Wavelength conversion device

Abstract

Provided is a wavelength conversion device that makes it possible to highly accurately measure the temperature of a wavelength conversion element in the wavelength conversion device in a non-contact manner using an etalon filter. Specifically, provided is a wavelength conversion device (200) that inputs and outputs visible light and near-infrared light, the wavelength conversion device (200) comprising: a wavelength conversion element (101) configured to convert the wavelengths of the visible light and the near-infrared light; an etalon filter (201) disposed on an optical path of either the wavelength-converted visible light or near-infrared light output from the wavelength conversion element; and a light receiving element (215) disposed on the output side of the etalon filter and configured to detect either a change in the wavelength of the visible light or a change in the intensity of amplified spontaneous emission (ASE) of the near-infrared light.

Description

Wavelength conversion device

[0001] The present disclosure relates to a wavelength conversion device using a nonlinear optical effect used in optical communication systems and optical measurement systems, and specifically relates to a configuration for measuring the temperature of a wavelength conversion element with high accuracy.

[0002] For the generation and modulation of coherent light spanning the ultraviolet region-visible region-infrared region-terahertz region for applications such as optical signal wavelength conversion, optical modulation, optical measurement, optical processing, medical treatment, and bioengineering in optical communication, many wavelength conversion devices as disclosed in Patent Document 1 and Patent Document 2 have been developed.

[0003] Many nonlinear optical elements are used as wavelength conversion elements employed in wavelength conversion devices, and various materials have been researched and developed for nonlinear optical elements. Oxide-based compound substrates such as lithium niobate (LiNbO₃) and periodically poled lithium niobate (PPLN) are known as promising materials with very high second-order nonlinear optical constants. As an example of an optical device utilizing the high nonlinear optical characteristics of such materials, wavelength conversion elements using second harmonic generation, difference frequency generation, and sum frequency generation based on quasi-phase matching are known.

[0004] When an optical waveguide made of lithium niobate or the like is used in a laboratory, a processed element (chip) can be installed and used as it is. However, when the optical waveguide is incorporated into a device or shipped as a commercial product, for product protection and convenience, it is common practice to implement packaging in which a group of related elements required for use are enclosed together in a single package container as a functional component called a module.

[0005] Fig. 1 shows the configuration of a conventional wavelength conversion device 100 including a wavelength conversion element. Fig. 1 is a top view of the wavelength conversion device 100. The wavelength conversion device 100 is an example of a 4-port module including an input port 109a for near-infrared light, an input port 109b for visible light, an output port 111a for near-infrared light, and an output port 111b for visible light. Arrows indicate the propagation direction of light.

[0006] The wavelength conversion device 100 comprises a wavelength conversion element 101, a temperature control element 103 such as a Peltier element, a carrier 105, and a temperature measuring instrument 107. The temperature control element 103 and the temperature measuring instrument 107 can be controlled and operated via pins 103p for the temperature control element and 107p for the temperature measuring instrument, respectively.

[0007] Japanese Patent Publication No. 2017-147299 Japanese Patent Publication No. 2018-190868

[0008] IH Malitson, “Interspecimen Comparison of the Refractive Index of Fused Silica,” J. Opt. Soc. Am. 55, 1205-1209 (1965)

[0009] In this wavelength conversion device 100, when high-intensity light propagates through the wavelength conversion element 101, light absorption occurs in the wavelength conversion element 101, generating heat. The characteristics of the wavelength conversion element vary greatly with temperature, and this heat generation causes changes in the optical characteristics of the wavelength conversion element, such as its refractive index. Therefore, conventional wavelength conversion devices 100 are provided with a temperature control element 103 to stabilize the temperature of the wavelength conversion element 101, and a carrier 105 to uniformly dissipate heat or cool the entire wavelength conversion element 101. The temperature control element 103 is controlled based on temperature data measured by a temperature measuring instrument 107 positioned near or connected to the wavelength conversion element 101, and adjusts the temperature of the wavelength conversion element 101.

[0010] However, if the temperature measuring instrument 107 is brought into contact with the wavelength conversion element 101 itself in order to measure its temperature with high accuracy, there is a possibility of damage or degradation of the element due to the contact itself. Also, if the temperature measuring instrument 107 is placed at a distance from the wavelength conversion element 101 as shown in Figure 1, a distance is created between the wavelength conversion element 101 and the temperature measuring instrument 107, which presents a problem in that the true temperature of the wavelength conversion element 101 cannot be measured properly.

