Abstract: An oscillator outputs an additional signal with a frequency which is higher than a frequency corresponding to a bandwidth of a frequency band allotted to an electrical signal to be transmitted and lower than a half of a lowest frequency of a frequency band allotted to the electrical signal to be transmitted. Thereby, if a second order intermodulation distortion between the additional signal and the electrical signal to be transmitted occurs, a frequency where distortion occurs is outside all of the frequency bands allotted to the electrical signal to be transmitted, and the occurring second order intermodulation distortion does not affect the electrical signal to be transmitted. Further, if the second order intermodulation distortion of the additional signal occurs, the frequency where distortion occurs is outside all of the frequency bands allotted to the electrical signal to be transmitted, and the occurring second order intermodulation distortion does not affect the electrical signal to be transmitted.

Abstract: An electrical signal to be frequency-modulated is branched into first and second signals. An FM laser 102 oscillates light having a wavelength .lambda.1 in a steady state condition, and outputs an optical signal obtained by converting an amplitude change in the inputted first signal into an optical intensity change and an optical frequency change. An optical detecting portion 106, to which the optical signal from the FM laser 102 and light having a wavelength .lambda.0 outputted from a local light source 104 are inputted, converts an optical intensity modulation component of the inputted optical signal as a current amplitude change by operating square-law detection characteristics, and generates a beat signal at a frequency corresponding to a difference in wavelength .DELTA..lambda. between the two inputted optical signals. A discrimination portion 110 discriminates using a threshold value generated on the basis of the second signal and converts the beat signal into the pulse signal.

Abstract: The present invention provides an amplifier capable of accurately reproducing a signal under various operating environments and an optical receiving circuit using the amplifier. The differential amplifier is constructed such that the amplification factor thereof is set to 0.5, and a variation occurring inside thereof is the same as a variation occurring inside of the differential amplifier. Respective output variations occurring in maximum value holding circuits due to a temperature variation and a power supply voltage variation are canceled by providing differential amplification in the differential amplifier. At this time, an output variation occurring in the differential amplifier is also canceled. Therefore, an output variation occurring in the differential amplifier is made equal in value to the output variation occurring in the differential amplifier, such that the same variation as a signal input is superimposed on the reference input fed to the differential amplifier.

Abstract: A signal processing circuit 113 subjects a transmission signal outputted from a signal source 111 and a carrier outputted from a carrier generation circuit 112 to predetermined signal processing, to generate a modulation signal amplitude-modulated by the transmission signal and so adapted that its envelop on the high level side (or on the low level side) has a shape analogous to the waveform of the transmission signal and its envelope on the low level side (or on the high level side) is at an approximately constant level. A light source 114 converts the modulation signal into a light intensity modulation signal, and outputs the light intensity modulation signal to an optical coupler 120. The above-mentioned signal processing is performed by the signal processing circuit 113, whereby the spectrum distribution of the light signal outputted from the light source 114 is dispersed, and the peak value of light spectra is decreased.

Abstract: When an electric signal outputted from a signal source (101) is converted to a light signal in an electrica-optical converting portion (104), a distortion component such as secondary or tertiary distortion is caused in the light signal to deteriorate transmission quality. Therefore, the light signal outputted from the electrica-optical converting portion (104) is further intensity-modulated with the same electric signal in an external light modulation portion (106) to forcibly cause a distortion which is out of phase with and of the same amplitude as the distortion component caused in the electrical-optical converting portion (104), thereby canceling the distortion component included in the light signal. Consequently, an optical transmission system capable of high-quality optical transmitting can be realized while employing a device having equivalent performance with the conventional devices.

Abstract: A center station 1 generates an all-channel signal 2 obtained by multiplexing signals on all channels, and transmits the signals to a selective distribution station 10 through 1 wire transmission line such as an optical fiber. Subscribers' transmitting devices 40.sub.1 to 40.sub.N transmit requests for channels to be received by corresponding subscribers' receiving devices 30.sub.1 to 30.sub.N to the selective distribution station 10 in a radio transmission system. The selective distribution station 10 selects the signals on the channels requested from the all-channel signal 2 in response to requests to receive channels serving as up-signals transmitted in a radio transmission system from the subscribers' transmitting devices 40.sub.1 to 40.sub.N, and distributes and transmits the selected signals to the subscribers' receiving devices 30.sub.1 to 30.sub.N as down-signals.

Abstract: A signal for which the amplitude of envelope becomes substantially 0 only for a certain period of time within the time of a period T, and a measured signal having a certain amplitude are synthesized, and the synthesized signal is optically transmitted. When a plurality of reflection points are present on a light transmission line, there is an increase in harmonic distortion or intermodulation distortion as well as in cross modulation distortion after receiving. This increase in cross modulation distortion causes an increase in variation of amplitude of the measured signal.

