Optical devices, methods for aligning optical devices

Abstract

The present invention comprises a wiring substrate (53) and an optically functional element (51) that has an input / output optical waveguide (511) for an optical signal and is flip-chip mounted on the wiring substrate (53), an end surface of the input / output optical waveguide (511) in the optically functional element (51) is butted and coupled with an end surface of another input / output optical waveguide (521), the wiring substrate (53) comprises aligning through-holes (531) that penetrate through the wiring substrate (53), and consistency or inconsistency between the position of the end surface of the input / output optical waveguide (511) and the position of the end surface of the other input / output optical waveguide (521) can be visually recognized via the alignment through-holes (531).

Description

Technical Field

[0001] The present disclosure relates to an optical device in which an optical functional element having an optical waveguide and an optical functional element are flip-chip mounted on a substrate.

Background Art

[0002] In recent years, with the spread of optical signal transmission using optical fibers, technologies for integrating a large number of optical circuits at high density have been demanded. As one of such optical circuits, a planar lightwave circuit (PLC) made of quartz or an optical circuit (System in Package: SiP) using silicon photonics is known. PLC is a waveguide-type optical device having low loss, high reliability, and high design freedom, and a PLC integrating functions such as a multiplexer / demultiplexer, a splitter / combiner, etc. is mounted on a transmission device at an optical communication transmission end. Although SiP is inferior to PLC in terms of low loss, it is an optical device having high design freedom and enabling a smaller optical circuit to be realized with a small optical waveguide bending radius. In addition, in the transmission device, as optical devices other than PLC and SiP, optical functional elements such as a photo diode (PD) that converts optical and electrical signals, a laser diode (LD), or an optical modulator are also mounted.

[0003] Toward further expansion of communication capacity, a high-functional optoelectronic integrated device integrating an optical waveguide such as a PLC that performs optical signal processing and an optical device such as a PD is demanded. This optical device performs high-speed optoelectronic conversion made of an InP-based material. As a platform for such an integrated optical device, PLC and SiP are promising, and an integrated optical device in which an InP optical modulator chip and a PLC chip are hybrid integrated has been proposed. Such an integrated optical device is described in, for example, Non-Patent Document 1.

[0004] In the integrated optical device described in Non-Patent Literature 1, a phase modulator is integrated on an InP chip, a polarization rotator and polarization beam combiner are integrated on a PLC, and the two chips are optically coupled via a lens. The method of using a PLC as a polarization Mux chip has a smaller mounting area compared to the conventional method of constructing polarization synthesis with a spatial optical system, and the integration into the optical circuit simplifies optical axis alignment. This form of optical coupling by combining a PLC and optical circuit elements such as InP has advantages in terms of device miniaturization and the freedom of optical circuit design. Furthermore, to expand communication capacity, integrated devices including PDs with waveguide structures suitable for broadband using InP-based materials and optical phase modulators with high-speed phase modulation capabilities have been developed. Moreover, in recent years, there has been a demand for integrated optical devices in which optical circuit elements are directly connected to each other without the use of lenses, in order to further miniaturize the devices. [Prior art documents] [Non-patent literature]

[0005] [Patent Document 1] E. Yamada et al., "112-Gb / s InP DP-QPSK modulator integrated with a silica-PLC polarization multiplexing circuit", Proc. Opt. Fiber Commun. Conf. Expo. Nat. Fiber Opt. Eng. Conf., Mar. 2012.) [Overview of the project]

[0006] Here, for example, if we consider the case of connecting a PLC and an InP-based optical functional element by butting their respective input and output optical waveguides, it is necessary to align and fix the optical waveguides while monitoring the intensity of the light that passes through the connection surface after inputting light to one of the optical elements. For example, butt connection of an optical fiber and a PLC requires alignment. Alignment is performed by adjusting the end face of the glass fiber block on which the fiber is fixed to the end face of the PLC to be parallel, then, while inputting light into the fiber, aligning the position of the optical output from the fiber with the input optical waveguide of the PLC, and adjusting the position to obtain optimal optical coupling while monitoring the output from the output optical waveguide connected to the input optical waveguide. After that, UV-curing adhesive is filled into the adjusted position and cured in a short time by irradiation with UV light, thereby bonding the two. If integration of optical functional elements made of Si or InP using the optical circuit of the PLC as a platform can be realized using such a butt coupling method, it will be possible to provide smaller integrated optical devices.

[0007] Furthermore, to increase the speed of the device, it is necessary to shorten the electrical wiring distance between the optical functional element and the IC that inputs and outputs electrical signals, in order to transmit high-speed signals with low loss. A configuration in which the IC and optical functional element are mounted on a substrate as a flip chip is suitable for transmitting signals with low loss because the IC and optical functional element can be connected over a short distance. Moreover, by using a SiP that integrates a polarization control optical circuit as an optical circuit element and connecting it to a flip-chip phase modulator with heterogeneous materials, it is possible to realize a small and high-speed optical device.

