JP2633384B2 - Optical wavelength converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical disc device, a laser beam printer,
The present invention relates to an optical wavelength converter used for products using laser light such as an optical measuring instrument, and more particularly, to an optical wavelength converter for shortening the wavelength of laser light by generating a sum frequency.

(Prior Art) In recent years, it has become possible to manufacture a small-sized semiconductor laser device capable of obtaining light of high intensity at low cost. For this reason, semiconductor laser devices have come to be widely used in general industrial equipment, consumer equipment, and the like, where it was conventionally difficult to use a semiconductor laser device as a light source in terms of cost. Among these devices, semiconductor laser devices are often used as light sources for information processing devices such as, for example, a light source for reading information of an optical disk device, a light source of a laser printer, or a light source of a device in the field of optical measurement.

As described above, in the device, higher performance can be expected as the diameter of the spot where the light emitted from the light source can be collected is smaller. By focusing the emitted light on a small spot, for example, increasing the recording density of the optical disk in an optical disk device, improving the resolution in a laser printer, and measuring in the optical applied measurement field such as interference measurement Accuracy can be improved.

Since the focused spot diameter (minimum focused diameter of light) is proportional to the wavelength of the laser light, a semiconductor laser capable of emitting shorter wavelength light is required to improve the performance of equipment using laser light. It is desirable to use an element.

At present, the semiconductor laser devices used in the above-described devices generally emit laser light having a wavelength of 780 to 830 nm. As a semiconductor laser device that can obtain laser light of a shorter wavelength than this, there is a semiconductor laser device using an InGaAlP-based semiconductor material, which emits laser light of a wavelength of 680 nm.

However, in order to put such a short-wavelength semiconductor laser device into practical use, it is necessary to solve many problems such as improving reliability. Semiconductor laser devices that emit light with shorter wavelengths are in the early stages of research, and there is no prospect of commercialization. Therefore, at this stage, a large-sized and inconvenient gas laser must be used in order to obtain emission light of a short wavelength such as green or blue.

As another method for obtaining laser light of a short wavelength, there is a method of converting the wavelength of laser light. This uses sum frequency generation, in which the light emitted from the light source irradiates the nonlinear optical material and the frequencies of the multiple lights are added.
In particular, the second harmonic generation in which two lights of the same frequency are added and the third harmonic generation in which three lights of the same frequency are added are often used. By using an optical wavelength converter utilizing the second harmonic generation, for example, YAG
The laser beam having a wavelength of 1.06 μm emitted from the laser is wavelength-converted to obtain a green laser beam having a wavelength of 0.53 μm, or the laser beam having a wavelength of 0.83 to 0.84 μm is converted to a wavelength of 0.415 μm.
A blue laser beam of about 0.42 μm can be obtained.

However, in general, such an optical wavelength conversion device using sum frequency generation has a low wavelength conversion efficiency, and therefore, it is an important major problem to convert light emitted from a semiconductor laser element with high efficiency. The wavelength conversion efficiency increases in proportion to the fundamental wave density, and the harmonic output increases in proportion to the square of the fundamental wave density. Therefore, in order to increase the wavelength conversion efficiency and the harmonic output, it is effective to increase the fundamental wave density by confining light by applying an optical waveguide structure to the optical wavelength converter.

However, in the optical wavelength converter having the optical waveguide formed as described above, it is difficult to guide the light emitted from the light source to the optical waveguide. For example, if the light incident end face is 0.5 ×
When light is guided to an optical wavelength converter having an optical waveguide having a size of 2 μm ² , it is necessary to condense the light to the light incident end face with an accuracy of 1 μm or less. It is difficult to adjust the focusing position with such accuracy, and it is also difficult to maintain this accuracy over a long period of time.

As a method for fundamentally solving such a problem, a method has been proposed in which a light source of a semiconductor laser device and an optical wavelength converter are integrally formed adjacently on the same substrate.

FIG. 7 is a sectional view of a conventional semiconductor laser-integrated optical wavelength converter in the optical waveguide direction.

