Optical Quadrature Amplitude Modulation Research Articles

QAM receiver based on light amplifiers measured with effective role of optical coherent duobinary transmitter

Abstract Effective role of optical duobinary transmitter with optical coherent quadrature amplitude modulation (QAM) receiver based on light amplifiers measured is stimulated by using optisystem simulation software version 13. Signal, noise power levels are stimulated after long haul fiber optic range up to 350 km distance. Measured light amplifiers, optical duobinary transmitters and optical QAM receiver are employed to measure the peak signal amplitude power (SAP) and noise signal power for bit rate transmission with 100 Gb/s based 350 km length. Maximum signal power level margin is enhanced with high data rates transmission.

Differential coding scheme based FSO channel for optical coherent DP-16 QAM transceiver systems

Abstract This article has indicated optical coherent differential polarization (DP) 16 quadrature amplitude modulation (QAM) transceiver systems with free-space optical (FSO) channel in the presence of differential coding scheme. The optical coherent DP 16-QAM receiver executes the reverse process conversion of the optical signal into an electrical one that is detected to the users. The proposed optical coherent DP-16 QAM transceiver systems based FSO channel model with differential coding has been presented and compared with the previous model. However, the simulation results have confidence realization about the superiority of the proposed simulation model. Hence the proposed optical coherent DP-16 QAM transceiver systems simulation model with differential coding is verified and validated the enhancement performance based on simulation performance parameters.

Scheme of coherent optical chaos communication

We propose and numerically demonstrate a scheme of coherent optical chaos communication using semiconductor lasers for secure transmission of optical quadrature amplitude modulation (QAM) signals. In this scheme, a laser intensity chaos and its delayed duplicate are used to amplitude-quadrature modulate a continuous-wave light to generate a chaotic carrier. High-quality chaotic carrier synchronization between the transmitter and receiver is guaranteed by laser intensity chaos synchronization, avoiding laser phase fluctuation. Decryption is implemented by a 90 deg optical hybrid using the synchronous chaotic carrier as local light. Secure transmission of an optical 40 Gb/s 16QAM signal is demonstrated by using a laser intensity chaos with a bandwidth of 11.7 GHz. The system performances are evaluated by analyzing a bit error ratio with different masking coefficients, signal rates, synchronization coefficients, parameter mismatches, and dispersion compensation. It is believed that this scheme can pave a way for high-speed optical chaos communication.

Performance enhancement of an optical high-order QAM channel by adding correlated data to robust neighboring BPSK or QPSK channels.

We numerically simulate and experimentally demonstrate an approach to potentially enhance the performance of a high-order quadrature amplitude modulation (QAM) channel by adding correlated data to other robust binary-phase-shift-keyed (BPSK) or quadrature-phase-shift-keyed (QPSK) channels. The correlated data are introduced by optically multiplying the BPSK or QPSK channels, already modulated with their own data, by the target high-order QAM data of the same baud rate. After joint detection and signal processing, a ∼3 dB optical signal-to-noise (OSNR) improvement is observed in simulations by comparing the performance of the target QAM channel (from 4QAM to 256QAM) with and without the use of channel correlation. We also experimentally demonstrate the scheme for a QPSK or a 16QAM target channel using BPSK correlated channels. A ≥2 dB OSNR improvement is observed.

Design and Performance Investigation of Intersatellite Optical Wireless Communication System Employing Modulation Techniques

This work is focused to carry out the investigation of coherent optical quadrature phase shift keying (CO-QPSK), coherent optical quadrature amplitude modulation (CO-QAM), CO-8-QAM, CO-8-PSK, CO-16-QAM and CO-16-PSK techniques on intersatellite optical wireless communication system using OptiSPICE and OptiSystem at 1550, 1064 and 850 nm. The maximum bit rate achieved for CO-QPSK and CO-QAM is 0.511 Tbps, CO-8-QAM and CO-8-PSK is 0.742 Tbps and CO-16-QAM and CO-16-PSK is 1 Tbps at maximum distance of 45,000 km. The performance of CO-16-PSK is better than other proposed techniques in terms of quality (Q) factor at 1550, 1064 and 850 nm wavelengths. There is 59.93, 27.95, 16.58, 7.26 and 4.26 % improvement in CO-16-PSK from CO-QPSK, CO-QAM, CO-8-QAM, CO-8-PSK and CO-16-QAM respectively in terms of signal to noise ratio (SNR) at 1550 nm wavelength. On comparing all the techniques, it is found that at acceptable bit error rate 0---10ź7, CO-16-PSK is better technique as compared to other proposed techniques in terms of bit rate, Q factor and SNR.

Hardware‐efficient frequency offset and phase noise mitigation in coherent optical quadrature amplitude modulation systems

A hardware-efficient adaptive algorithm for frequency offset and phase noise mitigation in coherent optical quadrature amplitude modulation systems is presented and analysed. Hardware efficiency for the mitigation of imperfections is achieved by computing directly the complex exponential, thus avoiding a CORDIC processor in the phase recovery loop. The design includes a square-root- and trigonometry-free update. Simulation results substantiate the theoretical findings.

Flexible quadrature amplitude modulation with semiconductor optical amplifier and electroabsorption modulator

Optical quadrature amplitude modulation (QAM) is experimentally demonstrated with a low-complexity modulator based on a semiconductor optical amplifier and electroabsorption modulator. Flexible amplitude/phase format transmission is achieved. The applicability of octary QAM for coherent optical access networks with sustainable 3 Gb/s per-user bandwidth is investigated for a long reach of 100 km, and its compatibility with a potentially high split is verified.