[0008] However, when connecting optical circuit elements or optical fibers to optical functional elements, it is necessary to pre-align the input / output optical waveguides of the optical functional element and the input / output optical waveguides of the optical circuit elements to a rough position where the light intensity of both can be confirmed. In the case of the flip-chip phase modulator described above, the optical waveguide surface is on the wiring board side, so the optical waveguide is not visible, making it impossible to observe from above and difficult to pre-align the optical waveguides.

[0009] This disclosure has been made in view of the above points, and aims to provide an optical device that is applicable to the integration of an optical functional element having an optical waveguide input / output structure and an optical circuit element having an optical waveguide input / output structure for inputting and outputting optical signals between the optical element and the optical circuit element, and that realizes end-face optical coupling by a structure that enables simple alignment when inputting and outputting optical signals between the optical element and the optical circuit by end-face connection.

[0010] To achieve the above objectives, one form of optical device disclosed herein is: An optical device that can be connected to an optical circuit element, The device comprises a wiring board and an optical functional element having an input / output optical waveguide for optical signals, and being mounted as a flip chip on the wiring board, wherein the end face of the input / output optical waveguide in the optical functional element is , the optical circuit element The end face of the input / output optical waveguide is butted and coupled to the wiring board, and the wiring board is provided with alignment through-holes that penetrate the wiring board, and the optical waveguide is connected through the alignment through-holes. Functional elements The position of the end face of the input / output optical waveguide and the Optical circuit elements The alignment or misalignment with the position of the end face of the input / output optical waveguide can be visually observed.

[0011] Furthermore, one embodiment of the optical device alignment method of this disclosure comprises a wiring board and an optical functional element having an optical signal input / output optical waveguide and mounted as a flip chip on the wiring board, A method for aligning an optical device to which the optical functional element and the optical circuit element are connected, The end face of the input / output optical waveguide in the optical functional element , the optical circuit element The end face of the input / output optical waveguide is butted and coupled, and the wiring board is provided with a centering through-hole that penetrates the wiring board, and the centering through-hole is connected to the Optical functional elements The position of the end face of the input / output optical waveguide and the Optical circuit elements This is performed in an optical device where the alignment or misalignment with the position of the end face of the input / output optical waveguide is visible. , Through the aforementioned through-hole for alignment Optical functional elements The end face of the input / output optical waveguide and 、 The aforementioned Optical circuit elements While visually observing the end faces of the input and output optical waveguides , the optical functional element Input / output optical waveguide and 、 The aforementioned Optical circuit elementsAfter adjusting the X-axis and Y-axis with the input / output optical waveguide, the above-mentioned Optical functional elements input / output optical waveguide and the above-mentioned Optical circuit elements Obtain the light intensity profile transmitted through the input / output optical waveguide, and align the peak of the light intensity profile in the Y-axis direction to perform pre-alignment death , Performs alignment using optical signals. .

[0012] According to the above form, it is applicable to the integration of an optical functional element having an optical waveguide input / output structure and an optical circuit element having an optical waveguide input / output structure for inputting and outputting an optical signal between the optical functional element and the optical circuit element. When performing optical signal input / output between the optical element and the optical circuit by end-face connection, it is possible to provide an optical device that realizes end-face optical coupling with a structure that enables simple alignment.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram showing a comparative example of the present disclosure. [Figure 2] It is a diagram showing another comparative example of the present disclosure. [Figure 3] (a), (b) are diagrams showing another comparative example of the present disclosure. [Figure 4] (a), (b) are diagrams showing another comparative example of the present disclosure. [Figure 5] (a), (b) and (c) are plan views for explaining the optical device of the first embodiment of the present disclosure. [Figure 6] (a), (b) are plan views for explaining the optical device of the second embodiment of the present disclosure. [Figure 7] (a), (b) are plan views for explaining the optical device of the second embodiment of the present disclosure. [Figure 8] It is a diagram showing the output light intensity profile obtained after performing the pre-alignment of the present embodiment. [Figure 9] It is a diagram showing the output light intensity profile of the comparative example.

Embodiments for Carrying Out the Invention

[0014] Prior to the description of the present disclosure, the comparative examples of the present disclosure will be described below with reference to the drawings. The drawings of the present disclosure are for explaining the configuration, the positional relationship of each part, the operation, the function, and the technical idea of the present disclosure, and do not limit the specific shape of the present disclosure, nor necessarily accurately represent its aspect ratio and the like.

[0015] [Comparative Example] FIG. 1 is a diagram showing a comparative example of the present disclosure, and shows a state in which an optical functional element 11 and an optical circuit element 12 are connected with different materials. The optical functional element 11 shown in FIG. 1 is a phase modulation chip, and is composed of InP in which Mach-Zehnder interferometers 112 and 113, which are phase modulators, are integrated, and includes an optical waveguide 111 that connects the Mach-Zehnder interferometers 112 and 113. The optical circuit element 12 is a polarization control chip, and integrates a polarization rotator 122, a polarization beam combiner (PBC) 123, and an optical waveguide 121. In both the comparative example and the embodiment, in the following description, the surface on which the Mach-Zehnder interferometers 112 and 113 shown in FIG. 2 are formed is defined as the surface of the optical functional element 11, and the surface on which the polarization rotator 122 and the polarization beam combiner 123 are mounted is defined as the surface of the optical circuit element 12. And the surface opposite to the surface is referred to as the back surface.

