Integrated optical device and method for aligning the same

Abstract

This integrated optical device is characterized in that an optical function element is provided with an optical waveguide that is composed of a core and a cladding and that is disposed on a substrate, and the optical function element includes: an optical signal input waveguide or output waveguide provided on an end face of the substrate; and a reflectance control body that is provided in the vicinity of the core and forms a region having a different reflectance than the core, the cladding, and the substrate when light is incident on the end face. The integrated optical device is also characterized in that the input waveguide or the output waveguide of the optical function element is butt-coupled and attached to a different waveguide via the end face.

Description

[Technical Field]

[0001] The present invention relates to an integrated optical device applicable to optical communication systems, and relates to an optical functional element formed of an optical waveguide and an integrated optical device in which the optical functional element is mounted. [Background technology]

[0002] In recent years, the widespread use of optical fiber transmission has led to a demand for technologies capable of integrating multiple optical circuits at high density. Examples of such technologies include silica-based planar lightwave circuits (PLCs) and silicon photonics-based SiPs. PLCs are waveguide-based optical devices with excellent features such as low loss, high reliability, and high design flexibility. In fact, transmission equipment at optical communication transmission ends incorporates PLCs that integrate functions such as multiplexers / demultiplexers, branchers, and couplers. While SiPs do not match PLCs in terms of low loss, they offer high design flexibility and enable even smaller optical circuits through their small waveguide bending radius. In addition to PLCs and SiPs, transmission equipment also incorporates optical functional elements such as photodiodes (PDs) that convert optical and electrical signals, laser diodes (LDs), and optical modulators. To further expand communication capacity, high-performance integrated optoelectronic devices are required that integrate optical waveguides, such as PLCs, for optical signal processing, with optical devices, such as PDs made of InP (indium phosphide) materials, for high-speed photoelectric conversion.

[0003] PLCs and SiPs are promising platforms for such integrated optical devices, and an integrated optical device that hybrid-integrates an InP optical modulator chip and a PLC chip has been proposed (Non-Patent Document 1). In the example of Non-Patent Document 1, a phase modulator is integrated on an InP chip, a polarization rotator (PR), and a polarization beam combiner (PBC) are integrated on a PLC, and the two chips are optically coupled via a lens. Using a PLC as a polarization combining chip requires a smaller mounting area than conventional polarization combining methods using spatial optics, and integrating it into an optical circuit simplifies optical axis alignment. Optically coupling such a combination of PLC and optical circuit elements such as InP offers advantages in terms of device miniaturization and optical circuit design flexibility. To expand communication capacity, integrated devices have been developed that include PDs with waveguide structures suitable for broadband use using InP-based materials, as well as optical phase modulators with high-speed phase modulation capabilities. Furthermore, in recent years, to achieve further miniaturization, integrated optical devices in which optical circuit elements are directly connected without lenses have become increasingly desirable.

[0004] This paper describes a method for coupling a PLC and an InP-based optical functional element by butting their input and output waveguides together without using a lens.

[0005] For example, when butt-connecting an optical fiber to a PLC, first the end face of the optical fiber block (made of glass) to which the optical fiber is fixed is adjusted so that it is parallel to the end face of the PLC. Next, while inputting light into the optical fiber, the optical output position of the optical fiber is aligned with the input waveguide at the end face of the PLC. While monitoring the output light from the output waveguide connected to that input waveguide, the position is adjusted to obtain optimal optical coupling. Then, while maintaining this position, a UV-curable adhesive is filled between the end face of the optical fiber block and the end face of the PLC, which is then cured and fixed in place in a short time by irradiating it with UV light.

[0006] If this butt coupling method could be used to integrate Si or InP optical functional elements on the optical circuit platform of a PLC, or to integrate InP optical functional elements on an SiP optical circuit platform, it would be possible to provide smaller integrated optical devices. However, when this butt coupling method is used to connect an optical functional element with an optical circuit element in a U-shaped folded configuration, in which the input and output waveguides are located on the same end face, as shown in Figure 1, the following problems arise.

[0007] Fig. 1 shows the optical circuit configuration of a conventional integrated optical device. In Fig. 1, a phase modulator chip 110, which is an optical functional element, includes an optical input waveguide 111 and first and second QPSK modulators 112 and 113, which phase-modulate and output the signal light from the optical input waveguide 111. The chip also includes two optical output waveguides 114 and 115, which output the output light from the first and second QPSK modulators. A polarization mux chip 120, which is an optical circuit element, includes a signal light input / output waveguide 121, phase-modulating light input waveguides 122 and 123, a polarization rotator 124 that rotates the TE light from the phase-modulating light input waveguide 123 to TM light, and a polarization beam combiner 125 that multiplexes the TE light from the phase-modulating light input waveguide 122 with the TM light from the polarization rotator 124. The signal light input / output waveguide 121 is connected to the optical input waveguide 111 and outputs the input signal light to the optical input waveguide 111. The phase-modulating optical input waveguides 122 and 123 are connected to the optical output waveguides 114 and 115, respectively. The signal light from the polarization beam combiner 125 is output from the signal light output waveguide 126.

[0008] To butt-couple and connect the optical input waveguide 111 and optical output waveguides 114 and 115 of the phase modulator chip 110 in Figure 1 to the signal light input / output waveguide 121 and phase modulation light input waveguides 122 and 123 of the polarization mux chip 120, it is necessary to input light into the optical input / output waveguide 121 of the polarization mux chip 120 and monitor the intensity of the light output from the signal light output waveguide 126 via the connection end face while moving the position of the phase modulator chip or the polarization mux chip on the XY plane to align the waveguides to be connected at the connection end face.

[0009] To monitor the optical intensity of an optical signal input through the signal light input / output waveguide 121, propagating to the signal light output waveguide 126, and outputting it, at least the optical input waveguide 111 and the signal light input / output waveguide 121, the optical output waveguide 114 and the phase-modulation optical input waveguide 122, and the optical output waveguide 115 and the phase-modulation optical input waveguide 123 must be pre-aligned to a rough position sufficient to check the optical intensity. Furthermore, because at least two connections (three connections in Figure 1) are made on the same connection surface, precise rotational alignment around the Z axis (Z-axis rotation) is also required. However, this alignment is typically performed by observing the connection end surface (XY plane) only from the top, making it difficult to achieve perfect Z-axis rotation. Therefore, when connecting to an optical functional device with a folded configuration, such as the phase modulator chip shown in Figure 1, gradual alignment is required through repeated fine adjustments of the Z-axis rotation. Thus, in order to realize compact integration by using end face connection and omitting spatial optical systems such as lenses, there is a problem in that a complicated alignment process is required.

