Optical device

Abstract

An optical device (3) disclosed in the present application comprises: an optical element (20); and an optical system (300) that condenses light of a first wavelength and light of a second wavelength at an incident end of the optical element. The optical system (300) is configured such that the condensing position of the light of the first wavelength and the condensing position of the light of the second wavelength are substantially the same. In one embodiment, the optical system includes a diffusion lens (301) that diffuses the light of the first wavelength, a collimating lens (12) that collimates the light of the second wavelength, and a condensing lens (14) that condenses the diffused light of the first wavelength and the collimated light of the second wavelength at substantially the same focal position. In another embodiment, the optical system includes a collimating lens (11) that collimates the light of the first wavelength, a collimating lens (12) that collimates the light of the second wavelength, and an achromatic lens (401) that condenses the collimated light of the first wavelength and the collimated light of the second wavelength at substantially the same focal position.

Description

Optical device

[0001] The present disclosure relates to an optical device, and more particularly to an optical device that inputs and outputs light of different wavelengths.

[0002] Conventionally, as an optical device that inputs and outputs light of different wavelengths, an optical device having a waveguide made of a nonlinear optical medium (hereinafter also referred to as a "nonlinear optical medium waveguide") is known (see, for example, Patent Documents 1 and 2). As one such optical device, there is known a wavelength conversion device in which light of wavelength λ1 (frequency ω1) and light of wavelength λ2 (frequency ω2) are input to a nonlinear optical medium waveguide to generate sum frequency (ω3=ω1+ω2) and difference frequency generation (ω1-ω2). As another optical device, there is known an optical parametric amplifier that utilizes an optical parametric process, that is, inputs light of wavelength λ3 (frequency ω3) and light of wavelength λ2 (frequency ω2) into a nonlinear optical medium waveguide, and outputs amplified light of wavelength λ2 (frequency ω2) and light of wavelength λ1 (frequency ω1).

[0003] A schematic configuration of a conventional optical device will be described with reference to FIG. 1. FIG. 1(a) is a top view, and FIG. 1(b) is a cross-sectional view taken along section line Ib-Ib. As shown in FIG. 1(a), the optical device 1 includes an optical system 10, an optical element 20, and a package 40. In the package 40, together with the optical system 10 and the optical element 20, a thermistor and a Peltier element (not shown) for controlling the operating temperature of the optical element 20 are mounted.

[0004] The optical system 10 includes a collimating lens 11 disposed at the exit end of an optical fiber 30 through which light of wavelength λ1 propagates, a collimating lens 12 disposed at the exit end of an optical fiber 31 through which light of wavelength λ2 propagates, a dichroic mirror 13 configured to transmit the light of wavelength λ1 converted into parallel light by the collimating lens 11 and reflect the light of wavelength λ2 converted into parallel light by the collimating lens 12, and a condensing lens 14 that condenses the light of wavelength λ1 and the light of wavelength λ2 coming from the dichroic mirror 13.

[0005] The optical element 20 includes a substrate 21 and a nonlinear optical medium waveguide 22 disposed on the substrate 21. The nonlinear optical medium waveguide 22 can be, for example, LiNbO3, LiTaO3, LiNb(x)Ta(1-x)O3 (0≦x≦1), or one of these containing at least one additive selected from the group consisting of Mg, Zn, Sc, and In. In one example, the optical element 20 can be a periodically polled lithium niobate (PPLN) waveguide in which a LiTaO3 substrate as the substrate 21 and a ZnO-doped LiNbO3 having a periodically reversing polarization structure as the nonlinear optical medium waveguide 2 are directly joined. Figure 1(b) shows a nonlinear optical medium waveguide 22 with a ridge waveguide structure, but bulk crystals can also be used if it is possible to confine the propagating light and suppress its spread.

[0006] In the optical device 1 shown in Figure 1, light with wavelength λ1 emitted from the optical fiber 30 becomes free-space light and is converted into parallel light by the collimating lens 11. Similarly, light with wavelength λ2 emitted from the optical fiber 31 becomes free-space light and is converted into parallel light by the collimating lens 12. The light with wavelengths λ1 and λ2, converted into parallel light, are focused by the focusing lens 14 and coupled to the nonlinear optical medium waveguide 22.

