Abstract: An apparatus for modulating a beam of light with balanced push-pull mechanism. The apparatus includes a first waveguide comprising a first PN junction on a silicon-on-insulator substrate and a second waveguide comprising a second PN junction on the silicon-on-insulator substrate. The second PN junction is a replica of the first PN junction shifted with a distance. The apparatus further includes a first source electrode and a first ground electrode coupled respectively with the first PN junction and a second source electrode and a second ground electrode coupled respectively with the second PN junction. The apparatus additionally includes a third ground electrode disposed near the second PN junction at the distance away from the second ground electrode, wherein the first ground electrode, the second ground electrode, and the third ground electrode are commonly grounded to have both PN junctions subjected to a substantially same electric field varied in ground-source-ground pattern.

Abstract: A hybrid MOS optical modulator. The optical modulator includes an optical waveguide, a cathode comprising a first material and formed in the optical waveguide, and an anode comprising a second material dissimilar from the first material and formed in the optical waveguide, the anode adjoining the cathode, a capacitor being defined between the anode and the cathode.

Abstract: An optical modulation apparatus includes an optical modulation unit that includes a plurality of ring optical modulators which are coupled in cascade to each other and the ring optical waveguides of which have round-trip lengths different from each other, and a controller that performs, for at least one of the ring optical modulators, first resonance wavelength adjustment control to adjust the resonance wavelength of the ring optical modulator to one input light wavelength, performs second resonance wavelength adjustment control to specify the ring optical modulator that exhibits a minimum current amount required for the adjustment of the resonance wavelength of the ring optical waveguide to the one input light wavelength from among the ring optical modulators and adjust the resonance wavelength of the specified ring optical modulator to the one input light wavelength, and performs modulation driving control for the specified ring optical modulator.

Abstract: An optical control device is provided which can suppress crosstalk between electrodes without increasing the entire size of the device itself. The optical control device includes a substrate having an electro-optical effect, an optical waveguide formed in the substrate, and a modulation electrode modulating optical waves propagating in the optical waveguide. The modulation electrode includes at least two signal electrodes and ground electrodes arranged to interpose the signal electrodes therebetween. The optical control device further includes an electrical connection member that electrically connects the ground electrode disposed between the two signal electrodes to other ground electrodes and that is disposed to cross over part of the signal electrode.

Abstract: Electro-optic (EO) modulator and related device structures which can be used in conjunction with high EO materials to lower switching voltage and improve related performance parameters.

Abstract: Provided are examples of light modulators and optical apparatuses that may include the light modulators. A light modulator may include a plasmonic nano-antenna and an element for changing plasmon resonance characteristics of the plasmonic nano-antenna. The plasmon resonance characteristics of the plasmonic nano-antenna may be changed due to a change in refractive index of the element, and thus light may be modulated.

Abstract: An overvoltage protection component may be in a SOI layer, a portion of the SOI layer forming the core of an optical waveguide. This component may be made of semiconductor regions of different doping types and/or levels, at least one of these regions corresponding to at least a portion of the waveguide core.

Abstract: The invention is a surface plasmon resonance (SPR) sensor to determine the presence and quantity of biological or chemical entities in an analyte. The sensor comprises a metal periodic structure deposited as a thin layer of a noble metal, comprising a one dimensional array of nanoslits or a two dimensional array of nanoholes on a transparent dielectric substrate, a nm-thick layer of transparent dielectric protection layer on top of the metal periodic structure and a functionalization layer, which acts as a binding layer to biological or biochemical entities in an analyte that is in contact with the functionaliztion layer.

Abstract: A plasmonic device having a transparent conducting oxide (TCO) waveguide and a tunable voltage applied across the TCO and a metal layer for modulating an input optical signal.

Abstract: A touch panel includes a substrate; and a sensing electrode with a conductive pattern on the substrate, wherein the sensing electrode includes: an electrode layer; and a first buffer layer on the electrode layer.

Abstract: A second insulating film, which includes a hollowed portion inside in a region where the high mesa ridge type optical element is formed, is formed. By using the second insulating film as a mask and etching, a concave portion is formed in the transparent waveguide layer and the upper cladding layer below the hollowed portion. The modulator layer having the Al-based material is formed. By etching with the modulator layer formed in the concave portion being covered with the third insulating film, the modulator layer formed outside the concave portion is removed. By etching with the modulator layer formed in the concave portion being covered with the fourth insulating film, the ridge of the semiconductor laser is formed without exposing the modulator layer formed in the concave portion.

