JP2005189812A - Wavelength division multiplexer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent characteristic deterioration depending on a polarization surface when combining or separating light having more than two wavelength bands with one optical component, and to provide an optical component for wavelength division multiplexing which achieves good wavelength division multiplexing characteristics with a small size and an excellent storage characteristic. <P>SOLUTION: The wavelength division multiplexer includes a single optical substrate or a plurality of optical substrates integrated together, on which the first optical filter and the second optical filter are placed. The center wavelengths of three wavelength bands, λ1, λ2, and λ3, satisfy: 0.92≤λ2/λ1≤1.08, and 0.20≤λ3/λ1≤0.92 or 1.08≤λ3/λ1≤5.00. The first optical filter A combines or separates light of λ3 and two-wavelength multiplexed light of λ1 and λ2. The second optical filter B combines or separates light of λ1 and light of λ2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wavelength multiplexer / demultiplexer.

A dielectric multilayer film is generally used as an antireflection film on the surface of a spectacle lens, a color separation filter for a TV deposited on a glass substrate, or the like. For example, there are color separation filters used for liquid crystal projectors and cameras. Alternatively, a laser detection mirror used in a DVD (Digital Versatile Disk) device or the like has a configuration in which a dielectric multilayer film is sandwiched between two prism-shaped glass substrates, and light is incident on the dielectric multilayer film. It can be incident.
In the communication field, the introduction of wavelength multiplexing optical communication technology is being promoted. Among them, in order to separate light of different wavelengths, a filter in which a dielectric multilayer film serving as an edge filter or a bandpass filter is formed on a glass substrate has become necessary.

In optical communication, combining three-terminal modules in cascade enables multiplexing / demultiplexing of band light of a plurality of wavelengths. However, since at least one three-terminal module less than the number of multiplexing / demultiplexing is required, the apparatus cost is increased, the accommodation area is increased, and the installation cost is also considered to be increased.
Further, as disclosed in Patent Document 1 and Non-Patent Document 1, a module that multiplexes and demultiplexes a plurality of wavelengths by incorporating a plurality of bandpass filters and edge filters in a single module has been proposed. However, since the light separation angle is small, it is necessary to take a long optical path when incorporating a laser for transmission and a diode for reception, which causes a problem that the apparatus becomes large and the installation cost increases.
On the other hand, if the device is to be miniaturized, it is necessary to use a laser / diode array, which causes an increase in cost. In order to reduce the size without increasing the device cost, it is necessary to increase the light separation angle. In this case, there arises a problem that the difference between the P and S waves of the emitted light increases and the multiplexing / demultiplexing characteristics deteriorate.

Patent Document 2 discloses a method for improving the problem of characteristic degradation depending on P and S polarization at a high divergence angle, that is, a high incident angle, that is, a problem that the amplitude wavelength characteristic of the emitted light largely deviates depending on the polarization direction of the incident light. Proposed. In Patent Document 2, Si is used for the high refractive index layer of the dielectric multilayer filter. However, as disclosed in Patent Document 2, when TiO ₂ or SiO ₂ is used for the low refractive index layer, when left at a high temperature and high humidity of 85 ° C. and 85% RH for a long time, TiO ₂ and SiO ₂ Oxygen diffuses toward the high refractive index layer. This causes a decrease in the refractive index of the Si and Ge layers, a wavelength shift due to an increase in the refractive index of the low refractive index layer, and a change in optical characteristics. Moreover, since ZnS and ZnSe have weak adhesion to SiO ₂ and TiO _2, they also cause a problem that they are easily peeled off.

Here, if the incident medium is air having a refractive index of 1, the characteristic difference due to the difference in polarization direction can be reduced. However, in recent optical parts, the degree of integration has been increased due to miniaturization, and the filter is often used by directly joining to other optical parts, fiber capillaries, prisms, lenses, and waveguides. In this case, in order to make the incident medium air, it is necessary to have an air sandwich structure. In the case of an air sandwich structure, an antireflection film is formed between the joint surfaces in order to suppress amplitude fluctuation due to multiple reflection. Since this antireflection film is optimized for air having a refractive index of 1, if the resin or the like at the time of joining enters the light passage surface, the transmission characteristics deteriorate. Therefore, it is necessary to have a joining structure that does not allow the resin to go around, which increases the cost.
JP-A-8-82711 JP 2000-162413 A Yoichi Fujii "Optical engineering" Agne Jofusha 1993 (169 pages)

  The present invention has been invented in view of the above situation, and improves the characteristic deterioration depending on the polarization plane when performing multiplexing / demultiplexing of light of three or more waves with one optical component, and is small in size. A multilayer filter and optical components for multiplexing / demultiplexing that have excellent multiplexing / demultiplexing characteristics, have a high degree of freedom in selecting bonding materials when bonding multiple substrates, and have excellent storage characteristics even when light is transmitted. The purpose is to provide.

  On the other hand, the present invention has been invented in view of the above situation, and improves the characteristic deterioration depending on the polarization plane when performing multiplexing / demultiplexing of band light of three or more waves with one optical component, Accordingly, an object of the present invention is to provide a multilayer filter and an optical component for multiplexing / demultiplexing that are small and have excellent multiplexing / demultiplexing characteristics.

  A wavelength multiplexer / demultiplexer according to the present invention is a wavelength multiplexer / demultiplexer that demultiplexes wavelength multiplexed light having at least three wavelength bands into a predetermined band and / or combines wavelength multiplexed light with the wavelength multiplexed light. The duplexer has a structure in which one optical substrate or a plurality of optical substrates are integrated, and the first optical filter A and the second optical filter B having at least two different characteristics supported on the optical substrate. When the center wavelengths of the three wavelength bands are λ1, λ2, and λ3, 0.92 ≦ λ2 / λ1 ≦ 1.08 and 0.20 ≦ λ3 / λ1 ≦ 0.92 or 1.08 ≦ λ3 / λ1 ≦ 5.00, the first optical filter A is disposed on the optical path of the three wavelength-multiplexed lights, and the light having a central wavelength of λ3 is the wavelength band Or combined with two wavelength multiplexed lights whose center wavelengths are λ1 and λ2. The second optical filter B is disposed on the optical path of the two wavelength-multiplexed lights, and the two wavelength-multiplexed lights are combined or separated into light having center wavelengths λ1 and λ2 in the wavelength band. It is a wave. With such a configuration, it is possible to improve the problem that the amplitude wavelength characteristic of the emitted light deviates due to the polarization plane, S wave, and P wave of the incident light.

Further, in the present invention, the first optical filter A reflects a light having a central wavelength of the wavelength band of λ3 out of three wavelength multiplexed light as a form of a wavelength multiple demultiplexer. The center wavelength of the band transmits two wavelength multiplexed lights of λ1 and λ2, and the second optical filter B is the center of the wavelength band of the two wavelength multiplexed lights transmitted through the first optical filter A. Reflects light having a wavelength of λ2 and transmits light having a central wavelength of λ1 in the wavelength band. The refractive index of the incident medium of the first optical filter A is n _A , and the light to the first optical filter A The angle formed by the three wavelength multiplexed light and the normal line of the filter surface of the first optical filter A is θ _A , the refractive index of the incident medium of the second optical filter B is n _B , and the second optical Two wavelength multiplexed lights to filter B and second optical filter When the angle between the normal to the filter surface of the B and _{θ B, θ A ≧ 15 °} , n A · Sinθ A ≦ 0.95, θ B ≧ 15 °, and n B · sin [theta _B ≦ 0.85 It is desirable to do.

  Furthermore, in the above embodiment, it is preferable that 60 ° ≦ α ≦ 120 °, where α is an angle formed between the first optical filter A and the second optical filter B.

Further, the present invention, as another form of the wavelength multiplexing demultiplexer, the first optical filter A transmits light having a central wavelength of λ3 among the three wavelength multiplexed light, The wavelength band reflects two wavelength-multiplexed lights whose center wavelengths are λ1 and λ2, and the second optical filter B is the wavelength band of the two wavelength-multiplexed lights reflected from the first optical filter A. And the light having the center wavelength in the wavelength band of λ1 is reflected, the refractive index of the incident medium of the first optical filter A is n _A , and the first optical filter A The angle formed by the three wavelength multiplexed light and the normal line of the filter surface of the first optical filter A is θ _A , the refractive index of the incident medium of the second optical filter B is n _B , and the second Two wavelength multiplexed lights to the optical filter B and the second optical filter When the angle between the normal of the filter surface of the filter B was _{θ B, θ A ≧ 5 °} , n A · Sinθ A ≦ 0.95, θ B ≧ 5 °, n B · Sinθ B ≦ 0.85 Is desirable.

Further, in the above embodiment, when the angle formed by the first optical filter A and the second optical filter B is α, α ≧ θ _A +5 and 10 ° ≦ α ≦ 90 ° are preferable. .

  On the other hand, a wavelength multiplexer / demultiplexer according to the present invention is a wavelength multiplexer / demultiplexer that demultiplexes wavelength multiplexed light composed of at least three wavelength bands into a predetermined band or / and combines with wavelength multiplexed light. The wavelength multiplexer / demultiplexer has a structure in which one optical substrate or a plurality of optical substrates are integrated, and includes at least two first optical filters A and second optical filters B supported on the optical substrate, When the central wavelengths of the three wavelength bands are λ1, λ2, and λ3, 0.94 ≦ λ2 / λ1 ≦ 0.98 and 0.20 ≦ λ3 / λ1 ≦ 0.94, One optical filter A is disposed on the optical path of the three wavelength-multiplexed lights, and combines light having a center wavelength of λ1 with two wavelength-multiplexed lights having center wavelengths of λ2 and λ3. Wave or demultiplexing, the second optical filter B is One of is disposed on the optical path of the wavelength-multiplexed light, the two wavelength-multiplexed light, the center wavelength of said wavelength band is to multiplex or demultiplex the light of λ2 and [lambda] 3. With such a configuration, it is possible to improve the problem that the amplitude wavelength characteristic of the emitted light deviates due to the polarization plane, S wave, and P wave of the incident light.

