Return-to-zero Differential Phase-shift Keying Research Articles

Modulator-Free Variable Multi-Rate FSO Communication 1 km Outfield Demonstration Based on Chirp-Managed Laser

Due to the high energy efficiency per bit and high sensitivity, Return-to-zero differential-phase-shift-keying (RZ-DPSK) is perfectly suitable for free-space laser communications. However, the conventional generation method of RZ-DPSK optical signal requires two modulators, which is costly, bulky, and heavy, significantly hindering the application of RZ-DPSK in size, weight, and power (SWaP)-constrained satellite platforms. In this paper, we propose and experimentally demonstrate a modulator-free variable multi-rate RZ-DPSK free-space optical (FSO) communication system based on chirp-managed laser (CML). Based on the proposed scheme, an FSO outfield experiment over 1 km has been successfully undertaken, achieving receiving sensitivities of −48.9 dBm and −45.6 dBm at 2.5 Gbps and 5 Gbps, with bit error rate (BER) of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> without forward error correction (FEC), respectively. The performance of the proposed system is also investigated by studying the eye diagrams under two different test conditions of back-to-back transmission and 1-km free space transmission. In addition to the small size, lightweight and low cost, the proposed scheme shows great potential for a variety of FSO communication applications ranging from Cube-Star to larger satellite laser communication platforms.

Performance Comparison of Different Modulation Schemes in High-Speed MDM Based Radio Over FSO Transmission Link Under the Effect of Atmospheric Turbulence Using Aperture Averaging

In this work, we investigate the performance comparison of different modulation schemes viz. non return-to-zero (NRZ), alternate mark inversion (AMI), return-to-zero differential phase shift keying (RZ-DPSK), and non return-to-zero differential phase shift keying (NRZ-DPSK) in a 2 × 40 Gbps–40 GHz Radio over free space optics (RoFSO) transmission link incorporating mode division multiplexing (MDM) of two distinct Hermite Gaussian (HG) modes (HG00 and HG01) under the influence of different atmospheric turbulence conditions. Further, the effect of increasing receiver antenna aperture diameter on the link performance is investigated and compared for all four modulation schemes under different turbulence conditions. It is observed that as the strength of the atmospheric turbulence increases, the performance of the link degrades whereas the Bit error rate and the Quality Factor (Q Factor) of the received signal are significantly improved by increasing the receiver aperture diameter. Among the four modulation schemes, link with NRZ-DPSK modulation scheme gives the best performance under the influence of atmospheric turbulence followed by RZ-DPSK, AMI, and NRZ scheme. Also, the proposed NRZ-DPSK scheme based MDM-RoFSO link is investigated under different weather conditions and the results are compared with the previously reported works in the literature.

On the performance of blue–green waves propagation through underwater optical wireless communication system

The present study proposed a high-data-rate underwater optical wireless communication (UOWC) system to propagate the laser blue–green waves through water. The presented study not only focuses on analysis of challenges in UOWC link including attenuation, absorption, scattering and turbulence model, but also investigates the performance of the proposed system using two different methods of balanced modulation schemes. Spectrum efficiency of the system can be improved by using appropriate modulation formats. Return-to-zero differential phase shift keying (RZ-DPSK) and non-return-to-zero differential phase shift keying (NRZ-DPSK) schemes are two modulation formats that we investigate them to improve the characteristics of the proposed UOWC system. The paper explains a real model and exhaustive analysis for advanced UOWC works by using channel model and modulation formats for presented underwater link. Performance of the proposed system under different modulation schemes and physical aspects of UOWC is studied with several parameters like max quality factor, min bit error rate (BER) and eye diagram. For clear ocean, the performance of the proposed system is good and min BER less than 10−90 for two modulation formats. Generally, results at different condition show that the operation of NRZ-DPSK modulation has better performance than RZ-DPSK scheme.

Comparison of DPSK and RZ-DPSK Modulations in Optical Channel with Speed of 10 Gbps

This article is devoted to the problematic of error rate and modulations in optical communication. Optic waveguide shows insufficiencies in high speed transfers manifested by corrupted transfer. Although modern technological processes contributed to lowering these insufficiencies, it would be uneconomical to completely reconstruct the optical network infrastructure. The solution is only partial so we approach more economical methods, such as modulations. The article works with a 10 Gbps channel with two modulation types, namely DPSK (Differential Phase Shift Keyed) and RZ-DPSK (Return to Zero-Differential Phase Shift Keyed). These modulations are evaluated and compared according to BER (Bit Error Rate) and Q-factor.

