Raman enhanced polarization-insensitive wavelength conversion based on two-pump four-wave mixing

Xiaojie Guo; Chester Shu

doi:10.1364/OE.24.028648

1. Introduction

Fiber-based four-wave mixing (FWM) has been widely explored for various functionalities of optical signal processing, such as all-optical regeneration [1], optical phase conjugation (OPC) [2], wavelength conversion [3], multicasting [4] and sampling [5]. In particular, OPC has been extensively studied recently in view of its great potential to compensate Kerr nonlinearity distortions in high-capacity wavelength division multiplexing (WDM) systems [6–9]. All-optical wavelength conversion has also attracted much research interest as one of the enabling technologies to improve the efficiency of optical networks [10–12]. Besides wide operation bandwidth and transparency to data rate and modulation format for practical applications, a recent study has verified that the FWM-based wavelength converter is as cascadable as erbium-doped fiber amplifiers (EDFAs) by increasing the conversion efficiency [13].

Polarization-insensitive feature and high conversion efficiency are of critical importance for FWM-based optical signal processing in practical applications. The conversion efficiency, defined as the output power of the idler with respect to the input power of the signal, is strongly dependent on the polarization alignment between the signal and the pump. Two-orthogonal-pump FWM is a well-known scheme to mitigate the intrinsic polarization dependence of the FWM process [14]. However, the nonlinear coefficient of the two-orthogonal-pump FWM is only one third of that in a two-parallel-pump FWM process, resulting in a weak idler. A straightforward solution to this drawback is to use two intensified pumps achieved by powerful EDFAs. Meanwhile, different techniques are often used to suppress stimulated Brillouin scattering (SBS) since the pump power for sufficient conversion efficiency usually surpasses the SBS threshold of the highly nonlinear fiber (HNLF). One of the common techniques is to apply frequency dithering to the narrow-linewidth pump so that the pump spectrum is broadened beyond the SBS gain bandwidth. Since simple pump frequency dithering transfers phase noise to the idler, counter-phase dithering scheme [15] is necessary to avoid degradation of the idler. Apart from frequency dithering, specialty fiber with different stresses along its length [16] has also been developed for SBS suppression. Conversion efficiency of 10 dB has been demonstrated without pump dithering but using four strained fiber pieces with a sophisticated design [17]. On the other hand, using a polarization diversity loop scheme is an alternative way to realize polarization-insensitive FWM [18, 19]. Similar to the two-orthogonal-pump FWM, this scheme requires a high pump power to achieve relatively large conversion efficiency so that SBS suppression is demanded. When SBS suppression is applied, the pump power is still limited because the SBS effect in the counter-propagation scheme will induce more severe signal distortion than in the unidirectional configuration [20].

Apart from the use of strong FWM pumps, backward Raman amplification has been proposed as another way to improve the conversion efficiency in a degenerate FWM process [21]. This approach is particularly attractive when the FWM pump is located outside the gain spectrum of the EDFA [22]. Recently, we have reported performance improvement of a phase-sensitive fiber optical parametric amplifier by applying backward Raman amplification, where the gain extinction ratio was enhanced by 9.2 dB [23]. In this paper, we propose to use backward Raman amplification to enhance the conversion efficiency of two-orthogonal-pump FWM. Theoretical analysis and experimental demonstration are presented to show the feasibility in achieving polarization-insensitive and highly efficient FWM with the assistance of Raman pump. We also discuss the impact of the settings of the Raman pump power and the FWM pump powers on the performance of wavelength conversion.

2. Theory

The schematic of using a Raman pump to enhance the efficiency of polarization-insensitive FWM is shown in Fig. 1. In the orthogonally pumped FWM process, the parametric interaction corresponds to ω₁ + ω₂ = ω₃ + ω₄, where ω₁, ω₂, ω₃ and ω₄ are the optical frequencies of the two pumps, signal and idler, respectively. The pumps denoted as A_1,_x and A_2,_y are linear polarized along x axis and y axis, respectively, as shown in Fig. 1. In the following study, we use subscripts x or y to denote the components of the various fields along x axis or y axis. The incident signal with an arbitrary polarization can be considered as two orthogonal components, A_3,_x and A_3,_y. Hence, two orthogonal components of the idler, A_4,_x and A_4,_y, are generated through non-degenerate FWM processes corresponding to A_3,_y and A_3,_x, respectively. Meanwhile, the signal, the idler, and the orthogonal-polarized pumps are amplified by a depolarized Raman pump in the counter-propagating direction. Due to the random polarization of the Raman pump, the direct Raman gain for the Stokes waves (the FWM pumps, the signal and the idler) is independent of their polarization states. Taking Raman amplification into account, the orthogonally pumped FWM process can be described by the following set of coupled equations [24],

