Abstract

Reconfigurable optical add-drop filters in future intelligent and software controllable wavelength division multiplexing networks should support hitless wavelength switching and gridless bandwidth tuning. The hitless switching implies that the central wavelength of one channel can be shifted without disturbing data transmissions of other channels, while the gridless tuning means that the filter bandwidth can be adjusted continuously. Despite a lot of efforts, very few integrated optical filters simultaneously support the hitless switching of central wavelength and the gridless tuning of bandwidth. In this work, we demonstrate a hitless add-drop filter with gridless bandwidth tunability on the silicon-on-insulator (SOI) platform. The filter comprises the two identical multimode anti-symmetric waveguide Bragg gratings (MASWBG) which are connected to a loop. The phase apodization technique is utilized to weaken the intrinsic sidelobe interference of grating-based devices. By sequentially manipulating central wavelengths of the two MASWBGs with the thermo-optical effect, we can reconfigure the spectral response of the filter gridlessly and hitlessly. Specifically, the central wavelength of the device is shifted by 14.5 nm, while its 3 dB bandwidth is tuned from 0.2 nm to 2.4 nm. The dropping loss and the sidelobe suppression ratio (SLSR) are dependent on the bandwidth selected. Measured variation ranges of dropping loss and SLSR are from -1.2 dB to -2.5 dB and from 12.8 dB to 21.4 dB, respectively. The hitless wavelength switching is verified by a data transmission measurement at a bit rate of 25 Gbps.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

Due to the explosive increase in the number of mobile terminals and the rapid developments of multimedia applications and cloud computing services, the demand for transmission capacity and bandwidth of optical networks grows exponentially. The wavelength division multiplexing (WDM) technology has emerged as the most widely used solution to fulfill the ever-growing demand for bandwidth [14]. A key device in a WDM network is the optical add/drop multiplexer (OADM). It can selectively drop/add an individual or multiple wavelength channels at a network node without performing the expensive optical-to-electrical-to-optical (OEO) conversion.

Wavelength channels are pre-determined and fixed for a static OADM, thus valuable optical spectrum resources cannot be used effectively [5,6]. In contrast, a reconfigurable optical add/drop multiplexer (ROADM) enables the flexible allocation of optical bandwidth, and thus is strongly desired by the next-generation optical network with intelligence and software controllability [710]. An ideal ROADM is required to be colorless, directionless, contentionless, and gridless (CDCG) [11].

To date, various ROADMs have been demonstrated by utilizing different technologies such as photonic integrated circuit (PIC) [12,13], micro-electro-mechanical systems (MEMS) [10,14], and liquid crystals (LC) [9,15]. ROADMs based on MEMS or LC rely on bulky free-space optics, and therefore suffer from high assembly costs and limited stabilities. In contrast, the PIC technology enables on-chip ROADMs with a compact footprint, low cost, and high reliability. Plenty of integrated ROADMs have been demonstrated on almost all material platforms available for photonic integration, including silicon-on-insulator (SOI) [13,16], silica [17,18], Polymer [12], InP [19], and $\rm {Si}_3{\rm{N}}_4$ [20]. Among them, the SOI platform possesses the advantage of high integration density thanks to its large refractive index contrast [21]. More importantly, the large thermo-optic coefficient ($\sim 1.84\times 10^{-4}/K$) of silicon allows controlling the light propagation route on the chip by simply heating the waveguide with high power efficiency.

A CDCG ROADM requires the reconfiguration of the add-drop filter to be implemented hitlessly, i.e., tuning central wavelength or bandwidth of one channel should not disturb data transmissions in any other wavelength channels. Many schemes have been proposed to realize integrated reconfigurable add-drop filters on SOI. For example, a 1$\times$2 wavelength-selective switch with a flexible grid is reported in [22]. It consists of six 1$\times$32 arrayed waveguide gratings (AWG) and 32 MZI switches. The total footprint hence is as large as 3.0$\times$5.5 $mm^2$. However, this scheme doesn’t support gridless bandwidth tuning since the minimum grid size is constrained by the bandwidth of the AWG. Reconfigurable silicon add-drop filters can also be realized by utilizing microring resonators. Based on the principle of multi-channel-spectrum combination, multiply microring resonators are cascaded in [23] to form a filter whose bandwidth can be tuned gridlessly from 0.6 nm to 2.4 nm. However, the hitless switching of the central wavelength is impossible with this scheme. To realize the hitless reconfiguration, microring resonators are incorporated with interferometric input couplers to manipulate coupling coefficients between bus waveguides and resonators [24,25]. Before reconfiguring a channel, one can at first disable this channel by making its microring resonators operate in the undercoupled regime. In this manner, the reconfiguration won’t disturb transmissions of optical signals in the bus waveguide. Another solution enabling hitless reconfiguration is based on the bypass switch [26,27]. One arm of the switch provides the by-path route, while the other arm is loaded with an microring resonators based tunable add-drop filter. One can switch all incident optical signals to the by-path route, and then shifts the central wavelength of the add-drop filter hitlessly. However, the optical switches and tunable add-drop filter must be operated synchronously, which results in a response time delay making the operation more complicated, and the drive voltage is up to 40 V. We note that the hitless add-drop filters reported in [26,27] are unable to alter their bandwidths. To the best of knowledge, although a lot of efforts have been made, an integrated hitless add-drop filter that supports the gridless tuning of bandwidth and central wavelength hasn’t been demonstrated.

In parallel, waveguide Bragg gratings have been investigated quite extensively to build high-performance optical filters on silicon [28,29], largely due to their box-like responses that are free of the free spectral range (FSR) limitation. Despite these advantages, a stand-alone silicon waveguide Bragg gratings with uniform corrugation doesn’t support the bandwidth tunability and suffers from a strong sidelobe interference [30]. These issues hinder the application of silicon waveguide Bragg gratings in CDCG ROADM systems. In our previous work [31], we have developed a phase apodization technology to suppress sidelobes in the transmission spectra of silicon waveguide Bragg gratings. A sidelobe suppression ratio (SLSR) of 18.5 dB is achieved. Furthermore, by connecting two multimode antisymmetric waveguide Bragg gratings (MASWBGs) into a loop and adjusting the misalignment between their central wavelengths, we have realized a bandwidth tuning range as wide as 12.0 nm in [32]. With the two issues regarding the sidelobe suppression and the bandwidth tunability being addressed, we are able to demonstrate an integrated hitless ROADM based on silicon MASWBGs in this work.

This work is organized as follows: In section 2, we discuss the operation principle and determine design parameters by numerical simulation. After that, we present the fabrication and measurement results of our device in section 3. Finally, we conclude the work and discuss the future perspective in section 4.

2. Operation principle and structure design

2.1 Device structure

A schematic diagram of our hitless ROADM is shown in Fig. 1(a). It contains two reconfigurable add-drop filters. Each filter is a closed-loop that comprises two identical MASWBGs and four mode (de)multiplexers. In principle, a group of such add-drop filters can be cascaded in series to build a multi-channel ROADM system. As a proof-of-concept, a two-channel ROADM is demonstrated in this work.

 figure: Fig. 1.

Fig. 1. Schematic diagrams of (a) the two-channel hitless ROADM, (b) (c) the adiabatic directional coupler, and (d) the phase apodized waveguide sidewall Bragg grating. In (a), arrows with different colors are used to indicate propagation routes of different wavelengths inside the device. The wavelength $\lambda _1$ meets phase matching conditions of both MASWBGs, $\lambda _2$ only meets the phase matching condition of MASWBG1 but does not meet that of MASWBG2, $\lambda _3$ do not meet the phase matching condition of MASWBG1.

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The operation principle of the reconfigurable add-drop filter can be understood by examining transmission routes of different wavelengths. At first, if the phase-matching condition of $(n_0 + n_1)/2=\lambda /\Lambda$ is satisfied for the MASWBG1, the incident (forward) TE0 mode is converted to the backward TE1 mode. Here $n_0$ and $n_1$ denote effective indexes of TE0 and TE1 modes, respectively, $\lambda$ is the resonance wavelength of the MASWBG, and $\Lambda$ is the grating period. Four adiabatic directional couplers (ADC) work as mode (de)multiplexers [33]. Their operation principle is illustrated in Figs. 1(b) and 1(c), where the TE1 mode in the wide tapered waveguide is coupled to the TE0 mode of the narrow tapered waveguide. Meanwhile, the TE0 mode can transmit through the wide tapered waveguide without being coupled to the narrow tapered waveguide. With the aid of the mode (de)multiplexer, the TE1 mode reflected by MASWBG1 is routed to MASWBG2 as the TE0 mode, and then is filtered again. As a result, only wavelength which meets phase matching conditions of both MASWBGs can exit from the drop port of the add-drop filter. The final spectrum obtained at the drop port can be regarded as the product of the responses of the two MASWBGs [32]. In this case, the propagation route of light is indicated by red arrows ($\lambda _1$) in Fig. 1(a). Similarly, if the signal at the wavelength ($\lambda _1$) is incident from Add1 port, it can be added to the bus waveguide after two grating assisted reflections.

