JP2019113623A - Characteristic stabilization method for wavelength conversion element - Google Patents

Abstract

To solve the problems that: a wavelength conversion element utilizing PPLN-WG of conventional technology indirectly generates light of wavelength 520 nm band of sum frequency light of input light and SHG light generated in the element, and a wavelength conversion device using an SHG process has oscillations of 520 nm caused in the element; the PPLN-WG causes variation in refractive index with intense input power and light damage such that wavelength conversion characteristics deteriorate is caused; temperature control means which avoids those increases in size and the wavelength conversion device increases in size to require a larger power consumption; and since a temperature adjustment mechanism is added on a core side, the wavelength conversion element increases in manufacturing cost.SOLUTION: A wavelength conversion element according to the present invention comprises, on a substrate end face including an end face of a waveguide, an AR film characterized in preventing second wavelength conversion light generated from input light and wavelength conversion light from being reflected. Focusing attention on sum frequency light of frequency 3ω generated when SHG light is generated by making communication-wavelength signal light etc., of high input power incident on a PPLN-WG, an AR film which prevents light of a frequency zone 3ω from being reflected to suppress heat generation caused by the sum frequency light is formed on both end faces of a waveguide.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a wavelength conversion element. Specifically, the present invention relates to a wavelength conversion element that outputs light in a wavelength band used in optical communication.

  Wavelength conversion technology using non-linear optical effects in optical materials and parametric amplification technology have various application fields, and research and development are actively conducted in many organizations and organizations. In addition, wavelength conversion technology that performs signal processing in the form of light without converting optical signals into electrical signals is also a key technology for high-speed large-capacity optical communication. The wavelength conversion element is actively considered as low-noise amplification applying wavelength conversion technology to the optical communication field, batch conversion of wavelength band of WDM signal, and the like, and is regarded as important as a communication element. Among them, wavelength conversion elements using periodically poled lithium niobate waveguides (PPLN-WG: Periodically Poled Lithium Niobate-Wave Guide) realize an increase in light intensity by increasing the optical power density by forming a waveguide, Higher wavelength conversion efficiencies can be realized by using a quasi phase matching technique. The wavelength conversion element using PPLN-WG attracts attention as a device which plays an important role in the field of next-generation optical fiber communication and the field of quantum computing.

  For example, in a phase sensitive optical amplifier (PSA: Phase Sensitive Amplifier) capable of low noise optical amplification, it is used as a parametric amplification element or an excitation light generation element, and a high gain low noise optical amplifier has been proposed. Also, in the field of quantum computing, using PPLN-WG in fiber ring resonators and using it as a parametric oscillator, a demonstration of extremely high-speed and large-capacity calculation has been reported compared to previous computers. There is. In order to further enhance the performance of the technology to which these wavelength conversion elements are applied, it is important to realize an element with higher wavelength conversion efficiency.

T. Inagaki, et al. "A coherent Ising machine for 2000-node optimization problems," Science 354, p. 603-606, 2016 T. Umeki, et al., “Phase sensitive degenerate parametric amplification using directly-bonded PPLN ridge waveguides,” Optics Express, 2011, Vol. 19, No. 7, pp. 6326-6332 K. Enbutsu, et al. “PPLN-Based Low-Noise In-Line Phase Sensitive Amplifier with Highly Sensitive Carrier-Recovery System,” IEICE Transactions on Communications, vol. E 99. B (2016) No. 8 pp. 1727- 1733

JP, 2015-215501, A

The wavelength conversion element using the second-order nonlinear optical effect can realize various operations such as wavelength (frequency) conversion and optical amplification. For example, light of frequency ω is input to generate light of double frequency 2ω, or two lights of input frequency ω ₁ and ω ₂ are input, and their sum wave number ω ₁ + ω ₂ or difference frequency ω It is possible to generate light of a frequency of _{1-? 2} . In addition, it is also possible to amplify the input light by entering strong light as excitation light.

FIG. 1 is a diagram showing the configuration of a wavelength conversion element using PPLN-WG according to the prior art. In FIG. 1, the wavelength conversion element 100 includes a waveguide core 102 having a periodically poled structure, which is fabricated on a substrate 101 such as a lithium niobate (LiNbO ₃ ) crystal. At the substrate end of the waveguide core 102, there is an end face 103 which is processed to be smooth in order to input and output light with low loss.

