Optical Frequency Division Multiplexing System Research Articles

Mitigation of Non Linear Effects Using Non Linear Transform in Dispersion Managed Coherent Optical OFDM Systems

It is very important to compensate the dispersion and non linearity present in the optical backhaul so that it is compatible with upcoming technologies. Optical Frequency Division Multiplexing (OFDM) is a physical layer, Multicarrier Modulation Technique (MCT) which is being widely used to design Back Bone (BB), Back Haul (BH) and Cognitive Optical Networks (CONs). Fiber nonlinearity present in dispersion managed links limits the capacity of an OFDM link, as it gets enhanced by high Peak to Average Power Ratio (PAPR) value of the transmitted signal. This work aims to decrease the PAPR value and hence in turn reduce the non linear impairments present in the coherent OFDM optical fiber link. In this work L2-by-3 non linear transform has been implemented to mitigate various fiber non linear effects through PAPR reduction.

Subcarriers-to-subcarriers beating interference cancellation in virtual single sideband optical frequency division multiplexing system

We propose and experimentally demonstrate the superior performance of a 40-Gbps 16-quadrature amplitude modulation virtual single sideband (VSSB) direct detection optical frequency division multiplexing system with symbol predistortion to mitigate subcarriers-to-subcarriers beating interference. The VSSB signal is generated in the electronic domain by combining the baseband orthogonal frequency division multiplexing signals and sinusoidal waves without a frequency gap to maximize the electrical and optical spectral efficiencies. The results show that 5-dB optical signal to noise ratio sensitivity improvement is obtained by using symbol predistortion.

Extension of the Transmission Length of Optical FDM System by using Distributed In-Line Group-Delay Equalizers

Optical frequency division multiplexing (FDM) transmission systems are promising to realize the large capacity. In such optical FDM transmission systems, the four-wave-mixing (FWM) occurs as a serious limiting factor. The FWM can be suppressed by the fiber dispersion, however, which must be compensated by the group-delay equalizers. In this paper, an optical FDM transmission system of equally spaced channels with the distributed in-line group-delay equalizers is proposed and evaluated by the computer simulations. The simulations show that in the optical FDM transmission system with the distributed in-line equalizers, both the FWM and the random interaction between the fiber dispersion and the XPM/SPM can be suppressed effectively. Consequently, the system makes the transmission length about 2.2 times longer than that of the systems with one receiving-end equalizer. Moreover, among the methods for realizing the middle-haul and large capacity systems, the optical FDM transmission system with the distributed in-line equalizers has been confirmed to be most promising.

Architectural framework for optical frequency division multiplexing systems based on regular space-frequency interconnections

The paper describes a multistage interconnection network (MIN) with regular interconnections in three dimensions (two space dimensions and the third dimension is the frequency) and dimension-dependent switches. (Regular interconnections mean that the same interconnection principles are applied throughout the stages of the MIN.) The frequency domain is organized by introducing artificial dimensions. The architecture is interpreted as an optical frequency division multiplexing (OFDM) system with multidimensional interconnections and switches where the dimension is an additional design parameter. The multidimensional interconnections may be implemented using a combination of space and frequency channels. The frequency interconnections (data movements between channels) are expressed by the Kronecker product (KP) of permutation matrices. In this case the number of frequency conversion (FC) operations and the number of frequency channels crossed during the generation of interconnections and switching decreases. The architectural principles presented are of general interest for the study of transmission and processing in arbitrary large scale interconnection systems implemented in the 3-D physical space. >

Can multilevel signaling improve the spectral efficiency of ASK optical FDM systems?

The question of whether multilevel signaling can improve the spectral efficiency of optical frequency division multiplexing (FDM) systems is investigated. Multilevel amplitude-shift keying (ASK) and a receiver consisting of an optical channel selection filter (specifically, a single-stage Fabry-Perot), a pin diode for direct detection, and an integrator are assumed. It is also assumed that additive noise is negligible and that the major impairments are adjacent channel interference and intersymbol interference. The analysis shows that, for such a receiver, there is no advantage to going beyond binary signaling. It is also shown that this finding holds up when additive and phase noises and alternative approaches to filtering are considered. >

