Mach-Zehnder Delay Interferometer Research Articles

Optical Differential-Phase-Shift-Keying Demodulation Using a Silicon Microring Resonator

We have for the first time experimentally demonstrated an ultrasmall, low power penalty, and robust 10 - Gb/s differential-phase-shift-keying demodulator using a silicon-based microring resonator. The microring resonator is compatible with a wide range of signal bit rates. In optical transmission measurements with 11.6-km nonzero dispersion-shifted fiber, the microring resonator demodulator had comparative power penalty compared with a Mach-Zehnder delay interferometer both in single ended detection. Error-free detection was achieved.

Multi-format receiver for non-return-to-zero binary-phase-shift-keyed and non-return-to-zero amplitude-shit-keyed signals

A Multi-format receiver for both non-return-to-zero binary-phase- shift-keyed (NRZ-BPSK) signal and non-return-to-zero amplitude-shift- keyed (NRZ-ASK) signal is demonstrated. Multi-format signal detection is based on incoherent BPSK demodulation and ASK-BPSK format conversion. Incoherent BPSK demodulation is realized by a Mach- Zehnder delay interferometer (MZDI) and a feedback decoder. Transmission experiments validate the feasibility of multi-format receiver. This receiver has potential to serve as a useful terminal block for all-optical wavelength division-multiplexed (WDM) networks.

Multichip Differential Phase-Shift-Keyed Transmission Over (Non)Linear Optical Channels

The recently introduced multichip differential phase-shift keying (MC-DPSK) optical transmission format, entailing the modulation of relative phases over a moving transmission window of successive chip intervals, is analytically and numerically analyzed. The maximum-likelihood optimal MC-DPSK receiver is derived and synthesized using integrated-optic Mach-Zehnder delay interferometers, whose electrical outputs are interpreted as generalized Stokes' parameters. The MC-DPSK performance over a nonlinear fiber channel, limited by the combination of amplified spontaneous emission noise and self-phase modulation, is further derived and simulated, demonstrating that the lowest complexity three-chip binary-phase MC-DPSK receiver provides an ~1-dB Q-factor advantage over conventional DPSK.

Direct Detection Frequency Discrimination Optical Receiver for Minimum-Shift Keying Format Transmission

An incoherent detection scheme based on frequency discrimination for minimum-shift keying (MSK) optical transmission systems is proposed to significantly extend the reach of uncompensated transmission distance. The receiver consists of dual narrowband optical filters in association with an optical delay line. This photonic front end operates based on frequency discrimination principles of matched filters, rather than relying on the phase of the optical carrier. Hence, its performance is less sensitive to the all-pass quadratic phase transfer function of the fiber transmission medium and is thus less susceptible to fiber chromatic dispersion. The photonic front-end optical receiver for 40-Gb/s optical MSK offers a dispersion tolerance of up to plusmn340 ps/nm for 1-dB power penalty at a bit-error rate of 10-9. This achievement is approximately five to seven times better than that of the existing value based on the Mach-Zehnder delay interferometer (MZDI) optical balanced receiver. Furthermore, the receiver is shown to be robust to polarization-mode dispersion.

A staggered differential phase-shift keying modulation format for 100Gbit/s applications

We propose and demonstrate by numerical simulation a new phase modulation format, the staggered differential phase-shift keying (SDPSK), for 100 Gbit/s applications. Non-return-to-zero (NRZ) SDPSK signals was generated by using two phase modulators, and return-to-zero (RZ) SDPSK signals with 50% duty cycle was generated by cascading a dual-arm Mach-Zehnder modulator. The demodulation of 2 bit/symbol can be simply achieved on 1 bit rate through only one Mach-Zehnder delay interferometer and a balanced receiver. By comparing the transmission characteristics of the two staggered phase modulation formats with those of NRZ-DPSK, RZ-DPSK, NRZ-DQPSK, and RZ-DQPSK, respectively, we show that, the SDPSK signal has similar chromatic dispersion and polarization-mode-dispersion tolerance to the DPSK signal with same NRZ or RZ shape, while the SDPSK signal has stronger nonlinear tolerance than the DPSK or DQPSK signal. In addition, the SDPSK signal has the best transmission performance when each signal was transmitted over 106km optical SMF+DCF, and then launched into a third-order Gaussian optical bandpass filter placed with beyond 125GHz bandwidth.

All-optical format conversion from inverse-return-to-zero to non-return-to-zero using a Mach-Zehnder delay interferometer

All-optical format conversion from inverse-return- to-zero inverse-RZ to non-return-to-zero NRZ is realized by using a half-bit-delay Mach-Zehnder delay interferometer. Experimental results demonstrate that the converted NRZ signal has better receiver sensitivity than the back-to-back inverse-RZ signal. © 2008 Society of Photo-Optical Instrumentation Engineers.

