Abstract: In an FEC frame structuring method, and an FEC multiplexer, the order of information is changed by a first interleaving circuit 32, a first error correction code is generated by an RS (239, 223) coding circuit 33, the order is rechanged to an original order by a first deinterleaving circuit 34, and a second error correction code is generated by an RS (255, 239) coding means 5. The second error correction code is decoded by an RS (255, 239) decoding circuit 11 to correct an error of information, the order of information is changed by a second interleaving circuit 35, the first error correction code is decoded by an RS (239, 223) decoding circuit 36 to correct a residual error of information, and the order is rechanged to an original order by a second interleaving circuit 37.

Abstract: Detection of an optical pulse position uses an optical pulse string with a determined repetitive ratio and an electric clock signal with a same frequency as the repetitive ratio of the optical pulse string. A phase of the electric clock signal oscillator is shifted and supplied to an optical modulator. The optical modulator modulates the optical pulse string based on the electric clock signal and outputs a modulated optical signal. A photo detector converts the modulated optical signal output from the optical modulator to an electric signal. The phase shift amount of the electric clock signal is controlled to maximize an output from the photo detector. Additionally, a dither signal may be used in the control of the phase shift, more than the optical modulator may be employed, and/or more than color light source may be employed. The use of at least one of feed forward and feedback control provided by maximizing an output of the photo detector allows an optical pulse having a short width to be realized.

Abstract: An optical wavelength division multiplexed signal amplifying repeater capable of doubling the number of wavelength division multiplexed signals that can be transmitted is disclosed. Optical signals of both 1.3 &mgr;m band and 1.55 &mgr;m band in the entered optical wavelength division multiplexed signals are amplified, while pumping lights capable of causing Raman amplification in the 1.3 &mgr;m band are coupled with the optical wavelength division multiplexed signals so as to cause the Raman amplification for the optical signals of the 1.3 &mgr;m band, such that a difference between the loss in the 1.3 &mgr;m band and the loss in the 1.55 &mgr;m band due to the optical fibers are compensated. An optical communication transmission line using such repeaters is also disclosed.

Abstract: A method to determine a discrimination threshold of a received signal input from an optical transmission line comprises steps of measuring a bit error rate of the received signal at each of a plurality of discrimination thresholds by changing a polarization direction of an optical signal to enter the optical transmission line to detect the worst bit error rate at each discrimination threshold, and searching a predetermined bit error rate from the plurality of the detected worst bit error rates and searching a discrimination threshold of the received signal according to the predetermined bit error rate.

Abstract: Detection of an optical pulse position uses an optical pulse string with a determined repetitive ratio and an electric clock signal with a same frequency as the repetitive ratio of the optical pulse string. A phase of the electric clock signal oscillator is shifted and supplied to an optical modulator. The optical modulator modulates the optical pulse string based on the electric clock signal and outputs a modulated optical signal. A photo detector converts the modulated optical signal output from the optical modulator to an electric signal. The phase shift amount of the electric clock signal is controlled to maximize an output from the photo detector. Additionally, a dither signal may be used in the control of the phase shift, more than the optical modulator may be employed, and/or more than color light source may be employed. The use of at least one of feed forward and feedback control provided by maximizing an output of the photo detector allows an optical pulse having a short width to be realized.

Abstract: Detection of an optical pulse position uses an optical pulse string with a determined repetitive ratio and an electric clock signal with a same frequency as the repetitive ratio of the optical pulse string. A phase of the electric clock signal oscillator is shifted and supplied to an optical modulator. The optical modulator modulates the optical pulse string based on the electric clock signal and outputs a modulated optical signal. A photo detector converts the modulated optical signal output from the optical modulator to an electric signal. The phase shift amount of the electric clock signal is controlled to maximize an output from the photo detector. Additionally, a dither signal may be used in the control of the phase shift, more than the optical modulator may be employed, and/or more than color light source may be employed. The use of at least one of feed forward and feedback control provided by maximizing an output of the photo detector allows an optical pulse having a short width to be realized.

Abstract: A wavelength division multiplexed optical processing device and an optical communication transmission path which are capable of significantly improving the transmission characteristic of wavelength division multiplexed optical signals. A wavelength division multiplexed optical processing device is formed by a first arrayed optical waveguide for demultiplexing entered wavelength division multiplexed optical signals, and outputting demultiplexed optical signals; a plurality of correction units for correcting respective optical signals demultiplexed by the first arrayed optical waveguide; and a second arrayed optical waveguide for multiplexing optical signals corrected by the correction unit, and outputting multiplexed optical signals.

