Optical Frequency Division Multiplexing Research Articles

Polarization multiplexed OFDM band interleaving enabled metro-access integrated networks

In this paper, we propose a novel “ring+tree” topology enabled optical metro-access integrated networks (MAIN), using polarization multiplexed band interleaving (PMBI) of optical multiband orthogonal frequency division multiplexing (MB-OFDM) technology. In this proposed MAIN, the services for downstream and upstream transmission are carried by two orthogonal polarization states, respectively. By utilizing the proposed structure in each central node (CN) with the common or low-order filters, the MAIN system with three CNs has been successfully simulated. Finally, the obtained results verify the feasibility of our proposed MAIN system with high spectral efficiency.

Pilot tone design for dispersion estimation in coherent optical fast OFDM systems

We show that inserting pilot tones with frequency intervals inversely proportional to the subcarrier index exhibits greatly improved dispersion estimation performance when compared to the equal spacing design in optical fast orthogonal frequency division multiplexing (F-OFDM). With the proposed design, a 20-Gbit/s four amplitude shift keying optical F-OFDM system with 840-km transmission without optical dispersion compensation is experimentally demonstrated. It is shown that a single F-OFDM symbol with six pilot tones can achieve near-optimal estimation performance for the 840-km dispersion. This is in contrast to the minimum of ten pilot tones using an equal spacing design with either cubic or Fourier-transform-based interpolation.

Advantage of Optical Fast OFDM Over OFDM in Residual Frequency Offset Compensation

We analyze the intercarrier interference (ICI) induced by residual frequency offset (RFO) in optical fast orthogonal frequency division multiplexing (F-OFDM) and compare this scheme with conventional OFDM in two scenarios: (1) the same RFO to subcarrier spacing ratio, and (2) the same discrete cosine or Fourier transform point size. In both scenarios, the ICI on a subcarrier in F-OFDM is dominated by the adjacent subcarriers, but the contribution to that in conventional OFDM is dispersed across the subcarriers. 19.5-GBaud 16QAM and 4ASK F-OFDM systems are investigated. 16QAM F-OFDM exhibits an RFO tolerance up to six times greater than that of 16QAM OFDM, when equalizers with the same tap number are used for the RFO compensation. 4ASK F-OFDM using 1-tap equalizers can achieve an RFO tolerance of up to four times greater than that of five-tap equalizer-based 4ASK OFDM.

Hadamard precoding for PAPR reduction in optical direct detection OFDM systems

The high peak-to-average power ration (PAPR) values of optical orthogond frequency division multiplexing (OFDM) signal limit the system nonlinear tolerance (NLT). In this paper, a novel method based on Hadamard precoding is proposed to reduce the peak-to-average power ratio in optical direct detection OFDM system. The proposed scheme is successfully applied to an experimental system of optical direct-detection OFDM signal transmission through fiber. In this experiment, the 2.5 Gbit/s binary phase shift keying (BPSK) optical OFDM signals with Hadamard precoding are generated and transmitted though a single mode fiber. The experimental results show that the proposed scheme can reduce PAPR by almost 1.5 dB. Meantime the received sensitivity is improved by 2 dB with 100 km fiber transmission compared with that of an ordinary optical direct detection OFDM system.

Offset-QAM based coherent WDM for spectral efficiency enhancement

Optically multiplexed multi-carrier systems with channel spacing reduced to the symbol rate per carrier are highly susceptible to inter-channel crosstalk, which places stringent requirements for the specifications of system components and hinders the use of high-level formats. In this paper, we investigate the performance benefits of using offset 4-, 16-, and 64-quadrature amplitude modulation (QAM) in coherent wavelength division multiplexing (CoWDM). We compare this system with recently reported Nyquist WDM and no-guard-interval optical coherent orthogonal frequency division multiplexing, and show that the presented system greatly relaxes the requirements for device specifications and enhances the spectral efficiency by enabling the use of high-level QAM. The achieved performance can approach the theoretical limits using practical components.

