Single-channel Transmission Research Articles

Mitigation of nonlinearities using conjugate data repetition.

We investigate a time-domain implementation of generalized phase-conjugated twin waves which we call conjugate data repetition. A theory based on time-domain perturbation analysis explaining the mitigation of nonlinear effects is provided, and the concept is evaluated using numerical simulations. Compared to PM-QPSK at the same channel bit rate, the single-channel transmission reach in a conventional system with standard single-mode fiber of conjugate data repetition-QPSK is increased by approximately a factor of 2.

Single-Channel 50G and 100G Discrete Multitone Transmission With 25G VCSEL Technology

This paper explores the feasibility of single-channel 50G and 100G transmission using 25G VCSEL technology. We show through experiments the practicality of 50G transmission through 100 m of OM3 multi-mode fiber. To address the question of whether single-channel 100G transmission is feasible, we show through simulation the needed reduction in relative intensity noise of 25G VCSELs and present a novel modulation technique which offers improved performance over conventional discrete multitone with little additional computational complexity.

Single channel 112Gbit/sec PAM4 at 56Gbaud with digital signal processing for data centers applications.

112Gbit/sec DSP-based single channel transmission of PAM4 at 56Gbaud over 15GHz of effective analog bandwidth is experimentally demonstrated. The DSP enables use of mature 25G optoelectronics for 2-10km datacenter intra-connections, and 8Tbit/sec over 80km interconnections between data centers.

Efficient Chromatic Dispersion Precompensation for Coherent Optical OFDM

To reduce the guard interval, short-cyclic-prefix coherent optical orthogonal frequency division multiplexing (CO-OFDM) divides a band into two subbands and precompensates for chromatic dispersion (CD) with timing offset. Implementation using full band inverse discrete Fourier transformations (IDFTs), however, can excessively increase hardware complexity. We propose an efficient hardware implementation of IDFT with timing offsets for short-cyclic-prefix CO-OFDM. In addition, the residual intersubband CD induced by quantized timing offset is compensated using subcarrier-based phase rotation. By increasing the number of subbands efficiently and compensating for the residual intersubband CD, the transmission performance can be improved. Simulation results show 112-Gb/s single-channel transmission over a 2250-km standard single-mode-fiber with polarization division multiplexing 16 quadrature amplitude modulation (PDM-16 QAM) using 128 DFT with a 16 guard interval.

Directional Transmission Based Optimization for the Hidden and Exposed Terminal Problems in Inter-Vehicular Communications

The intrinsic problems of hidden/exposed terminal may bring about threat of conflict in inter-vehicular communication, and thus decrease network throughput. In this paper, we take the unidirectional feature of road into consideration, design single-channel transmission scheme for decreasing communication conflicts with position information and directional antenna, including the identification and notification of relative positions among adjacent nodes, the identification of node transmission state, and the method of directional transmission scheduling. By simulation experiments of inter-vehicular communication in NS-2, we verify that this scheme can discern the hidden/exposed terminal nodes and decrease conflicts effectively, and thus improve network performance.

Analysis of intensity modulation performance in WDM-PON network

This paper mainly does research and analysis on anti-dispersive performance and anti-nonlinear performance for intensity modulation formats such as NRZ, RZ, CS-RZ, DRZ, MD-RZ in 40Gbps high-speed single-channel optical transmission system. It compares the five pattern modulation formats in dispersion tolerance, nonlinear tolerance, and advantages and disadvantages in transmission distance. Anti-nonlinear effect ability of CSRZ and RZ are stronger than that of NRZ code; in the single-channel transmission system, DRZ and improved modulation format MDRZ have better resistance for anti-nonlinear performance, so they are suitable for long-distance transmission. RZ has the minimum dispersion tolerance. NRZ has higher spectrum efficiency than RZ, and thus have a better dispersion tolerance. CSRZ code has higher spectral efficiency, higher dispersion tolerance and nonlinear tolerance than RZ code, making it more suitable for long distance transmission.

WDM optical steganography based on amplified spontaneous emission noise.

We propose and experimentally demonstrate a wavelength-division multiplexed (WDM) optical stealth transmission system carried by amplified spontaneous emission (ASE) noise. The stealth signal is hidden in both time and frequency domains by using ASE noise as the signal carrier. Each WDM channel uses part of the ASE spectrum, which provides more flexibility to apply stealth transmission in a public network and adds another layer of security to the stealth channel. Multi-channel transmission also increases the overall channel capacity, which is the major limitation of the single stealth channel transmission based on ASE noise. The relations between spectral bandwidth and coherence length of ASE carrier have been theoretically analyzed and experimentally investigated.

