JPH0593930A - Optical wavelength conversion element and production thereof - Google Patents

Abstract

PURPOSE:To approximate the aspect ratio of the beams emitted from optical waveguides to 1 relating to the wavelength conversion element formed by using a nonlinear optical effect and the process for production thereof. CONSTITUTION:Polarity inversion layers 3 are formed on an LiTaO3 substrate 1. The optical waveguides 2 formed by a proton exchange method are formed thereon. The thickness of the exit part 5 of the optical waveguides 2 is larger than the thickness of the optical waveguides and the aspect ratio of the beam of the higher harmonic waves P2 emitted therefrom is nearly 1. The aspect ratio of the beam emitted therefrom is approximate to 1 and the efficiency of utilizing the beam is greatly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength conversion element used in the field of optical information processing utilizing coherent light or in the field of optical measurement and control, and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 4 shows a block diagram of a conventional optical wavelength conversion element based on an optical waveguide. The harmonic generation (wavelength 0.42 μm) with respect to the fundamental wave having a wavelength of 0.84 μm will be described in detail below with reference to the drawings. (K.Mizuuchi, K.Yamamoto and TT
aniuchi, Applied Physics Letters, Vol 58, page 2732, June 1991 issue). As shown in Figure 4, LiTa
An optical waveguide 2 is formed on an O ₃ substrate 1, and a layer 3 (polarization inversion layer) whose polarization is periodically inverted is further formed on the optical waveguide 2. By compensating for the mismatch between the propagation constants of the fundamental wave P1 and the generated harmonic wave P2 by the periodic structure of the polarization inversion layer 3 and the non-polarization inversion layer 4, the harmonic wave P2 can be generated with high efficiency. When the fundamental wave P1 is incident on the incident surface 10 of the optical waveguide 2, the harmonic P2 is efficiently generated from the optical waveguide 2,
It operates as a light wavelength conversion element.

Such a conventional optical wavelength conversion element has an optical waveguide manufactured by the proton exchange method as a basic constituent element. A method of manufacturing this element will be described. First Li
Ta is periodically patterned on the TaO ₃ substrate 1 by using a normal photo process and dry etching. Next, the LiTaO ₃ substrate 1 on which the Ta pattern was formed was subjected to 260 in pyrophosphoric acid.
Proton exchange is performed at 30 ° C. for 30 minutes to form a 0.8 μm-thick proton exchange layer directly below the slit not covered with Ta. Then, heat treatment is performed at a temperature of 590 ° C. for 10 minutes. As a result, the domain inversion layer is formed. Just below the proton exchange layer, Li is reduced and the Curie temperature is lowered, so that polarization reversal can be partially performed. Then, Ta is removed by etching with a 1: 1 mixed solution of HF: HNF ₃ for 2 minutes.
Further, the optical waveguide 2 is formed in the polarization inversion layer by using proton exchange. By patterning Ta as a mask for the optical waveguide 2 in a stripe shape, the Ta mask has a width of 5
A slit having a size of μm and a length of 12 mm is formed. The substrate covered with this Ta mask is subjected to proton exchange at 260 ° C. for 16 minutes to form a 0.5 μm high refractive index layer. After removing the Ta mask, heat treatment is performed at 380 ° C. for 10 minutes. The region directly under the slit of the proton-exchanged protective mask becomes the optical waveguide 2 having a refractive index increased by about 0.03. The optical wavelength conversion element manufactured by this conventional method has a wavelength of 0.84 μm.
When the length of the optical waveguide 2 was 9 mm and the power of the fundamental wave P1 was 27 mW, the power of the higher harmonic wave P2 was 0.13 mW and the conversion efficiency was 0.5%. The conversion efficiency per 1W is 18% / W.

In addition, the generated SHG beam is NA
After collimating with a collimator lens of 0.3, NA0.
A focused beam up to the diffraction limit was obtained by focusing with the focus lens of No. 6.

[0005]

In the optical wavelength conversion element based on the above-mentioned optical waveguide, the harmonic beam emitted from the optical waveguide is not vertically and horizontally symmetrical but vertically (in the thickness direction of the optical waveguide). Is 30 degrees, horizontal (width direction of optical waveguide)
Was an asymmetric beam having a divergence angle of 7 degrees and an aspect ratio of 4. Therefore, there is a problem that the beam is kicked by the collimator lens in order to obtain the focused light up to the diffraction limit in both the vertical and horizontal directions, and the harmonic output used for the focused light is lost by about 40%.

