NRZ-DPSK Signals Research Articles

Multi-Channel NRZ/RZ-DPSK to CSRZ-DPSK Format Conversion Based on Nonlinear Polarization Rotation of SOA**Supported by the National Natural Science Foundation of China under Grant Nos 61425022, 61522501, 61675004, 61307086, 61475024, 61672290, 61475094 and 61605013, the National Basic Research Program of China under Grant Nos 2015AA015501, 2015AA015502, 2015AA015504, 2015AA016904 and 2015AA016901, and the Beijing Nova Program under Grant No Z141101001814048.

We present an all-optical nonreturn-to-zero/return-to-zero (NRZ/RZ) to carrier-suppressed return-to-zero (CSRZ) format conversion scheme for differential phase-shift keying (DPSK) signals. The conversion is based on nonlinear polarization rotation of a semiconductor optical amplifier (SOA). The 4-channel NRZ-DPSK or RZ-DPSK signals at 10 Gb/s are simultaneously converted to the corresponding CSRZ-DPSK signals, with −0.8 and 1.4 dB average power penalties, respectively. Additionally, high quality format conversion performances are shown with the optical spectra and eye diagrams.

Polarization-insensitive wavelength conversion of 40 Gb/s NRZ-DPSK signals in a silicon polarization diversity circuit.

Polarization insensitive wavelength conversion of a 40 Gb/s non-return-to-zero (NRZ) differential phase-shift keying (DPSK) data signal is demonstrated using four-wave mixing (FWM) in a silicon nanowire circuit. Polarization independence is achieved using a diversity circuit based on polarization rotators and splitters, which is fabricated by a simple process on the silicon-on-insulator (SOI) platform. Error-free performance is achieved with only 0.5 dB of power penalty compared to the wavelength conversion of a signal with well optimized input polarization. Additionally, data transmission over 161 km standard single-mode fiber (SSMF) is demonstrated at 40 Gb/s using optical phase conjugation (OPC) in the proposed circuit.

Silicon/Silica-Hybrid-Integrated Delay Line Interferometer for Demodulation of PSK Formats

We propose a 1-bit delay line interferometer (DLI) with a hybrid Mach–Zehnder structure for demodulation of phase-shift-keying (PSK) signals. Each arm contains silicon (Si)/Si-rich silica waveguides and spot size converters to generate optical delay using both of physical length and refractive index changes. This report covers the numerical analysis and experimental investigations, ranging from basic characterization to application. We employed a DLI with a free spectral range of 10.2 GHz in a demodulation experiment of 10.0-Gb/s NRZ-DPSK signals. As a result, very clear eye patterns and error-free operation are obtained from the C- to L-telecommunications bands with a device size per channel of 1.6 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{mm}^{2}$</tex></formula> . The novel and effective design provides a demodulator in simple and high-density device integration.

In-line residual chromatic dispersion measurement for NRZ-DPSK and RZ-DPSK signals using a novel RF spectrum phase detection technique

In this paper, a novel method of in-line chromatic dispersion (CD) measurement is proposed, we theoretically and experimentally demonstrated the CD measurement of 40-Gbit/s NRZ-DPSK and RZ-DPSK signals by a novel RF spectrum phase detection technique, this is performed using in-band tone monitoring RF, electrically down-converted to direct current (DC) or a low intermediate-frequency (IF) of less than 1MHz through electronic mixing with local oscillator (LO) of 5GHz. The measurement provides CD measuring range (±425ps/nm), and independent of the bit-rate and data format. In addition, the use of electronic mixer and low-speed detectors makes it cost effective for in-line CD measurement.

Amplitude regeneration of NRZ–DPSK signal with a feed-forward control circuit

An optical-and-electrical hybrid-type amplitude regenerator for an NRZ–DPSK signal suffering from optical amplifier noise is described. The system is a feed-forward control circuit composed of a coupler, a photo detector, and an intensity modulator, and works to suppress intensity fluctuations in a DPSK signal while preserving phase information. A schematic explanation of how the DPSK transmission performance is improved with intensity noise suppression during transmission is presented, and an experiment to demonstrate its effect is conducted.

Photonic crystal fiber based Mach-Zehnder interferometer for DPSK signal demodulation

We demonstrate a novel fiber-based in-line DPSK demodulator using an in-fiber Mach-Zehnder interferometer (MZI). The device is fabricated by mismatch splicing of a photonic crystal fiber (PCF) with standard single mode fibers. The spectral characteristics at different PCF lengths are analyzed. The envelope of the interference fringes show a period that is inversely proportional to the PCF length, and is attributed to the periodic coupling between the core mode and the cladding mode. Error free demodulations of 10-Gb/s RZ- and NRZ-DPSK signals have been demonstrated using the in-fiber PCF-MZI demodulator with only 3-m PCF to introduce 91-ps delay. Wideband DPSK demodulation has also been achieved.

