JP2001330744A - Optical waveguide device, method for manufacturing the same, light source using the same and optical system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve coupling efficiency and to lower return light noise in direct coupling of a semiconductor laser and an optical waveguide device. SOLUTION: The end face of a substrate formed with the optical waveguide and the end face of the optical waveguide are formed at different angles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a waveguide type optical device to which a coherent light source is applied and which is used in optical information processing and optical applied measurement fields, and a method of manufacturing the same. Further, the present invention relates to a light source and an optical system using a waveguide device.

[0002]

2. Description of the Related Art In many fields such as optical communication, optical sensors, waveguide lasers, and optical wavelength conversion, waveguide type optical devices using optical waveguides have been actively studied. As a feature of the waveguide type optical device, a high guided power density can be realized over a long interaction length by confining light in the optical waveguide. Various functional devices can be realized on the waveguide. Further, when a semiconductor laser is used as a light source, the size of the device can be reduced, and the application to a wide range of fields can be realized by reducing the cost and the size of the device. When a semiconductor laser is used as a light source of a waveguide type optical device, a major problem is the coupling of the optical waveguide with the semiconductor laser. Specifically, the problem of coupling is roughly classified into a problem of the coupling itself and a problem caused by the semiconductor laser. As a problem of the joining, there is a problem of the joining method. There are two coupling methods: coupling via a condensing optical system and direct coupling between the laser and the waveguide.The direct coupling method is used to realize miniaturization, stabilization, and cost reduction by reducing the number of parts. It is becoming mainstream. On the other hand, there is also a problem caused by the characteristics of the semiconductor laser. The spectrum of the semiconductor laser light is greatly affected by the reflected return light. When the emitted light of the semiconductor laser is reflected outside and returns to the laser itself, it affects the resonance state of the semiconductor laser and increases the noise of the laser light. Further, the output light has an effect of being multi-mode or changing the oscillation wavelength, thereby deteriorating the coherence of the oscillation light.

For this reason, in a waveguide type optical device used for communication, an isolator is inserted between the optical waveguide and the semiconductor laser via a lens system to reduce return light from the optical waveguide to the semiconductor laser. I have. Further, in the second harmonic generation (SHG) element utilizing the nonlinear optical effect, a larger problem occurs. As the SHG element, a quasi phase matching (QPM) SHG element using a periodically poled structure is mainly used as a method for realizing high efficiency, but the wavelength tolerance is extremely narrow, about 0.1 nm, The output fluctuates greatly due to the wavelength fluctuation of the semiconductor laser. Therefore, if the oscillation wavelength of the semiconductor laser is affected by the return light, there is a problem that it is difficult to stabilize the output. In order to prevent this, a method has been proposed in which the incident end face of the optical waveguide is polished obliquely so that the optical axis of the waveguide type optical device and the optical axis of the condensing optical system are inclined. For example, when an optical fiber used for communication is coupled to a semiconductor laser, the end face 33 of the fiber 30 is obliquely polished as shown in FIG. Noise was reduced.

[0004]

When a semiconductor laser beam is coupled to a waveguide type optical device, high efficiency coupling between the semiconductor laser and the optical waveguide is enabled, and return light to the semiconductor laser is prevented. A method for realizing stable oscillation is provided.

In the conventional method using a condensing optical system and an isolator, the number of components increases. Furthermore, when the number of parts increases, there is a problem that it is difficult to reduce the cost because the number of adjustment locations increases during assembly. In addition, there is a problem that in order to insert a condensing optical system and an isolator, the size of the device, including the focal length of the optical system, must be increased. Further, there is a problem that mechanical stability is deteriorated as the device becomes larger.

In the method of obliquely polishing the end face of a waveguide type optical device to reduce the reflected light returning from the end face, the optical axis of the waveguide type optical device and the optical axis of the condensing optical system are inclined. There is a problem that the optical system becomes complicated in this respect.
In addition, there is a problem that downsizing is difficult in that a light collecting optical system is required, and mechanical stability is deteriorated.

Furthermore, if the incident side and the outgoing side of the end face of the substrate are formed at different angles, there is a problem that the variation in element shape between the elements is greatly increased and a problem occurs in a mass production process. In order to mass-produce an optical waveguide device, a large number of devices having the same shape are formed on the same substrate to simplify the production process, and the devices are cut into individual devices by cutting. In particular, in the case of an optical waveguide device, it is necessary to optically polish the input and output end faces of the optical waveguide. Thereby, the accuracy of the cutting process can be improved and simplified. However, it is difficult to introduce this step in the case of a device in which the input / output section end faces of the substrate have different angles. In other words, when a bar-shaped substrate having different incident and exit end faces with different angles is manufactured and cut, a device having different lengths is formed depending on the location of the formed element,
It becomes difficult to produce a device having a uniform shape.

The present invention solves the above-mentioned problems, and provides a waveguide type optical device capable of performing stable operation by reducing reflected light returning to a semiconductor laser even when a simple optical system is used. Furthermore, even in direct coupling with a semiconductor laser that can be miniaturized, the reflected return light to the semiconductor laser is reduced,
It is another object of the present invention to provide an optical waveguide device capable of realizing high coupling efficiency, and a light source and an optical system using the same.