[0006]

According to the present invention, an optical wavelength conversion element capable of generating a beam having an aspect ratio close to 1 is added to the structure of the optical wavelength conversion element in order to solve the above problems. Is provided. That is, the present invention has means for providing a polarization inversion layer and an optical waveguide having a thickness d1 in a nonlinear optical crystal, and having a relation that the thickness d2 of the emitting portion of the optical waveguide is d2> d1.

[0007]

In the light wavelength conversion element of the present invention, the aspect ratio of the output beam, that is, the aspect ratio, can be brought close to 1 by increasing the thickness of the output portion of the optical waveguide of the light wavelength conversion element. The light wavelength conversion element having the above-described structure significantly improves the beam utilization efficiency.

[0008]

EXAMPLE As a first example, a method for manufacturing an optical wavelength conversion device of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an optical wavelength conversion element of the present invention. The domain-inverted layers 3 are periodically formed on the LiTaO ₃ substrate 1. This polarization inversion layer 3
The optical waveguide 2 is formed so as to traverse. The fundamental wave P1 enters from the incident surface 10 of the optical wavelength conversion element, is converted into a harmonic wave P2 by the optical waveguide 2, and is emitted from the exit surface 12 of the optical wavelength conversion element. A layer thicker than the optical waveguide 2 is formed near the emitting surface 12 as the emitting portion 5. Assuming that the thickness of the optical waveguide 2 is d1 and the thickness of the emitting portion 5 is d2, there is a relationship of d2> d1. By optimizing the thickness of d2, a beam of harmonic P2 that is vertically and horizontally symmetrical (aspect ratio 1) is emitted.

Next, a method of manufacturing the optical wavelength conversion device of the present invention will be described. FIG. 2 is a manufacturing process diagram thereof. In FIG. 3A, first, Ta6a is patterned on the LiTaO ₃ substrate 1 in a periodic pattern by using a normal photoprocess and dry etching. Next, LiTa having a pattern formed of Ta6a
Proton exchange is performed on the O ₃ substrate 1 at 260 ° C. for 30 minutes to form a 0.8 μm-thick proton exchange layer immediately below the slit, and then heat treatment is performed at a temperature of 590 ° C. for 10 minutes. Thereby, the domain inversion layer 3 is formed. Since the Li content of the proton exchange layer is reduced and the Curie temperature is lowered, polarization inversion can be partially performed. Next, 2 with a 1: 1 mixture of HF: HNF _3.
Etching for 6 minutes to remove Ta6a. Next, the optical waveguide 2 is formed in the polarization inversion layer 3 by using proton exchange. In the same figure (b), after Ta is patterned into a stripe shape as an optical waveguide mask, a Ta mask is formed with a width of 4 μm.
260 with a slit having a length of m and a length of 12 mm
Proton exchange was performed in pyrophosphoric acid at 16 ° C. for 16 minutes. Thereby, the high refractive index layer 7 having a thickness of 0.5 μm is formed. Next, after removing the Ta mask in the same figure (c), a pattern in which Ta8 having a thickness of 1000 A is patterned only on the emitting portion was subjected to a heat treatment for 30 seconds by an infrared heating device. Ta8 directly absorbs infrared rays and becomes higher in temperature than the optical waveguide 2. The optical waveguide had a temperature of 420 ° C., and the emitting portion had a temperature of 500 ° C. The heat treatment uniformizes the loss and reduces the non-linearity of the high refractive index layer 7. High refractive index layer 7 by heat treatment
Is 1.8 μm with a spread and refractive index increased by about 0.03
The optical waveguide 2 and the emitting portion 5 having a thickness of 4 μm. In this way, the thickness d2 of the emitting portion is larger than the thickness d1 of the optical waveguide because the relationship between the heat treatment temperatures T2 and T1 is T.
This is because 2> T1, which is a difference in diffusion rate and a difference in thickness. Finally, vapor-deposit SiO ₂ to 3000.
A was added.