Further, in the present invention, the first optical filter A reflects a light having a central wavelength of the wavelength band of λ1 out of three wavelength multiplexed light as a form of a wavelength multiple demultiplexer. The center wavelength of the band transmits two wavelength-multiplexed lights having wavelengths λ2 and λ3, and the second optical filter B is the center of the wavelength band among the two wavelength-multiplexed lights transmitted through the first optical filter A. Reflects light having a wavelength of λ2 and transmits light having a central wavelength of the wavelength band of λ3. The three wavelength multiplexed light to the first optical filter A and the filter surface of the first optical filter A When the angle formed with the normal line is θ _A , it is desirable that 5 ° ≦ θ _A ≦ 30 °.

Furthermore, in the above embodiment, the optical system further includes a mirror disposed on an optical path of light having a center wavelength of λ1 reflected by the first optical filter A, and the refractive index of the incident medium of the mirror is n _M , where n _M · Sinθ _M ≧ 1, θ _M , where θ _M is an angle formed between light having a central wavelength of λ1 reflected by the first optical filter A and a normal line of the mirror surface It is desirable that ≦ 85 °.

  Preferably, the first optical filter A is an edge filter, and the second optical filter B is a bandpass filter or an edge filter.

  According to the present invention, it is possible to provide a wavelength multiplexer / demultiplexer that can be miniaturized, demultiplexes or multiplexes at least three wavelength multiplexed light having excellent characteristics at low cost into light of three bands.

  The best mode for carrying out the present invention will be described below with reference to the drawings. The present invention can be applied to a wavelength multiplexer / demultiplexer that multiplexes and / or demultiplexes three different wavelengths. That is, the present invention can be applied to a wavelength multiplexer / demultiplexer that multiplexes and / or demultiplexes light having wavelengths that do not overlap with each other. Unless otherwise specified, the light of λ1, λ2, and λ3 means light in a band including the center wavelength.

Embodiment 1 of the Invention
FIG. 1 is a conceptual diagram showing an embodiment of a wavelength multiplexer / demultiplexer for demultiplexing or multiplexing wavelength multiplexed light having at least three wavelength bands according to the present invention. In FIG. 1, an optical substrate and the like are omitted to schematically show the wavelength multiplexer / demultiplexer.

As shown in FIG. 1, reference numeral 1 denotes a wavelength multiplexer / demultiplexer, and the wavelength multiplexer / demultiplexer 1 includes a first filter A11 and a second filter B21. Although not shown in this figure, as described later, the first filter A11 and the second filter B21 are supported by one optical substrate or a plurality of integrated optical substrates. Accordingly, the first filter A11 and the second filter B21 are configured so as to function as one optical element as a whole, and are reduced in size.
Reference numeral 33 denotes the direction in which the light of λ3 travels. The light is reflected by the first filter A11 and travels in the direction of 30. On the other hand, the lights of λ1 and λ2 are designed to travel from the 30 directions to the first filter A11. Accordingly, the light of λ3 is combined with the two wavelength multiplexed lights of λ1 and λ2 by the first filter A11, and three wavelength multiplexed lights are generated by the first filter A11.

Here, the center wavelengths of the three wavelength multiplexed lights of the present invention are 0.92 ≦ λ2 / λ1 ≦ 1.08, and 0.20 ≦ λ3 / λ1 ≦ 0.92 or 1.08 ≦ λ3 / λ1. ≦ 5.00. Since the light of λ1 and the light of λ2 do not overlap each other, λ1 ≠ λ2.
That is, in general, when separating two close bands such as 0.92 ≦ λ2 / λ1 ≦ 1.08, it is preferable to use an optical bandpass filter rather than an optical edge filter. Thereby, the transition width of transmission / reflection can be made steep. However, in the present invention, such an optical band-pass filter is separated from the band of λ1 · λ2 in the relationship of 0.20 ≦ λ3 / λ1 ≦ 0.92 or 1.08 ≦ λ3 / λ1 ≦ 5.00. It has been clarified that when the band is incident, it is difficult to obtain large transmittance and reflectance, and the characteristics are not stable.

On the other hand, the optical edge filter is suitable for separating light in two separate bands, and can have a very wide transmission band. However, when attempting to separate two waves that are close together, the number of layers increases, which makes it difficult to manufacture and is not suitable for use.
Therefore, the present inventors have found that a wavelength multiplexer / demultiplexer having excellent performance at low cost can be realized by adopting the following structure.

In FIG. 1, λ3 traveling from the direction 33 enters the first filter A11. Then, the two multiplexed λ1 and λ2 are incident on the first filter A11 from 30 directions. Accordingly, the first filter A11 is disposed on the optical path of wavelength multiplexed light in which light of three bands is multiplexed.
Here, the first filter A11 is an edge filter that combines or demultiplexes λ3 from λ1 and λ2. Therefore, for example, when the first filter A11 has a characteristic of reflecting λ3, the light is reflected on the surface of the first filter A11, and λ1 and λ2 are reflected in the 30 incident directions.
On the other hand, with respect to λ1 and λ2 that are adjacent wavelength bands, when the first filter A11 has a characteristic of transmitting λ1 and λ2, the two wavelength multiplexed lights are transmitted through the first filter A11. Accordingly, it is possible to demultiplex λ3 having a distant wavelength among the three wavelength multiplexed lights.

  Then, the two wavelength multiplexed lights 34 of λ1 and λ2 that have passed through the first filter A11 are incident on the second filter B21 disposed on the optical path. Here, the second filter B21 is a band-pass filter that can multiplex or demultiplex λ1 and λ2. For example, the second filter B21 has a characteristic of transmitting λ1 and reflecting λ2. Accordingly, the two wavelength multiplexed lights are demultiplexed into λ1 and λ2 by the second filter B21, and λ1 advances to 31 and λ2 advances to 32.

Here, if the angle θ _A is smaller than 15 °, the angle difference between the three wavelength multiplexed light and the transmitted light of λ3 becomes small, and the respective optical elements approach each other and are difficult to arrange. Therefore, the angle θ _A is preferably set to 15 ° or more. On the other hand, when the angle θ _A is increased, the incident angle to the first filter A11 is increased, so that the reflectance of the P-polarized light of the edge filter formed on the first filter A11 is decreased. According to the study, the upper limit of the angle theta _A is related to the refractive index _{n A} of the substrate _A, by a n A · sin [theta _A to 0.95 or less, a sufficient reflectance can be obtained in the P-polarized light.

Thus, n _A lower increases the degree of freedom in design of the angle theta _A is also the reflectivity of the n _A is lower the P-polarized light if using the same angle theta _A increases. Therefore, it is preferable that the refractive index n _A is low. The incident angle theta _A is preferably at least 20 _°, n _A · _Sinθ A is preferably preferably set to 0.8 or less.

If the angle θ _B is smaller than 15 °, the angle difference between the two-wavelength multiplexed light and λ2 becomes small, and the arrangement of elements becomes difficult. Therefore, the angle θ _B is preferably 15 ° or more. Meanwhile, since the incident angle to the second filter B21 when the angle theta _B increasing increases, characteristics of the band-pass filter which is formed on the second filter B21 is deteriorated.
According to the study, the upper limit of the angle theta _B is also the refractive index _{n B} of the second incident medium of the filter B21 is _related, if not the n _B · Sinθ B to 0.85 or less, the transmission band of the band-pass filter It became clear that it was difficult to flatten the characteristics. Furthermore, it has been clarified that sufficient values of P-polarized light and reflectivity cannot be obtained unless n _B · Sinθ _{B is set} to 0.85 or less.

Again, as the refractive index n _B of the second incident medium of the filter B21 is small, the degree of freedom in designing the angle theta _B increases. Further, the smaller the refractive index n _B of the incident medium of the second filter B21, the higher the flatness of the transmission band of the second filter B21 and the reflectance of P-polarized light in the reflection band. Therefore, it is preferable that the refractive index n _B is small. The incident angle theta _B is preferably at least 20 _°, n _B · _Sinθ B is preferably preferably set to 0.7 or less.

Further, when both the emission medium of the first filter A11 and the incident medium of the second filter B21 are air, the angle α for obtaining the incident angle θ _B can be obtained from the following equation 1.
α = θ _B + arcsin (n _A · sin θ _A ) (1)
Therefore, if the refractive index n _A of the substrate A and the incident angle θ _A to the first filter A 11 are set, the first filter A 11 and the second filter B 21 for obtaining a desired angle θ _B are formed. The angle α can be obtained by calculation. According to the study, the range of the effective angle α is 60 ° ≦ α ≦ 120 °, and preferably 70 ° ≦ α ≦ 100 °.

Embodiment 2 of the Invention
FIG. 2 is a conceptual diagram showing another embodiment of the wavelength multiplexer / demultiplexer according to the present invention. In this conceptual diagram, the wavelength multiplexer / demultiplexer 1 has a first filter A11 disposed on one surface of a single substrate C40 and a second filter B21 disposed on the other surface. An integrated structure is also possible.

