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Accepted papers to appear in an upcoming issue

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Coherent combining of second harmonic generators by active phase control of the fundamental waves

Alice Odier, Anne Durécu, Jean-Michel Melkonian, Laurent Lombard, Michel Lefebvre, and Pierre Bourdon

Doc ID: 292252 Received 07 Jun 2017; Accepted 21 Jul 2017; Posted 21 Jul 2017  View: PDF

Abstract: Coherent beam combining (CBC) by active phase control could be useful for power scaling fiber-laser-pumped optical frequency converters. However, a fast phase modulator operating at the frequency-converted wavelength, a non-standard component, would be necessary. Fortunately, nonlinear conversion processes rely on a phase-matching condition allowing for indirect phase control using standard phase modulators. In this paper, coherent combining of second harmonic generators is demonstrated in both birefringent and quasi phase matching schemes. Phase control operates at the fundamental wavelength, using all-fibered electro-optic modulators. An excellent beam combination is achieved with a residual phase error of λ/30 on the second harmonic wave.

Reflectionless and invisible potentials in photonic lattices

Stefano Longhi

Doc ID: 297397 Received 05 Jun 2017; Accepted 21 Jul 2017; Posted 21 Jul 2017  View: PDF

Abstract: An arbitrarily-shaped optical potential on a discrete photonic lattice, which transversely drifts at a speed larger than the maximum one allowed by the light cone of the lattice band, becomes reflectionless. Such an in- triguing result, which arises from the discrete transla- tional symmetry of the lattice, is peculiar to discretized light and does not have any counterpart for light scat- tering in continuous optical media. A drifting non- Hermitian optical potential of the Kramers-Kronig type is also an invisible potential, i.e. a discrete optical beam crosses the drifting potential without being distorted, delayed nor advanced.

All-fiber highly-chirped dissipative soliton generation in the telecom range

Denis Kharenko, Innokentiy Zhdanov, Anastasia Bednyakova, Evgeny Podivilov, Mikhail Fedoruk, Alexander Apolonskiy, Sergei Turitsyn, and Sergey Babin

Doc ID: 297821 Received 12 Jun 2017; Accepted 21 Jul 2017; Posted 21 Jul 2017  View: PDF

Abstract: A high-energy (0.93 nJ) all-fiber Erbium femtosecond oscillator operating in the telecom spectral range is proposed and realized. The laser cavity built of commercially available fibers and components combines non-PM and PM parts providing stable generation of highly-chirped (chirp parameter 40) pulses compressed in an output piece of standard PM fiber to 165 fs. The results of numerical simulation agree well with experiment. The analyzed intracavity pulse dynamics enables the classification of the generated pulses as dissipative solitons.

Binary zero-order diffractive and anti-reflective optical elements in silicon for the mid-infrared

Grégoire Smolik and Hans Peter Herzig

Doc ID: 297825 Received 19 Jun 2017; Accepted 21 Jul 2017; Posted 21 Jul 2017  View: PDF

Abstract: We propose a novel method for the design of binary 2-level diffractive optical elements that provide an efficient diffractive function while reducing the reflectivity of a high-index interface. The structure can be fabricated with a single patterning step and is particularly useful for the mid-infrared spectral range. The concept is based on zero-order transmission gratings using subwavelength micro-structures. To demonstrate the concept a Dammann grating has been realized in silicon and characterized in the mid-infrared by scanning the far-field intensity distribution.

Modelling of nonlinearity-compensated optical communication systems considering second-order signal-noise interactions

Nikita Shevchenko, Tianhua Xu, Domanic Lavery, Gabriele Liga, David Ives, Robert Killey, and Polina Bayvel

Doc ID: 296674 Received 24 May 2017; Accepted 20 Jul 2017; Posted 21 Jul 2017  View: PDF

Abstract: An analytical model considering modulation-dependent nonlinear effects and second-order interactions between signal and optical amplifier noise is presented for Nyquist-spaced wavelength-division-multiplexing optical communication systems. System performance of dual-polarisation (DP) modulation formats, such as DP-QPSK, DP-16QAM, and DP-64QAM is investigated using both the analytical model and numerical simulations. A good agreement between analytical and numerical results shows that, in the case of full-field nonlinearity compensation, accounting for second-order interactions becomes essential to predict system performance of both single-channel and multi-channel systems at optimum launched powers and beyond. This effect is validated via numerical simulations for signal bandwidths up to ~1 THz.

Endoscopic forward viewing optical coherence tomography and angiography with MHz swept source

Kaicheng Liang, Osman Ahsen, Zhao Wang, Hsiang-Chieh Lee, Wenxuan Liang, Benjamin Potsaid, Tsung-Han Tsai, Michael Giacomelli, Vijaysekhar Jayaraman, Hiroshi Mashimo, Xingde Li, and James Fujimoto

Doc ID: 296680 Received 26 May 2017; Accepted 20 Jul 2017; Posted 21 Jul 2017  View: PDF

Abstract: Endoscopic optical coherence tomography (OCT) instruments are mostly side viewing and rely on at least one proximal scan, limiting accuracy of volumetric imaging and en face visualization. Previous forward viewing OCT devices had limited imaging speeds. We report a forward viewing fiber scanning 3D-OCT probe with 900 μm field of view and 5 μm transverse resolution, imaging at 1 MHz axial scan rate in the human gastrointestinal tract. The probe is 3.3 mm diameter and 20 mm rigid length, enabling passage through the endoscopic channel. The scanner has 1.8 kHz resonant frequency, and each volumetric acquisition takes 0.17 sec with 2 volumes/sec display. 3D-OCT and angiography imaging of the colon was performed during surveillance colonoscopy.

Heatsink-free CW operation of injection microdisk lasers grown on Si substrate with emission wavelength beyond 1.3 µm

Natalia Kryzhanovskaya, Eduard Moiseev, Yulia Polubavkina, Mikhail Maximov, Marina Kulagina, Sergey Troshkov, Yirii Zadiranov, Yulia Guseva, Andrey Lipovskii, Mingchu Tang, Mengya liao, Jiang Wu, Siming Chen, Huiyun Liu, and Alexey Zhukov

Doc ID: 300606 Received 23 Jun 2017; Accepted 20 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: High-performance injection microdisk lasers grown on Si substrate are demonstrated for the first time. Continuous wave lasing in microlasers with diameters from 14 to 30 µm is achieved at room temperature. The minimal threshold current density of 600 A/cm2 (room temperature, continuous wave regime, heatsink-free uncooled operation) is comparable to that of high-quality microdisk lasers on GaAs substrates. Microlasers on silicon emit in the wavelength range of 1320-1350 nm via the ground state transition of InAs/InGaAs/GaAs quantum dots. High stability of the lasing wavelength (dλ/dI=0.1 nm/mA) and low specific thermal resistance of 4×10-3 оС×cm2/W are demonstrated.

Plasmon coherence determination by nanoscattering

Yahong Chen, andreas norrman, Sergey Ponomarenko, and Ari Tapio Friberg

Doc ID: 301066 Received 30 Jun 2017; Accepted 20 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: We present a simple and robust protocol to recover the second-order field correlations of polychromatic, statistically stationary surface plasmon polaritons (SPPs) from a spectrum measurement in the far zone of a dipolar nanoscatterer. The recovered correlations carry comprehensive information about the spectral, spatial, and temporal coherence of the SPPs. We also introduce and exemplify, for the first time, the two-point Stokes parameters associated with partially coherent SPP fields.

Kerr-lens mode-locked Tm³+:Sc₂O₃ single crystal laser in-band pumped by an Er:Yb fiber MOPA at 1611 nm

Masaki Tokurakawa, eisuke fujita, and Christian Kraenkel

Doc ID: 295658 Received 09 May 2017; Accepted 20 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: We demonstrate a Kerr-lens mode-locked Tm³+:Sc₂O₃ single crystal laser in-band pumped by an Er³+:Yb³+ fiber MOPA at 1611 nm. Pulses as short as 166 fs with an average output power of 440 mW are obtained. The spectral bandwidth and center wavelength are 28.2 nm and 2128 nm, respectively. At a longer pulse duration of 298 fs we obtain 1 W of average output power. The repetition rate is 95 MHz and the conversion efficiency against the absorbed pump power is as high as 47%. To the best of our knowledge, this is the first Kerr-lens mode-locked Tm³+ doped solid state laser.

