Optical device

Abstract

This optical device (100) comprises: a PLC (110); a protective film (104) partially provided on an upper surface of the PLC (110); a window region (105) which is an exposed region on the upper surface of the PLC (110) that lacks the protective film (104); and a glass block (107) which is secured onto the window region (105). The window region (105) at least partially borders at least one side on the upper surface of the PLC (110). An end surface of the glass block (107) is aligned with an end surface of the PLC (110) that has said one side on the upper side thereof. A fiber block (108) is fixed to the end surface of the PLC (110) and to the end surface of the glass block (107).

Description

Optical devices

[0001] This disclosure relates to optical devices.

[0002] Against the backdrop of the explosive growth of data communications, exemplified by the internet, optical communication networks are developing rapidly. In particular, wavelength division multiplexing (WDM) technology, which enables the transmission of signal light of multiple wavelengths in a single optical fiber, is important as a means of achieving high capacity in optical communications.

[0003] Wavelength multiplexing / demultiplexing elements and / or optical amplifiers play a crucial role in realizing WDM technology. When WDM technology is applied to transmission over distances of 100 km or more, optical amplifiers may be placed at regular intervals along the transmission fiber. In this case, the wavelength dependence of the gain spectrum significantly affects the Optical Signal-to-Noise Ratio (OSNR). Optical elements that provide gain equalization functions may be used to flatten the gain spectrum.

[0004] There are several methods for realizing various optical functional circuits that can be used in optical communication networks. For example, planar lightwave circuits (PLCs), which have optical waveguides made of silica glass formed on a planar substrate, are widely used as an advantageous method that combines multi-functionality, mass production capability, and low cost.

[0005] Silica-based PLCs utilize the same materials as optical fibers used in optical communications, thus enabling the realization of low-loss optical waveguides. Furthermore, because PLCs form optical waveguides on a planar substrate, it is easy to combine various functional elements, allowing for the reproducible fabrication of complex optical circuits. Wavelength multiplexing / demultiplexing elements and / or optical switches fabricated using PLCs are important optical devices in the construction of optical networks.

[0006] To connect a silica-based PLC to an external optical element, there is a method of connecting an optical fiber to the PLC. For example, as described in Patent Document 1, there is a method of bonding and fixing a fiber block containing an optical fiber array having the same inter-channel pitch as the PLC to the end face of the PLC.

[0007] Japanese Patent Publication No. 2014-48628

[0008] However, existing technologies have room for improvement, for example, in terms of the reliability of the optical properties of PLCs connected to fiber blocks (in other words, optical fibers) and the mechanical reliability of their connections.

[0009] Therefore, one of the purposes of this disclosure is to provide an optical device that improves both the reliability of its optical properties and its mechanical reliability.

[0010] Therefore, an optical device according to one aspect of the present disclosure comprises: a planar light wave circuit; a protective film partially provided on the upper surface of the planar light wave circuit; a window region which is an exposed area on the upper surface where the protective film is not provided, and the window region is at least partially in contact with at least one side of the upper surface; a glass block fixed on the window region, wherein the end face of the glass block is aligned with the end face of the glass block which has the side of the planar light wave circuit as its upper side; and a fiber block fixed to the end face of the planar light wave circuit and the end face of the glass block.

[0011] (A) is a side view showing an exemplary structure of an optical device according to the first embodiment, and (B) is a top view of the optical device. (A) is a side view showing an exemplary structure of a PLC constituting the optical device, (B) is a top view of the PLC, and (C) is a cross-sectional view obtained by cutting the PLC through the line segment A-A' in (B) with a plane perpendicular to the plane of the paper. This is a top view showing an example of a variation of the window area in the PLC. (A) is a side view showing an exemplary structure of a PLC constituting an optical device according to the second embodiment, (B) is a top view of the PLC, and (C) is a cross-sectional view obtained by cutting the PLC through the line segment B-B' in (B) with a plane perpendicular to the plane of the paper. This is a schematic diagram illustrating an example of a method for precisely controlling the load on the adhesive. This is a top view of an optical device as a modified example. This is a diagram showing an exemplary connection structure between a PLC and a fiber block.

[0012] Embodiments will be described in detail below with reference to the drawings. However, the accompanying drawings and the following description are provided for the benefit of those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter described in the claims. Furthermore, unnecessary details may be omitted. For example, detailed descriptions of already well-known matters or redundant descriptions of substantially identical configurations may be omitted.

[0013] Furthermore, in the drawings, identical or corresponding elements are appropriately denoted by the same reference numeral. The drawings are schematic, and the dimensional relationships or ratios of each element may differ from reality. There may also be differences in dimensional relationships or ratios between drawings. When numerical values ​​are given in the following explanation, these values ​​are merely examples, and other values ​​may be used additionally or as substitutes.

[0014] <Overview> As previously described, when a fiber block is bonded to the end face of a PLC, the bonding area to the end face of the PLC is insufficient, and therefore sufficient bonding strength may not be ensured. In such cases, for example, a glass block may be bonded to the upper surface of the PLC so that its end face is aligned with the end face of the PLC, thereby expanding the bonding area.

