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: In an optical fiber transmission line between two terminal stations, an input side wavelength converter for up-shifting a wavelength of a signal light is inserted at a front part of each of the optical amplifiers and an output side wavelength converter for down-shifting a wavelength of a signal light is inserted at a rear step of the optical amplifiers. Signal lights transmit in a wavelength band shorter or longer than the zero dispersion wavelength of the transmission optical fiber on said transmission optical fibers. The input side wavelength converter converts the wavelength of the signal lights from the transmission optical fibers within the amplifying bandwidth of the optical amplifiers and the output side wavelength converter returns the wavelength of the signal lights optically amplified by the optical amplifiers.

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: 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: A waveform converter includes a transmission-type InGaAsP electroabsorption optical modulator 10 using the Franz-Keldysh effect. Continuous light (probe light) 12 as a target of wavelength conversion is fed to an end surface 10a of the optical modulator 10 while a constant voltage of 3 V is applied to the optical modulator 10. An optical circulator 14 is supplied with original signal light (signal light to be waveform-converted) 16 through its terminal A, and delivers it from the terminal B thereof to another end surface 10b of the optical modulator 10. The optical modulator 10 gives a loss to the probe light 12 according to the intensity of the original signal light 16 and makes the waveform of the probe light 12 to be substantially the same as the original signal light. The probe light waveform-converted by the optical modulator 10 and output from the end surface 10b is fed to a terminal B of an optical circulator 14 as a waveform-converted light 18 and output from its terminal C.

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 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 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: 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: A bilateral optical transmission system for pulse information disclosed which can accommodate variations in the relationship between the down-link signal transmission rate and the up-link one. A single bilateral optical transmission line is laid between first and second positions. A transmission pulse train with pulse transmission time slots set therein at fixed time intervals is provided onto the transmission line from the first position. A return pulse train is retransmitted from the second position to the first position over the bilateral optical transmission line.

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.