Wave plate, wavelength selection switch, optical branch insertion device, and method for manufacturing wave plate

Abstract

To provide a wave plate that enables adjustment of an optical path difference between the transmitted light passing through a region having a formed pattern layer and the transmitted light passing through a region having no pattern layer formed.SOLUTION: Provided is a wave plate 10 comprising: a transparent substrate 11; a pattern layer 12 that is patterned on the transparent substrate 11; and a cured resin layer 13 that is formed in a region on the transparent substrate 11 where the pattern layer 12 is not formed. The pattern layer 12 has a retardation film 12b. When the main refractive indices of the retardation film 12b are Nx, Ny, and the refractive index of the cured resin layer 13 is Nr, the wave plate 10 satisfies formula Nx>Nr>Ny.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wavelength plate, a wavelength selective switch, an optical add-drop multiplexer, and a method for manufacturing a wavelength plate.

Background Art

[0002] In recent years, the traffic of data centers and mobile networks has been increasing rapidly. In the optical backbone networks that support these, high speed, large capacity, long distance, and reliability are essential. To meet these requirements, wavelength division multiplexing (WDM) signals are used in optical communication, and multiple optical signals can be transmitted through a single optical fiber. As a result, it is possible to increase the communication capacity without adding optical fibers. However, there is a problem that a large cost is required to reconstruct the form of the optical backbone network, and an optical add-drop multiplexer (ROADM) has been developed (see, for example, Non-Patent Document 1). ROADM can remotely select and switch the optimal transmission path of the WDM signal, and is used in optical communication as a technology that can flexibly reconstruct the optical backbone network. As a key device of ROADM, a wavelength selective switch (WSS) can be mentioned, which has functions of multiplexing, demultiplexing, and switching the optical signal path of each wavelength.

[0003] The WSS is, for example, a mechanism that causes light incident from an input port to be incident on an LCOS (Liquid Crystal on Silicon) as a switching element (optical beam deflector) via a plurality of optical elements, modulates the phase of the incident light with the LCOS, and causes the light to be incident on an arbitrary output port. Here, the LCOS that modulates the phase of the incident light has polarization dependence and operates only with polarized light in a specific direction, and it is necessary to incident polarized light that can be modulated by the LCOS. For this reason, the WSS requires a configuration for compensating the polarization state. The WSS includes, for example, a polarization beam splitter that separates incident light from a port array into two linearly polarized lights that are orthogonal to each other, a wave plate that rotates the direction of one of the separated linearly polarized lights by 90°, and a switching element (optical beam deflector) that modulates the phase of the incident light and causes the light to be incident on an arbitrary output port.

[0004] On the other hand, Patent Document 1 describes a half-wave plate including a transparent substrate, an optically anisotropic layer including a birefringent film, and a protective layer that is an atomic layer deposition layer of an inorganic compound and is in contact with the optically anisotropic layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, in order to apply the half-wave plate described in Patent Document 1 to a wavelength selection switch, it is conceivable to pattern the optically anisotropic layer. However, it is desired to adjust and reduce the optical path difference between the transmitted light that has passed through the region where the optically anisotropic layer is formed and the transmitted light that has passed through the region where the optically anisotropic layer is not formed. At this time, in order to correct the optical path difference, it is also conceivable to insert other optical elements, but adding new components becomes a factor in increasing costs.

[0008] An object of the present invention is to provide a wave plate capable of adjusting the optical path difference between the transmitted light that has passed through the region where the pattern layer is formed and the transmitted light that has passed through the region where the pattern layer is not formed.

Means for Solving the Problems

[0009] (1) A wave plate comprising a transparent substrate, a pattern layer formed with a pattern on the transparent substrate, and a cured resin layer formed in a region on the transparent substrate where the pattern layer is not formed, wherein the pattern layer has a retardation film, and when the main refractive indices of the retardation film are Nx and Ny and the refractive index of the cured resin layer is Nr, the formula Nx>Nr>Ny is satisfied.

[0010] (2) The wave plate according to (1), wherein the surface of the pattern layer is covered with a protective film.

[0011] (3) The wave plate according to (1) or (2), wherein the pattern layer further has an antireflection film disposed between the retardation film and the transparent substrate.

[0012] (4) The wave plate according to any one of (1) to (3), further comprising a second transparent substrate disposed on the side opposite to the transparent substrate with respect to the cured resin layer.