[0009]

In order to solve the above-mentioned problems, an optical waveguide device according to the present invention comprises a substrate, an optical waveguide formed near the surface of the substrate, and end faces on the incident side and the exit side of the substrate. And an optical waveguide end face formed on an incident side and an exit side end face of the optical waveguide, wherein the substrate end face has an area larger than the optical waveguide end face, and Alternatively, at least one end face on the emission side, a normal line of the substrate end face and a normal line of the optical waveguide end face are not parallel to each other.

A light source according to the present invention comprises: a semiconductor laser;
The optical waveguide device.

Further, an optical system according to the present invention comprises at least the optical waveguide device and a condensing optical system for condensing light emitted from the optical waveguide device onto an object to be observed. It is characterized in that the object to be observed has a confocal relationship.

Also, a method of manufacturing an optical waveguide device according to the present invention includes a step of forming an optical waveguide, and a step of forming an end face of a substrate after the formation of the optical waveguide, wherein the end face of the substrate is edged by an image processing apparatus. The incident end face of the optical waveguide is formed with reference to the intersection of the detected and ion-exchange shielding mask and the end face of the substrate whose edge has been detected.

Further, a method of manufacturing an optical waveguide device according to the present invention includes a step of forming an optical waveguide and a step of forming an end face of an incident portion after the formation of the optical waveguide. Is detected as an edge, and the substrate end face of the optical waveguide is formed with reference to the intersection of the ion exchange shielding mask and the end face of the incident part where the edge is detected.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention proposes an optical waveguide having a new structure in order to stably and efficiently couple a semiconductor laser in a waveguide type optical device.

In a waveguide type optical device using a semiconductor laser as a light source, it is effective to directly couple the semiconductor laser and the optical waveguide in order to reduce the size. However, it has been clarified that a new problem exists in the waveguide type optical device in which the semiconductor laser and the optical waveguide are directly coupled.

The first problem is a problem of returning light to the semiconductor laser. In the case of direct coupling, since the end face of the waveguide type optical device and the end face of the semiconductor laser are adjacent to each other, the influence of the reflected return light from the incident end face to the semiconductor laser is extremely small. However, when the light reflected from the emission-side end face of the optical waveguide returns to the semiconductor laser, the oscillation spectrum of the semiconductor laser is greatly affected. In the case of direct coupling, it is necessary to reduce the reflected return light from the end face of the optical waveguide on the emission side.

The second problem occurs when a waveguide type optical device is used in a confocal optical system. As shown in FIG. 4, the confocal optical system is an optical system in which the light source 26 and the irradiation body 29 are focused together, and is an optical system in which light exists between two focal points. When the confocal points each have a reflectance, a resonator structure is formed between the confocal points. When a slight vibration or disturbance of the resonator occurs, the phase of light existing in the resonator shifts, so that the intensity of light emitted from the resonator and from the resonator fluctuates due to an interference effect. As an example of using a waveguide type optical device in a confocal optical system, a waveguide type optical device such as S
The case where the HG element is used in an optical disk will be described.

The second harmonic emitted from the SHG element is focused by a focusing optical system and focused on an optical disk.
Detects pits on the optical disk. In this case, the SHG element and the optical disk form a confocal optical system. The problem here is the reflected light of the SHG element. When there is light reflected from the output end face or the input end face of the SHG element,
A resonator is formed in the confocal optical system. Therefore, the vibration noise of the resonator is mixed in the signal for detecting the pit of the optical disk. That is, it has been found that the vibration of the optical disk causes a change in the length of the resonator, which causes a power change, thereby changing the intensity of the detected light and greatly increasing the signal noise. Even a reflection of only 0.1% became a large noise component with respect to the detection signal of the optical disk.

In order to solve the first and second problems, the reflected return light at the entrance end face and the exit end face of the optical waveguide is reduced to 0.0.
It is necessary to reduce it to 1% or less. However, it is difficult to achieve this value with a high yield using a normal antireflection film. On the other hand, there is a method in which the end face of the optical waveguide is formed obliquely to the traveling direction of the waveguide. When the incident part of the optical waveguide is formed obliquely to the traveling direction of the waveguide, there is a problem that the coupling efficiency of the direct coupling between the optical waveguide and the semiconductor laser is greatly reduced.

In order to solve this problem, the end face of the substrate on the incident side of the waveguide is formed perpendicular to the traveling direction of the optical waveguide.
Only the end face of the substrate on the emission side was formed inclined with respect to the traveling direction of the waveguide. However, when a plurality of waveguide-type elements are formed on the same substrate in order to enhance the mass production effect, and cut out after the end face is formed, a problem arises in that the lengths of the substrates are different. The use of a substrate having a different angle only on one end surface has a problem that it is difficult to form a plurality of devices having the same length from a single substrate.

