Forward Error Correction Limit Research Articles

A novel architecture of satellite‐ground communication system at W‐band based on RF transparent demodulation technique

ABSTRACTWe proposed and experimentally demonstrated a novel architecture for the downlink of satellite‐ground communication system at W‐band (75–110 GHz). Radio‐frequency transparent demodulation technique and polarization multiplexing technique are used to reduce the ground system complexity. Quadrature phase shift keying signals (30 Gbaud/s) are transmitted over 15 m wireless link and 50 km fiber. The net bit rate of the whole system is 100 Gb/s while 20% overhead forward error correction (FEC) code is used. Bit‐rate‐error under FEC limit of 2 × 10−2 is achieved at the optical signal noise ratio of 21 dB. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:409–414, 2015

Adaptive-optics-based simultaneous pre- and post-turbulence compensation of multiple orbital-angular-momentum beams in a bidirectional free-space optical link

As a recently explored property of light, orbital angular momentum (OAM) has potential in enabling multiplexing of multiple data-carrying beams, to increase the transmission capacity and spectral efficiency of a communication system. For the use of OAM multiplexing in free-space optical (FSO) communications, atmospheric turbulence presents a critical challenge. In this paper, we experimentally demonstrate simultaneous pre- and post-turbulence compensation of multiple OAM beams, in a bidirectional free-space optical communications link, using a single adaptive optics (AO) system. Each beam carries a 100 Gbit/s signal, and propagates through an emulated atmospheric turbulence. A specifically designed AO system, which utilizes a Gaussian beam for wavefront sensing and correction, is built at one end of the bidirectional link. We show that this AO system can be used to not only post-compensate the received OAM beams, but also pre-compensate the outgoing OAM beams emitted from the same link end. Experimental results show that this compensation technique helps reduce the crosstalk onto adjacent modes by more than 12 dB, achieving bit error rates below the forward error correction limit of 1×10−3, for both directions of the link. The results of work might be helpful to future implementation of OAM multiplexing, in a high-capacity FSO bidirectional link affected by atmospheric turbulence.

Iterative intersymbol interference cancellation in vestigial sideband Nyquist–subcarrier modulation system

The intersymbol interference caused by dispersion, chirp, and a vestigial sideband filter in intensity modulation and a direct detection single carrier system is analyzed theoretically and numerically. An iterative nonlinear intersymbol interference cancellation technique is proposed and experimentally demonstrated in a 40-Gbps 16-QAM Mach-Zehnder modulator-based vestigial sideband intensity modulation and direct detection half-cycle Nyquist–subcarrier modulation system over a 100-km uncompensated standard single-mode fiber transmission for the first time. The experimental results show that 2.2-dB receiver sensitivity improvement is obtained at the forward error correction limit by using the iterative technique.

\(2 \times 100\) -Gb/s NRZ-OOK Integrated Transmitter for Intradata Center Connectivity

We demonstrate an integrated transmitter that can generate two 100-Gb/s optical channels with simple nonreturn-to-zero-ON-OFF keying format. The transmitter is based on the combination of an ultrafast electro-optic polymer platform for the photonic integration and the optical modulation with ultrafast InP-double heterojunction bipolar transistor electronics for the multiplexing and the amplification of the 100-Gb/s driving signals. Through error-free transmission of 2 × 80-Gb/s signals over 1 km of SMF and transmission of 2 × 100-Gb/s signals over 500 m of single-mode fiber with error performance way below the forward error correction limit, we reveal the potential of the approach for parallel 100-GbE optical interfaces in small footprint transceivers for intradata center networks.

High Speed WDM VLC System Based on Multi-Band CAP64 With Weighted Pre-Equalization and Modified CMMA Based Post-Equalization

Multi-user access is one of the key problems in the visible light communication (VLC). In this paper, we propose and experimentally demonstrate an approach for multi-user access based on multi-band CAP modulation over a wavelength division multiplexing (WDM) VLC system using a single RGB LED. In this scenario each wavelength will provide 3 sub-bands. Depending on the combination of the different wavelength and the sub-bands, a dynamic capacity can be achieved for up to 9 users access. At the transmitter a weighted pre-equalization method is proposed to overcome frequency attenuation of the LED, while at the receiver a post-equalizer based on modified cascaded multi-modulus algorithm (CMMA) is utilized. The experimental results show that the bit error rate (BER) for an over-all 1.35 Gb/s CAP64 signal over 30-cm transmission can be under the 7% forward error correction (FEC) limit of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The results clearly demonstrate the benefit and feasibility of the multi-band CAP modulation for the short range multi-user VLC systems.