40 Gb/s DWDM Structure with Optical Phase Configuration for Long-Haul Transmission System

AbstractWe propose the experimental transport of 48 channels with 40 Gbit/s dense wavelength-division multiplexing (DWDM) system that uses single-mode fiber (SMF) in combination with dispersion compensation fiber (DCF) which is a dispersion compensation device, in C and L band wavelength range to solve the dispersion program. The DWDM system scheme employing single Mach–Zehnder modulation (MZM) return-to-zero differential phase-shift keying (RZ-DPSK) modulation format with hybrid Raman/EDFA (Erbium-doped fiber amplifier) configuration to improve transmission signal, and employing an optical phase conjugation (OPC) configuration in the middle line. That can compensate for dispersion impairment and improve nonlinear effects to investigate transmission distance performances.

DWDM Transmission with LEAF and RDF Structure in 40 Gb/s Single MZM with RZ-DPSK Modulation

AbstractWe propose the experiment transport of 48 Chs 40 Gb/s dense wavelength division multiplexing (DWDM) system that uses larger effective area fiber (LEAF) in combination with reverse dispersion fiber (RDF), which is a dispersion compensation device, in C band (1,530–1,560 nm) and L band (1,570–1,610 nm) wavelength range to solve the dispersion program. The single Mach–Zehnder modulation (MZM) format with erbium-doped fiber amplifier (EDFA) configuration to generate return-to-zero differential phase-shift keying (RZ-DPSK) modulation signal can compensate dispersion impairment in 48×40 Gb/s DWDM system. The proposed 48×40 Gb/s DWDM system successfully employs single MZM RZ-DPSK modulation format to reduce modulation complex configuration with EDFA to promote the power signal and using LEAF and RDF in 28 spans over 3,360 km ultra-long-haul fiber transmission successfully.

A Symmetric RZ-DPSK Based Colorless NG-PON using Optical Carrier Suppression Scheme

In this paper a simultaneous transmission of a 10 Gbps RZ-DPSK data signal for downstream as well as for upstream is proposed and successfully simulated. An OCS (Optical Carrier Suppression) scheme for generation of second order dual side-band optical carrier is utilized by quadrupling a 10 GHz clockfrequency with a 10 GHz LN-MZM (Lithium-Niobate Mach-Zehnder-Modulator). The upper side second order band is used to generate a RZ-DPSK (Return to Zero-Differential Phase Shift Keying) data signal at the OLT (Optical Line Terminal). At the receiving ONU (Optical Network Unit) 50 km away from the OLT the unmodulated lower side second order band coupled with the downlink transmitted signal is utilized for the uplink modulation of 10 Gbps data in RZ-DPSK format. The simulation results show that the performance of the single-tone RZ-DPSK data modulation format is a suitable choice for the WDMPON (Wavelength Division Multiplexing-Passive Optical Network) link with a transmission span of 50 km. The proposed architecture eliminates the need of any pulse carver and mid-span power amplifiers along with the requirement of any power splitting device used in the ONU for colorless uplink transmission. In this scheme, high data rate transmission over long distance is achieved. This scheme merges the boundaries of local access networks and MAN (Metropolitan Area Networks). The proposed scheme is a highly robust, cost effective, backward compatible as well as future proof WDM-PON architecture.

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.

Symbol rate identification for auxiliary amplitude modulation optical signal

In this paper, we creatively propose and demonstrate a method for symbol rate identification (SRI) of auxiliary amplitude modulation (AAM) optical signal based on asynchronous delay-tap sampling (ADTS) and average magnitude difference function (AMDF). The method can accurately estimate symbol rate and has large transmission impairments tolerance. Furthermore, it can be realized in the digital signal processor (DSP) with low logical resources because of multiplication-free. In order to improve the accuracy of SRI, the peak to valley ratio (PTVR) of AMDF is introduced into our method for blind chromatic dispersion (CD) compensation. The results of the numerical simulations show that the overall maximum SRI error is smaller 0.079% for return-to-zero (RZ) on-off keying (OOK), RZ differential phase-shift keying (DPSK), RZ differential quadrature phase-shift keying (DQPSK) and RZ 16-ary quadrature amplitude modulation (QAM) with 50% duty cycles.

Mitigation of Fiber Nonlinearity Effects in Ultra High-Dense WDM System by Using Fractional Fourier Transform for 32 Channel System

