JPH086082A - Wavelength converter, wavelength converting method and bbo crystal for wavelength conversion - Google Patents

Abstract

PURPOSE: To enable a resonator to be synchronized with a small easy structure without lowering optical output of a changed wavelength. CONSTITUTION: A laser beam emitted from a laser beam machine 12 is made incident on a resonator 16, whose resonance frequency is modulated in the electrical field imparted to the a BBO crystal 14 inside the resonator 16. In the BBO crystal 14, a modulation electrode 32 is arranged, as is a feedback electrode 34, so that the laser beam modulated in the BBO crystal 14 is detected by a photodetector 18. With a signal proportional to the error of the resonance frequency obtained from the photodetector 18, an electrical field is imparted to the BBO crystal 14 through the electrode 32, thereby changing the resonator length, controlling by feeding back negatively against the resonance frequency of the resonator 16 that is determined by the BBO crystal 14 through the imparting of the electrical field, and making synchronization by maintaining the error nearly on a zero level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion device, a wavelength conversion method, and a BBO crystal for wavelength conversion. In particular, the light converted from the oscillation wavelength of incident light to a predetermined wavelength by the nonlinear optical effect is emitted light. The present invention relates to a wavelength conversion device for extracting as described above, a wavelength conversion method for extracting light having a predetermined wavelength converted to a different wavelength, and a wavelength conversion BBO crystal used when converting light having a predetermined wavelength to light having a different wavelength.

[0002]

BACKGROUND OF THE INVENTION Continuous visible laser light having a fundamental wavelength by wavelength conversion using a non-linear optical material such as a uniaxial crystal having optical anisotropy (non-linear optical effect). There is a wavelength conversion device that obtains ultraviolet light, which is the conversion wavelength, from the. This non-linear optical effect is a series of phenomena caused by the non-linear polarization induced in the non-linear optical material. By using the second-order nonlinear optical effect, the laser light can be wavelength-converted (second harmonic generation, sum frequency, difference frequency generation, etc.). For example, second harmonic generation (Second Harmonic Genera) using a non-linear optical material such as β barium borate crystal (β barium borate: BBO).
(tion: SHG) is generally used for wavelength conversion of light. That is, the simplest example of wavelength conversion is the second harmonic generation, in which the frequency of the converted light is twice that of the input light and the wavelength is half. In the following description, the wavelength conversion for generating the second harmonic will be briefly described as an example. However, when the incident light is composed of two wavelength components, the sum of light of the sum of the two wavelengths of the incident light is generated. The same applies to frequency generation and difference frequency generation for generating light having a wavelength that is the difference between the two wavelengths of incident light. Further, since most of the non-linear optical materials for generating the second harmonic wave have a crystal form, they are hereinafter referred to as crystals.

In the second-order non-linear optical effect, the amplitude of the induced non-linear polarization is proportional to the square of the amplitude of the electric field of the incident light, so the converted light power is the square of the input light power. , But the proportional coefficient is considerably smaller. Therefore, generally, the power of the light converted by the small conversion efficiency is small. Therefore, a resonator is provided outside the laser device to increase the power of laser light (hereinafter referred to as excitation light) incident on the crystal, and
Light having a frequency twice that of the second harmonic (hereinafter referred to as SHG light) is emitted.

However, as described above, in order to efficiently generate SHG light from a crystal using a resonator,
The resonant frequency of the resonator must be tuned to the frequency of the laser light incident on the resonator. To this end, it is necessary to detect the resonance frequency error in order to suppress the frequency shift of the laser light that enters the resonator, and to perform feedback control to tune the light frequency by changing the resonator length of the resonator. is there.

Therefore, the conventional wavelength conversion device 100 is
As shown in FIG. 13, the laser device 102 and the resonator 10
An electro-optical modulator (hereinafter, referred to as an EO modulator) 108 having an electro-optical effect is arranged between the first and second electrodes 6. Laser light L emitted from the laser device 102
0 passes through the EO modulator 108 and is incident on the resonator 106. On the extended optical path of the laser beam L1 emitted from the EO modulator 108, the photodetector 1 connected to the servo electric circuit 110 for driving the EO modulator 108, etc.
12 are arranged. The electric circuit 110 for servo is E
It is for applying an electric field to generate an electro-optical effect in the O modulator 108.

The resonator 106 is composed of an incident mirror 114, a sampling mirror 116, a first mirror 122 and a second mirror 124. The laser light L1 incident on the resonator 106 passes through the incident mirror 114, follows the optical path L1a, and reaches the sampling mirror 116. The sampling mirror 116 samples a part of the incident light and irradiates it to the photodetector 112, and reflects other light which is not sampled and guides it to the optical path L1b. The light reflected by the sampling mirror 116 reaches the first mirror 122. First mirror 122
Reflects all of it and guides it to the optical path L1c. The crystal 104 is disposed on the optical path L1c, and the light reflected by the first mirror 122 passes through the crystal 104 and reaches the second mirror 124. Therefore, the crystal 104 emits the SHG light converted according to the incident light together with the unconverted light. The second mirror 124 receives the crystal 104 of the incident light.
SHG that reflects and converts unconverted light in
The light L2 is transmitted. The light reflected by the second mirror 124 is guided to the optical path L1d and reaches the incident mirror 114. The incident mirror 114 has an incident optical axis parallel to the optical path L1d and a reflected optical axis parallel to the optical path L1a adjusted, and reflects the light following the optical path L1d and guides it to the optical path L1a.

In the wavelength converter 100 having such a configuration, the error of the resonance frequency is detected from the detection value of the photodetector 112. Based on the detection value of the photodetector 112, the EO modulator 108 is frequency-modulated (and phase-modulated) at a high frequency to modulate the laser light L0 (referred to as FM sideband method. Michio Oka and Shi.
geo Kubota; Jpn.J.Appl.Phys.31, p531,1992: R.Drever,
J.Hall, F.Kowalski, J.Hough, G.Ford, A.Munley and H.Wa
rd; Appl.Phys.B31, p97,1983).

However, the conventional wavelength conversion device 100
In the error detection in, there were the following problems.

Incident power is lost due to surface reflection and internal absorption of the EO modulator. This reduces the power of incident visible light and also the final SHG light output. Due to the optical aberration of the EO modulator, the wavefront of the laser light emitted from the EO modulator is disturbed, and the coupling efficiency of the laser light in the resonator is reduced. This also reduces the SHG light output. Since the EO modulator must be arranged between the laser device and the resonator, the device becomes large. The cost is high because the configuration of the EO modulator is required.

In the conventional wavelength converter 100, in the feedback control for tuning the frequency, the first mirror 122 constituting the resonator 106 is a piezo element (piezoelectric element, element for converting an electric signal into a displacement). And the first mirror 122 is displaced to change the resonator length and change the resonance frequency.