  FIG. 2 is a view showing the configuration of a wavelength conversion device including a wavelength conversion element using PPLN-WG according to the prior art. The wavelength conversion device 200 of FIG. 2 includes the wavelength conversion element 100 shown in FIG. 1 and, on the substrate end face 103 including the waveguide cross section of the wavelength conversion element, the input light to suppress the adverse effect of the return light. And anti-reflection (AR: Anti-Reflection) film 204a, 204b which suppressed the reflectance in the wavelength range of wavelength conversion light is formed. The two input lights 211 and 212 are combined by the combining means 201 and input to the wavelength conversion element. Further, the output light including the wavelength converted light output from the wavelength conversion element is separated by the demultiplexing means 202 into two output lights 213 and 214 and a wavelength converted light 215. The input light 211 and the output light 213, and the input light 212 and the output light 214 are in correspondence with each other. The functions to be realized differ depending on the wavelength relationship of each input light described above.

FIG. 3 is a diagram showing the relationship between input and output light of the wavelength conversion device using the second harmonic light generation process. The second harmonic generation (SHG) process is the most basic wavelength conversion process used in the wavelength conversion element. The wavelength conversion element in the wavelength conversion device 300 of FIG. 3 is the same as the wavelength conversion element 100 of FIG. 1, and AR films 304 a and 304 b are formed on two end faces of the waveguide, respectively. The wavelength conversion using the SHG process is different from the general configuration of the wavelength conversion device of FIG. 2 in that there is only one input light 311 of frequency ω _{1 as} the input light. From the demultiplexing unit 202 outputs, as the output light 213 of the frequency omega _1, and the second harmonic wave 214 of the frequency 2 [omega ₁ is output.

  FIG. 4 is a view showing an example of the characteristic of the AR film in the wavelength conversion element of the prior art. The wavelength-reflectance characteristic of AR film used when inputting signal light of 1550 nm which is a communication wavelength zone as input light is shown. The horizontal axis indicates the wavelength (nm), and the vertical axis indicates the reflectance (%). As shown in FIG. 4, the AR film in the wavelength conversion element exhibits low reflection characteristics in the wavelength band of 775 nm, which is half the wavelength of the input light, in addition to the 1550 nm band.

  FIG. 5 is a diagram showing a phase matching curve of a wavelength converter using the SHG process. The phase matching curve in case the input power of input light is 3 mW is shown. By applying the quasi phase matching technique, high SHG output is shown at the desired wavelength (1552.4 nm).

  In the wavelength conversion element, when the power of the input light is increased, a direct wavelength conversion phenomenon by the input light and an indirect wavelength conversion phenomenon by the generated wavelength-converted light and the input light occur simultaneously. The process of indirect wavelength conversion will be described using the SHG process for the sake of simplicity.

FIG. 6 is a diagram schematically showing the operation at the time of wavelength conversion operation using the SHG process. The configuration of the wavelength conversion device 600 is the same as that of the wavelength conversion device 300 using the SHG process shown in FIG. 3, except that the third output light 315 is included as an output of the wavelength conversion element. This is different from the operation described in. In the wavelength converter 600 of FIG. 6, when the power of the input light 311 of frequency ω ₁ is increased, the SHG light 214 of frequency 2ω ₁ generated in the wavelength conversion element and the input light 311 of frequency ω ₁ are generated. The sum frequency light 315 having the frequency ω ₁ + 2ω ₁ = 3ω ₁ is generated indirectly. The generation of such sum frequency light more notably occurs in the wavelength conversion element in which the wavelength conversion efficiency is enhanced by applying the waveguide formation and phase matching technology by PPLN-WG or the like. For example, when light of a communication wavelength band in the 1550 nm band is used as the input light 311 for a high efficiency element such as PPLN-WG, light of a wavelength of 520 nm is used as sum frequency light by the input light 311 and SHG light generated in the element. It occurs indirectly. In the wavelength converter using the SHG process, as shown in FIG. 6, the light of the wavelength 520 nm band of the sum frequency light repeats internal reflection, and in the worst case, oscillation occurs at the wavelength 520 nm in the element.

