JPH06151795A - Photodetector - Google Patents

Abstract

PURPOSE:To provide a photodetector, which has a large photodetecting sensitivity in specified directions and is given the angle dependency of an asymmetrical photodetecting sensitivity, by a method wherein a thin film having a tapered structure is provided on the photodetecting part of a substrate. CONSTITUTION:A photodetector consists of a low-refractive index layer 13 having a photodetecting part 12 on a substrate, a parallel plane part 13, which is laminated on the upper part of this photodetecting part 12 and is parallel to the substrate surface, and a tapered part 13b, which is not parallel to the plane part 13a, and a high- refractive index medium 14, which is provided on the upper parts of the parts 13a and 13b. The incident angle of the light in the medium 14 to the substrate surface out of incident lights, which intrude through this medium 14, are transmitted the part 13b and are incided in the part 12 from specified directions which are not vertical to the part 12, is set at a critical angle or larger, which is decided on the basis of the relation between the refractive indexes of the medium 14 and the layer 13, and the incident angle of the light in the medium 14 to the part 13b out of the incident lights is set at an angle smaller than a critical angle, which is decided on the basis of the relation between the refractive indexes of the medium 14 and the layer 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to optical communication, optical integrated circuits,
The present invention relates to a photodetector used for an optical information processing circuit or the like.

[0002]

2. Description of the Related Art An example of a conventional photodetector will be described with reference to FIG. FIG. 9 shows a cross section of a pin photodiode made of a Si substrate, which is composed of an n layer 1, an i layer 2, and a p layer 3 (light receiving portion 3). This Si
A SiO ₂ layer 4 is formed on the front surface of the substrate, and a back surface electrode 5 is formed on the back surface thereof. Moreover, a high refractive index medium 6 is formed on the upper portion of such a Si substrate. In addition,
The contact electrodes are omitted here.

Lights 7a to 7 traveling from the upper right side of FIG.
Lights 8a to 8c traveling from c and the same upper left portion are detected by the light receiving unit 3, and a photocurrent is generated thereby, and converted into an electric signal. In the light-receiving unit 3 thus formed on the Si substrate, since the Si substrate is generally flat, S
The light receiving sensitivity is highest for light in the direction perpendicular to the i substrate,
There is an angular dependence of the light-receiving sensitivity that the light-receiving sensitivity becomes smaller as the angle formed by the point-symmetrical with respect to the vertical line of the Si substrate and the perpendicular becomes larger (that is, as the light enters obliquely).

[0004]

In this case, if the Si substrate (hereinafter referred to as the substrate) is tilted, the angle dependency of its light-receiving sensitivity changes. Therefore, the substrate is tilted to change the angle dependency and the normal line of the substrate is changed. Although it is possible to make the light receiving sensitivity asymmetric with respect to the angle, there are restrictions on the arrangement of the substrate,
There is a drawback that one board cannot support multiple directions.
Further, only the light receiving portion on the substrate can be tilted with respect to the substrate so that the asymmetric light receiving sensitivity has an angle dependence, but the angle of the light receiving surface tilted on the substrate is the light receiving portion 3 (hereinafter referred to as a light receiving element). Unless the area of () is reduced to some extent, it is at most 10 and more degrees, and since the inclination also changes the light receiving sensitivity, for example, the light is incident on the substrate from the left and right at the same incident angle of 45 °. It is difficult to selectively detect light.

In view of the above, therefore, in the prior art, in order to make the light receiving element on the substrate have an asymmetric angle dependency of the light receiving sensitivity such that the light receiving sensitivity for light in a specific direction becomes large, Separately, optical components such as a lens, a diffraction grating, a slit, and a prism are provided in front of the incident direction so that light in a specific direction can easily enter the light receiving element. For example, when using a slit,
A slit with a knife edge is provided in front of the light receiving element on the substrate, and the light receiving element strongly receives the light on the side without the knife edge, which causes an asymmetric angle dependence in the light receiving sensitivity.

However, if these optical components are provided separately from the substrate for the light receiving element, the number of components increases, and in many cases it becomes difficult to provide other optical components. For example, by providing the slit, it becomes difficult to bring the prism or the diffraction grating into close contact with the light receiving element.

As an example of the light receiving element for detecting the guided light on the substrate, 10p-ZN-8, 1991, autumn, 52nd applied physics, titled "Waveguide type photodetector for integrated optical pickup" Some are disclosed by the applicant at academic conferences. In order to guide the guided light to the light receiving element efficiently, the shape of the substrate surface approaching the light receiving element is formed in a taper shape, and thereby the angle dependence is provided. Of course, the detection sensitivity of guided light has a planar angle dependency. However, since such a tapered substrate is generally produced by laminating and processing thin films, it is difficult to provide the optical component integrally with the light receiving element on the substrate.

[0008]

According to a first aspect of the invention, there is provided a light receiving portion formed on a substrate, and a taper which is not parallel to a parallel plane portion which is laminated on an upper portion including the light receiving portion and which is parallel to the substrate surface. A low refractive index layer having a high refractive index medium and a high refractive index medium provided on the parallel plane portion and the tapered portion of the low refractive index layer. The incident angle of light in the high refractive index medium with respect to the surface of the substrate out of the incident light that is transmitted through the tapered portion of the layer and is incident on the light receiving portion on the substrate from a specific direction that is not perpendicular to the light receiving portion is the high refractive index medium. And a large angle equal to or greater than a critical angle determined from the relationship of the refractive index of the low refractive index layer, and the incident angle of light in the high refractive index medium with respect to the tapered portion of the incident light is set to the high angle. Refractive index medium and low refractive index It is set to an angle smaller than the critical angle determined from the relationship between the refractive index of.

According to a second aspect of the invention, a low refraction having a light receiving portion formed on the substrate, a parallel flat portion parallel to the substrate surface and a taper portion which is laminated on the upper portion including the light receiving portion and is not parallel to the substrate surface. A low refractive index layer, a high refractive index medium provided on the parallel plane portion and the taper portion of the low refractive index layer, and a low refractive index medium provided on the high refractive index medium. From the low refractive index medium, the contact surface between the high refractive index medium and the low refractive index medium penetrates into a portion which is not parallel to the substrate, and penetrates the tapered portion of the low refractive index layer through the high refractive index medium. The incident angle of the light in the high refractive index medium with respect to the surface of the substrate among the incident light incident from a specific direction that is not perpendicular to the light receiving portion on the substrate is defined by the refraction of the high refractive index medium and the low refractive index layer. Above the critical angle determined from the relationship of the rates The angle of incidence of the light in the high refractive index medium with respect to the taper portion of the incident light is determined from the relationship between the high refractive index medium and the refractive index of the low refractive index layer. The angle was set smaller than the critical angle.