Abstract: An integrated optical linewidth reduction system detects/estimates the phase noise of an incoming optical signal and subtracts the detected phase noise from the phase noise of the incoming signal. A first coupler/splitter of the linewidth reduction system may split the incoming signal into first and second optical signals travelling through first and second optical paths. A second coupler/splitter may split the second optical signal into third and fourth optical signals travelling through third and fourth optical paths. The third optical path has a longer propagation delay than the fourth optical path. Two different coupling ratios of the third and fourth optical signals are used to generate an electrical signal representative of the phase noise of the incoming signal. A phase detector/estimator estimates the phase noise from the electrical signal. A phase modulator subtracts the detected/estimated phase noise from the phase noise of the incoming signal.

Abstract: An electro-refraction modulator includes a series of layers with different doping levels surrounding a single-crystal regrown p-n junction implemented in a silicon-on-insulator (SOI) technology. The regrown p-n junction is spatially abrupt and precisely defined, which significantly increases the tuning efficiency of the electro-refraction modulator while maintaining acceptable insertion loss. Consequently, the electro-refraction modulator (such as a resonator modulator or a Mach-Zehnder interferometer modulator) can have high bandwidth, compact size and reduced drive voltage. The improved performance of the electro-refraction modulator may facilitate silicon-photonic links for use in applications such as wavelength-division multiplexing.

Abstract: A system and methods for electro-optical modulation are presented. A first optical signal and a second optical signal are optically coupled to produce a local oscillator signal propagated in two signal paths. The local oscillator signal in the first signal path and the second signal path is electro-optically phase modulated with a radio frequency electrical signal to produce a first phase modulated optical signal and a second phase modulated optical signal respectively. The first phase modulated optical signal and the second phase modulated optical signal are optically coupled to produce an intensity modulated signal comprising an RF frequency of the radio frequency electrical signal frequency mixed by a local oscillator frequency of the local oscillator signal.

Abstract: A Mach-Zehnder type optical modulator according to the present invention is characterized by: that it comprises a beam splitting unit for splitting input light into two component light beams, a first waveguide and a second waveguide for guiding respective ones of the split component light beams, a beam combining unit for combining together the component light beams guided respectively by the first and second waveguides and outputting the combined light, a plurality of electrodes which are formed into electrode pairs as a result of being arranged on the first and second waveguides in a symmetric and parallel manner, and driving units for differentially driving respective ones of the electrode pairs in accordance with the magnitude relationships between the voltage of an input signal and respective ones of threshold voltages set individually for the electrode pairs; and that, by thus being driven differentially, the plurality of electrodes each apply a voltage for modulating the input light to the waveguide on

Abstract: The present invention is a method and an apparatus for optical modulation, for example for use in optical communications links. In one embodiment, an apparatus for optical modulation includes a first silicon layer having one or more trenches formed therein, a dielectric layer lining the first silicon layer, and a second silicon layer disposed on the dielectric layer and filling the trenches.

Abstract: An optical communication device has a pair of Mach-Zehnder optical modulators; a voltage monitor configured to monitor a voltage component acquired by optical-to-electric conversion of combined light output from the Mach-Zehnder optical modulators; a power monitor configured to monitor a power component acquired by square law detection of the optical-to-electric converted combined light from the Mach-Zehnder optical modulators; a first controller configured to control a substrate bias voltage or a driving amplitude applied to one of two waveguides of each of the Mach-Zehnder optical modulators based upon an output of the power monitor, and a second controller configured to control the substrate bias voltage or the driving amplitude applied to the other of the two waveguides of each of the Mach-Zehnder optical modulator based upon an output of the voltage monitor.

Abstract: A Mach-Zehnder modulator includes: a conductive semiconductor region disposed on a substrate; a first waveguide arm disposed on the conductive semiconductor region; a second waveguide arm disposed on the conductive semiconductor region; a first electrode disposed on the first waveguide arm, the first electrode receiving a first drive signal applied to the first waveguide arm; a second electrode disposed on the second waveguide arm, the second electrode receiving a second drive signal applied to the second waveguide arm; a first ground electrode disposed on the conductive semiconductor region, the first ground electrode being electrically connected to a reference potential; and a second ground electrode disposed on the conductive semiconductor region. The first and second drive signals constitute a differential signal. The second ground electrode is electrically connected to the first ground electrode via the conductive semiconductor region.

