JP6414295B2 - Optical device and optical device manufacturing method - Google Patents

Description

  The present invention relates to an optical device and an optical device manufacturing method.

  Conventionally, a light receiving element that receives light emitted from an optical waveguide is sometimes provided outside or on the front or side of the substrate having the optical waveguide. In this structure, the light receiving element is externally attached to the substrate. For this reason, the package of the optical device is increased by the amount of the light receiving element.

  By the way, in the structure in which the chip is mounted on the substrate by flip chip and the underfill material is filled between the two, an underfill material such as an adhesive is applied to the region where the underfill material is not filled by the groove provided in the substrate. Has been disclosed (for example, see Patent Document 1). Further, a technique for preventing the adhesive from flowing out to the reflection surface of the end portion of the optical waveguide by a convex portion provided at the end portion of the optical waveguide is disclosed (for example, see Patent Document 2).

JP 2003-243444 A JP 2008-145684 A

  You may make it adhere | attach a light receiving element on the surface of a board | substrate with an adhesive agent, for example, without providing a light receiving element in the outer side of a board | substrate. In this way, since the light receiving element can be accommodated in the size of the substrate, the package can be reduced in size. However, when light incident on the light receiving element from the optical waveguide passes through the adhesive containing bubbles, the light is irregularly reflected by the bubbles, so that the amount of light received by the light receiving element is reduced. When a groove is provided in the substrate to prevent the adhesive from flowing into the optical path from the optical waveguide to the light receiving element, the groove cannot be provided so as to cross the optical waveguide, so that the adhesive cannot be prevented from flowing in. There is a case.

  An object of the present invention is to provide an optical device capable of receiving light traveling in an optical waveguide with a light receiving element fixed to the surface of the substrate, and a method for manufacturing the optical device.

  In one proposal, the optical device includes an optical waveguide branched into signal light and monitor light, a reflection groove provided at a midway position of the optical waveguide of the monitor light, and the light emitted from the optical waveguide is reflected at the bottom surface, A substrate having an electro-optic effect, a light receiving element fixed to the substrate on the reflective groove, and a convex surface having a predetermined height so as to surround the reflective groove. A reflective groove protecting convex portion that is provided in contact with the light receiving element and prevents an adhesive that fixes the light receiving element to the substrate from flowing into a portion of the reflective groove where the light passes. The light emitted from the optical waveguide into the reflection groove is reflected on the bottom surface of the reflection groove while passing through the space in the reflection groove and is incident on the light receiving element. The wire is connected to the light receiving element at the position of It is a requirement to be connected by the bindings.

  According to this optical device, light traveling in the optical waveguide can be received by the light receiving element fixed to the substrate surface. Further, according to this method of manufacturing an optical device, it is possible to manufacture an optical device that can receive light traveling in the optical waveguide with a light receiving element fixed to the substrate surface.

FIG. 1 is a diagram illustrating an example of an optical device according to an embodiment. FIG. 2 is a diagram illustrating a first example of the LN modulator according to the embodiment. FIG. 3 is a diagram showing a cross section in the substrate thickness direction along the cutting line A-A ′ of FIG. 2. FIG. 4 is a diagram illustrating a second example of the LN modulator according to the embodiment. FIG. 5 is a diagram showing a cross section in the substrate thickness direction along the cutting line B-B ′ of FIG. 4. FIG. 6 is a diagram illustrating a third example of the LN modulator according to the embodiment. FIG. 7 is a diagram showing a cross section in the substrate thickness direction along the section line C-C ′ of FIG. 6. FIG. 8 is a diagram illustrating a fourth example of the LN modulator according to the embodiment, and is a diagram illustrating a cross section in the substrate thickness direction along the section line C-C ′ of FIG. 6. FIG. 9 is a diagram illustrating a first example of a pattern of a reflection groove protecting convex portion and a wiring protecting convex portion in the LN modulator according to the embodiment. FIG. 10 is a diagram illustrating a second example of the pattern of the reflection groove protecting convex portion and the wiring protecting convex portion in the LN modulator according to the embodiment. FIG. 11 is a diagram illustrating a third example of the pattern of the reflection groove protecting convex portion and the wiring protecting convex portion in the LN modulator according to the embodiment. FIG. 12 is a diagram illustrating a fourth example of the pattern of the reflection groove protecting convex portion and the wiring protecting convex portion in the LN modulator according to the embodiment. FIG. 13 is a diagram illustrating a fifth example of the pattern of the reflection groove protecting convex portion and the wiring protecting convex portion in the LN modulator according to the embodiment. FIG. 14 is a diagram illustrating a fifth example of the LN modulator according to the embodiment. FIG. 15 is a diagram illustrating a sixth example of the LN modulator according to the embodiment. FIG. 16 is a diagram illustrating a waveform in a state where the phase of the signal light and the monitor light are out of phase. FIG. 17 is a diagram illustrating a seventh example of the LN modulator according to the embodiment, and is a diagram illustrating a cross section in the substrate thickness direction along a cutting line A-A ′ of FIG. 2. FIG. 18 is a diagram (part 1) illustrating an example of the method of manufacturing the optical device according to the embodiment. FIG. 19 is a second diagram illustrating an example of the method of manufacturing the optical device according to the embodiment. FIG. 20 is a diagram (No. 3) illustrating an example of the optical device manufacturing method according to the embodiment.

  Exemplary embodiments of an optical device and a method for manufacturing the optical device will be described below in detail with reference to the accompanying drawings. In the following description of each embodiment, the same components are denoted by the same reference numerals, and redundant descriptions are omitted.

Example of Optical Device FIG. 1 is a diagram illustrating an example of an optical device according to an embodiment. As shown in FIG. 1, the optical device has an optical waveguide 2 that guides light and a reflection groove 3 that reflects light on a substrate 1. The substrate 1 has an electro-optic effect. A Z-cut crystal substrate such as LiNbO ₃ (hereinafter abbreviated as LN) or LiTaO ₂ is an example of the substrate 1 having an electro-optic effect.

  The reflection groove 3 is provided in a part of the optical waveguide 2. The reflection groove 3 has a bottom surface 4 on which light emitted from the optical waveguide 2 is reflected. The light receiving element 5 is fixed to the substrate 1 on the reflection groove 3. For example, a photodiode (PD) is an example of the light receiving element 5.