In the invention of claim 3, claim 1 or 2
In the invention described above, at least one intermediate layer is provided between the high refractive index medium and the low refractive index layer.

According to a fourth aspect of the invention, in the third aspect of the invention, at least one of the intermediate layers is formed of a high refractive index material, and the high refractive index material is formed on the substrate surface on which the light receiving portion is formed. One of the contact surfaces between the intermediate layer made of a refractive index substance and the low refractive index layer, or the contact surface between the intermediate layer made of the high refractive index substance and the intermediate layer made of a substance having a smaller refractive index than the lower layer. Parts or all of them are formed in non-parallel tapered parts, and a contact surface between the intermediate layer made of the high refractive index material and the high refractive index medium or the high refractive index medium with respect to the substrate surface on which the light receiving part is formed. Part or all of the contact surface between the intermediate layer made of a substance having a refractive index and the intermediate layer made of a substance having a similar refractive index to that of the upper layer was formed in parallel parallel plane portions.

According to the invention of claim 5, claim 1 or 2
In the invention described above, at least one intermediate layer is provided between the high refractive index medium and the low refractive index layer, and at least one of the intermediate layers is provided as a waveguide layer.

According to the invention of claim 6, claim 1 or 2
In the invention described above, at least one intermediate layer is provided between the high refractive index medium and the low refractive index layer, and at least one of the intermediate layers is provided as a waveguide layer, and the high refractive index medium is It is formed as a prism for optical coupling to the waveguiding layer, and an incident light coupling means for injecting incident light in a specific direction from the prism is provided, and the incident light coupling means intrudes through the prism. In order to detect the emitted light, a tapered light detecting portion was formed on the substrate surface on the lower surface of the prism.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, a guided light detecting means for detecting the guided light coupled to the waveguide layer from the light detecting portion via the prism is provided, and the guided light detecting means is provided. The optical coupling efficiency detecting means for obtaining the optical coupling efficiency is provided by the output information from the optical detector and the output information obtained from the light in the specific direction by the photodetector.

[0015]

According to the first aspect of the invention, since the low refractive index layer having the taper structure is formed around the light receiving portion, the light receiving sensitivity which is asymmetrical with respect to the incident light from the high refractive index medium in a specific direction is obtained. It becomes possible to provide angle dependency and to increase the light receiving sensitivity.

According to the second aspect of the present invention, there is provided a low refractive index layer having a tapered structure around the light receiving portion, and a contact surface between the high refractive index medium and the low refractive index medium which is not parallel to the substrate. Therefore, it becomes possible to have an asymmetric angle dependence of the light receiving sensitivity with respect to the incident light in a specific direction from the low refractive index medium.

In the third aspect of the invention, the provision of the intermediate layer makes it possible to function as a protective layer for the high refractive index medium and the substrate.

According to the fourth aspect of the invention, at least a part of the boundary surface on the low refractive index layer side of the intermediate layer made of the high refractive index medium is provided with a portion that is not parallel to the substrate.
It is possible to make the interface between the high refractive index medium and the intermediate layer parallel to the substrate.

According to the fifth aspect of the invention, since at least one of the intermediate layers is used as the waveguiding layer, it is possible to integrate the optical components at a high density.

According to the sixth aspect of the present invention, since the light detecting portion having the tapered structure is provided on the substrate on the lower surface of the prism, the light incident from the specific direction of the prism is directly coupled without being coupled to the waveguide layer. Can be detected.

According to the seventh aspect of the invention, output information obtained from light in a specific direction detected by the photodetector having a taper structure and guided light detected by the guided light detecting means are obtained. The output information and can be used to determine the optical coupling efficiency of the prism.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 will be described with reference to FIG. FIG. 1 shows a cross-sectional shape of this device. The Si substrate 9 serving as a substrate includes an n layer 10 and an i layer 10 from the lower layer side.
A layer 11 and a p layer 12 (hereinafter, referred to as a light receiving portion 12) are sequentially formed to form a pin photodiode. A low refractive index layer 13 is formed on the Si substrate 9 including the light receiving portion 12. This low refractive index layer 13
Is a parallel plane portion 1 parallel to the substrate surface of the Si substrate 9.
A tapered portion 13b that is not parallel to 3a is formed. A high refractive index medium 14 is provided on the parallel flat surface portion 13a and the tapered portion 13b of the low refractive index layer 13. A back surface electrode 15 is attached to the back surface side of the Si substrate 9. The taper shape of the low refractive index layer 13 can be relatively easily produced by etching a multilayer film having different etching rates at an angle of 5 ° or more.

Further, the following conditions are set here. The first condition is that of the incident light that enters from the high-refractive-index medium 14 and transmits through the tapered portion 13b of the low-refractive-index layer 13 and enters the light-receiving portion 12 on the Si substrate 9 from a specific direction that is not perpendicular to the substrate surface. The incident angle of light in the high-refractive index medium 14 is set to a larger angle than the critical angle determined from the relationship between the refractive indices of the high-refractive index medium 14 and the low-refractive index layer 13. In addition, as a second condition, of the incident light, the incident angle of the light in the high refractive index medium 14 with respect to the tapered portion 13b is defined as the high refractive index medium 14 and the low refractive index layer 1
The angle is set to be smaller than the critical angle determined from the relationship of the refractive index of 3.

In such a structure, first, the incident light will be described. In FIG. 1, light incident from the right side is indicated by incident light 16a, 16b, 16c, 16d, and light transmitted through the tapered portion 13b is indicated by light rays 17b, 17c, 17d. Of the light incident from the right side, the parallel flat surface portion 13a
The light reflected by is indicated by a light ray 17a. The light incident from the left side is incident light 18a, 18b, 18c, 18d, 18
The total reflection light reflected by the parallel plane portion 13a and the taper portion of the incident light 18a, 18b, 18c is indicated by the light ray 19
a, 19b, 19c, i of incident light 18d, 18e
The light transmitted through layer 11 is indicated by rays 19d and 19e. A ₁
˜A ₄ are perpendiculars to the substrate surface, and B ₁ and B ₂ are perpendiculars to the tapered portion 13b.

