Differential Phase-shift Keying Signals Research Articles

Semiconductor Optical Amplifier (SOA)-Driven Reservoir Computing for Dense Wavelength-Division Multiplexing (DWDM) Signal Compensation

Optical signal processing (OSP) technology is a crucial part of the optical switching node in the modern optical-fiber communication system, especially when advanced modulation formats, e.g., quadrature amplitude modulation (QAM), are applied. However, the conventional on–off keying (OOK) signal is still widely used in access or metro transmission systems, which leads to the compatibility requirement of OSP for incoherent and coherent signals. In this paper, we propose a reservoir computing (RC)-OSP scheme based on nonlinear mapping behavior through a semiconductor optical amplifier (SOA) to deal with the non-return-to-zero (NRZ) signals and the differential quadrature phase-shift keying (DQPSK) signals in the nonlinear dense wavelength-division multiplexing (DWDM) channel. We optimized the key parameters of SOA-based RC to improve compensation performance. Based on the simulation investigation, we observed a significant improvement in signal quality over 10 dB compared to the distorted signals on each DWDM channel for both the NRZ and DQPSK transmission cases. The compatible OSP achieved by the proposed SOA-based RC could be a potential application of the optical switching node in the complex optical fiber communication system, where incoherent and coherent signals meet.

Single Wavelength Simultaneous Optical Intensity-Polarization-Phase Modulation for Multi-Dimensional Optical Transmission

We propose a novel multi-dimensional optical transmission system based on a direct detection system. In the proposed system, quadrature phase shift keying (QPSK), binary polarized intensity rotational frequency shift keying (PIRBFSK), and binary differential phase shift keying (DBPSK) signals modulated by optical intensity, polarization, and phase are simultaneously transmitted for optical multi-dimensional transmission. The signal transmission performance of the proposed modulation technique and the possible interference of each dimension modulation were numerically and experimentally analyzed. The performance of the proposed system was verified using the bit error rate (BER), eye diagram, and spectrum of the received multi-dimensional signal.

High wavelength-resolved state of polarization monitoring method based on stimulated Brillouin scattering effect

A state of polarization (SOP) monitoring method with high wavelength resolution, based on the stimulated Brillouin scattering (SBS) in optical fiber is presented. By scanning the wavelength of pump which stimulates SBS effect, the signal spectrum with high resolution of ~ 0.1 pm can be obtained. Then, through measuring the signal spectra under six specific polarization states of pump, the Stokes vectors of each wavelength component of signal are retrieved. The results show that a mean error which is 0.018 is achieved for the wavelength-resolved SOP monitoring of a 40-Gb/s nonreturn-to-zero differential quadrature phase-shift keying (NRZ-DQPSK) signal. This monitoring method provides effective capability for estimation of polarization mode dispersion (PMD).

DPSK over inverse pulse position modulation with high extinction ratio for optical label switching

AbstractOptical label switching (OLS) is a promising solution for rapidly growing packet based internet traffic and data switching in data center. Most proposed schemes apply orthogonal modulation, which superimpose a nonamplitude modulated label signal onto a Manchester coded or pulse position modulated (PPM) ASK payload signal. The extinction ratio (ER) has to be reduced for overlaid signal. To avoid the quality degradation of payload signal from low ER, a differential phase shift keying (DPSK) over inverse PPM is proposed in this paper. Due to the high mark ratio of the inverse PPM, the proposed DPSK over inverse PPM modulation achieves a high ER for the ASK signal while induces limited crosstalk to the DPSK signal. Compare with the previously proposed schemes, the test results show the proposed DPSK over inverse 4PPM modulation achieves an optimum ER improvement of at least 6 dB to support an extended of at least 10.5 km.

All-optical 3R regeneration for DPSK signal based on a semiconductor optical amplifier scheme.

This paper presents experimental demonstration of an all-optical 3 R (re-amplification, re-shaping, re-timing) regeneration scheme for differential phase-shift keying (DPSK) signals, which consists of a clock recovery module and a phase-regeneration module. The clock recovery module is based on a mode-locked fiber laser, and the optical clock is extracted with low timing jitter of 29 ps from a degraded 10 Gb/s DPSK signal. The phase regenerator consists of a one-bit delay interferometer demodulation stage and a semiconductor optical amplifier in which cross-phase modulation and nonlinear polarization rotation occur simultaneously. The results show that, after 3 R regeneration, the receiver sensitivity is improved by more than 1.6 dB for a bit error rate of 1 E-9.