  In the optical device shown in FIG. 1, at least a part of the light 6 a that has traveled in the optical waveguide 2 is caused by the medium of the optical waveguide 2 and the medium of the space 7 in the reflection groove 3 at the end face of the reflection groove 3. The light is refracted at a determined refraction angle and is emitted into the reflection groove 3. The light 6 b incident on the reflection groove 3 travels toward the bottom surface 4 of the reflection groove 3 and is reflected on the bottom surface 4 of the reflection groove 3 while passing through the space 7 in the reflection groove 3.

  The light 6c reflected by the bottom surface 4 of the reflection groove 3 travels upward. In the example shown in FIG. 1, the light receiving element 5 is, for example, a back-illuminated type element. Therefore, the light 6 c reflected by the bottom surface 4 of the reflecting groove 3 is reflected in the space 7 in the reflecting groove 3 on the back surface of the light receiving element 5. The light is refracted at a refraction angle determined by the medium and the medium of the light receiving element 5 and enters the light receiving element 5. The light 6 d incident on the light receiving element 5 enters the light receiving portion 8 of the light receiving element 5.

  According to the optical device shown in FIG. 1, the light traveling from the optical waveguide 2 is fixed to the surface of the substrate 1 in order to reflect the light emitted from the optical waveguide 2 on the bottom surface 4 of the reflection groove 3 and to go upward. The received light receiving element 5 can receive light.

The optical device shown in FIG. 1 is, for example, a LiNbO ₃ external modulator (hereinafter referred to as an LN modulator), an optical modulator using a polymer material or a semiconductor material such as InP or Si, or a PLC (Planar Lightwave Circuit), planar light. The present invention can be applied to an optical device such as a Mach-Zehnder variable optical attenuator formed by a circuit). The case where the optical device shown in FIG. 1 is applied to an LN modulator for coherent communication having a polarization multiplexing function will be described below.

First Example of LN Modulator FIG. 2 is a diagram illustrating a first example of the LN modulator according to the embodiment. FIG. 3 is a diagram showing a cross section in the substrate thickness direction along the cutting line AA ′ in FIG. 2. The cutting line AA ′ is a direction in the vicinity of the light receiving element 5 that passes through the light receiving element 5 and is parallel to the input direction of light input to the LN modulator or the output direction of signal light output from the LN modulator. Extend to. Therefore, in FIG. 3, the vicinity of the light receiving element 5 passes through the light receiving element 5 and is parallel to the input direction of light input to the LN modulator or the output direction of signal light output from the LN modulator. A cut section is shown.

  As illustrated in FIGS. 2 and 3, the LN modulator includes, for example, an X-polarization IQ modulation unit optical waveguide 11 and a Y-polarization IQ modulation unit optical waveguide 12 on a substrate 1. A modulation electrode (not shown) is provided on the X-polarization IQ modulator optical waveguide 11 and the Y-polarization IQ modulator optical waveguide 12, respectively. X-polarized signal light is output from the optical waveguide 11 for X-polarization IQ modulation section. Y-polarized signal light is output from the optical waveguide 12 for Y-polarization IQ modulation section. The X-polarized signal light and the Y-polarized signal light output from the LN modulation area may be multiplexed, for example, in a polarization multiplexing unit (not shown).

  The monitoring light receiving element 5 includes an optical waveguide 2 branched from the X-polarization IQ modulation unit optical waveguide 11 for monitoring and an optical waveguide 2 branched from the Y-polarization IQ modulation unit optical waveguide 12 for monitoring. Is provided.

  The reflection groove 3 is formed below the light receiving element 5 in the monitoring optical waveguide 2. The reflection groove 3 may be formed shallower than the thickness of the optical waveguide 2 or may be formed to the same depth as the thickness of the optical waveguide 2. The depth of the reflection groove 3 may be, for example, about 1 to 15 μm. If the depth of the reflection groove 3 is about 1 to 15 μm, at least part of the light 6 a that has traveled through the optical waveguide 2 is emitted into the reflection groove 3. A portion through which light passes in the space 7 in the reflection groove 3 may be filled with air.

  In the reflection groove 3, an end surface from which light is emitted from the optical waveguide 2 is an inclined surface 13 that refracts light emitted from the optical waveguide 2 toward the bottom surface 4 of the reflection groove 3. As a result, the light 6 b emitted from the optical waveguide 2 and entering the reflection groove 3 can be advanced toward the bottom surface 4 of the reflection groove 3.

The inclined surface 13 forms an angle smaller than the angle at which the light 6 a traveling in the optical waveguide 2 is totally reflected by the inclined surface 13 with respect to the thickness direction of the substrate 1. For example, when a portion where light passes in the space 7 in the reflection groove 3 is filled with air, the refractive index of LiNbO ₃ is 2.2 and the refractive index of air is 1, so Due to the difference, the angle at which the light 6 a traveling in the optical waveguide 2 is totally reflected by the inclined surface 13 is 27.85 ° with respect to the thickness direction of the substrate 1.

  Therefore, the angle formed by the inclined surface 13 with respect to the thickness direction of the substrate 1 may be smaller than 27.85 °. If the inclined surface 13 is inclined at an angle smaller than 27.85 ° with respect to the thickness direction of the substrate 1, the light 6 a traveling in the optical waveguide 2 is prevented from being totally reflected by the inclined surface 13. 2 can be emitted into the reflection groove 3.

  The angle formed by the inclined surface 13 with respect to the thickness direction of the substrate 1 may be set to, for example, 5 ° to 20 °. In this way, even when the inclination of the inclined surface 13 deviates from the set value due to an error in manufacturing the reflection groove 3, the angle at which the inclined surface 13 forms with respect to the thickness direction of the substrate 1 is the angle at which total reflection occurs. That is, the angle can be smaller than 27.85 °.

  In the reflection groove 3, a reflection film 14 is provided on the inner surface except for the inclined surface 13 from which light is emitted from the optical waveguide 2. Since the reflectance at the bottom surface 4 of the reflection groove 3 is improved by the reflection film 14, the amount of light 6c reflected by the bottom surface 4 of the reflection groove 3 can be increased. The reflective film 14 may be made of a metal such as Au (gold).

  The reflective film 14 is a light shielding film that blocks light from entering the reflective groove 3 from the bottom surface 4 of the reflective groove 3. As a result, of the light 6 a that has traveled in the optical waveguide 2, the light traveling in the optical waveguide 2 without being emitted from the inclined surface 13 of the reflection groove 3 penetrates into the reflection groove 3 from the bottom surface 4 of the reflection groove 3. Can be prevented.