Next, the geometrical rays of the incident light as described above will be mainly described. The low refractive index layer 13 having a taper structure may actually be thinner than the wavelength, and in this case, it must be treated as a wave optics. This geometrical explanation is sufficient as the basic principle because the choice is made to be larger or smaller than the critical angle of reflection. However, when the low-refractive index layer 13 is sufficiently thin with respect to the wavelength, the electric field strength due to the evanescent wave may be large even in the lower layer of the low-refractive index layer 13, and for example, this may be the p-layer of the light-receiving unit 12. For example, absorption of light occurs, and photocurrent is generated even with incident light having a critical angle of total reflection or more. Therefore, the thickness of the low refractive index layer 13 on the light receiving portion 12 is set to be at least 1 of the wavelength.
By setting the thickness to / 4 or more, the electric field intensity in the lower layer due to the incident light becomes relatively small, so that the absorption in the lower layer becomes small and the light receiving portion 12 is affected by the difference between the critical angle and the incident angle. It becomes possible to give the angle dependence of the light receiving sensitivity. In addition, the low refractive index layer 13 on the light receiving portion 12
If the thickness is 1 or more times the wavelength, a sufficiently large SN ratio can be obtained. Further, the SN ratio hardly changes at a thickness of several times the wavelength, and the state is the same as in the case of bulk.

Next, the basic operating principle of the present apparatus (the two setting conditions described above) will be described. High refractive index medium 14
As a high refractive index flint glass of LaSF (21) manufactured by OHARA INC. (N = 1.84491, 632.8n)
m) is used. As a glass similar to this, TaSF (9) glass (n = 1.8) manufactured by Hoya Co., Ltd.
4493, 632.8 nm) may be used. Further, the low refractive index layer 13 having the tapered portion 13b is formed by plasma CVD of SiON at a substrate temperature of 300 °, and the refractive index is set to n = 1.453. In this case, the critical angle theta, a ^{θ = sin ~ 1 (1.453 /} 1.845) = 51.95 °. And now, from the high refractive index medium 14 to the Si substrate 9
It is assumed that light rays are incident at an incident angle of 55 °. The angle θ ₁ of the tapered portion 13b of the low refractive index layer 13 is 11.31 °
And ^{(tan ~ 1 (0.2))} , the thickness of the parallel plane portion 13a is not a taper of the low refractive index layer 13 is set to 4 [mu] m.

First, the reason why the light beam incident on the Si substrate 9 from the left side is not absorbed by the light receiving portion 12 will be described. Of the incident light incident from the left side, the incident light 1 incident on the parallel plane portion 13a of the low refractive index layer 13 having the tapered portion 13b 1
8a and 18b are light rays having an incident angle θ ₂ = 55.0 °, which is larger than the critical angle θ = 52.0 °, so that they are totally reflected at a reflection angle 55.0 °, and are rays 19a and 19b. Become. Further, of the incident light incident from the left side, the incident light 18c incident on the taper portion 13b has an incident angle θ ₃ = 66.
It is a ray of 3 °, which is larger than the critical angle θ = 52.0 °, and is totally reflected at a reflection angle of 66.3 °.
c. Considering the substrate, the incident angle is 55 ° and the reflection angle is 77.6. Thus, from the left side, the Si substrate 9
The light incident on the low-refractive index layer 13 at an incident angle of 55 ° is
The light is not totally reflected by and is not absorbed by the light receiving unit 12.

On the other hand, of the incident light incident from the right side, the incident light 16a incident on the non-tapered portion of the low refractive index layer 13 having the tapered portion 13b has an incident angle θ ₄ =
It is a ray of 55.0 °, which has a critical angle θ = 52.0 °.
Since it is larger, it is totally reflected at a reflection angle of 55 °
a. In addition, among the incident lights that are incident from the right side, the incident lights 16b, 16c, and 16d that are incident on the tapered portion 13b.
Is a light beam with an incident angle θ ₅ = 43.7 °, which is smaller than the critical angle θ = 52.0 °, and therefore has an exit angle 61.3 °.
Are transmitted and become light rays 17b, 17c, 17d. Considering the substrate, the incident angle of the light rays 17b, 17c, 17d is 55 °, which is refracted by the tapered portion 13b,
This time, it is incident on the light receiving portion 12 at the incident angle θ ₆ and is absorbed, whereby a photocurrent flows.

In this case, as described above, in reality, as the film thickness becomes thinner, it becomes different from the geometrical ray,
In the thin film portion having the tapered portion 13b, the light beam is transmitted through the low refractive index layer 13 and absorbed by the lower Si substrate 9 even though the incident angle of the light beam is a total reflection condition larger than the critical angle θ. To be done. For example, the light rays 18d and 18e incident from the left side on the taper portion 13b of the low refractive index layer 13 which is ¼ or less of the wavelength of light having a small film thickness are light rays 19d,
It becomes 19e and enters the i layer 11 and is absorbed. this is,
The light rays incident from the right side are the same, and the asymmetric light receiving characteristic is lost. For this reason, the light receiving portion 12 formed of the p layer is not provided in the thin film thickness portion, or the area of the light receiving portion 12 is made sufficiently small to reduce the excess light to the required amount. It is necessary to.

As described above, by forming the low refractive index layer 13 having a taper structure around the light receiving portion 12,
It is possible to make the light receiving sensitivity asymmetric with respect to the incident light from the high refractive index medium 14 in a specific direction, and to further increase the light receiving sensitivity.

Further, at least one light receiving portion 12 is provided in the thin portion of the low refractive index layer 13, and the incident light is incident from the output information and the output information of the light receiving portion 12 having an asymmetrical characteristic. The characteristic can be detected. In addition, the low refractive index layer 13
Although the taper portion 13b of 1 has been described as one plane,
By using a flat surface or a curved surface having two or more different surface directions and providing two or more light receiving portions 12, it is possible to selectively detect light in two or more directions. Further, when the incident angle on the light receiving section 12 is large and part of the incident light is reflected on the surface to reduce the light receiving sensitivity, an antireflection layer is provided between the light receiving section 12 and the low refractive index layer 13. By providing at least one layer, most of the reflected light can be guided to the light receiving unit 12.

