WO2023105722A1 - Wavelength conversion apparatus - Google Patents

Wavelength conversion apparatus Download PDF

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WO2023105722A1
WO2023105722A1 PCT/JP2021/045384 JP2021045384W WO2023105722A1 WO 2023105722 A1 WO2023105722 A1 WO 2023105722A1 JP 2021045384 W JP2021045384 W JP 2021045384W WO 2023105722 A1 WO2023105722 A1 WO 2023105722A1
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wavelength conversion
wavelength
temperature
conversion element
light
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PCT/JP2021/045384
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French (fr)
Japanese (ja)
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晃次 圓佛
啓 渡邉
修 忠永
拓志 風間
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日本電信電話株式会社
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Priority to JP2023565813A priority Critical patent/JPWO2023105722A1/ja
Priority to PCT/JP2021/045384 priority patent/WO2023105722A1/en
Publication of WO2023105722A1 publication Critical patent/WO2023105722A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/37—Non-linear optics for second-harmonic generation

Definitions

  • the present disclosure relates to a wavelength conversion device that applies the second-order nonlinear optical effect.
  • Wavelength conversion technology that applies the second-order nonlinear optical effect is used in various fields such as wavelength conversion of optical signals in optical communication, optical processing, medical care, and biotechnology.
  • the wavelength range of light that is the target of wavelength conversion extends from the ultraviolet range to the visible, infrared, and terahertz ranges.
  • Wavelength conversion technology that applies second-order nonlinear optical effects can convert light in wavelength ranges that cannot be directly output by semiconductor lasers. Often used for production.
  • the wavelength conversion technology that applies this second-order nonlinear optical effect can be used when sufficient power cannot be obtained even in a wavelength band that can be directly generated by a semiconductor laser.
  • a wavelength conversion technique that applies this second-order nonlinear optical effect is used when performing wavelength conversion by generating a difference frequency, which will be described later, or amplification using a parametric effect.
  • a wavelength conversion device that performs these wavelength conversion techniques incorporates a wavelength conversion element based on the second-order nonlinear optical effect.
  • Typical materials applied to wavelength conversion elements include lithium niobate (LiNbO 3 ), which has a large nonlinear constant . Due to its high conversion efficiency, it is widely used in commercial light sources.
  • DFG Difference Frequency Generation
  • an optical parametric amplifier can also be configured in which a second-order nonlinear medium is placed in a resonator, only ⁇ 1 is input, and ⁇ 2 and ⁇ 3 that satisfy (Equation 2) are generated.
  • PSD Phase Sensitive Amplifier
  • PSA two optical amplification operations are known.
  • One is an operation using degenerate parametric amplification in which a signal light and pumping light having half the wavelength of the signal light are input to a second-order nonlinear medium and the signal light is amplified (see, for example, Non-Patent Document 1).
  • the other is an operation using non-degenerate parametric amplification in which a pair of signal light and idler light and pumping light having a wavelength that is the sum frequency of the signal light and idler light are input and the signal light and idler light are amplified.
  • a pair of signal light and idler light is generated by the DFG described above.
  • DFG and parametric amplification are mainly used.
  • signal light and idler light exist in the communication wavelength band of 1.55 ⁇ m band, so pumping light is required to be light in the 0.78 ⁇ m band.
  • SHG light obtained by wavelength-converting a light source in the communication wavelength band is generally used as the excitation light having a half wavelength of the communication wavelength band.
  • Such pumping light is required to have high power and low noise from the viewpoint of achieving high gain and low noise in an optical amplifier such as a PSA.
  • FIG. 1 is a diagram showing the basic configuration of a wavelength conversion device 100 that generates a second harmonic (SHG light) of input light by SHG.
  • the wavelength conversion device 100 includes a wavelength conversion element 102 that converts the wavelength of the excitation light 101, an optical filter 104 that transmits only the wavelength-converted light 103 output from the wavelength conversion element 102, and the temperature of the wavelength conversion element 102. and a temperature controller 105 to control.
  • the wavelength-converted light 103 that is most efficiently converted at the wavelength that satisfies the phase matching condition is output.
  • residual pumping light 106 which is a residual component of the pumping light 101, can also be output from the wavelength conversion element 102 at the same time.
  • This residual pumping light 106 is removed by the optical filter 104 because it adversely affects optical amplification characteristics when input as pumping light of an optical amplifier such as a PSA.
  • the wavelength conversion characteristics depend on the temperature of the wavelength conversion element 102, so the temperature is controlled by the temperature controller 105 so as to maintain the phase matching condition.
  • the temperature controller 105 can be, for example, a Peltier element or a heater.
  • wavelength-converted light for example, wavelength-converted light 103 shown in FIG. 1 generated by a wavelength conversion device (for example, wavelength conversion device 100 shown in FIG. 1) is used as excitation light.
  • the input pumping light wavelength-converted light
  • the temperature controller for example, the temperature controller 105 shown in FIG. 1
  • the phase matching conditions that have been satisfied due to temperature fluctuations and optical loss of the wavelength conversion element due to environmental temperature fluctuations, etc. collapses, and the power of the wavelength-converted light may become unstable. Therefore, it is necessary to compensate for these instabilities and fluctuations.
  • FIG. 2 is a diagram showing the configuration of a conventional wavelength conversion device 200 for stabilizing wavelength-converted light.
  • the wavelength conversion device 200 has the configuration of the wavelength conversion device 100 shown in FIG.
  • a computing device 204 that generates a feedback signal for controlling the temperature of the temperature controller 105 by computation based on the output of 203 and transmits the feedback signal to the temperature controller 105 .
  • the temperature of the wavelength conversion element 102 is periodically detuned in the positive and negative directions at regular intervals, and based on the power fluctuation of the wavelength-converted light 103 caused by the temperature detuning. Accordingly, the temperature controller 105 is configured to be feedback-controlled.
  • FIG. 3A and 3B show the behavior of the wavelength-converted light when the temperature of the wavelength conversion element is detuned.
  • FIG. 3A shows the temperature dependence of the phase control curve of the wavelength conversion device.
  • b) shows an enlarged view near the peak in FIG. 3(a)
  • FIG. 3(c) shows the relationship between the detuning temperature and the output of wavelength-converted light.
  • T 0 is the temperature that satisfies the phase matching condition
  • T 0 + ⁇ T is the temperature of the wavelength conversion element that has changed from T 0 to the high temperature side
  • T is the temperature of the wavelength conversion element that has changed from T 0 to the low temperature side. 0 - ⁇ T, respectively.
  • T 0 + ⁇ T is the temperature of the wavelength conversion element that has changed from T 0 to the low temperature side.
  • the phase matching wavelength is indicated by a dashed line.
  • the phase matching curve in the wavelength conversion element shifts linearly with the temperature of the wavelength conversion element. It can be said that the amount of wavelength shift per unit temperature is generally determined by the physical parameters of the second-order nonlinear medium applied to the wavelength conversion element.
  • the conventional wavelength conversion device 200 periodically detunes the temperature of the wavelength conversion element 102 in the positive and negative directions, and changes the power as shown in FIG.
  • the temperature fluctuation of the wavelength conversion element 102 is calculated from the quantity).
  • a feedback signal is generated based on the calculation result, and the temperature controller 105 is controlled by the feedback signal, thereby further stabilizing the power of the output wavelength-converted light 103 .
  • the present disclosure has been made in view of the problems described above, and an object of the present disclosure is to provide a wavelength conversion device that performs wavelength conversion using SFG, and is capable of reducing the power attenuation of output wavelength-converted light.
  • An object of the present invention is to provide a wavelength conversion device capable of suppressing noise more than the conventional one.
  • the present disclosure provides a wavelength conversion device for inputting excitation light and outputting wavelength-converted light by sum-frequency generation, wherein the wavelength conversion element performs wavelength conversion based on the second-order nonlinear optical effect.
  • a temperature controller for controlling the temperature of the wavelength conversion element, a detector for detecting the power of residual excitation light transmitted through the wavelength conversion element, and an arithmetic unit for generating a control signal for the temperature controller based on the output of the detector.
  • the computing device generates a control signal for detuning the temperature of the wavelength conversion element to the temperature regulator, based on the power fluctuation of the residual excitation light that occurs in response to the temperature detuning of the wavelength conversion element.
  • the temperature fluctuation of the wavelength conversion element is calculated, and based on the temperature fluctuation, a control signal for controlling the temperature controller is generated so that the temperature of the wavelength conversion element becomes a temperature that corrects the fluctuation of the phase matching condition of the wavelength conversion element.
  • a wavelength conversion device configured to generate a wavelength is provided.