  A buffer layer and an Si layer 15 may be provided on the surface of the substrate 1. Of the buffer layer and the Si layer 15, the buffer layer can prevent light absorption loss due to, for example, electrodes provided on the substrate surface or electrical wiring, and can achieve impedance matching. For example, temperature drift can be suppressed by the Si layer. The light receiving element 5 may be fixed to the substrate 1 by bonding the back surface of the light receiving element 5 to the buffer layer and the Si layer 15 with, for example, an adhesive 16.

  On the surface of the substrate 1, strictly speaking, on the surface of the buffer layer and the Si layer 15, the light receiving element electrical wires 17, 18, the X polarization IQ modulation unit optical waveguide 11 and the Y polarization IQ modulation unit optical waveguide 12 are provided. A modulation electrode (not shown) is provided on each of the above. One end of a metal wire 19 is connected to the light receiving element electrical wires 17 and 18 by wire bonding. The other end of the wire 19 is connected to the anode or cathode electrode 20 of the light receiving element 5 by wire bonding. That is, the light receiving element electrical wires 17 and 18 and the light receiving element 5 are electrically connected by the wire 19. The light receiving element electrical wires 17 and 18 are electrically connected to terminals of a package that houses the LN modulator.

  At least a part of the electrode 20 of the light receiving element 5 may be placed on the adhesive 16, and the adhesive 16 may support the electrode 20 of the light receiving element 5 from below. By doing so, the ultrasonic wave can be applied more strongly to the electrode 20 of the light receiving element 5 during wire bonding than when the electrode 20 of the light receiving element 5 is hollow, so that the bonding of the wire 19 by wire bonding is possible. Strength can be increased.

  According to the LN modulator shown in FIGS. 2 and 3, the light 6 b emitted from the optical waveguide 2 and entering the reflecting groove 3 is reflected by the reflecting film 14 on the bottom surface 4 of the reflecting groove 3 and directed upward. The light traveling in the optical waveguide 2 can be received by the light receiving element 5 fixed to the surface of the substrate 1. Further, according to the LN modulator shown in FIG. 2 and FIG. 3, since the portion through which light passes in the space 7 in the reflection groove 3 is filled with air, the portion through which light passes, for example, in the adhesive There is nothing that causes diffuse reflection of light such as bubbles. Therefore, since the light passing through the space 7 in the reflection groove 3 enters the light receiving element 5 without irregular reflection, the amount of light received by the light receiving element 5 can be increased.

  For example, the light receiving sensitivity of the monitoring light when the light leaking from the optical waveguide is received by the light receiving element is approximately 50 mA / W, whereas the LN modulator shown in FIGS. Since the amount of light received by the element 5 increases, the light receiving sensitivity of the monitoring light is improved to approximately 200 mA / W. Further, according to the LN modulator shown in FIGS. 2 and 3, since the light receiving element 5 is provided on the surface of the substrate 1, the LN modulator is accommodated as compared with the case where the light receiving element 5 is provided outside the substrate 1. The package to be made can be downsized.

Second Example of LN Modulator FIG. 4 is a diagram illustrating a second example of the LN modulator according to the embodiment. FIG. 5 is a diagram showing a cross section in the substrate thickness direction along the cutting line BB ′ of FIG. The cutting line BB ′ is the same as the cutting line AA ′ described above. Accordingly, FIG. 5 shows a cross section similar to FIG.

  As shown in FIGS. 4 and 5, in the second example of the LN modulator, the light receiving element 5 has the light receiving portion 8 facing the bottom surface 4 of the reflection groove 3 and is bonded to the electrode of the light receiving element 5 by flip chip bonding. 20 and the light receiving element electrical wirings 17 and 18 are fixed to the substrate 1 in an electrically connected state. An underfill agent may be filled in a joint portion between the electrode 20 of the light receiving element 5 and the light receiving element electrical wirings 17 and 18. Then, since the bonding strength between the electrode 20 of the light receiving element 5 and the light receiving element electrical wirings 17 and 18 increases, the light receiving element 5 can be firmly fixed to the substrate 1.

  In this case, if the underfill agent flows into a portion where light passes through the space 7 in the reflection groove 3, the light may be irregularly reflected by bubbles in the underfill agent. Therefore, it is preferable that the underfill agent does not flow into a portion where light passes in the space 7 in the reflection groove 3.

  The light receiving element 5 is provided with a dummy electrode other than the electrode 20 used for bonding to the light receiving element electrical wirings 17 and 18, and the dummy electrode is bonded to the substrate 1 by flip chip bonding. Also good. Also by doing in this way, the light receiving element 5 can be firmly fixed to the substrate 1. In addition, when the bonding strength is increased by providing a dummy electrode, it is not necessary to use an underfill agent, so that the underfill agent can be prevented from flowing into a portion of the space 7 in the reflection groove 3 through which light passes. it can.

  Other configurations are the same as those of the first example of the LN modulator shown in FIGS. Therefore, the overlapping description is omitted.

  According to the LN modulator shown in FIGS. 4 and 5, even when the light receiving element 5 is fixed to the surface of the substrate 1 by flip chip bonding, the light traveling through the optical waveguide 2 can be received by the light receiving element 5. it can. Further, according to the LN modulator shown in FIGS. 4 and 5, the mounting area of the light receiving element 5 can be reduced by flip-chip bonding, so that the LN modulator can be reduced in size. Therefore, the LN modulators shown in FIGS. 4 and 5 are suitable for applications that require further miniaturization.

Third Example of LN Modulator FIG. 6 is a diagram illustrating a third example of the LN modulator according to the embodiment. FIG. 7 is a diagram showing a cross section in the substrate thickness direction along the cutting line CC ′ of FIG. The cutting line CC ′ is the same as the cutting line AA ′ described above. Accordingly, FIG. 7 shows a cross section similar to FIG.

  As shown in FIGS. 6 and 7, the third example of the LN modulator has a reflection groove protecting convex portion 21 around the reflection groove 3. The reflection groove protecting convex portion 21 may protrude from the surface of the substrate 1 in a bank shape, for example, and may surround the reflection groove 3 on the inner side of the portion bonded by the adhesive 16. The reflection groove protecting convex portion 21 is, for example, a modulation electrode on each of the light receiving element electrical wirings 17 and 18 or the X polarization IQ modulation portion optical waveguide 11 and the Y polarization IQ modulation portion optical waveguide 12. It may be made of the same material. For example, the reflection groove protecting convex portion 21 may be made of a metal such as Au.