Abstract: A microwave frequency component includes a thin layer of dielectric material arranged between an earth electrode and a control electrode controlling a microwave frequency electrical signal such that the earth electrode extends over a first face, called the lower face, of the thin layer of dielectric material, and the control electrode extends longitudinally over a second face, called the upper face, of the thin layer of dielectric material. The microwave frequency component is such that it includes a set of at least two shielded coplanar electrodes extending along the entire length of the control electrode, to each side of and at an equal distance from the control electrode.

Abstract: A multi-wavelength surface plasmon laser that simultaneously emits surface plasmons having a large number of wavelengths and includes an active layer whose thickness changes with position, and a metal cavity whose length changes with position so that light of different wavelengths is emitted according to position. Surface plasmons are generated at the interface between a metal layer and a semiconductor layer in response to the light of different wavelengths. The surface plasmons having different wavelengths may be resonated in the metal cavity whose length changes with position and may be emitted to the outside.

Abstract: A method of operating a wavelength swept source apparatus includes generating a single mode light, and generating a basic optical comb including light rays having identical frequency differences with adjacent light rays by modulating the generated single mode light. The method further includes generating other optical combs that include the same number of light rays as that of light rays of the optical comb that has a frequency band different from that of the basic optical comb, and is distributed in a frequency band wider than that in which the basic optical comb is distributed, by modulating the light rays of the basic optical comb. The light rays of the basic optical comb and the light rays included in the other optical combs are sequentially emitted according to frequencies of the light rays of the basic optical comb and the light rays included in the other optical combs.

Abstract: According to embodiments of the present invention, a method for forming an optical modulator is provided. The method includes providing a substrate, implanting dopants of a first conductivity type into the substrate to form a first doped region, implanting dopants of a second conductivity type into the substrate to form a second doped region, wherein a portion of the second doped region is formed over and overlaps with a portion of the first doped region to form a junction between the respective portions of the first doped region and the second doped region, and wherein a remaining portion of the second doped region is located outside of the junction, and forming a ridge waveguide, wherein the ridge waveguide overlaps with at least a part of the junction.

Abstract: An optical modulator device made on large core silicon fin waveguide platform and its fabrication methods. The optical device includes two silicon optical coupling waveguides each having a lower ridge and an upper ridge, two mode transformers respectively connecting the coupling waveguides with an optical modulator waveguide. The optical modulator waveguide has a silicon fin waveguide structure with a narrower fin structure on top of a wider lower ridge structure. Each coupling waveguide and the corresponding mode transformer form a two-stage horizontal taper structure, namely a taper in the lower ridge of the coupling waveguide and a taper of the mode transformer. The light travelling in the coupling waveguide with majority of light in the upper ridge can gradually shift to the lower ridge of the optical modulator where an electro-optic region is positioned. The electro-optic region changes its optical property in response to an applied electric field.

Abstract: A tunable laser includes a substrate comprising a silicon material, a gain medium coupled to the substrate, wherein the gain medium includes a compound semiconductor material, and a waveguide disposed in the substrate and optically coupled to the gain medium. The tunable laser also includes a first wavelength selective element characterized by a first reflectance spectrum and disposed in the substrate and a carrier-based phase modulator optically coupled to the first wavelength selective element. The tunable laser further includes a second wavelength selective element characterized by a second reflectance spectrum and disposed in the substrate, an optical coupler disposed in the substrate and optically coupled to the first wavelength selective element, the second wavelength selective element, and the waveguide, and an output mirror.

Abstract: A Mach-Zehnder modulator arrangement includes at least one electro-optic Mach-Zehnder modulator having a first optical waveguide forming a first modulator arm and a second optical waveguide forming a second modulator arm. A travelling wave electrode arrangement includes first waveguide electrodes for applying a voltage across the first optical waveguide and second waveguide electrodes for applying a voltage across the second optical waveguide. The first waveguide electrodes are capacitively coupled to the second waveguide electrodes. A driver unit supplies an alternating voltage to the travelling wave electrode arrangement. The driver unit includes a first output port coupled to the first waveguide electrodes and a second output port coupled to the second waveguide electrodes. The driver unit supplies a first varying signal to the first waveguide electrodes via the first output port and a second varying signal to the second waveguide electrodes via the second output port.