[0011] This disclosure addresses the above-mentioned issues and provides a wavelength conversion device configuration that can measure temperature with high accuracy using an etalon filter instead of conventional temperature measuring instruments such as thermistors.

[0012] According to an embodiment for achieving this objective, the present invention provides a wavelength conversion device for inputting and outputting visible light and near-infrared light, comprising: a wavelength conversion element configured to convert the wavelengths of visible light and near-infrared light; an etalon filter disposed on the optical path of either the wavelength-converted visible light or the near-infrared light output from the wavelength conversion element; and a photodetector disposed on the output side of the etalon filter and configured to detect either a change in the wavelength of the visible light or a change in the intensity of the naturally radiated amplified light (ASE) of the near-infrared light.

[0013] The invention described in claim 2 provides a wavelength conversion device according to claim 1, further comprising a waveplate disposed between a wavelength conversion element and an etalon filter, and an optical element disposed on the output side of the waveplate.

[0014] The invention described in claim 3 provides a wavelength conversion device according to claim 1, further comprising a first temperature control element connected to at least one surface of the wavelength conversion element and configured to control the wavelength conversion element to a predetermined temperature.

[0015] The invention described in claim 4 provides a wavelength conversion device according to claim 3, further comprising a first carrier disposed between the wavelength conversion element and the first temperature control element, configured to make the temperature of the entire wavelength conversion element uniform.

[0016] The invention described in claim 5 provides a wavelength conversion device according to claim 1, further comprising a second temperature control element connected to at least one surface of the etalon filter and configured to control the etalon filter to a predetermined temperature.

[0017] The invention described in claim 6 provides a wavelength conversion device according to claim 5, further comprising a second carrier disposed between an etalon filter and a second temperature control element and configured to make the temperature of the entire etalon filter uniform, and a temperature measuring instrument connected to at least one surface of the second carrier and configured to measure the temperature of the etalon filter and control the second temperature control element.

[0018] The invention described in claim 7 provides a wavelength conversion device according to claim 2, further comprising an angle adjustment mechanism for adjusting the waveplate to an arbitrary angle, wherein the angle adjustment mechanism adjusts the waveplate based on the output of either the output port or the photodetector.

[0019] Figure 1 is a top view showing a conventional wavelength conversion device. Figure 2(a) is a top view showing the configuration of a wavelength conversion device in one operational configuration, (b) is a graph showing the wavelength (λ) shift of the second harmonic detected by the photodetector due to the temperature change of the wavelength conversion element, and (c) is a graph showing the conversion formula and trend for converting the temperature characteristics of the phase matching curve into a temperature difference. Figure 3(a) is a top view showing the configuration of another wavelength conversion device in one operational configuration, and (b) is a graph showing the trend of the ASE spectrum intensity changing as the temperature changes. Figure 4 is a top view showing a modified configuration of a wavelength conversion device in one operational configuration. Figure 5 is a top view showing another modified configuration of a wavelength conversion device in one operational configuration. This figure shows the temperature change measurement mechanism using an etalon filter.

[0020] The embodiments of the wavelength conversion device of this disclosure will be described in detail below with reference to the figures. However, it will be obvious to those skilled in the art that the present invention is not limited to the embodiments described below, and that the embodiments and details can be modified in various ways without departing from the spirit of the invention disclosed herein. Furthermore, configurations of different embodiments can be combined as appropriate.

[0021] The operating principle of the present invention is described below. First, the etalon filter used for temperature measurement will be explained.

[0022] An etalon filter is a component that selectively transmits light of a specific wavelength using optical interference. Typically, an etalon filter consists of two parallel optical surfaces (e.g., glass) with a certain space between them, allowing interference to enhance or suppress specific wavelengths. This filter transmits only light of a specific wavelength through the interference effect, while other wavelengths are reflected or absorbed.

[0023] The basic principle of an etalon filter is based on interference. Specifically, the etalon structure causes interference in multiple paths as light travels, reflecting off two parallel reflective surfaces. As light travels back and forth within the etalon, the light reflected from the reflective surfaces interferes with the light traveling forward. This interference effect is related to the wavelength of light, as the space within the etalon (the thickness of the interference filter) is associated with the wavelength of light. Therefore, interference at specific wavelengths can be amplified and transmitted. Consequently, etalon filters have high wavelength selectivity, allowing for very precise transmission of light of specific wavelengths.

