JPH07114049A - Flush type optical waveguide - Google Patents

Abstract

PURPOSE:To enhance coupling efficiency by sticking the front surfaces of respective flush type optical waveguide elements to each other to eliminate the change in the refractive indices at the boundaries of the optical waveguides. CONSTITUTION:The front surface 13 and the front surface 14 are disposed to face each other and are aligned in such a manner that the optical waveguide 15 and the optical waveguide 16 overlap on each other. The front surface 13 and the front surface 14 are fixed to each other by optical glue, for example, resin cured by UV rays. As a result, the refractive index distribution of a vertical direction is nearly symmetrical in the front surfaces 13, 14 as a border, and the waveguide mode is symmetrical form in the optical waveguide 17. Then, the coupling efficiency is higher if light is coupled to the optical waveguide 17 of the optical waveguide element 100 than in the case of coupling of the light to the optical waveguide 15 of the optical waveguide element 18 or coupling of the light to the optical waveguide 16 of the optical waveguide element 19. Then, the performance of the optical waveguide type device is improved and the man-hours for operation at the time of element assembly are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device, a laser printer, and other optical application devices, and more particularly to a waveguide type optical integrated device used as a light source thereof.

[0002]

2. Description of the Related Art Gas lasers, semiconductor lasers, SHG lasers and the like are used as light sources for optical application devices. SH
G lasers are roughly classified into three types, and the waveguide type among them is to obtain SHG by making laser light enter an optical waveguide. Further, not limited to the waveguide type SHG laser,
Optical waveguides are used in various fields such as optical communication.

Several methods have been proposed for producing an optical waveguide. Nishihara Hiro et al., "Optical Integrated Circuits" (198
5 years), the basic structure of the three-dimensional optical waveguide is (1) embedded type (FIG. 2 (a)), (2) ridge type (FIG. 2 (b)), (3) ) There is a loading type (FIG. 2C), and a three-dimensional optical waveguide is manufactured by a method such as ion exchange, Ti diffusion, and proton exchange depending on the desired optical waveguide structure and its material.

For example, in Japanese Patent Laid-Open No. 3-287141, as shown in FIG. 3, lithium tantalate (LiTaO ₃ ) is used.
An example is described in which an optical waveguide is formed on a substrate by proton exchange (a method in which Li ions of LiTaO ₃ and protons are partially replaced).

[0005]

However, the prior art has the following problems. That is, in an optical system using an optical waveguide element, it is important to increase the ratio of light incident on the optical waveguide (coupling efficiency).

According to the method shown in FIG. 3, the optical waveguide can be manufactured only so that the upper surface 36 of the optical waveguide and the upper surface 37 of the substrate are aligned with each other. Therefore, the refractive index distribution in the substrate depth direction, which is seen by the cutting line shown in FIG. 4A, greatly changes on the optical waveguide and the upper surface of the substrate as shown in FIG. 4B. Therefore, the intensity distribution of light (waveguide mode) propagating in a state of being confined in the optical waveguide has an asymmetrical shape when viewed along the cutting line shown in FIG. 4 (a) (see Nishihara Hiro et al. Circuit "(1985)).

In most cases, the intensity distribution of the light emitted from the light source that is incident on the optical waveguide is biaxially symmetric when observed in a plane perpendicular to the light traveling direction. For example, when an optical system as shown in FIG. 5 is assembled, the ratio of light incident on the optical waveguide (coupling efficiency)
Is largely due to the magnitude of the overlap integral value of the y-direction intensity distribution of the light of the incident light source and the guided mode. In this case where the intensity distribution of the guided mode is asymmetric, the overlap integral value is smaller and the coupling efficiency is smaller than in the case where the waveguide mode is symmetrical. Further, not only the buried type optical waveguide but also the ridge type or the loading type optical waveguide, since the upper surface of the optical waveguide is basically an air layer, the same discussion as above can be made.

Further, for example, Electronics Letters Vol. 25, pp. 731 to 7
As discussed on page 32, a ferroelectric material having a spontaneous polarization, for example, a LiTaO ₃ substrate 31 using a polarization inversion grating 33 in which the direction of the spontaneous polarization is periodically inverted is used. There is a method in which the harmonics are phase-matched, the optical waveguide 32 is formed on this substrate by the proton exchange method, the fundamental wave 34 is incident on one end face of the optical waveguide, and the second harmonic 35 is taken out. The generation efficiency of the second harmonic becomes better as the overlap between the guided mode of the fundamental wave and the guided mode of the second harmonic in the optical waveguide increases. As described above, the shape of the fundamental wave guided mode changes depending on the refractive index distribution of the optical waveguide and its surroundings. However, when the upper surface of the optical waveguide is air, the fundamental wave guided mode and the second harmonic guided mode are formed. The overlap with is small and the generation efficiency is small.