As shown in FIG. 2, λ3 light incident from the direction 33 passes through the first filter A11 and is combined with λ1 and λ2 incident from the substrate side to form three wavelength multiplexed light. On the other hand, the two-wavelength multiplexed light of λ1 and λ2 reflected from the first filter A11 is guided to the second filter B21, and the second filter B21 combines or demultiplexes the light of λ1 and λ2.
Here, a short-wavelength transmission type optical edge filter is disposed as the first filter A11, and an optical bandpass filter is disposed as the second filter B21.
In FIG. 2, the filter surface of the first filter A11 and the filter surface of the second filter B21 do not intersect directly, but as shown by the broken line, these surfaces are extended so as to intersect at an angle α. Also good.

The three wavelength multiplexed lights enter / exit from the entrance / exit surface C41 of the substrate C40. The incident / exit surface C41 is provided so as to be perpendicular to the three wavelength-multiplexed lights, but this may be an angle inclined by 1 ° to 10 °.
Three wavelength multiplexed lights connected to the wavelength multiplexer / demultiplexer are incident / exited on the incident / exit surface C41. As this method, there is a method in which three wavelength multiplexed light guided by an optical fiber or the like is converted into parallel light using a collimator lens or the like and guided to the first filter A11. As another method, the ferrule of the optical fiber is fixed to the incident / exit surface C41 by a method such as adhesion or fusion, and diffused light having a spread angle determined by the NA of the optical fiber is guided to the first filter A11. Etc.

The three wavelength multiplexed lights, which are the incoming and outgoing lights, are set to enter or exit at an angle of θ _A with respect to the normal line of the filter surface of the first filter A11. At that time, the light of λ1 and λ2 of the three wavelength-division-multiplexed light is reflected at an angle theta _A at the substrate side of the first filter A11, it is guided to the second filter B21 propagated through the substrate. If light of λ3 from another light source is mixed in the three wavelength multiplexed lights in the same direction as λ1 and λ2, the light is transmitted through the first filter A11 and emitted in the 33 direction, so the problem is reduced.

The light of λ3 passes through the first filter A11 and is combined with the light of λ1 and λ2 to become three wavelength multiplexed lights.
If the angle θ _A is smaller than 5 °, the angle difference between the three wavelength multiplexed lights and the two wavelength multiplexed lights λ1 and λ2 becomes small. For this reason, arrangement | positioning of 2nd filter B21 becomes difficult because the optical path of 2nd filter B21 and 3 wavelength multiplexing light approaches. Therefore, the angle θ _A should be 5 ° or more.

On the other hand, when the angle θ _A is increased, the incident angle to the first filter A11 is increased, so that the reflectance of the P-polarized light of the edge filter formed on the first filter A11 is decreased.
According to the study, the upper limit of the angle theta _A is related to the refractive index n _A of the substrate A, unless a n A _· sin [theta _A to 0.95 or less, clear that no sufficient reflectance can be obtained in the P-polarized light It became. Thus, n _A lower increases the degree of freedom in design of the angle theta _A is also the reflectivity of the n _A is lower the P-polarized light if using the same angle theta _A increases. Therefore, n _A is preferably lower. The incident angle theta _A is preferably not more than 10 _°, n _A · _Sinθ A is preferably preferably set to 0.8 or less.
In addition, the transmission light of λ3 is refracted when passing through the first filter A11 and is incident on the substrate C40. The incident angle of the transmission light on the substrate surface must be determined in consideration of the refraction angle at that time. Therefore, it is preferable that the variation in the refractive index n _C of the substrate C40 is small.

On the other hand, the light that has been reflected by the first filter A11 and becomes the two-wavelength multiplexed light of λ1 and λ2 is incident on the second filter B21 at an angle θ _B formed with the normal line of the filter surface of the second filter B21. Incident. The second filter B21 can multiplex or demultiplex the two-wavelength transmitted light by using an optical bandpass filter that transmits one of the bands λ1 and λ2 and reflects the other.
When the angle θ _B is smaller than 5 °, the angle difference between the light in the band of λ 2 that is the reflected light of the second filter B 21 and the two-wavelength multiplexed light becomes small. For this reason, since light in the band of λ2 enters the first filter A11, the angle θ _B is preferably set to 5 ° or more.

Meanwhile, since the incident angle to the second filter B21 when the angle theta _B increasing increases, characteristics of the band-pass filter which is formed on the second filter B21 is deteriorated. According to the study, the upper limit of the angle θ _B is also related to the refractive index n _B of the incident medium of the second filter B 21, and the transmission band of the band-pass filter is required unless n _B · Sin θ _A is 0.85 or less. It became clear that it was difficult to flatten the characteristics. Furthermore, it has been clarified that sufficient values of P-polarized light and reflectivity cannot be obtained unless n _B · Sinθ _{A is set} to 0.85 or less.

Again, as the refractive index n _B of the second incident medium of the filter B21 is small, the degree of freedom in designing the angle theta _B increases. Furthermore, the flatness of the transmission band of the second filter B21 and the reflectance of P-polarized light in the reflection band can be increased. Therefore, it is better that the refractive index n _B is small. The incident angle theta _B is preferably 10 ° or _more, n _B · _Sinθ B is preferably preferably set to 0.7 or less.

In this embodiment, when the incident medium of the first filter A11 and the incident medium of the second filter B21 are the same medium, the angle α for obtaining the incident angle θ _B can be obtained from the following equation 2. .
α = θ _A + θ _B (2)
Therefore, if the incident angle θ _A to the first filter A 11 is set, the angle α formed by the first filter A 11 and the second filter B 21 for obtaining the desired angle θ _B can be easily obtained by calculation. be able to. According to the study, the range of the effective angle α is 20 ° ≦ α ≦ 90 °, preferably 30 ° ≦ α ≦ 75 °, and more preferably 35 ° ≦ α ≦ 60 °.

  Further, the angle at which the light in the band of λ1 is refracted can be controlled by setting the emission surface C42 to be a surface inclined with respect to the second filter B21. Therefore, the emission angle of λ1 can be adjusted by setting this angle. In FIG. 2, the angle of the exit surface C42 is parallel to the filter surface of the second filter B21.

The refractive index n _C of the substrate C40 affects the emission angle of λ2. When the variation in the refractive index n _C of the substrate C40 is large, the emission angle of λ2 varies, so that a material having a small variation in refractive index is preferably used as the material for the substrate C40. Further, when the exit surface C42 is not subjected to AR coating, in order to suppress the reflection at the exit surface C42, the refractive index n _C of the substrate C40 is lower is better.

Embodiment 3 of the Invention
FIG. 3 is a conceptual diagram showing another embodiment of the wavelength multiplexer / demultiplexer according to the present invention. The three wavelength multiplexed lights are combined or demultiplexed by the first filter A11 with the λ1 light 31 and the two wavelength multiplexed lights 34 with λ2 and λ3, and the two wavelength multiplexed lights 34 are further converted into the second filter B21. Thus, the light 32 of λ2 and the light 33 of λ3 are multiplexed or demultiplexed.

  Here, the center wavelengths of the above three wavelength multiplexed lights of the present invention are 0.94 ≦ λ2 / λ1 ≦ 0.98, and have a relationship of 0.20 ≦ λ3 / λ1 ≦ 0.94. This is because, in the present invention, since the wavelength multiplexed light is structured to be multiplexed / demultiplexed by the edge filter, it is difficult to separate at a wavelength in a band closer than the above due to its characteristics.

In general, in the configuration as shown in FIG. 3, when one band is multiplexed or demultiplexed by the first filter A11, the angle θ _A formed by the normal line of the first filter A11 and the above three wavelength multiplexed lights is set. When the angle is 45 °, the reflected light can be extracted perpendicularly to the three wavelength multiplexed light, which is preferable because the optical elements can be easily arranged.

When two close bands such as 0.94 ≦ λ2 / λ1 ≦ 0.98 are separated by the first filter A11, when a general optical edge filter is used at an incident angle of 45 °, S polarization The characteristics of P-polarized light deviate greatly. Therefore, there arises a problem that the optical characteristics of the multiplexer / demultiplexer greatly vary depending on the polarization state of the light. As a method corresponding to this, a method of designing an optical edge filter having a small difference between the characteristics of S-polarized light and P-polarized light is conceivable.
However, in the case of such a filter, the reflectance of the reflection band is usually low. Therefore, in order to obtain sufficient reflectance, a method using a special film material in which the refractive index of the high refractive index film of the filter is 3 or more can be considered. Alternatively, a method of forming an edge filter having 100 or more layers can be considered, but the manufacturing cost is greatly increased by using any method.

Further, according to the study by the present inventors, even if the reflectance can be improved by any of the above methods, when the angle θ _{A is set} to 45 °, the incident angle fluctuates by 1 degree due to manufacturing variation. As a result, the transition wavelength of the edge filter greatly deviates. For this reason, when an attempt is made to use a filter that separates two close wavelengths satisfying 0.94 ≦ λ2 / λ1 ≦ 0.98, if the incident angle slightly deviates from the set value, the variation in characteristics increases. It became clear that it was not suitable for use.
According to the study by the present inventors, it has been found that in order to solve this problem, it is necessary to set the angle θ _A to the smallest possible angle of 30 ° or less. That is, if the angle θ _A is greater than 30 °, the first filter A11 has a large difference between the characteristics of S-polarized light and P-polarized light. Further, when the incident angle is deviated, the optical characteristic is deteriorated due to the large deviation of the edge portion in the wavelength direction.

