Differential Phase-shift Keying Signals Research Articles

Simultaneous DPSK demodulation and wavelength conversion scheme for Rayleigh backscattering noise mitigation in WDM-PON

We propose a scheme for mitigating Rayleigh backscattering noise and demodulating differential phase-shift keying (DPSK) signals in wavelength-division-multiplexed passive optical networks (WDM-PONs) with injection-locked Fabry-Perot laser diodes (FP-LDs). Signal demodulation and wavelength conversion are simultaneously realized on the basis of the frequency deviation and red shift of longitude modes in the FP-LDs. Experimental results demonstrate that the demodulation and wavelength conversion of 2.5-Gb/s DPSK signals are achieved. A power penalty of about 1.6 dB at a bit error rate of 10-9 is measured after transmission over 25-km single mode fiber.

Fiber-based optical parametric amplif ier for 40-Gb/s NRZ-DPSK signal transmission system employing QC-LDPC codes

In this letter, we investigate quasi-cyclic low-density parity-check (QC-LDPC) codes in a 40-Gb/s nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) signal transmission system based on a fiber-based optical parametric amplifier (FOPA). A constructed algorithm of QC-LDPC codes according to the optimizing set of shift values on the circulant permutation matrix (CPM) of the basis matrix is proposed. Simulation results prove that the coding gain in the encoded system can be realized at 10.2 dB under QC-LDPC codes with a code rate of 5/6 when the bit error rate (BER) is 10-9. In addition, the error-floor level originating from the uncoded system is suppressed.

Broadband Modulation Performance of 100-GHz EO Polymer MZMs

We experimentally characterize the performance of 100-GHz electro-optical polymer Mach-Zehnder modulators in both dual-drive and single-drive versions using broadband modulation. For the dual-drive version, we measure bit-error rate (BER) at 80 Gbit/s for differential phase-shift keying (DPSK) and >; 90 Gbit/s for on-off keying (OOK). The eye diagrams of 100 Gbit/s OOK and S21 measurement of up to 110-GHz further indicate a response bandwidth of >;100 GHz. Tunable-chirp operation is also demonstrated by changing the phase and amplitude of each driving signal. For the single-drive version, a BER of 10-9 is achieved for both 100-Gbit/s OOK and DPSK signals without optical or electrical equalization. The single-drive version shows a 7-dB bandwidth of >; 110-GHz and a chirp factor of as low as -0.02.

Reconfigurable crystal-based demodulator for both differential-phase-shift keying and differential-quadrature-phase-shift keying formats: principle, design and performance

A reconfigurable demodulator for both differential-phase-shift keying (DPSK) and differential-quadrature-phase-shift keying (DQPSK) formats is theoretically and experimentally presented. In this crystal-based demodulator, a rotatable quarter-wave plate is implemented to switch the operation of the device between DPSK and DQPSK modes. To mitigate polarisation-dependent-frequency shift (PDFS), the authors control uniformity of optical path length differences for the orthogonal polarisation states in the delay crystal, a liquid crystal phase-tuning retarder is used to improve the tuning time. The design and fabrication consideration of this device are also discussed. The packaged device has a low PDFS of within ±0.2 GHz over C-band, fast tuning time of 20.5 ms, error-free demodulation of optical transponder unit-3 DPSK and DQPSK signals can be achieved.

Generation and transmission of DPSK signals using a directly modulated passive feedback laser

The generation of differential-phase-shift keying (DPSK) signals is demonstrated using a directly modulated passive feedback laser at 10.709-Gb/s, 14-Gb/s and 16-Gb/s. The quality of the DPSK signals is assessed using both noncoherent detection for a bit rate of 10.709-Gb/s and coherent detection with digital signal processing involving a look-up table pattern-dependent distortion compensator. Transmission over a passive link consisting of 100 km of single mode fiber at a bit rate of 10.709-Gb/s is achieved with a received optical power of -45 dBm at a bit-error-ratio of 3.8 × 10(-3) and a 49 dB loss margin.