[0024] The wavelength selectivity of an etalon filter allows for highly accurate measurement of temperature changes in a wavelength conversion element. For example, when the temperature of a wavelength conversion element changes, the frequency and intensity of the light output from the element change with temperature. When the light output from the wavelength conversion element is incident on an etalon filter, the fringe period after passing through the etalon filter fluctuates according to the amount of change in frequency and intensity. Finally, the fluctuation in the fringe period of the etalon filter can be converted into the temperature change in the wavelength conversion element.

[0025] Non-patent document 1 shows the relationship between the refractive index (n) and the wavelength (λ) in an etalon filter (in the case of quartz (SiO2)) (see Equation 1). In other words, because the frequency of light incident on the etalon filter changes with temperature, the fringe period after transmission through the etalon filter also changes. The temperature coefficient of the wavelength conversion element is 0.14 nm / °C, and it can be seen that the wavelength of the second harmonic output from the wavelength conversion element changes by 0.14 nm per 1°C. For example, if the wavelength of the signal input to an etalon filter with a length of 500 μm changes from 775 nm (reference temperature, e.g., 20°C) to 775.3 nm, the period (v) of the signal detected by the photodiode (PD) via the etalon filter changes from 206.2183217 GHz to 206.2191028 GHz. The period difference (Δv) is 781 kHz, and when the temperature change is converted using the temperature coefficient mentioned above, it corresponds to a difference of 2.14 °C (see Figure 6).

[0026]

[0027] Therefore, by using an etalon filter, it is possible to measure the temperature change in a wavelength conversion element (more precisely, the wavelength change of the wavelength conversion element in response to temperature changes) with high precision.

[0028] The embodiments of this disclosure will now be described with reference to the drawings. There are two main types of embodiments described below. One involves placing an etalon filter in the visible light optical path and utilizing the second harmonic generation (SHG) of visible light, while the other involves placing an etalon filter in the near-infrared light optical path and utilizing amplified spontaneous emission (ASE) of near-infrared light. The wavelength conversion device utilizing SHG will be described in the first and third embodiments, and the wavelength conversion device utilizing ASE will be described in the second and fourth embodiments.

[0029] (First Embodiment) Figure 2(a) is a top view showing the configuration of a wavelength converter 200 according to the first embodiment of the present disclosure. The wavelength converter 200 according to this embodiment is a four-port wavelength converter equipped with an input port 109a for near-infrared light and an input port 109b for visible light, as well as an output port 111a for near-infrared light and an output port 111b for visible light. The arrows indicate the direction of light propagation.

[0030] A four-port wavelength converter that inputs and outputs visible and near-infrared light is a device that converts light of different wavelengths. Typically, it utilizes the nonlinear optical properties of wavelength conversion elements to convert light of a specific wavelength to another. Representative techniques include four-wave mixing, difference frequency generation, and second-order nonlinear effects (e.g., color filters, parametric oscillation). This makes it possible to convert light with a specific wavelength (e.g., visible light) to another wavelength (near-infrared light).

[0031] A four-port wavelength converter typically has two input ports 109a and 109b and two output ports 111a and 111b. For example, near-infrared light can be input to one input port 109a, and visible light to the other input port 109b. Different wavelengths can then be output to the output ports; for example, near-infrared light can be output to one output port 111a, and visible light to the other output port 111b. Conversion between these ports can be performed, for example, from visible light to near-infrared light, or vice versa.

[0032] The wavelength conversion device 200 comprises a wavelength conversion element 101, a first temperature control element 103 for stabilizing the temperature of the wavelength conversion element 101, and a first carrier 105 for uniformly dissipating heat or cooling the entire wavelength conversion element 101. The first temperature control element 103 can be controlled and operated via a pin 103p for the first temperature control element. Here, the wavelength conversion element 101 is a nonlinear optical element whose material contains at least one of LiNbO3, KNbO3, LiTaO3, LiNb(x)Ta(1-x)O3 (0≦x≦1), or KTiOPO4, or whose material contains at least one of the group consisting of Mg, Zn, Sc, and In as an additive.

[0033] The wavelength conversion device 200 includes an etalon filter 201 for measuring the temperature of the wavelength conversion element 101. The etalon filter 201 itself also has a temperature dependence, and in order to eliminate the influence of this temperature dependence and measure only the temperature of the wavelength conversion element 101, a second carrier 205 and a second temperature control element 203 connected to the second carrier 205 are provided on one side of the etalon filter 201. The second carrier 205 is equipped with a second temperature measuring instrument 207 for monitoring the temperature of the etalon filter 201 or the temperature of the vicinity, and maintains the etalon filter 201 at a constant temperature based on the temperature information measured by the second temperature measuring instrument 207.