On the other hand, when the angle θ _{A is set} to 30 ° or less, the angle between the three wavelength multiplexed lights 30 and the light 31 reflected from the first filter A11 becomes small. For this reason, it is difficult to arrange an optical element that receives the light 31 of λ1. If the angle θ _A is too small, the angle difference between the three wavelength multiplexed light 30 and the light reflected by the first filter A11 becomes small. For this reason, in the case of the structure shown in FIG. 26, the light travels not to the mirror 12 but to the joint surface between the substrate A and the substrate C, so the angle θ _A is preferably 5 ° or more.
The present inventors have found that by adopting the following structure, a wavelength multiplexer / demultiplexer having low cost and excellent performance can be realized. Specifically, the angle θ _{A is set} to 5 ° to 30 °, preferably 10 ° to 25 °, and the mirror 12 is disposed on the optical path of the λ1 light 31 reflected by the first filter A11. As a result, the reflected light 35 can be extracted at a large angle with respect to the three wavelength multiplexed lights, and a wavelength multiplexer / demultiplexer excellent in performance at low cost is realized.

As shown in FIG. 3, the three wavelength multiplexed lights that are incident and outgoing light are set to enter or exit at an angle θ _A with respect to the normal line of the filter surface of the first filter A11. At that time, among the three wavelength multiplexed lights, the light of λ1 and λ2 travels from the direction 30 to the first filter A11 at an angle of θ _A formed with the normal line of the first filter A11. The first filter A11 reflects the light of λ1 in the direction of 31, and the reflected light of λ1 is reflected by the mirror 12 arranged on the optical path and proceeds in the direction of 35. Therefore, the angle between the light of λ1 and the three wavelength multiplexed lights 30 can be made large and almost perpendicular, and the design of the member is further facilitated.

The light of λ2 passes through the first filter A11 and proceeds to the second filter B21, and the light of λ2 is reflected in the direction of 32 by the second filter B21. The light of λ3 travels from the direction 33 to the second filter B21, passes through the second filter B21 and the first filter A11, and travels in the direction 30.
At this time, the light of λ3 transmitted through the second filter B21 is combined with the light of λ2, and two wavelength multiplexed light 34 is generated by the second filter B11. Further, the two wavelength multiplexed lights transmitted through the first filter A11 are combined with the light of λ1, and three wavelength multiplexed lights 30 are generated by the first filter A11. If the light of λ3 from another light source is mixed in the three wavelength multiplexed lights in the same direction as λ1 and λ2, it passes through the first filter A11 and the second filter B21 and is emitted in the 33 direction. Therefore, the problem is reduced.

In the present embodiment, a total reflection mirror can be obtained by setting the angle at which the light of λ1 is incident on the mirror 12 to a predetermined angle. In this case, it is preferable to polish the surface of the mirror 12 to be a flat surface because it is not necessary to form a film having a high reflectivity, and the manufacturing cost can be reduced. For this purpose, when the refractive index of the medium incident on the mirror 12 is n _M and the angle between the light of λ 1 reflected from the first filter A 11 and the normal of the mirror surface is θ _M , n _M · Sin θ _It is preferable that _M ≧ 1.
Here, when gradually increasing the theta _M, the angle between the light and the mirror 12 of λ1 reflected by the first filter A11 is reduced. Therefore, even if the incident positions of the three wavelength multiplexed lights 30 are slightly shifted at the time of manufacture, the position where the light 31 of λ1 and the mirror 12 come into contact with each other greatly varies, and the manufacture becomes difficult. Therefore, the angle theta _M is preferably set to a 85 ° or less. Preferably _{n M} · _Sinθ M ≧ 1.1, preferably set to θ _M ≦ 75 °.

  In the present invention, it is also possible to reverse the direction of light entering and exiting, in which case the above multiplexing or demultiplexing is demultiplexing or multiplexing, respectively. In the above description, the light of λ3 and λ1 and λ2 are incident on the wavelength multiplexer / demultiplexer 1 (first filter A11) from different directions. Of course, it is possible to enter 1 (first filter A11). In this case, it means that there are three or more wavelength division multiplexed lights in advance.

The filter used in the present invention has a structure in which a high refractive index film and a low refractive index film are laminated on a substrate. Examples of the material for the high refractive index film include oxides such as Ta oxide, Ti oxide, Ce oxide, Hf, Zr oxide, Nb oxide, Yb oxide, and Cr oxide, nitrides such as Si nitride and Ge nitride, and Si carbide. And at least one selected from semiconductors such as carbides such as ZnS, ZnSe, GaP, InP, GaAs, GaAl, and GaN, and mixtures thereof.
On the other hand, the material of the low refractive index film includes oxides such as Si oxide, Al oxide, Mg oxide, and Ge oxide, Ca fluoride, Ba fluoride, Ce fluoride, Mg fluoride, Na fluoride, There is at least one selected from fluorides such as Nd fluoride, Na ₅ Al ₃ F ₁₄ , and Na ₃ AlF ₆ , and mixed materials thereof.
In addition, although it is preferable to use the same kind as each refractive index film | membrane, if it is a material with a similar refractive index, it is also possible to substitute a part with refractive index film | membrane which consists of other materials. In addition, it is desirable to use oxides, nitrides, carbides, and fluorides in order to improve storage characteristics in a high temperature and high humidity environment.

Both optical filters of the present invention are examples of dielectric multilayer thin film filters, and are produced, for example, by a vacuum film forming method. As the vacuum film forming method, various film forming methods such as a vacuum evaporation method, a sputtering method, a chemical vapor deposition method, and a laser brazing method can be used. When using vacuum deposition, ion is applied to the substrate using ion plating, a cluster ion beam method, or another ion gun that ionizes part of the vapor flow and applies a bias to the substrate to improve film quality. It is effective to use ion-assisted deposition.
Examples of the sputtering method include a DC reactive sputtering method, an RF sputtering method, and an ion beam sputtering method. Further, examples of the chemical vapor phase method include a plasma polymerization method, a light-assisted vapor phase method, a thermal decomposition method, and a metal organic chemical vapor phase method. In addition, the film thickness of each refractive index film | membrane can be made into a desired film thickness by changing the vapor deposition time etc. at the time of film formation.

In addition to optical glass and crystallized glass such as quartz glass and borosilicate glass, the substrate may be a semiconductor substrate such as Si wafer, GaAs wafer, GaIn wafer, SiC wafer, LiNbO ₃ , LiTaO ₃ , TiO ₂ , SrTiO ₂ . ₃ , oxide single crystals such as Al ₂ O ₃ and MgO, polycrystalline substrates, fluoride single crystal substrates such as CaF ₂ , MgF ₂ , BaF ₂ and LiF, polycrystalline substrates, chlorides such as NaCl, KBr and KCl Any substrate can be used as long as it is transparent in the use band, such as a bromide single crystal, another crystal substrate, a plastic such as acrylic, amorphous polyolefin, and polycarbonate.

  Embodiments of the present invention described above will be described below with reference to the drawings. Further, the present invention is not limited to these examples. The material used for the filter described in the examples was Si oxide with a refractive index of 1.46, Nb oxide with 2.21 and quartz glass (refractive index of 1.44) for the substrate. The refractive index of air was 1.00.

すなわちλ１の帯域は１５４０〜１５６０ｎｍの範囲の光を受信用に使用し、その中心波長は１５５０ｎｍである。同様に、λ２の帯域は１４８０〜１５００ｎｍの範囲の光を受信用に使用し、その中心波長は１４９０ｎｍである。更に、λ３の帯域は１２６０〜１３６０ｎｍの範囲の光を送信用に使用し、その中心波長は１３１０ｎｍである。そして、使用する帯域のそれぞれの中心波長の間には、λ２／λ１＝０．９６、λ３／λ１＝０．８５の関係がある。 Further, the band handled by the wavelength multiplexer / demultiplexer 1 according to the embodiment described below is as shown in Table 1 below.

That is, the band of λ1 uses light in the range of 1540 to 1560 nm for reception, and its center wavelength is 1550 nm. Similarly, in the band of λ2, light in the range of 1480 to 1500 nm is used for reception, and its center wavelength is 1490 nm. Furthermore, the band of λ3 uses light in the range of 1260 to 1360 nm for transmission, and its center wavelength is 1310 nm. And there are relationships of λ2 / λ1 = 0.96 and λ3 / λ1 = 0.85 between the center wavelengths of the bands to be used.

In the wavelength multiplexer / demultiplexer that handles the three bands having the relationship shown in Table 1, it is necessary to adopt a configuration that can handle each of the adjacent λ1 and λ2 bands and the λ3 band that is farther away. .
FIG. 4 is a schematic diagram showing an example of the wavelength multiplexer / demultiplexer 1 according to the present invention. The wavelength multiplexer / demultiplexer 1 is configured by fixing two optical substrates, a substrate A10 and a substrate B20, in a V shape by a method such as adhesion at an angle α.
Specifically, the first filter A11 is disposed on the inner surface of the V shape on the substrate A10, and the second filter B21 is disposed on the inner surface of the V shape on the other substrate B20. By fixing the substrate A10 and the substrate B20, the two optical substrates are integrated.

Λ3 reflected by the first filter A11 is combined with λ1 and λ2, and becomes three wavelength multiplexed light. The two wavelength-multiplexed lights having the bands of λ1 and λ2 are transmitted through the first filter A11 and guided to the second filter B21, and the second filter B21 is demultiplexed into light of the bands of λ1 and λ2.
Here, the first filter A11 is a long wavelength transmission type optical edge filter, and the second filter B21 is an optical bandpass filter.
In FIG. 4, the second filter B21 is disposed on the joint surface between the substrate A10 and the substrate B20. However, the second filter B21 may not be disposed on the joint surface. The first filter A11 and the second filter B21 were formed on the substrate by a vacuum film formation method.