In PPLN-WG, a strong input power causes a change in refractive index, causing a problem of optical damage that degrades wavelength conversion characteristics. It is known that LiNbO ₃ (LN) crystals cause photoinduced refractive index change, so-called light damage, even with relatively weak visible laser light irradiation. In order to avoid optical damage, in many PPLN-WGs, LN doped with several mol /% of MgO and ZnO is periodically poled and used as a core. However, LN crystals doped with MgO and ZnO can not ignore the influence of light absorption in visible light as compared to LN crystals not doped. In the wavelength conversion element, light of a wavelength of 520 nm band corresponding to the above-mentioned visible light, green color, is absorbed and generated to generate a temperature distribution in the element. Spatial distribution occurs in refractive index through thermal optics, and phase matching can not be achieved at a desired wavelength, and the phase matching wavelength shifts. The output of the SHG light to be used decreases, which causes the performance of the wavelength conversion element to decrease.

  FIG. 7 is a diagram showing an example of the phase matching characteristic when the phase matching condition is shifted due to the high light input level. The phase matching characteristics were evaluated when light having an input power of 1 W was incident at a wavelength of 1550 nm as the input light 311. In comparison with FIG. 5, it is clear that the second harmonic output level is significantly reduced and the conversion efficiency of the wavelength conversion element is reduced. With regard to the problem of temperature distribution generation due to absorption of green light of wavelength 520 nm band, temperature control means such as a large Peltier element is used to suppress temperature distribution generation in the wavelength conversion element in order to make temperature distribution uniform. A way to avoid it has been taken. However, with the increase in the size of the temperature control means, the size of the entire wavelength conversion device including the wavelength conversion element has been increased, and an increase in the power consumption of the device has been unavoidable.

  As a method of controlling the temperature of the element more efficiently, a technology has been proposed in which a temperature control mechanism is installed on the core side to make the temperature distribution uniform (Patent Document 1). However, in the method of controlling the temperature of the core, it is necessary to deposit a metal film on the core, and there is a problem that the manufacturing cost of the wavelength conversion element is increased.

  The present invention has been made in view of such problems, and realizes simplification of the configuration, reduction in power consumption, and cost reduction while preventing the performance deterioration of the wavelength conversion element.

  In order to achieve the object of the present invention, the invention according to claim 1 is a waveguide using a second-order nonlinear optical material, and an input light formed on an end face of the waveguide. A first wavelength-converted light generated by input light, and an anti-reflection film that suppresses reflection of light in each wavelength band of the second wavelength-converted light generated by the input light and the first wavelength-converted light; It is a wavelength conversion element characterized by having.

  The invention according to claim 2 is the wavelength conversion element according to claim 1, wherein the wavelength band of the second wavelength-converted light includes communication bands including O band, E band, S band, C band, and L band. Corresponding to three times the frequency band of the signal light used in

  The invention according to claim 3 is formed on a waveguide using a second-order nonlinear optical material, an end face of the waveguide, and generates a difference frequency with respect to an input light of a communication wavelength band and the input light. Or excitation light for phase sensitive amplification, and reflection prevention for suppressing reflection of light in each wavelength band of wavelength converted light generated by the input light and the excitation light and belonging to a frequency band three times as high as the input light It is a wavelength conversion element characterized by including a film.

  The invention according to claim 4 is the wavelength conversion element according to any one of claims 1 to 3, wherein the waveguide using the second-order nonlinear optical material is a periodically poled lithium niobate waveguide. It features.

  The invention according to claim 5 is the wavelength conversion element according to claim 4, wherein the core of the waveguide is doped with ZnO or MgO.

  The invention according to claim 6 is the wavelength conversion element according to any one of claims 1 to 5, wherein the waveguide using the second-order nonlinear optical material is manufactured by direct bonding.

  As described above, according to the present invention, simplification of the configuration of the wavelength conversion element and the wavelength conversion device, reduction in power consumption and cost reduction are realized.

