Integrated optical device and method for manufacturing the same

Abstract

Provided is an integrated-type optical device that, when butt-connecting waveguides, can conveniently connect the same, and achieves stable optical coupling. An optical circuit and an optical function element are butt-connected in this integrated-type optical device, said optical circuit performing optical signal processing and being provided on a substrate that does not transmit ultraviolet-region to visible-region light, and said optical function element comprising a material that does not transmit ultraviolet-region to visible-region light. In the optical circuit, a butt joint retaining substrate that transmits ultraviolet-region to visible-region light is installed in a groove that extends to a connection end surface in which a waveguide for input / output is formed, and the connection end surface of the optical circuit and an end surface of the butt joint retaining substrate are machined to be flush. The optical circuit and the optical function element are fixed by using UV light which has been transmitted by the butt joint retaining substrate to cure a UV-curable adhesive agent which has been filled in at the connection end surface.

Description

[Technical field]

[0001] The present invention relates to an integrated optical device and a manufacturing method thereof, and more particularly to an integrated optical device that can be applied to an optical communication system and that incorporates an optical circuit element formed of an optical waveguide and an optical functional element such as a photodiode or an optical modulator, and a manufacturing method thereof. [Background technology]

[0002] In recent years, with the spread of optical fiber transmission, there is a demand for technology to integrate a large number of optical circuits at high density, and silica-based planar lightwave circuits (PLCs) and silicon photonics (SiPs) are well known. PLCs are waveguide-type optical devices with excellent characteristics such as low loss, high reliability, and high design freedom. Transmission equipment at the transmission end of optical communication systems is equipped with PLCs that integrate optical circuits such as multiplexers / demultiplexers, branchers, and couplers. SiPs are optical devices that do not match PLCs in terms of low loss, but have high design freedom and can realize even smaller optical circuits due to their small waveguide bending radius. In addition to PLCs and SiPs, transmission equipment also includes optical devices such as photodiodes (PDs) and laser diodes (LDs) that convert optical and electrical signals, and optical functional elements such as optical modulators.

[0003] To further expand communication capacity, there is a demand for high-performance optoelectronic integrated devices that integrate optical waveguides such as PLCs that perform optical signal processing and optical devices such as PDs that perform high-speed photoelectric conversion and are made of InP-based materials. PLCs and SiPs are seen as promising platforms for such integrated optical devices, and optoelectronic integrated devices that hybridly integrate light-receiving and emitting element chips with PLC chips and SiP chips have been proposed.

[0004] For example, in the example described in Patent Document 1, a 45-degree mirror is provided in a partial region of the waveguide, a PD chip is mounted on the waveguide, and the light propagating through the optical waveguide is converted vertically by the mirror to perform optical coupling with the PD. As in this example, an optical device configuration in which a PLC and an optical functional element such as a PD are combined and mounted has advantages in terms of miniaturization of the device and freedom of design of the optical circuit.

[0005] To expand communication capacity, multi-channel integrated optical devices have been developed by optically coupling and mounting PLCs, which integrate optical circuits such as optical signal multiplexing / demultiplexing functions, with multiple optical functional elements in an array. In recent years, in order to achieve even higher speeds and higher functionality, there has been a demand for the integration of PDs with a waveguide structure suitable for broadband using InP-based materials and optical functional elements including a waveguide structure such as an optical phase modulator with high-speed phase modulation function. To integrate optical functional elements, for example, it is necessary to butt-couple the input / output waveguides of PLCs, SiPs, and optical functional elements made of Si or InP-based materials, and fix the waveguides together.

[0006] Generally, UV-curable adhesives are used to connect PLC and SiP substrates together, and to connect PLC and SiP to optical functional elements. For example, when butt-connecting an optical fiber to a PLC waveguide, after alignment, the end face of the fiber block made of glass to which the optical fiber is fixed and the end face of the PLC are filled with UV-curable adhesive, and the adhesive is cured by irradiating with ultraviolet light (UV light). UV-curable adhesives can be cured in a short time, so they can be bonded more easily than heat-curable adhesives. If such butt-connection can be used to realize an optical integrated circuit that integrates a PLC with an optical circuit and an optical functional element, or an optical integrated circuit that integrates a SiP with an optical circuit and an optical functional element, it will be possible to provide more functional optical devices.

