Carrier-suppressed Return-to-zero Research Articles

Transmitter diversity and OAM incorporated 40 Gbps free space optical system

Abstract The present research evaluates optical angular momentum’s (OAM) performance in challenging atmospheric conditions and emphasizes its significance in free space optical (FSO) communication systems. It has been demonstrated that implementing the transmitter diversity (TD) technique effectively suppresses inter-channel interference, improving system performance as a whole. The best option among the studied encodings is found to be the combination of non-return-to-zero (NRZ) and carrier suppressed RZ (CSRZ), which performs better in a variety of weather scenarios and covers a wide FSO range from 72 m to 1450 m. Proposed system offered distance enhancement of 81.25 % under clear sky, 16.66 % under light rain, 10.22 % under moderate rain, 3.4 % under heavy rain, 10 % under light haze, 4 % under moderate haze, 4.44 % under heavy haze, 12.5 % under light fog, 4 % under moderate fog, 7.8 % under heavy fog, 5.8 % under light dust, 7.6 % under medium dust and 12.5 % under heavy dust as compared to existing workIn particular, during bad weather, this research offers significant insights into the design and optimisation of high-speed FSO systems.

Few-mode fiber Bragg grating-based simultaneous multichannel CSRZ to NRZ format conversion scheme for LP01 and LP11.

We propose what we believe is a novel format conversion scheme using a few-mode fiber Bragg grating (FM-FBG) that can perform multichannel format conversion from carrier-suppressed return-to-zero (CSRZ) to non-return-to-zero (NRZ) for both LP01 and LP11. The multichannel spectral response of FM-FBG is designed according to the algebraic difference between the CSRZ and NRZ spectra outlines. Additionally, the FM-FBG response spectra of LP11 are designed to shift with that of LP01 by the WDM-MDM channel spacing for filtering both modes together. Numerical results demonstrate the successful conversion of both LP01 and LP11 channels, carrying four channels of 200-GHz-spaced CSRZ signals at 40 Gbit/s, into NRZ signals with a high Q-factor (exceeding 14 dB), and the converted NRZ signals exhibit clean and open eye diagrams. Furthermore, the performance analysis also shown that our proposed FM-FBG is robust to central wavelength detuning.

Design of Ultra Dense WDM Optical Communication System to Reduce Signal Impairments Using DCF and Repeater Techniques

Linear and non-linear impairments are the major problems that affected the dense wavelength division multiplexing (DWDM) system performance. In this simulation designs, two different compensation techniques have been proposed to eliminate signal impairments. The repeater technique was proposed to reduce non-linear effects like four-wave mixing (FWM) which cause transfer power from DWDM channels to another new channels. The dispersion compensation fiber (DCF) technique was used to reduce dispersion effects which cause signal pulse broadening over long transmission distances. Also, three different modulation formats and four frequency separations were used to determine which modulation scheme is more compatible with the compensation techniques. The results is calculated in term of quality factor against power and noetic that the carrier suppressed return to zero (CSRZ) format offers the best performance with the DCF technique with 32.1804 Q-factor at 15dBm threshold power then, the differential phase shift keying (DPSK) format is compatible with the repeater technique with 27.7959 quality factor and 14dBm threshold power. Index Terms— Dense Wavelength Division Multiplexing (DWDM), Dispersion Compensation Fiber DCF, Repeater, and Non-linear Effects.