FIG. 1 is a view showing the configuration of a prior art PPLN-WG wavelength conversion element. FIG. 2 is a view showing a wavelength converter including a PPLN-WG wavelength conversion element. FIG. 3 is a diagram showing an input / output relationship of a device using a second harmonic light generation process. FIG. 4 is a view showing an example of the characteristic of the AR film in the wavelength conversion element of the prior art. FIG. 5 is a diagram showing a phase matching curve of a wavelength conversion device using an SHG process. FIG. 6 is a diagram schematically showing the operation at the time of wavelength conversion using the SHG process. FIG. 7 is a diagram showing a phase matching characteristic in which the phase matching condition is shifted with high light input. FIG. 8 is a diagram showing the configuration of the wavelength conversion element according to the first embodiment of the present invention. FIG. 9 is a view showing AR film reflection characteristics of the wavelength conversion element according to the first embodiment. FIG. 10 is a diagram showing the phase matching characteristic of the SHG light of the first embodiment. FIG. 11 is a view showing the configuration of the wavelength conversion element of the second embodiment. FIG. 12 is a diagram showing the configuration of the wavelength conversion element of the third embodiment. FIG. 13 is a diagram showing the configuration of the wavelength conversion element of the fourth embodiment.

  The wavelength conversion element of the present invention includes an AR film having a characteristic of preventing reflection of the second wavelength-converted light generated from the input light and the wavelength-converted light on the substrate end surface including the end surface of the waveguide. As also shown in FIG. 2, on the input / output end face of the optical element of the prior art, in order to suppress the adverse effect of the reflected return light of the used optical frequency band such as the input signal light to the wavelength conversion element, An AR film formed of a film or the like is applied. For example, when the SHG process is used in PPLN-WG used for wavelength conversion, an AR film is formed for two frequency bands: the frequency (fundamental wave frequency) ω of input signal light and the frequency 2ω of SHG light. The inventors paid attention to light of frequency 3ω of sum frequency light generated when SHG light is generated by causing signal light of a communication wavelength of high input power and the like to be incident on PPLN-WG. By applying an AR film having the characteristic of preventing reflection of light in the 3ω frequency band to suppress heat generation due to light of the 3ω frequency on the end face of the waveguide, oscillation or heat generation generated in PPLN-WG It has been found that the reduction of the wavelength conversion efficiency can be avoided.

  The light in the above-mentioned 3ω frequency band, which gives the AR film a characteristic of preventing reflection, corresponds roughly to a frequency three times the frequency band used for optical communication (1⁄3 in wavelength) ). Therefore, it corresponds to a frequency band three times the signal light frequency used in the communication wavelength including the O band, the E band, the S band, the C band, and the L band. In the following description, although an example of preventing reflection of C-band (1550 nm band) signal light and its third harmonic green light is described, the present invention is not limited to the configuration of C-band signal light.

  It is used in the prior art without the application of complicated and expensive temperature control technology such as using the large temperature control device considered in the prior art or installing the temperature control mechanism on the core side The problem of wavelength conversion efficiency reduction due to the indirect generation of sum frequency light can be solved by a simple method of merely changing the design of the dielectric multilayer film.

  The light conversion element of the present invention and wavelength conversion devices of various configurations and functions using the same will be described below with reference to the drawings and detailed embodiments.

First Embodiment
In each embodiment of the present invention described below, a direct junction ridge type PPLN-WG is used as a wavelength conversion element. The direct bonding method is a method of bonding by surface-to-surface attractive force by first superimposing wafers subjected to surface treatment using chemicals. Bonding is performed at normal temperature, but since the bonding strength of the wafer at this time is small, heat treatment at high temperature is performed to improve the bonding strength. The technique of direct bonding which can firmly bond the substrates together without using an adhesive or the like has features such as high resistance to optical damage, long-term reliability, and ease of device design. In addition, for example, in light generation in the mid-infrared region by a differential frequency generation (DFG) mechanism, it is considered promising from the viewpoint of being able to avoid mixing of impurities and absorption of an adhesive or the like.

FIG. 8 is a diagram showing the configuration of the wavelength conversion element according to the first embodiment of the present invention. The wavelength conversion device 800 including the wavelength conversion element of FIG. 8 is operated to generate excitation light necessary for the PSA by the wavelength conversion element, and generates SHG light from the input light 312 which is fundamental light of wavelength 1550 nm (ω ₁ ). Do. In order to generate excitation light of wavelength 775 nm necessary for PSA operation, fundamental wave light 312 of input power 2 W at wavelength 1550 nm (ω ₁ ) which is light of communication wavelength band to PPLN-WG 102 is input. The fundamental wave light 312 generates SHG light (2ω ₁ ) in the PPLN-WG 102, and the demultiplexing means 202 outputs residual fundamental wave light 213 (ω ₁ ) and SHG light 214 (2ω ₁ ). In the wavelength conversion element of the present invention, AR films 804 a and 804 b are formed on the input and output end faces of the 101 substrate in order to generate SHG light efficiently and stably.

