Wavelength multiplexer / demultiplexer

Abstract

To provide a wavelength division multiplexer that can suppress an increase in insertion loss occurring when an environment temperature of a wavelength selection filter changes.SOLUTION: A wavelength division multiplexer comprises: a first collimator; M second collimators; M wavelength selection filters; and a base plate. The base plate has a loading plane where M wavelength selection filters are loaded. Each of M wavelength selection filters has a light transmissive substrate 41 and a multilayer film 42. The substrate includes: a first principal plane 41a and a second principal plane 41b that face each other in a first direction X; and a bottom plane 41c that connects the first principal plane and the second principal plane, and faces the loading plane 51. The multilayer film is formed on the first principal plane. Each of M wavelength selection filters is fixed on the loading plane by a cured product of an adhesive agent 60. In at least one wavelength selection filter of M wavelength selection filters, the cured product of the adhesive agent is in contact with the bottom plane and in non-contact with the multilayer film.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a wavelength multiplexer / demultiplexer.

Background Art

[0002] A wavelength multiplexer / demultiplexer used in an optical communication system using a wavelength division multiplexing method or the like is known (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1). The wavelength multiplexer / demultiplexer multiplexes a plurality of optical signals having different wavelengths into a wavelength division multiplexed optical signal, or demultiplexes a wavelength division multiplexed optical signal including a plurality of optical signals having different wavelengths into each optical signal.

[0003] The wavelength multiplexer / demultiplexer includes a plurality of wavelength selection filters each having an optically transparent substrate and a multilayer film formed on the surface of the substrate that transmits only an optical signal in a predetermined transmission wavelength band. The plurality of wavelength selection filters are arranged, for example, in two rows on a base plate, and are arranged such that their positions in the arrangement direction are staggered between the rows. For example, when a plurality of optical signals having different wavelengths are multiplexed, each optical signal is input from a corresponding collimator to a wavelength selection filter, and each optical signal that has passed through the wavelength selection filter is multiplexed with other optical signals while being reflected by the multilayer film of another wavelength selection filter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a wavelength multiplexer / demultiplexer as described above, each wavelength selection filter is fixed to a base plate by, for example, a cured product of an adhesive. When the environmental temperature changes while each wavelength selection filter is fixed to the base plate, the inclination of the multilayer film with respect to the optical signal incident on the wavelength selection filter may change. Specifically, when the environmental temperature becomes lower than room temperature (for example, 25°C), the multilayer film inclines away from the base plate, and when the environmental temperature becomes higher than room temperature, the multilayer film inclines closer to the base plate. As a result, the optical path of the reflected light from the multilayer film changes from the original optical path, and the insertion loss due to the wavelength selection filter increases.

[0007] An object of the present disclosure is to provide a wavelength multiplexer / demultiplexer capable of suppressing an increase in insertion loss that occurs when the environmental temperature of a wavelength selection filter changes.

Means for Solving the Problems

[0008] The present disclosure provides, as one aspect, a wavelength multiplexer / demultiplexer. The wavelength multiplexer / demultiplexer includes a first collimator, M (where M is an integer of 2 or more) second collimators, M wavelength selective filters, and a base plate. The first collimator has a first optical waveguide and a collimating lens optically coupled to an end of the first optical waveguide. Each of the M second collimators has a second optical waveguide and a collimating lens optically coupled to an end of the second optical waveguide. The M wavelength selective filters transmit optical signals in mutually different transmission wavelength bands and reflect optical signals in wavelength bands other than their respective transmission wavelength bands. The base plate has a mounting surface on which the M wavelength selective filters are placed. The optical path connecting the first collimator and the first second collimator passes through the first wavelength selective filter. The optical path connecting the m-th (m = 1, ···, M - 1) wavelength selective filter and the (m + 1)-th second collimator passes through the (m + 1)-th wavelength selective filter. Each of the M wavelength selective filters has an optically transparent substrate and a multilayer film. The substrate includes a first main surface and a second main surface facing each other in a first direction, and a bottom surface connecting the first main surface and the second main surface and facing the mounting surface. The multilayer film is formed on the first main surface and is configured to transmit optical signals in a specific transmission wavelength band and reflect optical signals in wavelength bands other than the specific transmission wavelength band. Each of the M wavelength selective filters is fixed to the mounting surface by a cured adhesive. In at least one of the M wavelength selective filters, the cured adhesive contacts the bottom surface and does not contact the multilayer film.

Effects of the Invention

[0009] According to the present disclosure, it is possible to provide a wavelength multiplexer / demultiplexer that can suppress an increase in insertion loss that occurs when the environmental temperature of the wavelength selective filter changes.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. A wavelength multiplexer according to an embodiment of the present disclosure includes a first collimator, M (M is an integer of 2 or more) second collimators, M wavelength selection filters, and a base plate. The first collimator has a first optical waveguide and a collimating lens optically coupled to an end of the first optical waveguide. Each of the M second collimators has a second optical waveguide and a collimating lens optically coupled to an end of the second optical waveguide. The M wavelength selection filters transmit optical signals in mutually different transmission wavelength bands and reflect optical signals in other wavelength bands except for their respective transmission wavelength bands. The base plate has a mounting surface on which the M wavelength selection filters are mounted. The optical path connecting the first collimator and the first second collimator passes through the first wavelength selection filter. The optical path connecting the m-th (m = 1, ···, M - 1) wavelength selection filter and the (m + 1)-th second collimator passes through the (m + 1)-th wavelength selection filter. Each of the M wavelength selection filters has an optically transparent substrate and a multilayer film. The substrate includes a first main surface and a second main surface facing each other in a first direction, and a bottom surface connecting the first main surface and the second main surface and facing the mounting surface. The multilayer film is formed on the first main surface and is configured to transmit an optical signal in a specific transmission wavelength band and reflect an optical signal in other wavelength bands except for the specific transmission wavelength band. Each of the M wavelength selection filters is fixed to the mounting surface by a cured product of an adhesive. In at least one of the M wavelength selection filters, the cured product of the adhesive contacts the bottom surface and does not contact the multilayer film.

[0012] In this wavelength multiplexer / demultiplexer, in at least one of the M wavelength selection filters, the cured product of the adhesive contacts the bottom surface of the substrate of the wavelength selection filter and does not contact the multilayer film. Since the cured product of the adhesive does not contact the multilayer film, the multilayer film is not restricted to the placement surface of the base plate by the cured product of the adhesive. Therefore, when thermal deformation of the substrate occurs due to a change in the environmental temperature, the stress generated in the multilayer film is reduced. As a result, in the above wavelength multiplexer / demultiplexer, the inclination of the multilayer film when the environmental temperature changes is suppressed. Therefore, in the above wavelength multiplexer / demultiplexer, even when the environmental temperature changes, it is difficult for an optical path shift of the optical signal reflected by the wavelength selection filter to occur, and an increase in the insertion loss due to the wavelength selection filter can be suppressed.

[0013] As one embodiment, the substrate may include a first side surface and a second side surface that face each other in a second direction intersecting the first direction. In the at least one wavelength selection filter, the cured product of the adhesive may contact the first side surface and the second side surface. According to this embodiment, since the cured product of the adhesive contacts not only the bottom surface of the substrate but also the first side surface and the second side surface of the substrate, the contact area between the wavelength selection filter and the cured product of the adhesive increases, and the wavelength selection filter is more firmly fixed to the base plate by the cured product of the adhesive. Therefore, for example, even when a physical external force is applied to the wavelength selection filter, it is difficult for the position and orientation of the wavelength selection filter to shift, and an increase in the insertion loss due to the wavelength selection filter can be suppressed.

[0014] As an embodiment, the first main surface may include an exposed area where no multilayer film is formed. The cured product of the adhesive may be in contact with the exposed area. In this embodiment, the first main surface may include a first portion facing the second main surface in a first direction and a second portion that extends inclined with respect to the first portion and the bottom surface and connects the first portion and the bottom surface. The second portion may include the exposed area. According to this embodiment, since the cured product of the adhesive is in contact not only with the bottom surface of the substrate but also with a part of the first main surface, the contact area between the wavelength selection filter and the cured product of the adhesive increases, and the wavelength selection filter is more firmly fixed to the base plate by the cured product of the adhesive. Therefore, for example, even when a physical external force is applied to the wavelength selection filter, it is difficult for the position and orientation of the wavelength selection filter to deviate, and an increase in insertion loss due to the wavelength selection filter can be suppressed.

[0015] In the above embodiment, the portion in contact with the exposed area in the cured product of the adhesive may be located more than 300 μm away from the center of the first main surface when viewed from the first direction. According to this embodiment, since the portion in contact with the exposed area in the cured product of the adhesive is located at a certain distance from the center of the first main surface, it is possible to suppress the light signal passing through the wavelength selection filter from being blocked by the cured product of the adhesive.

[0016] As one embodiment, each of the M wavelength selection filters may be formed on the second major surface and may have an antireflection film configured to prevent reflection of an optical signal on the second major surface. In the at least one wavelength selection filter, the cured product of the adhesive may be in contact with the surface facing the mounting surface of the antireflection film. According to this embodiment, since the cured product of the adhesive is in contact not only with the bottom surface of the substrate but also with the surface facing the mounting surface of the antireflection film, the contact area between the wavelength selection filter and the cured product of the adhesive increases, and the wavelength selection filter is firmly fixed to the base plate by the cured product of the adhesive. Therefore, for example, even when a physical external force is applied to the wavelength selection filter, displacement of the position and orientation of the wavelength selection filter is less likely to occur, and an increase in insertion loss due to the wavelength selection filter can be suppressed.

[0017] As one embodiment, in the at least one wavelength selection filter, the cured product of the adhesive may be in contact with the surface on the side opposite to the second major surface of the antireflection film. According to this embodiment, since the cured product of the adhesive is in contact not only with the bottom surface of the substrate but also with the surface on the side opposite to the second major surface of the antireflection film, the contact area between the wavelength selection filter and the cured product of the adhesive increases, and the wavelength selection filter is firmly fixed to the base plate by the cured product of the adhesive. Therefore, for example, even when a physical external force is applied to the wavelength selection filter, displacement of the position and orientation of the wavelength selection filter is less likely to occur, and an increase in insertion loss due to the wavelength selection filter can be suppressed.

[0018] In the above embodiment, the portion of the cured product of the adhesive in contact with the antireflection film may be located 300 μm or more away from the center of the second major surface when viewed from the first direction. According to this embodiment, since the portion of the cured product of the adhesive in contact with the antireflection film is located at a certain distance from the center of the second major surface, it is possible to suppress the optical signal passing through the wavelength selection filter from being blocked by the cured product of the adhesive.

[0019] As one embodiment, the adhesive may contain an ultraviolet curable resin. According to this embodiment, the adhesive can be quickly cured by irradiating the adhesive with ultraviolet rays. Therefore, during the process of curing the adhesive, it is difficult for the position and orientation of the wavelength selection filter to shift, and an increase in insertion loss due to the wavelength selection filter can be suppressed.

[0020] As one embodiment, the adhesive may contain a filler made of silica. According to this embodiment, since silica is a material with a relatively small coefficient of linear expansion, thermal deformation of the cured product of the adhesive due to changes in environmental temperature is suppressed. Therefore, even when the environmental temperature changes, it is difficult for the position and orientation of the wavelength selection filter fixed by the cured product of the adhesive to shift, and an increase in insertion loss due to the wavelength selection filter can be suppressed.

[0021] In the above embodiment, the content of the filler with respect to the volume of the adhesive may be 50% by volume or more. According to this embodiment, thermal deformation of the cured product of the adhesive due to changes in environmental temperature is further suppressed. Therefore, it is even more difficult for the position and orientation of the wavelength selection filter to shift when the environmental temperature changes, and an increase in insertion loss due to the wavelength selection filter can be further suppressed.

[0022] As one embodiment, the distance between the bottom surface and the placement surface may be 50 μm or more. According to this embodiment, it is difficult for the influence of thermal deformation of the base plate due to changes in environmental temperature to reach the wavelength selection filter. Therefore, even when the environmental temperature changes, it is difficult for the position and orientation of the wavelength selection filter to shift, and an increase in insertion loss due to the wavelength selection filter can be suppressed.