Abstract: A fiber-optic surface plasmon resonance sensor may include an optical fiber and a surface plasmon excitation layer. The optical fiber may include a core, a cladding surrounding the core, and a depression. The surface plasmon excitation layer may include a first excitation layer, a second excitation layer and an optical waveguide layer between the first excitation layer and the second excitation layer. Incident light incident through the core may be coupled to the surface plasmon excitation layer at a specific angle of incidence and wavelength satisfying the surface plasmon resonance condition. Depending on the polarizing direction of the incident light, an s-polarized component may be coupled to the guided-wave mode in the optical waveguide layer constituting the surface plasmon excitation layer.

Abstract: A Mach-Zehnder optical modulator includes a join-and-branch portion; two light wave guides connected with the join-and-branch portion; an output light waveguide connected with the join-and-branch portion; arm electrodes respectively provided on the two light waveguides; and a ground electrode that is provided at an edge of at least one of the arm electrodes along the light waveguide, is spaced from the arm electrode and is grounded.

Abstract: An photonic RF circulator is described that provides greater than 40 db of isolation between a Received RF signal and a Transmitted RF signal in a simultaneous transmit and receive device. The photonic RF circulator uses light modulated in an optical waveguide grating where the Received RF signal co-propagates with the light and the Transmitted RF signal counter-propagates with the light. Variations described within provide for broadening the bandwidth of the T/R isolation and rejection of various noise sources.

Abstract: Mach-Zehnder optical modulators and IQ modulators based on a series push-pull travelling wave electrode are provided. The modulator includes a conductive backplane providing an electrical signal path. One or more voltage control taps are electrically connected to the conductive backplane within an area underneath the travelling wave electrode and provide an equalizing DC control voltage to the conductive backplane. In other variants, a plurality of conductive backplane segments are provided, and at least one voltage control tap is electrically connected to each conductive backplane segment within an area underneath the travelling wave electrode and provides a DC control voltage to the corresponding conductive backplane segment.

Abstract: An integrated optical circuit includes an optically transparent substrate including: an input face, an output face, an upper face and a lower face, the upper and lower faces extending between the input and output faces; at least one optical waveguide which includes at least one first end situated on the input face and a second end situated on the output face; and at least one optical attenuation zone able to attenuate an optical signal transmitted via the substrate to the outside of the waveguide. The waveguide has a non-rectilinear optical path between the first and second end, the attenuation zone extends from the upper face to the lower face, and is positioned on a straight line segment joining the first and second end of the optical waveguide, the waveguide and the attenuation zone having respective dimensions such that the attenuation zone does not cut the waveguide.

Abstract: An optical module includes a waveguide substrate including an optical waveguide and electrodes that apply electronic signals to the optical waveguide; a relay substrate disposed adjacent to the waveguide substrate; a terminal substrate disposed adjacent to the waveguide substrate and opposite to the relay substrate across the waveguide substrate; and a carrier substrate on which the waveguide substrate, the relay substrate, and the terminal substrate are mounted. The electrodes have a first interconnect unit from the relay substrate to the terminal substrate via the waveguide substrate and second interconnect units from the first interconnect unit and branching on the terminal substrate. Among the second interconnect units, a first interconnect branch includes a capacitor and a terminal resistor; and a second interconnect branch is connected to an interconnect of the carrier substrate via a bias resistor, passes under the waveguide substrate to a DC electrode for bias-adjusting on the relay substrate.

Abstract: A variable capacitance element includes a piezoelectric substrate, a buffer layer located on the piezoelectric substrate with an orientation, a dielectric layer located on the buffer layer and having a relative dielectric constant that varies in accordance with an applied voltage, and a first electrode and a second electrode arranged to apply an electric field to the dielectric layer.

Abstract: The present optical modulator includes an optical waveguide core made of a semiconductor material, an electrode, and a plurality of channels made of a semiconductor material doped in an n type or a p type and electrically connecting the optical waveguide core and the electrode to each other. The plurality of channels are provided in a spaced relationship from each other along a propagation direction of light; the optical waveguide core includes a doped region doped in the n type or the p type and a non-doped region. The doped region and the non-doped region are disposed alternately along the propagation direction of light. Each of the plurality of channels is connected to the doped region.