The optical signal is severely degraded when transmitted in the fiber due to both the linear and nonlinear distortions. It is well known that, the linear distortions in single mode fiber include chromatic dispersion (CD) and polarization-mode dispersion (PMD) while self-phase modulation (SPM), cross phase modulation (XPM) and four-wave mixing (FWM) are considered the most among nonlinear distortions. A method called Fractional Fourier Transform (FRFT) has been applied to mitigate fiber nonlinearity impairments. In this work, 10 Gb/s optical fiber system with five spans, each of length 60 km, for three types of modulation formats (Return-to-Zero Differential Phase Shift Keying (RZ-DPSK), Return-to-Zero Differential Quaternary Phase Shift Keying (RZ-DQPSK) and Carrier-Suppressed Return-to-Zero (CSRZ)), single and multi-channel transmission systems are designed and simulated using “OptiSystem (2011) version 10.0” software package. The BER of thirty two channel systems (channel No.16) at bit rate 10 Gb/s per channel, 300 km link length of CSRZ modulation format with channel spacing of 50 GHz at SNR 10 dB without FRFT is 10-4.6 and 10-6.4 with FRFT. The BER of thirty two channel system (channel No.16) at bit rate 10 Gb/s per channel, 300 km link length of CSRZ modulation format with channel spacing of 25 GHz at SNR 10 dB without FRFT is 10- 2.56 and 10-3.24 with FRFT.

Experimental Investigation of All-Optical NRZ-DPSK to RZ-DPSK Format Conversion Based on TOAD

We propose and experimentally demonstrate a novel all-optical non-return-to-zero differential-phase-shift-keying (NRZ-DPSK) to return-to-zero differential-phase-shift-keying (RZ-DPSK) format conversion scheme. This scheme is based on the terahertz optical asymmetric demultiplexer (TOAD). A 10 Gb/s converted RZ-DPSK signal is obtained with a wide duty cycle tuning range from 16% to 66%. For all converted RZ-DPSK signals, the receiver sensitivities at BER of 10−9 are 0.4 to 1.7 dB higher compared with the original NRZ-DPSK signal. The clear and open eye diagrams are presented to demonstrate the high quality format conversion performance. Moreover, the optical spectra show that this conversion is in a wavelength-preserving operation.

All-optical pulsewidth-tunable wavelength conversion of return-to-zero differential phase-shift keying signal

We demonstrate the wavelength conversion of return-to-zero differential phase-shift keying (RZ-DPSK) signal with the pulsewidth-tunable operation using a Raman amplifier (RA)-based ultrashort pulse compressor and a highly nonlinear fiber (HNLF)-based four-wave mixing (FWM) switch. The wavelength of the input RZ-DPSK signal is converted to new wavelengths owing to the FWM effect in HNLF. On the other hand, the pulsewidth of the wavelength-converted RZ-DPSK signal is tuned from 10 to 3 ps by using the ultrashort pulse source based on RA-based adiabatic soliton pulse compression. The bit error rate characteristics of the input RZ-DPSK and the wavelength-converted RZ-DPSK signals with different pulsewidths are measured and error-free operations are achieved in all cases. The optical spectra, autocorrelation traces, and clear and opening eye diagrams show high conversion performance with wide-range pulsewidth tunability.

Investigation of Stimulated Brillouin Scattering Effect on Different Modulation Formats

In this study, the impact of Stimulated Brillouin Scattering (SBS) and effective core area and the Brillouin gain coefficient on On-Off Key (OOK) and phase modulation formats is investigated. In comparison with OOK formats, Return to Zero-Differential Phase Shift Keying (RZ-DPSK) revealed more robustness against the SBS effect with regards to jitter. The generated jitter due to power increment from 0 to 6 dBm was measured. The results show 0.1232, 0.1054, 0.0683 and 0.0544 bit period jitter for NRZ-OOK, RZ-OOK 0.5, NRZ-DPSK and RZ DPSK respectively. Furthermore, it is shown that SBS effect changes the behavior of system with regards to bit rate variation. It is shown that lower bit rate, does not guarantee higher performance. For instance, while the log BER at 2 Gb/sec is -11 for RZ-OOK 0.5, -9 for CSRZ,-10 for NRZ-DPSK and -16 for RZ-DPSK, at 8 Gb/sec they hit a peak with -16, -20, -21 and -36, respectively.

Tunable modulation format conversion based on spectral line-by-line pulse shaper for all-optical signal processing

A tunable modulation format converter based on spectral line-by-line pulse shaper is proposed to realize different format conversions. The pulse shaper works as a format converter by setting its frequency response equivalent to the transform function between two formats. The working principles show that the format converter is suitable for different formats by adjusting its frequency response. Examples of format conversion from return to zero differential phase-shift keying (RZ-DPSK) to on-off keying (OOK) with different data packets and from return to zero (RZ) to non-return to zero (NRZ) are given. The results show that the format converter is not only suitable for different formats but also for random data packets.

