JPH04257283A - Optical parametric oscillating device - Google Patents

Abstract

PURPOSE:To reduce Fresnel loss without varying the projecting position of output light and permit a wide wavelength variable range. CONSTITUTION:Excitation light from excitation light sources 20 and 22 excites a pair of nonlinear optical crystals 31 and 32. Two beams of light (signal light and idler light) generated by the nonlinear optical crystals are resonated in a closed-loop optical path formed by resonating mirrors M1, M2, M3 and M4. Therefore, the generated light is a wave proceeding in one direction and not easily disturbed. Rotating devices 24a and 24 are used for varying the resonance conditions of the generating light, and the pair of nonlinear optical crystals 31 and 32 are rotated in synchronism in the opposite direction to the optical path. Thus, optical path deviation caused by the one nonlinear optical crystal can be compensated by the other crystal. The projection position of the output light outputted in response to the resonance conditions is not influenced by the wavelength variation.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical parametric oscillation device, and more particularly to an optical parametric oscillation device capable of continuously changing the output wavelength by rotating an optical medium such as a nonlinear optical crystal.

0002

[Prior art and problems to be solved by the invention] Figure 1
shows a conventional example of this type of optical parametric oscillator.

FIG. 1(a) shows a standing wave type optical parametric oscillator. Excitation light λp from a predetermined light source passes through mirror 2 and enters nonlinear optical crystal 4, where it undergoes an optical parametric process to generate signal light λs and idler light λi. Excitation light λp of the light that has passed through mirror 6 is cut by filter 8, and the remaining signal light λs and idler light λi are taken out as output light. In this case, the wavelengths of the signal light λs and the idler light λi are determined by conditions such as the arrangement of the mirrors 2 and 6 and the nonlinear optical crystal 4 that constitute the resonator. Therefore, if the nonlinear optical crystal 4 is rotated in a plane parallel to the drawing, the wavelengths of the output lights λs and λi can be continuously changed. However, in the optical parametric oscillator shown in FIG. 1(a), there is a problem in that an optical axis shift occurs between the excitation light and the output light depending on the amount of rotation of the crystal 4, and the emission position of the beam changes. Ta. Furthermore, since the resonator is a reciprocating type, there is a problem that Fresnel loss increases at the end face of the crystal 4, and that the going and returning light interfere with each other, deteriorating the state of the output light. .

FIG. 1(b) shows a two-crystal standing wave type optical parametric oscillator. This device improves the drawbacks of the device shown in FIG. 1(a). The same parts as those in the device in FIG. 1(a) are given the same reference numerals, and the description thereof will be omitted. In this device, two nonlinear optical crystals 4a and 4b are arranged between mirrors 2 and 6 constituting a resonator, and these are rotated by the same amount in opposite directions. Therefore, although the problem of the beam emission position fluctuating has been solved, the same problems as in the apparatus of FIG. 1(a) remain in other respects. Moreover, since two nonlinear optical crystals 4a and 4b are used, the structure results in a further increase in Fresnel loss.

FIG. 1(c) shows a monolithic optical parametric oscillator. This device improves the drawbacks of the device shown in FIG. 1(b). In the case of this device, excitation light λp from a light source enters the nonlinear optical crystal 14 via the first surface 14a, is reflected by the second and third surfaces 14b and 14c, and travels in a loop-shaped optical path in one direction. Proceed to. A signal light λs and an idler light λi are emitted from the first surface. In this case, since the phase matching condition is no longer satisfied when the crystal 14 is rotated, the wavelengths of the output lights λs and λi are tuned by changing the temperature of the crystal 14 itself. For this reason, problems related to Fresnel loss and the like are solved, but the wavelength of the output light can hardly be varied, and the time response is also not good.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical parametric oscillator that has low Fresnel loss, does not change the output position of output light, and has a wide wavelength variable range.

[0007]

[Means for Solving the Problems] In order to solve the above problems, an optical parametric oscillator according to the present invention provides (a) 1
or two or more pairs of nonlinear optical media; (b) an excitation light source that generates excitation light of a predetermined wavelength to excite the nonlinear optical medium; and (c) two or more pairs of generated light (signals) generated from the nonlinear optical medium by the excitation light. (d) resonating means (for example, a mirror, etc.) for resonating at least one of the light and the idler light in a closed loop optical path passing through the nonlinear optical medium;
A rotating means is provided for rotating each pair of nonlinear optical media synchronously in opposite directions with respect to the optical path to change the wavelength of the generated light output from the resonant means.