\frac{d A_{1, x}}{d z} = i γ [P_{1, x} + 2 (b P_{R} + \frac{P_{2, y}}{3})] A_{1, x} + \frac{1}{2} (g_{1} P_{R} - α) A_{1, x},

\frac{d A_{2, y}}{d z} = i γ [P_{2, y} + 2 (b P_{R} + \frac{P_{1, x}}{3})] A_{2, y} + \frac{1}{2} (g_{2} P_{R} - α) A_{2, y},

\frac{d A_{3, x}}{d z} = i 2 γ (P_{1, x} + b P_{R} + \frac{P_{2, y}}{3}) A_{3, x} + i \frac{2}{3} γ A_{1, x} A_{2, y} A_{4, y}^{*} e^{- i Δ β z} + \frac{1}{2} (g_{3} P_{R} - α) A_{3, x},

\frac{d A_{4, y}}{d z} = i 2 γ (P_{2, y} + b P_{R} + \frac{P_{1, x}}{3}) A_{4, y} + i \frac{2}{3} γ A_{1, x} A_{2, y} A_{3, x}^{*} e^{- i Δ β z} + \frac{1}{2} (g_{4} P_{R} - α) A_{4, y},

\frac{d A_{3, y}}{d z} = i 2 γ (P_{2, y} + b P_{R} + \frac{P_{1, x}}{3}) A_{3, y} + i \frac{2}{3} γ A_{1, x} A_{2, y} A_{4, x}^{*} e^{- i Δ β z} + \frac{1}{2} (g_{3} P_{R} - α) A_{3, y},

\frac{d A_{4, x}}{d z} = i 2 γ (P_{1, x} + b P_{R} + \frac{P_{2, y}}{3}) A_{4, x} + i \frac{2}{3} γ A_{1, x} A_{2, y} A_{3, y}^{*} e^{- i Δ β z} + \frac{1}{2} (g_{4} P_{R} - α) A_{4, x} .

In the above equations,

A_{i, j}

(

i = 1, 2, 3, 4

and

j = x, y

) denotes the complex amplitude of the pumps, signal and idler,

P_{R}

is the input power of the Raman pump,

b

is an averaging factor for cross-phase modulation induced by the Raman pump,

g_{j} (j = 1, 2, 3, 4)

is the Raman gain coefficient,

α

is the attenuation of the fiber, and

Δ β

is the phase mismatch determined by fiber dispersion. The powers of the two orthogonal FWM pumps are denoted by

P_{1, x}

and

P_{2, y}

, respectively. From Eq. (4) to Eq. (6), one can find that the two pairs of signal and idler, (A_3, _x, A_4, _y) and (A_4, _x, A_3, _y), are evolving along the propagation direction in the same manner. It implies that the idler components along the x- and y- axis are generated with the same conversion efficiency. The polarization-insensitive feature of two-orthogonal-pump FWM process is maintained under the backward Raman pumping.

Fig. 1 Schematic of Raman-enhanced polarization-insensitive two-pump FWM.

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On the other hand, the orthogonal-polarized components of the idler, A_4, _x and A_4, _y, are generated through the FWM process and also amplified by the Raman pump. In the FWM process, the power of the idler is determined by the powers of the two FWM pumps and the signal that are intensifying along the fiber due to the Raman gain. As a result, the total idler power will be increased directly by the Raman gain and indirectly through the FWM process, i.e., the conversion efficiency is increased.