Lean Analogue Receiver for Coherent Optical Analogue Radio-over-Fiber Transmission

Bernhard Schrenk, Markus Hofer, and Thomas Zemen

Doc ID: 297584 Received 06 Jun 2017; Accepted 19 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: A lean receiver for low-cost coherent optical applications is presented. Conceptual simplicity is guaranteed through use of a monolithic integrated externally modulated laser. Local oscillator and fast photodetector are provided by the distributed feedback section and electro-absorption modulator of the monolithic laser. The injection locking feature, which is obtained in virtue of the in-line configuration of the receiver, guarantees exact frequency translation during coherent reception and obviates the need for digital signal processing typically employed for the purpose of signal recovery. The proposed receiver is experimentally demonstrated for wired multi-carrier and analogue transmission of wireless radio signals. Nyquist-shaped frequency division multiplexing with data rates of up to 10 Gb/s and real-time transmission of 64-ary quadrature amplitude modulated narrowband orthogonal frequency division multiplexed radio signals is shown for an optical loss budget of 31 dB.

Investigating the impact of initial geometric layout on topology-optimized metagrating performance

Jianji Yang and Jonathan Fan

Doc ID: 298102 Received 27 Jun 2017; Accepted 19 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: Topology optimization is a powerful inverse design technique in metasurface engineering and can transform an initial layout into a high performance device. With this method, devices are optimized within a local design phase space, making the identification of suitable initial geometries essential. In this Letter, we examine the impact of initial geometric layout on the performance of large-angle (75 degree) topology-optimized metagrating deflectors. We find that when conventional metasurface designs based on dielectric nanoposts are used as initial layouts for topology optimization, the final devices have efficiencies around 66%. In contrast, when random initial layouts are used, the final devices have ultra-high efficiencies that can reach 94%. Our numerical experiments suggest that device topologies based on conventional metasurface designs may not be suitable to produce ultra-high efficiency, large-angle metasurfaces. Rather, initial geometric layouts with non-trivial topologies and shapes are required.

Silicon nanobeam cavity for ultra-localized light-matterinteraction

Weiwei Zhang, samuel serna, Xavier LE ROUX, Laurent Vivien, and Eric Cassan

Doc ID: 292967 Received 26 Apr 2017; Accepted 19 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: In this work, we theoretically and experimentally demonstrate an air mode silicon nanobeam cavity design unusually with dielectric mirrors. This designcombines an extremely strong localization of light matter interaction in the cavity center and a reduced sensitivity of the resonator wavelength to temperature or top cladding material refractive index variations. Theproposed approach allows an accurate control of the resonator cavity quality factor combined with a flexible choice of the cavity effective mode volume. Qfactors higher than 50,000 have been determined for such cavities and mode volumes smaller than (λ/n)^3 were achieved in the investigated configurations. Such a cavity design provides a robust approach to study thehybrid integration of various active materials in the silicon platform, including carbone nanotubes, III-V nanowires, graphene, etc, for light emission, modulation or detection

Precision wander model of beam wave in the weak to strong turbulence of atmosphere

Qiu Wang, Yun Zhu, and YiXin Zhang

Doc ID: 296928 Received 29 May 2017; Accepted 19 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: We present a new beam wander model valid in all irradiance fluctuation regions by using extended Rytov theory with large-scale and small-scale filters. Comparing the calculated results of our wander model and commonly used models with the experiment data obtaining in the case of different propagation distance, waist radius of beam wave, the outer scale of turbulence and turbulence strength, our new theory gives better agreement with the experimental results than others do.

Axial sub-Fourier focusing of an optical beam

Thomas Zacharias, Barak Hadad, Alon Bahabad, and Yaniv Eliezer

Doc ID: 300414 Received 20 Jun 2017; Accepted 18 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: We demonstrate experimentally the generation of an optical beam having an axial focusing which is narrower than the Fourier limit. The beam is constructed from a superposition of Bessel beams with different longitudinal wave vectors, realizing a super-oscillatory axial intensity distribution. Such beams can be useful for microscopy and for optical particle manipulation

Multifrequency Excitation and Detection Scheme in Apertureless Scattering Near Field Scanning Optical Microscopy

Hadar Greener, Michael Mrejen, Uri Arieli, and Haim Suchowski

Doc ID: 298072 Received 20 Jun 2017; Accepted 18 Jul 2017; Posted 19 Jul 2017  View: PDF

Abstract: Near-field scanning optical microscopy has revolutionized the study of fundamental physics, as it is the only optical non-invasive nanoscale-resolved imaging technique. However, its resolution remains strongly limited by the poor discrimination of weak near-field optical signals from far-field background. Here, we theoretically and experimentally demonstrate a multifrequency excitation and detection scheme in apertureless near field optical microscopy, that exceeds current state of the art sensitivity and background suppression. We achieved a two-fold enhancement in sensitivity, and deep sub-wavelength resolution of λ/ 0 in optical measurements. This method offers rich control over experimental degrees of freedom, breaking the ground for non-interferometric complete phase and amplitude retrieval of the near field signal.

1.5 kW efficient CW Nd:YAG planar waveguide MOPA laser

Juntao Wang, Zhenhai Wu, Hua Su, Tangjian Zhou, jun lei, Wenqiang Lv, Jing He, Liu Xu, Yuejian Chen, Dan Wang, Lixin Tong, Hao Hu, Qingsong Gao, and Chun Tang

Doc ID: 292148 Received 13 Jun 2017; Accepted 18 Jul 2017; Posted 18 Jul 2017  View: PDF

Abstract: In this Letter we report a 1064 nm continuous wave (CW) Nd:YAG planar waveguide laser with an output power of 1544 W based on the structure of master oscillator power amplification (MOPA). A fiber laser is acted as the seeder source, and the waveguide laser amplifier is performed with the pumping of diode laser arrays (DLAs). . The dimension of the waveguide is 1 mm (T) × 10 mm (W) × 60mm (L), and the dual end oblique pumping is adopted with different angles. After a single pass amplification, the power is scaled from 3 W to 1544 W with the pump power of 2480 W, leading to an optical to optical efficiency of 49%. At the maximum output, the beam quality M2 are measured to be 2.8 and 7.0 in the guided direction and the unguided direction, respectively. To the best of our knowledge, it is up to now the highest output power in Nd:YAG planar waveguide laser.

High-sensitivity and large-dynamic-range refractive index sensors employing weak composite Fabry-Perot cavities

Pengcheng Chen, Xuewen Shu, Haoran Cao, and Kate Sugden

Doc ID: 295907 Received 12 May 2017; Accepted 17 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: Most sensors face a common tradeoff between high sensitivity and large dynamic range. We demonstrate here an all-fiber refractometer based on a composite intrinsic Fabry-Perot interferometer (FPI), which possesses the co-existence advantages of high sensitivity and large dynamic range. Since the two composite cavities have a large cavity length difference, one can observe both fine and coarse fringes, which correspond to the long cavity and short cavity, respectively. Due to the short FPI and the use of an intensity demodulation method, the different fine fringe dips correspond to a series of quasi-continuous highly sensitive zones for refractive index measurement. By calculating the parameters of the composite FPI, we find that the range of the ultra-sensitive zones can be considerably adjusted. Experimental trends are in good agreement with the theoretical predictions. The co-existence of high sensitivity and large dynamic range in a composite FPI is of great significance to practical RI measurement.

Accurate analysis of mechanical stress in dielectric multilayers

Thomas Begou and Julien Lumeau

Doc ID: 300906 Received 23 Jun 2017; Accepted 17 Jul 2017; Posted 18 Jul 2017  View: PDF

Abstract: We present a systematic study of stress coefficient of dielectric materials (SiO2, Nb2O5 and HfO2). In particular, we show a thickness dependence of the stress coefficient on layer thickness which shows that the determination of this coefficient is complex and requires careful analysis. We then apply the different models of stress coefficient to multilayer structures and show that stress-induced deformation can be precisely predicted in final components with a few percent accuracy.

