Wavelength selection element and manufacturing method therefor

Abstract

To provide a wavelength selection element comprising two substrates that are reliably aligned and fixed to each other with a predetermined distance therebetween, and to provide a method of manufacturing the same.SOLUTION: A wavelength selection element comprises a pair of light-transmissive substrates 11 having principal surfaces that face each other with a gap therebetween; a pair of reflective films 12 formed on the opposing principal surfaces to face each other with an optical distance therebetween; a bonding section 13 designed to bond the pair of substrates together and made of a curable adhesive having a cured hardness that is less than that of the pair of substrates; and a contact section 14 at which the pair of substrates come into direct contact with each other to define the gap.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a wavelength selection element such as an optical filter and a method for manufacturing the same. [Background technology]

[0002] An optical filter is, for example, an optical element configured to selectively emit only light of a predetermined wavelength (wavelength band) from incident light. For example, a wavelength selection element such as an optical filter has a configuration in which a pair of reflective films facing each other are arranged. For example, the pair of reflective films are arranged with a gap therebetween. Also, the distance between the reflective films is set according to the wavelength of the light to be extracted.

[0003] For example, Patent Document 1 discloses an optical device having a first base on which a movable plate having a first light reflecting portion is provided so as to be displaceable in its thickness direction, and a second base on which a second light reflecting portion is provided and opposed to the first light reflecting portion across an optical gap, and the first and second bases are bonded together via a bonding film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-134025 A Summary of the Invention [Problem to be solved by the invention]

[0005] The distance between the reflective films (optical gap) is closely related to the wavelength of the light (electromagnetic wave) to be extracted, i.e., the wavelength selection characteristics (filtering characteristics). In order to reliably extract only electromagnetic waves of a specific wavelength, it is preferable that the optical gap between the reflective films is constant throughout the entire area of ​​the film.

[0006] Also, as described in Patent Document 1, for example, there is known a technique for forming an optical filter by forming a reflective film on each of a plurality of (for example, two) substrates and bonding the substrates together. In such a configuration, the precision of the optical gap is affected by the positional relationship between the substrates, for example, the parallelism of the two substrates.

[0007] In order to improve filtering characteristics, it is preferable that the substrates are fixed to each other so as to reliably form a desired optical gap, that the positions of the substrates are reliably determined, and that the substrates can be easily bonded to each other without, for example, requiring a complex device.

[0008] The present invention has been made in view of the above-mentioned points, and has an object to provide a wavelength selecting element in which substrates are reliably positioned and fixed at a desired interval, and a manufacturing method thereof. Another object of the present invention is to provide a wavelength selecting element in which substrates are reliably and easily positioned and fixed at a desired interval, and which has high wavelength selecting characteristics, and a manufacturing method thereof. [Means for solving the problem]

[0009] The invention described in claim 1 is characterized by comprising a pair of light-transmitting substrates having main surfaces facing each other with a gap therebetween, a pair of reflective films formed on the opposing main surfaces and facing each other at an optical distance, a joint portion that bonds the pair of substrates to each other and is made of a curing adhesive that has a hardness after curing lower than that of the pair of substrates, and an abutment portion where the pair of substrates directly abut against each other to define a gap.

[0010] The invention described in claim 9 is characterized by comprising a first reflective film formation step of forming a first reflective film on a first main surface of a first substrate; a second reflective film formation step of forming a second reflective film in a recess of a second substrate having a second main surface with a recess; a coating step of coating a bonding member made of a curing adhesive having a hardness after curing lower than that of the first substrate on an area outside the recess on the second main surface of the second substrate; a butting step of directly butting the first main surface against the second main surface so that the first and second reflective films face each other at an optical distance; and a bonding step of curing the bonding member and bonding the first and second substrates. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1A is a schematic top view of a wavelength selection element according to a first embodiment, FIG. 1B is a cross-sectional view of the wavelength selection element according to the first embodiment, and FIG. 1C is a partially enlarged cross-sectional view of the wavelength selection element according to the first embodiment. [Diagram 2] 3A to 3C are schematic diagrams illustrating the operation of the wavelength selection element according to the first embodiment. [Diagram 3] 3A to 3C are diagrams illustrating steps of a manufacturing method for a wavelength selecting element according to the first embodiment. [Figure 4] 5(a) to 5(d) are diagrams illustrating a method for manufacturing a wavelength selecting element according to the first embodiment. [Diagram 5] 1A and 1B are schematic cross-sectional views of a wavelength selection element according to Example 1 and a comparative example thereof, respectively. [Figure 6] 1A and 1B are a schematic top view and a schematic cross-sectional view, respectively, of a wavelength selection element according to a modified example of the first embodiment. [Figure 7] 10(a) and 10(b) are a schematic top view and a schematic cross-sectional view, respectively, of a wavelength selection element according to Example 2. FIG. [Figure 8] 10(a) and 10(b) are schematic cross-sectional views of a wavelength selection element according to Example 2 and a comparative example thereof, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below with reference to the embodiments. EXAMPLES

