Nonlinear optical device

Abstract

A nonlinear optical device (1) comprises: a nonlinear optical waveguide (2); a multiplexing / demultiplexing mirror (3) that reflects signal light emitted from an optical fiber (10) to cause the signal light to enter the nonlinear optical waveguide (2), and transmits excitation light emitted from an optical fiber (11) to cause the excitation light to enter the nonlinear optical waveguide (2); and a multiplexing / demultiplexing mirror (4) that reflects the signal light emitted from the nonlinear optical waveguide (2) to cause the signal light to enter an optical fiber (12), and transmits the excitation light emitted from the nonlinear optical waveguide (2) to cause the excitation light to enter an optical fiber (13).

Description

Nonlinear Optical Devices

[0001] The present invention relates to a nonlinear optical device used in an optical communication system or an optical control system.

[0002] Many nonlinear optical and electro-optical devices are being developed to generate and modulate coherent light ranging from the ultraviolet to the visible, infrared, and terahertz regions in fields such as optical signal wavelength conversion and optical modulation in optical communications, optical measurement, optical processing, medicine, and bioengineering. Various materials are being researched and developed as nonlinear optical and electro-optical media for use in such devices.

[0003] Lithium niobate (LiNbO ３ Oxide-based compound substrates such as GaN, GaN-based GaN, and GaN-based GaN substrates have very high second-order nonlinear optical constants and electro-optic constants and are known as promising materials. Periodically poled lithium niobate (PPLN) is known as an example of an optical device that utilizes this high nonlinearity. PPLN can realize second harmonic generation (SHG), difference frequency generation (DFG), and sum frequency generation (SFG), and is known to be able to realize wavelength conversion devices.

[0004] By using a wavelength conversion device with high wavelength conversion efficiency, it is possible to construct an amplifier for signal light, called an optical parametric amplifier, by transferring energy from pump light to signal light. In particular, phase-sensitive amplifiers, which have amplification characteristics that correspond to the phase relationship between pump light and signal light, are expected to be a technology that can achieve low-noise optical amplification. Furthermore, the degenerate optical parametric amplification process can generate photon pairs with quantum correlation, and can generate non-classical states such as squeezed light generation and heralded single-photon states. The light that can be generated by the degenerate optical parametric amplification process is expected to be an important resource for optical quantum computers and quantum optical sensing technologies.

[0005] In recent years, wavelength conversion devices have been implemented as optical fiber-coupled modules, and by improving compatibility with various optical fiber devices, research and development in application fields has been accelerating (Non-Patent Document 1).

[0006] As mentioned above, there are high expectations for nonlinear optical devices incorporating nonlinear optical waveguides made of ferroelectric materials such as lithium niobate. A conventional nonlinear optical device 100, as shown in Figure 11, is composed of lenses 101-106, wavelength multiplexing / demultiplexing mirrors (dichroic mirrors) 107-110, and a nonlinear optical waveguide 111.

[0007] Signal light enters nonlinear optical device 100 from optical fiber 112, and pump light enters nonlinear optical device 100 from optical fiber 113. The signal light is converted into parallel light by lens 101, reflected by dichroic mirror 107, and incident on dichroic mirror 108. The pump light is converted into parallel light by lens 102 and incident on dichroic mirror 108. The signal light and pump light are combined by dichroic mirror 108, condensed by lens 103, and incident on nonlinear optical waveguide 111.

[0008] In the nonlinear optical waveguide 111, the signal light is amplified by the parametric effect with the pump light and exits the nonlinear optical waveguide 111. At this time, not all of the pump light contributes to amplification; part of the pump light also exits the nonlinear optical waveguide 111 together with the amplified signal light. The light exiting the nonlinear optical waveguide 111 is focused by lens 104 and separated into pump light and signal light by dichroic mirror 109. The signal light is focused by lens 105, exits the nonlinear optical device 100, and enters optical fiber 114. The pump light is reflected by mirror 110, focused by lens 106, exits the nonlinear optical device 100, and enters optical fiber 115.