All-Optical Wavelength-Shift-Free NRZ-DPSK to RZ-DPSK Format Conversion with Pulsewidth Tunability by an SOA-Based Switch

We demonstrate an all-optical non-return-to-zero differential phase shift keying (NRZ-DPSK) to return-to-zero differential phase shift keying (RZ-DPSK) format conversion with wavelength-shift-free and pulsewidth tunable operations by using a semiconductor optical amplifier (SOA)-based switch. An NRZ-DPSK signal is injected into the SOA-based switch with an RZ clock, and is converted to RZ-DPSK signal owing to the nonlinear effects inside the SOA. In this scheme, the wavelength of the converted RZ-DPSK signal is maintained as the original wavelength of the input NRZ-DPSK signal during the format conversion. Moreover, the pulsewidth of the converted signal is tunable in a wider operating range from 30 to 60 ps. The format conversion with pulsewidth tunability is based on cross-phase modulation (XPM) and cross-gain modulation (XGM) effects in the SOA. The clear eye diagrams, optical spectra and the bit-errorrate (BER) characteristics show high conversion performance with the wide pulsewidth tuning range. For all cases of the converted RZ-DPSK signal with different pulsewidths, the receiver sensitivities at a BER of 10−9 for the converted RZ-DPSK signal were 0.7 to 1.5 dB higher than the receiver sensitivity of the input NRZ-DPSK signal. key words: Differential phase shift keying (DPSK), format conversion, wavelength-shift-free, pulsewidth tunable operation, cross-phase modulation (XPM), cross-gain modulation (XGM)

Simultaneous multi-channel RZ-OOK/DPSK to NRZ-OOK/DPSK format conversion based on integrated delay interferometers and arrayed-waveguide grating

Format conversion is enabling function at the interface of different networks with different optimal modulation formats. Meanwhile, multi-channel signal processing function has its special significance for dense wavelength division multiplexing networks. In this paper, we designed and fabricated a delay interferometer cascaded with an arrayed-waveguide grating based on silicon on insulator. The 4-channel return-to-zero on-off keying (RZ-OOK) to non-return-to-zero on-off keying (NRZ-OOK) and return-to-zero differential phase shift keying (RZ-DPSK) to non-return-to-zero differential phase shift keying (NRZ-DPSK) format conversions at 40 Gbit/s were realized with this integrated device, the output eye diagrams showed a good conversion performance. Thanks to the mature fabrication technology, this device shows great potential for its small size, low power consumption and possibility of monolithic integration.

Simultaneous Demultiplexing and Demodulation of 10 Gbit/s RZ-DPSK Signal using Arrayed Waveguide Gratings

We propose and demonstrate simultaneous demultiplexing and demodulation of wave length division multiplexed (WDM) return-to-zero differential phase-shift keying (RZ-DPSK) signal by a standard Arrayed Waveguide Gratings (AWG) at 10 Gbit/s data rate using ITU grid of 100 GHz channel spacing. Simulation results show error free transmission in a distance of 25 km with negligible power penalty and improved receiver sensitivity. The propose scheme is cost effective in term of component counts, hence reduces the deployment cost significantly.

An Ultracompact OSNR Monitor Based on an Integrated Silicon Microdisk Resonator

Optical signal-to-noise ratio (OSNR) monitoring is essential for control and management of dynamic optical networks. Small footprint, low cost, and less power consumption are always desirable for such monitoring system. In this paper, we demonstrate an integrated dispersion-insensitive in-band OSNR monitor based on a compact silicon microdisk resonator (MDR) with only 5-μm radius. The MDR (Q ~ 54 000) functions as an ultranarrow bandpass filter in the measurement of the OSNR. The monitoring performance is evaluated in a 10-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) system and is shown to be insensitive to chromatic dispersion from 0 to 850 ps/nm. The input power requirement of the monitor is also studied, which is consistent with the desire for low-power operation. Finally, we analyze the sensitivity of this technique for various Q factors of the MDRs. The results indicate that the sensitivity of this scheme can be improved with higher Q factors.

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).

Simulation and comprehensive assessment of single channel RZ-DPSK optical link by dispersion management with channel bit rate beyond 40 Gbits/s

This paper studied the influence of return to zero-differential phase-shift-keying (RZ-DPSK) data format on techniques of pre-, post- and pre/post combination dispersion compensation for faithful transmission of optical signal at 80 and 100 Gbits/s channel bit rate via simulation. The purpose of this study was to find out the dispersion compensation techniques for optimal transmission with the interaction effects of self-phase modulation (SPM) and amplifier spontaneous emission (ASE) for RZDPSK encoded optical data. By the simulation method, it was found out that the RZ-DPSK data format can be allowed with a transmission distance of about 700 km of standard single mode fiber (SMF) at 100 Gbits/s, and it can be provided with farther transmission distance of more than 1000 km at 80 Gbits/s with the combination of the pre- and post-compensation technique. To efficiently suppress the effect of ASE and improve optical signal-tonoise ratio (OSNR), the bandwidth frequency of optical receiver filter was found to be at least equal to bit rate.