[0034] The wavelength conversion device 200 includes a waveplate 209 positioned to adjust the polarization angle of the wavelength-modified visible light output from the wavelength conversion element 101, thereby determining the amount of light incident on the output port 111b for visible light and the etalon filter 201. The angle-adjusted light is then split by an optical element (e.g., a polarizing beam splitter (PBS)) 211 located on the output side of the waveplate 209 into light traveling to the output port 111b and light traveling to the etalon filter 201. The light then output through the etalon filter 201 is detected by a photodetector (e.g., a photodetector) 215 located on the output side of the etalon filter 201.

[0035] The temperature measurement mechanism of the wavelength conversion device 200 in this embodiment will be described below. In this embodiment, the temperature of the wavelength conversion element 101 is measured using visible light output through the wavelength conversion element 101. Therefore, the etalon filter 201 is placed on the optical path of the visible light. However, in the following description, the propagation of light from the input port to the wavelength conversion element 101 will be omitted, and the mechanism for measuring the temperature of the wavelength conversion element 101, which is the objective of this embodiment, will be described, focusing on the output light from the wavelength conversion element 101 onwards.

[0036] To measure the temperature of the wavelength conversion element 101, the etalon filter 201 needs to be placed on the visible light optical path. Therefore, the visible light needs to be branched into a separate optical path for temperature measurement. However, since the wavelength-changed visible light output from the wavelength conversion element 101 is unipolarized (one of either vertical or horizontal polarization), it is difficult to branch it simply using an optical element such as a PBS. Therefore, a waveplate 209 is placed on the output side of the wavelength conversion element 101, and after adjusting the amount of light sent to the etalon filter 201 and the amount of light sent to the visible light output port 111b, the light is branched into two optical paths by an optical element 211 provided on the output side of the waveplate 209.

[0037] One of the branched visible light beams is incident on an etalon filter 201 located in a separate optical path. As described above, the output (especially the wavelength) of the etalon filter 201 fluctuates with temperature changes. Specifically, when the temperature of the wavelength conversion element 101 deviates from a certain reference temperature (20°C in this embodiment), the phase matching wavelength changes, and the wavelength of the light transmitted through the etalon filter 201 changes (see Figure 2(b)). As a result, the period of the etalon fringe also changes. For example, as shown in Figure 6, when the wavelength of the light transmitted through the etalon filter 201 changes from 775 nm to 775.3 nm, the period of the light transmitted through the etalon filter 201 changes from 206.2183217 GHz to 206.2191028 GHz. The difference in period (Δν) at this time is 781.0382 kHz.

[0038] By converting this period difference into a temperature difference from the temperature characteristics of the phase matching curve, the actual temperature of the wavelength conversion element 101 can be accurately measured (see Figure 2(c)). For example, since the temperature coefficient of a known etalon filter is 0.14 nm / °C, the period difference of 781.0382 kHz in the example corresponds to 2.142857°C, and the measured temperature of the wavelength conversion element 101 is 22.142857°C.

[0039] (Second Embodiment) Figure 3(a) is a top view showing the configuration of a wavelength converter 300 according to a second embodiment of the present disclosure. The wavelength converter 300 according to this embodiment is a four-port type wavelength converter, similar to the wavelength converter 200 according to the first embodiment. The arrows indicate the direction of light propagation.

[0040] The main difference between the wavelength conversion device 300 according to this embodiment and the wavelength conversion device 200 according to the first embodiment is that the etalon filter 201 for temperature measurement is placed on the optical path of near-infrared light, and the intensity fluctuation of the near-infrared ASE is used to measure the temperature of the wavelength conversion element 101. Therefore, the wavelength conversion devices according to the first and second embodiments have the same components, but only the placement of the etalon filter 201 is different.

[0041] As shown in Figure 3(a), in order to split the near-infrared light, the waveplate 209 and the optical element 211 are positioned between the wavelength conversion element 101 and the output port 111a for near-infrared light. Specifically, the wavelength conversion device 300 includes a waveplate 209 positioned to adjust the polarization angle of the wavelength-changed near-infrared light output from the wavelength conversion element 101 to determine the amount of light incident on the output port 111a for near-infrared light and the etalon filter 201. The angle-adjusted light is then split by an optical element (e.g., a polarizing beam splitter (PBS)) 211 positioned on the output side of the waveplate 209 into light that travels to the output port 111a and light that travels to the etalon filter 201. Subsequently, the light output through the etalon filter 201 is detected by a photodetector (e.g., a photodetector) 215 positioned on the output side of the etalon filter 201.