[0023] As one embodiment, the coefficient of linear expansion of the base plate is 15.0×10 -6It may be less than (1 / K). According to this embodiment, thermal deformation of the base plate due to changes in the environmental temperature is suppressed. Therefore, even when the environmental temperature changes, displacement of the position and orientation of the wavelength selection filter disposed on the base plate hardly occurs, and an increase in insertion loss due to the wavelength selection filter can be suppressed.

[0024] As one embodiment, the wavelength multiplexer may further include a third collimator optically coupled to the M-th wavelength selection filter. According to this embodiment, by using the third collimator as an upgrade port, the number of channels of the wavelength multiplexer can be increased as needed.

[0025] As one embodiment, an optical element having a reflecting surface extending along a predetermined direction may be further provided when viewed from the thickness direction of the base plate. Each of the M second collimators and the M wavelength selection filters may be arranged side by side along a predetermined direction when viewed from the thickness direction of the base plate. The first collimator, the M second collimators, and the M wavelength selection filters may be located on the same side of the reflecting surface when viewed from the thickness direction of the base plate. The reflecting surface may change the direction of the optical path connecting the first collimator and the first second collimator, and the direction of the optical path connecting the m-th (m = 1, ···, M - 1) wavelength selection filter and the (m + 1)-th second collimator. According to this embodiment, miniaturization of the wavelength multiplexer can be achieved as compared with the case where the odd-numbered second collimators and wavelength selection filters and the even-numbered second collimators and wavelength selection filters are arranged to face each other.

[0026] In the above embodiment, the odd-numbered wavelength selection filters may be different in position in the thickness direction of the base plate from the even-numbered wavelength selection filters. The base plate may be disposed between the odd-numbered wavelength selection filters and the even-numbered wavelength selection filters. According to this embodiment, when viewed from the thickness direction of the base plate, the odd-numbered wavelength selection filters can be arranged so as to overlap a part of the even-numbered wavelength selection filters, and further miniaturization of the wavelength multiplexer can be achieved.

[0027] As one embodiment, the at least one wavelength selection filter may be at least any one of the wavelength selection filters from the first to the (M / 2)-th. According to this embodiment, an increase in insertion loss due to the wavelength selection filter can be effectively suppressed.

[0028] As one embodiment, the number of the at least one wavelength selection filter may be (M / 2) or more. According to this embodiment, an increase in insertion loss due to the wavelength selection filter can be more reliably suppressed.

[0029] As one embodiment, the base plate may include a first base plate on which M wavelength selection filters are placed, and a second base plate that is separate from the first base plate and on which the first collimator and M second collimators are placed. According to this embodiment, it becomes possible to independently design the first base plate on which the wavelength selection filter is placed and the second base plate on which the first collimator and the second collimators are placed. Thereby, the degree of freedom in arranging the wavelength selection filter, the first collimator, and the second collimators can be improved.

[0030] As one embodiment, the wavelength multiplexer may further include a housing in which the first collimator, M second collimators, M wavelength selection filters, and the base plate are accommodated in an internal space. The internal space may be sealed. According to this embodiment, for example, oxidation of the base plate accommodated in the internal space can be suppressed, and deterioration of the characteristics of the wavelength multiplexer can be suppressed.

[0031] [Details of Embodiments of the Present Disclosure] A specific example of the wavelength multiplexer / demultiplexer according to the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these examples, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

[0032] <First Embodiment> FIG. 1 is a schematic plan view of a wavelength multiplexer / demultiplexer 1 according to the first embodiment. FIG. 2 is a schematic cross-sectional view of the wavelength multiplexer / demultiplexer 1 shown in FIG. 1. FIG. 3 is a schematic view of the wavelength multiplexer / demultiplexer 1 with the illustration of the base plate 50 and the housing 70 omitted. The wavelength multiplexer / demultiplexer 1 is, for example, a MUX / DEMUX module used in an optical communication system. The wavelength multiplexer / demultiplexer 1 has at least one of a function of multiplexing M optical signals having different wavelengths to generate a wavelength-division multiplexed optical signal, and a function of demultiplexing a wavelength-division multiplexed optical signal including M optical signals having different wavelengths into individual optical signals. The wavelength multiplexer / demultiplexer 1 includes a first collimator 10, M second collimators 20(1) to 20(M), M wavelength selection filters 40(1) to 40(M), a base plate 50, a joining member 60, and a housing 70. M is an arbitrary integer of 2 or more, and in the present embodiment, M = 12.

[0033] FIG. 4 is a cross-sectional view of the first collimator 10 and the second collimators 20(1) to 20(M). The first collimator 10 has an optical fiber 11 (first optical waveguide), a first collimating lens 12, a ferrule 13, and a capillary 14.

[0034] The optical fiber 11 is, for example, a single-mode optical fiber made of glass. The optical fiber 11 has a core extending in the optical waveguide direction and a cladding covering the periphery of the core. The ferrule 13 is formed in a substantially cylindrical shape. The ferrule 13 has a first end face 13a and a second end face 13b that intersect the central axis of the ferrule 13, and an outer peripheral face 13c that is a cylindrical surface connecting the first end face 13a and the second end face 13b. The ferrule 13 is attached to the tip of the optical fiber 11. A through hole is formed in the ferrule 13 along the central axis of the ferrule 13. The optical fiber 11 is inserted through the through hole of the ferrule 13. The central axis of the ferrule 13 coincides with the optical axis AX1 of the optical fiber 11. The end face of the optical fiber 11 is exposed from the ferrule 13 at the first end face 13a and is polished together with the first end face 13a to be flush with the first end face 13a. The end face of the optical fiber 11 and the first end face 13a are inclined with respect to a virtual plane H1 perpendicular to the optical axis AX1 of the optical fiber 11. The inclination angle of the first end face 13a with respect to the virtual plane H1 may be, for example, 6° or more and 10° or less, or may be 8°. A joining member 15 for fixing the optical fiber 11 to the ferrule 13 is disposed on the second end face 13b. The joining member 15 is a cured product of a resin adhesive. The ferrule 13 is formed of, for example, glass such as quartz or ceramic such as zirconia.

[0035] The first collimating lens 12 is a lens component formed in a substantially cylindrical shape and is optically coupled to the optical fiber 11. The first collimating lens 12 is formed of glass such as quartz, for example. The first collimating lens 12 has a first end face 12a and a second end face 12b that intersect the central axis of the first collimating lens 12, and an outer peripheral face 12c that is a cylindrical face connecting the first end face 12a and the second end face 12b. The first end face 12a is spherical and functions as a convex lens. The second end face 12b faces the end face of the optical fiber 11 and is optically coupled to the end face. The second end face 12b is inclined with respect to the virtual plane H1. The inclination angle of the second end face 12b with respect to the virtual plane H1 may be, for example, 6° or more and 10° or less, or may be 8°. In the present embodiment, the second end face 12b is parallel to the first end face 13a of the ferrule 13.

[0036] The capillary 14 is a substantially cylindrical member that houses the first collimating lens 12 and the ferrule 13. The capillary 14 is formed of glass such as quartz or metal such as SUS, for example. The first collimating lens 12 is inserted from the first opening 14a of the capillary 14. The ferrule 13 is inserted from the second opening 14b of the capillary 14. The outer peripheral face 12c of the first collimating lens 12 and the outer peripheral face 13c of the ferrule 13 are in contact with the inner peripheral face 14c of the capillary 14. The end face of the optical fiber 11 and the second end face 12b of the first collimating lens 12 face each other in the internal space of the capillary 14. The capillary 14 holds the first collimating lens 12 and the ferrule 13 so that the optical axis AX1 of the optical fiber 11 and the central axis of the first collimating lens 12 coincide with each other.

[0037] The second collimators 20(1) to 20(M) have the same configuration as the first collimator 10 described above. The second collimators 20(1) to 20(M) include an optical fiber 21 (second optical waveguide), a second collimating lens 22, a ferrule 23, and a capillary 24.

[0038] The optical fiber 21 has the same configuration as the above-described optical fiber 11. The ferrule 23 is formed in a substantially cylindrical shape. The ferrule 23 has a flat first end face 23a and a second end face 23b that intersect the central axis of the ferrule 23, and an outer peripheral face 23c that is a cylindrical surface connecting the first end face 23a and the second end face 23b. The ferrule 23 is attached to the tip of the optical fiber 21. A through hole is formed in the ferrule 23 along the central axis of the ferrule 23. The optical fiber 21 is inserted into the through hole of the ferrule 23. The central axis of the ferrule 23 coincides with the optical axis AX1 of the optical fiber 21. The end face of the optical fiber 21 is exposed from the ferrule 23 at the first end face 23a and is polished together with the first end face 23a to be flush with the first end face 23a. The end face of the optical fiber 21 and the first end face 23a are inclined with respect to a virtual plane H1 perpendicular to the optical axis AX1 of the optical fiber 21. The inclination angle of the first end face 23a with respect to the virtual plane H1 may be, for example, 6° or more and 10° or less, or may be 8°. A joining member 25 for fixing the optical fiber 21 to the ferrule 23 is disposed on the second end face 23b. The joining member 25 is a cured product of a resin-based adhesive. The ferrule 23 is formed of, for example, glass such as quartz or ceramic such as zirconia.

[0039] The second collimating lens 22 is a lens component formed in a substantially cylindrical shape and is optically coupled to the optical fiber 21. The second collimating lens 22 is formed of, for example, glass such as quartz. The second collimating lens 22 has a first end face 22a and a second end face 22b that intersect the central axis of the second collimating lens 22, and an outer peripheral face 22c that is a cylindrical surface connecting the first end face 22a and the second end face 22b. The first end face 22a is spherical and functions as a convex lens. The second end face 22b faces the end face of the optical fiber 21 and is optically coupled to the end face. The second end face 22b is inclined with respect to the virtual plane H1. The inclination angle of the second end face 22b with respect to the virtual plane H1 may be, for example, 6° or more and 10° or less, or may be 8°. In the present embodiment, the second end face 22b is parallel to the first end face 23a of the ferrule 23.

[0040] The capillary 24 is a substantially cylindrical member that houses the second collimating lens 22 and the ferrule 23. The capillary 24 is formed of glass such as quartz or metal such as SUS. The second collimating lens 22 is inserted from the first opening 24a of the capillary 24. The ferrule 23 is inserted from the second opening 24b of the capillary 24. The outer peripheral surface 22c of the second collimating lens 22 and the outer peripheral surface 23c of the ferrule 23 are in contact with the inner peripheral surface 24c of the capillary 24. The end face of the optical fiber 21 and the second end face 22b of the second collimating lens 22 face each other in the internal space of the capillary 24. The capillary 24 holds the second collimating lens 22 and the ferrule 23 so that the optical axis AX1 of the optical fiber 21 and the central axis of the second collimating lens 22 coincide with each other.

[0041] FIG. 5 is a perspective view showing the wavelength selection filters 40(1) to 40(M). FIG. 6 is a cross-sectional view of the wavelength selection filters 40(1) to 40(M). The wavelength selection filters 40(1) to 40(M) transmit optical signals in different transmission wavelength bands and reflect optical signals in other wavelength bands except for their respective transmission wavelength bands. The wavelength selection filters 40(1) to 40(M) are fixed to the mounting surface 51 of the base plate 50 described later by the joining member 60. The wavelength selection filters 40(1) to 40(M) have a substrate 41, a multilayer film 42, and an antireflection film 43.