[0009] In a configuration such as nonlinear optical device 100 in which multiple lenses 101-106 and dichroic mirrors 107-110 are individually arranged, signal light passes through or is reflected at least six times at the interface between the optical components and air before being coupled to nonlinear optical waveguide 111. For this reason, conventional nonlinear optical device 100 has had the problem of large loss of signal light. When considering applications to photonic technology, etc., it is necessary to reduce loss of signal light as much as possible and realize a low-loss nonlinear optical device.

[0010] Takahiro Kashiwazaki et al., “Fabrication of low-loss quasi-single-mode PPLN waveguide and its application to a modularized broadband high-level squeezer”, Applied Physics Letters, vol.119, 251104, 2021

[0011] The present invention has been made to solve the above problems, and has an object to provide a low-loss nonlinear optical device.

[0012] A nonlinear optical device of the present invention comprises a nonlinear optical waveguide, a first multiplexing / demultiplexing mirror configured to reflect signal light output from a first optical fiber to input it into the nonlinear optical waveguide and to transmit pump light output from a second optical fiber to input it into the nonlinear optical waveguide, and a second multiplexing / demultiplexing mirror configured to reflect the signal light output from the nonlinear optical waveguide to input it into a third optical fiber and to transmit the pump light output from the nonlinear optical waveguide to input it into a fourth optical fiber, wherein the first multiplexing / demultiplexing mirror couples the signal light and the pump light to the nonlinear optical waveguide so that the optical axes of the signal light and the pump light input to the nonlinear optical waveguide coincide with the optical axis of the nonlinear optical waveguide, and the second multiplexing / demultiplexing mirror separates the signal light and the pump light output from the nonlinear optical waveguide, and couples the signal light to the third optical fiber and the pump light to the fourth optical fiber.

[0013] According to the present invention, by combining the conventionally used lens and mirror into one, the number of times that the signal light passes through the interface between the optical component and the air can be reduced, thereby reducing the loss of the signal light and realizing a low-loss nonlinear optical device.

[0014] FIG. 1 is a block diagram showing the configuration of a nonlinear optical device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of a multiplexing / demultiplexing mirror according to the first embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of a nonlinear optical device according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view showing an example of a multiplexing / demultiplexing mirror and a signal light reflecting mirror according to the second embodiment of the present invention. FIG. 5 is a cross-sectional view illustrating a parabolic curved surface. FIG. 6 is a cross-sectional view showing an example of a multiplexing / demultiplexing mirror and a signal light reflecting mirror according to a third embodiment of the present invention. FIG. 7 is a cross-sectional view showing an example of a multiplexing / demultiplexing mirror and a signal light reflecting mirror according to the third embodiment of the present invention. FIG. 8 is a block diagram showing the configuration of a nonlinear optical device according to a fourth embodiment of the present invention. FIG. 9 is a block diagram showing the configuration of a nonlinear optical device according to a fifth embodiment of the present invention. FIG. 10 is an enlarged view of the input side of the nonlinear optical device according to the fifth embodiment of the present invention. FIG. 11 is a block diagram showing the configuration of a conventional nonlinear optical device.

[0015] [First Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of a nonlinear optical device according to a first embodiment of the present invention. The nonlinear optical device 1 includes a nonlinear optical waveguide 2, a multiplexing / demultiplexing mirror 3 that reflects signal light output from an optical fiber 10 to input it into the nonlinear optical waveguide 2 and transmits pump light output from an optical fiber 11 to input it into the nonlinear optical waveguide 2, and a multiplexing / demultiplexing mirror 4 that reflects the signal light output from the nonlinear optical waveguide 2 to input it into an optical fiber 12 and transmits the pump light output from the nonlinear optical waveguide 2 to input it into an optical fiber 13.

[0016] The multiplexing / demultiplexing mirror 3 couples the signal light and the pump light to the nonlinear optical waveguide 2 so that the optical axes of the signal light and the pump light incident on the nonlinear optical waveguide 2 coincide with the optical axis of the nonlinear optical waveguide 2. The multiplexing / demultiplexing mirror 4 separates the signal light and the pump light output from the nonlinear optical waveguide 2, and couples the signal light to the optical fiber 12 and the pump light to the optical fiber 13.

