Differential Phase-shift Keying Modulation Format Research Articles

Design of DWDM optical communication systems with different modulation formats using DCF and a repeater.

The dense wavelength division multiplexing (DWDM) technique has been used to provide a large capacity and low bandwidth loss for optical communication systems. In this paper, simulation designs by Optisystem15.0 of carrier-suppressed return to zero (CSRZ), differential phase shift keying (DPSK), and intensity modulation is proposed to determine which modulation format is more compatible with four and eight DWDM channels for transmitting an optical signal over 400km distance. For a long optical path, the dispersion compensation fiber (DCF) technique is proposed to eliminate dispersion effects and increase the possibility of transmitting multiple optical wavelengths over long single-mode fiber. Optical amplifiers are used to amplify the optical signal with a distorted signal and process the attenuation caused by the long transmission distance. In DCF network design, CSRZ offers the best performance because of the large quality factor (24.560) and high threshold power (15dBm), which make the system compatible with increased distance between the transmitter and receiver; next is intensity modulation with a 24.5604 quality factor and 13dBm threshold power value; DPSK comes in last with the worst performance, with a quality factor of 10 at 13dBm power due to non-linear effects, especially non-linear phase noise. In the repeater design, the DPSK modulation format has the best performance with a large quality factor of 20.7913 at a high threshold power of 14dBm for 150GHz spacing; this is because the repeater technique is compatible with reducing the non-linear effects of the DPSK format. CSRZ and intensity modulation have the same performance with a 12 quality factor at 4dBm power for intensity modulation and 3dBm power for CSRZ modulation.

Performance Comparison of Free-Space Optical (FSO) Communication Link Under OOK, BPSK, DPSK, QPSK and 8-PSK Modulation Formats in the Presence of Strong Atmospheric Turbulence

Abstract Free-space optical (FSO) communication system provides several advantages over radio frequency (RF) system offering high bandwidth, low cost, small space requirements and more secure transmission which is free from Electromagnetic Interference (EMI). However, when the transmitted light signal passes through the atmosphere it experiences attenuation and fluctuations due to atmospheric turbulence. This paper analyzes the bit error rate (BER) performance of FSO communication systems under strong atmospheric turbulence for on-off keying (OOK), binary phase-shift keying (BPSK), differential phase shift keying (DPSK), quadrature phase shift keying (QPSK) and 8-phase shift keying (8-PSK) for link distances of 500, 1,000, 1,500 and 2,000 m. The probability density function (pdf) of the received irradiance is modelled using the gamma-gamma distribution model. It is found that the system exhibits the best BER performance and compensates the lowest power penalty at BER of 10 - 9 for BPSK modulation compared with other modulation techniques which makes BPSK more appropriate to be used with FSO turbulent system.

Performance Evaluation of OOK, DPSK and Duo-binary Modulation Format based Mixed-Line-Rate (MLR) Optical Network

With the steady increase in the heterogeneous Internet traffic, the optical wavelength division multiplexed (WDM) networks based on a mixed line rate (MLR) strategy have emerged as an efficient-solution. Also, with the migration from the legacy to the higher line rate(s), the advanced modulation format(s) (MF) is/are required. However, use of appropriate MF(s) for the higher line rate(s) still remains an open problem. In this article, we compare the performance of an On-Off Keying (OOK), Differential Phase Shift Keying (DPSK) and Duo-binary (DB) MF based MLR network in the presence of various physical layer impairment(s) (PLIs) for which, we propose a mathematical model based on various MFs. As a novelty, we validate the proposed theoretical model’s results by comparing them with the results obtained through simulations from OptSim, which has not been conducted in any existing study(s) thus far. Our simulation results show that the DB MF is perfectly suitable for high spectral-efficient MLR systems owing to its high resistance to various PLIs.

4 × 10 Gbps WDM repeaterless transmission system using asymmetrical dispersion compensation for rural area applications

We demonstrate experimentally 4 × 10 Gbps wavelength division multiplexing repeaterless transmission system using non-return-to-zero differential phase-shift keying modulation format over 300-km standard single-mode fiber. The channels used were 1546.9, 1547.7, 1548.51 and 1549.2 nm with 100 GHz spacing. In this system design, a dispersion compensation module is used; multi-channel-chirped fiber Bragg grating was deployed with asymmetrical configuration with different compositions of dispersion values at the transmitting and the receiving sides. The transmission system was pumped bidirectionally with 1445 and 1455 nm wavelength in a forward direction, and three pump wavelengths of 1430, 1440 and 1450 nm are deployed for the backward direction. The total on–off Raman gain is 47 dB from total pump power of 1.862 W. The result for dispersion pre-compensation of − 2006.0 and − 2338.3 ps/nm has minimal effect on nonlinearity showing the best performance for 300-km repeaterless transmission system.