Research on the Modulation Performance in GPON System

This paper mainly does research and analysis on anti-dispersive performance and anti-nonlinear performance for intensity modulation formats such as NRZ, RZ, CS-RZ, DRZ, MD-RZ in 40Gbps high-speed single-channel optical transmission system. It compares the five pattern modulation formats in dispersion tolerance, nonlinear tolerance, and advantages and disadvantages in transmission distance. Anti-nonlinear effect ability of CSRZ, RZ are stronger than that of NRZ code; in the single-channel transmission system, DRZ and improved modulation format MDRZ have better resistance foranti-nonlinear performance, so they are suitable for long-distance transmission. RZ has the minimum dispersion tolerance. NRZ than RZ has higher spectrum efficiency than RZ, and thus have a better dispersion tolerance. CSRZ code has higher spectral efficiency, higher dispersion tolerance and nonlinear tolerance than RZ code, making it more suitable for long distance transmission.

Digital subcarrier multiplexing for fiber nonlinearity mitigation in coherent optical communication systems.

In this work we experimentally investigate the improved intra-channel fiber nonlinearity tolerance of digital subcarrier multiplexed (SCM) signals in a single-channel coherent optical transmission system. The digital signal processing (DSP) for the generation and reception of the SCM signals is described. We show experimentally that the SCM signal with a nearly-optimum number of subcarriers can extend the maximum reach by 23% in a 24 GBaud DP-QPSK transmission with a BER threshold of 3.8 × 10(-3) and by 8% in a 24 GBaud DP-16-QAM transmission with a BER threshold of 2 × 10(-2). Moreover, we show by simulations that the improved performance of SCM signals is observed over a wide range of baud rates, further indicating the merits of SCM signals in baud-rate flexible agile transmissions and future high-speed optical transport systems.

Bit Error Rate Estimation Methods for QPSK CO-OFDM Transmission

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) is an attractive transmission technique to virtually eliminate intersymbol interference caused by chromatic dispersion and polarization-mode dispersion. Design, development, and operation of CO-OFDM systems require simple, efficient, and reliable methods of their performance evaluation. In this paper, we demonstrate an accurate bit error rate estimation method for QPSK CO-OFDM transmission based on the probability density function of the received QPSK symbols. By comparing with other known approaches, including data-aided and nondata-aided error vector magnitude, we show that the proposed method offers the most accurate estimate of the system performance for both single channel and wavelength division multiplexing QPSK CO-OFDM transmission systems.

Unrepeatered DPSK transmission over 360 km SMF-28 fibre using URFL based amplification.

Unrepeatered 42.7 Gb/s per channel RZ-DPSK transmission over standard SMF-28 fibre with novel URFL based amplification using fibre Bragg gratings is investigated. OSNR and gain performance are studied experimentally and through simulations. Error free transmission for 16 channels across the full C-band with direct detection was experimentally demonstrated for 280 km span length, as well as 6-channel transmission at 340 km and single-channel transmission up to 360 km (75 dB) without employing ROPA or specialty fibres.

CO-OFDM Technology Long Distance Transmission System

Analysis of CO-OFDM single-mode optical fibre transmission system mode l, studied the timing deviation on the system synchronization performance, and used the Zadoff-Chu pilot sequence to realize the system synchronization, and concludes that the four QAM is to achieve 100 Gbps long distance transmission of the optimal modulation mode. In addition, the Zadoff-Chu pilot frequency sequence also has a constant amplitude, zero auto correlation properties, which can reduce the amplifier nonlinear effects, improve the performance of channel estimation. Based on Optisystem software simulation platform, built based on the CO-OFDM technology transfer rate for 100 Gbps long distance transmission system simulation system, and research the transmission distance for 1000 km error performance and the relationship between the transmission power. We research in single channel transmission and WDM transmission system of the two cases, random filling and consistent filling ef fect the performance of the system.

Rate-Adaptive Coded Modulation for Fiber-Optic Communications

Rate-adaptive optical transceivers can play an important role in exploiting the available resources in dynamic optical networks, in which different links yield different signal qualities. We study rate-adaptive joint coding and modulation, often called coded modulation (CM), addressing non-dispersion-managed (non-DM) links, exploiting recent advances in channel modeling of these links. We introduce a four-dimensional CM scheme, which shows a better tradeoff between digital signal processing complexity and transparent reach than existing methods. We construct a rate-adaptive CM scheme combining a single low-density parity-check code with a family of three signal constellations and using probabilistic signal shaping. We evaluate the performance of the proposed CM scheme for single-channel transmission through long-haul non-DM fiber-optic systems with electronic chromatic-dispersion compensation. The numerical results demonstrate improvement of spectral efficiency over a wide range of transparent reaches, an improvement over 1 dB compared to existing methods.