However, since the first mirror 122 has an inertial mass, the high-frequency response deteriorates and frequency fluctuations occur. Further, it is difficult to follow the frequency fluctuation of incident light at a frequency of several kilohertz or higher due to the physical properties of the piezo element, and frequency fluctuations also occur. Due to fluctuations in these frequencies, the intensity (power) of the SHG light that is the output light fluctuates, or the servo control fails,
There was a problem that it could be out of sync.

In consideration of the above facts, the present invention has a compact and easy structure without lowering the optical output of the converted wavelength.
It is an object of the present invention to obtain a wavelength conversion device and a wavelength conversion method that can efficiently convert incident light into light of a conversion wavelength.

Further, it is an object to obtain a BBO crystal for wavelength conversion for facilitating the change of the resonance length used when converting the incident light into the light of the conversion wavelength.

[0014]

In order to achieve the above object, the present inventor has conducted various investigations, and as a result, paying attention to the phenomenon of electro-optical effect occurring in a nonlinear optical crystal, attempting all investigations, and specifically It was established as a wavelength converter. Specifically, the wavelength conversion device of the present invention is arranged on the emission side of the light emission means for emitting light of the fundamental wavelength, and uses the optical path length of light passing through the inside as a resonance length to cause resonance according to the resonance length. A resonance means having a frequency and having a plurality of reflection means for internally reflecting the light; and a resonance means disposed on the optical path of the light passing through the inside of the resonance means and having optical anisotropy. And a nonlinear optical material that emits incident light and light having at least one conversion wavelength different from that of the light, and the nonlinear optical material such that the resonance frequency of the resonance means is tuned to the light having the fundamental wavelength. An electric field applying means for applying an electric field to the electric field.

According to a second aspect of the invention, the electric field applying means applies an electric field for modulating the resonance length to the nonlinear optical material so that the resonance frequency of the resonance means is tuned to the light of the fundamental wavelength. Can be granted.

According to a third aspect of the invention, there is further provided photodetection means arranged on the exit side of the nonlinear optical material for detecting the intensity of incident light, and the electric field applying means modulates the resonance frequency. To the non-linear optical material, the resonance frequency obtained from the intensity of the detected light and the first electric field applying means for applying an electric field to the non-linear optical material are matched to the non-linear optical material. It can be configured by a second electric field applying means for applying an electric field.

In a fourth aspect of the invention, a BBO crystal can be used as the nonlinear optical material.

According to a fifth aspect of the present invention, the resonance means has a cross-sectional shape of a light beam different from a cross-sectional shape of an incident light beam with respect to a plane disposed on the exit side of the nonlinear optical material and passing through the optical axis. As described above, the reflection / transmission means for reflecting the light of the basic wavelength and transmitting the light of the conversion wavelength, and the basic incident on the nonlinear optical material disposed between the nonlinear optical material and the light emitting means. Reflects the light reflected by the reflection / transmission means so as to have a cross-sectional shape of a light beam that passes through an optical path that substantially matches the reference optical path through which the light of the wavelength passes and that substantially matches the cross-sectional shape of the light beam of the fundamental wavelength. Reflection means for

According to a sixth aspect of the present invention, in the wavelength conversion device according to the fifth aspect, at least one of the reflection / transmission means and the reflection means of the resonance means emits light incident from a predetermined direction and at the same time. The reflecting member includes a transmitting member that emits light incident from a direction different from the direction as reflected light, and a reflecting member that reflects the light emitted from the transmitting member from a predetermined direction and guides the light to the transmitting member. It is characterized in that an odd number of light collecting portions for collecting light are located between the transmitting member and the transmitting member, and the total number of light collecting portions for collecting light inside the resonance means is an even number.

The wavelength conversion method of the invention described in claim 7 is
The incident light is converted into the converted wavelength light by using a nonlinear optical material which has optical anisotropy and emits the incident light and the light having at least one conversion wavelength different from the wavelength of the incident light. In the wavelength conversion method, a light having a fundamental wavelength is incident on the nonlinear optical material, and an electric field for modulating a resonance length is applied to the nonlinear optical material so that the light having the fundamental wavelength resonates.

The BBO crystal according to the eighth aspect of the present invention is provided in a wavelength conversion device that emits light converted from a fundamental wavelength to a different wavelength so that the optical path length is changed by applying an electric field.

[0022]

In the wavelength conversion device of the present invention, the resonance means is arranged on the emission side of the light emission means such as a laser device for emitting light of the fundamental wavelength. The resonance means has a resonance frequency corresponding to the resonance length with an optical path length of light passing through the interior as a resonance length, and includes a plurality of reflection means for internally reflecting the light. A non-linear optical material is arranged on the optical path of the light passing through the inside of the resonance means. The nonlinear optical material has optical anisotropy and emits incident light and light having at least one conversion wavelength different in wavelength. An electric field is applied to this nonlinear optical material by the electric field applying means so that the resonance frequency of the resonance means is tuned to the light of the fundamental wavelength. Therefore, the resonance means can be tuned only by the electric field applied to the nonlinear optical material, and it is possible to provide a wavelength conversion device that can be easily tuned without newly providing an electro-optic modulator.

In the wavelength converter, as described in claim 2, the electric field applying means modulates the resonance length into the nonlinear optical material so that the resonance frequency of the resonance means is tuned to the light of the fundamental wavelength. You may make it provide the electric field for this. In this way, if an electric field is applied to the nonlinear optical material,
The light emitted from the non-linear optical material can be modulated, which can change the resonance length and tune the resonance frequency of the resonance means.

Further, as described in claim 3, the wavelength conversion device further comprises a photodetector arranged on the exit side of the non-linear optical material for detecting the intensity of incident light.
The electric field applying means applies the electric field to the nonlinear optical material to modulate the resonance frequency, and the resonance frequency obtained from the intensity of the detected light and the resonance frequency obtained from the intensity of the detected light are matched with each other. It may be configured by a second electric field applying means for applying an electric field to the nonlinear optical material. According to this structure, the resonance frequency of the resonance means can be easily detected. That is, the light emitted from the nonlinear optical material is modulated by the electric field applied by the first electric field applying means. Therefore, the light detecting means detects the intensity of light according to this modulation. The shift of the resonance frequency can be detected from the intensity of the light according to the modulation, and the error between the resonance frequency obtained from the intensity of the detected light and the frequency of the light of the fundamental wavelength can be detected. Therefore, the resonance frequency of the resonance means can be tuned to the light of the fundamental wavelength by applying the electric field corresponding to this error to the nonlinear optical material by the second electric field application means.

Here, reference (Chris A. Ebbers; Appl. Phy
s. Lett. 52, p1948, 1988), the influence of the electro-optical effect was not taken into consideration because the nonlinear optical crystal, especially the BBO crystal had a small electro-optical effect. In the wavelength converter of the present invention, the electric field is applied to the nonlinear optical material by the electric field applying means so that the resonance frequency of the resonance means is tuned to the light of the fundamental wavelength. This nonlinear optical material is used as a nonlinear optical material as BB as described in claim 4.
You may comprise using O crystal. With such a configuration, it is possible to configure a non-linear optical material that has a small electro-optical effect and is not used for tuning as described above to function as a conventional electro-optical modulator.

