Abstract: There are provided an optical transfer characteristic measuring method and apparatus capable of measuring an optical transfer characteristic of an optical device on optical frequency axis in wide optical frequency bandwidth with high resolution. There are provided a variable wavelength sweep type light source capable of switching the wavelength of an optical signal generated therefrom stepwise and sweeping the optical frequency of the optical signal in a predetermined frequency range, and a variable wavelength reference light source capable of switching the wavelength of an optical signal generated therefrom stepwise and not capable of sweeping the optical frequency of the optical signal.

Abstract: An object of the present invention is to simplify the addition of a node. Nodes (14-1˜14-8) connect to a ring (12) through optical add/drop multiplexers (10-b 1˜10-8). A new ring (20) is constructed next to the ring (12). Disposed on the ring (20) are an optical add/drop multiplexer (28) corresponding to a to-be-added node (26) and an optical add/drop multiplexer (30) to connect the ring (20) with the ring (12). The optical add/drop multiplexer (30) connects with the node (14-5) connecting the ring (12) through a connector (32). The connector (32) mediates signals between the node (14-5) and the optical add/drop multiplexer (30) bidirectionally.

Abstract: An apparatus for monitoring and measuring condition of a plurality of optical transmission lines individually according to this invention comprises at least one reflecting means having a predetermined reflection bandwidth arranged on each of said optical transmission lines; an optical pulse tester for outputting probe pulse light having predetermined wavelength in the reflection bandwidth of said reflecting means, and analyzing the reflected light of said probe pulse light in a time domain; optical coupling means for adding said probe pulse light from said optical pulse tester and a signal light, and coupling it to each of optical transmission lines through optical dividing means, along with coupling the reflected light of said probe pulse light to said optical pulse tester; and a plurality of optical filters arranged on the input end of each of said optical transmission lines for transmitting wavelength of signal light to be transmitted on their respective optical transmission lines and the predetermined wav

Abstract: Disposing optical fiber gratings 10a each reflecting a wavelength &lgr;1 which is different from a signal wavelength &lgr;s along an optical fiber line 10 at suitable intervals and positions. The wavelength &lgr;s of signal light is not reflected by the grating 10a, but transmitted through the optical fiber line 10. An optical pulse tester 14 outputs probe pulse lights of wavelengths &lgr;0, &lgr;1, which are different from the signal wavelength &lgr;s, at slightly different times. The probe lights of the wavelengths &lgr;0, &lgr;1 are input into the optical fiber line 10 through an optical adding and dividing device 16 and transmitted through the optical fiber line 10. Reflected light of the wavelength &lgr;1 of probe light contains therein reflection pulses of the grating 10a, and each reflection pulse serves as a position reference. The probe light of the wavelength &lgr;0 does not contain reflection light of the grating 10a.

Abstract: The self-oscillation frequencies of injection-locked laser devices 5-1 through 5-M are preset to the frequency of the signal light to be transmitted by the optical add-drop device, and the self-oscillation frequencies of the injection-locked laser devices 6-1 through 6-N are preset to the frequency of the signal light to be branched by this device. Wavelength-division multiplexed signal light inputted from an input optical line 1 is split in an optical splitter 2 and inputted to the injection-locked laser devices. Signal light whose wavelength has been set for the injection-locked laser devices 5-1 through 5-M is amplified by these injection-locked laser devices 5-1 through 5-M and inputted to an optical combiner 10. Signal light whose wavelength has been set for the injection-locked laser devices 6-1 through 6-N is outputted to branching optical lines 8-1 through 8-N.

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: 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 communication system in which the degradation of the signal-to-noise-ratio during transmission is alleviated. An optical signal from an optical transmitter is propagated over a transmission line comprising optical fibers and optical amplifiers, and received by an optical receiver. The signal-to-noise ratio is improved by inserting an injection-locked laser device at a specified point on the optical transmission line, improving the transmission characteristics of the optical communication system.

Abstract: The coherent optical receiver is characterized in that it comprises a local oscillator light, source, for amplifying a local oscillator light a light combining/dividing unit, a dual balanced receiver which comprises two optical detectors, and an electrical amplifier. Therefore, the coherent optical receiver has the characteristic that the length of the non-repeating section of an optical communication system including the device and employing heterodyne detection can be increased, or the dynamic range of an optical measuring system including this receiver and employing heterodyne detection can be widened.

Abstract: An optical frequency multiplex carrier control system which permits high-accuracy, high-speed stabilization control of the frequency of an optical signal. Based on the fact that the time waveform of the output signal from scanning type Fabry-Perot which receives the output optical signal from an optical frequency multiplexer is composed of pulse signals corresponding to an optical frequency standard and spectrum multiplex carriers of the output optical signal, the time intervals between the pulse corresponding to the optical frequency standard and pulses corresponding to the spectra of a scanning signal and each multiplexed carrier are measured by a counter having a high-accuracy clock, and variations in the optical frequency scanning region of the scanning type Fabry-Perot and in each carrier frequency with respect to the optical frequency standard are detected by hardware, with high accuracy, as variations in the pulse intervals, thereby stabilizing the frequencies of the multiplexed optical carriers.

Abstract: A method of optical phase detection, in which a signal light polarized linearly and a local light emitted from a local light laser light source are combined with each other so that an in-phase component and a quadrature component, which is 90 degrees behind the local light in phase and is combined with the signal light, are taken out; and the in-phase component is demodulated while the phase of the signal light and that of the local light are synchronized with each other through the use of the in-phase component and the quadrature component, in which the signal light and the local light are separated into mutually-perpendicular P-polarized and S-polarized components by first and second polarization beam splitters; the phases of the P-polarized or S-polarized components are regulated by first and second optical phase compensation plates so that the polarized components of the signal light are kept in phase with each other, but the polarized components of the local light have a phase difference of 90 degrees be

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: In measurement method of dispersion characteristics of an optical fiber, a laser for measurement connected to one end of the fiber and variable in output light wavelength and an oscillation for modulating a measurement light signal sent out from the laser are provided. The modulation frequency of the output from the oscillator is used as an reference electric signal. A measuring light signal obtained through the modulator 8 and transmitted through the fiber is converted into an measuring electric signal. And the characteristics is measured from the phase difference between the reference electric signal and the measuring electric signal, wherein an external modulator, an optical divider and a monitoring section are provided. The modulator modulates the measuring light signal sent out from the laser and having a narrow spectral linewidth. The divider divides the output light signal from the modulator, at a prescribed ratio.

Abstract: In a controller for a semiconductor laser light source, a portion of light emitted from the source is fed back to regulate the spectral line width of the source and to regulate the oscillation frequency of the source in terms of the phase of the portion or the driving current for the source, the very small portion of the light is allowed to pass through an external resonator so as to be subjected to optical frequency discrimination by an optical frequency discriminator, the portion does not need to be divided from a communication signal light. Therefore, the communication signal light can be undergo a loss.

Abstract: A polarization diversity light receiving system using base combining is disclosed, which is arranged so that the control signal for the local oscillator laser is the sum of squared values of received signals.