JP5904901B2 - Optical coupling circuit element and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical coupling circuit element and a manufacturing method thereof. More specifically, the present invention relates to an optical coupling circuit element including a mirror structure for converting an optical path of light and coupling it to a photodiode (also referred to as “PD” in this specification) and a manufacturing method thereof.

  In recent years, with the spread of optical fiber transmission, a technique for integrating a large number of optical functional elements at a high density is required. As one of such techniques, a quartz-based planar optical waveguide circuit (hereinafter also referred to as PLC (Planar Lightwave Circuit)) is known. The PLC has excellent features such as low loss, high reliability, and high design freedom, and is promising as a platform for integrating multiple functions.

  Actually, the optical receiver at the transmission terminal station includes an optical module including a light receiving element such as a PD, a light emitting element such as a laser diode (hereinafter also referred to as an LD), a multiplexer / demultiplexer, a branching / coupling device, an optical modulation A PLC on which a functional element such as a container is formed is mounted by optical coupling. Further, for example, in a node device in the wavelength division multiplexing transmission system, a large number of PDs are integrated and mounted in order to monitor the light intensity of a plurality of optical waveguides in the PLC.

  As a structure that enables optical coupling between the optical waveguide and the light receiving and emitting optical element, a reflection mirror that converts the optical path in a direction perpendicular to the substrate surface as shown in FIG. Proposed structures have been proposed. As shown in FIG. 1, light traveling through an optical waveguide composed of a lower clad 102, a core 103, and an upper clad 104 is reflected perpendicularly to the substrate surface by a mirror 105 to the PD light receiving unit 106. Bonding structures have been proposed.

  The conditions required when manufacturing the optical path conversion mirror will be described. For example, the optical path conversion mirror used in the optical waveguide circuit of the above-described node device needs to satisfy the following various conditions.

  First, the node device has both optical waveguides to be monitored and optical waveguides that are not monitored, so that the optical waveguides that are not monitored are affected both physically and optically. It must be possible to extract light from any optical waveguide.

  Secondly, high positional accuracy and angular accuracy are required for optical coupling with the array type PD.

  Thirdly, high mirror surface roughness accuracy is required to prevent an increase in light receiving loss and deterioration of crosstalk in the PD.

  Fourth, for miniaturization and integration, it is required that the PD can be mounted in the vicinity of the optical path conversion mirror (for example, in a PD light receiving part having a light receiving diameter of 20 μm, the PD light receiving part extends from the end of the optical waveguide. The distance is preferably 10 μm to 100 μm).

  Fifth, it is desirable to fix the mirror so as not to cause misalignment in alignment and usage environment conditions when the PD is mounted.

  Sixth, it is desirable that the mirror can be added with a lens effect and a filter effect in order to increase the functionality of the optical waveguide circuit.

  A method for manufacturing a structure that reflects light in an optical coupling circuit will be described. As such a method, (1) a method of forming a groove inclined in the direction perpendicular to the substrate by machining with a dicing saw or the like in the PLC, and inserting a thin film reflection filter into the groove, (2) A method of forming a micromirror by laser ablation at one end of a polymer waveguide. (3) A groove is dug to the substrate surface by etching at the end of the waveguide, and a slope using the surface tension of the resin is formed in the groove. (4) a method of forming a mirror on this slope, (4) a method of forming a groove inclined at an angle with respect to the vertical direction of the substrate by etching at the end of the waveguide, and forming a reflector by a metal vapor deposition film or the like on the end surface. Proposed.

  Although the method (1) is simple, there is a possibility that the optical waveguide other than the desired optical waveguide may be cut together at the end of the waveguide, and there is a problem that the application is limited.

  The method (2) can be applied only to polymer waveguides, and there is a problem that processing by laser ablation is extremely difficult in a silica-based optical waveguide that is most expected as a practical PLC.

  The method (3) can be widely applied to various waveguide materials including a silica-based optical waveguide, and a structure that can be easily manufactured has also been proposed (see, for example, Patent Document 1). Patent Document 1 proposes an optical path conversion mirror having a structure in which a resin inclined surface is used as a mirror support, and having high mirror surface accuracy and high alignment accuracy with an optical waveguide, and has high performance and high productivity. However, since light passes through a plurality of interfaces having different refractive indexes before reaching the optical element, there is a possibility that insertion loss and reflection loss are increased.