[0010] 2 and 3, a proposal has been made to provide an input-side alignment through port 215 and an output-side alignment through port 216 near the optical input waveguide 211 and optical output waveguide 214 of a phase modulator chip 210, which is an optical functional element. Fig. 2 shows the output-side alignment, and Fig. 3 shows the input-side alignment. In Fig. 2, input light is input through the output waveguide 226 of the polarization Mux chip 220, and while monitoring the output light from the output-side alignment through port 216, the polarization Mux chip 220 or the phase modulator chip 210 is moved in the X and Y directions to align the phase-modulating light input waveguide 222 of the polarization Mux chip 220 with the output-side alignment through port 216 of the phase modulator chip 210. In Figure 3, input light 229 is input through signal light input / output waveguide 221 of polarization Mux chip 220, and output light 219 from input-side alignment through port 215 is monitored while moving polarization Mux chip 220 or phase modulator chip 210 in the X and Y directions to align signal light input / output waveguide 221 of polarization Mux chip 220 with input-side alignment through port 215 of phase modulator chip 210. By performing input-side alignment and output-side alignment separately, the degree of deviation in Z-axis rotation can be confirmed from the position and movement of the fine adjustment table after each alignment. This makes it easy to align Z-axis rotation, allowing us to move on to the process of aligning the input / output waveguides of the optical functional element and the optical circuit element without having to make repeated fine adjustments.

[0011] Furthermore, as shown in Figure 4, a tap port 411 for output-side alignment and a tap port 412 for input-side alignment are provided on a phase modulator chip 410, which is an optical functional element, and the input light input to the polarization mux chip 420 is monitored to be output via each tap port while the polarization mux chip 220 or the phase modulator chip 210 is moved in the X and Y directions to perform input-side alignment and output-side alignment, respectively. This also makes it possible to check the amount of deviation in Z-axis rotation from the position of the micro-adjustment table after alignment and to perform Z-axis rotation alignment.

[0012] However, when aligning the optical functional elements shown in Figures 2 to 4 by providing an alignment through port or tap port, it is necessary to separately place an optical fiber or PD at the output position of the through port or tap port and monitor the output light for alignment. Furthermore, the alignment setup, such as switching between input and output alignment and installing the optical fiber or PD, becomes complicated. Furthermore, the optical waveguide circuit for the through port or tap port must be placed inside the optical functional element, which hinders miniaturization. Furthermore, when providing an alignment tap port as shown in Figure 4, part of the signal light is tapped for alignment, which increases the loss from the signal light path.

[0013] As described above, in the past, when using a PLC or SiP platform to achieve hybrid integration of optical circuit elements integrating polarization control circuits and other devices with optical functional elements such as optical modulators, butt-joining optical waveguides without using a lens required complex alignment processes and cumbersome settings, and also posed problems such as hindering miniaturization. [Prior art documents] [Non-patent literature]

[0014] [Non-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. Summary of the Invention

[0015] The present invention has been made in view of the above problems, and aims to provide an integrated 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 / outputting optical signals between the optical functional element and the optical circuit element, and that realizes end-face optical coupling by a structure that enables simple alignment when inputting / outputting optical signals between the optical functional element and the optical circuit element by end-face connection.

[0016] In order to achieve the above object, the present invention is characterized by having the following configuration.

[0017] (Configuration 1) In an optical functional element having an optical waveguide made of a core and a clad provided on a substrate, an input waveguide or an output waveguide for an optical signal provided on an end surface of the substrate; Core Both sides When light is incident on the end face, the reflectance of the core, cladding, and substrate is different from that of the substrate. A plurality of regions each having different reflectances of On the end face a reflectance control body that forms a reflectance control signal; the plurality of regions are arranged along the end face such that the reflectance decreases in the order from the region closest to the core to the region farthest from the core; An integrated optical device, characterized in that an input waveguide or an output waveguide of an optical functional element is butt-coupled and bonded to another waveguide via an end face.

[0018] (Configuration 2) An optical functional element in which an optical waveguide consisting of a core and a clad is provided on a substrate. an input waveguide or output waveguide for optical signals provided on the end face of the substrate; Core Both sides When light is incident on the end face, the reflectance of the core, cladding, and substrate is different from that of the substrate. A plurality of regions each having different reflectances of On the end face and a reflectance control body that forms the reflectance control element. The plurality of regions are arranged along the end face such that the reflectance decreases in the order from the region closest to the core to the region farthest from the core. an optical functional element; In the alignment for butt-coupling through an end face with an optical circuit element having an input waveguide or an output waveguide for connection, monitoring the optical intensity of the reflected return light branched by a circulator or coupler disposed at the optical input of the optical circuit element; An alignment method for an integrated optical device, characterized in that an optical functional element or an optical circuit element is scanned while being moved, and alignment is performed by estimating the correspondence between the scanning position and the position of an area with different reflectivity formed by a reflectivity control body on the end face from the position where the light intensity profile of the reflected return light corresponding to the cross-sectional shape of the end face becomes the peak.

[0019] According to the present invention, when integrating an optical functional element such as an optical modulator having an optical waveguide input / output structure with an optical circuit element having a polarization control circuit, it is possible to provide an optical waveguide component that realizes simple and highly efficient optical coupling by butt-joining the respective waveguides to input / output optical signals between the optical functional element and the optical circuit element. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 shows the optical circuit configuration of an integrated optical device in which a conventional optical functional element and an optical circuit element are connected by butt coupling using a U-shaped folded configuration in which input and output waveguides are arranged on the same end face. [Figure 2] FIG. 2 is a diagram showing the optical circuit configuration of an integrated optical device in which alignment through ports are provided near the optical input and optical output waveguides of a conventional optical functional element. [Figure 3] FIG. 3 is a diagram showing the optical circuit configuration of an integrated optical device in which alignment through ports are provided near the optical input and optical output waveguides of a conventional optical functional element. [Figure 4] FIG. 4 is a diagram showing the optical circuit configuration of an integrated optical device in which a conventional optical functional element is provided with an alignment tap port. [Figure 5] FIG. 5 is a diagram showing an optical circuit configuration of an integrated optical device according to an embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an input / output structure for aligning the input / output portion of an optical functional element according to an embodiment of the present invention. [Figure 7]FIG. 7 is a diagram showing a profile of the intensity of reflected returning light when the intensity of reflected returning light is scanned while moving the optical function element or optical circuit element of the integrated optical device according to the embodiment of the present invention along the X-axis and Y-axis. [Figure 8] FIG. 8 is a diagram showing an optical circuit configuration of an integrated optical device according to the embodiment. [Figure 9] FIG. 9 is a diagram showing the relationship between the scanning position of the connection end face of the input / output structure for aligning the optical functional element of Example 1 and the intensity profile of the reflected returning light corresponding to the scanning position. [Figure 10] FIG. 10 is a diagram showing the relationship between the scanning position on the connection end face of the input / output part of the optical functional element of Comparative Example 1 and the intensity profile of the reflected returning light corresponding to the scanning position. [Figure 11] FIG. 11 is a diagram showing an aligning input / output structure according to the second embodiment. [Figure 12] FIG. 12 is a diagram showing the relationship between the scanning position of the connection end face of the input / output structure for aligning the optical functional element of Example 2 and the intensity profile of the reflected returning light corresponding to the scanning position. [Figure 13] FIG. 13 is a diagram showing an aligning input / output structure according to the third embodiment. [Figure 14] FIG. 14 is a diagram showing the relationship between the scanning position of the connection end face of the input / output structure for aligning the optical functional element of Example 3 and the intensity profile of the reflected returning light corresponding to the scanning position. [Figure 15] FIG. 15 is a diagram showing a boundary scan of the alignment input / output structure of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0022] 5 and 6 show, for illustrative purposes, one embodiment of the present invention.