A DPSK demodulator for biomedical application

SummaryIn this study, a differential phase‐shift‐keying (DPSK) demodulator, which is implemented by digital circuit, is proposed. A differential voltage clipper is used to generate narrow pulses at the extremum of the received modulated signal. Regarding the DPSK signal, the outputs of the clipper have double frequency. In order to halve the frequency, a frequency divider is applied to get synchronous clock. Two binary counters are used to detect phase variation; the data are recovered after two times sampling. This technique removes the need for voltage controlled oscillator (VCO). The proposed demodulator is postlayout simulated in a 0.18‐μm CMOS process, with a power of 64 μW and active area of 68 × 70 μm2. The demodulator recovers 10 Mb/s data rate at 10‐MHz carrier frequency using a 1.8‐V power supply.

Fast Digital Algorithms for the Noncoherent Demodulation of the Differential Phase-Shift Keyed Binary Signals

In this paper, the fast digital algorithms for noncoherent demodulation of the binary and four position differential phase-shift keyed signals providing the minimum number of arithmetic operations over the carrier period have been studied. The properties of the demodulator responses have been considered and the expressions for the incorrect reception probability have been found while the useful signal is distorted by Gaussian white noise. It is shown that the presented algorithms realize the functional frequency selection, they provide a potential interference immunity against Gaussian noises and, as a result, they implement an optimal signal extraction in broad-band noises. Operability and efficiency of the introduced demodulators have been confirmed by experimental data obtained from statistical simulation.

Performance Comparison of All-Optical Amplify-and-Forward Relaying FSO Communication Systems With OOK and DPSK Modulations

All-optical amplify-and-forward (OAF) relaying technique can amplify and filter the attenuated optical signal in optical domain, and thus is regarded as a simple way to extend the transmission distance of free-space optical (FSO) communication systems. At the relaying node, however, the incident background radiation and the amplified spontaneous emission noise of the deployed erbium-doped fiber amplifier will deteriorate the optical signal-to-noise, therefore causing the degradation of the system's bit error ratio (BER). In this paper, we perform simulations and experiments on FSO system with on-off keying (OOK) and differential phase-shift keying (DPSK) signals, focusing on the receiving sensitivity loss (RSL) of the OAF-assisted dual-hop system. Taking the BER level of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> as the reference, we find that the DPSK system suffers more than 8 dB RSL at the data rate of 5 Gb/s in simulation, while the OOK system gets less than 1 dB RSL at the same data rate. In the following experiments, the obtained results exhibit that RSL of DPSK system is nearly 10 dB, which of OOK system is less than 1.5 dB, shown similarly property to the simulations.

Transmission Performance of 112 Gb/s POLMUX QPSK Signal in OOK/DPSK WDM System

AbstractIn this article, the impact of cross-phase modulation (XPM) and cross-polarization modulation (XpolM) on transmission of 112 Gb/s polarization multiplexed quadrature phase shift keying (POLMUX QPSK) signal in a wavelength division multiplexing (WDM) system has been investigated. This WDM system comprises of on-off keying (OOK) or differential phase shift keying (DPSK) channels. It is observed that the effects of XPM and XpolM are greatly reduced in a hybrid system of co-propagating OOK and DPSK channels. This is due to the dominance of phase modulation of DPSK signals rather than the intensity modulated OOK signals. The error vector magnitude (EVM) of the received optical signal is evaluated for the increase in number of neighbouring OOK and DPSK channels respectively within a bandwidth of 350 GHz. Also, the effect of increase in bit rate for two neighbouring OOK and DPSK channels has been observed individually on the 112 Gb/s POLMUX QPSK signal. It is concluded that DPSK signals display an improvement of −9.44 dB in EVM over OOK signals when there are eight neighbouring channels in the transmission system.

Performance investigation of 110-Gbps optical MSK system using a Quad Mach-Zehnder IQ modulator

In this paper, numerical simulation is conducted to investigate the generation, transmission and detection of a 110 Gbps optical Minimum Shift Keying (MSK) signal. The transmitter has been designed using a Quad Mach-Zehnder IQ Modulator. At the transmitter, a 110 Gbps optical MSK signal with constant envelope and a continuous phase is generated by combining signals of I-arm and $$90^\circ$$ phase shifted of Q-arm. Error-free transmission of 110 Gbps optical MSK signal is achieved after traversing a distance of 240 km, also a comparison is made with respect to Differential Phase Shift Keying (DPSK) to show its effectiveness. At the receiver side, the original signal is recovered through a balanced detection method, with a power penalty of around 3.34 dB. Also, BER curves of different bit rates for MSK are studied ranging from 40 to 120 Gbps and found that maximum 110 Gbps can be achieved error-free. The optical spectrum of both MSK and DPSK signals are observed and found that MSK is having narrower main lobes with smaller side lobes compared with that of DPSK, which in turn results in an increase in spectral efficiency and reduction in intersymbol interference.