A 20-Mb/s VLC Link With a Polymer LED and a Multilayer Perceptron Equalizer

This letter experimentally demonstrates a visible light communication system using a 350-kHz polymer light-emitting diode operating at a total bit rate of 19 Mb/s with a bit error rate (BER) of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> and 20 Mb/s at the forward error correction limit for the first time. This represents a remarkable net data rate gain of ~55 times. The modulation format adopted is ON-OFF keying in conjunction with an artificial neural network classifier implemented as an equalizer. The number of neurons used in the experiment is varied from the set N = {5, 10, 20, 30, 40} with 40 neurons offering the best performance at 19 Mb/s and the BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> .

A 10-Gb/s Silicon Microring Resonator-Based BPSK Link

We design and demonstrate for the first time an end- to-end binary phase-shift keying (BPSK) link based on silicon microring resonators, with an operational bit-rate at 10 Gb/s. The obtained bit-error-rate is below the forward error correction limit, validating the practical application of the demonstrated technique. Performance comparisons to conventional BPSK modulation and demodulation techniques are also made. The microring-based BPSK link promises a compact, energy efficient, and low-cost interconnect solution for high-capacity transceivers.

Demonstration of 6.25 Gbaud advanced modulation formats with subcarrier multiplexed technique on silicon Mach-Zehnder modulator.

Silicon Mach-Zehnder modulators (Si MZMs) with good linearity are designed and fabricated. 6.25 Gbaud Nyquist 16, 32 and 64-Quadrature Amplitude Modulation (QAM) optical signals were successfully generated by intensity modulation from the Si MZM, and the effective data rates are 22.61 Gb/s, 28.26 Gb/s and 33.91 Gb/s respectively. The subcarrier multiplexed technique and direct detection scheme were employed in this experiment. After 53.1 km transmission, the BERs of 16-QAM and 32-QAM are both below the 7% hard-decision forward error correction limit, while the back-to-back BER of 64-QAM is well below the 20% soft-decision forward error correction limit. These results demonstrated that the Si MZM can be used in the high-capacity low-cost short-haul intensity modulation and direct detection system.

Stealth transmission of temporal phase en/decoded polarization-modulated-code-shift-keying optical-code-division multiple-access signal over synchronous digital hierarchy network with asynchronous detection

An innovative approach for security-enhanced optical stealth transmission in a synchronous digital hierarchy network is proposed and experimentally investigated. The security enhancement is achieved through a signal modulation format, so-called polarization-modulated-code-shift-keying, which is implemented with two superstructured fiber Bragg gratings-based optical-code-division multiple-access encoders and a polarization modulator. The proposed modulation format can provide a constant energy level for both bits 0’s and 1’s, which avoids secure vulnerability of single-stealth-user with on-off-keying modulation before coupling into the host channel and after the cascade of filters. Moreover, a self-made cost-effective gain-switched distributed feedback laser with relatively narrow spectrum is first employed as a stealth optical source, which greatly reduces the system cost and complexity. The stealth signal is recovered and detected asynchronously. The experimental results show high secure performance and robustness against eavesdropping, while keeping a bit error rate below forward error correction limit.

Experimental Demonstration of Nonlinearity and Phase Noise Tolerant 16-QAM OFDM W-Band (75–110 GHz) Signal Over Fiber System

We propose a nonlinearity and phase noise tolerant orthogonal frequency division multiplexing (OFDM) W-band signal over fiber system based on phase modulation and photonic heterodyne up-conversion techniques. By heterodyne mixing the phase-modulated optical OFDM signal with a free-running laser in the photodiode, the constant envelope OFDM W-band wireless signal is obtained to suppress the nonlinear impairments. Moreover, the phase noises of the beating lasers appear as additive terms to the desired signal, and could be easily filtered out without complex phase noise estimation and compensation algorithms. In our experiment, 4 Gb/s QPSK and 8 Gb/s 16-QAM constant envelope OFDM W-band signals are transmitted over 22.8 km single mode fiber and 2.3 m air distance with achieved bit-error-rate performance below the forward error correction limit.