[0023] In this embodiment, in an optical functional element having an optical waveguide provided on a substrate, an alignment input / output structure including an input waveguide or output waveguide for inputting or outputting a signal to or from an optical circuit element is provided near one end face of the substrate constituting the optical functional element.

[0024] FIG. 5 shows the optical circuit configuration of an integrated optical device comprising a phase modulator chip 510, which is an optical functional element of this embodiment, and a polarization Mux chip 520, which is an optical circuit element.

[0025] A phase modulator chip 510, which is an optical functional element, includes an optical input waveguide 511, a first QPSK modulation unit 512, and a second QPSK modulation unit 513, which phase-modulate and output the signal light from the optical input waveguide 511. The chip also includes two optical output waveguides 514 and 515, which output the output light from the first and second QPSK modulation units. A polarization mux chip 520, which is an optical circuit element, includes a signal light input / output waveguide 521, phase-modulating light input waveguides 522 and 523, a polarization rotator 524 that rotates the TE light from the phase-modulating light input waveguide 523 to TM light, a polarization beam combiner 525 that combines the TE light from the phase-modulating light input waveguide 522 with the TM light from the polarization rotator 524, and a signal light output waveguide 526 that outputs the light from the polarization beam combiner.

[0026] In this embodiment, alignment input / output structures 531 and 532 are provided near an optical input waveguide 511 and an optical output waveguide 514 on the side of a connection end face 530 which is an input / output section of a phase modulator chip 510, respectively.

[0027] FIG. 6(a) is a top view of an aligning input / output structure 600 (531 or 532 in FIG. 5) of this embodiment provided in the input / output section of an optical functional element, and FIG. 6(b) is a view of the aligning input / output structure 600 of this embodiment as viewed from the connection end face side. As shown in FIGS. 6(a) and 6(b), the aligning input / output structure of this embodiment has reflectance control bodies 610 and 611 provided near the core 602 on the connection end face 530 side of the substrate of the optical functional element. The reflectance control bodies 610 and 611 form an area having a different reflectance from the core 602, cladding, and substrate when light is incident on the connection end face. The procedure for aligning the optical functional element of this embodiment via the connection end face of the input / output waveguide for connecting the optical circuit element (polarization mux chip 520) with the optical functional element is as follows. As shown in Figure 5, a circulator 541, coupler, or the like is arranged in a signal light input / output waveguide 521 of a polarization mux chip 520, which is an optical circuit element, to branch the reflected return light, and the intensity of the reflected return light is scanned while the optical functional element or optical circuit element is moved along the X-axis or Y-axis. During this process, the intensity of the reflected return light from the end face equipped with an alignment input / output structure including a reflectivity controller changes depending on the structure. Similarly, a circulator 542, coupler, or the like is arranged in a signal light output waveguide 526 of the polarization mux chip 520 to branch the reflected return light, and the intensity of the reflected return light is scanned while the optical functional element or optical circuit element is moved along the X-axis or Y-axis.

[0028] 7A and 7B are diagrams showing the reflected return light intensity profile obtained when the reflected return light intensity is scanned while the optical functional element or optical circuit element is moved along the X and Y axes, as described above. Fig. 7A shows the X-direction scan, and shows the reflected return light intensity profile obtained when light from the input / output waveguides of the optical circuit element is moved and scanned along the X axis on lines A-A', B-B', and C-C'.

[0029] Figure 7(b) is a diagram showing Y-direction scanning, showing the reflected light intensity profile scanned by moving light from the input and output waveguides of the optical circuit element along the Y axis on lines D-D' and E-E'.

[0030] 7(a) and 7(b), the profile of the reflected return light intensity reflects the structure of the end face that includes the reflectance control body, and the reflected return light intensity increases particularly when scanning an area that includes the reflectance control body. As a result, the contrast in the reflected return light intensity at the boundary between the reflectance control body and other areas increases, and the presence of the reflectance control body makes it easy to estimate which position on the connection end face the scanned area corresponds to.

[0031] Therefore, the input / output waveguides of the optical functional element equipped with the input / output alignment structure of this embodiment and the input / output waveguides of the optical circuit element can be aligned in advance, including Z-axis rotation alignment, to a position sufficient for light transmission between the butt-coupled input / output waveguides. Then, as shown in FIG. 1, more precise alignment can be performed by inputting signal light and monitoring the output light. As described above, this embodiment, as shown in FIGS. 2 to 4, enables highly accurate alignment with a simple configuration and procedure without the need for a separate alignment port or the like. Note that in this embodiment, the input / output waveguides of the optical functional element have a U-shaped folded configuration in which the optical input waveguide 511 and the optical output waveguide 514 are located on the same connecting end face 530, but other configurations are also possible. For example, the folded configuration may be U-shaped or have other shapes, as long as a path is formed through which light input to the optical input waveguide is output from the optical output waveguide. Furthermore, the input and output waveguides of the optical functional element may be located on different end faces, or only one of the input or output waveguides of the optical functional element may be provided with an output alignment structure. Furthermore, the output alignment structure of this embodiment may be used to perform only alignment for butt-connecting either the input or output waveguide of the optical functional element with a waveguide of an optical circuit element. Furthermore, although this embodiment has described a case where the input / output waveguides of the optical functional element and the input / output waveguides of the optical circuit element are butt-coupled, the waveguides butt-coupled with the input / output waveguides of the optical functional element may be waveguides included in optical elements other than optical circuits, and the waveguides may be not only waveguides formed on a substrate but also optical fibers, etc.