[0042] The substrate 41 is formed of a light-transmissive material. The light-transmissive material is, for example, glass. Having light transmissivity means transmitting 95% or more of the light of the target wavelength. The substrate 41 has light transmissivity in a wavelength band including all the wavelengths included in the wavelength-division multiplexed optical signal, for example. The substrate 41 is formed in a substantially rectangular parallelepiped shape. The substrate 41 has a first main surface 41a, a second main surface 41b, a bottom surface 41c, a first side surface 41e, and a second side surface 41f. The first main surface 41a and the second main surface 41b face each other in the X direction (the first direction). In the following description, the direction perpendicular to the X direction is the Y direction, and the direction perpendicular to the X direction and the Y direction is the Z direction. The first main surface 41a and the second main surface 41b have a rectangular shape when viewed from the X direction. The first main surface 41a has a convex curved surface shape facing outward of the substrate 41 as shown in FIG. 6. The second main surface 41b is formed flat along the Y direction and the Z direction.

[0043] The bottom surface 41c connects the first main surface 41a and the second main surface 41b and faces the mounting surface 51 of the base plate 50, which will be described later, in the Z direction. The bottom surface 41c is formed flat along the X direction and the Y direction. The first side surface 41e and the second side surface 41f face each other in the Y direction (the second direction). Each of the first side surface 41e and the second side surface 41f connects the first main surface 41a and the second main surface 41b and extends flat along the X direction and the Z direction. When viewed from the X direction, the width of the substrate 41 along the Y direction may be, for example, 0.8 mm or more and 2 mm or less, and the width of the substrate 41 along the Z direction may be, for example, 0.8 mm or more and 2 mm or less. The maximum thickness of the substrate 41 along the X direction may be, for example, 0.5 mm or more and 2 mm or less.

[0044] The multilayer film 42 is a band-pass filter configured to transmit only optical signals in a specific transmission wavelength band and reflect optical signals in other wavelength bands. The multilayer film 42 is composed of a number of thin film filters (TFFs) laminated together. The thin film filters are formed of a dielectric. The number of layers of the thin film filters constituting the multilayer film 42 is, for example, 100 layers or more. The thickness of the multilayer film 42 is, for example, 30 μm or more and 100 μm or less. The multilayer film 42 is formed directly on the first main surface 41a of the substrate 41 and is in contact with the first main surface 41a. The multilayer film 42 extends along the first main surface 41a and has a convex curved surface shape facing away from the first main surface 41a as shown in FIG. 6. In the present embodiment, the multilayer film 42 is formed over the entire first main surface 41a.

[0045] The multilayer film 42 has a first surface 42a, a second surface 42b, and a third surface 42c. The first surface 42a is the surface on the side of the first main surface 41a of the substrate 41 and is in contact with the first main surface 41a. The second surface 42b is the surface on the side opposite to the first main surface 41a. The third surface 42c is the surface facing the mounting surface 51 of the base plate 50 and connects the first surface 42a and the second surface 42b. In the present embodiment, the third surface 42c is flush with the bottom surface 41c of the substrate 41.

[0046] FIG. 7 is a graph showing the transmission wavelength bands of the multilayer films 42 included in the wavelength selection filters 40(1) to 40(M). In FIG. 7, the horizontal axis represents the wavelength and the vertical axis represents the light transmittance. FIG. 7 shows the transmission wavelength bands F(1) to F(M) corresponding to the wavelength selection filters 40(1) to 40(M) respectively, and the signal wavelengths λ1 to λ of the optical signals. Mis shown. As shown in FIG. 7, the multilayer film 42 has different transmission wavelength bands F(1) to F(M) for each of the wavelength selection filters 40(1) to 40(M). Different transmission wavelength bands mean that the center wavelengths of the transmission wavelength bands are different, including cases where the transmission wavelength bands overlap near the short wavelength end and the long wavelength end in the transmission wavelength bands. In the present embodiment, the widths of the transmission wavelength bands F(1) to F(M) are equal to each other. The transmission wavelength bands F(1) to F(M) each include the signal wavelengths λ1 to λ M respectively. As an example, the center wavelengths of the transmission wavelength bands F(1) to F(M) are the signal wavelengths λ1 to λ M respectively.

[0047] The antireflection film 43 is configured to prevent reflection of the optical signal on the second main surface 41b. The antireflection film 43 is an AR (Anti-Reflection) film formed by laminating a plurality of thin film filters. The thin film filter is formed of a dielectric. The number of layers of the thin film filter constituting the antireflection film 43 is, for example, 10 layers or less. The thickness of the antireflection film 43 is, for example, 0.1 μm or more and 3 μm or less. The antireflection film 43 is directly formed on the second main surface 41b of the substrate 41 and is in contact with the second main surface 41b. The antireflection film 43 extends along the second main surface 41b. In the present embodiment, the antireflection film 43 extends flatly along the Y direction and the Z direction. In the present embodiment, the antireflection film 43 is formed over the entire second main surface 41b.

[0048] The antireflection film 43 has a first surface 43a, a second surface 43b, and a third surface 43c. The first surface 43a is the surface on the second main surface 41b side of the substrate 41 and is in contact with the second main surface 41b. The second surface 43b is the surface on the side opposite to the second main surface 41b. The third surface 43c is the surface facing the mounting surface 51 of the base plate 50 and connects the first surface 43a and the second surface 43b. In the present embodiment, the third surface 43c is flush with the bottom surface 41c of the substrate 41.

[0049] In the wavelength selection filters 40(1) to 40(M), in order to suppress fluctuations in the transmission wavelength band due to temperature changes, the substrate 41 is formed of a material having a relatively large linear expansion coefficient so that the expansion of the multilayer film 42 itself and the contraction of the multilayer film 42 due to the influence of the expansion of the substrate 41 cancel each other out. Therefore, the substrate 41 usually has a larger linear expansion coefficient than the multilayer film 42. The wavelength selection filters 40(1) to 40(M) are formed through a process of cooling the substrate 41 and the multilayer film 42 after forming the multilayer film 42 on the first main surface 41a of the substrate 41 at a predetermined film formation temperature. At this time, due to the difference in the linear expansion coefficients between the substrate 41 and the multilayer film 42, a convex warp occurs on the first main surface 41a of the substrate 41 and the multilayer film 42. In particular, the multilayer film 42 suitable for DWDM (Dense-WDM) signals with a narrow wavelength interval is formed thicker than the antireflection film 43 because more than 100 thin film filters are laminated to obtain steep transmission characteristics, and thus warping due to the difference in the linear expansion coefficients is likely to occur. The radius of curvature of the first surface 42a and the second surface 42b of the multilayer film 42 becomes a small value of about 1 m, for example. Due to the warp of the multilayer film 42, the wavelength selection filters 40(1) to 40(M) act as a reflective concave lens with respect to the optical signal incident from the antireflection film 43 side.

[0050] As shown in FIG. 1, the base plate 50 is a plate-like member on which the first collimator 10, the second collimators 20(1) to 20(M), and the wavelength selection filters 40(1) to 40(M) are placed, and is fixed to a housing 70 described later. The thickness direction of the base plate 50 coincides with the Z direction. In the present embodiment, the base plate 50 has a rectangular shape with rounded corners when viewed from the Z direction. The shape of the base plate 50 is not limited, and it may be, for example, a square shape or an elliptical shape. The base plate 50 has a flat mounting surface 51 extending along the X direction and the Y direction. The first collimator 10, the second collimators 20(1) to 20(M), and the wavelength selection filters 40(1) to 40(M) are placed on the mounting surface 51. The base plate 50 may be formed of a material having a relatively small coefficient of linear expansion, such as stainless steel such as SUS430 and SUS410, glass, or invar. The coefficient of linear expansion of the base plate 50 may be, for example, 15.0×10 -6 (1 / K) or less.

[0051] The joining member 60 is a cured product of an adhesive and is a member for fixing the wavelength selection filters 40(1) to 40(M) to the mounting surface 51 of the base plate 50. Here, the "adhesive" refers to the composition of the joining member 60 in the state before curing (uncured). The joining member 60 is formed by curing the adhesive. The joining member 60 suppresses the movement and orientation variation of the wavelength selection filters 40(1) to 40(M) with respect to the mounting surface 51. As shown in FIG. 6, the joining member 60 is disposed between the bottom surface 41c of the substrate 41 and the mounting surface 51 of the base plate 50. The joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42 and the antireflection film 43. The joining member 60 is in direct contact with the bottom surface 41c. Hereinafter, the surface combining the bottom surface 41c of the substrate 41, the third surface 42c of the multilayer film 42, and the third surface 43c of the antireflection film 43 is referred to as the bottom surface 40c of the wavelength selection filters 40(1) to 40(M). When viewed from the Z direction, the contact area of the bottom surface 40c with the joining member 60 may be 70% or less of the entire area of the bottom surface 40c, or may be 50% or less of the area.

[0052] In the present embodiment, in all the wavelength selection filters 40(1) to 40(M), the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42. Therefore, in at least any one of the first wavelength selection filter 40(1) to the (M / 2)-th wavelength selection filter 40(M / 2), the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42. Further, among the M wavelength selection filters 40(1) to 40(M), in (M / 2) or more wavelength selection filters 40(1) to 40(M), the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42. Note that in at least one of the wavelength selection filters 40(1) to 40(M) among all the wavelength selection filters 40(1) to 40(M), it is sufficient that the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42.

[0053] The adhesive that constitutes the joining member 60 contains, for example, an adhesive resin. The adhesive resin contained in the adhesive may be an ultraviolet curable resin that cures when irradiated with ultraviolet light. When the adhesive contains an ultraviolet curable resin, for example, in a state where the adhesive is disposed between the bottom surface 41c and the mounting surface 51, the joining member 60 is formed by irradiating the adhesive with ultraviolet light. The adhesive contains a filler 65 for preventing thermal deformation of the joining member 60 due to changes in environmental temperature. The filler 65 is also contained in the joining member 60 which is a cured product of the adhesive. The filler 65 has a coefficient of linear expansion smaller than that of the adhesive resin. The material of the filler 65 is, for example, silica. The shape of the filler 65 may be, for example, spherical or polygonal. The average particle diameter of the filler 65 may be, for example, 10 μm or more. The average particle diameter of the filler 65 is the average value of the equivalent diameter of the projected area measured by the microscopic method, or the average value of the equivalent diameter of the spherical volume measured by the laser diffraction scattering method. The content of the filler 65 with respect to the volume of the adhesive may be, for example, 50% by volume or more, or 70% by volume or more. The content of the filler 65 with respect to the volume of the joining member 60 after curing may be equivalent to the content of the filler 65 with respect to the volume of the adhesive before curing. For example, when the content of the filler 65 with respect to the volume of the adhesive is 50% by volume or more, the content of the filler 65 with respect to the volume of the joining member 60 may also be 50% by volume or more.

[0054] The thickness of the joining member 60 is larger than the average particle diameter of the filler 65 and may be, for example, 30 μm or more, or 50 μm or more. The thickness of the joining member 60 is the maximum thickness in the Z direction of the joining member 60 located between the bottom surface 41c and the mounting surface 51. Therefore, when the thickness of the joining member 60 is 30 μm or more, the maximum distance in the Z direction between the bottom surface 41c and the mounting surface 51 is at least 30 μm or more. From the viewpoint of suppressing thermal deformation of the wavelength selection filters 40(1) to 40(M) due to heat from the base plate 50, it is preferable that the maximum distance in the Z direction between the bottom surface 41c and the mounting surface 51 is large, and may be, for example, 30 μm or more, or 50 μm or more.

[0055] As shown in FIGS. 1 and 2, the housing 70 is formed in a box shape having an internal space S. The internal space S is, for example, sealed. Further, the internal space S is filled with an inert gas such as nitrogen. The housing 70 houses the first collimator 10, the second collimators 20(1) to 20(M), the wavelength selection filters 40(1) to 40(M), and the base plate 50 in the internal space S. The housing 70 has a main body 71 having an opening 71a and a lid 72 closing the opening 71a. The main body 71 has a bottom plate 73 extending along the X and Y directions and side walls 74 extending along the Z direction from the outer edge of the bottom plate 73. A plurality of recesses 74b recessed toward the bottom plate 73 are formed in the end surface 74a of the side wall 74 in the Z direction. The optical fiber 11 and the optical fiber 21 are inserted into the plurality of recesses 74b.