Secondly, if a wavelength only meets the phase matching condition of MASWBG1 but does not meet that of MASWBG2, the light would propagate through MASWBG2 in the TE0 mode. After passing through two another adiabatic directional couplers, the light is converted to the TE1 mode and then is launched into the other end of MASWBG1. Since the phase matching condition of MASWBG1 is well satisfied, the TE1 mode is reflected back as the TE0 mode. The adiabatic directional coupler then allows the TE0 mode to directly exit from the through port of this stage. In this case, the propagation route of light is marked by yellow arrows ($\lambda _2$) in Fig. 1(a).

At last, incident light which wavelength do not meet the phase matching condition of MASWBG1 directly transmit through this stage as indicated by orange arrows ($\lambda _3$) in Fig. 1(a).

According to the operation principle described above, spectra obtained at the drop and the through ports of the add-drop filter are complementary to each other. In the following two sub-sections, we discuss how to suppress the sidelobes by optimizing the waveguide Bragg gratings, and then explain how to accomplish the hitless and gridless tuning of central wavelength and the bandwidth.

2.2 Phase apodization technology

It is known that the spectral response of a uniform Bragg grating presents strong sidelobes besides its main band due to discontinuities of the coupling coefficient at the two ends of the grating. These sidelobes would cause crosstalks between adjacent channels. Many apodization techniques have been developed to weaken discontinuities of coupling coefficients, such as modulating the duty cycle or the recessing amplitude of the grating corrugation [34,35]. However, these techniques inevitably vary local average effective indexes of waveguide Bragg gratings along the axial direction. After the apodization, the average index at the central part of the waveguide Bragg grating is usually higher than those at the two ends. As a result, the resonance wavelength at the central part of the waveguide Bragg gratings shifts to the long wavelength side. On the short wavelength side, the central part of the waveguide Bragg gratings is transparent, thus a FP cavity is established between the two ends. The FP cavity effect finally leads to strong side lobes on the left side of the transmission window [36]. Briefly, only side lobes on the long wavelength side of the transmission band can be suppressed by conventional apodization techniques.

To eliminate the coupling coefficient discontinuities without changing the local average effective index of the waveguide Bragg gratings, the waveguide width and the amplitude of the grating corrugation recessing are modulated simultaneously in [37]. However, this configuration requires a very high fabrication precision so as to realize a sub-20 nm feature size. To solve this issue, we have demonstrated a phase apodization technique to manipulate the coupling coefficient. An advantage of this technique is that the local average refractive index of the waveguide Bragg gratings remains a constant along the axial direction [31]. Therefore, sidelobes on both sides of the passband can be suppressed effectively.

The phase apodized sidewall waveguide Bragg gratings is depicted in Fig. 1(d). The waveguide supports propagations of TE0 and TE1 modes. A lateral misalignment $\Delta s$ is introduced between grating corrugations on the two sides of the waveguide. It is modulated by a Gaussian function along the axial direction:

$$\Delta s = \frac{\Lambda}{2}\cdot e^{\frac{-b(z-L/2)^2}{L^2}}$$
Here $\Lambda$ and $L$ denote the period and the total length of the MASWBG, $b$ denotes the apodization strength. Equation (1) implies that the grating corrugations are exactly asymmetrical $(\Delta s=\Lambda /2)$ in the middle of the MASWBG, so the coupling strength between the symmetrical TE0 mode and the asymmetrical TE1 mode reaches its maximum value. In contrast, the grating corrugations are symmetrical $(\Delta s \approx 0)$ at the two ends of the MASWBG, so no coupling occurs between orthogonal TE0 and TE1 modes. The coupling coefficient between TE0 and TE1 modes in the phase apodized grating can be calculated as [38]:
$$\kappa=| \frac{\kappa_0}{2}- \frac{\kappa_0}{2}e^{i\cdot \frac{2\pi\Delta s}{\Lambda}} |=\kappa_0\sin{\pi \Delta s/ \Lambda}$$
Here $\kappa _0$ represents the maximal coupling coefficient in the middle of the MASWBG. It is determined by the spatial overlap between the two mode profiles and the dielectric perturbation in the transversal plane. Equation (2) implies that the coupling strength is apodized by gradually tuning the misalignment $\Delta s$ along the grating. It is noteworthy that the phase apodization technique doesn’t alter the local average effective index of the waveguide Bragg grating, so the detrimental FP cavity effect is avoided.

2.3 Hitless operation of the ROADM

In Fig. 1(a), the two MASWBGs which compose a reconfigurable add-drop filter are identical in design. Their central wavelengths are controlled independently by two metallic heaters. According to the operation principle described in section 2.1, the final spectrum obtained at the drop port of the add-drop filter is determined by the overlapping between the responses of the two MASWBGs. Therefore, the bandwidth of the add-drop filter can be tuned by introducing an offset between the central wavelengths of the two MASWBGs, while the position of the passband can be shifted by tuning the central wavelengths of the two MASWBGs collectively.

If the central wavelengths of the two MASWBGs are completely misaligned so that there is no overlapping between their passbands, the add-drop filter is in the "transparent" state by permitting all wavelengths to pass. This feature enables us to reconfigure the device hitlessly. Specifically, when switching the central wavelength of one add-drop filter, one just needs to tune the two MASWBGs of this add-drop filter sequentially rather than simultaneously. During such a tuning process, the two constituent MASWBGs are not aligned until the tuning is completed, so the add-drop filter remains in the "transparent" state. Therefore, data transmissions at all other wavelength channels are not disturbed.

To obtain optimal design parameters of the add-drop filter, we perform simulations by utilizing the three-dimensional (3D) finite-difference time-domain (FDTD) method. According to simulation results, waveguide widths of the adiabatic directional couplers are chosen to be $\omega _1=0.6\ \mu$m, $\omega _2=0.45\ \mu$m, $\omega _3=1.2\ \mu$m, and $\omega _4=0.1\ \mu$m, the length $L_t$ and the gap width $g$ of the adiabatic directional couplers are 205.6 $\mu$m and 0.13 $\mu$m, respectively. The length $L$, the period $\Lambda$ and the corrugation width $\Delta \omega$ of the MASWBG are 472 $\mu$m, 0.295 $\mu$m, and 0.14 $\mu$m.

The simulated spectral response at the drop port of the MASWBG is plotted in Fig. 2(a). We define the SLSR as the ratio between peak powers of the passband and the strongest sidelobe in the wavelength range of interest. Thanks to the phase apodization technology, sidelobes on both sides of the passband are suppressed successfully to produce an SLSR of 20.5 dB. Simulated dropping loss and 3 dB bandwidth are 0.2 dB and 3.2 nm, respectively. Two such MASWBGs then are connected to form a reconfigurable add-drop filter. Its response is simulated in Figs. 2(b)–2(d) at different operating states. In Fig. 2(b), the two MASWBGs have an identical central wavelength, so their filtering spectra overlap completely. Since the same filtering process occurs twice, we obtain a much steeper response which is favorable to practical WDM systems. Another benefit is that the SLSR is improved to $\sim 39.0$ dB. The resultant 3 dB bandwidth of 2.8 nm represents the widest bandwidth that can be achieved by this design. In Fig. 2(c), the central wavelengths of the two MASWBGs are offset by 0.5 nm, the 3 dB bandwidth of the add-drop filter thus shrinks to 1.7 nm. Corresponding dropping loss and SLSR are 0.55 dB and 22.1 dB, respectively. In Fig. 2(d), the central wavelengths of the two MASWBGs are completely misaligned. It can be seen that almost no light (< -20 dB) can leak from the drop port of the filter. This channel hence is at the "Off" state to permit all wavelengths to pass. It should be noted that spectral response of practical MASWBGs cannot be ideally box-shaped. Therefore, at the band edge of MASWBG1, the incident light is partially reflected and partially transmitted. A portion of the reflected light can propagate anticlockwise along the loop, and then enters the other end of MASWBG1, where it is reflected to the through port. In the through port, this portion of the light interferes with the portion that directly transmits through MASWBG1. The interference gives rise to transmission fluctuations in the final transmission spectrum. To suppress this effect, an independent heater (Heater3) is used to control the relative phase between the lights that propagate through different paths so that they can interfere destructively in the through port.

 figure: Fig. 2.

Fig. 2. Simulated spectral responses at drop ports of (a) a single MASWBG, (b) the add-drop filter with the central wavelengths of the two MASWBG being well aligned, (c) the add-drop filter with the central wavelengths of the two MASWBG being offset by 0.5 nm, (d) the filter with the central wavelengths of the two MASWBGs being offset by 3.5 nm.