  In addition, the third example of the LN modulator may have a wiring protection convex portion 22 between a portion where the adhesive 16 is bonded and the light receiving element electric wires 17 and 18. The wiring protection convex portion 22 may protrude from the surface of the substrate 1 in a bank shape, for example, and may surround the light receiving element 5 outside the portion where the adhesive 16 is bonded. The wiring protecting convex portion 22 is, for example, a light receiving element electrical wiring 17, 18 or a modulation electrode on each of the X polarization IQ modulation section optical waveguide 11 and the Y polarization IQ modulation section optical waveguide 12. It may be made of the same material. For example, the wiring protecting convex portion 22 may be made of a metal such as Au.

  Other configurations are the same as those of the first example of the LN modulator shown in FIGS. Therefore, the overlapping description is omitted. As in the second example of the LN modulator shown in FIGS. 4 and 5, the light receiving element 5 is fixed to the substrate 1 by flip chip bonding, and the reflection groove protecting convex portion 21 flows into the underfill agent. May be prevented.

  According to the LN modulator shown in FIGS. 6 and 7, the reflective groove protecting convex portion 21 can prevent the adhesive 16 from flowing into a portion through which light passes in the space 7 in the reflective groove 3. Therefore, there is nothing that causes diffuse reflection of light, such as bubbles in the adhesive, in a portion where light passes in the space 7 in the reflection groove 3. Therefore, since the light passing through the space 7 in the reflection groove 3 enters the light receiving element 5 without irregular reflection, the amount of light received by the light receiving element 5 can be increased. Further, according to the LN modulator shown in FIG. 6 and FIG. 7, the adhesive 16 can be prevented from flowing out to the light receiving element electric wires 17 and 18 by the wiring protecting convex portion 22. Further, since the light receiving element 5 is placed on the reflection groove protecting convex portion 21, the height of the light receiving element 5 can be set to the height of the reflection groove protecting convex portion 21. Therefore, the height of the light receiving element 5 can be adjusted by adjusting the height of the reflection groove protecting convex portion 21.

FIG. 8 is a diagram illustrating a fourth example of the LN modulator according to the embodiment, and illustrates a cross section in the substrate thickness direction along the section line CC ′ in FIG. 6. FIG. FIG. 8 shows a cross section similar to FIG.

  As shown in FIG. 8, the fourth example of the LN modulator has multiple reflection groove protecting convex portions 21 around the reflection groove 3. In the example shown in FIG. 8, the reflection groove protecting convex portions 21 are provided double below the light receiving element 5, but may be provided three or more. One of the multiple reflection groove protecting convex portions 21 may be provided directly below the electrode 20 of the light receiving element 5. Other configurations are the same as those of the third example of the LN modulator shown in FIGS. Therefore, the overlapping description is omitted.

  According to the LN modulator shown in FIG. 8, the reflection groove protecting convex portion 21 can prevent the adhesive 16 from flowing into the portion of the space 7 in the reflection groove 3 where light passes. As in the third example of the LN modulator shown in FIG. 7, the amount of light received by the light receiving element 5 can be increased. Further, according to the LN modulator shown in FIG. 8, the electrode 20 of the light receiving element 5 is supported from below by the reflection groove protecting convex portion 21 immediately below the light receiving element 5. Compared with a certain case, ultrasonic waves can be applied more strongly to the electrode 20 of the light receiving element 5 during wire bonding. Therefore, the bonding strength of the wire 19 by wire bonding can be increased.

  Instead of providing the reflection groove protecting convex portion 21 directly below the electrode 20 of the light receiving element 5, a pedestal that supports the electrode 20 of the light receiving element 5 from below is provided, so that the electrode 20 of the light receiving element 5 can be attached to the electrode 20 during wire bonding. You may make it make an ultrasonic wave act stronger. Even if it does in this way, compared with the case where the lower part of the electrode 20 of the light receiving element 5 is hollow, the joining strength of the wire 19 by wire bonding can be raised.

  When the light receiving element 5 is fixed to the substrate 1 by flip chip bonding as in the second example of the LN modulator shown in FIG. 4 and FIG. The protective convex portions 21 may be provided in multiple. In this case, the underfill agent can be prevented from flowing into the reflection groove 3 by the reflection groove protecting convex portion 21.

FIG. 9 is a first example of the pattern of the reflective groove protecting convex portion and the wiring protecting convex portion in the LN modulator according to the embodiment. It is a figure which shows the example of. In FIG. 9, a portion to which the light receiving element 5 is attached is shown enlarged, and the light receiving element 5, the light receiving portion 8 of the light receiving element 5, and the electrode 20 of the light receiving element 5 are indicated by virtual lines.

  As shown in FIG. 9, in the first example of the pattern of the reflective groove protecting convex portion and the wiring protecting convex portion, the reflective groove protecting convex portion 21 surrounds the reflective groove 3 inside the light receiving element 5. Is provided. Further, the wiring protecting convex portion 22 is provided outside the light receiving element 5 so as to surround, for example, two light receiving elements 5.

  The reflection groove protecting convex portion 21 is provided directly below the electrode 20 of the light receiving element 5 and also serves as a pedestal that supports the electrode 20 of the light receiving element 5 from below. The height of the reflective groove protecting convex portion 21 or the wiring protecting convex portion 22 is not particularly limited, but may be, for example, 5 μm or more and 40 μm or less. If it does so, it can prevent that the adhesive agent 16 flows in into the reflective groove 3 by the convex part 21 for reflective groove protection. Further, the adhesive 16 can be prevented from flowing out to the light receiving element electric wires 17 and 18 by the wiring protecting convex portion 22. In FIG. 9, reference numeral 23 denotes an optical waveguide that guides X-polarized signal light or Y-polarized signal light output from the LN modulator.

Second Example of Patterns of Reflective Groove Protection Protrusions and Wiring Protection Protrusions FIG. 10 shows a second pattern of reflective groove protection convexes and wiring protection convex parts in the LN modulator according to the embodiment. It is a figure which shows the example of. In FIG. 10, the portion to which the light receiving element 5 is attached is shown enlarged, and the light receiving element 5, the light receiving portion 8 of the light receiving element 5, and the electrode 20 of the light receiving element 5 are indicated by virtual lines.

