Abstract: The present invention has an object to obtain an optical signal quality supervisory device that supervises the quality of an optical signal simply, efficiently and with high accuracy without inviting an increase in cost, an increase in circuit scale and increase in power consumption. The bit rate of the optical supervisory channel is made lower than the bit rate of the optical main channel that is transmitted over an optical communication system, but the reception electric band width of a receiver that receives the optical supervisory channel is made equal to or wider than the reception electric band width of a receiver that receives the optical main channel. Also, the optical supervisory channel is made up of an SOH (section over head) frame to detect an error of the BIP (bit interleaved parity) byte of SOH, thereby supervising the quality of the optical communication system, in particular, the light wave network.

Abstract: Detection of an optical pulse position uses an optical pulse string with a determined repetitive ratio and an electric clock signal with a same frequency as the repetitive ratio of the optical pulse string. A phase of the electric clock signal oscillator is shifted and supplied to an optical modulator. The optical modulator modulates the optical pulse string based on the electric clock signal and outputs a modulated optical signal. A photo detector converts the modulated optical signal output from the optical modulator to an electric signal. The phase shift amount of the electric clock signal is controlled to maximize an output from the photo detector. Additionally, a dither signal may be used in the control of the phase shift, more than the optical modulator may be employed, and/or more than color light source may be employed. The use of at least one of feed forward and feedback control provided by maximizing an output of the photo detector allows an optical pulse having a short width to be realized.

Abstract: An optical switching system is implemented by providing a transmitting section with a preparatory transmitted optical signal selector and a working transmitted optical signal splitter, which are each implemented by a 1×2 optical space switch, and by providing a receiving section with a receiving optical switch which is implemented by a 2×2 optical space switch, and with a preparatory receiving optical gate which is implemented by a 1×2 optical space switch. This makes it possible to switch between the working system and preparatory system without employing any 4×4 optical space switch, thereby implementing a practical optical switching system without causing such problems as communication interruption during maintenance or impairment of transmission path working efficiency.

Abstract: A dispersion compensation device comprises a chirped grating, and a first optical unit for guiding at least a lightwave signal with a wavelength of &lgr;i that needs a positive dispersion compensation and is applied thereto to one end portion of the chirped grating whose grating pitch is shorter, and for furnishing light reflected by the chirped grating to outside the device. The device further comprises a second optical unit for guiding at least a lightwave signal with a wavelength of &lgr;i that needs a negative dispersion compensation and is applied thereto to another end portion of the chirped grating whose grating pitch is longer, and for furnishing light reflected by the chirped grating to outside the device. Both the first and second optical units can be either optical circulators or optical couplers.

Abstract: Detection of an optical pulse position uses an optical pulse string with a determined repetitive ratio and an electric clock signal with a same frequency as the repetitive ratio of the optical pulse string. A phase of the electric clock signal oscillator is shifted and supplied to an optical modulator. The optical modulator modulates the optical pulse string based on the electric clock signal and outputs a modulated optical signal. A photo detector converts the modulated optical signal output from the optical modulator to an electric signal. The phase shift amount of the electric clock signal is controlled to maximize an output from the photo detector. Additionally, a dither signal may be used in the control of the phase shift, more than the optical modulator may be employed, and/or more than color light source may be employed. The use of at least one of feed forward and feedback control provided by maximizing an output of the photo detector allows an optical pulse having a short width to be realized.

Abstract: Detection of an optical pulse position uses an optical pulse string with a determined repetitive ratio and an electric clock signal with a same frequency as the repetitive ratio of the optical pulse string. A phase of the electric clock signal oscillator is shifted and supplied to an optical modulator. The optical modulator modulates the optical pulse string based on the electric clock signal and outputs a modulated optical signal. A photo detector converts the modulated optical signal output from the optical modulator to an electric signal. The phase shift amount of the electric clock signal is controlled to maximize an output from the photo detector. Additionally, a dither signal may be used in the control of the phase shift, more than the optical modulator may be employed, and/or more than color light source may be employed. The use of at least one of feed forward and feedback control provided by maximizing an output of the photo detector allows an optical pulse having a short width to be realized.

Abstract: An optical switch includes a light emitter for emitting light and light receivers. A reflector is used for changing a path of light emitted from the light emitter. The reflector is held by a permanent magnet having first and second magnetic poles of opposite polarities. A supporting member is provided for the reflector and the first permanent magnet so that the reflector and the first permanent magnet can move between a first position and a second position. In the first position, the reflector and the first permanent magnet interact so the emitted light travels into one light receiver of the light receivers. On the other hand, in the second position, the reflector and the first permanent magnet interact so the emitted light travels into another of the light receivers. The switch further includes an electromagnet for generating first and second magnetic fields selectively for moving the reflector and the first permanent magnet between the first and second positions.

Abstract: When an intensity modulating operation and a phase modulating operation are carried out by employing a 2-electrode MachZehnder type optical modulator preferably a LN-MZ type optical modulator, a drive signal of this 2-electrode LN-MZ type optical modulator is produced from an intensity modulation signal and a phase modulation signal with a low loss and a simple arrangement.