[0032] As described above, in the embodiment of the present invention, a reflectance control body is provided near the core of an input / output waveguide as an alignment input / output structure in an optical functional element. Then, light from the input / output waveguide of the optical circuit element is irradiated onto the connection end face of the optical functional element on which the reflectance control body is provided, and the end face shape and the core position can be easily estimated by using the intensity profile of the reflected return light, the intensity of which corresponds to the reflectance at the irradiation position. Furthermore, since this embodiment utilizes the return light intensity profile, it is not necessary to provide a separate alignment port or the like in the optical functional element, as in the conventional examples shown in FIGS. 2 to 4 .

[0033] When a waveguide is butt-coupled to the input / output waveguide of an optical functional element equipped with the input / output alignment structure of this embodiment, the positions of the waveguides to be butt-coupled can be pre-aligned in advance to a position where more precise alignment can be performed by inputting signal light and monitoring the output.

[0034] Furthermore, in connecting optical functional elements equipped with the alignment input / output structure of this embodiment, rough alignment is performed in advance, including rotational alignment around the Z axis, in addition to the X and Y directions, prior to precise alignment. Therefore, fine adjustment is not required in the subsequent precise alignment, and the alignment time can be shortened.

[0035] Generally, PLCs have a cross-sectional structure in which a thin SiO2 film is deposited on a Si or SiO2 substrate to a thickness of approximately 20 μm as an underclad, 3 to 10 μm as a core, and approximately 20 μm as an overclad. The optical circuit element targeted by the present invention is assumed to be a PLC formed on a Si substrate of this size. Furthermore, a Si photonics optical circuit element is assumed to have a structure in which a SOI layer of SiO2 is deposited on a Si substrate to a thickness of several μm as an underclad, a core of Si to a thickness of several hundred nanometers, and an overclad of SiO2 to a thickness of several μm. Furthermore, optical functional elements using InP as a substrate generally have a structure in which an InP substrate is used as an underclad, a core of compound semiconductor to a thickness of several hundred nanometers, InP to a thickness of several hundred nanometers, and an overclad of SiN or SiO2, and metal patterns serving as electrodes are provided on the front and back surfaces. The optical functional element targeted by the present invention is also assumed to be an optical functional element based on an InP substrate of this size. In the present invention, the waveguides formed on the end faces of the substrates of the optical functional element and optical circuit element having such a structure and size are assumed to be input / output waveguides for inputting and outputting optical signals, and therefore the waveguides must be optically coupled with an alignment accuracy of about 1 / 10 of the mode field at the end faces.

[0036] The reflectance control element of the input / output alignment structure of the present embodiment can be formed, for example, by providing grooves in the cladding (including undercladding and overcladding) and passivation on both sides of the core that constitutes the input / output waveguide at the connection end face of the optical functional device. The reflectance can be controlled by filling the grooves with a material with a refractive index different from that of the substrate, core, and cladding. The groove depth is preferably not too far from the bottom surface of the core, so that the core position can be easily determined from the intensity profile of the reflected light. For example, the groove depth is preferably approximately twice the distance from the substrate surface to the bottom surface of the core. Furthermore, the groove width (dimension in the X direction) should be large enough to cause a change in the intensity of the reflected light. However, if it is too large, scanning will take a long time. Therefore, it is preferable that the width be approximately the same as the distance in the X direction from the core center to the core-side end face of the groove. The distance in the X direction from the core center to the core-side wall surface of the groove should be as small as possible without affecting the mode field of the core, so that the core position can be easily determined from the intensity profile of the reflected light. Furthermore, in order to make it easier to estimate the core position, it is desirable that the grooves be arranged symmetrically with respect to the core.

[0037] The connection end face of an optical functional element to which an optical circuit element is connected is generally provided with an antireflection coating to reduce reflected light due to end face reflection. This antireflection coating is designed to match the refractive index of the core, cladding, and the adhesive used for fixing the connection end face. Therefore, the intensity of reflected reflected light from the portion of the connection end face corresponding to the core or cladding is low. On the other hand, because the refractive index of the reflectance control body is significantly different from that of the core or cladding, the intensity of reflected reflected light from the portion corresponding to the reflectance control body is greater than that of the portion corresponding to the core or cladding. Thus, since the portion with high reflected reflected light intensity from the position of the reflectance control body can be used as a landmark, it is desirable to provide the reflectance control body near the core to estimate the core position from the profile of the reflected reflected light intensity. As described above, the reflectance control body can be easily formed, for example, by forming a groove in the cladding and filling the groove with a resin with a refractive index of approximately 1.5. On the other hand, if the difference in refractive index between the resin and the core or cladding is small, the groove can be formed without filling it with resin, and the groove wall can be made a reflective surface due to the difference in refractive index between the groove end face and air, allowing it to function as a reflectance control element. When using an ultraviolet-curable resin or the like as an adhesive for the connecting end face, alignment can be achieved by filling the adhesive between the connecting end faces. In this case, if the groove is formed up to the connecting end face, it may be filled with the adhesive used to fix the connecting end face, and it may no longer function as a reflection control element. To prevent this from happening, when forming only a groove, it is desirable to form the groove offset from the connecting end face. Furthermore, when forming a reflectance control element using only a groove, it is desirable to form the wall of the groove on the connecting end face side, which serves as a reflective surface, parallel to the connecting end face.

[0038] In this embodiment, even in a U-shaped waveguide layout in which the input and output parts of the optical functional element are on the same connection surface, it is possible to obtain the reflected return light intensity profiles on both the input and output sides, and estimate the positions of each core from the reflected return light intensity profiles, thereby making it possible to adjust the Z-axis rotational deviation in advance.

[0039] In this way, in an integrated optical device in which optical functional elements that perform optical signal processing and optical circuit elements that are provided on a substrate are hybridly integrated, by providing a reflectance control body near the input / output waveguide as an input / output structure for aligning the optical functional elements, the profile of the reflected light returning from the end face has a large contrast in the reflected light intensity at the boundary of the end face structure, making it easy to estimate the core position without providing an alignment port and enabling efficient alignment in butt coupling, making it possible to provide an integrated optical device achieved by simple butt optical coupling. [Example]

[0040] Example 1 is an integrated optical device comprising an optical circuit element constituted by a SiP chip having optical waveguides for inputting and outputting signal light and corresponding input / output optical waveguides for butt-coupling, and an optical functional element constituted by an InP chip having an input / output alignment structure including input / output waveguides for optical signals that are butt-coupled with the input / output optical waveguides for butt-coupling of the optical circuit element.