Ultra-long haul high speed 96 × 40 GB/s radio over IsOWC system employing advanced modulation scheme

Abstract This paper successfully demonstrates that point-to-point (P2P) superdense wavelength division multiplexing (SDWDM) based on the radio over intersatellite optical wireless communication (Ro-IsOWC) system of 96 channels separated by a 100 GHz bandwidth with 40 GB/s data rate on each stream at a 10,000 km link range has been designed and investigated. The performance of the proposed work has been evaluated by considering the comparison of advanced modulation schemes such as carrier-suppressed return-to-zero (CSRZ), duobinary return-to-zero (DRZ), and modified duobinary return-to-zero (MDRZ) with an optical preamplifier on the bases of bit error rate (BER), quality factor, eye height, and optical signal-to-noise ratio (OSNR) in the clear weather condition. Moreover, the effects of internal parameters such as transceiver aperture diameter and gain of an optical amplifier also have been analyzed with an optimized modulated system. Apart from this, the system performance also has been assessed under varying data rates and OWC frequency ranges with the best-suited modulation format. It has been found that the CSRZ modulation format has shown robust performance and can achieve BER as better as 10−09 with a 5.5 dB quality factor for all wavelengths. It also has been observed that the quality of the received signal deteriorates below an unacceptable value for data rate and link distance beyond 40 GB/s and 10,000 km, respectively.

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 ENHANCEMENT OF DWDMFSO SYSTEM UNDER DIVERSE WEATHER CONDITIONS WITH OPTIMIZED MODULATION FORMAT

This paper is successfully demonstrating simulating comparison and investigation of 48 channels of dense wavelength division multiplexing free space optical (DWDM−FSO) network with a 10 GB/s data rate on each channel separated by 100 GHz frequency spacing under a clear sky, haze and light rain climate conditions. Apart from this, comparison of a series of modulation formats such as non−return to zero (NRZ), return to zero (RZ), carrier suppressed return to zero (CSRZ), Soliton pulse, and offset quadrature phase shift keying (OQPSK) have been performed and optimized the performance of the designed system with best suited modulated system. The performance of the proposed work has been evaluated in terms of bit error rate (BER), quality factor (Q), signal−to−noise ratio (SNR), received signal power and eye diagrams. It has been observed that OQPSK modulated system has shown more robust performance as compared to other line encoding techniques. The minimum simulation work reports for OQPSK modulated system have been recorded with the acceptable performance BER ≤ 10−10, Q ≥ 6 dB at the 2000 meters FSO link range.

Performance Comparison of Different Modulation Formats for a 40 Gbps Hybrid Optical CDMA/DWDM System against ISI and FWM

This paper carries out a numerical simulation investigating three different modulation formats: carrier suppressed return to zero (CSRZ), modified duobinary return to zero (MDRZ) and return to zero (RZ). The purpose of this investigation is to find the optimum modulation format for the hybrid optical code division multiple accesses–dense wavelength division multiplexing (optical CDMA/DWDM) system with the implementation of an electro-optic phase modulator (EOPM) at a data rate of 40 Gbps per channel, with a transmitted power of 22 dBm and transmission distance of 105.075 km. The results revealed that CSRZ was superior to MDRZ and RZ and was more tolerant to optical fiber nonlinearity. Furthermore, unlike the DWDM systems, the performance of the proposed hybrid system based RZ format was better than the performance of MDRZ. Hence, the CSRZ modulation format is the best candidate for the optical CDMA/DWDM with EOPM module due to its high performance.

Performance Improvement Using DCSRZ at 10 GHz OCDMA Transmission Link

In this paper, a method based upon combination of duo-binary (DB) and carrier suppressed return-to-zero (CSRZ) format has been proposed that has significantly improved the performance of optical code division multiple access (OCDMA) system by means of two dimensional (2D) codes based on two parameters; wavelength and time. The various investigations divulge that highest Q2 (dB) of minimum and maximum value [18,23]; [14,17]; [9,12] and [1,6] has been obtained at a power variation of -10 to 20 dBm f or DCRZ, DB, CSRZ and RZ modulation formats respectively for a communication distance of 80 kilometers. It has also been identified that maximum OSNR of [37-29] dB is obtained by using DCSRZ modulation format for the same distance. The maximum opening of eye for DCSRZ format has further proved its robustness to suppress the channel impairments at a high-power level of 20 dBm for 10 GHz optical CDMA systems.

