Optical Frequency Division Multiplexing Transmission Research Articles

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.

622 Mbit/s‐sixteen‐channel FDM coherent optical transmission system using two‐section MQW DFB‐LDs

AbstractA light source and optical frequency control technique needed for realizing the optical frequency division multiplexing transmission (Optical FDM) is developed and experiments of a 622 Mbit/s‐sixteen‐channel FDM coherent optical transmission based on the heterodyne detection are conducted. the transmission is configured such that sixteen 1.55 μm wavelength two‐section MQW DFB‐laser diode (LD) are multiplexed by a star coupler. the wavelength of each LD was spaced at 10 GHz intervals with the frequency fluctuation kept under + 100 MHz by the optical frequency control circuit that uses a scanning Fabry‐Perot interferometer. the receiver configuration has a delay‐line demodulator, polarization diversity, and a frequency discriminator with no dead bands. For the station light source, the two‐section MQW DFB‐LD was tuned, which is the same as the transmitter, using current and temperature control. Random channels could selectively be received with a receiver sensitivity of ‐39.3 dBm. It was verified that 16 channels of 622 Mbit/s high‐vision (Japanese standard HDTV) signal could be transmitted through 110 km of 1.3 μm zero dispersion fiber without signal degradation.

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.

Theoretical analysis of triple-coupler ring-based optical guided-wave resonator

A comprehensive theoretical analysis of the triple-coupler ring-based optical guided-wave resonator (TCRR) is presented. Channel-passing and channel-dropping transmittance characteristics of the TCRR are derived by using a combination of transfer matrix and chain matrix formulations. The dependence of the transmittance characteristics on the amplitude coupling ratios of the three directional couplers are investigated, and optimum design relationships are determined. It is shown that the TCRR is ideally a nonterminating filter at antiresonance. An extensive comparison between the TCRR and a double-coupler ring resonator (DCRR) with same radius of curvature, waveguide propagation loss, coupling loss and finesse, is carried out. It is shown that the TCRR, by suitably sizing its waveguide lengths, has a free spectral range double that of the DCRR and features also higher transmission at resonance and better extinction ratio. These characteristics make the TCRR particularly advantageous for frequency selective filtering applications in optical frequency division multiplexing transmission systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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>

Cross-phase modulation influence on a two-channel optical PSK homodyne transmission system

The residual amplitude modulation of adjacent channels causes cross-phase modulation which is responsible for degradation in the error rate performance of a phase detection system. This influence on a two-channel 10 Gb/s optical phase-shift-keying (PSK) homodyne transmission system was experimentally evaluated. A penalty was observed for more than 6 dBm fiber input power with 28% residual amplitude modulation passing through a 100 km dispersion shifted-fiber. Since cross-phase modulation does not require phase matching, which is required for four-wave mixing, the optical frequency range in which the influence occurs is broadband. These results show that residual amplitude modulation in synchronous optical frequency division multiplexing transmission systems severely limits the fiber input power.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A wide-FSR waveguide double-ring resonator for optical FDM transmission systems

A wide free-spectral-range (FSR) waveguide double-ring resonator (DRR) is investigated for use in optical frequency-division multiplexing (OFDM) transmission systems. It consists of two ring resonators with different radii and three directional couplers. The FSR is determined by the least common multiple of the FSRs of the two ring resonators. In order to determine the parameters of the DRR, transmission equations of the DRR, which have different radii, are derived by using the scattering matrix. The dependence of the transmittance characteristics of the DRR on the amplitude coupling coefficients of directional couplers and on the propagation loss of the ring waveguides is studied. The design guidelines for OFDM transmission systems are described. >

A wide-band guided-wave periodic multi/demultiplexer with a ring resonator for optical FDM transmission systems

A wide-band guided-wave periodic multi/demultiplexer with a ring resonator for optical frequency-division-multiplexing (FDM) transmission systems is demonstrated. This periodic multi/demultiplexer consists of a Mach-Zehnder interferometer and ring resonator. It has a flat wide bandwidth and sharp cutoff regions. The authors describe theoretical analysis, design method, and experimental results of the multi/demultiplexer. The fabricated periodic multi/demultiplexer with a ring resonator has 5-GHz channel frequency separation at the 1.55- mu m wavelength region. Measured average loss was 4.8-dB and the average crosstalk was -13.2 dB. At 0.5-dB loss up from the minimum loss level, a width of 4.0 GHz was measured. This '0.5-dB bandwidth' is 1.8 times wider than that of the conventional Mach-Zehnder type periodic multi/demultiplexer. >

Wideband guided-wave periodic multi/demultiplexer with a ring cavity for optical FDM transmission systems

A guided-wave periodic multi/demultiplexer with a ring cavity for optical frequency-division-multiplexing (FDM) transmission systems is demonstrated. The frequency spacing is 5 GHz at the 1.55 μm wavelength region and the bandwidth is 1.8 times as wide as that of conventional periodic filters with simple Mach-Zehnder interferometer structure.

Observation of crosstalk due to four-wave mixing in a laser amplifier for FDM transmission

Crosstalk due to four-wave mixing in a semiconductor laser amplifier for optical FDM (frequency-division multiplexing) transmission is reported. Even when a laser amplifier is used in constant-power modulated FDM transmission, four-wave mixing in the amplifier causes channel crosstalk. In an experiment on three-channel amplification, where signals are frequency-modulated, a crosstalk of – 30 dB is measured. This crosstalk is strongly dependent on channel separation and optical power

5 GHz-spaced, eight-channel, guided-wave tunable multi/demultiplexer for optical FDM transmission systems

A 5GHz-spaced, eight-channel, guided-wave tunable multi/demultiplexer for optical frequency-division-multiplexing (FDM) transmission systems is demonstrated. It is constructed with high-silica channel waveguides and thin-film heaters loaded on the waveguides for frequency tuning