This optical wavelength converter integrated with a semiconductor laser is manufactured as follows. First, Ga _0.7 Al _0.3 As was placed on a GaAs substrate 190.
First cladding layer 191, GaAs active layer 192, and Ga _0.7 Al _0.3 As
The second cladding layer 193 is sequentially grown to form a semiconductor laser device structure. After that, a part of the semiconductor laser device structure is removed by etching, and then a ZnS first cladding layer 195, a ZnSe _0.1 S _0.9 core layer 196, and a ZnS second cladding layer 197 are grown thereon to form an optical wavelength converter. Form the structure. At this time, the GaAs active layer 192 and the ZnSe _0.1 S _0.9 core layer 19
6 means that each layer is grown so that the height from the substrate is almost equal. Then, after being divided into chips, TiO ₂ —SiO ₂ that reflects the fundamental wave is placed on the end face 701 of the semiconductor laser element region.
The multilayer reflection film 198 is formed on the end face 702 of the optical wavelength conversion region, and the TiO ₂ —SiO ₂ multilayer reflection film 199 for transmitting harmonics is formed on the end surface 702, thereby obtaining a semiconductor laser integrated optical wavelength conversion device.

The light generated in the semiconductor laser element region of this semiconductor laser integrated wavelength converter is directly injected into an optical waveguide (ie, ZnSe _0.1 S _0.9 core layer 196) formed of a non-linear optical material and converted into a harmonic therein. Then, the light is emitted from the end face 702.

(Problems to be Solved by the Invention) In order to perform wavelength conversion with high efficiency in an optical wavelength conversion device, it is necessary to match the phase of a fundamental wave with the phase of a harmonic in an optical waveguide. In the optical wavelength converter described above,
This is not taken into account. Therefore, when a non-linear optical material having no or very little birefringence in a single crystal state, such as ZnSSe or ZnCdS, is used as an optical waveguide, the birefringence caused by the structural anisotropy of the optical waveguide is Very small. For this reason, it is difficult to match the phase of the fundamental wave with the phase of the higher harmonic wave using birefringence. As described above, these nonlinear optical materials have a high nonlinear optical coefficient, but when used as the optical waveguide of the above-mentioned conventional optical wavelength converter, the phases of the fundamental wave and the harmonic wave are mismatched. Therefore, the light injected into this optical waveguide is once converted from a fundamental wave to a harmonic, and the generated harmonic is converted back to a fundamental wave, based on the wavelength of the introduced light and the nonlinear optical material used. Will be repeated at a cycle determined depending on. As a result, the light emitted from the end face 702 of the light wavelength conversion area is not practically subjected to wavelength conversion, and the wavelength conversion efficiency of the light wavelength conversion device becomes extremely poor.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an optical wavelength conversion device that exhibits high conversion efficiency even when using a nonlinear optical material having a small birefringence such as ZnSSe or ZnCdS. To provide.

(Means for Solving the Problems) The present invention has a first clad layer, a core layer, and a second clad layer formed on a semiconductor substrate, and applies laser light to an optical waveguide composed of the core layer. What is claimed is: 1. An optical wavelength conversion device for performing wavelength conversion into a second harmonic by introducing the same, wherein an amorphous layer having a predetermined length in an optical waveguide direction is provided between the semiconductor substrate and the first cladding layer. The core layer is provided periodically at predetermined intervals along the optical waveguide direction, and the core layer is a single crystal or a polycrystal having a uniform orientation on the substrate, and is amorphous or poorly oriented on the non-crystal. An optical wavelength conversion device formed in a polycrystalline form, thereby achieving the above object.

In the optical wavelength conversion device, a semiconductor laser device may be provided adjacent to the laminated structure, and laser light from the device may be introduced into the optical waveguide.

The length of the amorphous layer and the interval at which the amorphous layer is formed on the substrate are determined by the amorphous layer formation period (層) obtained by the following equation.