Direct coupling of tomography and ptychography

Doga Gursoy

Doc ID: 296918 Received 06 Jun 2017; Accepted 16 Jul 2017; Posted 18 Jul 2017  View: PDF

Abstract: A generalization of the ptychographic phase problem is presented in recovering three-dimensional (3D) refractive properties of an object in a tomography setting. This approach allows to reconstruct 3D objects by fully ignoring the data redundancy condition in the form of overlapping areas of adjacent scan tiles, enabling highly flexible acquisition patterns, and can pave the way for sparse data collection with significantly less radiation dose.

Enhanced depth-of-field of integral imaging microscope using bifocal holographic optical element- micro lens array

Ki-Chul Kwon, Young-Tae Lim, Chang-Won Shin, Munkh-Uchral Erdenebat, Jae-Moon Hwang, and Nam Kim

Doc ID: 297187 Received 05 Jun 2017; Accepted 16 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: We propose and implement an integral imaging microscope with extended depth-of-field using a bifocal holographic micro lens array. The properties of the two micro lens arrays are switched via peristrophic multiplexing, where different properties of the micro lens array are recorded onto the single holographic optical element. The recorded micro lens array properties are perpendicular to each other: after the first mode is recorded, the holographic optical element is rotated by 90° clockwise, and the second mode is recorded. Experimental results confirm that the depth-of-field of integral imaging microscopy system is extended successfully by using the bifocal micro lens array.

Optical frequency combs generated mechanically

Misha Sumetsky

Doc ID: 296977 Received 29 May 2017; Accepted 15 Jul 2017; Posted 18 Jul 2017  View: PDF

Abstract: An elongated bottle microresonator with nanoscale parabolic effective radius variation can possess series of dense equally spaced optical eigenfrequencies which separation can match the eigenfrequency of its axially symmetric acoustic mode. It is shown that this acoustic mode can parametrically excite optical modes and give rise to a highly equidistant and moderately broadband optical frequency comb with the teeth spacing independent of the input laser power and the amplitude of mechanical vibrations.

Fano-resonance-based mode-matching hybrid metasurface for enhanced second-harmonic generation

Zhi Li, Wenwei Liu, Zhancheng Li, Hua Cheng, Shuqi Chen, and jianguo tian

Doc ID: 301177 Received 28 Jun 2017; Accepted 14 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: Plasmonic nanostructures have been considered as potential candidates for enhancing the nonlinear upconversion rate at nanoscale levels due to their strong near-field enhancement. Here, we propose a Fano-resonance-based mode-matching hybrid metasurface that combines the advantages of Fano resonances and mode-matching for boosting second-harmonic conversion. A confined and strong near-field intensity is generated by gold nanoantennas within the volume of polycrystalline zinc sulfide nanoparticles, thus resulting in a larger effective second-harmonic coefficient. The combination of the abovementioned features allows for the realization of a second-harmonic generation (SHG) conversion efficiency of 5.55 × 10−8, and the SHG signal is twice that obtained with dipole hybrid metasurfaces. Our designed metasurface may pave the way for optimizing nonlinear light–matter interactions at the nanoscale.

Two-Photon Absorption and Subband Photodetection in Monolayer MoS₂

FENG ZHOU and Wei Ji

Doc ID: 296622 Received 01 Jun 2017; Accepted 14 Jul 2017; Posted 18 Jul 2017  View: PDF

Abstract: We develop a theoretical model to quantify the two-photon absorption (2PA) coefficients of monolayer MoS₂. Based on two-dimensional excitons, our model reveals the 2PA coefficient spectrum on the order of 0.01 ~ 0.1 cm/MW in the near-infrared for monolayer MoS₂. As compared to the band theory for bulk semiconductors, these coefficients are enhanced by at least one order of magnitude. Our model is in agreement with light-intensity-dependent photocurrent measurements on a monolayer-MoS₂, subband photodetector with femtosecond laser pulses.

Quantum temporal imaging by four-wave mixing

Junheng Shi, Giuseppe Patera, Mikhail Kolobov, and Shensheng Han

Doc ID: 300727 Received 27 Jun 2017; Accepted 14 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: We investigate temporal imaging of broadband squeezed light by four-wave-mixing. We consider two possible imaging configurations: phase-conjugating and phase-preserving. Both of these configurations have been successfully used for temporal imaging of classical temporal waveforms.We demonstrate that for quantum temporal imaging, precisely, temporal imaging of broadband squeezed light, these two schemes have very different behavior: the phase-conjugating configuration deteriorates squeezing, while the phase-preserving leaves it intact. These results are very important for applications of temporal imaging for quantum communications and quantum information processing.

SPARSE (Spatially PhAse-Retarded Spectroscopic Ellipsometry) for real-time film analysis

Ki-Nam Joo, Young Ho Yun, and Dae Hee Kim

Doc ID: 298317 Received 16 Jun 2017; Accepted 14 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: In this letter, we propose a novel type of spectroscopic ellipsometer, named as SPARSE based on the spatial polarization distribution opposed to the temporal polarization changes. SPARSE can collect all information, necessary to characterizing film structures, with a single image acquisition and it has the benefit of real-time measurements. For the verification, feasible experiments with single film layered CRMs and multi-layered film specimens were carried out.

Modulated Vortex Six-Wave Mixing

Dan Zhang, xing liu, LINGMENG YANG, XINGHUA Li, Zhaoyang Zhang, and Yanpeng Zhang

Doc ID: 296136 Received 29 May 2017; Accepted 14 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: We experimentally generated vortex six-wave mixing (SWM) signal via Photonic Band Gap (PBG) structure in an atomic ensemble for the first time. The output of SWM carrying orbital angular momentum-transmitted from the orbital angular momenta of probe beam has the interaction with the nonlinear effect in hot rubidium atomic system. Our results show that spatial SWM image can be modulated by the detuning and the power of related generating fields. Also, the nonreciprocal specialty of the SWM signal is observed here. Such characteristics can be used in information communication potentially.

Spectral broadening of picosecond pulses forming dispersive shock waves in optical fibers

Alexandre Parriaux, Matteo Conforti, Abdelkrim Bendahmane, Julien Fatome, Christophe Finot, Stefano Trillo, Nathalie Picque, and Guy Millot

Doc ID: 296357 Received 19 May 2017; Accepted 13 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: We investigate analytically, numerically and experimentally the spectral broadening of pulses that undergo the formation of dispersive shocks, addressing in particular pulses in the range of tens of ps generated via electro-optic modulation of a continuous-wave laser. We give an analytical estimate of the maximum spectral extension and show that super-Gaussian waveforms favor the generation of flat-topped spectra. We also show that the weak residual background of the modulator produces undesired spectral ripples. Spectral measurements confirm our estimates and agree well with numerical integration of the nonlinear Schrödinger equation.

High Extinction ratio TE/TM selective Bragg grating filters on silicon-on-insulator

Charalambos Klitis, Giuseppe Cantarella, Michael Strain, and Marc Sorel

Doc ID: 295587 Received 10 May 2017; Accepted 13 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: We report on the design and fabrication of TE and TM polarisation selective Bragg gratings filters in the form of sinusoidal perturbations on the waveguide sidewall and etched holes on the top of the waveguide respectively. Combining the two geometries on a silicon-on-insulator waveguide resulted in Bragg grating filters with high extinction ratios of approximately 60 dB.

Nano/micro dual-scale textured antireflective subwavelength structures in anisotropically etched GaAs

Kyunghwan Kim, Yunwon Song, and Jungwoo Oh

Doc ID: 300601 Received 23 Jun 2017; Accepted 13 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: Light absorption enhancement by surface texturing is widely used to improve the performance of optoelectronic devices. In this study, we demonstrate nano/micro dual-scale textured GaAs by integrating triangular GaAs by orientation-dependent wet etching and subwavelength nanoholes by metal-assisted chemical etching (MacEtch). This is the first report on nano/micro dual-scale textured GaAs. The reflectance was adjusted by controlling the aspect ratio of the nanoholes by varying the MacEtch duration. The combination of the microstructure and subwavelength structures significantly reduced the solar weighted reflectance of GaAs by 72%.