[0016] Signal light (TE polarization (transverse electric field polarization)) is input from the optical waveguide 121, and is input to the polarization rotator 122 and the polarization beam combiner 123 through the Mach-Zehnder interferometers 112 and 113, respectively. The TE polarization input to the polarization rotator 122 is converted into TM polarization (transverse magnetic field polarization) and input to the polarization beam combiner 123. TE polarization and TM polarization are output as signal light from the polarization beam combiner 123.

[0017] Furthermore, in order to increase the speed of the device, it is necessary not only to increase the speed of the optical functional element 11 itself, but also to shorten the distance of the wires (electrical wiring) 21 between the optical functional element 11 and the driver IC 20 that is connected to the optical functional element 11 to input and output electrical signals, in order to transmit high-speed signals with low loss. Figure 2 is a plan view showing a known structure in which the driver IC 20, optical functional element 11 and optical circuit element 12 are integrated on a substrate 10. In the structure shown in Figure 2, the optical functional element 11 and the driver IC 20 are mounted face up and connected by wire bonding, but the wires 21 need to be several hundred micrometers long, and it is difficult to design signal lines that match the high frequency, so the loss becomes a problem in bandwidths of 50 GHz or higher.

[0018] In the structure shown in Figure 2, variations in the length of the wire 21 can cause variations in transmission characteristics for each channel. Taking this into consideration, there is a structure in which the driver IC 20 and the optical functional element 11 are mounted as a flip chip on a substrate 30 equipped with wiring 31, as shown in Figure 3(a). In the structure shown in Figure 3(a), the surface of the optical functional element 11 is connected toward the surface of the wiring substrate 30 where the wiring 31 is formed. Figure 3(b) shows the state in which the optical functional element 11 and driver IC 20 shown in Figure 3(a) are connected to the wiring substrate 30. In the top view, the back surface of the optical functional element 11 is visible.

[0019] Connections are made using metal bumps 32 or solder. Therefore, the configuration shown in Figure 3(a) allows for short-distance connection of the optical functional element 11 to the wiring board 30. Furthermore, the wiring 31 on the wiring board 30 can be designed with width and pitch to match high frequencies, making it suitable for low-loss signal transmission. In the example shown in Figure 3, the optical functional element 11 is used as a phase modulator, and by mounting it on the wiring board 30 with a driver IC 20 and a flip chip, it becomes possible to connect the two with ideal electrical wiring. Moreover, the configuration shown in Figure 3(a) enables the realization of a compact and high-speed optical device by integrating optical circuit elements together.

[0020] Figures 4(a) and 4(b) illustrate the connection of the optical circuit element 12 to the configuration shown in Figure 3(a). Figure 4(a) is a plan view of the configuration shown in Figure 3(a) and the optical circuit element 12 as seen from the surface of the wiring board 30. Figure 3(b) is a plan view of the configuration shown in Figure 3(a) as seen from the back of the wiring board 30. When connecting the optical circuit element 12 or optical fiber to the optical functional element 11, it is necessary to pre-align the input / output optical waveguides of the optical functional element 11 and the input / output optical waveguides of the optical circuit element 12 to a rough position where the light intensity of both can be confirmed. In the case of the optical functional element 11 of the flip-chip phase modulator described above, the surface on which the input / output optical waveguides are formed faces the surface of the wiring board 30, and the input / output optical waveguides are not visible from the top surface. Therefore, in the alignments shown in Figures 4(a) and 4(b), it is not possible to observe the input and output optical waveguides from above, making it difficult to pre-align the input and output optical waveguides.

[0021] To address the above issues, one could consider providing alignment marks on the back surface of the substrate of the optical functional element 11 and the optical circuit element 12, indicating the connection positions, and performing pre-alignment without confirming the positions of the input and output optical waveguides. However, forming alignment marks on the back surface of the substrate requires the addition of a separate process to the processing steps on the substrate surface, leading to a more complex and costly manufacturing process.

[0022] Another possible configuration to address the above issues is to design the input / output optical waveguides of the optical circuit element 12 to be located outside the wiring board 30. With such a configuration, the input / output optical waveguides are not hidden by the wiring board 30, and pre-alignment can be performed while confirming the position of the input / output optical waveguides. However, with such a configuration, the chip of the optical circuit element 12 cannot be placed in the center of the wiring board 30, reducing the design flexibility. This becomes a problem when arranging chips at high density. Furthermore, when mounting the optical functional element 11 and optical circuit element 12 on the wiring board 30 using flip chips and soldering, there is a problem that the adhesive deteriorates due to the heat generated by soldering if the optical functional element 11 and optical circuit element 12 are connected before being mounted on the wiring board 30.

