All-optical OFDM Research Articles

All-Optical OFDM Generation for IEEE802.11a Based on Soliton Carriers Using Microring Resonators

The optical carrier generation is the basic building block to implement all-optical orthogonal frequency-division multiplexing (OFDM) transmission. One method to optically generate single and multicarriers is to use the microring resonator (MRR). The MRRs can be used as filter devices, where generation of high-frequency (GHz) soliton signals as single and multicarriers can be performed using suitable system parameters. Here, the optical soliton in a nonlinear fiber MRR system is analyzed, using a modified add/drop system known as a Panda ring resonator connected to an add/drop system. In order to set up a transmission system, i.e., IEEE802.11a, first, 64 uniform optical carriers were generated and separated by a splitter and modulated; afterward, the spectra of the modulated optical subcarriers are overlapped, which results one optical OFDM channel band. The quadrature amplitude modulation (QAM) and 16-QAM are used for modulating the subcarriers. The generated OFDM signal is multiplexed with a single-carrier soliton and transmitted through the single-mode fiber (SMF). After photodetection, the radio frequency (RF) signal was propagated. On the receiver side, the RF signal was optically modulated and processed. The results show the generation of 64 multicarriers evenly spaced in the range from 54.09 to 55.01 GHz, where demodulation of these signals is performed, and the performance of the system is analyzed.

Flexible all-optical frequency allocation of OFDM subcarriers

We investigate the underlying mechanism that allows OFDM subcarriers in an all-optical OFDM system to be assigned to any optical frequency using an optical filter, even if that frequency is not generated by the comb-line source feeding the filters. We confirm our analysis using simulations, and present experimental results from a 252-subcarrier system that uses a mode-locked laser (MLL) as the comb source and a wavelength selective switch. The experimental results show that there is no correlation between the programmed frequency offset between a subcarrier and nearest comb line, and the received signal quality. Thus, subcarriers could be inserted into unused portions of an optical transmission system's spectrum without restriction on their particular center frequencies. Any percentage of cyclic prefix can be added to the OFDM symbol simply by reprogramming the optical filter to give wider subcarrier frequency spacing than the comb line spacing, which is useful for tailoring the CP to the dispersion of various optical transmission paths, to maximize the spectral efficiency. Finally, the MLL's center frequency need not be locked to a system reference.

All-optical OFDM demultiplexing by spectral magnification and band-pass filtering

We propose a simple OFDM receiver allowing for the use of standard WDM receivers to receive spectrally advanced OFDM signals. We propose to spectrally magnify the optical-OFDM super-channels using a spectral telescope consisting of two time-lenses, which enables reduced inter-carrier-interference in subcarrier detection by simple band-pass filtering. A demonstration on an emulated 100 Gbit/s DPSK optical-OFDM channel shows improved sensitivities after 4-times spectral magnification.

The improvement of Nyquist pulse shaping for all-optical OFDM system in multi-users network

The all-optical orthogonal frequency division multiplexing has a better spectral efficiency and a lower response requirement of modulators for high capacity transmission. In the system, the optical filter will degrade the performance of subcarriers which are far away from the center carrier. We proposed an improvement method of all-optical OFDM scheme using Nyquist pulse shape in the pulse source generator. Comparing a Nyquist shape pulse with a Gauss pulse in a 4×100Gb/s DP-QPSK all-optical sampling OFDM system, the side lobe of transmitted spectrum can be effective suppressed, and the optical power will be more focused on the effective frequency band. By coherent receiver, the results show that the Nyquist pulse shaping can improve the OSNR and transmission performance of subcarriers which deviate mostly from the center frequency of optical filter. This improvement is of great benefit for multi-users system.

Proposal and Performance Evaluation of an Efficient RZ-DQPSK Modulation Scheme in All-Optical OFDM Transmission Systems

A return-to-zero differential quadrature phase-shift keying (DQPSK) modulation scheme is proposed for all-optical orthogonal frequency-division multiplexing transmission systems. The system uses coupler-based inverse fast Fourier transform/fast Fourier transform to support a 700 km single-mode fiber link and a transmission rate of 40??Gb/s without any nonlinear compensation. The performance of the proposed system is evaluated using simulation and four performance measures are obtained, namely, the eye diagram, the eye-opening penalty (EOP), the power spectral broadening, and the bit error rate (BER). The effect of self-phase modulation is taken into account in the performance evaluation. In addition, the performance of the proposed system is compared to that of a traditional one adopting a non-return-to-zero DQPSK scheme. Our results reveal that the proposed system outperforms the traditional one in all four aforementioned performance measures, yet the spectral efficiency is almost preserved. Specifically, for an input average power of 12 dBm, a reduction in both the required optical-signal-to-noise ratio of about 4 dB (to achieve a BER of 10?6) and the EOP of about 5 dB are reported when adopting the proposed system, as compared to the traditional one.