[0017] 2 is a cross-sectional view of the multiplexing / demultiplexing mirrors 3 and 4, cut along a plane including the optical axis of the light incident on the nonlinear optical waveguide 2, the optical axis of the light exiting the nonlinear optical waveguide 2, and the optical axis of the nonlinear optical waveguide 2. The curved surfaces (signal light reflecting surfaces) 30 and 40 of the multiplexing / demultiplexing mirrors 3 and 4 closer to the nonlinear optical waveguide 2 are coated with a coating film that reflects the signal light and transmits the pump light. On the other hand, the curved surfaces 31 and 41 of the multiplexing / demultiplexing mirrors 3 and 4 farther from the nonlinear optical waveguide 2 are coated with a coating film that transmits the pump light. The formation of these coating films enables the realization of optical devices with even lower loss. The coating film is preferably a dielectric multilayer film.

[0018] When designing the multiplexing / demultiplexing mirror 3, the shape of the curved surface 30 is determined so that the signal light is efficiently coupled to the nonlinear optical waveguide 2, and then the shape of the curved surface 31 is determined so that the pump light is efficiently coupled to the nonlinear optical waveguide 2.

[0019] An example of the shape of the curved surface 30 is an elliptical surface having two focal points. An elliptical surface focuses light emitted from one focal point at the other focal point. Therefore, the optical fiber 10, the multiplexing / demultiplexing mirror 3, and the nonlinear optical waveguide 2 are arranged so that one focal point of the curved surface 30 coincides with the center position of the output end face of the optical fiber 10, and the other focal point of the curved surface 30 coincides with the center position of the input end face of the nonlinear optical waveguide 2. This makes it possible to achieve highly efficient coupling between the optical fiber 10 and the nonlinear optical waveguide 2.

[0020] The shape of the multiplexing / demultiplexing mirror 4 is the same as that of the multiplexing / demultiplexing mirror 3. The nonlinear optical waveguide 2, the multiplexing / demultiplexing mirror 4, and the optical fiber 12 are arranged so that one focal position of the curved surface 40 of the multiplexing / demultiplexing mirror 4 coincides with the center position of the output end face of the nonlinear optical waveguide 2, and the other focal position of the curved surface 40 coincides with the center position of the input end face of the optical fiber 12. This makes it possible to achieve highly efficient coupling between the nonlinear optical waveguide 2 and the optical fiber 12.

[0021] As described above, in this embodiment, by combining the conventionally used lens and mirror into one, it is possible to reduce the number of times that the signal light passes through the interface between the optical component and the air, which is the main cause of loss, and therefore it is possible to reduce the loss of the signal light and realize a low-loss nonlinear optical device.

[0022] 3 is a block diagram showing the configuration of a nonlinear optical device according to a second embodiment of the present invention. A nonlinear optical device 1a of this embodiment has at least one signal light reflecting mirror 5 inserted between an optical fiber 10 for inputting signal light and a multiplexing / demultiplexing mirror 3a, and at least one signal light reflecting mirror 6 inserted between a multiplexing / demultiplexing mirror 4a and an optical fiber 12 for outputting signal light.

[0023] As in the first embodiment, the multiplexing / demultiplexing mirror 3a couples the signal light and the pump light to the nonlinear optical waveguide 2 so that the optical axes of the signal light and the pump light incident on the nonlinear optical waveguide 2 coincide with the optical axis of the nonlinear optical waveguide 2. The multiplexing / demultiplexing mirror 4a separates the signal light and the pump light output from the nonlinear optical waveguide 2, and couples the signal light to the optical fiber 12 and the pump light to the optical fiber 13.