As described above, the electro-optical effect of the BBO crystal changes according to the applied electric field, but the BBO crystal is not limited to tuning the resonance frequency. That is, as described in claim 8, a BBO crystal may be provided in a wavelength conversion device that emits light converted from a fundamental wavelength to a different wavelength so that the optical path length is changed by applying an electric field. With such a configuration, the BBO crystal can be used as an optical path length changing element with good responsiveness. Therefore, the wavelength conversion device can be applied to minute and high-speed control for changing the optical path length.

In the wavelength conversion device, as described in claim 5, the wavelength conversion device may be composed of a resonance means including a reflection / transmission means and a reflection means.

The reflection / transmission means is disposed on the exit side of the nonlinear optical material and reflects the light of the fundamental wavelength so that the cross-sectional shape of the light flux is different from the cross-sectional shape of the incident light flux with respect to the plane passing through the optical axis. At the same time, the light of the converted wavelength is transmitted. Therefore, of the light from the light emitting means to the reflection / transmission means on the outward path,
The reflection / transmission means reflects only the light of the fundamental wavelength. Since the reflected light flux at the time of this reflection has a cross-sectional shape of the light flux different from the shape of the incident light flux, the light reflected by the reflection / transmission means and traveling toward the nonlinear optical material side as a return path is subject to conditions such as phase matching of the nonlinear optical material. No match. Therefore, the generation of light having at least one conversion wavelength different from the fundamental wavelength on the return path becomes substantially zero.

The reflecting means is disposed on the incident side of the non-linear optical material and passes through an optical path which substantially coincides with the reference optical path through which the light of the fundamental wavelength incident on the non-linear optical material passes, and the luminous flux of the fundamental wavelength light. The light reflected by the reflection / transmission means is reflected so that the cross-sectional shape of the light flux is substantially the same as the cross-sectional shape of. Therefore, the light from the reflecting / transmitting means to the reflecting means as the return path is reflected so as to have the cross-sectional shape of the light flux of the light going from the light emitting means to the non-linear optical material side as the going path. Therefore, in the reflecting means, the light reflected after traveling on the return path from the reflecting / transmitting means and the light incident from the light emitting means are matched, and the matched light is directed to the nonlinear optical material. As a result, of the light of the fundamental wavelength, the light that was desired to be converted into the light of the converted wavelength when traveling in the forward path will again travel in the forward path, and in the nonlinear optical material, for example, in one direction of the forward path. Will generate light of at least one conversion wavelength different from the fundamental wavelength.

Each of the reflection / transmission means and the reflection means of the resonance means can be constituted by a curved surface such as a spherical surface, and the focal length and the reflection optical axis of each can be substantially matched. With such a configuration, the resonance means can be configured as a so-called confocal resonator, and light can circulate inside the resonance means to confine incident light.

At least one of the reflection / transmission means and the reflection means of the resonance means emits the light incident from the predetermined direction and the light from a direction different from the predetermined direction as described in claim 6. A transmitting member that emits light as reflected light, and a reflecting member that reflects the light emitted from the transmitting member from a predetermined direction and guides the light to the transmitting member. Between the reflecting member and the transmitting member. It can be configured such that an odd number of light-collecting portions where light is collected are located and the total number of light-collecting portions where light is collected is even. The condensing portion where the light is condensed inside means that at least one of the reflection / transmission means and the reflection means emits light incident from a predetermined direction and reflects light incident from a direction different from the predetermined direction. And a transmission member formed of a lens and a reflection surface that emits light as a reflection member, and a reflection member having a reflection surface that reflects the light emitted from the transmission member from a predetermined direction and guides the light to the transmission member. It refers to a light condensing portion where light is condensed between the member. With such a configuration, the resonance means can be configured as a so-called double confocal resonator, and light circulates inside the resonance means even when the incident optical axis is slightly deviated, The incident light can be confined.

As described above, when the resonance means includes the reflection / transmission means and the reflection means, the reflection means and the reflection / transmission means generate light of at least one conversion wavelength different from the fundamental wavelength such as SHG light. The light transmitted through the non-linear optical material is radiated toward the non-linear optical material again through the reflection means and the reflection / transmission means without matching the conditions such as phase matching, and the light of the converted wavelength is concentrated in the non-linear optical material. Since it does not pass through, it is possible to obtain an inexpensive wavelength conversion device that is easy to adjust with a simple configuration.
Instability due to the interference effect does not occur because the converted wavelength light is not generated bidirectionally.

Further, in the wavelength conversion method of the invention described in claim 7, the incident light and the light having at least one conversion wavelength different in wavelength from the incident light are emitted. When the light incident using the nonlinear optical material is converted into the light of the conversion wavelength, the light of the fundamental wavelength is incident on the nonlinear optical material and the resonance length is modulated so that the light of the fundamental wavelength resonates. An electric field for applying to the nonlinear optical material. Therefore, the resonance length can be modulated when the incident light is converted into the light of the conversion wavelength, and the light of at least one conversion wavelength can be converted into the light modulated according to the resonance length according to the applied electric field. You can

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings. The first embodiment is one in which the present invention is applied to a wavelength conversion device including a ring resonator.

As shown in FIG. 1, the wavelength conversion device 10 of this embodiment comprises a laser device 12 as a light emitting means, a resonator 16 as a resonance means, and a servo electric circuit 20. A resonator 16 is disposed on the laser beam emitting side of the laser device 12. From this laser device 12, the frequency (for example, about 6 × 10 ¹⁴ Hz)
The laser light is emitted.

The resonator 16 is the resonator 10 shown in FIG.
The configuration is the same as that of 0, and includes an entrance mirror 22, a sampling mirror 24, a first mirror 26, and a second mirror 28. The laser light L0 emitted from the laser device 12 is incident on the resonator 16 and the incident mirror 2
2 and the optical path L1a, and the sampling mirror 24
To The sampling mirror 24 samples (transmits) a part of the incident light and reflects the other unsampled light to guide it to the optical path L1b. Optical path L1
A photodetector 18 as a photodetector is provided on the extension of a, and the light sampled by the sampling mirror 24 is irradiated. The light reflected by the sampling mirror 18 reaches the first mirror 26. First mirror 2
6 reflects all of them and guides them to the optical path L1c. A BBO crystal 14 as a nonlinear optical material is provided on the optical path L1c.
Is arranged, and the light reflected by the first mirror 26 passes through the BBO crystal 14 and reaches the second mirror 28. Therefore, in the BBO crystal 14, S converted according to the incident light is converted.
HG light is emitted together with unconverted light. Second mirror 2
Reference numeral 8 reflects the unconverted light in the BBO crystal 14 of the incident light and transmits the converted SHG light L2. The light reflected by the second mirror 28 is guided to the optical path L1d and reaches the entrance mirror 22. The incident mirror 22 has an incident optical axis parallel to the optical path L1d and a reflected optical axis parallel to the optical path L1a adjusted, and reflects the light following the optical path L1d to guide it to the optical path L1a.