As shown in FIG. 4, in this embodiment, two optical filters having different characteristics are supported on a substrate in which two optical substrates are joined together. As a result, downsizing is achieved. Further, since the bonding surface of the substrate is not an optical path, the degree of freedom in selecting the bonding material is increased, and the deterioration of the optical characteristics due to the deterioration of the bonding material can be reduced, and the storage characteristics are excellent.
Although the cutting surface A13 is provided on the substrate A10 so that the three-wavelength multiplexed light can easily enter, this need not be provided. When the cutting surface A13 is provided, the angle of the cutting surface A13 can be set to be perpendicular to the three wavelength multiplexed lights or inclined by 1 ° to 10 °. The cutting surface A13 allows three wavelength multiplexed lights, which are transmission / reception lights connected to the wavelength multiplexer / demultiplexer 1, to enter and exit.

As a method of entering and emitting, there is a method in which three-wavelength multiplexed light guided by an optical fiber or the like is converted into parallel light using a collimator lens or the like and guided to the first filter A11. As another method, a method is adopted in which a ferrule of an optical fiber is fixed to the cutting surface A13 by a method such as adhesion or fusion, and diffused light having a divergence angle determined by the NA of the optical fiber is guided to the first filter A11. be able to.
The three wavelength multiplexed lights that are the input / output signal lights are set so as to be incident at an angle θ _A with respect to the normal line of the first filter A11. At this time, light in the 1550 nm and 1490 nm bands among the three wavelength multiplexed lights is transmitted through the first filter A11 and guided to the second filter B21. Therefore, even if tentatively the three wavelength-division-multiplexed optical bandwidth of light having a center wavelength of 1310nm of other light sources have been mixed, are reflected at an angle theta _A, can be emitted from the substrate A10.

Light in a band of 1310nm to be used for transmission is transmitted through the optical substrate A10, at an angle theta _A incident on the first filter A11, enters the optical fiber that has sent the three wavelength-multiplexed light after reflection at an angle theta _A Angled to do.
In this example, the optical substrate was quartz and the angle θ _A was set to 30 °. Therefore, n _A · sin θ _A = 0.72. Note that it is preferable that the 1310-nm band transmission light be incident on the substrate with P-polarized light because reflection on the substrate surface can be reduced and transmission loss can be reduced.

On the other hand, the light that has passed through the first filter A11 and has become two wavelength multiplexed lights of 1550 nm and 1490 nm is incident on the second filter B21 at an angle θ _B formed with the normal line of the surface of the second filter B21. To do. The second filter B21 can be an optical bandpass filter that transmits either the 1550 nm band or the 1490 nm band and reflects the other. Thereby, two wavelength division multiplexed lights can be demultiplexed. In this example, the bandpass filter was designed to transmit light in the 1550 nm band and reflect the 1490 nm band.

If the emission medium and the second incident medium of the filter B21 of the first filter A11 as in this embodiment both the air and the angle for obtaining the incident angle theta _B alpha can be obtained from equation 1 above .
In this embodiment, θ _A = 30 ° and n _A = 1.44, so α = 76.1 ° was set in order to set the angle θ _B to 30 °. Here, n _B · sin θ _B = 0.5.

In this embodiment, the emission medium of the first filter A11 and the incidence medium of the second filter B21 are both air, but an optical material such as another optical substrate is disposed on the emission surface of the second filter B21. It can be configured such as. Thus, may be different the emission medium and the second incident medium of the filter B21 of the first filter A11, in which case, it is possible to vary the angle theta _B by the refractive index and the shape of the optical material to be placed there It is.

  Further, the light in the band of λ1 transmitted through the second filter B21 may be reflected by the back surface B24 at a rate of several percent of the reflectance and then transmitted through the second filter B21 to reach the direction of λ2. When light in this λ1 band is mixed with the light receiving element of λ2, crosstalk may occur. If this crosstalk becomes a problem, AR coating may be applied to the back surface B24, or the substrate B may be cut into a rough surface in the shape of the cutting surface B25 so that the light reflected from the back surface B24 is scattered. .

  The refractive index of the substrate B20 affects the emission angle of λ1, which is light in the 1550 nm band. When the variation in the refractive index of the substrate B20 is large, the emission angle of λ1 varies, so it is preferable to use a material with a small variation in refractive index as the material used for the substrate B20. The value of the refractive index of the substrate B20 is not particularly problematic because it does not affect the characteristics of the first filter A11 and the second filter B21. However, when the AR coating is not applied to the back surface B24, the refractive index of the substrate B10 is preferably low in order to suppress reflection on the back surface B24.

FIG. 5 shows the characteristics of the long-wavelength transmission type optical edge filter used in the first filter A11 of the present embodiment. The incident medium is quartz (refractive index 1.44), the incident angle θ _A = 30 °, and the output medium is air. The low refractive index material used is oxidized Si having a refractive index of 1.46, and the high refractive index material is oxidized Nb having a refractive index of 2.21.
FIG. 6 shows the characteristics of the optical bandpass filter used for the second filter B21 of this embodiment. The incident medium is air, the incident angle θ _B = 30 °, the output medium is quartz, the high refractive index material is oxidized Nb, and the low refractive index material is oxidized Si. The refractive index of the used material is 2.21 for the high refractive index film, 1.46 for the low refractive index film, and 1.44 for quartz.
FIG. 7 shows the characteristics of a transmission signal in the 1310 nm band in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1260 to 1360 nm, which is the band to be used, both P-polarized light and S-polarized light have low transmission loss and good multiplexing characteristics.
FIG. 8 shows the characteristics of received signals in the bands of 1490 nm and 1550 nm in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1480 to 1500 nm for 1490 nm received light and in the range of 1540 to 1560 nm for 1550 nm received light, both P-polarized light and S-polarized light have low transmission loss and good demultiplexing characteristics. Yes.

FIG. 9 is a schematic diagram showing another example of the wavelength multiplexer / demultiplexer according to the present invention.
All optically the same as FIG. 4 except that the V-shaped method is different. Therefore, both the substrate A and the substrate B are quartz having a refractive index of 1.44, θ _A = 30 °, θ _B = 30 °, n _A · Sin θ _A = 0.72, n _B · Sin θ _B = 0.5, α = 76.1 °. Also in the present embodiment, the same optical characteristics as in the first embodiment can be obtained.

FIG. 10 is a schematic diagram showing another example of the wavelength multiplexer / demultiplexer according to the present invention.
The substrate A10 is quartz, the incident angle to the first filter A11 is 30 °, the substrate B20 is quartz, and the incident angle to the second filter B21 is 30 °. Therefore, n _A · Sinθ _A = 0.72, n _B · Sinθ _B = 0.72, and the angle α formed by the first filter A11 and the second filter B21 is 60 °.
FIG. 11 shows the characteristics of the long wavelength transmission type optical edge filter used in the first filter A11 of the present embodiment. The incident medium is quartz (refractive index 1.44), the incident angle θ _A = 30 °, and the output medium is quartz. The low refractive index material used is Si oxide having a refractive index of 1.46, and the high refractive index material is Ta oxide having a refractive index of 2.15.
FIG. 12 shows the characteristics of the optical bandpass filter used for the second filter B21 of this embodiment. The incident medium is quartz, the incident angle θ _B = 30 °, the output medium is air, the high refractive index material is Ta oxide, and the low refractive index material is Si oxide. The refractive index of the used material is 2.15 for the high refractive index film, 1.46 for the low refractive index film, and 1.44 for quartz.
FIG. 13 shows the characteristics of the transmission signal in the 1310 nm band in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1260 to 1360 nm, which is the band to be used, both P-polarized light and S-polarized light have low transmission loss and good multiplexing characteristics.
FIG. 14 shows the characteristics of the received signals in the bands of 1490 nm and 1550 nm in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1480 to 1500 nm for 1490 nm received light and in the range of 1540 to 1560 nm for 1550 nm received light, both P-polarized light and S-polarized light have low transmission loss and good demultiplexing characteristics. Yes.

Example 4 is a case where the wavelength multiplexer / demultiplexer 1 according to the second embodiment of the invention shown in FIG. 2 is used.
In the wavelength multiplexer / demultiplexer 1, a first filter A11 is disposed on one surface of a single optical substrate C40, and a second filter B21 is disposed on the other surface. For the three-wavelength multiplexed light that is the incoming / outgoing light, first, the first filter A11 separates the band of λ3 from the three-wavelength multiplexed light that is the incoming / outgoing light. The separated two-wavelength multiplexed light, which is the remaining band of λ1 and λ2, is guided to the second filter B21 and is demultiplexed into light of the bands of λ1 and λ2 by the second filter B21. Here, a short-wavelength transmission type optical edge filter is disposed as the first filter A11, and an optical bandpass filter is disposed as the second filter B21.
The three wavelength multiplexed lights enter / exit from the entrance / exit surface C41 of the substrate C40. In this embodiment, the incident / exit surface C41 is provided to be perpendicular to the three wavelength multiplexed lights.

