Abstract: An optical system includes an optical module having an optical reception unit that receives input light and output an electric signal related to received input light, and a processing unit having an identification unit that performs identification processing based on a threshold value on the electric signal input via a reception signal path from the optical reception unit. The optical module includes a threshold calculation unit that calculates the threshold value based on the electric signal from the optical reception unit and a signal path characteristic of the reception signal path from the optical reception unit to the identification unit, and the identification unit of the processing unit performs the identification processing based on the threshold value calculated by the threshold calculation unit. Thereby, the threshold value is optimized when the identifier is provided in the unit as a connection destination of the optical module.

Abstract: According to an optical-receiving apparatus including an APD converting input light into an electric signal and a bias-voltage-control method used for the optical-receiving apparatus, a multiplication factor appropriate for the APD is predetermined and a multiplication factor used for the APD can be maintained at the level of the predetermined multiplication factor at all times according to a change in the ambient temperature of the APD so that the intensity of input light-transmitted to the APD can be monitored with accuracy. The optical-receiving apparatus further includes a bias circuit generating a bias voltage applied to the APD based on a control signal, a temperature-monitor circuit monitoring the ambient temperature, and an operating circuit that stores data on the predetermined multiplication factor and that controls the bias circuit so that the multiplication factor corresponding to the monitored temperature becomes the predetermined multiplication factor.

Abstract: A module is configured to be attached to a cage. A handle is rotatable about a rotation shaft between an accommodated position where the module is mounted to the cage and a withdrawal position where the module can be withdrawn from the cage. A resiliently-bendable tongue piece performs engagement and disengagement between the module and the cage. A notch portion is provided to the tongue piece. A press portion is provided to the handle on a circumference having a center located on the rotation shaft of the handle, the press portion configured to contact with the notch portion when the handle is at the accommodated position. A cam rotatable with the handle so as to resiliently bend the tongue piece.

Abstract: An optical system includes an optical module having an optical reception unit that receives input light and output an electric signal related to received input light, and a processing unit having an identification unit that performs identification processing based on a threshold value on the electric signal input via a reception signal path from the optical reception unit. The optical module includes a threshold calculation unit that calculates the threshold value based on the electric signal from the optical reception unit and a signal path characteristic of the reception signal path from the optical reception unit to the identification unit, and the identification unit of the processing unit performs the identification processing based on the threshold value calculated by the threshold calculation unit. Thereby, the threshold value is optimized when the identifier is provided in the unit as a connection destination of the optical module.

Abstract: A module is configured to be attached to a cage. A handle is rotatable about a rotation shaft between an accommodated position where the module is mounted to the cage and a withdrawal position where the module can be withdrawn from the cage. A resiliently-bendable tongue piece performs engagement and disengagement between the module and the cage. A notch portion is provided to the tongue piece. A press portion is provided to the handle on a circumference having a center located on the rotation shaft of the handle, the press portion configured to contact with the notch portion when the handle is at the accommodated position. A cam rotatable with the handle so as to resiliently bend the tongue piece.

Abstract: According to an optical-receiving apparatus including an APD converting input light into an electric signal and a bias-voltage-control method used for the optical-receiving apparatus, a multiplication factor appropriate for the APD is predetermined and a multiplication factor used for the APD can be maintained at the level of the predetermined multiplication factor at all times according to a change in the ambient temperature of the APD so that the intensity of input light-transmitted to the APD can be monitored with accuracy. The optical-receiving apparatus further includes a bias circuit generating a bias voltage applied to the APD based on a control signal, a temperature-monitor circuit monitoring the ambient temperature, and an operating circuit that stores data on the predetermined multiplication factor and that controls the bias circuit so that the multiplication factor corresponding to the monitored temperature becomes the predetermined multiplication factor.