[0015] By adhesively fixing the fiber block to both the end face of the glass block and the end face of the PLC, a sufficient bonding area can be secured, thereby achieving sufficient adhesive strength to be reliable against vibration or shock, for example.

[0016] Figure 7 shows an exemplary connection structure between the PLC 710 and the fiber block 708. Figure 7 is a side view of the optical device 700, which includes the fiber block 708 and the PLC 710. In Figure 7, the X-axis defines the width direction of the optical device 700, the Y-axis defines the height (or thickness) direction of the optical device 700, and the Z-axis defines the direction of light propagation in the optical device 700.

[0017] The PLC 710 includes, for example, a substrate 701 and a cladding layer 702 formed on the substrate 701. A core (not shown in Figure 7) is provided inside the cladding layer 702.

[0018] A glass block 707 is fixed to the upper surface of the cladding layer 702 by adhesive 7007. Here, the glass block 707 is positioned and bonded in such a way that one of its end faces aligns with the end face of the PLC 710 (in other words, that each end face forms a coplanar plane).

[0019] The fiber block 708 is then bonded and fixed to both the end face of the PLC 710 and the end face of the glass block 707 using adhesive 7008. The fiber block 708 has one or more optical fibers 709 that can be used to connect to other optical elements.

[0020] Thus, in the optical device 700 illustrated in Figure 7, by using the glass block 707 to expand the bonding area for the fiber block 708, sufficient connection strength can be achieved to ensure or guarantee mechanical reliability against vibration or shock, for example.

[0021] On the other hand, when using optical functional elements based on silica-based PLCs in optical networks, the optical devices may be required to ensure not only mechanical reliability but also long-term reliability of their optical properties in environments such as high temperature and high humidity.

[0022] For example, in a PLC, grooves may be formed in the cladding layer on one or both sides along the optical waveguide core to achieve an adiabatic mechanism or polarization rotation function. When grooves are present in the cladding layer, water molecules that enter from the side walls of the grooves can easily reach the interior of the core. As a result, a change in the refractive index of the core may occur, which can alter (e.g., degrade) the intended optical properties of the PLC.

[0023] Therefore, when grooves are present near the core, the reliability of long-term optical properties under high-temperature and high-humidity environments tends to decrease compared to cases where grooves are not present near the core. For this reason, it may be considered to form a protective film, for example, made of a material with excellent gas barrier properties, covering not only the top surface of the cladding layer but also the side walls and bottom surfaces of the grooves. The protective film can prevent or suppress the penetration of water molecules into the optical waveguide core, thereby ensuring the long-term reliability of optical properties under high-temperature and high-humidity environments.

[0024] For the protective film, for example, silicon nitride, which is known as a material film with excellent gas barrier properties, may be used. Silicon nitride is a compound of nitrogen and silicon, and may also be called "silicon nitride" or "silicon nitride (SiN)".

[0025] By forming a silicon nitride protective film on the upper surface of a quartz-based PLC, it becomes possible to suppress or mitigate changes in optical properties even in high-temperature and high-humidity environments. Therefore, it is possible to improve the long-term reliability of optical properties in high-temperature and high-humidity environments.

[0026] Here, even when a protective film is formed on the upper surface of the PLC, it may be required to expand the bonding area of ​​the fiber block 708 to the PLC 710 using the glass block 707, similar to the structure illustrated in Figure 7. This is because expanding the bonding area ensures sufficient bonding strength between the PLC 710 and the fiber block 708, thereby improving mechanical reliability.

[0027] However, generally speaking, films made of silicon nitride have inferior adhesion to adhesives made of organic materials compared to films made of quartz glass. Therefore, when bonding glass blocks 707 to a silicon nitride protective film, it may not be possible to ensure sufficient adhesive strength.

[0028] Therefore, for example, if vibration or shock is applied to the optical device 700, to which the PLC 710 and the glass block 707 are bonded together, one or both of the glass block 707 and the fiber block 708 may detach from the PLC 710. In other words, the mechanical reliability of the optical device 700 may not be sufficiently ensured.

[0029] Thus, when a silicon nitride protective film is applied to the PLC710 to ensure the long-term reliability of optical properties in high-temperature and high-humidity environments, the mechanical reliability against vibration or shock in the optical fiber connection may decrease. In other words, there is room for improvement in balancing the long-term reliability of optical properties and the mechanical reliability of optical devices.

[0030] Therefore, the following describes several exemplary embodiments of optical devices that can improve the mechanical reliability against vibration or shock in optical fiber connections while ensuring the long-term reliability of optical properties in high-temperature and high-humidity environments.