Cascaded and Multisection Sagnac Interferometers for Scalable and Tunable All-Optical OFDM DEMUX

With cascaded and multisection Sagnac interferometers, all-optical fast Fourier transform (FFT) has been demonstrated for optical demultiplexing (DEMUX) of orthogonal frequency division multiplexing (OFDM) signals. The transmission characteristics of the interferometers have been investigated theoretically and experimentally. The scalability and tunability of the all-optical OFDM DEMUX are analyzed and demonstrated for 5-channel OFDM signals.

Transmission performance of a 400 Gbit s−1 all-optical orthogonal frequency division multiplexing system

The performance of a 400 Gbit s−1 all-optical orthogonal frequency division multiplexing (AO-OFDM) transmission system is researched with the effects of chromatic dispersion, fiber nonlinearities and amplified spontaneous emission (ASE) noise. The numerical simulation results show that the AO-OFDM system can provide a higher spectral efficiency (SE) and a better sensitivity than a dense wavelength division multiplexing (DWDM) system. The accumulated dispersion tolerance of the system reaches 330 ps nm−1. When transmitted over single-span 80 km single-mode fiber (SMF), AO-OFDM signals have a 1.5 dB power penalty at BER=10−3 due to the fiber Kerr nonlinearities, and the receiver sensitivity of the AO-OFDM system is obviously degraded with increasing incident optical power. In multispan transmission, the interaction of the fiber Kerr nonlinearity with the ASE noise is analyzed. A 1320 km maximum transmission distance is realized at 0 dBm incident optical power. The transmission discount due to the ASE noise and fiber nonlinearities in the AO-OFDM system is calculated. Fiber Kerr nonlinearities impose a greater limitation on the performance of the AO-OFDM system for long-distance transmission. All results clearly indicate the feasibility of AO-OFDM technology for next generation 400 Gbit s−1 fiber communication and multiservice networks.

Optical orthogonal frequency division multiplexed transmission using all‐optical discrete Fourier transform

Orthogonal frequency division multiplexing (OFDM) can provide spectrally efficient communication channels because it can utilize carrier orthogonality and various impairment mitigation methods. An optical OFDM signal can be generated electronically to multiplex lower-rate carriers. In recent advancements, OFDM signals are also shown to be generated and demultiplexed by all-optical discrete Fourier transform (DFT), overcoming the speed limit of electronics for >Tbps capacity. High-performance DFT devices, such as arrayed waveguide grating (AWG) or planar lightwave circuit (PLC), are critically required to obtain strong orthogonality for scalable all-optical OFDM (AO-OFDM) system implementations. Advanced techniques such as coherent modulation and detection with digital impairment mitigation are also important for long-reach AO-OFDM transmissions. More recently, optical superchannel schemes have been introduced utilizing coherent detection for multi-Tbps AO-OFDM transmissions. This paper reviews the device and system aspects for the AO-OFDM technology, including a generalized theoretical model to provide an indepth understanding.

High-Capacity Fiber Field Trial Using Terabit/s All-Optical OFDM Superchannels With DP-QPSK and DP-8QAM/DP-QPSK Modulation

We report the results of two separate field trials aimed to achieve high fiber capacity over long-haul distances. In the first trial, 22 all-optical orthogonal frequency-division multiplexing superchannels with hybrid dual-polarization 8 quadrature amplitude modulation and dual-polarization quadrature phase-shift-keying (DP-QPSK) modulation were generated using a novel flexible format superchannel transmitter design. The signal carrying net 21.7 Tb/s data was transmitted over 1503 km of dispersion uncompensated field-installed standard single-mode fiber with the aid of hybrid Raman and erbium-doped fiber amplifier (EDFA) amplification and digital coherent detection. In the second trial, we extended the transmission distance to over 2531 km of field fiber using only EDFA for loss compensation. The increase in reach was achieved by reducing the net total data rate to 16.2 Tb/s and modulating the optical superchannel subcarriers with DP-QPSK only. To the best of our knowledge, we achieved the highest capacity field trial record to date at 21.7 Tb/s in the first trial, while the achieved capacity-distance product of 40.9 Pb/s ·km in the second trial is also the highest reported to date.

