Abstract: Reduction of output power of light with a wavelength converted is suppressed, which is caused by a pyroelectric effect that occurs when a temperature of a wavelength conversion element including a ferroelectric substrate is changed.

Abstract: A method for adjusting a transmission wavelength of signal light transmitted through an optical waveguide device provided with one or more optical waveguides through which the signal light having a wavelength of 1520 nm to 1560 nm and blue light having a wavelength of 375 nm to 455 nm pass, a groove through which the waveguide passes, and resin filled in the groove, including a step of passing the signal light and the blue light through the same or mutually different one or more optical waveguides and of passing the signal light and the blue light through the same or mutually different resin, the latter step changing a refractive index of the resin by irradiating the resin with the blue light so as to change the transmission wavelength of the signal light transmitted through the resin in accordance with a change in the refractive index of the resin.

Abstract: With a wavelength conversion device based on a nonlinear optical effect, when arrayed waveguides including an intended nonlinear waveguide are fabricated, unwanted slab waveguides are inevitably formed. The slab waveguides can cause an erroneous measurement in the selection of a waveguide having desired characteristics from the arrayed waveguides. The erroneous measurement can lead to redoing steps for fabricating the wavelength conversion device and a decrease in the yield and inhibit the evaluation of the characteristics in selection of the waveguide and the subsequent fabrication of the wavelength conversion device from being efficiently performed. A wavelength conversion device according to the present invention includes a plurality of waveguides formed on a substrate, and a plurality of slab waveguides that are arranged substantially in parallel with and spaced apart from the plurality of waveguides, and each of the slab waveguides has a grating structure that reflects light of a particular wavelength.

Abstract: According to the present disclosure, it is possible to realize an optical communication system in which a relay-type PSA and homodyne detection are efficiently combined using a single phase synchronization mechanism. Intensity noise and phase noise can be suppressed to a very low level, and accurate transmission of signals with increased multiplicity is enabled. By utilizing the features of the PSA to extract the phase of a single carrier using the sum frequency light of the signal light and its phase-conjugated light, the number of pilot carriers can be reduced compared to the configuration of the conventional optical communication system, and it is possible to suppress unnecessary nonlinear noise.

Abstract: A highly-efficient ridge waveguide includes a base substrate of a single-crystal and a core substrate made of a nonlinear optical medium, the base substrate and the core substrate being directly bonded, and includes a thin film layer formed on a surface of the core substrate on the upper side of a periodically polarization-reversed structure, and becomes a wavelength conversion element. A direct bonding method through thermal diffusion is applied to bonding. The core substrate has a ridge structure formed in a light propagating direction and a reversed structure formed by processing this. A surface of the core substrate is ground and a thin film layer is formed on the ground surface. A core formed by digging a core layer of the core substrate in an unbonded state is provided on an upper surface of an undercladding layer of the base substrate in a bonded state. Two side surfaces of the core are in contact with an air layer.

Abstract: Provided is an optical waveguide circuit in which the space between waveguides, a waveguide groove, or the space between fibers is filled with a resin where a wavelength shifts to positive (shifts backward) instead of a conventional resin where a wavelength shifts to negative (shifts forward), to return a refractive index having decreased by an instantaneous change to the original refractive index. In the filling resin with which the space between the waveguides, the waveguide groove, the space between the fibers, or the space between the fiber and the waveguide is filled, upon input of light, a refractive index of a portion through which the light passes instantaneously decreases, and then the refractive index gradually increases to compensate the initial decrease in the refractive index.

Abstract: A wavelength conversion optical element using a nonlinear optical effect of a device structure in which wavelength conversion efficiency rises as targeted when the length of a waveguide is increased is provided. The element adopts a waveguide structure using lithium niobate of a second-order nonlinear optical material. Wavelength conversion regions are formed to correspond to two linear waveguides extending in parallel to each other on a plane of the planar structure and correspond to the lengths of the two linear waveguides. One end side of the linear waveguide is an incident side of excitation light and one end side of the linear waveguide is an emission side of wavelength converted light. The linear waveguides excluding the incident side and the emission side are joined by a bent waveguide.