  • FIG. 1 is a diagram showing the basic configuration of a wavelength conversion device that generates a second harmonic (SHG light) of input light by SHG;
  • FIG. 1 is a diagram showing the configuration of a wavelength conversion device for stabilizing wavelength-converted light according to the prior art;
  • FIG. 3A is a diagram showing the behavior of wavelength-converted light when the temperature of the wavelength conversion element is detuned,
  • FIG. 3A shows the temperature dependence of the phase control curve of the wavelength conversion device,
  • FIG. 3(a) shows an enlarged view near the peak, and
  • FIG. 3(c) shows the relationship between the detuning temperature and the output of wavelength-converted light.
  • FIG. 4 is a diagram showing power spectra of wavelength-converted light and residual pumping light in the vicinity of a phase matching wavelength;
  • 1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure;
  • FIG. 1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure;
  • FIG. 1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure;
  • FIG. 1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure;
  • FIG. 1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure;
  • the wavelength conversion device is the same as the conventional technology in that the temperature of the wavelength conversion element is periodically detuned and the temperature regulator is feedback-controlled based on the power fluctuation due to the detuning.
  • the wavelength conversion device detects the residual pumping light that has been removed by an optical filter or the like in the past, and is feedback-controlled based on the power fluctuation of the residual pumping light that accompanies periodic detuning. , unlike the prior art.
  • the wavelength conversion device generates wavelength-converted light by SHG. play.
  • FIG. 4 is a diagram showing power spectra of wavelength-converted light and residual pump light in the vicinity of the phase matching wavelength. It should be noted that each spectrum in the drawing is a spectrum when the wavelength conversion device 500 described later is used.
  • the temperature that satisfies the phase matching condition is T 0
  • the temperature of the wavelength conversion element that has changed from T 0 to the higher temperature side is T 0 + ⁇ T
  • the temperature of the conversion element is shown as T 0 - ⁇ T, respectively.
  • the power spectrum of the residual excitation light is a distribution showing a dip (minimum value) in the phase matching wavelength when the temperature of the wavelength conversion element is T0 .
  • the wavelength conversion device is configured to control the temperature of the wavelength conversion element by monitoring the residual excitation light.
  • the wavelength conversion device in this embodiment has the same basic configuration as the wavelength conversion device 200 described above. configured to be
  • FIG. 5 is a diagram showing the configuration of a wavelength conversion device 500 according to one embodiment of the present disclosure.
  • the wavelength conversion device 500 includes a wavelength conversion element 102 that performs wavelength conversion on input light 101 including excitation light 101, and wavelength-converted light 103 out of the output light output from the wavelength conversion element 102. Then, based on a dichroic mirror 501 that reflects the residual excitation light 106, a detector 502 that detects the residual excitation light 106 split by the dichroic mirror 501, and the output of the detector 502, the temperature controller 105 is calculated. and an arithmetic device 204 that generates a feedback signal for temperature control and transmits the feedback signal to the temperature controller 105 .
  • the basic configuration of the wavelength conversion device 500 is similar to that of a conventional wavelength conversion device (for example, the wavelength conversion device 200). However, it differs from the conventional wavelength conversion device in that it includes a dichroic mirror 501 instead of the optical filter 104 and does not require an averaging device 203 for stabilizing fluctuations in the phase noise of light to be detected.
  • the wavelength conversion element 102 included in the wavelength conversion device 500 can be, for example, a ridge waveguide using LiNb 3 having a periodically poled structure as a second-order nonlinear medium.
  • the second-order nonlinear medium of the wavelength conversion element 102 is not limited to this, and LiTaO 3 or LiNb(x)Ta(1 ⁇ x)O 3 (where 0 ⁇ x ⁇ 1).
  • at least one element selected from the group consisting of Mg, Zn, Sc and In may be added as an additive.
  • Wavelength conversion is performed using the wavelength conversion device 500 having such a configuration, and SHG light is generated as the wavelength-converted light 103 .
  • the temperature of the wavelength conversion element 102 is periodically detuned by the temperature controller 105 to vary the spectrum of the residual excitation light 106 near the phase matching wavelength.
  • the fluctuation behavior is monitored by the detector 502 , and the arithmetic unit 204 generates a feedback signal based on the output of the detector 502 to control the temperature regulator 105 .
  • the wavelength of the pumping light 101 may be any wavelength in the range from the O band to the L band among optical communication wavelengths.
  • the wavelength-converted light 103 output from the wavelength conversion device 500 is stabilized by suppressing fluctuations in power due to environmental temperature and optical loss. Furthermore, as described above, since the wavelength conversion device 500 does not monitor the output wavelength-converted light 103, power attenuation of the wavelength-converted light 103 that occurs in the conventional technology is also suppressed. Therefore, it becomes possible to supply the stable wavelength-converted light 103 to the outside such as the PSA more efficiently than before.
  • the wavelength conversion device 500 does not use an averaging device (eg, averaging device 203) like the conventional wavelength conversion device (eg, wavelength conversion device 200), and the stability of the wavelength-converted light 103 equivalent to that of the conventional one can be obtained. can be realized.
  • averaging device eg, averaging device 203
  • the power of the residual excitation light 106 is larger than that of the wavelength-converted light 103, as shown in FIG. Since the power of this residual excitation light 106 has a value so large that noise can be ignored, it is not necessary to stabilize fluctuations due to phase shift noise. Therefore, the wavelength conversion device 500 does not require an averaging device, which also has the advantage of simplifying the system configuration.
  • FIG. 6 is a diagram showing the configuration of a wavelength conversion device 600 according to an embodiment of the present disclosure.
  • the wavelength conversion device 600 in this embodiment has, in addition to the structure of the wavelength conversion device 500, an optical fiber 602 that introduces the input light 101 into the metal casing 601 and an optical fiber 602 that outputs the light.
  • excitation light collimating lens 603 for collimating the excitation light focus lens 604 arranged to focus the collimated excitation light on the wavelength conversion element 102, output light from the wavelength conversion element 102 (wavelength converted light 103 and the residual excitation light 106), a focus lens 606 arranged to focus the wavelength-converted light 103 out of the output light collimated by the collimating lens 605 to the output end,
  • An optical fiber 607 that guides the wavelength-converted light 103 condensed by the focus lens 606 to the outside, a mirror 608 that reflects the residual excitation light 106 out of the output light collimated by the collimator lens 605, and a mirror 608 that reflects the residual excitation light 106.
  • a focus lens 609 arranged to condense the residual excitation light 106 collected by the focus lens 609 to the output end, a fiber 610 for guiding the residual excitation light 106 condensed by the focus lens 609 to the detector 502, and the outside of the metal housing 601. and a plurality of optical windows 611 for inputting and outputting light to and from the interior. Since the excitation light 101 and the residual excitation light 106 have the same wavelength, it is preferable to use the same optical fibers 602 and 610 in terms of optical design.
  • the dichroic mirror 501 is inside the metal housing 601 and installed between the collimator lens 605 and the focus lens 606 . Further, in the wavelength conversion device 600 of this embodiment, the detector 502 and the arithmetic device 204 are installed outside the metal housing 601 , and the detector 502 is optically connected to the optical fiber 610 .
  • the arithmetic device 204 is communicably connected to the temperature controller 105 in the same manner as the wavelength conversion device 200 and the wavelength conversion device 500, so that the temperature controller 105 can receive the feedback signal generated by the arithmetic device 204.
  • the form of the feedback signal may be an electrical signal or an optical signal.
  • the electrical signal is transmitted to the temperature controller 105 via a terminal installed on the metal housing 601, and the metal housing 601 and the terminal are electrically insulated. required).
  • wavelength conversion device 600 configured in this way is used, as in the first embodiment, if wavelength conversion is performed to generate SHG light, a conventional wavelength conversion device (for example, the wavelength conversion device 200) can be used. , a stable wavelength-converted light 103 can be generated.
  • the wavelength conversion device 600 does not monitor the output wavelength-converted light 103, so it is possible to perform wavelength conversion while suppressing the power attenuation of the wavelength-converted light 103.
  • the wavelength conversion device 600 does not require an averaging device, and therefore has the advantage of simplifying the system configuration.
  • the wavelength conversion device 600 has a structure in which the mechanism for wavelength conversion and the mechanism for demultiplexing the output light from the wavelength conversion element are hermetically sealed inside the metal housing 601 . Therefore, it is possible to generate the wavelength-converted light 103 that is more stable than the wavelength conversion device 500 without being easily affected by external temperature fluctuations and the like.
  • the wavelength conversion device relates to the wavelength conversion device 600 described in the second embodiment, in which the detector 502 for detecting the residual excitation light 106 is installed inside the metal housing 601 .