  The method (4) is a method of performing mirror processing after processing an optical element after attaching an epitaxial film which is an element of the optical element, and a wafer process can be adopted. Therefore, it is advantageous in that both high-precision PD processing and mirror processing can be achieved (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

JP 2012-042515 A

Yuki Kurata, Keisuke Nasu, Munehisa Tamura, Yoshifumi Muramoto, Haruki Yokoyama, "High-speed InP-PD integrated silica-based PLC device using heterogeneous technology", Shinsokai, 2011, C-3-33 (2011) Kurata, Yu; Nasu, Yusuke; Tamura, Munehisa; Yokoyama, Haruki; Muramoto, Yoshifumi, "Heterogeneous Integration of High-Speed InP PDs on Silica-Based Planar Lightwave Circuit Platform", Proc. ECOC2011, Th.12, LeSaleve.5 , (2011)

  However, in the method (4) in which the groove inclined to the vertical direction of the substrate is formed by etching at the end of the waveguide and the reflector made of a metal vapor deposition film or the like is formed on the end surface, high-precision PD processing and Although mirror processing is compatible, there is a problem that the scattering angle of light after mirror reflection becomes large because only a flat mirror can be formed (see FIG. 2A). When the light scattering angle is increased, the light receiving diameter of the PD light receiving unit 206 has to be increased, and there is a problem that a PD element band cannot be obtained sufficiently (the PD element band is inversely proportional to the light receiving area).

  The present invention has been made in view of such a problem, and an object of the present invention is to satisfy the requirements for the optical path conversion mirror used in the optical waveguide circuit of the node device described above, and to have a light collecting property. And an optical waveguide circuit including the same.

The present invention relates to a substrate, an optical waveguide formed on the substrate, an optical element on the optical waveguide, and bonded only to the convex end surface of the optical waveguide in order to reflect light that propagates through the optical waveguide and couple it to the optical element. And an optical coupling circuit including a core and a clad, and the mirror is in a normal direction (z-axis direction) of a surface of the substrate on which the optical waveguide is formed. And the optical element is a photodiode (hereinafter referred to as PD), and the light receiving portion of the PD includes a p-contact layer and an n-contact layer, and the p-contact layer Is circular, and the n-contact layer has a curved structure along the circular shape of the p-contact layer .

The present invention relates to a substrate, an optical waveguide formed on the substrate, an optical element on the optical waveguide, and bonded only to the convex end surface of the optical waveguide in order to reflect light that propagates through the optical waveguide and couple it to the optical element. The optical waveguide is a multimode waveguide composed of a core and a clad , and a plurality of reflection directions differ from mode to mode on the end face of the optical waveguide. A mirror having a curved surface is provided, and the mirror is curved with respect to a normal direction (a z-axis direction) of a surface of the substrate on which the optical waveguide is formed .

The present invention relates to a substrate, an optical waveguide formed on the substrate, an optical element on the optical waveguide, and bonded only to the convex end surface of the optical waveguide in order to reflect light that propagates through the optical waveguide and couple it to the optical element. An optical coupling circuit including a core and a clad, and the mirror is in a normal direction (z-axis direction and the normal direction of the surface of the substrate on which the optical waveguide is formed) And is formed away from the end of the core from which the light of the optical waveguide is emitted .

The present invention relates to a substrate, an optical waveguide formed on the substrate, an optical element on the optical waveguide, and only bonded to a convex end surface of the optical waveguide in order to reflect light coupled to the optical waveguide and couple it to the optical element. The optical waveguide includes a core and a clad, and further includes a high dopant layer at two positions separated from the core in the y-axis direction by a predetermined distance. The mirror has a direction (y-axis) perpendicular to two axes of the normal direction (z-axis direction) of the surface of the substrate on which the optical waveguide is laminated and the extension direction (x-axis direction) of the optical waveguide. Characterized by being curved with respect to the direction)

The present invention relates to a substrate, an optical waveguide formed on the substrate, an optical element on the optical waveguide, and only bonded to a convex end surface of the optical waveguide in order to reflect light coupled to the optical waveguide and couple it to the optical element. An optical coupling circuit including a core and a clad, and the mirror is in a normal direction (z-axis direction) of a surface of a substrate on which the optical waveguide is stacked. ) And a direction perpendicular to the two axes of the optical waveguide extension direction (referred to as the x-axis direction) (referred to as the y-axis direction), and the optical element is a photodiode (hereinafter referred to as PD). The PD light receiving portion is composed of a p-contact layer and an n-contact layer, the p-contact layer is circular, and the n-contact layer is along the circular shape of the p-contact layer. Characterized by having a curved structure .

The present invention relates to a substrate, an optical waveguide formed on the substrate, an optical element on the optical waveguide, and only bonded to a convex end surface of the optical waveguide in order to reflect light coupled to the optical waveguide and couple it to the optical element. The optical waveguide is a multimode waveguide composed of a core and a clad , and a plurality of reflection directions differ from mode to mode on the end face of the optical waveguide. A mirror having a curved surface is provided, and the mirror has two axes: a normal direction of the surface of the substrate on which the optical waveguide is stacked (referred to as the z-axis direction) and an extension direction of the optical waveguide (referred to as the x-axis direction) It is characterized by being curved with respect to a direction perpendicular to the y-axis direction.

The present invention relates to a substrate, an optical waveguide formed on the substrate, an optical element on the optical waveguide, and only bonded to a convex end surface of the optical waveguide in order to reflect light coupled to the optical waveguide and couple it to the optical element. An optical coupling circuit including a core and a clad, and the mirror is in a normal direction (z-axis direction) of a surface of a substrate on which the optical waveguide is stacked. ) And the end of the core from which the light of the optical waveguide exits , which is curved with respect to a direction (referred to as the y-axis direction) perpendicular to two axes of the optical waveguide extension direction (referred to as the x-axis direction) It is formed away from.