[0013] FIG. 1(a) is a diagram showing a schematic top view of a wavelength selection element 10 according to the first embodiment. FIG. 1(b) is a cross-sectional view of the wavelength selection element 10. FIG. 1(b) is a cross-sectional view taken along line VV in FIG. 1(a). FIG. 1(c) is a partially enlarged cross-sectional view showing an enlarged portion surrounded by a dashed line in FIG. 1(b). The configuration of the wavelength selection element 10 will be described with reference to FIGS. 1(a) to (c). The wavelength selection element 10 is, for example, an optical filter.

[0014] The wavelength selection element 10 has a pair of light-transmitting substrates (hereinafter, sometimes referred to as a substrate pair) 11 facing each other. The substrate pair 11 is made of, for example, quartz, borosilicate glass, silicon, or the like. As shown in FIG. 1(b), the substrate pair 11 has a structure in which a flat-plate-shaped first substrate 11A and a second substrate 11B are arranged facing each other. In this specification, light-transmitting property refers to a property of transmitting at least a part of electromagnetic waves including light (visible light).

[0015] 1(b), the substrate pair 11 has a pair of main surfaces (hereinafter, sometimes referred to as a main surface pair) PP that face each other with a gap GP. The main surface pair PP is composed of a first main surface PL1 provided on the first substrate 11A and a second main surface PL2 provided on the second substrate 11B. In other words, the wavelength selecting element 10 has first and second substrates 11A and 11B that respectively have first and second main surfaces PL1 and PL2 that face each other with a gap GP.

[0016] In this embodiment, the first main surface PL1 is made up of a central portion of one main surface (first main surface) MS1 of the first substrate 11 A. Also, in this embodiment, as shown in Figures 1 (b) and (c), a recess is provided in a main surface (second main surface) MS2 of the second substrate 11B that faces the main surface PL1 (main surface MS1), and the bottom surface of the recess is the second main surface PL2.

[0017] In this embodiment, as shown in Fig. 1(a), the first and second substrates 11A and 11B have rectangular outer shapes. Also, as shown in Fig. 1(b), in this embodiment, the first and second main surfaces PL1 and PL2 are arranged parallel to each other. Also, the second main surface PL2 has a circular shape.

[0018] The wavelength selection element 10 has a pair of reflective films (hereinafter, sometimes referred to as a reflective film pair) 12 that have a property of selectively transmitting electromagnetic waves. The reflective film pair 12 constitutes, for example, a Fabry-Perot etalon. Each of the reflective film pair 12 is, for example, a thin film made of Ag and an alloy containing Ag, and is a reflective film (reflective film) that has transparency. In this embodiment, the reflective film pair 12 has a circular shape when viewed from a direction perpendicular to the reflective film pair 12.

[0019] 1(b), the reflective film pair 12 is formed on the main surfaces PL1 and PL2 of the substrate pair 11 and is disposed opposite to each other at an optical distance DT. More specifically, the reflective film pair 12 is composed of a first reflective film 12A provided on the first main surface PL1 of the first substrate 11A and a second reflective film 12B provided on the second main surface PL2 of the second substrate 11B. In this embodiment, the first and second reflective films 12A and 12B are disposed such that their opposing surfaces are parallel to each other.

[0020] The wavelength selection element 10 also has a joint 13 that joins the first and second substrates 11A and 11B to each other. As shown in Fig. 1(a) in this embodiment, the joint 13 is made up of a plurality of joint pieces 13A scattered in a direction parallel to the substrate pair 11. Hereinafter, the joint 13 refers to both the joint 13 and the joint pieces 13A.

[0021] The reflective film pair 12 is provided in the center of the substrate pair 11, and the bonding portion 13 is formed in the peripheral region of the substrate pair 11. As shown in Fig. 1(b) , in this embodiment, the bonding portion 13 is sandwiched between the first and second substrates 11A and 11B. That is, the substrate pair 11 is bonded to each other between the first and second substrates 11A and 11B.