  • FIG. 7 is a diagram showing the configuration of a wavelength conversion device 700 according to an embodiment of the present disclosure.
  • the wavelength conversion device 700 in this embodiment is the same as the wavelength conversion device 600 described in the second embodiment, except that the detector 502 for detecting the residual excitation light 106 is inside the metal casing 601. It has an installed structure.
  • the detector 502 included in the wavelength conversion device 700 is a large diameter detector.
  • the mirror 608, the focus lens 609, the optical window 611 installed between the mirror 608 and the focus lens 609, and the optical fiber 610, which are included in the wavelength conversion device 600, are unnecessary. becomes.
  • the wavelength conversion device 700 having such a configuration has the advantage of simplifying the optical alignment compared to the wavelength conversion device 600 described in the second embodiment. That is, the wavelength conversion device 600 requires alignment for introducing the residual pumping light 106 demultiplexed from the output light into the optical fiber 610.
  • the detector 502 installed in the wavelength conversion device 700 is Since it is a detector with a large aperture that can receive collimated light, it can be optically coupled with passive alignment. As a result, the lead time for module mounting can be shortened.
  • wavelength conversion device 700 if wavelength conversion is performed by using such a wavelength conversion device 700 to generate SHG light in the same manner as in the first and second embodiments, a conventional wavelength conversion device (for example, wavelength Similar to the converter 200), it is possible to generate stable wavelength-converted light 103.
  • a conventional wavelength conversion device for example, wavelength Similar to the converter 200
  • the wavelength conversion device can stabilize the power of the wavelength-converted light while suppressing the power attenuation of the output wavelength-converted light. Since such a wavelength converter can efficiently supply input light to an optical amplifier such as a PSA, it is expected to be applied to the light source of an optical amplifier.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

According to the present disclosure, provided is a wavelength conversion apparatus to which excitation light is inputted and which outputs wavelength-converted light by sum frequency generation, the wavelength conversion apparatus comprising: a wavelength conversion element which performs wavelength conversion on the basis of a second-order nonlinear optical effect; a temperature controller which controls the temperature of the wavelength conversion element; a detector which detects power of residual excitation light transmitted through the wavelength conversion element; and a computation device which generates a control signal for the temperature controller on the basis of output of the detector, wherein the computation device is configured to generate a control signal for causing the temperature controller to detune the temperature of the wavelength conversion element, compute a change in the temperature of the wavelength conversion element on the basis of a change in the power of the residual excitation light produced in response to detuning of the temperature of the wavelength conversion element, and on the basis of the temperature change, generate a control signal for controlling the temperature controller such that the temperature of the wavelength conversion element becomes a temperature at which a change in the phase matching condition of the wavelength conversion element is corrected, thereby making it possible to suppress power attenuation of outputted wavelength-converted light compared to the prior art.

Description

波長変換装置Wavelength converter
　本開示は、二次非線形光学効果を応用した波長変換装置に関する。 The present disclosure relates to a wavelength conversion device that applies the second-order nonlinear optical effect.
　二次非線形光学効果を応用した波長変換技術は、光通信における光信号の波長変換、光加工、医療、生物工学など、様々な分野で利用されている。波長変換の対象となる光の波長域は、紫外域から可視域、赤外域、テラヘルツ域に及び、二次非線形光学効果を応用した波長変換技術は、半導体レーザでは直接出力できない波長域の光の生成にしばしば利用される。一方、この二次非線形光学効果を応用した波長変換技術は、半導体レーザによって直接生成することが可能な波長帯であっても、それだけでは十分なパワーが得られない場合には利用され得る。例えば、光通信システムにおいては、後述する差周波発生による波長変換や、パラメトリック効果を利用した増幅を行う際に、この二次非線形光学効果を応用した波長変換技術が利用される。これらの波長変換技術を行う波長変換装置では、二次非線形光学効果に基づいた波長変換素子が組み込まれる。波長変換素子に適用される代表的な材料には、大きな非線形定数を有するニオブ酸リチウム（ＬｉＮｂＯ３）が挙げられ、ＬｉＮｂＯ３を適用した周期分極反転光導波路構造を有する波長変換装置は、その波長変換効率の高さから、市販されている光源に広く適用されている。 Wavelength conversion technology that applies the second-order nonlinear optical effect is used in various fields such as wavelength conversion of optical signals in optical communication, optical processing, medical care, and biotechnology. The wavelength range of light that is the target of wavelength conversion extends from the ultraviolet range to the visible, infrared, and terahertz ranges. Wavelength conversion technology that applies second-order nonlinear optical effects can convert light in wavelength ranges that cannot be directly output by semiconductor lasers. Often used for production. On the other hand, the wavelength conversion technology that applies this second-order nonlinear optical effect can be used when sufficient power cannot be obtained even in a wavelength band that can be directly generated by a semiconductor laser. For example, in an optical communication system, a wavelength conversion technique that applies this second-order nonlinear optical effect is used when performing wavelength conversion by generating a difference frequency, which will be described later, or amplification using a parametric effect. A wavelength conversion device that performs these wavelength conversion techniques incorporates a wavelength conversion element based on the second-order nonlinear optical effect. Typical materials applied to wavelength conversion elements include lithium niobate (LiNbO 3 ), which has a large nonlinear constant . Due to its high conversion efficiency, it is widely used in commercial light sources.
　以下に、二次非線形光学効果を応用した波長変換の原理について述べる。二次非線形光学効果では、波長λ１の光と波長λ２の光を二次非線形媒質に入力し、新たな波長λ３を発生させる。このような波長変換のうち、（式１）で表される波長変換は、和周波発生（Sum Frequency Generation：以下、ＳＦＧという）と呼ばれる。 The principle of wavelength conversion using the second-order nonlinear optical effect will be described below. In the second-order nonlinear optical effect, light of wavelength λ 1 and light of wavelength λ 2 are input into a second-order nonlinear medium to generate a new wavelength λ 3 . Among such wavelength conversions, the wavelength conversion represented by (Equation 1) is called sum frequency generation (hereinafter referred to as SFG).
　１／λ３＝１／λ１＋１／λ２　　　（式１）
特に、λ１＝λ２を満たす波長変換は、第２高調波発生（Second Harmonic Generation：以下、ＳＨＧという）と呼ばれる。 1/λ 3 =1/λ 1 +1/λ 2 (equation 1)
In particular, wavelength conversion that satisfies λ 1 =λ 2 is called Second Harmonic Generation (hereinafter referred to as SHG).
　一方、（式２）を満たす波長変換は、差周波発生（Difference Frequency Generation：以下、ＤＦＧという。）と呼ばれる。 On the other hand, wavelength conversion that satisfies (Formula 2) is called Difference Frequency Generation (hereinafter referred to as DFG).
　１／λ３＝１／λ１－１／λ２　　　（式２）
このＤＦＧにおける波長λ１の光は励起光、波長λ２の光は信号光、波長λ３の光はアイドラ光と呼ばれる。さらに、二次非線形媒質を共振器の中に入れてλ１のみ入力し、（式２）を満たすλ２およびλ３を発生させる、光パラメトリック増幅器を構成することもできる。 1/λ 3 =1/λ 1 −1/λ 2 (equation 2)
In this DFG, the light of wavelength λ 1 is called excitation light, the light of wavelength λ 2 is called signal light, and the light of wavelength λ 3 is called idler light. Furthermore, an optical parametric amplifier can also be configured in which a second-order nonlinear medium is placed in a resonator, only λ 1 is input, and λ 2 and λ 3 that satisfy (Equation 2) are generated.
　近年、通信分野で用いられる波長変換装置は、波長変換効率の向上により、二次非線形光学効果による光増幅が可能となっている。この光増幅を行う光増幅器は、位相感応光増幅器（Phase Sensitive Amplifier：以下、ＰＳＡという）と呼ばれ、入力光の信号ノイズ比を劣化させることなく増幅することが可能であることから、従来まで多用されてきたエルビウム添加光ファイバ増幅器（Erbium-Doped Fiber Amplifier：以下、ＥＤＦＡという）に代わる長距離伝送用光増幅器として期待されている。 In recent years, wavelength conversion devices used in the field of communication have become capable of optical amplification due to second-order nonlinear optical effects due to improvements in wavelength conversion efficiency. An optical amplifier that performs this optical amplification is called a Phase Sensitive Amplifier (PSA). It is expected as an optical amplifier for long distance transmission to replace the widely used erbium-doped fiber amplifier (hereinafter referred to as EDFA).