FIG. 9 is a view showing the reflection characteristic of the AR film of the wavelength conversion element of the first embodiment. In addition to 1550 nm of input fundamental wave light and 775 nm of SHG light, AR films 804 a and 804 b in FIG. 8 have low reflection characteristics also near the wavelength 517 nm of sum frequency light of input light and SHG light. That is, the first wavelength-converted light (SHG light 214) generated on the end face of the waveguide and generated by the input light (fundamental light 312), and the light generated by the input light and the first wavelength-converted light An AR film is provided to suppress the reflection of light in each wavelength band of the two wavelength converted lights (sum frequency light). By providing the AR films 804a and 804b, in the PPLN-WG 102, from the SHG light (2ω ₁ ) as the input light 312 (ω ₁ ) and the first wavelength converted light, the wavelength 3ω ₁ as the sum frequency light is further added. Even when the second wavelength-converted light is generated, it is output from the demultiplexing means 202 as the output light 315 to the outside of the wavelength conversion element. Therefore, even in the configuration of the present embodiment that inputs fundamental wave light with a power as high as 2 W and generates wavelength-converted light with high output, the level of light near the wavelength 517 nm (3ω ₁ ) corresponding to green drops significantly, Also, no absorption occurs in the PPLN-WG 102 by the nonlinear optical material. There is no heat generation due to light near the wavelength 517 nm (3ω ₁ ). There is no change in the temperature distribution of the wavelength conversion element.

  FIG. 10 is a diagram showing phase matching characteristics of SHG light in the wavelength conversion element of the first embodiment. By forming AR films 804a and 804b having low reflection characteristics in the three wavelength bands as shown in FIG. 9 on the end face of the waveguide, the residual component of 517 nm in PPLN-WG102 is reduced, and the related art A high SHG output can be stably generated without the temperature control means and temperature control mechanism required by the technology. That is, even if there is no external temperature control means of the wavelength conversion element of the prior art or the temperature control mechanism fabricated in the core, high levels of SHG output over the prior art can be obtained only by providing the AR films 804a and 804b. The Specifically, the temperature control means of the prior art and the wavelength conversion element with a temperature control mechanism have been limited to about 150 mW SHG output, whereas the present invention obtained 500 mW SHG output.

Second Embodiment
The wavelength conversion element of the present invention can be used for wavelength conversion devices of various forms and functions using the wavelength conversion element. Hereinafter, an example of usage of a wavelength conversion element different from the first embodiment will be described. The second embodiment shows an example applied to an optical parametric amplification (OPA) section in PSA.

  FIG. 11 is a diagram showing the configuration of the wavelength conversion element according to the second embodiment of the present invention. The wavelength conversion device using the wavelength conversion element of the present invention is an example in which an AR film is applied to the parametric amplification unit 1100 in PSA using PPLN-WG102. In the parametric amplification unit 1100, the wavelength conversion element operates to amplify signal light with a wavelength of 1552 nm to low noise by parametric interaction. As an input light 1111 to the beam combining means 201, signal light with an input power of 15 dBm at a wavelength of 1550 nm in the communication wavelength band and excitation light 1112 with a wavelength of 776 nm are inputted. In the wavelength conversion element PPLN-WG 102, the signal light 1111 was amplified to low noise by parametric amplification.