Next, an embodiment of the present invention will be described with reference to FIG. The description of the same parts as those of the invention according to claim 1 (see FIG. 1) is omitted, and the same reference numerals are used for the same parts.

In FIG. 2, a parallel plane portion 13a and a taper portion 13b are provided on the pin photodiode formed by the Si substrate 9.
A low-refractive index layer 13 having, and a parallel plane portion 14a and taper portions 14b and 14c provided on the low-refractive index layer 13.
And a high refractive index medium 14 having
It is composed of a low refractive index medium 20 provided above. In this case, the light incident from the right side is the incident light 21a and 21b, and the light transmitted through the high refractive index medium 14 is the light rays 22a and 2b.
2b, and the light transmitted through the low refractive index layer 13 is a light ray 22. Further, the light incident from the left side is the incident light 23a, 23
b, and the light transmitted through the high refractive index medium 14 is the light ray 24.
a and 24b. In this case, the perpendicular to the parallel plane portion 14a is indicated by A ₁ , and the perpendiculars to the tapered portions 14b and 14c are indicated by B ₁ and B ₂ . C _{1 to} C ₄ are perpendiculars to the substrate surface, and D ₁ is a perpendicular to the tapered portion 13b.
θ ₁ and θ ₂ are tapered portions 14 b and 14 of the high refractive index medium 14.
c is the angle formed between the low refractive index layer 13, θ _{3 to} θ ₇ are the respective incident angles, and θ _{8 to} θ ₁₀ are the refracted angles.

The low refractive index medium 20 is made of air,
The refractive index n = 1.000. The high refractive index medium 14 is made of high refractive index flint glass and has a refractive index n = 1.895.
And It is assumed that the angles θ ₁ and θ ₂ are both 45 °, and that the plane of the parallel plane portion 14a is parallel to the substrate surface.
The incident angles θ ₅ and θ ₇ here are set to 63.68 °.

In such a structure, first, the reason why the light incident from the left side is not absorbed by the light receiving portion 12 will be described. Of the light rays incident from the left, the light ray 23a incident on the tapered portion 14b which is not parallel to the substrate has an incident angle θ ₃
= 18.68 °, which is the refracted refraction angle θ
It becomes the light ray 24a of ₈ = 10.00 °. This ray 24a
Is a light beam having an incident angle θ ₄ = 55 ° with respect to the substrate, so that when it is incident on the low refractive index layer 13, it is reflected at the boundary portion of this layer regardless of whether it is the tapered portion 13b. Therefore, the light is not absorbed by the light receiving unit 12.

On the other hand, among the light rays incident from the right, the light rays 21a and 21b incident on the taper portion 14c.
Is a light ray with an incident angle θ ₆ = 18.68 °, which is a refracted light ray 22a, 22b with a refraction angle θ ₁₀ = 10.00 °.
Becomes These rays 22a and 22b have an incident angle θ ₁₁ = 55 ° with respect to the substrate. Since the incident portion of the light ray 22a is the parallel plane portion 13a, the incident angle θ ₁₁ = 55 ° to the low refractive index layer 13 is larger than the critical angle θ = 52.0 °, so that the light beam 22a is totally reflected. . Since the incident position of the light ray 22b is the tapered portion 13b, the incident angle θ ₁₂ = 4
It is 3.7 °, and an angle θ ₁₃ = 6 given by transmission and refraction.
It becomes 1.0 °, enters the light receiving portion 12 at an incident angle θ ₁₄ , and is absorbed by the light receiving portion 12, whereby a photocurrent is generated.

The light ray 23b which is incident on the plane-parallel portion 14a from the left side has an incident angle θ = 63.68 °, which travels at an angle θ ₉ = 29.0 ° given by being transmitted and refracted, When this enters the low-refractive index layer 13, since it is smaller than the critical angle θ, it is transmitted and enters the light-receiving portion 12, whereby a photocurrent is generated. In this case, even if the optical component made of the high-refractive index medium 14 and the substrate are not horizontal, light is easily transmitted to the light receiving section 12 depending on the incident angle of the incident light beam, so that the plane-parallel portion 14 a with respect to the light receiving section 12 is formed. It is necessary to set the position and area appropriately. A light shielding layer or a reflective layer may be provided in this portion.

As described above, by providing the low-refractive index layer 13 having a tapered structure and the high-refractive index layer 14 having a portion not parallel to the Si substrate 9 around the light receiving portion 12, The angle dependence of the light receiving sensitivity can be imparted to the incident light from the low refractive index medium 20 in a specific direction.

If the boundary between the optical component composed of the high-refractive index medium 14 and the low-refractive index medium 20 is only a portion parallel to the substrate such as the parallel plane portion 14a, it is not a tapered portion. Regardless of this, all the light becomes smaller than the critical angle θ and passes through the low-refractive index layer 13, so that it is not possible to fabricate a detection device having an asymmetric angle dependence of the light-receiving sensitivity, so caution is required.

Next, an embodiment of the invention described in claim 3 will be described with reference to FIG. The description of the same parts as those in the first and second aspects of the present invention is omitted, and the same parts are designated by the same reference numerals.

Here, at least one intermediate layer is provided between the high refractive index medium 14 and the low refractive index layer 13. That is, the intermediate layer here is a layer in which two layers of the high refractive index intermediate layer 25 and the low refractive index intermediate layer 26 are provided. In this case, the light incident from the right side is the incident light 27, the light transmitted through the high refractive index intermediate layer 25 is a light ray 28, and the light transmitted through the low refractive index intermediate layer 26 is a light ray 29, which has a low refractive index. The light transmitted through the layer 13 is a light ray 30. θ
₁ and θ ₂ are incident angles, and θ ₃ is a refraction angle.
The high refractive index intermediate layer 25 has the same refractive index n = 1.895 as the high refractive index medium 14, and the low refractive index intermediate layer 26 has the same refractive index n = 1.453 as the low refractive index layer 13. The incident angle of light from the right side is θ ₁ = 55 °. Further, A ₁ and A ₂ indicate perpendiculars to the substrate surface, and B ₁ indicates perpendiculars to the tapered portion 14b.