Two-stage Crosstalk Mitigation in an Orbital Angular Momentum-based Free-space Optical Communication System

Zhen Qu and Ivan Djordjevic

Doc ID: 301010 Received 26 Jun 2017; Accepted 13 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: We propose and experimentally demonstrate a two-stage crosstalk mitigation method in an orbital angular momentum (OAM) based free-space optical (FSO) communication system, which is enabled by combining spatial offset and low-density parity-check (LDPC) coded nonuniform signaling. Different from traditional OAM multiplexing, where the OAM modes are centrally aligned for co-propagation, the adjacent OAM modes (OAM states 2 and -6, and OAM states -2 and 6) in our proposed scheme are spatially offset to mitigate the mode crosstalk. Different from traditional rectangular modulation formats, which transmit equidistant signal points with uniform probability, the 5-quadrature amplitude modulation (5-QAM) and 9-QAM are introduced to relieve crosstalk induced performance degradation. The 5-QAM and 9-QAM formats are based on Huffman coding technique, which can potentially achieve great crosstalk tolerance by combining them with corresponding nonbinary LDPC codes. We demonstrate that crosstalk can be reduced by 1.6 dB and 1 dB via spatial offset for OAM states ±2, and ±6, respectively. Compared to quadrature phase shift keying (QPSK) and 8-QAM formats, the LDPC coded 5-QAM and 9-QAM are able to bring 1.1 dB and 5.4 dB performance improvements in the presence of atmospheric turbulence, respectively.

Bi-directional top hat D-Scan: single beam accurate characterization of nonlinear waveguides

Nicolas Dubeuil and Samuel Serna Otálvaro

Doc ID: 295339 Received 15 May 2017; Accepted 12 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: The characterization of a third order nonlinear integrated waveguide is reported for the first time by means of a top-hat Dispersive-Scan (D-Scan) technique, a temporal analog of the top-hat Z-Scan. With a single laser beam, and by carrying two counter-directional nonlinear transmissions to assess the input and output coupling efficiencies, a novel procedure is described leading to an accurate measurement of the TPA figure of merit, the effective Two-Photon Absorption (TPA) and optical Kerr (including the sign) coefficients. The technique is validated in a silicon strip waveguide for which the effective nonlinear coefficients are measured with an accuracy of ±10%.

Pump-linewidth-tolerant wavelength multicasting using soliton Kerr frequency combs

Peicheng Liao, Changjing Bao, Arne Kordts, Maxim Karpov, Martin Pfeiffer, Lin Zhang, Yinwen Cao, Ahmed Almaiman, Amirhossein Mohajerin Ariaei, Moshe Tur, Martin Fejer, Tobias Kippenberg, and Alan Willner

Doc ID: 296958 Received 29 May 2017; Accepted 12 Jul 2017; Posted 19 Jul 2017  View: PDF

Abstract: We experimentally demonstrate pump-linewidth-tolerant wavelength multicasting using microresonator-based soliton Kerr frequency combs. When Kerr comb lines serve as coherent pumps in a periodically poled lithium niobate waveguide, the linewidth of the multicast signal almost remains that of the original signal at different linewidths of Kerr combs ranging from 100 kHz to 1 MHz. However, in the conventional multicasting where free-running (FR) pumps are used, the linewidth of the converted signal significantly increases. Furthermore, the error vector magnitude (EVM) performance demonstrates eight-fold error-free multicasting of 10 Gbaud 16-quadrature amplitude modulation signals, even when the linewidths of Kerr combs are as broad as 1 MHz (no Kalman filtering algorithm in the receiver). In contrast, the EVM performance of the signal copy is degraded with a FR laser as a dummy pump.

Beam folding analysis and optimization of mask-enhanced toroidal multipass cells

Manuel Graf, Herbert Looser, Lukas Emmenegger, and Bela Tuzson

Doc ID: 297089 Received 12 Jun 2017; Accepted 12 Jul 2017; Posted 19 Jul 2017  View: PDF

Abstract: We present computational and experimental investigations of the beam folding properties and fringe suppression capabilities in monolithic toroidal multipass cells when combined with absorption masks.Coherent field simulations based on Fresnel-Huygens theory were performed to understand the effect of multiple field truncations in such an optically semi-unstable mirror arrangement.The explicit numerical calculation of the radiation field at each reflection allows detailed optimization and performance analysis.We experimentally verified the evolving irradiance distributions and identified optimal initial field configurations. Furthermore, we suggest a proxy to estimate the noise level for specific initial conditions.These insights pave the way to a better optical performance and thus to even more lightweight and compact designs of this multipass cell type.

Optical time domain reflectometry based on Brillouin dynamic grating in an elliptical-core two-mode fiber

Kwang Yong Song and Yong Hyun Kim

Doc ID: 292998 Received 18 Apr 2017; Accepted 12 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: Optical time domain reflectometry based on Brillouin dynamic grating (BDG-OTDR) in an elliptical-core two-mode fiber (e-core TMF) is proposed and experimentally demonstrated for discriminative measurement of strain and temperature distribution. Acoustic gratings are generated by the spontaneous Brillouin scattering of a pump pulse in the LP01 mode of x- and y-polarizations, which are used to reflect a probe pulse in the LP11 mode of x-polarization by intermodal BDG operation. Distribution maps of intermodal and polarization birefringence are acquired by analyzing the two BDG spectra, which are used to separately measure the temperature and strain distributions. In experiments distributed measurement of intermodal BDG spectra along a 95 m e-core TMF is performed with 2 m spatial resolution, where strain and temperature coefficients of the BDG spectral shift are measured to be ‒0.085 MHz/με, +7.6 MHz/°C for the pump-probe of the LP01y-LP11x mode, and ‒0.093 MHz/με, +4.3 MHz/°C for the LP01x-LP11x mode, respectively. Distribution maps of the strain and temperature variation along the TMF are separately obtained by matrix calculation using the four coefficients with an error of ±119.3 με in strain and ±1.5 °C in temperature, respectively.

Dual-angle, spectral reconstruction imaging method for the determination of dielectric thin film thickness

Jennifer Kruschwitz and Roy Berns

Doc ID: 296757 Received 26 May 2017; Accepted 12 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: The thickness of optical films, such as dielectrics, can be determined by the use of a profilometer or by a spectrophotometer. Some physical or optical methods used for film thickness determination can be destructive, time consuming, and/or expensive depending on the method used. Digital cameras are becoming more common in everyday use due to their accessibility and low cost. This work reviews a simple method for determining the physical thickness of a dielectric film on a silicon wafer using two images from a digital camera.

Beyond the perturbative description of the nonlinear optical response of low-index materials

Orad Reshef, Enno Giese, M. Zahirul Alam, Israel De Leon, Jeremy Upham, and Robert Boyd

Doc ID: 295952 Received 30 May 2017; Accepted 11 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: We show that standard approximations in nonlinear optics are violated for situations involving a small value of the linear refractive index. Consequently, the conventional equation for the intensity-dependent refractive index, n(I) = n0 + n2I, becomes inapplicable in epsilon-near-zero and low-index media, even in the presence of only third-order effects. For the particular case of indium tin oxide, we find that the χ(3), χ(5) and χ(7) contributions to refraction eclipse the linear term; thus, the nonlinear response can no longer be interpreted as a perturbation in these materials. Although the response is non-perturbative, we find no evidence that the power series expansion of the material polarization diverges.

Transmissive single-beam-splitter resonator optic gyro based on hollow-core photonic-crystal fiber

Hongchen Jiao, Li Shuang Feng, Junjie Wang, Kai Wang, and Yang Zhaohua

Doc ID: 292219 Received 11 Apr 2017; Accepted 11 Jul 2017; Posted 11 Jul 2017  View: PDF

Abstract: We propose a transmissive single-beam-splitter resonator optic gyro based on a hollow-core photonic-crystal fiber (HCPCF), which is a new regime of resonator fiber optical gyros based on HCPCF (HC-RFOG), for the first time. We evaluate the transfer function of this novel transmissive single-beam-splitter resonator, and the resonance characteristics are simulated to optimize the element parameters. We utilize a micro-optical coupler formed by pairs of lenses and one filter to realize this novel resonator. Our approach yields a finesse of 12 and a transmittance of about 5%. Based on this novel resonator, we construct a HC-RFOG, and we simulate and analyze the effects of polarization noise on the gyro system. In addition, effective method to suppress polarization noise are employed and their efficacy confirmed by experiments. A bias stability of 1.3 °/h is successfully demonstrated, which is the best result reported to date, to the best of our knowledge, for RFOGs based on a HCPCF resonator.