[0041] An example of such an integrated optical device is the integrated optical modulation device shown in Figure 5 as one embodiment of the present invention. This integrated optical modulation device is composed of a phase modulation waveguide that changes the phase of light in response to an electrical signal and an optical waveguide for butt coupling, and uses an optical modulation element as an optical functional element, in which the input and output waveguides for the optical signal are arranged on one end face in a U-shaped optical waveguide configuration. Light input to the input waveguide of the optical circuit element is optically coupled to the optical modulation element side via the butt coupling section, converted into a phase-modulated optical signal by the phase modulation waveguide, optically coupled to the optical circuit element again via the butt coupling section, and then polarization-combined by the polarization rotator and polarization beam combiner before being output.

[0042] Here, as a connection test device, an integrated optical device was constructed using an optical functional element composed of a U-shaped folded waveguide obtained by removing the phase modulation section from such an integrated optical modulation device, and an optical circuit element including a signal light input / output waveguide and a butt-coupling input / output waveguide, excluding the polarization rotator and polarization beam combiner. Then, the alignment of the butt-coupling between the optical functional element and the optical circuit element of this integrated optical device was performed by creating one having an input / output alignment structure including a reflectance control element as Example 1, and one having no reflectance control element as a comparative example, and measuring the profile of the intensity of the reflected return light from the connection end face of each.

[0043] 8 is a diagram showing the optical circuit configurations of the integrated optical devices of Example 1 and Comparative Example 1. The optical circuit element 820 is a Si photonics chip having a platform measuring 2.5 mm in length, 2.0 mm in width, and 0.6295 mm in thickness, in which a 3.0 μm-thick SiO2 underclad, a 0.22 μm-thick and 0.5 μm-wide Si core, and a 1.5 μm-thick SiO2 overclad are formed on a 0.625 mm-thick Si substrate.

[0044] The optical signal input and output of the optical circuit element 820 is performed from one long side, and the other long side is connected to an optical functional element. The connection end faces are polished for connection to the optical functional element. The optical circuit element 820 is provided with a signal light input waveguide 821, a signal light output waveguide 822, and, as input and output waveguides for butt coupling, a butt coupling input waveguide 823 and a butt coupling output waveguide 824.

[0045] Furthermore, S-shaped waveguide structures 825, 826 are provided between the signal light input waveguide 821 and the butt coupling input waveguide 823, and between the signal light output waveguide 822 and the butt coupling output waveguide 824. Due to this S-shaped optical waveguide structure, the optical axes of the signal light input waveguide 821 and the butt coupling input waveguide 823, and the optical axes of the signal light output waveguide 822 and the butt coupling output waveguide 824 are shifted, making it possible to prevent stray light and the like.

[0046] The optical functional element 810 to be butt-coupled to the optical circuit element 820 is an InP chip measuring 2.5 mm in length, 4.0 mm in width, and 0.25 mm in substrate thickness, with an InP substrate as underclad, a compound semiconductor core 2.0 μm in width and 0.3 μm in thickness, and InP deposited to a thickness of 2.0 μm as overclad.

[0047] An optical input waveguide 811 and an optical output waveguide 812 are provided on one of the short sides of optical functional element 810 as input / output waveguides to be butt-coupled with the butt-coupling input / output waveguide of the optical circuit element. The input / output waveguide composed of optical input waveguide 811 and optical output waveguide 812 is U-shaped, and an optical signal propagates from optical input waveguide 811 to optical output waveguide 812. Input / output alignment structures 831 and 832 are provided near optical input waveguide 811 and optical output waveguide 812 on connecting end face 830, which is one end face of optical functional element 810. As shown in FIG. 9 , input / output alignment structures 831 and 832 are provided on both sides of each waveguide with reflectance control bodies, each composed of grooves 904 and 905 filled with a resin having a refractive index of 1.5. This reflectance control element forms an area with a different reflectance from core 902, cladding, and the substrate when light is incident on the connection end face. The groove is formed 2 μm deeper than the bottom surface of core 902, with a distance of 3 μm from the center of the core to the groove wall surface and a groove width of 2 μm. Note that the dimensions of each part of the optical functional element and optical circuit element described above are shown for illustrative purposes only and may be other than these.

[0048] 9A and 9B are diagrams showing the relationship between the scanning position of the connection end face of the alignment input / output structure of the optical functional element in Example 1 and the intensity profile of the reflected returning light corresponding to the scanning position. Fig. 9A shows the X scan, and Fig. 9B shows the Y scan.

[0049] The lower diagrams of Figures 9(a) and 9(b) show the structure and each scanning position of aligning input / output structures 831 and 832 provided near the optical input waveguide 821 and optical output waveguide 822, which are the input / output waveguides of the optical functional element of Example 1, as viewed from the connection end face side.

[0050] In the input / output alignment structure of Example 2, a reflectance control element is formed on both sides of core 902 in waveguide region 903, which is made up of core 902 and the surrounding cladding layer, and which is a region that propagates light in the input / output waveguide. Grooves 904 and 905 are formed in the same manner as the reflectance control element in the output alignment structure of the embodiment shown in FIG.

[0051] FIG. 10 shows the relationship between the scan position on the connection end face of the input / output section of the optical functional element of Comparative Example 1 and the reflected return light intensity profile corresponding to the scan position. For comparison with Example 1, Comparative Example 1 is an integrated circuit device in which an optical functional element and an optical circuit element having the same structure as Example 1 are connected, but no reflectance control element is provided. Similar to FIG. 9, FIGS. 10(a) and 10(b) show the scan positions and the reflected return light intensity profile corresponding to the scan positions for X scan and Y scan, respectively. The structural diagrams at the bottom of FIGS. 10(a) and 10(b) show the structure of the optical functional element of Comparative Example 1 as seen from the connection end face side near the optical input waveguide and optical output waveguide. In FIGS. 10(a) and 10(b), no reflectance control element is formed on either side of the core 1002.

[0052] (Acquisition of reflected light intensity profile for pre-alignment) Next, a method for performing pre-alignment for butt-coupling the input / output waveguides of an optical functional element and the waveguides of an optical circuit element will be described using Example 1. For input-side pre-alignment in the integrated circuit device of Example 1, as shown in Fig. 8, light with a wavelength of 1.55 µm was input from the signal light input waveguide 821 of the optical circuit element 820 via a circulator 841, and the optical circuit element was scanned in the X and Y directions while acquiring the intensity of the reflected return light, thereby acquiring a profile of the intensity of the reflected return light from the connection end face on the input side of the optical functional element. Similarly, for output-side pre-alignment, light was input from the signal light output waveguide 822 of the optical circuit element via a circulator 842, and the intensity of the reflected return light was acquired, thereby also acquiring a profile of the intensity of the reflected return light from the connection end face on the output side of the optical functional element.