[0023] As described above, when hybridizing optical functional elements such as optical modulators with optical circuit elements such as PLCs and SiPs that integrate polarization control circuits, flip chips are suitable for inputting and outputting high-speed signals. However, a challenge has been to easily match and couple the input and output optical waveguides. This disclosure focuses on this point and aims to provide an optical device that achieves highly efficient optical coupling by easily matching and coupling the input and output optical waveguides of optical functional elements and optical circuit elements mounted on a wiring board using a flip chip.

[0024] [First Embodiment] Figures 5(a), 5(b), and 5(c) are plan views illustrating an optical device according to a first embodiment of the present disclosure. The optical device of this embodiment comprises a wiring board 53, an optical functional element 51, an optical circuit element 52, and a driver IC 55. The optical functional element 51 and the driver IC 55 are connected by a wire 56. The optical functional element 51 may have a configuration similar to, for example, the phase modulation chip shown in Figure 1, and is equipped with an optical waveguide for inputting and outputting optical signals, with its end face located at its end. The optical circuit element 52 may be a polarization control chip similar to, for example, the optical circuit element 12 shown in Figure 1, and is equipped with an optical waveguide for inputting and outputting optical signals, with its end face located at its end. The explanation of Figures 5(a) to 5(c) will be given with the front of the page as "top" and the back as "bottom".

[0025] Figure 5(a) shows the back surface of the wiring board 53, where the wiring is formed, relative to the surface on which the input / output optical waveguides of the optical functional element 51, optical circuit element 52, and IC driver 55 are formed. Figure 5(b) shows the configuration shown in Figure 5(a) rotated 180 degrees towards the viewer around the Z-axis. In Figure 5(b), the back surface of the wiring board 53 and the optical functional element 51, optical circuit element 52, and driver IC 55, which are located below the wiring board 53, are shown. The optical functional element 51 and optical circuit element 52 are flip-chip mounted so that their surfaces are in contact with the wiring board 53. As shown in Figures 5(a) and 5(b), the wiring board 53 has three through-holes 531 for alignment that penetrate through the wiring board 53. Figure 5(c) is an enlarged view of the through-holes 531 for alignment shown in Figure 5(b).

[0026] The end faces of the input / output optical waveguides in the optical functional element 51 are butted and coupled with the end faces of other input / output optical waveguides. In the examples shown in Figures 5(a) and 5(b), the other input / output optical waveguides are the input / output optical waveguides of the optical circuit element 52. As shown in Figure 5(c), the butted portion between the end faces of the input / output optical waveguides of the optical functional element 51 and the input / output optical waveguides of the optical circuit element 52 is visible through the alignment through-hole 531. In the first and second embodiments, the "butted portion" refers to the position where the end faces come into contact before being fixed with adhesive or the like. That is, the butted portion C of the input / output optical waveguide 511 on the optical functional element 51 side and the input / output optical waveguide 521 on the optical circuit element 52 side can be observed from the alignment through-hole 531. Here, "visible" means that the state can be observed visually or by camera from above the alignment through-hole 531.

[0027] As described above, in the first embodiment of the optical device, the input / output optical waveguide 511 of the optical functional element 11 and the input / output optical waveguide 521 of the optical circuit element 52 can be confirmed and pre-aligned from the wiring board 53 side through the alignment through-hole 531. When the flip chip is mounted on the wiring board 53, the surface on which the input / output optical waveguide of the optical functional element 51 is provided is covered by the wiring board 53. However, according to the first embodiment, since the alignment through-hole 531 corresponds to the coupling position of the input / output optical waveguides 511 and 512, the positions of the input / output optical waveguides 511 and 512 can be confirmed, and pre-alignment can be performed using the same procedure as known input / output optical waveguides that are not mounted on a flip chip.

[0028] With the configuration of the first embodiment, the input / output optical waveguide 511 of the optical functional element 51 and the input / output optical waveguide 521 of the optical circuit element 52 can be pre-aligned to positions that facilitate alignment. Therefore, according to the first embodiment, the initial alignment can be close to the position that will be aligned during alignment performed while inputting signal light and monitoring the output light. The first embodiment also enables highly accurate alignment with a simple configuration and procedure, even for optical functional elements 11 mounted as flip chips on a wiring board 53.

[0029] As described above, in the first embodiment, an optical functional element is flip-chip mounted on a wiring board, input and output optical waveguides are provided in the optical functional element, and alignment through-holes are provided at positions corresponding to the input and output optical waveguide positions on the wiring board. With this configuration, the alignment of the input and output optical waveguides can be performed from the back side of the wiring board while confirming the input and output optical waveguide positions through the alignment through-holes. This is the greatest feature of the first embodiment.

[0030] In the first embodiment, the position of the input / output optical waveguides covered by the wiring board can be easily confirmed by mounting the flip chip. This allows for pre-alignment, where the optical waveguide positions are pre-adjusted to a position that is easy to align. Pre-aligning the optical waveguides to be aligned to close positions is desirable because it reduces the time required for fine-tuning during subsequent alignment while monitoring the optical output of the signal light. As a result, butt coupling to the optical functional element mounted on the flip chip can be realized with a simple procedure.

