Abstract: The optical amplifier according to the present invention is constructed such that the amount of the electric current fed to the power feeding line 2a is first detected by the current detection means, and then a setting signal is generated to each of the bypass circuits 22 and 23 in accordance with the thus detected amount of the fed current, and thereafter the output level of each of the optical repeater circuits 11 and 12 is controlled respectively by the bypass circuits 22 and 23, so that the output level of these repeater circuits 11 and 12 can be controlled in accordance with the amount of the current fed to the power feeding line 2a.

Abstract: The optical amplifier according to the present invention is constructed such that the amount of the electric current fed to the power feeding line 2a is first detected by the current detection means, and then a setting signal is generated to each of the bypass circuits 22 and 23 in accordance with the thus detected amount of the fed current, and thereafter the output level of each of the optical repeater circuits 11 and 12 is controlled respectively by the bypass circuits 22 and 23, so that the output level of these repeater circuits 11 and 12 can be controlled in accordance with the amount of the current fed to the power feeding line 2a.

Abstract: The optical amplifier according to the present invention is constructed such that the amount of the electric current fed to the power feeding line 2a is first detected by the current detection means, and then a setting signal is generated to each of the bypass circuits 22 and 23 in accordance with the thus detected amount of the fed current, and thereafter the output level of each of the optical repeater circuits 11 and 12 is controlled respectively by the bypass circuits 22 and 23, so that the output level of these repeater circuits 11 and 12 can be controlled in accordance with the amount of the current fed to the power feeding line 2a.

Abstract: An optical repeater monitoring system, according to the invention, comprises an oscillating source, a reference signal transmitter for transmitting a reference signal of a predetermined frequency generated from an output of the oscillating source to a first optical fiber, and an optical repeater. The optical repeater has a first photodetector for converting light from the first optical fiber into an electrical signal, a reference signal extractor for extracting a component of the reference signal from an output of the first photodetector, a carrier generator for generating a carrier from an output of the reference signal extractor, a monitor signal modulator for modulating the carrier generated by the carrier generator with a monitor signal showing a operating state of the optical repeater, a transmitter for transmitting an output of the monitor signal modulator to a second optical fiber.

Abstract: A control signal superimposer for superimposing a control signal on a signal light, comprising a pumping light source for generating a pumping light with intensity fluctuation in accordance with the control signal; a Raman amplification medium pumped by the pumping light from the pumping light source for Raman-amplifying the signal light; a combiner for combining the pumping light output from the pumping light source and the signal light to be Raman-amplified and then supplying them to the Raman amplification medium; and an optical filter for extracting the signal light component from the output light of the Raman amplification medium and terminating the pumping light component.

Abstract: An optical amplifying transmission system comprising a first optical amplifying transmission line including a first optical amplifier, a second optical amplifying transmission line including a second optical amplifier, a pumping light generator for generating pumping lights to be supplied to said first and second amplifiers, the powers of the pumping lights being variable, and first and second terminal stations which connect respectively to both ends of said first and second optical amplifying transmission lines.

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 oscillator oscillates at a predetermined reference frequency, and a reference signal light sender generates light (reference signal light) of a specific wavelength deeply modulated by output from the oscillator. A frequency divider frequency-divides the output from the oscillator into a certain number, and outputs a tone signal of a predetermined measurement frequency. Output from the frequency divider is applied to selected one of a plurality of optical transmission signal senders via one of a plurality of switches, and is used to slightly intensity-modulate a corresponding optical transmission signal. An optical divider in an optical repeater outputs most of output light from an optical amplifier onto an optical fiber transmission line toward a terminal station, and applies small amounts of the light to a measuring circuit.

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: 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: An optical transmission device using return-to-zero optical pulses as transmission optical pulses, which is capable of enhancing a transmission distance as well as a wavelength range with satisfactory transmission characteristics and enabling an easy realization of the wavelength division multiplexing optical transmission. The optical transmission device is formed by an optical transmitter for transmitting transmission optical pulses by superposing digital data signals onto return-to-zero optical pulses, and a modulator for applying one of a phase modulation and a frequency modulation in synchronization with a transmission rate of the transmission optical pulses, to the transmission optical pulses transmitted by the optical transmitter. This optical transmission device can be utilized in forming a wavelength division multiplexing optical transmission apparatus and an optical transmission system.

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 pulse generator, capable of generating ultrashort optical pulses suitable for optical soliton transmission, includes a DFB laser 10 for continuous laser oscillation, an electroabsorbtion modulator 12 for creating a sequence of optical pulses of the pulse width 14.6 ps from optical output of the laser 10. Output from an optical modulator 12 enters into a dispersion decreasing fiber 16 via an optical isolator 14. The dispersion decreasing fiber 16 has chromatic dispersion that decreases from 13.7 ps/nm/km to 2.3 ps/nm/km with distance, and its fiber length is 15 km. Pump laser beams from pump lasers 20, 24 are introduced to the dispersion decreasing fiber 16 by optical couplers 18, 22, and the fiber 16 functions as a Raman amplifier. When the Raman gain is 2.4 dB, the pulse width is compressed from 14.6 ps to 5.8 ps, approximately, even when the power of input pulses to the dispersion decreasing fiber 16 complies with the soliton condition.

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: Incident light 1 is inputted to an electro-absorption-type optical modulator 4 via an optical circulator 2 and a lens 3, and subjected to intensity modulation that corresponds to a modulation signal 8. The optical signal outputted by the electro-absorption-type optical modulator 4 is inputted to a Faraday rotator 6 via a lens 5, and the plane of polarization is rotated 45.degree.. The optical signal transmitted by the Faraday rotator 6 is totally reflected by a totally reflecting mirror 7, inputted for the second time to the Faraday rotator 6, then passed through the lens 5 after the plane of polarization has been rotated 45.degree. by this Faraday rotator 6, and readmitted by the electro-absorption-type optical modulator 4. The output of the electro-absorption-type optical modulator 4 is emitted via the lens 3 and the optical circulator 2. The polarization dependence of insertion loss can be eliminated because the plane of polarization is rotated 90.degree.