The first mirror 26 of the resonator 16 is attached to a mount device (not shown) which is displaceable, and the mount device (not shown) is mounted on the body of the resonator 16 via a piezo element 30. Piezo element 30
Is for changing the resonator length by displacing the first mirror 26 and changing the resonance frequency, and is connected to the servo electric circuit 20. Resonator 1
The BBO crystal 14 of No. 6 is provided with two electrodes 32 and 34, which are connected to the servo electric circuit 20. The photodetector 18 is also connected to the servo electric circuit 20. These electrodes 3
2, 34 and the electric circuit for servo 20 constitute an electric field applying means. Further, the electrode 32 and the electric circuit for servo 20 constitute a first electric field applying means, and the electrode 34
The servo electric circuit 20 constitutes a second electric field applying means.

Next, the operation of the wavelength conversion device 10 of this embodiment will be described. As described above, the resonator 16 is used to
In order to efficiently generate SHG light from the crystal 14,
The frequency of the laser light incident on the resonator 16 is set to the resonator 16
Since the resonance frequency of the resonator 16 must be tuned, the error of the resonance frequency of the resonator 16 is detected and
Feedback control to tune is required.

First, in order to maintain the condition for tuning the resonance frequency of the resonator 16 to the frequency of the laser light incident on the resonator 16, the deviation of the resonance frequency (error signal) is detected. The FM sideband method described above is used for this detection.

In the present embodiment, the laser light emitted from the laser device is directly incident on the resonator 16 without being frequency-modulated, and the BBO crystal 14 disposed inside the resonator 16 is directly exposed. By modulating, the resonance frequency of the resonator 16 is modulated. That is, B
The refractive index of the BO crystal 14 changes due to the electro-optic effect when an electric field is applied. The optical path length of the BBO crystal 14 changes due to the change in the refractive index of the BBO crystal 14, and the optical path length of the resonator 16, that is, the resonator length changes.
The resonance frequency of changes. Since the BBO crystal 14 has a high frequency response, the resonance frequency can be modulated with a high frequency by applying a high frequency electric field to the BBO crystal 14. In this embodiment, the electrode 32 provided on the BBO crystal 14 is used as an electrode for modulation, and an electric field is applied to the BBO crystal 14 via the electrode 32. The laser light modulated at high frequency in the BBO crystal 14 is detected by the photodetector 18 to obtain a signal proportional to the error in the resonance frequency of the resonator 16.

Next, the feedback control using the electro-optical effect of the BBO crystal 14 will be described. As mentioned above, B
The BO crystal 14 has a phenomenon in which the refractive index changes due to the generation of an electro-optical effect by applying an electric field. By this phenomenon, the optical resonator length can be changed. Therefore, a signal proportional to the error of the resonance frequency obtained from the photodetector 18 is changed in the cavity length (through the electrode 32, the BBO
A signal proportional to the error with respect to the resonance frequency of the resonator 16 determined by the BBO crystal 14 by applying the electric field.
That is, by performing the negative feedback control, the error can always be maintained near zero (servo control).

In this embodiment, 2 provided on the BBO crystal 14 is used.
Of the two electrodes 32 and 34, the electrode 32 is set for modulation and the separate electrode 34 is set for feedback as described above. A signal is supplied to this electrode 34, and an electric field proportional to the error signal is applied to the BBO crystal 14. The feedback control by the electro-optical effect of the BBO crystal 14 can effectively give a higher frequency than the control by the piezo element 30.

Conventionally, in order to control the resonator length, a method has been used in which a mirror forming a resonator is mounted on a piezo element and the mirror is actually moved. However, in the conventional piezo element, a mechanical method is used. For some reason, the response of several kilohertz was the limit of high frequency driving. In this embodiment, since the BBO crystal 14 is directly controlled, even if the fluctuation of the frequency of the laser light has a component of several kilohertz or more, it can be controlled well.

The BBO crystal 1 is used to control the resonator length.
The range of change of the resonator length can be set larger in the control by the piezo element 30 than in the control by the electro-optical effect of 4. Therefore, in this embodiment, in consideration of the mechanical control range of the piezo element 30, feedback control is performed by the piezo element 30 on the low frequency side, and feedback control is performed by using the electro-optical effect of the BBO crystal 14 on the high frequency side. In order to maximize the effect of the efficient control in the optimum frequency range, both are controlled together.

The resonator 16 has a thickness of 9 m.
The BBO crystal 14 is formed by m, and the frequency of the high frequency modulation applied to the BBO crystal 14 is 2 MHz and the amplitude is 15 V (peak
As a result of conducting an experiment by setting -to-peak), good operation can be obtained.

Next, the operation of the wavelength conversion device 10 will be further described along with an example of a specific configuration of the servo electric circuit 20.

The servo electric circuit 20 shown in FIG. 2 includes a high frequency oscillator 42. This high-frequency oscillator 42 is connected to the BBO crystal 14 via the EO element driver 40.
Of the double-balanced mixer (hereinafter referred to as DBM) 44. The other input end of the DBM 44 is the photodetector 1
It is connected so that the signal from 8 may be input. DB
M44 is a low-pass filter (hereinafter referred to as LPF).
The LPF 46 is connected to the LPF 48 and a high pass filter (hereinafter referred to as HPF) 52. The LPF 48 is connected to the piezo element 30 via a piezo element driver 50. The HPF 52 is connected to the electrode 34 of the BBO crystal 14 via the EO element driver 54.

One of the electric signals 60 (see FIG. 3) of a predetermined frequency (for example, 2 MHz) output from the high frequency oscillator 42 is output to the electrode 32 of the BBO crystal 14 via the EO element driver 40, and at the same time, to the DBM 44. It is output to one input terminal. The DBM 44 outputs a signal corresponding to the product of the signal detected by the photodetector 2 and the electric signal 60 of a predetermined frequency output from the high frequency oscillator 42.

When a high frequency electric field is applied to the BBO crystal 14 which is an EO element arranged in the resonator 16, the resonator length of the resonator 16 is modulated according to the magnitude of the electric field,
As a result, the center frequency of the resonator 16 temporally fluctuates from the reference frequency f0. That is, when the frequency of the incident laser light and the resonance frequency of the resonator 16 match, that is, the resonator length of the resonator 16 matches an integer multiple of the wavelength of the incident laser light (hereinafter, resonance condition 4), the signal waveform of the photodetector 18 (the portion above the frequency f0 in FIG. 4) when the resonator length is longer than the center value around the frequency f0 as shown by the signal 62B in FIG. The amplitude value has a shape that substantially matches the shape of the signal waveform of the photodetector 18 (the portion below the frequency f0 in FIG. 4) when it is short. Therefore, the transmission frequency characteristic distribution 64 of the resonator 16 has a substantially symmetrical waveform about the frequency f0.
Therefore, the high frequency output is the product of the strengths of the electric fields. Therefore, in the output of the DBM 44, the contributions of the positive portion and the negative portion are equal, and the average value becomes substantially 0 (see the signal 66B in FIG. 5).