Coherent Optical OFDM Transmission Up to 1 Tb/s per Channel

Coherent optical frequency-division multiplexing (CO-OFDM) is one of the promising pathways toward future ultrahigh capacity transparent optical networks. In this paper, numerical simulation is carried out to investigate the feasibility of 1 Tb/s per channel CO-OFDM transmission. We find that, for 1 Tb/s CO-OFDM signal, the performance difference between single channel and wavelength division multiplexing (WDM) transmission is small. The maximum Q is 13.8 and 13.2 dB respectively for single channel and WDM transmission. We also investigate the CO-OFDM performance on the upgrade of 10-Gb/s to 100-Gb/s based DWDM systems with 50-GHz channel spacing to 100-Gb/s systems. It is shown that due to the high spectral efficiency and resilience to dispersion, for 100-Gb/s CO-OFDM signals, only 1.3 dB Q penalty is observed for 10 GHz laser frequency detuning. A comparison of CO-OFDM system performance under different data rate of 10.7 Gb/s, 42.8 Gb/s, 107 Gb/s and 1.07 Tb/s with and without the impact of dispersion compensation fiber is also presented. We find that the optimum fiber launch power increases almost linearly with the increase of data rate. 7 dB optimum launch power difference is observed between 107 Gb/s and 1.07 Tb/s CO-OFDM systems.

Dual-band OOFDM system based on tandem single-sideband modulation transmitter

We demonstrate an optical orthogonal frequency division multiplex (OOFDM) transmitter using a simple dual-electrode Mach- Zehnder modulator (MZM) to perform tandem single-sideband optical modulation. This allows a doubling of transmission capacity. A commercial optical transmitter card, equipped with an on-board arbitrary waveform generator, is used for the system test. A proof-of-concept transmission experiment is conducted using a fiber-optic re-circulating loop.

121.9-Gb/s PDM-OFDM Transmission With 2-b/s/Hz Spectral Efficiency Over 1000 km of SSMF

We discuss optical multi-band orthogonal frequency division multiplexing (OFDM) and show that by using multiple parallel OFDM bands, the required bandwidth of the digital-to-analogue/ analogue-to-digital converters and the required cyclic prefix can significantly be reduced. With the help of four OFDM bands and polarization division multiplexing (PDM) we report continuously detectable transmission of 10 times121.9-Gb/s (112.6-Gb/s without OFDM overhead) at 50-GHz channel spacing over 1,000-km standard single mode fiber (SSMF) without any inline dispersion compensation. In this experiment 8 QAM subcarrier modulation is used which confines the spectrum of the 121.9 Gb/s PDM-OFDM signal within a 22.8 GHz optical bandwidth. Moreover, we propose a digital signal processing method to reduce the matching requirements for the wideband transmitter IQ mixer structures required for PDM-OFDM.

All optical discrete Fourier transform processor for 100 Gbps OFDM transmission

Optical orthogonal frequency division multiplex (OFDM) symbol generation by all-optical discrete Fourier transform (DFT) is proposed and investigated for 100-Gbps transmission performance. We discuss a design example for a 4x25Gbps OFDM transmission system and its performance comparison with that for a 100-Gbps single-channel return-to-zero data transmission in an optically amplified system.

Multiplexed reflectometric fiber optic frequency-modulated continuous-wave interferometric displacement sensor

A practical double-sensor multiplexed fiber optic displacement sensor is reported. The sensor is based on the principles of optical frequency-modulated continuous-wave (FMCW) interference and frequency-division multiplexing. The beat signals from the individual sensors are assigned in the frequency domain and separated with different electrical bandpass filters. The displacements of the targets can be determined simultaneously by detecting the phase shifts of the corresponding beat signals. The cross talks between the individual sensors are analyzed algebraically and with a phasor diagram. An accuracy of 0.05 µm in a dynamic range of 1000 µm is achieved.

Highly spectrum efficient OFDM/PDM wireless networks by using optical SSB modulation

Optical frequency division multiplexing (OFDM) wireless access network using optical single-sideband modulation is proposed, which allows to deliver different wireless signals from a central station to each base station over an optical fiber network. The optical single-sideband (SSB) OFDM can achieve the highest spectrum efficiency of 0.25 b/s/Hz. A 0.25 b/s/Hz has been experimentally verified by the error-free transport of two-channel 4.98 Gb/s BPSK signal on 10 GHz wireless carrier with the frequency channel interval of 20 GHz at 1550 nm over 50 km-long standard single-mode fiber link. Furthermore, it has been also experimentally confirmed that by introducing the polarization division multiplexing (PDM), the ultimate spectrum efficiency of 0.5 b/s/Hz can be achieved by the hybrid OFDM/PDM.

Minimum channel spacing in an ofdm cpfsk optical coherent system

Channel spacing in optical frequency-division multiplexed (OFDM) coherent optical systems with continuous-phase frequency-shift-keying (CPFSK) is obtained both theoretically and experimentally. The bit error ratio is derived taking into account the non-Gaussian interference statistics, expressed in terms of the Marcum Q-function, and the sensitivity penalty is reported as a function of the signal-to-interference ratio and the channel spacing for different IF filters. Laboratory demonstration of a state-of-the-art fully engineered two-channel 2.5 Gb s-1 CPFSK coherent system at 1550 nm has been performed, showing an inter-channel crosstalk measurement in agreement with the theoretical analysis. A 0.1 nm channel spacing is experimentally confirmed.