[0042] The temperature measurement mechanism of the wavelength conversion device 300 in this embodiment will now be described. In this embodiment, the temperature of the wavelength conversion element 101 is measured using near-infrared light output through the wavelength conversion element 101. Therefore, the etalon filter 201 is placed on the optical path of the near-infrared light.

[0043] For temperature measurement of the wavelength conversion element 101, the etalon filter 201 needs to be arranged on the optical path of near-infrared light. Therefore, the near-infrared light needs to be branched into a separate optical path for temperature measurement. However, since the wavelength-converted visible light output from the wavelength conversion element 101 is single-polarized light (one polarization of vertical polarization or horizontal polarization), it is difficult to simply branch the light with an optical element such as a PBS. Therefore, after arranging a wave plate 209 on the output side of the wavelength conversion element 101 and adjusting the amount of light sent to the etalon filter 201 and the amount of light sent to the near-infrared light output port 111a, the light is branched into two optical paths by an optical element 211 provided on the output side of the wave plate 209.

[0044] One of the branched near-infrared light beams enters the etalon filter 201 arranged in a separate optical path. As described above, an etalon filter is a filter that utilizes the light interference effect, and functions to enhance light of a specific wavelength (or wavelength range) and suppress light of other wavelengths. In other words, the etalon filter exhibits the strongest transmission at the designed wavelength, and has lower transmittance at other wavelengths.

[0045] For example, when the temperature of the wavelength conversion element 101 deviates from a certain reference temperature (20° C. in the present embodiment), the phase matching wavelength changes, and the wavelength of light transmitted through the etalon filter 201 changes from 775 nm to 775.3 nm. In this case, the ASE intensity of light output at the constant reference temperature deviates from the design value, so the ASE intensity of light output via the etalon filter 201 changes (see FIG. 3b). Therefore, by converting the temperature characteristic of the ASE intensity into a temperature difference, the actual temperature of the wavelength conversion element 101 can be accurately measured.

[0046] (Third Embodiment) FIG. 4 is a top view showing the configuration of a modified wavelength conversion device 400 of the wavelength conversion device 200 according to the first embodiment of the present disclosure. The wavelength conversion device 400 according to the present embodiment has substantially the same configuration as the wavelength conversion device 200 according to the first embodiment, except that it includes a wave plate angle adjustment mechanism 401 capable of adjusting the wave plate 209.

[0047] The wavelength plate angle adjustment mechanism 401 can compensate for variations in the characteristics of the wavelength conversion element 101 mounted therein when the wavelength conversion device 400 is actually manufactured or produced. In order to detect visible light or near-infrared light with a light-receiving element, a light intensity above a certain level is required. However, when the angle of the wavelength plate 209 is fixed, there is a risk that light cannot be detected by the light-receiving element when a wavelength conversion element having slightly different characteristics is mounted. Therefore, the wavelength plate angle adjustment mechanism 401 ensures normal operation of the wavelength conversion device 400 after manufacture or production.

[0048] In FIG. 4, the wavelength plate angle adjustment mechanism 401 is illustrated as being formed on one side surface of the wavelength conversion device 400, but without being limited thereto, it may be formed on the top surface or the bottom surface of the wavelength conversion device 400. Further, although the wavelength plate angle adjustment mechanism 401 is illustrated on the outer surface of the wavelength conversion device 400, it may be formed on the inner surface thereof.

[0049] The wavelength plate angle adjustment mechanism 401 is electrically or mechanically connected to the wavelength plate 209, and adjusts the angle of the wavelength plate 209 based on the light intensity detected by the light-receiving element 215. Alternatively, the wavelength plate angle adjustment mechanism 401 may adjust the angle of the wavelength plate 209 based on the light intensity detected at the output port 111b for visible light.

[0050] (Fourth Embodiment) FIG. 5 is a top view showing the configuration of a modified wavelength conversion device 500 of the wavelength conversion device 300 according to the second embodiment of the present disclosure. The wavelength conversion device 500 according to the present embodiment has substantially the same configuration as the wavelength conversion device 300 according to the second embodiment described above, except that it includes a wavelength plate angle adjustment mechanism 401 capable of adjusting the wavelength plate 209.

