JPH0375609A - Waveguide type photodetecting element and production thereof - Google Patents

Abstract

PURPOSE:To reduce the number of stages and to provide a cost reduction by adopting the constitution having microreflecting pats formed in the waveguide in correspondence to the spacings between the adjacent photodetectors of plural photodetectors. CONSTITUTION:This element has the waveguide 1, a waveguide reflecting optical system 100 formed as the end face of the waveguide 1, the plural photodetectors 2a to 2d provided in the waveguide 1 or in proximity to the waveguide 1 and the microreflecting parts 4ab, 4cd formed in the waveguide 1 in correspondence to the spacings between the adjacent photodetectors. Guided light is converged not by refraction but by reflection in this case and, therefore, the function of the waveguide reflecting optical system 100 does not change at all even if the optical wavelength changes. Since the waveguide reflecting optical system 100 is formed as the end face of the waveguide layer, the production thereof is easy. The decreased number of stages, the improved accuracy and the decreased fluctuations at time of mass production are obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveguide type photodetector element that is most suitable for constructing an optical integrated pickup, an optical spectrum analyzer, etc., and a method for manufacturing the same.

[Conventional technology]

2. Description of the Related Art A waveguide type photodetecting element has been proposed, which confines light in a waveguide and guides the guided light, and condenses the guided light by refracting or diffracting it using a waveguide optical system. The use of such a waveguide-type photodetector allows the optical system to be made smaller and lighter. .

○QE85-72. As seen in P2O-46 (1985) J, etc., application to optical integrated pickups for optical disks, etc. is expected.

Incidentally, in the optical integrated pickup described above, a waveguide layer is laminated on a buffer layer of a thermal oxide film formed on the surface of a silicon (S, t) substrate to form a slab-type leading waveguide, and a light beam is incident on the waveguide by a light beam irradiation means. , the light reflected by the optical disk is guided into the optical waveguide by a waveguide optical system such as a condensing grating coupler, and is focused near the light receiving surface of a plurality of photodetectors such as photodiodes formed on the substrate. It is designed to obtain recording information signals and servo signals for tracking and focusing.

In addition, the waveguide optical system may include a prism coupler or a normal grating coupler and a waveguide lens (mode index lens, Luneburg lens, geodesic lens, etc.) instead of the condensing grating coupler.
A method using a combination with a grating lens, etc.) is known.

However, when using the above-mentioned waveguide lens as a waveguide optical system, various problems such as those described below occur.

For example, among the waveguide lenses mentioned above, mode index lenses and Luneburg lenses require extremely high precision in refractive index control during their manufacturing process, but high precision refractive index control is not possible with current technology. It is difficult and difficult to put into practical use at this stage in terms of mass production. Additionally, a geodesic lens is a waveguide lens made by adding a depression to a waveguide, and since the shape of the depression is aspherical, it is difficult to process and requires precision cutting followed by a polishing process. For this reason, mass production is difficult, and cost reduction is also difficult.

Although grating lenses are relatively easy to manufacture and can be realized at low cost, their lens action depends on the wavelength of light, and when the wavelength of light changes, the focal length changes. However, as is well known, semiconductor lasers commonly used as light sources for waveguide optical elements have the property of wavelength shifting due to temperature changes. Therefore, when using grating lenses, extremely high precision It is necessary to perform temperature control or to use a DFB semiconductor laser without wavelength shift 1-, which poses the problem of increasing the size and cost of the device.

Therefore, in order to solve the above-mentioned problem, a waveguide layer provided on the substrate and a waveguide optical system for condensing the guided light guided through the waveguide layer are provided. The present inventors have proposed a waveguide type photodetecting element characterized in that the wave optical system is a waveguide reflective optical system formed as the end face of the waveguide layer (Japanese Patent Application No. 1-10360). This waveguide-type photodetector is extremely useful as a waveguide-type photodetector because it can be easily realized at low cost, and an ordinary semiconductor laser can be used as a light source.

[Problem to be solved by the invention]

By the way, the problems related to the waveguide optical system can be solved by adopting the above-mentioned waveguide reflective optical system, but one problem that makes it difficult to put the waveguide type photodetector into practical use is that there is a portion between the photodetectors that cannot receive light. There is a problem in that this causes a decrease in detection sensitivity and a detection error.

That is, in the above-mentioned optical integrated pickup, etc., due to the formation of a plurality of photodetectors, it is inevitable that a non-photodetectable area of several μm or more will occur at the boundary between the photodetectors. Therefore, when used as an optical pickup for an optical disk, a problem arises in that the sensitivity of the focus error signal is particularly reduced or becomes insensitive, which hinders its practical use.