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3. Fabrication and performance characterization

3.1 Device fabrication

The two-channel ROADM is fabricated on an SOI substrate with a 220-nm-thick top silicon layer and a 2-$\mu$m-thick SiO2 layer. At first, waveguides are patterned by E-beam lithography (EBL) and inductively coupled plasma dry-etching. After that, a 2.2-$\mu$m-thick SiO2 cladding layer is deposited by plasma-enhanced chemical vapor deposition (PECVD). A 100-nm-thick TiW alloy layer is deposited on top of the SiO2 cladding layer, and then is patterned by the lift-off technique to form the metallic heater. Finally, TiW/Al metal routing layers with thicknesses of 200 nm/500 nm are evaporated on top of the TiW alloy heater to form the contact. The resistance of the heater is measured to be $\sim 470\ \Omega$. Design parameters validated by the simulation in sub-section 2.3 are utilized for the practical device. A microscope image of the fabricated device is shown in Fig. 3 together with scanning electron microscope (SEM) images of the grating corrugation and the mode (de)multiplexer. The total footprint of the device is 2.0$\times$0.7 mm.

 figure: Fig. 3.

Fig. 3. (a) Microscope image of the two-channel ROADM. (b-d) SEM images of the grating corrugation at different positions of the MASWBG. (e) SEM image of the mode (de)multiplexer.

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3.2 Characterization of the phase apodization technology

In order to experimentally verify the effect of phase apodization technology, we measure and compare spectral responses of a phase apodized MASWBG and a reference uniform MASWBG. Dimensions of multimode waveguide, corrugation width and grating period of the two MASWBGs are identical, which are $1.2 \ \mu$m $\times 472\ \mu$m, $\ 0.14\ \mu$m, and $0.295\ \mu$m, respectively. The value of the apodization coefficient is 10.

The measured spectra at drop ports of the two devices are displayed in Fig. 4, where the total coupling loss of the two fiber grating couplers has been normalized. The uniform MASWBG in Fig. 4(a) presents a very poor SLSR of only 4.0 dB. In contrast, the phase apodization technology successfully suppresses side lobes on both sides of the passband in Fig. 4(b). The measured SLSR is better than 22.3 dB.

 figure: Fig. 4.

Fig. 4. Spectral responses of (a) the reference uniform MASWBG, (b) the phase apodized MASWBG, and the wavelength resolution is 0.1 nm.

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The individual MASWBG in Fig. 4(b) presents a relatively large 3 dB bandwidth of 2.8 nm. From the view point of increasing the channel density, a narrow 3 dB bandwidth is desirable. This can be realized by simultaneously weakening the coupling coefficient and increasing the coupling length. However, a weak coupling coefficient is implemented by reducing the corrugation width, and thus demands a high fabrication resolution. In [6], we have already demonstrated an individual silicon waveguide Bragg grating based filter with a 3 dB bandwidth as narrow as 0.9 nm. The device uses a very narrow corrugation width of 25 nm and a grating length of 900 $\mu$m. Its performance hence is susceptible to the fabrication imperfection. The purpose of this work is to demonstrate the hitless and gridless reconfigurability rather than realizing a narrow bandwidth. In order to reduce the process risk, we use conservative design parameters which then lead to a relatively wide passband in Fig. 4(b).

3.3 Characterization of bandwidth and central wavelength tunabilities

In this sub-section, we characterize bandwidth and center wavelength tunabilities of the fabricated two-channel ROADM shown in Fig. 3. The measured spectral responses at the drop port of channel 1 are displayed in Fig. 5. In Fig. 5(a), heating voltages applied on the two MASWBGs of channel 1 are equal, so there is no offset between the central wavelengths of the two MASWBGs. Channel 1 thus presents the maximum 3 dB bandwidth of 2.4 nm. The dropping loss at the center of the passband is $\sim$ -1.2 dB, while the intra band ripples are less than 0.7 dB. Thanks to the phase apodization technique, a SLSR of 21.4 dB is achieved. We note that measured dropping loss and bandwidth basically agree with the simulation results in subsection 2.3. However, the measured SLSR of 21.4 dB is inferior to the 39 dB SLSR simulated in Fig. 2(b). We attribute the discrepancy to phase noises in practical gratings, which can be induced by sidewall roughness, thickness non-uniformity of the Si layer, field stitching error of the electron beam lithography, and so on [39]. By tuning the central wavelengths of the two MASWBGs equally, we sweep the passband of channel 1 with a grid spacing of 3.2 nm (400 GHz) in Fig. 5(a). The adjacent channel isolation, which is defined as the minimum ratio (in dB) of the dropped optical power at the center of the passband to that at the adjacent wavelength grid [40], is over 31.5 dB.

 figure: Fig. 5.

Fig. 5. Experimental results of tuning central wavelength and bandwidth of channel 1. (a)/(b)/(c) 3 dB bandwidths of pass bands are 2.4/0.7/0.2 nm, and the wavelength resolution are 0.1/0.05/0.05 nm. (d) Relationships between the dropping loss, ripples and SLSR with the 3dB bandwidth of the add-drop filter as a variable.

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In Figs. 5(b) and 5(c), the two MASWBGs of channel 1 are heated with different powers so as to change the 3 dB bandwidth. Measured 3 dB bandwidths are 0.7 nm and 0.2 nm in Figs. 5(b) and 5(c), respectively. When shifting the passband center of channel 1, we make sure the difference in the central wavelengths of the two MASWBGs is fixed, so the bandwidth of channel 1 remains unchanged. In Fig. 5(b), the central wavelength of the 0.7-nm-wide passband is swept with a grid spacing of 1.6 nm (200 GHz). Channel dropping losses at the 8 grid wavelengths vary between -1.4 dB and -2.3 dB, intra band ripples are less than 1.7 dB, while the SLSRs and the adjacent channel isolation are both $\sim$ 13.1 dB, respectively. In Fig. 5(c), the central wavelength of the 0.2-nm-wide passband is swept with a grid spacing of 0.8 nm (100 GHz). Channel dropping losses at the 16 grid wavelengths are between -1.2 dB and -2.5 dB. Intra band ripples are less than 1.9 dB, while the SLSRs and the adjacent channel isolation are $\sim$ 12.8 dB and 19 dB, respectively. It is worthy to note that as the 3 dB bandwidth decreases from 2.4 nm to 0.2 nm, the shape factor defined as the ratio of -3 dB bandwidth to -10 dB bandwidth deteriorates from 0.89 in Fig. 5(a) to 0.2 in Fig. 5(c). This detrimental effect is universal for bandwidth tunable filters based on the operation principle of controlling the spectral overlap of two sub-filters [28,32]. The issue can be alleviated by improving the roll-off factor of the MASWBG unit. For example, the integral layer peeling algorithm is used to design a Bragg grating filter on SOI with box shape passband in [41]. This technique can be utilized in our future design.

We summarize dependences of dropping loss, intra band ripple and SLSR on the 3 dB bandwidth in Fig. 5(d). It can be found in Fig. 5(d) that the intra band ripple is enhanced as the 3 dB bandwidth decreases. This can be attributed to the fact that both the thermal crosstalk and the resistivity distribution of the heater cannot be exactly uniform along the grating. When the heater works, there is a weak longitudinal fluctuation of the thermal field which adds a phase noise to the refractive index perturbation of the grating. As we increase the heating power to reduce the 3 dB bandwidth, the phase noise scales up and thus enhances the intra band ripple. Similar phenomena have been reported in pervious works [6,42]. To improve the uniformity of the thermal field, one can globally optimize the mask layout and improve the quality of the metallic heater. By taking the measurement error and the random intra band ripple into account, we find in Fig. 5(d) that the dropping loss basically remains unchanged as the 3 dB bandwidth decreases. There is an abrupt deterioration of the SLSR as the 3 dB bandwidth starts to decrease from 2.4 nm to 2.0 nm. After that, the SLSR is almost a constant. The reason is that with a misalignment between the central wavelengths of the two MASWBGs, the roll-off characteristic of the final spectrum is determined by the superposition between the band edge of one MASWBG and the flat band top of the other MASWBG. Therefore, the rejection effect is weakened at wavelengths in proximity to the passband. The thermal tuning efficiency of the ROADM is $\sim 35$ mW/nm.

Transmissions of high-speed data signals through the ROADM are characterized by the setup shown in Fig. 6(a). The output of a tunable laser (TSL-510) is launched into the commercial LiNbO3 modulator which is driven by a pseudorandom bit sequences (PRBS) signal with a pattern length of $2^{31}-1$. The modulation format is non-return-to-zero (NRZ) on-off keying (OOK). The modulated light is sent to a polarization controller before being coupled into the DUT. The output wavelength of the tunable laser is aligned to the central wavelength of channel 1. The modulated light dropped by channel 1 then is coupled out from the chip to an Erbium-doped Fiber Amplifier (EDFA). After that, an optical bandpass filter with a bandwidth of 0.8 nm is used to suppress the amplified spontaneous emission noise (ASE). A variable optical attenuator controls the power level of the amplified optical signal. Finally, the signal is launched into a sampling oscilloscope with an optical head (Keysight, DCA-X 86100D) for the eye diagram analysis.

 figure: Fig. 6.

Fig. 6. (a) Setup for the high-speed data transmission measurement. The setup includes a tunable laser, two polarization controllers (PC), a LiNbO3 modulator, a bit pattern generator (BPG), an Er-doped fiber amplifier (EDFA), a tunable bandpass filter, a variable optical attenuator (VOA), and a wide-bandwidth oscilloscope. (b) Eye diagrams of data signals dropped by channel 1 at different data rates and bandwidths.