Spectral efficiency of optical FDM systems impaired by phase noise

The required frequency spacings between channels in an optical frequency division multiplexing (FDM) network are considered. The minimum permissible spacings consistent with meeting bit error rate (BER) objectives are derived. The assumed transmission uses on-off keying (OOK), at a data rate 1/T (in bits per second), via external modulation of a laser source having linewidth beta (in hertz). The assumed receiver consists of an optical channel selection filter followed by a p-i-n photodiode and a postdetection integrate-and-dump circuit. The analysis estimates the adjacent channel interference (ACI)-induced floor on BER for the middle of three FDM channels, as a function of frequency spacing and linewidth-to-bit rate ratio ( beta T). For BER=10/sup -9/ and beta T ranging from 0.32 to 5.12, the required channel spacing ranges from 5.2 to 27.5 bit rates. The multiplying factors associated with using (wide-deviation) frequency shift keying (FSK), coherent (heterodyne) detection, and infinitely many FDM channels, respectively, are estimated to be 2.0, at most 3.0, and at most 1.37. >

Advanced technology for fiber optic subscriber systems

Key issues in handling optical frequencies for broadband communication services and constructing optical frequency-division multiplexing (OFDM) systems are discussed. The configuration of OFDM transmission systems, their use of multichannel frequency stabilization, multiplexer/demultiplexer, tunable filters, and common amplification systems, and the effects of optical-fiber nonlinearities of OFDM systems are described. The applicability of OFDM to various kinds of telecommunication networks, such as high-capacity end-to-end transmission, information distribution, multinode networks and subscriber systems of both transfer and access networks is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Generation and evaluation of d-dimensional (d ≥ 3) optical shuffle patterns

We use d-dimensional shuffle patterns to describe optical frequency division multiplexing. A complexity measure is derived from the geometry of common shuffle patterns and is extended to evaluate d-dimensional shuffle patterns. The least complexity of the generated patterns is determined with respect to the size and the dimension of the data sets. Trade-offs between the dimension of the data sets and the frequency-conversion-based processing of the pattern generation are discussed. A comparison of multiplexing on vectors and arrays is presented. The relation of the complexity analysis to the design of optical frequency division multiplexing systems is briefly discussed.

Design and performance of FSK-direct detection scheme for optical FDM systems

The authors describe the design and performance of an optical frequency-division-multiplexing (FDM) system that uses a frequency-shift-keying (FSK) direct detection scheme. This system utilizes a Mach-Zehnder type periodic filter as a channel selective filter and optical frequency discriminator. Requirement conditions for laser diode linewidth, frequency deviation, channel frequency spacing, detuning of optical filters, and signal power variance are discussed. These characteristics are experimentally confirmed using planar waveguide type filters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transmission limitations due to fiber nonlinearities in optical FDM systems

Transmission limitations due to stimulated Brillouin scattering and four-wave mixing processes are investigated for optical frequency division multiplexing (FDM) systems. The applicability of the dispersion-shifted (DS) and nondispersion-shifted (NDS) fibers is discussed, taking account of channel frequency separation, total channel numbers, input signal power, transmission length, and receiver sensitivity degradation. Experimental results on Brillouin gain spectra and the wave generation efficiency in four-wave mixing processes are also presented to discuss the applicability of the two types of single-node fiber. It was found that NDS fibers operated at a wavelength of 1550 nm can be widely deployed in multichannel systems both for the long-haul and information distribution transmissions, if the signal waveform distortion due to fiber chromatic dispersion is precluded. The delay equalizer will be useful for a high-speed system employing bit rates over 10 Gb/s and repeaterless spans over 300 km. For such an application, DS fiber is preferable. Concerning information distribution network applications, the NDS fiber should be more attractive as a transmission medium for FDM system applications. >

Optical heterodyne image-rejection receiver for high-density optical frequency division multiplexing system

An optical heterodyne image-rejection receiver (IRR) for high-density optical frequency division multiplexing (OFDM) systems is described. The IRR was realized using balanced receivers, which showed more than 18-dB suppression over the 1.5-3.0-GHz IF region. Measured crosstalk penalties in a two-channel 560 Mb/s differential phase-shift keyed (DPSK) heterodyne optical communication system were realized for the first time. The crosstalk penalties in an OFDM system are estimated theoretically with and without the IRR. The required channel spacing and number of channels that can be accommodated in the 10-nm tuning range of the local laser are presented. A particular configuration of the IRR, its operation, and its performance limitations are discussed. The experimental results for image-rejection reception in a two-channel 560-Mb/s DPSK system are also given. Crosstalk penalties are estimated experimentally and compared to the theoretical calculation. Since the conventional configurations of the IRR are very sensitive to the polarization fluctuation of the transmitted signals, polarization-insensitive IRRs are proposed and their features are considered.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Channel allocation and crosstalk penalty in coherent optical frequency division multiplexing systems

We theoretically studied the crosstalk penalty of coherent optical frequency division multiplexing systems by varying the intermediate frequency and the channel spacing. Our results, applicable to ASK, PSK and CPFSK modulation formats, provide a quantitative criterion for designing a practical multichannel coherent lightwave system.