[0056] The lid 72 is formed in a plate shape and is attached to the main body 71 so as to close the opening 71a with the optical fiber 11 and the optical fiber 21 inserted into the recesses 74b. The gap between the surface of the recess 74b and the surface of the lid 72 may be sealed with a sealing member such as resin. The sealing member suppresses the entry of outside air, moisture, and dust into the internal space S and, when the internal space S is filled with an inert gas, the outflow of the inert gas from the internal space S.

[0057] Subsequently, the arrangement modes of the first collimator 10, the second collimators 20(1) to 20(M), and the wavelength selection filters 40(1) to 40(M) will be described. As shown in FIG. 1, the second collimators 20(1) to 20(M) are arranged in two rows, the first row L11 and the second row L12, when viewed from the Z direction. Specifically, the odd-numbered second collimators 20(1), 20(3), ···, 20(M - 1) are arranged in a row in this order and constitute the first row L11. The even-numbered second collimators 20(2), 20(4), ···, 20(M) are arranged in a row in this order and constitute the second row L12. The arrangement directions of the first row L11 and the second row L12 in the present embodiment are the Y direction and coincide with each other.

[0058] The wavelength selection filters 40(1) to 40(M) are arranged in two columns, namely the first column L21 and the second column L22, when viewed from the Z direction, similar to the second collimators 20(1) to 20(M). Specifically, the odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) are arranged in a row in this order, forming the first column L21. The even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M) are arranged in a row in this order, forming the second column L22. In the present embodiment, the arrangement directions of the first column L21 and the second column L22 are in the Y direction and coincide with each other. The wavelength selection filters 40(1) to 40(M) are arranged such that their positions in the arrangement direction alternate between the first column L21 and the second column L22.

[0059] The antireflection films 43 of the wavelength selection filters 40(1), 40(3), ···, 40(M - 1) in the first column L21 face the second column L22. The antireflection films 43 of the wavelength selection filters 40(2), 40(4), ···, 40(M) in the second column face the first column L21. In the Y direction, the wavelength selection filter 40(2) is located between the wavelength selection filter 40(1) and the wavelength selection filter 40(3). The same applies to the subsequent wavelength selection filters 40(3) to 40(M - 1). That is, in the Y direction, the m-th (m = 2, ···, M - 1) wavelength selection filter 40(m) is located between the wavelength selection filter 40(m - 1) and the wavelength selection filter 40(m + 1). When viewed from the Z direction, the first column L21 and the second column L22 of the wavelength selection filters 40(1) to 40(M) are arranged between the first column L11 and the second column L12 of the second collimators 20(1) to 20(M).

[0060] The first collimator 10 is arranged on the straight line connecting the wavelength selection filter 40(1) and the second collimator 20(1) when viewed from the Z direction. The first collimator 10 is linearly and spatially optically coupled to the first second collimator 20(1) via the first wavelength selection filter 40(1). That is, the optical path connecting the first collimator 10 and the second collimator 20(1) passes through the wavelength selection filter 40(1). The wavelength selection filter 40(1) is optically coupled to the first collimator 10 on the second main surface 41b side of the substrate 41 and is optically coupled to the second collimator 20(1) on the first main surface 41a side of the substrate 41.

[0061] The second main surface 41b of the substrate 41 of the wavelength selection filter 40(1) is linearly and spatially optically coupled to the second second collimator 20(2) via the second wavelength selection filter 40(2). That is, the optical path connecting the second main surface 41b of the substrate 41 of the wavelength selection filter 40(1) and the second collimator 20(2) passes through the wavelength selection filter 40(2). The wavelength selection filter 40(2) is optically coupled to the wavelength selection filter 40(1) on the second main surface 41b side of the substrate 41 and is optically coupled to the second collimator 20(2) on the first main surface 41a side of the substrate 41. The same optical coupling applies to the third and subsequent second collimators 20(3) to 20(M) and wavelength selection filters 40(3) to 40(M).

[0062] In other words, the above configuration is as follows. The second main surface 41b of the substrate 41 of the m-th (m = 1, ···, M - 1) wavelength selection filter 40(m) is linearly and spatially optically coupled to the (m + 1)-th second collimator 20(m + 1) via the (m + 1)-th wavelength selection filter 40(m + 1). That is, the optical path connecting the second main surface 41b of the substrate 41 of the wavelength selection filter 40(m) and the second collimator 20(m + 1) passes through the wavelength selection filter 40(m + 1). The wavelength selection filter 40(m + 1) is optically coupled to the wavelength selection filter 40(m) on the second main surface 41b side of the substrate 41 and is optically coupled to the second collimator 20(m + 1) on the first main surface 41a side of the substrate 41.

[0063] Referring to FIG. 8, the operation of the wavelength multiplexer / demultiplexer 1 when multiplexing a plurality of optical signals will be described. FIG. 8 shows the operation of the wavelength multiplexer / demultiplexer 1 when multiplexing M optical signals Sλ1 to Sλ that have different wavelengths from each other. M In this case, first, the M-th optical signal Sλ M is output from the M-th second collimator 20(M) and reaches the M-th wavelength selection filter 40(M). The optical signal Sλ M passes through the wavelength selection filter 40(M) and reaches the (M-1)-th wavelength selection filter 40(M-1), and is reflected by the multilayer film 42 of the wavelength selection filter 40(M-1).

[0064] At the same time, the (M-1)-th optical signal Sλ M-1 is output from the (M-1)-th second collimator 20(M-1) and reaches the wavelength selection filter 40(M-1). The optical signal Sλ M-1 passes through the wavelength selection filter 40(M-1) and is multiplexed with the optical signal Sλ M . The multiplexed light reaches the (M-2)-th wavelength selection filter 40(M-2) and is reflected by the multilayer film 42 of the wavelength selection filter 40(M-2).

[0065] At the same time, the (M-2)-th optical signal Sλ M-2 is output from the (M-2)-th second collimator 20(M-2) and reaches the wavelength selection filter 40(M-2). The optical signal Sλ M-2 passes through the wavelength selection filter 40(M-2) and is multiplexed with the optical signals Sλ M and Sλ M-1 . Thereafter, in the same manner, the optical signals are sequentially multiplexed up to the first optical signal Sλ1, and a wavelength-division multiplexed optical signal is generated. The generated wavelength-division multiplexed optical signal reaches the first collimator 10 from the wavelength selection filter 40(1) and is output to the outside of the wavelength multiplexer / demultiplexer 1 via the optical fiber 11.

[0066] Referring to FIG. 9, the operation of the wavelength multiplexer / demultiplexer 1 when demultiplexing a plurality of optical signals will be described. FIG. 9 shows the operation of the wavelength multiplexer / demultiplexer 1 when demultiplexing M optical signals Sλ1 to Sλ that have different wavelengths from each other. MIt is a diagram showing the operation of the wavelength multiplexer / demultiplexer 1 when demultiplexing. In this case, first, the wavelength-division multiplexed optical signal including the optical signals Sλ1 to Sλ M is output from the first collimator 10 and reaches the wavelength selection filter 40(1). The first optical signal Sλ1 passes through the wavelength selection filter 40(1) and is output to the outside of the wavelength multiplexer / demultiplexer 1 via the optical fiber 21 of the second collimator 20(1).

[0067] The remaining optical signals Sλ2 to Sλ M are reflected by the multilayer film 42 of the wavelength selection filter 40(1) and reach the wavelength selection filter 40(2). The second optical signal Sλ2 passes through the wavelength selection filter 40(2) and is output to the outside of the wavelength multiplexer / demultiplexer 1 via the optical fiber 21 of the second collimator 20(2). The remaining optical signals Sλ3 to Sλ M are reflected by the multilayer film 42 of the wavelength selection filter 40(2) and reach the third wavelength selection filter 40(3). Thereafter, the optical signals Sλ M are sequentially demultiplexed in the same manner until, and each optical signal Sλ1 to Sλ M is output to the outside of the wavelength multiplexer / demultiplexer 1.

[0068] The effects obtained by the wavelength multiplexer / demultiplexer 1 of the present embodiment described above will be described together with the problems of the conventional wavelength multiplexer / demultiplexer. First, the wavelength selection filter 140 of the conventional wavelength multiplexer / demultiplexer will be described with reference to FIG. 28. FIG. 28 is a diagram showing the wavelength selection filter 140 provided in the conventional wavelength multiplexer / demultiplexer. FIG. 28 shows how the shape of the wavelength selection filter 140 is deformed as the environmental temperature changes. In the (a) part of FIG. 28, the wavelength selection filter 140 under a room temperature (for example, 25°C) environment is shown, in the (b) part, the wavelength selection filter 140 under a temperature lower than the room temperature (for example, -40°C) environment is shown, and in the (c) part, the wavelength selection filter 140 under a temperature higher than the room temperature (for example, 85°C) environment is shown.

[0069] The wavelength selection filter 140 has the same configuration as the above-described wavelength selection filters 40(1) to 40(M). Specifically, the wavelength selection filter 140 has a substrate 141, a multilayer film 142, and an antireflection film 143, and is fixed to the mounting surface 151 of the base plate 150 by a joining member 160. The conventional wavelength multiplexer is different from the wavelength multiplexer 1 in that the joining member 160 is in contact with the multilayer film 142 and the antireflection film 143 of the wavelength selection filter 140. The joining member 160 is in contact with the bottom surface 141c of the substrate 141, the multilayer film 142, and the antireflection film 143.

[0070] As shown in part (a) of FIG. 28, in a room temperature environment, the tangent plane H2 of the second surface 142b at the intersection of the second surface 142b of the multilayer film 142 and the optical axis AX2 of the optical signal incident on the wavelength selection filter 140 is perpendicular to the optical axis AX2. On the other hand, as shown in parts (b) and (c), in a low temperature environment and a high temperature environment, the tangent plane H2 is inclined with respect to the optical axis AX2. As described above, the substrate 141 is formed of a material having a relatively large linear expansion coefficient. The multilayer film 142 deforms following the thermal deformation of the substrate 141 due to a change in the environmental temperature. In a low temperature environment, the multilayer film 142 deforms so that the curvature increases, and in a high temperature environment, the curvature of the multilayer film 142 decreases. At this time, since the end portion of the wavelength selection filter 140 near the base plate 150 is fixed (constrained) to the mounting surface 151 of the base plate 150 by the joining member 160, in a low temperature environment, the tangent plane H2 is inclined so that the angle (angle α in FIG. 28) formed with the optical axis AX2 is larger than 90°. In a high temperature environment, the tangent plane H2 is inclined so that the angle α formed with the optical axis AX2 is smaller than 90°. That is, in a low temperature environment, the multilayer film 142 inclines away from the mounting surface 151, and in a high temperature environment, the multilayer film 142 inclines closer to the mounting surface 151. Such an unintended inclination of the multilayer film 142 due to a temperature change causes an optical path shift of the optical signal reflected from the wavelength selection filter 140 and increases the insertion loss by the wavelength selection filter 140.

[0071] In contrast, in the wavelength multiplexer / demultiplexer 1 according to the present embodiment, in at least one of the M wavelength selection filters 40(1) to 40(M), the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42. Since the joining member 60 is non-contact with the multilayer film 42, the multilayer film 42 is not restricted by the joining member 60 to the mounting surface 51 of the base plate 50. Therefore, when thermal deformation of the substrate 41 occurs due to a change in the environmental temperature, the stress generated in the multilayer film 42 is reduced. As a result, in the wavelength multiplexer / demultiplexer 1, the inclination of the multilayer film 42 when the environmental temperature changes is suppressed. Thus, in the wavelength multiplexer / demultiplexer 1, even when the environmental temperature changes, it is difficult for an optical path shift of the optical signal reflected by the wavelength selection filters 40(1) to 40(M) to occur, and an increase in insertion loss due to the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0072] Further, in the present embodiment, the adhesive constituting the joining member 60 contains an ultraviolet curable resin. In this case, the adhesive can be quickly cured by irradiating ultraviolet rays to the adhesive. Therefore, during the process of curing the adhesive, it is difficult for the position and orientation of the wavelength selection filters 40(1) to 40(M) to shift, and an increase in insertion loss due to the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0073] Further, in the present embodiment, the adhesive constituting the joining member 60 may contain a filler 65 made of silica. In this case, since silica is a material having a relatively small coefficient of linear expansion, thermal deformation of the joining member 60 due to a change in the environmental temperature is suppressed. Therefore, even when the environmental temperature changes, it is difficult for the position and orientation of the wavelength selection filters 40(1) to 40(M) fixed by the joining member 60 to shift, and an increase in insertion loss due to the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0074] In addition, in the present embodiment, the content of the filler 65 with respect to the volume of the adhesive constituting the joining member 60 may be 50% by volume or more. In this case, the thermal deformation of the joining member 60 due to changes in the environmental temperature is further suppressed. Therefore, when the environmental temperature changes, the displacement of the positions and orientations of the wavelength selection filters 40(1) to 40(M) is less likely to occur, and an increase in the insertion loss caused by the wavelength selection filters 40(1) to 40(M) can be further suppressed.