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By configuring the bandwidth of channel 1 to be 2.4/0.7/0.2 nm (corresponding spectral responses have been presented in Fig. 5), we capture eye diagrams of dropped signals at three different data rates of 10/25/32 Gbps. The results are displayed in Fig. 6(b). As we increase the data rates or reduce the bandwidth of the filter, the signal quality deteriorates to some degree. However, Q factors of all measured eye diagams are higher than 6, so dropped data signals can be regarded as error free. It is observed that timing jitters of data signals dropped by channel 1 are slightly larger than those of the B2B signals. The reason is that Bragg gratings usually present strong group velocity dispersions [43,44]. As analyzed in [45], the group velocity dispersion would broaden the pulse and finally increases the timing jitter. However, clearly open eye diagrams with Q factors better than 7 are obtained at all different bandwidths and data rates.

3.4 Characterization of the hitless reconfiguration

In this sub-section, we demonstrate the hitless operation of the two-channel ROADM. Spectral responses measured at drop ports of the two channels before and after the hitless switching are illustrated in Fig. 7(a). At the initial state, passbands of both channels are configured with a width of 2.4 nm. Their centers locate at 1543.7 nm and 1546.9 nm to implement a channel spacing of 400 GHz. At the final state, the central wavelength of channel 1 is shifted by two grids from 1543.7 nm to 1550.1 nm. When switching the central wavelength of channel 1, we should avoid disturbing the data transmission in channel 2.

 figure: Fig. 7.

Fig. 7. Hitless switching of the central wavelength of channel 1, and the wavelength resolution of the spectrum is 0.1nm. (a) Spectra measured at the drop ports of the two channels before and after the hitless switching. (b) Spectral responses of channel 1 in 6 intermediate states. (c) Spectral responses of channel 2 in 6 intermediate states. The inset shows the time response of the heater.(d) Spectral responses of the through port in 6 intermediate states. (e) the eye mask of channel 1 and channel 2.

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As already discussed in section 2.3, we switch the central wavelength of channel 1 hitlessly through three tuning steps: At first, the central wavelength of MASWBG2 is shifted to a wavelength that is beyond the target wavelength of 1550.1 nm, e.g., 1554.9 nm here. Secondly, the central wavelength of MASWBG1 is shifted to the target wavelength of 1550.1 nm. Finally, the central wavelength of MASWBG2 is moved backward to 1550.1 nm by turning down the heating power. During such a tuning process, the central wavelengths of the two MASWBGs are always misaligned, so channel 1 remains in the "off" state which is transparent for all wavelengths. It is worthy to note that the central wavelength of MASWBG2 is shifted excessively to the right side of the target wavelength of 1550.1 nm in step 1, and then it is moved back to 1550.1 nm in step 3. The reason for adopting this strategy is that we want passbands of the two MASWBGs to overlap from the right side of the target wavelength in step 3. By this manner, we can minimize the disturbance to the passband of channel 2, which locates closely on the left side of the target wavelength of channel 1. However, for multi-channel systems, it is necessary to increase the roll-off factor of the individual MASWBG so as to minimize the impact of wavelength switching on adjacent channels. For example, the integral layer peeling algorithm developed in [41] can be utilized to improve the spectral shape factor of the MASWBG.

To verify the hitless operation, we pick up six typical intermediate states and record corresponding spectral responses at all three output ports, i.e., one through port and two drop ports. These six states are listed in Table 1, while the measured spectra are displaced in Figs. 7(b)–7(d). For most intermediate states in Fig. 7(b), i.e., states 3, 4 and 5, there is almost no optical signal being dropped by channel 1, and the in-band isolation is over 24.4 dB. However, the spectral response at state 2 (the blue curve in Fig. 7(b)) exhibits a weak peak. The reason is that passbands of the two constituent MASWBGs are not completely separated from each other in this state. In the wavelength range where band edges of the two MASWBGs still overlap, a small portion of the light leaks from the drop port and thus leads to a peak in the blue curve of Fig. 7(b). The measured spectral responses at the drop port of channel 2 and the through port of the device are displayed in Figs. 7(c) and 7(d), respectively. It is obvious that the response of channel 2 remains almost unchanged from state 1 to state 6. Therefore, the hitless operation is verified. We note that although channel 2 and channel 1 share the identical design, the add-drop filter of channel 2 is unable to provide a box-like response as well as channel 1. A possible reason is that waveguide Bragg gratings of channel 2 suffer from stronger random phase noises than channel 1.

We test the temporal response of the heater with an individual MASWBG. The result is plotted in the inset of Fig. 7(c). The rising and falling times are 16.7 $\mu$s and 6.7 $\mu$s, respectively. As listed in Tabel 1, the wavelength switching process contains three wavelength tuning steps. Therefore, the aggregate time to switch the wavelength of one channel is $\sim 40.1$ $\mu$s.

Tables Icon

Table 1. Heating voltages and central wavelengths of the two MASWBG at six intermediate states.

To further validate that the central wavelength of channel 1 is switched hitlessly, we characterize qualities of 25 Gb/s data signals dropped by the two channels at the 6 intermediate states. Measured eye diagrams are displayed in Fig. 7(e). As shown in Fig. 7(b), the central wavelength of channel 1 is switched from 1543.7 nm to 1550.1 nm. By setting the wavelength of the laser to these two values, we capture eye diagrams of data signals dropped by channel 1 before and after the wavelength switching. As shown in the first row of Fig. 7(e), the Q factors of the eyes before and after the wavelength switching are 13.7 and 13.1, respectively. Therefore, the deterioration of the channel quality is insignificant as we tune the central wavelength.

On the other hand, we fix the incident wavelength at the passband center of channel 2, i.e., 1546.9 nm, and then measures eye diagrams of data streams dropped by channel 2 at the six states listed in Tabel 1. The results are displayed in the second row of Fig. 7(e). As we expected, switching the central wavelength of channel 1 makes almost no impact on the data transmission in channel 2. The Q factors measured at the six states are 12.5, 11.5, 10, 9.1, 11.3, 11.7. We note that compared with other states, the Q factor measured at state 4 degrades slightly. The reason is that the optical signal needs to transmit through channel 1 before being dropped by channel 2. At state 4, the MASWBG1 of channel 1 exhibits the same central wavelength of 1546.9 nm as channel 2. The corresponding optical path inside channel 1 for this wavelength is indicated in the inset of Fig. 2(d). The optical signal experiences two grating assisted reflections and makes a full circle inside channel 1. Therefore, the light is subject to an additional dropping loss of around 1.1 dB after transmitting through channel 1. Due to the reduction of the optical power entering channel 2, the quality of the dropped data signal worsens a little bit. However, signal qualities at channel 2 are good enough to support the error-free operation in all six states. To alleviate this issue, it is suggested to reduce losses of the MASWBG and the adiabatic directional coupler by further optimizing their designs.

It is observed in Fig. 7(c) that the passband of channel 2 is subject to a jitter of around 0.2 nm during the wavelength switching of channel 1. This is attributed to the thermal crosstalk between the two channels. Such a jitter is tolerable for the 2.4 nm bandwidth in Fig. 7. However, if the 3 dB bandwidth is configured to be 0.2 nm, the jitter would deteriorate the quality of the signal dropped by channel 2. In the future design, it is necessary to increase the spacing between two add-drop filters so as to suppress their thermal crosstalk.

4. Conclusion

In summary, we demonstrate a hitless and gridless two-channel ROADM based on phase apodized MASWBGs. The reconfigurability of the device is characterized by the static spectral response and dynamic data transmission measurements. In Table 2, the performance of our device is compared favorably with reported ROADMs on silicon. The comparison manifests that this work is a very competitive candidate for the CDCG-ROADM by simultaneously supporting hitless and gridless reconfiguration. Furthermore, our device possesses the advantages of the wider bandwidth tuning range, lower dropping loss, and fewer controlling electrodes.

Tables Icon

Table 2. Comparison of the reported ROADMs on silicon

Two wavelength channels are demonstrated in this work. However, in principle, our scheme has good scalability to allow integrating more wavelength channels. Due to the intrinsic sensitivity of waveguide Bragg gratings to phase noises induced by processing errors, the shape of the spectrum of channel 2 is inferior to that of channel 1. In order to implement more wavelength channels, improving the processing quality and suppressing the susceptibility to the phase noises are suggested for our future work.

Funding

This work was supported by the National Key Research and Development Program of China (2018YFB2200600); Natural Science Foundation of Fujian Province (2019J01796); Fujian Province New Century Talent Foundation; Zhangping Qimai Foundation.

Acknowledgments

The authors would like to thank Dr. Bing Wei, Training Platform of Information and Microelectronic Engineering in Polytechnic Institute of Zhejiang University.

Disclosures

The authors declare no conflicts of interest.