Phase regeneration of DPSK signals in a highly nonlinear lead-silicate W-type fiber

We experimentally demonstrate phase regeneration of a 40-Gb/s differential phase shift keying (DPSK) signal in a 1.7-m long highly nonlinear lead silicate W-type fiber using a degenerate two-pump phase-sensitive amplifier (PSA). Results show an improvement in the Error Vector Magnitude (EVM) and a reduction of almost a factor of 2 in the phase noise of the signal after regeneration for various noise levels at the input.

All-Optical Signal Regenerator for Differential Phase-Shift Keying Format Employing a Differential Encoding Circuit With SOA-MZIs

We propose and demonstrate the all-optical differential phase-shift keying (DPSK) signal regenerator with differential encoder employing a newly proposed all-optical T-type flip-flop (T-FF). The proposed configuration of an all-optical T-FF employs a counter-faced configuration of two semiconductor optical amplifier Mach–Zehnder interferometers (SOA-MZIs) to realize a short feedback path without loopback waveguide for high-speed operation. Numerical simulation reveals that it can operate as a T-FF at a bit-rate of 10-Gb/s under the condition of a carrier life time of 10 ps. We also experimentally demonstrate the operation of the proposed all-optical T-FF at a bit-rate of 2 Gb/s with a fiber-based experimental setup. Finally, we demonstrate the possibility of a DPSK signal regenerator with the combination of the proposed all-optical T-FF and the standard SOA-MZI by numerical simulations, which can drastically improve the quality of a DPSK signal degraded in transmission. We believe that the proposed configuration of an all-optical DPSK regenerator is promising for future optical networks.

Distributed parametric amplifier for RZ-DPSK signal transmission system

We have experimentally demonstrated a single pump distributed parametric amplification (DPA) system for differential phase shift keying (DPSK) signal in a spool of dispersion-shifted fiber (DSF). The gain spectrum of single pump DPA is thoroughly investigated by both simulation and experiment, and a possible reference for optimal input pump power and fiber length relationship is provided to DPA based applications. Furthermore, DPSK format is compared with on-off keying (OOK) within DPA scheme. Eight WDM signal channels at 10-Gb/s are utilized, and approximately 0.5-dB power penalties at the bit-error rate (BER) of 10(-9) are achieved for return-to-zero DPSK (RZ-DPSK), comparing to larger than 1.5-dB with OOK format. In order to improve the system power efficiency, at the receiver, the pump is recycled by a photovoltaic cell and the converted energy can be used by potential low-power-consuming devices, i.e sensors or small-scale electronic circuits. Additionally, with suitable components, the whole DPA concept could be directly applied to the 1.3-μm telecommunication window along the most commonly used single-mode fiber (SMF).

Chromatic Dispersion Monitoring for NRZ-DPSK System Using Asynchronous Amplitude Histogram Evaluation

We propose and demonstrate a chromatic dispersion (CD) monitoring technique for a nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) signal generated with a Mach-Zehnder modulator at 40 Gb/s by analyzing the waveform overshoot after transmission. Without demodulating the NRZ-DPSK signal, the CD up to 120 ps/nm is monitored experimentally via the amplitude of the overshoot. Furthermore, based on the asynchronous amplitude histogram (AAH) evaluation method, a novel histogram processing method, which is more convenient, is proposed and investigated. Experimental results show that the monitoring scheme for CD is independent of optical signal-to-noise ratio (OSNR) within a certain range. This technique needs neither demodulating the signal nor extracting the synchronous clock, and it can be applied to high-order modulation formats at different bit rates.

Generation of Return-to-Zero Optical Pulses Using Directly Modulated Chirp Managed Laser

We propose and experimentally demonstrate the generation of return-to-zero (RZ) optical pulses with duty cycles of 33% and 67% using a directly modulated chirp managed laser (CML) driven by a sinusoidal signal at half pulse rate. No external pulse carver is required. The transmission performance of a 10-Gb/s RZ differential phase-shift keying (RZ-DPSK) signal based on CML pulses is also investigated. It shows comparable fiber chromatic dispersion tolerance and fiber nonlinearity robustness in single-channel test, compared with the conventional RZ-DPSK signal generated, via an external pulse carver.