[0007] For example, if the optical device 1 is an optical parametric amplifier, signal light is input from optical fiber 30 and pump light is input from optical fiber 31. In this case, the relationship between the wavelength λ1 of the signal light and the wavelength λ2 of the pump light is λ1 ≈ 2λ2.

[0008] Japanese Patent Publication No. 2011-128368, Patent No. 7417160

[0009] The focal point of a focusing lens shifts according to the wavelength of light. Figure 2 shows the relationship between wavelength and focal point shift due to aberration in the focusing lens 14. If the optical device 1 described above is an optical parametric amplifier, and the wavelength λ1 of the signal light is 1.5 μm and the wavelength λ2 of the pump light is 0.8 μm, then the focal point of the pump light shifts by about 0.1 mm from the focal point of the signal light.

[0010] Figure 1 shows that the focal point of light with wavelength λ1 is located at the end face of the nonlinear optical medium waveguide 22, while the focal point of light with wavelength λ2 is shifted between the focusing lens 14 and the nonlinear optical medium waveguide 22. The coupling efficiency of light with wavelength λ1 to the nonlinear optical medium waveguide 22 is high, while the coupling efficiency of light with wavelength λ2 is low. As a result, the wavelength conversion efficiency and light intensity amplification factor of the optical element 20 decrease.

[0011] This disclosure has been made in view of these problems and aims to provide an optical device that can suppress the difference in coupling efficiency between light of different wavelengths.

[0012] To achieve this objective, an optical device in one embodiment of the present disclosure includes an optical element and an optical system that focuses light of a first wavelength and light of a second wavelength onto the incident end of the optical element. The optical system is configured such that the focusing position of the light of the first wavelength and the focusing position of the light of the second wavelength are substantially the same.

[0013] As described above, according to one embodiment of the present disclosure, it is possible to suppress the difference in coupling efficiency between light of different wavelengths.

[0014] This figure illustrates the schematic configuration of a conventional optical device, where (a) is a top view and (b) is a cross-sectional view along the cross-sectional line Ib-Ib. This figure shows the relationship between wavelength and focal shift due to aberrations in the focusing lens. This figure shows the schematic configuration of an optical device according to one embodiment of the present disclosure. This figure shows the schematic configuration of an optical device according to another embodiment of the present disclosure. This figure illustrates the achromatic lens used in the optical device of Figure 4. This figure shows the relationship between wavelength and focal shift due to aberrations in the achromatic lens of the optical device of Figure 4. This figure illustrates a modified form of the optical device of Figure 4.

[0015] Embodiments of this disclosure will be described in detail below with reference to the drawings. Identical or similar reference numerals indicate identical or similar elements, and repeated descriptions may be omitted. Numerical values ​​and materials in the following description are illustrative, and other numerical values ​​and materials may be used in embodiments of this disclosure without departing from the spirit of this disclosure.

[0016] The optical devices according to various embodiments of the present disclosure include an optical element and an optical system that focuses light of a first wavelength and light of a second wavelength onto the incident end of the optical element. The optical system is configured such that the focusing position of the light of the first wavelength and the focusing position of the light of the second wavelength are substantially the same.

[0017] (First Embodiment) Referring to Figure 3, this is a schematic diagram showing the general configuration of an optical device according to one embodiment of the present invention. The optical device 3 in Figure 3 includes an optical system 300, an optical element 20, and a package 40. The optical element 20 and the package 40 are the same as those of the optical device 1 in Figure 1, so their description is omitted.

[0018] The optical system 300 includes a diffusion lens 301 positioned at the output end of an optical fiber 30 through which light of wavelength λ1 is guided, a collimating lens 12 positioned at the output end of an optical fiber 31 through which light of wavelength λ2 is guided, a dichroic mirror 13 configured to transmit the light of wavelength λ1 converted into diffuse light by the diffusion lens 301 and reflect the light of wavelength λ2 converted into parallel light by the collimating lens 12, and a focusing lens 14 that focuses the light of wavelength λ1 and the light of wavelength λ2 from the dichroic mirror 13.