References

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4. J. Mikkelsen, A. Bois, T. Lordello, D. Mahgerefteh, S. Menezo, and J. Poon, “Polarization-insensitive silicon nitride mach-zehnder lattice wavelength demultiplexers for cwdm in the o-band,” Opt. Express 26(23), 30076–30084 (2018). [CrossRef]  

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13. D. Wu, Y. Wu, Y. Wang, J. An, and X. Hu, “Reconfigurable optical add-drop multiplexer based on thermally tunable micro-ring resonators,” Opt. Commun. 367, 44–49 (2016). [CrossRef]  

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30. H. Qiu, G. Jiang, T. Hu, H. Shao, P. Yu, J. Yang, and X. Jiang, “Fsr-free add–drop filter based on silicon grating-assisted contradirectional couplers,” Opt. Lett. 38(1), 1–3 (2013). [CrossRef]  

31. J. Jiang, H. Qiu, G. Wang, Y. Li, T. Dai, D. Mu, H. Yu, J. Yang, and X. Jiang, “Silicon lateral-apodized add–drop filter for on-chip optical interconnection,” Appl. Opt. 56(30), 8425–8429 (2017). [CrossRef]  

32. J. Jiang, H. Qiu, G. Wang, Y. Li, T. Dai, X. Wang, H. Yu, J. Yang, and X. Jiang, “Broadband tunable filter based on the loop of multimode bragg grating,” Opt. Express 26(1), 559–566 (2018). [CrossRef]  

33. Y. Ding, J. Xu, F. Da Ros, B. Huang, H. Ou, and C. Peucheret, “On-chip two-mode division multiplexing using tapered directional coupler-based mode multiplexer and demultiplexer,” Opt. Express 21(8), 10376–10382 (2013). [CrossRef]  

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References

  • View by:

  1. A. Liu, L. Liao, Y. Chetrit, J. Basak, H. Nguyen, D. Rubin, and M. Paniccia, “Wavelength division multiplexing based photonic integrated circuits on silicon-on-insulator platform,” IEEE J. Sel. Top. Quantum Electron. 16, 23–32 (2010).
    [Crossref]
  2. D. Dai, J. Wang, S. Chen, S. Wang, and S. He, “Monolithically integrated 64-channel silicon hybrid demultiplexer enabling simultaneous wavelength-and mode-division-multiplexing,” Laser Photonics Rev. 9(3), 339–344 (2015).
    [Crossref]
  3. F. Horst, W. M. Green, S. Assefa, S. M. Shank, Y. A. Vlasov, and B. J. Offrein, “Cascaded mach-zehnder wavelength filters in silicon photonics for low loss and flat pass-band wdm (de-) multiplexing,” Opt. Express 21(10), 11652–11658 (2013).
    [Crossref]
  4. J. Mikkelsen, A. Bois, T. Lordello, D. Mahgerefteh, S. Menezo, and J. Poon, “Polarization-insensitive silicon nitride mach-zehnder lattice wavelength demultiplexers for cwdm in the o-band,” Opt. Express 26(23), 30076–30084 (2018).
    [Crossref]
  5. A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
    [Crossref]
  6. D. Mu, H. Qiu, J. Jiang, X. Wang, Z. Fu, Y. Wang, X. Jiang, H. Yu, and J. Yang, “A four-channel dwdm tunable add/drop demultiplexer based on silicon waveguide bragg gratings,” IEEE Photonics J. 11, 1–8 (2019).
    [Crossref]
  7. D. K. Tripathi, P. Singh, N. Shukla, and H. Dixit, “Reconfigurable optical add and drop multiplexers a review,” ECIJ 3(1), 1 (2014).
    [Crossref]
  8. C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
    [Crossref]
  9. S. Frisken, G. Baxter, D. Abakoumov, H. Zhou, I. Clarke, and S. Poole, “Flexible and grid-less wavelength selective switch using lcos technology,” in 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference (IEEE, 2011), pp. 1–3.
  10. D. M. Marom, D. T. Neilson, D. S. Greywall, C.-S. Pai, N. R. Basavanhally, V. A. Aksyuk, D. O. López, F. Pardo, M. E. Simon, Y. Low, P. Kolodner, and C. A. Bolle, “Wavelength-selective 1 x k switches using free-space optics and mems micromirrors: theory, design, and implementation,” J. Lightwave Technol. 23(4), 1620–1630 (2005).
    [Crossref]
  11. S. Perrin, “The need for next-generation roadm networks,” Heavy Reading, September (2010).
  12. J.-U. Shin, Y.-T. Han, S.-P. Han, S.-H. Park, Y. Baek, Y.-O. Noh, and K.-H. Park, “Reconfigurable optical add-drop multiplexer using a polymer integrated photonic lightwave circuit,” ETRI J 31(6), 770–777 (2009).
    [Crossref]
  13. D. Wu, Y. Wu, Y. Wang, J. An, and X. Hu, “Reconfigurable optical add-drop multiplexer based on thermally tunable micro-ring resonators,” Opt. Commun. 367, 44–49 (2016).
    [Crossref]
  14. J. Li, A. Liu, W. Zhong, Q. Zhang, and C. Lu, “Mems switch based serial reconfigurable oadm,” Opt. Commun. 230(1-3), 81–89 (2004).
    [Crossref]
  15. N. A. Riza and S. Yuan, “Reconfigurable wavelength add-drop filtering based on a banyan network topology and ferroelectric liquid crystal fiber-optic switches,” J. Lightwave Technol. 17(9), 1575–1584 (1999).
    [Crossref]
  16. M. Geng, L. Jia, L. Zhang, L. Yang, P. Chen, T. Wang, and Y. Liu, “Four-channel reconfigurable optical add-drop multiplexer based on photonic wire waveguide,” Opt. Express 17(7), 5502–5516 (2009).
    [Crossref]
  17. M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
    [Crossref]
  18. Y. Goebuchi, T. Kato, and Y. Kokubun, “Fast and stable wavelength-selective switch using double-series coupled dielectric microring resonator,” IEEE Photonics Technol. Lett. 18(3), 538–540 (2006).
    [Crossref]
  19. D. Rabus, M. Hamacher, H. Heidrich, and U. Troppenz, “Box-like filter response of triple ring resonators with integrated soa sections based on gainasp/inp,” in Conference Proceedings. 14th Indium Phosphide and Related Materials Conference (Cat. No. 02CH37307) (IEEE, 2002), pp. 479–482.
  20. E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
    [Crossref]
  21. H. Subbaraman, X. Xu, A. Hosseini, X. Zhang, Y. Zhang, D. Kwong, and R. T. Chen, “Recent advances in silicon-based passive and active optical interconnects,” Opt. Express 23(3), 2487–2511 (2015).
    [Crossref]
  22. C. R. Doerr, L. L. Buhl, L. Chen, and N. Dupuis, “Monolithic flexible-grid 1×2 wavelength-selective switch in silicon photonics,” J. Lightwave Technol. 30(4), 473–478 (2012).
    [Crossref]
  23. T. Dai, A. Shen, G. Wang, Y. Wang, Y. Li, X. Jiang, and J. Yang, “Bandwidth and wavelength tunable optical passband filter based on silicon multiple microring resonators,” Opt. Lett. 41(20), 4807–4810 (2016).
    [Crossref]
  24. M. A. Popović, T. Barwicz, F. Gan, M. S. Dahlem, C. W. Holzwarth, P. T. Rakich, H. I. Smith, E. P. Ippen, and F. X. Kärtner, “Transparent wavelength switching of resonant filters,” in Conference on Lasers and Electro-Optics (Optical Society of America, 2007), p. CPDA2.
  25. D. O. M. de Aguiar, M. Milanizadeh, E. Guglielmi, F. Zanetto, G. Ferrari, M. Sampietro, F. Morichetti, and A. Melloni, “Automatic tuning of silicon photonics microring filter array for hitless reconfigurable add–drop,” J. Lightwave Technol. 37(16), 3939–3947 (2019).
    [Crossref]
  26. H. A. Haus, M. A. Popovic, and M. R. Watts, “Broadband hitless bypass switch for integrated photonic circuits,” IEEE Photonics Technol. Lett. 18(10), 1137–1139 (2006).
    [Crossref]
  27. R. Chatterjee, M. Yu, A. Stein, D.-L. Kwong, L. C. Kimerling, and C. W. Wong, “Demonstration of a hitless bypass switch using nanomechanical perturbation for high-bitrate transparent networks,” Opt. Express 18(3), 3045–3058 (2010).
    [Crossref]
  28. J. St-Yves, H. Bahrami, P. Jean, S. LaRochelle, and W. Shi, “Widely bandwidth-tunable silicon filter with an unlimited free-spectral range,” Opt. Lett. 40(23), 5471–5474 (2015).
    [Crossref]
  29. M. Hammood, A. Mistry, M. Ma, H. Yun, L. Chrostowski, and N. A. Jaeger, “Compact, silicon-on-insulator, series-cascaded, contradirectional-coupling-based filters with> 50 db adjacent channel isolation,” Opt. Lett. 44(2), 439–442 (2019).
    [Crossref]
  30. H. Qiu, G. Jiang, T. Hu, H. Shao, P. Yu, J. Yang, and X. Jiang, “Fsr-free add–drop filter based on silicon grating-assisted contradirectional couplers,” Opt. Lett. 38(1), 1–3 (2013).
    [Crossref]
  31. J. Jiang, H. Qiu, G. Wang, Y. Li, T. Dai, D. Mu, H. Yu, J. Yang, and X. Jiang, “Silicon lateral-apodized add–drop filter for on-chip optical interconnection,” Appl. Opt. 56(30), 8425–8429 (2017).
    [Crossref]
  32. J. Jiang, H. Qiu, G. Wang, Y. Li, T. Dai, X. Wang, H. Yu, J. Yang, and X. Jiang, “Broadband tunable filter based on the loop of multimode bragg grating,” Opt. Express 26(1), 559–566 (2018).
    [Crossref]
  33. Y. Ding, J. Xu, F. Da Ros, B. Huang, H. Ou, and C. Peucheret, “On-chip two-mode division multiplexing using tapered directional coupler-based mode multiplexer and demultiplexer,” Opt. Express 21(8), 10376–10382 (2013).
    [Crossref]
  34. D. Wiesmann, C. David, R. Germann, D. Emi, and G. Bona, “Apodized surface-corrugated gratings with varying duty cycles,” IEEE Photonics Technol. Lett. 12(6), 639–641 (2000).
    [Crossref]
  35. C. Greiner, T. W. Mossberg, and D. Iazikov, “Bandpass engineering of lithographically scribed channel-waveguide bragg gratings,” Opt. Lett. 29(8), 806–808 (2004).
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  36. T. Erdogan, “Fiber grating spectra,” J. Lightwave Technol. 15(8), 1277–1294 (1997).
    [Crossref]
  37. M. Strain and M. Sorel, “Integrated iii–v bragg gratings for arbitrary control over chirp and coupling coefficient,” IEEE Photonics Technol. Lett. 20(22), 1863–1865 (2008).
    [Crossref]
  38. X. Wang, Y. Wang, J. Flueckiger, R. Bojko, A. Liu, A. Reid, J. Pond, N. A. Jaeger, and L. Chrostowski, “Precise control of the coupling coefficient through destructive interference in silicon waveguide bragg gratings,” Opt. Lett. 39(19), 5519–5522 (2014).
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  39. A. D. Simard, N. Ayotte, Y. Painchaud, S. Bedard, and S. LaRochelle, “Impact of sidewall roughness on integrated bragg gratings,” J. Lightwave Technol. 29(24), 3693–3704 (2011).
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  40. R. Boeck, J. Flueckiger, L. Chrostowski, and N. A. Jaeger, “Experimental performance of dwdm quadruple vernier racetrack resonators,” Opt. Express 21(7), 9103–9112 (2013).
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  41. A. D. Simard, M. J. Strain, L. Meriggi, M. Sorel, and S. LaRochelle, “Bandpass integrated bragg gratings in silicon-on-insulator with well-controlled amplitude and phase responses,” Opt. Lett. 40(5), 736–739 (2015).
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  42. M. Boroojerdi, M. Ménard, and A. Kirk, “Wavelength tunable integrated add-drop filter with 10.6 nm bandwidth adjustability,” Opt. Express 24(19), 22043–22050 (2016).
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  43. S. Khan, M. A. Baghban, and S. Fathpour, “Electronically tunable silicon photonic delay lines,” Opt. Express 19(12), 11780–11785 (2011).
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  44. S. Khan and S. Fathpour, “Demonstration of tunable optical delay lines based on apodized grating waveguides,” Opt. Express 21(17), 19538–19543 (2013).
    [Crossref]
  45. E. Krune, K. Jamshidi, K. Voigt, L. Zimmermann, and K. Petermann, “Jitter analysis of optical clock distribution networks in silicon photonics,” J. Lightwave Technol. 32(22), 4378–4385 (2014).
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2019 (3)