Whispering-gallery-mode laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry

Gang Zhao, Thomas Hausmaninger, Weiguang Ma, and Ove Axner

Doc ID: 297247 Received 01 Jun 2017; Accepted 11 Jul 2017; Posted 12 Jul 2017  View: PDF

Abstract: Whispering-gallery-mode (WGM) lasers are a type of laser that has an exceptionally narrow line width. Noise-immune cavity-enhanced optical heterodyne molecular spectrometry, which is a detection technique with extraordinary properties that benefit from narrow line width lasers, has been realized with a WGM laser. By locking to a cavity with a finesse of 55 000, acetylene and carbon dioxide could be simultaneous detected down to an unprecedented detection sensitivity of 6.6×10-14 cm-1 over 150 s, corresponding to 5 ppt of C₂H₂.

Noninvasive measurement of tissue blood oxygenation with Cerenkov imaging during therapeutic radiation delivery

Xiaofeng Zhang, Sai Kit Lam, Gregory Palmer, Shiva Das, Mark Oldham, and Mark dewhirst

Doc ID: 300529 Received 20 Jun 2017; Accepted 11 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: Tumor tissue oxygenation significantly affects the outcome of radiotherapy. Real-time monitoring of tumor hypoxia is highly desirable for effective radiotherapy and is the basis for improved treatment because hypoxic tumor cells are more resistant to radiation damage than fully oxygenated cells. We propose to use Cerenkov imaging to monitor tumor hypoxia by means of tissue blood oxygenation without the need for any exogenous contrast agent. Using a rodent hypoxia model, we demonstrate that Cerenkov imaging can be used as a noninvasive and noncontact method to measure tissue blood oxygenation level during radiation delivery. The data from Cerenkov imaging were validated using near infrared spectrometry methods. The results demonstrate the feasibility of using Cerenkov imaging to monitor tumor hypoxia during therapeutic radiation delivery.

5 W output power from a double-clad hybrid fiber with Yb-doped phosphate core and silicate cladding

Longfei Wang, Dongbing He, Lei Zhang, Chunlei Yu, Suya Feng, Meng Wang, Danping Chen, and Lili Hu

Doc ID: 298131 Received 14 Jun 2017; Accepted 10 Jul 2017; Posted 11 Jul 2017  View: PDF

Abstract: We report on, for the first time to knowledge, realization of laser from an Yb-doped phosphate core/silicate cladding double-clad hybrid fiber. 5 W output power was extracted with 14.6% slope efficiency and laser spectrum of 1027 nm central wavelength from a 20 cm long single-mode fiber with ~10 μm core diameter in a 20%-4% laser cavity. The laser efficiency at 1027 nm can be significantly enhanced and the laser at ~1018 nm might also be realized by correspondingly manipulating and optimizing the laser oscillator.

Improved performance of transparent conducting AZO/Cu/AZO multilayer thin films by inserting a metal Ti layer for flexible electronics

Shihui Yu, Yifan Liu, Haoran Zheng, Lingxia Li, and Yongtao Sun

Doc ID: 294966 Received 04 May 2017; Accepted 10 Jul 2017; Posted 12 Jul 2017  View: PDF

Abstract: In order to improve the performance of transparent conductive Al doped ZnO (AZO)/Cu/Al doped ZnO multilayer thin films, multilayer thin films of titanium–embedded AZO/Cu/AZO structures have been designed and deposited onto flexible polycarbonate substrates to develop an indium free transparent flexible electrode. The effect of Ti layer on the structural, optical and electrical properties of multilayer thin films was investigated. The experiments revealed that the AZO/Ti/Cu/AZO fabricated in argon-oxygen mixtures has the best performance (figure of merit of 3. ×10–2 Ω–1): resistivity of 3.85×10–5 Ω∙cm, sheet resistance of 4.31 Ω/sq., carrier concentration of 1.65×1022 cm–3, mobility of 9.87 cm2/Vs, and acceptable average transmittance of above 82 % in the visible range.

Generating broadband vortex modes in ring core fiber by using plasmonic q-plate

Jingfu Ye, Yan Li, Yanhua Han, Duo Deng, Xiaoya Su, He Song, Jianmin Gao, and Shiliang Qu

Doc ID: 295214 Received 08 May 2017; Accepted 10 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: A mode convertor was proposed and investigated for generating vortex modes in ring core fiber based on plasmonic q-plate (PQP), which is composed of specially organized L-shaped resonator (LSR) arrays. Multicore fiber was used to split fundamental mode in Single Mode Fiber (SMF) and the LSR arrays were used to convert phases of these fundamental modes in multicore fiber. The transmitted fundamental modes with gradient phase distribution behind PQP can be considered as the incident light for generating broadband vortex modes in ring core fiber. The topological charges of generated vortex modes can be various by using an optical PQP with different q and the chirality of the generated vortex mode can be controlled by the handedness of the incident circularly polarized light. The operation bandwidth is 800nm in the range of 1200nm-2000nm, which covers six communication bands from O to U band. The separation of vortex modes also was discussed by using dual ring core fiber. The mode convertor is of potential interest for connecting traditional network and vortex communication network.

Efficient method for the measurement of lifetime optical damage performance of thin film coatings from laser damage size analysis

Selim Elhadj and Jae Hyuck Yoo

Doc ID: 297335 Received 06 Jun 2017; Accepted 10 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: A laser damage test method based on damage size analysis is described that simplifies the derivation of the lifetime optical damage threshold of film materials critical in the design of devices used in high rep-rate, high power laser systems. The Damage Size Analysis (DSA) method presented here is solely based on imaging to measure the damage site size produced from exposure to a known Gaussian shaped beam with a fixed, systematically selected fluence well above the ablation threshold. The method locates the damage boundary produced from repeated exposures, using images with high contrast, and maps it to the beam profile to extract a lifetime laser damage fluence threshold value. We validate the DSA approach using a few relevant transparent film material systems and by comparing it to the standard S/1 laser damage test method. The DSA method can be more efficient and accelerate materials development and validation necessary to support the design of high power optoelectronics devices.

A tunable photonic radiofrequency filter with complementary bandpass and bandstop responses

Peixuan Li, Wei Pan, Xihua Zou, Lianshan Yan, and Yan Pan

Doc ID: 297969 Received 12 Jun 2017; Accepted 10 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: A photonic radiofrequency (RF) filter with two complementary bandpass and bandstop responses, capable of simultaneously providing a single transmission channel at one port and a notch rejection channel at the other port, is proposed. An integrated polarization division-multiplexing Mach–Zehnder modulator and the in-fiber stimulated Brillouin scattering effect are used to control the amplitudes and phases of the RF modulation sidebands along two orthogonal states of polarization, to generate two complementary bandpass and bandstop responses at two output ports, respectively. Experiments are then performed. Two complementary responses are simultaneously generated in a high frequency resolution of ~20 MHz, with a rejection over 35 or 51 dB being achieved for the passand or stopband. A tunable central frequency to the bandpass and bandstop responses is also demonstrated within the range from 3 to 15 GHz.

Extreme events induced by collisions in a forced semiconductor laser

Pierre Walczak, Cristina Rimoldi, François Gustave, Lorenzo Columbo, Massimo Brambilla, Franco Prati, Giovanna Tissoni, and Stephane Barland

Doc ID: 295158 Received 10 May 2017; Accepted 10 Jul 2017; Posted 10 Jul 2017  View: PDF

Abstract: We report on the experimental study of an optically driven multimode semiconductor laser with 1 m cavity length. We observed a spatiotemporal regime where real time measurements reveal very high intensity peaks in the laser field. Such a regime, which coexists with the locked state and with stable phase solitons, is characterized by the emergence of extreme events which produce a heavy tail statistics in the probability density function. We interpret the extreme events as collisions of spatiotemporal structures with opposite chirality. Numerical simulations of the semiconductor laser model, showing very similar dynamical behavior, substantiate our evidences and corroborate the description of such interactions as collisions between coherent solitonic structures with different phase rotations.

