Abstract: An optical modulator includes an optical phase modulator which applies an operating voltage to at least one arm so as to modulate an optical phase of an optical signal transmitted via at least one arm and an optical phase adjuster which applies a voltage below the operating voltage to at least one arm so as to adjust an operating point. In the optical phase adjuster, an optical phase coarse adjuster applies a voltage below the operating voltage to at least one arm so as to change an optical phase of an optical signal by 180° or more, while an optical phase fine adjuster applies a voltage below the operating voltage to at least one arm so as to changer an optical phase of an optical signal by 90° or less. Thus, it is possible to automatically calibrate an operating point of an optical modulator with low power consumption.

Abstract: An object of the present invention is to provide an electro-optical modulator that allows high-speed carrier injection into a silicon-containing i-type amorphous semiconductor, particularly a-Si:H, and has little optical loss. An electro-optical modulator comprises: a substrate 201; an optical waveguide comprising a silicon-containing i-type amorphous semiconductor 204 formed on the substrate; and a silicon-containing p-type semiconductor layer 203 and a silicon-containing n-type semiconductor layer 205 arranged apart from each other with the silicon-containing optical waveguide comprising an i-type amorphous semiconductor 204 interposed therebetween and constituting optical waveguides together with the silicon-containing optical waveguide comprising an i-type amorphous semiconductor. The silicon-containing p-type semiconductor layer 203 and/or silicon-containing n-type semiconductor layer 205 are a crystalline semiconductor layer.

Abstract: Provided is a silicon-based electro-optic modulator which is small in size and capable of high speed operation. A first silicon semiconductor layer (120) doped to exhibit a first type of conductivity and a second semiconductor layer (160) doped to exhibit a second type of conductivity are at least partly stacked together, and a relatively thin dielectric (150) is formed at the interface between the stacked first and second silicon semiconductor layers (120, 160). The first silicon semiconductor layer (120) has a rib waveguide shape (130) comprising a rib portion (131) and slab portions (132). A first heavily doped region (140) formed by a high concentration doping process is arranged at a location, in the first silicon semiconductor layer (120), neighboring to each of the slab portions (132). The first heavily doped region (140) has almost the same height as that of the rib portion (131) of the rib waveguide (130).

Abstract: A waveguide-coupled MSM-type photodiode of the present invention comprises a structure in which a semiconductor light-absorbing layer and an optical waveguide core layer are adjacent and optically coupled to each other, has formed metal-semiconductor-metal (MSM) junctions which are arranged at an interval on the semiconductor light-absorbing layer, and is characterized in that of the MSM electrodes arranged at the interval, a voltage is set so that a reverse bias is applied to those MSM electrodes that are arranged on a light incidence side.

Abstract: In a region in which silicon semiconductor layers having first and second conductive types are stacked, a concavoconvex structure including a Si1-xGex (x=0.01 to 0.9) layer is formed on a surface of the first silicon semiconductor layer, a relatively thin dielectric is formed on the concavoconvex structure, and a silicon semiconductor layer having the second conductive type is further stacked.

Abstract: An optical receiver circuit has a function of converting a differential optical signal into a differential current signal. The optical receiver circuit has a pair of light-receiving elements including first and second light-receiving elements operable to convert an optical signal into a current signal and a pair of signal lines. An anode of the first light-receiving element and a cathode of the second light-receiving element are connected to a first signal line of the pair of signal lines via first and second AC coupling capacitors, respectively. A cathode of the first light-receiving element and an anode of the second light-receiving element are connected to a second signal line of the pair of signal lines via third and fourth AC coupling capacitors, respectively. Differential signal currents are generated in the first and second signal lines in response to reception of differential optical signals inputted into the first and second light-receiving elements.

Abstract: An optical end coupling type silicon optical integrated circuit is provided using an SOI substrate. This optical integrated circuit is constituted so as to connect with an external optical circuit at an end coupling part and have signal light incident to an optical circuit that includes a curved part. In the plane of the optical integrated circuit, the position of one end coupling part selected from among any thereof and the position of any multimode optical waveguide element to which a respective optical waveguide is connected via a respective curved part satisfy a positional relationship defined on the basis of a beam divergence angle [theta] of stray light.

