Abstract: An optical transmitter for providing a signal light with a reduced degree of polarization, the transmitter being used as a transmitting terminal of an optical repeater system that encompasses optical amplifiers at a signal light transmitter, the optical transmitter includes an optical source for transmitting a signal light source; and a degree of polarization reducing circuit including a polarizing beam splitter splitting the signal light source from the optical source means into a first polarized component and a second polarized component that are orthogonal to each other; a first optical path transmitting the first polarized component input from the polarizing beam splitter while maintaining the polarization plane of the first polarized component; a second optical path, which is spatially separate from the first optical path, transmitting the second polarized component input from the polarizing beam splitter while maintaining the polarization plane of the second polarized component; and a polarizing beam mi

Abstract: To perform waveform shaping, retiming and amplification of the transmitted pulse signal of a binary PCM fiber optic communication employing an optical pulse signal which has a pulse duty factor within 1 with respect to a time slot, an optical waveform shaping device is proposed in which the optical pulse signal is branched by an optical branch circuit into two optical signals. The one transmitted optical signal passes through a photodetector, a band-pass filter for extracting the fundamental frequency component of the signal, an amplifier and a delay circuit, so that the signal is converted to a sinusoidal voltage synchronized with the optical pulse signal. The other optical signal passes through a semiconductor electrical absorption type optical modulator which is driven by the sinusoidal voltage and a DC voltage, so that the width of a gate waveform is changed by controlling the amplitude of the sinusoidal voltage and the DC voltage.

Abstract: Apparatus for monitoring a plurality of optical repeaters of an optical communication system in which each said repeater directly amplifies an optical signal transmitted in an optical fiber and passing through the respective optical repeater, including an optical division circuit for dividing an outgoing main line signal and a monitoring signal, a format conversion circuit by which monitoring information is converted into binary information, a previous modulation circuit by which a monitoring signal is modulated with a sine wave, a comparison circuit which compares the monitoring signal with a reference voltage, a voltage controlled amplifier which amplifies the modulated monitoring signal, an automatic gain control circuit which regulates the output from the outgoing optical repeater, and an outgoing optical repeater which includes a stimulating light source, a wave synthesizer and a doped optical fiber.

Abstract: In a long-distance high-speed optical communication scheme in which multiple optical amplifiers are provided at a large number of stages in optical fibers, an optical signal from a light source which has a desired small line width and oscillates at a single wavelength is modulated at a high speed by an external modulator and then transmitted in the fibers which are dispersion shifted optical fibers, the zero-dispersion wavelength in which is set to be larger than the oscillation wavelength of the light source. Therefore, noises and the modulation instability, which would occur due to the phase fluctuation in the oscillation wavelength of the light source, and the influence of a waveform distortion due to the dispersion in the optical fibers can be avoided to make it possible for the first time in history to transmit the optical signals at the high-speed in the long-distance optical communication system employing the optical amplifiers.

Abstract: A pumping light source drive system is disclosed for driving pumping light sources of an optical amplifier which is composed of a rare earth doped optical fiber doped with a rare earth element and said pumping light sources. The pumping light sources are always held in operation. The output signal power at the output of the rare earth doped optical fiber or the combined power of the pumping light sources is detected and compared with a predetermined reference power to control the output power of the pumping light sources, so that the output signal power or the combined power of the pumping light sources reaches a predetermined value.

Abstract: A system for measuring laser spectrum is disclosed in which the laser light to be measured is branched into one branched light and the other branched light so that the laser spectrum of the light is measured from a beat output resulting from mixing a delayed light obtained by delaying the one branched light for a certain period of time with the other branched light undelayed. In accordance with the present invention, the delay time of the delayed light undergoes such variations as to assume a value equal to an integral multiple of a fixed delay time by the use of an optical directional coupler.

Abstract: Delay time variation in an optical fiber digital communication system which includes optical regenerative repeaters is measured at one of terminal ends having reference clock signal. A monitor signal which depends upon the delay time variation is provided at the farthest repeater in an area where delay time is subject to secular change by dividing reference clock signal from said terminal end, and said monitor signal is returned to the terminal end from said farthest repeater, and the terminal end compares the returned monitor signal with the divided reference signal by using a phase comparator to provide measure of delay time variation.

Abstract: A signal coupler couples more than three transmitter-receivers through optical fiber cables and at least one repeater on a bit-multiplex system, by exchanging or reallocating each time slot according to a transmission station and the related destination. The coupler has a means to release the bit-multiplexing (or demultiplex) the signals from each transmitter by deriving the control clock signals from the information signals themselves. The coupler also has a means for multiplexing the bit signals for each destination by automatically adjusting the phase relationships among the released signals (demultiplexed signals) for bit-synchronization using a delay circuit.

Abstract: In a transmission system, which includes one or more digital repeaters in a transmission line and a digital multiplex/demultiplex branching unit, a code for supervising the digital repeater or repeaters in an in-service state is transmitted according to a data sequence signal obtained through bit-by-bit time-division multiplexing of at least two different kinds of digital signals. The supervisory code has a configuration of a transmission line code obtained by dividing the digital signals into blocks of bits corresponding in number to the sum (n.times.m'+1) of the product of the number n of channels of the digital signals and positive odd number m' and one and adding after each of the blocks a number of parity bits (supervisory bits) corresponding to the respective digital signals equal to the number of the channels, i.e., has a bit configuration of n(m'+1)+1.

Abstract: A mount arrangement of a semiconductor laser and an optical fiber as a unitary structure. A substrate has a submount disposed thereon mounting a semiconductor laser. The laser is fixed on the submount by a fusion-welding material. A fiber submount is disposed on the substrate in the vicinity of the semiconductor laser submount. An optical fiber is fixed to the fiber submount with its optical axis coaxial with the optical axis of the output light of the semiconductor laser. The fiber submount includes a material for fixing the optical fiber and has a melting point such that it will not affect the coaxial optical alignment of the semiconductor laser and the optical fiber and the fixing between the substrate, the laser submount and between the laser submount and semiconductor laser during fabrication.

Abstract: A coupling system for the output light of a semiconductor laser, characterized in that an end portion of an optical fiber is made as a focusing lens to be coupled with the output light from an active layer of the semiconductor laser is formed so that, at least in a plane parallel to the optical axis of the output light and perpendicular to the junction plane of the semiconductor laser, the width of the end portion continuously decreases towards its tip to provide a required curvature at the tip and that the distribution of light of the semiconductor laser and that of the optical fiber and the focusing lens are matched with each other in the plane perpendicular to the junction plane of the semiconductor laser. The end portion of the optical fiber defining the focusing lens may be formed to have a fixed width in a plane parallel to the junction plane of the semiconductor laser.

Abstract: An optical switch for switching laser beams, having a transparent glass plate with a reflection film on the surface of the same has been found. When the reflection film is at the first position, the first input beam is coupled with the output beam through the transparent glass plate, while the second input beam is prevented by said reflection film. When the reflection film is at the second position, the first input beam is prevented by said reflection film, and the second input beam is coupled with the output beam through the reflection by said reflection film. Thus, according to the displacement of the transparent glass plate together with the reflection film, the input beams are switched. Due to the above operational principle, the output optical level does not decrease even during the transient time, and then, the present optical switch is utilized in an optical repeater for digital communication.