  In the present invention, the curved mirror surface is formed by changing the position where the resist film is formed in the mirror forming portion in accordance with the angle of the mirror to be formed. Such a curved mirror surface can greatly improve the light condensing property (see FIG. 2B). As a result, the light receiving diameter of the PD light receiving unit 206 can be reduced.

  In addition, it is possible to form a curved mirror surface by arranging a high dopant layer having an etching rate faster than that of the optical waveguide portion in the vicinity of the optical waveguide in the vicinity of the mirror manufacturing position, and the same effect as described above can be obtained. .

  According to the method of the present invention, the mirror surface can be formed after the optical element is arranged in the optical waveguide portion. Therefore, the mirror formation conditions and shape can be changed with high accuracy in accordance with the production state of each optical element. It is possible.

It is a figure explaining the structure provided with the reflective mirror which reflects light and couple | bonds with PD based on a prior art. (A) is a figure explaining the subject of a prior art, (b) is a figure explaining the effect of this invention. It is a figure explaining the basic structure of the optical coupling circuit element based on the 1st Embodiment of this invention. It is a figure explaining the method to produce the optical coupling circuit element based on the 1st Embodiment of this invention. It is a figure explaining the optical coupling circuit element based on the 1st Embodiment of this invention. It is a figure explaining the method to produce the optical coupling circuit element based on the 2nd Embodiment of this invention. It is a figure explaining the optical coupling circuit element based on the 2nd Embodiment of this invention. It is a figure explaining the optical coupling circuit element based on the 3rd Embodiment of this invention. It is a figure explaining the method to produce the optical coupling circuit element based on the 3rd Embodiment of this invention. It is a figure explaining the structure of the optical waveguide used in order to produce the optical coupling circuit element based on the 4th Embodiment of this invention. It is a figure explaining the optical waveguide used in order to produce the optical coupling circuit element based on the 4th Embodiment of this invention. It is a figure explaining the optical coupling circuit element based on the 4th Embodiment of this invention. It is a figure explaining the structure of the optical coupling circuit element based on the 4th Embodiment of this invention. It is a figure for demonstrating PD which comprises the optical coupling circuit element based on the 5th Embodiment of this invention. It is a figure explaining the structure of the optical coupling circuit element based on the 6th Embodiment of this invention. It is a figure explaining the optical coupling circuit element based on the 6th Embodiment of this invention. It is a figure explaining the optical coupling circuit element based on the 7th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 3 shows a basic configuration of the optical coupling circuit element according to the present embodiment. The optical coupling circuit element according to this embodiment includes a substrate 301, an optical waveguide formed on the substrate 301, and an optical element 306 disposed on the optical waveguide. A curved mirror 305 is formed at the end of the optical waveguide near the optical element 306.

  As the substrate 301, a Si substrate is used.

  The optical waveguide includes a lower clad 302, a core 303, and an upper clad 304. The material of the optical waveguide is quartz glass. A (planar) optical circuit using a silica-based waveguide is called a silica-based PLC (Planar Lightwave Circuit).

  The mirror 305 is produced by forming an oblique groove in the optical waveguide by anisotropic etching and depositing a metal on the end of the optical waveguide. An example of anisotropic etching is anisotropic plasma etching. Au, Al, etc. can be used as the metal to be deposited. A method for manufacturing the mirror will be described in detail later. The mirror 305 has a curved surface, and has a focal position with respect to propagating light near the core portion 303 or the optical element 306 of the optical waveguide.

  The optical element 306 is PD or LD.

  Light traveling through the optical waveguide is reflected by the mirror 305 and coupled to the optical element 306. Since the mirror 305 has a focal position in the vicinity of the optical element, the light is reflected by the mirror 305 and then condensed and coupled to the optical element 306. Therefore, if the optical element is a PD, the speed of the PD can be increased.

  FIG. 4 shows an example of a method for producing an optical coupling circuit element according to the present invention.

  First, on the Si substrate 401, a lower clad 402 (thickness: 30 μm), a core 403 (thickness: 4.5 μm, width: 4.5 μm), and an upper clad 404 (thickness: 20 μm) are sequentially formed. A film is formed to produce an optical waveguide, and an optical element is placed on the produced optical waveguide. In the example shown in FIG. 4, a PD 405 is used as an optical element (see FIG. 4A).

  Next, a photoresist 406 is applied to the entire Si substrate (including the optical waveguide and the PD 405) on which the quartz-based waveguide is mounted. After the exposure, development is performed to remove the photoresist in a portion where a groove for forming a mirror (also referred to as “mirror groove” in this specification) is formed. A portion from which the photoresist is removed to form the mirror groove is referred to as a mirror opening 407 (see FIG. 4B).

  Using the remaining photoresist 406 as a mask, anisotropic plasma etching is performed from the mirror opening 407 to form a mirror groove 408 having an angle of 30 degrees with respect to the extending direction of the optical waveguide (see FIG. 4C). .