Abstract: An optical modulator includes a plurality of electrode pads arranged in a zigzag alignment; two arms which are partially bent to circumvent the electrode pads so as to carry out optical phase modulation at various parts based on voltages input via the electrode pads; an optical branch structure branching the arms; and an optical coupling structure aggregating the arms together. Each arm is made of a silicon-base electro-optic element including a substrate; a first conductive semiconductor layer having a rib waveguide structure; a dielectric layer deposited on the rib waveguide structure; and a second conductive semiconductor layer deposited on the dielectric layer. The first conductive semiconductor layer is connected to first electrode wires via first contacts, while the second conductive semiconductor layer is connected to second electrode wires via second contacts. Thus, it is possible to miniaturize the optical modulator which can operate at a low voltage.

Abstract: An optical modulator includes a plurality of electrode pads arranged in a zigzag alignment; two arms which are partially bent to circumvent the electrode pads so as to carry out optical phase modulation at various parts based on voltages input via the electrode pads; an optical branch structure branching the arms; and an optical coupling structure aggregating the arms together. Each arm is made of a silicon-base electro-optic element including a substrate; a first conductive semiconductor layer having a rib waveguide structure; a dielectric layer deposited on the rib waveguide structure; and a second conductive semiconductor layer deposited on the dielectric layer. The first conductive semiconductor layer is connected to first electrode wires via first contacts, while the second conductive semiconductor layer is connected to second electrode wires via second contacts. Thus, it is possible to miniaturize the optical modulator which can operate at a low voltage.

Abstract: An optical modulator includes an optical phase modulator which applies an operating voltage to at least one arm so as to modulate an optical phase of an optical signal transmitted via at least one arm and an optical phase adjuster which applies a voltage below the operating voltage to at least one arm so as to adjust an operating point. In the optical phase adjuster, an optical phase coarse adjuster applies a voltage below the operating voltage to at least one arm so as to change an optical phase of an optical signal by 180° or more, while an optical phase fine adjuster applies a voltage below the operating voltage to at least one arm so as to changer an optical phase of an optical signal by 90° or less. Thus, it is possible to automatically calibrate an operating point of an optical modulator with low power consumption.

Abstract: An output monitoring method for an optical modulator includes: branching light into first and second lights; modulating a phase of the first light within a first waveguide; modulating a phase of the second light within a second waveguide; multiplexing the first and second lights to generate interference light, and outputting the interference light from first and second output ports; detecting a difference or ratio between a portion of the interference light from the first output port and a portion of the interference light from the second output port; and setting an operating point of light based on the detected difference or ratio; and controlling phase modulation of follow-on light that propagates through the first and second waveguides so as to keep the operating point constant.

Abstract: In order to provide an optical sending circuit which has a small size and can carry out long haul transmission and which can reduce a stray light and an optical cross talk noise generated in an optical transmission line, the optical sending circuit includes: a first EA modulator whose reverse bias voltage is changed by a first data signal; a second EA modulator whose reverse bias voltage is changed by a second data signal; a first optical transmission line which inputs a light to be modulated, which is to be modulated by the first EA modulator, to the first EA modulator; a second optical transmission line which is connected with an output of the first EA modulator, and transfers an optical signal modulated by the first data signal; and a third optical transmission line which is connected with an output of the second EA modulator.

Abstract: Provided is a connecting channel that has manufacturing tolerance, can suppress light loses, improves reliability of the connecting channel, and connects an optical device and an optical waveguide. The connecting channel includes first silicon layer (3) that has rib-shaped part (3?) extending in a longitudinal direction of the connecting channel, and second silicon layer (6) that is stacked on first silicon layer (3) to partially overlap rib-shaped part 3?, and extends in the longitudinal direction. Second silicon layer (6) has tapered part (W) tapered toward one end in the longitudinal direction, and is located away from an upper portion of rib-shaped part (3?) at an end surface of one end in the longitudinal direction.