The present invention has been made in view of the above circumstances, and provides a waveguide type photodetector element that can simultaneously solve the problems related to the waveguide optical system and the problem of the generation of dead areas between the photodetectors, and The purpose is to provide a manufacturing method thereof.

[Means to solve the problem]

In order to achieve the above object, the waveguide type photodetecting element according to the present invention includes a waveguide, a waveguide reflection optical system formed as an end face of a waveguide layer of the waveguide, and a waveguide purse string or a waveguide reflective optical system formed as an end face of a waveguide layer of the waveguide. a plurality of photodetectors provided close to the wavepath;
The waveguide is characterized by having a minute reflection section formed in the waveguide corresponding to between adjacent photodetectors.

Further, the method for manufacturing the waveguide type photodetecting element is characterized in that the waveguide reflection optical system and the minute reflection section are simultaneously formed in the same process.

[For production]

In the waveguide type photodetecting element according to the present invention, the waveguide optical system is a waveguide reflective optical system formed as the end face of the waveguide layer as described above, and the waveguide light guided through the waveguide layer is guided by the waveguide optical system. It is reflected by the wave path reflection optical system and focused on one point.

In this way, the waveguide light is focused by reflection rather than refraction, so even if the optical wavelength changes, the function of the waveguide reflective optical system does not change at all. Further, since the waveguide reflective optical system is formed as an end face of the waveguide layer, its fabrication is also easy.

Further, in the waveguide type photodetecting element according to the present invention, since the structure has a minute reflection section formed in the waveguide corresponding to between adjacent photodetectors of a plurality of photodetectors, the minute reflection section acts to reflect the guided light reaching the non-photodetectable portion between the photodetectors toward the light-receiving surface of the photodetector, and effectively eliminates the non-photodetectable portion.

In addition, in the waveguide-type photodetecting element having the above configuration, if the manufacturing process for forming the waveguide reflective optical system and the manufacturing process for forming the minute reflective part are performed separately, similar steps will be repeated. When using methods such as photolithography, it is necessary to align the mask between the steps, and the accuracy of the detection system decreases and varies due to alignment errors. However, in the method for manufacturing a waveguide type photodetecting element according to the present invention, the waveguide reflection optical system and the minute reflection section are simultaneously formed in the same process, which reduces the number of steps. This makes it possible to reduce the amount of noise, improve accuracy, and reduce variation during mass production.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

First, a method for manufacturing a waveguide type photodetecting element according to the present invention will be briefly explained.

The structure and manufacturing method of the waveguide reflection optical system of the waveguide type photodetecting element according to the present invention are disclosed in the earlier application (Japanese Patent Application No. 1-10360).
For example,
Photolithographic techniques are used. in this case,
Basically, a waveguide reflective optical system is formed as an end face of a waveguide layer through processes such as etching or diffusion according to the mask shape.

On the other hand, the minute reflection section formed between adjacent photodetectors can be realized with the same cross-sectional structure as the waveguide reflection optical system described above. This means that the waveguide reflective optical system and the minute reflective section can be formed simultaneously in the same manufacturing process.

More specifically, this means that it is sufficient to simply add the pattern of the minute reflective portions 4ab to a photomask having a pattern for forming the waveguide reflective optical system.

Incidentally, the planar shapes of the two types of reflection parts, the waveguide reflection optical system and the minute reflection part, can be arbitrarily determined independently of each other, as described in the earlier application. Any combination of total reflection and normal reflection is possible.

At this time, when laminating metal reflective layers, etc., it may be necessary to make the cross-sectional shapes of the two different (i.e., the presence or absence of a metal reflective layer). Since the mask pattern can be made to meet the requirements of both parties, there is no increase in the overall number of steps.

Hereinafter, description will be made based on specific examples.

FIG. 1 is a plan configuration diagram schematically showing the main parts of a waveguide-type photodetector according to an embodiment of the present invention, including a waveguide reflection optical system 100 that utilizes total reflection, and a photodetector 2a. , 2b
This is an example in which minute reflecting portions 4ab and 4cd are formed in the waveguide 1 at positions corresponding to dead portions 3ab and 3cd between 2c and 2d.

In the waveguide type photodetector element having the configuration shown in FIG. 1, light incident from the right side in the figure is reflected and focused by the parabolic end surface 100 of the waveguide l, and when the light flux is parallel light, , are focused on the vertices of minute reflection parts 4ab and 4cd. Here, minute reflection parts 4ab and 4cd
are photodetectors 2a, 2b and 2c.