2018 (2)

2017 (1)

2016 (3)

2015 (4)

2014 (3)

X. Wang, Y. Wang, J. Flueckiger, R. Bojko, A. Liu, A. Reid, J. Pond, N. A. Jaeger, and L. Chrostowski, “Precise control of the coupling coefficient through destructive interference in silicon waveguide bragg gratings,” Opt. Lett. 39(19), 5519–5522 (2014).
[Crossref]

D. K. Tripathi, P. Singh, N. Shukla, and H. Dixit, “Reconfigurable optical add and drop multiplexers a review,” ECIJ 3(1), 1 (2014).
[Crossref]

E. Krune, K. Jamshidi, K. Voigt, L. Zimmermann, and K. Petermann, “Jitter analysis of optical clock distribution networks in silicon photonics,” J. Lightwave Technol. 32(22), 4378–4385 (2014).
[Crossref]

2013 (5)

2012 (1)

2011 (2)

2010 (2)

R. Chatterjee, M. Yu, A. Stein, D.-L. Kwong, L. C. Kimerling, and C. W. Wong, “Demonstration of a hitless bypass switch using nanomechanical perturbation for high-bitrate transparent networks,” Opt. Express 18(3), 3045–3058 (2010).
[Crossref]

A. Liu, L. Liao, Y. Chetrit, J. Basak, H. Nguyen, D. Rubin, and M. Paniccia, “Wavelength division multiplexing based photonic integrated circuits on silicon-on-insulator platform,” IEEE J. Sel. Top. Quantum Electron. 16, 23–32 (2010).
[Crossref]

2009 (2)

M. Geng, L. Jia, L. Zhang, L. Yang, P. Chen, T. Wang, and Y. Liu, “Four-channel reconfigurable optical add-drop multiplexer based on photonic wire waveguide,” Opt. Express 17(7), 5502–5516 (2009).
[Crossref]

J.-U. Shin, Y.-T. Han, S.-P. Han, S.-H. Park, Y. Baek, Y.-O. Noh, and K.-H. Park, “Reconfigurable optical add-drop multiplexer using a polymer integrated photonic lightwave circuit,” ETRI J 31(6), 770–777 (2009).
[Crossref]

2008 (1)

M. Strain and M. Sorel, “Integrated iii–v bragg gratings for arbitrary control over chirp and coupling coefficient,” IEEE Photonics Technol. Lett. 20(22), 1863–1865 (2008).
[Crossref]

2007 (1)

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

2006 (2)

Y. Goebuchi, T. Kato, and Y. Kokubun, “Fast and stable wavelength-selective switch using double-series coupled dielectric microring resonator,” IEEE Photonics Technol. Lett. 18(3), 538–540 (2006).
[Crossref]

H. A. Haus, M. A. Popovic, and M. R. Watts, “Broadband hitless bypass switch for integrated photonic circuits,” IEEE Photonics Technol. Lett. 18(10), 1137–1139 (2006).
[Crossref]

2005 (3)

E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
[Crossref]

M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
[Crossref]

D. M. Marom, D. T. Neilson, D. S. Greywall, C.-S. Pai, N. R. Basavanhally, V. A. Aksyuk, D. O. López, F. Pardo, M. E. Simon, Y. Low, P. Kolodner, and C. A. Bolle, “Wavelength-selective 1 x k switches using free-space optics and mems micromirrors: theory, design, and implementation,” J. Lightwave Technol. 23(4), 1620–1630 (2005).
[Crossref]

2004 (2)

J. Li, A. Liu, W. Zhong, Q. Zhang, and C. Lu, “Mems switch based serial reconfigurable oadm,” Opt. Commun. 230(1-3), 81–89 (2004).
[Crossref]

C. Greiner, T. W. Mossberg, and D. Iazikov, “Bandpass engineering of lithographically scribed channel-waveguide bragg gratings,” Opt. Lett. 29(8), 806–808 (2004).
[Crossref]

2003 (1)

C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
[Crossref]

2000 (1)

D. Wiesmann, C. David, R. Germann, D. Emi, and G. Bona, “Apodized surface-corrugated gratings with varying duty cycles,” IEEE Photonics Technol. Lett. 12(6), 639–641 (2000).
[Crossref]

1999 (1)

1997 (1)

T. Erdogan, “Fiber grating spectra,” J. Lightwave Technol. 15(8), 1277–1294 (1997).
[Crossref]

Abakoumov, D.

S. Frisken, G. Baxter, D. Abakoumov, H. Zhou, I. Clarke, and S. Poole, “Flexible and grid-less wavelength selective switch using lcos technology,” in 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference (IEEE, 2011), pp. 1–3.

Abdalla, S.

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

Aksyuk, V. A.

An, J.

D. Wu, Y. Wu, Y. Wang, J. An, and X. Hu, “Reconfigurable optical add-drop multiplexer based on thermally tunable micro-ring resonators,” Opt. Commun. 367, 44–49 (2016).
[Crossref]

Analui, B.

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

Assefa, S.

Ayotte, N.

Baek, Y.

J.-U. Shin, Y.-T. Han, S.-P. Han, S.-H. Park, Y. Baek, Y.-O. Noh, and K.-H. Park, “Reconfigurable optical add-drop multiplexer using a polymer integrated photonic lightwave circuit,” ETRI J 31(6), 770–777 (2009).
[Crossref]

Baghban, M. A.

Bahrami, H.

Bailey, J.

C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
[Crossref]

Baker, N.

E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
[Crossref]

Balmater, E.

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

Barwicz, T.

