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: An optical access system is disclosed in which subscribers' terminals and optical coupler-splitters of nodes are maintenance-free and required control is effected on the part of the central office alone. At a first position, down-link optical digital signals are generated, which are made "1s" every n bits (n being an integer equal to greater than 2). The optical digital signals, except a train of optical pulses every n bits, are sent as down-link information over a transmission line. At a second position, the optical digital signals, except the optical pulse train, are demodulated from the transmitted down-link optical digital signals, and in an optical gate circuit on which the down-link optical digital signals are incident, up-link optical digital signals based on up-link message data is formed in synchronization with the optical pulses corresponding to every n-th bits and is transmitted to the first position over the transmission line.

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: To enable the filtering of a light signal without using an optical bandpass filter, the present invention provides the following construction: a light signal transmitted through an optical fiber enters an injection-locked laser device which is locked to the wavelength of the light signal to oscillate synchronously with the light signal; the locked light signal enters a light frequency discriminator to transform the frequency-modulated signal into an intensity modulated signal, and it enters a light receiver to be demodulated. Since the injection-locked laser device emits only a locked oscillation light signal, the received light signal can be extracted without using an optical bandpass filter.

Abstract: An optical short pulse reshaping device capable of effectively eliminating noise from or reshaping of input optical short pulses of a pulse width of picosecond order shorter than a carrier life time. The device comprises: a semiconductor laser element, means for injecting an electric current to the semiconductor laser element for obtaining an oscillation state of the semiconductor laser element, means for injecting into the semiconductor laser element input optical short pulses of a wavelength shorter than that of the oscillation light of said semiconductor laser element, and means for taking out optical short pulses emitted from the semiconductor laser element in distinction from its oscillation output light.

Abstract: To enable the surveillance of a long-distance optical fiber line that a method using the reflection lights and Rayleigh backscatter lights cannot cover, a plurality of optical reflection elements P1-Pn are interposed in the optical fiber line at each specific distance. Each of the optical reflection elements P1-Pn reflects only a light signal of one of specific wavelengths .lambda.1-.lambda.n on a constant level. Light pulses of the specific wavelengths .lambda.1-.lambda.n are transmitted to the optical fiber line to measure intensities of the light pulses reflected by the optical reflection elements P1-Pn. From the measurement, surveillance of the optical fiber line can be done between the transmitter and each of positions of the optical reflection elements P1-Pn. The reflectance of the optical reflection elements P1-Pn can be set to 100%, and the surveillance becomes possible even if the length of the optical fiber line exceeds 200 km.

Abstract: An equipment for facsimile call service of a telephone exchange which can apply an unique charging system to a facsimile call by distinguishing the facsimile call from ordinary speech calls, notify a caller of cause when occurring a failure in transmitting the facsimile call, and advise the caller on the way to eliminate the cause.

Abstract: In an optical frequency stabilizing device for stabilizing optical frequencies of transmission lasers even when optical frequency reference is shut off, an optical shutter 44 is normally held in its open state to pass optical frequency reference light from an optical network to an injection-locked laser device 42. An optical multiplexer 46 multiplexes outputs of a injection-locked laser device 42 and transmission laser devices 40-1 through 40-3, and an optical frequency discriminator 48 scans optical output of the multiplexer 46. Opto-electrically converted output of a photodetector 52 is applied to a control device 50 which controls driving currents, etc. of the laser devices 40-1 through 40-3 to adjust optical output frequencies of the laser devices 40-1 to 40-3 to predetermined values relative to the optical output frequency of the injection-locked laser device 42. The control device 50 also closes the optical shutter 44 for a moment, and adjusts the driving current, etc.

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: In an optical wavelength monitoring apparatus for easily monitoring wavelength deviation, light introduced from a laser source 10 to an optical transmission line 12 is divided by directional couplers 14, 20. Optical output of the directional coupler 14 is converted into an electrical signal by a photodiode 16, and logarithmic-amplified by a logarithmic amplifier 18. Optical output of the directional coupler 20 is introduced to a photodiode 26 via an optical filter 24. The optical filter 24 is an optical element whose transmittance decreases as the incident light deviates from a specific wavelength .lambda.a. Optical output from the optical filter 24 is converted into an electrical signal by a photodiode 26, and logarithmic-amplified by a logarithmic amplifier 28. A differential amplifier 30 outputs a difference between outputs of the amplifiers 18, 28.

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: An encoding control unit obtains a quantization step size and a video encoding rate Rc on the basis of various kinds of conditions including a transmission time and image quality specified through an input unit by a user, and property of image contents from a signal compression processing unit. Next, the video encoding rate Rc is compared with a network transmission rate Rt which is obtained through a network IF unit. Then, if the transmission rate Rt of the network is smaller than the video encoding rate Rc and is present in the range any of values of which is equal to or larger than the value smaller than Rc by a predetermined quantity, then the quantization step size is corrected in such a way that the video encoding rate Rc is equal to or smaller than the transmission rate Rt of the network, or in such a way that the video encoding rate Rc is increased.

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.

Abstract: An optical switch is formed by: at least one switch driving circuit for generating ultrasonic waves; at least one electric acousto-optic element forming at least one diffraction grating therein upon being applied with the ultrasonic waves generated by the switch driving circuit; at least one polarization rotator for rotating a polarization plane of a first primary diffracted light produced by the diffraction grating, by 90.degree.

Abstract: The purpose of the invention is to detect a surveillance signal in a shorter time without lowering the usable merit of wavelength. The transmission signal transmitting through the optical fiber transmission lines is specified as a light FDM signal multiplexed in wavelength, and the surveillance light signal is interposed in the middle of two adjacent channel slots. The surveillance light signal is produced such that the spread spectrum is applied to the surveillance carrier and thereby a light signal is modulated in intensity. The light FDM signal and surveillance light signal are turned to the facing transmission lines in the optical repeaters to be received by each terminal station, and the modulation rate of the surveillance light signal can be made deeper so that the surveillance signal can be detected in a shorter time.

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 frequency shifter which has no insertion loss polarization dependency and no polarization mode dispersion is formed by: at least one ultrasonic wave generator for generating ultrasonic waves; at least one electric acousto-optic element forming at least one diffraction grating therein upon being applied with the ultrasonic waves generated by the ultrasonic wave generator; at least one polarization rotator for rotating a polarization plane of a first primary diffracted light produced by the diffraction grating, by 90.degree.

Abstract: An optical add/drop multiplexer device which is capable of extracting or inserting optical signals of arbitrary wavelength and having a wavelength selection characteristic with a narrow bandwidth, and which is compact in size and highly reliable. The device is formed by a substrate member; a plurality of optical waveguides, formed over the substrate member in layers with a prescribed interval along a direction perpendicular to a plane of the substrate member, each optical waveguide having a portion arranged in parallel and in proximity to an adjacent optical waveguide to form a coupling section; and a diffraction grating member, provided at the coupling section and having a prescribed period along a light propagation direction, for reflecting light signals with a specific wavelength among light signals entered from one of adjacent optical waveguides to another one of the adjacent optical waveguides.