To investigate the enhancement in the conversion efficiency by the assistance of Raman gain, we derive an analytical solution for the idler from the above set of coupled equations. To simplify the derivation, we assume that the Raman gain is flat, i.e. $g_{j} = g_{R} (j = 1, 2, 3, 4)$ . By rewriting Eq. (1) and Eq. (2) in terms of powers and phases of the waves, we can obtain an expression for both FWM pumps,

P_{j, k} (z) = P_{j, k} (0) \exp {(g_{R} P_{R} - α) z},

where

(j, k) = (1, x)

or

(2, y)

, and

P_{j, k} (0)

denotes the input power of the pump. Due to the Raman gain, the effective power of each FWM pump for the idler generation is higher than the input pump power

P_{j, k} (0)

. In order to simplify the procedures to obtain an analytical expression for the conversion efficiency, we assume that the FWM pump powers are constant as path average power in Eq. (3) to Eq. (6). The path average power of each FWM pump is given by

P_{j, k}^{a v e} = η_{j, k} P_{j, k} (0)

, where

η_{j, k} = [\exp (g_{R} P_{R} - α) L - 1] / [(g_{R} P_{R} - α) L]

and

L

is the length of the fiber. We can then solve the pair of coupled equations for (A_3, _x, A_4, _y) by the procedures similar to Ref [21]. and obtain the output power of A_4, _y:

P_{4, y} (L) = \frac{4}{9} γ^{2} L^{2} P_{1, x}^{a v e} P_{2, y}^{a v e} P_{3, x} (0) \exp {(g_{R} P_{R} - α) L},

where

P_{3, x} (0)

is the input power of the signal component A_3, _x. Similarly, the output power of another idler component A_4, _x is given by

P_{4, x} (L) = \frac{4}{9} γ^{2} L^{2} P_{1, x}^{a v e} P_{2, y}^{a v e} P_{3, y} (0) \exp {(g_{R} P_{R} - α) L},

where

P_{3, y} (0)

is the input power of the signal component A_3,_y. According to Eq. (8) and Eq. (9), the conversion efficiency

G_{i}

has the same form for both orthogonal-polarized components of the signal, i.e., the FWM process with Raman assistance is polarization-independent. The expression for the conversion efficiency is

G_{i} = \frac{4}{9} γ^{2} L^{2} η_{1, x}^{} η_{2, y}^{} P_{1, x}^{} (0) P_{2, y}^{} (0) \exp {(g_{R} P_{R} - α) L} .

As compared to the case without Raman amplification, the conversion-efficiency enhancement factor with the Raman pump (denoted as

ξ

) is

ξ = η_{1, x}^{} η_{2, y}^{} \exp {(g_{R} P_{R} - α) L} .

In Eq. (11),

η_{1, x}^{}

and

η_{2, y}^{}

indicate the indirect improvement of conversion efficiency through Raman gain on the FWM pumps, and the last term indicates the conversion efficiency enhancement by direct Raman amplification of the idler. From Eq. (11), one can conclude that the conversion efficiency is enhanced by increasing the Raman gain.

It should be noted that $g_{R}$ in Eq. (10) and Eq. (11) is an effective Raman gain coefficient but not the gain coefficient in the small-signal condition, especially when the FWM pumps are relatively large. Actually, the Raman gain gradually saturates with the increase of the FWM pump powers. When the depletion of Raman pump is significant, $G_{i}$ and $ξ$ would be overestimated if we use a Raman gain coefficient in the small-signal condition to calculate their values from Eq. (10) and Eq. (11). The effective Raman gain coefficient can be approximately expressed by $g_{R}^{e f f} = \ln (G_{R, s a t}^{}) / (P_{R} L)$ , where $P_{R}$ is the input power of the Raman pump. Here the saturated Raman gain $G_{R, s a t}^{}$ can be obtained from the following approximate expression [25]

G_{R, s a t}^{} = \frac{(1 + r) G_{R}^{1 + r}}{1 + r G_{R}^{1 + r}},

where

r = λ_{S t o k e s} P_{i n, S t o k e s} / (λ_{R} P_{R})

,

P_{i n, S t o k e s}

is the input power of the Stokes signal, and

λ_{S t o k e s}

and

λ_{R}

are the wavelengths of the Stokes signal and the Raman pump, respectively. Therefore, by using the calculated

g_{R}^{e f f}

, we can predict the conversion efficiency and its enhancement due to Raman amplification from Eq. (10) and Eq. (11).