In such a structure, the incident light 27 incident from the right side to the portion where the boundary surface between the high refractive index intermediate layer 25 and the low refractive index intermediate layer 26 is not parallel to the substrate surface is at the point P. Since there is no change in the refractive index, it travels straight through the high-refractive-index intermediate layer 25 and becomes a light ray 28 that is incident at the position of point Q at an incident angle θ ₂ = 43.7 °. Since it is smaller than the critical angle given by the layer 26,
The light ray 28 is transmitted and refracted to become a light ray 29 given at a refraction angle θ ₃ , and enters the position of point R, and since the refractive index does not change at this position, the light ray 28 goes straight through the low refractive index layer 13
It becomes 0, and it is incident on the light receiving part 12 at an incident angle θ ₄ , and the light receiving part 1
2, which results in photocurrent. On the other hand, a light ray (not shown) incident from the left side is totally reflected because the incident angle from the high refractive index intermediate layer 25 to the low refractive index intermediate layer 26 is larger than the critical angle, and is absorbed by the light receiving unit 12. It will not be done. Therefore, the light receiving unit 12 has an asymmetric angle dependency of the light receiving sensitivity.

In this case, even if the refractive index of the intermediate layer does not have a value equal to that of the high refractive index medium 14 or the low refractive index layer 13, the taper angle given by the low refractive index layer 13 is at least at one boundary surface. Due to the difference, the incident angle of the incident light beam needs to be larger or smaller than the critical angle. The intermediate layer may be either the low refractive index intermediate layer 26 or the high refractive index intermediate layer 25, or may have three or more layers. In this case as well, it is necessary that the incident angle of the incident light beam be larger or smaller than the critical angle due to the difference in taper angle provided by the low refractive index layer 13 in at least one layer or the boundary surface of the medium. Furthermore, if the intermediate layers are sufficiently thin, it is possible to cause total internal reflection by gradually changing the refractive index of the multilayer intermediate layer, in which case the transmittance is increased.

As described above, by providing the high refractive index intermediate layer 25 and the low refractive index intermediate layer 26 between the high refractive index medium 14 and the low refractive index layer 13, the high refractive index medium 14 is provided.
It can also serve as a protective layer for the Si substrate 9.

Next, an embodiment of the invention described in claim 4 will be described with reference to FIG. The description of the same parts as those in the first to third aspects of the present invention is omitted, and the same parts are designated by the same reference numerals.

Here, at least one of the intermediate layers described in the above-mentioned embodiment of claim 3 is formed of a high refractive index material. That is, the high refractive index medium 1
A high-refractive-index intermediate layer 31 made of a high-refractive-index material was provided as an intermediate layer between 4 and the low-refractive-index layer 13. Further, here, with respect to the substrate surface on which the light receiving section 12 is formed, the contact surface between the high refractive index intermediate layer 31 and the low refractive index layer 13 (or the high refractive index intermediate layer 31 and the lower layer thereof). Part or all of the contact surface with the intermediate layer made of a substance having a small refractive index is formed in the non-parallel tapered portion 13b, and the light receiving portion 12 is further formed.
The contact surface between the high-refractive-index intermediate layer 31 and the high-refractive-index medium 14 (or the high-refractive-index intermediate layer 31 and a material having a refractive index similar to that of the upper layer) on the substrate surface on which A part or the whole of the contact surface with the intermediate layer) is formed in the parallel plane portion 14a.

The high-refractive-index intermediate layer 31 includes the high-refractive-index medium 14
With the same refractive index n = 1.895 and the incident light from the right 32
The incident angle of θ ₁ = 55 °. Further, the boundary surface between the high refractive index intermediate layer 31 and the high refractive index medium 14 is assumed to be parallel to the substrate. A ₁ and A ₂ are perpendiculars to the substrate surface, and B ₁ is a perpendicular to the tapered portion 13b.

In such a structure, the light incident from the right side is the incident light 32, and since there is no change in the refractive index at the position of point P, it travels straight through the high refractive index intermediate layer 31 and becomes a light ray 33 at point Q. It is incident on the position at an incident angle θ ₂ = 43.7 °. Since this is smaller than the critical angle given by the high-refractive index intermediate layer 31 and the low-refractive index layer 13, the light ray 33 is transmitted and refracted to become the light ray 34 given by the refraction angle θ ₃ , and the light receiving unit 12
Is incident and absorbed at an incident angle given by θ ₄ , which causes a photocurrent. On the other hand, a light ray (not shown) incident from the left side has an incident angle from the high-refractive index intermediate layer 31 to the low-refractive index layer 13 that is larger than the critical angle, so that the light ray is totally reflected and absorbed by the light receiving unit 12. There is no end. For this reason, the light receiving section 12 has an asymmetric angle dependency of the light receiving sensitivity.

Next, an embodiment of the invention described in claim 5 will be described with reference to FIG. The description of the same parts as those in the first to fourth aspects of the present invention is omitted, and the same parts are designated by the same reference numerals.

Here, low refractive index intermediate layers 35 and 36 are provided between the high refractive index medium 14 and the low refractive index layer 13 as intermediate layers consisting of two layers having slightly different refractive indexes. . In this case, the low refractive index intermediate layer 36 is a waveguide layer. 37a and 37b are guided lights, and A is the guided lights 37a. It shows the traveling direction A of 37b. Light incident from the right side is incident light 38, and the incident position of this incident light 38 on the low refractive index intermediate layer 35 is point P, and further,
The light transmitted through the low refractive index intermediate layer 36 and the low refractive index layer 13 is a light ray 39. In this case, the low-refractive-index intermediate layer 35 has a refractive index n = 1.453, the low-refractive-index intermediate layer 36 has a refractive index n = 1.500, and each has a thickness of 2 μm. The refractive index of the high refractive index medium 14 is n = 1.895, and the incident angle of light from the right side is θ ₁ = 55 °. In this case, B ₁ indicates a perpendicular line to the tapered portion 14b.

