JPH062341U - Optical parametric oscillator - Google Patents

Abstract

(57) [Summary] [Objective] To realize an oscillator that can obtain optical parametric oscillation with a light source with a lower power density than before. In an optical parametric oscillator for generating pumping light into a nonlinear optical crystal to generate signal light and idler light having different wavelengths, in addition to the resonator for the signal light and the idler light, a resonator for the pumping light is used. In addition, the nonlinear optical crystal is cut at an angle matched to the pumping optical path in order to minimize the loss of the pumping light due to surface reflection when the pumping light is incident on the nonlinear optical crystal. It is what

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical parametric (hereinafter simply referred to as OP) oscillation used as a wavelength tunable light source, and more particularly to a device capable of further increasing the output value of OP oscillation with low-power pumping light. .

[0002]

[Prior art]

OP oscillation is a method of injecting pumping laser light (wavelength λ _p ) into a nonlinear optical crystal to generate two lights of different wavelengths (signal light λ _s and idler light λ _i ). It has been used as a variable method.

3A and 3B are configuration diagrams showing a conventional example of such an OP oscillator. 3A and 3B, C is a nonlinear optical crystal, M _a and M _b are high transmittance for the pumping light λ _p , and high reflectance for the signal light λ _s and the idler light λ _i. The mirror M _c has a high reflectance for the pumping light λ _p and a high transmittance for the signal light λ _s and the idler light λ _i . z represents the crystal axis of the nonlinear optical crystal C, and angle θ represents the phase matching angle. Further, the pumping light λ _p is made incident on the nonlinear optical crystal C in accordance with an angle θ that can achieve phase matching with the signal light λ _s and the idler light λ _i . The polarization states of the three light waves are determined by the conditions of phase matching.

In such a configuration, when the power density of the pumping light λ _p exceeds the OP oscillation threshold value in the nonlinear optical crystal C, the signal light λ _s and the idler light λ _i oscillate. Amplification of the signal light λ _s and the idler light λ _i is performed by forming a resonator for each wavelength outside the crystal and increasing the power density of the pumping light λ _p . FIG. 3 (a) shows a structure in which the pumping light λ _p passes through the crystal once. In this case, the pumping light λ _p has a power density exceeding the oscillation threshold as shown in the following equation. There must be. P _s / ω _s = P _i / ω _i = (P _pth / ω _p ) · (P _p / P _pth -1) where P is the optical power, ω is the frequency of each light wave, and the subscript s is the signal light. i is idler light, p is pumping light, and pth is an oscillation threshold. Further, in FIG. 3B, a mirror M _c is provided to turn back the pumping light λ _p to increase the power density of the pumping light in the nonlinear optical crystal C.

[0005]

[Problems to be solved by the device]

 However, the OP oscillator shown in the above-mentioned prior art requires a light source having a power density that satisfies the oscillation threshold, and a CW (Continuous Wave) having a relatively low power density with respect to pulsed light is required. It was difficult to use as a wavelength tunable light source that requires a low power density for laser and measurement.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to make it possible to obtain OP oscillation with a light source having a lower power density than before.

[0007]

[Means for Solving the Problems]

 The configuration of the present invention for solving the above-mentioned problems is an OP oscillator for generating pumping light into a nonlinear optical crystal to generate signal light and idler light having different wavelengths. Providing a resonator for the pumping light, and pumping the nonlinear optical crystal to minimize the loss of the pumping light due to surface reflection when the pumping light enters the nonlinear optical crystal. It is characterized by being cut at an angle that matches the optical path.

[0008]

[Action]

 In the present invention, an external resonator for pumping light is incorporated in the OP oscillator to increase the power density of the pumping light in the crystal, enabling OP oscillation with lower pumping power.

[0009]

【Example】

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the OP oscillator of the present invention. In FIG. 1, the same elements as those in FIG. 3 are designated by the same reference numerals, and duplicate description will be omitted. In FIG. 1, M ₁ and M ₂ are mirrors having a high transmittance for pumping light and a high reflectance for signal light and idler light. M ₃ is a mirror having a high reflectance for pumping light and a high transmittance for signal light and idler light. M ₄ and M ₅ are mirrors having a high reflectance for pumping light. a to h indicate points where light passes and is reflected. Further, in the nonlinear optical crystal C _1, light transmitted between points c → e has an incident angle of 0 ° at point d, and light transmitted between points g → c has an incident angle of 0 ° at point h. As you can see, each is cut.

