Abstract: An optical phase modulator (2) includes a first 2×2 Mach-Zehnder optical phase modulation unit (10). The first 2×2 Mach-Zehnder optical phase modulation unit (10) includes a first 2×2 multimode interference waveguide (11), a second 2×2 multimode interference waveguide (14), a pair of first arm waveguides (12, 13), and first modulation electrodes (15, 16). A first output port (an output port 17d) of the first 2×2 Mach-Zehnder optical phase modulation unit (10 ) is a cross port to a first input port (an input port 17a) of the first 2×2 Mach-Zehnder optical phase modulation unit (10).

Abstract: A multi-mode interferometric optical waveguide device includes: a multi-mode interferometric optical waveguide which includes a first reflective surface; a first single-mode waveguide connected to the multi-mode interferometric optical waveguide; and a second single-mode waveguide connected to the multi-mode interferometric optical waveguide and oppose the first reflective surface. Consequently, the multi-mode interferometric optical waveguide device can propagate light from the first single-mode waveguide to the second single-mode waveguide, with further reduced optical losses.

Abstract: A multi-mode interference multiplexer/demultiplexer can suppress reflected return light while guiding light to a single-mode waveguide. The multi-mode interference multiplexer/demultiplexer includes a multi-mode waveguide, a first single-mode waveguide connected to a first end, a second single-mode waveguide opposing the first single-mode waveguide, a third single-mode waveguide connected to a second end, a reflecting surface opposing the third single-mode waveguide, and a fourth single-mode waveguide connected to a side end. Light entering from the second or third single-mode waveguide is reflected off the reflecting surface and forms an image at a first connection on a side end of the fourth single-mode waveguide.

Abstract: A multi-mode interference multiplexer/demultiplexer can suppress reflected return light while guiding light to a single-mode waveguide. The multi-mode interference multiplexer/demultiplexer includes a multi-mode waveguide, a first single-mode waveguide connected to a first end, a second single-mode waveguide opposing the first single-mode waveguide, a third single-mode waveguide connected to a second end, a reflecting surface opposing the third single-mode waveguide, and a fourth single-mode waveguide connected to a side end. Light entering from the second or third single-mode waveguide is reflected off the reflecting surface and forms an image at a first connection on a side end of the fourth single-mode waveguide.

Abstract: A semiconductor laser according to the present invention includes an active layer, a guide layer laminated on the active layer, a diffraction grating formed along a light emission direction in the guide layer, an upper electrode provided above the guide layer, and a lower electrode provided below the active layer. The diffraction grating includes a current-injection diffraction grating and current-non-injection diffraction gratings provided both in front of and in back of the current-injection diffraction grating. Phase shifters are individually provided at a central portion of the current-injection diffraction grating and at boundaries between the current-injection diffraction grating and the current-non-injection diffraction gratings. The upper electrode is provided above the current-injection diffraction grating and is not provided above the current-non-injection diffraction gratings.

Abstract: A first arm portion and a second arm portion are provided so as to have a distance therebetween greater than a distance between input ends of two output waveguides and greater than a distance between an output end of a first output portion and an output end of a second output portion, the first arm portion forming a traveling path of light from one of the two output waveguides to the first output portion through a first optical amplifier, the second arm portion forming a traveling path of light from another one of the two output waveguides to the second output portion through a second optical amplifier. The first optical amplifier and the second optical amplifier have curved portions in which the first output portion and the second output portion are curved in a direction toward each other, and the first optical amplifier and the second optical amplifier respectively output light from the output end of the first output portion and the output end of the second output portion.

Abstract: A first arm portion and a second arm portion are provided so as to have a distance therebetween greater than a distance between input ends of two output waveguides and greater than a distance between an output end of a first output portion and an output end of a second output portion, the first arm portion forming a traveling path of light from one of the two output waveguides to the first output portion through a first optical amplifier, the second arm portion forming a traveling path of light from another one of the two output waveguides to the second output portion through a second optical amplifier. The first optical amplifier and the second optical amplifier have curved portions in which the first output portion and the second output portion are curved in a direction toward each other, and the first optical amplifier and the second optical amplifier respectively output light from the output end of the first output portion and the output end of the second output portion.