The above problem has become a significant problem in a waveguide type optical wavelength conversion device. A typical example of an optical wavelength conversion element is a quasi-phase matching type (hereinafter referred to as QPM) which realizes highly efficient wavelength conversion by taking phase matching between a fundamental wave and a harmonic by using a periodic domain-inverted structure as a nonlinear grating. In an optical wavelength conversion element (hereinafter, referred to as an SHG element), the phase matching wavelength range in which wavelength conversion can be realized with high efficiency is as narrow as about 0.1 nm. Therefore, even if the oscillation wavelength of the semiconductor laser slightly fluctuates due to the return light from the waveguide, the output of the SHG element greatly fluctuates, and stable operation becomes difficult.

In order to solve the above problems, the point of the present invention is that, in the substrate on which the optical waveguide is formed, the substrate end face and the optical waveguide end face are formed at different angles. Another feature is that a configuration is adopted that facilitates direct coupling between the optical waveguide device and the semiconductor laser. In the following embodiments, each point will be described.

(Embodiment 1) Here, a light source using an optical waveguide device of the present invention will be described. The configuration of the optical waveguide device of the present invention will be described with reference to FIG. In FIG. 1, 1 is a LiNbO ₃ substrate, 2 is an optical waveguide, 3 is a periodically poled structure, 4 is an incident end face of the optical waveguide, 5 is an emission end face of the optical waveguide, 6 is an incident end face of the substrate, 7
Is an emission end face of the substrate, and 8 is a semiconductor laser.

An optical wavelength conversion device having a periodically poled structure having a nonlinear optical effect is taken as an example of an optical waveguide device. The light in the 800 nm wavelength band emitted from the semiconductor laser 8 is coupled to the optical waveguide 2 through the incident end face 4 of the optical waveguide, and is converted by the periodic polarization inversion structure 3 into light having a wavelength half that of the incident light. Are emitted from the emission end face 7 of the optical waveguide. The optical waveguide is formed by proton exchange and has a size of about 5 μm in width and about 2 μm in depth.

The semiconductor laser is an AlGaAs laser, and the coupling efficiency between the optical waveguide and the semiconductor laser increases as the distance between the end face of the optical waveguide and the emission end face of the semiconductor laser increases. In order to achieve a coupling efficiency of 50% or more, it is necessary to make the distance close to 3 μm or less.
% Or less is required to achieve 2% or less. Since the efficiency of the optical wavelength conversion element is proportional to the square of the coupling efficiency with the semiconductor laser, high-efficiency coupling is indispensable.

Further, in coupling the semiconductor laser and the optical waveguide, reduction of return light to the semiconductor laser is a major problem. When the light emitted from the semiconductor laser returns to the semiconductor laser, the noise of the semiconductor laser greatly increases. In order to prevent this, a method of forming the emission end face of the optical waveguide at an angle to the traveling direction of the optical waveguide has been conventionally used.

When the angle formed between the normal to the exit end face of the waveguide and the traveling direction of the optical waveguide is 3 ° or more, the return light is approximately 1/1.
In the case of a communication device or the like, the noise needs to be further reduced. Return light noise is reduced depending on the angle.

Conventionally, the end face of the optical waveguide is formed on the end face of the substrate. Therefore, the normal to the end face of the substrate and the normal to the end face of the optical waveguide were in the same plane, and were therefore parallel to each other. However, in the case of direct coupling with a semiconductor laser, the method of forming the emission part of the optical waveguide obliquely is as follows: (1) Both the input part and the emission part of the optical waveguide are formed obliquely. (2) The output part of the optical waveguide is formed obliquely, and the input part is formed perpendicular to the waveguide. However, in any of the methods, the oblique exit end face becomes a serious problem.

In the method (1), the formation of a waveguide element is easy. The method of (1) is adopted in the case of ordinary lens coupling or in the case of coupling between an optical fiber and a waveguide device.
However, this method has a problem that the coupling efficiency is extremely reduced in direct coupling with the semiconductor laser.

For example, when the end face of the optical waveguide formed on the LiNbO ₃ substrate is inclined at about 4 ° with respect to the optical waveguide, the light emitted from the semiconductor laser is coupled with the optical waveguide in a state having the highest coupling with the optical waveguide. When the semiconductor laser is brought closer, the angle between the end face of the semiconductor laser and the end face of the optical waveguide is about 8 ° according to Snell's law.

On the other hand, the semiconductor laser chip has a width of 200 μm.
When the distance is about m, the distance between the semiconductor laser and the end face of the optical waveguide is at least 12 μm. For this reason, the coupling efficiency of the direct coupling is extremely reduced to about 10%. On the other hand, the distance between the optical waveguide and the semiconductor laser can be reduced to 1 μm or less by bringing the end face of the optical waveguide and the semiconductor laser close to each other, but the coupling efficiency is reduced to about half due to the angle with the optical waveguide. Will drop.

On the other hand, the method (2) allows the semiconductor laser and the optical waveguide to be coupled with high efficiency because the incident portion is vertical. In addition, since return light from the emission portion of the optical waveguide to the semiconductor laser can be prevented, stable oscillation of the semiconductor laser can be achieved. However, if both end faces of the substrate have different angles, it becomes an obstacle to mass production of device fabrication.