Simulative Analysis of Robustness of Various Modulation Formats for Optical CDMA using 2D Codes for Different Encoders at 10Gbps

This paper reports the simulative analysis of NRZ, RZ, carrier-suppressed RZ (CSRZ) and duo-binary (DB) modulation formats for optical code division multiple access (OCDMA) system for two different types of encoders at 10 Gbps. The investigations reveal that highest Q2(dB) of the order of 16.5;14.5;6.2 and 3.8 has been obtained when we use combination of optical filters and time delay components as optical encoders in OCDMA system for CSRZ, DB, RZ and NRZ formats respectively. It is also observed that for fiber Bragg grating (FBG’s) as optical encoders, Q2 (dB) of the order of 17.7;11.8;7 and 4 is achieved in case of DB, CSRZ, RZ and NRZ formats respectively. CSRZ and duo-binary formats have shown the robustness over other formats for OCDMA system using filter, time delay components and fiber Bragg gratings (FBGs) as optical encoders respectively. The maximum eye opening in case of these formats further proved their efficiency.

A New Suppression approach of FWM Crosstalk Effect in Optical Communication Link based on Polarization combiner Method

To meet the growing needs of internet data, optical communication systems have become the backbone of modern communications networks. At the present time, the dense wavelength division multiplexing (DWDM) technique has been used to increase the number of channels, but the nonlinear effects have a great impact that limits the performance of doubling the DWDM system. The four wave mixing (FWM) is the most harmful and dangerous as the effect of FWM increases on the system the greater the optical connection distances. The new approach of pairing groups of different optical signals was investigated to suppress the FWM effect. The simulation was conducted for an 8-channel system with a total data rate (80Gb/s). A comparative study was conducted on the suppression of FWM by the difference in the power inputs (-0.5 to 20) dBm. The robustness of the proposed technique was examined using two forms of modulation (Carrier Suppressed Return to Zero (CSRZ) and Duo Binary Modulation class -1(DBM-1)) techniques, with optical fiber system of (1,2,5) spans, each of length 60 Km, with spacing between the channels 50GHz. The power of FWM was significantly reduced with the CSRZ & DBM-1 techniques to less than (47.97%, 41.38 %) respectively, at an input power of 12.5 dBm. The performance of the proposed system with the polarization technique was improved by the rate of the quality factor (Q-factor of (91.59%, 78.67%) for the same sequence of modulation.

Comparative Analysis of DCF based Dispersion Compensation Techniques in Optical Fiber Communication Link using Different Input Transmitter Conditions at 10 Gbps

In this paper, Dispersion Compensating Fiber (DCF) based various dispersion compensating techniques (pre, post and symmetrical) with different modulation format like Non Return to Zero(NRZ), Return to Zero(RZ), Carrier Suppressed Return to Zero(CSRZ) and Duo Binary(DB) along with PN, FCC and Walsh code input sequences are implemented. Simulation and analysis of these implemented techniques were done at 10 Gbps bit rate and input laser power ranging from 1 mW to 10 mW at transmission distance of 240 km using BER Analyzer in Optisystem 17.0 software. Comparison between different techniques was done in terms of Q factor and BER versus input CW laser power for different modulations and input sequences. From the analysis, it is concluded that when Walsh code as user defined input sequence are used for all the implementation, it gives higher value of Q factor and lower value of Bit Error Rate as compared to PN and FCC codes for most of the input CW laser power.

Performance Analysis of Modulation Formats for Next Generation RoF Systems

Radio over fiber (RoF) has found to be one of the most effective communication techniques. It has the tendency to incorporate both optical fiber and free space radio paths. In this research article, importance, benefits, and applications of RoF system are discussed in detail for futuristic networks. The performance of RoF system is visualized by modulating the data with the RF signal having same frequency at both transmitter and receiver ends. Initially, the performance is checked using non-return to zero (NRZ) format and later compared with duobinary (DB) and carrier suppressed return to zero (CSRZ). Various simulations are performed which directly affect the system performance. Important parameters such as RoF link distance, data rate, transmitter power, amplifier gain, and RF signal frequency are tested. The operation is carried out at 1550 nm wavelength and 30 GHz RF frequency. System is optimized to receive the transmitted waveforms successfully. Simulations are performed in Optisystem 17.0 and MATLAB. For the analysis, the results are plotted using Q-factor and BER values.

