JPH03219215A - Wavelength converting element - Google Patents

Abstract

PURPOSE:To attain the conversion efficiency to increasingly higher harmonic waves by having double resonators for both of a basic wave and the higher harmonic wave. CONSTITUTION:This converting element has a light source 21 to admit the basic wave into a nonlinear optical crystal 25, the nonlinear optical crystal 25 which converts the basic wave to the higher harmonic wave and the double resonators 23, 24 to both of the basic wave and the higher harmonic wave. Namely, the basic wave omega from a light source 11 is resonated by the resonator 23 of the basic wave to prevent the dissipation to the outside and to improve the absorption of the omega to the nonlinear optical crystal 25. Further, the 2omega of a high output is obtd. by providing the resonator 24 for the second harmonic wave 2omega. The conversion efficiency is improved in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a wavelength conversion element using a nonlinear optical crystal, and in particular, high wavelength conversion by configuring a double resonator for both the second harmonic and the fundamental wave. The present invention relates to a wavelength conversion element that can obtain efficiency.

[Prior Art] The basic configuration of a conventional resonant wavelength conversion element is shown in Fig. 1. A fundamental wave emitted from a light source such as a semiconductor laser (LD) 1 is converged by a coupling optical system such as a convex lens 2, and is incident on a resonator mirror 4, 4° for the resonator for the fundamental wave, and the KNbOa disposed inside the resonator. The light is incident on a nonlinear optical crystal 3 such as At this time, if the reflectance of the resonant mirror 4 on the light source side to the fundamental wave is rln+ln, and the reflectance of the resonant mirrors 4' to the fundamental wave is rout, and the transmittance of the nonlinear optical crystal 3 is t, then the relationship rln = j2rout is established. Normally, rout is approximately 100% and t is approximately 99%. At this time, the phase shift amount ψ inside the resonator is O, which is the strongest resonance state.

With this configuration, the fundamental wave ω inside the resonator is hardly dissipated to the outside of the resonator, and the second harmonic 2ω is outputted with high efficiency.

[Problems to be Solved by the Invention] An object of the present invention is to provide a novel wavelength conversion element that achieves higher harmonic conversion efficiency than conventional wavelength conversion elements.

[Means for Solving the Problems] The present invention provides a light source that inputs a fundamental wave into a nonlinear optical crystal;
The present invention provides a wavelength conversion element comprising a nonlinear optical crystal that converts a fundamental wave into a harmonic wave, and a double resonator for both the fundamental wave and the harmonic wave.

Various embodiments of the double resonator type wavelength conversion element of the present invention are shown in FIGS. 3 to 10. In the figure, the solid line light represents the fundamental wave ω, and the broken line light represents the second harmonic 2ω. The transmittance of the nonlinear optical crystal with respect to ω is t = 99%, and the reflectance of the light source side and output side of the pair of resonator mirrors 23.23' with respect to ω and 2ω is rz3(ω).

r2x°(ω), r2s (2ω), r2m'(2ω
), and a pair of resonator mirrors for ω and 2ω 24.2
The reflectance on the light source side and output side of 4' is r24(ω) + r
24° (ω).

If rz< (2ω), rz4'(2ω), in Fig. 3, rimo(ω) = 99.9%, rza
((aJ) ”: t” rz 3(ω)=98%
, rz4'(2ω)=99%, r24(2ω)=99.
It is 9%. Here, r24(ω) → 0%, r23(2ω
) Saki O%.

In FIG. 4, r2t°(ω) = 99.9%.

rz3(ω) ”t2rxs°(ω)=98%, r24
°(2ω)=99%, rz4(2ω)=99.9%. Here, r2t (2(IJ)”=0%,
rzs' (2CJ) 'W 0%.

Let r24(ω)→0%.

In Figure 5, r23° (ω) = 99.9% r2x
(ω) = t"ras' (ω) = 98%, ra4'(
2ω)=99%, r24(2ω)=99.9%. Here, rza(ω) hto%, r,,' (ω)
“FO%.

In the case of FIG. 6, similarly to the above, the resonator mirror pair 26.2
The reflectance for 6° ω and 2ω is r26(ω).

r2m' (ω), rza (2ω), raa' (
2ω), rxao(ω) = 99.9%, r
za(ω)=t”rtao(ω)=98%, rzs
' (2ω) = 99%, rts (2ω) = 99.
It is 9%.