Measurable lower limit of thin film conductivity with parallel plate waveguide terahertz time domain spectroscopy

Masayoshi Tonouchi, Shohei Ohashi, Iwao Kawayama, Hironaru Murakami, Annick Degardin, Alain Kreisler, and Manjakavahoaka Razanoelina

Doc ID: 295526 Received 10 May 2017; Accepted 09 Jul 2017; Posted 10 Jul 2017  View: PDF

Abstract: Parallel plate waveguide (PPWG) in the terahertz (THz) time domain spectroscopy (TDS) is a powerful tool to investigate the properties of thin and low conductive materials. In this letter, we determine the lower limit of detection of the PPWG – THz – TDS approach. We provide a closed-form expression of the minimal measurable conductivity by the system. The experimental results of amorphous YBa2Cu3O7-δ films indicate that the factors limiting the spectroscopic modality is the waveguide device misalignment. On the other hand, the expression of the minimal detectable conductivity provides a clear scheme of optimization by increasing the waveguide length and therefore enhancing the sensitivity of the system.

Photo-induced terahertz radiation and negative conductivity dynamics in Heusler alloy Co2MnSn film

Shunnong Zhang, Zuanming Jin, Xiumei Liu, Wanying Zhao, Xian Lin, Chao Jing, and Guo-Hong Ma

Doc ID: 295524 Received 09 May 2017; Accepted 09 Jul 2017; Posted 12 Jul 2017  View: PDF

Abstract: We report the broadband terahertz (THz) radiation in ferromagnetic half-metallic Heusler alloy Co2MnSn thin film upon the irradiation of a femtosecond laser pulse at room temperature. The magnetic-, sample symmetry-, and pump fluence-dependent THz emission reveal that the THz radiation is originated from the magnetic-dipole radiation, i.e. the light-induced sub-picosecond demagnetization. In addition, by optical pump-THz probe spectroscopy, we found that the photo-excited increase of the scattering rate of hot carriers, thereby leads to the photo-induced negative THz conductivity in Co2MnSn thin film.

Distributed Feedback Lasers with AlternatingLaterally-Coupled Ridge-Waveguide Surface Gratings

Topi Uusitalo, Heikki Virtanen, Maija Karjalainen, Sanna Ranta, Jukka Viheriala, and Mihail Dumitrescu

Doc ID: 297668 Received 13 Jun 2017; Accepted 09 Jul 2017; Posted 18 Jul 2017  View: PDF

Abstract: Distributed feedback lasers with laterally-coupledridge waveguide surface gratings having the protrusions placed alternately on the lateral sides of the ridgeare demonstrated. This configuration enables the fabrication of gratings with wider trenches than in the gratings having the protrusions placed symmetrically onboth sides of the ridge. The design strategy and coupling coefficient calculations are discussed. The outputcharacteristics of fabricated lasers show lower threshold currents and higher slope efficiencies for deviceswith 1st-order alternating gratings than for those with3rd-order symmetrical gratings having comparable grating trench widths.

All-Positive-Coefficient Microwave Photonic Filter with Rectangular Response

Zhijing Zhu, Hao Chi, Tao Jin, Shilie Zheng, Xiaofeng Jin, and Xianmin Zhang

Doc ID: 297790 Received 09 Jun 2017; Accepted 07 Jul 2017; Posted 11 Jul 2017  View: PDF

Abstract: In conventional approaches to realizing microwave photonic filters (MPFs) with rectangular response, both positive and negative coefficients should be included in the systems, which is a difficulty in the incoherent MPFs. Electrical or optical ways to realize the MPFs with bipolar taps, such as those using balanced detectors or based on two opposite modulation slopes of dual-input Mach-Zehnder modulators, usually involve more components compared to the MPFs with all positive coefficients. In this letter, a design of MPFs with rectangular response using all positive coefficients is proposed. There is only one optical link as well as one photodetector utilized in the approach, which largely simplifies the filter structure. Experimental demonstrations of 55-positive-tap MPFs with different passbands are presented to verify the feasibility and potential of the approach.

Multi-band perfect plasmonic absorptions using rectangular graphene gratings

Sheng-Xuan Xia, Xiang Zhai, Yu Huang, Jian Liu, wang lingling, and Shuangchun Wen

Doc ID: 301023 Received 26 Jun 2017; Accepted 07 Jul 2017; Posted 07 Jul 2017  View: PDF

Abstract: We propose to achieve multi-band perfect plasmonic absorptions with peak absorptivity >99% via the excitation of standing-wave graphene surface plasmon polaritons (SWGSPPs) using single-layer graphene-based rectangular gratings. For the case with continuous gratings, perfect absorptions are only allowed for even-order modes, while the absorptions are quite low for odd-order modes because the fields are out-of-phase. However, for gratings with bottom-open configuration, four-band perfect absorptions containing both the even- and odd-order modes can be realized, which are found to be highly sensitive to the incident angle. The simulated results agree very well with the theoretic analyses by considering the phase path of the plasmonic waves. This multi-band absorber is a promising candidate for future plasmonic devices.

Genetic-algorithm-optimized wideband on-chip polarization rotator with an ultrasmall footprint

Zejie Yu, Haoran Cui, and Xiankai Sun

Doc ID: 298221 Received 16 Jun 2017; Accepted 06 Jul 2017; Posted 10 Jul 2017  View: PDF

Abstract: Polarization control of light waves is an important technique in optical communication and signal processing. On-chip polarization rotation from the fundamental transverse-electric (TE0) mode to the fundamental transverse-magnetic (TM0) mode is usually difficult because of their large effective refractive index difference. Here, we demonstrate an on-chip wideband polarization rotator to convert the TE0 mode into the TM0 mode within a footprint of 0.96 × 4.2 μm2 designed with a genetic algorithm. In simulation the optimized structure achieves polarization rotation with a minimum conversion loss of 0.7 dB and the 1-dB bandwidth of 157 nm. Experimentally, our fabricated devices have demonstrated the expected polarization rotation with a conversion loss of ~2.5 dB in the measured wavelength range of 1440–1580 nm, where the smallest value reaches ~2 dB. The devices require only a single step of lithography and etch in fabrication, and thus can serve as a generic approach and standard module for controlling light polarization in integrated photonic circuitry.

Inline self-diffraction dispersion-scan of over octave-spanning pulses in the single-cycle regime

Miguel Canhota, Francisco Silva, Rosa Weigand, and Helder Crespo

Doc ID: 296643 Received 24 May 2017; Accepted 06 Jul 2017; Posted 07 Jul 2017  View: PDF

Abstract: We present an implementation of dispersion-scan based on self-diffraction (SD d-scan) and apply it to the measurement of over octave-spanning sub-4-fs pulses. The results are compared with second-harmonic generation (SHG) d-scan. The efficiency of the SD process is derived theoretically and compared with the spectral response retrieved by the d-scan algorithm. The new SD d-scan has a robust inline setup and enables measuring pulses with over-octave spectra, single-cycle durations and wavelength ranges beyond those of SHG crystals, such as the ultraviolet and the deep-ultraviolet.

Ultra-compact multimode silicon bent waveguide with ultralow inter-mode crosstalk

Chunlei Sun, Yu Yu, Guanyu Chen, and Xinliang Zhang

Doc ID: 297371 Received 05 Jun 2017; Accepted 06 Jul 2017; Posted 07 Jul 2017  View: PDF

Abstract: We propose and experimentally demonstrate a sharply bent multimode silicon waveguide by introducing a pair of mode converters (MCs). The principle of the multimode bend is based on the eigenmodes conversion between straight and bent waveguides, and the particle swarm optimization is adopted to engineer the geometry. The device is fabricated on standard silicon-on-insulator platform using one lithography/etching, and no additional steps are required. The measured results show the insertion loss is <0.2 dB, and the inter-mode crosstalk is < -22 dB with bend radius of 5 µm, from 1500 to 1600 nm. A comparable performance can be achieved using conventional scheme with 40 µm radius.