[0031] Generally, the cross-sectional structure of a PLC is constructed by depositing a thin film of SiO2 as an undercladding of approximately 20 μm, as a core of 3 μm to 10 μm, and as an overcladding of approximately 20 μm on a Si or SiO2 substrate. The first embodiment assumes a PLC formed on a Si substrate. In Si photonics optical circuit elements, several μm of SiO2 forming an SOI layer as an undercladding, several hundred nanometers of Si forming a core, and several μm of SiO2 as an overcladding are deposited on the Si substrate. In optical functional elements using an InP substrate, the InP substrate is used as an undercladding, several hundred nanometers of compound semiconductor forming a core, and InP as an overcladding or SiN or SiO2 as a passivation layer are deposited. Metal patterns that serve as electrodes are provided on the front and back surfaces.

[0032] Furthermore, in the first embodiment, an optical waveguide formed in the edge region of the substrate is assumed to be an input / output optical waveguide for inputting and outputting optical signals. The input / output optical waveguide is optically coupled with other input / output optical waveguides by a mode field at the edge. The wiring board is used to input and output electrical signals to the chip. Such a wiring board may be a ceramic substrate made of a ceramic material such as aluminum nitride or aluminum oxide, or an organic substrate based on epoxy, on which a metal wiring pattern is provided and laminated. Conductivity between each laminated layer is provided by conductive vias, which are created by providing through holes in each substrate and coating or filling the surface with a conductive material.

[0033] Alignment through-holes are formed by providing through-holes in a wiring board at a location where the part that serves as a marker for the optical functional element can be identified during pre-alignment for alignment. A typical through-hole via is a conductive via filled with a light-impermeable conductive material for the purpose of electrically connecting the front and back surfaces of the substrate. In contrast, for alignment through-holes in the first embodiment, it is desirable that the conductive material is not filled, or that the material is light-transmitting, in order to confirm the surface of the optical functional element. The position of the alignment through-hole is preferably at the input / output optical waveguide position of the optical functional element. However, in the first embodiment, alignment through-holes may be formed in the process of forming conductive vias and used as alignment through-holes without filling them with conductive material, thereby simplifying the manufacturing process.

[0034] Thus, in the first embodiment, in an optical device that hybridizes optical functional elements and optical circuit elements, alignment through-holes are provided in the wiring board at the positions of the input and output optical waveguides of the optical functional elements mounted as flip chips on the wiring board. Therefore, in the first embodiment, butt optical coupling with optical functional elements and optical fibers can be performed by checking the optical waveguide position from the wiring board side, pre-aligning to a rough alignment position, and then transitioning to alignment by optical signals. As a result, the first embodiment enables efficient alignment in butt coupling and makes it possible to provide an optical device that is coupled by simple butt optical coupling.

[0035] Furthermore, according to the first embodiment, in order to obtain the above-mentioned effects, it is not necessary to provide a marker on the back surface of the optical functional element to serve as a guide for alignment, nor is it necessary to restrict the mounting position of the optical functional element in order to confirm the input / output optical waveguide. In this respect, the first embodiment is superior to the known techniques mentioned above.

[0036] [Second Embodiment] The second embodiment differs from the first embodiment in that it provides alignment markers corresponding to both optical functional elements and optical circuit elements, and forms alignment through-holes on the wiring board at positions corresponding to the alignment markers. In this configuration, the alignment markers can be observed through the alignment through-holes.

[0037] Figures 6(a), 6(b), 7(a), and 7(b) are plan views illustrating the optical device of the second embodiment. The optical device of the second embodiment comprises a wiring board 63, an optical functional element 61, and an optical circuit element 62. Figure 6(a) shows the optical functional element 61 and the optical circuit element 62 mounted on the surface of the wiring board 63. The optical functional element 61 and the optical circuit element 62 are flip-chip mounted on the wiring board 63, and their surfaces are in contact with the wiring board 63. The optical circuit element 62 includes optical waveguides for input and output of optical signals, and corresponding input and output optical waveguides for butt coupling. Figure 6(b) shows the wiring board 63 viewed from the back. Figure 7(a) shows the wiring board 63 and the optical functional element 61 and optical circuit element 62 located beneath the wiring board 63 viewed from the back of the wiring board 63. Figure 7(b) is a view from the surface of an optical device in which an optical functional element 61 and an optical circuit element 62 are coupled together. However, the optical device shown in Figure 7(b) is a device for connection testing in the second embodiment, and has a configuration in which the phase modulation section, polarization rotator, and polarization beam combiner are removed from the optical functional element of the integrated optical modulation device (shown in Figure 1).