The dead part 3ab and 3cd between 2d is apparently zp
It functions to set the voltage to "O".

The waveguide reflection optical system 100 and the minute reflection section 4ab.

4cd is formed by etching at least the thickness of the waveguide layer of the waveguide structure according to a mask pattern. At this time, it is only necessary to form those patterns on the same photomask.

Next, FIG. 2 is an example of a waveguide reflection optical system using normal reflection, and furthermore, it is a parabolic waveguide layer end face 101.
In this example, it is separated from the metal reflective layer 110. At this time, a similar metal reflective layer may or may not be provided on the minute reflective portions 4ab and 4cd. This is because the minute reflective portions 4a are formed on the photomask on which the metal reflective layer 110 is formed.
b, can be arbitrarily selected depending on whether or not to form a 4cd metal layer pattern.

Next, FIG. 3 shows the shape of the minute reflection section 4, the photodetector 2a,
This shows the relationship with 2b.

Here, the minute reflection part 4 has two reflection surfaces, and the planar shape of these reflection surfaces may be a straight line as shown in FIG. However, the angle of incidence relative to the incident light must be greater than or equal to the total reflection angle when using total reflection, and 45° when using normal reflection.
It is sufficient if it is at least °.

Further, FIG. 3(B) shows an example in which the apexes of the two reflecting surfaces are located near the line connecting the front edges of the photodetectors 2a and 2b.

Further, in this example, the minute reflection section 4 and the photodetector 2a.

In order to absorb the positioning error with 2b, a margin is provided in the shape of the minute reflection part 4 so that each has an overlapping range. Note that although the vertex position changes slightly due to alignment errors, the functions of apparently removing the dead area and effectively utilizing the amount of incident light are not lost.

The above description has been given using an example of optical pink-up in which a minute reflective portion is formed in the vicinity of the focal point of a waveguide reflective optical system constituting a condensing element system using photolithography, but the present invention is not limited to this. It can be applied to waveguide-type photodetecting elements in general, such as other processing methods, other configurations of waveguide reflection optical systems and positional relationships with minute reflection parts, and other devices such as optical spectrum analyzers.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a novel waveguide type photodetection element that includes a waveguide reflection optical system and a minute reflection section corresponding to the dead section between a plurality of photodetectors. be able to.

Furthermore, according to the present invention, since the waveguide reflective optical system and the minute reflective part corresponding to the dead part between the plurality of photodetectors are simultaneously formed in the same manufacturing process, each process is performed separately. The number of steps can be reduced, and throughput and costs can be reduced compared to the case where this method is used.

In addition, simultaneous processing eliminates the need for mutual alignment, which improves the performance of the waveguide photodetector, that is, increases the detection accuracy, and eliminates individual detection accuracy differences and deviations in the detection center during mass production. We can expect a reduction in variations in transfer, etc.

In the case of photolithography, the alignment accuracy for each mask is generally one order of magnitude worse than the dimensional and positional accuracy of the photomask.

Therefore, for items that require extremely high precision in their positional relationship, such as the waveguide reflective optical system and minute reflective parts, it is better to form them using a single photomask than when forming them separately using separate masks. The relative positional accuracy of these will be improved as described above, and the factors that cause variations from job to job will also be eliminated.

This is true not only for photolithography but also for other mechanical processing methods or mechanical masking methods.

[Brief explanation of drawings]

FIG. 1 is a plan configuration diagram schematically showing the main parts of a waveguide type photodetector according to an embodiment of the present invention, and FIG. 2 is a plan view schematically showing a main part of a waveguide type photodetector according to another embodiment of the present invention. FIG. 3 is a plan configuration diagram schematically showing the main part, and is a diagram for explaining the relationship between the shape of the minute reflection part and the photodetector. 1... Waveguide, 2a, 2b, 2c, 2d...
...Photodetector, 3.3ab, 3cd...Photodetection insensitive portion, 4,4ab,4cd...Waveguide reflective optical system, 100.101...Waveguide reflective optical system, L.・・・
・Incoming light. Fig. 3 (4) 11γ−−

Claims (1)

[Scope of Claims] 1. A waveguide, a waveguide reflection optical system formed as an end face of a waveguide layer of the waveguide, and a plurality of photodetectors provided in the waveguide or close to the waveguide. A waveguide-type photodetecting element having a micro-reflection portion formed in the waveguide corresponding to a space between adjacent photodetectors. 2. A method for manufacturing a waveguide type photodetecting element according to claim 1, characterized in that the waveguide reflective optical system and the minute reflection section are simultaneously formed in the same process. manufacturing method.