Bit-Rate-Variable DPSK Demodulation Using Silicon Microring Resonators With Electro-Optic Wavelength Tuning

We demonstrate a bit-rate-variable differential phase-shift keying (DPSK) demodulator based on silicon microring resonators (MRRs) with an integrated diode for wavelength tuning. The resonance wavelength of the MRR may be tuned by carrier injection and depletion. Error-free operations (bit error rate <;10-9) have been achieved for all tuning wavelengths. In addition, the proposed scheme can demodulate DPSK signals over a wide range of bit rates from below 25 to 40 Gb/s.

All-optical simultaneous drop and wavelength conversion of DPSK data

We demonstrate an all-optical scheme for the simultaneous drop and wavelength conversion of bursts of data from a continuous stream of differential phase-shift keyed (DPSK) signals. This function is obtained in a single semiconductor optical amplifier Mach-Zehnder interferometer thanks to proper nonlinear interaction of the data stream and an optical gate signal at different wavelength. Fast switching-time enabling wavelength shifting operation on continuous DPSK data stream at 10 and 40 Gb/s without any bit loss is reported. Corresponding measured power penalties are negligible at 10 Gb/s and about 1.7 dB at 40 Gb/s.

Bit-Rate Flexible Demodulation of DPSK Signals Based on Phase Sensitive Gain in Cascaded Four-Wave Mixing

We demonstrate bit-rate flexible demodulation of differential phase-shift keying (DPSK) signals in a linear structure. The demodulator utilizes a tunable optical delay based on the combination of wavelength conversion in a photonic crystal fiber and dispersion in a short section of single-mode fiber. Error-free demodulations for return-to-zero-DPSK signals at both 25 and 40 Gb/s have been successfully achieved.

Reconfigurable Four-Input Photonic Logic Minterms and Maxterms Generation Using SOAs

A generation approach of photonic logic minterms and maxterms, which is fully reconfigured minterms and maxterms for four-input 40-Gb/s differential phase-shift keying (DPSK) signals, has been demonstrated based on delay interferometers and semiconductor optical amplifiers. The maxterms are directly derived by inverting the corresponding minterms, according to their complementary characteristics. Reconfigurations of the scheme, enabled by tuning either the phase shift of delay interferometer or input wavelength, are shown among 16 minterms, as well as corresponding maxterms. A full set of minterms and maxterms are captured with clear open eye diagrams and extinction ratios of over 10 and 8 dB, respectively, which indicate the potential of further realizing arbitrary complex logic operations.

Influence of Fiber-Bragg Grating-Induced Group-Delay Ripple in High-Speed Transmission Systems

The implementation of a chirped fiber-Bragg grating (FBG) for dispersion compensation in high-speed (up to 120&#x00A0;Gbit/s) transmission systems with differential and coherent detection is, for the first time, experimentally investigated. For systems with differential detection, we examine the influence of group-delay ripple (GDR) in 40&#x00A0;GBd 2-, 4-, and 8-ary differential phase shift keying (DPSK) systems. Furthermore, we conduct a nonlinear-tolerance comparison between the systems implementing dispersion-compensating fibers and FBG modules, using a 5&#x00D7;80&#x00A0;Gbit/s 100-GHz-spaced wavelength division multiplexing 4-ary DPSK signal. The results show that the FBG-based system provides a 2 dB higher optimal launch power, which leads to more than 3&#x00A0;dB optical signal-to-noise ratio (OSNR) improvement at the receiver. For systems with coherent detection, we evaluate the influence of GDR in a 112&#x00A0;Gbit/s dual-polarization quadrature phase shift keying system with respect to signal wavelength. In addition, we demonstrate that, at the optimal launch power, the 112&#x00A0;Gbit/s systems implementing FBG modules and that using electronic dispersion compensation provide similar performance after 840 km transmission despite the fact that the FBG-based system delivers lower OSNR at the receiver. Lastly, we quantify the GDR mitigation capability of a digital linear equalizer in the 112 Gbit/s coherent systems with respect to the equalizer tap number (Ntap). The results indicate that at least Ntap=9 is required to confine Q-factor variation within 1&#x00A0;dB.