[0019] In the optical device 3 shown in Figure 3, light of wavelength λ1 emitted from the optical fiber 30 becomes free-space light and is converted to diffused light by the diffusion lens 301. Meanwhile, light of wavelength λ2 emitted from the optical fiber 31 becomes free-space light and is converted to parallel light by the collimating lens 12. The light of wavelength λ1 converted to diffused light and the light of wavelength λ2 converted to parallel light are focused by the focusing lens 14 and coupled to the nonlinear optical medium waveguide 22.

[0020] In the optical device 1 of Figure 1, the optical system 10 was configured so that both light of wavelength λ1 and light of wavelength λ2 were incident on the focusing lens 14 as parallel light. In the optical device 3 of this embodiment, the light of wavelength λ1 is converted into diffuse light by the diffusion lens 301, and the configuration is such that the focusing position of the light of wavelength λ1 by the focusing lens 14 is approximately the same as the focusing position of the parallel light of wavelength λ2.

[0021] As described above, according to the configuration of the optical device 3 of this embodiment, as shown in Figure 3, the shift in the focal position between light of different wavelengths λ1 and λ2 can be reduced to approach zero. Therefore, it is possible to suppress the difference in coupling efficiency between light of different wavelengths in the optical device 3. As a result, the wavelength conversion efficiency and light intensity amplification rate of the optical element 20 are improved.

[0022] (Second Embodiment) Referring to Figure 4, this is a schematic diagram showing the general configuration of an optical device according to another embodiment of the present invention. The optical device 4 in Figure 4 includes an optical system 400, an optical element 20, and a package 40. The optical element 20 and the package 40 are the same as those of the optical device 1 in Figure 1, so their description is omitted.

[0023] The optical system 400 includes a collimating lens 11 positioned at the output end of an optical fiber 30 that guides light of wavelength λ1, a collimating lens 12 positioned at the output end of an optical fiber 31 that guides light of wavelength λ2, a dichroic mirror 13 configured to transmit the light of wavelength λ1 converted into parallel light by the collimating lens 12 and reflect the light of wavelength λ2 converted into parallel light by the collimating lens 12, and an achromatic lens 401 that focuses the light of wavelength λ1 and the light of wavelength λ2 from the dichroic mirror 13 to substantially the same focal position.

[0024] Figure 5 shows a schematic configuration of an achromatic lens. The achromatic lens 401 is a lens made by bonding together multiple media with different refractive indices for different wavelengths (multiple media with different wavelength dispersions).

[0025] Figure 6 shows the relationship between wavelength and focal shift in the achromatic lens 401. As shown in Figure 6, the achromatic lens 401 can be configured to focus light of different wavelengths to approximately the same focal position. Even when the optical device 4 described above is an optical parametric amplifier, that is, when the wavelength λ1 of the signal light is 1.5 μm and the wavelength λ2 of the pump light is 0.8 μm, the focal position of the wavelength λ2 of the pump light can be approximately the same as the end face of the nonlinear optical medium waveguide 22.

[0026] In the optical device 4 shown in Figure 4, light with wavelength λ1 emitted from the optical fiber 30 becomes free-space light and is converted into parallel light by the collimating lens 11. Similarly, light with wavelength λ2 emitted from the optical fiber 31 becomes free-space light and is converted into parallel light by the collimating lens 12. Both the light with wavelength λ1 and the light with wavelength λ2, converted into parallel light, are focused by the achromatic lens 401 and coupled to the nonlinear optical medium waveguide 22.

[0027] As explained above, the optical device 4 in Figure 4 converts both light of wavelength λ1 and light of wavelength λ2 into parallel light, similar to the optical device 1 in Figure 1, but the focusing lens 14 in Figure 1 is replaced with an achromatic lens 401.