In order to obtain high amplification gain with the phase sensitive amplifier, it is necessary to input high level excitation light 1112 to PPLN-WG102. At this time, as described in FIG. 6, in addition to the amplification action of the signal light 1111, the sum frequency light (ω ₁ + ω ₂ ) of the signal light 1111 (ω ₁ ) and the excitation light 1112 (ω ₂ ) in the wavelength conversion element Will occur. Therefore, green light of 517 nm is generated in addition to the light of wavelengths 1552 nm and 776 nm, and oscillation and heat generation occur in the wavelength conversion element. In the parametric amplification unit 1100 of the present embodiment, AR films 1104 a and 1104 b having low reflection characteristics for the signal light 1111, the excitation light 1112, and their sum frequency light at the input / output end of PPLN-WG 102 used for parametric amplification. Formed. That is, input light in the communication wavelength band (signal light 1111), excitation light (excitation light 1112) for generating a difference frequency with respect to the input light or performing phase sensitive amplification, and generated by the input light and the excitation light And an AR film for suppressing the reflection of light in each wavelength band of the wavelength-converted light (corresponding to the output light 1115) belonging to a frequency band three times the input light.

  The demultiplexing means 202 outputs an output light 1113 as amplified signal light and an output light 1114 as excitation light. Furthermore, by providing the AR films 1104a and 1104b, the 517 nm green light generated in the PPLN-WG 102 is output to the outside as the output light 1115 without staying in the wavelength conversion element. By forming the AR films 1104a and 1104b, it was possible to stably realize a high PSA gain of 25 dB by inputting 1 W of excitation light 1112 without the temperature control means and temperature adjustment mechanism required in the prior art. .

Third Embodiment
FIG. 12 is a diagram showing the configuration of the wavelength conversion element according to the third embodiment of the present invention. The wavelength conversion device using the wavelength conversion element of the present invention applies the AR film to the carrier extraction unit 1200 in the in-line type PSA (Non-Patent Document 3) that relays and amplifies BPSK signals to low noise using PPLN-WG102. It is an example. The carrier extraction unit 1200 of the inline type PSA sends PPLN-WG 102 as input light to the multiplexing means 201, a part of the signal light 1211 (ω ₁ ) of wavelength 1536 nm and local oscillation light of wavelength 1534 nm (hereinafter referred to as local light And 1212 (ω ₂ ) to extract a carrier wave of wavelength 1538 nm. More specifically, carrier wave 1213 of wavelength 1538 nm is extracted from BPSK modulated signal 1211 by cascade wavelength conversion operation of SHG mechanism and difference frequency generation (DFG) mechanism generated in one PPLN-WG 102.

In order to increase the carrier extraction sensitivity in the carrier extraction unit 1200, it is necessary to input high-level local light 1212 and light of 10 dBm is input. In this case, in addition to local light SHG light and signal light differential frequency light 1214 generated by SHG / DFG cascade wavelength conversion, sum frequency light 1215 (2ω ₂ + ω ₁ ) of local light SHG light and signal light, local light And sum frequency light 1215 (3ω ₂ ) of SHG light is generated. Therefore, in addition to the wavelengths 1536 nm and 776 nm, green light of 512 nm is generated and oscillates and generates heat in the wavelength conversion element.

  In the carrier wave extraction unit 1200 which is the wavelength conversion device of the present embodiment, an AR film having low reflection characteristics for the wavelength band of 512 nm in addition to the wavelengths 1536 nm and 767 nm at the input / output terminal of PPLN-WG 102 used for parametric amplification. 1204a and 1204b were formed. That is, the first wavelength-converted light (SHG light) formed on the end face of the waveguide and generated by the first input light (signal light 1211), the second input light (local light 1212), and The AR film is provided to suppress the reflection of light in each wavelength band of the first wavelength-converted light (sum frequency light 1215) generated by the first input light and the first wavelength-converted light. By this AR film, the green light of 512 nm generated in the PPLN-WG 102 is output to the outside as the output light 1215 without staying in the wavelength conversion element. As a result, the carrier of the BPSK signal can be extracted with high sensitivity and stability without the temperature control means and temperature control mechanism required in the prior art.

Fourth Embodiment
FIG. 13 is a diagram showing the configuration of the wavelength conversion element according to the fourth embodiment of the present invention. The wavelength conversion device using the wavelength conversion element of the present invention is an example in which an AR film is applied to the excitation light generation unit 1300 in an in-line type PSA that relays and amplifies a BPSK signal using PPLN-WG 102 to low noise. In the excitation light generation unit 1300 of the in-line PSA, the sum frequency light of carrier light 1311 (ω ₁ ) of wavelength 1538 nm and local light 1312 (ω ₂ ) of wavelength 1534 nm extracted from the BPSK signal as input to the multiplexing means 201 It generates (wavelength 1536 nm) and supplies energy to the parametric amplification unit.

