Abstract: A modulated electrical signal Smod produced upon amplitude-modulating a subcarrier having a high frequency (for example, a millimeter-wave band) by a baseband signal SBB to be transmitted and a main carrier MC outputted from a light source are inputted to an external optical modulating portion in an optical transmitter. The external optical modulating portion amplitude-modulates the main carrier MC by the modulated electrical signal Smod, to output a double-modulated optical signal OSdmod to an optical filter portion. The optical filter portion passes only a component of one of sidebands included in the double-modulated optical signal OSdmod, and outputs the component to an optical fiber as an optical signal OS. An optical/electrical converting portion in an optical receiver optical/electrical-converts the optical signal OS transmitted through the optical fiber, to directly obtain a baseband signal SBB.

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: In FIG. 5, a plurality of signal sources 21.sub.1 to 21.sub.N each generate a carrier with different frequencies. A pulse signal generating portion 23 generates a pulse signal with the same period and time width as those of a horizontal synchronizing signal in NTSC system color television broadcasting. Delay devices 32.sub.1 to 32.sub.N delay timing of the pulse signal for a randomly predetermined delay amount. Level adjuster 52.sub.1 to 52.sub.N generate a modulating signal by adjusting each pulse base of the delayed pulse signal for a level within a range between 12.5% and 74.375% with respect to a pulse top. Modulators 42.sub.1 to 42.sub.N output a signal obtained by modulating the carrier with the modulating signal. A multiplex portion 24 multiplexes the modulated signals to output a resultant signal as a test signal. The error rate of a QAM signal is evaluated with the test signal.

Abstract: In a system for simultaneously optically transmitting a plurality of digital modulation signals using an analog SCM transmission technique, the degree of degradation of the waveform of a transmission signal or the magnitude of distortion thereof differs depending on bands, whereby there arises a difference in transmission quality among channels. Therefore, an analog signal to be transmitted is converted into a digital signal by an analog-to-digital converting portion, after which the digital signal is divided, by a hierarchy separating portion, into a plurality of groups of digital information depending on degrees of importance in constructing the original analog signal. A modulating portion digitally modulates carriers having different frequencies which are respectively assigned to the groups of digital information. A multiplexing portion frequency-multiplexes and simultaneously optically transmits all the digital modulation signals.

Abstract: A branch portion 107 branches a modulating signal into two signals in opposite phases. One of them is inputted to an FM laser element 102. The other one is adjusted in propagation delay and in amplitude and then is inputted to an IM suppressing laser element 110. The FM laser element 102 outputs an optical-frequency-modulated signal around a wavelength .lambda.1, whose optical intensity is also modulated. A local light source 104 outputs light at a wavelength .lambda.0, which is different from the oscillation wavelength .lambda.1 of the FM laser element 102 by .DELTA..lambda.. The IM suppressing laser element 110 outputs an optical-intensity-modulated signal. The three lights are combined and inputted to a photodetection portion 106.

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: The present invention provides an optical disc comprising a main-image signal recording area holding a signal of a main image for a display, and a sub-image signal recording area holding a signal of a sub image to be displayed including an image of a time counted down in accordance with a progress of a sub-image signal reproduction. Furthermore it provides an image signal transmitting apparatus for repeatedly transmitting a main-image signal and a sub-image signal one after the other by utilizing such optical disc, the image signal transmitting apparatus comprising a image signal reproduction device for reproducing the main-image signal and the sub-image signal, a cycle time memory for memorizing a main-image signal transmission cycle, and a control device for obtaining a time difference between the cycle and time required for the main-image signal reproduction as well as control the image signal reproduction device.

Abstract: A picture image distributing apparatus provided within a passenger moving vehicle, consists of: a head end portion for multichannel FDM picture image signals; an electrical optical for converting the FDM picture image signals into optical signals; an optical amplifier for optically amplifying the optical outputs; one optical fiber transmission path connected to optical taps of unequal distribution for branching halfway on one portion of the optical power except for the branching at a final point, an optical/electrical converter for receiving optical signals branched at the final point or halfway so as to convert them into electrical signals; and a passenger seat picture image receiving terminal connected to the optical/electrical converter so as to receive the electrical signals.

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: There is provided a peak compression circuit including detection device for detecting that value of an input signal has exceeded a predetermined set value, a pulse generation device for generating, based on the result of the detection, a pulse signal constituted of frequency components which have no substantial adverse influence on the input signal and having a polarity in a direction of reducing the parts of the input signal exceeding the predetermined set value, a delay device for delaying the input signal so that there is a phase match between the generated pulse signal and the portions of the input signal exceeding the predetermined set value and an addition device for adding the delayed input signal and the pulse signal. There is further provided a light transmitter including the peak compression circuit and a light source for outputting a light signal which has been intensity-modulated by the output signal of the peak compression circuit.

Abstract: A light-receiving module includes: a pigtail optical fiber including a core portion for transmitting an optical signal and a cladding portion covering a side face of the core portion; an optical connector provided at a first end of the pigtail optical fiber for optically connecting a transmitting optical fiber with the end of the pigtail optical fiber; a light-receiving device having a light-receiving face for receiving the optical signal propagating through the core portion and for converting the optical signal into an electric signal; an optical coupling system for converging the optical signal emitted from a second end of the pigtail optical fiber onto the light-receiving face of the light-receiving device; and means for preventing light propagating through the cladding portion from reaching the light-receiving face of the light-receiving device so that the optical signal propagating through the core portion does not interfere with the light propagating through the cladding portion on the light-receiving f

Abstract: The present invention provides an optical disc comprising a main-image signal recording area holding a signal of a main image for a display, and a sub-image signal recording area holding a signal of a sub image to be displayed including an image of a time counted down in accordance with a progress of a sub-image signal reproduction. Furthermore it provides an image signal transmitting apparatus for repeatedly transmitting a main-image signal and a sub-image signal one after the other by utilizing such optical disc, the image signal transmitting apparatus comprising a image signal reproduction device for reproducing the main-image signal and the sub-image signal, a cycle time memory for memorizing a main-image signal transmission cycle, and a control device for obtaining a time difference between the cycle and time required for the main-image signal reproduction as well as control the image signal reproduction device.

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: A pay-channel transmission system for a CATV has an optical transmission unit and an optical receiver unit. The optical transmission unit includes pay-channel television signals optically multiplexed by a .lambda..sub.1 wavelength semiconductor laser and non-pay-channel television signals optically multiplexed by a .lambda..sub.2 wavelength semiconductor laser. The optical receiver unit includes an optical filter for filtering the .lambda..sub.1 wavelength data. Thus, a non-subscriber having the optical filter is prevented from receiving the pay-channel television signals, and a subscriber having no optical filter is able to receive both the pay-channel television signals and non-pay-channel television signals.

Abstract: There is provided a method of multiplexing digital signals which includes multiplexing serial digital signals of a plurality of channels having a given transmission rate and each of which has frame synchronizing signals to a single serial signal, converting signals excluding the frame synchronizing signals of one selected channel to a format which allows inverse-conversion and which does not allow detection of the frame synchronizing signals and using the frame synchronizing signals of the one selected channel as frame synchronizing signals of the single serial signal. There is also provided apparatus for performing the method which includes circuitry for the steps referred to above.