Abstract: To provide a block gain equalizer, which controls an amount of gain slope, and does not cause any loss in an optical signal. A block gain equalizer 201 branches an optical signal transmitted from an optical fiber transmission path 101N by an optical coupler 112 to take out a supervisory signal 119 by a band pass filter. An electric signal 122 after this photoelectric conversion is inputted into a gain control circuit 207 to read slope correction data for flattening the gain. The gain control circuit 207 supplies a gain control signal 208 to a semiconductor laser 204 to drive it by power which corresponds to the gain slope for flattening the gain, for pumping an erbium doped fibers 202 in accordance with a backward pumping system. Thereby, the block gain equalizer 201 is capable of flattening the frequency characteristic without any loss in optical signal. It is also possible to adjust the gain by an attenuator as required. Also, for the pumping system, various systems can be adopted.

Abstract: An optical control apparatus having an optical reflector for selectively reflecting signal light having a specific wavelength, transmitting and outputting signal light having another wavelength and a saturable absorber for transmitting and outputting the transmitted signal light when an output level of the transmitted signal light is equal to or larger than a predetermined threshold value.

Abstract: The present invention minimizes trouble and loss caused by a failure polarization scrambler.

Abstract: An optical switch with simple circuit structure and increased a response speed is disclosed. This optical switch comprises a light combiner for combining a light signal &lgr;S and a control light &lgr;C and outputting a combined signal, and a saturable absorption type optical device provided with an input port and an output port, and outputs a light signal based on the combined light signal outputted from the light combiner. When an input power of the light signal &lgr;S is at a region where a light signal applied to the saturation absorption type optical device is attenuated, the light intensity of the control signal &lgr;C is set to the OFF state, and when the input power of the light signal &lgr;S is at a region where a light signal applied to said saturation absorption type optical device transmits therethrough, the light intensity of said control signal &lgr;C is set to the ON state.

Abstract: An optical gain equalizer is provided with an erbium doped optical fiber (EDF). The gain equalizer selects two lights out of wavelength division multiplexed light, controls pumping light to EDF based upon the result of the comparison of the levels and flattens the inclination of the gain of the wavelength division multiplexed light. Another optical gain equalizer is provided with EDF and a variable attenuator. The optical gain equalizer selects two lights out of wavelength division multiplexed light and attenuates the wavelength division multiplexed light based upon the result of comparing the levels of the two lights. The power of pumping light to EDF that amplifies wavelength division multiplexed light is controlled based upon this attenuation and the inclination of the gain of the wavelength division multiplexed light is flattened.

Abstract: To provide a block gain equalizer, which controls an amount of gain slope, and does not cause any loss in an optical signal. A block equalizer 201 branches an optical signal transmitted from an optical fiber transmission path 101N by an optical coupler 112 to take out a supervisory signal 119 by a band pass filter. An electric signal 122 after this photoelectric conversion is inputted into a gain control circuit 207 to read slope correction data for flattening the gain. The gain control circuit 207 supplies a gain control signal 208 to a semiconductor laser 204 to drive it by power which corresponds to the gain slope for flattening the gain, for pumping an erbium doped fibers 202 in accordance with a backward pumping system. Thereby, the block gain equalizer 201 is capable of flattening the frequency characteristic without any loss in optical signal. It is also possible to adjust the gain by an attenuator as required. Also, for the pumping system, various systems can be adopted.

Abstract: An optical switch includes a saturable absorption type optical element provided with a saturable absorption region, and a band-block optical filter to which signal light composed of at least one wavelength light having an optical power in the absorption region of the saturable absorption type optical element and control light whose optical power is set such that a total power of the signal light and the control light comes within a transmission region of the saturable absorption type optical element and which is composed of either one of two wavelength lights different from that of the signal light are inputted and which transmits therethrough the signal light and the control light which is composed only of one of the wavelength lights and outputs the transmitted signal light and control light to the saturable absorption type-optical element. ON/OFF of the signal light is controlled by varying the wavelength of the control light.

Abstract: A cable branching unit which enables the exchange of signals through normal cables without suspending the power supply even when a short mode fault is caused in a cable branching from the cable branching unit. The cable branching unit branches a first cable into a second and a third cable and comprises a band pass filter for extracting a control signal multiplexed among signals transmitted from the first land station through the first cable, and a relay short circuits, to a ground, one or both of the cable connected to the second land station and the cable connected to the third land station, according to the control signal extracted by the band pass filter.

Abstract: In an optical branching/multiplexing apparatus, to effect harmful influence to transferring characteristic of optical signal of wavelength penetrated through an optical branching device is prevented. At the optical branching device, a specific wavelength signal is subjected to an optical-branching, while another wavelength signal with exception of the specific wavelength is penetrated in wavelength division multiplexed main input signal. Multiplexed input signal is amplified by an optical amplifier 7 with variable gain, before amplified signal is divided by a photo coupler to be applied to the optical multiplexing device and to the other hand input sides of a comparator.

Abstract: A branching system having an optical ADM, where the optical ADM comprises a first optical circulator being connected to a main signal transmission line input, a first FBG having an input which is an output of the first optical circulator, an optical isolator having an input which is an output of the first FBG, a second optical FBG having an input which is an output of the optical isolator and a second optical circulator having an input which is an output of the second FBG. With this structure, the optical amplifier is able to detect whether the branch transmission line is being cut off due to obstructions. Thus, even if a detour route of light being branched off at the optical circulator is generated, for the light is intercepted by the optical isolator, there should be no generation of a loop. Thus, deterioration on the transmission feature of the main transmission line can be prevented.

Abstract: It is the object of the invention to provide a wavelength stability circuit used in a WDM optical transmission system, in which the spacing of wavelengths between adjacent optical signals are always so controlled as to keep a prescribed value. The two optical signals with different wavelengths are respectively generated by two laser diodes and multiplexed by an optical coupler. A portion of the multiplexed optical signals is supplied to an optical heterodyne detection circuit, where the spacing of the wavelengths between the two optical signals is detected. The spacing of the wavelengths between the optical signals is converted into an electrical signal by an O/E converter and a frequency counter, and the electrical signal is compared with a standard voltage in a comparator.