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 that restrains output power of light that has a wavelength converted from reducing due to a pyroelectric effect when a temperature of a wavelength conversion element including a ferroelectric substrate is changed is a wavelength conversion device that 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: 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: There is provided an optical waveguide chip. In the optical waveguide chip, an optical waveguide circuit includes a substrate, a lower clad layer laminated on the substrate, a core layer that is laminated on the lower clad layer and corresponds to a propagation path of an optical signal, and an upper clad layer laminated on the core layer; the upper and lower clad layers in a region that does not correspond to the propagation path of the optical signal are removed across to an edge of the chip; the region from which the upper and lower clad layers have been removed is filled with a light absorbing material; and a height of the filled light absorbing material is higher than a height of an uppermost surface of the upper clad layer.

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: 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 configuration of an excitation light generation device for providing an excitation light having a good SN ratio to a PSA is disclosed. Further, a configuration of a relay amplifier of the PSA including the excitation light generation device is also shown. The following disclosure includes the excitation light generation device, an optical amplification device including the excitation light generation device, and an optical transmission system. More specifically, the excitation light generation device for maintaining the SN ratio of the excitation light in a high state by utilizing an optical sensitive amplification function with respect to the excitation light generated by an optical phase lock loop is disclosed. The excitation light generation device of the present disclosure generates a local oscillation excitation light using the OPLL and having a sufficiently high SN ratio, which makes an inherent low noise operation of the PSA possible even to a signal light having a high SN ratio.

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 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.