A WDM-PON with DPSK modulated downstream and OOK modulated upstream signals based on symmetric 10 Gbit/s wavelength reused bidirectional reflective SOA

We investigate a wavelength-division-multiplexing passive optical network (WDM-PON) with centralized lightwave and direct detection. The system is demonstrated for symmetric 10 Gbit/s differential phase-shift keying (DPSK) downstream signals and on-off keying (OOK) upstream signals, respectively. A wavelength reused scheme is employed to carry the upstream data by using a reflective semiconductor optical amplifier (RSOA) as an intensity modulator at the optical network unit (ONU). The constant-intensity property of the DPSK modulation format can keep high extinction ratio (ER) of downstream signal and reduce the crosstalk to the upstream signal. The bit error rate (BER) performance of our scheme shows that the proposed 10 Gbit/s symmetric WDM-PON can achieve error free transmission over 25-km-long fiber transmission with low power penalty.

Performance analysis of hybrid WDM-OTDM optical multicast overlay system employing 120 Gbps polarization and subcarrier multiplexed unicast signal with 40 Gbps multicast signal

In this paper, we have propose and investigated the performance of hybrid WDM-OTDM optical multicast overlay system which employs 120Gbps unicast and 40Gbps multicast data operating over SMF+DCF and amplifier link in C-band. The polarization and subcarrier multiplexed modulation formats are used to obtain 120Gbps unicast data and DPSK (differential phase shift keying) modulation format for 40Gbps multicast data transmission. In multicast operation, DPSK data is superimposed on to multiplexed unicast data channels. The impact of extinction ratio, input power and transmission distance on the performance of proposed system in terms of output optical power, BER and Q-factor has been investigated for both unicast and multicast data. We have also concluded that polarization and subcarrier multiplexed modulation formats are promising option to increase per channel capacity and less vulnerable to CD and PMD. In addition, the proposed system using hybrid modulation techniques offers higher bandwidth utilization efficiency at higher per channel data rate than conventional modulation formats.

Effects of ASE on DPSK Modulation Formats with Different Duty-Ratio in Optical Transmission System

In optical networks, erbium-doped fiber amplifiers (EDFAs) are used to provide a wide and flat gain spectrum. Amplified Spontaneous Emission (ASE) emitted from EDFA adds to signal and grows rapidly. This accumulated ASE noise may limit the effective amplification due to saturation effect and affects the receivers bit error ratio (BER). In this paper, we show the impact of ASE noise in transmission fiber by using three different modulation formats: 33%DPSK, 66%DPSK and DPSK. In recent years, optical fiber communication system began to use the DPSK (Differential Phase Shift Keying) format to replace the traditional OOK format, which has been intensively investigated in numerical and experimental works.

Stimulated Raman crosstalk in bi-directional pumped distributed Raman amplifier for DPSK and OOK modulation format

Novel closed form formulae are derived to study crosstalk degradation due to stimulated Raman scattering (SRS) in WDM systems employing bi-directional pumped distributed Raman amplifier (DRA). They are applied to evaluate the crosstalk performance of different modulation formats, especially differential phase-shift keying (DPSK) and ON–OFF keying (OOK), which are widely used in optical communication. Further, SRS crosstalk is evaluated for different data rates and pulse shapes prevalent in optical data transmission. Next, crosstalk is calculated for different pumping schemes as special cases of bi-directional pumped DRA. The study shows that minimum SRS crosstalk can be achieved for 40Gb/s RZ-DPSK signal with 33.3% duty cycle in WDM system employing backward pumped DRA.

Investigation of Transparency of FWM in SOA to Advanced Modulation Formats Involving Intensity, Phase, and Polarization Multiplexing

We experimentally investigate the real transparency of four-wave mixing (FWM) in semiconductor optical amplifiers to modulation formats involving intensity, phase, and polarization multiplexing. We exploit two different FWM polarization-independent schemes (that make use of two pumps) to wavelength-convert 40 Gb/s single-polarization and 80 Gb/s polarization-multiplexed signals in case of both nonreturn-to-zero <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</i> keying (NRZ-OOK) and NRZ differential phase-shift keying modulation formats. We found that, although FWM conversion is transparent to modulation formats employing phase and intensity, polarization-multiplexed signals pose serious limitations to all-optical processing transparency.

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.

