Abstract: The present invention relates to an optical cross connect unit comprising M wavelength separating sections for receiving multiplexed optical signals each having N kinds of wavelengths different from each other through M optical fibers, respectively, and for wavelength-separating each of the multiplexed optical signals into N optical signals, M optical reproduction relay sections each for conducting an optical reproduction and relay in a manner of making a conversion of each of the N optical signals, wavelength-separated in each of the wavelength separating sections, into an electric signal and then modulating it with a desired optical wavelength, a refill section for mutually refilling M sets of optical signals optically reproduced and relayed in the optical reproduction relay sections, a focusing section for focusing the M sets of optical signals refilled in the refill section, and a light source unit for supplying input lights having desired wavelengths to be modulated in the M optical reproduction relay se

Abstract: An optical amplifier of a wavelength-division multiplexing transmission system that includes a pre-stage optical amplifying unit and a post stage optical amplifying unit. The pre-stage optical amplifying unit has a rare-earth element doped optical fiber and a pump light source for inputting a pump light to the rare-earth element doped optical fiber. The post-stage optical amplifying unit has a second rare-earth element doped optical fiber and a pump light source for inputting a pump light to the second rare-earth element doped optical fiber. The pre-stage optical amplifying unit and the post-stage optical amplifying unit are optically connected by a detachable optical coupling device. In addition, a gain equalizing unit, positioned on an output side of the optical fibers, compensates for wavelength-dependency of a gain characteristic of the optical fibers.

Abstract: In an OADM system, an OADM device includes an AOTF. The AOTF can select an optional wavelength by changing the frequency of an RF signal to be applied. An optical signal having a specified wavelength can be dropped from a wavelength-multiplexed optical signal input from an input terminal, or a wavelength-multiplexed optical signal input from an add port can be multiplexed with a through optical signal. However, considering the increase in coherent cross talk, the AOTF should be exclusively used for dropping in an actual device configuration. Otherwise, a drop optical signal is branched by an optical coupler with the wavelength selected by a tributary station. Thus, the wavelength selected by the tributary station can be extracted by the AOTF from the through optical signal.

Abstract: A gain equalizer which equalizes gain versus wavelength characteristics of an optical amplifier. The gain versus wavelength characteristics of the optical amplifier include first, second and third gain peaks in a wavelength band with the second gain peak being between the first and third gain peaks. The optical amplifier amplifies an input signal in accordance with the gain versus wavelength characteristics to produce an output signal. The gain equalizer includes first, second and third optical filters having first, second and third transparency characteristics, respectively. The first, second and third transparency characteristics are periodic waveforms having different periods related to the wavelength difference between the first and third gain peaks. The second transparency characteristic is a periodic waveform having a period equal to 1/(2n) of the period of the waveform of the first transparency characteristic.

Abstract: The output level of pumping light supplied from a pumping light source is varied using a variable attenuator, which is controlled by a variable attenuator driver circuit. By separating a portion containing the pumping light source from a portion containing an amplification medium, it becomes possible to prevent heat emitted by the pumping light source from adversely affecting the amplification medium. By arranging the portion containing the pumping light source such that a pumping light source or sources can be added when necessary, optical transmission system requirements of having more pumping light sources for system upgrade can be accommodated readily. By packaging portions containing amplification media, an optical amplifier can be made small.

Abstract: The output level of pumping light supplied from a pumping light source is varied using a variable attenuator, which is controlled by a variable attenuator driver circuit. By separating a portion containing the pumping light source from a portion containing an amplification medium, it becomes possible to prevent heat emitted by the pumping light source from adversely affecting the amplification medium. By arranging the portion containing the pumping light source such that a pumping light source or sources can be added when necessary, optical transmission system requirements of having more pumping light sources for system upgrade can be accommodated readily. By packaging portions containing amplification media, an optical amplifier can be made small.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: The present invention relates to a method for transmitting a supervisory optical signal. A first optical amplifier for a first band (e.g., a conventional band: C band) determining a noise characteristic and a gain efficiency is provided. A second optical amplifier for a second band (e.g., a long wavelength band: L band) determining a noise characteristic and a gain efficiency is provided. The supervisory optical signal is processed in relation to one of the first and second optical amplifiers superior in at least one of the noise characteristic and the gain efficiency to the other. According to this method, undue degradation in the noise characteristic and the gain efficiency can be prevented to maintain a good transmission quality of a main signal.

