Naoya Henmi

Degradation of bit-error rate in coherent optical communications due to spectral spread of the transmitter and the local oscillator

In coherent optical communication schemes, the FM noises of the transmitter and/or the local oscillator seriously deteriorate the receiver sensitivity. A theory is developed describing the effect of the FM noise on the bit-error rate (BER) performance of various heterodyne and homodyne schemes. To verify the theory, the BER of a phase-shift keying (PSK) heterodyne system is measured. The feasibility of the PSK scheme using semiconductor lasers is also discussed on the basis of analysis and experimentation.

Prechirp technique for dispersion compensation for a high-speed long-span transmission

Dispersion compensation by the prechirp technique is theoretically investigated, and experimental results are discussed. An improvement of more than two times was observed for dispersion-limited transmission lengths in 5-Gb/s, 150-km and 10-Gb/s, 50-km transmission with a semiconductor electroabsorption external modulator and a normal fiber. An allowable transmission fiber dispersion of 10000 ps/nm and 2.5 Gb/s is estimated by computer simulation with this prechirp technique.<<ETX>>

Prechirp technique as a linear dispersion compensation for ultrahigh-speed long-span intensity modulation directed detection optical communication systems

Prechirp technique, as a linear dispersion compensation for intensity modulation direct detection (IM-DD) optical transmission systems, has been investigated theoretically and experimentally. This technique is based on a predistortion technique in an optical transmitter. Implementation to the ordinary IM-DD optical transmitter, which uses an external intensity modulator, is easily realized merely by adding a small injection current modulation to a semiconductor laser diode, allowable optical transmission fiber dispersion will be more than doubled with this technique, modified prechirp technique, which utilizes a time division superimposing prechirped bit streams, has also been investigated to achieve greater dispersion compensation capability. >

A new design arrangement of transmission fiber dispersion for suppressing nonlinear degradation in long-distance optical transmission systems with optical repeater amplifiers

The invention of the erbium-doped fiber amplifier has opened the possibility of constructing long-distance optical transmission systems with 1.5-mm zero-dispersion wavelength shifted fibers. In such systems, nonlinear degradation due to four-wave mixing and self-phase modulation strictly limits the total span of systems and the length of the optical repeater spacing. There are proposals to use slightly normal group velocity dispersion fibers (D >

High receiver sensitivity at 10 Gb/s using an Er-doped fiber preamplifier pumped with a 0.98 mu m laser diode

The authors report the realization of an extremely high receiver sensitivity at 10 Gb/s by using an erbium doped fiber (EDF) preamplifier pumped with a 0.98 mu m laser diode. The obtained EDF input sensitivity is -37.2 dBm (147 photons/bit). In addition, the importance of minimizing reflection from amplifier fiber ends is shown. >

Photonic wavelength-division and time-division hybrid switching system utilizing coherent optical detection

The application of coherent optical detection to a photonic wavelength-division (WD) and time-division (TD) hybrid switching system for a large-capacity switching is studied. Wavelength switching time is 1.8 ns, and the wavelength is stable after wavelength switching as wide as 3-4 AA. The results suggest the feasibility of switching over 20 channels (TD 4 channels, WD approximately 6 channels) for 100-Mb/s signals. This channel number can be increased to 256 channels (WD 64 channels) in view of the maximum wavelength sweep range (40 AA) of wavelength tunable laser diodes obtained so far.<<ETX>>

Rayleigh scattering influence on performance of 10 Gb/s optical receiver with Er-doped optical fiber preamplifier

The achievement of -30.8 dBm (630 photon/bit) receiver sensitivity at 10 Gb/s, with an Er/sup 3+/-doped optical fiber preamplifier, is discussed. This is an 8.3-dB sensitivity improvement over the avalanche-photodiode/FET receiver. Power penalties caused by a noise increase due to Rayleigh backscattering by the transmission optical fiber have been evaluated. Approximately -30-dB Rayleigh scattering from a 20-km optical fiber resulted in a 3.5-dB power penalty for a 25-dB-gain optical amplifier.<<ETX>>

The influence of directly modulated DFB LD sub-mode oscillation on long-span transmission system

Error-rate floors have been observed in several long-span transmission experiments at 500 Mb/s, using 1.5- mu m distributed-feedback laser diodes (DFB LDs) and 1.3- mu m zero dispersion optical fibers. It is proposed that for the threshold gain difference between main and submode (for DFB LDs), Delta alpha is a good parameter to specify the submode oscillation characteristics. It is experimentally and theoretically confirmed that the threshold gain difference Delta alpha must be greater than 5-6 cm/sup -1/, to avoid the error rate floor at 500 Mb/s. It was also confirmed that lambda /4 phase-shifted DFB LDs can easily satisfy this condition. >

A 2.56-Tb/s multiwavelength and scalable switch-fabric for fast packet-switching networks

We propose an implementation of a terabits-per-second crossbar-equivalent switch-fabric for packet-switching networks. It consists of switch-modules employing semiconductor optical amplifier gates (SOAGs), arrayed waveguide grating routers, and multiple wavelength-channels. It offers large modularity and a small internal loss. The number of SOAGs in a 256/spl times/256 switch-fabric is one-eighth that of a conventional switch-fabric. Scalability up to 2.56 Tb/s is demonstrated by a 10 Gb/s transmission experiment in which the input level into the switch-module was observed to possess a dynamic range of 6 dB.

Optical cross-connect system incorporated with newly developed operation and management system

The optical cross-connect (OXC) system described in this paper increases the operation flexibility and reliability of the trunk-line optical networks used for data communication. It features an OXC node comprised of a photonic switching network and a conventional electric switching network that are connected hierarchically. The operation and management scheme proposed for this OXC system uses the concept of an optical path and an optical section. The OXC system allows hitless network reconfiguration by switching the photonic switches gradually and without interference effects. An experimental OXC network showed that a broken optical path is restored, by rerouting, within 50 ms. Experiments using a LiNbO/sub 3/ 8/spl times/8 photonic switch matrix also showed that the OXC system provides photonic hitless switching. These results confirm the feasibility of flexibly reconfigurable and fast-restorable OXC systems.