JPS63269132A - Optical integrated circuit - Google Patents

Abstract

PURPOSE:To provide a simple optical system with a waveform converting function by transmitting the distribution of an electric field as Gauss's distribution in a light guide at the time of coupling light radiated into a substrate at a fixed angle by Cherenkov radiation with another light guide. CONSTITUTION:When laser light with 0.8mum wavelength is made incident from a semiconductor laser upon a secondary higher harmonic generating light guide 2, the light are guided into the light guide 2, generates secondary higher harmonic with 0.4mum and radiates the higher harmonic into the substrate as substrate radiation light 6 at a fixed angle by Cherenkov radiation. The light 6 are made incident upon a blaze grating 4 formed in a single mode three-dimensional light guide 3, coupled with a proton replacement single mode three-dimensional light guide 3 and transmitted as wave-guided light 7. The light 7 are radiated to the external at the end face of the light guide 3 as radiation light 8. Since the space distribution shape of light intensity at the end face of the light guide 3 is similar to a circle, astigmatism at the time of concentrating light by means of the lens system can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical integrated circuit having a wavelength conversion function of converting light into light of a different wavelength, and is particularly used for writing and erasing information on optical discs, etc. The present invention relates to an optical integrated circuit that can be used as a short wavelength laser light source for optical pickup.

2. Description of the Related Art In recent years, the importance of optical information processing and the like has been increasing, and there are expectations for the development of optical integrated circuits and the like having a wavelength conversion function. Especially for optical pickups used for optical discs, etc.
There is a demand for a short wavelength laser light source that is expected to improve recording density, and the development of particularly high-performance second harmonic generation elements is expected. (Radiation Science Research Group Material R886-21
) Highly efficient second harmonic generation elements using optical waveguides have already been developed, but since the second harmonic is generated by Cerenkov radiation, the wavefront of the second harmonic light is Because of the distortion, it is difficult to focus the light onto an optical disk using a normal optical lens system, making it difficult to apply it to optical pickup.

FIG. 5 shows the structure of a second harmonic generation element using a conventional optical waveguide. 51 is a lithium niobate substrate;
52 is a proton exchange optical waveguide. The first laser beam 53 incident on the optical waveguide 52 is converted into a half-wavelength second harmonic by the nonlinear optical effect of the optical waveguide 52, and is emitted into the substrate at a constant angle by Cerenkov radiation.

Problems to be Solved by the Invention However, the primary light propagating through the optical waveguide is gradually converted into second harmonic laser light as it propagates (because of this,
The light intensity is gradually attenuated, and as a result, the light intensity of the second harmonic is also gradually attenuated. Further, since the second harmonic is radiated from the entire optical waveguide at a constant angle, the intensity distribution of the second harmonic output light becomes asymmetrical in the vertical direction at the output end face, as shown at 55. Therefore, the near-field pattern at the exit end face has a shape close to a crescent moon shape, which is far from a circle, and has a large astigmatism when stopped by a lens system. Therefore, when applying this element to optical pickup, etc., it is impossible to focus the laser beam onto a disk with a spot diameter of 1 μm or less using a normal lens system, and a complicated optical system is required. Not only is this difficult, but it also requires an expensive optical system such as an aspherical lens and precise optical axis alignment technology.

The present invention solves these problems and realizes a high-performance optical integrated circuit having wavelength conversion functions such as second harmonic generation. The present invention provides an optical integrated circuit for a small short wavelength laser light source.

Means for Solving the Problems The present invention is an optical integrated circuit formed by including a plurality of optical waveguides on a substrate. A first optical waveguide having a nonlinear effect capable of converting the wavelength of light and radiating the wavelength-converted secondary light to the outside of the optical waveguide, and at least one of the plurality of optical waveguides. The optical integrated circuit is characterized in that the optical integrated circuit is an optical waveguide which couples the wavelength-converted second light and propagates the light as guided light.

Furthermore, the present invention can have the following aspects.

(2) The first nonlinear optical waveguide and the second optical waveguide through which the second wavelength-converted light propagates are arranged in close proximity to each other in a pair.

(2) The first nonlinear optical waveguide is formed near the first surface of the substrate, and the light wavelength-converted in the first nonlinear optical waveguide is radiated into the substrate, and the second optical waveguide is formed near the first surface of the substrate. It is formed near the second surface of the substrate.

■The first or second optical waveguide is formed near the surface of the substrate, and the second or first optical waveguide is formed on the first or second optical waveguide with a buffer layer interposed therebetween. .

■ A grating that has an effective periodic refractive index distribution with respect to the propagation direction of light is formed in a part of the second optical waveguide, and the second wavelength is converted and radiated due to the diffraction effect of the grating. The next light is coupled to the guided light of the second optical waveguide.

■The grating is characterized by being a blaze grating.

(2) The second optical waveguide through which the wavelength-converted light propagates is a single mode three-dimensional optical waveguide.

(2) The second optical waveguide through which the wavelength-converted light propagates is a two-dimensional optical waveguide.