[0031] <First Embodiment> Figure 1(A) is a side view showing an exemplary structure of the optical device 100 according to the first embodiment, and Figure 1(B) is a top view of the optical device 100. Figure 2(A) is a side view showing an exemplary structure of the PLC 110 constituting the optical device 100, Figure 2(B) is a top view of the PLC 110, and Figure 2(C) is a cross-sectional view obtained by cutting the PLC 110 with a plane perpendicular to the plane of paper passing through the line segment A-A' in Figure 2(B).

[0032] In Figures 1(A), 1(B), and 2(A) to 2(C), the X-axis defines the width direction of the optical device 100, the Y-axis defines the height (or thickness) direction of the optical device 100, and the Z-axis defines the direction of light propagation in the optical device 100. The directions defined by the X-axis, Y-axis, and Z-axis are the same in the drawings used in the following explanation.

[0033] As shown in Figures 1(A) and 2(A), for example, the PLC 110 includes a substrate 101, a cladding layer 102 formed on the substrate 101, and a protective film 104 formed to partially cover the upper surface of the cladding layer 102.

[0034] Inside the cladding layer 102, there is at least one core 103, as illustrated in Figure 2(C). The core 103 may extend in the Z-axis direction (in other words, the longitudinal direction of the PLC 110) as shown in Figures 1(B) and 2(B).

[0035] As an example, when the upper surface of the cladding layer 102 is divided into two regions in the Z-axis direction, the protective film 104 is formed in the region farther from the end face of the PLC 110 to which the fiber block 108 is connected, and not in the region 105 closer to the end face.

[0036] The region 105 where the protective film 104 is not formed is the region where the upper surface of the cladding layer 102 is exposed, and will be referred to as the "window region 105" for convenience below. The upper edge of the end face of the PLC 110 on the side to which the fiber block 108 is connected forms one side of the window region 105.

[0037] In other words, as illustrated in Figures 1(B) and 2(B), the window region 105 is in contact with the short side of the PLC 110 that forms the end face to which the fiber block 108 is connected, and with a portion of each of the two long sides that face each other in the X-axis direction, as shown in the illustration in Figures 1(B) and 2(B) when viewed from above.

[0038] Further, as illustrated in FIG. 1(B), FIG. 2(B) and FIG. 2(C), a groove 106 is provided along the core 103 on at least one side of a part of the PLC 110 (e.g., the clad layer 102). There is no limitation on the depth of the groove 106; for example, the groove 106 has a depth from the upper surface of the clad layer 102 to a position directly above the substrate 101. The side walls and bottom surface of the groove 106, together with the upper surface of the clad layer 102, are covered by a protective film 104.

[0039] As illustrated in FIG. 1(A) and FIG. 1(B), a glass block 107 is adhered and fixed to the upper surface portion of the clad layer 102 corresponding to the window region 105 by an adhesive 1007. For example, the glass block 107 has a rectangular parallelepiped shape, and is positioned such that one of rectangular end faces facing each other in the Z-axis direction is aligned with the end face of the PLC 110 in the Y-axis direction, in other words, in the height (or thickness) direction.

[0040] Therefore, the end face of the PLC 110 and the end face of the glass block 107 form the same plane in the XY plane. In other words, the end face of the PLC 110 on the side to which the fiber block 108 is connected is expanded in the height direction by the end face of the glass block 107.

[0041] The fiber block 108 is fixed by an adhesive 1008 to both the end face expanded in the height direction as described above, that is, both the end face of the PLC 110 and the end face of the glass block 107 that form the same plane.

[0042] The fiber block 108 includes one or more optical fibers 109 that can be used for connection with other optical elements. For example, the fiber block 108 may incorporate an optical fiber array having the same inter-channel pitch as the PLC 110.

[0043] It should be noted that the glass block 107 may be understood as a non-limiting example of an auxiliary member or component for expanding the end face of the PLC 110 on the side to which the fiber block 108 is connected. Such an auxiliary member or component may be referred to as an "end face expansion auxiliary member" for convenience. The end face expansion auxiliary member is not limited to being made of glass, and only needs to have a material or surface with good adhesiveness to the adhesive 1008.

[0044] The size (area) of the window region 105 in a top view is not limited as long as it is large enough to accommodate the glass block 107. However, when the glass block 107 is bonded and fixed to the upper surface portion of the cladding layer 102 corresponding to the window region 105, it is desirable to minimize the exposed area of ​​the cladding layer 102 where the protective film 104 is absent as much as possible within a finite range.

[0045] For example, the larger the exposed area of ​​the cladding layer 102, the easier it is for water molecules to penetrate into the interior of the cladding layer 102 and / or the core 103 in a high-temperature, high-humidity environment, which can easily alter the optical properties of the PLC 110. Therefore, as a non-limiting example, it is desirable that the in-plane distance in the Z-axis direction between the glass block 107 and the protective film 104 on the upper surface of the cladding layer 102 be 2 mm or less.

[0046] The substrate 101 constituting the PLC 110 can be made of any material as long as it is a substrate with a smooth surface on which a glass layer that will become the cladding layer 102 can be molded directly above it, but as an unspecified example, a silicon substrate is preferred. The materials constituting the cladding layer 102 and core 103 of the PLC 110 are, for example, materials based on silica-based glass such as SiO2 or SiOx.