  The mirror groove processing (oblique groove processing) using this anisotropic plasma etching is performed as follows. After the etching chamber (hereinafter also referred to as “chamber”) is evacuated to a vacuum, an etching gas is introduced and a high frequency voltage is applied to generate plasma in the chamber. Thereafter, an electric field is induced in the chamber by applying a voltage to electrodes provided so that the electrode surfaces are parallel to the upper and lower portions of the chamber. Then, ions in the plasma are attracted to the electrode according to the electric field. Since ions are attracted and accelerated perpendicularly to the bottom surface (lower electrode) of the chamber, the ions collide with the object to be etched only from one direction, and anisotropic etching proceeds. Accordingly, by inclining and installing the PLC to be processed in the chamber, the ions collide obliquely with the PLC, the etching is performed obliquely, and oblique groove processing becomes possible.

  Next, the photoresist is washed with a resist removing solution to remove all the resist once. After removing the resist, the photoresist 406 is applied again to the entire Si substrate (including the optical waveguide and the PD 405). At this time, exposure / development is performed so that the width of the mirror opening 407 is about 20 μm wider in the direction of the PD 405 than when the mirror opening was previously formed (FIG. 4B). (See FIG. 4 (d)).

  After forming the mirror opening by a photo process, a mirror groove 408 having an angle of 45 degrees with respect to the optical waveguide extension direction is formed by anisotropic plasma etching (see FIG. 4E).

  Next, the photoresist is washed with a resist removing solution to remove all the resist once. After removing the resist, the photoresist 406 is applied again to the entire Si substrate (including the optical waveguide and the PD 405). At this time, exposure / development is performed so that the width of the mirror opening 407 is about 11 μm wider in the PD 405 direction than when the mirror opening was previously formed (FIG. 4D). (See FIG. 4 (f)).

After forming the mirror opening by a photo process, a mirror groove 408 having an angle of 60 degrees with respect to the direction of extension of the optical waveguide is formed by anisotropic plasma etching. Thereby, the surface which consists of three surfaces can be obtained in the optical waveguide end near PD405 (refer FIG.4 (g)). Wet etching uses chemicals, and the etching proceeds by a chemical reaction with the etching site. Examples of the oxide film etching solution include an NH4F: HF: H2O aqueous solution and an HF: H2O aqueous solution. The etching rate can be adjusted by changing the mixing ratio of the solution.

  Next, Au is vapor-deposited on the surface consisting of three surfaces to form a highly reflective mirror. By performing wet etching before Au deposition, an entirely curved mirror surface can be obtained (see FIG. 4H).

  The manufactured mirror reflects the light propagating from the optical waveguide, and has a curved surface so as to focus on the PD light receiving surface centering around the wavelength of about 1300 nm.

  In the example shown in FIG. 4, a three-sided mirror surface was obtained by performing anisotropic plasma etching three times, but a more versatile mirror surface by performing anisotropic plasma etching more than three times. Can be obtained. In this case, it is necessary to satisfy the following (Formula 1).

Here, n is an integer equal to or greater than 1, and D _{n + 1} = 0. Hereinafter, (Equation 1) will be described with reference to FIG.

L _n is a parameter indicating the extent to which the photoresist is applied in the n-th anisotropic plasma etching, and the distance from the PD to the mirror opening set in the n-th anisotropic plasma etching Represents.

D _n is a parameter indicating the depth to which the mirror groove is formed in the n-th anisotropic plasma etching, and the surface of the optical waveguide on which the PD is disposed and the n-th anisotropic plasma etching. Represents the distance between the lower end of the mirror surface formed by

θ _n is a parameter indicating the etching angle at the n-th anisotropic plasma etching, and represents the angle of the mirror surface formed by the n-th anisotropic plasma etching with respect to the optical waveguide extension direction.

In the case of the above-described embodiment (when a mirror surface having three surfaces is obtained by performing anisotropic plasma etching three times), n = 1 to 3, D ₁ = 50 μm, D ₂ = 29 μm, D ₃ = 27 μm, θ ₁ = 30 °, θ ₂ = 45 °, θ ₃ = 60 °, L ₁ = 86.6 μm, L ₂ = 65.4 μm, and L ₃ = 54.0 μm.

  In this embodiment, the coupling loss from the optical waveguide to the PD is 0.7 dB (1300 nm).

(Second Embodiment)
In the first embodiment, anisotropic plasma etching is performed a plurality of times to obtain a multi-surface mirror surface, and then wet etching is performed to obtain a generally curved surface. In this embodiment, as shown in FIG. 6, after obtaining a mirror surface composed of multiple surfaces by performing anisotropic plasma etching a plurality of times, by cutting only the periphery of each vertex of the mirror surface by wet etching, A mirror surface comprising a plurality of curved surfaces is formed.

  Since only the periphery of each vertex of the mirror surface is wet-etched, the wet etching of this embodiment basically reduces the etching amount as compared with the case of the first embodiment. Further, after forming the mirror surface, a metal film (Au, Al, etc.) can be deposited as necessary to improve the reflectance.