3. Experimental setup and results

We conduct experiments to demonstrate the two-orthogonal-pump FWM under backward Raman amplification. The experimental setup is depicted in Fig. 2. Two tunable lasers (TL1 and TL2) are used to generate two continuous-wave (CW) FWM pumps. The wavelengths are 1550.0 nm (P1) and 1547.9 nm (P2), which are spaced almost symmetric to the zero-dispersion wavelength of the HNLF. The two pumps are combined by a polarization beam splitter to ensure that their polarization states are orthogonal. Since the output power of TL2 is relatively low, an EDFA (not shown in Fig. 2) is used after the laser to produce a sufficiently high pump power. A 40Gb/s non-return-to-zero differential phase-shift keying (NRZ-DPSK) signal is produced by modulating a third tunable laser TL3 at 1556.6 nm with a Mach-Zehnder modulator. A polarization scrambler is used to vary the polarization state of the signal. The signal and the orthogonally polarized pumps are combined by a coupler and then launched into a HNLF. The HNLF has a length of 1 km, an attenuation coefficient of 0.79 dB/km, and a nonlinear coefficient of 11.7 W⁻¹km⁻¹. The zero-dispersion wavelength and the dispersion slope are 1549 nm and 0.019 ps• km⁻¹nm⁻², respectively. The SBS threshold of the HNLF is 13.3 dBm at which a distortion begins to develop on the idler. At the HNLF output, a 1455-nm CW fiber laser serving as the Raman pump is launched into the HNLF from the opposite direction through an optical circulator. The FWM pumps, the signal and the generated idler are extracted by the same optical circulator and then split by a 90/10 coupler. The 10% portion is analyzed by an optical spectrum analyzer (OSA) and the 90% portion is directed to an optical bandpass filter (OBPF) to select the converted idler for measurement.

Fig. 2 Experimental setup on Raman-enhanced two-orthogonal-pump FWM. TL: tunable laser; PC: polarization controller; PBS: polarization beam splitter; MZM: Mach-Zehnder modulator; PRBS: pseudorandom binary sequence; PS: polarization scrambler; HNLF: highly nonlinear fiber; OBPF: optical band pass filter; OSA: optical spectrum analyzer.

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First, we compare the FWM processes when the Raman pump is turned off and turned on. In the experiment, the FWM pumps have the same power of 5.3 dBm at the input of the HNLF and the input power of the Raman pump is 30.3 dBm. Figure 3 shows the FWM spectra when the polarization scrambler is turned off. The idler generated from the two-pump FWM process (ω₁ + ω₂ = ω₃ + ω₄) is indicated by a dashed box. Without the Raman pump, the idler is very weak with a conversion efficiency of −29.4 dB. When the Raman pump is turned on, the two FWM pumps are amplified by 13.5 dB and 13.3 dB, respectively. The idler power is increased by 29.1 dB to a level nearly equal to the input signal power. The conversion efficiency is significantly enhanced with the Raman assistance. Due to the direct Raman amplification, the signal power is increased by 14.3 dB, while the optical signal-to-noise ratio (OSNR) is degraded by the spontaneous noise from the Raman pump. Although the spontaneous noise is also introduced to the idler under Raman amplification, we observed an improvement of the idler OSNR. It is because the idler not only experiences direct Raman gain but also grows more efficiently owing to the amplified FWM pumps. In addition, one can find two other idlers (denoted as I1 and I2) close to the polarization-insensitive idler in Fig. 3. They are generated from two degenerate FWM processes (2P2→S + I1 and 2P1→S + I2), which are polarization sensitive. Also, there are two residual idlers (denoted as I3 and I4) around the signal, which are generated from the FWM processes (P1 + S→P2 + I3 and P2 + S→P1 + I4).

Fig. 3 Output FWM spectra with Raman pump (w. Raman) and without Raman pump (w/o Raman). The polarization-insensitive idler is indicated by a dashed box.

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In order to verify the polarization-insensitive performance of the Raman-enhanced two-orthogonal-pump FWM, we vary the polarization states of the input signal and measure the output powers of the converted idler. The results are plotted in Fig. 4. The input signal power is −5.0 dBm. In the absence of Raman pump, the variation of the idler power is ± 0.2 dB when the polarization state of the signal is changed. With the Raman pump, the output power of the idler varies by ± 0.3 dB around −5.7 dBm against the polarization state of the input signal. It confirms the polarization-insensitive property of the two-orthogonal-pump FWM under Raman assistance. For various polarization states, the output power of the idler with Raman pump is ~29.0 dB higher than the one without Raman assistance, owing to the Raman enhancement in conversion efficiency.