Λ = mλ / 2 (N _2w −N _w ), (m = 1,3,5,...) Where λ is the wavelength of the fundamental wave, N _w is the equivalent refractive index of the fundamental wave, and N
_2w is the harmonic equivalent refractive index, and m is the order. The value of m is preferably 1, but may be an odd number such as 3 or 5. It is desirable that both the length of the amorphous layer and the optical waveguide direction and the distance between the amorphous layer and the amorphous layer be Λ / 2.

As the material of the substrate used in the present invention, GaAs, ZnSe, Ga
P. The amorphous layer may be any layer that does not grow single crystal on these substrates, for example, SiO ₂ , Al ₂ O ₃ , S
Examples of such materials include i, Mo, and W, and materials such as GaAs, ZnS, and ZnSe formed under conditions that do not allow epitaxial growth.

Non-linear optical materials are used for the first cladding layer, the core layer, and the second cladding layer, and examples thereof include ZnS and ZnSSe, and compound semiconductors such as CdS, ZnCds, ZnTe, and ZnSTe.

(Operation) In the optical wavelength conversion device of the present invention, an amorphous layer is provided periodically on the substrate along the optical waveguide direction. When the first cladding layer, the core layer, and the second cladding layer are sequentially grown thereon, the non-crystal layer becomes amorphous or polycrystalline with poor orientation, and the exposed substrate becomes monocrystalline. Alternatively, each of the above-mentioned layers is formed in a polycrystalline form having a uniform orientation.

Since the nonlinear optical coefficient of a nonlinear optical material formed in an amorphous state or a polycrystalline state with poor orientation is almost zero, the core layer (that is, the optical waveguide) has a nonlinear optical coefficient having a thickness of Λ / 2. A region having the non-linear optical coefficient having a thickness of Λ / 2 and a region having a non-linear optical coefficient are arranged alternately along the optical waveguide direction.

When a laser beam is introduced into such an optical waveguide, the wavelength is converted from a fundamental wave to a higher harmonic in a region having a nonlinear optical coefficient, and the wavelength is not converted in a region adjacent to this having no nonlinear optical coefficient. , The generated harmonics are kept without being converted back to the fundamental wave, as a result,
Strong harmonics can be obtained.

As described above, when the light wavelength conversion portion is manufactured by the crystal growth method, harmonics can be obtained by breaking the crystallinity of the light wavelength conversion portion at a constant period. In such a case, it is generally said that the quasi-phase matching condition is satisfied.

(Example) An example of the present invention will be described below.

Embodiment 1 FIG. 1 is a sectional view of an optical wavelength converter according to an embodiment of the present invention in the optical waveguide direction, and FIG. 2 is a sectional view of the optical wavelength converter in a direction perpendicular to the optical waveguide direction. In the layered structure in the figure, the shaded portions indicate amorphous or polycrystalline crystals with poor orientation, and the other portions indicate single-crystal or polycrystalline crystals with uniform orientation. Show.

This optical wavelength converter was manufactured as follows.
First, TiO ₂ was deposited on the surface of the GaAs substrate 10. The surface was covered with a resist to form a grating pattern having a groove in a direction perpendicular to the optical waveguide direction, and then the TiO ₂ film was dry-etched to form a TiO ₂ amorphous layer 11. At that time, the light waveguide direction of the length 104, and the substrate exposed portion of the light waveguide direction of the length of the TiO ₂ amorphous layer 11 (i.e. a TiO ₂ amorphous layer 11, the distance between the TiO ₂ amorphous layer 11) 105 Are both 0.68 μm
(Λ = 1.36 μm). On top of this, using MOCVD, Z
An nS first cladding layer 12, a ZnS _0.8 Se _0.2 core layer 13, and a ZnS second cladding layer 14 were sequentially grown.