On the other hand, when the resonator length is longer than the resonance condition, the resonance frequency of the resonator 16 shifts to the negative side as shown by the signal 62C in FIG. Therefore, the resonator length is shifted to the negative side, and the signal of the photodetector 18 becomes large, so that DB
The output of M44 will shift to the positive side on average (see signal 66C in FIG. 5). Similarly, when the resonator length is shorter than the resonance condition, the resonance frequency of the resonator 16 shifts to the positive side as shown by the signal 62A in FIG. Therefore, the resonator length shifts to the positive side, the signal of the photodetector 18 becomes small, and the output of the DBM shifts to the negative side on average (see the signal 66A in FIG. 5).

Therefore, the output of the LPF 46, which provides a value obtained by averaging the output of the DBM 44 over time, shows the length of the resonator from the resonance condition of the resonator 16. Therefore, if the feedback control for changing the resonator length of the resonator 16 is reversely performed using the signal indicating the length of the resonator, the resonator length is always controlled to resonate with the frequency of the incident laser light. can do.

In order to change the resonator length by using the signal output from the DBM 44, the mount device as the support mechanism for the first mirror 26 constituting the resonator is proportional to the voltage as described above. In addition to being composed of a piezo element (electrostrictive element or electromagnetic element) that moves in parallel, a rotatable glass plate having a refractive index distributed from a low refractive index to a high refractive index in the circumferential direction is placed in the resonator 16. There is a method of adjusting the rotation angle by a voltage, or a method of combining a plurality of these mechanisms.

In the wavelength conversion device 10 of this embodiment, the BBO
Although the case where control is performed using both the crystal 14 (EO element) and the piezo element 30 has been described, as shown in FIG. 6, the simplest configuration is as follows without controlling the piezo element 30. Amplify the signal at point F to
A voltage may be applied to the electrode 34 arranged on the crystal 16.

As described above, the wavelength conversion device of this embodiment is
A BBO crystal (non-linear crystal) arranged in the resonator is provided with two electrodes for high frequency modulation and for applying a tuning signal (DC and low frequency components). As a result, it is possible to provide a compact and inexpensive wavelength conversion device that converts laser light of a predetermined wavelength into SHG light by the non-linear effect in the BBO crystal without disposing the EO modulator required in the conventional wavelength conversion device. can do.

Further, by applying an electric field to the BBO crystal by two electrodes for high frequency modulation and for applying a tuning signal, high frequency modulation becomes possible, tuning becomes easy, and the output of the obtained SHG light is increased. You can Further, since the followability of servo control is improved due to the possibility of modulation at high frequency, the intensity of output light can be stabilized and the stability of servo control can be improved.

When the stability of this servo control is improved, it becomes possible to use even a resonator having a small tuning width. A resonator for a wavelength conversion device having a high conversion efficiency for obtaining ultraviolet light from visible light generally has a small tuning width. Therefore, according to this embodiment, it is easy to realize a wavelength conversion device having a high conversion efficiency for obtaining ultraviolet light from visible light.

In the above embodiments, the case where the present invention is applied to the ring type resonator has been described, but the present invention is not limited to this, and the present invention is also applicable to the confocal type resonator described below. It is an applicable resonator. If the following confocal resonator is used, it is possible to construct a compact wavelength converter having a smaller number of parts and fewer moving parts than the wavelength converter of the above-mentioned embodiment. A wavelength conversion device 11 using this confocal resonator will be described as a second embodiment of the present invention. Since the present embodiment has substantially the same configuration as the above-described embodiments, the same portions are denoted by the same reference numerals, and only resonators having different configurations will be described below.

As shown in FIG. 7, the wavelength conversion device 11 of this embodiment includes a laser device 12 which emits laser light of a predetermined wavelength. A collimator lens system 74 is arranged on the emission side of the laser device 12. The collimator lens system 74 is composed of a concave lens 70 as a diffusing means and a convex lens 72 as a condensing means, and the concave lens 70 and the convex lens 72 are arranged in this order. The laser light emitted from the laser device 12 is a concave lens 7
After being diffused by 0, it is condensed by the convex lens 72. The collimator lens system 74 is for adjusting the wavefront of light and the beam diameter of the laser light, and forms a condensing portion having a beam waist where the laser light is concentrated on the exit side of the collimator lens system 74. The laser device 12 and the collimator lens system 74 constitute a light emitting means.

A resonator 76 is arranged on the laser light emitting side of the collimator lens system 74. This resonator 7
Reference numeral 6 denotes a first mirror 78 and a second mirror 7 arranged in order from the laser light emission side of the collimator lens system 74.
It is composed of nine. The first mirror 78 and the second mirror 79 are formed by curved spherical mirrors having the same radius of curvature. Therefore, the first mirror 78 and the second mirror 7
The focal lengths of 9 are the same. In the resonator 76 of this embodiment, the first mirror 78 and the second mirror 79 are arranged so that their focal positions coincide with each other, and their centers of curvature coincide with each other on the same line. A so-called confocal resonator is formed. The resonator 76 is arranged so that a light condensing portion, which is a beam waist where the laser light is concentrated, is located near the focal position.

A sampling mirror 68 is arranged between the convex lens 72 and the resonator 76.
The photodetector 1 is provided on the reflection side of the sampling mirror 68.
8 are provided.

In this embodiment, the first mirror 78 and the second mirror 78
The radius of curvature of each of the mirrors 79 of the collimator lens system 7 is
4 is set to be larger than the curvature of the wavefront of the laser light emitted from the laser beam. Therefore, in each of the first mirror 78 and the second mirror 79, the curvature of the wavefront of the light when incident is changed at the time of reflection.

A BBO crystal 14 is arranged in the vicinity of the above-mentioned beam waist where the beam waist is located so that the beam waist is located inside the BBO crystal 14. BBO
Crystal 14 has a sufficiently large acceptance angle.
The O-crystal 14 efficiently outputs the SHG light of the conversion wavelength obtained from the laser light (excitation light) of the fundamental wavelength due to the nonlinear optical effect when the laser light matching the large acceptance angle is incident. Further, the BBO crystal 14 is provided with two electrodes 32 and 34.
Is connected to the servo electric circuit 20. The photodetector 18 is also connected to the servo electric circuit 20.
Next, the operation of the resonator 76 of this embodiment will be described. The laser beam L emitted from the collimator lens system 74 is transmitted through the first mirror 78 while the beam diameter is gradually reduced, reaches the inside of the BBO crystal 14, and a beam waist is formed in the BBO crystal 14. Further, the laser light L that has passed through the first mirror 78 acts as the excitation light L1 for obtaining the SHG light of the conversion wavelength in the BBO crystal 14.
In this BBO crystal 14, due to the nonlinear optical effect, SH
G light L2 is generated. The generated SHG light L2 passes through the second mirror 79 and is used as output light (light in the direction of the white arrow B in FIG. 7). The excitation light L1a that has not been converted into the SHG light L2 is reflected by the second mirror 79 and the curvature of the wavefront is changed. When the curvature of the wavefront is changed, the beam diameter is changed so as to be expanded in the diffusion direction without being changed in the reduction direction. The excitation light L1b having the changed wavefront curvature is transmitted through the BBO crystal 14 and
To the mirror 78. In the first mirror 78, the excitation light L1b is reflected with its curvature changed so that it matches the curvature of the wavefront of the laser light L (that is, the excitation light L1) emitted from the collimator lens system 74. . Both of the excitation lights L1 and L1a reach the BBO crystal 14. In this way, the excitation light circulates in the resonator.

