Planar lightwave circuit component

Abstract

The present invention includes: a planar lightwave circuit 111 including an optical waveguide formed on a substrate; and a mount member 101 having an upper surface for holding the planar lightwave circuit 111. The upper surface of the mount member 101 includes a recess region 101b extending from one end surface 101c toward an end surface 101d side facing the end surface 101c. The planar lightwave circuit 111 is fixed to, on the recess region 101b, at least a portion of a non-recess region 101a excluding the recess region 101b of the mount member 101.

Description

Planar Lightwave Circuit Components

[0001] The present disclosure relates to a planar lightwave circuit component, and more particularly to a planar lightwave circuit component in which a planar lightwave circuit is mounted on a substrate.

[0002] Planar lightwave circuits (PLCs) are known for realizing various optical functional devices required in optical communication networks. They are constructed by forming quartz waveguides on a substrate. These circuits are widely used due to their versatility, mass production, and low cost. When constructing optical functional devices using these PLCs, the PLC is adhesively fixed on a mount. However, this configuration significantly changes the characteristics of the PLC due to changes in ambient temperature. Because PLCs are composed of a silicon substrate and a quartz glass layer, which have relatively large differences in thermal expansion coefficients, they are prone to significant warpage and thermal expansion due to changes in ambient temperature. In this case, adhesively fixing the entire bottom surface of the PLC to a mount suppresses warpage and thermal expansion, resulting in significant changes in the stress on the optical waveguide layer.

[0003] In contrast to this, in Patent Document 1, in a planar lightwave circuit, only the area near one end face that needs to be firmly fixed to prevent misalignment of the optical axis with other optical elements is adhesively fixed to the mount, and the other areas of the planar lightwave circuit are left floating in the air.This minimizes the impact of stress changes on the part of the optical circuit that has optical functions, even if the planar lightwave circuit is distorted or warped due to changes in environmental temperature, and suppresses deterioration of the characteristics of the optical function circuit.

[0004] Furthermore, in optical communication networks, wavelength division multiplexing (WDM) technology, which allows many wavelength signals to be transmitted through a single fiber, is effective in increasing the capacity of optical communications. Wavelength multiplexing / demultiplexing elements and optical amplifiers play an important role in realizing WDM technology. In particular, applying WDM technology to transmissions over distances of 100 km or more requires optical amplifiers to be placed at regular intervals within the transmission fiber, and the wavelength dependence of their gain spectrum significantly affects the optical signal-to-noise ratio (OSNR). A gain equalizer that flattens the gain spectrum is described in Non-Patent Document 1.

[0005] The aforementioned gain equalizer has a drawback in that it has a large loss due to its configuration in which Mach-Zehnder interferometers are connected in multiple stages. This is due to the fact that optical signals are essentially discarded at the output ports of each stage of the Mach-Zehnder interferometer that are not connected. For example, Non-Patent Document 2 discloses a lattice filter circuit as such a gain equalizer.

[0006] JP 2013-7797 A

[0007] K. Suzuki, T. Kitoh, S. Suzuki, Y. Inoue, Y. Hbbino, T. Shibata, A. Mori, and M. Shimizu. 2002), paper IThG2.TR Schlipf, MW Street, J. Pandavenes, R. McBride, and DRS Cumming, "Design and Analysis of a Control System for an Optical Delay-Line Circuit Used as Reconfigurable Gain Equalizer," Journal of Lightwave Technology, Vol. 21, Issue 9, pp. 1944 (2003).

[0008] However, in the configuration described in Patent Document 1, because most of the planar lightwave circuit is suspended in midair, when vibrations of frequencies near the natural frequency of the planar lightwave circuit components act, large vibrations act on the planar lightwave circuit and the mount, which can cause problems such as peeling of the adhesive fixing portion to the mount. Furthermore, if the planar lightwave circuit is equipped with a phase shifter, power sharing to this phase shifter is required. Therefore, if most of the planar lightwave circuit is suspended in midair, the planar lightwave circuit may warp or thermally expand due to changes in environmental temperature, which could result in a stable power supply failure if the power supply unit becomes misaligned.

[0009] In this way, there is a risk that the function of a planar lightwave circuit component in which a planar lightwave circuit is adhesively fixed to a mount may be impaired by vibration, shock, or the like.