[0007] Fig. 1 shows a conventional butt connection between a SiP chip and an InP chip. Fig. 1(a) is a top view, and Fig. 1(b) is a cross-sectional view along the waveguide to be connected. The SiP chip 10 has an optical waveguide formed on a Si substrate 11, in which a lower clad layer 12, a waveguide core 13, and an upper clad layer 14 are laminated. The InP chip 20 is an optical functional element in which a waveguide core 22 is formed on an InP substrate 21. As shown in Fig. 1(a), the waveguides are aligned, a UV-curable adhesive 31 is filled between the end faces of both chips, and UV light is irradiated.

[0008] However, the optical circuit formed on the SiP chip 10 has a clad layer constituting a waveguide, which is transparent from the ultraviolet region to the near infrared region. 2 However, the substrate is often made of Si, which absorbs light from the ultraviolet to the visible range. The substrate of an optical functional element made of InP is also made of a material that is not transparent from the ultraviolet to the visible range, such as Si or InP. Therefore, even if UV light is irradiated, it does not pass through the substrates of both chips (10, 20), and therefore does not reach most of the adhesive region A, as shown in FIG. 1(b). This causes a problem that the UV curing adhesive 31 cannot be completely cured, and sufficient adhesive strength cannot be obtained.

[0009] Fig. 2 shows a conventional connection method using a butt-coupled holding substrate. Fig. 2(a) is a top view, and Fig. 2(b) is a cross-sectional view along the waveguide to be connected. A butt-coupled holding substrate 32 made of a glass substrate that transmits UV light is mounted under the InP substrate 21 of the InP chip 20. When the two chips are bonded, the butt-coupled holding substrate 32 is also butted at the same time, filled with UV-curable adhesive 31, and irradiated with UV light. Since the UV light transmits through the butt-coupled holding substrate 32, the two chips (10, 20) and the butt-coupled holding substrate 32 can be firmly bonded and fixed.

[0010] However, it is difficult to completely align the adhesive surfaces of the InP chip 20 and the butt-coupled holding substrate 32 with respect to the SiP chip 10. In addition, since InP is a material that easily breaks due to external force, it is also difficult to align the adhesive surfaces by polishing or dicing after mounting the InP chip 20 on the butt-coupled holding substrate 32. If the adhesive surfaces are not aligned, for example, if the adhesive surface of the butt-coupled holding substrate 32 protrudes beyond the adhesive surface of the InP chip 20, the distance between the two chips (10, 20) increases, the gap between the waveguides to be connected increases, and the loss due to radiation of the propagating light increases. In this way, if the adhesive surfaces cannot be aligned, there is a problem that the misalignment of the adhesive surfaces varies each time an optical device is manufactured, causing a variation in connection loss.

[0011] In addition, although the adhesive surface of the butt-joint holding substrate 32 can be fixed, the InP chip 20 itself does not transmit UV light, so that uncured UV-curable adhesive 31 still remains on the adhesive surface of the InP chip 20, and therefore this method was not suitable for butt-jointing from the viewpoint of long-term reliability. Thus, in an optical integrated circuit in which a PLC or SiP in which an optical circuit is integrated is hybrid-integrated with an optical functional element, it has been a challenge to realize an integrated optical device in which optical waveguides are stably butt-jointed and fixed. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2005-70365 A Summary of the Invention

[0013] An object of the present invention is to provide an integrated optical device and a manufacturing method thereof, which is an optical integrated circuit mounting an optical circuit having a waveguide structure and optical functional elements such as a light receiving / emitting element and an optical modulator, and which can be easily connected when butt-connecting the waveguides and realizes stable optical coupling.