The three-wavelength multiplexed light that is the input / output signal light is set to enter or exit at an angle θ _A with respect to the normal line of the first filter A11. At that time, the light in the band having the center wavelengths of 1550 nm and 1490 nm among the three wavelength multiplexed lights is reflected at the angle θ _A on the substrate side of the first filter A11, propagates in the substrate, and propagates through the second filter B21. Led to. If light in a band having a center wavelength of 1310 nm of another light source is mixed in the three-wavelength multiplexed light in the same direction as λ1 and λ2, it is transmitted through the first filter A11 and emitted.
On the other hand, light in a band of central wavelength 1310nm used for transmission is set to emit at an angle theta _A from the first filter A11. As a result, the light transmitted through the first filter A11 coincides with the optical path through which the light of λ1 and λ2 propagates, and the light having the center wavelength of 1310 nm is incident on the optical fiber that has transmitted the three wavelength multiplexed light. Is done.

In this embodiment, the substrate C is made of quartz, and the angle θ _A is set to 30 °. Therefore, n _A · sin θ _A = 0.72. Note that transmission light having a center wavelength of 1310 nm is preferable, and reflection of the substrate surface can be reduced by making P-polarized light incident on the substrate C40, so that transmission loss can be reduced.
The transmitted light having the center wavelength of 1310 nm band is refracted through the first filter A11 and incident on the substrate C.

On the other hand, the light that is reflected by the first filter A11 and becomes two wavelength multiplexed lights having the center wavelengths of 1550 nm and 1490 nm is the second angle at θ _B formed by the normal line of the surface of the second filter B21. The light enters the filter B21. The second filter B21 is designed as a bandpass filter so as to transmit light of 1550 nm and reflect a band of 1490 nm.
If the incident medium and the second incident medium of the filter B21 of the first filter A11 as in this example were the same medium, the angle for obtaining the incident angle theta _B alpha can be determined from equation 2 above . In this embodiment, θ _A = 30 °, so α = 42 ° in order to set the angle θ _B to 12 °. In the present embodiment, the angle of the exit surface C42 is parallel to the filter surface of the second filter B21.

FIG. 15 shows the characteristics of a short wavelength transmission type optical edge filter used in the first filter A11 of the present embodiment. The incident medium is quartz (refractive index 1.44), the incident angle θ _A = 30 °, and the output medium is air. The low refractive index material used is oxidized Si having a refractive index of 1.46, and the high refractive index material is oxidized Nb having a refractive index of 2.21.
FIG. 16 shows the characteristics of the optical bandpass filter used for the second filter B21 of this embodiment. The incident medium is quartz, the incident angle θ _B = 12 °, the output medium is air, the high refractive index material is oxidized Nb, and the low refractive index material is oxidized Si. The refractive index of the used material is 2.21 for the high refractive index film, 1.46 for the low refractive index film, and 1.44 for quartz.
FIG. 17 shows the characteristics of the transmission signal in the band whose center wavelength is 1310 nm in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1260 to 1360 nm, which is the band to be used, both P-polarized light and S-polarized light have low transmission loss and good multiplexing characteristics.
FIG. 18 shows the characteristics of received signals in the bands of 1490 nm and 1550 nm in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1480 to 1500 nm for 1490 nm received light and in the range of 1540 to 1560 nm for 1550 nm received light, both P-polarized light and S-polarized light have low transmission loss and good demultiplexing characteristics. Yes.

FIG. 19 is a schematic diagram showing another example of the wavelength multiplexer / demultiplexer according to the present invention. Although the basic structure is the same as that of the fourth embodiment, a λ3 angle correction substrate 44 is disposed outside the first filter A11, and a λ2 angle correction substrate 43 is disposed outside the second filter B21.
The λ3 angle correction substrate 44 is used when it is desired to set the angle between λ3 and the three wavelength multiplexed lights to a predetermined angle, but may not be used when the angle may be the same as that of the fourth embodiment. . The λ3 angle correction substrate 44 is made of the same material as the substrate C40 but may have a different refractive index.

Further, in order to fix the λ3 angle correction substrate 44 and the substrate C40, a first filter A11 and an optically transparent bonding material are located between the two. The order of this bonding is preferably arranged in the order of the substrate C40, the first filter A11, the bonding material, and the λ3 angle correction substrate 44 from the substrate C40 side. Thereby, the transmission loss of about 1 to 5% in the bonding material can be reduced in the light of λ1 and λ2. Further, the substrate C40, the bonding material, the first filter A11, and the λ3 angle correction substrate 44 may be disposed in this order.
Further, when the light of λ3 is incident on the first filter A11, the light reflected with a reflectance of about 0 to 10% propagates in the direction of 32, and crosstalk occurs when mixed with the 32 light receiving elements. Sometimes. When this crosstalk becomes a problem, the surface on the exit surface C42 side of the λ3 angle correction substrate 44 may be cut into a rough surface so that the light reflected by the first filter A11 is scattered.

In this embodiment, the same quartz as the substrate C40 is used for the λ3 angle correction substrate 44, and the angle is set perpendicular to the three-wavelength multiplexed light.
Similarly, the λ2 angle correction substrate 43 is used when the angle between λ2 and the three-wavelength multiplexed light is desired to be a predetermined angle, but may not be used when the angle may be the same as that of the fourth embodiment. Good. As the material of the λ2 angle correction substrate 43, a material having the same refractive index as that of the substrate C40 can be used, but it may be different.

  Further, in order to fix the λ2 angle correction substrate 43 and the substrate C40, a second filter B21 and an optically transparent bonding material or the like are positioned between the two. It is preferable to arrange the bonding in the order of the substrate C40, the second filter B21, the bonding material, and the λ2 angle correction substrate 43 in this order from the substrate C40 side. % Transmission loss can be reduced. Further, the substrate C40, the bonding material, the second filter B21, and the λ2 angle correction substrate 43 may be disposed in this order.

In the present embodiment, the same quartz as that of the substrate C is used for the λ2 angle correction substrate 43, and the angle is set to be 36 ° in order to make the emission angle perpendicular to the three-wavelength multiplexed light. doing. Further, since the substrate C is quartz having a refractive index of 1.44, θ _A = 30 °, θ _B = 12 °, n _A · Sin θ _A = 0.72, n _B · Sin θ _B = 0.30, α = 42. °.
In this embodiment, it is possible to use a filter designed to match the emission medium of the edge filter of FIG. 15 and the bandpass filter of FIG. Therefore, the same optical characteristics as in Example 4 can be obtained.

FIG. 20 is a schematic diagram showing another example of the wavelength multiplexer / demultiplexer according to the present invention. Although the basic structure is the same as that of the fourth embodiment, the optical substrate A10 and the optical substrate B20 are integrated with each other, and thus the size is reduced.
In this embodiment, the substrate A10 is quartz, the incident angle to the first filter A11 is 30 °, and the incident medium is air. Therefore, n _A · Sinθ _A = 0.5, the substrate B20 is quartz, and the second filter B21. Since the incident angle is 12 ° and the incident medium is air, n _B · Sinθ _B = 0.21, and the angle α formed by the first filter A11 and the second filter B21 is 42 °.
FIG. 21 shows the characteristics of the short wavelength transmission type optical edge filter used in the first filter A11 of the present embodiment. The incident medium is air, the incident angle θ _A = 30 °, and the output medium is quartz (refractive index 1.44). The low refractive index material used is oxidized Si having a refractive index of 1.46, and the high refractive index material is oxidized Nb having a refractive index of 2.21.
FIG. 22 shows the characteristics of the optical bandpass filter used for the second filter B21 of this embodiment. The incident medium is air, the incident angle θ _B = 12 °, the output medium is quartz, the high refractive index material is oxidized Nb, and the low refractive index material is oxidized Si. The refractive index of the used material is 2.21 for the high refractive index film, 1.46 for the low refractive index film, and 1.44 for quartz.
FIG. 23 shows the characteristics of the transmission signal in the 1310 nm band in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1260 to 1360 nm, which is the band to be used, both P-polarized light and S-polarized light have low transmission loss and good multiplexing characteristics.
FIG. 24 shows the characteristics of received signals in the bands of 1490 nm and 1550 nm in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1480 to 1500 nm for 1490 nm received light and in the range of 1540 to 1560 nm for 1550 nm received light, both P-polarized light and S-polarized light have low transmission loss and good demultiplexing characteristics. Yes.

FIG. 25 is a schematic diagram showing another example of the wavelength multiplexer / demultiplexer according to the present invention. Although the basic structure is the same as that of the fourth embodiment, the optical substrate A10 and the optical substrate B20 are integrated with each other, and thus the size is reduced.
Substrate A is quartz, the incident angle to the first filter A11 is 30 °, and the incident medium is air, so that n _A · Sinθ _A = 0.5, the substrate B is quartz, and the incident angle to the second filter B21 is 8 ° and the incident medium is quartz. Therefore, n _B · Sinθ _B = 0.20, and the angle α formed by the first filter A11 and the second filter B21 is 42 °.
In this embodiment, each filter used in Embodiment 6 can be used. Therefore, the same optical characteristics as in Example 6 can be obtained.

Example 8 is a case where the wavelength multiplexer / demultiplexer 1 according to Embodiment 3 of the present invention is used.
FIG. 26 is a schematic diagram showing another example of the wavelength multiplexer / demultiplexer according to the present invention. The wavelength multiplexer / demultiplexer 1 is configured by fixing four optical substrates, the substrate A10, the substrate B20, the substrate C40, and the substrate D45 with an optically transparent bonding material or the like.
A first filter A11 is disposed between the substrate A10 and the substrate B20, and a second filter B21 is disposed between the substrate B20 and the substrate D45. Further, the mirror 12 is disposed on the surface on the substrate A10 side in contact with the bonding surface between the substrate A10 and the substrate C40.