Fig. 4 Output power of the converted idler against polarization state of the input signal. Input signal power is −5.0 dBm.

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To further study the performance of polarization-insensitive FWM with Raman enhancement, we evaluate the quality of the converted idlers by eye diagrams and bit-error-rate (BER) measurement. Figure 5(a)(i) and Fig. 5(a)(ii) show the eye diagrams of the converted idlers when the polarization scrambler is turned on and turned off, respectively. The eye diagrams are widely opened and almost the same in both cases. The results indicate that the operation is polarization-insensitive. As compared to the eye diagram of the input signal shown in Fig. 5(a)(iii), we observe little quality degradation in the converted idlers. The corresponding BER curves are plotted in Fig. 5(b), where we observe a power penalty of 0.7 dB at the error-free detection level when the polarization state of the input signal is scrambled. The low power penalty of the converted idler is attributed to the high OSNR resulted from the Raman-enhanced conversion efficiency.

Fig. 5 (a) Eye diagrams and (b) BER measurement of the input signal (B2B, back to back), and the converted idlers in Raman-enhanced two-orthogonal-pump FWM when polarization scrambling of the input signal is turned off (Fixed) and turned on (Scrambled).

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4. Discussion

We then investigate the effect of the FWM pump powers and the Raman pump power on the overall conversion efficiency ( $G_{i}$ ) and the conversion-efficiency enhancement factor ( $ξ$ ) of the polarization-insensitive FWM under Raman assistance. To comprehensively study the impact of the pump powers on $ξ$ and $G_{i}$ , numerical simulations are conducted by solving the nonlinear Schrödinger equation [21]. Figure 6(a) shows the contour map of $ξ$ for different FWM pump and Raman pump powers. In the simulation, the powers of the two FWM pumps are equal. As shown in Fig. 6(a), for a given FWM pump power, $ξ$ grows with the increase of Raman pump power. However, for a fixed Raman pump power, $ξ$ decreases with the increase of FWM pump power. It can be explained by the depletion of the Raman pump. With a higher FWM pump power, the Raman gain tends to saturate, i.e., the effective value of $g_{R}$ in Eq. (11) is reduced. As a result, maximum enhancement of the conversion efficiency can be obtained at the upper-left corner of the contour map, representing the combination of strong Raman pump and weak FWM pumps. The contour map for the overall conversion efficiency $G_{i}$ is plotted in Fig. 6(b). In contrast to $ξ$ , $G_{i}$ achieves higher values at the upper-right corner of the contour map. It is because $G_{i}$ increases with both the input FWM pumps and the Raman pump as indicated by Eq. (10). Therefore, we can obtain higher conversion efficiency in this region at the expense of the conversion-efficiency enhancement.

Fig. 6 Simulated contour maps of (a) conversion-efficiency enhancement factor ( $ξ$ ) and (b) overall conversion efficiency ( $G_{i}$ ) in the FWM with Raman assistance. $ξ$ and $G_{i}$ are expressed in dB.

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Apart from the consideration of the conversion efficiency and its enhancement, the noise on the converted idler induced by the pumps should be minimized. The noise is influenced by the choice of the FWM pump power and Raman pump power. Since the Raman pump is much stronger than the FWM pumps, it is the main contribution of the noise. Without considering the spontaneous noise from the Raman pump, a high OSNR can be obtained using the combination of strong FWM pumps and strong Raman pump due to the high conversion efficiency. However, the spontaneous Raman noise becomes significant and cannot be neglected when the Raman pump power grows to a relative large value. There is a compromise between the noise and the conversion efficiency in choosing the powers of the FWM pumps and the Raman pump.

Another nonlinear effect, stimulated Brillouin scattering (SBS), also has a strong impact on the performance of the converted idler. For FWM pumps with a fixed power level at the HNLF input, their powers will gradually grow along the fiber with the increase of the Raman pump and eventually surpass the SBS threshold. The SBS effect will deplete the FWM pumps and also introduce noise to the converted idler. It should be avoided by using a moderate Raman pump; otherwise, the quality of the converted idler will be degraded. In general, for a better performance of the idler, the powers of the Raman pump and the FWM pumps should be moderate, i.e., lie in the central portion of the contour maps.