　ＰＳＡでは、２つの光増幅動作が知られている。１つは、二次非線形媒質へ信号光及び信号光の半分の波長を有する励起光を入力し、信号光を増幅する縮退パラメトリック増幅を利用した動作である（例えば、非特許文献１参照）。もう１つは、信号光とアイドラ光のペア及び信号光とアイドラ光の和周波となる波長を有する励起光を入力し、信号光及びアイドラ光を増幅する非縮退パラメトリック増幅を利用した動作である（例えば、非特許文献２参照）。信号光とアイドラ光のペアは、上述のＤＦＧによって生成される。 In PSA, two optical amplification operations are known. One is an operation using degenerate parametric amplification in which a signal light and pumping light having half the wavelength of the signal light are input to a second-order nonlinear medium and the signal light is amplified (see, for example, Non-Patent Document 1). The other is an operation using non-degenerate parametric amplification in which a pair of signal light and idler light and pumping light having a wavelength that is the sum frequency of the signal light and idler light are input and the signal light and idler light are amplified. (For example, see Non-Patent Document 2). A pair of signal light and idler light is generated by the DFG described above.
　通信分野において二次非線形光学効果に基づいた波長変換技術を用いる場合、主にＤＦＧ及びパラメトリック増幅が用いられる。ＤＦＧ及びパラメトリック増幅では、信号光及びアイドラ光が１．５５μｍ帯の通信波長帯に存在するため、励起光は０．７８μｍ帯の光であることが要求される。この通信波長帯の半分の波長を有する励起光は、通信波長帯の光源を波長変換したＳＨＧ光を用いることが一般的である。そして、このような励起光に対しては、ＰＳＡなどの光増幅装置において高利得・低ノイズ性を実現するという観点から、高パワー・低ノイズ性が要求されている。 When using wavelength conversion technology based on second-order nonlinear optical effects in the field of communications, DFG and parametric amplification are mainly used. In DFG and parametric amplification, signal light and idler light exist in the communication wavelength band of 1.55 μm band, so pumping light is required to be light in the 0.78 μm band. SHG light obtained by wavelength-converting a light source in the communication wavelength band is generally used as the excitation light having a half wavelength of the communication wavelength band. Such pumping light is required to have high power and low noise from the viewpoint of achieving high gain and low noise in an optical amplifier such as a PSA.
　図１は、ＳＨＧにより、入力光の第２高調波（ＳＨＧ光）を発生させる波長変換装置１００の基本構成を示した図である。波長変換装置１００は、励起光１０１に対して波長変換を行う波長変換素子１０２と、波長変換素子１０２から出力される波長変換光１０３のみを透過させる光学フィルタ１０４と、波長変換素子１０２の温度を制御する温調器１０５とを含む。波長変換素子１０２に入力光１０１を入力すると、位相整合条件を満たす波長において最も効率的に変換される波長変換光１０３が出力される。このとき、波長変換素子１０２からは、励起光１０１の残留成分である残留励起光１０６も同時に出力され得る。この残留励起光１０６は、ＰＳＡなどの光増幅装置の励起光として入力されると光増幅特性に悪影響を及ぼすため、光学フィルタ１０４によって除去される。また、波長変換素子１０２における波長変換では、波長変換素子１０２の温度に波長変換特性が依存するため、温調器１０５によって、位相整合条件を維持するように温度制御される。温調器１０５は、例えば、ペルチェ素子やヒータなどであり得る。 FIG. 1 is a diagram showing the basic configuration of a wavelength conversion device 100 that generates a second harmonic (SHG light) of input light by SHG. The wavelength conversion device 100 includes a wavelength conversion element 102 that converts the wavelength of the excitation light 101, an optical filter 104 that transmits only the wavelength-converted light 103 output from the wavelength conversion element 102, and the temperature of the wavelength conversion element 102. and a temperature controller 105 to control. When the input light 101 is input to the wavelength conversion element 102, the wavelength-converted light 103 that is most efficiently converted at the wavelength that satisfies the phase matching condition is output. At this time, residual pumping light 106, which is a residual component of the pumping light 101, can also be output from the wavelength conversion element 102 at the same time. This residual pumping light 106 is removed by the optical filter 104 because it adversely affects optical amplification characteristics when input as pumping light of an optical amplifier such as a PSA. In wavelength conversion in the wavelength conversion element 102, the wavelength conversion characteristics depend on the temperature of the wavelength conversion element 102, so the temperature is controlled by the temperature controller 105 so as to maintain the phase matching condition. The temperature controller 105 can be, for example, a Peltier element or a heater.
　ＰＳＡなどの光増幅器における光増幅では、励起光として波長変換装置（例えば、図１に示される波長変換装置１００）によって生成された波長変換光（例えば、図１に示される波長変換光１０３）が用いられ得る。この場合、光増幅器によって生成される増幅光の安定性を確保するため、入力される励起光（波長変換光）は、安定したパワーを有する光であることが求められる。しかしながら、温調器（例えば、図１に示される温調器１０５）を作動させていても、環境温度の揺らぎなどによる波長変換素子の温度変動や光損失などにより、満足されていた位相整合条件が崩れ、波長変換光のパワーが不安定となり得る。そのため、これらの不安定性・変動を補償する必要がある。 In optical amplification in an optical amplifier such as a PSA, wavelength-converted light (for example, wavelength-converted light 103 shown in FIG. 1) generated by a wavelength conversion device (for example, wavelength conversion device 100 shown in FIG. 1) is used as excitation light. can be used. In this case, in order to ensure the stability of the amplified light generated by the optical amplifier, the input pumping light (wavelength-converted light) is required to have stable power. However, even if the temperature controller (for example, the temperature controller 105 shown in FIG. 1) is operated, the phase matching conditions that have been satisfied due to temperature fluctuations and optical loss of the wavelength conversion element due to environmental temperature fluctuations, etc. collapses, and the power of the wavelength-converted light may become unstable. Therefore, it is necessary to compensate for these instabilities and fluctuations.
　図２は、従来技術による、波長変換光を安定化させるための波長変換装置２００の構成を示す図である。波長変換装置２００は、図１に示される波長変換装置１００の構成に加え、出力された波長変換光１０３の一部を分波する分波器２０１と、分波器２０１によって分波された波長変換光１０３の一部を検波する検波器２０２と、検波器２０２の出力に対し、波長変換光１０３の位相ノイズの揺らぎを安定化するための平均化を行う平均化装置２０３と、平均化装置２０３の出力に基づいて、演算により温調器１０５の温度制御を行うためのフィードバック信号を生成し、温調器１０５にフィードバック信号を送信する演算装置２０４と、をさらに含む。このように構成された波長変換装置２００では、定期的に一定間隔で波長変換素子１０２の温度が正負の方向に離調され、温度の離調に伴って生じる波長変換光１０３のパワー変動に基づいて、温調器１０５がフィードバック制御されるように構成されている。 FIG. 2 is a diagram showing the configuration of a conventional wavelength conversion device 200 for stabilizing wavelength-converted light. The wavelength conversion device 200 has the configuration of the wavelength conversion device 100 shown in FIG. A detector 202 for detecting a part of the converted light 103, an averaging device 203 for averaging the output of the detector 202 for stabilizing fluctuations in the phase noise of the wavelength-converted light 103, and an averaging device. A computing device 204 that generates a feedback signal for controlling the temperature of the temperature controller 105 by computation based on the output of 203 and transmits the feedback signal to the temperature controller 105 . In the wavelength conversion device 200 configured as described above, the temperature of the wavelength conversion element 102 is periodically detuned in the positive and negative directions at regular intervals, and based on the power fluctuation of the wavelength-converted light 103 caused by the temperature detuning. Accordingly, the temperature controller 105 is configured to be feedback-controlled.