M. A. Popović, T. Barwicz, F. Gan, M. S. Dahlem, C. W. Holzwarth, P. T. Rakich, H. I. Smith, E. P. Ippen, and F. X. Kärtner, “Transparent wavelength switching of resonant filters,” in Conference on Lasers and Electro-Optics (Optical Society of America, 2007), p. CPDA2.

Basak, J.

A. Liu, L. Liao, Y. Chetrit, J. Basak, H. Nguyen, D. Rubin, and M. Paniccia, “Wavelength division multiplexing based photonic integrated circuits on silicon-on-insulator platform,” IEEE J. Sel. Top. Quantum Electron. 16, 23–32 (2010).
[Crossref]

Basavanhally, N. R.

Baxter, G.

S. Frisken, G. Baxter, D. Abakoumov, H. Zhou, I. Clarke, and S. Poole, “Flexible and grid-less wavelength selective switch using lcos technology,” in 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference (IEEE, 2011), pp. 1–3.

Bedard, S.

Boeck, R.

Bois, A.

Bojko, R.

Bolle, C. A.

Bona, G.

D. Wiesmann, C. David, R. Germann, D. Emi, and G. Bona, “Apodized surface-corrugated gratings with varying duty cycles,” IEEE Photonics Technol. Lett. 12(6), 639–641 (2000).
[Crossref]

Boroojerdi, M.

Buhl, L. L.

Cappuzzo, M.

M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
[Crossref]

C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
[Crossref]

Chatterjee, R.

Chen, E.

M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
[Crossref]

C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
[Crossref]

Chen, L.

Chen, P.

Chen, R. T.

Chen, S.

D. Dai, J. Wang, S. Chen, S. Wang, and S. He, “Monolithically integrated 64-channel silicon hybrid demultiplexer enabling simultaneous wavelength-and mode-division-multiplexing,” Laser Photonics Rev. 9(3), 339–344 (2015).
[Crossref]

Chetrit, Y.

A. Liu, L. Liao, Y. Chetrit, J. Basak, H. Nguyen, D. Rubin, and M. Paniccia, “Wavelength division multiplexing based photonic integrated circuits on silicon-on-insulator platform,” IEEE J. Sel. Top. Quantum Electron. 16, 23–32 (2010).
[Crossref]

Chrostowski, L.

Clarke, I.

S. Frisken, G. Baxter, D. Abakoumov, H. Zhou, I. Clarke, and S. Poole, “Flexible and grid-less wavelength selective switch using lcos technology,” in 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference (IEEE, 2011), pp. 1–3.

Da Ros, F.

Dahlem, M. S.

M. A. Popović, T. Barwicz, F. Gan, M. S. Dahlem, C. W. Holzwarth, P. T. Rakich, H. I. Smith, E. P. Ippen, and F. X. Kärtner, “Transparent wavelength switching of resonant filters,” in Conference on Lasers and Electro-Optics (Optical Society of America, 2007), p. CPDA2.

Dai, D.

D. Dai, J. Wang, S. Chen, S. Wang, and S. He, “Monolithically integrated 64-channel silicon hybrid demultiplexer enabling simultaneous wavelength-and mode-division-multiplexing,” Laser Photonics Rev. 9(3), 339–344 (2015).
[Crossref]

Dai, T.

David, C.

D. Wiesmann, C. David, R. Germann, D. Emi, and G. Bona, “Apodized surface-corrugated gratings with varying duty cycles,” IEEE Photonics Technol. Lett. 12(6), 639–641 (2000).
[Crossref]

de Aguiar, D. O. M.

Ding, Y.

Dixit, H.

D. K. Tripathi, P. Singh, N. Shukla, and H. Dixit, “Reconfigurable optical add and drop multiplexers a review,” ECIJ 3(1), 1 (2014).
[Crossref]

Doerr, C.

C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
[Crossref]

Doerr, C. R.

Driessen, A.

E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
[Crossref]

Dupuis, N.

Earnshaw, M.

M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
[Crossref]

Emi, D.

D. Wiesmann, C. David, R. Germann, D. Emi, and G. Bona, “Apodized surface-corrugated gratings with varying duty cycles,” IEEE Photonics Technol. Lett. 12(6), 639–641 (2000).
[Crossref]

Erdogan, T.

T. Erdogan, “Fiber grating spectra,” J. Lightwave Technol. 15(8), 1277–1294 (1997).
[Crossref]

Fathpour, S.

Ferrari, G.

Flueckiger, J.

Frisken, S.

S. Frisken, G. Baxter, D. Abakoumov, H. Zhou, I. Clarke, and S. Poole, “Flexible and grid-less wavelength selective switch using lcos technology,” in 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference (IEEE, 2011), pp. 1–3.

Fu, Z.

D. Mu, H. Qiu, J. Jiang, X. Wang, Z. Fu, Y. Wang, X. Jiang, H. Yu, and J. Yang, “A four-channel dwdm tunable add/drop demultiplexer based on silicon waveguide bragg gratings,” IEEE Photonics J. 11, 1–8 (2019).
[Crossref]

Gan, F.

M. A. Popović, T. Barwicz, F. Gan, M. S. Dahlem, C. W. Holzwarth, P. T. Rakich, H. I. Smith, E. P. Ippen, and F. X. Kärtner, “Transparent wavelength switching of resonant filters,” in Conference on Lasers and Electro-Optics (Optical Society of America, 2007), p. CPDA2.

Geng, M.

Germann, R.

D. Wiesmann, C. David, R. Germann, D. Emi, and G. Bona, “Apodized surface-corrugated gratings with varying duty cycles,” IEEE Photonics Technol. Lett. 12(6), 639–641 (2000).
[Crossref]

Geuzebroek, D. H.

E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
[Crossref]

Gloeckner, S.

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

Goebuchi, Y.

Y. Goebuchi, T. Kato, and Y. Kokubun, “Fast and stable wavelength-selective switch using double-series coupled dielectric microring resonator,” IEEE Photonics Technol. Lett. 18(3), 538–540 (2006).
[Crossref]

Gomez, L.

M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
[Crossref]

C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
[Crossref]

Green, W. M.

Greiner, C.

Greywall, D. S.

Griffin, A.

M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
[Crossref]

Guckenberger, D.

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

Guglielmi, E.

Hamacher, M.

D. Rabus, M. Hamacher, H. Heidrich, and U. Troppenz, “Box-like filter response of triple ring resonators with integrated soa sections based on gainasp/inp,” in Conference Proceedings. 14th Indium Phosphide and Related Materials Conference (Cat. No. 02CH37307) (IEEE, 2002), pp. 479–482.

Hammood, M.

Han, S.-P.

J.-U. Shin, Y.-T. Han, S.-P. Han, S.-H. Park, Y. Baek, Y.-O. Noh, and K.-H. Park, “Reconfigurable optical add-drop multiplexer using a polymer integrated photonic lightwave circuit,” ETRI J 31(6), 770–777 (2009).
[Crossref]

Han, Y.-T.

J.-U. Shin, Y.-T. Han, S.-P. Han, S.-H. Park, Y. Baek, Y.-O. Noh, and K.-H. Park, “Reconfigurable optical add-drop multiplexer using a polymer integrated photonic lightwave circuit,” ETRI J 31(6), 770–777 (2009).
[Crossref]

Harrison, M.

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

Haus, H. A.

H. A. Haus, M. A. Popovic, and M. R. Watts, “Broadband hitless bypass switch for integrated photonic circuits,” IEEE Photonics Technol. Lett. 18(10), 1137–1139 (2006).
[Crossref]

He, S.

D. Dai, J. Wang, S. Chen, S. Wang, and S. He, “Monolithically integrated 64-channel silicon hybrid demultiplexer enabling simultaneous wavelength-and mode-division-multiplexing,” Laser Photonics Rev. 9(3), 339–344 (2015).
[Crossref]

Heidrich, H.

D. Rabus, M. Hamacher, H. Heidrich, and U. Troppenz, “Box-like filter response of triple ring resonators with integrated soa sections based on gainasp/inp,” in Conference Proceedings. 14th Indium Phosphide and Related Materials Conference (Cat. No. 02CH37307) (IEEE, 2002), pp. 479–482.

Holzwarth, C. W.

M. A. Popović, T. Barwicz, F. Gan, M. S. Dahlem, C. W. Holzwarth, P. T. Rakich, H. I. Smith, E. P. Ippen, and F. X. Kärtner, “Transparent wavelength switching of resonant filters,” in Conference on Lasers and Electro-Optics (Optical Society of America, 2007), p. CPDA2.

Horst, F.

Hosseini, A.

Hu, T.

Hu, X.

D. Wu, Y. Wu, Y. Wang, J. An, and X. Hu, “Reconfigurable optical add-drop multiplexer based on thermally tunable micro-ring resonators,” Opt. Commun. 367, 44–49 (2016).
[Crossref]

Huang, B.

Iazikov, D.

Ippen, E. P.

M. A. Popović, T. Barwicz, F. Gan, M. S. Dahlem, C. W. Holzwarth, P. T. Rakich, H. I. Smith, E. P. Ippen, and F. X. Kärtner, “Transparent wavelength switching of resonant filters,” in Conference on Lasers and Electro-Optics (Optical Society of America, 2007), p. CPDA2.