Multi Impairment Monitoring for Optical Networks

As optical networks become more complex, the need for in-line monitoring of more than just channel wavelength, power and OSNR becomes compelling. In this paper we describe an asynchronous delay tap sampling technique coupled with statistical machine learning that enables a single monitor to measure multiple simultaneous impairments on multiple formats. We demonstrate the technique for simultaneous measures of CD and 1st order PMD on a 40 Gbit/s NRZ-DPSK signal.

Low-timing-jitter all-optical clock recovery for 40 Gbits/s RZ-DPSK and NRZ-DPSK signals using a passively mode-locked quantum-dot Fabry–Perot semiconductor laser

We investigate experimentally all-optical clock recovery for return-to-zero (RZ) and nonreturn-to-zero (NRZ) differential phase-shift keying (DPSK) signals at 40 Gbits/s using a passively mode-locked quantum-dot Fabry-Perot (QD-FP) semiconductor laser. The QD-FP laser exhibits a beat spectrum linewidth of 80 kHz, which enables a recovered clock signal with a root-mean-square timing jitter of 160 fs for the RZ-DPSK signal and 240 fs for the NRZ-DPSK signal. The timing jitter of the recovered clock signal is characterized for different values of the input signal power and the input signal optical signal-to-noise ratio.

High-Order Ultrawideband Pulse Generation from NRZ-DPSK Signals

A simple method to generate ultrawideband (UWB) doublet and triplet from nonreturn-to-zero (NRZ) differential phase shift keying (DPSK) signals is proposed and experimentally demonstrated. The proposed configuration consists of a Mach–Zehnder modulator (MZM) to generate NRZ-DPSK signals, a section of single-mode fibre to form a microwave bandpass filter, which is used to generate doublet pulses, and a Gaussian optical bandpass filter (OBF), which serves as a frequency discriminator to generate higher-order UWB pulses. A pair of polarity-reversed triplet pulses is achieved by locating the optical carrier at the positive and negative linear slopes of the OBF, where the OBF detuning is 0.12 nm and -0.2 nm, respectively. The spectra of the pair of UWB triplets have a central frequency of 5 GHz and 5.6 GHz, and have a -10 dB bandwidth of 6.9 GHz and 8.1 GHz, respectively. The UWB pulses remain doublet shape when the light wavelength is located at the peak of the OBF. The spectrum of the doublet has a central frequency of 5.6 GHz and a -10 dB bandwidth of 6.9 GHz.

Phase Regeneration of NRZ-DPSK Signals Based on Symmetric-Pump Phase-Sensitive Amplification

Symmetric-pump phase-sensitive amplification (SP-PSA) is investigated experimentally. Symmetric pump waves are derived using carrier-suppressed return-to-zero modulation. The SP-PSA is used for phase regeneration of a phase-noise degraded nonreturn-to-zero differential phase-shift keying signal, significantly improving signal quality

Slow light on Gbit/s differential-phase-shift-keying signals

We demonstrate, via simulation and experiment, slowing down of a phase-modulated optical signal. A 10.7-Gb/s NRZ-DPSK signal can be delayed by as much as 42 ps while still achieving error free via broadband SBS-based slow light. We further analyze the impact of slow-light-induced data-pattern dependence on both constructive and destructive demodulated ports. By detuning the SBS gain profile, we achieve 3-dB Q-factor improvement by the reduction of pattern dependence. Performance comparison between NRZ-DPSK and RZ-DPSK shows that robustness to slow-light-induced pattern dependence is modulation format dependent.

Comparison of Cross-Gain Modulation Effect of Manchester-Duobinary, RZ-DPSK, NRZ-DPSK, RZ, and NRZ Modulation Formats in SOAs

Conventional on-off keyed signals, such as return-to-zero (RZ) and nonreturn-to-zero (NRZ) signals are susceptible to cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) due to pattern effect. In this letter, XGM effect of Manchester-duobinary, RZ differential phase-shift keying (RZ-DPSK), NRZ-DPSK, RZ, and NRZ signals in SOAs were compared. The experimental results confirmed the reduction of crosstalk penalty in SOAs by using Manchester-duobinary signals