Normally, when fabricating a waveguide type device, after performing a process process on a wafer, the device is cut into a chip size by a dicing saw. Since the chip is cut out in the same width and length direction as the substrate, the side surfaces of the substrate are formed in the same plane. Therefore, in order to cut out chips of the same shape, both end faces of the element must be parallel. A waveguide device requires a certain length in the waveguide direction. If the end faces of the substrate are not parallel and have an angle, the element length differs depending on the location, so that an element having the same shape cannot be cut out.

Further, in the waveguide type device, it is necessary to mirror-finish the end face of the waveguide to reduce the coupling loss due to the disturbance of the wavefront at the time of inputting and outputting light. In order to perform mirror finishing, a polishing step of the waveguide end face by polishing is required. To perform the polishing with high accuracy, a certain processing area is required. In addition, there is a problem that the peripheral portion of the processing surface cannot be used because the polishing process is likely to be disturbed in the peripheral portion of the processing area, and there is a problem that the peripheral portion of the processing surface cannot be used. Is adopted.

In the polishing process, it is difficult to process a waveguide device having non-parallel end faces. When both end faces of a substrate formed by a series of waveguide devices are polished, the element length of the formed waveguide device differs depending on the location. After cutting out devices with different angles, polishing both end faces to different angles complicates the process and at the same time has a problem in reducing the area of the end faces, so the element area increases and the material cost increases. . In addition, there is a problem that the miniaturization of the device is hindered.

In order to solve these problems, a structure shown in FIG. 1 is proposed. That is, the end face of the substrate and the end face of the optical waveguide are formed at different angles. Both end faces of the substrate are formed parallel to each other so that the substrate can be easily cut out, and end faces of the waveguide are formed at different angles. Considering the NA of the optical waveguide, the end face of the waveguide is formed larger than the cross section of the optical waveguide so that the outgoing light is not affected at the exit surface and the incident light is not affected at the incident portion. First, the emission unit will be described. The merits of forming the normal line between the end face of the optical waveguide and the end face of the substrate at the emission part are the following three points.

The return light to the semiconductor laser can be reduced.

By reducing the distance between the semiconductor laser and the optical waveguide, the coupling efficiency can be improved.

By forming the both end surfaces of the substrate so as to be parallel, it is easy to cut out the substrate, to reduce the size of the element,
The manufacturing process can be simplified and cost reduction can be achieved by mass production. There is a sufficient merit even if it is formed only in the emission part.

Next, a description will be given of the merits of the case where the light emitting device is formed at the incident portion. The merit of forming the substrate end face and the waveguide end face at different angles in the incident portion has two advantages in addition to the fact that the substrate end face can be formed in parallel. First
Is that direct coupling with a semiconductor laser is facilitated.

FIG. 2 shows how the semiconductor laser and the optical waveguide are coupled. The end face 4 of the optical waveguide 2, the end face 6 of the substrate, and the semiconductor laser 8 are fixed close to each other. With respect to the traveling direction of the optical waveguide 2, the normal to the optical waveguide end face 4 and the substrate end face 6
Are formed at different angles.

The semiconductor laser is adjusted so that the maximum coupling efficiency can be obtained by moving the semiconductor laser along the substrate end surface after contacting the substrate end surface. If the angle of the end face of the substrate is formed at an optimum angle, it is not necessary to adjust the inclination of the semiconductor laser, and the adjustment process can be simplified.

Another advantage is that the destruction of the semiconductor laser during direct coupling of the semiconductor laser is extremely reduced. Since the end surface of the optical waveguide is slightly depressed with respect to the substrate end surface, the end surface of the light emitting portion of the semiconductor laser does not contact the substrate. Therefore, the end face of the semiconductor laser can be brought close to the end face of the optical waveguide without being destroyed.

Next, the optimal relationship between the end face of the substrate, the end face of the optical waveguide, and the traveling direction of the waveguide at the incident portion will be described.
In order to obtain the maximum coupling efficiency with the optical waveguide when the semiconductor laser is pressed perpendicularly to the end face of the optical waveguide device, there is an appropriate relationship between the end face of the optical waveguide, the end face of the substrate, and the optical waveguide. The light traveling direction is refracted at an interface having a different refractive index according to Snell's law on the substrate end face. Therefore, in order to efficiently couple outgoing light from the semiconductor laser to the optical waveguide, a specific relationship between the angle of each surface and the refractive index must be satisfied. This relationship will be described with reference to FIG.

The effective refractive index of the optical waveguide for the light emitted from the semiconductor laser is N1, the acute angle between the normal to the substrate end face 6 and the normal to the optical waveguide end face 4 is θ3, and the normal to the substrate end face 4 and the light guide When an acute angle between the propagation direction of the waveguide 2 and θ2 is an acute angle between a normal line of the optical waveguide end face 4 and the propagation direction of the optical waveguide 2, θ1 + θ2 = θ3 (1) sin (θ3) = N1 * sin (θ1) (Equation 2) is satisfied.