[0022] 1(b), the first and second substrates 11A and 11B have abutment portions 14 that directly abut against each other to define the gap GP. The first and second substrates 11A and 11B are directly abutted against each other (contacted) by the abutment portions 14. The height of the gap GP, i.e., the opposing distance between the first and second main surfaces PL1 and PL2, is determined by the abutment portions 14. Therefore, the optical distance DT between the reflective films 12A and 12B, i.e., the cavity spacing, is determined by the abutment portions 14.

[0023] In this embodiment, the abutting portion 14 is provided so as to surround the outer periphery of the reflective film pair 12. Specifically, for example, the abutting portion 14 is formed in an annular shape so as to surround the outer periphery of the first reflective film 12A in a plane parallel to the first main surface PL1. Also, the bonding portion 13 is formed outside the abutting portion 14. That is, in this embodiment, the abutting portion 14 is provided between the bonding portion 13 and the reflective film pair 12 when viewed from a direction perpendicular to the reflective film pair 12.

[0024] 1(b), the abutting portion 14 is a portion where a protrusion PJ with a flat top surface protruding from a main surface (second main surface PL2) of one substrate (second substrate 11B in this embodiment) of the substrate pair 11 abuts against a main surface MS1 (first main surface PL1) of the other substrate (first substrate 11A in this embodiment). The protrusion PJ abuts against the first substrate 11A at its top surface to define (form) a gap GP.

[0025] Here, the protrusion PJ and the abutment portion 14 will be described with reference to Fig. 1(c). Note that the first substrate 11A is not shown in Fig. 1(c). In this embodiment, the protrusion PJ is a portion that protrudes from the arrangement surface (bonding surface) of the bonding portion 13 of the second substrate 11B and the second main surface PL2. Specifically, in this embodiment, the protrusion PJ is a portion of the main surface MS2 that remains by forming a recess in the main surface MS2 of the second substrate 11B.

[0026] The abutment portion 14 functions as a positioning portion for the reflective film pair 12 in the opposing direction of the first and second substrates 11A and 11B (a direction perpendicular to the first and second substrates 11A and 11B). On the other hand, the bonding portion 13 functions as a positioning portion for the reflective film pair 12 in a direction parallel to the substrate pair 11. That is, the position of the reflective film pair 12 in the direction perpendicular to the substrate pair 11 is determined by the abutment portion 14, and the position of the reflective film pair 12 in the direction parallel to the substrate pair 11 is determined by the bonding portion 13.

[0027] Next, the operation of the wavelength selection element 10 will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view similar to Fig. 1(b), but hatching is omitted. Fig. 2 is a diagram showing a schematic diagram of the process from when the input light IL enters the wavelength selection element 10 until it is extracted to the outside as selected light SL. First, the input light IL enters the wavelength selection element 10 via the first substrate 11A. After transmitting through the first substrate 11A, the input light IL transmits through the first reflective film 12A of the reflective film pair 12.

[0028] The input light IL is repeatedly reflected multiple times between the first and second reflecting films 12A and 12B. At this time, of the input light IL, light with a wavelength corresponding to the optical distance DT (optical gap) of the reflecting film pair 12 remains, and light with other wavelengths is attenuated. This remaining light with a wavelength passes through the second reflecting film 12B as selected light SL. Then, after passing through the second reflecting film 12B, the selected light SL is emitted from the second substrate 11B. In this way, the wavelength selection element 10 selectively outputs (transmits) the incident light (electromagnetic wave).

[0029] Fig. 3 is a flow diagram showing a manufacturing flow of the manufacturing method of the wavelength selecting element 10. Figs. 4(a) to (d) are cross-sectional views showing the first or second substrate 11A or 11B during the manufacturing of the wavelength selecting element 10. The manufacturing method of the wavelength selecting element 10 will be described with reference to Fig. 3 and Figs. 4(a) to (d). In Fig. 4(b), the shape of the second substrate 11B before processing is shown by a dashed line.

[0030] [Step of forming first reflective film 12A] First, the first reflective film 12A is formed on the first substrate 11A (FIG. 3, step S11). FIG. 4(a) is a cross-sectional view showing the first substrate 11A on which the first reflective film 12A is formed. Specifically, first, a flat plate-shaped first substrate 11A is prepared by performing chemical mechanical polishing on both main surfaces and planarizing them. Next, the first reflective film 12A is formed on one of the main surfaces (first main surface) MS1 of the first substrate 11A. In this embodiment, the center of the main surface MS1 is set as the first main surface PL1, and a circular Ag film is formed on the first main surface PL1 to form the first reflective film 12A.