Tunable, low phase noise microwave signals from an optically injected semiconductor laser with opto-electronic feedback

Joseph Suelzer, Thomas Simpson, Preetpaul Devgan, and Nicholas Usechak

Doc ID: 296915 Received 12 Jun 2017; Accepted 06 Jul 2017; Posted 20 Jul 2017  View: PDF

Abstract: We experimentally demonstrate the generation of microwave signals with linewidths below 3 Hz and a tuning range over 35 GHz from a semiconductor laser subject to optical injection and opto-electronic feedback. In this work, the feedback loop uses neither a microwave spectral filter or an amplifier to achieve a reduction in the microwave linewidth of six orders of magnitude.Two microwave frequencies, 25.4 GHz and 45.9 GHz, are chosen to highlight single sideband phase measurements of -105 dBc/Hz and -95 dBc/Hz at a 10-kHz offset, respectively. Finally, we demonstrate that longer-term stability can be further improved via asymmetric mutual injection.

Pulse Shaping of Broadband Adiabatic SHG in Ti-Sapphire Oscillator

assaf levanon, Asaf Dahan, achia nagler, erga lifshitz, eyal bahar, Michael Mrejen, and Haim Suchowski

Doc ID: 296064 Received 26 May 2017; Accepted 05 Jul 2017; Posted 05 Jul 2017  View: PDF

Abstract: We experimentally demonstrate an efficient broadband second harmonic generation process with tunable mode-locked Ti: sapphire oscillator. We have achieved a robust broadband and efficient flat conversion of more than 35nm wavelength, by designing an adiabatic aperiodically poled potassium titanyl phosphate (KTP) crystal. Moreover, we have shown that with such efficient flat conversion, we can shape and control broadband second harmonic pulses. More specifically, we assign spectral-phase of abs-value and π-step, which allows wavelength tunable intense pump-probe and amplitude modulation of the broadband second harmonic output. Such spectral phases serve as a proof of concept for other pulse-shaping application for nonlinear spectroscopy and imaging.

Sub-100 fs Tm:MgWO4 laser at 2017 nm mode-locked by a graphene saturable absorber

Yicheng Wang, Weidong Chen, Mark Mero, lizhen zhang, Haifeng Lin, zhoubin lin, Zhang Ge, Fabian Rotermund, Young Cho, Pavel Loiko, Xavier Mateos, Uwe Griebner, and Valentin Petrov

Doc ID: 298181 Received 15 Jun 2017; Accepted 05 Jul 2017; Posted 14 Jul 2017  View: PDF

Abstract: We present the first sub-100 fs bulk solid-state laser in the 2 μm spectral range employing the monoclinic Tm3+-doped MgWO4 crystal as an active medium. By applying a graphene-based saturable absorber and chirped mirrors for dispersion management, stable self-starting mode-locked operation at 2017 nm was achieved. Nearly Fourier-limited pulses as short as 86 fs featuring a bandwidth of 53 nm (FWHM) were generated at a repetition rate of 76 MHz. A pulse energy of 1.1 nJ was achieved at 87 MHz for a pulse duration of 96 fs. The mode-locked Tm3+:MgWO4 laser exhibits excellent stability with a fundamental beat note extinction ratio of 80 dBc above noise level.

Polarization management to mitigate misalignment induced fringe fading in fiber-based optical coherence tomography

Nanshuo Wang, Xinyu Liu, Qiaozhou Xiong, Jun Xie, shi chen, and Linbo Liu

Doc ID: 296067 Received 17 May 2017; Accepted 03 Jul 2017; Posted 05 Jul 2017  View: PDF

Abstract: In fiber-based optical coherence tomography (OCT), the interference fringes suffer from the fading effect due to misalignment of the light polarization states between the reference and sample arms, resulting in sensitivity degradation and image intensity variation. We theoretically and experimentally analyzed the relation between the misalignment and the fading coefficient. Assuming that the variation of the light polarization in single mode fiber was a random process, we statistically quantified the fading effect. Furthermore, in OCT configuration based on Michelson interferometer, we reported an interesting observation, that the polarization states of light travelling a round trip in SMF are not evenly distributed on the Poincare sphere. Based on this observation, we demonstrated the existence of an optimal output polarization state of the reference arm to mitigate the fading effect. We demonstrated that in an optimal setup, the statistical average SNR could be 3.5 dB higher than a setup without proper polarization management.

Sparsity-promoting BAE method for compensating for the mismodeling of optical properties in FMT

wenhao Xie, Yong Deng, dongmei yan, Xiaoquan Yang, and Qingming Luo

Doc ID: 295221 Received 08 May 2017; Accepted 03 Jul 2017; Posted 05 Jul 2017  View: PDF

Abstract: In fluorescence molecular tomography, the quality of image reconstruction of fluorophore distributions is heavily reduced by the mismodeling of inaccurately-known tissue optical properties. We propose an efficient sparsity-promoting Bayesian approximation error (spBAE) method to compensate for this mismodeling. In the spBAE method, sparsity prior was incorporated into the framework of the BAE method by varying the parameters of the prior of the solution with iterations. In vivo experiments demonstrate that this new method can effectively restrain the artifacts in image reconstruction.

Signal-to-noise ratio enhancement of stimulated Brillouin scattering based pulse compression of ultrabroad microwave signal by use of dispersion compensation fiber

Yi Ji, Weiwen Zou, Xin Long, and Jianping Chen

Doc ID: 296183 Received 22 May 2017; Accepted 02 Jul 2017; Posted 03 Jul 2017  View: PDF

Abstract: The signal-to-noise ratio (SNR) of all-optical pulse compression of broadband microwave signals based on stimulated Brillouin scattering (SBS) is theoretically analyzed. According to numerical simulation, it is found that the SNR is dominantly determined by the Brillouin gain coefficient gB. With the improvement of gB, the SNR is evidently enhanced and the bandwidth of SBS-based pulse compression is consequently enlarged. Experiments are implemented by use of dispersion compensation fiber (DCF) with higher gB rather than single mode fiber. The experimental results show that better SNR of the compressed signal is obtained and the system bandwidth is extended up to 5 GHz.

Angularly dense comb-like enhanced absorption of graphene monolayer with attenuated-total-reflection configuration

Gaige Zheng, Jiawei Cong, Yunyun Chen, Linhua Xu, and Shao Rong Xiao

Doc ID: 297760 Received 08 Jun 2017; Accepted 01 Jul 2017; Posted 10 Jul 2017  View: PDF

Abstract: Multiline absorber based on the excitation of guided-mode resonance of one-dimensional photonic crystals (1D-PhCs) including surface graphene monolayer under the attenuated-total-reflection (ATR) configuration is proposed and demonstrated. By carefully designing the structure parameters of the 1D-PhCs, the guided mode can be modulated by the periodic distribution of refractive index. Our results reveal that the critical coupling of the guided resonance in periodical PhCs to graphene produces the perfect absorption. The number of absorption peaks within photonic band corresponds to the number of unit cells. An ultrahigh Q-factor value of 4.75×10^6 is obtained at resonance with unity absorption, which could serve as a promising replacement of metallic thin film as a sensor probe for future biosensing applications.

Incoherent lensless imaging via coherency back-propagation

Ayman Abouraddy, Andre Beckus, Hasan Kondakci, Morgan Monroe, Nafiseh Mohammadian, George Atia, and Ahmed Elhalawany

Doc ID: 295169 Received 11 May 2017; Accepted 30 Jun 2017; Posted 10 Jul 2017  View: PDF

Abstract: The two-point complex coherence function constitutes a complete representation for scalar quasi-monochromatic optical fields. Exploiting dynamically reconfigurable slits implemented with a digital micromirror device, we report on measurements of the complex two-point coherence function for partially coherent light scattering from a `scene' comprising one or two objects at different transverse and axial positions with respect to the source. Although the intensity shows no discernible shadows in absence of a lens, numerically back-propagating the measured complex coherence function allows estimating the objects' sizes and locations -- and thus the reconstruction of the scene.

Zak phase induced multiband waveguide by two-dimensional photonic crystals

yu yang, Tao Xu, yun xu, and Zhihong Hang

Doc ID: 296214 Received 05 Jun 2017; Accepted 28 Jun 2017; Posted 05 Jul 2017  View: PDF

Abstract: Interface states in photonic crystals provide efficient approaches to control the flow of light. Photonic Zak phase determines the bulk band properties of photonic crystals and by assembling two photonic crystals with different bulk band properties together, deterministic interface states can be realized. By translating each unit cell of a photonic crystal by half the lattice constant, another photonic crystal with identical common gaps but different Zak phase at each photonic band can be created. By assembling these two photonic crystals together, multiband waveguide can thus be easily created and then experimentally characterized. Our experimental results have good agreement to numerical simulations and the propagation properties of these measured interface states indicate that this new type of interface states will be a good candidate for future applications of optical communications.