Up to 112 Gbit/s single wavelength channel transmission in the 1310 nm wavelength domain

ABSTRACTIn this article, we present up to 112 Gbit/s single wavelength channel on‐off keying transmission in the 1310‐nm wavelength domain utilizing polarization multiplexing over distances 25–38 km of standard single mode fiber. Excellent operation of the system is demonstrated. The proposed solution can be successfully utilized in data communications transmission. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:263–265, 2014

Intrachannel cross-phase modulation-induced phase shift in high-speed dispersion-managed optical fiber transmission system

We investigate the intrachannel cross-phase modulation (IXPM)-induced phase shift in optical return-to-zero pulse propagating in a periodically dispersion-managed long-haul optical fiber transmission line. Necessary dynamical equations for various pulse parameters have been derived using variational analysis to estimate the phase shift. These equations are solved by the Runge–Kutta method. The analytical result is verified by numerical simulation based on split-step Fourier method. We therefore explore the effects of various parameters, such as transmission distance, input power, duty cycle, dispersion map strength, and residual dispersion, on phase shift for a 40 Gb/s single-channel transmission system. We also check the impact of variation of bit rate on phase shift. We find that IXPM-induced phase shift can be mitigated by proper adjustment of dispersion management and different pulse parameters like duty cycle, dispersion map strength, and peak power.

A single-channel 128 Tbit/s-58 km transmission in the 11 μm band with wideband GVD and slope compensation

We describe a 1.28 Tbit/s single-channel transmission in the 1.1 μm band that uses a high-Δ single-mode step-index fiber (SIF) and ytterbium-doped fiber amplifiers (YDFAs). A 650 fs signal pulse was generated from a 10 GHz mode-locked Yb fiber laser (Yb MLFL) that was soliton-compressed by using an anomalous dispersion photonic crystal fiber (PCF). The dispersion of the SIF was compensated over a bandwidth as broad as 2.1 THz with two cascaded chirped fiber Bragg gratings (FBGs). In addition, an enhanced pre-chirping technique was newly adopted for the precise elimination of the large waveform distortion caused by the dispersion slope. As a result, 320 Gbit/s-161 km and 1.28 Tbit/s-58 km transmissions were successfully achieved.

Information-rate analysis of a fiber-optic transmission system including 2R signal regenerators

Performance of a single-channel fiber-optic transmission system in which signal regenerators are periodically inserted is analyzed in terms of information rate (IR) considering channel memory. Limitations in using regenerators in a system having non-zero residual dispersion between the regenerators are discussed. It is shown that a type of signal impairment caused by the interaction between the transmission-fiber dispersion and the regenerator nonlinearity is pattern-dependent and will be mitigated by the use of sequence estimation after detection at the receiver.

Hybrid mid-link spectral inverter to compensate for linear and nonlinear distortions for efficient transmission performance in 224 Gbit/s DP-16QAM system

The hybrid mid-link spectral inversion (H-MLSI) and digital signal processing techniques to compensate for the optical Kerr effects in 224 Gbit/s DP-16QAM transmission over 640 km of single-mode fiber are numerically evaluated. Digital signal processing methods, i.e., electronic dispersion compensation (EDC) and digital backward propagation (DBP) techniques, are implemented. The system is evaluated for diverse signal input launch powers for both single-channel and multichannel transmission in which five channels are multiplexed with a channel spacing of 100 GHz with central wavelength at 1550 nm. The system performance is enumerated by monitoring the bit error ratio. From the results, it is clear that the nonlinear threshold point is improved by 2 and 3 dBm signal power by using H-MLSI and DBP, respectively, with 20 steps per fiber span as compared to EDC. Furthermore, we have also evaluated the DBP complexity as compared to H-MLSI and the resultant impact on maximum transmission distance. Moreover, the performance penalty coming from the span-offset of H-MLSI can be reduced by employing DBP to compensate for the residual Kerr effects.

640 Gbaud (128 Tbit/s/ch) optical Nyquist pulse transmission over 525 km with substantial PMD tolerance

We report a substantial increase in PMD tolerance in a single-channel ultrahigh-speed transmission using optical Nyquist pulses. We demonstrate both analytically and experimentally a large reduction in depolarization-induced crosstalk with optical Nyquist pulses, which is one of the major obstacles facing polarization-multiplexed ultrashort pulse transmission. By taking advantage of the high PMD tolerance, a low-penalty 1.28 Tbit/s/ch optical Nyquist TDM transmission at 640 Gbaud was achieved over 525 km.

Comparison of 128-SP-QAM and PM-16QAM in long-haul WDM transmission

We investigate 128-level set-partitioning quadrature amplitude modulation (128-SP-QAM) experimentally and compare the performance to polarization-multiplexed 16QAM both at the same bit rate and at the same symbol rate. Using a recirculating loop we study both single channel and wavelength-division multiplexing (WDM) transmission and demonstrate a reach of up to 2680 km at a bit-error rate of 10(-3) for 128-SP-QAM. We confirm that 128-SP-QAM has an increased sensitivity compared to PM-16QAM and show that the maximum transmission distance can be increased by more than 50 % at the same bit rate for both single channel and WDM transmission. We also investigate the performance at the same symbol rate as a possible fall back solution in a degrading link.