Theories and applications of chromatic dispersion penalty mitigation in all optical OFDM transmission system

Fiber chromatic dispersion (CD) in optical OFDM transmission degrades carrier orthogonality, resulting in a system penalty. Such penalty can be mitigated by per-carrier delay precompensation and spectrum filtering. We present a theoretical model to investigate the CD impairment in all-optical OFDM system, and demonstrate experimentally that both methods restore performance without overhead or guard interval.

Demonstration and performance investigation of all-optical OFDM systems based on arrayed waveguide gratings

We experimentally demonstrate an 8 x 12.5 Gbit/s all-optical orthogonal frequency-division multiplexing (AO-OFDM) system using arrayed waveguide gratings (AWGs), which perform discrete Fourier transform (DFT) and inverse DFT (IDFT) of a signal directly in the optical domain. The experimental results show that frequency orthogonality of OFDM sub-channels is degraded in the AWG due to the slab-diffraction effect. To restore the frequency orthogonality and improve the system performance, we propose and demonstrate a waveform reshaping scheme, that improve the bit-error-rate (BER) from 10(-4) to 10(-6). We also experimentally investigate the influence of frequency mismatch between the OFDM signal and AWG at the receiver. The measured BER shows a serious degradation from 10(-6) to 10(-4) in case of ± 1.88 GHz frequency mismatch. To keep the BER under 10(-5), the frequency mismatch should be smaller than ± 0.5 GHz ( ± 4% of the channel spacing).

The validity of “Odd and Even” channels for testing all-optical OFDM and Nyquist WDM long-haul fiber systems

We investigate experimentally the validity of testing all-optical OFDM and Nyquist WDM systems using interleaved test channels derived from only two data sources. These "odd and even" channels are insufficiently decorrelated, so experiments underestimate the inter-carrier interference (ICI). Additionally, numerical simulations demonstrate that using odd and even channels generates stronger nonlinear distortions during transmission, causing an unrealistically large penalty in the nonlinearity-limited region.

What else can an AWG do?

The present paper aims to describe other functionalities for an arrayed waveguide grating (AWG)-based device, showing that this widely used configuration can be designed not only to frequency multiplex/demultiplex wavelength division multiplexing (WDM) signals, but also to perform the discrete Fourier transform (DFT) and the discrete fractional Fourier transform (DFrFT) of a signal, in all-optical orthogonal frequency division multiplexing (OFDM) systems. In addition 1 × N and N × N phased array switches architectures are described, as well as a new configuration to perform polarization diversity demultiplexing. Finally, a general approach, based on an analogy with the finite impulse response (FIR) filter approach, is presented to design optical modulators for any modulation format, using either phase modulators (PM) or electro-absorption modulators (EAM).

Study of the all-optical high-speed OFDM transmission system based on MAMSK modulation

In this paper, an all-optical orthogonal frequency division multiplexing (OOFDM) system based on the multi-amplitude minimum shift keying (MAMSK) modulation is proposed. A scheme to realize MAMSK is designed, and the influence of modulation index on the performance of MAMSK is discussed. Numerical simulations and analysis are performed, and the comparison between the MAMSK-OOFDM and the MAMSK-WDM system is made. The lowest value of the BER of MAMSK-OOFDM is 3.98×10−6, while that of MAMSK-WDM is 7.94×10−4 when the input power is 0.8 mw and dispersion is completely compensated. The results show that, for its multi-level amplitude and excellent spectrum efficiency, MAMSK-OOFDM can greatly mitigate the effects caused by dispersive and nonlinear phenomena, and it can also effectively improve the capacity of the system.