  The light of λ1 that is the received light travels from the direction 30 to the first filter A11 and is reflected by the first filter A11. As a result, the light of λ1 that is the received light is demultiplexed, reflected by the mirror 12, and emitted in the direction of 31. Similarly, the light of λ2, which is the received light, travels from the direction 30 and passes through the first filter A11 and is reflected by the second filter B21. As a result, the light of λ2 that is the received light is demultiplexed and then emitted in the direction of 32. The light of λ3 that is the transmitted light travels from the direction 33 to the second filter B21, passes through the second filter B21 and the first filter A11, and travels in the direction 30.

  Here, the first filter A11 and the second filter B21 are short-wavelength transmission type optical edge filters having different characteristics. The first filter A11 and the second filter B21 are formed on the substrate by a vacuum film forming method. Therefore, as shown in FIG. 26, in this embodiment, two optical filters having different characteristics are supported on a substrate in which four optical substrates are joined and integrated, thereby achieving miniaturization. In addition, since the position where light of each wavelength enters or exits the substrate is away from the substrate bonding surface, the influence of the wraparound of the bonding material can be reduced even if the size is reduced.

The entrance / exit surface C41 on which the three wavelength multiplexed lights 30 enter / exit the substrate C40 can be made perpendicular to the three wavelength multiplexed lights 30 or at an angle inclined by 1 ° to 10 ° relative thereto. The incident / exit surface C41 allows incident / exit of three wavelength multiplexed lights, which are transmission / reception lights connected to the wavelength multiplexer / demultiplexer 1.
As a method of entering and emitting, there is a method in which three wavelength multiplexed lights guided by an optical fiber or the like are converted into parallel light using a collimator lens or the like and guided to the first filter A11. As another method, a method is adopted in which the ferrule of the optical fiber is fixed to the entrance surface C41 by a method such as adhesion or fusion and diffused light having a spread angle determined by the NA of the optical fiber is guided to the first filter A11. Can do.

A substrate C40 is bonded to the substrate A10 so that the three wavelength multiplexed light can easily enter. However, when the three wavelength multiplexed light 30 is used as a parallel light by a collimator lens or the like, the substrate C40 is not provided. Also good. At this time, if loss due to reflection on the surface of the substrate A10 becomes a problem, an AR coat may be provided on the surface of the mirror 12 of the substrate A10.
The three wavelength multiplexed lights enter and exit the first filter A11 at an angle θ _A from the incident medium having the refractive index n _A of the substrate A10, and light in the 1550 nm band used for reception is demultiplexed by reflection. The remaining two lights in the 1310 nm and 1490 nm bands are transmitted through the first filter A11. Therefore, the first filter A11 was designed as a short wavelength transmission type optical edge filter.
In this embodiment, the angle theta _A is set to 20 °. In addition, when the optical edge filter is used at oblique incidence, if the refractive index of the incident medium is increased, the difference between the S-polarized light and the P-polarized light increases, and the transition wavelength of the edge filter also varies when the angle θ _A varies. growing. Therefore, the optical substrate is made of quartz having a low refractive index.

The light of λ1 reflected by the first filter A11 proceeds to the mirror 12. The mirror 12 can be configured by forming a metal film or a dielectric multilayer film having a high reflectance, or by forming a total reflection mirror satisfying the value of the incident angle θ _M 13 of n _M · Sin θ _M ≧ 1. Here, the value of the angle θ _M can be obtained from the following Expression 3 using the angles α and θ _A formed by the first filter A 11 and the mirror 12.
θ _M = θ _A + α (3)
On the other hand, in order to arrange an element that receives the light 31 of λ1 in a compact manner, it is preferable that the angle formed by the light 30 and the light 31 of λ1 is a right angle. For this purpose, the exit surface A14 may be parallel to the light 30 and the angle α may be set to 45 °.
In this embodiment, α = 45 °, θ _M = 65 °, and since the incident medium of the first filter A11 and the mirror 12 is the same quartz, n _A = n _M = 1.44, so n _M · Sinθ _M = 1.31. Therefore, the mirror 12 is a total reflection mirror. This eliminates the need for forming a high reflectivity film, thereby reducing the manufacturing cost.

In the case of the total reflection mirror, the substrate A10 may be burned due to aging and the optical characteristics of the mirror 12 may be deteriorated. In that case, a dielectric thin film such as Si oxide or a metal thin film such as Au may be formed on the surface of the mirror 12 as a protective film.
In particular, when a dielectric thin film having a refractive index close to the refractive index of the substrate A10, such as Si oxide, is formed, even if the protective film covers the bonding surface between the substrate A10 and the substrate C40, the protective films for the three wavelength multiplexed light Reflection at the surface is reduced. Thereby, the fall of the transmittance | permeability can be suppressed. Therefore, since the protective film can be formed on the entire surface of the mirror 12 of the substrate A10, it is not necessary to mask the film formation region, and the manufacturing cost can be reduced.

Two bands multiplexed light 34 of λ2 and λ3 transmitted through the first filter A11 is incident on the second filter B21 at an angle theta _B from the incident medium of index _{n B} of the substrate B20. Then, the light in the 1490 nm band used for reception is demultiplexed by reflection, and the light in the 1310 nm band is transmitted. Therefore, the second filter B21 was designed as a short wavelength transmission type optical edge filter.
In this embodiment, .lambda.2 since band (1490 nm) and [lambda] 3 (1310 nm) is away, adverse effects even by increasing the angle theta _B optical properties undergo is small. Therefore, the angle θ _{B is set} to 45 °, and the optical substrate is the same quartz as the substrate A10. Furthermore, if light of λ3 is incident as P-polarized light, a filter with low transmittance of S-polarized light can be used in the band of λ3 if the transmittance of P-polarized light is high. Therefore, a filter having a small number of stacked layers and a wide transition width can be used, so that the manufacturing cost of the second filter B21 can be reduced.

  In this embodiment, quartz is used for all the substrates in order to make the light of λ3 transmitted through all the substrates go straight. However, substrates having different refractive indexes may be mixed. In that case, by changing the angle of the incident surface D47 to give a refraction angle, the angles of λ3 and the three wavelength multiplexed lights 30 can be made parallel.

  The light in the band of λ3 advances from the direction 33 and is reflected by the second filter B21 at a reflectance of several percent, but reaches the second filter B21 after being reflected by the cutting surface D46 at a reflectance of several percent. There is. The light in the λ3 band may be mixed with the λ2 light 32 by passing through the second filter B21. When this crosstalk becomes a problem, the cutting surface D46 may be cut into a rough surface so that light is scattered, or an AR coating may be provided to reduce reflection.

  In addition, with respect to the light of λ1, which is a band of 1550 nm, it may be necessary to obtain high isolation in order to maintain high separation from transmitted / received light of other bands. In this case, a band pass filter that transmits the band of λ1 may be further disposed on the emission surface A14. Similarly, when it is necessary to increase the isolation of light of λ2 which is 1490 nm, a band pass filter may be further arranged on the exit surface B23.

FIG. 27 shows the characteristics of the short wavelength transmission type optical edge filter used in the first filter A11 of this embodiment. The incident and output media are quartz with a refractive index of 1.44, and the incident angle θ _A = 20 °. The low refractive index material used was Si oxide with a refractive index of 1.46, and the high refractive index material was oxidized Nb with a refractive index of 2.21.
FIG. 28 shows the characteristics of the short wavelength transmission type optical edge filter used for the second filter B21 of the present embodiment. The incident and exit media are quartz with a refractive index of 1.44, the incident angle θ _B = 45 °, the low refractive index material used is oxidized Si with a refractive index of 1.46, and the high refractive index material is oxidized with a refractive index of 2.21. Nb.
FIG. 29 shows the characteristics of a transmission signal in the 1310 nm band in the wavelength multiplexer / demultiplexer of this embodiment. It can be seen that in the range of 1260 to 1360 nm, which is the band to be used, both P-polarized light and S-polarized light have low transmission loss and have good multiplexing characteristics.
FIG. 30 shows the characteristics of received signals in the bands of 1490 nm and 1550 nm in the wavelength multiplexer / demultiplexer of the present embodiment. In the range of 1480 to 1500 nm for received light of 1490 nm and in the range of 1540 to 1560 nm for received light of 1550 nm, both P-polarized light and S-polarized light have low transmission loss and good demultiplexing characteristics. I understand that.

  In addition to the wavelengths used in the above-described embodiments, it is possible to similarly multiplex / demultiplex wavelength-multiplexed light in a band having a relationship of the center wavelength ratio of the present invention with an edge filter. Further, by combining with a filter having other characteristics, multiplexed light of three or more waves can be multiplexed / demultiplexed by a downsized wavelength multiplexer / demultiplexer.