However, this relationship is for the case where air is present between the semiconductor laser and the end face of the waveguide. For example, when the space is filled with an adhesive having a refractive index of N2, the relationship of equation 2 is N2 * sin. (Θ3) = N1 * sin (θ1). When the space between the semiconductor laser and the waveguide device is filled with the filler, it is less susceptible to disturbance and the influence of dust and the like can be removed. Also, by selecting a material having an appropriate refractive index, an antireflection effect can be obtained, which is effective.

The area of the end face of the optical waveguide is formed smaller than the end face of the substrate. The reason is that when the semiconductor laser is fixed by direct bonding, the laser is pressed against the end face of the substrate to take a reference. Here, the reference plane is the end face of the substrate. Since the end face of the optical waveguide is deeper than the end face of the substrate, the position of the laser and the waveguide can be minimized without the active layer of the semiconductor laser hitting the substrate.

To use the reference plane, if the area of the end face of the optical waveguide is too large, the laser falls into the concave portion of the end face of the optical waveguide. It is desirable that the size of the end face of the optical waveguide be sufficiently larger than the area of the actual end face of the optical waveguide and smaller than the area of the end face of the substrate of the semiconductor laser. At least, when the semiconductor laser is arranged at an appropriate position, it is necessary that a substrate end face portion of the waveguide serving as a reference plane of the semiconductor laser exists.

Further, the end face of the waveguide must be formed slightly larger than the actual end face of the waveguide (the cross section of the actual optical waveguide). The reason is that the light emitted from the waveguide becomes divergent light and spreads. If the area of the waveguide end face is made equal to the area of the waveguide cross section, the spread beam may hit the substrate when emitted from the recessed optical waveguide end face.

When hitting the substrate, the wavefront is disturbed, so that there is a problem that the light condensing characteristic is deteriorated. The same applies to the incident part. In order to prevent the incident light from being kicked by the substrate, the end face of the waveguide needs to be larger than the actual cross section of the waveguide. Even when a waveguide end face is actually formed, it is preferable to form a slightly larger end face than to form a waveguide end face having the same shape as the waveguide section.

By forming the end face of the waveguide at the inclined portion at the incident portion, optical system noise when the waveguide device is used in a confocal optical system can be greatly reduced. When a waveguide device is used in a confocal optical system, the reflected light from the end face of the waveguide causes an interference effect in the optical system and becomes a noise component as described above, but the end face of the waveguide is formed obliquely. Thus, the light reflected from the end face can be greatly reduced. The confocal optical system is an optical system that condenses light and uses it by hitting an object, and is an optical system generally used, such as an optical system that utilizes the light condensing characteristics, a length measuring device, and an optical disk. .

The substrate preferably has a refractive index of 2 or more. When the refractive index is 2 or more,
The inclination of the beam entering and exiting the waveguide is more than twice as large as the inclination of the end face of the waveguide. The greater the inclination of the beam, the greater the attenuation of the return light. It is preferable to use a material having a large refractive index because the return light can be greatly attenuated by a slight inclination of the waveguide end face.

The inclination of the waveguide end face, that is, the angle θ1 between the waveguide propagation direction and the waveguide end face, is preferably 2 ° or more. When the angle is 2 ° or more, the return light can be reduced to several tenths. More preferably, the angle is about 5 ° to 10 °. In order to completely remove the return light noise of the semiconductor laser, the return light amount needs to be -40 dB or less. This value can be realized when the antireflection coat and the polishing angle are 5 ° or more. However, forming an angle of 10 ° or more requires a large inclination of the waveguide, and increases the area of the substrate. This is because problems such as distortion of the output beam occur.

Further, when the normal line of the substrate end face and the normal line of the waveguide end face are not parallel to the waveguide traveling direction, the direct coupling with the semiconductor laser is facilitated as shown in FIG. In addition, return light noise can be reduced, and at the same time, light noise can be significantly reduced even when used in a confocal optical system. Furthermore, by making the structures of the incident part and the outgoing part equal, it becomes possible to match the directions of the incident light and the outgoing light in the same direction. As a result, when an optical system is formed using an optical waveguide device, angle adjustment is facilitated.

Forming the end face of the substrate and the end face of the waveguide at different angles, that is, by different processes eliminates the need to use an optical polishing process for device formation, thereby simplifying the process and improving mass productivity. The end face of the waveguide used for inputting and outputting light has a size of at most about 10 μm square. If an optical surface is formed over this area, input and output of light can be performed efficiently. However, actually, the entire surface of the end face of the substrate is formed by optical polishing, which requires a complicated and time-consuming optical polishing process. However, the configuration of the present invention has an advantage that a device can be formed by mirror-finishing only the waveguide end face.

Next, a method for manufacturing the waveguide device will be described. In order to form the end face of the optical waveguide and the end face of the substrate at different angles, it is difficult to form the end face by ordinary edge polishing. As a manufacturing method, there are a method using grinding using a dicing saw, a method using plasma etching used in a semiconductor process, a laser processing, and the like. The method of forming by a grinding process is a method of forming a cut surface by a kind of grinding process of a mechanical process. Since the end face of the waveguide has a thickness of at most several μm and a distance of about 10 μm, the mirror-finished surface is easy because the cut surface is small. After each surface of the optical waveguide is formed by grinding, the substrate end surface is cut and formed. It can be machined with high precision and has excellent mass productivity.