The optical waveguide 2 and the emitting portion 5 are manufactured by the steps as described above. The thickness d of this optical waveguide 2 is 1.
The thickness is 8 μm, which is smaller than the thickness of the domain inversion layer 3 of 2.0 μm, and the wavelength is effectively converted. The period of the domain inversion layer 3 is 10.
It is 8 μm and operates for a wavelength of 0.84 nm. Further, there is no change in the refractive index of the non-polarization inversion layer 4 and the polarization inversion layer 3 of the optical waveguide 2, and the propagation loss when light is guided is small. A surface perpendicular to the optical waveguide 2 was optically polished to form an entrance surface 10 and an exit surface 12. In this way, the light wavelength conversion element can be manufactured. The length of this element is 10 mm. Semiconductor laser light (wavelength 0.84 μ as fundamental wave P1
When m) was guided from the incident part, it propagated in a single mode, and the harmonic P2 having a wavelength of 0.42 μm was taken out of the substrate from the emitting part. The propagation loss of the optical waveguide 2 was as small as 1 dB / cm, and the harmonic P2 was effectively extracted. Basic wave 40mW
A harmonic of 1 mW (wavelength 0.42 μm) was obtained at the input of.
The divergence angle of the emitted harmonic beam is 10 in the thickness direction.
The beam was a substantially symmetrical beam with an aspect ratio of 1.4 in the width direction and 7 degrees in the width direction. This beam was collimated by a collimator lens of NA 0.5 and condensed by a focus lens of NA 0.6, and a beam with a spot size of 0.6 μm up to the diffraction limit was obtained. The utilization efficiency was 95%. FIG. 3 shows the relationship between the thickness of the optical waveguide and the aspect ratio. By thus increasing the thickness of the optical waveguide of the emitting portion, the aspect ratio can be brought close to 1.

An infrared heating device capable of rapid heating and capable of utilizing the infrared absorption of metal is suitable for carrying out such a treatment.

Next, a second embodiment using the method of manufacturing an optical wavelength conversion device of the present invention will be described. The configuration of the light wavelength conversion element is similar to that of the first embodiment. The optical waveguide 2 was manufactured by proton exchange in phosphoric acid and then heat-treated for 10 minutes using a heater having a temperature distribution. The temperature on the optical waveguide is 380 ° C., and the temperature on the emitting portion is 450 ° C. The produced optical waveguide has a thickness of 2.2 μm, a width of 4 μm and a length of 9 mm, and an emission portion has a thickness of 3.5 μm, a width of 5 μm and a length of 1 mm. The period of polarization inversion is 3.6 μm, and the thickness of the polarization inversion layer is 1.5 μm. The conversion efficiency in this example is high for a wavelength of 840 nm, and is 10% at a 40 mW input because the first-order polarization inversion period is used. The aspect ratio of the emitted beam was 1.7, and the utilization efficiency at the time of condensing was 90%. There was no optical damage and the harmonic output was very stable.

In the embodiment, LiTa is used as the nonlinear optical crystal.
Although O ₃ is used, it is also applicable to ferroelectrics such as LiNbO ₃ , KNbO ₃ and KTP.

[0014]

As described above, according to the optical wavelength conversion element of the present invention, the aspect ratio of the beam emitted can be made closer to 1 by increasing the thickness of the emission part of the optical waveguide of the optical wavelength conversion element. You can As a result, the utilization efficiency of the beam emitted from the light wavelength conversion element can be greatly improved, and its practical value is extremely large.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical wavelength conversion device according to a first embodiment of the present invention.

FIG. 2 is a process drawing of the method for manufacturing the optical wavelength conversion device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between optical waveguide thickness and aspect ratio.

FIG. 4 is a configuration diagram of a conventional optical wavelength conversion element.

[Explanation of symbols]

1 LiTaO ₃ substrate 2 optical waveguide 3 polarization inversion layer 5 emission part P1 fundamental wave P2 harmonic

Claims (4)

[Claims] 1. A nonlinear optical crystal having a domain-inverted layer and an optical waveguide having a thickness d ₁ , wherein the thickness d ₂ of the emitting portion of the optical waveguide has a relationship of d ₂ > d _1. Optical wavelength conversion element. 2. A high refractive index layer is formed by a proton exchange method in a nonlinear optical crystal having a polarization inversion layer, and then an optical waveguide is formed at a heat treatment temperature T1 and an emission portion is formed at a heat treatment temperature T2.
A method of manufacturing an optical wavelength conversion element, characterized in that the heat treatment temperature is set so that the relationship of T2> T1 is satisfied. 3. The nonlinear optical crystal is LiNb _x Ta _1-x O.
_{3. The} method for producing an optical wavelength conversion element according to claim 1 or an optical wavelength conversion element according to claim 2, which is a (0 ≦ X ≦ 1) substrate. 4. The method for manufacturing a light wavelength conversion element according to claim 2, wherein the heat treatment is performed using an infrared heating device.