All-optical OFDM Research Articles

Optical orthogonal division multiplexing for long haul optical communications: A review of the first five years

Optical OFDM was proposed for dispersion compensation in long-haul optical communications systems in 2006 in two forms, one using direct-detection and the other using coherent detection. Since then there has been extensive innovation towards developing intermediate forms of optical OFDM that are more suited to specific applications. This review paper presents our view on the developments in optical OFDM for long-haul optical transmission applications. It covers the basic elements of radio OFDM before concentrating on direct detection optical OFDM and its development, followed by coherent optical OFDM. All-optical OFDM is then considered, together with optical methods of generating and separating the OFDM subcarriers. The paper then discusses the critical issue of nonlinear degradation due to the Kerr effect in optical fibers and reviews recent innovations to mitigate the effects of fiber nonlinearity. Finally some future research directions are discussed.

All-optical OFDM transmitter design using AWGRs and low-bandwidth modulators

An Arrayed-Waveguide Grating Router (AWGR) can be used as a demultiplexer for an optical OFDM system, as it provides both the serial-to-parallel converter and the optical Fourier transform (FT) in one component. Because an inverse FT is topologically identical to a Fourier transform, the AWGR can also be used as a FT in an OFDM transmitter. In most all-optical OFDM systems the optical modulators are fed with CW tones; however, the subcarriers (SC) will only be perfectly orthogonal if the bandwidth of the data modulators is similar to the total bandwidth of all subcarriers. Using simulations, this paper investigates the reduction in modulator bandwidth that could be achieved if the modulators are placed before an AWGR designed as a FT. This arrangement also allows the complex (IQ) modulators to be replaced with simpler and more-compact phase modulators. We show that these design improvements enable 7.5-GHz bandwidth modulators to be used in a 4 × 10 Gsymbol/s (80 Gbit/s) per polarization per wavelength system.

All-optical OFDM transmission of 7 x 5-Gb/s data over 84-km standard single-mode fiber without dispersion compensation and time gating using a photonic-integrated optical DFT device

We implement dispersion-tolerant and time-gating-free all-optical OFDM transmission using a photonic-integrated discrete Fourier transform (DFT) device. We show that 35-Gb/s OFDM data having near-unity spectral efficiency can be transmitted all-optically with 1-dB dispersion margin of ~1000 ps/nm. The passive-optical DFT circuit is implemented using multi-mode interference (MMI) couplers on a high index-contrast silica integrated-optic platform. We also propose a photonic DFT circuit based on an NxN MMI device capable of simultaneous channelization of OFDM signals into N subcarriers.

Experimental implementation of an all-optical OFDM system based on time lens

A real time all-optical orthogonal frequency division multiplexing (OOFDM) system based on two time lenses is experimentally demonstrated. At the transmitter, groups of initial optical pulses are transformed into OOFDM symbols by a continuous inverse Fourier transform (IFT) device, which consists of the first a quadratic phase modulator and two high dispersive elements. After transmission, a continuous Fourier transform (FT) device, consisting of another quadratic phase modulator and two high dispersive elements, rebuilds the initial optical pulses at the receiver. The electrical sinusoidal waveform employed in the FT module at the receiver is obtained directly from the transmitter with certain phase shift. In the system, the guard interval is necessary for each OOFDM symbol to ensure the initial pulses are operated FT/IFT under a parabolic waveform driving and to have more Fourier transformation time window. Experiment results show that 8 × 2.5 Gb/s signals successfully transmit through 200-km-G.655 fibers without any dispersion compensation, with the BER being 10 − 12 .