[0038] As shown in Figure 7(b), the optical circuit element 62 includes an input optical waveguide 621a for signal light, an output optical waveguide 621c, and corresponding butt-coupled input / output optical waveguides 621b and 621d, respectively. The optical functional element 61 includes butt-coupled optical waveguides 611a and 611b that butt-couple with the butt-coupled input / output optical waveguides 621b and 621d. The optical functional element 61 and the optical circuit element 62 are mounted on a wiring board 63 as flip chips, as shown in Figures 6(a) and 7(a). The wiring board 63 inputs and outputs electrical signals between the optical functional element 61 and the optical circuit element 62.

[0039] The optical device of the second embodiment may be an optical modulation device that combines an optical functional element 61 and an optical circuit element 62. When the optical device of the second embodiment is an optical modulation device, the optical functional element 61 is composed of a phase-modulating optical waveguide that changes the phase of light by receiving an electrical signal from the wiring board 63 and an optical waveguide for butt coupling, and the input and output optical waveguides 611a and 611b are arranged on one end face in a U-shaped optical waveguide arrangement. When the optical device of the second embodiment is an optical modulation device, the light input to the butt-to-input and output optical waveguides 621b and 621d of the optical circuit element 62 is optically coupled to the optical functional element 61 via the butt coupling section, then converted into a phase-modulated optical signal by the phase-modulating optical waveguide, optically coupled again to the optical circuit element 62 via the butt coupling section, and polarized combined by a polarization rotator and a polarization beam combiner and output.

[0040] As shown in Figure 7(b), the surface of the optical functional element 61 is provided with connection pads 613 for flip-chip mounting onto the wiring board 63. As shown in Figure 6(b), the surface of the wiring board 63 is provided with connection pads 633 that are electrically connected to the connection pads 613. As shown in Figure 6(a), the optical functional element 61 and optical circuit element 62 and the wiring board 63 are electrically connected via the connection pads 613 and 633. In addition, the wiring board 63 has four alignment through-holes 632 formed therein, similar to the first embodiment. The alignment through-holes 632 are through-holes that penetrate the wiring board 63, similar to the first embodiment.

[0041] As a platform for the optical circuit element 62, a SiP chip with dimensions of 2.5 mm in length and 2.0 mm in width can be used. The second embodiment uses a Si photonics chip in which a 3.0 μm thick SiO2 undercladding, a 0.22 μm thick Si core with a width of 0.5 μm, and a 1.5 μm thick SiO2 overcladding are formed on a Si substrate with a thickness of 0.625 mm.

[0042] The optical circuit element 62 inputs and outputs signal light from one long side and connects the other long side to the optical functional element 61. The connection surface is polished for connection. The optical waveguide structure from the input optical waveguide 621a to the butt-alignment input / output optical waveguide 621b, and from the output optical waveguide 621c to the butt-alignment input / output optical waveguide 621d, is S-shaped. Markers 625 are provided near the butt-alignment input / output optical waveguides 621b and 621d. Markers 625 serve as guides when the optical circuit element 62 is aligned with the optical functional element 61.

[0043] The optical functional element 61 is an InP chip with dimensions of 2.5 mm in length, 4.0 mm in width, and a substrate thickness of 0.25 mm. The InP chip has an InP substrate as the undercladding, a compound semiconductor core with a width of 2.0 μm and a thickness of 0.3 μm, and an overcladding of 2.0 μm of deposited InP. Butt-joint input / output optical waveguides 611a and 611b are provided on the short side. Markers 615 are also provided near the butt-joint input / output optical waveguides 611a and 611b. Markers 615 are paired with marker 625 on the optical circuit element 62 and serve as a guide when aligning with the optical circuit element 62. Markers 615 and 625 together are referred to as the alignment marker 65.

[0044] The wiring board 63 is made of a ceramic aluminum nitride substrate with dimensions of 4.0 mm in length, 8.0 mm in width, and a substrate thickness of 0.45 mm. Connection pads 633 and alignment through-holes 632 are formed on this substrate. The connection pads 633 are gold pads. The alignment through-holes 632 are φ150 μm through-holes that penetrate the substrate.

[0045] In the flip-chip mounting of the optical functional element 61 onto the wiring board 63, gold bumps approximately 20 μm in height are formed on the connection pads 633 of the wiring board 63 using the ball-forming function of a wire bonder. The flip-chip optical functional element 61 is mounted onto the wiring board 63 by connecting the connection pads 633 and 613 via the gold bumps using thermocompression bonding.

[0046] The alignment through-holes 632 of the wiring board 63 are formed at positions corresponding to the alignment markers 65 or the abutting portions of the input / output optical waveguides for the abutting of the optical functional elements 61 and optical circuit elements 62. Therefore, as shown in Figure 6(a), the alignment markers 65 can be seen from the back surface of the wiring board 63 through the alignment through-holes 632. In the second embodiment as well, the abutting portions of the input / output optical waveguides for the abutting of the optical functional elements 61 and optical circuit elements 62 can be seen through the alignment through-holes 632.