[0075] In addition, in the present embodiment, the distance between the bottom surface 41c of the substrate 41 and the mounting surface 51 of the base plate 50 may be 50 μm or more. In this case, it is difficult for the influence of the thermal deformation of the base plate 50 due to changes in the environmental temperature to reach the wavelength selection filters 40(1) to 40(M). Specifically, the influence of the thermal deformation of the base plate 50 can be absorbed by the joining member 60. Therefore, even when the environmental temperature changes, the displacement of the positions and orientations of the wavelength selection filters 40(1) to 40(M) is less likely to occur, and an increase in the insertion loss caused by the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0076] In addition, in the present embodiment, the linear expansion coefficient of the base plate 50 may be 15.0×10 -6 (1 / K) or less. In this case, the thermal deformation of the base plate 50 due to changes in the environmental temperature is suppressed. Therefore, even when the environmental temperature changes, the displacement of the positions and orientations of the wavelength selection filters 40(1) to 40(M) arranged on the base plate 50 is less likely to occur, and an increase in the insertion loss caused by the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0077] In addition, in the present embodiment, in at least any one of the wavelength selection filters 40(1) to 40(M / 2) from the first to the (M / 2)-th, the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42. For example, as described with reference to FIG. 9, a plurality of optical signals Sλ1 to Sλ MWhen demultiplexing a wavelength-division multiplexed optical signal including [it] while sequentially transmitting it from the wavelength selection filter 40(1) to the wavelength selection filter 40(M), the displacement in position and orientation of the wavelength selection filters arranged on the upstream side of the optical path (for example, the wavelength selection filters 40(1) to 40(M / 2)) increases the insertion loss significantly compared to the displacement in position and orientation of the wavelength selection filters arranged on the downstream side of the optical path (for example, the wavelength selection filters 40(M / 2 + 1) to 40(M)). In the wavelength multiplexer / demultiplexer 1 according to the present embodiment, in at least any one of the first to (M / 2)-th wavelength selection filters 40(1) to 40(M / 2) arranged on the upstream side of the optical path, the joining member 60 is non-contact with the multilayer film 42. Therefore, it is difficult for displacement in position and orientation to occur in the wavelength selection filters 40(1) to 40(M / 2) arranged on the upstream side of the optical path, and an increase in insertion loss due to the wavelength selection filters 40(1) to 40(M) can be effectively suppressed.

[0078] Also, in the present embodiment, the number of wavelength selection filters 40(1) to 40(M) in which the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the multilayer film 42 is (M / 2) or more. In this case, an increase in insertion loss due to the wavelength selection filters 40(1) to 40(M) can be more reliably suppressed.

[0079] Also, in the present embodiment, the wavelength multiplexer / demultiplexer 1 further includes a housing 70 in which the first collimator 10, M second collimators 20(1) to 20(M), M wavelength selection filters 40(1) to 40(M), and a base plate 50 are housed in the internal space S. The internal space S is sealed and further filled with an inert gas. In this case, for example, oxidation of the base plate 50 housed in the internal space S can be suppressed, and deterioration of the characteristics of the wavelength multiplexer / demultiplexer 1 can be suppressed.

[0080] <First Modified Example> Referring to FIGS. 10 and 11, a first modification of the wavelength multiplexer according to the first embodiment will be described. FIG. 10 is a perspective view showing wavelength selection filters 40(1) to 40(M) according to the first modification. FIG. 11 is a view of the wavelength selection filters 40(1) to 40(M) according to the first modification as seen from the antireflection film 43 side.

[0081] In this modification, the bonding member 60 is in contact not only with the bottom surface 41c of the substrate 41 but also with the second surface 43b and the third surface 43c of the antireflection film 43. The bonding member 60 is in direct contact with the second surface 43b and the third surface 43c. FIG. 11 shows the center C1 of the second main surface 41b of the substrate 41 when viewed from the X direction and a virtual circle H3 centered on the center C1. The optical signals transmitted through the wavelength selection filters 40(1) to 40(M) pass through, for example, the center C1. In this embodiment, the radius of the virtual circle H3 is 300 μm. The contact portion 61 of the bonding member 60 in contact with the antireflection film 43 is located outside the virtual circle H3 when viewed from the X direction. That is, the contact portion 61 is located more than 300 μm away from the center C1 of the second main surface 41b when viewed from the X direction.

[0082] In this modification, the bonding member 60 is in contact with the second surface 43b and the third surface 43c of the antireflection film 43. In this case, the contact area between the wavelength selection filters 40(1) to 40(M) and the bonding member 60 increases, and the wavelength selection filters 40(1) to 40(M) are firmly fixed to the base plate 50 by the bonding member 60. Therefore, even when a physical external force is applied to the wavelength selection filters 40(1) to 40(M), for example, it is difficult for the position and orientation of the wavelength selection filters 40(1) to 40(M) to shift, and an increase in insertion loss due to the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0083] Further, in this modified example, the contact portion 61 of the bonding member 60 that is in contact with the antireflection film 43 is located more than 300 μm away from the center C1 of the second main surface 41b when viewed in the X direction. In this case, since the contact portion 61 of the bonding member 60 is located at a certain distance from the center C1 of the second main surface 41b, it is possible to suppress the light signal passing through the wavelength selection filters 40(1) to 40(M) from being blocked by the bonding member 60.

[0084] <Second Modified Example> Referring to FIG. 12, a second modified example of the wavelength multiplexer according to the first embodiment will be described. FIG. 12 is a perspective view showing the wavelength selection filters 40(1) to 40(M) according to the second modified example. In the second modified example, the bonding member 60 is in contact with not only the bottom surface 41c of the substrate 41 but also the first side surface 41e and the second side surface 41f of the substrate 41. The bonding member 60 is in direct contact with the first side surface 41e and the second side surface 41f.

[0085] In this modified example, the bonding member 60 is in contact with the first side surface 41e and the second side surface 41f of the substrate 41. In this case, the contact area between the wavelength selection filters 40(1) to 40(M) and the bonding member 60 increases, and the wavelength selection filters 40(1) to 40(M) are firmly fixed to the base plate 50 by the bonding member 60. Therefore, even when a physical external force is applied to the wavelength selection filters 40(1) to 40(M), for example, it is difficult for the positions and orientations of the wavelength selection filters 40(1) to 40(M) to deviate, and an increase in the insertion loss due to the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0086] <Third Modified Example> Referring to FIG. 13, a third modified example of the wavelength multiplexer according to the first embodiment will be described. FIG. 13 is a perspective view showing the wavelength selection filters 40(1) to 40(M) according to the third modified example.

[0087] In this modification example, the joining member 60 is in contact with not only the bottom surface 41c of the substrate 41, but also the second surface 43b and the third surface 43c of the antireflection film 43, and the first side surface 41e and the second side surface 41f of the substrate 41. The joining member 60 is in direct contact with the second surface 43b and the third surface 43c, and the first side surface 41e and the second side surface 41f. Similar to the first modification example, the contact portion 61 of the joining member 60 in contact with the antireflection film 43 is located more than 300 μm away from the center C1 of the second main surface 41b when viewed in the X direction.

[0088] In this modification example, the joining member 60 is in contact with the second surface 43b and the third surface 43c of the antireflection film 43, and the first side surface 41e and the second side surface 41f of the substrate 41. In this case, the contact area between the wavelength selection filters 40(1) to 40(M) and the joining member 60 increases, and the wavelength selection filters 40(1) to 40(M) are firmly fixed to the base plate 50 by the joining member 60. Therefore, for example, even when a physical external force is applied to the wavelength selection filters 40(1) to 40(M), it is difficult for the positions and orientations of the wavelength selection filters 40(1) to 40(M) to deviate, and an increase in the insertion loss caused by the wavelength selection filters 40(1) to 40(M) can be suppressed.

[0089] Also, in this modification example, the contact portion 61 of the joining member 60 in contact with the antireflection film 43 is located more than 300 μm away from the center C1 of the second main surface 41b when viewed in the X direction. In this case, since the contact portion 61 of the joining member 60 is located at a certain distance from the center C1 of the second main surface 41b, it is possible to suppress the light signal passing through the wavelength selection filters 40(1) to 40(M) from being blocked by the joining member 60.

[0090] <Second Embodiment> Referring to FIGS. 14 to 16, the wavelength multiplexer according to the second embodiment will be described. FIG. 14 is a perspective view showing wavelength selection filters 40A(1) to 40A(M) according to the second embodiment. FIG. 15 is a cross-sectional view of the wavelength selection filters 40A(1) to 40A(M) according to the second embodiment. FIG. 16 is a view of the wavelength selection filters 40A(1) to 40A(M) as seen from the multilayer film 42 side according to the second embodiment. In the following description, the differences from the wavelength selection filters 40(1) to 40(M) according to the first embodiment will be mainly described, and the description of the similar points will be omitted.

[0091] The wavelength selection filters 40A(1) to 40A(M) have a substrate 41A, a multilayer film 42, and an antireflection film 43, similar to the wavelength selection filters 40(1) to 40(M). The substrate 41A has a first main surface 410a, a second main surface 41b, a bottom surface 41c, a first side surface 41e, and a second side surface 41f. As shown in FIG. 15, the first main surface 410a of the substrate 41A includes a first portion 411 facing the second main surface 41b in the X direction and a second portion 412 extending inclined with respect to the first portion 411 and the bottom surface 41c.

[0092] The first portion 411 has a convex curved surface shape facing outward of the substrate 41. The second portion 412 is a flat surface inclined with respect to the X direction and the Z direction. The second portion 412 is located closer to the bottom surface 41c than the first portion 411 and connects the first portion 411 and the bottom surface 41c. The second portion 412 is formed, for example, by chamfering the corner of the substrate 41A. FIG. 16 shows the center C2 of the first main surface 410a of the substrate 41A as seen from the X direction and a virtual circle H4 centered on the center C2. The optical signal transmitted through the wavelength selection filters 40A(1) to 40A(M) passes through, for example, the center C2. In this embodiment, the radius of the virtual circle H4 is 300 μm. The second portion 412 is located outside the virtual circle H4 as seen from the X direction. That is, the second portion 412 is located more than 300 μm away from the center C2 of the first main surface 410a as seen from the X direction.

[0093] The multilayer film 42 is formed on the first portion 411 and is not formed on the second portion 412. That is, the second portion 412 includes an exposed area that is exposed from the multilayer film 42. In the present embodiment, the entire second portion 412 corresponds to the exposed area. As an example, the multilayer film 42 may be formed by removing, by etching, the portion located on the second portion 412 after being formed on the first portion 411 and the second portion 412.

[0094] The joining member 60 is in contact with the bottom surface 41c of the substrate 41 and the second portion 412 of the first main surface 410a, and is not in contact with the multilayer film 42. The joining member 60 is in direct contact with the bottom surface 41c and the second portion 412. The contact portion 62 of the joining member 60 that is in contact with the exposed area (second portion 412) is located outside the virtual circle H4 when viewed in the X direction. That is, the contact portion 62 is located more than 300 μm away from the center C2 of the first main surface 410a when viewed in the X direction.