[0014] In order to achieve the above object, one embodiment of the present invention provides an integrated optical device in which an optical circuit for performing optical signal processing provided on a substrate that does not transmit light in the ultraviolet to visible ranges is butt-connected to an optical functional element made of a material that does not transmit light in the ultraviolet to visible ranges, the optical circuit having a groove reaching a connection end face on which an input / output waveguide is formed, and a butt-connection holding substrate that transmits light in the ultraviolet to visible ranges. fixed the connection end face of the optical circuit and the end face of the butt-joint holding substrate are processed to be flush with each other, and the optical circuit and the optical functional element are fixed to each other by a UV-curable adhesive applied to the connection end face and cured by UV light transmitted through the butt-joint holding substrate; The groove is formed from the upper clad layer and the lower clad layer forming the input / output waveguide to a part of the substrate, except for a region in which a waveguide core of the input / output waveguide is formed, the butt-coupled holding substrate is fixed so as to be accommodated in the groove, and the depth of the groove and the thickness of the butt-coupled holding substrate are equal to or greater than the thickness of the optical functional element. It is characterized by: [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing a conventional butt joint between a SiP chip and an InP chip. [Diagram 2] FIG. 2 is a diagram showing a conventional connection method using a butt joint holding substrate; [Diagram 3] FIG. 3 is a diagram showing a butt connection between a SiP chip and an InP chip according to an embodiment of the present invention; [Figure 4] FIG. 4 is a diagram showing a butt connection between a SiP chip and an InP chip according to the first embodiment; [Diagram 5] FIG. 5 is a diagram showing the results of evaluating the coupling loss of the integrated optical device according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0017] FIG. 3 shows the butt joint between the SiP chip and the InP chip according to one embodiment of the present invention. FIG. 3(a) is a top view, FIG. 3(b) is a cross-sectional view along B-B' in FIG. 3(a), and FIG. 3(c) is a cross-sectional view along C-C' in FIG. 3(a). The SiP chip 40 has an optical waveguide formed on a Si substrate 41, in which a lower clad layer 42, a waveguide core 43, and an upper clad layer 44 are laminated. The SiP chip 40 has a groove 45 formed thereon that reaches the connection end surface of the substrate, which is the bonding surface, and butt joint holding substrates 33a and 33b made of glass substrates are fixed thereto. The InP chip 20 is an optical functional element in which a waveguide core 22 is formed on an InP substrate 21. As shown in FIG. 3(a), the waveguides of both chips (20, 40) are aligned with each other at the butt joint portion, which is the bonding surface, and a UV curing adhesive 31 is filled between the end surfaces of both chips and cured by irradiating ultraviolet light (UV light).

[0018] As shown in FIG. 3(a), the groove 45 of the SiP chip 40 is formed to reach the connection end surface of the substrate, which is the bonding surface, except for the region in which the waveguide core 43, which is the input / output waveguide, is formed. As shown in FIG. 3(b), the groove 45 is formed in the upper clad layer 4, which forms the waveguide. 4. The groove 45 is formed not only on the upper cladding layer 42 but also over a part of the Si substrate 41. The butt-joint holding substrate 33 is fixed in this groove 45, and the connection end surface of the SiP chip 40, which serves as the bonding surface, and the end surface of the butt-joint holding substrate 33 are made flush with each other by polishing or dicing.

[0019] As shown in FIG. 3(a), the waveguides are aligned at the butt joint of both chips (40, 20), UV curing adhesive 31 is filled between the end faces of both chips, and UV light is irradiated. Most of the UV curing adhesive 31 filled between the end faces is hardened by the UV light transmitted through butt joint holding substrates 33a, 33b. Therefore, it is possible to bond with the UV curing adhesive 31 without providing a glass substrate for fixing on the InP chip 20 side, and it is possible to realize a butt joint with sufficient adhesive strength. The bonding surfaces of the SiP chip 40 can be stably connected because the Si substrate 41 and the butt joint holding substrate 33 are aligned by polishing or dicing.

[0020] According to this embodiment, both chips can be easily connected to each other, and an integrated optical device can be obtained that realizes stable optical coupling from the viewpoint of long-term reliability.

[0021] Generally, the cross-sectional structure of a PLC is made of Si or SiO 2 On the substrate, SiO 2 The SiP has a cross-sectional structure in which a SiO 2 thin film is deposited on a Si substrate as a lower clad layer, 3 to 10 μm as a waveguide core, and 20 μm as an upper clad layer. 2 The thickness is several μm, the waveguide core is several hundred nm, and the upper cladding layer is SiO 2 Furthermore, in optical functional devices using InP as a substrate, the InP substrate is used as the lower cladding layer, a compound semiconductor is deposited to a thickness of several hundred nm as the waveguide core, InP is used as the upper cladding layer, and SiN or SiO is used as the passivation. 2 is deposited.