Based on the above discussion, the powers of the Raman pump and the FWM pumps should be carefully selected in generating an idler with a high conversion efficiency and improved noise performance. Moderate pump power is favorable since the overall conversion efficiency, the enhancement of the conversion efficiency and the OSNR of the idler can reach a relative high level in this case. Apart from numerical simulation, we also conduct experiments to study the performance at different combinations of the Raman pump power and the FWM pump power. Table 1 are five combinations of the powers investigated in the experiment. The conversion-efficiency enhancement factor $ξ$ is plotted in Fig. 7 and compared with the simulated and analytical results. The analytical results obtained from Eq. (11) are in good agreement with the experimental and simulated results. Thus, we can roughly predict the enhancement of the conversion efficiency due to the Raman pump based on the analytical expression in Section 2.

Table 1. Parameters for five cases of power combination

View Table

Fig. 7 Experimental, analytical and simulated results of the conversion-efficiency enhancement factor $ξ$ for different FWM pump powers. The corresponding Raman pump powers are shown in Table 1.

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In addition to the measurement of $G_{i}$ , the quality of the idler is also quantified by measuring the eye signal-to-noise ratio (SNR) from the oscilloscope. Figure 8 shows the experimental results. For a combination of weak FWM pump and strong Raman pump (Case 1), we observe a relative low idler SNR although the conversion efficiency is the highest among the five cases. The low SNR can be attributed to large spontaneous noise originated from the strong Raman scattering. Improved performances of the output idler with a SNR around 7.6 are obtained from Case 2 to Case 4, where moderate powers are selected for the two types of pumps. In these cases, although the conversion efficiency is slightly lower than that in Case 1, the moderate Raman pump induces little noise to the idler so that the idler SNR is maintained at a high level. In Case 5, the Raman pump is set to be the same as that in Case 4, while the FWM pump is increased to 8.0 dBm. We find that the conversion efficiencies are nearly equal in Case 4 and Case 5. However, the idler SNR in Case 5 is worse than that in Case 4, as shown in Fig. 8 (a). A possible reason is that the backward SBS becomes significant with the higher FWM pump input in Case 5, resulting in the degradation of the idler quality. Also, the FWM pumps are depleted by the backward SBS so that the measured conversion efficiency is 1.8-dB lower than the one in the numerical simulation where the SBS effect is not included. The experimental results imply that moderate pump powers are promising for optimized performance of polarization-independent wavelength conversion based on Raman-enhanced two-orthogonal-pump FWM.

Fig. 8 (a) Measured idler SNR and (b) overall conversion efficiency ( $G_{i}$ ) for different combinations of FWM pump power and Raman pump power. Insets are eye diagrams of the idler at different values of SNR.

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For the application with multiple input signals, we should avoid the generation of spurious idlers around the signal and around the idler of interest as shown in Fig. 3. It could be achieved by increasing the spectral separation of the two pumps and locating the signal between the pumps. In the case with widely separated FWM pumps, it should be noted that polarization mode dispersion (PMD) in the HNLF may degrade the performance of the Raman-enhanced two-orthogonal-pump FWM by introducing polarization sensitivity to the conversion efficiency. In a given HNLF, the orthogonality of the two FWM pumps may be broken when there is a large spectral separation between them. Accordingly, the conversion efficiency will vary with the polarization state of the input signal. Nevertheless, the FWM pumps in this work are spectrally close so that the polarization dependence of the conversion efficiency is negligible. The issues associated with PMD are not discussed here but will be further studied in our future work.

5. Conclusion

In this work, backward Raman amplification has been successfully applied to enhance the conversion efficiency in the two-orthogonal-pump FWM scheme. The polarization-insensitive feature is well preserved in the presence of the Raman pump. Wavelength conversion with ~0dB conversion efficiency and negligible polarization dependency has been demonstrated in a highly nonlinear fiber without pump frequency dithering. The impact of the Raman pump power and the FWM pump powers on the performance of wavelength conversion has also been addressed through theoretical analysis and experiments. The results indicate that the powers of both the FWM and Raman pumps should be carefully selected to ensure high conversion efficiency and low excess noise for performance optimization. Moderate pump powers without introducing significant spontaneous noise and stimulated Brillouin scattering are preferable in the Raman-enhanced polarization-insensitive FWM process.