[0009]

According to the present invention, the upper surfaces of two embedded optical waveguide elements are bonded to each other, that is, the surfaces 13 and 14 in FIG. One optical waveguide is provided.

According to the present invention, in at least one of the two embedded optical waveguide elements, the cross-sectional shape of the optical waveguide near at least one of the light incident end and the light emitting end of the optical waveguide. In the element whose element changes toward the end portion of the optical waveguide, by laminating the upper surfaces of the optical waveguide elements together, one optical waveguide having a waveguide mode close to a symmetrical shape is provided.

Further, according to the present invention, at least one of the two embedded optical waveguide elements is a nonlinear optical element having periodic spontaneous polarization reversal, and the upper surfaces of the optical waveguide elements are bonded to each other. This provides one optical waveguide having high second harmonic generation efficiency.

[0012]

According to the present invention, by bonding the upper surfaces of two embedded optical waveguide elements to each other, a large change in the refractive index at the boundary surface of the optical waveguide is eliminated, and the intensity distribution of the light from the incident light source and the guide of the optical waveguide are eliminated. The coupling efficiency can be increased by increasing the overlap integral value with the intensity distribution of the wave mode.

Further, according to the present invention, at least one of the two embedded optical waveguide elements is a non-linear optical element having periodic spontaneous polarization reversal, and the upper surfaces of the optical waveguide elements are bonded to each other. This eliminates a large change in the refractive index at the boundary surface of the optical waveguide and increases the overlap between the guided mode of the fundamental wave and the guided mode of the second harmonic in the optical waveguide, thereby increasing the efficiency of the second harmonic generation. Can be increased.

Further, according to the present invention, the SH using at least one of the two embedded optical waveguide elements is a nonlinear optical element having periodic spontaneous polarization reversal.
The spot diameter on the disc is 0.5 μm by using the G laser as a light source for an optical information recording / reproducing device.
Since the size can be made small, the recording density can be increased four times that of the conventional one. Further, by using the SHG laser as the light source of the laser beam printer, high definition printing can be achieved.

[0015]

EXAMPLE Next, a waveguide type SHG laser is adopted as a light source of an optical application apparatus, for example, an optical information recording / reproducing apparatus, and the buried type optical waveguide according to the present invention is used as a waveguide element of the waveguide type SHG laser. An embodiment will be described with reference to the drawings.

(Embodiment 1) FIG. 1A is a sectional view showing an embodiment of an embedded optical waveguide according to the present invention.
FIG. 1B is a perspective view of the optical element of FIG. In FIG. 1, 11 and 12 are Zcut LiTaO ₃ single crystal substrates whose surfaces 13 and 14 are + c-planes. The + c plane is one of the planes perpendicular to the direction of spontaneous polarization of a uniaxial ferroelectric crystal such as LiTaO ₃ . Reference numerals 15 and 16 are channel type optical waveguides produced by proton exchange, for example, width 4 μm, thickness 3
It is an optical waveguide of μm. The surface 13 and the surface 14 are opposed to each other, the optical waveguide 15 and the optical waveguide 16 are aligned so as to overlap each other, and the surface 13 and the surface 14 are fixed to each other with an optical glue, for example, a resin that is cured by ultraviolet rays.

As a result, the refractive index distribution in the up-down direction becomes nearly symmetrical with respect to the surface 13 (14), and the optical waveguide 17
The guided mode at is symmetric. Therefore, when the light is coupled to the optical waveguide 17 of the optical waveguide element 100, the coupling is greater than when the light is coupled to the optical waveguide 15 of the optical waveguide element 18 or the optical waveguide 16 of the optical waveguide element 19. Efficiency has increased.

(Embodiment 2) FIG. 6A is a sectional view showing an embodiment of the embedded optical waveguide according to the present invention.
FIG. 6B is a perspective view of the optical element of FIG. In FIG. 6, reference numerals 61 and 62 denote ZcutLiTaO ₃ single crystal substrates whose surfaces 63 and 64 are + c planes. Reference numerals 65 and 66 are channel type optical waveguides produced by proton exchange. The optical waveguide 65 has a length of 20 mm and is approximately 2 mm from at least one waveguide end portion toward the other waveguide end portion.
The cross-sectional shape gradually changes over the length of mm, for example, the width is reduced from 4 μm to 2 μm, and the thickness is reduced from 3 μm to 2 μm.
01 is configured.