Abstract: A downsized, low-power electro-optical modulator that achieves reducing both of the additional resistance in the modulation portion and the optical loss each caused by electrodes at the same time is provided. The electro-optical modulator includes a rib waveguide formed by stacking a second semiconductor layer 9 having a different conductivity type from a first semiconductor layer 8 on the first semiconductor layer 8 via a dielectric film 11, and the semiconductor layers 8 and 9 are connectable to an external terminal via highly-doped portions 4 and 10, respectively. In a region in the vicinity of contact surfaces of the semiconductor layers 8 and 9 with the dielectric film 11, a free carrier is accumulated, removed, or inverted by an electrical signal from the external terminal, and whereby a concentration of the free carrier in an electric field region of an optical signal is modulated, so that a phase of the optical signal can be modulated.

Abstract: A waveguide-coupled MSM-type photodiode of the present invention comprises a structure in which a semiconductor light-absorbing layer and an optical waveguide core layer are adjacent and optically coupled to each other, has formed metal-semiconductor-metal (MSM) junctions which are arranged at an interval on the semiconductor light-absorbing layer, and is characterized in that of the MSM electrodes arranged at the interval, a voltage is set so that a reverse bias is applied to those MSM electrodes that are arranged on a light incidence side.

Abstract: In a region in which silicon semiconductor layers having first and second conductive types are stacked, a concavoconvex structure including a Si1-xGex (x=0.01 to 0.9) layer is formed on a surface of the first silicon semiconductor layer, a relatively thin dielectric is formed on the concavoconvex structure, and a silicon semiconductor layer having the second conductive type is further stacked.

Abstract: An optical modulator according to the present invention is configured at least by a semiconductor layer subjected to a doping process so as to exhibit a first conductivity type, and a semiconductor layer subjected to a doping process so as to exhibit a second conductivity type. Further, in the optical modulator, at least the first conductivity type semiconductor layer, a dielectric layer, the second conductivity type semiconductor layer, and a transparent electrode optically transparent in at least a near-infrared wavelength region are laminated in order.

Abstract: To provide an optical modulator having a reduced size and reduced power consumption and capable of being easily connected to a waveguide and a method of manufacturing the optical modulator. The optical modulator has at least semiconductor layer (8) having a rib-shaped portion and doped so as to be of a first conduction type, dielectric layer (11) laid on first-conduction-type semiconductor layer (8), and semiconductor layer (9) laid on dielectric layer (11), having the width at the side opposite from dielectric layer (11) increased relative to the width of the rib-shaped portion, and doped so as to be of a second conduction type.

Abstract: The present invention provides a photodetector which solves the problem of low sensitivity of a photodetector, an optical communication device equipped with the same, and a method for making the photodetector, and a method for making the optical communication device. The photodetector includes a substrate, a lower cladding layer arranged on the substrate, an optical waveguide arranged on the lower cladding layer, an intermediate layer arranged on the optical waveguide, a optical absorption layer arranged on the intermediate layer, a pair of electrodes arranged on the optical absorption layer, and wherein the optical absorption layer includes a IV-group or III-V-group single-crystal semiconductor, and the optical absorption layer absorbs an optical signal propagating through the optical waveguide.

Abstract: A semiconductor light receiving element comprises: a substrate, a semiconductor layer of a first conductivity type formed on the substrate, a non-doped semiconductor light absorbing layer formed on the semiconductor layer of the first conductivity type, a semiconductor layer of a second conductivity type formed on the non-doped semiconductor light absorbing layer, and an electro-conductive layer formed on the semiconductor layer of the second conductivity type. A plurality of openings, periodically arrayed, are formed in a laminated body composed of the electro-conductive layer, the semiconductor layer of the second conductivity type, and the non-doped semiconductor light absorbing layer. The widths of the openings are less than or equal to the wavelength of incident light, and the openings pass through the electro-conductive layer and the semiconductor layer of the second conductivity type to reach the non-doped semiconductor light absorbing layer.