Next, after forming a striped resist pattern along the optical waveguide direction on the surface of the ZnS second cladding layer 14, the ZnS
The second clad layer 14, the ZnS _0.8 Se _0.2 core layer 13, the ZnS first clad layer 12, and the TiO ₂ amorphous layer 11 are removed by reactive ion beam etching (RIBE) to form a striped optical waveguide stack 201. did. Then, a ZnS _0.9 Se _0.1 burying layer 15 was grown on the exposed substrate by MOCVD to bury the optical waveguide stack 201. After the wafer on which the optical wavelength conversion element structure is formed is cleaved and divided into chips, TiO on the light incident end face 101 is used to suppress the reflection of the fundamental wave.
_An optical wavelength conversion device was obtained by forming a _2- SiO ₂ multilayer anti-reflection film 17 and a TiO ₂ -SiO ₂ multilayer anti-reflection film 18 on the light emitting end face 102 for suppressing reflection of harmonics.

FIG. 3 is a schematic diagram showing a system for wavelength-converting light emitted from a light source using the optical wavelength converter of the present invention.

An experiment of converting the wavelength of laser light using the obtained optical wavelength converter was performed. The laser beam 301 having an output of 100 mW emitted from the GaAlAs-based semiconductor laser device 30 was transmitted through the collimator lens 35 and the focusing lens 36 sequentially, and was condensed on the optical waveguide entrance end face of the optical wavelength converter 20. Then, when the temperature of the optical wavelength converter 20 was changed between 0 and 50 ° C., the second harmonic having a wavelength of 432 nm was 2.3 mW at about 32 ° C.
Of the output. In addition, the temperature of the optical wavelength converter is set to 25
When the injection current to the semiconductor laser element was changed at each temperature by fixing the temperature to 1 to 35 ° C. every 1 ° C., the second harmonic having an output of 0.5 mW or more was obtained at each temperature. This indicates that even when this optical wavelength conversion device is used at an environmental temperature near room temperature, it can be handled by adjusting the injection current to the semiconductor laser element.

The obtained second harmonic could be exposed to almost the diffraction limit.

Embodiment 2 In this embodiment, an example of a semiconductor laser-integrated optical wavelength converter in which a semiconductor laser element and an optical wavelength converter are integrally formed on the same substrate will be described.

FIG. 4 is a sectional view in the optical waveguide direction of a semiconductor laser-integrated optical wavelength converter according to another embodiment of the present invention, and FIG. 5 shows an example of a semiconductor laser element region of the semiconductor laser-integrated optical wavelength converter. FIG. 3 is a cross-sectional view in a direction perpendicular to the optical waveguide direction.
In the laminated structure of the wavelength conversion region 402 in FIG. 4, the hatched portions indicate amorphous or polycrystalline crystals with poor orientation, and the other portions are single crystals or polycrystalline with uniform orientation. Shows the crystals formed.

This optical wavelength converter was manufactured as follows.
First, an n-GaAs current block layer 52 was formed on a p-GaAs substrate 50, and the current block layer 52 was etched to form a V-shaped stripe groove 53. On top of that, p-Ga _0.65
Al _0.35 As First cladding layer 54, undoped Ga _0.92 Al _0.08 As
Active layer 55, n-Ga _0.65 Al _0.35 As second cladding layer 56 and n
-The GaAs cap layer 57 was sequentially grown by the liquid layer growth method. At this time, the thickness of the n-type cap layer 57 was formed to 5 μm. Thereafter, an n-side Au / AuZn electrode 70 was provided on the surface of the n-type cap layer 57, and a p-side AuGe / Ni electrode 71 was provided on the back surface of the p-GaAs substrate 50 to obtain a semiconductor laser device structure. Such a structure
Called VSIS structure.