[0053] In the optical functional element of Example 1, the reflected return light intensity is high in the region where the reflectance control body is formed. Therefore, in the reflected return light intensity profile of the X-scan in FIG. 9( a), when scanning along line B-B', two peaks corresponding to the reflectance control body appear in the reflected return light intensity profile BB'. Since the scan positions of these two peaks correspond to the position of the reflectance control body, the position of the reflectance control body can be estimated from the return light intensity profile. Furthermore, from the relationship between the scan positions shown in the lower diagram and the core 902 and grooves 904 and 905, it can be estimated that the core is located between the scan positions of the two peaks corresponding to the position of the reflectance control body. Next, in the reflected return light intensity profile of the Y-scan in FIG. 9( b), when scanning along line D-D', one peak corresponding to the reflectance control body appears in the reflected return light intensity profile DD'. Since the scan position of this peak corresponds to the position of the reflectance control body, the position of the reflectance control body can be estimated. From the positional relationship between the core 902 and the groove 904 shown in the structural diagram, it can be estimated that the core is located at the center of the peak of the reflected return light intensity profile DD'.

[0054] In Example 1, the core position is estimated based on the position of the reflectance control element estimated using the intensity profile of the reflected return light at the connecting end face of the optical functional element. Then, based on the estimated core position, the pre-alignment is completed by correcting the misalignment of the input and output waveguides for butt-coupling of the optical circuit element that are butt-coupled to the input and output waveguides of the optical functional element, respectively. At this time, the Z-axis rotational deviation can be calculated based on the relationship between the core position estimated from the intensity profiles of the reflected return light on the input and output waveguide sides and the scan coordinates.

[0055] In contrast, the optical functional device of the comparative example does not have an alignment input / output structure equipped with a reflectance control element. Therefore, even if the reflected return light intensity profile is acquired using the same method as in Example 1, the reflected return light intensity profile BB' obtained by scanning line B-B' of the X-scan return light intensity profile in FIG. 10(a) and the reflected return light intensity profile CC' obtained by scanning line C-C' are almost identical. Therefore, in Comparative Example 1, which lacks a reflectance control element, it is not possible to determine the position on the end face where the X-scan was performed (on line B-B' or line C-C') based on the reflected return light intensity profile of the X-direction scan, as in Example 1. Furthermore, since there is no peak in the reflected return light intensity profile as in Example 1, it is not possible to estimate the core position. Similarly, using the Y-scan return light intensity profile in FIG. 10(b), the reflected return light intensity profile DD' obtained by scanning line D-D' and the reflected return light intensity profile EE' obtained by scanning line E-E' are almost identical. Therefore, even from the Y-scan return light intensity profile, it is impossible to determine at which position on the end face the Y-scan was performed (on the D-D' line or the E-E' line). As mentioned above, the connection end face of the optical functional device is provided with an anti-reflection coating, and the reflectivity of the connection end face is lower than that of air, so the reflected return light intensity changes at the boundary between the overclad and air. Therefore, the core position can be roughly estimated by assuming that the Y-axis scan position where the reflected return light intensity changes is the boundary between the overclad and air and using it as a reference. However, the difference in the reflected return light intensity between air and the overclad is small, and the reflected return light intensity changes gradually, making it difficult to accurately estimate the core position. In particular, during the pre-alignment stage, the connecting adhesive used to secure the connecting end faces of the optical functional device and the optical circuit element is often not introduced. In such cases, the reflectivity of the connection end face with an anti-reflection coating, which is designed assuming the presence of a connecting adhesive, is high, and the difference in the reflected return light intensity between air and the overclad is small.

[0056] As described above, by using an optical functional element provided with an input / output alignment structure including the reflectance control element and input / output waveguides of Example 1 to construct an integrated circuit device in which the input / output waveguides of an optical circuit element are butt-coupled, pre-alignment can be easily performed based on the relationship between the core position estimated based on the reflected return light intensity profile and the scan coordinates, making it possible to perform pre-alignment with high accuracy without providing an alignment port, and making it possible to provide an integrated optical device achieved by simple butt-optical coupling. [Example]

[0057] Example 2 is an integrated optical device including an optical circuit element formed by a SiP chip having the same optical waveguides for inputting and outputting signal light as in Example 1 and corresponding input / output optical waveguides for butt coupling, and an optical functional element formed by an InP chip having an input / output structure for alignment including input / output optical waveguides for optical signals that are butt-coupled with the input / output optical waveguides for butt coupling of the optical circuit element. In Example 2, instead of the reflectance control body of the input / output structure for alignment of Example 1, a reflectance control body is provided that is formed by a plurality of grooves of different lengths that are formed side by side along the light propagation direction of the waveguide on both sides of the core of the waveguide. The structures, sizes, etc. of the optical circuit element and the optical functional element of the integrated optical device of Example 2 are the same as those of Example 1, except for the reflectance control body.

[0058] FIG. 11 is a diagram illustrating an aligning input / output structure according to a second embodiment. FIG. 11(a) is a top view of the aligning input / output structure 1100, and FIG. 11(b) is a view of the aligning input / output structure 1100 as viewed from the connection end face. The aligning input / output structure according to the second embodiment includes a reflectance control element formed on both sides of a waveguide region 1103, which includes a core 1102 and a cladding layer surrounding the core 1102, along the light propagation direction of the waveguide formed by the waveguide region. In the aligning input / output structure illustrated in FIG. 11, three grooves (grooves 1104, 1105, 1106) and three grooves (grooves 1107, 1108, 1109) are formed on both sides of the waveguide core. The widths of the three grooves, which are the dimensions parallel to the top surface of the substrate and the connection end face (the X direction in the figure), are different from each other. The bottom of each groove is formed 2 μm deeper than the bottom of core 1102, the distance from the core center to the wall surface of each groove on the core side is 2 μm, and the length in the Z direction is 1.5 μm. The widths of each groove are 2 μm, 4 μm, and 6 μm, respectively, from the side closer to the end face. Note that the dimensions of each part of the optical functional element and optical circuit element of the integrated optical device of Example 2 are shown for illustrative purposes only and may be other dimensions.