With the first mirror 78 and the second mirror 79
Is the curvature R of the wavefront of the incident laser light L._LIs the first
Smaller than the curvature of the mirror 78 and the second mirror 79.
(See FIG. 8). Therefore, with the second mirror 79
Curvature R of the wavefront of the reflected light _BThe incident laser
Curvature of light wavefront R_LGet bigger. Therefore, the above incident
When the beam diameter of the laser beam and the resonator conditions are
(Solid line in FIGS. 7 and 8) and return path (one-dot chain in FIGS. 7 and 8)
Line) and the beam diameter of the beam waist is changed. this
BBO crystal 14 is placed at the position of the beam waist and SHG
When light is generated, S generated for each of the forward and backward paths
Since the acceptance angle of the crystal is large enough for HG optical power,
The area of the beam diameter at the beam waist of each excitation light
Inversely proportional. That is, as in this example,
So that the beam diameter of the beam waist of
By setting the input laser light, the laser beam with a small beam diameter
Excitation in the direction in which the laser light travels (the direction of the white arrow A in FIG. 7)
In order to generate SHG light (harmonic output) only in the luminous
The power of is concentrated. For example, the bee on the outbound path and the inbound path
By setting the ratio of the size of the um diameter to 1: 3 (1: 5)
SHG light (harmonic output) is 9: 1 (25: 1)
So 90% (96%) of the converted power goes in one direction
concentrate.

As described above, according to the wavelength conversion device of this embodiment, since the resonator functioning as the confocal resonator is used as the external resonator for wavelength conversion, the return path is changed by the mirror provided in the resonator. The curvature of the wavefront of the laser light reflected toward the beam can be different from the curvature of the wavefront of the incident light and the excitation light, and is generated by passing through the crystal arranged near the beam waist. The SHG light will be concentrated only on the outward path. Therefore, using a resonator provided with a pair of curved surfaces that function as a confocal system, a crystal is arranged near the focal point of the resonator, and a radius of curvature different from that of the curved surface, that is, a radius of curvature smaller than that of the curved surface. The wavelength of the light can be converted with high efficiency by simply adjusting the incident laser light so as to achieve a simple and simple configuration without requiring complicated adjustment.

As an example of a practical confocal system configuration,
As shown in FIG. 9, a parallel plane-shaped BBO connection with a thickness y is formed.
Radius of curvature R at a distance x from one surface of crystal 14_MThe first
The mirror 78 of No. 1 is arranged,
Radius R at an interval z from one surface_MSecond mirror of
79 is provided to form the resonator 76. At this time, BB
Refractive index n of O crystal 14₂Surrounding materials up to the mirror and crystal
Medium n₁Refraction considering the interface refraction
Rate n = n₂/ N₁Is the radius of curvature R of the mirror _MAnd spacing
x and z are (R_M= X + y / n + z).

In the above embodiment, the case where the BBO crystal 14 is disposed near the focal points of the mirrors 78 and 24 having the same radius of curvature has been described, but the present invention is a resonator provided with the mirror as a separate body. It is not limited to disposing the crystal therein, and only the BBO crystal 14 may be processed to form the resonator 76. That is, the BBO crystal 14 is polished and coated so that the end surface on the laser light incident side and the end surface on the emission side of the BBO crystal 14 have a radius of curvature R _M.
It is also possible to form the resonator only with four. For example, as shown in FIG. 10, if the end face 20a on the incident side and the end face 20b on the emitting side of one crystal have a radius of curvature R _M and are polished so that the center of curvature becomes the center of the opposing end faces. A monolithic confocal resonator can be formed.

In this case, the laser light passing through the inside of the resonator always propagates in the crystal. However, since the crystal has the phase matching condition, only when the phase matching condition is satisfied, , Efficient SHG light is generated, and the effective portion (distance) of the crystal that generates this SHG light
Will match the thickness y in FIG.

The crystal itself is processed as described above,
Although the resonator may be formed by only the crystal, it is not easy to polish the spherical surface of the crystal, and the crystal other than the effective portion (y) where the SHG light is efficiently generated is wasted. Therefore, the resonator is not composed of only the crystal, but only the central portion (y) is formed of the crystal, and the blocks (x, z) serving as the surrounding mirrors are composed of a transparent medium such as glass having the same refractive index. It is also effective to do. This glass is generally easy to be spherically polished. By doing so, the required capacity of the crystal can be reduced and the crystal can be effectively used. Also,
The crystal may be flat-polished, and the glass may be easily spherical-polished. Therefore, the manufacturing of the resonator is facilitated.

Next, a third embodiment will be described. The present invention is applied to a double confocal resonator which is an application of a confocal system. Since the third embodiment has substantially the same structure as the above-mentioned embodiment, only the resonator having a different structure will be described.

As shown in FIG. 11, a resonator 77 is arranged on the laser beam emitting side of the collimator lens system 74. The resonator 77 of this embodiment includes a first mirror 78,
It is composed of a second mirror 79 and a lens 80 having a focal length d. In the resonator 77 of this embodiment, the first mirror 7
8 and the second mirror 79 are arranged such that the positions of the centers of curvature coincide with each other, and the lens 80 is arranged at the positions of the centers of curvature to form a so-called double confocal resonator. There is. Further, in the vicinity of the condensing position of the lens 80, B
The BO crystal 14 is arranged.

Next, the operation of the wavelength conversion device of this embodiment will be described together with the behavior of laser light. Collimator lens system 7
The laser beam L emitted from the laser beam 4 passes through the first mirror 78 with the beam diameter gradually decreasing, is once condensed, and then diffuses to reach the lens 80. In the lens 80, the incident laser beam is condensed, and the beam diameter gradually decreases to reach the inside of the BBO crystal 14, and a beam waist is formed in the BBO crystal 14. In this BBO crystal 14,
The SHG light L2 is generated by the nonlinear optical effect. The generated SHG light L2 passes through the second mirror 79. SH
The excitation light L1a that has not been converted into the G light L2 is reflected by the second mirror 79 and the curvature of the wavefront is changed. When the curvature of the wavefront is changed, the beam diameter is changed so as to be expanded in the diffusion direction without being changed in the reduction direction. The excitation light L1b with the wavefront curvature changed is B
The light passes through the BO crystal 14 and reaches the lens 80. Lens 8
At 0, the incident laser light is collected and emitted to the first mirror 78. The first mirror 78 reflects the incident laser light and changes the curvature of the wavefront.
That is, the excitation light L1b is reflected with the curvature of the wavefront thereof changed so as to match the curvature of the wavefront of the laser light L (that is, the excitation light L1) emitted from the collimator lens system 74. Both the excitation lights L1 and L1a are condensed by the lens 80 and reach the BBO crystal 14. in this way,
The excitation light circulates in the resonator 77.