An optical OFDM multiplexer and 16 × 10 Gb/s OOFDM system using serrodyne optical frequency translation based on LiNbO 3 phase modulator

This paper proposes an all-optical orthogonal frequency division multiplexing (OFDM) multiplexer based on sawtooth wave driving LiNbO 3 phase modulators by using serrodyne optical frequency translation. This multiplexer has high integration ability. The designing concept and implementation method have been discussed. A 16 × 10 Gb/s optical OFDM system is designed based on this multiplexer. Transmission characteristics, including tolerances of polarization mode dispersion (PMD) and nonlinear impairments have been studied numerically. Simulations show that the PMD tolerance is about 42 ps. The spectral efficiency reaches 1 bit/s/Hz with binary modulation format.

Optical FFT/IFFT circuit realization using arrayed waveguide gratings and the applications in all-optical OFDM system

Arrayed waveguide gratings (AWG) are widely used as wavelength division multiplexers (MUX) and demultiplexers (DEMUX) in optical networks. Here we propose and demonstrate that conventional AWGs can also be used as integrated spectral filters to realize a Fast Fourier transform (FFT) and its inverse form (IFFT). More specifically, we point out that the wavelength selection conditions of AWGs when used as wavelength MUX/DEMUX also enable them to perform FFT/IFFT functions. Therefore, previous research on AWGs can now be applied to optical FFT/IFFT circuit design. Compared with other FFT/IFFT optical circuits, AWGs have less structural complexity, especially for a large number of inputs and outputs. As an important application, AWGs can be used in optical OFDM systems. We propose an all-optical OFDM system with AWGs and demonstrate the simulation results. Overall, the AWG provides a feasible solution for all-optical OFDM systems, especially with a large number of optical subcarriers.

PAPR Reduction in All-optical OFDM Systems Based on Phase Pre-emphasis

This paper investigates the peak-to-average power ratio (PAPR) theory in all-optical orthogonal frequency division multiplexing (OFDM) optical fibre communication systems. We find out that phase pre-emphasis could effectively reduce PAPR in all-optical OFDM communication systems which employ intensity modulation-direct detection (IM-DD) method. An equation is developed and proposed to calculate suitable phasing values for pre-emphasis. Furthermore, we find out that phase pre-emphasis cannot reduce PAPR effectively in all-optical OFDM systems that employ Phase Shift Keying (PSK) or Quadracture Amplitude Modulation (QAM) method.

全光采样OFDM系统性能分析

The performance of a novel all-optical sampling orthogonal frequency division multiplexing (OFDM) system is proposed and analyzed. Time delays and phase shifters are used to realize all optical forward/inverse discrete Fourier transform (DFT/IDFT). Different system configurations are tested and analyzed to optimize the performance, including the system capacity, modulation formats, DFT/IDFT constructions, and the width of the sample pulse. The 50- and 100-Gb/s real-time all-optical sampling (AOS) OFDM systems are investigated. All results are analyzed, and useful suggestions are offered for future high-speed applications.

High-Capacity Wireless Signal Generation and Demodulation in 75- to 110-GHz Band Employing All-Optical OFDM

We present a radio-frequency (RF) and bit-rate scalable technique for multigigabit wireless signal generation based on all-optical orthogonal frequency-division multiplexing (OFDM) and photonic up-conversion. Coherent detection supported by digital signal processing is used for signal demodulation and data recovery. In order to demonstrate the RF frequency scalability and bit-rate transparency, the system is tested at 60 GHz and in the 75- to 110-GHz band at the baud rates of 5 and 10 Gbaud. In terms of the bit rate, the proposed system is experimentally tested up to 40 Gb/s for wireless signal generation and demodulation. The wireless transmission is not considered in this letter. Additionally, a novel digital carrier phase/frequency recovery structure is employed to enable robust phase and frequency tracking between the beating lasers.