[0022] The waveguides reaching the end faces of the respective substrates are used as input / output waveguides for inputting and outputting optical signals, and are optically coupled by the mode field at the end faces. In the region where the input / output waveguides are formed, grooves are formed on both sides of the waveguide core at intervals that do not affect the mode field, reaching the connection end faces.

[0023] A butt-joint holding substrate made of a material transparent from the ultraviolet region to the visible region is mounted in this groove, and is preferably made of, for example, quartz glass.

[0024] The length of the groove and the butt-coupled holding substrate parallel to the waveguide core, the depth of the groove, and the thickness of the butt-coupled holding substrate are set so that the UV light irradiated from the top surface of the chip can irradiate the UV curing adhesive filled between the end faces of the substrate. In the above-mentioned embodiment, in order to increase the strength of adhesion and fixation with the InP chip 20, which is an optical functional element, it is desirable that the depth of the groove and the thickness of the butt-coupled holding substrate 33 are equal to or greater than the thickness of the InP chip 20.

[0025] It is more efficient to form the grooves and mount the butt-coupled holding substrate while the wafer is in its wafer state or while multiple chips are cut in a row, rather than for each chip cut from the wafer. If the grooves can be formed and the butt-coupled holding substrate can be mounted as one step in the wafer processing process, the connection end surface of the optical circuit and the connection end surface of the butt-coupled holding substrate can be made flush by chipping the wafer by dicing or the like. In addition, a highly flat bonding surface can be formed by polishing the end surface.

[0026] Also, a light-shielding film that transmits or absorbs near-infrared light can be formed on the surface opposite to the adhesive surface of the butt-joint holding substrate 33, i.e., on the end surface on the side of the optical circuit integrated in the SiP chip 40. For example, a metal film does not transmit near-infrared light, and therefore can prevent stray light generated in the optical circuit of the SiP chip 40 from leaking to the optical functional element side of the InP chip 20. As a result, for example, when a PD is integrated in the optical functional element, the characteristics of the optical functional element can be improved by preventing stray light that becomes noise in the signal light from reaching the PD.

[0027] In this way, an integrated optical device in which an optical circuit for performing optical signal processing provided on a substrate that does not transmit light in the ultraviolet to visible ranges and an optical functional element made of a material that does not transmit light in the ultraviolet to visible ranges are hybrid-integrated has a butt-coupled holding substrate that transmits light in the ultraviolet to visible ranges mounted in a groove that reaches the connection end face of the optical circuit in which the input / output waveguide is formed. The end face of the butt-coupled holding substrate and the connection end face of the optical circuit are processed so as to be flush with each other, and the UV-curable adhesive filled between the end faces is cured by UV light that has passed through the butt-coupled holding substrate. Since most of the UV-curable adhesive can be cured, there is no variation in connection loss due to misalignment of the connection end faces, and the input / output waveguide of the optical circuit and the input / output waveguide of the optical functional element can be accurately coupled. In addition, since sufficient adhesive strength can be obtained, an integrated optical device that enables a person to realize stable optical coupling from the viewpoint of long-term reliability can be obtained. EXAMPLES

[0028] An example of the integrated optical device of this embodiment will be described. The optical functional element is an optical modulation element composed of a waveguide constituting a phase modulator that changes the phase of light by inputting an electric signal, and an input / output waveguide connected to the phase modulator. The SiP chip is composed of an optical circuit that processes a plurality of signal lights, and an input / output waveguide connected to the optical circuit, and is equipped with a butt-coupled holding substrate. The signal light output from the output optical waveguide of the optical circuit is coupled to the input optical waveguide of the optical functional element through the butt coupling portion, and is input to the optical modulation element. The phase-modulated signal light is input again to the optical circuit from the output optical waveguide of the optical functional element through the butt coupling portion. In this way, the integrated optical device is an optical integrated circuit in which the SiP chip and the optical functional element transmit and receive signal light through the butt coupling portion.