Funding

National Natural Science Foundation of China (NSFC) (61505070); Research Grants Council of Hong Kong, China (GRF Grants CUHK 416213, 14206614).

References and links

1. R. Slavik, F. Parmigiani, J. Kakande, C. Lundstrom, M. Sjodin, P. A. Andrekson, R. Weerasuriya, S. Sygletos, A. D. Ellis, L. Gruner-Nielsen, D. Jakobsen, S. Herstrom, R. Phelan, J. O’Gorman, A. Bogris, D. Syvridis, S. Dasgupta, P. Petropoulos, and D. J. Richardson, “All-optical phase and amplitude regenerator for next-generation telecommunications systems,” Nat. Photonics 4(10), 690–695 (2010). [CrossRef]

2. B. P. P. Kuo, E. Myslivets, A. O. J. Wiberg, S. Zlatanovic, C. S. Bres, S. Moro, F. Gholami, A. Peric, N. Alic, and S. Radic, “Transmission of 640-Gb/s RZ-OOK channel over 100-km SSMF by wavelength-transparent conjugation,” J. Lightwave Technol. 29(4), 516–523 (2011). [CrossRef]

3. H. N. Tan, K. Tanizawa, T. Inoue, T. Kurosu, and S. Namiki, “No guard-band wavelength translation of Nyquist OTDM-WDM signal for spectral defragmentation in an elastic add-drop node,” Opt. Lett. 38(17), 3287–3290 (2013). [CrossRef] [PubMed]

4. L. Liu, E. Temprana, V. Ataie, A. O. J. Wiberg, B. P. P. Kuo, E. Myslivets, N. Alic, and S. Radic, “All optical wavelength multicaster and regenerator based on four-mode phase-sensitive parametric mixer,” Opt. Express 23(24), 30956–30969 (2015). [CrossRef] [PubMed]

5. M. Sköld, M. Westlund, H. Sunnerud, and P. A. Andrekson, “All-optical waveform sampling in high-speed optical communication systems using advanced modulation formats,” J. Lightwave Technol. 27(16), 3662–3671 (2009). [CrossRef]

6. K. Solis-Trapala, M. Pelusi, H. N. Tan, T. Inoue, and S. Namiki, “Optimized WDM transmission impairment mitigation by multiple phase conjugations,” J. Lightwave Technol. 34(2), 431–440 (2016). [CrossRef]

7. I. Sackey, F. Da Ros, J. Karl Fischer, T. Richter, M. Jazayerifar, C. Peucheret, K. Petermann, and C. Schubert, “Kerr nonlinearity mitigation: mid-link spectral inversion versus digital backpropagation in 5×28-GBd PDM 16-QAM signal transmission,” J. Lightwave Technol. 33(9), 1821–1827 (2015). [CrossRef]

8. M. F. Stephens, M. Tan, I. Phillips, S. Sygletos, P. Harper, and N. J. Doran, “1THz-bandwidth polarization-diverse optical phase conjugation of 10x114Gb/s DP-QPSK WDM signals,” in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optical Society of America, 2014), paper W3F.6. [CrossRef]

9. H. Hu, R. M. Jopson, A. Gnauck, M. Dinu, S. Chandrasekhar, X. Liu, C. Xie, M. Montoliu, S. Randel, and C. McKinstrie, “Fiber nonlinearity compensation of an 8-channel WDM PDM-QPSK signal using multiple phase conjugations,” in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optical Society of America, 2014), paper M3C.2. [CrossRef]

10. S. Namiki, T. Kurosu, K. Tanizawa, S. Petit, G. Mingyi, and J. Kurumida, “Controlling optical signals through parametric processes,” IEEE J. Sel. Top. Quantum Electron. 18(2), 717–725 (2012). [CrossRef]

11. E. Ciaramella, “Wavelength conversion and all-optical regeneration: achievements and open issues,” J. Lightwave Technol. 30(4), 572–582 (2012). [CrossRef]

12. S. Namiki, K. Solis-Trapala, H. N. Tan, M. Pelusi, and T. Inoue, “Multi-channel cascadable parametric signal processing for wavelength conversion and nonlinearity compensation,” J. Lightwave Technol., in press (2016).