In such a structure, the incident angle of the light ray 38 incident on the position P from the right side with respect to the substrate is θ ₁ =
Since it is 55 °, the incident angle at the point Q to the low-refractive index intermediate layer 35 is 43.7 °, and the refraction angle is 61.3 °, and the light ray 39 proceeds. When this light ray 39 enters the low refractive index intermediate layer 36, the refraction angle at the point R is 58.2.
However, when the light enters the low refractive index layer 13, it changes in the opposite direction by about 3.1 °, which is in the same direction as the straight direction, and enters the light receiving portion 12. on the other hand,
Light rays (not shown) incident from the left side are included in the low refractive index intermediate layer 3
5 and total reflection occurs at the interface between the low refractive index intermediate layer 36 and the light receiving portion 12. Therefore, the intermediate layer having such a structure does not interfere with the asymmetric angle dependence of the light receiving sensitivity of the light receiving section 12. In reality, since the film thickness is small, it is necessary to treat it as a wave optics. However, with such a thickness, the light from the right side to the tapered portion 14b is transmitted to the light receiving section 12, and the light from the left side is transmitted. There is no change in total reflection.

In this case, the low-refractive-index intermediate layer 36 functions as a waveguide layer because it has a slightly smaller refractive index than the low-refractive-index intermediate layers 35 and 13 above and below it.
When HeNe laser light is coupled from the left side to the low-refractive-index intermediate layer 36, which is the waveguide layer, from the left side by the end-face coupling method, the guided light 37a having a predetermined electric field intensity distribution proceeds in the direction A of the arrow and has a tapered shape. The light travels like the guided light 37b. Further, when the incident light 38 is a thin laser beam light, it is given with an electric field intensity distribution like 40, and thereafter,
The light beam 39 is overlapped with the guided light 37b in the vicinity of the broken line of the low refractive index intermediate layer 36, but unlike the electrons, they are separated without affecting each other due to the characteristics of the light, and the guided light 37b is moved right along the waveguide layer. The light ray 39 reaches the light receiving portion 12 and is absorbed. Such crossing of light makes it possible to provide many functions within a very small area, and it is possible to fabricate an advanced optical integrated circuit.

However, since the laser beam may be coupled to the waveguide layer under a specific condition, at this time, the film thickness, incident angle, refractive index, etc. of the low refractive index intermediate layers 35, 36 may be changed. Good. Further, by providing a light receiving portion different from the light receiving portion 12 in the thin portion 41 of the low refractive index layer 13, light is transmitted through the thin portion 41 and absorbed, whereby the guided light 37b is absorbed. It can also be detected.

As described above, by using at least one of the intermediate layers as the waveguiding layer, it becomes possible to integrate the optical components at a high density.

Next, an embodiment of the invention described in claim 6 will be described with reference to FIGS. 6 and 7. The description of the same parts as those in the first to fifth aspects of the present invention will be omitted, and the same reference numerals will be used for the same parts.

Here, an example of the configuration when applied to a prism coupling device is shown. That is, the low-refractive index layer 13 is formed on the Si substrate 9, and two low-refractive-index intermediate layers 35 and 36 having slightly different refractive indexes as intermediate layers are laminated on the low-refractive index layer 13. ing. The low refractive index intermediate layer 36 is provided as a waveguide layer. Part of the low-refractive-index intermediate layers 35 and 36 serves as a photodetector 42 formed in a tapered shape. A low refractive index layer 43 for sufficiently confining the guided light a is formed on a part of the surface of the low refractive index intermediate layer 35. Si substrate 9 which is the traveling direction of the guided light a
An optical information processing means 44 is provided near the end of the. Further, a prism 45 made of a high refractive index medium is provided above the photodetector 42. This prism 45
An objective lens 46 forming a part of the incident light coupling means is arranged in order to guide a light beam from a specific direction to the. Further, FIG. 7 shows the Si substrate 9 with the prism 45 removed.
FIG. 3 is a top view of the extraction electrode 4 in the light receiving part 12.
7 is connected, and the light receiving unit 12 is arranged so that the beam 48 (same as the light rays 51a and 51b) reflected from the optical disk 55 can be incident. Hatching area 49
Indicates the range in which the guided light a propagates.

In this case, 50a to 50c are prisms 45.
Is a light ray having a Gaussian distribution 51 incident from the air which is a low refractive index medium, and 52a and 52b are light rays 50a.
.About.50c are rays reflected after being coupled to the waveguiding layer or rays corresponding to total reflection rays, and 53a. Reference numeral 53b is a light ray that has passed through the objective lens 46, and dashed lines 54a and 54b are light reflected by the optical disk 55, and 56a and 5b.
Reference numeral 6b is a light beam that has passed through the objective lens 46 again.

The low-refractive-index intermediate layer 36 has a smaller refractive index than the surroundings and serves as a waveguide layer. The prism 45, the low-refractive-index intermediate layer 36, and the low-refractive-index layer 43 guide the light rays 50a to 50c to the waveguide layer. To form a prism coupling part for coupling to. At this time, the thickness of the low-refractive-index intermediate layer 35 is assumed to be relatively smaller than the wavelength. Further, in order to increase the coupling efficiency, the incident angle of the beam on the substrate, the refractive index of the prism 45, and the refractive index and thickness of the low refractive index intermediate layers 35 and 36 are optimized in advance. Further, the incident angle θ _{1 at} which the light ray 50a enters the prism 45 is set to 90 ° in order to reduce stray light due to reflection.

In such a structure, of the light rays 50a to 50c that enter the substrate from the right side, the light ray 50c that enters the tapered photodetecting section 42 is absorbed by the light receiving section 12 and passes through the extraction electrode 47 to the electric circuit. Then, the change in the light intensity of the light ray 50c can be detected.
Further, among the light rays 50a to 50c that have entered the substrate from the right side, the light rays 50a and 50b that have entered the areas other than the tapered photodetector 42 are condensed by the high NA objective lens 46 and become the light rays 53a and 53b. To form a light spot of several μm, which is irradiated onto the surface of the optical disk 55. The light rays 54a and 54b reflected by the optical disk 55 again pass through the objective lens 46 and become light rays 56a and 56b, which are input-coupled or totally reflected to the waveguide layer. At this time, since the low-refractive index layer 43 exists on the low-refractive-index intermediate layer 35 of the gap layer, the guided light a coupled to the waveguide layer propagates through the waveguide layer without being output-coupled, and Guided light a with intensity distribution 57
Becomes The guided light a is processed by the optical information by being detected by the optical information processing means 44.

