Abstract: Excitation light is split into two components with mutually orthogonal polarization. One component is fed clockwise and the other component is fed counterclockwise into a polarization maintaining loop. An optical conversion generation unit including two second-order nonlinear optical media disposed on opposite sides of a half-wave plate in the loop generates up-converted light from each excitation component by second harmonic generation, and generates down-converted light from the up-converted light by spontaneous parametric down conversion. A polarization manipulation unit manipulates the polarization direction of at least one of the excitation or down-converted components. The clockwise and counterclockwise components of the down-converted light are recombined and output as quantum entangled photon pairs having substantially the same wavelength as the excitation light.

Abstract: Excitation light is split into two components with mutually orthogonal polarization. One component is fed clockwise and the other component is fed counterclockwise into a polarization maintaining loop. A second-order nonlinear optical medium disposed in the loop generates up-converted light from each excitation component by second harmonic generation, and generates down-converted light from the up-converted light by spontaneous parametric down conversion. A polarization manipulation unit manipulates the polarization direction of at least one of the excitation or down-converted components. The clockwise and counterclockwise components of the down-converted light are recombined and output as quantum entangled photon pairs having substantially the same wavelength as the excitation light. The optical components can be optimized for operation at this wavelength without the need to consider the shorter wavelength of the up-converted light.

Abstract: A CS optical pulse train generation method, which is able to change the half width of an optical pulse constituting a CS optical pulse train, and which is compact and has low power consumption. A distributed Bragg reflector semiconductor laser utilized in this method is one which is constituted comprising an optical modulation region, a gain region, a phase control region, and a distributed Bragg reflector region. Current is injected into the gain region by way of a p-side electrode and a n-side common electrode by a constant current source, forming the population inversion required for laser oscillation. Optical modulation required to manifest mode locking is carried out in the optical modulation region. A diffraction grating is formed in the distributed Bragg reflector region.

Abstract: An optical m-ary modulator includes an optical loop forming a polarization maintaining closed optical path. A loop input-output unit splits linearly polarized input signal light into a first component and a second component and feeds the first and second components into the optical loop in opposite directions. A pair of phase modulators modulate the first and second components according to respective control signals. The loop input-output unit recombines the modulated first and second components. The optical phase bias unit creates a phase difference between the first and second components so that they combine to form an m-ary modulated optical signal. Since the first and second components travel around the same optical path, when they recombine their phases are correctly aligned, making the modulator immune to environmental effects and permitting the use of high-speed optical modulation techniques.

Abstract: The present invention is an optical clock signal extraction device, comprising first conversion means and second conversion means for enabling to extract an optical clock signal without depending on the polarization direction of an input optical signal. The first conversion means comprises a first optical converter and a continuous wave light source of which wavelength is ?2, where an input optical signal of which wavelength is ?1 and continuous wave light of which wavelength is ?2 are input to the first optical converter, and an intermediate optical signal of which wavelength is ?2 is generated and output without depending on the polarization direction of the input optical signal. The second conversion means has a second optical converter, where the intermediate optical signal is input to the second optical converter, and an optical clock signal of which wavelength is ?3 is generated and output by the passive mode locking operation of the second optical converter.

Abstract: The present invention provides an optical switch in which a switching operation is not affected even when the polarization state of a control light varies. The optical switch comprises a loop-form optical waveguide loop circuit formed from an optical nonlinear medium, control light input means of phase control means for inputting the control light into the optical waveguide loop circuit, and a wavelength demultiplexing/multiplexing circuit. The optical waveguide loop circuit is constituted by an optical path formed from a first optical fiber extending from an optical demultiplexer/multiplexer to the control light input means, an optical path formed from a second optical fiber extending from the control light input means to the wavelength demultiplexing/multiplexing circuit, and an optical path formed from a fourth optical fiber extending from the wavelength demultiplexing/multiplexing circuit and returning to the optical demultiplexer/multiplexer.