In such a configuration, the incident pumping light λ _p passes through the point a, partially passes through the point c and is divided into the point d, and the other portion is reflected into the point b. The light transmitted through the point d enters the point c via the points e → f → g → h. At point c, part of the light is transmitted, point b is reflected, and part is reflected, and the process proceeds from point d → e → f → g → h. On the other hand, the light reflected at the point c 1 is reflected at the point b 1 and is returned to the point c 2. Part of the light is reflected at point c to point a, and part of light is transmitted to proceed to points c → h → g → f → e → d → c. However, the light traveling from the point c to the point a does not participate in parametric oscillation. The light incident from the point d 1 to the point c is partially transmitted through the point c, is partially reflected at the point a, and is partially reflected at the point c 1 to proceed to points c → h → g → f → e → d. This series of optical paths is shown in FIG.

Here, the loss due to absorption and scattering of the pumping light in the crystal is represented by α, and the mirror M ₁ , M₂Transmittance at t, mirror M₃, M_Four, M_FiveWhere r is the reflectance at point c and r is the reflectance at point c_c, Transmittance t_cFurther, the power density of the pumping light existing between the points c → d (including the light passing between the points d → c) is determined by setting the reflectance at the points h and d to 0 and the transmittance to 1. First, when the incident light amount of the pumping light is P, the light amounts of to shown in FIG._cLight intensity of t · P = tr²αr_cLight amount of α · (light amount) = tr²αr_cLight amount of α · (light amount) = tr²αr_cLight amount of α · (light amount) = tr²αt_crt_cαtr²Light amount of α · (light amount) = tr²αt_crt_cαtr²Light amount of α · (light amount of) = r_cαtr²Light amount of α · (light amount of) = r_crr_cαtr²Light amount of αt · P = r_cαtr²α ・ (light intensity) Also, the power density P of the pumping light existing between points c → d (or between points d → c)_cdBecomes ++++++++++++++++++++ (1). By substituting each light quantity of ~ into this equation (1) and rearranging it, P_cd= {Αt / (1-α²tr²r_c) ・ (T_c+ Α^Fivet³r⁷t_c ³r_c+ Α³t²r^Fivet_c ³+ Αtr³r_c ²) ・ P (2)

At this time, for example, the values of the respective variables in the equation (2) are α = 0.99, t = 0.99, r = 0.99, and the incident angle at the point c is the Brewster angle. If close values t _c = 0.1 and r _c = 0.9, then P _cd = 5.9 · P. This means that a laser light source with a power density of 0.17 (1 / 5.9) times the oscillation threshold can satisfy the OP oscillation threshold. In the case of FIG. 3B, which is the method, in the ideal state, a light source of 0.5 times the oscillation threshold value is required, whereas in the above embodiment, the power density is about 3 times that. It becomes possible to oscillate with a light source that is about twice as low.

As described above, in the above embodiment, since the pump oscillator has a resonant structure for pumping light, it has the effect of amplifying the power density of the pumping light, and is more effective than an OP oscillator having no resonant structure. OP oscillation light can be obtained with a light source having a lower power density. Further, even in the structure of the nonlinear optical crystal, since the pumping light entrance / exit surface is a flat surface, the processing is easy and mass production at a lower cost is possible.

[0014]

[Effect of device]

 As described above in detail with reference to the embodiments, according to the present invention, it is possible to realize an OP oscillator in which OP oscillation can be obtained with a light source having a power density lower than that of the conventional one.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an OP oscillator of the present invention.

FIG. 2 is a diagram showing an optical path of pumping light of the apparatus shown in FIG.

FIG. 3 is a configuration diagram of a conventional OP oscillator.

[Explanation of symbols]

C ₁ Non-linear optical crystal M _{1 to} M ₅ mirrors a to h Light passing and reflecting points

Claims (1)

[Scope of utility model registration request] 1. An optical parametric oscillator for injecting pumping light into a nonlinear optical crystal to generate signal light and idler light having different wavelengths, wherein a resonance of the pumping light is provided in addition to the resonator for the signal light and the idler light. And that the nonlinear optical crystal is cut at an angle matched to the pumping optical path in order to minimize the loss of the pumping light due to surface reflection when the pumping light is incident on the nonlinear optical crystal. An optical parametric oscillator characterized by.