In grinding, attention should be paid to improving the mirror surface of the processed surface. The end face formation by the grinding process has a problem that the mirror finish is deteriorated because a slight processing flaw is left. This disturbs the wavefront of the incoming and outgoing light, which may cause problems such as deterioration of the coupling efficiency and deterioration of the outgoing light wavefront. As a method for preventing this, chemical etching is used in combination.

The first method is a method of performing grinding while using an abrasive having a melting property of the substrate at the time of grinding.
Is a method of slightly dissolving the substrate surface with a fusible etching solution for the substrate after the grinding process, whereby the mirror surface of the ground surface is greatly improved.

Edge processing utilizing dry etching is also possible. A method of forming the end face of a semiconductor laser or the like by dry etching has been reported, and it is easy to form the end face of the waveguide by dry etching. Since the etching depth for forming the waveguide end face is about several μm, the end face formation by dry etching is also easy. Since the entire wafer can be patterned and etched at once by using the photolithography method, mass productivity is excellent.

End face processing by laser is also possible. As the laser, a laser having a wavelength in the absorption wavelength range of the substrate is used.
In particular, an excimer laser has a short wavelength and a high energy density of light, and thus is suitable for mirror finishing. For example, LiNbO
_When processing _three substrates, the absorption wavelength of LiNbO ₃ : 0.1.
An ArF laser having a wavelength shorter than 3 μm is used. Wavelength 0.2
When a laser of 5 μm was used, the processed surface was slightly uneven, and it was difficult to process a mirror surface. This is because laser processing is performed mainly on thermal destruction due to laser absorption, and the mirror surface of the end face is degraded due to reattachment of the substrate melted by the laser. On the other hand, ArF has an oscillation wavelength of 0.2 μm or less, and can chemically decompose and remove a LiNbO ₃ substrate. Since the decomposed LiNbO ₃ does not adhere again to the substrate, the etched surface becomes a mirror surface, and light can be input and output with high efficiency. In addition, since the wavefront of the light emitted from the waveguide device is hardly disturbed, light with high coherence can be used, so that emitted light having excellent light-collecting characteristics can be realized.

(Embodiment 2) Here, a method for forming the position of the end face of the optical waveguide with high precision will be described. FIG.
As is clear from the configuration of the light source shown in FIG. 1, the positional relationship between the optical waveguide end face, the substrate end face, and the optical waveguide needs to be formed with high precision. Specifically, the width of the optical waveguide is on the order of several μm, and the positional relationship between the semiconductor laser and the optical waveguide is 0.1 μm.
Unless the alignment is accurate with the order of m, high-efficiency coupling cannot be realized. Therefore, the positional relationship between the optical waveguide end face and the substrate end face and the optical waveguide must be formed with an accuracy of 1 μm or less. In the present embodiment, a method for forming a waveguide end face and a substrate end face with high accuracy using an optical waveguide mask will be described.

A method of manufacturing an optical waveguide using ion exchange will be described as a method of manufacturing an optical waveguide. When the optical waveguide is formed by ion exchange, the pattern of the optical waveguide is selectively exchanged using an ion shielding mask such as a metal mask. Usually, the mask pattern is removed after ion exchange, but a method for forming an end face using this mask pattern is proposed.

For example, after ion exchange, a substrate end face is first formed. To form the end face of the substrate, the substrate is cut by a dicing saw to form an end face. The surface accuracy of the end face of the formed substrate must be finished to a surface roughness of 1 μm or less because it is necessary to consider the alignment with the semiconductor laser at the incident portion. The angle between the end face of the substrate and the optical waveguide can be accurately formed by the mask pattern. Next, the end face of the incident part of the optical waveguide is formed. By recognizing the intersection between the substrate end face and the waveguide by image processing, the alignment can be performed with high accuracy of about 0.1 μm. An optical waveguide end face is formed based on this point. Thereafter, the device is formed by removing the mask.

There is also a method of forming a substrate end face after forming a waveguide end face. After ion exchange, an end face of the optical waveguide is formed based on the ion exchange mask pattern. The formation is performed by the above-described dry etching, dicing, laser processing, or the like. Since the wafer can be processed as it is, the process is facilitated and mass production is possible. Thereafter, an image of the intersection between the optical waveguide and the end face of the waveguide is detected, and the end face of the substrate is formed based on this point. Since the substrate end face requires cutting of the substrate, it is formed by dicing. When this method is used, there is an advantage that the alignment when forming the waveguide end face for the first time can be performed with relatively low accuracy.

In the case where mirror polishing is performed near the edge of the substrate, chipping and cracking of the substrate frequently occur near the edge, causing a problem of lowering the production yield of the element.
This problem can be solved by forming a substrate end surface (not a mirror finish) after forming the waveguide end surface. The waveguide, the substrate end face, and the waveguide end face can be formed with high accuracy by performing high-precision alignment by image detection when forming the substrate end face. When a metal mask is used as an ion exchange mask,
An ion shielding effect can be obtained at about 0 nm. This does not hinder the formation of the waveguide end face and the substrate end face.