Abstract: An optical modulator includes, a first polarization separation and combination portion, a second polarization separation and combination portion, a first polarization plane-maintaining optical fiber, a second polarization plane-maintaining optical fiber, a third polarization plane-maintaining optical fiber of which a first end is coupled with the second input and output terminal of the second polarization separation and combination portion, the third polarization plane-maintaining optical fiber including a first optical coupler, to which control light that is linearly polarized light is input, a fourth polarization plane-maintaining optical fiber of which a first end is coupled with the third input and output terminal of the second polarization separation and combination portion; and a first polarization plane conversion portion that optically communicates with a second end of the third polarization plane-maintaining optical fiber and a second end of the fourth polarization plane-maintaining optical fiber.

Abstract: The device is structured to have a first electric modulation signal generator, a second electric modulation signal generator, a two-mode beat light source and an optical intensity modulator. The first electric modulation signal generator generates and outputs a first electric modulation signal. The second electric modulation signal generator generates and outputs a second electric modulation signal of a same frequency as the first electric modulation signal and to which a phase difference of ? radians is provided (? is a real number satisfying 0????). The two-mode beat light source is driven by the first electric modulation signal, and generates and outputs two-mode beat light. The two-mode beat light is inputted to the optical intensity modulator, and the optical intensity modulator generates and outputs a CS optical pulse train. Light transmittance of the optical intensity modulator is modulated by the second electric modulation signal.

Abstract: To provide an optical clock signal extracting device with a simple configuration, by which an optical clock signal may be extracted without depending on the polarization direction of an input optical signal. A current is injected to a gain region 30 through an n-type common electrode 12 and a p-type electrode 24 in the gain region 30 by a constant current source 28. A reverse-bias voltage is applied by a constant voltage source 26 to a saturable absorption region 32 through the p-type electrode 12 and the n-type common electrode 72 in the saturable absorption region 32. An optical waveguide 16 in the gain region is formed with bulk crystal or a quantum well structure into which extension strain is introduced, and an optical waveguide 18 in the saturable absorption region is formed with a quantum well structure into which extension strain is introduced.

Abstract: An optical clock signal recovery apparatus includes a mode-locked semiconductor laser that generates an optical pulse train polarized in a first direction. Optical components of the apparatus transmit a component of an input optical signal polarized in a second direction, perpendicular to the first direction, into the mode-locked semiconductor laser while blocking the component of the input optical signal polarized in the first direction, and transmit light exiting the mode-locked semiconductor laser polarized in the first direction, while blocking light exiting the mode-locked semiconductor laser polarized in the second direction. The transmitted exiting light is output as a recovered optical clock signal.

Abstract: The present invention provides an optical switch in which a switching operation is not affected even when the polarization state of a control light varies. The optical switch includes a loop-form optical waveguide loop circuit formed from an optical nonlinear medium, a control light input arrangement for inputting the control light into the optical waveguide loop circuit and serving as a phase control arrangement, a wavelength demultiplexing/multiplexing circuit, and a phase bias circuit.

Abstract: An optical clock signal regeneration device, which includes a mode-locking laser element, a signal light provision component and an optical clock signal formation component, is provided. The signal light provision component includes a birefringent medium, at which a polarization group delay time between orthogonal polarization signals, which is caused by a difference in refractive indices between orthogonal optical axes, is a natural number multiple of a signal time interval of an inputted signal light, and, on the basis of orthogonal polarization signal light obtained by passing input signal light which is inputted from outside through the birefringent medium, provides at least a signal light component with a light polarization direction that matches an oscillation polarization direction of the mode-locking semiconductor laser to the mode-locking laser element.

Abstract: A CS optical pulse train generation method, which is able to change the half width of an optical pulse constituting a CS optical pulse train, and which is compact and has low power consumption. A distributed Bragg reflector semiconductor laser utilized in this method is one which is constituted comprising an optical modulation region, a gain region, a phase control region, and a distributed Bragg reflector region. Current is injected into the gain region by way of a p-side electrode and a n-side common electrode by a constant current source, forming the population inversion required for laser oscillation. Optical modulation required to manifest mode locking is carried out in the optical modulation region. A diffraction grating is formed in the distributed Bragg reflector region.