[0031] [Step of forming the protrusion PJ and the second reflective film 12B] Next, the protrusions PJ and the second reflective film 12B are formed on the second substrate 11B (FIG. 3, step S12). FIG 4(b) is a cross-sectional view showing the second substrate 11B on which the protrusions PJ and the second reflective film 12B are formed.

[0032] Specifically, first, a flat plate-shaped second substrate 11B is prepared by performing chemical mechanical polishing on both main surfaces to flatten them. Next, a recess (first recess) RC1 is formed in the center of a main surface (second main surface) MS2 of the second substrate 11B. In addition, a recess (second recess) RC2 is formed in the peripheral region of the main surface MS2. The recesses RC1 and RC2 can be formed by, for example, partially removing the main surface MS2 of the second substrate 11B by etching or the like.

[0033] An area where the recesses RC1 and RC2 are not formed is left on the main surface MS2 of the second substrate 11B. This remaining main surface MS2 becomes a protrusion PJ that protrudes relatively from the recesses RC1 and RC2. The bottom surface of the recess RC1 becomes the second main surface PL2. A flattening process may be performed on the bottom of the recess RC1 to obtain a desired flatness. In this manner, the protrusion PJ is formed on the second substrate 11B.

[0034] [Step of forming second reflective film 12B] Next, the second reflective film 12B is formed on the second main surface PL2, which is the bottom surface of the recess RC1. In this embodiment, the second reflective film 12B is formed by forming a circular Ag film on the second main surface PL2. In this embodiment, the second reflective film 12B has the same shape and size as the first reflective film 12A.

[0035] [Joining material BD coating process] Next, a bonding material BD is applied to the second substrate 11B (FIG. 3, step S13). FIG 4(c) is a cross-sectional view showing the second substrate 11B in a state where the bonding material BD has been applied.

[0036] Specifically, the bonding member BD is applied to an area outside the recess RC1 on the main surface MS2 of the second substrate 11B. In this embodiment, the bonding member BD is applied to the bottom surface of the recess RC2 formed on the main surface MS2 of the second substrate 11B. In this embodiment, a curable adhesive made of an ultraviolet-curable resin material is used as the bonding member BD.

[0037] The bonding material BD was applied to multiple locations on the bottom surface of the recess RC2. The viscosity and amount of the bonding material BD was adjusted so that the height of the bonding material BD exceeded the height of the protrusion PJ (main surface MS2) as shown in Fig. 4(c). The application process of the bonding material BD, the butting process and the bonding process described below were performed in the air.

[0038] [Butting Process and Bonding Process of First and Second Substrates 11A and 11B] Next, the first and second substrates 11A and 11B are butted against each other (FIG. 3, step S14). With the first and second substrates 11A and 11B butted against each other, the bonding material BD is cured to bond the first and second substrates 11A and 11B to each other (FIG. 3, step S15). FIG. 4(d) is a cross-sectional view showing the bonded first and second substrates 11A and 11B.

[0039] Specifically, first, the first and second substrates 11A and 11B are butted together so that the first and second reflective films 12A and 12B face each other. In this embodiment, the main surface MS1 of the first substrate 11A is directly butted (contacted) against the protrusion PJ of the second substrate 11B. In this embodiment, pressure is applied to the first and second substrates 11A and 11B, so that the main surface MS1 of the first substrate 11A comes into contact with the entire top surfaces of the protrusions PJ of the second substrate 11B. This forms the abutment portion 14.

[0040] During this butting step, the bonding member BD on the second substrate 11B was brought into contact with the main surface MS1 of the first substrate 11A. Specifically, by butting the main surface MS1 of the first substrate 11A against the second substrate 11B in the state shown in Fig. 4(c), the bonding member BD was first brought into contact with the first substrate 11A, and then the protrusion PJ was butted against the first substrate 11A.

[0041] By forming the abutting portion 14 in the abutting step, the gap GP between the first and second main surfaces PL1 and PL2 and the optical distance DT between the first and second reflecting films 12A and 12B are formed (determined).

[0042] Next, the bonding member BD is cured to bond the first and second substrates 11A and 11B together, forming the bonding portion 13. In this embodiment, ultraviolet light is irradiated onto the ultraviolet curable resin serving as the bonding member BD after the abutment portion 14 has been formed. This causes the bonding member BD to cure, forming the bonding portion 13, and bonding the first and second substrates 11A and 11B together. Through these steps, the wavelength selection element 10 is formed.