All-optical sampling OFDM system performance analysis

All-optical sampling OFDM system performance analysis

全光采样OFDM系统性能分析

全光采样OFDM系统性能分析

Trigonometric Transforms for High-Speed Optical Networks: All-Optical Architectures and Optical OFDM

In this paper, it is shown that the use of real trigonometric transforms can advantageously replace the Fourier transform in optical communication systems, for both all-optical and electronic signal processing. All-optical discrete Hartley transform (DHT) and discrete Cosine transform (DCT) architectures for high-speed optical signal processing, filtering and data compression are given and compared to fiber Fourier processing. A trigonometric transform-based orthogonal frequency division multiplexing (OFDM) transmission system is also presented. The modulation/demodulation is performed by using the fast Hartley transform (FHT) algorithm. The simplified scheme and the real processing make it suitable for direct detection optical systems.

Design of arrayed-waveguide grating routers for use as optical OFDM demultiplexers

All-optical OFDM uses optical techniques to multiplex together several modulated lightsources, to form a band of subcarriers that can be considered as one wavelength channel. The subcarriers have a frequency separation equal to their modulation rate. This means that they can be demultiplexed without any cross-talk between them, usually with a Discrete Fourier Transform (DFT), implemented optically or electronically. Previous work has proposed networks of optical couplers to implement the DFT. This work shows that the topology of an Arrayed Grating Waveguide Router (AWGR) can be used to perform the demultiplexing, and that the AWGR can be considered as a serial-to-parallel converter followed by a DFT. The simulations show that the electrical bandwidths of the transmitter and receiver are critical to orthogonal demultiplexing, and give insight into how crosstalk occurs in all-optical OFDM and coherent-WDM systems using waveforms and spectra along the system. Design specifications for the AWGR are developed, and show that non-uniformity will lead to crosstalk. The compensation of dispersion and the applications of these techniques to 'coherent WDM' systems using Non-Return to Zero modulation is discussed.

Novel 64×2.5 Gb/s all-optical OFDM symbol generator based on triangle waveform driving-LiNbO3 modulators

We propose a novel and simple all-optical 160-Gb/s orthogonal frequency division multiplexing (OFDM) symbol generator which is based on discrete triangle waveform driving-LiNbO3 modulators to realize largerange linear optical shift. The entire system needs 64 discrete modulators: at the transmitter, a 2.5-Gb/s optical duobinary (ODB) modulator for data modulation and a 2.5-Gb/s triangle waveform driving-LiNbO3 phase modulator for phase shift to generate each subcarrier; and at the receiver, a 2.5-GHz optical band pass filter (OBPF) using Faraday anomalous dispersion optical effect to separate them. Excellent bit error rate (BER) is observed after 1060 km of transmission without any dispersion compensation.

Experimental implementation of an all-optical OFDM system based on time lenses

Experimental implementation of an all-optical OFDM system based on time lenses

A planar waveguide optical discrete Fourier transformer design for 160 Gb/s all-optical OFDM systems

A cost-effective all-optical discrete Fourier transformer (ODFT) is designed based on a silicon planar lightwave circuit (PLC), which can be applied to all-optical orthogonal frequency division multiplexing (OFDM) transmission systems and can be achieved by current techniques. It consists of 2 × 2 directional couplers, phase shifters and optical delay lines. Metal-film heaters are used as phase shifters, according to the thermooptic effect of SiO 2. Based on the ODFT, a 160 Gb/s OFDM system is set up. Simulation results show excellent bit error rate (BER) and optical signal-to-noise ratio (OSNR) performances after 400 km transmission.

All-optical orthogonal frequency multiplexing scheme with cyclic postfix based on fiber Bragg gratings

A novel all-optical orthogonal frequency division multiplexing (AO-OFDM) scheme is proposed and demonstrated. Ultrashort optical pulses are used as samples for optical discrete Fourier transform (DFT) and the inverse DFT process. Different subcarrier channels can be parallelly processed by fiber Bragg gratings. A 20-Gb/s two subcarrier AO-OFDM experiment is carried out with narrowband filtering and optical cyclic postfixes (CP) inserted. Experimental results show that this scheme has good spectral efficiency. Furthermore, the received signals have better eye diagrams and bit error rate performance with the help of CP. This scheme can be used in high-speed optical transmission systems.