[0059] Each groove is formed at a position away from the connecting end face (offset from the connecting end face), and none of the grooves reaches the end face. The grooves constituting the reflectance control element of Example 2 are not filled with resin as in Example 1, and therefore an interface between the substrate material and air is formed on the wall surface of the groove. The wall surface of each groove closer to the connecting end face serves as a reflective surface, and light irradiated onto the connecting end face is reflected by this groove wall to become reflected returning light. It is desirable that the wall surface of each groove constituting the reflective surface closer to the connecting end face be formed parallel to the connecting end face. The closer the groove is to the connecting end face, the closer the connecting end face and the reflective surface are, resulting in a greater reflected returning light intensity, and the farther the groove is from the connecting end face, the smaller the reflected returning light intensity. Therefore, as shown in Figure 11(b), on both sides of the core on the input / output end face, reflectance control body 1120 consisting of regions 1110, 1111, and 1112, each with a different reflectance, and reflectance control body 1121 consisting of regions 1113, 1114, and 1115, each with a different reflectance, are formed.

[0060] FIG. 12 is a diagram showing the relationship between the scan position of the connection end face of the alignment input / output structure of the optical functional element of Example 2 and the reflected return light intensity profile corresponding to the scan position. FIG. 12 shows the reflected return light intensity profile of Example 2 obtained by the same method as Example 1. FIG. 12(a) shows the X scan, and FIG. 12(b) shows the Y scan. From the reflected return light intensity profile of FIG. 12(a), it can be estimated that in Example 2, as in Example 1, a core is located between the two peaks BB' in the reflected return light intensity profile of the X scan. From the reflected return light intensity profile of FIG. 12(b), it can be estimated that a core is located at the center of the peaks DD' in the reflected return light intensity profile of the Y direction scan.

[0061] As described above, the reflectance control body of Example 2 has three regions with different reflectances, with the reflectance of region 1110 close to the core and region 1113 being the highest, followed by regions 1111 and 1114, and regions 1112 and 1115 in that order.

[0062] 12(a), scanning along line B-B' of the X-scan, each region is scanned in turn, and the reflected return light intensity profile BB' shows that the reflected return light intensity rises sharply from the estimated core center toward the periphery, and then gradually drops in a stepped pattern. By utilizing the shapes of the two peaks in this reflected return light intensity profile, it is easier to determine the scan position in Example 2 than in Example 1.

[0063] In Example 1, the two peaks of the reflected return light intensity profile of the X-scan are both symmetrical. Therefore, if the reflected return light intensity is acquired at the first scan position and then the acquired reflected return light intensity decreases as the scan position is slid to the right, it is impossible to determine whether the scan position is approaching the core (at a position corresponding to the peak on the left) or away from the core (at a position corresponding to the peak on the left). For this reason, in Example 1, it is necessary to acquire and check the reflected return light intensity profile by sliding the scan position significantly, which takes time to check the scan position.

[0064] In contrast to this, in Example 2, if the reflected return light intensity is acquired at the initial scan position, and then the reflected return light intensity acquired while sliding the scan position to the right suddenly decreases, it can be determined that the scan position is approaching the core (at a position corresponding to the peak on the left).If the reflected return light intensity gradually decreases in stages, it can be determined that the scan position is moving away from the core (at a position corresponding to the peak on the right).

[0065] Each groove constituting the reflectance control element of Example 2 is formed at a position away from the connecting end face (offset from the connecting end face), and none of the grooves reaches the end face. Therefore, the grooves of Example 2 are designed to prevent the flow of adhesive, such as ultraviolet-curable resin, used to fix the connecting end face. As described above, when ultraviolet-curable resin or the like is used as the adhesive for the connecting end face, the adhesive may be pre-filled between the connecting end faces before alignment. Even in such a case, it is possible to prevent the adhesive from flowing into the groove, reducing the refractive index difference between the end face of the groove and the medium inside the groove, resulting in a clear reflected light profile.

[0066] As described above, by using an optical functional element provided with an input / output alignment structure including the reflectance control element and input / output waveguide of Example 2, and measuring the profile of the reflected return light when butt-coupled with an optical circuit element, it is possible to perform accurate pre-alignment without providing an alignment port, and it is possible to provide an integrated optical device achieved by simple butt-coupling. [Example]

[0067] Example 3 is an integrated optical device including an optical circuit element formed by a SiP chip having the same optical waveguides for inputting and outputting signal light as in Example 1 and corresponding input / output optical waveguides for butt coupling, and an optical functional element formed by an InP chip having an input / output structure for alignment including input / output waveguides that are butt-coupled with the input / output optical waveguides for butt coupling of the optical circuit element. In Example 3, instead of the reflectance control body of the input / output structure for alignment of Example 1, a reflectance control body formed by grooves having multiple bottom surfaces with different depths is provided on both sides of the core of the input / output waveguide. The structures, sizes, etc. of the optical circuit element and the optical functional element of the integrated optical device of Example 3 are the same as those of Example 1, except for the reflectance control body.

[0068] 13A and 13B are diagrams showing an aligning input / output structure of Example 3. Fig. 13A is a diagram showing the aligning input / output structure 1300 as seen from above, and Fig. 13B is a diagram showing the aligning input / output structure 1300 as seen from the connection end face side.

[0069] The input / output structure for alignment of Example 3 includes reflectance control body 1330 formed by groove 1310 and reflectance control body 1340 formed by groove 1320 on both sides of core 1302 in waveguide region 1303 which is made up of core 1302 and the surrounding clad layer that constitutes the region through which light propagates. This reflectance control body forms a region whose reflectance differs from that of the core, clad, and substrate when light is incident on the connection end face.

[0070] In the alignment input / output structure shown for example in FIG. 13, groove 1310 on both sides of the waveguide has bottom surfaces 1311 and 1312 with two different depths, and groove 1320 has bottom surfaces 1321 and 1322 with two different depths. The distance from the core center to the wall surface on the core side of each of grooves 1310 and 1320 is 2 μm, and the groove length is 5 μm. The bottom surfaces of grooves 1310 and 1320 are composed of a surface that is 2 μm deeper than the bottom surface of the core and a surface that is 6 μm deeper than the bottom surface of the core, and each bottom surface has a width of 2 μm. The dimensions of the components described above for the optical functional element and optical circuit element of the integrated optical device of Example 3 are shown for illustrative purposes only and may be other dimensions.

[0071] Fig. 14 shows the scan position of the connection end face of the alignment input / output structure of the optical functional element in Example 3 and the reflected return light intensity profile corresponding to the scan position. In Example 3, the reflected return light intensity profile was obtained by the same method as in Example 1. Fig. 14(a) shows the reflected return light intensity profile of the X scan in Example 3, and Fig. 14(b) shows the reflected return light intensity profile of the Y scan in Example 3.