Abstract: An equalizing apparatus for equalizing gains of wideband wavelength-division multiplexed light and for improving the S/N ratio comprises a plurality of optical amplifyer for optically amplifying light in different wavelength groups, respectively; and multiplexer for multiplexing optically amplified light from said plurality of optically amplifying means.

Abstract: When an intensity modulating operation and a phase modulating operation are carried out by employing a 2-electrode MachZehnder type optical modulator preferably a LN-MZ type optical modulator, a drive signal of this 2-electrode LN-MZ type optical modulator is produced from an intensity modulation signal and a phase modulation signal with a low loss and a simple arrangement.

Abstract: A new two-way WDM optical transmission system is provided. The WDM optical transmission system comprises a two-way optical fiber cable, a first dispersion compensation optical fiber (DCOF) connected to one end of the optical fiber cable, a second DCOF connected to another end of the optical fiber cable, a chromatic dispersion compensating transmitter unit and a chromatic dispersion compensating receiver unit. The two-way optical fiber cable comprises a plurality of segments. The first DCOF is connected to one end of the optical fiber cable and has a compensation amount of a half of a one segment dispersion D.sub.c of the optical fiber cable. The second DCOF is connected to another end of the optical fiber cable and has the compensation amount of the half of the one segment dispersion D.sub.c. And the chromatic dispersion compensating transmitter unit compensates accumulated residual chromatic dispersions to be caused by higher-order wavelength dispersion of the optical fiber cable at each signal wavelength.

Abstract: This invention provides the gain equalizer positioned to an optical amplifying transmission line for equalizing gains of said optical amplifying transmission line, comprising a plurality of first optical filters varying transmittance periodically in at least predetermined wavelength range, and one or more second optical filters that their transmittance peaks at a wavelength substantially coinciding to the predetermined transmittance bottom wavelength of the first optical filters and decreases in a predetermined range at both side of the predetermined transmittance bottom wavelength.

Abstract: An optical transmission system comprises transmission optical fibers 14 connected between an optical transmission terminal 10 and an optical receiving terminal 12 via optical amplifying repeaters 16, and equalizing fiber 18 each connected in each equalizing interval. The equalizing fiber 18 is typically located at the terminal end of each equalizing interval. Each transmission optical fiber 14 is a dispersion-shifted fiber whose wavelength dispersion is substantially zero in a specific band, for example, 1.5 .mu.m. The optical amplifying repeaters 16 include an optical amplifier, and a dispersion compensating optical element having wavelength dispersion characteristics that exhibit an inclination opposite from that of wavelength characteristics of wavelength dispersion of the transmission optical fiber 14 (more specifically, a minus inclination with respect to the wavelength). The dispersion compensating optical element compensates offset values of cumulative wavelength dispersion among different wavelengths.

Abstract: An optical transmission system for optical transmission with the capacity of 100 Gb/S over a distance of 9,000 km or more includes an light sending station for outputting an optical signal in the band of 1.55 .mu.m, and an light receiving station connected to the light sending station by an optical fiber transmission line. The optical fiber transmission line includes a plurality of transmission optical fibers connected by optically amplifying repeaters. Each transmission optical fiber is a single-mode optical fiber having an effective cross-sectional area of 80 .mu.m.sup.2 or more. Each optically amplifying repeater includes an erbium-doped optical fiber for pumping in 0.98 .mu.m, WDM coupler for demultiplexing and multiplexing 1.55 .mu.m and 0.98 .mu.m wavelengths, optical isolator and gain equalizing filter, which are connected in series, so as to locate output light from an pumping laser for oscillation in 0.98 .mu.m onto the erbium-doped optical fiber through the WDM coupler.

Abstract: The present invention is directed towards an optical ADM apparatus provided with a narrow band-pass filter which is capable of minimizing declination of the transmission characteristics. An optical transmission prohibiting element composed of an optical isolator and a fiber grating is connected in series to the downstream of a fiber grating interposed between two optical circulators. The drop light is reflected by the fiber grating and released from an output optical fiber of the optical circulator. A leak component of the drop light having passed through the fiber grating appears on the side of the isolator and runs across the isolator to the other fiber grating. Most of the leak component is however reflected by the fiber grating while its small portion enters the optical circulator via the fiber grating. The small portion of the leak component is as small as negligible and will hardly interfere with the add light. The optical transmission prohibiting element may be an optical circulator.