As described above, by setting the refractive index of the photodetector 42 to be larger than the value required for coupling, the light beam can be directly incident on the photodetector 42. At this time, the light beam is reflected by the optical disk 55. Since the reflected light rays 56a and 56b become return light and are incident on the light detection unit 42 again, it becomes difficult to detect the light amount of light directly incident from an LD (laser diode) (not shown). It becomes difficult to control, and it becomes necessary to separately prepare a half mirror and provide a front PD (not shown). Therefore, in this embodiment, as described above, the photodetector 4
By forming 2 in a taper shape, the light beam 50c from the LD can be directly detected without being affected by the returning light, which allows the light beam 50c to act as a front PD (not shown). Since it can be integrated on top, further miniaturization can be achieved.

Next, an embodiment of the invention described in claim 7 will be described with reference to FIG. The description of the same parts as those in the first to sixth aspects of the present invention will be omitted, and the same reference numerals will be used for the same parts.

Here, the following mechanism is added to the configuration of the prism coupling device of FIG. 6 described above.
That is, the guided light receiving portion 58 as the guided light detecting means for detecting the guided light a coupled to the waveguide layer a from the light detecting portion 42 via the prism 45 is provided. This guided light receiving section 58
Is provided on a taper portion 60 connected to the extraction electrode 59 and formed by thinly forming the low refractive index layer 13 of the substrate. Further, an optical coupling efficiency detecting means (not shown) for obtaining the optical coupling efficiency is provided by the output information from the guided light receiving portion 58 and the output information obtained from the light in the specific direction by the light detecting portion 42. This optical coupling efficiency detecting means is included in the optical information processing means 44.

In such a structure, the optical disk 55
Light from the same direction as the light rays 56a and 56b due to the reflected light from the light receiving portion 1 passes through the light detecting portion 42 having a tapered shape.
2 is detected. The guided light a in the waveguide layer composed of the low-refractive-index intermediate layer 36 partially penetrates the guided light a into the tapered portion 60 while advancing in the direction of the optical information processing means 44 and receives the guided light. It is detected by the unit 58. These detected 2
The light coupling efficiency can be calculated by obtaining the ratio of the two lights by the light coupling efficiency detection means using one light. Thereby, the prism coupling device and the LD or the optical disk 55
The coupling efficiency of the prism coupling device can be adjusted by changing the positional relationship between the objective lens 46 and the objective lens 46.

[0064]

The invention according to claim 1 has a light receiving portion formed on a substrate, and a parallel flat portion parallel to the substrate surface and a taper portion which is laminated on the upper portion including the light receiving portion. The low refractive index layer and a high refractive index medium provided on the parallel plane portion and the tapered portion of the low refractive index layer, and the taper of the low refractive index layer penetrating from the high refractive index medium. The incident angle of light in the high refractive index medium with respect to the surface of the substrate out of the incident light that is transmitted through the portion and is incident on the light receiving portion on the substrate from a specific direction that is not perpendicular to the high refractive index medium and the low refractive index. The angle of incidence of light in the high refractive index medium with respect to the taper portion of the incident light is set to a large angle equal to or greater than a critical angle determined from the relationship of the refractive index of the high refractive index medium and the high refractive index medium. Relationship of refractive index of the low refractive index layer Since it is set to an angle smaller than the critical angle determined from the above, it is possible to have an asymmetric light-reception sensitivity with respect to incident light from a high-refractive-index medium in a specific direction, and to increase the light-reception sensitivity. It is a thing.

According to a second aspect of the present invention, a low refraction having a light receiving portion formed on a substrate, a parallel flat portion parallel to the substrate surface and a tapered portion which is laminated on an upper portion including the light receiving portion and which is not parallel to the substrate surface. An index layer, and a high refractive index medium provided on the parallel plane portion and the tapered portion of the low refractive index layer,
The high-refractive index medium is provided on the low-refractive-index medium, and the low-refractive-index medium penetrates into a portion where the contact surface between the high-refractive-index medium and the low-refractive-index medium is not parallel to the substrate. In the high-refractive-index medium in the high-refractive-index medium of the incident light that passes through the taper part of the low-refractive-index layer through the high-refractive-index medium and enters from the specific direction that is not perpendicular to the light-receiving part on the substrate. The incident angle of light at a large angle equal to or greater than the critical angle determined from the relationship between the high refractive index medium and the refractive index of the low refractive index layer, and the incident light with respect to the tapered portion Since the incident angle of light in the high refractive index medium is set to an angle smaller than the critical angle determined from the relationship between the refractive index of the high refractive index medium and the low refractive index layer, a specific direction from the low refractive index medium Received light asymmetric with respect to incident light It is capable to have an angle dependence of the degree.

According to the invention of claim 3, in the invention of claim 1 or 2, since at least one intermediate layer is provided between the high refractive index medium and the low refractive index layer, the high refractive index is high. It can serve as a protective layer for a medium or a substrate.

According to a fourth aspect of the present invention, in the third aspect of the invention, at least one of the intermediate layers is formed of a high refractive index material, and the high refractive index material is formed on the substrate surface on which the light receiving portion is formed. One of the contact surfaces between the intermediate layer made of a refractive index substance and the low refractive index layer, or the contact surface between the intermediate layer made of the high refractive index substance and the intermediate layer made of a substance having a smaller refractive index than the lower layer. Parts or all of them are formed in non-parallel tapered parts, and a contact surface between the intermediate layer made of the high refractive index material and the high refractive index medium or the high refractive index medium with respect to the substrate surface on which the light receiving part is formed. Since a part or all of the contact surface between the intermediate layer made of a refractive index material and the intermediate layer made of a material having a similar refractive index to that of the upper layer is formed on parallel plane portions parallel to each other, the high refractive index medium and the intermediate The interface with the layers can be parallel to the substrate It is intended.

According to a fifth aspect of the present invention, in the first or second aspect of the present invention, at least one intermediate layer is provided between the high refractive index medium and the low refractive index layer. Since at least one layer is provided as the waveguiding layer, the optical components can be integrated with high density.