Simultaneous optimisation of filter bandwidths and interferometer free spectral range for DPSK and DQPSK modulation

The authors investigate the optimal bandwidths for transmitter and receiver filters for differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) optical modulation in dense wavelength-division multiplexing (WDM) scenarios. Single-channel setups were investigated as reference. Simultaneously, the optimal free spectral range (FSR) of the delay interferometer (DI) needed at the receiver for both modulation formats was searched. Transmitter (Tx) and receiver (Rx) optimal setups were focused and the propagation effects were not considered. It is demonstrated that the optimal FSR, in general, is larger than the symbol rate for both DPSK and DQPSK modulation formats.

A Novel Dispersion-Free Interleaver for Bidirectional DWDM Transmission Systems

We propose a novel dispersion-free interleaver using optical delay lines by accurately locating the zeros in the transfer function. It has been implemented with the design of interleaver pairs with the same amplitude responses but opposite phase responses for bidirectional dense wavelength-division multiplexed (DWDM) transmission systems. The measured results are consistent with device simulation. We have further modified the original three-port design using unidirectional amplification, and a fourport interleaver has been built and demonstrated to achieve bidirectional DWDM transmission. In this paper, we fully studied and verified the applications of our four-port interleavers in bidirectional transmission. We demonstrated a bidirectional strain-line system over 210 km and a recirculating loop transmission over a 500-km standard single-mode fiber using 10-Gb/s on-off keying signals. Furthermore, we also demonstrated return-to-zero differential phase-shift keying (DPSK) and nonreturn-to-zero DPSK modulation formats for more than 230 km of transmission. For comparison, the different amplification functions, such as the erbium-doped fiber amplifier and the semiconductor optical amplifier, have also been probed in this paper. The experimental results have clearly illustrated the desirable functions of this novel bidirectional amplifier in this dispersion-free interleaver.

Bidirectional ROF Links Using Optically Up-Converted DPSK for Downstream and Remodulated OOK for Upstream

We propose a novel radio-over-fiber system to provide full-duplex services by using optical differential phase-shift keying modulation format at the central station for downstream and on-off keying remodulation of the downlink carrier at the base station (BS) for upstream. The optical carrier suppression modulation scheme is employed to simultaneously generate and up-convert 40-GHz optical millimeter wave. As the same optical carrier is used for both uplink and downlink, no additional light source is required at the BS, which greatly reduces the cost and simplifies the overall system. Simulations and experimental results show that the bidirectional 2.5-Gb/s data is successfully transmitted over 40-km single-mode fiber (SMF-28) with less than 2-dB power penalty

Interleaved Bidirectional Transmission of 16 $\times$ 10-Gb/s DWDM Signals Using DPSK Modulation Format and In-line Semiconductor Optical Amplifiers

We have performed both experimental and numerical analyses of interleaved bidirectional transmission of 16 times 10-Gb/s dense-wavelength-division-multiplexed (DWDM) signals using differential-phase-shift-keying (DPSK) modulation format and in-line semiconductor optical amplifiers (SOAs). The constant intensity of DPSK-modulated DWDM signals enabled us to mitigate the crosstalk effects in the bidirectional SOA. We have demonstrated error-free bidirectional transmission of 16 channels over an 80-km single-mode fiber (SMF) with matching dispersion-compensating fiber and in-line amplification provided by an SOA. SOAs can be used for bidirectional transmission if the facet reflections can be controlled. In order to understand further the effect of the SOA facet reflectivity on transmission results, we developed a simulation model for our system. Based on the good agreement between our simulation and experimental results, we have found out that the system reflections can be minimized by careful optimization of the bias current and reflectivity of the SOA

Stokes space optimal detection of multidifferential phase and polarization shift keying Modulation

A unified framework is developed for optimizing the bit error rate incurred in the simultaneous differential modulation of the optical resources of polarization (pol.), phase, and amplitude over channels wherein the optical phase slowly wanders relative to the symbol rate, as applicable to high-bit-rate optical transmission. The modulation formats of pol. shift keying (POLSK), differential phase shift keying (DPSK), and amplitude shift keying (ASK), as well as recent and novel combinations thereof, are interpreted as instances of a new conceptual format called multichip differential state of POLSK, whereby it is the states of pol. in a block of D time slots that are differentially modulated and detected block-by-block. The classical description of pol. in terms of the four Stokes parameters (SPs), recently extended to D/sup 2/ generalized SPs, underlies the conception of optimal receivers for these schemes. The theory is applied to rigorously establish the optimality of known POLSK receivers, to identify new optimal receiver structures for multipower POLSK, and to assess the optimality of recently introduced differential phase ASK and multichip DPSK modulation formats.