The optical waveguide 66 gradually changes its cross-sectional shape, for example, from a width of 4 μm to a width of 2 μm, over a length of about 2 mm from the waveguide end portion of the light incident end in the light propagation direction. The waveguide is configured so that the thickness is reduced from 3 μm to 0 μm. The surface 63 and the surface 64 are opposed to each other, and the optical waveguide 65 and the optical waveguide 66 are aligned so as to overlap each other, and the surface 63 and the surface 64 are fixed to each other with an optical glue, for example, a resin that is cured by ultraviolet rays.

As a result, the refractive index distribution in the up-down direction becomes nearly symmetrical with respect to the surface 63 (64), and the optical waveguide 67
The waveguide mode at the waveguide end portion 602 of 1 is close to a symmetric shape. Therefore, the optical waveguide 6 of the optical waveguide element 600 is
When light is coupled to 7, the optical waveguide 65 of the optical waveguide element 68 is
When coupling light to the optical waveguide 66 of the optical waveguide element 69
The coupling efficiency was higher than that in the case of coupling light to. Further, since the optical waveguide 66 has a wider width and a shorter length than the optical waveguide 16 of the first embodiment, the precision of alignment when the optical waveguide 65 and the optical waveguide 66 are overlapped is reduced.

(Embodiment 3) FIG. 7A is a sectional view showing an embodiment of the embedded optical waveguide according to the present invention.
7B is a perspective view of the optical device of FIG. 7A. In FIG. 7, 71 and 72 are ZcutLiTaO ₃ single crystal substrates whose surfaces 73 and 74 are + c planes. 75 and 76 are channel type optical waveguides produced by proton exchange. The optical waveguide 75 has a length of 20 mm, and its cross-sectional shape gradually changes from the one end of the waveguide to the other end of the waveguide by about 5 mm, for example, a width of 4 μm.
The waveguide end portion 701 is configured so that the width becomes narrower from m to 2 μm and the thickness becomes thinner from 3 μm to 2 μm. The optical waveguide 76 has a length of 20 mm, and its cross-sectional shape gradually changes from the one waveguide end portion to the other waveguide end portion over a length of 20 mm, for example, from a width of 4 μm to a width of 2 μm. Narrower and 3 μm thick
To 2 μm, the waveguide is formed.

The surface 73 and the surface 74 are opposed to each other, and the optical waveguide 75 and the optical waveguide 76 are aligned so as to overlap each other, and the surface 73 and the surface 74 are fixed to each other with an optical glue, for example, a resin which is cured by ultraviolet rays.

As a result, the refractive index distribution in the up-down direction becomes nearly symmetrical with respect to the surface 73 (74), and the optical waveguide 77
The waveguide mode at the waveguide end portion 702 of is close to symmetric. Therefore, the optical waveguide 7 of the optical waveguide element 700 is
When light is coupled to 7, the optical waveguide 75 of the optical waveguide element 78
When the light is coupled to the optical waveguide 76 of the optical waveguide element 79
The coupling efficiency was higher than that in the case of coupling light to. Furthermore, since the optical waveguide 76 has a wider width and changes more gently than the optical waveguide 16 of the first embodiment, the alignment accuracy when the optical waveguide 75 and the optical waveguide 76 are overlapped is reduced.

(Embodiment 4) FIG. 8A is a sectional view showing an embodiment of the embedded optical waveguide according to the present invention, and FIG.
FIG. 9 is a perspective view of the optical element of FIG. In FIG.
81 and 82 are ZcutLiTaO ₃ single crystal substrates whose surface 83 is + c plane and whose surface 84 is −c plane. 85 is LiT
For aO ₃ single crystal thin film, spontaneous polarization is usually upward. 8
Reference numeral 6 denotes a portion where the polarization is inverted, and the polarization is downward in this portion. The period is Λ. Journal of Applied Physics
ics) Vol. 40, No. 2, pages 720 to 734, the sign of the nonlinear optical coefficient coincides with the direction of spontaneous polarization in the case of a ferroelectric crystal of space group R3c such as LiTaO ₃ .

Therefore, the nonlinear optical coefficients of the substrate and the optical waveguide of this embodiment are also periodically inverted. 87
Is a channel-type optical waveguide manufactured by proton exchange, and both the fundamental wave and the second harmonic wave are confined in this portion and propagate. Face the surface 83 and the surface 84,
Optical glue, for example, a surface 83 made of a resin that is cured by ultraviolet rays.
And surface 84 are secured to each other.