Abstract: An optical transmitter comprises an amplitude modulation unit performing amplitude modulation of only a one-side amplitude of a main signal with a low-frequency signal having a predetermined frequency. An optical modulator receives an input signal generated after the one-side amplitude modulation, and modulates an incoming light in response to the received signal in accordance with a predetermined modulation-characteristic curve to output an optical output signal. An operating point control unit applies a predetermined bias voltage to the optical modulator to control a level of the input signal substantially applied to the modulation-characteristic curve so that the one-side amplitude of the main signal is applied to a minimum portion of the modulation-characteristic curve of the optical modulator.

Abstract: An optical receiving device which is improved in the accuracy of optical input interruption detection as well as in the alarm response and thus is capable of high-quality detection of interruption of the optical input. A light receiving element receives an optical signal and converts it into an electrical signal. A bias control section stabilizes a bias voltage applied to the light receiving element against variations in temperature and power supply. An optical input interruption protection section protects the light receiving element using a protective voltage so that the light receiving element may not be broken due to an excessive rise of the bias voltage when the optical input is interrupted. An alarm issuing section monitors the photocurrent of the light receiving element and issues an alarm on detecting an interruption of the optical input when the bias voltage and the protective voltage become equal to each other.

Abstract: An optical transmitter comprises an amplitude modulation unit performing amplitude modulation of only a one-side amplitude of a main signal with a low-frequency signal having a predetermined frequency. An optical modulator receives an input signal generated after the one-side amplitude modulation, and modulates an incoming light in response to the received signal in accordance with a predetermined modulation-characteristic curve to output an optical output signal. An operating point control unit applies a predetermined bias voltage to the optical modulator to control a level of the input signal substantially applied to the modulation-characteristic curve so that the one-side amplitude of the main signal is applied to a minimum portion of the modulation-characteristic curve of the optical modulator.

Abstract: An optical receiving device which is improved in the accuracy of optical input interruption detection as well as in the alarm response and thus is capable of high-quality detection of interruption of the optical input. A light receiving element receives an optical signal and converts same into an electrical signal. A bias control section stabilizes a bias voltage applied to the light receiving element against variations in temperature and power supply. An optical input interruption protection section protects the light receiving element by means of a protective voltage so that the light receiving element may not be broken due to an excessive rise of the bias voltage when the optical input is interrupted. An alarm issuing section monitors the photocurrent of the light receiving element and issues an alarm on detecting an interruption of the optical input when the bias voltage and the protective voltage become equal to each other.

Abstract: Disclosed is a laser diode protecting circuit adapted to prevent a laser diode from producing an excessive emission when the laser diode is driven at low temperature, thereby assuring that the laser diode will not be damaged or degraded in terms of its characteristic. When the laser diode is started at low temperature, a laser diode protecting circuit has a power monitor circuit for monitoring backward power of the laser diode and a laser diode current limiting circuit for limiting the laser diode current when the backward power becomes equal to the set power. When the laser diode temperature subsequently rises and the backward power falls below the set power, an automatic current control circuit performs automatic current control in such a manner that the laser diode current attains a set current value.

Abstract: An optical transmitter, a terminal-station apparatus having the optical transmitter, and an optical communication system employing the terminal-station apparatus. The optical transmitter comprises: a light-source unit for generating an optical signal; a monitor unit for monitoring a parameter depending on the wavelength of the optical signal; a judgment unit for determining as to whether or not the monitored parameter satisfies a predetermined condition; and a shut-off unit for shutting off the optical signal in case the monitored parameter does not satisfy the predetermined condition. By using the optical transmitter, it can be possible to prevent crosstalk from occurring between WDM (Wavelength Division Multiplexing) channels in the optical communication system.

Abstract: An optical transmitter and an optical communication system, each for providing a good transmission characteristic of a main signal and allowing suppression of SBS (stimulated Brillouin scattering). The optical transmitter comprises a light source for outputting a carrier beam, an optical modulator for modulating the carrier beam based on a main signal and sending out an optical signal into an optical fiber transmission line, an oscillator for outputting a low frequency signal, a first circuit for frequency or phase modulating the carrier beam based on the low frequency signal, and a second circuit for superposing an opposite phase signal having a phase opposite to that of the low frequency signal with the main signal and supplying a resulting signal to the optical modulator.