[0047] In the second embodiment, a marker 615 formed on the optical functional element 61 and a marker 625 formed on the optical circuit element 62 are positioned so that they can be seen through the alignment through-hole 632. The optical functional element 61 and the optical circuit element 62 are then pre-aligned by adjusting their positions so that the markers 615 and 625 properly form the alignment marker 65. In such a process, it is preferable that the markers 615 and 625 are symmetrical with respect to an axis perpendicular to the opposing direction of the optical functional element 61 and the optical circuit element 62, and have similar shapes. This is because it is easier to visually determine whether the shape formed by bringing the markers 615 and 625 together is appropriate.

[0048] In the second embodiment, a transparent material that transmits visible light is provided on the back surface of the wiring board 63 and in a position that covers the alignment through-hole 632. Here, "cover" is not limited to a configuration in which the transparent material covers the alignment through-hole 632, but may also be a configuration in which the transparent material fills the alignment through-hole 632. In the second embodiment, the transparent material is a thin-film glass substrate 635 with a thickness of 0.03 μm. With this configuration, in the second embodiment, even when the wiring board 63 is attached to another substrate with a thermally conductive adhesive, the thermally conductive adhesive can be prevented from entering the alignment through-hole 632. [Examples]

[0049] Next, embodiments of the present disclosure will be described. This embodiment is applied to pre-alignment in the alignment of butt coupling of an optical functional element and an optical circuit element mounted as a flip chip on a wiring board, in which the positions of each input and output optical waveguide are aligned to a position where alignment by optical signal is possible. In this embodiment, the input and output optical waveguides were observed through alignment through holes to evaluate whether pre-alignment was possible. The optical functional element in this embodiment is a test device obtained by removing the polarization rotator and polarization beam combiner from a phase modulation chip, as described in the second embodiment. The optical functional element in this embodiment comprises a signal optical input / output optical waveguide and an input / output optical waveguide for butt coupling. In this embodiment, the optical functional element is an InP chip and the optical circuit element is a SiP chip.

[0050] For butt coupling of an InP chip to an SiP chip, the connection end faces of the SiP chip and InP chip are observed from the back side of the wiring board through alignment through-holes, and the end faces of the input and output optical waveguides are brought close together. After this, the operator observes two alignment through-holes and pre-aligns the wiring board horizontally so that the input and output optical waveguides align at each of them.

[0051] At this time, if the end faces do not align when one of the two through-holes for alignment is aligned, it is determined that the Z-axis rotation is misaligned, and the Z-axis rotation is adjusted to align them. Subsequent alignment is performed by inputting 1.55 μm wavelength light from the signal light input optical waveguide of the SiP chip, propagating it through the InP chip, and monitoring the light intensity output from the signal light output optical waveguide. In this alignment, first, the output light intensity profile in the Y-axis direction is obtained, and the alignment is adjusted to a rough alignment position by positioning so that the output light intensity peaks. After that, the alignment is completed by adjusting the alignment of the X and Y axes and the Z-axis rotation so that the output light intensity is maximized, and adjusting the gap between the end faces to the design position (1 μm).

[0052] Furthermore, pre-alignment using alignment markers involves observing the alignment markers through the alignment through-holes and adjusting the X and Z axis rotations so that the alignment markers on the InP chip and SiP chip are in the design position. This type of alignment allows for pre-alignment similar to pre-alignment performed by observing the end faces of the input and output optical waveguides.

[0053] The butt joint between the SiP chip and the InP chip is fixed by filling the space between the SiP chip and the InP chip with a UV-curable adhesive that is transparent in the infrared region, and then curing the adhesive by irradiating it with UV light. At this time, an anti-reflective film corresponding to the refractive index of the resin being filled is provided on the end face of the input / output optical waveguide of the InP chip. Along with such an optical device, the discloser of this embodiment separately prepared a wiring board without alignment through-holes and confirmed the difference in the complexity of alignment with and without alignment through-holes.

[0054] Figure 8 shows the output light intensity profile in the Y-axis direction obtained after pre-alignment by observing the input / output optical waveguides using the alignment through-hole as described above, and the output light intensity profile in the Y-axis direction obtained after pre-alignment by observing the alignment marker through the alignment through-hole. The solid line in the figure shows the result of alignment performed while visually observing the butt joint of the input / output optical waveguides through the alignment through-hole. The dashed line shows the result of alignment performed while visually observing the alignment marker through the alignment through-hole. Note that both profiles were obtained by first aligning using the butt joint, then separating the chip, and finally using the alignment marker. In Figure 8, the horizontal axis shows the scan position in the Y-axis direction, and the vertical axis shows the light intensity obtained at the scan position.

[0055] As shown in Figure 8, although the initial position in the Y-axis direction is offset from the peak, the pre-alignment ensures that the X-axis and Z-axis rotational positions are almost perfectly aligned. Therefore, the peak position of the output light intensity can be confirmed by acquiring the Y-axis profile only once. In this embodiment, the alignment can then be further adjusted by adjusting the Z-axis rotation to quickly complete the centering process.

