JP2014153430A - Integrated type light receiving element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized integrated type light receiving element having a good crosstalk characteristic.SOLUTION: An integrated type light receiving element comprises: a substrate 12; optical waveguides 17 (each of which includes a core part 16 and a clad 14) formed on the substrate 12; mirrors 18 each of which is disposed at the end of the optical waveguide 17; and a plurality of PDs 22 (each including a PD receiving part 20) arranged on the optical waveguide 17 side by side. The mirror 18 flips up light for the PDs 22 propagating the core part 16 by reflection. The integrated type light receiving element is manufactured through the steps in which the plurality of mirrors 18 corresponding to the plurality of core parts 16 respectively are each formed with an oblique mirror groove by anisotropic etching, the mirrors are formed by metal deposition, superfluous mirrors are removed by laser ablation, and the like.

Description

  The present invention relates to an integrated light receiving element, and in particular, from a light receiving element such as a planar lightwave circuit and a photodiode (also referred to as “PD” in this specification) used in the fields of optical communication and optical information processing. The present invention relates to an integrated light receiving element.

  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 lightwave circuit (also referred to as “PLC” (Planar Lightwave Circuit) in this specification) is known. The PLC has excellent characteristics such as low loss, high reliability, and high design flexibility, 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 (also referred to as “LD” in this specification), a multiplexer / demultiplexer, a branching / combining unit. And a PLC on which functional elements such as an optical modulator and an optical modulator are formed are mounted by optical coupling.

  Further, for example, in a node device in the wavelength division multiplex 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.

  Structures as shown in FIGS. 1 and 2 have been proposed as structures enabling optical coupling between an optical waveguide and a light receiving (emitting) light element. This structure is manufactured by providing an oblique groove (also referred to as “mirror groove” in this specification) in an optical waveguide by anisotropic etching, and depositing a metal or a multilayer film on the side surface of the oblique groove. be able to. A mirror can be manufactured by using the deposited metal or multilayer film as a reflecting surface that changes the optical path in a direction perpendicular to the substrate surface.

  FIG. 1 is a perspective view of a structure including a mirror that reflects light and couples to a PD according to the prior art, FIG. 2 is a diagram illustrating the same structure, and FIG. 1A is a top view. (B) is a front view, (c) is a cross-sectional view taken along the cross-sectional line AA ′ of (a).

  The structure shown in FIGS. 1 and 2 includes a substrate 12, an optical waveguide 17 on the substrate 12 (the optical waveguide 17 is composed of a core portion 16 and a cladding portion 14), and a mirror provided at the end of the optical waveguide 17. 18 and a plurality of PDs 22 arranged side by side on the optical waveguide 17 (the PD 22 includes the PD light receiving unit 20).

  1 and 2, the direction in which the core portion 16 extends is the x-axis direction, the normal direction of the surface 12 of the substrate on which the optical waveguide 17 is laminated is the z-axis direction, and the direction perpendicular to the x-axis and the z-axis. The coordinate axes are set so that is in the y-axis direction. This coordinate axis is assumed to be set similarly in the following description.

  As the substrate 12, a Si substrate or the like can be used. The optical waveguide 17 is composed of a plurality of core parts 16 and a clad part 14, and realizes a multi-channel. The light propagating through the core portion 16 is reflected by the mirror 18 to change the optical path, and is coupled to the PD light receiving portion of the corresponding PD 22.

Japanese Patent No. 3834024

  In a conventional integrated light-receiving element (structure shown in FIGS. 1 and 2 in which a planar mirror is attached over the entire surface of the waveguide end in an oblique groove), light scattering due to surface roughness of the mirror surface, or There is a problem that the crosstalk characteristics between channels deteriorate due to the light that leaks from the core part and propagates through the cladding part (also referred to as “stray light” in this specification) reflected by the mirror.

  The present invention has been made in view of these problems, and an object of the present invention is to provide an integrated light-receiving element having a small size and good crosstalk characteristics.

  The present invention relates to a substrate, an optical waveguide composed of a clad portion on the substrate and a plurality of core portions, and a plurality of mirrors corresponding to each of the plurality of core portions for reflecting light propagating through the plurality of core portions. And a plurality of PDs corresponding to each of the plurality of mirrors for coupling the light reflected by the mirror on the optical waveguide, wherein the optical waveguide has an oblique groove formed therein. And a mirror is formed at the end of the optical waveguide in the oblique groove.