In the case of FIG. 7, the optical film for the double resonator is directly formed on the light source side and output side end faces of the nonlinear optical crystal 25, and the reflectance is 26.26' for the pair of mirrors in FIG. The same is true.

In Figures 3 to 7, the reflectance of the mirror pair for the fundamental wave ω is (light source side) = t2 (output side), and the second harmonic wave 2ω
The reflectance of the pair of mirrors on the output side is made slightly lower than on the light source side. Further, when 2ω passes through a mirror for ω, and conversely, when ω passes through a mirror for 2ω, the reflectances for 2ω and ω are preferably set to approximately 0, respectively.

8 to 10 show a ring-shaped double resonator, and the light source of the fundamental wave is not particularly shown, but is located on the left side of the figure. ω and 2ω are the same optical axis.

In the case of FIG. 8, the ring-shaped resonator is composed of four mirrors, and the reflectance of each of mirrors 41, 42, 43, and 44 for ω and 2ω is set to r4. (ω).

Tar (2ω), r4□(ω), r4z(2ω)+
r41(ω).

r4s (2ω), r4. (ω), r44(2ω
), then r4□(ω)=99.9%, r43(ω)
=99.9%, r44(ω)=99.9%, r41(ω
)=t xr4g(ω)xr4x(ω)Xr44(ω)
=98.7%, and r4+(2ω)=99.9%
, r4□(2ω)=99.9%, r43(2ω)=99
．． 9%, r4. (2ω)=99.9%, r,,
(2ω) has a slightly lower reflectance than the others.

In FIG. 9, the ring-shaped resonator is composed of three mirrors, and the reflectance of each of mirrors 46, 47, and 48 with respect to ω and 2ω is r46(ω).

r4a (2ω), r,, (ω), r4. (2ω)
, r, , (ω).

r4. (2ω), then r4. (ω)=99.9%
, r4g(ω)=99.9%, r4. (ω)=txr4
t(ω)
9%, r4m (2ω) = 99.9%, and ra7(
2ω) is slightly lower than the others.

In FIG. 10, optical films are directly formed on the light source side and output side end faces of the nonlinear optical crystal 45, and on one end face forming a triangular ring with them, and the reflectance of each is as shown in FIG. Same as in case.

The nonlinear optical crystal 45 may be placed somewhere on the optical axis of the fundamental wave within the ring resonator, but it is preferable that the mirrors on both sides of the nonlinear optical crystal 45 have concave inner surfaces to converge the light.

In the present invention, various gas lasers, solid-state lasers, liquid lasers, dye lasers, etc. can be used as light sources in addition to LDs, but LDs are preferable in terms of compactness and weight reduction, and examples of nonlinear optical crystals include KNbOs and KTiOPO4.
, KH2PO4, β-BaB204LtNbO, crystals, etc. can be used.

[Operation] When the fundamental wave ω is multiplied by multiple reflections within the resonator, the electric field strength increases and the wavelength conversion efficiency increases.

On the other hand, it is known that when the second harmonic intensity becomes strong (ie, the conversion efficiency from the fundamental wave ω to the second harmonic 2ω increases).

Therefore, by further providing a second harmonic resonator to form a double resonator, the conversion efficiency can be further improved.

[Example] A first example of the present invention is shown in FIG. The LDII of the light source of the fundamental wave ω (wavelength 842 nm) has 5pectra
- An injection locked array LD in which 5DL-3420G manufactured by Diode Lab was injection-locked with HLP-1400 manufactured by Hitachi was used.

In order to prevent the influence of the returned light of ω, a Faraday isolator 12 is used, and the ω is converged by a converging lens with a focal length f=10 cm, and is incident on the KNbO, 14 of the nonlinear optical crystal. An optical film is formed on the end face on the light source side of KNbO,14 and the end face on the output side of the second harmonic 2ω (wavelength 421 nm), and the reflectance rln on the light source side and the reflectance rout on the output side are ω. , 2ω, respectively ran(ω)=
98%, rout (ω) = 99.9%, r, l,
(2ω) = 99.9%.

rout (2CLI) = 99%. KNb
The transmittance of Os to ω is 99%, and rln(ω)
= 0.99”rou (ω) = 0.98 and 98
%.