  As shown in FIG. 10, in the second example of the pattern of the reflective groove protecting convex portion and the wiring protecting convex portion, the reflective groove protecting convex portion 21 is provided in a double manner. Therefore, even if the adhesive 16 gets over the outer reflection groove protecting convex portion 21 and flows into the outer reflection groove protecting convex portion 21, the inner reflection groove protecting convex portion 21 causes the adhesive 16 to enter the reflecting groove 3. 16 can be prevented from flowing. The pattern shown in FIG. 10 is suitable when the amount of the adhesive 16 is large. The reflection groove protecting convex portion 21 may be provided in three or more layers.

  In addition to the reflection groove protecting projection 21, a pedestal 24 that supports the electrode 20 of the light receiving element 5 from below is provided directly below the electrode 20 of the light receiving element 5. The height of the base 24 may be the same as the height of the reflection groove protecting convex portion 21. The pedestal 24 can be made of, for example, the same material as the modulation electrodes on each of the light receiving element electrical wires 17 and 18 or the X polarization IQ modulation unit optical waveguide 11 and the Y polarization IQ modulation unit optical waveguide 12. It may be. For example, the base 24 may be made of a metal such as Au. By providing the pedestal 24, ultrasonic waves can be applied more strongly to the electrode 20 of the light receiving element 5 during wire bonding than when the bottom of the electrode 20 of the light receiving element 5 is hollow. Strength can be increased.

  In the example shown in FIG. 10, the wiring protection convex portion 22 is single, but may be multiplexed. If it does so, the capability to prevent the adhesive agent 16 from flowing out to the electric wiring 17 and 18 for light receiving elements can be made high. Further, the height of the wiring protecting convex portion 22 may be made higher than the height of the reflecting groove protecting convex portion 21. Also by doing so, the ability to prevent the adhesive 16 from flowing out to the light receiving element electrical wirings 17 and 18 can be enhanced. For example, the height of the reflective groove protecting convex portion 21 may be 5 μm, and the height of the wiring protecting convex portion 22 may be 20 μm.

Third Example of Patterns of Reflective Groove Protection Protrusions and Wiring Protection Protrusions FIG. 11 shows a third pattern of reflective groove protection convexes and wiring protection convex parts in the LN modulator according to the embodiment. It is a figure which shows the example of. In FIG. 11, the portion to which the light receiving element 5 is attached is shown enlarged, and the light receiving element 5, the light receiving portion 8 of the light receiving element 5, and the electrode 20 of the light receiving element 5 are indicated by virtual lines.

  As shown in FIG. 11, in the third example of the pattern of the reflective groove protecting convex portion and the wiring protecting convex portion, the reflective groove protecting convex portion 21 and the wiring protecting convex portion 22 are provided in a ladder shape. . The wiring protecting projections 22 are provided so as to extend along the light receiving element electrical wirings 17 and 18, and a plurality of reflection groove protecting projections 21 are hung between the pair of wiring protecting projections 22. Has been passed.

  There are a plurality of reflective groove protecting convex portions 21 between the adhesion portion by the adhesive 16 and the reflective groove 3, and even if the adhesive 16 flows between the adjacent reflective groove protecting convex portions 21, the adhesive 16 is reflected. Since it flows along the groove protecting convex portion 21, the adhesive 16 can be prevented from flowing into the reflection groove 3. For example, the height of the reflective groove protecting convex portion 21 may be 5 μm, and the height of the wiring protecting convex portion 22 may be 20 μm.

FIG. 12 illustrates a fourth example of the pattern of the reflective groove protecting convex portion and the wiring protecting convex portion in the LN modulator according to the embodiment. It is a figure which shows the example of. In FIG. 12, a portion to which the light receiving element 5 is attached is shown enlarged, and the light receiving element 5, the light receiving portion 8 of the light receiving element 5, and the electrode 20 of the light receiving element 5 are indicated by virtual lines.

  As shown in FIG. 12, in the fourth example of the pattern of the reflective groove protecting convex portion and the wiring protecting convex portion, the reflective groove protecting convex portion 21 surrounds the reflective groove 3 twice, and the outer reflection thereof The groove protecting convex portion 21 also serves as a pedestal that supports the electrode 20 of the light receiving element 5 from below. In addition, the surface of the substrate 1 has, for example, a bank-like convex portion 25 surrounding a region where the adhesive 16 is applied. The adhesive 16 is applied to a closed region surrounded by the convex portion 25. For example, the convex portions 25 are provided on the substrate 1 at locations corresponding to the four corners of the light receiving element 5. The height and material of the convex part 25 may be the same as the convex part 21 for reflection groove protection, for example.

  In the example shown in FIG. 12, with respect to the light receiving element 5 on the side close to the light receiving element electrical wirings 17 and 18, a convex part 26 connecting the convex part 25 and the convex part 25 is formed on the light receiving element electrical wirings 17 and 18. It is provided in parallel to. Accordingly, when the adhesive 16 flows out from the closed region surrounded by the convex portion 25, the flowed out adhesive 16 flows along the convex portion 26, and thus the flowed out adhesive 16 flows into the light receiving element electrical wirings 17, 18. Can be prevented from flowing toward.

  In addition, with respect to the light receiving element 5 on the side far from the light receiving element electrical wirings 17 and 18, a convex part 27 extends outward from each convex part 25. This is because, since the light receiving element electrical wires 17 and 18 are separated from each other, when the adhesive 16 flows out from the closed region surrounded by the convex portion 25, the flowed out adhesive 16 may flow outward. It is.

  Since the application area | region of the adhesive agent 16 is surrounded by the convex part 25, it can prevent that the adhesive agent 16 apply | coated to this application | coating area | region flows into the reflective groove | channel 3. Further, when the adhesive 16 is applied to the substrate 1, the convex portion 25 serves as a mark of the application region, and a container for receiving the adhesive 16 by the convex portion 25 can be formed. Therefore, an appropriate amount of the adhesive 16 can be easily applied. Can do.

FIG. 13 is a fifth example of the pattern of the reflective groove protecting convex portion and the wiring protecting convex portion in the LN modulator according to the embodiment. It is a figure which shows the example of. In FIG. 13, the portion to which the light receiving element 5 is attached is shown enlarged, and the light receiving element 5, the light receiving portion 8 of the light receiving element 5, and the electrode 20 of the light receiving element 5 are indicated by virtual lines.

