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: M wavelength separating sections receive multiplexed optical signals each having N kinds of wavelengths different. Each of the multiplexed optical signals are separated into N optical signals. M relays conduct optical reproduction and relay to convert each of the N optical signals into electric signals and then produce optical signals modulated with desired optical wavelengths. A refill section mutually refills M sets of the reproduced and relayed optical signals. A focusing section focuses the M sets of optical signals refilled in the refill section. A light source supplies input lights having desired wavelengths, which lights are modulated in the relays. The light source includes N light sources outputting N kinds of optical wavelengths. A multiplexer/brancher multiplexes the lights from the N light sources to produce a multiplexed light and branches the multiplexed light into M×N distributed lights. M wavelength filters distribuitively receive N distributed lights of the M×N distributed lights.

Abstract: In an optical amplifier for use in, for example, a wavelength multiplexing optical communication system, in order to allow an excitation light source to be enlargeable or removable in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation, there are included an optical amplifying section (2) for amplifying and outputting inputted signal light, a plurality of excitation light sources (3, 4) and an excitation light source control section (5) for controlling operations of the excitation light sources (3, 4), wherein the excitation light sources are composed of a main excitation light source (3) and an auxiliary excitation light source (4), and the excitation light source control section (5) is equipped with a control section (7) which, when the number of channels in the inputted signal light is equal to or less than a predetermined number of channels, executes control whereby the main excitation light source (3) supplies excitation

Abstract: A light branching/inserting apparatus which can easily control light signal wavelengths, and which can branch, insert or transmit light signals having an optional wavelength and optional multiplexed number, by using a wavelength selection filter utilizing acousto-optic effects.

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: 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: In an optical amplifier for use in, for example, a wavelength multiplexing optical communication system, in order to allow an excitation light source to be enlargeable or removable in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation, there are included an optical amplifying section (2) for amplifying and outputting inputted signal light, a plurality of excitation light sources (3, 4) and an excitation light source control section (5) for controlling operations of the excitation light sources (3, 4), wherein the excitation light sources are composed of a main excitation light source (3) and an auxiliary excitation light source (4), and the excitation light source control section (5) is equipped with a control section (7) which, when the number of channels in the inputted signal light is equal to or less than a predetermined number of channels, executes control whereby the main excitation light source (3) supplies excitation

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: 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: 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: The invention provides a remote control device of an acousto-optic tunable filter, which comprises an acousto-optic tunable filter interpolated in an optical transmission line, capable of controlling an output state of an input light signal by being supplied with a surface acoustic wave control signal through a control port; a surface acoustic wave control signal source to generate the surface acoustic wave control signal, which is provided at a remote place from the acousto-optic tunable filter; and a control unit that receives an information of the surface acoustic wave control signal from the surface acoustic wave control signal source through remote transmission means, and supplies the surface acoustic wave control signal to the control port of the acousto-optic tunable filter.

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 rare earth element doped fiber forming an optical amplifier is pumped with a plurality of pumping lights to prevent drop of the inversion population ratio in the length direction of the rare earth element doped fiber.

Abstract: An optical wavelength selective control apparatus has a plurality of wavelength selective optical filters connected to one another to extract an optical signal at an arbitrary wavelength from wavelength division multiplexed signals according to a frequency signal for selecting a wavelength, and a frequency oscillator for outputting a signal at a frequency corresponding to a wavelength of the optical signal to be extracted to each of the wavelength selective optical filters as a frequency signal for selecting a wavelength, thereby performing a wavelength selecting process highly accurately with the wavelength selective optical filter.

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 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: An optical transmitting device which combines a plurality of signal lights, each having a different, corresponding, frequency, into a wavelength division multiplexed signal light. The frequencies are spaced apart from each other in a manner with eliminates the effects of four-wave mixing (FWM). More specifically, the difference in frequencies of any pair-combination of the signal lights is different from the difference in frequencies between any other pair-combination of the signal lights. Moreover, the plurality of signal lights include n signal lights having respectively corresponding frequencies f1 through fn arranged in order from f1 to fn along a frequency spectrum, where frequencies f1 through fn−1 have respectively corresponding integer spacing coefficients m1 through mn−1, and frequencies fi and fi+1 are separated by mi·&Dgr;fS−F, where i=1 to (n−1) and &Dgr;fS−F is a unit of spacing between frequencies.

Abstract: A remote control device of an acousto-optic tunable filter includes an acousto-optic tunable filter, a surface acoustic wave control signal source and a control unit. The acousto-optic tunable filter receives an output light signals from an optical transmission line and has a control port to control and outputs state of the light signal received from the optical transmission line, based on a surface acoustic wave control signal received through the control port. The surface acoustic wave control signal source generates the surface acoustic wave control signal and is provided at a remote place from the acousto-optic tunable filter. The control unit receives information regarding the surface acoustic wave control signal generated by the surface acoustic wave control signal source and supplies the surface acoustic wave control signal to the control port of the acousto-optic tunable filter.

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.