[0010] The present disclosure has been made in view of the above points, and aims to provide a planar lightwave circuit component whose function is not impaired by vibrations or the like.

[0011] In order to achieve the above object, one form of the planar lightwave circuit component of the present invention includes a planar lightwave circuit including an optical waveguide formed on a substrate, and a mount member having a holding surface for holding the planar lightwave circuit, the holding surface of the mount member including a recessed region extending from one end face toward the side opposite the end face, and the planar lightwave circuit is fixed on the recessed region and to at least a portion of a non-recessed region of the mount member excluding the recessed region.

[0012] According to the above embodiment, it is possible to provide a planar lightwave circuit component whose function is not impaired by vibration or the like.

[0013]

[0023] Figures for explaining a planar lightwave circuit component of a first embodiment, where (a) is a plan view, and (b) and (c) are cross-sectional views. Figures for explaining a planar lightwave circuit component of a second embodiment, where (a) is a plan view, and (b) and (c) are cross-sectional views. Figures for explaining a planar lightwave circuit component of a third embodiment, where (a) is a plan view, and (b) is a cross-sectional view. Figures for explaining modified examples of a mounting member. Figures for explaining a comparative example of the present disclosure, where (a) is a top view, and (b) is a cross-sectional view.

[0014] Hereinafter, first to third embodiments of the present disclosure (hereinafter also collectively referred to as the present embodiments) will be described. The drawings used in the present embodiments are intended to explain the configuration, arrangement, function, effect, and technical concept of the embodiments, and do not limit the specific shapes and dimensional ratios of the configurations.

[0015] 1(a), 1(b), and 1(c) are diagrams illustrating a planar lightwave circuit component 1 according to a first embodiment, with FIG. 1(a) being a plan view, FIG. 1(b) being a cross-sectional view taken along the arrow line Ib-Ib' in FIG. 1(a), and FIG. 1(c) being a cross-sectional view taken along the arrow line Ic-Ic' in FIG. 1(a). In the first embodiment, the direction of the z-axis of the x, y, and z coordinates shown in FIG. 1 is defined as "up," and the plan view of FIG. 1(a) is a top view showing a top view of the planar lightwave circuit component. The back surface of the planar lightwave circuit component 1, as opposed to its top surface, is also referred to as the "bottom surface." In this embodiment, FIGS. 1(a) to 1(c) are collectively referred to as "FIG. 1."

[0016] Furthermore, in this embodiment, a device having an optical functional circuit including an optical waveguide on a flat substrate is referred to as a planar lightwave circuit, and a planar lightwave circuit fixed to a mounting member is referred to as a planar lightwave circuit component. The substrate is, for example, a silicon substrate, and the optical functional circuit is configured on the substrate using a quartz-based material. However, this embodiment is not limited to this configuration and may include a combination of quartz and other materials.

[0017] As shown in FIG. 1 , a planar lightwave circuit component 1 includes a planar lightwave circuit 111 including an optical waveguide formed on a substrate, and a mounting member 101 that holds the planar lightwave circuit 111. In FIG. 1 , the substrate of the planar lightwave circuit 111 and the cladding and core that constitute the optical waveguide are not shown. The mounting member 101 has a rectangular shape when viewed from above. The rectangular upper surface serves as a holding surface that holds the planar lightwave circuit 111. The holding surface includes a recessed region 101b that extends from one end surface toward the opposing side. In the mounting member 101 of the first embodiment, the upper and lower surfaces of the recessed region 101b are penetrated. Note that the first embodiment illustrates an example in which the planar lightwave circuit component 1 forms a recessed region 101b that extends from the end surface 101c shown in FIG. 1( a) toward the opposing end surface 101d.

[0018] In the first embodiment, the recessed region 101b is formed by cutting out from the end face 101c toward the opposite end face 101d. Note that this embodiment is not limited to this configuration, and the mounting member 101 may be initially molded and processed to have the recessed region 101b. Furthermore, the recessed region 101b is not limited to being formed on the end face 101c, and may be formed to include other end faces. In this embodiment, the region of the mounting member 101 excluding the recessed region 101b is referred to as the non-recessed region 101a. The planar lightwave circuit 111 is located on the recessed region 101b and is fixed to at least a portion of the non-recessed region 101a of the mounting member 101. In other words, the planar lightwave circuit 111 of the first embodiment is disposed so as to straddle the recessed region 101b of the mounting member 101, and is adhesively fixed to the non-recessed region 101a excluding the recessed region 101b. As a result, stress relief regions 112 corresponding to the recessed regions 101b are formed in the planar lightwave circuit component 1.