[0095] In the present embodiment, the first main surface 410a of the substrate 41A includes an exposed area where the multilayer film 42 is not formed, and the joining member 60 is in contact with the exposed area. Also, in the present embodiment, the first main surface 410a includes a first portion 411 that faces the second main surface 41b in the X direction, and a second portion 412 that extends inclined with respect to the first portion 411 and the bottom surface 41c of the substrate 41A and connects the first portion 411 and the bottom surface 41c. The second portion 412 includes the exposed area. In this case, since the joining member 60 is in contact not only with the bottom surface 41c of the substrate 41A but also with a part of the first main surface 410a, the contact area between the wavelength selection filters 40A(1) to 40A(M) and the joining member 60 increases, and the wavelength selection filters 40A(1) to 40A(M) are firmly fixed to the base plate 50 by the joining member 60. Therefore, for example, even when a physical external force is applied to the wavelength selection filters 40A(1) to 40A(M), it is difficult for the position and orientation of the wavelength selection filters 40A(1) to 40A(M) to deviate, and an increase in insertion loss due to the wavelength selection filters 40A(1) to 40A(M) can be suppressed.

[0096] In addition, in the present embodiment, the contact portion 62 in contact with the exposed region of the joining member 60 is located more than 300 μm away from the center C2 of the first main surface 410a when viewed in the X direction. In this case, since the contact portion 62 of the joining member 60 is located at a certain distance from the center C2 of the first main surface 410a, it is possible to suppress the optical signal passing through the wavelength selection filters 40A(1) to 40A(M) from being blocked by the joining member 60.

[0097] <First Modified Example> With reference to FIG. 17, a first modified example of the wavelength multiplexer according to the second embodiment will be described. FIG. 17 is a perspective view showing the wavelength selection filters 40A(1) to 40A(M) according to the first modified example.

[0098] In this modified example, the joining member 60 is in contact with not only the bottom surface 41c of the substrate 41A and the second portion 412 of the first main surface 410a, but also the second surface 43b and the third surface 43c of the antireflection film 43. The joining member 60 is in direct contact with the second surface 43b and the third surface 43c. The contact portion 61 of the joining member 60 in contact with the antireflection film 43 is located more than 300 μm away from the center C1 of the second main surface 41b when viewed in the X direction.

[0099] In this modified example, the joining member 60 is in contact with the second surface 43b and the third surface 43c of the antireflection film 43. In this case, the contact area between the wavelength selection filters 40A(1) to 40A(M) and the joining member 60 increases, and the wavelength selection filters 40A(1) to 40A(M) are firmly fixed to the base plate 50 by the joining member 60. Therefore, for example, even when a physical external force is applied to the wavelength selection filters 40A(1) to 40A(M), it is difficult for the position and orientation of the wavelength selection filters 40A(1) to 40A(M) to deviate, and an increase in the insertion loss due to the wavelength selection filters 40A(1) to 40A(M) can be suppressed.

[0100] In addition, in this modified example, the contact portion 61 of the bonding member 60 that contacts the antireflection film 43 is located at a distance of 300 μm or more from the center C1 of the second main surface 41b when viewed in the X direction. In this case, since the contact portion 61 of the bonding member 60 is located at a certain distance from the center C1 of the second main surface 41b, it is possible to suppress the light signal passing through the wavelength selection filters 40A(1) to 40A(M) from being blocked by the bonding member 60.

[0101] <Second Modified Example> Referring to FIG. 18, a second modified example of the wavelength multiplexer according to the second embodiment will be described. FIG. 18 is a perspective view showing the wavelength selection filters 40A(1) to 40A(M) according to the second modified example. In the second modified example, the bonding member 60 is in contact with not only the bottom surface 41c of the substrate 41A and the second portion 412 of the first main surface 410a, but also the first side surface 41e and the second side surface 41f of the substrate 41A. The bonding member 60 is in direct contact with the first side surface 41e and the second side surface 41f.

[0102] In this modified example, the bonding member 60 is in contact with the first side surface 41e and the second side surface 41f of the substrate 41A. In this case, the contact area between the wavelength selection filters 40A(1) to 40A(M) and the bonding member 60 increases, and the wavelength selection filters 40A(1) to 40A(M) are firmly fixed to the base plate 50 by the bonding member 60. Therefore, for example, even when a physical external force is applied to the wavelength selection filters 40A(1) to 40A(M), it is difficult for the position and orientation of the wavelength selection filters 40A(1) to 40A(M) to shift, and an increase in insertion loss due to the wavelength selection filters 40A(1) to 40A(M) can be suppressed.

[0103] <Third Modified Example> Referring to FIGS. 19 and 20, a third modified example of the wavelength multiplexer according to the second embodiment will be described. FIG. 19 is a perspective view showing the wavelength selection filters 40A(1) to 40A(M) according to the third modified example. FIG. 20 is a cross-sectional view of the wavelength selection filters 40A(1) to 40A(M) according to the third modified example.

[0104] In this modified example, the joining member 60 is in contact with not only the bottom surface 41c of the substrate 41A and the second portion 412 of the first main surface 410a, but also the second surface 43b and the third surface 43c of the antireflection film 43, and the first side surface 41e and the second side surface 41f of the substrate 41A. The joining member 60 is in direct contact with the second surface 43b and the third surface 43c, and the first side surface 41e and the second side surface 41f. Similar to the first modified example, the contact portion 61 of the joining member 60 in contact with the antireflection film 43 is located at a distance of 300 μm or more from the center C1 of the second main surface 41b when viewed in the X direction.

[0105] In this modified example, the joining member 60 is in contact with the second surface 43b and the third surface 43c of the antireflection film 43, and the first side surface 41e and the second side surface 41f of the substrate 41A. In this case, the contact area between the wavelength selective filters 40A(1) to 40A(M) and the joining member 60 increases, and the wavelength selective filters 40A(1) to 40A(M) are firmly fixed to the base plate 50 by the joining member 60. Therefore, for example, even when a physical external force is applied to the wavelength selective filters 40A(1) to 40A(M), it is difficult for the position and orientation of the wavelength selective filters 40A(1) to 40A(M) to deviate, and an increase in the insertion loss caused by the wavelength selective filters 40A(1) to 40A(M) can be suppressed.

[0106] Also, in this modified example, the contact portion 61 of the joining member 60 in contact with the antireflection film 43 is located at a distance of 300 μm or more from the center C1 of the second main surface 41b when viewed in the X direction. In this case, since the contact portion 61 of the joining member 60 is located at a certain distance from the center C1 of the second main surface 41b, it is possible to suppress the light signal passing through the wavelength selective filters 40A(1) to 40A(M) from being blocked by the joining member 60.

[0107] <Third Embodiment> Referring to FIG. 21, the wavelength multiplexer / demultiplexer according to the third embodiment will be described. FIG. 21 is a schematic cross-sectional view of the wavelength multiplexer / demultiplexer 1B according to the third embodiment. In the following description, the differences from the wavelength multiplexer / demultiplexer 1 according to the first embodiment will be mainly described, and the description of the same points will be omitted.

[0108] The wavelength multiplexer / demultiplexer 1B includes a first collimator 10, M second collimators 20(1) to 20(M), M wavelength selection filters 40(1) to 40(M), a base plate 50B, a joining member 60, and a housing 70. The wavelength multiplexer / demultiplexer 1B is different from the wavelength multiplexer / demultiplexer 1 of the first embodiment in terms of the configuration of the base plate 50B.

[0109] The mounting surface 51B of the base plate 50B has a first mounting portion 52a and a pair of second mounting portions 52b. The first mounting portion 52a is located between the pair of second mounting portions 52b in the X direction. The first mounting portion 52a and the second mounting portions 52b extend flatly along the X direction and the Y direction. The height of the first mounting portion 52a in the Z direction with reference to the bottom plate 73 of the housing 70 is different from the height of the second mounting portions 52b. The first mounting portion 52a is located farther from the bottom plate 73 than the second mounting portions 52b. That is, the thickness of the portion of the base plate 50 corresponding to the first mounting portion 52a is larger than the thickness of the portion corresponding to the second mounting portions 52b. The first mounting portion 52a and the pair of second mounting portions 52b are connected by a pair of stepped surfaces 52c.

[0110] The wavelength selection filters 40(1) to 40(M) are mounted on the first mounting portion 52a, and the second collimators 20(1) to 20(M) are mounted on the pair of second mounting portions 52b. Specifically, the odd-numbered second collimators 20(1), 20(3), ···, 20(M - 1) are mounted on one of the second mounting portions 52b, and the even-numbered second collimators 20(2), 20(4), ···, 20(M) are mounted on the other second mounting portion 52b. The first collimator 10 (see FIG. 1) is further mounted on the other second mounting portion 52b.

[0111] In this embodiment, the base plate 50B has a first mounting portion 52a and a second mounting portion 52b that are at different heights from the bottom plate 73. The wavelength selection filters 40(1) to 40(M) are mounted on the first mounting portion 52a, and the first collimator 10 and the second collimators 20(1) to 20(M) are mounted on the second mounting portion 52b. In this case, the wavelength selection filters 40(1) to 40(M) mounted on the first mounting portion 52a and the first collimator 10 and the second collimators 20(1) to 20(M) mounted on the second mounting portion 52b can be properly optically coupled. For example, generally, since the sizes of the wavelength selection filters 40(1) to 40(M) in the Z direction are smaller than the sizes of the first collimator 10 and the second collimators 20(1) to 20(M), by designing the base plate 50 such that the first mounting portion 52a is higher than the second mounting portion 52b, the optical axes of the wavelength selection filters 40(1) to 40(M) and the optical axes of the first collimator 10 and the second collimators 20(1) to 20(M) can be properly aligned.

[0112] <Fourth Embodiment> Referring to FIG. 22, the wavelength multiplexer / demultiplexer according to the fourth embodiment will be described. FIG. 22 is a schematic cross-sectional view of the wavelength multiplexer / demultiplexer 1C according to the fourth embodiment. In the following description, the differences from the wavelength multiplexer / demultiplexer 1 according to the first embodiment will be mainly described, and the description of the same points will be omitted.

[0113] The wavelength multiplexer / demultiplexer 1C includes a first collimator 10, M second collimators 20(1) to 20(M), M wavelength selection filters 40(1) to 40(M), a base plate 50C, a joining member 60, and a housing 70. The wavelength multiplexer / demultiplexer 1C is different from the wavelength multiplexer / demultiplexer 1 of the first embodiment in terms of the configuration of the base plate 50C.

[0114] The base plate 50C has a main base plate 55 disposed on the bottom plate 73 of the housing 70, a first base plate 56 disposed on the main base plate 55, and a pair of second base plates 57. The main base plate 55, the first base plate 56, and the second base plates 57 are plate-like members extending along the X direction and the Y direction. The main base plate 55 is fixed to the bottom plate 73, and the first base plate 56 and the second base plates 57 are fixed to the main base plate 55. The first base plate 56 is separate from the pair of second base plates 57 and is located between the pair of second base plates 57 in the X direction.

[0115] The first base plate 56 has a mounting surface 56a on which the wavelength selection filters 40(1) to 40(M) are mounted. The mounting surface 56a extends flatly along the X direction and the Y direction. Each of the pair of second base plates 57 has a mounting surface 57b on which the second collimators 20(1) to 20(M) are mounted. The mounting surface 57b extends flatly along the X direction and the Y direction. The odd-numbered second collimators 20(1), 20(3), ···, 20(M - 1) are mounted on the mounting surface 57b of one of the second base plates 57, and the even-numbered second collimators 20(2), 20(4), ···, 20(M) are mounted on the mounting surface 57b of the other second base plate 57. The first collimator 10 (see FIG. 1) is further mounted on the mounting surface 57b of the other second base plate 57.

[0116] The height of the mounting surface 56a in the Z direction with reference to the bottom plate 73 of the housing 70 is different from the height of the mounting surface 57b. The mounting surface 56a is located farther from the bottom plate 73 than the mounting surface 57b. That is, the thickness of the first base plate 56 is larger than the thickness of the second base plate 57.