[0024] In this embodiment, by inserting the signal light reflecting mirrors 5 and 6, the optical fiber 10 for inputting signal light and the optical fiber 11 for inputting pumping light can be arranged parallel or nearly parallel, and the optical fiber 12 for outputting signal light and the optical fiber 13 for outputting pumping light can be arranged parallel or nearly parallel. Therefore, in this embodiment, the nonlinear optical device 1a can be made compact and have a structure that is easy to mount.

[0025] 4 is a cross-sectional view of the multiplexing / demultiplexing mirrors 3a, 4a and the signal light reflecting mirrors 5, 6, cut along a plane including the optical axis of the light incident on the nonlinear optical waveguide 2, the optical axis of the light exiting the nonlinear optical waveguide 2, and the optical axis of the nonlinear optical waveguide 2. As in the first embodiment, a coating film that reflects the signal light and transmits the pump light is formed on the curved surfaces (signal light reflecting surfaces) 30a, 40a of the multiplexing / demultiplexing mirrors 3a, 4a that are closer to the nonlinear optical waveguide 2. A coating film that transmits the pump light is formed on the curved surfaces 31a, 41a of the multiplexing / demultiplexing mirrors 3a, 4a that are farther from the nonlinear optical waveguide 2. A coating film that reflects the signal light is formed on the curved surfaces 50, 60 of the signal light reflecting mirrors 5, 6, on which the signal light is incident.

[0026] When designing the multiplexing / demultiplexing mirror 3 a and the signal light reflecting mirror 5, the shapes of the curved surfaces 30 a and 50 are determined so that the signal light is efficiently coupled to the nonlinear optical waveguide 2, and then the shape of the curved surface 31 a is determined so that the pump light is efficiently coupled to the nonlinear optical waveguide 2.

[0027] An example of the shape of the curved surfaces 30a, 50 is a parabolic curved surface as shown in Figure 5. A parabolic curved surface focuses incident parallel light onto a focal point. Furthermore, light emitted from the focal point becomes parallel light when reflected by the parabolic curved surface. Therefore, the optical fiber 10, the multiplexing / demultiplexing mirror 3a, the signal light reflecting mirror 5, and the nonlinear optical waveguide 2 are arranged so that the focal position of the curved surface 50 coincides with the center position of the output end face of the optical fiber 10, and the focal position of the curved surface 30a coincides with the center position of the input end face of the nonlinear optical waveguide 2. This allows for highly efficient coupling between the optical fiber 10 and the nonlinear optical waveguide 2.

[0028] The shape of the multiplexing / demultiplexing mirror 4a is the same as that of the multiplexing / demultiplexing mirror 3a, and the shape of the signal light reflecting mirror 6 is the same as that of the signal light reflecting mirror 5. The nonlinear optical waveguide 2, the multiplexing / demultiplexing mirror 4a, the signal light reflecting mirror 6, and the optical fiber 12 are arranged so that the focal position of the curved surface 40a of the multiplexing / demultiplexing mirror 4a coincides with the center position of the output end face of the nonlinear optical waveguide 2, and so that the focal position of the curved surface 60 coincides with the center position of the input end face of the optical fiber 12. This makes it possible to achieve highly efficient coupling between the nonlinear optical waveguide 2 and the optical fiber 12.

[0029] In this embodiment, the insertion of the signal light reflecting mirrors 5 and 6 increases the degree of freedom in the arrangement of the mirrors, thereby greatly reducing the difficulty of fabricating the nonlinear optical device 1a.

[0030] [Third Example] When a signal light reflecting mirror is inserted as in the second example, it is not necessary to make both the signal light reflecting surface of the multiplexing / demultiplexing mirror and the signal light reflecting surface of the signal light reflecting mirror curved; one of the reflecting surfaces may be flat (with an infinite radius of curvature).

[0031] 6 and 7 are cross-sectional views of the multiplexing / demultiplexing mirrors 3b and 4b and the signal light reflecting mirrors 5b and 6b of this embodiment, taken along a plane including the optical axis of the light entering the nonlinear optical waveguide, the optical axis of the light exiting the nonlinear optical waveguide, and the optical axis of the nonlinear optical waveguide. In the examples of Figures 6 and 7, the signal light reflecting surfaces 30b and 40b of the multiplexing / demultiplexing mirrors 3b and 4b are flat. An example of the shape of such multiplexing / demultiplexing mirrors 3b and 4b is a plano-convex lens.