[0019] As a result, thermal expansion and warping that may occur in the planar lightwave circuit 111 due to changes in environmental temperature, etc., are not suppressed by the mounting member 101 in the stress relief region 112 but are released as they are, thereby reducing internal stress in the planar lightwave circuit 112. At the same time, even if the planar lightwave circuit component 1 is subjected to vibration or impact at a frequency close to its natural frequency, the entire planar lightwave circuit 112 is adhesively fixed to the non-recessed region 101a, thereby preventing problems such as the planar lightwave circuit 112 peeling off from the mounting member 101 due to the vibration or impact. In comparison with the comparative example described below, in the comparative example, only the vicinity of the end of the planar lightwave circuit is adhesively fixed to the mounting member, and the area of ​​the adhesively fixed portion is small, making the planar lightwave circuit more likely to peel off from the mounting member if it resonates due to vibration or impact. Furthermore, in the comparative example, the planar lightwave circuit has a so-called cantilever shape, making it more susceptible to resonance due to vibration or impact.

[0020] 1(b) shows a cross section of the recessed region 101b of the planar lightwave circuit component 1, and Fig. 1(c) shows a cross section of the non-recessed region 101a. The planar lightwave circuit 111 is adhered and fixed to the upper surface of the mounting member 101 with adhesive 103, but as is clear from Figs. 1(b) and 1(c), the entire lower surface is fixed to the non-recessed region 101a, and the recessed region 101b is not fixed to the mounting member 101, leaving a space 102 below.

[0021] According to the first embodiment, the planar lightwave circuit 111 is fixed to the mount member 101 with sufficient strength, ensuring resistance to vibration and shock due to the natural frequency. Furthermore, when an electric wiring board for power supply is mounted on the mount member 101, misalignment between the electric wiring board and the planar lightwave circuit can be suppressed even when the ambient temperature changes, enabling a stable power supply. At the same time, in the stress relief region 112 of the planar lightwave circuit 111, warping and thermal expansion that occur in the planar lightwave circuit 111 when the ambient temperature changes are suppressed by the mount member 101, and stress changes that occur can be alleviated.

[0022] That is, in the first embodiment, the recessed region 101b of the mount member 101 is formed so as to extend from the end face 101c toward the end face 101d, so that the planar lightwave circuit can be fixed in the non-recessed region 101a formed so as to sandwich the recessed region 101b. Therefore, even if large vibrations are applied to the planar lightwave circuit 111 and the mount member 101, vibration of the planar lightwave circuit 111 can be suppressed, and peeling of the adhesive fixation to the mount member 101 can be prevented.

[0023] Next, the alignment of the planar lightwave circuit 111 with the mounting member 101 in the first embodiment will be described. In all of the examples shown in Fig. 1, the planar lightwave circuit 111 is fixed so as to be positioned outside the mounting member 101 at the end face 101d. In such a case, the length by which the planar lightwave circuit 111 projects outside the mounting member 101 is preferably less than 1000 times the thickness of the adhesive 103, and is, for example, about 1 mm.

[0024] The above configuration is based on the following technical concept. That is, if the planar lightwave circuit is located inside the mounting member, the adhesive area with the mounting member is increased, improving the fixing force and improving resistance to vibration and shock. Furthermore, if the end face of the planar lightwave circuit is located outside the mounting member, it can be expected that the degree of freedom in connecting to other elements at that end face will be increased. However, if the end face of the planar lightwave circuit extends too far from the mounting member, it will hinder resistance to vibration and shock. For this reason, in the first embodiment, the extension amount of the planar lightwave circuit is defined in relation to the thickness of the adhesive layer.