[0008]

[Operation] The optical parametric oscillator described above causes the generated light generated from the nonlinear optical medium to resonate within a closed loop optical path. Therefore, the generated light is a wave that travels in one direction and is less susceptible to disturbance. Also, in order to change the wavelength of the generated light, each pair of nonlinear optical media is rotated synchronously in opposite directions with respect to the optical path described above, so that the optical path generated by one medium of each pair of nonlinear optical media is The shift can be compensated for by the other medium. Therefore, the output position of the output light hardly changes.

[0009]

Embodiment FIG. 2 is a diagram showing the configuration of an optical parametric oscillator according to a first embodiment.

The laser light source 20 is composed of, for example, an Nd-YAG laser, and generates a laser beam of about 1064 nm. This excitation light is transmitted to a second harmonic generator (SHG) 2
2, it is converted into excitation light λp with a wavelength of 532 nm. S.H.
The excitation light λp emitted from G22 has its beam diameter narrowed by a collimator 23 and enters a ring-shaped resonator 30 forming a closed loop optical path. This ring type resonator 30 has 4
It is composed of mirrors M1, M2, M3, and M4. The mirror M1 transmits the excitation light λp, but hardly transmits other light such as the signal light λs and the idler light λi to be generated within the ring resonator 30. Mirrors M2 and M3 receive excitation light λp and signal light λs.
, and serves as a total reflection mirror for idler light λi and the like. The mirror M4 has a high reflectance for the excitation light λp and a transmittance of 50 to 80% for the signal light λs and idler light λi to be generated. Thereby, only the signal light λs and the idler light λi can be extracted as output light. Mirror M1
, M2, a first non-linear optical crystal body 31 made of a rectangular parallelepiped KTP crystal or the like is interposed. This first non-linear optical crystal body 31 is placed on the first rotary table 24a,
Rotate in a plane parallel to the drawing. A second non-linear optical crystal body 32 made of a KTP crystal or the like having the same shape and the same extension angle is also interposed between the mirrors M3 and M4. This second non-linear optical crystal 32 is placed on the second rotating table 24b and rotates in a direction opposite to the first non-linear optical crystal 31 in a plane parallel to the drawing.

FIG. 3 is a diagram showing details of the ring-shaped resonator 30, non-linear optical crystals 31, 32, etc. of FIG. 2.

[0012] First and second rotary tables 24a, 2
4b is driven by a belt 24c provided around it. In this case, the first and second rotary tables 2
4a and 24b are used, and since the belt 24c is crossed between each rotary table 24a and 24b, the amount of rotation of these rotary tables 24a and 24b is the same, and the rotation directions are opposite. It has become. In addition,
The amount and direction of rotation of the second rotary table 24b are precisely controlled by the motor 26 and belt 28. The first and second non-linear optical crystals 31 and 32 placed on the first and second rotary tables 24a and 24b rotate together with these rotary tables 24a and 24b, so the amounts of rotation thereof are equal; The direction of rotation is opposite. Therefore, the angles formed by the first and second non-linear optical crystals 31 and 32 with respect to the optical axis of the resonant light are always equal to each other. That is, the angle θ formed by the crystal axis of the first non-linear optical crystal 31 with respect to the optical axis of the resonant light, and the angle θ formed by the crystal axis of the second non-linear optical crystal 32 with respect to the optical axis of the resonant light. are equal. Moreover, since the same rectangular parallelepiped nonlinear optical crystals are used as the first and second nonlinear optical crystals 31 and 32, even if the angle θ changes, the mirror M1 and the first nonlinear optical crystal 31 The optical path of the resonant light between the mirror M4 and the second non-linear optical crystal 32 does not change.

The operation of the optical parametric oscillator according to the first embodiment will be briefly explained below.