[0029] Fig. 4 shows the butt connection between the SiP chip and the InP chip according to the first embodiment. Fig. 4(a) is a top view, and Fig. 4(b) is a cross-sectional view taken along line B-B' in Fig. 4(a). The size of the SiP chip 50 is 2.5 mm in length and 2.0 mm in width. A SiO 2 a lower cladding layer 52 of 0.22 μm thick and 0.5 μm wide, a Si waveguide core 53 of 1.5 μm thick and SiO 2 4(a), waveguide cores 53a and 53b having an S-shaped waveguide structure are formed up to the end face of the SiP chip 50 as input / output waveguides of an optical circuit formed in the SiP chip 50.

[0030] The SiP chip 50 has grooves 55 formed therein that reach the connection end surface of the substrate, which is the bonding surface, and butt-joint holding substrates 73a-73c made of glass substrates are fixed thereto. As shown in FIG. 4(b), three grooves 55 are provided with a depth of 0.27 mm in the vertical direction of the substrate. The length of the grooves 55 parallel to the waveguide cores 53 is 0.5 mm, and the length parallel to the end surface is 1.0 mm between the input / output waveguides and 0.7 mm outside the input / output waveguides. The width of the region where the waveguide cores 53, which are the input / output waveguides, are formed and where the grooves 55 are not formed is 0.05 mm.

[0031] The butt-coupled holding substrates 73a-73c are 0.02 mm smaller in both length and width than the groove 55, and are made of synthetic quartz with a plate thickness of 0.3 mm. The butt-coupled holding substrate 73 is mounted in the groove 55 and fixed with adhesive 56. The end face of the butt-coupled holding substrate 73 and the connection end face of the SiP chip 50 are polished so as to be flush with each other. By making the plate thickness of the butt-coupled holding substrate 73 larger than the plate thickness of the InP chip 60, the entire end face of the InP chip 60 can be bonded, leading to improved adhesive strength.

[0032] The size of the InP chip 60 is 2.5 mm long, 4.0 mm wide, and 0.25 mm thick. An InP substrate 61 is used as a lower cladding layer, and a waveguide core 62 made of a compound semiconductor having a thickness of 0.3 μm and a width of 2.0 μm, and an upper cladding layer of InP having a thickness of 2.0 μm are deposited on the InP substrate 61. The optical functional element of Example 1 is a device for connection testing, and has a structure having only a U-shaped folded waveguide that inputs the signal light output from the SiP chip 50 directly to the SiP chip 50.

[0033] A method of butt-coupling the InP chip 60 to the SiP chip 50 will be described. First, the connection end faces of the SiP chip 50 and the InP chip 60, which are to be butt-coupled portions, are observed from above, and the input / output waveguides of each are pre-aligned. Next, signal light for alignment is input to the optical circuit of the SiP chip 50, and the signal light output from one side of the Si waveguide core 53 to the folded waveguide (waveguide core 62) of the InP chip 60 is input again to the optical circuit from the other Si waveguide core 53, and the output of the optical circuit is monitored. The positions of the input / output waveguides of the SiP chip 50 and the InP chip 60 are precisely aligned so that the optical intensity of this monitor light is maximized.

[0034] A UV-curable adhesive 71 that is transparent in the infrared region is filled between the end faces of the SiP chip 50 and the InP chip 60. Next, the UV-curable adhesive 71 is cured by irradiating the butt joint with UV light via a butt joint holding substrate 73. By using a butt joint holding substrate 73 that is transparent from the ultraviolet region to the visible region, UV light can be irradiated onto almost the entire connection end face of the butt joint, and the UV-curable adhesive 71 can be cured sufficiently.

[0035] It is preferable that the surface of the butt joint holding substrate 73 is a polished surface so that the state of the connection end face of the butt joint part, such as the filling state of the UV curing adhesive 71, can be directly confirmed by a camera, etc. Also, it is preferable to form an anti-reflection film corresponding to the refractive index of the UV curing adhesive 71 to be filled on the end face of the butt joint part where the waveguide core 62 of the InP chip 60 is formed.

[0036] FIG. 5 shows the results of evaluating the coupling loss of the integrated optical device according to Example 1. Five integrated optical devices according to Example 1 were fabricated, and a signal light with a wavelength of 1.55 μm was input to the optical circuit of the SiP chip 50 and input again to the optical circuit via the folded waveguide of the InP chip 60, and the optical intensity of the signal light output from the optical circuit of the SiP chip 50 was measured. For comparison, five conventional integrated optical devices shown in FIG. 2 were fabricated and evaluated in the same manner as above. The horizontal axis of FIG. 5 is the optical device number of each integrated optical device, and the vertical axis is the insertion loss when the InP chip 60 is butt-connected to the SiP chip 50, and the difference from the average insertion loss is shown.

