Abstract
Polarization-insensitive (PI) phase-transmultiplexing (PTM) of a 10-Gb/s return-to-zero ON-OFF keying (RZ-OOK) pump and a 10-Gb/s RZbinary phase-shift keying (RZ-BPSK) probe to 20-Gb/s RZ-quadrature-PSK (RZ-QPSK) has been successfully demonstrated for the first time in a passive, birefringent AlGaAs waveguide, utilizing PI cross-phase modulation (PI-XPM). For differential QPSK (DQPSK)-detection, a 10 − 9-BER pre-amplified receiver sensitivity penalty of ≈ 2.5 dB for the in-phase component and ≈ 4.9 dB for the quadrature component were found. The penalties were relative to the FPGA-precoded RZ-DQPSK baseline for a pump-probe detuning of ≈ 12 nm, when the probe state of polarization was scrambled and the pump was launched off-axis into the waveguide.
Highlights
Advances in nonlinear optical signal processing (NOSP) techniques, along with device design, have made polarization-insensitive (PI)-NOSP possible
highly nonlinear fiber (HNLF) is a passive device, it lacks the sufficient deterministic differential group delay (DGD) to enable the type of PI-NOSP demonstrated in [8,9], which may be achieved with an external birefringence, or a polarization diversity loop
Since the receiver response can vary with different signal dutycycles [32], the RZ-BPSK and RZ-QPSK signals used for the baseline measurements were generated using the Ergo-XG laser that served as the probe in the PTM RZ-QPSK experiment
Summary
Advances in nonlinear optical signal processing (NOSP) techniques, along with device design, have made polarization-insensitive (PI)-NOSP possible. It was found that circular birefringence could be induced in a highly nonlinear fiber by twisting the fiber, and the birefringence could be used to reduce the polarization sensitivity of NOSP [6] Another technique, first demonstrated by Lenihan et al [7,8], utilized the inherent birefringence of a PCF to enable PI-NOSP, which eliminated the need for a polarization diversity loop, or an external birefringence. Signals can have unpredictable SOPs. HNLF is a passive device, it lacks the sufficient deterministic DGD to enable the type of PI-NOSP demonstrated in [8,9], which may be achieved with an external birefringence, or a polarization diversity loop. A 10−9-BER penalty of ≈2.5 dB for the in-phase component and ≈4.9 dB for the quadrature component were found when the pump was launched off-axis into the waveguide at a pump-probe detuning of ≈12 nm, while the probe SOP was randomized
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