Next, a resist turn is formed on the surface of the n-side Au / AuZn electrode 70 so as to cover the semiconductor laser element region 401, and the n-side Au / AuZn electrode 70 in a region not covered with the resist is formed by wet etching. After removal and subsequent RIBE, the n-type cap layer 57, the n-Ga _0.65 Al _0.35 As second cladding layer 56, the undoped Ga _0.92 Al _0.08 As active layer 55, p
-Ga _0.65 Al _0.35 As The first cladding layer 54 and the n-GaAs current block layer 52 were removed to expose the p-GaAs substrate 50. Then, as an optical waveguide laminated structure, a ZnS-ZnSe superlattice in which a ZnS _0.7 Se _0.3 first cladding layer 62, a thin layer of ZnS (thickness of 100 mm) and a thin layer of ZnSe (thickness of 50 mm) are alternately stacked for 50 periods. A wavelength conversion region 402 was formed in the same manner as in Example 1 except that the core layer 63 and the ZnS _0.7 Se _0.3 second cladding layer 63 were grown. At this time, each layer of the optical waveguide laminated structure was grown so that the height of the undoped Ga _0.92 Al _0.08 active layer 55 from the center of the substrate and the height of the ZnS-ZnSe superlattice core layer 63 from the center were equal. I let it. After cleaving the wafer in the direction perpendicular to the optical waveguide direction and dividing it into chip rows, a high reflection film for the fundamental wave is formed on the end face 403 of the semiconductor laser element region 401.
On the light emitting end face 404 of the wavelength conversion region 402, an antireflection film 76 for harmonics was formed. This anti-reflection film 76
It is desirable that the film be a highly reflective film for the fundamental wave. Thereafter, the chip array was divided to obtain a semiconductor laser integrated optical wavelength converter.

The chip of the optical wavelength converter integrated with a semiconductor laser was mounted on a stem, and dry nitrogen was sealed therein to package a hermetic seal.

When a current of 120 mA was passed through the obtained optical wavelength converter and the temperature was changed in the range of 0 to 55 ° C, a second harmonic having an output of 0.8 mW was generated at about 27 ° C. Outgoing light wavelength is 434
nm.

Embodiment 3 In this embodiment, another example of a semiconductor laser-integrated optical wavelength converter in which a semiconductor laser element and an optical wavelength converter are integrally formed on the same substrate will be described.

FIG. 6 is a cross-sectional view in a direction perpendicular to the optical waveguide direction, showing another example of the semiconductor laser element region of the semiconductor laser integrated optical wavelength converter.

This optical wavelength converter was manufactured as follows.
On an n-GaAs substrate 80, an n-GaAs buffer layer 81, an n-Al _0.6 Ga _0.4 As cladding layer 82, a non-doped Al _y Ga
_1-y As layer 83 (in the growth direction, y = 0.6 → 0 continuously changed), In _0.15 Ga _0.85 As active layer 84 (thickness 100 mm), non-doped Al _y Ga _1-y As layer 85 (growth) In the direction, y is changed continuously from 0 to 0.6), and a p-Al _0.6 Ga _0.4 As clad layer 86 and a p-GaAs cap layer 87 are sequentially grown. Next, p-Al _0.6 Ga _0.4 As
The ridge cladding layer 86, and a p-GaAs cap layer 87 is etched, the surface other than the top surface of the ridge, SiO ₂
An insulating film 88 was formed.

Such a structure is called a GRIN-SCH structure. The active layer 84 of this embodiment is an InGaAs quantum well layer. InGaAs is GaAs
However, when formed in a very thin film such as a quantum well, the lattice is distorted and no lattice defect occurs. Note that an n-GaAs layer may be provided instead of the SiO ₂ insulating film 88.

Generally, a semiconductor laser device having an InGaAs strained quantum well structure emits light having a wavelength of 0.9 to 1.1 μm.

Next, as in the second embodiment, a part of the semiconductor laser device structure was removed by etching to expose the n-GaAs substrate 80. The length of the TiO ₂ amorphous layer 11 in the optical waveguide direction 10
4, and the length of the exposed portion of the substrate in the optical waveguide direction (ie, TiO ₂
The distance between the amorphous layer 11 and the TiO ₂ amorphous layer 11) 105 is 0.84
μm (Λ = 1.68 μm), and Zn _0.42 Cd _0.58 S first cladding layer, ZnS _0.06 Se
An optical wavelength conversion region was produced in the same manner as in Example 2 except that a _0.94 core layer and a Zn _0.42 Cd _0.58 S second cladding layer were grown. After that, the p-side Au / AuZn electrode 1
00, and an n-side AuGe / Ni electrode 101 was provided on the substrate surface side.