According to a sixth aspect of the present invention, in the invention according to the first or second aspect, at least one intermediate layer is provided between the high refractive index medium and the low refractive index layer. At least one layer is provided as a waveguide layer, and the high refractive index medium is formed as a prism for optical coupling to the waveguide layer,
Incident light coupling means for allowing incident light in a specific direction to enter from this prism is provided, and a taper is formed on the substrate surface on the lower surface of the prism for detecting the incident light entering through the prism by the incident light combining means. Since the light detecting portion having the shape is formed, the light incident from the specific direction of the prism can be directly detected without being coupled to the waveguide layer.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, a guided light detecting means for detecting guided light coupled to the waveguide layer from the light detecting portion via the prism is provided, and the guided light detecting means is provided. Since the optical coupling efficiency detecting means for determining the optical coupling efficiency from the output information from the light and the output information obtained from the light in the specific direction by the light detecting portion is provided, the specific direction detected by the light detecting portion having the taper structure is provided. The optical coupling efficiency of the prism can be obtained by using the output information obtained from the light and the output information obtained from the guided light detected by the guided light detecting means.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a photo-detecting device which is an embodiment of the invention described in claim 1.

FIG. 2 is a cross-sectional view showing a configuration of a photo-detecting device according to an embodiment of the invention as set forth in claim 2.

FIG. 3 is a cross-sectional view showing a configuration of a photo-detecting device which is an embodiment of the invention described in claim 3.

FIG. 4 is a cross-sectional view showing a configuration of a photo-detecting device according to an embodiment of the invention as set forth in claim 4.

FIG. 5 is a cross-sectional view showing the configuration of a photo-detecting device which is an embodiment of the invention as set forth in claim 5.

FIG. 6 is a sectional view showing the structure of a photodetector according to an embodiment of the present invention.

FIG. 7 is a plan view showing the shape of a substrate with a prism removed.

FIG. 8 is a cross-sectional view showing the configuration of a photo-detecting device according to an embodiment of the invention as set forth in claim 7.

FIG. 9 is a sectional view showing a shape of a light receiving element which is a conventional example.

[Explanation of symbols]

 9 substrate 12 light receiving part 13 low refractive index layer 13a parallel plane part 13b taper part 14 high refractive index medium 20 low refractive index medium 25, 26 intermediate layer 31 high refractive index material 35 intermediate layer 36 intermediate layer (waveguide layer) 42 light Detector 45 Prism 46 Incident light coupling means 58 Guided light detection means

Claims (7)

[Claims] 1. A low-refractive index layer having a light-receiving portion formed on a substrate, a low-refractive-index layer laminated on the upper portion including the light-receiving portion and having a parallel flat portion parallel to the substrate surface and a taper portion not parallel to the low-refractive-index layer. The high refractive index medium is provided on the parallel plane portion and the tapered portion of the refractive index layer, penetrates from the high refractive index medium, passes through the tapered portion of the low refractive index layer, and passes through the substrate. Of the incident light incident from a specific direction that is not perpendicular to the light receiving part, the incident angle of light in the high refractive index medium with respect to the substrate surface is determined from the relationship between the refractive index of the high refractive index medium and the low refractive index layer. The angle of incidence of light in the high refractive index medium with respect to the tapered portion of the incident light is set to a large angle equal to or greater than the determined critical angle, and the refractive indices of the high refractive index medium and the low refractive index layer are set. From the critical angle determined from the relationship A photodetector characterized by being set to a small angle. 2. A low refractive index layer having a light receiving portion formed on a substrate, a parallel plane portion parallel to the substrate surface and a tapered portion which is laminated on the upper portion including the light receiving portion, and the low refractive index layer. The high refractive index medium provided on the parallel plane portion and the tapered portion of the refractive index layer, and the low refractive index medium provided on the high refractive index medium, The contact surface between the high-refractive index medium and the low-refractive index medium penetrates into a portion that is not parallel to the substrate, penetrates the tapered portion of the low-refractive index layer through the high-refractive index medium, and is transferred onto the substrate. The incident angle of light in the high refractive index medium with respect to the substrate surface, out of the incident light incident from a specific direction not perpendicular to the light receiving portion, is determined from the relationship between the refractive index of the high refractive index medium and the low refractive index layer. Set to a larger angle than the critical angle, and Of the incident light, the incident angle of light in the high refractive index medium with respect to the tapered portion is set to an angle smaller than a critical angle determined from the relationship between the refractive index of the high refractive index medium and the low refractive index layer. A photodetector characterized by the above. 3. The photodetector according to claim 1, wherein at least one intermediate layer is provided between the high refractive index medium and the low refractive index layer. 4. At least one of the intermediate layers is made of a high-refractive index material, and an intermediate layer made of the high-refractive index material and a low-refractive index layer are formed on the surface of the substrate on which the light receiving portion is formed. The contact surface, or a part or all of the contact surface between the intermediate layer made of the high refractive index substance and the intermediate layer made of a substance having a smaller refractive index than that of the lower layer is formed in a non-parallel tapered portion, and With respect to the surface of the substrate on which the light receiving section is formed, a contact surface between the intermediate layer made of the high refractive index material and the high refractive index medium, or the intermediate layer made of the high refractive index material and the upper layer 4. The photodetector according to claim 3, wherein a part or all of the contact surface with the intermediate layer made of a substance having a refractive index of a certain degree is formed in parallel parallel plane portions. 5. At least one intermediate layer is provided between the high refractive index medium and the low refractive index layer, and at least one of the intermediate layers is provided as a waveguide layer. Item 1. The photodetector according to item 1 or 2. 6. At least one intermediate layer is provided between the high refractive index medium and the low refractive index layer, and at least one of the intermediate layers is provided as a waveguide layer, and the high refractive index medium is provided. It is formed as a prism for optical coupling to the waveguiding layer, and an incident light coupling means for injecting incident light in a specific direction from the prism is provided, and the incident light coupling means intrudes through the prism. 3. The photodetector according to claim 1, wherein a taper-shaped photodetector is formed on the substrate surface of the lower surface of the prism to detect the emitted light. 7. A guided light detecting means for detecting guided light coupled to a waveguide layer from a light detecting portion via a prism is provided, and output information from the guided light detecting means and light in a specific direction is detected by the light detecting portion. 7. The photo-detecting device according to claim 6, further comprising a photo-coupling efficiency detecting means for obtaining a photo-coupling efficiency based on the obtained output information.