Abstract: An apparatus includes a transducer including a plasmonic funnel having first and second ends with the first end having a smaller cross-sectional area than the second end, and a first section positioned adjacent to the first end of the plasmonic funnel, and a first waveguide having a core, positioned to cause light in the core to excite surface plasmons on the transducer.

Abstract: An optical module includes a waveguide substrate having an optical waveguide and electrodes that apply electronic signals to the optical waveguide; a relay substrate disposed adjacently to the waveguide substrate; and a termination substrate disposed sandwiching the waveguide substrate with the relay substrate. The electrodes respectively have a first wiring portion connected from the relay substrate through the waveguide substrate to the termination substrate and a second wiring portion extending from the first wiring portion and branching on the termination substrate. In the second wiring portion, one branched wiring portion has a capacitor and a termination resistor, and another branched wiring portion extends through a bias resistor to a DC electrode on the relay substrate. The second wiring portion is divided into a first group extending in a first direction along the optical waveguide and a second group extending in a direction opposite to the first direction.

Abstract: An object of the present invention is to provide a manufacturing method of an optical waveguide element whose DC drift is suppressed, and to provide a manufacturing method of an optical waveguide element, capable of adjusting DC drift in the middle of manufacturing processes so as to improve a fabrication yield. The method of manufacturing an optical waveguide element comprises a step of forming an optical waveguide in a substrate having an electro-optic effect, a step of forming a buffer layer, and a step of forming an electrode, in which one stage or a plurality of stages of an interface diffusion layer heat adjustment step (S1, S2) for adjusting a concentration distribution of a specific substance in the buffer layer by heating is included after the buffer layer is formed.

Abstract: An electric-pulse-induced-resistance change device (EPIR device) is provided which is a resistance switching device. It has a buffer layer inserted between a first active resistance switching layer and a second active resistance switching layer, with both active switching layers connected to electrode layers directly or through additional buffer layers between the active resistance switching layers and the electrodes. This device in its simplest form has the structure: electrode-active layer-buffer layer-active layer-electrode. The second active resistance switching layer may, in the alternative, be an ion donating layer, such that the structure becomes: electrode-active layer-buffer layer-ion donating layer-electrode. The EPIR device is constructed to mitigate the retention challenge.

Abstract: An optical coherent transceiver comprising a polarization and phase-diversity coherent receiver and a polarization and phase-diversity modulator on the same substrate interfaced by three grating couplers, on grating coupler coupling in a signal, one grating coupler coupling in a laser signal, and a third grating coupler coupling out a modulated signal.

Abstract: A multi-wavelength distributed Bragg reflector (DBR) semiconductor laser is provided where DBR heating elements are positioned over the waveguide in the DBR section and define an interleaved temperature profile that generates multiple distinct reflection peaks corresponding to distinct temperature dependent Bragg wavelengths associated with the temperature profile. Neighboring pairs of heating elements of the DBR heating elements positioned over the waveguide in the DBR section are spaced along the direction of the axis of optical propagation by a distance that is equal to or greater than the laser chip thickness b to minimize the impact of thermal crosstalk between distinct temperature regions of the interleaved temperature profile.

Abstract: An electro-optic Mach-Zehnder modulator arrangement includes first and second optical waveguides forming, respectively, first and second arms of the Mach-Zehnder modulator. An electrode arrangement includes a first waveguide electrode output port coupled to the first waveguide electrodes a second waveguide electrode arranged on top of a capacitive segment of the first and the second optical waveguides, respectively, such that a voltage can be applied across the capacitive segments of the first and second optical waveguide. At least one driver unit supplies a voltage to the electrode arrangement. The driver unit includes first and second output ports coupled, respectively, to the first and second waveguide electrodes. The driver unit supplies first and second varying signals to the first and second waveguide electrodes via the first and second output ports, respectively. A non-grounded conductive region connects the capacitive segments of the first and second optical waveguides to each other.

Abstract: An optical modulator and a method for manufacturing an optical modulator are provided.

Abstract: Photonic modulators and methods of modulating an input optical signal are provided. A photonic modulator includes at least one modulator section and differential drive circuitry. The at least one modulator section includes a P-type layer and an N-type layer forming a PN junction in the modulator section. The differential drive circuitry is electrically coupled to the P-type layer and the N-type layer of the at least one modulator section.