[0032] As in the first and second embodiments, a coating film that reflects the signal light and transmits the pump light is formed on the signal light reflecting surfaces 30b, 40b of the multiplexing / demultiplexing mirrors 3b, 4b. A coating film that transmits the pump light is formed on the curved surfaces 31b, 41b opposite the signal light reflecting surfaces 30b, 40b of the multiplexing / demultiplexing mirrors 3b, 4b. A coating film that reflects the signal light is formed on the curved surfaces 50b, 60b of the signal light reflecting mirrors 5b, 6b, on which the signal light is incident.

[0033] When designing the multiplexing / demultiplexing mirror 3b and the signal light reflecting mirror 5b, the shape of the curved surface 50b is determined so that the signal light is efficiently coupled to the nonlinear optical waveguide 2, and then the shape of the curved surface 31b is determined so that the pump light is efficiently coupled to the nonlinear optical waveguide 2.

[0034] In the second embodiment, the curved surfaces 30a, 31a, and 50 are described as being parabolic surfaces, but in this embodiment, the signal light is focused only by the structure of the curved surface 50b of the signal light reflecting mirror 5b. Therefore, if the curved surface 50b is made an elliptical surface, the signal light can be focused at the center of the incident end face of the nonlinear optical waveguide 2, thereby achieving highly efficient coupling between the optical fiber 10 and the nonlinear optical waveguide 2. The shape of the multiplexing / demultiplexing mirror 4b is the same as that of the multiplexing / demultiplexing mirror 3b, and the shape of the signal light reflecting mirror 6b is the same as that of the signal light reflecting mirror 5b.

[0035] [Fourth Example] Figure 8 is a block diagram showing the configuration of a nonlinear optical device according to a fourth example of the present invention. This example is a specific example of the third example. Lithium niobate doped with ZnO was used as the material for the nonlinear optical waveguide 2 of the nonlinear optical device 1b of this example. The material for the nonlinear optical waveguide 2 may also be a ferroelectric material such as lithium tantalate or potassium titanyl phosphate.

[0036] The optical fiber 10 for inputting signal light and the optical fiber 12 for outputting signal light were polarization-maintaining fibers for optical communication in the 1.56 μm band. The optical fiber 11 for inputting pumping light and the optical fiber 13 for outputting pumping light were polarization-maintaining fibers capable of propagating light with a wavelength of 780 nm in single mode. In this example, the signal light wavelength was set to approximately 1560 nm and the pumping light wavelength was set to approximately 780 nm, but it goes without saying that these wavelengths are not necessarily limited to these.

[0037] In this embodiment, no optical components through which signal light passes are used, so that loss of signal light, which occurs in conventional nonlinear optical devices, is not observed, and the effect of the present invention was confirmed.

[0038] 9 is a block diagram showing the configuration of a nonlinear optical device according to a fifth embodiment of the present invention. This embodiment is a specific example of the second embodiment. The nonlinear optical waveguide 2 and optical fibers 10 to 13 used are the same as those used in the fourth embodiment.

[0039] 10 is an enlarged view of the input side of the nonlinear optical device 1a of this embodiment. As explained in the second embodiment, the signal light reflecting surfaces 50 and 60 of the signal light reflecting mirrors 5 and 6 and the signal light reflecting surfaces 30a and 40a of the multiplexing / demultiplexing mirrors 3a and 4a are parabolic curved surfaces. Therefore, it is necessary to collimate the pump light so that it is incident on the multiplexing / demultiplexing mirror 3a. Therefore, a lens 7 that converts the pump light into collimated light is inserted between the optical fiber 11 for inputting the pump light and the multiplexing / demultiplexing mirror 3a.