  Such an optical coupling circuit element having a mirror surface composed of a plurality of curved surfaces can be applied to a receiving circuit for separating multimodes. Referring to FIG. 7, an optical coupling circuit device according to this embodiment includes an Si substrate 701, an optical waveguide (lower cladding 702 (thickness: 20 μm)) formed on the Si substrate 701, and a core 703 (thickness). : 6.0 μm, width: 12.0 μm), upper clad 704 (thickness: 20 μm)), fundamental mode reception PD 705 and higher order mode reception PD 706 arranged on the optical waveguide, and mirror 707. The mirror 707 has a plurality of curved surfaces.

  As shown in FIG. 7, in the light propagation distribution, a large amount of light in the fundamental mode is distributed near the center of the core, while light in the higher order mode is distributed in a wider range. Therefore, by forming the curved surfaces forming the mirror surface at positions where the light propagation distribution of the fundamental mode is high or positions where the light propagation distribution of the higher order mode is high, the direction in which the light of the fundamental mode is reflected and the height of the reflection are high. The direction in which the light of the next mode is reflected can be made different. The fundamental mode light 708 reflected by the mirror 707 is coupled to the fundamental mode reception PD 705. The higher-order mode light 709 reflected by the mirror 707 is coupled to the higher-order mode reception PD 706.

  As a matter of course, in some cases, a part of the higher-order mode light is coupled to the fundamental mode reception PD, but by comparing with the reception characteristics of the higher-order mode reception PD, the fundamental mode light in the fundamental mode reception PD Only components can be extracted to improve reception characteristics.

  In this embodiment, the coupling loss from the optical waveguide to the PD is 0.7 dB (1550 nm) in the fundamental mode reception PD, and 1.0 dB (1550 nm) in the high-order mode reception PD.

(Third embodiment)
As shown in FIG. 8, the optical coupling circuit element according to the present embodiment includes a Si substrate 801, a first waveguide layer 802 on the Si substrate 801, and a second conductor on the first waveguide layer 802. It comprises a waveguide layer 803, a third waveguide layer 804 on the second waveguide layer 803, a PD 806 disposed on the third waveguide layer 804, and a mirror 807 having a plurality of curved surfaces. A high-dopant layer 805 is provided between the first waveguide layer 802 and the second waveguide layer 803 and between the second waveguide layer 803 and the third waveguide layer 804. It is laminated between. Ge, B, P, F, etc. can be used as the dopant material. Since these dopant substances may be added to the core or the clad portion of the optical waveguide, in that case, it is necessary to make them higher than their addition amount. However, since the etching rate differs even if the addition amount per unit volume is the same depending on the substance to be added, it is necessary to select a dopant substance according to the required etching amount. In addition, when a high etching rate is desired, it is desirable to add 1 mol% or more.

  The light that passes through the first waveguide layer 802, the light that passes through the second waveguide layer 803, and the light that passes through the third waveguide layer 804 are reflected in different directions by the mirror 807 and correspond to each other. Combine to individual PD.

  FIG. 9 shows a method for producing the optical coupling circuit element according to this embodiment. Also in this embodiment, similarly to the above-described embodiment, anisotropic plasma etching is performed a plurality of times to obtain a multi-surface mirror surface, and then a curved mirror surface is formed by wet etching. However, in the structure according to the present embodiment, since the high dopant layer is stacked between the waveguide layer, the portion of the high dopant layer is preferentially shaved in the wet etching process. . By utilizing this property, a mirror having a plurality of curved surfaces can be obtained.

  In this embodiment, the coupling loss from the optical waveguide to the PD is 0.8 dB (1480 nm) for the first waveguide layer and 0.9 dB (1300 nm) for the second waveguide layer. The waveguide layer was 1.0 dB (1550 nm).

(Fourth embodiment)
In the first to third embodiments described above, the mirror surface curved with respect to the normal direction of the surface of the substrate on which the optical waveguide is formed (also referred to as “vertically curved mirror surface” in this specification). Formed. In this embodiment, a mirror surface that is curved with respect to a direction perpendicular to both the normal direction of the surface of the substrate on which the optical waveguide is formed and the extension direction of the core (in this specification, “mirror surface that is curved in the horizontal direction”). Or “mirror surface curved in the lateral direction”).

  In order to obtain a mirror surface curved in the horizontal direction, the optical waveguide used in this embodiment has a structure shown in FIG.

  FIG. 10A is a top view of the optical waveguide used in the present embodiment. FIG. 10B is a front view of the optical waveguide used in this embodiment. FIG. 10C is a cross-sectional view of the optical waveguide used in this embodiment, taken along a cross-sectional line A-A ′ in FIG. In FIG. 10, the direction in which the core extends is the x-axis direction, the normal direction of the surface (not shown) of the substrate on which the waveguide is disposed is the z-axis direction, and the direction perpendicular to the x-axis and z-axis is the y-axis direction. The coordinate axes are set so that This coordinate axis is set similarly in the following description.

