Abstract: The I phase modulator modulates a phase based on the bias voltage in which a first modulation signal and a first pilot signal are inherent and the Q phase modulator modulates a phase based on the bias voltage in which a second pilot signal different from the first pilot signal and a second modulation signal are inherent. A time-average power synchronous detection unit detects an optical power at a timing at which the positivity and negativity of the voltages of both pilot signals become the same, and an optical power when the positivity and negativity of the voltages of both pilot signals are opposite. The bias voltage control unit controls the bias voltage so that the difference between both the optical powers becomes small based on the detection result of the time-average power synchronous detection unit.

Abstract: An optical transceiver has a projection covering member that can suppress EMI noise radiated from a pig-tail part. An elastic covering member covers a projection which includes an optical coupler of an optical sub assembly. The covering member is made of a conductive elastic material having a predetermined resistivity. At least a part of an outer circumference surface of the elastic covering member comes into intimate contact with an outer periphery of a conductive opening part of a case for the optical transceiver while an inner circumference surface of the elastic covering member comes into intimate contact with the projection.

Abstract: To achieve a size-reduction of an optical module having a circuit that generates a high-frequency clock signal for controlling optical modulation by an optical modulator and to suppress radiation of electromagnetic waves from the optical module. A through-hole via is formed on a multilayer printed circuit board so as to be insulated from a plurality of grounded wiring layers by an anti-pad. A coaxial connector and an intensity modulation control IC that generates a high-frequency clock signal are provided on the multilayer printed circuit board. The high-frequency clock signal is input to the coaxial connector through a micro-strip line formed on the multilayer printed circuit board. An open stub connected to the through-hole via is provided on a wiring layer between a first wiring layer and a second wiring layer among the plurality of wiring layers.

Abstract: When designing a demodulator for a DPSK-modulated signal, it is required that optical phase modulation is performed fast and the demodulator has a long lifetime. To achieve this object, a delay line interferometer inside the demodulator performs adjustment of phase difference between two split lights caused to interfere, using a first optical phase modulation unit such as a Piezo actuator and a second optical phase modulation unit such as a heating element that operates slower in modulation speed than the first optical phase modulation unit and is slower in deterioration speed.

Abstract: To reduce emission of an unintentional electromagnetic wave even if a frequency of a clock signal being output is high, a printed circuit board (10) includes: a substrate (101); signal output circuits (102 and 103) formed on the substrate (101), for outputting a clock signal; power supply wirings (109 and 110) for connecting the signal output circuits (102 and 103) and a power source; and trap filters (107 and 108) provided to the power supply wirings (109 and 110), for attenuating a frequency component corresponding to a frequency of the clock signal.

Abstract: Provided are an optical transceiver and a projection covering member that can suppress EMI noise radiated from a pig-tail part. An elastic covering member for covering a projection which includes an optical coupler of an optical sub assembly is made of a conductive elastic material having predetermined resistivity. At least a part of an outer circumference surface of the elastic covering member comes into intimate contact with an outer periphery of a conductive opening part of a case while an inner circumference surface of the elastic covering member contacts with the projection.

Abstract: A laser light source outputs a virtually linearly-polarized light beam that has plural mode components arranged at an interval of an almost equal angular frequency. A polarization dispersion device is connected to the laser light source in such a way that a polarization axis of the polarization dispersion device is at 45° with respect to a polarization axis of the light beam output from the laser light source. This polarization dispersion device effects on the light beam output from the laser light source a polarization mode dispersion that is not in the vicinity of (2?/??), where ?? is a mode interval angular frequency.

Abstract: An optical fiber propagates and amplifies a second signal light that is a wavelength-multiplexed signal of a first signal light of a plurality of wavelengths and a reference light that is out of a wavelength range of amplification. An excitation light source outputs an excitation light for amplifying the second signal light. A beam splitter splits a portion of the second signal light into the first signal light and the reference light. A signal light level detecting unit detects a level of the first signal light. A reference light level detecting unit detects a level of the reference light. A signal level setting unit calculates a target value for constantly maintaining a Raman gain, and controls the output level of the excitation light in such a way that the first signal level matches with the target value.

Abstract: An optical fiber propagates and amplifies a second signal light that is a wavelength-multiplexed signal of a first signal light of a plurality of wavelengths and a reference light that is out of a wavelength range of amplification. An excitation light source outputs an excitation light for amplifying the second signal light. A beam splitter splits a portion of the second signal light into the first signal light and the reference light. A signal light level detecting unit detects a level of the first signal light. A reference light level detecting unit detects a level of the reference light. A signal level setting unit calculates a target value for constantly maintaining a Raman gain, and controls the output level of the excitation light in such a way that the first signal level matches with the target value.

Abstract: In an non-polarized pump light source (5), a laser light source (1) transmits a virtually linearly-polarized light beam that has plural mode components arranged at an interval of an almost equal angular frequency. The transmitted light beam of the laser light source (1) is connected with a polarization dispersion device (3) in such a way that the polarization axes of the transmitted light beam and the polarization dispersion device (3) meet to form a 45° angle. In the polarization dispersion device (3), when the mode interval angular frequency is considered to be &Dgr;&ohgr;, the polarization mode dispersion that is not in the vicinity of (2&pgr;/&Dgr;&ohgr;) is effected on the incident light from the laser light source (1). As a result, though the optical path difference between the two polarization modes becomes less than the coherent length, an effectively non-polarizing light is transmitted as a pump light from the non-polarized pump light source (5).