[0025] Furthermore, the first embodiment is not limited to an example in which the planar lightwave circuit 111 is positioned outside the mount member 101. The planar lightwave circuit 111 may be fixed to the mount member 101 so that the end face on the end face 101d side is aligned with the end face 101d of the mount member 101. Furthermore, the planar lightwave circuit 111 may be fixed to the mount member 101 so that the end face on the end face 101d side is positioned inside the end face 101d of the mount member 101.

[0026] As described above, in the first embodiment, the planar lightwave circuit 111 is fixed to the mount member 101 with sufficient strength, ensuring resistance to vibration and shock due to the natural frequency. Furthermore, when an electric wiring board for power supply is mounted on the mount member 101, misalignment between the electric wiring board and the planar lightwave circuit 111 can be suppressed even when the ambient temperature changes, enabling a stable power supply. At the same time, in the stress relief region 112 of the planar lightwave circuit 111, warping and thermal expansion that occur in the planar lightwave circuit 111 when the ambient temperature changes are suppressed by the mount member 101, and stress changes that occur can be alleviated.

[0027] Second Embodiment Next, a second embodiment of the present disclosure will be described. FIGS. 2(a), 2(b), and 2(c) are diagrams illustrating a planar lightwave circuit component 2 according to a second embodiment of the present disclosure. FIG. 2(a) is a plan view, FIG. 2(b) is a cross-sectional view taken along the line IIb-IIb' in FIG. 2(a), and FIG. 2(c) is a cross-sectional view taken along the line IIc-IIc' in FIG. In the drawings of the second embodiment, some of the common descriptions explained in the first embodiment will be omitted. As shown in FIG. 2, the planar lightwave circuit component 2 according to the second embodiment includes a planar lightwave circuit 211 and a mounting member 201 having an upper surface that holds the planar lightwave circuit 211. The upper surface of the mounting member 201 includes a recessed region 201b extending from one end surface 201c toward the side opposite the end surface 201c. The planar lightwave circuit 211 is fixed on the recessed region 201 b and to at least a part of the non-recessed region 201 a of the mounting member 201 with adhesive 203 .

[0028] The second embodiment differs from the first embodiment in that, while the recessed region 101b in the first embodiment is a through-hole, the recessed region 201b does not penetrate the mounting member 201. That is, the recessed region 201b in the second embodiment has a thickness t2, and the thickness t1 of the non-recessed region 201a is greater than the thickness t2 of the recessed region 201b. In other words, the mounting member 201 in the second embodiment has a recessed structure in which the recessed region 201b starts from the top surface of the mounting member 201, does not penetrate to the bottom surface, and has a surface 201c that is lower than the top surface. Note that the second embodiment does not limit the step between the top surface and surface 201c of the mounting member 201 as long as the bottom surface of the planar lightwave circuit 211 does not contact surface 201c.

[0029] 2(b) and 2(c), in the second embodiment, the portion of the planar lightwave circuit 211 above the recessed region 201a becomes a stress relief region 212 that contacts the space 202. Therefore, similar to the first embodiment, the second embodiment can suppress warping and distortion of the planar lightwave circuit 211 regardless of changes in the environmental temperature. Furthermore, in the second embodiment, the recessed region 201b does not penetrate through the board, but is dug out to leave the surface 201c, so that the strength of the mount member 201 can be increased compared to the mount member 101.

[0030] (Third Embodiment) The third embodiment differs from the first and second embodiments in that a lattice filter type optical circuit is mounted as the planar lightwave circuit 311. Here, the lattice filter type optical circuit will be described.

[0031] A lattice filter optical circuit is composed of N directional couplers and N-1 arm waveguides, each consisting of two waveguides sandwiched between them. The phase of the light propagating through the arm waveguide is controlled by applying heat to one of the arm waveguides. This phase control is performed by a phase shifter that utilizes a change in refractive index due to the thermo-optic effect. The control adjusts the phase difference between the optical signals propagating through the two waveguides that make up the arm waveguide, adjusting the interference state in the downstream directional coupler and controlling the transmission spectrum for each wavelength.