  As shown in FIG. 13, in the fifth example of the pattern of the reflection groove protecting convex portion and the wiring protecting convex portion, the wiring protecting convex portion 22 projects outward in the region where the adhesive 16 is applied. Thereby, the area | region where the adhesive agent 16 is apply | coated is expanded. The pattern shown in FIG. 13 is suitable when the amount of the adhesive 16 is large.

FIG. 14 is a diagram illustrating a fifth example of the LN modulator according to the embodiment. As shown in FIG. 14, the fifth example of the LN modulator is a light receiving unit having two light receiving units 8 instead of the two light receiving elements 5 in the first example of the LN modulator shown in FIG. 2. The element 28 is used. The light receiving element 28 may have the same length as the width of the substrate 1 in the input direction of the light input to the LN modulator or the direction intersecting the output direction of the signal light output from the LN modulator. . In this case, the light receiving element 28 may be fixed to the substrate 1 by applying the adhesive 16 from the side surface of the substrate 1.

  Other configurations are the same as those of the first example of the LN modulator shown in FIGS. Therefore, the overlapping description is omitted. In the second example of the LN modulator shown in FIGS. 4 and 5, the third example of the LN modulator shown in FIGS. 6 and 7, or the fourth example of the LN modulator shown in FIG. A light receiving element 28 having two light receiving portions 8 may be used.

FIG. 15 is a diagram illustrating a sixth example of the LN modulator according to the embodiment. FIG. 16 is a diagram illustrating a waveform in a state where the phase of the signal light and the monitor light are out of phase. In FIG. 16, the horizontal axis represents the voltage applied to the Mach-Zehnder interferometer, and the vertical axis represents the optical output power. As shown in FIG. 15, the sixth example of the LN modulator has a guard groove 29 immediately before the light receiving element 5 in the first example of the LN modulator shown in FIG. 2.

  Unnecessary light may be generated due to, for example, a coupling loss component of input light or an excessive loss component of a coupler. When unnecessary light enters the reflection groove 3 and is received by the light receiving element 5, the phase of the monitor light shifts as shown in FIG. 16, and the phase of the signal light and the monitor light is in an ideal state, that is, The phase difference between the signal light and the monitor light may deviate from the state of 180 °. If the phase of the signal light and the monitor light deviates from the ideal state, it becomes difficult to control the operating point of the LN modulator. Therefore, when unnecessary light is generated, it is preferable to prevent unnecessary light from entering the reflection groove 3. By providing the guard groove 29, it is possible to suppress unnecessary light from entering the reflection groove 3.

  Other configurations are the same as those of the first example of the LN modulator shown in FIGS. Therefore, the overlapping description is omitted. 4 and 5, the third example of the LN modulator shown in FIGS. 6 and 7, the fourth example of the LN modulator shown in FIG. 8, or FIG. 14. The guard groove 29 may be provided also in the fifth example of the LN modulator shown in FIG.

Seventh Example of LN Modulator FIG. 17 is a diagram showing a seventh example of the LN modulator according to the embodiment, and shows a cross section in the substrate thickness direction along the section line AA ′ of FIG. FIG. FIG. 17 shows a cross section similar to FIG. As shown in FIG. 17, the seventh example of the LN modulator is one in which the space 7 of the reflection groove 3 is filled with the adhesive 16 in the first example of the LN modulator shown in FIG. 3. When the space 7 of the reflection groove 3 is filled with the adhesive 16, it is preferable that the adhesive 16 does not contain bubbles.

  For example, when the depth of the reflection groove 3 is 3 μm, the angle formed by the inclined surface 13 of the reflection groove 3 with respect to the thickness direction of the substrate 1 varies in the range of 10 ° to 15 °. In this case, the optical path of the light 6b incident from the center of the inclined surface 13 into the reflection groove 3 is indicated by a two-dot chain line in FIG. When the space 7 of the reflection groove 3 is filled with the adhesive 16, variation in the arrival position when the light 6 b that has entered the reflection groove 3 from the center of the inclined surface 13 reaches the light receiving unit 8 of the light receiving element 5. Is, for example, 31 μm.

  On the other hand, in the case of the same variation in the first example of the LN modulator shown in FIG. 3, the optical path of the light 6b that has entered the reflecting groove 3 from the central portion of the inclined surface 13 is indicated by a two-dot chain line in FIG. Show. When the space 7 of the reflection groove 3 is filled with air, the variation in the arrival position when the light 6b incident into the reflection groove 3 from the central portion of the inclined surface 13 reaches the light receiving portion 8 of the light receiving element 5 is as follows. For example, 13 μm.

  Therefore, when the light receiving portion 8 of the light receiving element 5 is wide, both the first example of the LN modulator and the seventh example of the LN modulator can be used. On the other hand, when the light receiving portion 8 of the light receiving element 5 is narrow, it is preferable to use the first example of the LN modulator.

  Other configurations are the same as those of the first example of the LN modulator shown in FIGS. Therefore, the overlapping description is omitted. 4 and 5, a third example of the LN modulator shown in FIGS. 6 and 7, a fourth example of the LN modulator shown in FIG. 8, and FIG. 14. Also in the fifth example of the LN modulator shown or the sixth example of the LN modulator shown in FIG. 15, the space 7 of the reflection groove 3 may be filled with an adhesive 16 that does not contain bubbles.

Example of Manufacturing Method of Optical Device FIGS. 18 to 20 are diagrams illustrating an example of a manufacturing method of the optical device according to the embodiment.

  In FIG. 18, first, a substrate 1 is prepared as indicated by reference numeral 101. Next, as indicated by reference numeral 102, for example, Ti (titanium) is deposited on the surface of the substrate 1 to generate a Ti film 31 having a thickness of, for example, 1000 mm. Next, as indicated by reference numeral 103, a photoresist 32 is applied on the Ti film 31 to a thickness of, for example, about 1 μm, the photoresist 32 is patterned by a photolithography method, and the Ti film 31 is formed by dry etching or wet etching. Pattern it.

  When the Ti film 31 is patterned, a general directional coupler such as an optical modulator, an optical switch, a filter, or a variable optical attenuator, or a Mach-Zehnder interferometer using a Y branch is formed. Next, as indicated by reference numeral 104, for example, Ti is diffused into the substrate 1 at a temperature of 1000 ° C. to 1100 ° C. to form the optical waveguide 2. The optical waveguide 2 includes, for example, an optical waveguide 11 for an X polarization IQ modulator, an optical waveguide 12 for a Y polarization IQ modulator, and a monitor branching from these optical waveguides 11 and 12 of the LN modulator shown in FIG. The optical waveguide 2 is included. The optical waveguide 2 may be formed using Mg (magnesium) instead of Ti, or the optical waveguide 2 may be formed by a proton exchange method.