[0047] The material constituting the protective film 104 is not limited to any material that has excellent gas barrier properties and can prevent or suppress changes in optical properties caused by water molecules penetrating into the cladding layer 102 and the core 103 under high temperature and high humidity conditions. As a non-limiting example, silicon nitride is useful as the material for the protective film 104.

[0048] Although not shown in Figures 1(A), 1(B), and 2(A) to 2(C), other elements, such as a thermo-optical phase shifter and / or power supply wiring, may be formed on the upper surface of the PLC 110.

[0049] Furthermore, in Figure 1(B), the PLC 110 and the fiber block 108 are machined so that their respective connection end faces are perpendicular to the longitudinal direction (Z-axis direction) of the PLC 110 (parallel to the X-axis direction). However, the connection end faces may also be oblique end faces at an angle offset from the X-axis direction. For example, to prevent reflected light from the connection end face from becoming backlight, the connection end face may be machined at an angle of 8° or 10° with respect to the X-axis direction of the PLC 110.

[0050] <Role of the grooves and the effect of covering the side walls of the grooves with a protective film> The grooves 106 of the cladding layer 102 may be formed to obtain a heat insulating effect or a polarization rotation function. For example, when a part of the optical waveguide in the PLC 110 is to function as a phase shifter, a heater element may be mounted on the surface of the cladding layer 102 on top of the optical waveguide core 103.

[0051] By driving the heater element and transferring heat to the core 103, a portion of the optical waveguide can function as a phase shifter utilizing the thermo-optic effect. However, if the heat generated by driving the heater element is dissipated through the cladding layer 102, the core 103 cannot be heated efficiently, which may reduce the power efficiency of the thermo-optic phase shifter.

[0052] Therefore, in order to efficiently heat the core 103, grooves (which may also be called "insulating grooves") 106 can be formed in the cladding layers 102 on both sides of the core 103 in the region where the heater element is mounted, in order to improve heat insulation.

[0053] The formation of the insulating groove 106 prevents or suppresses heat from the heater element from being dissipated through the cladding layer 102. Therefore, it becomes possible to efficiently heat the core 103, thereby improving the power efficiency of the thermo-optical phase shifter.

[0054] On the other hand, the presence of the insulating groove 106 makes it easier for water molecules to penetrate from the side walls of the insulating groove 106 and reach the interior of the core 103. When water molecules penetrate the interior of the core 103, a change in the refractive index of the core 103 may occur, potentially degrading its optical properties.

[0055] Therefore, if the insulating groove 106 is formed in the PLC 110, the long-term reliability of the optical properties in a high-temperature, high-humidity environment may decrease compared to when the insulating groove 106 is not formed.

[0056] Therefore, a protective film 104 made of a material such as silicon nitride, which has excellent gas barrier properties, is formed so as to cover not only the upper surface of the cladding layer 102 but also the side walls and bottom surface of the heat insulating groove 106, as illustrated in Figure 2(C).

[0057] Since the side walls and bottom surface of the insulating groove 106 are covered with the protective film 104, the probability of water molecules reaching the core 103 and penetrating into the core 103 is reduced, thereby ensuring the long-term reliability of the optical properties in high-temperature and high-humidity environments.

[0058] Furthermore, even if the protective film 104 is formed only on the side walls of the heat insulating groove 106, the reliability of the optical properties can be improved. However, if the protective film 104 is formed to cover not only the side walls of the heat insulating groove 106, but also the bottom surface of the heat insulating groove 106 and the entire upper surface of the cladding layer 102 excluding the window region 105, it contributes to further improvement in the reliability of the optical properties.

[0059] Therefore, it is preferable that the protective film 104 is formed on the side walls of the groove 106 and its surroundings, and further preferable that it is formed on the entire area of ​​the upper surface of the cladding layer 102, which is a glass layer, excluding the window region 105.

[0060] <Regarding grooves for obtaining polarization rotation function> In the manufacture of quartz-based optical waveguides by flame deposition, soot glass, which will become the lower cladding layer, is deposited on a silicon substrate by flame deposition, and the soot-like soot glass is converted into transparent glass by being held in a high-temperature atmosphere.

[0061] Subsequently, a core glass layer is deposited on top of the lower cladding layer in the same manner as the lower cladding layer, and the desired core pattern is formed using techniques such as photolithography and reactive ion etching.

[0062] Then, a glass layer that will form the upper cladding layer is deposited on the lower cladding layer and the top of the core, for example, by flame deposition, thereby forming an optical waveguide.

[0063] Generally, the temperature at which glass becomes transparent is 1000°C or higher. Therefore, during the process of each layer becoming transparent, the silicon substrate expands at high temperatures (above 1000°C), and the stress is released in that state, resulting in transparent glass. After that, it is rapidly cooled to form the glass film.