Abstract: The present invention relates to an optical cross connect unit comprising M wavelength separating sections for receiving multiplexed optical signals each having N kinds of wavelengths different from each other through M optical fibers, respectively, and for wavelength-separating each of the multiplexed optical signals into N optical signals, M optical reproduction relay sections each for conducting an optical reproduction and relay in a manner of making a conversion of each of the N optical signals, wavelength-separated in each of the wavelength separating sections, into an electric signal and then modulating it with a desired optical wavelength, a refill section for mutually refilling M sets of optical signals optically reproduced and relayed in the optical reproduction relay sections, a focusing section for focusing the M sets of optical signals refilled in the refill section, and a light source unit for supplying input lights having desired wavelengths to be modulated in the M optical reproduction relay se

Abstract: This invention discloses an optical transmission device used for bi-directional optical communications. The optical transmission device comprises a uni-directional optical signal processing unit for performing specified optical signal processing for optical signals transmitted in a single direction and a uni-direction/bi-direction changing unit for unifying the flows of clockwise and counterclockwise optical signals in a single direction, inputting these flow-unified optical signals to the uni-directional optical signal processing unit and dividing the flow of optical signals from the uni-directional optical signal processing unit between clockwise and counterclockwise directions. Bi-directional wavelength-division multiplexing optical communications can be performed by unifying the transmission routes (flows) of optical signals transmitted in two ways in a single direction and using the existing optical transmission device for uni-directional optical communications.

Abstract: The output level of pumping light supplied from a pumping light source is varied using a variable attenuator, which is controlled by a variable attenuator driver circuit. By separating a portion containing the pumping light source from a portion containing an amplification medium, it becomes possible to prevent heat emitted by the pumping light source from adversely affecting the amplification medium. By arranging the portion containing the pumping light source such that a pumping light source or sources can be added when necessary, optical transmission system requirements of having more pumping light sources for system upgrade can be accommodated readily. By packaging portions containing amplification media, an optical amplifier can be made small.

Abstract: A computer-controlled optical amplifying apparatus, which includes an optical amplifying unit including an optical amplifying medium and an optical amplifying control unit controlling the optical amplifying unit under the control of a computer. This optical amplifying control unit is constituted by a status monitoring unit for monitoring the status, an optical output control unit for controlling the optical amplifying unit in accordance with the result of monitoring of status; and a status restoring unit for initializing the control status of the optical output control unit by initializing the computer when detecting an occurrence of the abnormal status by the result of monitoring of status and restoring the optical output control unit to the control status before occurrence of the related abnormal status within a relaxation time inherent in the optical amplifying medium occurring accompanied with this initialization.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: Multi-wavelength light is transmitted from a sending station to a receiving station. An erbium-doped optical fiber is installed on the transmission path that connects the sending station and the receiving station. Pump light is supplied from a light source installed in the receiving station to the erbium-doped optical fiber. In the receiving station, the multi-wavelength light is decomposed into the component wavelength signals. The light level of each component wavelength signal is detected, and the power of the light emitted by the light source is controlled so as to equalize those light levels.

Abstract: Disclosed is a bidirectional optical amplifier circuit having a function that achieves reliable detection of reflections from an exposed end at low cost. Received optical power is detected; if the detected power is less than a prescribed discrimination level, it is then decided that the detected light is not received signal light but transmitted signal light sent in the direction opposite from it and reflected at an exposed fiber end, and the bias current for a laser diode in the opposite path is reduced to lower the optical output level of an EDF.

Abstract: A computer-controlled optical amplifying apparatus, which includes an optical amplifying unit including an optical amplifying medium and an optical amplifying control unit controlling the optical amplifying unit under the control of a computer. This optical amplifying control unit is constituted by a status monitoring unit for monitoring the status, an optical output control unit for controlling the optical amplifying unit in accordance with the result of monitoring of status; and a status restoring unit for initializing the control status of the optical output control unit by initializing the computer when detecting an occurrence of the abnormal status by the result of monitoring of status and restoring the optical output control unit to the control status before occurrence of the related abnormal status within a relaxation time inherent in the optical amplifying medium occurring accompanied with this initialization.

Abstract: The invention provides an optical transmission method and apparatus suitable for use with a terminal station apparatus for an optical communication system for a very long distance of up to several thousands kilometers across an ocean as well as an optical amplification method and apparatus suitable for use with a repeater for an optical communication system. The methods and apparatus are improved in that the excessive loss in an optical amplifier and the variation of the branching ratio are suppressed to suppress the variation of the gain to suppress the polarization dependency of the loss or the gain on a transmission line of the optical communication system. The optical transmission apparatus comprises a depolarized light source for outputting depolarized light, and an external modulator for modulating light from the depolarized light source.

Abstract: In a light signal reception apparatus having a light surge eliminating function and provided in an optical transmission system, the apparatus of the present invention can effectively eliminate a light surge accidentally included in a light signal. The apparatus includes: an optical amplifying unit for receiving a light signal and amplifying it to a predetermined level; an optical filtering unit operatively connected to the optical amplifying unit for eliminating the light surge and passing through the light signal; an opto-electrical converting unit operatively connected to the optical filtering unit for converting the light signal to an electrical signal; and a monitoring unit operatively connected to the optical amplifying unit for monitoring a fluctuation of the light signal, and controlling a transmission wavelength characteristic of the optical filtering unit or a wavelength of the light signal in order to eliminate the light surge.

Abstract: A heterodyne receiver including a frequency discriminator adapted such that a signal to be subjected to frequency discrimination is divided into two signals and mixed together after one of the divided signals has been given a delay time, and additionally provided with a filter, of which a cutoff frequency is determined according to the delay time, disposed in the front stage. This results in both improvement of accuracy in frequency identification and expansion of the capture range.