Abstract: An optical module includes two components that are optically connected, and includes a glass layer disposed in a region including an optical connection portion between the two components, at least one component includes a thin tube through which outside air is introduced, and an end face of the thin tube is in contact with the glass layer.

Abstract: A wavelength conversion device includes a second-order nonlinear optical medium with a polarization inversion structure, wherein the wavelength conversion device performs wavelength conversion between three wavelengths according to a relationship of 1/?1=1/?2+1/?3, a polarization inversion period ? of the polarization inversion structure is divided into 2a regions, and when the 2a regions divided from the polarization inversion period ? each has a width ratio of an inverted region and a non-inverted region of r to 1?r (where 0?r?1), a ratio value r is set such that, when one period in phase of a sine function from 0 to 2? is divided into 2a regions, a value of the sine function in a center of each divided region is (1?2r)±0.1.

Abstract: An optical signal processing device includes: a light source which generates a fundamental wave light; an optical modulator which modulates the fundamental wave light, and generates a fundamental wave light having a plurality of carriers synchronized in phase; an optical filter which passes through required components among the plurality of carriers; a first second-order nonlinear optical element on which a light which passes through the optical filter is incident, and which generates a second harmonic of the fundamental wave light; and a second second-order nonlinear optical element on which a signal light and the second harmonic are incident, the second second-order nonlinear optical element performing nondegenerate parametric amplification, wherein the second second-order nonlinear optical element has an output unit for picking up a wavelength converted light corresponding to difference in frequency between the signal light and the second harmonic or an amplified light of the signal light.

Abstract: A wavelength conversion device that restrains output power of light when a temperature of a wavelength conversion element, including a ferroelectric substrate, is changed. The wavelength conversion device includes, in a casing, the wavelength conversion element, a temperature control element that controls a temperature of the wavelength conversion element, a static elimination mechanism, and a surface potential measurement mechanism, and eliminates static electricity by driving the static elimination mechanism when the surface potential measurement mechanism detects a change in surface potential of the wavelength conversion element.

Abstract: To provide a planar lightwave circuit capable of being optically connected to a semiconductor optical element or an optical wiring component in a simple, precise, and stable manner without an increase in circuit footprint or the number of fabrication steps or a deterioration of characteristics. By arranging a dummy optical waveguide having a mirror function in the vicinity of an input/output waveguide of an optical functional circuit forming the planar lightwave circuit, a semiconductor optical element or an optical wiring component can be easily aligned with and fixed to the optical functional circuit by monitoring the reflection light intensity from the dummy optical waveguide. When the optical functional circuit has a plurality of input/output waveguides to be optically connected, each input/output waveguide can be identified if the dummy optical waveguides having the mirror function have different reflection properties (such as reflectance, width, position, or reflection wavelength).

Abstract: An optical module includes a planar lightwave circuit optically connected to an optical fiber; a fiber block to which the optical fiber is fixed; and a glass layer that bonds and fixes the fiber block and the planar lightwave circuit. The glass layer is provided in a portion through which light passes between the optical fiber and the planar lightwave circuit in a gap between the connection end face of the fiber block and the connection end face of the planar lightwave circuit. The optical module further includes a thin tube. The thin tube may be provided to penetrate the fiber block. The thin tube can be provided so as to penetrate the planar lightwave circuit or a fixture plate mounted on the planar lightwave circuit.

Abstract: A planar optical waveguide device which has improved resistance to optical loss and improved stability of the entire system of balanced homodyne detection is realized. An embodiment is an optical waveguide device for measurement of squeezed light using balanced homodyne detection, including an amplifier circuit that is connected to a signal light input port for inputting the squeezed light and performs phase-sensitive amplification, and a multiplexing/demultiplexing circuit that is connected to a local oscillator optical input port and an output of the amplifier circuit, has local oscillator light and the amplified squeezed light incident on the circuit, and outputs the light interfering with each other to two output ports.