Mixed Line-Rate Transmission (112-Gb/s, 450-Gb/s, and 1.15-Tb/s) Over 3560 km of Field-Installed Fiber With Filterless Coherent Receiver

We report the first superchannel field experiment where two multicarrier signals at 450 Gb/s and 1.15 Tb/s are copropagated with 112-Gb/s neighbors over 45 × 79.1 km spans of field-installed fiber with erbium-doped fiber amplifiers after each span. The superchannels use zero-guard interval all-optical orthogonal frequency-division multiplexing, with each optically generated subcarrier modulated by dual-polarization quadriphase-shift-keying signals (DP-QPSK). The heterogeneous data-rate channels are aggregated using wavelength selective switch in a flexible grid wavelength-division multiplexing architecture. The net spectral efficiencies of the channels vary from 2 b/s/Hz for the 112-Gb/s channels, to 3.33 b/s/Hz for the 1.15-Tb/s superchannel. We demonstrate that any of the signals can be detected using a common filterless digital coherent receiver. In particular, tuning a local oscillator laser midway between two optically generated subcarriers enables the coherent receiver (with proper signal-processing algorithm) to demodulate two subcarriers in one data capture. This allows flexible downconversion across the whole signal band. Our results show that superchannels can coexist harmoniously with 100 G DP-QPSK signals. Even though the superchannels use the same modulation format per subcarrier as the 100 G signals, the absence of guard bands enables higher spectral efficiency that is achievable with single-carrier modulation with minimal sacrifice in reach.

High-Capacity 60 GHz and 75–110 GHz Band Links Employing All-Optical OFDM Generation and Digital Coherent Detection

The performance of wireless signal generation and detection at millimeter-wave frequencies using baseband optical means is analyzed and experimentally demonstrated. Multigigabit wireless signal generation is achieved based on all-optical orthogonal frequency division multiplexing (OFDM) and photonic upconversion. The received wireless signal is optically modulated and detected using digital coherent detection. We present a theoretical model, ultimate performance limitations based on simulations as well as experimental validation of the proposed architecture. In order to demonstrate the RF scalability and bit-rate transparency of our proposed approach, we experimentally demonstrated generation and detection in the 60 GHz and 75-110 GHz band of an all-optical OFDM quadrature phase shift keying, with two and three subcarriers, for a total bit rate over 20 Gb/s.

160 km all-optical OFDM transmission system with inline chromatic dispersion compensation

An experimental demonstration of an all-optical sampling orthogonal frequency division multiplexing (AOS-OFDM) transmission system with inline chromatic dispersion (CD) compensation is carried out to test the nonlinear influence. With five subcarriers non-return-to-zero (NRZ) modulated, the total bit rate is 50 Gb/s without polarization multiplexing. The receiver end is highly simplified with direct detection using optical Fourier transform filter. After transmission in 160-km standard single-mode fiber (SSMF) link with 130-ps/nm residual CD, an optimum input optical power for the system performance is achieved.

Long-haul transmission of 35-Gb/s all-optical OFDM signal without using tunable dispersion compensation and time gating

We propose that the optical OFDM technique using all optical discrete Fourier transform (DFT) has potential as a viable alternative for upgrading long-haul optical transmission systems towards 100-Gb/s. We demonstrate transmission of 35-Gb/s (7 x 5 Gb/s NRZ-OOK) all-optical OFDM signal over ~2000-km dispersion-managed span without using tunable dispersion compensation and time gating. We achieve bit error ratio of 1.2x10(-3) (7x10(-3)) for transmission over 1980-km (2310-km) all-EDFA amplified span consisting of standard single mode fiber (SSMF) and dispersion compensating fiber (DCF). We also study the nonlinear penalty impacting the all-optical OFDM transmission and discuss potential method for its mitigation.

Transmission of Spectral Efficient Super-Channels Using All-Optical OFDM and Digital Coherent Receiver Technologies

A 1.5 Tb/s super-channel is generated using all-optical orthogonal frequency-division multiplexing (OFDM) and dual-polarization 16QAM modulation without guard interval. We investigated the effects of DSP oversampling and receiver bandwidth using experimental results and numerical simulations to evaluate our receiver design. The super-channel is transmitted over 1200 km of standard single-mode fiber on existing 100 GbE network using only 200 GHz of optical bandwidth and detected using digital coherent receiver, achieving a spectral efficiency of 7 bit/s/Hz the highest reported to date for all-optical OFDM techniques.

5×200Gbit/s all-optical OFDM transmission using a single optical source and optical Fourier transform real-time detection

An all-optical sampling OFDM scheme using PolMux-DQPSK format with single source is proposed and experimentally demonstrated. 5 × 200 Gb/s AOS-OFDM signal with spectral efficiency of 3.07 bit/s/Hz is successfully transmitted over an 80 km SMF link with real-time detection by optical Fourier transform filters. Furthermore, this scheme can coexist with traditional WDM channels and be a promising technique for seamless upgrade of transmission date rate.