Single- and Dual-Channel DPSK Signal Amplitude Regeneration Based on a Single Semiconductor Optical Amplifier

We experimentally demonstrate that, based on operational condition optimization, a common quantum well (QW) semiconductor optical amplifier (SOA) has the ability of amplitude regeneration for return-to-zero (RZ) differential phase shift keying (DPSK) signals. For a single-channel RZ-DPSK regeneration scheme, a significant eye-opening enhancement and a negative power penalty of about 1.0 dB are obtained. For dual-channel RZ-DPSK regeneration, it can also be found that the eye-opening improvement and power penalty decrease in each channel. In addition, the DPSK regeneration scheme based on a single QW SOA is quite simple and stable.

Polarization insensitive wavelength multicasting of DPSK signal using four-wave mixing in a birefringent photonic crystal fiber

We demonstrate polarization-insensitive wavelength multicasting of differential phase-shift keying (DPSK) signal based on four-wave mixing (FWM) in a highly nonlinear, birefringent photonic crystal fiber (PCF). The 10-Gbit/s RZ-DPSK input signal is copied to 8 wavelength channels through FWM with three optical pumps. The pump wavelengths are unequally spaced to avoid undesirable crosstalk from pump-to-pump beatings. The dependence of conversion efficiency on input signal polarization is suppressed by exploiting the PCF birefringence together with control of the pump polarizations. All pump polarizations are aligned at 45 degrees to the principal axes of the PCF. Open eyes and error-free results are obtained in all the 8 multicast channels for polarization-scrambled RZ-DPSK input signal.

Performance Improvement of DPSK Signal Reception Using Reconfigurable Multiple Bit Differential Detection in the Presence of Carrier Frequency Offset

In this paper we propose a reconfigurable multiple bit differential detection (MBDD) algorithm with diversity reception in the form of postdetection equal-gain combining (EGC) that can be used for the differential phase shift keying (DPSK) signal reception in the presence of significant frequency offsets. The proposed algorithm is based on the MBDD algorithm with the introduction of a mechanism for the estimation of the frequency offset. The algorithm is checking N c frequency offsets around zero offset and chooses the one that is the most likely. The analysis shows that the receiver with the proposed algorithm provides signal reception with almost equal quality in a wide range of carrier frequency offsets around zero frequency offset.

RZ-DQPSK Signal Amplitude Regeneration Using a Semiconductor Optical Amplifier

An all-optical return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) signal regeneration scheme is experimentally demonstrated. Thanks to the gain saturation effect, common quantum-well semiconductor optical amplifiers have the ability to regenerate the amplitude distorted RZ-DQPSK signal, so amplitude noise can be reduced while phase information will not be distorted. A significant eye-opening improvement and a negative power penalty of about 1 dB can be achieved for an 80 Gb/s RZ-DQPSK signal.

High-speed addition/subtraction/complement/doubling of quaternary numbers using optical nonlinearities and DQPSK signals

We propose an innovative approach to implementing multiple arithmetic functions of quaternary numbers using optical nonlinearities and differential quadrature phase-shift keying (DQPSK) signals. By adopting 100 Gbit/s DQPSK signals (A, B) and exploiting nondegenerate four-wave mixing (FWM) for addition/subtraction and degenerate FWM for complement and doubling in a single highly nonlinear fiber, we demonstrate 50 Gbaud/s simultaneous quaternary addition (A+B), dual-directional subtraction (A-B, B-A), complement (-A, -B), and doubling (2B). Power penalties less than 4 dB (addition), 3 dB (dual-directional subtraction), 2 dB (complement), and 3.1 dB (doubling) are observed at a bit-error rate of 10(-9).