  In order to generate this sum frequency light, it is necessary to input both of the extracted carrier light and local light to the PPLN-WG 102 at a high level. For this reason, in the excitation light generation unit 1300, in addition to the sum frequency light of wavelength 1536 nm, the third harmonic of the carrier wave, the third harmonic of the local light, further the SHG light of the carrier and the sum frequency light of the local light, the carrier and the local light It generates up to light 1316 in the wavelength 512 nm band, which is the sum frequency light of SHG light.

  In the excitation light generation unit 1300 which is the wavelength conversion device of the present embodiment, an AR film 1304 a having a low reflectance in the wavelength band of 512 nm in addition to the wavelengths 1536 nm and 767 nm at the input / output end of PPLN-WG 102 used for parametric amplification. , 1304b. That is, the first wavelength-converted light (SHG light) formed on the end face of the waveguide and generated by the first input light (carrier light 1311), the second input light (local light), and the first wavelength light The AR film is provided to suppress the reflection of light in each wavelength band of the second wavelength-converted light (sum frequency light) generated by the first input light and the first wavelength-converted light. With this AR film, the green light of 512 nm generated in the PPLN-WG 102 is output to the outside of the wavelength conversion element as the output light 1316 without staying in the wavelength conversion element. This suppresses the heat generation of the element by the light of the wavelength 512 nm band which is the sum frequency light of the SHG light of the carrier wave and the sum frequency light of the local light, the carrier wave and the SHG light of the local light generated in PPLN-WG102. By providing the AR films 1304a and 1304b in the excitation light generation unit 1300, high sum frequency conversion is realized without the temperature control means and temperature adjustment mechanism required in the prior art, and relay amplification gain is increased by 16 dB. Was realized.

  As described above in detail, it is possible to use a large-sized temperature control device by changing the design of the AR film (dielectric multilayer film) used in the prior art by the wavelength conversion element of the present invention. It is possible to avoid the problem that the sum frequency light is indirectly generated and the performance of the wavelength conversion element is degraded without applying a complicated and expensive temperature control technology such as installing a temperature control mechanism. Since the temperature control device and the temperature control mechanism can be omitted, simplification and cost reduction of the wavelength conversion element and the wavelength conversion device can be realized.

  The invention is generally applicable to communication systems. In particular, it can be used for an optical communication device of an optical communication system.

100 wavelength conversion element 101 substrate 102 waveguide core (PPLN-WG)
103 End faces 104a, 104b, 804a, 804b, 1104a, 1104b, 1204a, 1204b, 1304a, 1304b Antireflection films 200, 300, 600, 800, 1100, 1200, 1300 Wavelength conversion device 201 Wavelength combining means 202 Wavelength demultiplexing means

Claims (6)

A waveguide using a second-order nonlinear optical material,
Formed on the end face of the waveguide,
First input light,
First wavelength-converted light generated by the second input light, and
What is claimed is: 1. A wavelength conversion element comprising: an antireflective film for suppressing light reflection in each wavelength band of the first wavelength-converted light generated by the first input light and the first wavelength-converted light.   The wavelength band of the second wavelength-converted light corresponds to three times the frequency band of the signal light used in the communication wavelength including O band, E band, S band, C band, and L band. The wavelength conversion element according to claim 1. A waveguide using a second-order nonlinear optical material,
Formed on the end face of the waveguide,
Input light in the telecommunication wavelength band,
Excitation light for generating a difference frequency or phase sensitive amplification for the input light;
And a reflection preventing film for suppressing the reflection of light in each wavelength band of wavelength converted light which is generated by the input light and the excitation light and belongs to a frequency band three times as high as the input light. element.   The wavelength conversion element according to any one of claims 1 to 3, wherein the waveguide using the second-order nonlinear optical material is a periodically poled lithium niobate waveguide.   The wavelength conversion element according to claim 4, wherein the core of the waveguide is doped with ZnO or MgO.   The wavelength conversion element according to any one of claims 1 to 5, wherein the waveguide using the second-order nonlinear optical material is manufactured by direct bonding.

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