Stable and wavelength-tunable RSOA- and SOA-based fiber ring laser

In this work, we propose and experimentally investigate a wavelength-tunable fiber ring laser architecture by using the reflective semiconductor optical amplifier (RSOA) and semiconductor optical amplifier (SOA). Here, the wavelength tuning range from 1538.03 to 1561.91nm can be obtained. The measured output power and optical signal to noise ratio (OSNRs) of the proposed fiber laser are between -0.8 and -2.5 dBm and 59.1 and 61.0dB/0.06nm, respectively. The power and wavelength stabilities of the proposed laser are also studied. In addition, the proposed laser can be directly modulated at 2.5Gbit/s quadrature phase shift keying-orthogonal frequency-division multiplexing (QPSK-OFDM) signal and 20–50km single-mode fiber (SMF) transmissions are achieved within the forward error correction (FEC) limit without dispersion compensation. It could be a cost-effective and promising candidate for the standard-reach and extended-reach wavelength division multiplexed passive optical network (WDM-PON).

Visible light communications: real time 10 Mb/s link with a low bandwidth polymer light-emitting diode

This paper presents new experimental results on a polymer light-emitting diode based visible light communications system. For the first time we demonstrate a 10 Mb/s link based on the on-off keying data format with real time equalization on a field programmable gate array. The 10 Mb/s transmission speed is available at a bit error rate less than 4.6 × 10(-3), which is the limit for forward error correction. At a BER of 10(-6) a transmission speed of 7 Mb/s is readily achievable.

Optimized 481 Mb/s visible light communication system using phosphorescent white LED

We demonstrate a visible light communication system based on DC-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) and achieve a bit rate of 481 Mb/s at a communication distance of 65 cm by employing single 1-W commercial phosphorescent light-emitting diode (LED). The average bit error rate of the received data is 2.3×10-3, which is below the forward error correction limit, 3.8×10-3. The effect of ­signal clipping in DCO-OFDM system is studied and resource allocation algorithms are utilized. At least 13% capacity improvement can be obtained by suitable signal clipping and resource allocation.

High Bandwidth Visible Light Communications Based on a Post-Equalization Circuit

A research in extending bandwidth of the visible light communication (VLC) system that uses phosphorescent white LED has been reported in this letter. Slow response of the phosphorescent component limits the modulation bandwidth of white LED to the lower MHz range. In this letter, we present a post-equalization circuit that contains two passive equalizers and one active equalizer. With blue-filtering and the post-equalization circuit, a bandwidth of 151 MHz has been achieved in our VLC system, which allows OOK-NRZ data transmission up to 340 Mb/s. The VLC link operates at 43 cm using a single one Watt white LED, and the bit-error-ratio was below 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , which is within the forward error correction limit.

Experimental evaluation of prefiltering for 56 Gbaud DP-QPSK signal transmission in 75 GHz WDM grid

We investigate optical prefiltering for 56Gbaud (224Gbit/s) electrical time-division multiplexed (ETDM) dual polarization (DP) quaternary phase shift keying (QPSK) transmission. Different transmitter-side optical filter shapes are tested and their bandwidths are varied. Comparison of studied filter shapes shows an advantage of a pre-emphasis filter. Subsequently, we perform a fiber transmission of the 56Gbaud DP QPSK signal filtered with the 65GHz pre-emphasis filter to fit the 75GHz transmission grid. Bit error rate (BER) of the signal remains below forward error correction (FEC) limit after 300km of fiber propagation.