[0040] Furthermore, since the signal light reflecting surface 40a of the multiplexing / demultiplexing mirror 4a is a parabolic curved surface, the pump light emitted from the multiplexing / demultiplexing mirror 4a becomes parallel light, and therefore it is necessary to focus the pump light. Therefore, a lens 8 for focusing the pump light is inserted between the multiplexing / demultiplexing mirror 4a and the optical fiber 13 for outputting the pump light. In this embodiment, too, no loss of signal light, which occurs in conventional nonlinear optical devices, was observed, confirming the effects of the present invention.

[0041] Some or all of the above embodiments may be described as, but are not limited to, the following supplementary notes.

[0042] (Supplementary Note 1) A nonlinear optical device of the present invention comprises a nonlinear optical waveguide, a first multiplexing / demultiplexing mirror configured to reflect signal light output from a first optical fiber to input it into the nonlinear optical waveguide and to transmit pump light output from a second optical fiber to input it into the nonlinear optical waveguide, and a second multiplexing / demultiplexing mirror configured to reflect the signal light output from the nonlinear optical waveguide to input it into a third optical fiber and to transmit the pump light output from the nonlinear optical waveguide to input it into a fourth optical fiber, wherein the first multiplexing / demultiplexing mirror couples the signal light and the pump light to the nonlinear optical waveguide so that the optical axes of the signal light and the pump light input to the nonlinear optical waveguide coincide with the optical axis of the nonlinear optical waveguide, and the second multiplexing / demultiplexing mirror separates the signal light and the pump light output from the nonlinear optical waveguide, and couples the signal light to the third optical fiber and the pump light to the fourth optical fiber.

[0043] (Supplementary Note 2) In the nonlinear optical device described in Supplementary Note 1, a coating film that reflects signal light and transmits pump light is formed on a signal light reflecting surface, which is a surface of the first and second multiplexing / demultiplexing mirrors that is closer to the nonlinear optical waveguide, and a coating film that transmits pump light is formed on a surface of the first and second multiplexing / demultiplexing mirrors opposite to the signal light reflecting surface.

[0044] (Supplementary Note 3) In the nonlinear optical device according to Supplementary Note 1, the signal light reflecting surfaces of the first and second multiplexing / demultiplexing mirrors, which are surfaces closer to the nonlinear optical waveguide, are elliptical curved surfaces.

[0045] (Supplementary Note 4) The nonlinear optical device described in Supplementary Note 1 further includes a first signal light reflecting mirror inserted between the first optical fiber and the first multiplexing / demultiplexing mirror and configured to reflect signal light from the first optical fiber and make it incident on the first multiplexing / demultiplexing mirror, and a second signal light reflecting mirror inserted between the second multiplexing / demultiplexing mirror and the third optical fiber and configured to reflect signal light from the second multiplexing / demultiplexing mirror and make it incident on the third optical fiber.

[0046] (Supplementary Note 5) In the nonlinear optical device described in Supplementary Note 4, the signal light reflecting surfaces of the first and second multiplexing / demultiplexing mirrors, which are surfaces closer to the nonlinear optical waveguide, and the signal light reflecting surfaces of the first and second signal light reflecting mirrors are parabolic curved surfaces.

[0047] (Supplementary Note 6) In the nonlinear optical device described in Supplementary Note 4, the signal light reflecting surfaces of the first and second multiplexing / demultiplexing mirrors, which are surfaces closer to the nonlinear optical waveguide, are flat, and the signal light reflecting surfaces of the first and second signal light reflecting mirrors are elliptically curved surfaces.

[0048] (Supplementary Note 7) The nonlinear optical device described in Supplementary Note 5 further includes a first lens inserted between the second optical fiber and the first multiplexing / demultiplexing mirror and configured to convert the pump light from the second optical fiber into parallel light, and a second lens inserted between the second multiplexing / demultiplexing mirror and the fourth optical fiber and configured to focus the pump light from the second multiplexing / demultiplexing mirror.

[0049] (Supplementary Note 8) In the nonlinear optical device according to any one of Supplementary Notes 1 to 7, the nonlinear optical waveguide is made of lithium niobate, lithium tantalate, or potassium titanyl phosphate.