  The optical waveguide used in this embodiment is composed of a core 1001 and a clad 1002 as in the first embodiment (see FIG. 10C). However, the optical waveguide used in this embodiment is provided with high dopant layers 1003-1 and 1003-2 in the periphery of the core 1001 at the end of the optical waveguide near the location where the PD will be disposed in the future. This is different from the first embodiment in terms of points (see FIGS. 10A and 10B).

  As shown in FIG. 10A and FIG. 10B, the optical waveguide used in this embodiment is located at a predetermined distance from the core 1001 along the y-axis direction (two locations around the core). High dopant layers 1003-1 and 1003-2.

  The optical waveguide shown in FIG. 10 can be manufactured by film deposition or the like, as in general waveguide manufacturing. Further, the optical waveguide shown in FIG. 10 can also be manufactured by injecting a dopant after preparing an optical waveguide composed of a core and a clad. Ge, B, P, and F can be used as the dopant. Since these dopant substances may be added to the core or the clad portion of the optical waveguide, in that case, it is necessary to make them higher than their addition amount. However, since the etching rate differs even if the addition amount per unit volume is the same depending on the substance to be added, it is necessary to select a dopant substance according to the required etching amount. In addition, when a high etching rate is desired, it is desirable to add 1 mol% or more.

  FIG. 11 shows a front view (FIG. 11A) of the optical waveguide used in the present embodiment and a graph of the dopant (B) concentration with respect to the position in the y-axis direction (FIG. 11B).

  An optical coupling circuit element manufactured using the optical waveguide shown in FIGS. 10 and 11 will be described. An optical waveguide used in this embodiment is manufactured on a Si substrate, and a PD is arranged on the manufactured optical waveguide. Next, anisotropic plasma etching is performed once to form an oblique groove with respect to the optical waveguide. Next, a metal film (Au, Al, etc.) is deposited on the surface formed by anisotropic plasma etching to form a mirror. The manufacturing process is the same as that of the first embodiment except that the number of times of anisotropic plasma etching is one and the structure of the optical waveguide to be used is different.

  FIG. 12 shows the configuration of the optical coupling circuit element according to this embodiment after the manufacturing process. FIG. 12 is a top view of the optical coupling circuit element according to the present embodiment (the substrate is not shown).

  As described above, the optical waveguide used in this embodiment has a configuration in which a high dopant layer is provided around the core at the end of the optical waveguide near the location where the PD is disposed. In the anisotropic plasma etching for forming the mirror surface, the high dopant layer is preferentially cut, so that the vicinity of the cladding and the edge of the high dopant layer is cut more than the vicinity of the core. By utilizing this property, it is possible to form a surface curved in the plane direction.

  In this embodiment, the coupling loss from the optical waveguide to the PD is 0.7 dB (1300 nm).

  This embodiment can be used with the first embodiment. Specifically, a mirror surface curved in both the vertical direction and the horizontal direction can be formed by performing anisotropic plasma etching a plurality of times on the optical waveguide used in the present embodiment. . Thereby, the shape of the mirror part in which light reflects can be made into a spherical shape.

  FIG. 13 is a diagram illustrating a structure of an optical coupling circuit element including a spherical mirror. FIG. 13A is a top view of the optical coupling circuit element. FIG. 13B is a front view of the optical coupling circuit element. FIG. 13C is a cross-sectional view of the optical coupling circuit element taken along a cross-sectional line A-A ′ in FIG. With the spherical mirror structure, the signal light can be condensed in the vertical direction and the horizontal direction.

  In the above-described embodiment, an optical waveguide provided with a high dopant layer is used to form a mirror that is curved in the horizontal direction. However, a photomask designed so that a curved structure can be formed instead of the high dopant layer. A mirror curved in the horizontal direction can also be formed by using.

(Fifth embodiment)
In this embodiment, the mirror structure curved in the horizontal direction according to the fourth embodiment is used together with a PD having a specific structure. As a result, it is possible to arrange a plurality of PDs close to each other while improving the light collecting characteristics.

  FIG. 14A is a top view of a state in which light reflected by a plane mirror is coupled to a PD light receiving unit having a conventional structure. In FIG. 14A and later-described FIG. 14B, the components other than the mirror and the light receiving unit are omitted for illustration. The PD light receiving unit includes a p contact layer 1401 and an n contact layer 1402. The p contact layer 1401 has a circular shape when viewed from above. Since the light 1411 reflected by the plane mirror 1403 is not particularly collected, the n-contact layer 1402 must have a linear shape along the plane of the plane mirror 1403 (see FIG. 14A).

  On the other hand, in this embodiment, the light 1411 reflected by the curved mirror 1404 is collected and coupled to the PD light receiving unit (see FIG. 14B). The p contact layer 1401 has a circular shape when viewed from above. The n contact layer 1402 has a curved shape along the circular shape of the p contact layer 1401. With this configuration, the distance from the mirror surface to the PD light receiving unit can be made equal and short, so that it is possible to improve the coupling rate of received light to the PD and the light receiving characteristics of high-speed signals.