Influence of the dynamic response of the Fabry-Perot filter on the performance of an OFDM-DD network

An analysis of the transient response of a Fabry-Perot filter (FPF) is presented. The impact of this phenomenon on the performance of optical frequency division multiplexing (OFDM) networks with direct detection is then analyzed. Results show that the transient effect of the filter can induce a considerable power penalty in OFDM networks when high bit rates are transmitted.

An optical FDM-based self-healing ring network employing arrayed waveguide grating filters and EDFA's with level equalizers

An optical frequency-division multiplexing (OFDM) based self-healing unidirectional ring network is designed and its performance is verified. It employs arrayed waveguide grating add/drop multiplexers (ADMs) and erbium-doped fiber amplifiers (EDFAs) with waveguide level equalizers in each remote node. The route diversity configuration is employed to make the network robust and bit loss-free route switching is performed. The level diagram reproducibility for each OFDM channel is guaranteed by the waveguide-level equalizers. Successful transmission performance confirms the effectiveness of the proposed system.

Integrated-optic versus microoptic devices for fiber-optic telecommunication systems: a comparison

We assess the relative merits and prospects of integrated-optics in comparison with microoptic and fiber-based techniques. Firstly, the market for fiber-optic components for telecommunications is analyzed. Secondly, the technological issues which make integrated optics quite different from integrated electronics will be discussed. Thirdly, a specific comparison between the potential of the competing optical technologies will be made for the polarization-diversity hybrid and the optical wavelength (de)multiplexer, two optical devices used in networks that are based on optical frequency division multiplexing (OFDM).

128‐channel, 480‐km optical frequency division multiplexing transmission employing 0.98‐μm pumped erbium‐doped fiber amplifiers and a gain equalizer

AbstractIn optical frequency division multiplexing (FDM) transmission systems using optical amplifiers, the transmission distance is limited mainly by gain‐tilt of erbiumdoped fiber amplifiers (EDFAs), accumulations of the ASE noise, and crosstalk due to the four‐wave mixing (FWM). Especially when dispersion‐shifted fibers are used, the transmission distance is limited by the decrease of the allowable input level to the fiber due to the FWM. It is shown here that a 0.98‐μm pumped EDFA has a smaller gain‐tilt accumulation and is suitable for optical FDM transmission. Level diagram is designed taking into account the ASE noise and the FWM crosstalk accumulation; the relationship between fiber‐EDFA input level and the receiver sensitivity is investigated. A 128‐channel optical FDM transmission experiment with 10‐GHz spacing was carried out, and it is demonstrated that all channels can be successfully transmitted through 480 km of dispersion‐shifted fiber with a power penalty of less than 1 dB by using a tunable gain equalizer.

60 GHz band millimetre-wave signal generation and transport over optical frequency division multiplexing networks

A novel optical generation and optical frequency division multiplexing (OFDM) transport of 60 GHz band millimetre (mm)-wave signals is proposed and experimentally demonstrated over 40 km long singlemode optical fibre. The generated mm-wave signals with the narrow linewidths of < 300 Hz are obtained.

A simple expression for optical FDM network scale considering fiber four-wave mixing and optical amplifier noise

Possible transmission distance and number of channels are studied in optical FDM (frequency division multiplexed) systems. Optical amplifier noise and fiber four-wave mixing, which respectively restrict input power to a repeater and input power to a fiber, are taken into account. A simple analytical expression is derived for evaluating FDM network scale by using a Gaussian noise approximation. Calculation examples are also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An optical infrastructure for future telecommunications networks

For the transport of the increasing traffic volume caused by existing and new narrowband services and evolving broadband services, the enhancement of the existing public telecommunication transport network is necessary. For this purpose an optical network layer with cross-connect and add/drop functionalities will be added to the existing transport network. A comparative analysis of space, time, and optical frequency division multiplexing has shown that for the time being optical frequency multiplexing is best suited for the realization of that new network layer. This multiplexing scheme offers the greatest advantages such as very high bandwidth utilization in the fiber and simple and efficient cross-connecting of high bitrate streams. In the near future, technology will be mature enough for the realization of a demonstrator network based on optical frequency division multiplexing. The functionalities of the optical network are evaluated and the results clearly show that optical frequency conversion and regeneration should be provided by the optical network. The article also deals with the realization aspects (cross-connecting, supervision, and operation and maintenance) of an optical node. >

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.