Abstract: An optical add/drop multiplexing scheme capable of reducing the degradation of the transmission characteristic due to the beat noises caused by the interference of the fiber grating leakage components. An optical add/drop multiplexing device is formed by a high speed polarization scrambler for entering signal lights with a data modulation at a high speed bit rate applied thereto, and scrambling polarization states of entered signal lights at high speed, and an optical add/drop element for receiving the signal lights with the polarization states scrambled by the high speed polarization scrambler, and carrying out an add/drop multiplexing operation for signal lights in a specific wavelength among received signal lights.

Abstract: Wavelength multiplexed optical signals which are input into a first optical amplifier from an optical transmission terminal device over an optical fiber are differently amplified in respective wavelengths due to unevenness of gain of the optical amplifiers and then output. By providing M-transmission optical filters having an M-type transmission characteristic to cancel gain deviation of the optical amplifiers in respective wavelengths, a flat gain characteristic can be achieved even after the optical signals are transmitted via a plurality of optical amplifiers and a plurality of M-transmission optical filters. Also, by removing ASE in a wavelength range of 1.53 .mu.m which prevents signal amplification in a wavelength range of 1.55 .mu.m, the wavelength multiplexed optical signals which are sufficiently amplified can be transmitted to an optical reception terminal device over the optical fiber.

Abstract: An optical transmitter which reverses the ON-OFF state of the optical intensity of a bright soliton lightwave and generates a dark soliton lightwave having an optical phase shift, an optical receiver for the dark soliton lightwave, and a superfast, high-capacity optical transmission system which is capable of increasing the soliton pulse array density while suppressing timing jitter. The optical transmission system is provided with the optical transmitter which transmits a dark soliton lightwave having digital information, the optical receiver which receives the dark soliton lightwave as a return-to-zero pulse and a transmission optical fiber interconnecting the transmitter and the receiver.

Abstract: The object of the present invention is to provide an optical transmitter which enables the reduction of the strong dependency of the transmission characteristic on the high-speed polarization scrambler driving signal phase. The light outputted from a light source is converted to a RZ pulse by an electro-absorption modulator. The RZ pulse is modulated by a data modulator, and the polarization thereof is scrambled in a high-speed electro-optic polarization scrambler and outputted from the output terminal thereof. Since, in the present invention, the light is once changed to a RZ pulse, the strong dependency of the optical signal transmission characteristic on the high-speed polarization scrambler driving signal phase can be reduced. Further, if the phase of the RZ pulse in the NRZ modulation signal is made to synchronize with the rising edge or the falling edge of the NRZ signal, the dependency on the high-speed polarization scrambler driving signal phase can be further reduced.

Abstract: An optical submarine branching unit employing an optical circuit structure which is small in the number of optical components used, permits reduction of optical insertion loss and is well compatible with the ADD/DROP function suitable for use in wavelength multiplex transmission. An optical fiber pair provided in an optical submarine cable connecting between first and second points is branched toward a third point, an optical circulator capable of reversing the direction of rotation of an optical input/output is provided as optical switching means by which, in the event of a failure in the branch transmission system having the branched optical fiber pair, the optical fiber pair is connected between the first and second points directly without being branched to the third point.

Abstract: An object of the present invention is to provide an optical add-drop multiplexer capable of giving improved characteristics with a simple, inexpensive arrangement which needs not a corresponding number of optical bandpass filters to the wavelength components of a light signal to be carried. The wavelength components .lambda.1 to .lambda.n of an input n-wave signal is received by an input optical fiber and transmitted through an optical circulator and an optical fiber to an optical bandpass filter which allows a specific wavelength .lambda.1 to pass but rejects the other wavelengths .lambda.2 to .lambda.n. While the rejected wavelengths .lambda.2 to .lambda.n are returned back to the optical fiber, the specific wavelength .lambda.1 runs through another optical fiber and another optical circulator and then is dropped from an output optical fiber. Meanwhile, another signal component of the wavelength .lambda.