13. H. N. Tan, T. Inoue, K. Solis-Trapala, S. Petit, Y. Oikawa, K. Ota, S. Takasaka, T. Yagi, M. Pelusi, and S. Namiki, “On the cascadability of all-optical wavelength converter for high-order QAM formats,” J. Lightwave Technol. 34(13), 3194–3205 (2016). [CrossRef]

14. K. Inoue, “Polarization independent wavelength conversion using fiber four-wave mixing with two orthogonal pump lights of different frequencies,” J. Lightwave Technol. 12(11), 1916–1920 (1994). [CrossRef]

15. M. C. Ho, M. E. Marhic, K. Y. K. Wong, and L. G. Kazovsky, “Narrow-linewidth idler generation in fiber four-wave mixing and parametric amplification by dithering two pumps in opposition of phase,” J. Lightwave Technol. 20(3), 469–476 (2002). [CrossRef]

16. L. Gruner-Nielsen, S. Dasgupta, M. D. Mermelstein, D. Jakobsen, S. Herstrom, M. E. V. Pedersen, E. L. Lim, S. Alam, F. Parmigiani, D. Richardson, and B. Palsdottir, “A silica based highly nonlinear fiber with improved threshold for stimulated Brillouin scattering,” in European Conference and Exhibition on Optical Communication (ECOC, 2010), pp. 1–3. [CrossRef]

17. C. Lundstrom, R. Malik, L. Gruner-Nielsen, B. Corcoran, S. L. I. Olsson, M. Karlsson, and P. A. Andrekson, “Fiber optic parametric amplifier with 10-db net gain without pump dithering,” IEEE Photonics Technol. Lett. 25(3), 234–237 (2013). [CrossRef]

18. K. K. Y. Wong, M. E. Marhic, L. Uesaka, and L. G. Kazovsky, “Polarization-independent fiber-optical parametric amplifier,” IEEE Photonics Technol. Lett. 14(11), 1506–1508 (2002). [CrossRef]

19. H. Nguyen Tan, T. Inoue, K. Tanizawa, S. Petit, Y. Oikawa, S. Takasaka, T. Yagi, and S. Namiki, “Counter-dithering pump scheme for cascaded degenerate FWM based wavelength converter,” in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optical Society of America, 2014), paper W3F.4. [CrossRef]

20. M. Jazayerifar, I. Sackey, R. Elschner, S. Warm, C. Meuer, C. Schubert, and K. Petermann, “Impact of SBS on polarization-insensitive single pump optical parametric amplifiers based on a diversity loop scheme,” in European Conference and Exhibition on Optical Communication (ECOC, 2014), paper Tu.4.6.4. [CrossRef]

21. C. J. S. de Matos, D. A. Chestnut, P. C. Reeves-Hall, and J. R. Taylor, “Continuous-wave-pumped Raman-assisted fiber optical parametric amplifier and wavelength converter in conventional dispersion-shifted fiber,” Opt. Lett. 26(20), 1583–1585 (2001). [CrossRef] [PubMed]

22. J. F. L. Freitas, M. B. C. e Silva, S. R. Lüthi, and A. S. L. Gomes, “Raman enhanced parametric amplifier based S–C band wavelength converter: experiment and simulations,” Opt. Commun. 255(4–6), 314–318 (2005). [CrossRef]

23. X. Fu, X. Guo, and C. Shu, “Raman-enhanced phase-sensitive fibre optical parametric amplifier,” Sci. Rep. 6, 20180 (2016). [CrossRef] [PubMed]

24. G. P. Agrawal, Nonlinear Fiber Optics (4th Edition) (Academic, 2006).

25. C. Headley and G. P. Agrawal, Raman Amplification in Fiber Optical Communication Systems (Elsevier Academic, 2005).

Raman enhanced polarization-insensitive wavelength conversion based on two-pump four-wave mixing

Abstract

1. Introduction

2. Theory

3. Experimental setup and results

4. Discussion

5. Conclusion

Funding

References and links

Cited By

Figures (8)

Tables (1)

Equations (12)

Optics Express

	Case 1	Case 2	Case 3	Case 4	Case 5
FWM pump (dBm)	4.0	5.3	6.0	7.0	8.0
Raman pump (dBm)	31.4	30.4	29.8	29.4	29.4