[0064] At temperatures above 1000°C, the silicon substrate expands and then contracts as it cools. Meanwhile, the glass in each cladding layer, having a lower coefficient of thermal expansion than silicon, is compressed while being constrained by the silicon substrate.

[0065] Therefore, the glass layer is subjected to compressive stress from the silicon substrate. This compressive stress is particularly pronounced in the horizontal direction of the substrate (in the XZ plane), and the core is also subjected to compressive stress in the horizontal direction of the substrate. On the other hand, in the vertical direction of the substrate (in the Y axis direction), the glass layer is not constrained by the silicon substrate and is subjected to stress at the side walls of the core due to the difference in the coefficient of thermal expansion between the upper cladding layer and the core.

[0066] Since both the upper cladding layer and the core are primarily composed of quartz, the difference in their coefficients of thermal expansion is smaller compared to the interface between the silicon substrate and the glass layer, resulting in only relatively small stresses being applied in the direction perpendicular to the substrate.

[0067] Thus, the internal stress applied to the core differs in the horizontal and vertical directions of the substrate. This anisotropy of internal stress is one of the causes of birefringence in optical waveguides and can lead to the polarization dependence of various optical elements as described above.

[0068] This polarization dependence follows a physical phenomenon called the photoelastic effect and can be represented by the refractive index distribution in a specific direction. For example, the stress distribution in the X, Y, and Z axes can be expressed as σ X (X, Y), σ Y (X, Y), σ Z The refractive index distribution n is expressed by (X, Y) and the photoelastic coefficients, which are determined by the material, are expressed by C1 and C2. In this case, the refractive index distribution n in the X-axis and Y-axis directions is expressed by (X, Y).X (X,Y), n Y (X,Y) are respectively given by the following formula (1) and formula (2).

[0069]

[0070] Refractive index distribution n X (X,Y) and n Y (X,Y) corresponds to the birefringence after stress application. Further, n X0 (X,Y) and n Y0 (X,Y) respectively represent the refractive index distributions in the X-axis direction and the Y-axis direction before stress application.

[0071] Here, consider a case where, as shown in, for example, FIG. 1(B), FIG. 2(B) and FIG. 2(C), a groove 106 is formed along the optical waveguide core 103 in the cladding layer 102 near one side of the optical waveguide core 103. Due to the formation of the groove 106, the internal stress in the horizontal direction is released on the side where the groove 106 is provided. On the other hand, relatively large stress can be localized at the side wall of the groove 106 and at the position of the lower cladding layer 102 near the boundary of the silicon substrate 101.

[0072] When viewed from the position of the core 103, the localized stress exists at a position obliquely below the substrate 101 side in the direction where the groove 106 is provided, for example, at the position surrounded by the dotted line 201 in FIG. 2(C), so that an asymmetric stress exists with respect to the light propagation direction (Z-axis direction). Accordingly, the stress birefringence provided by the above-described photoelastic effect also has an axially asymmetric distribution with respect to the light propagation direction.

[0073] Such an axially asymmetric stress birefringence distribution provides the effect of rotating the axis of birefringence of the optical waveguide. In other words, while in existing optical waveguides the principal axes of birefringence are horizontal and vertical relative to the substrate, forming the groove 106 on one side of the optical waveguide core 103 to make the stress distribution asymmetric allows the principal axis of birefringence to be tilted.

[0074] Since the stress distribution depends on the distance between the optical waveguide core 103 and the groove 106, adjusting this distance allows the tilt degree of the principal axis of birefringence to be changed.

[0075] When linearly polarized light passes through a birefringent object with a tilted principal axis, the angle θ between the polarization direction of the input light and the principal axis of the birefringent object, and the magnitude of birefringence Δn are defined. eff Furthermore, the polarization state of light propagating through a birefringent object changes depending on the propagation distance L of the light within the birefringent object.

[0076] For example, if these relationships satisfy equation (3) below, a linearly polarized wave with a polarization direction rotated by 2θ relative to the input linearly polarized wave is output from the birefringent object. kΔn eff L = π (3)

[0077] Here, in equation (3), k represents the wavenumber of the input light. Using this characteristic, θ, Δn eff By individually adjusting L, it is possible to obtain the desired amount of polarization rotation for an input linearly polarized wave.

[0078] However, if a groove (which may also be called a "side groove") 106 is formed in the cladding layer 102 on one side of the core 103 to obtain polarization rotation functionality, water molecules can easily penetrate from the side wall of the side groove 106 and reach the interior of the core 103. As a result, the refractive index of the core 103 may change, and its optical properties may change (for example, deteriorate).

[0079] Therefore, even when a single groove 106 for obtaining polarization rotation function is formed in the cladding layer 102, the long-term reliability of the optical properties under high temperature and high humidity conditions may decrease compared to when no groove 106 is formed, similar to the case where an "adiabatic groove" is formed.