As an example of a practical double confocal system configuration, the resonator 76 can be formed by processing only the BBO crystal 14. That is, as in the first embodiment, BB
It is also possible to form a resonator with only the BBO crystal 14 by polishing and coating the end surface of the O crystal 14 on the laser light incident side and the end surface on the emission side of the O crystal 14 so as to have a curvature radius R _M. For example, as shown in FIG. 12, the end surface 14a on the laser light incident side and the end surface 14b on the exit side of one BBO crystal 14 have a radius of curvature R _M, and the center of curvature is the center of the opposing end surface. Grind. This has the same configuration as that of FIG. 10 described above. Figure 10
The difference between the resonator of FIG. 12 and the resonator of FIG. 12 lies in the direction of phase matching.

In the BBO crystal 14 shown in FIG. 12, as in the above-described embodiment, the whole resonator is not formed of a single crystal, but only the central portion (y) is a nonlinear optical crystal. The surrounding portion may be made of glass or another material having the same refractive index. Further, instead of processing only the crystal as described above, only the central portion (y) is formed of the crystal and the blocks (x, z) serving as the surrounding mirrors are formed of glass having the same refractive index. Is also effective.

In the above embodiments, the shape of the beam diameter is not mentioned, but the present invention does not specify the applicable shape of the beam diameter. That is, in the confocal resonator and the double confocal resonator, the laser light (Gaussian beam) that makes one round trip through the resonator has exactly the same beam diameter and curvature as the incident laser light. This property can also be applied to the case where the beam diameter and the radius of curvature are not the same in the vertical direction and the horizontal direction of the laser beam, that is, the elliptic beam.
Therefore, it can be applied as it is even when an elliptical focus is formed in the crystal. As is well known, the light collecting method for this purpose is as follows.
A cylindrical system for changing the shape of the beam diameter is provided in the middle of the laser device 12 and the BBO crystal 14,
The shape of the beam diameter of the beam waist may be set to a predetermined shape.

As described above, in the above embodiment, the Fabry-Perot resonator having a simple structure is used to change the curvatures of the wavefronts of the incident light and the emitted light in the mirror to thereby obtain the unidirectional SHG light. Can occur.
Therefore, even though it is a Fabry-Perot type resonator, since the SHG light is not folded back inside the resonator, there is no instability due to the interference effect generated by the laser light in the forward path and the return path. Further, as compared with the conventional wavelength converter using a ring resonator that requires complicated adjustment to obtain high output, it is cheaper and easier to adjust, and used for frequency conversion of light in a desired wavelength range. You can Furthermore, in the case of a device using a double confocal resonator, even if the incident laser beam deviates from the set position or direction, it automatically acts as a resonator, so it is possible to make fine adjustments. Without
Easy to assemble. Furthermore, it can be realized by monolithically forming the resonator integrally with the crystal, that is, forming the resonator by one solid around the crystal.

Therefore, Fabry-Pero
In a wavelength conversion device using a non-linear optical effect that uses a t) type or a reciprocating type resonator, the size of the beam waist is different between the laser light traveling back and forth in the resonator in the going (outward) direction and the returning (returning) direction. By differently setting the optical system of the resonator and the beam diameter of the incident light and the radius of curvature of the wavefront, the resulting new wavelength of light (ie,
The wavelength of light can be converted by making the power of (SHG light) mainly concentrated in one direction.

The BBO crystal 1 used in the above examples
Non-linear optical materials other than 4 include KDP, KTP, LiN
bO ₃ etc.

The confocal resonator described above can be applied to wavelength conversion of various lasers. For example, blue-near ultraviolet light can be obtained by frequency multiplication of an infrared-red semiconductor laser, and deep ultraviolet light can be obtained by frequency multiplication of a green-blue laser. Therefore, it can be applied to the production of semiconductor elements, material processing, display devices, printing devices, three-dimensional hologram reproducing devices, photochemistry, measurement, reaction monitors, etc. using these lights. In particular, blue-near ultraviolet light can be obtained by frequency multiplication of an infrared-red semiconductor laser, and its output can be used for high-density optical recording. Further, deep ultraviolet light obtained by frequency multiplication of green-blue light is suitable for use in manufacturing semiconductor devices, processing materials, and the like.

Although the embodiments of the present invention have been described above, the embodiments of the present invention have various technical aspects as described below in addition to the technical matters corresponding to the claims. It is a thing.

The resonance means is disposed on the exit side of the non-linear optical material, reflects the light of the fundamental wavelength so that the light flux has a shape different from the shape of the incident light flux, and transmits the light of the converted wavelength. Reflection / transmission means, disposed between the non-linear optical material and the light emission means, pass through an optical path substantially coincident with a reference optical path through which light of a fundamental wavelength incident on the non-linear optical material passes, and the basic And a reflection means for reflecting the light reflected by the reflection / transmission means so that the shape of the light flux of the light of the wavelength substantially matches the shape of the light flux.

Thus, the resonance means is composed of the reflection / transmission means and the reflection means. The reflection / transmission means is disposed on the exit side of the nonlinear optical material, reflects the light of the fundamental wavelength so that the light flux has a shape different from the shape of the incident light flux, and transmits the light of the converted wavelength. Therefore, of the light that goes from the light emitting means to the reflection / transmission means on the outward path, the reflection / transmission means reflects only the light of the fundamental wavelength. Since the reflected light flux at the time of this reflection has a light flux shape different from that of the incident light flux, the light reflected by the reflection / transmission means and traveling toward the nonlinear optical material side as the return path does not meet the conditions such as phase matching of the nonlinear optical material. I will not do it. Therefore, the generation of light having at least one conversion wavelength different from the fundamental wavelength on the return path becomes substantially zero. The reflecting means is disposed on the incident side of the nonlinear optical material, passes through an optical path that substantially coincides with the reference optical path through which the light of the fundamental wavelength incident on the nonlinear optical material passes, and has the shape of the light flux of the fundamental wavelength. The light reflected by the reflection / transmission means is reflected so that the light fluxes have substantially the same shape. Therefore, the light from the reflection / transmission means to the reflection means as a return path is
It is reflected in the form of a light flux of light traveling from the light emitting means to the non-linear optical material side as an outward path. Therefore, in the reflecting means, the light reflected after traveling on the return path from the reflecting / transmitting means and the light incident from the light emitting means are matched, and the matched light is directed to the nonlinear optical material. As a result, of the light of the fundamental wavelength, the light that was desired to be converted into the light of the converted wavelength when traveling in the forward path will again travel in the forward path, and in the nonlinear optical material, for example, in one direction of the forward path. Will generate at least one converted wavelength of light that is different from the fundamental wavelength.