[0032] However, in a lattice filter optical circuit, if the interference state differs depending on the polarization direction of the light propagating within the optical circuit, a problem occurs in that the final output transmission spectrum becomes polarization dependent. The polarization dependency of the transmission spectrum appears as polarization dependent loss (PDL). In particular, in a lattice filter optical circuit with a large number of stages, the PDL generated in one arm waveguide is amplified with each lattice stage, resulting in a large PDL for the entire lattice filter optical circuit. PDL occurs when birefringence exists within the optical waveguide and there is a difference in the effective refractive index depending on the polarization of the propagating optical signal. Here, the birefringence Δn of the optical waveguide is eff is defined by equation (1).

[0033] In equation (1), n y is the effective refractive index in the Y direction, n x is the effective refractive index in the X direction. If (effective refractive index in the Y direction) > (effective refractive index in the X direction), the birefringence Δn eff is a positive value, and when (effective refractive index in the Y direction) < (effective refractive index in the X direction), the birefringence Δ neff is a negative value. Δ neffIn an optical waveguide where θ is not zero, two orthogonal polarization modes, called the TM mode having an electric field component perpendicular to the substrate surface and the TE mode having an electric field component in the horizontal direction, propagate.

[0034] An (N-1)-stage lattice filter optical circuit is composed of N directional couplers and N-1 arm waveguides, each consisting of two waveguides sandwiched between them. In the i-th arm waveguide, the phase difference Θ between the upper arm waveguide and the lower arm waveguide is i is expressed by equation (2).

[0035] In equation (2), λ is the wavelength of light, n eff is the effective refractive index of the optical waveguide, ΔL i is the difference in length between the upper and lower arm waveguides in the i-th arm waveguide, φ i is the phase difference applied between the arms by controlling the phase shifter in the i-th arm waveguide. When birefringence exists in the optical waveguide and the effective refractive index of the TE mode and the effective refractive index of the TM mode differ from each other, the phase difference expressed by equation (2) differs depending on the polarization mode, and therefore the interference state in the subsequent directional coupler differs depending on the polarization mode, resulting in PDL.

[0036] On the other hand, in an optical waveguide interferometer, polarization dependence also occurs due to asymmetric polarization rotation between the interfering arms. As is generally known in polarization-maintaining fibers, polarization rotation in an optical waveguide is suppressed by finite birefringence. Therefore, even if the absolute value of the birefringence expressed by equation (1) is reduced and the difference in interference state due solely to birefringence is eliminated, polarization dependence still occurs due to the influence of polarization rotation.

[0037] The following circuit configuration can be used to eliminate the PDL that occurs in lattice filter optical circuits. A planar lightwave circuit is configured with two lattice filter optical circuits of the same design and a folded connection structure that connects them. The folded connection structure has the function of rotating the polarization direction of the propagating light by approximately 90°. With this configuration, light that was in TE mode when passing through the first lattice filter optical circuit undergoes a polarization rotation of approximately 90° in the folded connection structure and passes through the second lattice filter optical circuit as TM mode. Therefore, the PDL that occurs in the first lattice filter optical circuit is canceled out by the PDL that occurs in the second lattice filter optical circuit. Overall, a planar lightwave circuit with low PDL can be realized.

[0038] Here, we will explain a method for providing the function of rotating the polarization direction in a folded connection structure. In a silica-based optical waveguide circuit, even if the structural birefringence due to the optical waveguide structure is zero, stress birefringence occurs because compressive stress in the horizontal direction of the substrate acts on the core due to the different thermal expansion coefficients of the substrate material, cladding material, and core material. In particular, when a flame deposition method or the like is used to form the cladding layer or core layer of the optical waveguide, high-temperature processes are included during the fabrication of the optical waveguide, resulting in large compressive stress at room temperature and a significant increase in birefringence. As such, birefringence occurs in the core of a silica-based optical waveguide, with the main axis being either perpendicular to or horizontal to the substrate.

[0039] When a groove is formed along the core in the cladding of an optical waveguide where birefringence occurs, asymmetric stress is applied to the optical waveguide core, tilting the principal axis of birefringence. The degree of stress application depends on the distance from the waveguide core to the groove, and adjusting this distance can change the degree of tilt of the principal axis of birefringence.

[0040] When linearly polarized light passes through a birefringent object whose principal axis of birefringence is tilted, the angle θ between the polarization direction of the input light and the principal axis of the birefringent object, and the magnitude of birefringence Δ neffThe polarization state of light propagating through a birefringent object changes depending on the propagation distance L in the birefringent object. In particular, when these relationships satisfy equation (3), a linearly polarized wave is output whose polarization direction is rotated by 2θ relative to the input linearly polarized wave.