Abstract: A Peltier control circuit detects a temperature of a device combined with a Peltier device and controls a current flowing through the Peltier device so as to keep the temperature of the device at a predetermined value. The circuit has a temperature sensing section for detecting the temperature of a device, a comparing section for comparing a temperature detection value with a predetermined temperature reference value, a limiting section for providing a comparison output with the limitation of a current flowing through the Peltier device and providing the limitation with a predetermined temperature characteristics, and a driving section for providing the Peltier device with an input or output driving current in accordance with the comparison output via the limiting section.

Abstract: An optical transmitter comprises a first unit for generating an optical signal having a bandwidth given by a main signal, a second unit modulating the optical signal according to a control signal to extend the bandwidth of the optical signal, a third unit extracting backward light including SBS(stimulated Brillouin scattering) light generated in an optical fiber transmission line, and a fourth unit performing feedback control so that the power of the SBS light becomes substantially constant. Through the structure of the optical transmitter good transmission characteristics of a main signal are obtained and the suppression of the SBS is allowed.

Abstract: In a light transmitter comprises an automatic bias control circuit which automatically controls a bias for an external modulator, a part of a light output/input signal of the external modulator is branched to detect an electrical monitor signal and a gain control signal is generated in inverse proportion to the level of the monitor signal to control the gain of the automatic bias control circuit.

Abstract: In controlling a discrimination level V.sub.1, V.sub.1 is controlled so that discrimination results based on discrimination levels V.sub.1 +.DELTA.V and V.sub.1 -.DELTA.V each become equal to the discrimination result based on the discrimination level V.sub.1. If the discrimination result based on V.sub.1 +.DELTA.V does not agree with the discrimination result based on V.sub.1, V.sub.1 is lowered, and if the discrimination result based on V.sub.1 -.DELTA.V does not agree with the discrimination result based on V.sub.1, V.sub.1 is raised. In controlling a discrimination phase .PHI..sub.1, .PHI..sub.1 is controlled so that discrimination results based on discrimination phases .PHI..sub.1 +.DELTA..PHI. and .PHI..sub.1 -.DELTA..PHI. each become equal to the discrimination result based on the discrimination phase .PHI..sub.1. If the discrimination result based on .PHI..sub.1 +.DELTA..PHI. does not agree with the discrimination result based on .PHI..sub.1, .PHI..sub.

Abstract: The optical amplifier includes a doped fiber doped with a rare earth element, a pumping light source, means for introducing signal light and pumping light into the doped fiber, detection means for detecting whether or not amplified signal light is included in light outputted from the doped fiber, and means for decreasing the intensity of the pumping light when it is detected that amplified signal light is not included. It can be possible to eliminate an influence of an optical surge arising from a characteristic of the doped fiber.

Abstract: An optical transmitter for optimizing the duty ratio of a high-speed optical transmission signal has an output unit for providing an optical output signal according to an electric signal, a monitor circuit for providing an output representative signal related to the output of the output unit, a driver for determining the logical value of each bit of an input data signal according to a reference voltage and driving the output unit according to the determination, an input signal detector for providing an input representative signal according to the input data signal, and a duty ratio controller for comparing the input and output representative signals with each other and controlling the reference voltage to the driver so that the difference between the input and output representative signals is reduced, to thereby optimize the duty ratio of the optical output signal.

Abstract: A Peltier control circuit detects a temperature of a device combined with a Peltier device and controls a current flowing through the Peltier device so as to keep the temperature of the device at a predetermined value. The circuit has a temperature sensing section for detecting the temperature of a device, a comparing section for comparing a temperature detection value with a predetermined temperature reference value, a limiting section for providing a comparison output with the limitation of a current flowing through the Peltier device and providing the limitation with a predetermined temperature characteristics, and a driving section for providing the Peltier device with an input or output driving current in accordance with the comparison output via the limiting section.