We have developed a depolarization technique to achieve polarization-insensitive wavelength conversion using four-wave mixing in an optical fiber. A maximum conversion efficiency of -11.79 dB was achieved over a 3 dB bandwidth of 26 nm in a 100-m-long dispersion-flattened photonic crystal fiber. The polarization-dependent conversion efficiency was less than 0.38 dB and the measured power penalty for a 10 Gbit/s NRZ signal was 1.9 dB. The relation between the conversion efficiency and the degree of polarization of the pump was also formulated.
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"Over the last few years, the CARS microscopy with PCFs has been developed to simplify the system and reduce the costs. Up to now, some frequency conversion techniques based on the supercontinuum [18– 23] or the non-supercontinuum24252627282930 have been used to generate the pump and Stokes beams. The selective spectral filtering of supercontinuum can obtain the desired wavelengths, but the temporal width can be elongated as well as the decreased spectral energy, and the noise amplification is remarkable due to the complex nonlinear optical process. "
[Show abstract][Hide abstract]ABSTRACT: The polarization maintaining photonic crystal fiber (PM-PCF) with two zero dispersion wavelengths is designed and fabricated by the improved stack-and-draw technology in our laboratory. The broadband blue-shifted and red-shifted dispersive waves (DWs) are efficiently generated from soliton self-frequency shift (SSFS) along the slow axis of PM-PCF. By optimizing the pump parameters and the fiber length, the polarized DWs centered in the normal dispersion region can be used as the pump and Stokes pulses for the high resolution coherent anti-Stokes Raman scattering (CARS) microscopy. Moreover, it is demonstrated that the widely tunable relevant CARS wavelengths can be obtained by adjusting the pump wavelength. The CARS microscopy based on DWs can find important applications in detecting the biological and chemical samples with the C = N, S-H, C-H, and O-H stretch vibration resonances of 2100 to 2400 cm(-1), 2500 to 2650 cm(-1), 2700 to 3000 cm(-1), and 3000 to 3750 cm(-1).
Full-text · Article · Jan 2013 · Progress In Electromagnetics Research
"Another method to overcome the polarization dependence is polarization diversity, in which the pump is split into two orthogonal states that independently interact with the data –. A related approach is to depolarize the pump pulse train, which requires a fiber delay that is longer than the coherence length of the pump laser . In fibers that are significantly longer than the birefringence correlation length, the random polarization mode dispersion can cause the polarization dependence to average out, leading to polarization-independent operation . "
[Show abstract][Hide abstract]ABSTRACT: We present a theoretical, numerical, and experimental investigation of the polarization dependence of cross-phase modulation in nonlinear birefringent fibers. Two new methods are described for producing a polarization-independent spectral shift through cross-phase modulation of a weak probe signal by a copropagating strong optical pulse. The birefringence of the fiber and spectral separation between the pump and probe signals are shown to play a critical role in determining the polarization dependence of the cross-phase modulation process. The methods are experimentally verified in two different highly nonlinear fibers, and are used to achieve polarization-independent optical switching at speeds of up to 160 Gb/s.
Full-text · Article · Jun 2008 · IEEE Journal of Selected Topics in Quantum Electronics
"One problem with fiber-based nonlinear devices is that they typically depend on the input polarization state, which can vary unpredictably in installed fiber systems. In response to this, a number of schemes have been proposed such as polarization diversity , twisting of the nonlinear fiber , , and depolarization of the clock pulses  . Any of these can eliminate the polarization dependence, but generally require added complexity in the device. "
[Show abstract][Hide abstract]ABSTRACT: We describe an all-optical 80-Gb/s time-division demultiplexer, which utilizes cross-phase modulation in a commercial photonic crystal fiber. Compared to back-to-back 10-Gb/s measurements, the demultiplexer achieves better than a 2.5-dB power penalty for all eight channels. More importantly, we demonstrate a novel scheme for polarization-insensitive operation, which uses only the birefringence of the fiber itself and proper alignment of the clock pulse polarization. Using this technique, the polarization sensitivity of the converted power is found to be less than 0.4 dB, allowing for error-free demultiplexing even while the data polarization state is scrambled