Jaeger, N. A.

Jamshidi, K.

E. Krune, K. Jamshidi, K. Voigt, L. Zimmermann, and K. Petermann, “Jitter analysis of optical clock distribution networks in silicon photonics,” J. Lightwave Technol. 32(22), 4378–4385 (2014).
[Crossref]

Jean, P.

Jia, L.

Jiang, G.

Jiang, J.

Jiang, X.

Kärtner, F. X.

M. A. Popović, T. Barwicz, F. Gan, M. S. Dahlem, C. W. Holzwarth, P. T. Rakich, H. I. Smith, E. P. Ippen, and F. X. Kärtner, “Transparent wavelength switching of resonant filters,” in Conference on Lasers and Electro-Optics (Optical Society of America, 2007), p. CPDA2.

Kato, T.

Y. Goebuchi, T. Kato, and Y. Kokubun, “Fast and stable wavelength-selective switch using double-series coupled dielectric microring resonator,” IEEE Photonics Technol. Lett. 18(3), 538–540 (2006).
[Crossref]

Kelderman, H.

E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
[Crossref]

Khan, S.

Kimerling, L. C.

Kirk, A.

Klein, E. J.

E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
[Crossref]

Kokubun, Y.

Y. Goebuchi, T. Kato, and Y. Kokubun, “Fast and stable wavelength-selective switch using double-series coupled dielectric microring resonator,” IEEE Photonics Technol. Lett. 18(3), 538–540 (2006).
[Crossref]

Kolodner, P.

Koumanset al., R. G.

A. Narasimha, B. Analui, Y. Liang, T. J. Sleboda, S. Abdalla, E. Balmater, S. Gloeckner, D. Guckenberger, M. Harrison, and R. G. Koumanset al., “A fully integrated 4×10-gb/s dwdm optoelectronic transceiver implemented in a standard 0.13μm cmos soi technology,” IEEE J. Solid-State Circuits 42(12), 2736–2744 (2007).
[Crossref]

Krune, E.

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D. Mu, H. Qiu, J. Jiang, X. Wang, Z. Fu, Y. Wang, X. Jiang, H. Yu, and J. Yang, “A four-channel dwdm tunable add/drop demultiplexer based on silicon waveguide bragg gratings,” IEEE Photonics J. 11, 1–8 (2019).
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M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
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Voigt, K.

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D. Dai, J. Wang, S. Chen, S. Wang, and S. He, “Monolithically integrated 64-channel silicon hybrid demultiplexer enabling simultaneous wavelength-and mode-division-multiplexing,” Laser Photonics Rev. 9(3), 339–344 (2015).
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D. Dai, J. Wang, S. Chen, S. Wang, and S. He, “Monolithically integrated 64-channel silicon hybrid demultiplexer enabling simultaneous wavelength-and mode-division-multiplexing,” Laser Photonics Rev. 9(3), 339–344 (2015).
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D. Wu, Y. Wu, Y. Wang, J. An, and X. Hu, “Reconfigurable optical add-drop multiplexer based on thermally tunable micro-ring resonators,” Opt. Commun. 367, 44–49 (2016).
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Appl. Opt. (1)

ECIJ (1)

D. K. Tripathi, P. Singh, N. Shukla, and H. Dixit, “Reconfigurable optical add and drop multiplexers a review,” ECIJ 3(1), 1 (2014).
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ETRI J (1)

J.-U. Shin, Y.-T. Han, S.-P. Han, S.-H. Park, Y. Baek, Y.-O. Noh, and K.-H. Park, “Reconfigurable optical add-drop multiplexer using a polymer integrated photonic lightwave circuit,” ETRI J 31(6), 770–777 (2009).
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IEEE J. Sel. Top. Quantum Electron. (2)

M. Earnshaw, M. Cappuzzo, E. Chen, L. Gomez, A. Griffin, E. Laskowski, A. Wong-Foy, and J. Soole, “Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module,” IEEE J. Sel. Top. Quantum Electron. 11(2), 313–322 (2005).
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A. Liu, L. Liao, Y. Chetrit, J. Basak, H. Nguyen, D. Rubin, and M. Paniccia, “Wavelength division multiplexing based photonic integrated circuits on silicon-on-insulator platform,” IEEE J. Sel. Top. Quantum Electron. 16, 23–32 (2010).
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IEEE J. Solid-State Circuits (1)

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IEEE Photonics J. (1)

D. Mu, H. Qiu, J. Jiang, X. Wang, Z. Fu, Y. Wang, X. Jiang, H. Yu, and J. Yang, “A four-channel dwdm tunable add/drop demultiplexer based on silicon waveguide bragg gratings,” IEEE Photonics J. 11, 1–8 (2019).
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C. Doerr, L. Stulz, D. Levy, L. Gomez, M. Cappuzzo, J. Bailey, R. Long, A. Wong-Foy, E. Laskowski, E. Chen, S. Patel, and T. Murphy, “Eight-wavelength add-drop filter with true reconfigurability,” IEEE Photonics Technol. Lett. 15(1), 138–140 (2003).
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Y. Goebuchi, T. Kato, and Y. Kokubun, “Fast and stable wavelength-selective switch using double-series coupled dielectric microring resonator,” IEEE Photonics Technol. Lett. 18(3), 538–540 (2006).
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E. J. Klein, D. H. Geuzebroek, H. Kelderman, G. Sengo, N. Baker, and A. Driessen, “Reconfigurable optical add-drop multiplexer using microring resonators,” IEEE Photonics Technol. Lett. 17(11), 2358–2360 (2005).
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D. Dai, J. Wang, S. Chen, S. Wang, and S. He, “Monolithically integrated 64-channel silicon hybrid demultiplexer enabling simultaneous wavelength-and mode-division-multiplexing,” Laser Photonics Rev. 9(3), 339–344 (2015).
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Opt. Commun. (2)

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J. Li, A. Liu, W. Zhong, Q. Zhang, and C. Lu, “Mems switch based serial reconfigurable oadm,” Opt. Commun. 230(1-3), 81–89 (2004).
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Figures (7)

Fig. 1.
Fig. 1. Schematic diagrams of (a) the two-channel hitless ROADM, (b) (c) the adiabatic directional coupler, and (d) the phase apodized waveguide sidewall Bragg grating. In (a), arrows with different colors are used to indicate propagation routes of different wavelengths inside the device. The wavelength $\lambda _1$ meets phase matching conditions of both MASWBGs, $\lambda _2$ only meets the phase matching condition of MASWBG1 but does not meet that of MASWBG2, $\lambda _3$ do not meet the phase matching condition of MASWBG1.
Fig. 2.
Fig. 2. Simulated spectral responses at drop ports of (a) a single MASWBG, (b) the add-drop filter with the central wavelengths of the two MASWBG being well aligned, (c) the add-drop filter with the central wavelengths of the two MASWBG being offset by 0.5 nm, (d) the filter with the central wavelengths of the two MASWBGs being offset by 3.5 nm.
Fig. 3.
Fig. 3. (a) Microscope image of the two-channel ROADM. (b-d) SEM images of the grating corrugation at different positions of the MASWBG. (e) SEM image of the mode (de)multiplexer.
Fig. 4.
Fig. 4. Spectral responses of (a) the reference uniform MASWBG, (b) the phase apodized MASWBG, and the wavelength resolution is 0.1 nm.
Fig. 5.
Fig. 5. Experimental results of tuning central wavelength and bandwidth of channel 1. (a)/(b)/(c) 3 dB bandwidths of pass bands are 2.4/0.7/0.2 nm, and the wavelength resolution are 0.1/0.05/0.05 nm. (d) Relationships between the dropping loss, ripples and SLSR with the 3dB bandwidth of the add-drop filter as a variable.
Fig. 6.
Fig. 6. (a) Setup for the high-speed data transmission measurement. The setup includes a tunable laser, two polarization controllers (PC), a LiNbO3 modulator, a bit pattern generator (BPG), an Er-doped fiber amplifier (EDFA), a tunable bandpass filter, a variable optical attenuator (VOA), and a wide-bandwidth oscilloscope. (b) Eye diagrams of data signals dropped by channel 1 at different data rates and bandwidths.
Fig. 7.
Fig. 7. Hitless switching of the central wavelength of channel 1, and the wavelength resolution of the spectrum is 0.1nm. (a) Spectra measured at the drop ports of the two channels before and after the hitless switching. (b) Spectral responses of channel 1 in 6 intermediate states. (c) Spectral responses of channel 2 in 6 intermediate states. The inset shows the time response of the heater.(d) Spectral responses of the through port in 6 intermediate states. (e) the eye mask of channel 1 and channel 2.

Tables (2)

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Table 1. Heating voltages and central wavelengths of the two MASWBG at six intermediate states.

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Table 2. Comparison of the reported ROADMs on silicon

Equations (2)

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Δ s = Λ 2 e b ( z L / 2 ) 2 L 2
κ = | κ 0 2 κ 0 2 e i 2 π Δ s Λ | = κ 0 sin π Δ s / Λ

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