Centralized Optical-Frequency-Comb-Based RF Carrier Generator for DWDM Fiber-Wireless Access Systems

In this paper, we report on a gigabit capacity fiber-wireless system that enables smooth integration between high-speed wireless networks and dense wavelength-division-multiplexing (DWDM) access networks. By employing a centralized optical frequency comb, both the wireline and the wireless services for each DWDM user can be simultaneously supported. Besides, each baseband channel can be transparently upconverted to multiple radio-frequency (RF) bands for different wireless standards, which can be flexibly filtered at the end user to select the on-demand RF band, depending on the wireless applications. For demonstration, we transmit a 2.5&#x2009;&#x2009;Gbit/s signal through the proposed system and successfully achieve a bit-error-rate (BER) performance well below the 7% overhead forward error correction limit of the BER of 2&#xD7;10&#x2212;3 for both the wireline and the wireless signals in the 60&#xA0;GHz band after 25&#xA0;km single-mode fiber plus up to 6&#xA0;m wireless distance.

Up to 64 QAM/32 Gbaud flexible dual polarization transmitter for future elastic optical networks

Next generation elastic optical networks will very likely require dual polarization (DP) optical transmitter with inherent flexibility to dynamically change its baud rate and/or modulation format. We develop a prototype of compact flexible DP M-ary quadrature amplitude modulation (MQAM) optical transmitter and demonstrate its reconfigurability to accommodate baud rates ranging from 8 to 32 Gbaud/s using the same hardware. The prototype has another advantage in that the modulation format can also be dynamically changed from binary phase shift keying up to 64 quadrature amplitude modulation (QAM) for single and DPs, all over a single optical carrier. This allows the generation of variable data rate up to 384-Gb/s over a single wavelength. Experimental results show that for the most challenging setting of DP-64 QAM/32 Gbaud, the worst case values of error vector magnitude and bit error rate are 6.7 and 3×10 −2 , respectively. For less stringent settings, i.e., lower baud rate and/or lower modulation format, forward error correction limit error free transmission is easily obtained. Further results are also reported to demonstrate transmitter flexibility and software definability, by measuring symbol streams showing instantaneous swapping between modulation schemes with a swapping time less than 10 symbols duration, i.e., 0.3 ns.

WDM-OFDM-PON Based on Compatible SSB Technique Using a Mode Locked Comb Source

We report on a wavelength division multiplexed-orthogonal frequency division multiplexed-passive optical network (WDM-OFDM-PON), for downstream transmission, based on a tunable mode locked comb source. The 12.75 Gb/s compatible single side-band (SSB) OFDM signal is used to modulate 10 comb tones separated by 10 GHz. Net spectral efficiencies of 1.12 and 1 bit/s/Hz were achieved in conjunction with the use of low complexity electronics. Transmission over 50 and 87 km of standard single mode fiber was successfully demonstrated. The incurred penalty after transmission over 50 km was at a bit error rate (BER) of 3×10-3, relative to the back-to-back case. All channels after 87 km transmission achieved performance below the 20% forward error correction (FEC) limit.

A single-channel 192 Tbit/s, 64 QAM coherent optical pulse transmission over 150 km using frequency-domain equalization

We demonstrate a single-channel 1.92 Tbit/s, 64 QAM coherent optical pulse optical time-division multiplexing (OTDM) transmission by utilizing frequency-domain equalization (FDE). FDE makes it possible to compensate precisely for the waveform distortions caused by hardware imperfections thus greatly improving the error vector magnitude (EVM) of the demodulated 64 QAM signal compared with that obtained with a conventional FIR filter. As a result, a coherent 64 QAM OTDM transmission over 150 km with a bit error rate of below the forward error correction limit of 2 x 10⁻³ (requiring 7% overhead) was achieved for the first time.

Pilot-symbols-aided cycle slip mitigation for DP-16QAM optical communication systems

A pilot-symbols-aided phase unwrapping (PAPU), which utilizes the time-division multiplexed pilot symbols that are transmitted with data, is proposed to do cycle slip detection and correction with the carrier phase estimation (CPE). Numerical simulations for 10 Gbaud dual-polarization 16-ary quadrature amplitude modulation (DP-16QAM) systems show that the block averaging quadrature phase-shift keying (QPSK) partitioning with PAPU greatly eliminates the performance degradation caused by cycle slips, maintains a low CS probability with less influence of filter length, and achieves a bit-error-rate (BER) performance below soft-decision forward error correction (FEC) limit 2 × 10⁻² at 15 dB optical signal-to-noise ratio with only 1.56% overhead and 6 MHz combined laser linewidth.