The excitation light λp that has passed through the mirror M1 is transmitted through the first non-linear optical crystal 31 and then passes through the mirror M2.
, M3 and is transmitted through the second non-linear optical crystal body 32. This excitation light λp is further reflected by mirror M4, passes through mirror M1, and enters ring-shaped resonator 30.
Emit outside.

The excitation light λp incident on the non-linear optical crystals 31 and 32 generates a signal light λs and an idler light λi of a predetermined wavelength. It is oscillated and amplified within. A portion of the signal light λs and the idler light λi pass through the mirror M4 and are emitted to the outside of the ring resonator 30.

In this case, even if the angle θ changes, the mirror M4
Since the optical path of the resonant light between the ring-shaped resonator 30 and the second non-linear optical crystal 32 does not change, the output positions of the output lights λs and λi emitted to the outside of the ring-shaped resonator 30 do not change. Also, 2
Since the two non-linear optical crystals 31 and 32 mutually have oscillation and amplification effects, the intensity of the output light can be increased. Furthermore, in the ring resonator 30, since the resonant light travels in only one direction, the Fresnel loss per nonlinear optical crystal is halved compared to a reciprocating resonator. Furthermore, since it is a ring-shaped resonator, disturbance is less likely to occur in the signal light λs and the idler light λi that are resonated and amplified.

FIG. 4 is a diagram showing the configuration of an optical parametric oscillator according to a second embodiment. Note that the difference between the second embodiment and the first embodiment is mainly in the ring-shaped resonator.
Identical parts are denoted by the same reference numerals and explanations will be omitted.

As shown in the figure, the ring-shaped resonator has a triangular shape made up of three mirrors M1', M2', and M3'. A first non-linear optical crystal 31 is arranged between mirrors M1' and M2', and mirror M2
A second non-linear optical crystal 32 is placed between M3' and M3'. Therefore, the excitation light λp incident on the mirror M1' enters the second non-linear optical crystal 32, is reflected by the mirrors M3' and M2', and enters the first non-linear optical crystal 31. As a result, signal light λs and idler light λi of a predetermined wavelength are generated, and are oscillated and amplified within this triangular ring-shaped resonator 30. Note that the angles of the first and second non-linear optical crystals 31 and 32 are changed so that they are both equal to the optical path of the resonant light.

Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments.

For example, the ring resonator can have any polygonal shape. Furthermore, a pair of non-linear optical crystals may be arranged on one side of the polygonal ring-shaped resonator. Furthermore, one non-linear optical crystal may be arranged on each side of the polygonal ring-shaped resonator, and a suitable pair of these non-linear optical crystals may be rotated with respect to each other for optical path compensation.

Furthermore, various types of laser light sources can be used as the excitation light source. Furthermore, various nonlinear optical media can be used as the nonlinear optical crystal disposed within the ring resonator.

[0022]

[Effects of the Invention] According to the optical parametric oscillator of the present invention, since the generated light is resonated within the loop-shaped optical path,
This generated light is a wave that travels in one direction and is less susceptible to disturbance, making it possible to obtain stable and high output light. In addition, since the optical path deviation caused by one medium in each pair of nonlinear optical media is compensated for by the other medium, the output position of the output light hardly changes, and the output position of the output light is free from wavelength dependence. No light source can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional optical parametric oscillator.

FIG. 2 is a diagram schematically showing an optical parametric oscillator according to a first embodiment.

FIG. 3 is an enlarged view of main parts of the optical parametric oscillator shown in FIG. 2;

FIG. 4 is a diagram schematically showing an optical parametric oscillator according to a second embodiment.

[Explanation of symbols]

21, 22, 23...excitation light source 24a, 24b, 26... Rotating means 31, 32...a pair of nonlinear optical media

Claims (1)

[Claims] 1. One or more pairs of nonlinear optical media, an excitation light source that generates excitation light of a predetermined wavelength to excite the nonlinear optical medium, and two generators generated from the nonlinear optical medium by the excitation light. at least one of the lights,
Resonating means for resonating within a closed loop optical path passing through the nonlinear optical medium, and each pair of the nonlinear optical medium being rotated synchronously in opposite directions with respect to the optical path to change the wavelength of the generated light output from the resonating means. An optical parametric oscillator comprising: a rotation means for rotating the oscillator.