A simple experimental scheme for M-QAM optical signals generation

A simple scheme to generate optical quadrature amplitude modulation (QAM) signals is proposed based on different types of delay interferometers (DIs). The simulated results show that 16QAM, 64QAM and 256 QAM optical signals can be generated by 2×2, 3×3 and 4×4 DI, respectively, and the outputs of the proposed scheme are similar to those of the conventional schemes. The operation principle is discussed and the transmission properties of the square 16QAM as well as 64QAM signals are analyzed and compared with common approach.

Performance analysis of coherent optical 8-star QAM systems using decision-aided maximum likelihood phase estimation

An approximate bit-error rate (BER) expression of 8-star quadrature amplitude modulation (QAM) in the presence of a phase estimation error is derived. The accuracy of the approximate BER is verified via numerical integration of the conditional BER and the Monte-Carlo (MC) simulations. This approximation allows quick estimation of the BER performance and prediction of laser linewidth tolerance, and also facilitates optimization of the ring ratio.

Blind Carrier Frequency Offset Estimation Based on Eighth-Order Statistics for Coherent Optical QAM Systems

We propose a carrier frequency offset estimation (FOE) algorithm based on eighth-order statistics for optical quadrature amplitude modulation (QAM) signals. The FOE algorithm does not involve fast Fourier transformation and can be implemented by hardware with little memory and computation resources. Simulation results show that in a 10.709-GBaud/s optical 16-QAM system, carrier frequency offset ranging between ± 1.25 GHz can be estimated with a uniform standard deviation of 2 MHz when the optical signal-to-noise ratio is 17 dB and 410 symbols are utilized.

A Method for Generating Arbitrary Optical Signal Constellations Using Direct Digital Drive

A digitally operated optical quadrature-amplitude modulation (QAM) modulator based on a single multielectrode Mach-Zehnder modulator is presented. Generation and performance of 64QAM are studied in detail. Simulation results show that a single modulator with 13 electrodes, each of which is driven by either one of the voltages 0 or 1.68 vπ, provides close-to-ideal 64QAM constellation despite the inherent nonlinearity of the modulator. Moreover, employing a sufficient number of electrodes, close to ideal error performance can be obtained for any constellation order, or shape. Simulations results are demonstrated for several different square constellations: 16QAM and 256QAM, and nonsquare constellations: 32QAM and 128QAM. A brief discussion on the utilization of the proposed scheme as a predistorter is also given.

A Simplified Feedforward Carrier Recovery Algorithm for Coherent Optical QAM System

A simplified quadrature amplitude modulation (QAM) feedforward carrier recovery algorithm is proposed. By introducing a new two-stage estimation structure and sliding-block approach, the required computational effort can be significantly reduced with a tolerable performance deterioration compared with the original algorithm. In order to choose the size of the sliding block properly, an analytical model is proposed that takes the optical SNR (OSNR) and the laser-linewidth-times symbol-rate product into account. The model reveals different influence of OSNR and the laser-linewidth-times symbol-rate product on the performance of any carrier recovery algorithm. The performance of the simplified algorithm is evaluated by Monte Carlo simulations for square 16-, 64-, and 256-QAM. The simulation results show that the computational effort for each symbol can be significantly reduced at the cost of a 11% reduction of laser linewidth tolerance.

Parallel Mach-Zehnder modulators for quadrature amplitude modulation

This paper describes optical quadrature amplitude modulation techniques using parallel Mach-Zehnder modulators (MZMs). Arbitrary constellations of optical signals can be generated by using a dual-parallel MZM which can independently control real and imaginary components of lightwaves, where each MZM should be driven by multi-level electric signals. Many parallel MZMs, such as quad-parallel MZMs, octet-parallel MZMs can synthesize optical multi-level signals from binary data stream generated by electronics designed for binary modulation formats. We also investigate characterization methods of parallel MZMs. Precise measurement of half-wave voltage, extinction ratio and chirp parameter of each MZM element can be achieved by using optical spectrum analysis.

Adaptive threshold adjustment for signaldistortion- free digital-coherent optical demodulation system

Optical quadrature amplitude modulation (QAM) attracts considerable attention in the enhancement of communications capacity, due to its high spectral efficiency. However, this modulation format is more sensitive to signal distortion than conventional formats, making it more difficult to create, transmit, and detect signals. In this paper, we propose an adaptive scheme for demodulation of the distorted optical signals with paying attention to use of DSP-technology. The scheme is based on the adjustment of the thresholds against the signal distortion. Successful demodulation of optical QAM signals is demonstrated with a sufficiently low bit-error rate.

Simple, low fluctuation voltage signal generation for 8-Gb/s quadrature amplitude modulation using dual-parallel Mach-Zehnder modulator

Optical quadrature amplitude modulation (QAM) has attracted considerable attention because of its high spectral efficiency. For high capacity, the modulation rate should also be enhanced, which requires the generation of high-baud-rate multilevel electric signals with high precision in amplitude. In this paper, we describe a method to reduce the amplitude fluctuation of the electric signal by adopting a return-to-zero (RZ) format. We also demonstrate 2.0-Gbaud optical QAM signal generation with a conventional dual-parallel Mach-Zehnder modulator (DPMZM) driven by the electric RZ data signals.