■A grating that radiates the propagating secondary light to the outside of the second optical waveguide is formed in a part of the second two-dimensional optical waveguide through which the wavelength-converted secondary light propagates. ing.

[Phase] The first nonlinear optical waveguide is an optical waveguide that generates a second harmonic.

(2) The first nonlinear optical waveguide is an optical waveguide containing lithium niobate as a main component.

Effect of the present invention The present invention guides light through a nonlinear optical waveguide, converts the wavelength due to the nonlinear optical effect, and radiates light into the substrate at a certain angle due to Cerenkov radiation. This method takes advantage of the fact that the electric field distribution propagates in a Gaussian distribution, so the wavefronts of the light emitted by the end face or grating coupler are aligned, and the light can be easily focused using a normal lens system or the like.

Example The present invention will be explained below based on examples.

FIG. 1 shows a schematic configuration of an optical integrated circuit having wavelength variation capability according to a first embodiment of the present invention. In Fig. 1, 1 is a lithium niobate substrate, 2 is a second harmonic generation optical waveguide formed by proton exchange, and 3 is a second harmonic generation optical waveguide formed by the proton exchange method, which generates a single mode for the second harmonic. In the three-dimensional optical waveguide through which the light propagates, 4 is a blaze grating.

Hereinafter, the principle of operation of this embodiment will be explained based on the sectional view of FIG. 2. When light 5 of a semiconductor laser with a wavelength of 0.8 μm is incident on the second harmonic generation optical waveguide 2, this laser light is guided through the optical waveguide 2 and generates a second harmonic with a wavelength of 0.4 μm, Cherenkov radiation is used to radiate light into the substrate at a constant angle as substrate radiation 6. This substrate emitted light 6 enters the blaze grating 4 formed in the single mode three-dimensional optical waveguide 3, is coupled with the proton exchange single mode three-dimensional optical waveguide 3 due to the diffraction effect, and propagates as guided light 7. This guided light 7 is further transferred to the three-dimensional optical waveguide 3.
It is emitted to the outside as radiation light 8 at the end face of the . As mentioned above, this waveguide is a single mode three-dimensional optical waveguide, so the spatial distribution shape of the light intensity at its end face is close to a circle, so there is no astigmatism when condensing light with a lens system. is getting smaller. As a result, the condensed spot diameter when stopped by a lens was about 0.5 μm, which was almost at the diffraction limit. As described above, it was possible to construct a high-performance wavelength conversion device that has small astigmatism and can exhibit the characteristics of a short wavelength light source.

In the above embodiments, the optical waveguide that propagates the second harmonic is a three-dimensional single mode waveguide, but new effects can be brought about by using a two-dimensional slab waveguide.

FIG. 3 shows an embodiment using a two-dimensional slab waveguide. 31 is a semiconductor laser, 32 is a lithium niobate substrate, 33 is a three-dimensional nonlinear optical waveguide formed by ion exchange on one side of the substrate, and 34 is a divergent second harmonic wave emitted from the nonlinear optical waveguide 33. A four-force grating coupler for coupling the optical waveguide 35 to the optical waveguide 35 described below. 35 is a slab waveguide formed on the back surface of the substrate. Further, 36 is a force grating coupler for emitting the second harmonic into space and focusing it on the surface of an optical disk or the like. Approximately 0.8 μm light emitted from the semiconductor laser 31 propagates through the optical waveguide 33 and is converted into approximately 0.4 μm laser light, which propagates through the optical waveguide 35 and passes through the four force grating 36. The light is radiated into space by a fogger and focused on the surface of an optical disk or the like. With this configuration, a short wavelength optical integrated pickup can be easily realized.

In the second embodiment, a force grating coupler having a light focusing function is used as the grating coupler, but it is also possible to use a parallel grating to emit the light into space as a parallel beam, and to collect the light with a lens system. .

In the first and second embodiments, a lithium niobate substrate is used to form a waveguide by ion diffusion, but this is only possible if the substrate is transparent to the second harmonic. isn't it. Furthermore, the nonlinear optical waveguide is not limited to the ion-exchange waveguide of lithium niobate, but it is also possible to use an optical waveguide formed of a medium having a nonlinear effect such as an oxide such as lithium tantalate, a ■-V group compound, or a II-Vl compound. is also possible. Further, the optical waveguide for propagating the second harmonic may be formed of any medium as long as it is transparent to the second harmonic.

Also, the nonlinear optical waveguide and the optical waveguide that propagates the second harmonic do not necessarily have to be formed on both sides of the substrate (
Both may be placed close to each other. A third embodiment in this case will be described using FIG. 4. 41 is GaAs
Substrate, 42 is ZnS layer, 43 is ZnS/Zn
Nonlinear optical waveguide with superlattice structure of S e, 44 is Zn5
eS solid solution pair layer, 45 is a Sin'' cladding layer, 46 is Si
The N optical waveguide layer 47 is a 5in2 cladding layer formed with a periodic structure. Further, 48 is a semiconductor laser having a wavelength band of 0.8 μm and having an active layer of AlGaAs, and is formed monolithically with the above-mentioned optical waveguide. The light emitted from the semiconductor laser propagates through 43 nonlinear optical waveguides, and the wavelength-converted light with a wavelength of 0.4 μm is coupled to the optical waveguide formed above it using the same principle and propagates through 46 optical waveguides. , is radiated from the end face 49. On the other hand, light that is somewhat attenuated due to wavelength conversion is emitted from the end face 50. According to this configuration, a three-wavelength laser light source can be easily formed and is expected to be used as a light source for optical pickup that can simultaneously record and erase information on an optical disc.