Abstract: A semiconductor laser according to the present invention includes an active layer, a guide layer laminated on the active layer, a diffraction grating formed along a light emission direction in the guide layer, an upper electrode provided above the guide layer, and a lower electrode provided below the active layer. The diffraction grating includes a current-injection diffraction grating and current-non-injection diffraction gratings provided both in front of and in back of the current-injection diffraction grating. Phase shifters are individually provided at a central portion of the current-injection diffraction grating and at boundaries between the current-injection diffraction grating and the current-non-injection diffraction gratings. The upper electrode is provided above the current-injection diffraction grating and is not provided above the current-non-injection diffraction gratings.

Abstract: A wavelength variable light source according to the present invention includes: an MMI that includes an input side and an output side, the input side connecting to one end of each of a plurality of MMI input waveguides, and the output side connecting to a plurality of MMI output waveguides, the MMI multiplexing light input from each of the MMI input waveguides and outputting the multiplexed light to each of the MMI output waveguides; a plurality of DFB-LDs connected to the other end of each of the MMI input waveguides, each of the MMI output waveguides performing a single mode oscillation at a different wavelength; and two SOAs respectively connected to two MMI output waveguides of the MMI output waveguides, and having different gains from each other.

Abstract: An optical semiconductor device includes: semiconductor lasers; a wave coupling section multiplexing light output by the semiconductor lasers; an optical amplifying section amplifying output light of the wave coupling section; first optical waveguides respectively optically connecting respective semiconductor lasers to the wave coupling section; a light intensity lowering section located in each of the first optical waveguides and lower light intensity of reflected light that is reflected at a reflecting point located in the optical semiconductor device and that returns to the respective semiconductor lasers; to decrease line width of the light output by the semiconductor lasers.

Abstract: An optical semiconductor device includes: semiconductor lasers; a wave coupling section multiplexing light output by the semiconductor lasers; an optical amplifying section amplifying output light of the wave coupling section; first optical waveguides respectively optically connecting respective semiconductor lasers to the wave coupling section; a light intensity lowering section located in each of the first optical waveguides and lower light intensity of reflected light that is reflected at a reflecting point located in the optical semiconductor device and that returns to the respective semiconductor lasers; to decrease line width of the light output by the semiconductor lasers.

Abstract: An optical semiconductor device includes: semiconductor lasers; a wave coupling section multiplexing light output by the semiconductor lasers; first optical waveguides respectively optically connecting respective semiconductor lasers to the wave coupling section; a phase regulator regulating phase of reflected light that is reflected at a reflecting point located in the optical semiconductor device and that returns to the semiconductor lasers; a second optical waveguide optically connecting the wave coupling section to the phase regulator; an optical amplifying section amplifying output light of the phase regulator; and a third optical waveguide optically connecting an output of the phase regulator to the optical amplifying section. The phase regulator adjusts the phase of reflected light that returns to the semiconductor lasers to decrease line width of the light output by the semiconductor lasers.

Abstract: A wavelength variable light source according to the present invention includes: an MMI that includes an input side and an output side, the input side connecting to one end of each of a plurality of MMI input waveguides, and the output side connecting to a plurality of MMI output waveguides, the MMI multiplexing light input from each of the MMI input waveguides and outputting the multiplexed light to each of the MMI output waveguides; a plurality of DFB-LDs connected to the other end of each of the MMI input waveguides, each of the MMI output waveguides performing a single mode oscillation at a different wavelength; and two SOAs respectively connected to two MMI output waveguides of the MMI output waveguides, and having different gains from each other.