[0041] In equation (3), k is the wave number of the input light. neff , L, it is possible to impart a desired polarization rotation to the input linearly polarized wave. A known gain equalizer using a lattice filter type optical circuit has realized a gain equalization function with small PDL by using the above configuration.

[0042] In a gain equalizer using a lattice filter optical circuit, the lattice filter optical circuit is adhesively fixed to a mount. This is to ensure a stable power supply to the thermo-optic phase shifter installed in the lattice filter optical circuit by fixing the lattice filter optical circuit to a common mount together with a power-supply PCB (Printed Circuit Board). The mount is usually made of a metal material such as stainless steel. In known lattice filter optical circuits, almost the entire bottom surface is fixed to the mount to ensure long-term reliability. This is also intended to prevent the temperature of the lattice filter optical circuit from rising above its heat-resistant temperature by using a highly thermally conductive paste as an adhesive to efficiently dissipate heat generated by the thermo-optic phase shifter formed in the lattice filter optical circuit to the outside.

[0043] Next, a third embodiment using the lattice filter type optical circuit described above will be described. Figures 3(a) and 3(b) are diagrams for explaining a planar lightwave circuit component 3 of the third embodiment, with Figure 3(a) being a top view and Figure 3(b) being a cross-sectional view taken along the arrow IIIb-IIIb' in Figure 3(a). Note that in the third embodiment, explanations that overlap with those in the first embodiment will be omitted.

[0044] As shown in Figures 3(a) and 3(b), the planar lightwave circuit component 3 of the third embodiment includes a planar lightwave circuit 311 and a mount member 301 having an upper surface that holds the planar lightwave circuit 311. The upper surface of the mount member 301 includes a recessed region 301b that extends from one end face 301c toward an end face 301d opposite the end face 301c. The planar lightwave circuit 311 is located on the recessed region 301b and is fixed to at least a portion of the non-recessed region 301a of the mount member 301 with adhesive 303. The planar lightwave circuit 311 on the recessed region 301b forms a stress relief region 312. The planar lightwave circuit 311 on the stress relief region 312 is in contact with the space 302.

[0045] The planar lightwave circuit 311 includes a substrate 311a and a clad 311b, and the clad 311b includes a core that becomes the optical waveguide 431. The clad layer and core layer of the optical waveguide may be formed by any method as long as they can form uniform and smooth layers. Examples of the formation method include flame deposition, chemical vapor deposition (CVD), and sputtering.

[0046] The planar lightwave circuit 311 includes an even number of lattice filter type optical circuits. The third embodiment includes two lattice filter type optical circuits 41 and 42, which are connected by a folded connection structure 43. The lattice filter type optical circuit 41 includes an input / output waveguide 411, N optical directional couplers 412, N-1 arm waveguides 413, and an input / output waveguide 414. The arm waveguide 413 is composed of two waveguides, at least one of which is equipped with a phase shifter 415. The optical directional coupler 412 corresponds to a two-input, two-output optical multiplexing / branching circuit.

[0047] The lattice filter type optical circuit 42 also includes an input / output waveguide 421, N optical directional couplers 422, N-1 arm waveguides 423, and an input / output waveguide 424. The arm waveguide 423 is composed of two waveguides, at least one of which is loaded with a phase shifter 425. In the above, N is an integer of 2 or more.

[0048] The lattice filter optical circuits 41 and 42 operate in the same manner. The propagation of signal light in the lattice filter optical circuits 41 and 42 will be described below using the lattice filter optical circuit 41. Signal light input from the input / output waveguide 411 passes through the optical directional coupler 412 and arm waveguide 413 in that order, and is output from the input / output waveguide 414. The phase shifter 415 controls the phase of the optical signal passing from the input / output waveguide 411 to the input / output waveguide 414. The principle of the phase shifter 415 is not important as long as it can control the phase of the optical signal that has passed through it, but it may be, for example, a thermo-optical phase shifter that uses heat generated by a heater and the thermo-optical effect.

