Abstract: A wavelength converter stabilizes output light intensity in which the light coupling efficiency to a light waveguide core is not easily varied. A mounting structure is adopted in which a substrate of a wavelength conversion element is a material with a lower refractive index for signal light than that of the core, and a support structure that suppresses elastic deformation by supporting the element through a contact at a tip end surface at a position corresponding to both end portions of the core at the occurrence of elastic deformation due to the thermal stress of the element is provided. The support structure is provided at a portion apart from a temperature control element at the top surface of a metal housing bottom surface member, and its top surface is disposed in the vicinity of a portion corresponding to both end portions of the core of the element in a support member.

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: A module structure that makes it easy to mount pigtail optical fibers by mounting a wavelength conversion apparatus, to enable adjustment of the path distance of optical signals, or to control the path distance of each individual polarization for polarization diversity control with high precision. The wavelength conversion apparatus is characterized in that when mounting a module having two or more input and output ports of a wavelength conversion apparatus, the module is configured to take out the input and output ports from two corresponding walls of the mounting housing, and also has a mechanism to control the path distance of at least one of the signal light and the excitation light input from each input and output port, and has a mechanism to separate the polarization of at least one of the signal light and the excitation light input from the ports and to control the path distance.

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: Stress applied to a wavelength conversion element is relaxed at the time of temperature control of the wavelength conversion element, and stable operation and improvement of long-term reliability of a wavelength conversion device are realized. A wavelength conversion device includes: a wavelength conversion element that receives excitation light and signal light and outputs wavelength-converted output signal light; a temperature control element that controls a temperature of the wavelength conversion element; an upper member that is provided between the wavelength conversion element and the temperature control element and transfers heat between the temperature control element and the wavelength conversion element; and a sheet-like adhesive sheet provided between the wavelength conversion element (and the upper member.

Abstract: In a nonlinear optical element, wavelength conversion efficiency is degraded by the heat generation caused when high-intensity converted waves are generated. Therefore, the present invention provides a wavelength conversion optical element that includes a periodically poled waveguide. In the wavelength conversion optical element, the periodically poled waveguide includes: a core that performs wavelength conversion on a fundamental wave that has entered the entrance end, and emits a converted wave from the exit end; and a cladding that covers the periphery of the core, and the structure of the element gradually changes so as to achieve quasi phase matching from the entrance end toward the exit end in the periodically poled waveguide.

Abstract: Provided is a wavelength conversion module that can be downsized by reducing the width of the housing and can reduce the mounting space. The wavelength conversion module including a wavelength conversion element includes: a lens barrel that is provided on a side surface of a metal housing and accommodates a lens for optically coupling the wavelength conversion element to an optical fiber; and a ferrule collar that is provided on the lens barrel and fixes a metal ferrule accommodating the optical fiber, and an input port and an output port are different from each other in any of the length in the optical axis direction of a plurality of the lens barrels, the length of a plurality of the metal ferrules, or a sum length of the lens barrels and the metal ferrules.

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: A balanced homodyne detection optical circuit according to the present disclosure is a planar optical waveguide circuit in which a circuit made of an optical waveguide including a dielectric or a semiconductor is formed on a substrate, the balanced homodyne detection optical circuit including an input port of local oscillator light and an input port of measurement light (squeezed light (including excitation light)), wherein a wavelength demultiplexing circuit which demultiplexes only the measurement light is arranged immediately after the input port of measurement light, a 50% multiplexing/demultiplexing circuit is arranged which causes squeezed light having been demultiplexed by the wavelength demultiplexing circuit and the local oscillator light to respectively branch at a branching ratio of 50% and to interfere with each other, and two output ports are arranged to which two outputs from the 50% multiplexing/demultiplexing circuit are guided.

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: 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 converter stabilizes output light intensity in which the light coupling efficiency to a light waveguide core is not easily varied. A mounting structure is adopted in which a substrate of a wavelength conversion element is a material with a lower refractive index for signal light than that of the core, and a support structure that suppresses elastic deformation by supporting the element through a contact at a tip end surface at a position corresponding to both end portions of the core at the occurrence of elastic deformation due to the thermal stress of the element is provided. The support structure is provided at a portion apart from a temperature control element at the top surface of a metal housing bottom surface member, and its top surface is disposed in the vicinity of a portion corresponding to both end portions of the core of the element in a support member.

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: 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: A balanced homodyne detection optical circuit according to the present disclosure is a planar optical waveguide circuit in which a circuit made of an optical waveguide including a dielectric or a semiconductor is formed on a substrate, the balanced homodyne detection optical circuit including an input port of local oscillator light and an input port of measurement light (squeezed light (including excitation light)), wherein a wavelength demultiplexing circuit which demultiplexes only the measurement light is arranged immediately after the input port of measurement light, a 50% multiplexing/demultiplexing circuit is arranged which causes squeezed light having been demultiplexed by the wavelength demultiplexing circuit and the local oscillator light to respectively branch at a branching ratio of 50% and to interfere with each other, and two output ports are arranged to which two outputs from the 50% multiplexing/demultiplexing circuit are guided.