As a result, the refractive index distribution in the up-down direction becomes nearly symmetrical with respect to the surface 83 (84), and the optical waveguide 88
The guided mode of the fundamental wave at is close to symmetric. Therefore, when the fundamental wave is coupled to the optical waveguide 88 of the optical waveguide element 800, compared to the case where the fundamental wave is coupled to the optical waveguide 87 of the optical waveguide element 89, the guided mode of the fundamental wave and the second harmonic wave are guided. The overlap with the mode in the waveguide became large, and the generation efficiency of the second harmonic became large.

(Embodiment 5) FIG. 9 is a diagram for explaining a method of ensuring the alignment accuracy in the process of stacking the waveguides in the fabrication of the embedded optical waveguide according to the present invention. In FIG. 9, 91 and 92 are ZcutLiTaO ₃ single crystal substrates whose surfaces 93 and 94 are + c-planes. 95 and 96 are channel type optical waveguides produced by proton exchange. Reference numerals 97 and 98 denote spherical convex portions arranged at a constant distance, for example, 2 mm from the center line of the waveguide 95, and these are made of, for example, Nb ₂ O using a complex conical surface opening mask. _It was made by sputtering and integrating ₅ .

99 and 90 are arranged at a fixed distance from the center line of the waveguide 96, for example, 2 mm each, and when the surfaces 93 and 94 are bonded together, 97 and 99, 98 and 90 are formed. Each is a spherical concave portion that is arranged so as to fit together. Spherical recesses 99 and 9
0 was cut with a diamond cutting tool in the same manner as in the method of manufacturing a geodesic lens, and the radius of 99 and 90 was made substantially equal to the radius of 97 and 98, respectively.
Therefore, when the surface 93 and the surface 94 are opposed to each other and the optical waveguide 95 and the optical waveguide 96 are aligned so as to overlap with each other, when the surface 93 and the surface 94 are fixed to each other with an optical glue, for example, a resin that is cured by ultraviolet rays. , 97 and 99,
By aligning the surface 93 and the surface 94 so that 98 and 90 fit into each other, the optical waveguide 95 and the optical waveguide 96 could be accurately overlapped. In addition, 97 and 98
The longer the distance between and, and the longer the distance between 99 and 90, the better the accuracy of alignment in the process of overlapping the waveguides.

[0029]

According to the present invention, the optical waveguide is manufactured so that the refractive index distribution in the cross-sectional direction of the embedded optical waveguide is substantially symmetrical, so that it is extremely simple and highly efficient between optical devices. The optical coupling can be performed, which contributes to the improvement of the performance of the optical waveguide type device and the reduction of the man-hours for assembling the element. Furthermore, if the embedded optical waveguide according to the present invention is used for a waveguide type wavelength conversion element, highly efficient wavelength conversion becomes possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a conventional example of a basic three-dimensional optical waveguide structure.

FIG. 3 is an explanatory diagram showing a conventional example of a wavelength conversion element in which an optical waveguide is formed by proton exchange.

FIG. 4 is an explanatory view showing a conventional example of a basic optical waveguide and its refractive index distribution.

FIG. 5 is an explanatory diagram showing an outline of an optical system that couples light from an incident light source to an optical waveguide device.

FIG. 6 is an explanatory diagram showing a second embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a third embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a fifth embodiment of the present invention.

[Explanation of symbols]

 11 ... Substrate, 15 ... Optical waveguide, 16 ... Optical waveguide.

Claims (5)

[Claims] 1. An optical waveguide comprising an optical substrate and an optical waveguide portion formed on or in the optical substrate and having a higher refractive index than the substrate, wherein the optical waveguide comprises:
The optical substrate comprises a plurality of optical substrates on which a channel type optical waveguide portion higher than the substrate is formed on at least a part of the main surface of the optical substrate, and the main surfaces of the plurality of substrates are bonded to each other. An embedded optical waveguide characterized by the above. 2. The embedded structure according to claim 1, wherein the size of at least one region of the channel type optical waveguide formed on or in the plurality of optical substrates changes in the light propagation direction. Type optical waveguide. 3. The embedded optical waveguide according to claim 1, wherein at least one of the plurality of optical substrates is a nonlinear optical crystal substrate having spontaneous polarization. 4. The optical waveguide section according to claim 3, wherein the optical waveguide portion formed on or inside one main surface of the nonlinear optical substrate, or a part of the nonlinear optical substrate and the spontaneous polarization of the optical waveguide portion are periodically inverted. Non-linear optical element. 5. A male-type spherical convex portion arranged in parallel with the optical waveguide portion is formed on the first optical substrate according to claim 1, 2, 3 or 4. Embedded type in which a spherical concave portion arranged parallel to the optical waveguide portion is formed, and the concave and convex portions of both substrates are aligned to align the positions of two optical waveguide portions formed on or inside both substrates. Manufacturing method of optical waveguide.