  Next, as indicated by reference numeral 105 in FIG. 19, a photoresist 33 is applied to the surface of the substrate 1, and the photoresist 33 is patterned by a photolithography method to form a pattern for forming the reflective grooves 3. Next, as shown by reference numeral 106, post-baking is performed to remove the solvent and developer remaining on the patterned photoresist 33, thereby improving the adhesion between the photoresist 33 and the substrate 1.

  Next, as indicated by reference numeral 107, the reflective groove 3 is formed by dry etching such as RIE (Reactive Ion Etching) using the patterned photoresist 33 as a mask. When the reflection groove 3 is formed, a guard groove 29 that suppresses unnecessary light from entering the reflection groove 3 may be formed. After the groove formation, as shown by reference numeral 108, the photoresist 33 used as a mask is removed.

  Next, as indicated by reference numeral 109 in FIG. 20, the buffer layer 34 is formed on the surface of the substrate 1 by, for example, sputtering or EB (Electron Beam) deposition. The thickness of the buffer layer 34 is optimized depending on the necessary band and the amount of electrical reflection, but may be, for example, about 0.5 μm to 1.0 μm.

  Next, as indicated by reference numeral 110, the Si layer 35 is generated on the surface of the buffer layer 34 by, for example, sputtering. The thickness of the Si layer 35 may be, for example, about 0.1 μm. The buffer layer 34 and the Si layer 35 become, for example, the buffer layer and the Si layer 15 of the LN modulator shown in FIG.

  Next, as indicated by reference numeral 111, Au is deposited on the surface of the Si layer 35 by, for example, an EB vapor deposition device to generate an Au film serving as a base for electrical wiring and electrodes. When generating the Au film for the electrode substrate, for example, the reflective film 14 of the LN modulator shown in FIG. 3 may be formed. The thickness of the Au film for the electrode base may be, for example, about 0.1 μm.

  Then, a photoresist is applied on the Au film for the electrode base, the photoresist is patterned by a photolithography method, and the Au film is patterned by etching, and then Au plating is performed. An electrode 36 is formed thereon. The thickness of the Au plating is optimized depending on the necessary band and the amount of electric reflection, but may be, for example, about 5 μm to 40 μm. The electrodes 36 include, for example, the light receiving element electrical wires 17 and 18 of the LN modulator shown in FIG. 2, the modulation electrode on the optical waveguide 11 for the X polarization IQ modulation unit, and the light for the Y polarization IQ modulation unit. A modulation electrode on the waveguide 12 is included. It should be noted that the film serving as a base of the electrical wiring or the electrode or the electrode 36 may be formed not only by Au but also by other metal such as Cu (copper).

  When the electrode 36 is formed, for example, the reflection groove protecting convex portion 21 and the wiring protecting convex portion 22 of the LN modulator shown in FIGS. 6 and 7 may be formed. Moreover, when forming the electrode 36, you may form the base 24 of the pattern shown, for example in FIG. Moreover, when forming the electrode 36, you may form the convex parts 25-27 of the pattern shown, for example in FIG. The thicknesses of the reflective groove protecting convex portion 21, the wiring protecting convex portion 22, the pedestal 24, and the convex portions 25 to 27 may be, for example, about 5 μm to 40 μm.

  Next, the substrate 1 is cut into optical device chips of a desired size. Next, the light receiving element 5 is fixed to the optical device chip by die bonding using the adhesive 16 or flip chip bonding. For example, in the case of the LN modulator shown in FIG. 6 or FIG. 7, a dispenser is used so that the adhesive 16 does not overflow from the reflective groove protecting convex portion 21 and the wiring protecting convex portion 22 to a desired position of the LN modulator chip. The adhesive 16 is applied using a device capable of controlling the volume.

  Then, the position of the light receiving element 5 is adjusted while recognizing an image with a camera so that the pattern of the surface of the light receiving element 5 comes to a desired position with reference to the corner of the pad of the light receiving element electrical wirings 17 and 18. The light receiving element 5 is arranged. For example, the center of the light receiving portion 8 of the light receiving element 5 may be a pattern for alignment. After the light receiving element 5 is arranged, the adhesive 16 is cured by irradiating ultraviolet rays, and the light receiving element 5 is fixed to the LN modulator chip. Thereafter, curing is performed by heat treatment. Finally, wire bonding is performed to electrically connect the electrode 20 of the light receiving element 5 and the electric wires 17 and 18 for the light receiving element.

  According to the optical device manufacturing method shown in FIGS. 18 to 20, it is possible to manufacture an optical device that can receive light traveling in the optical waveguide 2 by the light receiving element 5 fixed to the surface of the substrate 1. . In addition, according to the method of manufacturing an optical device shown in FIGS. 18 to 20, when the electrode 36 is formed, the reflective groove protecting convex portion 21, the wiring protecting convex portion 22, the pedestal 24, and the convex portions 25 to 27 are also formed. Therefore, it is not necessary to increase the number of processes. In addition, according to the method of manufacturing an optical device shown in FIGS. 18 to 20, the reflective film 14 is also formed when the base for the electrode is formed, so that the number of steps is not increased. Therefore, an increase in manufacturing cost can be suppressed.

  The following additional notes are further disclosed with respect to the embodiments including the above-described examples.

(Supplementary Note 1) An optical waveguide that guides light, and a reflection groove that reflects light emitted from the optical waveguide at a bottom surface, and has a substrate having an electro-optic effect, and is fixed to the substrate on the reflection groove A light receiving element, and the light emitted from the optical waveguide into the reflection groove is reflected on the bottom surface of the reflection groove while passing through the space in the reflection groove and is incident on the light receiving element. And optical device.

(Supplementary note 2) The optical device according to supplementary note 1, wherein a portion through which the light passes in a space in the reflection groove is filled with air.

(Additional remark 3) The end surface of the said reflective groove where light radiate | emits from the said optical waveguide is an inclined surface which refracts so that the light radiate | emitted from the said optical waveguide may go to the bottom face of the said reflective groove, It is characterized by the above-mentioned. The optical device according to 1 or 2.