It is the figure which showed the wavelength multiplexer / demultiplexer in Embodiment 1 of invention. It is the figure which showed the wavelength multiplexer / demultiplexer in Embodiment 2 of invention. It is the figure which showed the wavelength multiplexer / demultiplexer in Embodiment 3 of invention. 1 is a diagram illustrating a wavelength multiplexer / demultiplexer in Embodiment 1. FIG. FIG. 6 is a diagram illustrating characteristics of an optical edge filter that is the first filter A in the first embodiment. 6 is a diagram illustrating characteristics of an optical bandpass filter that is the second filter B in Embodiment 1. FIG. FIG. 5 is a diagram illustrating the characteristics of a transmission signal of the wavelength multiplexer / demultiplexer according to the first embodiment. FIG. 5 is a diagram illustrating characteristics of a received signal of the wavelength multiplexer / demultiplexer in the first embodiment. FIG. 5 is a diagram illustrating a wavelength multiplexer / demultiplexer according to a second embodiment. FIG. 10 is a diagram illustrating a wavelength multiplexer / demultiplexer in Example 3. FIG. 10 is a diagram illustrating characteristics of an optical edge filter that is the first filter A in the third embodiment. FIG. 10 is a diagram illustrating characteristics of an optical bandpass filter that is the second filter B in the third embodiment. FIG. 10 is a diagram illustrating characteristics of a transmission signal of a wavelength multiplexer / demultiplexer according to a third embodiment. FIG. 10 is a diagram illustrating characteristics of a received signal of a wavelength multiplexer / demultiplexer according to a third embodiment. FIG. 10 is a diagram showing characteristics of an optical edge filter that is a first filter A in Example 4. FIG. 10 is a diagram illustrating characteristics of an optical bandpass filter that is the second filter B in the fourth embodiment. It is the figure which showed the characteristic of the transmission signal of the wavelength multiplexer / demultiplexer in Example 4. It is the figure which showed the characteristic of the received signal of the wavelength multiplexer / demultiplexer in Example 4. FIG. 10 is a diagram illustrating a wavelength multiplexer / demultiplexer according to a fifth embodiment. FIG. 10 is a diagram illustrating a wavelength multiplexer / demultiplexer according to a sixth embodiment. FIG. 10 is a diagram illustrating characteristics of an optical edge filter that is a first filter A in Example 6. FIG. 10 is a diagram illustrating characteristics of an optical edge filter that is the second filter B in the sixth embodiment. It is the figure which showed the characteristic of the transmission signal of the wavelength multiplexer / demultiplexer in Example 6. It is the figure which showed the characteristic of the received signal of the wavelength multiplexer / demultiplexer in Example 6. FIG. 10 is a diagram illustrating a wavelength multiplexer / demultiplexer according to a seventh embodiment. FIG. 10 is a diagram illustrating a wavelength multiplexer / demultiplexer according to an eighth embodiment. FIG. 10 is a diagram showing characteristics of an optical edge filter that is a first filter A in Example 8. FIG. 10 is a diagram showing the characteristics of an optical edge filter that is the second filter B in Example 8. FIG. 10 is a diagram illustrating characteristics of a transmission signal of a wavelength multiplexer / demultiplexer according to an eighth embodiment. FIG. 10 is a diagram illustrating characteristics of a received signal of a wavelength multiplexer / demultiplexer according to an eighth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wavelength multiplexer / demultiplexer 10 ... Board | substrate A, 11 ... 1st filter A, 12 ... Mirror,
13 ... Cutting surface A, 14 ... Output surface A
20 ... Substrate B, 21 ... Second filter B, 23 ... Emission surface B, 24 ... Back surface B,
25 ... Cutting surface B
30 ... 3-wavelength multiplexed light, 31 ... λ1 band light, 32 ... λ2 band light, 33 ... λ3 band light,
34... Two-wavelength multiplexed light, 35... Λ1 band light reflected by a mirror 40... Substrate C, 41... Entrance / exit surface C, 42.
44 ... λ3 angle correction substrate, 45 ... substrate D, 46 ... cutting surface D, 47 ... incident surface D

Claims (10)

A wavelength multiplexer / demultiplexer that demultiplexes wavelength multiplexed light composed of at least three wavelength bands into a predetermined band and / or combines wavelength multiplexed light with the wavelength multiplexed light;
The wavelength multiplexer / demultiplexer has a structure in which one optical substrate or a plurality of optical substrates are integrated,
A first optical filter A and a second optical filter B having at least two different characteristics supported on the optical substrate;
When the center wavelengths of the three wavelength bands are λ1, λ2, and λ3, 0.92 ≦ λ2 / λ1 ≦ 1.08, and 0.20 ≦ λ3 / λ1 ≦ 0.92 or 1.08 ≦ λ3 / There is a relationship of λ1 ≦ 5.00,
The first optical filter A is disposed on the optical path of the three wavelength-multiplexed lights, and the light having the center wavelength of the wavelength band is λ3, and the two wavelength-multiplexed lights having the center wavelengths of the wavelength bands are λ1 and λ2. Combined or demultiplexed with
The second optical filter B is disposed on the optical path of the two wavelength-multiplexed lights, and the two wavelength-multiplexed lights are wavelengths that multiplex or demultiplex the lights with the center wavelengths of the wavelength bands λ1 and λ2. Multiplexer / demultiplexer. The first optical filter A reflects light having a central wavelength of λ3 among the three wavelength-multiplexed lights and transmits two wavelength-multiplexed lights having the central wavelengths of the wavelength bands of λ1 and λ2. And
The second optical filter B reflects light having a center wavelength of λ2 among the two wavelength multiplexed lights transmitted through the first optical filter A, and the center wavelength of the wavelength band is λ1. Of light,
The refractive index of the incident medium of the first optical filter A is n _A , and the angle formed by the three wavelength multiplexed lights to the first optical filter A and the normal line of the filter surface of the first optical filter A θ _A
The refractive index of the incident medium of the second optical filter B is n _B , and the angle formed by the two wavelength multiplexed lights to the second optical filter B and the normal line of the filter surface of the second optical filter B is θ _{When B}
θ _A ≧ 15 °,
n _A · Sinθ _A ≦ 0.95,
θ _B ≧ 15 °,
2. The wavelength multiplexer / demultiplexer according to claim 1, wherein n _B · Sinθ _B ≦ 0.85.   3. The wavelength multiplexer / demultiplexer according to claim 2, wherein 60 ° ≦ α ≦ 120 °, where α is an angle formed by the first optical filter A and the second optical filter B. 4. The first optical filter A transmits light having a central wavelength of λ3 among the three wavelength-multiplexed lights and reflects two wavelength-multiplexed lights having the central wavelengths of the wavelength bands of λ1 and λ2. And
The second optical filter B reflects light having a central wavelength of λ2 among the two wavelength multiplexed lights reflected from the first optical filter A, and the central wavelength of the wavelength band is λ1. Of light,
The refractive index of the incident medium of the first optical filter A is n _A , and the angle formed by the three wavelength multiplexed lights to the first optical filter A and the normal line of the filter surface of the first optical filter A θ _A
The refractive index of the incident medium of the second optical filter B is n _B , and the angle formed by the two wavelength multiplexed lights to the second optical filter B and the normal line of the filter surface of the second optical filter B is θ _{When B}
θ _A ≧ 5 °,
n _A · Sinθ _A ≦ 0.95,
θ _B ≧ 5 °,
2. The wavelength multiplexer / demultiplexer according to claim 1, wherein n _B · Sinθ _B ≦ 0.85. 5. The angle according to claim 4, wherein α ≧ θ _A +5 and 10 ° ≦ α ≦ 90 °, where α is an angle formed by the first optical filter A and the second optical filter B. Wavelength multiplexer / demultiplexer. A wavelength multiplexer / demultiplexer that demultiplexes wavelength multiplexed light composed of at least three wavelength bands into a predetermined band and / or combines wavelength multiplexed light with wavelength multiplexed light;
The wavelength multiplexer / demultiplexer has a structure in which one optical substrate or a plurality of optical substrates are integrated,
Comprising at least two first optical filter A and second optical filter B supported on the optical substrate;
When the center wavelengths of the three wavelength bands are λ1, λ2, and λ3, 0.94 ≦ λ2 / λ1 ≦ 0.98 and 0.20 ≦ λ3 / λ1 ≦ 0.94,
The first optical filter A is disposed on the optical path of the three wavelength-multiplexed lights, the light having the center wavelength of the wavelength band λ1 and the two wavelength-multiplexed lights having the center wavelengths of the wavelength bands λ2 and λ3. Combined or demultiplexed with
The second optical filter B is disposed on the optical path of the two wavelength-multiplexed lights, and the two wavelength-multiplexed lights are wavelengths that multiplex or demultiplex into the light having the center wavelengths of the wavelength bands λ2 and λ3. Multiplexer / demultiplexer. The first optical filter A reflects light having a center wavelength of λ1 among the three wavelength-multiplexed lights and transmits two wavelength-multiplexed lights having center wavelengths of λ2 and λ3. And
The second optical filter B reflects light having a center wavelength of λ2 among the two wavelength multiplexed lights that pass through the first optical filter A, and the center wavelength of the wavelength band is λ3. Of light,
When the angle formed by the three wavelength multiplexed lights to the first optical filter A and the normal line of the filter surface of the first optical filter A is θ _A ,
The wavelength multiplexer / demultiplexer according to claim 6, wherein 5 ° ≦ θ _A ≦ 30 °. A mirror disposed on an optical path of light having a center wavelength of λ1 reflected by the first optical filter A;
When the refractive index of the incident medium of the mirror is n _M , and the angle formed by the light having the center wavelength of λ1 reflected by the first optical filter A and the normal of the mirror surface is θ _M ,
n _M · Sinθ _M ≧ 1,
The wavelength multiplexer / demultiplexer according to claim 7, wherein θ _M ≦ 85 °.   9. The wavelength multiplexer / demultiplexer according to claim 6, wherein light incident on the wavelength multiplexer / demultiplexer of light having a center wavelength of λ3 in the wavelength band is P-polarized light. The first optical filter A is an edge filter,
The wavelength multiplexer / demultiplexer according to any one of claims 1 to 9, wherein the second optical filter B is a bandpass filter or an edge filter.

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