The metal mask is used for detecting the edge image.
Since high contrast can be obtained, there are also advantages such as easy high-accuracy image detection. By using the optical waveguide mask for image detection, high-precision positioning can be realized because alignment can be performed with the mask manufacturing accuracy.

As a method of forming an optical waveguide, it is also effective to use an optical waveguide having a protruding stripe structure on the substrate surface such as a loading or ridge waveguide. These waveguides are
After the formation of the waveguide, the position of the waveguide can be accurately detected. Since the waveguide end face and the substrate end face can be formed with high accuracy based on the position of the waveguide, there is an advantage that the optical waveguide end face portion can be easily detected by image detection.

(Embodiment 3) Here, an optical system using the light source of the present invention will be described. FIG. 3 illustrates an optical system for reading information from an optical disk. In FIG. 3, reference numeral 20 denotes FIG. 1 described in the first embodiment.
, 21 is a collimating lens, 22 is a detector, 23
Denotes a beam splitter, 24 denotes a condensing optical system, and 25 denotes an optical disk. The light emitted from the semiconductor laser 8 is incident on the light incident end 4.
And enters the waveguide 2 and is wavelength-converted by the domain-inverted structure 3. The wavelength-converted light is emitted from the emission end 5, collimated by the collimating optical system 21, and then focused on the surface of the optical disk 25 by the focusing optical system 24.
The light reflected here is collimated by the condensing optical system 24, then reflected by the beam splitter 23, and
2 and the information written on the surface of the optical disk 25 can be read.

The advantages of the optical system of the present invention are as follows.
Another problem is that there is no return light from the optical device and the optical system to the semiconductor laser. Conventional optical disks use a semiconductor laser as a direct light source. For this reason, there is a problem that returning light to the semiconductor laser significantly increases return light noise of the semiconductor laser. For this reason, a semiconductor laser requires a high frequency superimposing device, but an increase in light source noise due to high frequency superimposition cannot be avoided.

In the structure of the present invention, the light emitted from the semiconductor laser is partially reflected at the input end face and the output end face of the waveguide, but since the waveguide end face has an angle with respect to the waveguide, Light was not returned to the semiconductor laser, and light source characteristics with low noise were realized. Further, since the optical wavelength conversion element is used after converting the wavelength of a fundamental wave into a harmonic, the optical system is designed for the harmonic.

Accordingly, even when a fundamental wave that is not converted is partially emitted from the optical waveguide, the emitted light does not return to the semiconductor laser because it is not completely condensed and collimated by the collimating and condensing optical system. Therefore, the semiconductor laser can oscillate with low noise without being affected by the return light.

On the other hand, the configuration is also strong against interference noise in the confocal optical system. Optical disk 25
The optical system that converges light on the surface of the board constitutes a confocal optical system between the converging point and the exit or entrance of the optical waveguide. For this reason, if reflected light exists at each of the condensing points, a resonator is formed in the confocal optical system, and the intensity of light changes due to the interference effect, thereby causing noise.

However, in this configuration, since the exit end face of the optical waveguide is formed obliquely with respect to the optical axis, there is almost no reflected return light into the confocal optical system. Further, since the incident end face of the optical waveguide is also formed obliquely with respect to the optical waveguide, there is almost no reflected light to the confocal optical system.

Therefore, a low-noise optical system can be constructed.
Further, by forming the end face of the substrate and the end face of the optical waveguide at different angles, it is possible to make the light exit direction perpendicular to the end face of the substrate while preventing the end face reflection of the optical waveguide. Therefore, there is an advantage that the optical axis of the light source can be easily set with reference to the end face of the substrate. The formation of the grating structure on the end face of the substrate also has the advantage that the optical axis of the light source can be easily adjusted while observing the reflected return light from the substrate. Such characteristics can be realized because of an optical system using a waveguide device in which the waveguide end face and the substrate end face are formed at different angles.

[0075]

As described above, by forming the end face of the substrate and the end face of the waveguide at an angle, direct coupling between the semiconductor laser and the optical waveguide is facilitated, and the practical effect is large.

Further, by using a light source in which the optical waveguide device and the semiconductor laser are combined, it is possible to greatly reduce the noise of the optical system, to form an optical system with low noise, and to obtain a large practical effect. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a light source formed by an optical waveguide device of the present invention.

FIG. 2 is a diagram showing a state of direct coupling between a semiconductor laser and an optical waveguide;

FIG. 3 is a configuration diagram of an optical system according to the present invention.

FIG. 4 is a diagram showing a confocal optical system.