In this example, the wavelength is 0.8 with AlGaAs as the active layer.
Although a μm band semiconductor laser is used, the present invention is not limited to this, but an AlGa1nP semiconductor laser with a 0.6 μm band can also be used as a 0.3 μm band light source, so the effect is even greater. Furthermore, in this embodiment, the semiconductor laser is monolithically integrated;
There is no problem with a hybrid configuration like 2 and 2.

As described in detail, according to the present invention, astigmatism is small;
It is possible to provide an optical integrated circuit having a wavelength conversion function that allows light to be focused with a simple optical system, and its practical effects are great, for example, as an element for picking up short wavelength light.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of essential parts of an optical integrated circuit according to a first embodiment of the present invention, FIG. 2 is a sectional view of FIG. 1, and FIG. 3 is a schematic perspective view of an optical integrated circuit according to a second embodiment of the present invention. FIG. 4 is a schematic cutaway view of the third embodiment of the present invention, and FIG. 5 is a schematic perspective view of a conventional wavelength conversion element. DESCRIPTION OF SYMBOLS 1... Lithium niobate substrate, 2... Proton exchange second harmonic generation optical waveguide, 3... Proton exchange single mode three-dimensional optical waveguide, 4... Blaze grating, 5... Input Laser light, 6...Substrate radiation light, 7.
... Waveguide light, 8 ... Synchrotron radiation, 31 ... Semiconductor laser, 32 ... Lithium niobate substrate, 33 ... Ion exchange three-dimensional nonlinear optical waveguide, 34 ... Four force grating coupler , 35 slab waveguide, 36...
・Force grating coupler, 41...
GaAS substrate, 42...ZnS layer, 43...Z n
S/ZnS e superlattice structure nonlinear optical waveguide, 44...Zn5eS solid solution pair layer, 45...5in2
Cladding layer, 46@...SiN optical waveguide layer, 47...S
in” cladding layer, 48...semiconductor laser. Name of agent: Patent attorney Toshio Nakao and one other person Figure 2 5 light 6 base # light

Claims (11)

[Claims] (1) A substrate is formed including a plurality of optical waveguides, and at least one optical waveguide among the plurality of optical waveguides converts the wavelength of the propagating primary light and converts the wavelength-converted secondary light. a first optical waveguide having a nonlinear effect capable of radiating the wavelength-converted second-order light to the outside of the optical waveguide; What is claimed is: 1. An optical integrated circuit characterized in that the optical integrated circuit is a second optical waveguide that propagates as guided light. (2) Claims characterized in that the first nonlinear optical waveguide and the second optical waveguide through which the second-order wavelength-converted light propagates are arranged in close proximity to each other in a pair. The optical integrated circuit according to item 1. (3) A first nonlinear optical waveguide is formed near the first surface of the substrate, and the light wavelength-converted in the first nonlinear optical waveguide is radiated into the substrate, and a second optical waveguide is formed in the vicinity of the first surface of the substrate. 3. The optical integrated circuit according to claim 2, wherein the optical integrated circuit is formed near the second surface of the substrate. (4) A first or second optical waveguide is formed near the surface of the substrate, and the second or first optical waveguide is formed on the first or second optical waveguide with a buffer layer interposed therebetween. The optical integrated circuit according to claim 2, characterized in that: (5) A grating having an effective periodic refractive index distribution in the light propagation direction is formed in a part of the second optical waveguide, and the wavelength of the wavelength-converted and radiated grating is formed by the diffraction effect of the grating. 5. The optical integrated circuit according to claim 1, wherein the secondary light is coupled with the guided light of the second optical waveguide. (6) The optical integrated circuit according to claim 5, wherein the grating is a blazed grating. (7) The optical integration according to any one of claims 1 to 6, wherein the second optical waveguide through which the wavelength-converted light propagates is a single mode three-dimensional optical waveguide. circuit. (8) Claim 1, characterized in that the second optical waveguide through which the wavelength-converted light propagates is a two-dimensional optical waveguide.
6. The optical integrated circuit according to any one of items 6 to 6. (9) A grating that radiates the propagating second-order light to the outside of the second optical waveguide is formed in a part of the second two-dimensional optical waveguide that propagates the wavelength-converted second-order light. The optical integrated circuit according to claim 8, characterized in that: (10) The optical integrated circuit according to claim 1, wherein the first nonlinear optical waveguide is an optical waveguide that generates a second harmonic. (11) The optical integrated circuit according to claim 1, wherein the first nonlinear optical waveguide is an optical waveguide containing lithium niobate as a main component.