Abstract: An optical semiconductor device includes: semiconductor lasers; a wave coupling section multiplexing light output by the semiconductor lasers; first optical waveguides respectively optically connecting respective semiconductor lasers to the wave coupling section; a phase regulator regulating phase of reflected light that is reflected at a reflecting point located in the optical semiconductor device and that returns to the semiconductor lasers; a second optical waveguide optically connecting the wave coupling section to the phase regulator; an optical amplifying section amplifying output light of the phase regulator; and a third optical waveguide optically connecting an output of the phase regulator to the optical amplifying section. The phase regulator adjusts the phase of reflected light that returns to the semiconductor lasers to decrease line width of the light output by the semiconductor lasers.

Abstract: An optical semiconductor device includes: semiconductor lasers separated into two groups; an optical coupler combining light output from the semiconductor lasers; an optical amplifier amplifying light output from the optical coupler; and waveguides respectively connecting the semiconductor lasers to the optical coupler. Each of the waveguides includes a respective bent waveguide. The bent waveguides have the same radius of curvature.

Abstract: An objective of the present invention is to provide an optical fiber sensor which has a simple configuration to enable sensitively measuring a refractive index of a measurement medium in a wide range of refractive indexes. An optical fiber sensor according to the present invention includes; an optical fiber having a core in which a short-period gratings are formed and a cladding, the optical fiber being made so that transmission loss occurs due to cladding-propagation-mode leakage at its cladding portion where the short-period gratings are formed; a light source from which light having a wavelength range of the cladding propagation mode is emitted; and a light receiving unit for receiving transmission or reflection light having passed through the cladding at the position where the short-period gratings are formed.

Abstract: An optical fiber sensor measuring refractive index of a medium with high sensitivity in a wide range. The optical fiber sensor includes an optical fiber causing a transmission loss due to leakage in the clad propagation mode from a portion of a core and a clad where a Bragg grating is provided, a light source permitting light in a wavelength band in the clad propagation mode to enter the optical fiber, and a light-receiving section receiving the transmitted or reflected light transmitted through the core and the clad at the portion where the Bragg grating is provided. The refractive index of the medium to be measured in contact with the clad is measured according to total intensity of the light received by the light-receiving section. The Bragg grating is inclined at a predetermined angle of inclination to the vertical line vertical to the length direction of the optical fiber.

Abstract: An objective of the present invention is to provide an optical fiber sensor which has a simple configuration to enable sensitively measuring a refractive index of a measurement medium in a wide range of refractive indexes. An optical fiber sensor according to the present invention includes; an optical fiber having a core in which a short-period gratings are formed and a cladding, the optical fiber being made so that transmission loss occurs due to cladding-propagation-mode leakage at its cladding portion where the short-period gratings are formed; a light source from which light having a wavelength range of the cladding propagation mode is emitted; and a light receiving unit for receiving transmission or reflection light having passed through the cladding at the position where the short-period gratings are formed.

Abstract: An optical fiber sensor measuring refractive index of a medium with high sensitivity in a wide range. The optical fiber sensor includes an optical fiber causing a transmission loss due to leakage in the clad propagation mode from a portion of a core and a clad where a Bragg grating is provided, a light source permitting light in a wavelength band in the clad propagation mode to enter the optical fiber, and a light-receiving section receiving the transmitted or reflected light transmitted through the core and the clad at the portion where the Bragg grating is provided. The refractive index of the medium to be measured in contact with the clad is measured according to total intensity of the light received by the light-receiving section. The Bragg grating is inclined at a predetermined angle of inclination to the vertical line vertical to the length direction of the optical fiber.

Abstract: An optical fiber sensor that can detect a liquid level or detect a property of liquid with high reliability even under a frequently vibrational environment. The optical fiber sensor includes an optical fiber that includes a core having an area where a grating is formed and a clad, the optical fiber being disposed so that at least a part of the area with the grating is immersed in liquid, a light source for making light incident to the optical fiber so that a cladding mode light having a wavelength band is generated by the grating, and a light receiving unit for detecting the intensity of light which is incident from the light source to the optical fiber and transmitted through the grating.