FIG. 5 is a configuration diagram of a conventional optical waveguide device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 LiNbO ₃ substrate 2 optical waveguide 3 periodic polarization reversal structure 4 incident end face of optical waveguide 5 emission end face of optical waveguide 6 incidence end face of substrate 7 emission end face of substrate 8 semiconductor laser 21 collimating lens 22 detector 23 beam splitter 24 condensing Optical system 25 Optical disk 26 Light source 27 Lens 28 Lens 29 Irradiator 30 Fiber 31 Core 32 Semiconductor laser 33 End face

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 5/022 G02B 6/12 BM (72) Inventor Yasuo Kitaoka 1006 Kazuma Kazuma, Kadoma, Osaka Matsushita Electric Within Sangyo Co., Ltd. (72) Inventor Kenichi Kasumi 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.F-term (reference) GA10 HA20 5D119 AA12 AA20 BA01 EC27 FA05 JA29 JA36 NA05 5F073 AB21 AB23 BA01 BA09 CA05 EA26 FA30

Claims (20)

[Claims] A substrate; an optical waveguide formed near a surface of the substrate; a substrate end surface formed on an incident side and an exit side end face of the substrate; and an incident side and an exit side end face of the optical waveguide. An end face of the optical waveguide, the end face of the substrate having a larger area than the end face of the optical waveguide, and at least one of the end faces on the incident side or the outgoing side, An optical waveguide device in which normals of optical waveguide end faces are not parallel to each other. 2. The optical waveguide according to claim 1, wherein the direction of travel of the optical waveguide, the normal of the substrate end face, and the normal of the optical waveguide end face are not parallel to each other on at least one of the incident side and the exit side of the substrate. An optical waveguide device according to any of the preceding claims. 3. The optical waveguide device according to claim 1, wherein an incident end face of the substrate and an exit end face of the substrate are parallel to each other. 4. The optical waveguide device according to claim 1, wherein an end face of the incident part and an end face of the emission part of the optical waveguide are parallel to each other. 5. An effective refractive index N1 with respect to guided light of the optical waveguide, and a normal line of the substrate end surface and a normal line of the optical waveguide end surface, on at least one of the incident side and the exit side of the substrate. The acute angle θ3, the acute angle θ2 between the normal to the end face of the substrate and the propagation direction of the optical waveguide, and the acute angle θ1 between the normal to the end face of the optical waveguide and the propagation direction of the optical waveguide are θ1 + θ2 = θ3 sin (θ3) = N1 * The optical waveguide device according to claim 1, wherein a relationship of sin (θ1) is satisfied. 6. The optical waveguide device according to claim 1, wherein an angle θ2 between a propagation direction of the optical waveguide and a normal to the end face of the optical waveguide has a value of 2 ° to 10 °. 7. The optical waveguide device according to claim 1, wherein the refractive index of said optical waveguide has a value of 2 or more. 8. The optical waveguide device according to claim 1, wherein a normal to the end face of the substrate and a normal to the end face of the optical waveguide are parallel to the surface of the substrate. 9. An optical waveguide device comprising: a substrate made of a nonlinear optical crystal; a periodically poled structure formed on the substrate; and the optical waveguide according to claim 1. Description: 10. A light source comprising: a semiconductor laser; and the optical waveguide device according to claim 1. 11. The semiconductor laser, wherein the semiconductor laser is directly bonded to the optical wavelength conversion element, and at least one of a width and a depth of the end face of the incident portion is smaller than a width or a thickness of a substrate of the semiconductor laser. Item 10. The light source according to item 10. 12. The optical waveguide device according to claim 1, further comprising: a light-condensing optical system for converging light emitted from said optical waveguide device onto an object to be observed. An optical system, wherein the optical waveguide device and the object to be observed have a confocal relationship. 13. The optical system according to claim 12, wherein said observed object is an optical disk. 14. An optical waveguide comprising: a step of forming an optical waveguide; and a step of forming an end face of the substrate after the formation of the optical waveguide, wherein an edge of the end face of the substrate is detected by an image processing device, and the ion exchange shielding mask and the edge are detected. A method of manufacturing an optical waveguide device, wherein an incident end face of an optical waveguide is formed based on a detected intersection of a substrate end face. 15. An image processing apparatus comprising: a step of forming an optical waveguide; and a step of forming an incident facet after the formation of the optical waveguide, wherein an edge of the incident facet is detected by an image processing apparatus. A method for manufacturing an optical waveguide device, wherein an end face of a substrate of an optical waveguide is formed with reference to an intersection of an end face of an incident portion where the edge is detected. 16. The step of forming the optical waveguide includes: a step of forming an ion exchange shielding mask on a substrate; and a step of performing ion exchange using the shielding mask and forming an ion exchange waveguide in a non-shielding portion. 2. The method according to claim 1, wherein
17. The method for manufacturing an optical waveguide device according to 5 or 16. 17. The method of manufacturing an optical waveguide device according to claim 15, wherein the step of forming the optical waveguide includes the step of forming a projection on the substrate. 18. The method according to claim 18, wherein at least one of the step of forming the end face of the optical waveguide and the step of forming the end face of the substrate includes:
16. The method for manufacturing an optical waveguide device according to claim 14, wherein grinding is performed. 19. The method of manufacturing an optical waveguide device according to claim 14, wherein the method of forming the optical waveguide end face uses an etching process. 20. The method of manufacturing an optical waveguide device according to claim 14, wherein the method of forming the end face of the optical waveguide uses laser processing using a laser having a wavelength of 200 nm or less.