Abstract: The present invention is an optical clock signal extraction device, comprising first conversion means and second conversion means for enabling to extract an optical clock signal without depending on the polarization direction of an input optical signal. The first conversion means comprises a first optical converter and a continuous wave light source of which wavelength is ?2, where an input optical signal of which wavelength is ?1 and continuous wave light of which wavelength is ?2 are input to the first optical converter, and an intermediate optical signal of which wavelength is ?2 is generated and output without depending on the polarization direction of the input optical signal. The second conversion means has a second optical converter, where the intermediate optical signal is input to the second optical converter, and an optical clock signal of which wavelength is ?3 is generated and output by the passive mode locking operation of the second optical converter.

Abstract: To provide an optical clock signal extracting device with a simple configuration, by which an optical clock signal may be extracted without depending on the polarization direction of an input optical signal. A current is injected to a gain region 30 through an n-type common electrode 12 and a p-type electrode 24 in the gain region 30 by a constant current source 28. A reverse-bias voltage is applied by a constant voltage source 26 to a saturable absorption region 32 through the p-type electrode 12 and the n-type common electrode 72 in the saturable absorption region 32. An optical waveguide 16 in the gain region is formed with bulk crystal or a quantum well structure into which extension strain is introduced, and an optical waveguide 18 in the saturable absorption region is formed with a quantum well structure into which extension strain is introduced.

Abstract: The present invention provides an optical switch whose operational characteristics do not change, and which is not affected by polarization cross talk, even when the wavelength of a signal light or the ambient temperature of the optical switch varies. The optical switch comprises first and second polarization splitting/combining modules, (10,18), first and second polarization-maintaining single-mode fibers (12, 16), a first polarization plane conversion portion (14), third and fourth polarization-maintaining single-mode fibers (22, 26), and a second polarization plane conversion portion (24).

Abstract: The present invention provides an optical switch in which a switching operation is not affected even when the polarization state of a control light varies. The optical switch comprises a loop-form optical waveguide loop circuit formed from an optical nonlinear medium, control light input means of phase control means for inputting the control light into the optical waveguide loop circuit, a wavelength demultiplexing/multiplexing circuit, and a phase bias circuit.

Abstract: The present invention generates optical pulses of which the wavelength width in the wavelength variable area is sufficiently wide and of which frequency chirping is suppressed enough to be used for optical communication systems. The present invention is constructed by an optical pulse generation section 101 including MLLD1, CW light source 19, first optical coupling means 110 and second optical coupling means 112. An optical wave guide 30 which includes an optical gain area 3, optical modulation area 2 and a passive wave-guiding area 4 is created in the MLLD. Constant current is injected into the optical gain area from the first current source 11 via the p-side electrode 9 and the n-side common electrode 7. Reverse bias voltage is applied to the optical modulation area 2 by a voltage source 12 via the p-side electrode 8 and the n-side common electrode.

Abstract: The present invention provides an optical switch in which a switching operation is not affected even when the polarization state of a control light varies. The optical switch comprises a loop-form optical waveguide loop circuit formed from an optical nonlinear medium, control light input means of phase control means for inputting the control light into the optical waveguide loop circuit, and a wavelength demultiplexing/multiplexing circuit. The optical waveguide loop circuit is constituted by an optical path formed from a first optical fiber extending from an optical demultiplexer/multiplexer to the control light input means, an optical path formed from a second optical fiber extending from the control light input means to the wavelength demultiplexing/multiplexing circuit, and an optical path formed from a fourth optical fiber extending from the wavelength demultiplexing/multiplexing circuit and returning to the optical demultiplexer/multiplexer.

Abstract: The present invention provides an optical switch whose operational characteristics do not change, and which is not affected by polarization cross talk, even when the wavelength of a signal light or the ambient temperature of the optical switch varies. The optical switch comprises first and second polarization splitting/combining modules 10, 18, first and second polarization-maintaining single-mode fibers 12, 16, a first polarization plane conversion portion 14, third and fourth polarization-maintaining single-mode fibers 22, 26, and a second polarization plane conversion portion 24. One end of the first polarization-maintaining single-mode fiber is connected to a second input/output terminal 10-2, one end of the second polarization-maintaining single-mode fiber is connected to a first input/output terminal 18-1, and the respective other ends of the first and second polarization-maintaining single-mode fibers are connected to each other via the first polarization plane conversion portion.