Abstract: An optical amplifier of the present disclosure includes a Raman amplification unit and a parametric amplification unit that is configured of a second-order nonlinear element including a PPLN waveguide. In the optical amplifier, second harmonic lights are generated from a fundamental wave light having a wavelength that is slightly detuned to a shorter wavelength side with respect to a phase matching wavelength of the second-order nonlinear element, and is utilized as excitation light for the parametric amplification unit. By utilizing the excitation light based on the fundamental wave light of the wavelength detuned from the phase matching wavelength, a phase matching curve can be obtained in a wide band in a difference frequency generation (DFG) process of the second-order nonlinear element. The reduction in conversion efficiency of the wavelength near the excitation light in the parametric amplification unit is compensated by the Raman amplification unit.

Abstract: Even when excitation light having large power is used, damage at the end face of the optical fiber is suppressed, and reduction in wavelength conversion efficiency and reduction in phase sensitive amplification gain are prevented. An embodiment of the present invention relates to a wavelength conversion apparatus for performing a wavelength conversion operation by inputting a fundamental wave and a second-order harmonic into a second-order nonlinear optical medium, the wavelength conversion apparatus comprising: a second-order harmonic input optical fiber optically coupled to a waveguide of the second-order nonlinear optical medium, for inputting the second-order harmonic into the waveguide; and a second-order harmonic output optical fiber optically coupled to a waveguide, for outputting the second-order harmonic output from the waveguide, wherein the second-order harmonic input optical fiber and the second-order harmonic output optical fiber are polarization maintaining fibers.

Abstract: A wavelength conversion device includes a second-order nonlinear optical medium with a polarization inversion structure, wherein the wavelength conversion device performs wavelength conversion between three wavelengths according to a relationship of 1/?1=1/?2+1/?3, a polarization inversion period ? of the polarization inversion structure is divided into 2a regions, and when the 2a regions divided from the polarization inversion period ? each has a width ratio of an inverted region and a non-inverted region of r to 1?r (where 0?r?1), a ratio value r is set such that, when one period in phase of a sine function from 0 to 2? is divided into 2a regions, a value of the sine function in a center of each divided region is (1?2r)±0.1.

Abstract: In a wavelength conversion apparatus, reflection suppressors are provided on surfaces of optical elements indicating lenses , dichroic mirrors , and sealing windows excluding a wavelength conversion element in the apparatus between optical fibers F1 and F2 on the input side and optical fibers F3 and F4 on the output side, and on end surfaces of the optical fibers F3 and F4 on the output side. With this, even when light having a wavelength of a sum frequency component of signal light and excitation light is generated at the operation time of wavelength conversion of the wavelength conversion element, because the reflection suppressors suppress the reflection of unwanted light of the wavelength band, the unwanted light is unlikely to return to the wavelength conversion element and it is also possible to suppress a situation in which the unwanted light is mixed into the optical fibers F3 and F4.

Abstract: Provided is a wavelength conversion element capable of achieving highly efficient wavelength conversion, without relying on a method of applying electric fields. A wavelength conversion element is formed of a second-order nonlinear optical crystal and has a z-axis, running along a direction of spontaneous polarization, within a substrate plane. The wavelength conversion element includes a waveguide in which, when a plurality of circles having their centers on a straight line parallel to the z-axis and having the same radius are depicted so that circumferences of the plurality of circles contact each other, semicircular waveguides corresponding to one semicircles of the circumferences with the straight line as a boundary, are alternately connected.

Abstract: A problem is to provide a planar lightwave circuit optical device capable of facilitating mounting of connection to a printed circuit board and realizing downsizing of a device chip. A planar lightwave circuit optical device of the present invention is characterized by mounting an electrical connector (FPC connector) by means of soldering on an electrode pad of an electrical wire connected to an electrical drive unit (such as a heater) in a device formed by using a planar lightwave circuit (PLC).