(Supplementary note 4) The supplementary note 3, wherein the inclined surface forms an angle smaller than an angle at which light traveling in the optical waveguide is totally reflected by the inclined surface with respect to a thickness direction of the substrate. Optical devices.

(Additional remark 5) It has a reflective groove protection convex part which prevents the adhesive which fixes the said light receiving element to the said board | substrate to the part which the said light passes in the space in the said reflective groove around the said reflective groove. The optical device according to any one of appendices 1 to 4, characterized in that:

(Additional remark 6) Between the electrical wiring for light receiving elements electrically connected to the said light receiving element, and the adhesion part by the said adhesive agent, the convex for wiring protection which prevents the said adhesive agent flowing out to the said electrical wiring for light receiving elements The light according to appendix 5, wherein the height of the wiring protection convex portion from the surface of the substrate is higher than the height of the reflective groove protective convex portion from the surface of the substrate. device.

(Appendix 7) The optical device according to appendix 5 or 6, wherein a wire is connected to the light receiving element by wire bonding on the adhesive or the convex portion for protecting the reflection groove.

(Supplementary note 8) The optical device according to any one of supplementary notes 1 to 6, wherein the light receiving element is fixed to the substrate by flip chip bonding.

(Supplementary note 9) The optical device according to supplementary note 3, wherein the inclined surface forms an angle of 5 ° to 20 ° with respect to a thickness direction of the substrate.

(Supplementary note 10) The optical device according to any one of supplementary notes 1 to 9, further comprising a reflective film on a bottom surface of the reflective groove.

(Additional remark 11) It has the optical waveguide which guides light, and the reflective groove which the light radiate | emitted from the said optical waveguide reflects on a bottom face, and is fixed to the said board | substrate on the said reflective groove on the board | substrate which has an electrooptic effect A light receiving element, and an optical device in which light emitted from the optical waveguide into the reflection groove is reflected on the bottom surface of the reflection groove while passing through the space in the reflection groove and is incident on the light reception element. In manufacturing, forming the optical waveguide in the substrate, forming the reflection groove in a part of the optical waveguide, forming electrodes and electrical wiring on the surface of the substrate, cutting the substrate into a chip, A method of manufacturing an optical device, comprising: fixing the light receiving element on the reflection groove of the chip, and electrically connecting the light receiving element and an electric wiring for the light receiving element of the chip.

(Additional remark 12) When forming the said electrode, the adhesive agent which fixes the said light receiving element to the said board | substrate around the said reflection groove prevents flowing into the part which the said light passes in the space in the said reflection groove The method for manufacturing an optical device according to appendix 11, wherein a convex for protecting the reflection groove is formed.

(Additional remark 13) Before forming the said electrode, while forming the base for electrodes in the formation location of the said electrode, a reflective film is formed in the bottom face of the said reflective groove | channel, The light of Additional remark 11 or 12 characterized by the above-mentioned Device manufacturing method.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3 Reflective groove 4 Bottom surface of reflective groove 5 Light receiving element 6a Light traveling in the optical waveguide 6b Light incident on the reflective groove 6c Light reflected on the bottom surface of the reflective groove 6d Light incident on the light receiving element 7 Space in reflection groove 13 Inclined surface 14 Reflective film 16 Adhesive 17, 18 Light-receiving element electrical wiring 19 Wire 21 Reflection groove protection convex portion 22 Wire protection convex portion 36 Electrode

Claims (6)

An optical waveguide branched into signal light and monitor light, and a reflection groove that is provided in the middle of the optical waveguide of the monitor light and reflects the light emitted from the optical waveguide at the bottom surface, and has an electro-optic effect A substrate,
A light receiving element fixed to the substrate on the reflection groove;
Provided in a convex shape having a predetermined height so as to surround the periphery of the reflective groove, the light receiving element is provided in contact with the convex surface, and an adhesive for fixing the light receiving element to the substrate is provided in the reflective groove. A reflective groove protection convex portion for preventing the light from flowing into a portion through which light passes,
Light emitted from the optical waveguide into the reflection groove is reflected on the bottom surface of the reflection groove while passing through the space in the reflection groove, and enters the light receiving element.
An optical device, wherein a wire is connected to the light receiving element by wire bonding on the position of the reflection groove protecting convex portion.   The optical device according to claim 1, wherein a portion through which the light passes in the space in the reflection groove is filled with air.   The end surface of the reflection groove from which light is emitted from the optical waveguide is an inclined surface that refracts light emitted from the optical waveguide toward the bottom surface of the reflection groove. The optical device according to.   The optical device according to claim 3, wherein the inclined surface forms an angle smaller than an angle at which light traveling in the optical waveguide is totally reflected by the inclined surface with respect to a thickness direction of the substrate. . Between the electrical wiring for the light receiving element electrically connected to the light receiving element and the bonding location by the adhesive, the wiring protective convex portion for preventing the adhesive from flowing out to the electrical wiring for the light receiving element ,
5. The optical device according to claim 4, wherein the height of the wiring protecting convex portion from the surface of the substrate is higher than the height of the reflecting groove protecting convex portion from the surface of the substrate. An optical waveguide branched into signal light and monitor light, and a reflection groove that is provided in the middle of the optical waveguide of the monitor light and reflects the light emitted from the optical waveguide at the bottom surface, and has an electro-optic effect A substrate, a light receiving element fixed to the substrate on the reflection groove, and an adhesive for fixing the light reception element to the substrate are provided in a space in the reflection groove. A projection for protecting the reflection groove that prevents the light from flowing into a portion through which the light passes, and the light emitted from the optical waveguide into the reflection groove is reflected in the middle of passing through the space in the reflection groove. In manufacturing an optical device that reflects on the bottom surface of the groove and enters the light receiving element,
Forming the optical waveguide on the substrate;
Forming the reflection groove in the middle of the optical waveguide for monitoring,
Forming the reflective groove protecting convex portion into a convex shape having a predetermined height so as to surround the reflective groove;
Forming electrodes and electrical wiring on the surface of the substrate;
Cutting the substrate into chips,
Fixing the light receiving element on the position of the reflective groove of the chip so as to contact the convex surface of the convex part for the reflective groove;
Electrically connecting the light receiving element and the electric wiring for the light receiving element of the chip;
A method of manufacturing an optical device, comprising: connecting a wire to the light receiving element by wire bonding on a position of the convex portion for protecting the reflection groove.

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