[0072] As described above, the reflectance control element of Example 3 is configured with a groove having two bottom surfaces with different depths. Therefore, as shown in FIG. 14(a), the reflected return light intensity profile of the X-scan shows two peaks in the reflected return light intensity profile BB' obtained by scanning along the B-B' line and the reflected return light intensity profile CC' obtained by scanning along the C-C' line. Therefore, in Example 3, as in Example 1, it can be estimated that a core is located between the two peaks of the reflected return light intensity profiles BB' and CC'. It can also be seen that the scan position of the reflected return light intensity profile with a narrow gap between the peaks is close to the core corresponding to the B-B' line. Furthermore, in the Y-scan reflected return light intensity profile, it can be estimated that a core is located at the center of the peak of the narrow peak EE' due to the difference in peak width between the reflected return light intensity profile DD' obtained by scanning along the D-D' line and the reflected return light intensity profile EE' obtained by scanning along the E-E' line. Thus, in Example 3, the core position can be estimated using the reflected return light intensity profile in the same way as in Example 1.

[0073] Furthermore, in Example 3, the grooves constituting the reflectance control body are configured to have bottom surfaces with multiple depths, and therefore the shape of the reflectance control body as viewed from the end face is stepped. Therefore, in Example 3, the core position can also be estimated by boundary scanning, in which the optical functional element or optical circuit element is scanned by shifting it in the X and Y directions while acquiring the reflected return light intensity, and the part where the reflected return light intensity changes significantly is found and traced.

[0074] This boundary scan will be described in detail below with reference to FIG. 15 . In the alignment input / output structure 1300 of the third embodiment, the portions where the reflected return light intensity changes significantly are either the boundary portions between the cladding and the reflectance control bodies 1330 and 1340, or the boundary portion on the upper surface of the cladding portion including the core 1302 between the reflectance control body 1330 and the reflectance control body 1340, as indicated by the dotted line A-A′ in FIG. 15 . Therefore, by sequentially tracing the portions where the reflected return light intensity changes significantly on the connection end face of the alignment input / output structure, the dotted line A-A′ including the boundary of the reflectance control body can be traced as shown in FIG. 15 . From the results of tracing these boundary portions where the reflected return light intensity changes significantly, it is possible to associate the positional relationship between the cross-sectional shape of the alignment input / output structure and the scan coordinates, and the core position can be estimated from this positional relationship.

[0075] Example 3 is a reflectance control body having a characteristic cross-sectional shape with two or more steps due to multiple bottom surfaces with different depths, and therefore has the following advantages over rectangular shapes such as those in Examples 1 and 2. Even if other reflective structures are present on the chip, the characteristic shape of the reflectance control body provides a clue for distinguishing the scanned portion from the other reflective structures and confirming that it is the reflectance control body. Furthermore, when tracing a boundary portion where the intensity of reflected return light changes significantly, it is easier to estimate which portion of the reflectance control body is being traced than with rectangular shapes such as those in Examples 1 and 2.

[0076] In this way, when the reflectance control body of Example 3 is used, it is possible to estimate the core position not only by repeating X-scans and Y-scans as in Example 1, but also by tracing the boundary where the intensity of the reflected return light changes significantly just once using boundary scanning to estimate the cross-sectional shape, thereby estimating the core position.

[0077] As described above, by using an optical functional element provided with an input / output alignment structure including a reflectance control element and an input / output waveguide according to Example 3, and measuring the profile of the reflected light when butt-coupled with an optical circuit element, it is possible to perform accurate pre-alignment without providing an alignment port, and an integrated optical device can be provided using simple butt-coupling optical coupling. [Industrial Applicability]

[0078] The present invention can be used in an integrated optical device applicable to an optical communication system, and particularly relates to an integrated optical device in which input / output waveguides of an optical functional element and input / output waveguides of an optical circuit element are butt-coupled by being aligned and bonded.

Claims

1. In an optical functional element having an optical waveguide made of a core and a clad provided on a substrate, an input waveguide or an output waveguide for an optical signal provided on an end surface of the substrate; a reflectance control body provided on both sides of the core, the reflectance control body forming a plurality of regions on the end face, the regions having different reflectances from the core, the cladding, and the substrate when light is incident on the end face; the plurality of regions are arranged along the end face such that the reflectance decreases in the order from the region closest to the core to the region farthest from the core, an integrated optical device, wherein the input waveguide or the output waveguide of the optical functional element is butt-coupled and bonded to another waveguide via the end face;

2. a path through which light input from the input waveguide is output from the output waveguide; the input waveguide and the output waveguide are provided on the end face, Signal light is input and output to and from the optical functional element via the end face.

2. The integrated optical device according to claim 1.

3. the substrate of the optical functional element is Si or InP, The other waveguide is provided on a Si substrate.

3. The integrated optical device according to claim 1 or 2.

4. 3. The integrated optical device according to claim 1, wherein the reflectance control body comprises grooves on both sides of the core, each groove having a depth equal to or greater than the bottom surface of the core, and each groove is filled with a resin having a refractive index different from that of the core, the cladding, and the substrate.

5. The reflectance control element is provided with grooves on both sides of the core, each groove having a depth equal to or greater than the bottom surface of the core, the grooves not reaching the end faces, and the wall surfaces of the grooves on the end face side are formed parallel to the end faces.

3. The integrated optical device according to claim 1 or 2.

6. An optical functional element having an optical waveguide made of a core and a clad provided on a substrate, an input waveguide or an output waveguide for an optical signal provided on an end surface of the substrate; an optical functional element including: a reflectance control body provided on both sides of the core, the reflectance control body forming a plurality of regions on the end face, the regions having different reflectances from the core, the cladding, and the substrate when light is incident on the end face, the plurality of regions being arranged along the end face such that the reflectance decreases in the order from the region closest to the core to the region farthest from the core; In the alignment for butt-coupling via the end face with an optical circuit element having an input waveguide or an output waveguide for connection, monitoring the optical intensity of the reflected return light branched by a circulator or coupler disposed at the optical input of the optical circuit element; By scanning while moving the optical functional element or the optical circuit element, the correspondence between the scanning position and the position of the region with different reflectance formed by the reflectance control body of the end face is estimated from the position where the light intensity profile of the reflected return light corresponding to the cross-sectional shape of the end face becomes a peak, and alignment is performed.

1. An alignment method for an integrated optical device, comprising:

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