　図３は、波長変換素子の温度が離調した場合の波長変換光の挙動を示した図であり、図３（ａ）は、波長変換装置の位相制御曲線の温度依存性を、図３（ｂ）は、図３（ａ）のピーク近傍の拡大図を、図３（ｃ）は、離調温度と波長変換光の出力との関係を、それぞれ示している。なお、図中では、位相整合条件を満足する温度をＴ０、Ｔ０から高温側に変動した波長変換素子の温度をＴ０＋ΔＴ、Ｔ０から低温側に変動した波長変換素子の温度をＴ０－ΔＴとして、それぞれ示している。また、図３（ｂ）では、位相整合波長が破線で示されている。図３（ａ）に示される通り、波長変換素子における位相整合曲線は、波長変換素子の温度に対して線形にシフトする。その単位温度当たりの波長シフト量は、概ね、波長変換素子に適用される二次非線形媒質の物理パラメータによって決まると言ってよい。従来技術である波長変換装置２００では、このような特性に基づき、波長変換素子１０２の温度を定期的に正負の方向に離調し、図３（ｃ）に示されるようなパワーの変動（変化量）から波長変換素子１０２の温度変動を演算する。そして、演算の結果に基づいてフィードバック信号を生成し、温調器１０５をフィードバック信号によって制御することで、出力される波長変換光１０３のパワーをさらに安定化させている。 3A and 3B show the behavior of the wavelength-converted light when the temperature of the wavelength conversion element is detuned. FIG. 3A shows the temperature dependence of the phase control curve of the wavelength conversion device. b) shows an enlarged view near the peak in FIG. 3(a), and FIG. 3(c) shows the relationship between the detuning temperature and the output of wavelength-converted light. In the figure, T 0 is the temperature that satisfies the phase matching condition, T 0 +ΔT is the temperature of the wavelength conversion element that has changed from T 0 to the high temperature side, and T is the temperature of the wavelength conversion element that has changed from T 0 to the low temperature side. 0 -ΔT, respectively. Also, in FIG. 3B, the phase matching wavelength is indicated by a dashed line. As shown in FIG. 3(a), the phase matching curve in the wavelength conversion element shifts linearly with the temperature of the wavelength conversion element. It can be said that the amount of wavelength shift per unit temperature is generally determined by the physical parameters of the second-order nonlinear medium applied to the wavelength conversion element. Based on these characteristics, the conventional wavelength conversion device 200 periodically detunes the temperature of the wavelength conversion element 102 in the positive and negative directions, and changes the power as shown in FIG. The temperature fluctuation of the wavelength conversion element 102 is calculated from the quantity). A feedback signal is generated based on the calculation result, and the temperature controller 105 is controlled by the feedback signal, thereby further stabilizing the power of the output wavelength-converted light 103 .
　しかしながら、このような従来技術による波長変換装置２００の構成では、波長変換光１０３の一部を分波することが必要であるため、波長変換光１０３のパワー減衰が生じるという課題がある。この減衰する分のパワーを補償するために、従来ではＥＤＦＡなどの光増幅器により、励起光１０１を増幅するといった施策が行われている。しかしながら、このような方法では、励起光１０１の増幅過程で自然放出光が励起光１０１に混入し、この自然放出光がパラメトリック過程を経て波長変換光のノイズを引き起こすといった課題があることが知られている。 However, with such a configuration of the wavelength conversion device 200 according to the prior art, since it is necessary to demultiplex a part of the wavelength-converted light 103, there is a problem that the power of the wavelength-converted light 103 is attenuated. In order to compensate for this attenuated power, conventional measures have been taken to amplify the pumping light 101 using an optical amplifier such as an EDFA. However, it is known that such a method has a problem that spontaneous emission light is mixed into the excitation light 101 during the amplification process of the excitation light 101, and this spontaneous emission light causes noise in the wavelength-converted light through a parametric process. ing.
　本開示は、上記のような課題に対して鑑みてなされたものであり、その目的とするところは、ＳＦＧによる波長変換を行う波長変換装置であって、出力される波長変換光のパワー減衰を従来よりも抑制することが可能な波長変換装置を提供することにある。 The present disclosure has been made in view of the problems described above, and an object of the present disclosure is to provide a wavelength conversion device that performs wavelength conversion using SFG, and is capable of reducing the power attenuation of output wavelength-converted light. An object of the present invention is to provide a wavelength conversion device capable of suppressing noise more than the conventional one.
　上記のような課題に対し、本開示では、励起光を入力し、和周波発生によって波長変換光を出力する波長変換装置であって、二次非線形光学効果に基づいて波長変換を行う波長変換素子と、波長変換素子の温度を制御する温調器と、波長変換素子を透過する残留励起光のパワー検出する検波器と、検波器の出力に基づいて温調器に対する制御信号を生成する演算装置と、を備え、演算装置は、温調器に波長変換素子の温度を離調させる制御信号を生成し、波長変換素子の温度の離調に応答して生じる残留励起光のパワー変動に基づいて波長変換素子の温度変動を演算し、温度変動に基づいて、波長変換素子の温度が波長変換素子の位相整合条件の変動を補正する温度となるように温調器を制御するための制御信号を生成するように構成される波長変換装置を提供する。 In order to solve the above-described problems, the present disclosure provides a wavelength conversion device for inputting excitation light and outputting wavelength-converted light by sum-frequency generation, wherein the wavelength conversion element performs wavelength conversion based on the second-order nonlinear optical effect. , a temperature controller for controlling the temperature of the wavelength conversion element, a detector for detecting the power of residual excitation light transmitted through the wavelength conversion element, and an arithmetic unit for generating a control signal for the temperature controller based on the output of the detector. and the computing device generates a control signal for detuning the temperature of the wavelength conversion element to the temperature regulator, based on the power fluctuation of the residual excitation light that occurs in response to the temperature detuning of the wavelength conversion element. The temperature fluctuation of the wavelength conversion element is calculated, and based on the temperature fluctuation, a control signal for controlling the temperature controller is generated so that the temperature of the wavelength conversion element becomes a temperature that corrects the fluctuation of the phase matching condition of the wavelength conversion element. A wavelength conversion device configured to generate a wavelength is provided.
ＳＨＧにより、入力光の第２高調波（ＳＨＧ光）を発生させる波長変換装置の基本構成を示した図である。1 is a diagram showing the basic configuration of a wavelength conversion device that generates a second harmonic (SHG light) of input light by SHG; FIG. 従来技術による、波長変換光を安定化させるための波長変換装置の構成を示す図である。1 is a diagram showing the configuration of a wavelength conversion device for stabilizing wavelength-converted light according to the prior art; FIG. 波長変換素子の温度が離調した場合の波長変換光の挙動を示した図であり、図３（ａ）は、波長変換装置の位相制御曲線の温度依存性を、図３（ｂ）は、図３（ａ）のピーク近傍の拡大図を、図３（ｃ）は、離調温度と波長変換光の出力との関係を、それぞれ示している。FIG. 3A is a diagram showing the behavior of wavelength-converted light when the temperature of the wavelength conversion element is detuned, FIG. 3A shows the temperature dependence of the phase control curve of the wavelength conversion device, FIG. 3(a) shows an enlarged view near the peak, and FIG. 3(c) shows the relationship between the detuning temperature and the output of wavelength-converted light. 位相整合波長近傍における波長変換光及び残留励起光のパワースペクトルを示す図である。FIG. 4 is a diagram showing power spectra of wavelength-converted light and residual pumping light in the vicinity of a phase matching wavelength; 本開示の一実施形態における波長変換装置の構成を示す図である。1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure; FIG. 本開示の一実施形態における波長変換装置の構成を示す図である。1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure; FIG. 本開示の一実施形態における波長変換装置の構成を示す図である。1 is a diagram showing the configuration of a wavelength conversion device according to an embodiment of the present disclosure; FIG.
　以下に、図面を参照しながら本開示の種々の実施形態について詳細に説明する。同一又は類似の参照符号は、同一又は類似の要素を示し重複する説明を省略する場合がある。以下の説明は、一例であって本開示の一実施形態の要旨を逸脱しない限り、一部の構成を省略若しくは変形し、又は追加の構成とともに実施することができる。 Various embodiments of the present disclosure will be described in detail below with reference to the drawings. Identical or similar reference numerals indicate identical or similar elements and redundant description may be omitted. The following description is an example, and part of the configuration can be omitted or modified, or implemented with an additional configuration, as long as it does not deviate from the gist of an embodiment of the present disclosure.
　本開示による波長変換装置は、定期的に波長変換素子の温度を離調し、その離調によるパワー変動に基づいて温調器をフィードバック制御するという点では、従来技術と同様である。しかしながら、本開示による波長変換装置は、従来は光学フィルタ等により除去していた残留励起光を検波し、定期的な離調に伴う残留励起光のパワー変動に基づいてフィードバック制御されるという点で、従来技術とは異なる。 The wavelength conversion device according to the present disclosure is the same as the conventional technology in that the temperature of the wavelength conversion element is periodically detuned and the temperature regulator is feedback-controlled based on the power fluctuation due to the detuning. However, the wavelength conversion device according to the present disclosure detects the residual pumping light that has been removed by an optical filter or the like in the past, and is feedback-controlled based on the power fluctuation of the residual pumping light that accompanies periodic detuning. , unlike the prior art.
　なお、本明細書の説明では、例として、波長変換装置はＳＨＧによる波長変換光を生成するものとして説明するが、これに限定はされず、ＳＦＧに基づく波長変換装置であれば、同様の効果を奏する。 In the description of this specification, as an example, the wavelength conversion device generates wavelength-converted light by SHG. play.