[0049] The input / output waveguide 414 of the lattice filter optical circuit 41 and the input / output waveguide 424 of the lattice filter optical circuit 42 are connected by a folded connection structure 43. The folded connection structure 43 allows light to propagate within the lattice filter optical circuit 41 and be output from the input / output waveguide 414, and then enter the lattice filter optical circuit 42 via the input / output waveguide 424. The folded connection structure 43 has the function of rotating the polarization direction of the propagating light by approximately 90°.

[0050] Here, a specific example of the folded connection structure 43 will be described. In Fig. 3(a), an input / output waveguide 414 of a lattice filter type optical circuit 41 and an input / output waveguide 424 of a lattice filter type optical circuit 42 are connected by an optical waveguide 431. In the stress release region 312 where the optical waveguide 431 is located, the third embodiment has a groove 432 that runs along the optical waveguide 431. In the third embodiment, two locations along the y-axis of the continuous input / output waveguide 414, optical waveguide 431, and input / output waveguide 424 are respectively referred to as the input / output waveguides 414 and 424, and the portion between them along the x-axis is referred to as the optical waveguide 431.

[0051] In the third embodiment, in a lattice filter type optical circuit adhesively fixed to a mount member, grooves 432 that run along optical waveguides 431 are formed in the stress relief region 312. Therefore, in the third embodiment, stress changes that accompany adhesion to the mount member can be minimized, and asymmetric stresses applied to the optical waveguides can be appropriately controlled.

[0052] That is, in the third embodiment, because the folded connection structure 43 is provided within the stress relief region 312 of the planar lightwave circuit 311, it is less susceptible to stress changes due to changes in environmental temperature. Therefore, even after the planar lightwave circuit 311 is adhesively fixed to the mount member 301, it is possible to minimize changes in asymmetric stress applied to the optical waveguide 431 by the groove 432, and the amount of polarization rotation during propagation through the optical waveguide 431 in the groove 432 can be maintained at 90°. Such a third embodiment can realize a planar lightwave circuit with small PDL without impairing the function of canceling out the PDL generated in the lattice filter type optical circuit 41 and the lattice filter type optical circuit 42.

[0053] As described above, the third embodiment can realize long-term reliability against vibration and shock and stable power supply by adhesively fixing the lattice filter optical circuit to the mount. Furthermore, the third embodiment can provide a gain equalizer using a lattice filter optical circuit that achieves good optical characteristics such as low polarization dependent loss.

[0054] (Modifications) Next, modifications of the first, second, and third embodiments described above will be described. Figures 4(a), 4(b), and 4(c) are all top views of the mounting member, illustrating modifications of the mounting member. Similar to the first, second, and third embodiments, the mounting member 401 shown in Figure 4(a) has a rectangular upper surface in top view, with a rectangular recessed region 401b extending from end face 401c to end face 401d. The non-recessed region 401a of the mounting member 401 has regions extending to sandwich the recessed region 401b.

[0055] The mounting member of this embodiment is not limited to this configuration. For example, the outer shape of the mounting member obtained by overlapping the recessed and non-recessed regions (hereinafter referred to as the "outer shape") may be a polygonal shape, including a rectangle, or a circle. Furthermore, the shape of the recessed region may be any shape as long as it allows the desired optical circuit structure to be placed within the stress-relieved region of the planar lightwave circuit.

[0056] The mount member 402 shown in Fig. 4(b) has a rectangular outer shape and has a hexagonal recessed region 402b extending from end face 402c to end face 402d. Similar to recessed region 401a, the non-recessed region 402a of the mount member 402 has an area extending on either side of the recessed region. The mount member 403 shown in Fig. 4(c) has a rectangular outer shape and has an arc-shaped recessed region 403b extending from end face 403c to end face 403d. Similar to recessed regions 401a and 402a, the non-recessed region 403a of the mount member 403 is also formed to sandwich the recessed region.