  In addition, by providing the n contact layer with a curved shape along the circular shape of the p contact layer, the size of the PD can be made smaller than the size of the conventional PD (see FIG. 14C).

  Further, the coupling loss from the optical waveguide to the PD is 0.9 dB (1550 nm) in the structure shown in FIG. 14A, and 0.5 dB (1550 nm) in the structure shown in FIG. 14B. ) Was 25 GHz, whereas FIG. 14B was 54 GHz.

(Sixth embodiment)
In the present embodiment, the mirror structure curved in the horizontal direction described in the fourth embodiment is used together with the multimode waveguide. An optical coupling circuit element according to this embodiment is shown in FIG.

  FIG. 15A is a top view of the optical coupling circuit element according to the present embodiment. FIG. 15B is a front view of the optical coupling circuit element according to the present embodiment. FIG. 15C is a cross-sectional view of the optical coupling circuit element according to the present embodiment taken along a cross-sectional line A-A ′ in FIG.

  As shown in FIG. 15, the optical coupling circuit element according to this embodiment includes an optical waveguide composed of a core 1501 and a clad 1502, a PD 1504, and a mirror 1505.

  In this embodiment, the optical waveguide composed of the core 1501 and the clad 1502 is a multimode waveguide. As shown in FIG. 15B, the cross section of the core 1501 perpendicular to the light propagation direction is a horizontally long rectangle.

  The mirror 1505 has a structure curved in the horizontal direction. In the anisotropic plasma etching, it is described in the (fourth embodiment) to obtain a structure curved in the horizontal direction by utilizing the property that the high dopant layers 1503-1 and 1503-2 are preferentially shaved. . Multimode light propagating through the optical waveguide is reflected by the curved mirror 1505 and coupled to the PD 1504.

  In the present embodiment, an optical coupling circuit element having both a horizontally curved mirror and a multimode waveguide is used. FIG. 16B is a diagram illustrating the intensity distribution of multimode signal light propagating through a multimode waveguide having a rectangular cross section. FIG. 16C is a diagram showing the intensity distribution when the multimode signal light reflected by the mirror is coupled to the PD. As shown in FIGS. 16B and 16C, the multimode signal light is collected in the lateral direction by a curved mirror 1604. Therefore, the elliptical light field distribution can be converted into a circular light field distribution. Therefore, since the shape of the optical field can be converted in accordance with a circular PD light receiving unit whose manufacturing technique is mature, it contributes to miniaturization, speeding up, and high sensitivity of the PD.

  In this embodiment, the coupling loss from the optical waveguide to the PD was 0.7 dB (1480 nm).

(Seventh embodiment)
FIG. 17 shows the structure of the optical coupling circuit element according to this embodiment. As shown in FIG. 17, the mirror 1704 is formed at a location away from the end of the core 1701. The optical waveguide shown in FIG. 17 can be manufactured by film deposition or the like, as in general waveguide manufacturing.

  Light propagating through the core 1701 is emitted from the end portion of the core 1701, propagates through the waveguide between the end portion of the core 1701 and the mirror 1704, is reflected by the mirror 1704, and is coupled to the PD 1703. Since the mirror 1704 is located away from the end of the core 1701, the light propagates from the end of the core 1701 toward the mirror 1705, is once diffused and reflected by the mirror surface, and then collected and coupled to the PD 1704. . Compared with the reflected light when the core end face coincides with the mirror surface, the light that diffuses and propagates is reflected by the mirror over a larger area, so the influence of the surface roughness of the mirror surface is reduced. It is possible to suppress. Therefore, the light collection accuracy can be improved.

  In this embodiment, the coupling loss from the optical waveguide to the PD is 0.6 dB (1480 nm).

100 PLC
101 Substrate 102 Lower clad 103 Core 104 Upper clad 105 Mirror 106 PD light receiving portion 107 PD

200 PLC
201 Substrate 202 Lower clad 203 Core 204 Upper clad 205 Mirror 206 PD light receiving unit 207 PD

301 Substrate 302 Lower clad 303 Core 304 Upper clad 305 Mirror 306 Optical element

401 Si substrate 402 Lower clad 403 Core 404 Upper clad 405 PD
406 Photoresist 407 Mirror opening 408 Mirror groove

501 PD

601 Si substrate 602 Lower clad 603 Core 604 Upper clad 605 Mirror

701 Si substrate 702 Lower clad 703 Core 704 Upper clad 705 Basic mode reception PD
706 High-order mode reception PD
707 Mirror 708 Fundamental mode light reflected by mirror 709 High-order mode light reflected by mirror

801 Si substrate 802 First waveguide layer 803 Second waveguide layer 804 Third waveguide layer 805 High dopant layer 806 PD
807 mirror

1001 Core 1002 Clad 1003-1, 1003-2 High dopant layer

1101 Core 1102 Clad 1103-1, 1103-2 High dopant layer

1201 Core 1202 Clad 1203-1, 1203-2 High dopant layer 1204 PD
1205 mirror

1301 Core 1302 Clad 1303-1, 1303-2 High dopant layer 1304 PD
1305 Spherical mirror

1401 p contact layer 1402 n contact layer 1403 plane mirror 1404 curved mirror 1411 reflected light