Abstract: Video signals for broadcasting service with a plurality of channels are frequency-multiplexed into a predetermined broadcasting band, and converted into optical signals by an optical transmitter. At the same time, video signals for VOD service requested by a plurality of subscribers are selected, taken out, frequency-multiplexed within the VOD band, and converted into optical signals by an optical modulator. These two types of optical signals are transmitted to subscribers through the optical network. In each subscriber's household, either broadcasting signals or video signals for VOD service are reproduced and desired programs are selected in the tuners.

Abstract: In a fiber optic communication terminal composed of a light mixing part for mixing an input light signal and a light signal from own station, a detecting part for picking up a part of the output of the light mixing part to detect its quality deterioration, and a light source part in which the wavelength of output light is variable, increase of noise level or occurrence of bit error due to beat interference caused by mixing of input light signal and light signal from the own station is detected as quality deterioration in the detecting part, and by controlling the wavelength of the light source part accordingly, generation of beat interference can be prevented, and moreover by using a fiber optic communication terminal capable of maintaining the wavelength so that the signal quality may be the set value, the output light wavelength can be arranged at high density on the whole as a fiber optic communication system.

Abstract: The optical signal amplification apparatus of this invention includes a plurality of optical fiber amplifiers connected in series, each optical fiber amplifier including: an optical fiber doped with rare earth ions; and a pumping light source for emitting pumping light for exciting the optical fiber, wherein the power of signal light input into each optical fiber amplifier is set so that the value of a distortion component of the signal light output from the optical fiber amplifier is equal to the value of a distortion component of the signal light input into the optical fiber amplifier and that the distortion component of the signal light output from the optical fiber amplifier increases when the power of the signal light input into the optical fiber amplifier increases. An optical fiber transmission system including the optical signal amplification device is also provided.

Abstract: The present invention provides a cable broadcasting system and the transmission center employed therein. In the transmission center, plural images are divided into several groups in the same kinds and each image in one kind is repeated not simultaneously so that they are outputted as independent plural image signals, and the image that the subscribers have requested is selected from those plural image signals which is enciphered, modulated, and multiplexed to be transmitted in optical transmission lines through an available channel to the subscribers, while the transmission channel is validated as well as the enciphered image signal is deciphered at the subscribers' end in order to enable the subscribers to watch the image they have requested.

Abstract: An optical transmission system is disclosed wherein a multiplexed analog signal is supplied to a laser diode to modulate the intensity of a long-wavelength laser beam. A single mode optical fiber transmission medium has a first inclined end face at a proximal end and a second inclined end face at a distal end. The laser beam is coupled to the proximal end of the transmission medium by a coupling means including a single mode optical fiber connecting medium having one end connected to the laser diode and an opposite end having a third inclined end face complementary to the first inclined end face and a coupler for coupling the first and third inclined end faces in abutment relation.

Abstract: A semiconductor laser generating no intensity noise caused by reflected light and oscillating at a single frequency, wherein a cavity resonator is disposed externally of the semiconductor laser in order to suppress the oscillation frequency shift (chirping) of the semiconductor laser possibly induced with current modulation of the same.

Abstract: Apparatus for controlling humidity comprises a humidity sensing circuit including a humidity sensing element the electrostatic capacitance of which varies in accordance with the ambient relative humidity, and an air-conditioning system responsive to the sensed humidity. The humidity sensing element is charged and discharged repeatedly in accordance with a pulse train signal, and a period required for the voltage across the sensing element is measured during charging by a comparison between the voltage and a reference voltage. The pulse width or the reference voltage may be changed to select a desired reference humidity. A hysteresis characteristic may be given to render the operation of the circuit stable. When an SCR is controlled by the output signal of the humidity sensing circuit, the frequency of the pulse train signal is selected to be greater than four times the frequency of the voltage applied to the SCR.

Abstract: Apparatus for humidity detection comprises a humidity sensing element, the electrostatic capacitance of which varies in accordance with the ambient humidity, a fixed capacitor, first and second pulse generating circuits respectively responsive to the sensing element and the capacitor, and a computing circuit responsive to pulses from the first and second pulse generating circuit. The sensing element and the fixed capacitor are respectively charged via resistors to produce first and second pulses in accordance with voltage across the sensing element and the capacitor. The difference between the widths of the first and second pulses is detected in the computing circuit to produce an output pulse indicative of the relative humidity, thereby compensating for undesirable infuenece due to dielectric loss in the sensing element so as to accurately measure humidity irrespectively of the ambient temperature.

Abstract: Holographic reconstructing apparatus capable of exchanging a hologram memory plate and having a large memory capacity, wherein the position of the memory plate relative to an irradiating laser beam can be accurately controlled. A beam irradiated from a laser source is deflected by a light deflector and is selectively directed to a selected hologram to be read or directed intermittently to a region for dividing the laser beam into a plurality of laser beams. The intensity of each divided laser beam is detected by a light detector, and the detection signal is fed back to control the working point of the light deflector such that the center of the laser beam irradiates the center of the luminous laser beam dividing region. The working point is held until the light deflector again directs the laser beam to the dividing region so that the laser beam radiates a selected hologram on the hologram plate accurately.