[0057] (Comparative Example) Next, a comparative example to the embodiment described above will be described. FIG. 5(a) is a top view, and FIG. 5(b) is a cross-sectional view taken along the arrow VIb-VIb' in FIG. 5(a). The configuration shown in FIGS. 5(a) and 5(b) is described, for example, in Patent Document 1. In the planar lightwave circuit component shown in FIGS. 5(a) and 5(b), only the vicinity of the end of the planar lightwave circuit 611 is fixed to the mount member 601 with adhesive 603, and most of the area of ​​the planar lightwave circuit 611 is floating in midair. As a result, the area other than the adhesive-fixed area of ​​the mount member 601 is lowered by one step and is in contact with the space 602. This forms a stress relief area 612 in the planar lightwave circuit 611.

[0058] As described above, in a planar lightwave circuit component in which a large part of the planar lightwave circuit 611 is suspended in air, when a vibration or shock that coincides with the resonant frequency occurs, the planar lightwave circuit 611 resonates, and sufficient vibration or shock resistance cannot be obtained. Furthermore, when power sharing to a phase shifter is required, as in a lattice filter type optical circuit, warping or thermal expansion of the planar lightwave circuit 611 occurs, making it impossible to supply stable power.

[0059] On the other hand, the planar lightwave circuit component of this embodiment has a recessed region on the upper surface of the mounting member, which allows for the formation of a stress relief region while also forming a non-recessed region that does not vibrate in three directions around the stress relief region. In particular, by using a lattice filter type optical circuit in the planar lightwave circuit, it is possible to achieve long-term reliability against vibration and shock and a stable power supply while maintaining the characteristic of eliminating PDL.

[0060] 1, 2, 3 Planar lightwave circuit component 41, 42 Lattice filter type optical circuit 43 Folded connection structure 101, 201, 301, 401, 402, 403, 601 Mounting member 101a, 201a, 301a, 401a, 402a, 403a Non-recessed region 101b, 201b, 301b, 401b, 402b, 403b Recessed region 101c, 101d, 201c, 201d, 301c, 301d, 401c, 401d, 402c, 402d, 403c, 403d End face 102, 202, 302 Space 103, 203, 303, 603 Adhesive 111, 211, 311, 611 Planar lightwave circuit 112, 212, 312, 612 Stress relief region 311a Substrate 311b Cladding 411, 414, 421, 424 Input / output waveguide 412, 422 Optical directional coupler 413, 423 Arm waveguide 415, 425 Phase shifter 431 Optical waveguide 432 Groove portion

Claims

1. A planar optical waveguide component including a planar optical waveguide formed on a substrate and a mount member having a holding surface for holding the planar optical waveguide, wherein the holding surface of the mount member includes a recessed region extending from one end face toward the side facing the end face, and the planar optical waveguide is fixed on the recessed region and at least a part of a non-recessed region of the mount member excluding the recessed region.

2. The planar optical waveguide component according to claim 1, wherein the planar optical waveguide is fixed to the mount member with an adhesive, and is fixed at any one of a position where the end face on the facing side coincides with the end face on the facing side of the mount member, a position where the end face on the facing side is inside the end face on the facing side of the mount member, and a position where the end face on the facing side is outside the end face on the facing side of the mount member by a length less than 1000 times the thickness of the adhesive.

3. The planar optical waveguide component according to claim 1, wherein the recessed region penetrates the mount member.

4. The planar optical waveguide component according to claim 1, wherein the recessed region does not penetrate the mount member, and the non-recessed region is thicker than the recessed region.

5. The planar optical waveguide component according to claim 1, wherein the planar optical waveguide includes a groove portion formed by removing a cladding layer along the optical waveguide included in the planar optical waveguide in a stress relaxation region overlapping the recessed region.

6. The planar optical waveguide component according to claim 5, wherein the planar optical waveguide includes a first optical circuit, a second optical circuit having the same structure as the first optical circuit, at least one output port provided in the first optical circuit, at least one input port provided in the second optical circuit, and a connecting optical waveguide connecting the output port and the input port, and the groove portion is formed along the connecting optical waveguide.

7. The planar optical waveguide component according to claim 6, wherein the first optical circuit and the second optical circuit have a 2-input 2-output optical multiplexing / demultiplexing circuit, the optical multiplexing / demultiplexing circuit is connected in series by arm waveguides, and at least one of the arm waveguides is provided with a phase shifter.

8. The planar optical waveguide component according to claim 1, wherein the substrate is a silicon-on-insulator substrate, and the optical waveguide is made of a quartz-based material.

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