[0051] The waveplate angle adjustment mechanism 401 can compensate for variations in the characteristics of the mounted wavelength conversion elements 101 when actually manufacturing or producing the wavelength conversion device 500. A certain level of light intensity is required for the photodetector to detect visible light or near-infrared light, but if the angle of the waveplate 209 is fixed, there is a risk that the photodetector may not be able to detect light when mounting wavelength conversion elements with slightly different characteristics. Therefore, the waveplate angle adjustment mechanism 401 guarantees the normal operation of the wavelength conversion device 500 after manufacturing or production.

[0052] In Figure 5, the waveplate angle adjustment mechanism 401 is shown to be formed on one side of the wavelength conversion device 500, but it is not limited to being formed on the top or bottom surface of the wavelength conversion device 500. Also, although the waveplate angle adjustment mechanism 401 is shown on the outer surface of the wavelength conversion device 500, it may be formed on the inner surface.

[0053] The waveplate angle adjustment mechanism 401 is electrically or mechanically connected to the waveplate 209 and adjusts the angle of the waveplate 209 based on the light intensity detected by the photodetector 215. Alternatively, the waveplate angle adjustment mechanism 401 may adjust the angle of the waveplate 209 based on the light intensity detected by the near-infrared light output port 111a.

[0054] (Additional Considerations) The above description of embodiments of the present invention is presented for illustrative purposes only and is not intended to be exhaustive or to limit to the exact forms disclosed. Those skilled in the art will understand that many modifications and changes are possible in light of the above disclosure.

[0055] Finally, the language used herein has been selected primarily for readability and instructional purposes, and may not be selected to describe or limit the subject matter of the invention. Therefore, the scope of the invention is intended to be limited by the appended claims, not by this detailed description. Accordingly, the disclosure of embodiments of the invention is intended to illustrate, not limit, the scope of the invention as described in the claims.

[0056] This provides a configuration for a wavelength conversion device that allows for non-contact and highly accurate measurement of the temperature of the wavelength conversion element in the wavelength conversion device using an etalon filter.

[0057] 100, 200, 300, 400, 500 Wavelength conversion device 101 Wavelength conversion element 103, 203 Temperature control element 103p, 203p Pins for temperature control element 105, 205 Carrier 107, 207 Temperature measuring instrument 107p, 207p Pins for temperature measuring instrument 109a Input port for near-infrared light 109b Input port for visible light 111a Output port for near-infrared light 111b Output port for visible light 201 Etalon filter 209 Waveplate 211 Optical element 213 Mirror 215 Photodetector 401 Mechanism for adjusting the angle of the waveplate

Claims

1. A wavelength conversion device for inputting and outputting visible light and near-infrared light, comprising: a wavelength conversion element configured to convert the wavelengths of the visible light and the near-infrared light; an etalon filter disposed on the optical path of either the wavelength-converted visible light or the near-infrared light output from the wavelength conversion element; and a photodetector disposed on the output side of the etalon filter and configured to detect either a change in the wavelength of the visible light or a change in the intensity of the naturally radiated amplified light (ASE) of the near-infrared light.

2. The wavelength conversion device according to claim 1, further comprising: a waveplate disposed between the wavelength conversion element and the etalon filter; and an optical element disposed on the output side of the waveplate.

3. The wavelength conversion device according to claim 1, further comprising a first temperature control element connected to at least one surface of the wavelength conversion element and configured to control the wavelength conversion element to a predetermined temperature.

4. The wavelength conversion apparatus according to claim 3, further comprising a first carrier disposed between the wavelength conversion element and the first temperature control element, configured to make the temperature of the entire wavelength conversion element uniform.

5. The wavelength conversion apparatus according to claim 1, further comprising a second temperature control element connected to at least one surface of the etalon filter and configured to control the etalon filter to a predetermined temperature.

6. The wavelength conversion apparatus according to claim 5, further comprising: a second carrier disposed between the etalon filter and the second temperature control element and configured to make the temperature of the entire etalon filter uniform; and a temperature measuring instrument connected to at least one surface of the second carrier and configured to measure the temperature of the etalon filter and control the second temperature control element.

7. The wavelength conversion device according to claim 2, further comprising: an angle adjustment mechanism provided for adjusting the waveplate to an arbitrary angle, wherein the angle adjustment mechanism adjusts the waveplate based on the output of either an output port or the photodetector.

8. The wavelength conversion device according to claim 1, wherein the wavelength conversion element contains at least one of LiNbO3, KNbO3, LiTaO3, LiNb(x)Ta(1-x)O3 (0≦x≦1), or KTiOPO4 as a material, or contains at least one of the group consisting of Mg, Zn, Sc, and In as an additive to the material.

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