Further, each of the reflection / transmission means and the reflection means of the resonance means is composed of, for example, a curved surface such as a spherical surface, and has a radius of curvature substantially matching with each other, and a focal length and a reflected optical axis of each curved surface It can be configured to be substantially coincident. With such a configuration, the resonance means can be configured as a so-called confocal resonator, and light can circulate inside the resonance means to confine incident light.

[0083]

As described above, according to the wavelength conversion device of the present invention, the resonance frequency of the resonance means is provided by applying an electric field to the nonlinear optical material so that the resonance frequency of the resonance means is tuned to the light of the fundamental wavelength. Can be tuned, so that there is an effect that a compact and inexpensive wavelength conversion device can be configured without providing an electro-optic modulator. Further, by applying an electric field to the nonlinear optical material so that the resonance frequency of the resonance means is tuned to the light of the fundamental wavelength, high frequency modulation in the nonlinear optical material becomes possible, and the intensity of the obtained modulated wavelength light is stabilized. There is an effect that can be supplied to.

Further, according to the wavelength conversion method of the present invention, light of the fundamental wavelength is incident on the nonlinear optical material, and an electric field for modulating the resonance length so that the light of the fundamental wavelength resonates is applied to the nonlinear optical material. Since the light is given, the resonance length can be modulated when the incident light is converted into the light having the conversion wavelength, and at least one light having the conversion wavelength is converted into the light modulated according to the resonance length according to the applied electric field. There is an effect that can be done.

Furthermore, when the BBO crystal for wavelength conversion of the present invention is used in a wavelength conversion device, there is an effect that the optical path length can be minutely and rapidly modulated.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a schematic configuration of a wavelength conversion device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an electric circuit for servo of FIG.

FIG. 3 is a diagram showing an output voltage waveform of a high frequency oscillator of an electric circuit for servo.

FIG. 4 is a characteristic diagram showing a temporal variation of a resonance frequency of a resonator.

FIG. 5 is a diagram showing an output voltage waveform of a DBM of an electric circuit for servo.

6 is a block diagram showing a schematic configuration of another example of the servo electric circuit of FIG. 1. FIG.

FIG. 7 is a conceptual diagram showing a schematic configuration of a wavelength conversion device according to a second embodiment of the present invention.

FIG. 8 is an image diagram showing a wavefront (equal phase surface) of laser light in a resonator.

FIG. 9 is an image diagram showing an example of a confocal resonator.

FIG. 10 is an image diagram showing a resonator in which a crystal and a mirror are integrated.

FIG. 11 is an image diagram showing a conceptual configuration of a double confocal resonator according to a third example.

FIG. 12 is an image diagram showing a double confocal resonator formed only of crystals.

FIG. 13 is a block diagram showing a schematic configuration of a conventional wavelength conversion device.

[Explanation of symbols]

 10 wavelength conversion device 12 laser device (light emission means) 14 BBO crystal (nonlinear optical material) 16 resonator (resonance means) 18 photodetector (light detection means) 20 servo electric circuit 32 electrode (first electric field applying means) ) 34 electrodes (first electric field applying means)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Taira 1623 Shimotsuruma, Yamato City, Kanagawa Prefecture 14 IBM Japan, Ltd. Tokyo Research Laboratory

Claims (8)

[Claims] 1. A light emitting means for emitting light of a fundamental wavelength is disposed on the light emitting side, and has a resonance frequency corresponding to the resonance length with an optical path length of light passing through the inside as a resonance length, and the inside has the resonance frequency. Resonant means having a plurality of reflecting means for reflecting light, and disposed on the optical path of light passing through the inside of the resonant means,
A nonlinear optical material having optical anisotropy and emitting incident light and light having at least one conversion wavelength different in wavelength from the light; and having a resonance frequency of the resonance means for light having the fundamental wavelength. An electric field applying means for applying an electric field to the nonlinear optical material so as to be tuned, and a wavelength conversion device comprising: 2. The electric field applying means applies an electric field for modulating the resonance length to the nonlinear optical material so that the resonance frequency of the resonance means is tuned to the light of the fundamental wavelength. The wavelength conversion device according to claim 1. 3. A light detecting means is further provided, which is arranged on the exit side of the non-linear optical material and detects the intensity of incident light.
The electric field applying means includes a first electric field applying means for applying an electric field to the nonlinear optical material to modulate the resonance frequency, a resonance frequency obtained from the intensity of the detected light, and a frequency of light having the fundamental wavelength. The wavelength conversion device according to claim 1, further comprising: a second electric field applying unit that applies an electric field to the nonlinear optical material so that 4. The wavelength conversion device according to claim 1, wherein a BBO crystal is used as the nonlinear optical material. 5. The light of the fundamental wavelength is arranged such that the resonance means has a cross-sectional shape of a light beam different from a cross-sectional shape of an incident light beam with respect to a plane disposed on the exit side of the nonlinear optical material and passing through the optical axis. A reference for transmitting light of the fundamental wavelength, which is disposed between the non-linear optical material and the light-exiting means, and which is reflected / transmitted by which the light of the converted wavelength is transmitted and which is transmitted through the non-linear optical material. Reflection means for reflecting the light reflected by the reflection / transmission means so as to have a cross-sectional shape of a light flux that passes through an optical path that substantially matches the optical path and that substantially matches the cross-sectional shape of the light flux of the fundamental wavelength. The wavelength conversion device according to claim 1, wherein 6. A transmission member, wherein at least one of the reflection / transmission means and the reflection means of the resonance means emits light incident from a predetermined direction and emits light incident from a direction different from the predetermined direction as reflected light. , A reflecting member that reflects the light emitted from the transmitting member in a predetermined direction and guides the light to the transmitting member, and a condensing portion where the light is condensed between the reflecting member and the transmitting member. The wavelength conversion device according to claim 5, wherein an odd number of light-collecting portions are located and the total number of light-collecting portions that are condensed inside the resonance unit is an even number. 7. The incident light is converted by using a non-linear optical material which has optical anisotropy and emits incident light and light having at least one conversion wavelength different from the wavelength of the incident light. A wavelength conversion method for converting light of a wavelength into light of a fundamental wavelength, which is incident on the nonlinear optical material,
A wavelength conversion method, wherein an electric field for modulating a resonance length is applied to the nonlinear optical material so that light having the fundamental wavelength resonates. 8. A BBO crystal for wavelength conversion, which is provided in a wavelength conversion device that emits light converted from a fundamental wavelength to a different wavelength so that the optical path length is changed by applying an electric field.