[0043] Here, the bonding portion 13 will be described. Fig. 5(a) is a schematic cross-sectional view of the wavelength selection element 10 according to this embodiment. The bonding portion 13 is made of a curing adhesive that has a hardness (softness) smaller than that of the first substrate 11A after curing. The bonding portion 13 also has elasticity after curing, and the elastic force F1 is smaller than the bending stress (bending reaction force) F2 generated in the first substrate 11A after bonding. This significantly improves the uniformity of the optical distance DT of the reflective film pair 12 after bonding, i.e., in the wavelength selection element 10 that has become a product.

[0044] Specifically, the bonding member BD, which is a curing adhesive that becomes the bonding portion 13, shrinks when cured compared to before curing. Therefore, a force acts on the bonding surface (contact surface) between the bonding portion 13 and the first substrate 11A, with the abutment portion 14 as a fulcrum, to deflect (bend) the first substrate 11A toward the second substrate 11B. The contraction force acting between the bonding member BD and the first substrate 11A when cured remains as an elastic force F1 even after curing. In addition, a reaction force (reaction force against bending) F2 that repels the elastic force F1 is generated in the first substrate 11A that receives the elastic force F1.

[0045] However, by using a material with a relatively low hardness (softness) for the bonding portion 13, the reaction force F2 generated in the first substrate 11A can be made larger than the elastic force F1 of the bonding portion 13. Therefore, the deformation of the first substrate 11A due to the hardening of the bonding member BD is suppressed, and the shape of the first substrate 11A is stabilized. This improves the parallelism of the first and second main surfaces PL1 and PL2, and the gap GP has high in-plane uniformity. Therefore, the parallelism of the optical distance DT between the first and second reflecting films 12A and 12B, that is, the in-plane (in-film) uniformity is greatly improved. Therefore, the substrates are reliably positioned and fixed at a desired interval.

[0046] For example, examples of adhesives that can be used for the joint 13 include acrylic adhesives and epoxy adhesives. Examples of a curing method for the joint 13 include ultraviolet curing and heat curing. The adhesive for the joint 13 is preferably made of a material having a glass transition point lower than the environmental temperature in which the wavelength selection element 10 (substrate pair 11) is used. For example, when the joint 13 is made of a resin material, the joint 13 becomes vitrified when the environmental temperature falls below the glass transition point, and loses the elastic force F1 described above.

[0047] 5(b) shows a schematic cross-sectional view of a wavelength selecting element 100 having a similar configuration to the wavelength selecting element 10, except that the wavelength selecting element 100 has a bonding portion 101 made of an adhesive having a hardness after hardening greater than that of the first substrate 11A, as a comparative example. In the wavelength selecting element 100 according to the comparative example, the elastic force F3 after hardening of the bonding portion 101 is greater than the reaction force F2 of the first substrate 11A. In this case, as shown in FIG. 5(b), the first and second substrates 11A and 11B are bonded together with the first substrate 11A in a curved (warped) state.

[0048] Therefore, when the bonding portion 101 is provided, the uniformity of the gap GP0 between the first and second main surfaces PL1 and PL2 decreases. Also, the uniformity of the optical distance DT0 between the first and second reflecting films 12A and 12B decreases. Therefore, the actual filtering characteristics of the wavelength selecting element 100 differ from the designed filtering characteristics, and there are cases where the selected light SL in the desired wavelength band cannot be extracted.

[0049] On the other hand, in the wavelength selection element 10, as described above, the first and second substrates 11A and 11B are joined by the joint 13 made of a curing adhesive having a hardness after curing smaller than that of the first substrate 11A. Therefore, the first and second substrates 11A and 11B are reliably fixed at a desired interval, and the first and second reflective films 12A and 12B can be arranged at a desired interval.

[0050] Moreover, the wavelength selection element 10 has abutment portions 14 where the first and second substrates 11A and 11B directly abut between the first and second reflecting films 12A and 12B and the joint portion 13. Therefore, the gap GP between the first and second main surfaces PL1 and PL2 and the optical distance DT between the first and second reflecting films 12A and 12B are reliably determined.

[0051] Moreover, it is preferable that the bonding portion 13 has a plurality of bonding pieces 13A scattered within the bonding region (in the embodiment, within the region between the first and second substrates 11A and 11B). This makes it possible to suppress variations in the bonding strength and positional accuracy between the first and second substrates 11A and 11B during manufacturing. Specifically, for example, the risk of foreign matter being mixed into the bonding portion 13 is reduced. Therefore, the wavelength selection characteristics are stabilized.