1501 Core 1502 Clad 1503-1, 1503-2 High dopant layer 1504 PD
1505 curved mirror

1601 Core 1602 Clad 1603 PD
1604 curved mirror

1701 Core 1702 Clad 1703 PD
1704 mirror

Claims (7)

A substrate,
An optical waveguide formed on the substrate;
An optical element on the optical waveguide;
A mirror formed so as to be joined only to the convex end surface of the optical waveguide in order to reflect and propagate the light propagating through the optical waveguide to the optical element;
An optical coupling circuit comprising:
The optical waveguide is composed of a core and a clad,
The mirror is curved with respect to the normal direction (the z-axis direction) of the surface of the substrate on which the optical waveguide is formed,
The optical element is a photodiode (hereinafter referred to as PD),
The light receiving portion of the PD is composed of a p contact layer and an n contact layer,
The p-contact layer is circular;
The n-type contact layer has a curved structure along the circular shape of the p-type contact layer.
A substrate,
An optical waveguide formed on the substrate;
An optical element on the optical waveguide;
A mirror formed so as to be joined only to the convex end surface of the optical waveguide in order to reflect and propagate the light propagating through the optical waveguide to the optical element;
An optical coupling circuit comprising:
The optical waveguide is a multi-mode waveguide composed of a core and a clad , and includes a mirror having a plurality of curved surfaces having different reflection directions for each mode on an end surface of the optical waveguide ,
The optical coupling circuit , wherein the mirror is curved with respect to a normal direction (a z-axis direction) of a surface of the substrate on which the optical waveguide is formed .
A substrate,
An optical waveguide formed on the substrate;
An optical element on the optical waveguide;
A mirror formed so as to be joined only to the convex end surface of the optical waveguide in order to reflect and propagate the light propagating through the optical waveguide to the optical element;
An optical coupling circuit comprising:
The optical waveguide is composed of a core and a clad,
The mirror is curved with respect to the normal direction (z-axis direction) of the surface of the substrate on which the optical waveguide is formed, and is formed apart from the core end portion from which the light of the optical waveguide is emitted. An optical coupling circuit. A substrate,
An optical waveguide formed on the substrate;
An optical element on the optical waveguide;
A mirror formed so as to be joined only to the convex end surface of the optical waveguide in order to reflect and propagate the light propagating through the optical waveguide to the optical element;
An optical coupling circuit comprising:
The optical waveguide is composed of a core and a clad, and further includes a high dopant layer at two positions away from the core along the y-axis direction ,
The mirror has a direction perpendicular to two axes (a normal direction of the surface of the substrate on which the optical waveguide is laminated (referred to as z-axis direction) and an extension direction of the optical waveguide (referred to as x-axis direction)). An optical coupling circuit which is curved with respect to the y-axis direction) . A substrate,
An optical waveguide formed on the substrate;
An optical element on the optical waveguide;
A mirror formed so as to be joined only to the convex end surface of the optical waveguide in order to reflect and propagate the light propagating through the optical waveguide to the optical element;
An optical coupling circuit comprising:
The optical waveguide is composed of a core and a clad,
The mirror has a direction perpendicular to two axes (a normal direction of the surface of the substrate on which the optical waveguide is laminated (referred to as z-axis direction) and an extension direction of the optical waveguide (referred to as x-axis direction)). curved in the y-axis direction)
The optical element is a photodiode (hereinafter referred to as PD),
The light receiving portion of the PD is composed of a p contact layer and an n contact layer,
The p-contact layer is circular;
The n-type contact layer has a curved structure along the circular shape of the p-type contact layer. A substrate,
An optical waveguide formed on the substrate;
An optical element on the optical waveguide;
A mirror formed so as to be joined only to the convex end surface of the optical waveguide in order to reflect and propagate the light propagating through the optical waveguide to the optical element;
An optical coupling circuit comprising:
The optical waveguide is a multi-mode waveguide composed of a core and a clad , and includes a mirror having a plurality of curved surfaces having different reflection directions for each mode on an end surface of the optical waveguide ,
The mirror has a direction perpendicular to two axes (a normal direction of the surface of the substrate on which the optical waveguide is laminated (referred to as z-axis direction) and an extension direction of the optical waveguide (referred to as x-axis direction)). An optical coupling circuit which is curved with respect to the y-axis direction) . A substrate,
An optical waveguide formed on the substrate;
An optical element on the optical waveguide;
A mirror formed so as to be joined only to the convex end surface of the optical waveguide in order to reflect and propagate the light propagating through the optical waveguide to the optical element;
An optical coupling circuit comprising:
The optical waveguide is composed of a core and a clad,
The mirror has a direction perpendicular to two axes (a normal direction of the surface of the substrate on which the optical waveguide is laminated (referred to as z-axis direction) and an extension direction of the optical waveguide (referred to as x-axis direction)). The optical coupling circuit is curved with respect to the y-axis direction) and is formed away from the end of the core from which the light of the optical waveguide is emitted.