80-GB all-optical serial-to-parallel convertor for QPSK signal based on cascaded phase modulators and optical f ilters

Abstract

An all-optical serial-to-parallel converter (SPC) utilizing two cascaded phase modulators and optical bandpass filters (OBPFs) is experimentally investigated and applied to demultiplex an 80-GBd optical timedivision multiplexing (OTDM) return-to-zero (RZ) differential quadrature phase-shift keying (QPSK) signal. Two 40-GBd OTDM tributaries are error-free demultiplexed with a power penalty of approximately 4 dB in the worst case. With its advantages of compact structure, high speed, low power penalty, simultaneous two-tributary operation, and no assistance from a light source, the SPC has potential for use in future OTDM networks. However, the performance of the SPC still needs improvement.OCIS codes: 320.7080, 320.1590, 060.5060. doi: 10.3788/COL201210.113201.The optical time-division multiplexing (OTDM) technique is seen as a very attractive candidate for increasing the bit-rate per wavelength channel further [1] . An all-optical serial-to-parallel converter (SPC) with multitributary demultiplexing capability and low power consumption is a key technique for OTDM networks. Most reported OTDM demultiplexers are designed for OTDM return-to-zero (RZ) on-off keying (OOK) signal and are not phase-preserved. Other reported demultiplexers, including those based on either electro-optical on-off gates utilizing electro-absorption modulator (EAM) [2] , phase modulator (PM) [3] , Mach-Zehnder modulator (MZM) [4] , and nonlinear effects, such as cross-phase modulation (XPM) [5] and four-wave mixing (FWM), are also incapable of multi-channel processing [6] . Thus, along with the application of multi-level modulation formats, such as differential quadrature phase-shift keying (DQPSK) in OTDM systems [1,7] , the development and investigation of schemes that are capable of demultiplexing, such OTDM signals with phase-preserving and multi-tributary processing capabilities, are necessary.In this letter, an all-optical SPC that uses two cascaded PMs and optical band-pass filters (OBPFs) is experimentally investigated for optical quadrature phase-shift keying (QPSK) signals. We demonstrate the application of the SPC for the simultaneous demultiplexing of two 40-GB base-rate OTDM tributaries from an 80-GB OTDM RZ-DQPSK signal. Error-free performances were obtained for both base-rate tributaries. The power penalty was approximately 4 dB in the worst case. The SPC features a compact structure, high speed, low power penalty, and simultaneous two-tributary operation capacity, without assistance from a light source. With the possible capability of cascading such SPCs to extract more OTDM tributaries simultaneously, the proposed scheme has potential for use in future OTDM networks. Figure 1 shows the experimental setup of the SPC for the demultiplexing of an 80-GBd OTDM RZ-DQPSK signal. An optical pulse train centered at 1 549.65 nm with a repetition rate of 40 GHz and a full-width at half-maximum (FWHM) of 8 ps was generated using an EAM driven by a 40-GHz sine signal. The pulse train was then linearly compressed into a FWHM of 3.5 ps by...