[0080] Therefore, by forming a protective film 104 made of a material such as silicon nitride, which has excellent gas barrier properties, not only on the upper surface of the cladding layer 102 but also on the side walls and bottom surfaces of the single groove 106, the intrusion of water molecules into the optical waveguide core 103 can be suppressed or inhibited.

[0081] Therefore, even when a single groove 106 for obtaining polarization rotation function is provided in the cladding layer 102, it is possible to improve the long-term reliability of the optical properties in high-temperature and high-humidity environments, similar to the case when an "adiabatic groove" is provided.

[0082] <Effects of the window region 105> As previously described, in the optical device 100 of the first embodiment, there is a window region 105 on the upper surface of the cladding layer 102 of the PLC 110 that is exposed without a protective film 104. This window region 105 is in contact with one side of the PLC 110 on the side to which the fiber block 108 is connected when viewed from above.

[0083] Generally, the silicon nitride protective film 104 has poorer adhesion to adhesives made of organic materials compared to a quartz glass material film. Therefore, if the entire upper surface of the cladding layer 102 is covered with the silicon nitride protective film 104 without forming a window region 105, the glass block 107 will be bonded and fixed to the protective film 104 by adhesive 1007. However, in that case, sufficient adhesive strength cannot be ensured, and if the optical device 100 is subjected to vibration or shock, the glass block 107 and fiber block 108 may peel off from the PLC 110.

[0084] In contrast, in the first embodiment, a window region 105 is formed on the upper surface of the PLC 110, in which a cladding layer 102, which is a glass layer, is exposed, and a glass block 107 is bonded and fixed to the glass layer 102 of the window region 105 by an adhesive 1007. Therefore, since the bond is to a quartz-based glass material film with good adhesion, sufficient adhesive strength can be ensured.

[0085] By ensuring sufficient adhesive strength for the glass block 107, the fiber block 108, which is bonded and fixed to both the end face of the glass block 107 and the end face of the PLC 110 by adhesive 1008, can also be fixed sufficiently firmly. Therefore, the mechanical reliability of the optical connection between the PLC 110 and the fiber block 108 (in other words, the optical fiber 109) is improved.

[0086] As described above, according to the first embodiment, it is possible to improve the long-term reliability of the optical properties of the PLC 110 in high-temperature and high-humidity environments, and to improve the mechanical reliability of the optical fiber connection to the PLC 110 against vibration or shock.

[0087] Furthermore, according to the first embodiment, in addition to ensuring sufficient adhesive strength between the PLC 110 and the glass block 107, it is possible to avoid or suppress the transmission of impact to the protective film 104 when connecting the glass block 107 and the fiber block 108.

[0088] For example, if the protective film 104 is made of silicon nitride material, due to the properties of the silicon nitride film, if a mechanical impact is applied through an object in contact with the film, a crack may occur starting from that contact point.

[0089] In other words, if the window region 105 is not formed and the glass block 107 is directly bonded and fixed to the protective film 104, the impact when the fiber block 108 is connected to the glass block 107 may be transmitted to the protective film 104, potentially causing cracks in the protective film 104.

[0090] If cracks occur in the protective film 104, not only may the PLC 110's resistance to high temperature and high humidity environments decrease, but the adhesive strength of the glass block 107 may also decrease due to damage to the protective film 104 located directly beneath the glass block 107.

[0091] Therefore, in the first embodiment, a structure is adopted in which the glass block 107 and the protective film 104 do not come into direct contact, as shown in Figures 1(A) and 1(B), for example. This non-contact structure prevents the impact that occurs when connecting the glass block 107 and / or the fiber block 108 to the PLC 110 from being transmitted to the protective film 104.

[0092] Therefore, it is desirable that the glass block 107 and the protective film 104 are not in contact even after the glass block 107 is fixed to the upper surface of the cladding layer 102 in the window region 105. For example, it is desirable that the glass block 107 and the protective film 104 are spaced about 1 mm apart in the in-plane distance of the upper surface of the cladding layer 102.

[0093] Furthermore, in order to avoid mechanical impact on the protective film 104, the window region 105 in which the glass layer 102 is exposed without the protective film 104 being formed may be provided in a strip shape along the outer circumference of the PLC 110 in a top view, as shown in Figure 3.

[0094] In other words, the protective film 104 may be formed on the upper surface of the PLC 110, avoiding the outer periphery of the PLC 110. In this case, the window region 105 will be in contact with each of the four sides of the PLC 110 in a top view. The presence of the window region 105 along the outer periphery of the PLC 110 in a top view prevents mechanical impact from being applied to the protective film 104 during handling of the PLC 110.

[0095] <Second Embodiment> Next, a second embodiment will be described with reference to Figure 4. Figure 4(A) is a side view showing an exemplary structure of the PLC 410 constituting the optical device according to the second embodiment, Figure 4(B) is a top view of the PLC 410, and Figure 4(C) is a cross-sectional view obtained by cutting the PLC 410 with a plane passing through the line segment B-B' in Figure 4(B) and perpendicular to the plane of the paper.