[0037] As is clear from Fig. 5, in the integrated optical device of Example 1, the loss difference is within ±0.4 dB, and it can be seen that it can be stably mounted. On the other hand, in the conventional integrated optical device, the variation is large at ±1.1 dB. As described above, in the conventional integrated optical device, the connection end face is misaligned by about 10 µm, the gap between the connected waveguides becomes large, and the insertion loss increases.

[0038] According to the integrated optical device of the first embodiment, by mounting a butt coupling holding substrate, both chips can be easily connected, and an integrated optical device with small loss variation and stable optical coupling can be obtained.

Claims

1. An integrated optical device in which an optical circuit for performing optical signal processing, which is provided on a substrate that does not transmit light in the ultraviolet to visible range, and an optical functional element made of a material that does not transmit light in the ultraviolet to visible range are butt-connected, a butt-coupled holding substrate that transmits light in the ultraviolet to visible ranges is fixed to a groove that reaches a connection end face in which an input / output waveguide is formed, and the connection end face of the optical circuit and an end face of the butt-coupled holding substrate are processed to be flush with each other; the optical circuit and the optical functional element are fixed to each other by a UV-curable adhesive applied to the connection end faces and cured by UV light transmitted through the butt-joint holding substrate; the groove is formed from the upper clad layer and the lower clad layer forming the input / output waveguide to a part of the substrate, except for a region in which a waveguide core of the input / output waveguide is formed, the butt-coupled holding substrate is in contact with at least the lower clad layer and is fixed so as to be housed in the groove, 2. An integrated optical device according to claim 1, wherein the depth of said groove and the thickness of said butt-joint holding substrate are equal to or greater than the thickness of said optical functional element.

2. the optical circuit includes a Si substrate; the optical functional element includes a Si or InP substrate; The butt-joint support substrate is made of SiO 2 2. The integrated optical device according to claim 1, comprising a substrate having a thickness greater than that of said optical functional element.

3. 3. The integrated optical device according to claim 1, wherein the butt-joint holding substrate has a light-shielding film for absorbing near-infrared light formed on a surface thereof opposite to the end surface flush with the connection end surface.

4. A method for manufacturing an integrated optical device in which an optical circuit for performing optical signal processing, which is provided on a substrate that does not transmit light in the ultraviolet to visible range, and an optical functional element made of a material that does not transmit light in the ultraviolet to visible range are butt-connected, comprising: the optical circuit reaches a connection end face on which an input / output waveguide is formed, and a butt-coupled holding substrate that transmits light in the ultraviolet to visible ranges is fixed in contact with at least the lower clad layer so as to be accommodated in a groove that is formed from the upper clad layer and the lower clad layer that form the input / output waveguide to a part of the substrate, except for a region in which a waveguide core of the input / output waveguide is formed, and the connection end face of the optical circuit and an end face of the butt-coupled holding substrate are processed to be flush with each other; a step of inputting light for alignment into the optical circuit, inputting the light again from the optical functional element through the input / output waveguide into the optical circuit, and monitoring the light output from the optical circuit; aligning the optical circuit and the input / output waveguide of the optical functional element so that the optical intensity of the monitored light is maximized; filling the connection end surface with a UV curable adhesive; and irradiating the connection end surface with UV light through the butt joint holding substrate to cure the UV curable adhesive.

2. A method for manufacturing an integrated optical device, comprising the steps of: forming a first substrate on a first surface of the substrate; forming a first substrate on the first surface of the substrate;

5. the optical circuit includes a Si substrate; the optical functional element includes a Si or InP substrate; The butt-joint support substrate is made of SiO 2 5. The method for manufacturing an integrated optical device according to claim 4, wherein the substrate is made of a substrate and has a thickness greater than that of the optical functional element.

6. 6. The method for manufacturing an integrated optical device according to claim 4, wherein the butt-joint holding substrate has a light-shielding film for absorbing near-infrared light formed on a surface thereof opposite to the end surface flush with the connection end surface.

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