A DPSK Receiver With Enhanced CD Tolerance Through Optimized Demodulation and MLSE

We experimentally demonstrate that a differential phase-shift keying (DPSK) receiver employing a Mach-Zehnder delay interferometer (MZDI) with a bit delay of less than one bit combined with maximum likelihood sequence estimation can considerably enhance the tolerance to chromatic dispersion (CD). Furthermore, we analyze the impact of sampling phase and optimize the MZDI bit delay for 10.7-Gb/s nonreturn-to-zero (NRZ)-DPSK demodulation. Our investigation shows that a 4000-ps/nm CD tolerance at 2-dB penalty is feasible for 10.7-Gb/s NRZ-DPSK.

Conversions among binary optical modulation formats

We study the intrinsic relations and conversions among different binary modulation formats such as non-return-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ), differential-phase-shift-keying (DPSK), duobinary, and alternate-mark-inversion (AMI). In particular, we experimentally demonstrate the new conversion from CSRZ to duobinary using a Mach-Zehnder delay interferometer (MZDI).

Multichip Differential Phase-Shift-Keyed Transmission Over (Non)Linear Optical Channels

The recently introduced multichip differential phase-shift keying (MC-DPSK) optical transmission format, entailing the modulation of relative phases over a moving transmission window of successive chip intervals, is analytically and numerically analyzed. The maximum-likelihood optimal MC-DPSK receiver is derived and synthesized using integrated-optic Mach-Zehnder delay interferometers, whose electrical outputs are interpreted as generalized Stokes' parameters. The MC-DPSK performance over a nonlinear fiber channel, limited by the combination of amplified spontaneous emission noise and self-phase modulation, is further derived and simulated, demonstrating that the lowest complexity three-chip binary-phase MC-DPSK receiver provides an ~1-dB Q-factor advantage over conventional DPSK.

40-Gb/s QPSK and 20-Gb/s PSK with inserted pilot symbols using self-homodyne detection

We proposed and experimentally demonstrated 40-Gb/s quadrature phase-shifted keying (QPSK) and 20-Gb/s binary phase-shifted keying (PSK) transmission systems with inserted pilot symbols, using a return-to-zero radio frequency (RZ-RF) driving signal in the transmitter and self-homodyne direct detection in the receiver. Different from other existing homodyne or conventional differential PSK/QPSK systems, the proposed PSK and QPSK modulation formats do not need any complicated pre-coder, post-processor or local oscillator. In the proposed QPSK systems, simultaneous detection of in-phase and quadature components is successfully achieved by using one Mach-Zehnder delay interferometer and following balanced detector, which significantly reduces the system complexity and implementation cost.

Simple method for mitigation of polarization crosstalk in silica planar lightwave circuit directional couplers

Polarization crosstalk in planar lightwave circuit directional couplers can cause significant polarization-dependence in interferometers that use them. We show a simple way to mitigate the polarization crosstalk without incurring a performance penalty or requiring extra fabrication steps. We demonstrate it on a 23-ps Mach-Zehnder delay interferometer

Polarization-insensitive planar lightwave circuit dual-rate Mach-Zehnder delay-interferometer

We demonstrate a silica waveguide Mach-Zehnder delay-interferometer that uses integrated switches to demodulate either 10- or 40-Gb/s differential phase-shift keyed signals. We achieved polarization insensitivity by using a half-wave plate and reducing polarization crosstalk in the couplers

Demodulation of DPSK signals up to 40 gb/s using a highly birefringent photonic bandgap fiber

Phase-to-intensity modulation conversion of differential phase-shift keying signals is successfully demonstrated at 10 and 40 Gb/s using a polarization Mach-Zehnder delay interferometer implemented with only 2.4 m of a highly birefringent air-guiding photonic bandgap (PBG) fiber. Such a PBG fiber exhibits a birefringence one order of magnitude larger than that of conventional polarization-maintaining fibers, thus enabling the realization of compact interferometers. Furthermore, its single material nature is expected to result in reduced temperature sensitivity.

A simple AMI-RZ transmitter based on single-arm intensity modulator and optical delay interferometer

In the paper, we propose and demonstrate a simple alternate-mark inversion return-to-zero (AMI-RZ) transmitter upgraded from existing plain RZ-OOK transmitter by employing an additional Mach–Zehnder delay interferometer (MZDI), eliminating the use of high-speed RF circuit and dual-drive Mach–Zehnder modulator. A delay-and-subtract operation is performed by the MZDI on the RZ-OOK signal to achieve alternating phases in successive mark pulses. The nonlinearity tolerance of the generated AMI-RZ signal was characterized by experiment at 10Gbs−1 and simulation at 40Gbs−1. The ghost-pulse, due to intra-channel four-wave-mixing (IFWM), with generated AMI-RZ and RZ-OOK formats was also investigated respectively at 40Gbs−1. The results showed that the generated AMI-RZ exhibited higher nonlinear tolerance over RZ-OOK, especially the tolerance against IFWM in the 40-Gbs−1 optical transmission system. This AMI-RZ transmitter scheme is simple, potentially low cost and can be integrated easily with the existing RZ-OOK transmitters for upgrading to AMI-RZ transmitters.

40 Gbit/s signal format conversion from NRZ to RZ using a Mach-Zehnder delay interferometer

40Gbit/s signal format conversion from NRZ to RZ using a Mach-Zehnder delay interferometer has been demonstrated for the first time. The converted RZ signal has high receiver sensitivity and shows significantly improved transmission performance.