[0117] In this embodiment, the base plate 50C includes a first base plate 56 on which M wavelength selection filters 40(1) to 40(M) are mounted, and a second base plate 57 that is separate from the first base plate 56 and on which the first collimator 10 and M second collimators 20(1) to 20(M) are mounted. In this case, it is possible to independently design the first base plate 56 on which the wavelength selection filters 40(1) to 40(M) are mounted and the second base plate 57 on which the first collimator 10 and the second collimators 20(1) to 20(M) are mounted. Thereby, the degree of freedom in arranging the wavelength selection filters 40(1) to 40(M), the first collimator 10, and the second collimators 20(1) to 20(M) can be improved.

[0118] <Fifth Embodiment> Referring to FIG. 23, the wavelength multiplexer according to the fifth embodiment will be described. FIG. 23 is a schematic diagram showing the configuration of the wavelength multiplexer 1D according to the fifth embodiment. In the following description, the differences from the wavelength multiplexer 1 according to the first embodiment will be mainly described, and the description of the same points will be omitted.

[0119] The wavelength multiplexer 1D further includes a third collimator 30 in addition to the configuration of the wavelength multiplexer 1 of the first embodiment. The third collimator 30 can be used as an upgrade port. The configuration of the third collimator 30 is the same as that of the first collimator 10. The third collimator 30 is disposed to face the second main surface 41b of the substrate 41 of the wavelength selection filter 40(M), and is optically coupled to the second main surface 41b of the substrate 41 of the wavelength selection filter 40(M) via a space.

[0120] In this embodiment, the wavelength multiplexer 1D further includes a third collimator 30 optically coupled to the M-th wavelength selection filter 40(M). In this case, by using the third collimator 30 as an upgrade port, the number of channels of the wavelength multiplexer 1D can be increased as needed.

[0121] <Sixth Embodiment> Referring to FIGS. 24 and 25, the wavelength multiplexer / demultiplexer according to the sixth embodiment will be described. FIG. 24 is a schematic plan view of the wavelength multiplexer / demultiplexer 1E according to the sixth embodiment. FIG. 25 is a schematic cross-sectional view of the wavelength multiplexer / demultiplexer 1E shown in FIG. 24. In the following description, the differences from the wavelength multiplexer / demultiplexer 1 according to the first embodiment will be mainly described, and the description of the same points will be omitted.

[0122] The wavelength multiplexer / demultiplexer 1E includes a first collimator 10, M second collimators 20(1) to 20(M), M wavelength selection filters 40(1) to 40(M), a base plate 50E, a joining member 60, a housing 70E, and an optical element 80. The base plate 50E has a first mounting surface 58a and a second mounting surface 58b that face each other in the Z direction. The first mounting surface 58a and the second mounting surface 58b extend flatly along the X direction and the Y direction. The first mounting surface 58a is located closer to the bottom plate 73 than the second mounting surface 58b. A hole 58c that opens on the first mounting surface 58a and the second mounting surface 58b is formed in the base plate 50E. The hole 58c is formed in a rectangular shape having a long side along the Y direction when viewed from the Z direction. An optical element 80, which will be described later, is disposed inside the hole 58c.

[0123] On the first placement surface 58a, a first collimator 10, odd-numbered second collimators 20(1), 20(3), ···, 20(M - 1), and odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) are placed. On the second placement surface 58b, even-numbered second collimators 20(2), 20(4), ···, 20(M) and even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M) are placed. That is, the odd-numbered second collimators 20(1), 20(3), ···, 20(M - 1) are different in position in the Z direction from the even-numbered second collimators 20(2), 20(4), ···, 20(M). Similarly, the odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) are different in position in the Z direction from the even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M). The base plate 50E is disposed between the odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) and the even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M). When viewed from the Z direction, the second collimators 20(1) to (M) are arranged in a row along the Y direction in this order. Similarly, when viewed from the Z direction, the wavelength selection filters 40(1) to 40(M) are arranged in a row along the Y direction in this order.

[0124] When viewed from the Z direction, the odd-numbered second collimators 20(1), 20(3), ···, 20(M - 1) may be arranged so as to overlap a part of the even-numbered second collimators 20(2), 20(4), ···, 20(M). Similarly, when viewed from the Z direction, the odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) may be arranged so as to overlap a part of the even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M).

[0125] A plurality of through holes 74c are formed in the side wall 74 of the housing 70E. The optical fibers 11 and 21 are inserted into the plurality of through holes 74c. A plurality of convex portions 75 are formed on the inner surface of the side wall 74. As shown in FIG. 25, every two of the plurality of convex portions 75 form a pair, and the paired convex portions 75 are arranged in the Z direction. The end portion of the base plate 50E is sandwiched between the paired convex portions 75, and the base plate 50E is fixed to the housing 70E in a state of being separated from the bottom plate 73.

[0126] The optical element 80 is an element that changes the direction of the optical path, and is a prism in this embodiment. The optical element 80 may be, for example, a mirror. The optical element 80 has a reflecting surface 81 extending along the Y direction. The reflecting surface 81 changes the direction of the optical path connecting the first collimator 10 and the first second collimator 20(1), and the direction of the optical path connecting the m-th (m = 1, ···, M - 1) wavelength selection filters 40(1) to 40(M - 1) and the (m + 1)-th second collimator 20(2) to (M). The first collimator 10, the second collimators 20(1) to (M), and the wavelength selection filters 40(1) to 40(M) are located on the same side with respect to the reflecting surface 81 when viewed from the Z direction.

[0127] Optical signals Sλ1 to Sλ M When demultiplexing, first, a wavelength-division multiplexed optical signal including the optical signals Sλ1 to Sλ M is output from the first collimator 10 and reaches the reflecting surface 81 of the optical element 80. The wavelength-division multiplexed optical signal is reflected by the reflecting surface 81 and reaches the wavelength selection filter 40(1). The optical signal Sλ1 passes through the wavelength selection filter 40(1) and is output to the outside of the wavelength multiplexer / demultiplexer 1E through the second collimator 20(1). The remaining optical signals Sλ2 to Sλ M are reflected by the wavelength selection filter 40(1), reflected again by the reflecting surface 81, and then reach the wavelength selection filter 40(2). Thereafter, the optical signals Sλ M are demultiplexed one wavelength at a time until Sλ, and output to the outside of the wavelength multiplexer / demultiplexer 1E.

[0128] Optical signals Sλ1 to SλM When multiplexing, first, the optical signal Sλ M is output from the second collimator 20(M) and reaches the wavelength selection filter 40(M). The optical signal Sλ M passes through the wavelength selection filter 40(M) and reaches the reflecting surface 81. The optical signal Sλ M is reflected by the reflecting surface 81, then reaches the wavelength selection filter 40(M - 1), and is reflected again by the wavelength selection filter 40(M - 1). At the same time, the optical signal Sλ M-1 reaches the wavelength selection filter 40(M - 1) from the second collimator 20(M - 1). The optical signal Sλ M-1 passes through the wavelength selection filter 40(M - 1) and is multiplexed with the optical signal Sλ M . Thereafter, the optical signal Sλ1 is multiplexed in the same manner in sequence, and a wavelength-division multiplexed optical signal is generated. The generated wavelength-division multiplexed optical signal reaches the reflecting surface 81 from the wavelength selection filter 40(1), is reflected by the reflecting surface 81, and then reaches the first collimator 10. The wavelength-division multiplexed optical signal is output from the first collimator 10 to the outside of the wavelength multiplexer 1E.

[0129] In this embodiment, the wavelength multiplexer / demultiplexer 1E further includes an optical element 80 having a reflecting surface 81 extending along the Y direction when viewed from the Z direction. Each of the M second collimators 20(1) to 20(M) and the M wavelength selection filters 40(1) to 40(M) are arranged side by side along the Y direction when viewed from the Z direction. The first collimator 10, the second collimators 20(1) to 20(M), and the wavelength selection filters 40(1) to 40(M) are located on the same side of the reflecting surface 81 when viewed from the Z direction. The reflecting surface 81 changes the direction of the optical path connecting the first collimator 10 and the first second collimator 20(1), and the direction of the optical path connecting the m-th (m = 1, ···, M - 1) wavelength selection filters 40(1) to 40(M - 1) and the (m + 1)-th second collimators 20(2) to 20(M). In this case, compared with the case where the odd-numbered second collimators 20(1), 20(3), ···, 20(M - 1) and wavelength selection filters 40(1), 40(3), ···, 40(M - 1) and the even-numbered second collimators 20(2), 20(4), ···, 20(M) and wavelength selection filters 40(2), 40(4), ···, 40(M) are arranged to face each other, the wavelength multiplexer / demultiplexer 1E can be miniaturized.

[0130] In this embodiment, the odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) are different in position in the Z direction from the even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M). The base plate 50E is disposed between the odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) and the even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M). In this case, when viewed from the Z direction, the odd-numbered wavelength selection filters 40(1), 40(3), ···, 40(M - 1) can be arranged so as to overlap a part of the even-numbered wavelength selection filters 40(2), 40(4), ···, 40(M), and the wavelength multiplexer / demultiplexer 1E can be further miniaturized.

[0131] Referring to FIGS. 26 and 27, the simulation results regarding the variation in the tilt angle of the multilayer film and the variation in the insertion loss due to the change in the environmental temperature will be described. In this simulation, for wavelength selective filters with different contact modes of the joining members, the amount of variation in the tilt angle of the multilayer film and the amount of variation in the insertion loss were calculated when the environmental temperature changed from 25°C to 85°C. FIG. 26 is a schematic diagram showing the contact mode of the joining member with respect to the wavelength selective filter. FIG. 27 is a diagram showing the relationship between the contact mode of the joining member and the amount of variation in the tilt angle of the multilayer film and the amount of variation in the insertion loss.

[0132] FIG. 26 shows the contact mode of the joining member with respect to the wavelength selective filter assumed in this simulation. The contact mode (a) shown in part (a) of FIG. 26 is the contact mode of the joining member 160 in the conventional wavelength multiplexer / demultiplexer. The wavelength selective filter 140 shown in part (a) of FIG. 26 has the same configuration as the wavelength selective filters 40(1) to 40(M) according to the first embodiment described above. The contact mode (a) is a mode in which the joining member 160 is in contact with the entire bottom surface 140c of the wavelength selective filter 140. That is, in the contact mode (a), the joining member 160 is in contact with the bottom surface 141c of the substrate 141, the third surface 142c of the multilayer film 142, and the third surface 143c of the antireflection film 143.

[0133] The contact mode (b) shown in part (b) of FIG. 26 and the contact mode (c) shown in part (c) of FIG. 26 are the contact modes of the joining member 60 according to the present disclosure. Specifically, the contact mode (b) and the contact mode (c) are modes in which the joining member 60 is non-contact with the multilayer film 42. The wavelength selection filters 40 shown in parts (b) and (c) of FIG. 26 have the same configuration as the wavelength selection filters 40(1) to 40(M) according to the first embodiment. In the contact mode (b), the joining member 60 contacts the bottom surface 41c of the substrate 41 and the third surface 43c of the antireflection film 43 and is non-contact with the multilayer film 42. In the contact mode (b), the contact area between the joining member 60 and the bottom surface 40c of the wavelength selection filter 40 is 50% or more of the area of the entire bottom surface 40c. In the contact mode (c), the joining member 60 contacts the bottom surface 41c of the substrate 41 and is non-contact with the third surface 42c of the multilayer film 42 and the third surface 43c of the antireflection film 43. In the contact mode (c), the contact area between the joining member 60 and the bottom surface 40c of the wavelength selection filter 40 is 50% or less of the area of the entire bottom surface 40c.

[0134] In this simulation, similar to the wavelength multiplexer 1 according to the first embodiment, the number of the wavelength selection filter and the second collimator was set to 12 (M = 12), and the amount of variation in the tilt angle of the multilayer film and the amount of variation in the insertion loss IL when the environmental temperature changed from room temperature (25°C) to high temperature (85°C) were calculated. The amount of variation in the tilt angle of the multilayer film is the difference between the angle of the multilayer film with respect to the mounting surface in the room temperature environment and the angle of the multilayer film with respect to the mounting surface in the high temperature environment. Also, the amount of variation in the insertion loss IL was calculated based on the value of the insertion loss at the channel port corresponding to the twelfth second collimator 20(12).