Theoretical investigation of optical wavelength conversion techniques for DPSK Modulation formats using FWM in SOAs and frequency comb in 10 gb/s transmission systems

We have investigated the wavelength conversion techniques for differential phase-shift keying (DPSK) modulation formats in 10 Gb/s transmission systems, compared with the non-return-to-zero (NRZ) modulation format. For the wavelength conversion of DPSK modulation formats, we employed the wavelength converters based on the four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) and the frequency comb generated by phase modulation. The power penalty at 10/sup -9/ bit error rate was used as a measure of the system performance degraded by the wavelength conversion. Our simulation results show that the DPSK modulation formats have a smaller power penalty than the NRZ modulation format for the wavelength conversion using the FWM effect in an SOA due to a much lower pattern effect. However, as the wavelength conversion uses the frequency comb generated by phase modulation, it has a similar power penalty compared with the NRZ modulation format. It is also shown that the DPSK modulation formats are possible to obtain the power penalty less than 0.4 dB for both wavelength conversion techniques.

1050-km WDM Transmission of 8&amp;lt;tex&amp;gt;$,times,$&amp;lt;/tex&amp;gt;10.709Gb/s DPSK Signal Using Cascaded In-Line Semiconductor Optical Amplifier

We have performed eight-channel wavelength-division-multiplexing transmission over 1050-km single-mode fiber using cascaded in-line semiconductor optical amplifier and differential phase-shift keying modulation format for the first time; more than 6 dB of power margin was achieved over forward-error correction threshold. Factors that affect the transmission performance were discussed. It was found that four-wave mixing is the main factor that limits the maximum transmission distance. Larger capacity distance product can be realized by further optimizing the configuration of transmission link.

Direct sequence spread spectrum differential phase shift keying SAW correlator on GaAs

This paper presents the design, fabrication, and experimental results for a differential phase shift keying (DPSK) single SAW-based correlator on GaAs for direct sequence spread spectrum applications. The DPSK modulation format allows for noncoherent data demodulation; the SAW device correlator acts as the despreader. Unlike the conventional technique of using two parallel correlators and a one data bit delay element, this new system uses two inline correlators. When implemented on SAW devices, this in-line structure has the advantage of an inherent one data bit delay, lower insertion loss, and less signal distortion than the parallel structure. The DPSK correlator is fabricated on a {100} cut GaAs substrate with SAW propagation in the 110 direction, Using this cut, which is widely used in electronics, Rayleigh waves are generated with a piezoelectric coupling coefficient of the same order as ST-cut quartz. The piezoelectric semiconductor GaAs is of great interest because it is the only substrate that can be used to integrate SAW devices directly with electronics on the same chip, resulting in smaller packaging, reduction of packaging parasitics, lower cost, and greater system integration. This paper presents experimental results for SAW in-line correlator structures on GaAs along with their despreading system performances. Experimental measurements in both the time and frequency domains were performed and were found to be in good agreement with theoretical predictions.

Analysis of a DPSK soliton transmission system

We present a closed form expression to analyse the error performance of a differential phase-shift keying (DPSK) digital modulation format in an optical soliton communication system. In the analysis we include the effect of Gordon-Haus jitter, which is mainly due to the amplified spontaneous emission noise of the amplifiers. Gordon-Haus jitter is found to be less significant when the bit period is 15 times greater than the jitter variance and becomes more significant when the signal-to-noise ratio is greater than 20 dB. Due to a good bit error rate (BER) performance (BER ≈ 10 −20at SNR= 21 dB), the DPSK modulation format has a potential application for a high-bit-rate and low-noise soliton communication system.

A differential-delay SAW correlator for combined DSSS despreading and DPSK demodulation

The design of a novel SAW (surface-acoustic-wave) component for the noncoherent detection of DS/SS (direct-sequence spread-spectrum) signals with a DPSK (differential phase-shift keying) modulation format is presented. In the considered differential-delay correlator, both the correlation function for despreading and the delay function for DPSK demodulation are merged into a single device. Due to the absence of a separate delay line, no bandwidth-limiting effects no high insertion losses occur in the delay branch of the DPSK demodulator. In addition, an exact match between the correlator output and its one-symbol-delayed replica is obtained. Experiments on an ST-quartz differential-delay correlator with a center frequency of 98.5 MHz, a chip rate of 12.3 MHz and a symbol rate of 195.4 kb/s demonstrated the operation of the device. >