[0096] The PLC 410 has a cladding layer 402 formed on a substrate (for example, a silicon substrate) 401 and a protective film 404 formed to cover the cladding layer 402. Furthermore, as illustrated in Figure 4(C), a core 403 is present inside the cladding layer 102, and a groove 406 is provided in the cladding layer 402 on at least one side of the core 403 along the core 403.

[0097] The substrate 401, cladding layer 402, core 403, protective film 404, and groove 406 correspond to the substrate 101, cladding layer 102, core 103, protective film 104, and groove 106 described above, respectively.

[0098] In the second embodiment, as illustrated in Figures 4(A) and 4(B), in a top view, there is a window region 405-1 in which the upper surface of the cladding layer 402 is exposed without a protective film 404 being formed, so as to be in contact with one of the two short sides of the PLC 410. This window region 405-1 corresponds to the window region 105 in the first embodiment.

[0099] In addition to window region 405-1, there is an additional window region 405-2 at a position that is point-symmetric with respect to the in-plane centroid of the upper surface of the PLC 410, where the upper surface of the cladding layer 402 is exposed without the protective film 404 being formed. This window region 405-2 is in contact with the other of the two short sides of the PLC 410 when viewed from above.

[0100] In other words, in the second embodiment, the protective film 404 is formed on the upper surface of the PLC 410, avoiding the longitudinal end regions of the PLC 410, thereby forming window regions 405-1 and 405-2 in which the cladding layer 402 is exposed in a strip shape at both end regions. In the following, when window regions 405-1 and 405-2 are not distinguished from each other, they may be collectively referred to as "window region 405".

[0101] One side of the window region 405, for example, window region 405-1 on the side to which the fiber block 108 is connected, as in the first embodiment, corresponds to the area to which the glass block 107 is bonded and fixed to its upper surface. Furthermore, both window regions 405-1 and 405-2 correspond to the areas to which the bottom surface of the base 5003, described later in Figure 5, contacts and pressure is applied.

[0102] Therefore, the area of ​​each window region 405 in a top view only needs to be sufficient to ensure that the glass block 107 and / or base 5003 are positioned so as not to touch the protective film 404, and these areas may be the same or different.

[0103] <Adhesion of PLC> When the PLC 410 is actually put into operation, it can be bonded and fixed to a mount. For example, in order to supply power to the thermo-optical phase shifter configured in the PLC 410, the PLC 410 may be fixed to a mount common to the power supply wiring board (PCB: Printed Circuit Board). Fixing to the mount allows for a stable power supply to the PLC 410.

[0104] The mount is constructed from a metal material such as stainless steel. When fixing the PLC 410 to the mount, it is expected that the entire bottom surface of the PLC 410 will be tightly secured to the mount in order to ensure long-term mechanical reliability.

[0105] Another reason for bonding the entire bottom surface of the PLC410 to the mount is, for example, to efficiently dissipate the heat generated by the thermo-optical phase shifter. For example, if the thermo-optical phase shifter is configured as a lattice filter type optical circuit, using a paste with high thermal conductivity as the adhesive applied to the entire bottom surface of the PLC410 allows the temperature of the lattice filter type optical circuit to be controlled so that it does not exceed its heat resistance temperature.

[0106] Because the PLC410 is composed of a silicon substrate and a quartz-based glass layer with significantly different coefficients of thermal expansion, it is prone to warping and / or thermal expansion due to changes in ambient temperature. Therefore, when the bottom surface of the PLC410 is bonded to a mount, warping and / or thermal expansion are suppressed, and as a result, the stress applied to the optical waveguide layer changes. Consequently, after bonding the PLC410 to the mount, its ambient temperature-dependent characteristics may differ from those before bonding.

[0107] To stabilize this characteristic change, the thickness of the adhesive used to bond the PLC410 to the mount is expected to be uniformly and quantitatively controlled across the entire bottom surface. This is because the stress applied to the optical waveguide layer is determined by the thickness of the adhesive.

[0108] One example of a method for uniformly and quantitatively controlling the thickness of an adhesive is to precisely control the load applied to the adhesive after it has been applied, in order to spread it evenly. Figure 5 is a schematic diagram illustrating an example of a method for precisely controlling the load applied to an adhesive.

[0109] As illustrated in Figure 5, the PLC 410 is placed on the mount 5001 via the uncured adhesive 5002. Above the PLC 410, for example, a weight 5004 is placed via a base 5003.

[0110] The base 5003 contacts, for example, window regions 405-1 and 405-2, which are positioned symmetrically with respect to the in-plane center of gravity of the PLC 410. Therefore, the load quantitatively controlled by the weight 5004 is applied uniformly to the adhesive 5002 applied to the bottom surface of the PLC 410. Thus, the method illustrated in Figure 5 allows for uniform and quantitative control of the adhesive thickness when the PLC 410 is bonded and fixed to the mount 5001.