Performance enhancement of ultra-dense WDM over FSO hybrid optical link by incorporating MIMO technique

Abstract Free-space optical (FSO) communication is a wireless optical data transmission technology with a high data transmission rate. It has received much attention in recent years as it is cost-effective and has license free operation. It is line of sight free-space communication technique where optical signal severely degraded from atmospheric losses especially due to weather conditions; hence it restricts the link range and data carrying capacity. Therefore, a 16-channel ultra-dense wavelength division multiplexing–free space optics (UWDM–FSO) system each having each 10 Gb/s data rate is proposed to enhance the capacity and performance of FSO system. To authenticate the performance of the proposed system, investigation for different modulation formats such as nonreturn to zero (NRZ), return to zero (RZ), carrier suppressed return to zero (CSRZ) and duo binary (DB) are reported. Further, to reduce the atmospheric interference, multiple input multiple output (MIMO) technique is integrated into the proposed system. The outcomes of MIMO–UWDM–FSO link revealed a significant improvement in the bit error rate (BER), eye diagram and Q-factor, under different weather conditions. It is also observed that NRZ modulation formats perform better than RZ, CSRZ and DB formats.

Performance of Carrier- Suppressed Return-to-Zero(CSRZ), Duo binary Return-to-Zero(DRZ) and Modified Duo binary Return-to-Zero(MDRZ) Modulation Methods in WDM-PON Systems

In this paper the different modulation techniques used in fiber optic technology are compared to check which one has the better bit error rate (BER). There are a number of different modulation techniques used in WDN-PON systems but here the comparison is made among carrier-suppressed return-to-zero (CSRZ), duobinary return-to-zero (DRZ) and modified duobinary return-to-zero (MDRZ) modulation. The comparison to determine which is better is made my performing simulations in OptiSystem version 17 software. OptiSystem 17 is the current version of the software at the time the simulations were being carried out. In the OptiSystem software an optical fiber system is simulated from transmitter all the way to receiver. In the experiment when checking the performance of the different modulation formats, the optical fiber and the receiver are left unchanged and only the transmitter part is changed according to the modulation format being simulated at that particular instance. The modulation in the transmitter is done by using proper components from the OptiSystem library which when organized in the right order will give out a signal modulated in a certain format by the time it is fed into the optical fiber. Knowing the performance of modulation can help in WDM PON where the network gets to use passive components as it goes to user. Since no active amplification or correction equipment is used in WDM-PON, therefore using the format with the best performance can help with performance of overall system.

224-Gbps single-photodiode PAM-4 transmission with extended transmitter bandwidth based on optical time-and-polarization interleaving.

We have proposed and demonstrated the optical time-and-polarization interleaving (OTPI) technique, which can effectively extend the transmitter bandwidth for an intensity modulation and direct detection (IM/DD) optical system. The 224-Gbit/s line-rate OTPI-PAM-4 signal is successfully transmitted over a 500-m standard single-mode fiber (SSMF) in the C band, using the transmitter with a bandwidth of 25 GHz and the receiver with a single photodiode. By using a 33%-return-to-zero (RZ) pulse train, a bit-error ratio (BER) below 7% hard-decision forward error correction (HD-FEC) threshold is achieved. BER below 20% soft-decision forward error correction (SD-FEC) threshold is also realized using a carrier suppressed return-to-zero (CSRZ) pulse train. The OTPI technique can also be used for more higher-order pulse amplitude modulation (PAM) formats, making it a promising technique for next-generation high-speed optical interconnects.