　ＳＨＧに基づく波長変換では、上述の通り、励起光の一部が残留励起光として波長変換素子を透過し、波長変換光（この場合、ＳＨＧ光）と同時に出力され得る。しかし、残留励起光のエネルギーの一部は、波長変換光に移行するため、波長変換素子を透過した残留励起光には位相整合条件を満たす波長近傍においてパワーが減衰する（この現象はポンプディプレッションと呼ばれる）。本発明者らは、このポンプディプレッションによるパワー減衰に着目し、この現象に基づいて、従来技術と同様に波長変換素子の温度をフィードバック制御できることを見出した。 In wavelength conversion based on SHG, as described above, part of the excitation light passes through the wavelength conversion element as residual excitation light and can be output simultaneously with the wavelength-converted light (SHG light in this case). However, since part of the energy of the residual pumping light is transferred to wavelength-converted light, the power of the residual pumping light that has passed through the wavelength conversion element is attenuated in the vicinity of the wavelength that satisfies the phase matching condition (this phenomenon is called pump depression). Called). The present inventors paid attention to the power attenuation due to this pump depression, and based on this phenomenon, found that the temperature of the wavelength conversion element can be feedback-controlled in the same manner as in the prior art.
　図４は、位相整合波長近傍における波長変換光及び残留励起光のパワースペクトルを示す図である。なお、図中における各スペクトルは、後述する波長変換装置５００を用いた場合のスペクトルである。また、図中では、図３と同様に、位相整合条件を満足する温度をＴ０、Ｔ０から高温側に変動した波長変換素子の温度をＴ０＋ΔＴ、Ｔ０から低温側に変動した波長変換素子の温度をＴ０－ΔＴとして、それぞれ示している。図中に示される通り、残留励起光のパワースペクトルは、波長変換素子の温度がＴ０であるとき、位相整合波長においてディップ（極小値）を示す分布であり、波長変換光と同様に、温度の変動に応じて線形にシフトする。そして、そのシフト量は、波長変換光のシフト量と一致していることが分かる。すなわち、波長変換素子の位相整合条件がどの程度ずれているかをモニタするためには、波長変換光に限らず、残留励起光をモニタすることによっても判断が可能であると言える。本開示による波長変換装置は、このような原理に基づき、残留励起光をモニタすることによって波長変換素子の温度を制御する構成となっている。 FIG. 4 is a diagram showing power spectra of wavelength-converted light and residual pump light in the vicinity of the phase matching wavelength. It should be noted that each spectrum in the drawing is a spectrum when the wavelength conversion device 500 described later is used. In the figure, as in FIG. 3, the temperature that satisfies the phase matching condition is T 0 , the temperature of the wavelength conversion element that has changed from T 0 to the higher temperature side is T 0 +ΔT, and the wavelength that has changed from T 0 to the lower temperature side The temperature of the conversion element is shown as T 0 -ΔT, respectively. As shown in the figure, the power spectrum of the residual excitation light is a distribution showing a dip (minimum value) in the phase matching wavelength when the temperature of the wavelength conversion element is T0 . shifts linearly with the variation of . It can be seen that the shift amount matches the shift amount of the wavelength-converted light. In other words, in order to monitor how much the phase matching condition of the wavelength conversion element deviates, it can be said that it is possible to make a determination by monitoring not only the wavelength-converted light but also the residual pumping light. Based on this principle, the wavelength conversion device according to the present disclosure is configured to control the temperature of the wavelength conversion element by monitoring the residual excitation light.
（第１の実施形態）
　以下に、本開示の第１の実施形態について、図面を参照して詳細に説明する。本実施形態における波長変換装置は、上述の波長変換装置２００と同様の基本構成を有する波長変換装置であるが、従来、光学フィルタで除去していた残留励起光を分波し、検波に用いているように構成されている。 (First embodiment)
A first embodiment of the present disclosure will be described in detail below with reference to the drawings. The wavelength conversion device in this embodiment has the same basic configuration as the wavelength conversion device 200 described above. configured to be
　図５は、本開示の一実施形態における波長変換装置５００の構成を示す図である。本実施形態における波長変換装置５００は、励起光１０１を含む入力光１０１に対して波長変換を行う波長変換素子１０２と、波長変換素子１０２から出力される出力光のうち、波長変換光１０３を透過し、残留励起光１０６を反射させるダイクロイックミラー５０１と、ダイクロイックミラー５０１によって分波された残留励起光１０６を検波する検波器５０２と、検波器５０２の出力に基づいて、演算により温調器１０５の温度制御を行うためのフィードバック信号を生成し、温調器１０５にフィードバック信号を送信する演算装置２０４と、を含む。図から理解できるように、波長変換装置５００の基本的な構成は、従来の波長変換装置（例えば、波長変換装置２００）と同様である。しかしながら、光学フィルタ１０４の代わりにダイクロイックミラー５０１を含むこと、検波する光の位相ノイズの揺らぎを安定化するための平均化装置２０３が不要であることが従来の波長変換装置とは異なる。 FIG. 5 is a diagram showing the configuration of a wavelength conversion device 500 according to one embodiment of the present disclosure. The wavelength conversion device 500 according to the present embodiment includes a wavelength conversion element 102 that performs wavelength conversion on input light 101 including excitation light 101, and wavelength-converted light 103 out of the output light output from the wavelength conversion element 102. Then, based on a dichroic mirror 501 that reflects the residual excitation light 106, a detector 502 that detects the residual excitation light 106 split by the dichroic mirror 501, and the output of the detector 502, the temperature controller 105 is calculated. and an arithmetic device 204 that generates a feedback signal for temperature control and transmits the feedback signal to the temperature controller 105 . As can be understood from the figure, the basic configuration of the wavelength conversion device 500 is similar to that of a conventional wavelength conversion device (for example, the wavelength conversion device 200). However, it differs from the conventional wavelength conversion device in that it includes a dichroic mirror 501 instead of the optical filter 104 and does not require an averaging device 203 for stabilizing fluctuations in the phase noise of light to be detected.
　波長変換装置５００に含まれる波長変換素子１０２は、例えば、周期分極反転構造を有するＬｉＮｂ３を二次非線形媒質とした、リッジ型導波路であり得る。但し、これに限定はされず、波長変換素子１０２の二次非線形媒質には、ＬｉＴａＯ３、或いはＬｉＮｂ（ｘ）Ｔａ（１－ｘ）Ｏ３（ここで、０≦ｘ≦１）のいずれか、または、これらにＭｇ、Ｚｎ、Ｓｃ、Ｉｎからなる群から選ばれた少なくとも一つの元素を添加物として含有したものであってもよい。 The wavelength conversion element 102 included in the wavelength conversion device 500 can be, for example, a ridge waveguide using LiNb 3 having a periodically poled structure as a second-order nonlinear medium. However, the second-order nonlinear medium of the wavelength conversion element 102 is not limited to this, and LiTaO 3 or LiNb(x)Ta(1−x)O 3 (where 0≦x≦1). Alternatively, at least one element selected from the group consisting of Mg, Zn, Sc and In may be added as an additive.
　このような構成を有する波長変換装置５００を用いて波長変換を行い、波長変換光１０３としてＳＨＧ光を生成する。このとき、定期的に波長変換素子１０２の温度を温調器１０５によって離調し、残留励起光１０６の位相整合波長近傍におけるスペクトルに変動を与える。そして、その変動挙動を検波器５０２でモニタし、検波器５０２の出力に基づいて演算装置２０４がフィードバック信号を生成し、温調器１０５を制御する。なお、励起光１０１の波長は、光通信波長のうち、ＯバンドからＬバンドの範囲におけるいずれかの波長であればよい。 Wavelength conversion is performed using the wavelength conversion device 500 having such a configuration, and SHG light is generated as the wavelength-converted light 103 . At this time, the temperature of the wavelength conversion element 102 is periodically detuned by the temperature controller 105 to vary the spectrum of the residual excitation light 106 near the phase matching wavelength. The fluctuation behavior is monitored by the detector 502 , and the arithmetic unit 204 generates a feedback signal based on the output of the detector 502 to control the temperature regulator 105 . The wavelength of the pumping light 101 may be any wavelength in the range from the O band to the L band among optical communication wavelengths.