  In one embodiment of the present invention, the width of each of the plurality of mirrors is wider than the full width at half maximum of the light intensity distribution of the light propagating through the core portion.

  In one embodiment of the present invention, the oblique grooves are filled with a light shielding agent.

  In one embodiment of the present invention, the oblique grooves are filled with an epoxy resin or a silicone resin.

  In the integrated light receiving element having the structure according to the present invention, an extra reflection film (mirror) is removed in order to reflect only necessary signal light.

  Accordingly, stray light is transmitted or absorbed without being reflected, and scattered light from the mirror surface is also reduced. This contributes to the improvement of crosstalk.

  As described above, it is possible to provide an integrated light receiving element having a small size and good crosstalk characteristics.

It is a perspective view explaining the structure provided with the mirror which reflects light and couple | bonds with PD based on a prior art. It is a figure explaining the structure provided with the mirror which reflects light and couple | bonds with PD based on a prior art, (a) is a top view, (b) is a front view, (c) is (a) Is a cross-sectional view taken along a cross-sectional line AA ′ of FIG. It is a perspective view explaining the structure of the integrated light receiving element based on this invention. It is a figure explaining the structure of the integrated light receiving element based on this invention, (a) is a top view, (b) is a front view, (c) is sectional drawing AA 'of (a). FIG. It is a figure explaining the manufacture flow of the integrated light receiving element based on this invention. It is a figure explaining the manufacturing method of the integrated light receiving element based on this invention.

  3 and 4 show the structure of the integrated light receiving element according to the present invention.

  FIG. 3 is a perspective view of the structure of the integrated light receiving element according to the present invention, FIG. 4 is a view for explaining the same structure, (a) is a top view, and (b) is a front view. (C) is sectional drawing in sectional line AA 'of (a).

  As shown in FIGS. 3 and 4, the integrated light-receiving element according to the present invention includes a substrate 12 and an optical waveguide 17 on the substrate 12 (the optical waveguide 17 includes a core portion 16 and a cladding portion 14). The mirror 18 is provided at the end of the optical waveguide 17 and a plurality of PDs 22 arranged side by side on the optical waveguide 17 (the PD 22 includes the PD light receiving unit 20).

  As the substrate 12, a Si substrate or the like can be used.

  The optical waveguide 17 includes a clad part 14 and a core part 16.

  The mirror 18 jumps up the light for PD 22 propagating through the core portion 16 by reflection. The mirror 18 is formed at the end of the optical waveguide 17 where one end of the core portion 16 and one end of the clad portion 14 exist.

  Here, in comparison with the conventional structure shown in FIGS. 1 and 2, the mirror is not a flat mirror over the entire surface of the waveguide end, but a plurality of mirrors corresponding to each of the plurality of core portions 16. Thus, the structure according to the present invention is different. The width of each mirror may be wider than the full width at half maximum of the light intensity distribution of light propagating through each of the core portions 16.

  Such a mirror 18 has (1) forming an oblique groove in the optical waveguide near the PD by anisotropic etching, and (2) metal (Au, Al, etc. as a metal) at the end of the optical waveguide exposed by the groove formation. Or by depositing a multilayer reflective film, and (3) removing excess mirrors by laser ablation or the like. A method for manufacturing the mirror will be described in detail later.

  In the “structure in which the mirror is formed over the entire surface of the waveguide end portion” shown in FIG. 1 and FIG. 2, the crosstalk characteristic between channels caused by reflection of stray light and coupling of the reflected stray light to the PD. There was a problem of deterioration. However, in the structure according to the present invention, stray light is not reflected by the mirror but is transmitted through the end of the waveguide and absorbed.

  In addition, in the “structure in which the mirror is formed over the entire surface of the waveguide end portion” shown in FIGS. 1 and 2, there is a problem of deterioration in crosstalk characteristics between channels due to light scattering by the plane mirror. . However, in the structure according to the present invention, since the mirror is formed by removing an excess portion, crosstalk between channels can be reduced.

  As shown in FIG. 4C, since the light is reflected by the mirror 18 so that the optical path of the light is parallel to the substrate main surface normal direction (z-axis direction), the angle formed between the substrate 12 and the mirror 18 is An element was fabricated by oblique etching so as to be 45 degrees. However, the angle formed between the substrate 12 and the mirror 18 may be an acute angle.