[0111] Here, the base 5003 is in direct contact with the window areas 405-1 and 405-2 of the PLC 410. However, if the entire upper surface of the PLC 410 were covered by the protective film 404, the protective film 404 and the base 5003 would be in direct contact.

[0112] If the protective film 404 is made of silicon nitride material, due to the properties of silicon nitride films, cracks may occur starting from the point of contact when a hard object comes into localized contact with it. Depending on the environment in which the PLC 410 is placed, these cracks may expand, impairing the inherent gas barrier properties of the entire film.

[0113] In contrast, in this embodiment, the base 5003 contacts the exposed cladding layer 402, i.e., the window regions 405-1 and 405-2, which are located at point-symmetric positions with respect to the in-plane centroid of the PLC 410, so that contact between the protective film 404 and the base 5003 can be avoided.

[0114] Therefore, it is possible to prevent cracks from occurring in the protective film 404, and to ensure the long-term reliability of the gas barrier properties of the protective film 404 and the optical properties of the PLC 410 in high-temperature and high-humidity environments.

[0115] As described above, according to the second embodiment, it is possible to realize an optical device that can stabilize changes in optical properties before and after adhesive mounting while ensuring the long-term reliability of optical properties in high-temperature and high-humidity environments.

[0116] <Modification> In each of the embodiments described above, an example was shown in which the window area 105 (or 305) in which one side in the X-axis direction, when viewed from above, is in contact with the entire upper edge of the end face of the PLC 110 (or 410) (in other words, the width of the PLC 110 and the width of the window area are the same in the X-axis direction).

[0117] However, the width of the PLC in the X-axis direction does not have to match the width of the window area. For example, the width of the window area in the X-axis direction may be appropriately set according to the width of the glass block and / or fiber block that are bonded to the PLC in the X-axis direction.

[0118] For example, in comparison with the structure illustrated in Figure 1(B) of the first embodiment, as shown in Figure 6, a window region 605 in which the cladding layer 102 is exposed may be formed in a region shorter than the width of the PLC 110.

[0119] In this case, when viewed from above, one side of the window region 605 in the X-axis direction will be partially in contact with the upper edge of the end face of the PLC 110. Furthermore, the protective film 104 may extend in a strip-like manner from both sides of the window region 605 in the X-axis direction, at a certain distance from the window region 605, until it reaches the end face of the PLC 110.

[0120] This structure, like the first embodiment, can improve the long-term reliability of optical properties in high-temperature and high-humidity environments, as well as the mechanical reliability of optical fiber connections against vibration or shock.

[0121] <Supplement> In this disclosure, the term "...region" may be appropriately replaced with "...part," and the term "...film" may be appropriately replaced with "...layer."

[0122] Furthermore, in this disclosure, the terms “connection” or “joining,” when used, should be understood to mean any direct or indirect “connection” or “joining” between two or more elements. For example, the terms should be understood to include indirect “connection” or “joining” between two elements that are mutually “connected” or “joined” by one or more intermediate elements.

[0123] While the Disclosure has been described in detail above, it will be apparent to those skilled in the art that the purpose and scope of this Disclosure are not limited to what has been described herein. This Disclosure can be implemented in modified and altered forms without exceeding the purpose and scope of this Disclosure as defined by the claims. Therefore, the descriptions in this Disclosure are for illustrative purposes only and are not intended to be restrictive in any way to the purpose and scope of this Disclosure.

[0124] This disclosure is useful, for example, as an optical device that can be used in optical communication technology.

[0125] 100, 700 Optical devices 101, 401, 701 Substrates 102, 402, 702 Cladding layers 103, 403, 703 Cores 104, 404 Protective films 105, 405-1, 405-2 Window regions 106, 406 Grooves 107, 707 Glass blocks 108, 708 Fiber blocks 109, 709 Optical fibers 110, 410, 710 Planar optical circuits (PLCs) 1007, 1008, 5002, 7007, 7008 Adhesives 5001 Mounts 5003 Bases 5004 Weights

Claims

1. An optical device comprising: a planar light wave circuit; a protective film partially provided on the upper surface of the planar light wave circuit; a window region which is an exposed area on the upper surface where the protective film is not provided, and the window region is at least partially in contact with at least one side of the upper surface; a glass block fixed on the window region, wherein the end face of the glass block is aligned with the end face of the glass block which has the side of the planar light wave circuit as its upper side; and a fiber block fixed to the end face of the planar light wave circuit and the end face of the glass block.

2. The optical device according to claim 1, wherein the planar light wave circuit comprises an optical waveguide having a core and a cladding layer, and grooves provided along the core in the cladding layer on one or both sides of the core, and the side walls of the grooves, or the side walls and bottom surface of the grooves, are covered by the protective film.

3. The optical device according to claim 1 or 2, wherein the window regions are provided at positions that are point-symmetric with respect to the in-plane centroid of the plane light wave circuit.

4. The optical device according to claim 1 or 2, wherein the plane light wave circuit is made of a silica-based material formed on a silicon substrate, and the protective film is made of a silicon nitride material.

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