このようにして、波長変換装置５００から出力される波長変換光１０３は、環境温度や光損失によるパワーの変動が抑制され、安定化する。さらに、上述の通り、波長変換装置５００は、出力される波長変換光１０３をモニタしていないため、従来技術では生じていた波長変換光１０３のパワー減衰も抑制される。したがって、安定した波長変換光１０３をＰＳＡなどの外部へ、従来よりも効率的に供給することが可能となる。 In this way, the wavelength-converted light 103 output from the wavelength conversion device 500 is stabilized by suppressing fluctuations in power due to environmental temperature and optical loss. Furthermore, as described above, since the wavelength conversion device 500 does not monitor the output wavelength-converted light 103, power attenuation of the wavelength-converted light 103 that occurs in the conventional technology is also suppressed. Therefore, it becomes possible to supply the stable wavelength-converted light 103 to the outside such as the PSA more efficiently than before.
　また、波長変換装置５００は従来の波長変換装置（例えば、波長変換装置２００）のように平均化装置（例えば、平均化装置２０３）を用いることなく、従来と同等な波長変換光１０３の安定性を実現することができる。これは、図４に示される通り、残留励起光１０６のパワーが、波長変換光１０３に比べて大きいことに起因する。この残留励起光１０６のパワーは、ノイズが無視できるほどに大きい値を有するため、位相シフトのノイズによる揺らぎを安定化することが不要である。したがって、波長変換装置５００は、平均化装置が不要であり、そのためシステム構成を簡素化できるという利点も有する。 In addition, the wavelength conversion device 500 does not use an averaging device (eg, averaging device 203) like the conventional wavelength conversion device (eg, wavelength conversion device 200), and the stability of the wavelength-converted light 103 equivalent to that of the conventional one can be obtained. can be realized. This is because the power of the residual excitation light 106 is larger than that of the wavelength-converted light 103, as shown in FIG. Since the power of this residual excitation light 106 has a value so large that noise can be ignored, it is not necessary to stabilize fluctuations due to phase shift noise. Therefore, the wavelength conversion device 500 does not require an averaging device, which also has the advantage of simplifying the system configuration.
（第２の実施形態）
　以下に、本開示の第２の実施形態について、図面を参照して詳細に説明する。本実施形態における波長変換装置は、波長変換を行う機構及び波長変換素子からの出力光を分波する機構を金属筐体の内部に気密封入することにより、波長変換光の安定性をさらに向上させた形態に関する。 (Second embodiment)
A second embodiment of the present disclosure will be described in detail below with reference to the drawings. In the wavelength conversion device of this embodiment, the stability of the wavelength-converted light is further improved by hermetically enclosing the mechanism for wavelength conversion and the mechanism for demultiplexing the output light from the wavelength conversion element inside the metal housing. concerning the form.
　図６は、本開示の一実施形態における波長変換装置６００の構成を示す図である。図中に示される通り、本実施形態における波長変換装置６００は、波長変換装置５００の構成に加え、入力光１０１を金属筐体６０１の内部へ導入する光ファイバ６０２と、光ファイバ６０２から出力される励起光をコリメートする励起光用コリメートレンズ６０３と、コリメートされた励起光を波長変換素子１０２に集光するように配置されたフォーカスレンズ６０４と、波長変換素子１０２からの出力光（波長変換光１０３及び残留励起光１０６を含む）をコリメートするコリメートレンズ６０５と、コリメートレンズ６０５によってコリメートされた出力光のうち、波長変換光１０３を出力端に集光するように配置されたフォーカスレンズ６０６と、フォーカスレンズ６０６によって集光された波長変換光１０３を外部へ導出する光ファイバ６０７と、コリメートレンズ６０５によってコリメートされた出力光のうち、残留励起光１０６を反射させるミラー６０８と、ミラー６０８によって反射された残留励起光１０６を出力端に集光するように配置されたフォーカスレンズ６０９と、フォーカスレンズ６０９により集光された残留励起光１０６を検波器５０２へ導くファイバ６１０と、金属筐体６０１の外部から内部及び内部から外部へ光を入出力するための複数の光学窓６１１と、をさらに含む。なお、励起光１０１と残留励起光１０６は、同じ波長を有する光であるため、光ファイバ６０２と光ファイバ６１０は、光学設計上、同じものを用いることが好適である。 FIG. 6 is a diagram showing the configuration of a wavelength conversion device 600 according to an embodiment of the present disclosure. As shown in the figure, the wavelength conversion device 600 in this embodiment has, in addition to the structure of the wavelength conversion device 500, an optical fiber 602 that introduces the input light 101 into the metal casing 601 and an optical fiber 602 that outputs the light. excitation light collimating lens 603 for collimating the excitation light, focus lens 604 arranged to focus the collimated excitation light on the wavelength conversion element 102, output light from the wavelength conversion element 102 (wavelength converted light 103 and the residual excitation light 106), a focus lens 606 arranged to focus the wavelength-converted light 103 out of the output light collimated by the collimating lens 605 to the output end, An optical fiber 607 that guides the wavelength-converted light 103 condensed by the focus lens 606 to the outside, a mirror 608 that reflects the residual excitation light 106 out of the output light collimated by the collimator lens 605, and a mirror 608 that reflects the residual excitation light 106. A focus lens 609 arranged to condense the residual excitation light 106 collected by the focus lens 609 to the output end, a fiber 610 for guiding the residual excitation light 106 condensed by the focus lens 609 to the detector 502, and the outside of the metal housing 601. and a plurality of optical windows 611 for inputting and outputting light to and from the interior. Since the excitation light 101 and the residual excitation light 106 have the same wavelength, it is preferable to use the same optical fibers 602 and 610 in terms of optical design.
　本実施形態における波長変換装置６００では、ダイクロイックミラー５０１は、金属筐体６０１の内部であり、且つコリメートレンズ６０５とフォーカスレンズ６０６との間に設置される。また、本実施形態における波長変換装置６００では、検波器５０２及び演算装置２０４は、金属筐体６０１の外部に設置され、検波器５０２は、光ファイバ６１０と光学的に接続されている。 In the wavelength conversion device 600 of this embodiment, the dichroic mirror 501 is inside the metal housing 601 and installed between the collimator lens 605 and the focus lens 606 . Further, in the wavelength conversion device 600 of this embodiment, the detector 502 and the arithmetic device 204 are installed outside the metal housing 601 , and the detector 502 is optically connected to the optical fiber 610 .
　なお、演算装置２０４は、波長変換装置２００及び波長変換装置５００と同様に、温調器１０５と通信可能に接続されており、温調器１０５は演算装置２０４が生成したフィードバック信号を受信できるように構成されている。フィードバック信号の形式は電気信号であってよく、光信号であってもよいが、いずれの場合であっても、金属筐体６０１によってフィードバック信号が遮蔽されないような機構が必要である（例えば、フィードバック信号が電気信号である場合、金属筐体６０１に設置された端子を介して、電気信号が温調器１０５に送信されるように構成され、且つ金属筐体６０１と端子は電気的に絶縁されていることが必要である）。 Note that the arithmetic device 204 is communicably connected to the temperature controller 105 in the same manner as the wavelength conversion device 200 and the wavelength conversion device 500, so that the temperature controller 105 can receive the feedback signal generated by the arithmetic device 204. is configured to The form of the feedback signal may be an electrical signal or an optical signal. When the signal is an electrical signal, the electrical signal is transmitted to the temperature controller 105 via a terminal installed on the metal housing 601, and the metal housing 601 and the terminal are electrically insulated. required).
　このように構成された波長変換装置６００を用いても、第１の実施形態と同様に、波長変換を行ってＳＨＧ光を生成すれば、従来技術による波長変換装置（例えば、波長変換装置２００）と同様に、安定した波長変換光１０３を生成することができる。 Even if the wavelength conversion device 600 configured in this way is used, as in the first embodiment, if wavelength conversion is performed to generate SHG light, a conventional wavelength conversion device (for example, the wavelength conversion device 200) can be used. , a stable wavelength-converted light 103 can be generated.
　また、波長変換装置６００は、波長変換装置５００と同様に、出力される波長変換光１０３をモニタしていないため、波長変換光１０３のパワー減衰を抑制した上での波長変換が可能である。加えて、波長変換装置６００は、波長変換装置５００と同様に、平均化装置が不要であるため、システム構成を簡素化できるという利点も有する。 Also, similarly to the wavelength conversion device 500, the wavelength conversion device 600 does not monitor the output wavelength-converted light 103, so it is possible to perform wavelength conversion while suppressing the power attenuation of the wavelength-converted light 103. In addition, similarly to the wavelength conversion device 500, the wavelength conversion device 600 does not require an averaging device, and therefore has the advantage of simplifying the system configuration.