[0050] The present invention can be applied to wavelength conversion devices and the like.

[0051] 1, 1a, 1b... nonlinear optical device, 2... nonlinear optical waveguide, 3, 3a, 3b, 4, 4a, 4b... multiplexing / demultiplexing mirror, 5, 5b, 6, 6b... signal light reflecting mirror, 7, 8... lens, 10 to 13... optical fiber.

Claims

1. A non-linear optical waveguide, a first multiplexer / demultiplexer mirror configured to reflect signal light emitted from a first optical fiber and cause the reflected signal light to enter the non-linear optical waveguide, and to transmit pump light emitted from a second optical fiber and cause the transmitted pump light to enter the non-linear optical waveguide, and a second multiplexer / demultiplexer mirror configured to reflect signal light emitted from the non-linear optical waveguide and cause the reflected signal light to enter a third optical fiber, and to transmit pump light emitted from the non-linear optical waveguide and cause the transmitted pump light to enter a fourth optical fiber. The first multiplexer / demultiplexer mirror couples the signal light and the pump light to the non-linear optical waveguide such that the optical axes of the signal light and the pump light incident on the non-linear optical waveguide coincide with the optical axis of the non-linear optical waveguide. The second multiplexer / demultiplexer mirror separates the signal light and the pump light emitted from the non-linear optical waveguide, couples the signal light to the third optical fiber, and couples the pump light to the fourth optical fiber. A non-linear optical device characterized by the above.

2. The non-linear optical device according to claim 1, wherein a coating film that reflects signal light and transmits pump light is formed on a signal light reflection surface, which is a surface of the first and second multiplexer / demultiplexer mirrors closer to the non-linear optical waveguide, and a coating film that transmits pump light is formed on a surface of the first and second multiplexer / demultiplexer mirrors opposite to the signal light reflection surface. A non-linear optical device characterized by the above.

3. The non-linear optical device according to claim 1, wherein a signal light reflection surface, which is a surface of the first and second multiplexer / demultiplexer mirrors closer to the non-linear optical waveguide, is an elliptical curved surface. A non-linear optical device characterized by the above.

4. The non-linear optical device according to claim 1, further comprising a first signal light reflection mirror inserted between the first optical fiber and the first multiplexer / demultiplexer mirror and configured to reflect signal light from the first optical fiber and cause the reflected signal light to enter the first multiplexer / demultiplexer mirror, and a second signal light reflection mirror inserted between the second multiplexer / demultiplexer mirror and the third optical fiber and configured to reflect signal light from the second multiplexer / demultiplexer mirror and cause the reflected signal light to enter the third optical fiber. A non-linear optical device characterized by the above.

5. In the nonlinear optical device according to claim 4, the signal light reflecting surface, which is the surface of the first and second multiplexing / demultiplexing mirrors closer to the nonlinear optical waveguide, and the signal light reflecting surfaces of the first and second signal light reflecting mirrors are parabolic surfaces. A nonlinear optical device characterized by this.

6. In the nonlinear optical device according to claim 4, the signal light reflecting surface, which is the surface of the first and second multiplexing / demultiplexing mirrors closer to the nonlinear optical waveguide, is a plane, and the signal light reflecting surfaces of the first and second signal light reflecting mirrors are elliptical surfaces. A nonlinear optical device characterized by this.

7. In the nonlinear optical device according to claim 5, a first lens inserted between the second optical fiber and the first multiplexing / demultiplexing mirror and configured to convert the excitation light from the second optical fiber into parallel light, and a second lens inserted between the second multiplexing / demultiplexing mirror and the fourth optical fiber and configured to condense the excitation light from the second multiplexing / demultiplexing mirror are further provided. A nonlinear optical device characterized by this.

8. In the nonlinear optical device according to any one of claims 1 to 7, the nonlinear optical waveguide is made of lithium niobate, lithium tantalate, or potassium titanyl phosphate. A nonlinear optical device characterized by this.

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