[0028] According to the configuration of the optical device 4 of this embodiment, as shown in Figure 4, the shift in the focal position between light of different wavelengths λ1 and λ2 is reduced to nearly zero. Therefore, it is possible to suppress the difference in coupling efficiency between light of different wavelengths in the optical device 4. As a result, the wavelength conversion efficiency and light intensity amplification rate of the optical element 20 are improved. Furthermore, the optical system 400 of the optical device 4 of this embodiment can be configured to propagate light of different wavelengths in parallel through space, enabling the securing of positional displacement tolerance and simplification of implementation.

[0029] (Modified Forms) Referring to Figure 7, modified forms of the optical devices in Figures 3 and 4 will be described. As shown in Figure 7, an achromatic lens 701 and dichroic mirrors 702 and 703 can be arranged on the output side of the optical element 20.

[0030] If the optical device is an optical parametric amplifier, and the wavelength λ1 of the signal light is 1.5 μm and the wavelength λ2 of the pump light is 0.8 μm, then the optical element 20 outputs residual pump light (wavelength λ2), amplified signal light (wavelength λ1), and idler light (wavelength λ3).

[0031] The light with wavelengths λ1, λ2, and λ3 emitted from the optical element 20 becomes free-space light, which is then converted into parallel light by the achromatic lens 701.

[0032] The dichroic mirror 702 is configured to reflect the remaining pump light (wavelength λ2) and transmit the amplified signal light (wavelength λ1) and idler light (wavelength λ3).

[0033] The dichroic mirror 703 is configured to reflect idler light (wavelength λ3) and transmit amplified signal light (wavelength λ1).

[0034] In this way, the achromatic lens 701 can extract light of different wavelengths output from the optical element 20 as parallel light. Furthermore, the dichroic mirrors 702 and 703 can separate light of a desired wavelength.

[0035] This disclosure makes it possible to provide an optical device that can suppress the difference in coupling efficiency between light of different wavelengths.

[0036] 1, 3, 4 Optical devices 10, 300, 400, 700 Optical systems 11, 12 Collimating lenses 13, 702, 703 Dichroic mirrors 14 Focusing lenses 20 Wavelength conversion elements 21 Substrates 22 Nonlinear optical medium waveguides 30, 31 Optical fibers 40 Packages 301 Diffusing lenses 401, 701 Achromatic lenses

Claims

1. An optical device comprising: an optical element; and an optical system for focusing light of a first wavelength and light of a second wavelength at the incident end of the optical element, wherein the optical system is configured such that the focusing position of the light of the first wavelength and the focusing position of the light of the second wavelength are substantially the same.

2. The optical device according to claim 1, comprising: a diffusion lens for diffusing light of the first wavelength; a collimating lens for making light of the second wavelength parallel; and a focusing lens for focusing the diffused light of the first wavelength and the parallelized light of the second wavelength at substantially the same focal position.

3. The optical device according to claim 1, comprising: a collimating lens that makes light of the first wavelength into parallel light; a collimating lens that makes light of the second wavelength into parallel light; and an achromatic lens that focuses the light of the first wavelength and the light of the second wavelength, which have been made into parallel light, to substantially the same focal position.

4. The optical device according to claim 1, further comprising a second optical system for converting light of multiple wavelengths emitted from the optical element into parallel light, wherein the second optical system includes an achromatic lens.

5. The optical device according to claim 1, wherein the light of the first wavelength is signal light, the light of the second wavelength is pump light, and the optical element has an optical parametric amplification function for amplifying the signal light.

6. The optical device according to claim 1, wherein the optical device has a wavelength conversion function that generates a difference frequency from the first wavelength and the second wavelength.

7. The optical device according to claim 1, wherein the optical device has a wavelength conversion function that generates a sum frequency from the first wavelength and the second wavelength.

8. The optical device according to claim 1, wherein the optical element comprises a nonlinear optical medium waveguide containing LiNbO3, LiTaO3, LiNb(x)Ta(1-x)O3 (0≦x≦1), or at least one selected from the group consisting of Mg, Zn, Sc, and In as an additive.

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