[0052] Furthermore, the abutment portion 14 is preferably a portion where the flat top surface of the protrusion PJ of the second substrate 11B (one substrate) abuts against the main surface MS1 of the first substrate 11A (the other substrate). In other words, the abutment portion 14 is preferably a portion formed by direct abutment of surfaces against each other.

[0053] For example, in this embodiment, the main surface MS1 of the first substrate 11A and the top surface of the protrusion PJ of the second substrate 11B that form the abutment portion 14 are surfaces of rigid bodies that have been flattened by chemical mechanical polishing or the like. By directly abutting these highly flattened surfaces of the rigid bodies against each other, it is possible to obtain high parallelism between the first and second main surfaces PL1 and PL2, i.e., high parallelism between the first and second reflective films 12A and 12B.

[0054] In addition, in this embodiment, as described above, the manufacturing method of the wavelength selecting element 10 includes steps S13 to S15 of bonding the pair of substrates 11 using a bonding member BD made of a curing adhesive having a hardness after curing less than that of the pair of substrates 11. Therefore, without requiring complicated steps, expensive equipment, or a sophisticated manufacturing environment, the substrates are reliably and easily positioned and fixed at a desired interval to provide the wavelength selecting element 10 having high wavelength selection characteristics. In addition, by performing the butting step S14, the positioning accuracy of the substrates is further improved.

[0055] In this embodiment, the case where the abutting portion 14 is a portion of the pair of substrates 11 that directly abuts against each other has been described. However, for example, the abutting portion 14, i.e., the abutting portion (contact portion) of either the first or second substrate 11A or 11B, may be subjected to a surface treatment (surface processing) such as plating. In other words, it is sufficient that the rigid portions of the first and second substrates 11A and 11B abut against each other.

[0056] In this embodiment, the case has been described where the abutment portion 14 forms surface contact with the flat top surface of the protrusion PJ of the second substrate 11B and the main surface MS1 of the first substrate 11A, but the configuration of the abutment portion 14 is not limited to this. For example, the top surface of the protrusion PJ may have a curved shape, and the abutment portion 14 may be formed by point contact.

[0057] In this embodiment, the abutting portion 14 is formed in an annular shape on the outer periphery of the reflective film pair 12, but the configuration of the abutting portion 14 is not limited to this. For example, the abutting portion 14 may be formed intermittently on the outer periphery of the reflective film pair 12. The abutting portion 14 may be composed of a plurality of abutting pieces (not shown) provided on the outer side of the reflective film pair 12. That is, the first and second substrates 11A and 11B may abut against each other in a plurality of regions spaced apart from each other.

[0058] In addition, in this embodiment, the reflective film pair 12 has a circular planar shape, but the planar shape of the reflective film pair 12 is not limited to this. For example, the reflective film pair 12 may have a rectangular planar shape. In addition, the substrate pair 11 has been described and illustrated as having a rectangular planar shape, but the planar shape of the substrate pair 11 is not limited to this.

[0059] Although the case where the protrusions PJ are formed on the main surface MS2 of the second substrate 11B has been described, the protrusions PJ may be formed on the first substrate 11A. Also, the protrusions PJ may be formed on both the first and second substrates 11A and 11B, and the protrusions PJ may abut against each other to form the abutment portion 14.

[0060] In this embodiment, the wavelength selection element 10 has a pair of substrates 11 having optical transparency and main surfaces PL1 and PL2 facing each other with a gap GP therebetween, a pair of reflective films 12 formed on the facing main surfaces PL1 and PL2 and facing each other with an optical distance DT, a joint 13 made of a curing adhesive that bonds the pair of substrates 11 to each other and has a hardness after curing lower than that of the pair of substrates 11, and an abutment portion 14 where the pair of substrates 11 directly abut against each other to define the gap GP. Therefore, it is possible to provide a wavelength selection element in which the substrates are reliably positioned and fixed at a desired interval. EXAMPLES

[0061] Fig. 6(a) is a diagram showing a schematic top surface of a wavelength selection element 20 according to Example 2. Fig. 6(b) is a schematic cross-sectional view of the wavelength selection element 20. Fig. 6(b) is a cross-sectional view taken along line WW in Fig. 6(a). The wavelength selection element 20 has a similar configuration to the wavelength selection element 10, except for the configurations of the joint portion 22 and the abutment portion 23.

[0062] The wavelength selection element 20 has a pair of substrates (substrate pair) 21 consisting of first and second substrates 21A and 21B on which first and second reflective films 12A and 12B are provided. The bonding portion 22 has a first sub-bonding portion 22A provided so as to surround the reflective film pair 12, and a second sub-bonding portion 22B provided outside the first sub-bonding portion 22A and made of a curing adhesive having a higher hardness after curing than the first sub-bonding portion 22A.