A blocking filter 16 for a fundamental wave of 842 nm is arranged on the output side.

The wavelength of LDII was finely adjusted so that the 2ω blue light emission was the strongest, and the temperature of KNbo, 14 was tuned with a temperature control device 15 such as a Bertier effect element, and the result was 100.
5 mW of blue light was obtained for an ω input of mW.

A second embodiment is shown in FIG.

As a light source of the fundamental wave ω, 5pectra-Diode
Lab.

Hitachi's 5DL-3420C was replaced with Hitachi's HLP-1400
An injection-locked LD 31 was used.

Although not shown, a Faraday isolator 12 was placed between the LD 31 and the coupling optical system 32 in order to prevent the influence of the return light of ω. The wavelength of ω is 855 nm, and the light is focused to an appropriate beam diameter by a coupling optical system 32 consisting of a collimating lens, a cylindrical lens, and a spherical lens.

The ring resonator is composed of four mirrors 33, 34, 35, 36.

The reflectance of each mirror for ω and 2ω is r33(ω
)=95%, r3x (2ω)=99.9%, rs
4(ω)=99.9%, rs4(2ω)=99.9%
, ris(ω)=99.9%.

rss (2ω) = 99.9%, rxa (ω) = 99
．． 9%, rig(2ω)=99%.

The wavelength of LD31 was finely adjusted so that the 2ω blue light emission was the strongest, and the temperature of KNbo and 37 was tuned with a temperature control device such as a Peltier effect element, and the result was 100+n.
For W ω input, 4 mW of blue light (428 nm) was obtained.

[Effects of the Invention] The present invention causes the fundamental wave ω from a light source to resonate in a fundamental wave resonator, almost prevents it from dissipating to the outside, and improves the absorption of ω into the nonlinear optical crystal (and further reduces the absorption of the second harmonic). By providing a resonator for 2ω, there is an excellent effect that a high output of 2ω can be obtained.

[Brief explanation of drawings]

1 to 10 show embodiments of the present invention, and are side views of the basic configuration of a double resonant wavelength conversion element, and FIG. 11 is a side view of the basic configuration of a conventional example. 11...LD 14...KNbO,. Figure 3 Figure 3 Figure 0 Figure 0

Claims (7)

[Claims] (1) A wavelength conversion element comprising a light source that inputs a fundamental wave into a nonlinear optical crystal, a nonlinear optical crystal that converts the fundamental wave into a harmonic, and a double resonator for both the fundamental wave and the harmonic. (2) In a wavelength conversion element, a nonlinear optical crystal for converting a fundamental wave into a harmonic wave is arranged between a pair of resonators, and a light source for generating a fundamental wave is arranged outside one of the resonators. 2. The wavelength conversion element according to claim 1, further comprising a resonator that multiple-reflects a fundamental wave and a resonator that multiple-reflects harmonic waves as multiple resonators. (3) a pair of fundamental wave resonators that multiple-reflect the fundamental wave;
3. The wavelength conversion element according to claim 2, wherein a harmonic resonator for multiple reflection of harmonics is arranged on the same optical axis. (4) The wavelength conversion element according to claim 2, further comprising a pair of resonators that multiple-reflect both the fundamental wave and the harmonics. (5) For the fundamental wave resonator, the reflectance for the fundamental wave on the light source side is r_i_n, and the reflectance for the fundamental wave on the output side is r_i_n.
o_u_t, and if the transmittance of the fundamental wave to the fundamental wave inside the resonator is t, then r_i_n=t^2r_o_u_t, and the harmonic resonator has a smaller reflectance for harmonics on the output side than on the light source side. The wavelength conversion element according to any one of claims 2 to 4. (6) The wavelength conversion element according to any one of claims 2 to 5, wherein the fundamental wave and harmonic resonators are optical films formed on the light source side and output side end faces of the nonlinear optical crystal. (7) A ring-shaped resonator as a double resonator in which a fundamental wave and harmonics incident from the outside are circulated by at least three mirrors; A wavelength conversion element comprising a nonlinear optical crystal that converts waves into harmonics, and a light source that generates a fundamental wave and is placed outside the ring-shaped resonator.