Research on the output bit error rate of 2DPSK signal based on stochastic resonance theory

Binary differential phase-shift keying (2DPSK) signal is mainly used for high speed data transmission. However, the bit error rate of digital signal receiver is high in the case of wicked channel environment. In view of this situation, a novel method based on stochastic resonance (SR) is proposed, which is aimed to reduce the bit error rate of 2DPSK signal by coherent demodulation receiving. According to the theory of SR, a nonlinear receiver model is established, which is used to receive 2DPSK signal under small signal-to-noise ratio (SNR) circumstances (between −15 dB and 5 dB), and compared with the conventional demodulation method. The experimental results demonstrate that when the input SNR is in the range of −15 dB to 5 dB, the output bit error rate of nonlinear system model based on SR has a significant decline compared to the conventional model. It could reduce 86.15% when the input SNR equals −7 dB. Meanwhile, the peak value of the output signal spectrum is 4.25 times as that of the conventional model. Consequently, the output signal of the system is more likely to be detected and the accuracy can be greatly improved.

Experimental investigation of polarization insensitivity and cascadability with semiconductor optical amplifier-based differential phase-shift keyed wavelength converter

We experimentally investigate the polarization insensitivity and cascadability of an all-optical wavelength converter for differential phase-shift keyed (DPSK) signals for the first time. The proposed wavelength converter is composed of a one-bit delay interferometer demodulation stage followed by a single semiconductor optical amplifier. The impact of input DPSK signal polarization fluctuation on receiver sensitivity for the converted signal is carried out. It is found that this scheme is almost insensitive to the state of polarization of the input DPSK signal. Furthermore, the cascadability of the converter is demonstrated in a two-path recirculating loop. Error-free transmission is achieved with 20 stage cascaded wavelength conversions over 2800 km, where the power penalty is <3.4 dB at bit error rate of 10−9.

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.

Demonstration of Optical FEC Coding Scheme With Convolutional Code Consisting of a Signal Source

In this letter, we experimentally demonstrated an all-optical forward error correction (FEC) coding scheme with the $(7, 5)_{8}$ convolutional code using a single signal source to compensate time-dependent noise. The proposed coding scheme was comprised of optical XOR gates, delay lines, and optical wavelength converters, which are based on four-wave mixing in highly non-linear fibers. The temporal waveforms of the optical FEC coding scheme were experimentally achieved for 10 Gb/s return-to-zero differential phase shift keying (RZ-DPSK) signals modulated with $2^{23}-1$ , and the obtained idler signals accurately corresponded to the $(7, 5)_{8}$ code between any input signals. Under the optimized conditions of operational wavelengths, the proposed scheme theoretically offered 4.0 and 3.5 dB net coding gains for the conditions of BER $\geq 10^{-8}$ and BER $= 10^{-9}$ , respectively, owing to its small power penalties.

Noncoherent detection of DQPSK in OFDM systems using predictive VA

Noncoherent detection of differential quaternary phase shift keying (DQPSK) signals in OFDM systems is efficiently implemented using a predictive Viterbi algorithm (VA) operating on a trellis with just ST = MP−1 states instead of MP states, where M denotes an M-ary PSK constellation and P denotes the order of the prediction filter. The prediction filter coefficients are generated based on the channel DFT alone making a high SNR approximation, since the estimation of the noise-variance using training symbols results in loss of throughput.