Abstract: A light emitting control apparatus comprises a light emitting element which emits a light when an input electrical signal is converted into a light signal, a monitoring circuit which monitors the output level of the light emitting element, a sample-and-hold circuit which detects a peak value and is put into the sample mode when data of the monitoring circuit is in the mark state showing voltage and which is in turn put into the hold mode when the data is in the space state showing no voltage, and an amplifier which accomplishes negative feedback control of the output level of the light emitting element by using the output of the sample-and-hold circuit. Thus, the apparatus can quickly respond to a change of the input state and stabilize the output level of the light emitting element for a long time.

Abstract: A branch circuit is formed by forming an optical filter by means of connecting a wavelength selective reflector to between two units of directional coupler and further assembling three units of the optical filter.

Abstract: A branch circuit is formed by forming an optical filter by means of connecting a wavelength selective reflector to between two units of directional coupler and further assembling three units of the optical filter.

Abstract: A branch circuit is formed by forming an optical filter by means of connecting a wavelength selective reflector to between two units of directional coupler and further assembling three units of the optical filter.

Abstract: Reflectors each having a reflectance peak wavelength within a band of the wavelength characteristics of a laser amplification factor in the unsaturated state of each light source for excitation are provided between light sources for excitation and an optical coupler, and stable wavelength locking is effected by returning a portion of a small portion of excited light reflected by the reflectors into the light sources for excited light.

Abstract: This invention provides an optical amplifier which has low noise characteristics for a wide range of input signal electric power. The optical amplifier has a plurality of cascaded optical amplifying units, a signal level detector, and a pump-source controller. The pump-source controller changes controlling objects from a pump-source corresponding to a first one of the optical amplifying units to a pump-source corresponding to a second one of the optical amplifying units according to a detection level of the signal level detector from a low level to a high level. When the detection level is outside of a control object range, the optical amplifier controls an output from the pump-source to stabilize. When the detection level is within the control object range, the optical amplifier controls an output from a pump-source of each of optical amplifying units according to the detection level.

Abstract: A light amplifying apparatus adopting a redundant structure. Optical isolators 13, 14 are inserted between pump light sources 1, 2 and a photocoupler 4 so as to prevent injection locking, thereby preventing fluctuation of pump power.In another embodiment, optical fibers 15 adequately longer than the coherence length of the excitation light waves output from the pump light sources are provided. In still another embodiment, the frequency of the driving current for the pump light sources is modulated. In a further embodiment, wave plates 20, 21 are provided so as to circularly polarize the light waves output from the pump light sources clockwise and counterclockwise.

Abstract: An optical fiber which amplifies an input signal by a pump source, a compensation-signal source which injects a compensation-signal propagating contra-directionally with respect to the input signal Into the optical fiber, a gain detector which measures a spontaneous emission light of the pump source at an input side of the optical fiber and a compensation-signal source controller which controls output of the compensation-signal source based on output of the gain detector are provided. In addition, a coupler and a wavelength selective reflector which reflects a light of the same wavelength as the compensation-signal selectively, are provided at the input side of the optical fiber.

Abstract: An optical-fiber light amplifier using rare-earth-doped optical fibers. The light amplifier combines first and second excitation light from first and second sources to form combined excitation light and divides the combined excitation light for inverted distribution to both two optical fibers. The light entered one optical fiber and that entered the other optical fiber are polarized so as to be perpendicular to each other so that fluctuation of output level is prevented without mutual interference. Alternatively the first excitation light and the second excitation light may have different wavelengths; also in this case, fluctuation of level is prevented without any interference.

Abstract: Multiplex communication system for transmitting different signals through a plurality of channels comprises a transmitter and a receiver. The transmitter comprises a transmitting section for multiplexing and transmitting the different signals through the plurality of channels, and an adder for adding channel identification signals for identifying the respective channels to the signals to be transmitted through the respective channels. The receiver comprises a setting device for setting a desired channel, a detector for detecting the channel identification signals from the signals transmitted from the transmitter, and a channel selector for selecting the channel signal preset by the setting device in accordance with the outputs of the setting device and the detector.

Abstract: An optical-fiber light amplifier using rare-earth-doped optical fibers. The light amplifier combines first and second excitation light from first and second sources to form combined excitation light and divides the combined excitation light for inverted distribution to both two optical fibers. The light entered one optical fiber and that entered the other optical fiber are polarized so as to be perpendicular to each other so that fluctuation of output level is prevented without mutual interference. Alternatively the first excitation light and the second excitation light may have different wavelengths; also in this case, fluctuation of level is prevented without any interference.

Abstract: A optical signal from the input terminal 6a is amplified and goes through the optical fiber doped with rare earth. The excitation lights from the excitation light sources 2 and 3 are synthesized at the optical coupler 4 and outputted to the optical fiber doped with rare earth 1 through the optical coupler 5. A part of the light is branched from the optical coupler 11 to optical receiver 14 through the band pass light filter 13. The optical receiver 14 converts the received optical signal to an electrical signal and outputs it to the error signal output circuit 114. The receiving current is amplified in the error signal output circuit 114 and branched to the excitation light source output control circuits 9 and 10.