[0063] The first sub-bonding portion 22A has a similar configuration to the bonding portion 13 in the wavelength selection element 10. The first sub-bonding portion 22A is made of a curing type adhesive having a hardness after curing lower than that of the substrate pair 21. The second sub-bonding portion 22B is made of a curing type adhesive having a hardness after curing higher than that of the first sub-bonding portion 22A. In this embodiment, the second sub-bonding portion 22B is made of a total of four bonding pieces provided at each corner of the substrate pair 21.

[0064] In addition, in this embodiment, the abutment portion 23 provided on the substrate pair 21 of the wavelength selection element 20 has a first sub-abutment portion 23A provided between the reflective film pair 12 and the first sub-junction portion 22A and surrounding the reflective film pair 12, and a second sub-abutment portion 23B provided between the second sub-junction portion 22B and the first sub-abutment portion 23A.

[0065] In this embodiment, the first sub-abutment portion 23A has a configuration similar to that of the abutment portion 14 in the wavelength selection element 10, and is the portion where the first main surface PL1 (main surface MS1) of the first substrate 21A and the top of the protrusion (first protrusion) PJ of the second substrate 21B abut against each other.

[0066] In this embodiment, the second substrate 21B has a protrusion (second protrusion) PJ1 provided in an annular shape so as to surround a predetermined region at each corner of the main surface MS2 of the second substrate 21B. The second sub-abutment portion 23B is a portion where the first main surface PL1 of the first substrate 21A and the protrusion PJ1 of the second substrate 21B abut against each other. In addition, the second sub-bonding portion 22B of the bonding portion 22 is formed in the region surrounded by the protrusion PJ1.

[0067] In other words, the wavelength selecting element 20 has a joint 22 including first and second sub-joints 22A and 22B having different hardnesses from each other. The wavelength selecting element 20 also has first and second sub-abutment portions 23A and 23B as the abutment portion 23, and has portions where the first and second substrates 21A and 21B abut against each other at multiple points.

[0068] In this embodiment, both a high uniformity (parallelism) of the gap GP between the first and second main surfaces PL1 and PL2 of the substrate pair 21 and a strong bonding force of the substrate pair 21 are realized. Specifically, the first sub-bonding portion 22A of the bonding portion 22 and the first sub-abutting portion 23A of the abutting portion 23 are provided in consideration of the uniformity of the gap GP, as in the first embodiment. Meanwhile, the second sub-bonding portion 22B of the bonding portion 22 and the second sub-abutting portion 23B of the abutting portion 23 improve the bonding strength of the substrate pair 21.

[0069] In this manner, in this embodiment, the first and second substrates 21A and 21B are joined by the joint 22 consisting of a plurality of sub-joints. Therefore, it is possible to provide a wavelength selection element 20 in which the substrates are reliably positioned and fixed at a desired interval. EXAMPLES

[0070] Fig. 7(a) is a diagram showing a schematic top surface of a wavelength selection element 30 according to Example 3. Fig. 7(b) is a cross-sectional view of the wavelength selection element 30. Fig. 7(b) is a cross-sectional view taken along line XX in Fig. 7(a). The wavelength selection element 30 has a similar configuration to the wavelength selection element 10, except for the configurations of the substrate pair 31, the movable part 32, the support part 33, and the driving electrode 34. The substrate pair 31 is made of the same material as the substrate pair 11.

[0071] The wavelength selection element 30 is provided in an area inside the abutment portion 14 of the first substrate 31A, and has a movable portion 32 that displaces the first reflection film 12A in the film thickness direction of the first reflection film 12A, and a support portion 33 that movably supports the movable portion 32. The wavelength selection element 30 also has a drive electrode 34 consisting of first and second electrodes 34A and 34B that generates an electrostatic force that moves the movable portion 32.

[0072] 7(b), in this embodiment, the support portion 33 is made of a thin film portion provided on the outer periphery of the first reflective film 12A on the first substrate 31A. The movable portion 32 is a portion of the first substrate 31A inside the thin film portion as the support portion 33. The bottom surface of the movable portion 32 constitutes the first main surface PL1, and the first reflective film 12A is formed on the bottom surface of the movable portion 32.