When a current of 80 mA was passed through the obtained optical wavelength converter and the temperature was changed in the range of 0 to 50 ° C., a second harmonic having an output of 0.06 mW was generated at about 5 ° C. Outgoing light wavelength is 505n
m.

As described above, by integrating the InGaAs-based laser element having an emission wavelength of about 1 μm and the optical wavelength converter, the second embodiment is realized.
The second harmonic having a wavelength higher than the visibility was obtained. This wavelength is longer than the absorption edge of ZnS _0.06 Se _0.94 and Zn _0.42 Cd _0.58 S lattice-matched to GaAs. Therefore, by using a material such as ZnS _0.06 Se _0.94 or Zn _0.42 Cd _0.58 S as the second harmonic generation optical waveguide, n−
The deviation of the lattice spacing from the GaAs substrate 80 is kept low, and a high-quality optical waveguide can be formed.

The semiconductor laser-integrated optical wavelength converter of the present invention is provided with a semiconductor laser element region of any stripe structure such as a BH structure instead of the VSIS structure of the second embodiment and the GRIN-SCH structure of the third embodiment. Can be. Ga as substrate
An InGaAlP-based or InGaAsP-based semiconductor laser element region may be provided using a compound semiconductor other than As, for example, InP. In the manufacturing process, liquid phase growth, MOC
VD method, OMVPE method, ALE (Atomic Layer Epitaxy) method, MBE method,
Gas source MBE method and MEE (Migration Enhanced Epi
taxy) method can be used.

Further, the outgoing light having a wavelength of about 1 μm, such as a YAG laser, may be converted by using the optical wavelength converter having no semiconductor laser element region according to the present invention. In that case,
As the substrate, ZnSe may be used instead of GaAs, and it is preferable to use ZnSe as the core layer and adjust the mixed crystal ratio of the ZnCdS cladding layer so as to lattice match with ZnSe.

(Effects of the Invention) According to the present invention, in the optical waveguide of the optical wavelength conversion device, since the quasi-phase matching condition between the fundamental wave and the harmonic is satisfied, a nonlinear optical material such as ZnSSe or ZnCdS having a small birefringence is used. An optical wavelength conversion device that exhibits high conversion efficiency even when used as an optical waveguide is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical wavelength converter according to an embodiment of the present invention in the optical waveguide direction, FIG. 2 is a sectional view of the optical wavelength converter of the present invention in a direction perpendicular to the optical waveguide direction, and FIG. FIG. 4 is a schematic diagram showing a system for converting the wavelength of light emitted from a light source using the optical wavelength converter of the present invention, and FIG. 4 is a light guide of a semiconductor laser integrated optical wavelength converter according to another embodiment of the present invention. FIG. 5 shows an example of a semiconductor laser element region of a semiconductor laser-integrated optical wavelength converter. FIG. 5 is a cross-sectional view in a direction perpendicular to the optical waveguide direction. FIG. 6 shows a semiconductor laser-integrated optical wavelength converter. FIG. 7 is a cross-sectional view in a direction perpendicular to the optical waveguide direction, showing another example of the semiconductor laser element region of FIG. 10 GaAs substrate, 11 TiO ₂ amorphous layer, 12 ZnS first cladding layer, 13 ZnS _0.8 Se _0.2 core layer, 14 ZnS second cladding layer.

Claims (2)

(57) [Claims] A first cladding layer, a core layer, and a second cladding layer formed on a semiconductor substrate, wherein a second harmonic is introduced by introducing a laser beam into an optical waveguide formed of the core layer. An optical wavelength conversion device for performing wavelength conversion to an amorphous layer having a predetermined length in the optical waveguide direction between the semiconductor substrate and the first cladding layer. The core layer is provided periodically at intervals, and the core layer is formed as a single crystal or a polycrystal having uniform orientation on the substrate, and is formed as an amorphous or polycrystal having poor orientation on the non-crystal. Optical wavelength converter. 2. The optical wavelength conversion device according to claim 1, wherein a semiconductor laser device is provided on said semiconductor substrate adjacent to said laminated structure, and laser light from said device is introduced into said optical waveguide.