[0056] Figure 9 shows the light intensity profile for comparison with this embodiment. In Figure 9, the horizontal axis represents the Y-axis scan position, and the vertical axis represents the light intensity acquired at the scan position. When a through-hole for alignment is not used, the SiP chip and InP chip are observed from the back side and placed in approximate positions. After this, signal light is input from the SiP chip, and the Y-axis profile is acquired while moving the chip away from the initial position by ±2 μm in the X-axis direction to search for the peak position. Figure 9 shows the Y-axis profile for each amount of movement from the initial X-axis position. In Figure 9, the solid line profile represents a movement of 0 μm from the X-axis position, the dashed line profile represents a movement of -16 μm, the dashed line profile represents a movement of -18 μm, and the dashed line profile represents a movement of -20 μm.

[0057] As shown in Figure 9, although no peak was observed at 0 μm on the Y axis, the peak was finally confirmed when the X axis was moved 16 μm away from the initial position by repeated movements, and the maximum peak was obtained at -18 μm, allowing us to proceed to alignment. In the absence of a through-hole for alignment, the process becomes complicated because the light intensity profile must be acquired many times while moving the X axis before the peak can be confirmed. In contrast, when using a through-hole for alignment, as shown in Figure 8, the alignment position of the X axis can be set to an approximate position in advance, the peak can be confirmed with a single profile acquisition, and alignment can be performed with a simple procedure.

[0058] As described above, in this embodiment, the optical functional element mounted as a flip chip on a wiring board equipped with alignment through-holes allows observation of the optical waveguide and markers through the alignment through-holes from the wiring board side during butt coupling with the optical circuit element. Therefore, even when the flip chip is mounted on the wiring board and the markers cannot be seen from the back side, pre-alignment becomes possible, providing an optical device that simplifies butt optical coupling. [Explanation of symbols]

[0059] 10,30 boards 11,51,61 Optical Functional Elements 12,52,62 Optical circuit elements 20,55 Driver IC 21.56 wires 30, 53, 63 Wiring board 31 Wiring 32 Metal bumps 65. Marker for center alignment 111,121 Optical waveguide 112,113 Mach-Zehnder interferometer 122 Polarization Rotor 123 Polarization Beam Combiner 511,512,521 Input / output optical waveguide 531 Through-hole for centering 611a, 611b, 621b, 621d Optical waveguides for butt joints 613 Connection pad 621a Input Optical Waveguide 621c Output optical waveguide 615,625 markers 632 Through-hole for centering 633 Connection pad 635 Thin-film glass substrate

Claims

1. An optical device that can be connected to an optical circuit element, Wiring board and The system comprises an optical functional element having an optical waveguide for input and output of optical signals, and mounted as a flip chip on the wiring board, The end face of the input / output optical waveguide in the optical functional element is butted and coupled with the end face of the input / output optical waveguide of the optical circuit element. The aforementioned wiring board is provided with a through-hole for alignment that penetrates the wiring board, The alignment through-hole allows visual confirmation of whether the positions of the end faces of the input / output optical waveguides of the optical functional element and the input / output optical waveguides of the optical circuit element coincide or not. Optical devices.

2. The optical device according to claim 1, wherein the coupling portion between the end face of the input / output optical waveguide of the optical functional element and the end face of the input / output optical waveguide of the optical circuit element is visible through the alignment through-hole.

3. The optical device according to claim 1, wherein an alignment marker indicating the end face of the input / output optical waveguide of the optical functional element and an alignment marker indicating the end face of the input / output optical waveguide of the optical circuit element are visible through the alignment through-hole.

4. The optical device according to claim 3, wherein the alignment markers are provided on the optical functional element and the optical circuit element, respectively, and consist of two markers that are symmetrical with respect to an axis perpendicular to the opposing direction between the input / output optical waveguide of the optical functional element and the input / output optical waveguide of the optical circuit element, and have the same shape.

5. The optical device according to claim 1, wherein the through-hole for alignment is covered with a material that transmits visible light.

6. A method for aligning an optical device comprising a wiring board and an optical functional element having an optical signal input / output optical waveguide and mounted on the wiring board as a flip chip, wherein the optical functional element and the optical circuit element are connected, In an optical device in which the end faces of the input / output optical waveguides in the optical functional element are butted and coupled with the end faces of the input / output optical waveguides of the optical circuit element, the wiring board is provided with alignment through-holes that penetrate the wiring board, and the alignment or misalignment of the positions of the end faces of the input / output optical waveguides of the optical functional element and the input / output optical waveguides of the optical circuit element can be visually confirmed through the alignment through-holes, While visualizing the end faces of the input / output optical waveguides of the optical functional element and the input / output optical waveguides of the optical circuit element through the alignment through-hole, the X and Y axes of the input / output optical waveguides of the optical functional element and the input / output optical waveguides of the optical circuit element are adjusted, and then pre-alignment is performed by acquiring the light intensity profiles transmitted through the input / output optical waveguides of the optical functional element and the input / output optical waveguides of the optical circuit element and aligning the peaks of the light intensity profiles in the Y-axis direction. Performs alignment using optical signals. Method for aligning optical devices.

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