[0135] In this simulation, a simulation was performed assuming a multilayer film of two types of configurations (Configuration 1 and Configuration 2) with different materials and the like. Graph A in FIG. 27 is a graph showing the amount of variation in the tilt angle of the wavelength selection filter having the multilayer film of Configuration 1, and Graph B is a graph showing the amount of variation in the tilt angle of the wavelength selection filter having the multilayer film of Configuration 2. Graph C in FIG. 27 is a graph showing the amount of variation in the insertion loss IL when using the wavelength selection filter having the multilayer film of Configuration 1, and Graph D is a graph showing the amount of variation in the insertion loss IL when using the wavelength selection filter having the multilayer film of Configuration 2. The horizontal axis in FIG. 27 indicates the contact mode of the joining member, and the vertical axis indicates the amount of variation in the tilt angle (unit: deg) and the amount of variation in the insertion loss IL (unit: dB).

[0136] As shown in FIG. 27, compared with the contact mode (a), the contact modes (b) and (c) have smaller amounts of variation in the tilt angle of the multilayer film 42 and the amount of variation in the insertion loss IL. Specifically, compared with the contact mode (a), in the contact mode (b), the amount of variation in the tilt angle is about 20% smaller, and the amount of variation in the insertion loss IL is about 40% smaller. Also, compared with the contact mode (a), in the contact mode (c), the amount of variation in the tilt angle is about 60% smaller, and the amount of variation in the insertion loss IL is about 80% smaller. From the results of this simulation, it can be confirmed that by adopting the contact mode in which the joining member 60 is non-contact with the multilayer film 42, the amount of variation in the tilt angle of the multilayer film 42 and the amount of variation in the insertion loss IL when the environmental temperature changes become smaller. Also, from the results of the contact mode (b) and the contact mode (c) in this simulation, it can be confirmed that the smaller the ratio of the contact area of the joining member 60 to the entire area of the bottom surface 40c of the wavelength selection filter 40, the smaller the amount of variation in the tilt angle of the multilayer film 42 and the amount of variation in the insertion loss IL when the environmental temperature changes.

[0137] As described above, the embodiments of the present disclosure have been described in detail, but the present disclosure is not limited to the above embodiments and can be applied to various embodiments. For example, in each of the above embodiments, the joining member 60 is a single joining member formed integrally, but the joining member 60 may be composed of a plurality of separated joining members.

[0138] In the above-described first embodiment, the multilayer film 42 was formed over the entire first main surface 41a of the substrate 41. However, the first main surface 41a may include an exposed region where the multilayer film 42 is not formed. In this case, the bonding member 60 may be in contact with the exposed region of the first main surface 41a.

[0139] In the above-described sixth embodiment (see FIG. 24), the optical element 80 was a single optical element formed integrally. However, the optical element 80 may be composed of a plurality of optical elements. In this case, the plurality of optical elements may be arranged along the Y direction.

[0140] In each of the above-described embodiments, the case where the wavelength selection filter is a DWDM filter has been exemplified. However, the wavelength selection filter may be a filter having an arbitrary wavelength interval, such as a coarse wavelength division multiplexing (CWDM) filter.

Explanation of Reference Numerals

[0141] 1, 1B, 1C, 1D, 1E... wavelength multiplexer / demultiplexer 10... first collimator 11... optical fiber (first optical waveguide) 12... first collimating lens 12a, 13a, 22a, 23a... first end face 12b, 13b, 22b, 23b... second end face 12c, 13c, 22c, 23c... outer peripheral surface 13, 23... ferrule 14, 24... capillary 14a, 24a... first opening 14b, 24b... second opening 14c, 24c... inner peripheral surface 15, 25... bonding member 20(1) to 20(12)... second collimator 21... optical fiber (second optical waveguide) 22... second collimating lens 30... third collimator 40, 40(1) to 40(12), 40A(1) to 40A(12), 140... Wavelength selection filter 40c, 140c... Bottom surface 41, 41A, 141... Substrate 41a, 410a... First main surface 41b... Second main surface 41c, 141c... Bottom surface 41e... First side surface 41f... Second side surface 42, 142... Multilayer film 42a... First surface 42b, 142b... Second surface 42c, 142c... Third surface 43, 143... Anti-reflection film 43a... First surface 43b... Second surface 43c, 143c... Third surface 50, 50B, 50C, 50E, 150... Base plate 51, 51B, 56a, 57b, 151... Mounting surface 52a... First mounting portion 52b... Second mounting portion 52c... Step surface 55... Main base plate 56... First base plate 57... Second base plate 58a... First mounting surface 58b... Second mounting surface 58c... Hole portion 60, 160... Joining member 61, 62... Contact portion 65... Filler 70, 70E... Housing 71a... Opening 72... Cover 73... Bottom plate 74... Side wall 74a... End face 74b... Recess 74c... Through hole 75... Protrusion 80... Optical element 81... Reflective surface 411... First part 412... Second part AX1…Optical axis AX2…Optical axis C1…Center C2…Center F(1)~F(12)…Transmission wavelength band H1…Virtual plane H2…Contact plane H3…Virtual circle H4…Virtual circle L11…First column L12…Second column L21…First column L22…Second column S…Internal space

Claims

1. A first collimator having a first optical waveguide and a collimating lens optically coupled to an end of the first optical waveguide, M (M is an integer of 2 or more) second collimators each having a second optical waveguide and a collimating lens optically coupled to an end of the second optical waveguide, M wavelength selection filters that transmit optical signals in different transmission wavelength bands and reflect optical signals in other wavelength bands excluding their respective transmission wavelength bands, A base plate having a mounting surface on which the M wavelength selection filters are mounted, Comprising, The optical path connecting the first collimator and the first of the second collimators passes through the first of the wavelength selection filters, The optical path connecting the m-th (m = 1,..., M - 1) wavelength selection filter and the (m + 1)-th second collimator passes through the (m + 1)-th wavelength selection filter, Each of the M wavelength selection filters includes an optically transparent substrate including a first main surface and a second main surface facing each other in a first direction, and a bottom surface connecting the first main surface and the second main surface and facing the mounting surface, and a multilayer film formed on the first main surface and configured to transmit an optical signal in a specific transmission wavelength band and reflect an optical signal in other wavelength bands excluding the specific transmission wavelength band, and is fixed to the mounting surface by a cured product of an adhesive, In at least one of the M wavelength selection filters, the cured product of the adhesive contacts the bottom surface and does not contact the multilayer film, The substrate includes a first side surface and a second side surface facing each other in a second direction intersecting the first direction, In the at least one wavelength selection filter, the cured product of the adhesive contacts the first side surface and the second side surface, wavelength multiplexer / demultiplexer.

2. A first collimator having a first optical waveguide and a collimating lens optically coupled to an end of the first optical waveguide, M (M is an integer of 2 or more) second collimators each having a second optical waveguide and a collimating lens optically coupled to an end of the second optical waveguide, M wavelength selection filters that transmit optical signals in different transmission wavelength bands and reflect optical signals in other wavelength bands excluding their respective transmission wavelength bands, A base plate having a mounting surface on which the M wavelength selection filters are mounted, Comprising, The optical path connecting the first collimator and the first second collimator passes through the first wavelength selection filter. The optical path connecting the m-th (m = 1,..., M - 1) wavelength selection filter and the (m + 1)-th second collimator passes through the (m + 1)-th wavelength selection filter. Each of the M wavelength selection filters includes a light-transmissive substrate having a first main surface and a second main surface facing each other in a first direction, and a bottom surface connecting the first main surface and the second main surface and facing the placement surface, and a multilayer film formed on the first main surface and configured to transmit an optical signal in a specific transmission wavelength band and reflect optical signals in other wavelength bands excluding the specific transmission wavelength band, and is fixed to the placement surface by a cured product of an adhesive. In at least one of the M wavelength selection filters, the cured product of the adhesive contacts the bottom surface and does not contact the multilayer film. Each of the M wavelength selection filters has an antireflection film formed on the second main surface and configured to prevent reflection of an optical signal on the second main surface. In the at least one wavelength selection filter, the cured product of the adhesive contacts the surface of the antireflection film facing the placement surface, wavelength multiplexer / demultiplexer.

3. The first main surface includes an exposed region where the multilayer film is not formed. The cured product of the adhesive contacts the exposed region. The wavelength multiplexer / demultiplexer according to claim 1 or claim 2.

4. The first main surface includes a first portion facing the second main surface in the first direction, and a second portion extending inclined with respect to the first portion and the bottom surface and connecting the first portion and the bottom surface. The second portion includes the exposed region. The wavelength multiplexer / demultiplexer according to claim 3.

5. The portion of the cured product of the adhesive contacting the exposed region is located more than 300 μm away from the center of the first main surface when viewed from the first direction. The wavelength multiplexer / demultiplexer according to claim 3 or claim 4.

6. In the at least one wavelength selection filter, the cured product of the adhesive contacts the surface of the antireflection film opposite to the second main surface. The wavelength multiplexer / demultiplexer according to claim 2.

7. The portion of the cured adhesive in contact with the antireflection film is located at a distance of 300 μm or more from the center of the second main surface when viewed from the first direction, according to the wavelength multiplexer of claim 2 or claim 6.

8. The wavelength multiplexer according to any one of claims 1 to 7, wherein the adhesive contains an ultraviolet curable resin.

9. The wavelength multiplexer according to any one of claims 1 to 8, wherein the adhesive contains a filler made of silica.

10. The wavelength multiplexer according to claim 9, wherein the content of the filler with respect to the volume of the adhesive is 50% by volume or more.

11. The wavelength multiplexer according to any one of claims 1 to 10, wherein the distance between the bottom surface and the placement surface is 50 μm or more.

12. The linear expansion coefficient of the base plate is 15.0×10 －６ (1 / K) or less. The wavelength multiplexer according to any one of claims 1 to 11.

13. The wavelength multiplexer according to any one of claims 1 to 12, further comprising a third collimator optically coupled to the Mth wavelength selection filter.

14. When viewed from the thickness direction of the base plate, it further comprises an optical element having a reflecting surface extending along a predetermined direction. Each of the M second collimators and the M wavelength selection filters are arranged side by side along the predetermined direction when viewed from the thickness direction of the base plate. The first collimator, the M second collimators, and the M wavelength selection filters are located on the same side with respect to the reflecting surface when viewed from the thickness direction of the base plate. The reflecting surface changes the direction of the optical path connecting the first collimator and the first second collimator, and the direction of the optical path connecting the mth (m = 1,..., M - 1) wavelength selection filter and the (m + 1)th second collimator, according to the wavelength multiplexer of any one of claims 1 to 13.

15. The odd-numbered wavelength selection filters are different in position in the thickness direction of the base plate from the even-numbered wavelength selection filters. The base plate is disposed between the odd-numbered wavelength selection filters and the even-numbered wavelength selection filters, according to the wavelength multiplexer of claim 14.

16. The at least one wavelength selection filter is at least any one of the wavelength selection filters from the first to the (M / 2)th, according to the wavelength multiplexer of any one of claims 1 to 15.

17. The number of the at least one wavelength selection filter is (M / 2) or more, and the wavelength multiplexer / demultiplexer according to any one of claims 1 to 16.

18. The base plate includes a first base plate on which the M wavelength selection filters are placed, and a second base plate that is separate from the first base plate and on which the first collimator and the M second collimators are placed, and the wavelength multiplexer / demultiplexer according to any one of claims 1 to 17.

19. The wavelength multiplexer / demultiplexer further includes a housing in which the first collimator, the M second collimators, the M wavelength selection filters, and the base plate are accommodated in an internal space, wherein the internal space is sealed, and the wavelength multiplexer / demultiplexer according to any one of claims 1 to 18.

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