The DPSK Signal Noncoherent Demodulation Receiver Based on the Duffing Oscillators Array

Chaotic communication requires the knowledge of corresponding phase relationship between the primary phase of Duffing oscillator’s internal driving force and the primary phase of the undetected signal. Currently, there is no method of noncoherent demodulation for DPSK (Differential Phase Shift Keying) signal and mobile communication signal by Duffing oscillator. To solve this problem, this study presents a noncoherent demodulation method based on the Duffing oscillators array and Duffing oscillator optimization. We first present the model of Duffing oscillator and its sensitivity to undetected signal primary phase. Then the zone partition is proposed to identify the Duffing oscillator’s phase trajectory, and subsequently, the mathematical model and implementation method of the Duffing oscillators array are outlined. Thirdly, the Duffing oscillator optimization and its adaptive strobe technique are proposed, also their application to DPSK signal noncoherent demodulation are discussed. Finally, the design of new concept DPSK chaotic digital receiver based on the Duffing oscillators array is presented, together with its simulation results obtained by using SystemView simulation platform. The simulation results suggest that the new concept receiver based on the Duffing oscillator optimization of Duffing oscillators array owns better SNR (signal-to-noise ratio) threshold property than typical existing receivers (chaotic or nonchaotic) in the AWGN (additive white Gaussian noise) channel and multipath Rayleigh fading channel. In addition, the new concept receiver may detect mobile communication signal.

Coherent Access: A Review

In this paper, we will address the benefits of the coherent detection in future optical access networks. The scarcity of the optical spectrum, the required flexibility, and constant evolution of requirements highlight the effectiveness of coherent techniques toward the future passive optical networks (PON). A set of architectures for coherent optical access networks will be presented and the key attributes of each scenario will be investigated. In addition, as a basis to decrease the cost of the local oscillator (LO) at customer side, we experimentally investigate the possibility of using a low-cost laser as LO with real-time detection of a Nyquist-shaped differential quadrature phase-shift keying (DQPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array. Moreover, we experimentally derive a set of optimized parameters and their impact on the network operation for coherent ultradense wavelength-division multiplexing (UDWDM) systems. The balance between the number of channels, power budget, and dynamic power range will be evaluated. Furthermore, we demonstrate a reconfigurable real-time receiver DSP for future flexible UDWDM-PON systems applying the DQPSK and D8PSK modulation formats. By reviewing some of the motivations for this technology, such as flexibility, spectral efficiency, as well as compatibility with software-defined networking, we show that this technology is approaching the required maturity.

Analysis of DWDM System Using DPSK Modulation Technique with Raman–EDFA Hybrid Optical Amplifier

AbstractThis paper evaluates the performance of differential phase shift keying (DPSK) optical system based on Raman–erbium-doped fiber amplifier (EDFA) hybrid optical amplifier (HOA) is obtained at 64×20 Gbps with 0.1 THz channel spacing. A DPSK signal with bit rate of 20 Gbps is transmitted up to 210 km at 0 dBm signal input power and up to 166 km at –10 dBm signal input power with acceptable quality factor and bit error rate (BER). It is also found that the transmission distance up to 264 km has been covered at 10 dBm signal input power using Raman–EDFA HOA.

Ultrafast gain recovery in a QW-SOA and its application for 40 Gb/s regenerative format conversion from NRZ-DPSK to RZ-OOK

We propose a scheme to realize gain recovery of the order of a few picoseconds in a typical quantum well semiconductor optical amplifier (QW-SOA) using a pump signal with amplitude dips. In the scheme, the gain recovery is determined by the fast carrier density depletion and carrier temperature heating processes. The ultrafast gain recovery is numerically verified by a completed model combining the QW band structure calculation with rate equations in the QW-SOA. In practice, a pump signal with amplitude dips can be partly characterized by a non-return-to-zero differential phase-shift keying (NRZ-DPSK) signal generated by a Mach–Zehnder modulator. Therefore, we experimentally demonstrate 40 Gb/s wavelength-converting and regenerative format conversion from NRZ-DPSK to return-to-zero on–off keying (RZ-OOK), which may be a key function to connect different kinds of modulation formats at gateway nodes between long-haul backbone networks and metro area networks.

Impact of Receiver on In-Band Crosstalk-Induced Penalties in Differentially Phase-Modulated Signals

The impact of optical receiver configuration on in-band crosstalk-induced penalty has been investigated in both theoretical and experimental analyses, for differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) signals. Previously it has been shown that DPSK signals are ~6 dB more tolerant to in-band crosstalk than on-off keying (OOK) signals. However, we find that the tolerance difference between the two signals is reduced to ~3 dB when the decision threshold of the receiver is optimized to minimize the bit-error rate for each signal. Then we derive simple equations for the in-band crosstalk-induced penalty in DPSK and DQPSK signals with two different optical receiver configurations: balanced and single-ended direct-detection receivers. We confirm that the penalties obtained from our simple equations agree well with the measured results.