Abstract: An optical device includes a ridge-like optical waveguide portion, a mesa protector portion that is arranged in parallel to the optical waveguide portion, a resin portion that covers upper parts of the mesa protector portion and is disposed at both sides of the mesa protector portion, an electrode that is disposed on the optical waveguide portion, an electrode pad that is disposed on the resin portion located at an opposite side to the optical waveguide portion with respect to the mesa protector portion, and a connection portion that is disposed on the resin portion and electrically connects the electrode to the electrode pad.

Abstract: An integrated optical device includes first, second, third, and fourth edge portions; a plurality of modulators each of which includes an optical waveguide and an electrode portion provided on the optical waveguide, the optical waveguide extending in a direction of a first axis; a plurality of electric signal input sections arrayed along the first edge portion extending in a direction of a second axis intersecting with the first axis, each of the electric signal input sections being connected to one of the electrode portions of the modulators; an optical signal input section; and an optical signal output section provided in the second edge portion extending in the direction of the second axis. The modulators are arrayed in the direction of the second axis. In addition, the optical signal input section is provided in one of the second edge portion, the third edge portion, and the fourth edge portion.

Abstract: An integrated waveguide device that creates entanglement between a sequence of periodically spaced (in time) photons in a single input and output mode. The device consists of a polarization maintaining integrated waveguide chip containing a number of delay lines, integrated multimode interferometers with the potential for rapid switching, a polarization controller, an entangling gate, and off chip computer logic and timing. The device is capable of creating a diverse array of outputs such as linear cluster states and ring cluster states in a single output mode.

Abstract: An optical control element capable of efficiently removing unnecessary higher mode light without complicating a manufacturing process of the optical control element is provided. The optical control element includes a substrate having an electro-optical effect, optical waveguides that are formed on the substrate, and a control electrode that controls light waves propagating through the optical waveguides, and the optical waveguides include an output waveguide portion which derives fundamental mode light, and a subsidiary waveguide portion which is connected to the output waveguide portion and derives higher mode light, and removal means is formed in contact with the subsidiary waveguide portion, for removing the higher mode light propagating through the subsidiary waveguide portion.

Abstract: An optical device includes first and second optical modulators formed on a substrate having electro-optical effect. The first optical modulator includes a first optical waveguide; a first signal electrode configured to provide a first data signal for the first optical waveguide; and a first DC electrode, arranged at an output side of the first signal electrode, and configured to provide first DC voltage for the first optical waveguide. The second optical modulator includes a second optical waveguide; a second signal electrode configured to provide a second data signal for the second optical waveguide; and a second DC electrode provided, arranged at an input side of the second signal electrode, and configured to provide second DC voltage for the second optical waveguide. Input portions of the first and second signal electrodes are arranged at a same side edge of the substrate.

Abstract: A photonic device having a wavelength-dependent transmission or filter characteristic, comprising: a Splitter Polarization Rotator (SPR) configured to receive an input wave having a first polarization and outputting a first wave having the first polarization and a second wave having a second polarization different from the first polarization; first and second waveguide arms connected to the SPR configured to propagate the first and second waves respectively; and a Polarization Rotator and Combiner for combining the propagated first and second waves; wherein the dimensions of the first waveguide arm and the second waveguide arm are selected to cancel the influence of an external effect on the wavelength-dependent characteristic. Another aspect of the invention relates to a method for reducing the sensitivity of said integrated photonic device, comprising splitting a polarized light beam, propagating light waves of different through two waveguide arms of specific dimensions, and recombining them.

Abstract: The invention relates to a process for fabricating a semiconductor ridge pin junction (20, 21). According to the invention, judicious choices are made when defining hard masks and the sequence in which resist masks are formed for implantation (doping) and etching, which choices enable the conventional photolithography technique to be used despite the low precision of mask alignment (±100 nm) relative to underlying regions. By virtue of the process according to the invention, a ridge pin junction is formed, at lower cost and with shorter production times than in the prior art, with doped regions precisely spaced apart from the edge of the ridge.

Abstract: An optical modulator includes a first graphene and a second graphene on an upper surface of a semiconductor layer, a first electrode on the first graphene, and a second electrode on the second graphene. Respective side surfaces of the first graphene and the second graphene are separated from each other. A first ridge portion of the semiconductor layer and a second ridge portion on the second graphene constitute an optical waveguide, and the first and second graphenes are on a center portion of the optical waveguide in a vertical direction to the semiconductor.