Electrically tunable whispering gallery mode microresonator based on grapefruit microstructured optical fiber infiltrated with nematic liquid crystals

Chengkun Yang, Hao Zhang, Bo Liu, Shiwei Lin, Yuetao Li, and Haifeng Liu

Doc ID: 297597 Received 06 Jun 2017; Accepted 28 Jun 2017; Posted 05 Jul 2017  View: PDF

Abstract: An electrically tunable whispering gallery mode (WGM) microresonator based on a HF-etched microstructured optical fiber (MOF) infiltrated with nematic liquid crystals (NLCs) is proposed and experimentally demonstrated. Experimentally results indicate that as the peak to peak voltage of the applied AC electric field increases from 160 V to 220 V, WGM resonance peaks gradually move toward shorter wavelength region by 0.527 nm with a wavelength sensitivity up to 0.01 nm/V for TM1 169 mode, and the Q-factor for each WGM resonance peak rapidly decreases with the increment of applied electric voltage. The proposed electrically controlled WGM tuning scheme shows linear resonance wavelength shift with good spectral reversibility, which makes it a promising candidate to serve as integrated functional photonic device in practical use and related fundamental scientific studies.

Modulation bandwidth enhancement for coupled twin-square microcavity lasers

Zhi-Xiong Xiao, Yong-Zhen Huang, Yue-De Yang, Min Tang, and Jin-Long Xiao

Doc ID: 295837 Received 12 May 2017; Accepted 27 Jun 2017; Posted 27 Jun 2017  View: PDF

Abstract: Modulation bandwidth enhancements are investigated for coupled twin-square microcavity lasers due to photon-photon resonance effect. For a coupled twin-square microcavity laser with the square side length of 20 µm, we demonstrate the increase of 3-dB modulation bandwidth from 9.6 GHz to 19.5 GHz with the photon-photon resonance frequency difference of 18.3 GHz, by adjusting resonance mode wavelength interval between two square microcavities. The enhanced modulation bandwidth is explained by rate equation analysis, and numerical simulations are conducted for large signal modulation with improved eye-diagrams at 40 Gbit/s.

Random medium model for cusping of plane waves

Jia Li and Olga Korotkova

Doc ID: 296424 Received 22 May 2017; Accepted 19 Jun 2017; Posted 20 Jul 2017  View: PDF

Abstract: We introduce a model for a three-dimensional (3D) Schell-type stationary medium whose degree of potential’s correlation satisfies the Fractional Multi-Gaussian (FMG) function. Compared with the scattered profile produced by the Gaussian Schell-model (GSM) medium, the Fractional Multi-Gaussian Schell-model (FMGSM) medium gives rise to a sharp concave intensity apex in the scattered field. This implies that the FMGSM medium also accounts for a larger than Gaussian’s power in the bucket (PIB) in the forwarding scattering direction, hence being a better candidate than the GSM medium for generating highly-concentrated (cusp-like) scattered profiles in the far zone. Compared to other mathematical models for the medium’s correlation function which can also produce similar cusped scattered profiles the FMG function offers unprecedented tractability being the weighted superposition of Gaussian functions. Our results provide useful applications to energy counter problems and particle manipulation by weakly scattered fields.

Long-wavelength-infrared solitons in air

Aleksandr Voronin and Aleksei Zheltikov

Doc ID: 296465 Received 22 May 2017; Accepted 17 Jun 2017; Posted 26 Jun 2017  View: PDF

Abstract: Dispersion and optical nonlinearity of atmospheric air in the long-wavelength infrared (LWIR) range are shown to enable unique soliton dynamics in freely propagating laser beams. Numerical analysis of three-dimensional spatiotemporal LWIR waveform evolution in air reveals soliton self-compression scenarios whereby ultrashort LWIR subterawatt pulses can be compressed to single-cycle terawatt field waveforms.

Femtosecond laser written waveguides deep inside silicon

F Omer Ilday, Ihor Pavlov, Onur Tokel, Viktor Kadan, Ghaith Makey, Ahmet Turnali, Özgün Yavuz, and Svitlana Pavlova

Doc ID: 294915 Received 28 Apr 2017; Accepted 16 Jun 2017; Posted 16 Jun 2017  View: PDF

Abstract: Photonic devices that can guide, transfer or modulate light are highly desired in electronics and integrated silicon photonics. Here, we demonstrate for the first time, to the best of our knowledge, creation of optical waveguides deep inside silicon using femtosecond pulses at a central wavelength of 1.5 $\mu$m. To this end, we use 350-fs-long, 2-$\mu$J pulses with a repetition rate of 250 kHz from an Er-doped fiber laser, which we focused inside silicon to create permanent modifications of the crystal. The position of the beam is accurately controlled with pump-probe imaging during fabrication. Waveguides of 5.5 mm length, and 20 $\mu$m diameter were created by scanning the focal position along the beam propagation axis. The fabricated waveguides were characterized with a continuous-wave laser operating at 1.5 $\mu$m. The refractive index change inside the waveguide was measured with optical shadow-graphy, yielding a value of $6 \times 10^{-4}$; as well as by direct light coupling and far-field imaging, yielding a value of $3.5 \times 10^{-4}$. The formation mechanism of the modification is discussed.

Surface Nanoscale Axial Photonics at a capillary fiber

Misha Sumetsky, Tabassom Hamidfar, Artemiy Dmitriev, Brian Mangan, and Pablo Bianucci

Doc ID: 295540 Received 10 May 2017; Accepted 14 Jun 2017; Posted 16 Jun 2017  View: PDF

Abstract: We present the theory and first experimental demonstration of a sensing platform based on Surface Nanoscale Axial Photonics (SNAP) at a capillary fiber. The platform explores optical whispering gallery modes which circulate inside the wall of a capillary and slowly propagate along its axis. Due to the small thickness of the capillary wall, these modes are sensitive to spatial and temporal variations of refractive index of the media adjacent to the internal capillary surface. In particular, the developed theory allows to determine the internal effective radius variation of the capillary from the measured mode spectra. Experimentally, a SNAP resonator is created by local annealing of the capillary with a focused CO₂ laser followed by internal etching with hydrofluoric acid. The comparison of the spectra of this resonator in the cases when it is empty and filled with water allows us to determine the internal surface nonuniformity introduced by etching. The results obtained pave the way for a novel advanced approach in sensing of media adjacent to the internal capillary surface and, in particular, in microfluidic sensing.

Three-Dimensional Object Visualization and Detection in Low Light Illumination using Integral Imaging

Adam Markman, Xin Shen, and Bahram Javidi

Doc ID: 293203 Received 20 Apr 2017; Accepted 08 Jun 2017; Posted 11 Jul 2017  View: PDF

Abstract: Conventional two-dimensional (2D) imaging systems that operate in the visible spectrum may perform poorly in environments under low light illumination. In this work, we present the potential of passive three-dimensional (3D) synthetic aperture integral imaging (SAII) to perform 3D imaging of a scene under low light conditions in the visible spectrum and without the need for a photon counting or cooled CCD camera. Using dedicated algorithms, we demonstrate that the reconstructed 3D integral image is naturally optimum in a maximum likelihood sense in low light levels and in the presence of detector noise enabling object visualization in the scene. The conventional 2D imaging fails due to the limited number of photons. Using 3D imaging, we demonstrate the potential for 3D detection of objects behind occlusion in a photon-starved scene. To the best of our knowledge, this is the first report of experimentally using SAII sensing under low illumination conditions for 3D visualization and 3D object detection in the presence of obscurations with a conventional image sensor.

Partially coherent sources with circular coherence: comment

Milo Hyde and Santasri Bose-Pillai

Doc ID: 293282 Received 28 Apr 2017; Accepted 15 May 2017; Posted 11 Jul 2017  View: PDF

Abstract: In a recent paper [Opt. Lett. 42, 1512 (2017)], the authors present a new class of non-uniformly correlated sources with circular coherence. They also discuss a basic experimental set-up to synthesize such sources which uses the Van Cittert-Zernike theorem. Here, we present an alternative way to analyze these sources and a different way to generate them.

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