  FIG. 5 shows an example of a method for producing an integrated light receiving element according to the present invention.

  First, a clad part 14 and a core part 16 are formed on a substrate 12 such as a Si substrate to produce an optical waveguide 17, and a PD 22 is produced on the produced optical waveguide 17 (FIG. 5A). )).

  Next, a photoresist 24 is applied to the entire substrate 12 (including the optical waveguide 17 and the PD 22). After the exposure, development is performed, and the photoresist in the portion where the mirror groove for forming the mirror is formed is removed. In this specification, the portion where the photoresist is removed to form the mirror groove is referred to as a mirror opening (the mirror opening is indicated by reference numeral 26 in FIG. 5B).

  After the photoresist 24 is formed in a region other than the mirror opening 26, an oblique mirror groove 28 having an angle of 45 degrees with respect to the optical waveguide extension direction is formed by anisotropic etching (see FIG. 5C). Although a resist mask is used here, a metal mask can also be used, and the present invention is not limited by the mask material.

  Next, a metal is vapor-deposited on the waveguide end exposed in the mirror groove 28 to form a highly reflective mirror. Au or the like can be used as the metal to be deposited (see FIG. 5D). Alternatively, a mirror can be formed by depositing a multilayer reflective film by sputtering or the like.

  Then, the excess mirror is removed by laser ablation. As a result, a plurality of mirrors corresponding to each of the core portions 16 are created from one plane mirror formed over the entire surface of the waveguide end portion (see FIGS. 5E and 6). At this time, the width of each mirror is set to be wider than at least the full width at half maximum of the light intensity distribution of the light that propagates and reflects through the core portion. By doing so, it is possible to reflect an optical power of 96% or more. Further, if there is a mirror width that is about twice the full width at half maximum of the light intensity distribution of the light that propagates and reflects through the core, 99% or more of the optical power can be reflected. Further, it is desirable to form the mirror shape so as to correspond to the light intensity distribution. For example, when the light intensity distribution is elliptical, it is possible to improve the optical coupling efficiency with the PD by making the mirror shape seen from the x-axis direction also elliptical. As a laser used for ablation, a YAG laser having a wavelength of about 1.00 μm in the near infrared to infrared region can be used.

  Next, the photoresist is washed with a resist removing solution to remove all the resist once (not shown).

  The mirror groove 28 formed by anisotropic etching at the time of mirror formation may be filled with a light shielding agent. As the light-shielding agent, carbon black or a resin containing a pigment having absorption in the near infrared as a filler can be used. Alternatively, the mirror groove 28 may be filled with a resin having a refractive index close to that of the PLC (an epoxy resin or a silicone resin having a refractive index of 1.4 or more).

  In the above description, in the oblique mirror groove formed by anisotropic etching, metal is deposited over the entire surface of the waveguide end to form a plane mirror, and then the excess mirror is removed by laser ablation. A structure consisting of multiple mirrors was obtained.

  However, in the oblique mirror groove formed by anisotropic etching, before depositing the reflective film on the waveguide end, a mirror pattern mask for forming a plurality of mirrors is formed, and the reflective film is formed on the mask. It is also possible to obtain the structure shown in FIGS. 3 and 4 by depositing.

12 Substrate 14 Clad part 16 Core part 17 Optical waveguide 18 Mirror 20 PD light receiving part 22 PD
24 Photoresist 26 Mirror opening 28 Mirror groove

Claims (4)

A substrate,
On the substrate, an optical waveguide composed of a clad part and a plurality of core parts,
A plurality of mirrors corresponding to each of the plurality of core parts for reflecting light propagating through the plurality of core parts;
An integrated light receiving element comprising a plurality of PDs corresponding to each of the plurality of mirrors, on the optical waveguide, for coupling light reflected by the mirrors,
An oblique groove is formed in the optical waveguide,
An integrated light receiving element, wherein a mirror is formed at an end of the optical waveguide in the oblique groove.   2. The integrated light receiving element according to claim 1, wherein the width of each of the plurality of mirrors is wider than the full width at half maximum of the light intensity distribution of the light propagating through the core portion.   The integrated light receiving device according to claim 1, wherein the oblique grooves are filled with a light shielding agent.   The integrated light receiving device according to claim 1, wherein the oblique grooves are filled with an epoxy resin or a silicone resin.

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