　さらに、波長変換装置６００は、上述の通り、波長変換を行う機構及び波長変換素子からの出力光を分波する機構を金属筐体６０１の内部に気密封入した構造となっている。このため、外部温度の揺らぎ等の影響を受けにくく、波長変換装置５００よりも更に安定した波長変換光１０３を生成することが可能である。 Furthermore, as described above, the wavelength conversion device 600 has a structure in which the mechanism for wavelength conversion and the mechanism for demultiplexing the output light from the wavelength conversion element are hermetically sealed inside the metal housing 601 . Therefore, it is possible to generate the wavelength-converted light 103 that is more stable than the wavelength conversion device 500 without being easily affected by external temperature fluctuations and the like.
（第３の実施形態）
　以下に、本開示の第３の実施形態について、図面を参照して詳細に説明する。本実施形態による波長変換装置は、第２の実施形態で述べた波長変換装置６００において、残留励起光１０６を検波する検波器５０２が、金属筐体６０１の内部に設置された形態に関する。 (Third Embodiment)
A third embodiment of the present disclosure will be described in detail below with reference to the drawings. The wavelength conversion device according to this embodiment relates to the wavelength conversion device 600 described in the second embodiment, in which the detector 502 for detecting the residual excitation light 106 is installed inside the metal housing 601 .
　図７は、本開示の一実施形態における波長変換装置７００の構成を示す図である。図中に示される通り、本実施形態における波長変換装置７００は、第２の実施形態で述べた波長変換装置６００において、残留励起光１０６を検波する検波器５０２が、金属筐体６０１の内部に設置された構造を有する。ここで、波長変換装置７００が有する検波器５０２は、大口径の検波器である。また、このような構造となるに伴い、波長変換装置６００に含まれる、ミラー６０８、フォーカスレンズ６０９、ミラー６０８とフォーカスレンズ６０９との間に設置される光学窓６１１、及び、光ファイバ６１０は不要となる。 FIG. 7 is a diagram showing the configuration of a wavelength conversion device 700 according to an embodiment of the present disclosure. As shown in the figure, the wavelength conversion device 700 in this embodiment is the same as the wavelength conversion device 600 described in the second embodiment, except that the detector 502 for detecting the residual excitation light 106 is inside the metal casing 601. It has an installed structure. Here, the detector 502 included in the wavelength conversion device 700 is a large diameter detector. Further, with such a structure, the mirror 608, the focus lens 609, the optical window 611 installed between the mirror 608 and the focus lens 609, and the optical fiber 610, which are included in the wavelength conversion device 600, are unnecessary. becomes.
　このような構成を有する波長変換装置７００は、第２の実施形態で述べた波長変換装置６００に比べて、光学アラメントが簡素化されるという利点を有する。すなわち、波長変換装置６００では、出力光から分波された残留励起光１０６を光ファイバ６１０へ導入するための調芯が必要であったが、波長変換装置７００に設置される検波器５０２は、コリメート光を受光できるような大口径の検波器であるため、パッシブアライメントで光学結合することができる。その結果、モジュール実装のリードタイムを短縮することが可能となる。 The wavelength conversion device 700 having such a configuration has the advantage of simplifying the optical alignment compared to the wavelength conversion device 600 described in the second embodiment. That is, the wavelength conversion device 600 requires alignment for introducing the residual pumping light 106 demultiplexed from the output light into the optical fiber 610. However, the detector 502 installed in the wavelength conversion device 700 is Since it is a detector with a large aperture that can receive collimated light, it can be optically coupled with passive alignment. As a result, the lead time for module mounting can be shortened.
　また、このような波長変換装置７００を用いて、第１の実施形態及び第２の実施形態と同様に、波長変換を行ってＳＨＧ光を生成すれば、従来技術による波長変換装置（例えば、波長変換装置２００）と同様に、安定した波長変換光１０３を生成することが可能となる。 Further, if wavelength conversion is performed by using such a wavelength conversion device 700 to generate SHG light in the same manner as in the first and second embodiments, a conventional wavelength conversion device (for example, wavelength Similar to the converter 200), it is possible to generate stable wavelength-converted light 103. FIG.
　本開示による波長変換装置は、従来技術とは異なり、出力される波長変換光のパワー減衰を抑制しながらも、波長変換光のパワーを安定化させることが可能である。このような波長変換装置は、ＰＳＡなどの光増幅器へ効率的に入力光を供給できるため、光増幅器の光源への適用が見込まれる。 Unlike the conventional technology, the wavelength conversion device according to the present disclosure can stabilize the power of the wavelength-converted light while suppressing the power attenuation of the output wavelength-converted light. Since such a wavelength converter can efficiently supply input light to an optical amplifier such as a PSA, it is expected to be applied to the light source of an optical amplifier.

Claims (6)

  1. 　励起光を入力し、和周波発生によって波長変換光を出力する波長変換装置であって、
    　二次非線形光学効果に基づいて波長変換を行う波長変換素子と、
    　前記波長変換素子の温度を制御する温調器と、
    　前記波長変換素子を透過する残留励起光のパワー検出する検波器と、
    　前記検波器の出力に基づいて前記温調器に対する制御信号を生成する演算装置と、
    　を備え、
    　前記演算装置は、
    　　前記温調器に前記波長変換素子の温度を離調させる制御信号を生成し、
    　　前記波長変換素子の温度の離調に応答して生じる前記残留励起光のパワー変動に基づいて前記波長変換素子の温度変動を演算し、
    　　前記温度変動に基づいて、前記波長変換素子の前記温度が前記波長変換素子の位相整合条件の変動を補正する温度となるように前記温調器を制御するための制御信号を生成する、
    ように構成される、波長変換装置。     A wavelength conversion device for inputting excitation light and outputting wavelength-converted light by sum frequency generation,
    a wavelength conversion element that performs wavelength conversion based on a second-order nonlinear optical effect;
    a temperature controller for controlling the temperature of the wavelength conversion element;
    a detector for detecting the power of the residual excitation light transmitted through the wavelength conversion element;
    an arithmetic device that generates a control signal for the temperature controller based on the output of the detector;
    with
    The computing device is
    generating a control signal for causing the temperature regulator to detune the temperature of the wavelength conversion element;
    calculating the temperature fluctuation of the wavelength conversion element based on the power fluctuation of the residual excitation light generated in response to the temperature detuning of the wavelength conversion element;
    generating a control signal for controlling the temperature controller so that the temperature of the wavelength conversion element is a temperature that corrects the fluctuation of the phase matching condition of the wavelength conversion element based on the temperature fluctuation;
    A wavelength conversion device, configured to:
  2. 　前記波長変換素子、及び前記温調器を内部に気密封入する金属筐体と、
    　前記金属筐体に設置され、前記励起光、前記波長変換光、又は前記残留励起光を前記金属筐体の内部に入力、及び外部に出力させる光学窓と、
    をさらに備える、請求項１に記載の波長変換装置。     a metal housing that hermetically encloses the wavelength conversion element and the temperature controller;
    an optical window installed in the metal casing for inputting the excitation light, the wavelength-converted light, or the residual excitation light into the interior of the metal casing and outputting it to the outside;
    The wavelength conversion device of claim 1, further comprising:
  3. 　前記検波器が大口径の検波器であり、前記金属筐体の内部に設置される、請求項２に記載の波長変換装置。 The wavelength conversion device according to claim 2, wherein the detector is a large-diameter detector and is installed inside the metal housing.
  4. 　前記励起光の波長が、通信波長のうちＯバンドからＬバンドの範囲の波長である、請求項１乃至３のいずれか一項に記載の波長変換装置。 The wavelength conversion device according to any one of claims 1 to 3, wherein the wavelength of the excitation light is a wavelength in a range from O band to L band among communication wavelengths.
  5. 　前記波長変換素子は、二次非線形媒質を備えたリッジ型導波路であり、前記二次非線形媒質は、周期分極反転構造を有する、請求項１乃至４のいずれか一項に記載の波長変換装置。 5. The wavelength conversion device according to any one of claims 1 to 4, wherein said wavelength conversion element is a ridge-type waveguide provided with a second-order nonlinear medium, and said second-order nonlinear medium has a periodically poled structure. .
  6. 　前記二次非線形媒質に適用される材料が、ＬｉＮｂＯ３、ＬｉＴａＯ３、或いはＬｉＮｂ（ｘ）Ｔａ（１－ｘ）Ｏ３（ここで、０≦ｘ≦１）のいずれか、又はこれらにＭｇ、Ｚｎ、Ｓｃ、Ｉｎからなる群から選ばれた少なくとも一つの元素を添加物として含有した材料のいずれかである、請求項５に記載の波長変換装置。 The material applied to the second-order nonlinear medium is LiNbO 3 , LiTaO 3 , or LiNb(x)Ta(1−x)O 3 (where 0≦x≦1), or Mg, 6. The wavelength conversion device according to claim 5, wherein the material contains at least one element selected from the group consisting of Zn, Sc and In as an additive.
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