Performance investigation of optical wavelength conversion using a newly designed highly nonlinear ultra-flattened dispersion fibre

We report an analysis of the wavelength conversion using a newly designed highly nonlinear ultra-flattened dispersion fibre (HN-UFF) for different signal modulation formats. A new technical solution is presented for high bit rate wideband wavelength conversion without any additional pump signals. Two-channel 80 Gb s−1 modulated signals with differential quadrature phase shift keying (DQPSK) are considered for wavelength conversion using four wave mixing (FWM) technique in a newly designed HN-UFF without additional pump signals. It is found that even when the input signal frequency spacing is increased beyond 2 THz, DQPSK modulation with carrier-suppressed return-to zero (CSRZ), or CSRZ-DQPSK, gives a better value of flattened conversion efficiency and Q factor. The impact of input power on conversion efficiency and effective flatness is also investigated. The performance parameters, such as conversion efficiency, Q factor, log of bit error rate (BER), received signal power and power penalty, are analysed.

Performance Analysis of Duobinary and CSRZ Modulation Based Polarization Interleaving for High-Speed WDM-FSO Transmission System

Abstract In this paper, the bit error rate (BER) performance of Duobinary (DB) is compared with carrier-suppressed return-to-zero (CSRZ) based polarization interleaving (PI) schemes for high-speed transmission system. The system is integrated with wavelength-division multiplexing (WDM) scheme and PI scheme for free space optical communications (FSO). The simulation results show that DB offers betters BER performance compared to CSRZ in high-speed WDM-FSO-PI system.

Performance evaluation of 100 and 200-Gb/s WDM PM-QPSK transmission systems: tolerance analysis to the optical link impairments according to the optical carrier shape

Polarization-multiplexing quadrature phase shift keying (PM-QPSK) has become a key ingredient in the design of 100 and 200-Gb/s dense wavelength-division multiplexed (DWDM) networks. The performance of the system using these formats varies according to the shape of the pulses employed by the optical carrier: non-return to zero (NRZ), return to zero (RZ) or carrier-suppressed return to zero (CSRZ). In this paper, we analyse the tolerance of PM-QPSK to linear and nonlinear optical impairments, including amplified spontaneous emission (ASE) noise, crosstalk, distortion by optical filtering, chromatic dispersion (CD), polarization mode dispersion (PMD) and fibre Kerr nonlinearities. The simulation results show that RZ formats with a low-duty cycle have a higher tolerance to CD, PMD and intrachannel nonlinearities due to the reduction of pulse-to-pulse interaction. Conversely, the PM–NRZ-QPSK format has a higher spectral efficiency (SE) than other options and shows better tolerance to filtering distortion and CD in filterless networks.

Analytical study of DWDM optical long haul network with symmetrical dispersion compensation

Objective: To design 40 Gbps ultra-dense wavelength division multiplexed (DWDM) optical network for 32 and 64 channels. Methods: Proposed DWDM architecture supports three different advance modulation schemes with symmetrical dispersion compensation unit. Performance of proposed work has been investigated using parameters bit error rate (BER) and quality factor. For efficient analysis, we employ variation in channel spacing, transmission length of fiber and input laser power, which is resulted into some significant observations. Findings: Carrier Suppressed Return to Zero (CSRZ) scheme exhibits a good quality factor with maximum achievable distance up to 4250 km due to highest tolerance to nonlinear effects. Modified Duobinary Return to Zero (MDRZ) modulation scheme also provides a good quality factor with laser power variation due to high receiver sensitivity, but with limited reach upto 2750 km. While Duobinary Return to Zero (DRZ) scheme provides moderate transmission coverage up to 3750 km in comparison to CSRZ and MDRZ, with a lesser quality factor due to effect of Inter Symbol Interference (ISI). We observe that an increase in number of simultaneous users through the channels results into performance degradation. Application: This work delivers very huge data rate and good spectral efficiency to sustain the current high traffic growth. Keywords: Dispersion, Long Haul System, Optical Network, Symmetrical Compensation, DWDM

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.