[0073] In this embodiment, first and second electrodes 34A and 34B are provided between the movable part 32 and the reflective film pair 12, the electrodes being formed on the opposing main surfaces PL1 and PL2 of the substrate pair 31 and facing each other with a gap therebetween. The driving electrode 34 generates an electrostatic force that moves the movable part 32 and displaces the first reflective film 12A. Although not shown, the wavelength selecting element 30 has a driving circuit connected to the driving electrode 34.

[0074] When a voltage is applied to the drive electrode 34, an electrostatic force (e.g., electrostatic attraction) is generated between the first and second electrodes 34A and 34B. The support portion 33 is elastically deformed by the electrostatic force. As a result, the movable portion 32 moves (displaces) together with the first reflecting film 12A and the first electrode 34A, for example, toward the second substrate 31B. In this manner, the wavelength selection element 30 has a function of changing the optical distance DT between the first and second reflecting films 12A and 12B, and adjusting the wavelength of the electromagnetic wave (selected light SL) to be extracted. In other words, the wavelength selection element 30 is a wavelength-variable optical filter.

[0075] Fig. 8(a) is a schematic cross-sectional view of the wavelength selection element 30 when it is driven, that is, when the movable part 32 moves and the first reflection film 12A is displaced. Fig. 8(a) shows the state of the wavelength selection element 30 when the first reflection film 12A is displaced so that the optical distance DT1 is smaller than the optical distance DT.

[0076] Like the wavelength selecting element 10, the bonding portion 13 is made of a curing adhesive that has a hardness after curing that is smaller than that of the substrate pair 31. Therefore, as described with reference to Fig. 5(a), the elastic force F1 of the bonding portion 13 after curing is smaller than the bending reaction force F2 of the substrate pair 11. Therefore, the bonding portion 13 expands and contracts due to the bending stress generated in the first substrate 31A after curing while maintaining the bonding force (the figure shows an example of expansion).

[0077] In this way, even when the first substrate 31A is deformed by applying a deformation force (moving force) to it by the driving electrode 34, the joint 13 does not cause unnecessary deformation of the first substrate 31A. Therefore, the joint 13 and the abutting portion 14 can move the movable portion 32 so that the gap GP1 becomes an ideal distance, and the optical distance DT1 can be accurately changed.

[0078] FIG. 8(b) is a cross-sectional view showing a schematic state of a wavelength selection element 110 bonded by a bonding portion 101 instead of the bonding portion 13 during driving as a comparative example. First, when the bonding portion 101 is used, the first substrate 31A undergoes unnecessary deformation due to the curing shrinkage of the bonding portion 101 after the bonding portion 101 is cured. When the wavelength selection element 110 is driven in this state, not only is the gap GP2 of the substrate pair 31 non-uniform, but there is also a high possibility that the movable portion 32 moves with a displacement amount different from the designed displacement amount. Therefore, the optical distance DT2 of the reflective film pair 12 deviates from the designed uniformity and distance, and the desired filtering characteristics cannot be obtained.

[0079] On the other hand, since the joint 13 of the wavelength selection element 30 remains flexible even after hardening, the optical distance DT can be accurately adjusted to the designed optical distance DT1, and the degree of uniformity is also high.

[0080] Thus, in this embodiment, the wavelength selecting element 30 has a movable part 32 that is provided inside the abutment part 14 on one of the substrate pair 31 (the first substrate 31A in this embodiment) and displaces the optical distance DT of the reflective film pair 12. Therefore, even when the wavelength selection characteristics are changed by displacing the first reflective film 12A, for example, the wavelength selecting element 30 can be provided with the junction part 13 and the abutment part 14, in which the substrates are reliably positioned at a desired interval.

[0081] The above-described embodiments can be combined with each other. For example, the wavelength selection element 30 according to the third embodiment may have the joint 22 and the abutment portion 23 of the wavelength selection element 20 according to the second embodiment instead of the joint 13 and the abutment portion 14. [Explanation of symbols]

[0082] 10, 20, 30 Wavelength selection element 11, 21, 31 Pair of boards 11A, 21A, 31A First board 11B, 21B, 31B Second board 12 Pair of reflective films 12A First Reflection Film 12B Second reflective film PP Pair of main surfaces 13, 22 joint 14, 23 End 32 Moving parts 33 Support part

Claims

[Claim 1] A pair of light-transmitting substrates having main surfaces opposed to each other with a gap therebetween; a pair of reflective films formed on the opposing main surfaces and opposing each other with an optical distance therebetween; a bonding portion that bonds the pair of substrates to each other and is made of a curing adhesive having a hardness after curing that is smaller than that of the pair of substrates; abutting portion where the pair of substrates directly abut against each other to define the gap.

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