[0013] (5) The wave plate according to (4), further comprising an antireflection film disposed between the cured resin layer and the second transparent substrate.

[0014] (6) A wavelength selection switch comprising the retardation plate according to any one of (1) to (5).

[0015] (7) An optical branching / insertion device comprising the wavelength selection switch according to (6).

[0016] (8) A method for manufacturing a retardation plate according to any one of (1) to (5), the method including: forming a precursor of the pattern layer on the transparent substrate; laser processing the precursor of the pattern layer to form the pattern layer; and forming the cured resin layer in a region where the pattern layer is not formed on the transparent substrate, and forming the retardation film when forming the precursor of the pattern layer.

[0017] (9) The method for manufacturing a retardation plate according to (8), further including: sequentially forming an antireflection film and the retardation film when forming the precursor of the pattern layer; disposing a second transparent substrate on the side opposite to the transparent substrate with respect to the cured resin layer; and forming an antireflection film between the cured resin layer and the second transparent substrate.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a retardation plate capable of adjusting an optical path difference between transmitted light passing through a region where a pattern layer is formed and transmitted light passing through a region where the pattern layer is not formed.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0021] FIG. 1 shows a wavelength plate according to an embodiment of the present invention.

[0022] The wavelength plate 10 includes a transparent substrate 11, a pattern layer 12 formed with a pattern on the transparent substrate 11, and a cured resin layer 13 formed in a region on the transparent substrate 11 where the pattern layer 12 is not formed. Here, the cured resin layer 13 is also formed on the pattern layer 12. The pattern layer 12 has an antireflection film 12a and a retardation film 12b sequentially laminated on the transparent substrate 11, and the surface is covered with a protective film 12c. Here, the surface of the region on the transparent substrate 11 where the pattern layer 12 is not formed is also covered with the protective film 12c. On the cured resin layer 13 of the wavelength plate 10, an antireflection film 14 and a transparent substrate 15 are sequentially laminated. Further, antireflection films 16 and 17 are formed on the surfaces of the transparent substrates 11 and 15 on the sides not facing the antireflection films 12a and 14, respectively. Thereby, the transmittance of light in the use band of the wavelength plate 10 is improved.

[0023] At this time, when the principal refractive indices of the retardation film 12b are Nx and Ny, and the refractive index of the cured resin layer 13 is Nr, the formula Nx>Nr>Ny is satisfied. Therefore, the wavelength plate 10 can adjust the optical path difference (hereinafter referred to as the optical path difference) between the transmitted light passing through the region where the pattern layer 12 is formed and the transmitted light passing through the region where the pattern layer 12 is not formed.

[0024] For example, when Nx = 1.608, Ny = 1.492, Nr = 1.541, and the thickness of the retardation film 12b is 6 μm, the optical path difference in the ordinary light corresponding to the slow axis (Nx axis) is (1.608 - 1.541) × 6 = 0.402 [μm] This results in the optical path difference in the extraordinary light corresponding to the fast axis (Ny axis) being (1.541 - 1.492) × 6 = 0.294 [μm] This causes the optical path differences in the ordinary light and the extraordinary light to become smaller.

[0025] Here, in order to reduce the optical path differences in the ordinary light and the extraordinary light, the formula [(Nx + Ny) / 2] + 0.5 > Nr > [(Nx + Ny) / 2] - 0.5 is preferably satisfied, and the formula [(Nx + Ny) / 2] + 0.25 > Nr > [(Nx + Ny) / 2] - 0.25 is more preferably satisfied.

[0026] The birefringence (Nx - Ny) of the retardation film 12b is not particularly limited, but is, for example, 0.1 or more and 0.5 or less. The refractive index of the cured resin layer 13 is not particularly limited, but is, for example, 1.5 or more and 2.0 or less.

[0027] The retardation film 12b includes columnar portions and void portions provided between the columnar portions, and is formed by oblique vapor deposition of a dielectric material (see, for example, Patent Document 1). The refractive index of the dielectric material is not particularly limited, but is, for example, 1.5 or more. Examples of the dielectric material include, but are not limited to, Ta 2 O 5 , TiO 2 , SiO 2 , Al 2 O 3 , NbO 5 , MaF 2 and two or more of them may be used in combination. Among these, Ta with a refractive index of 2.25 2 O 5 is preferred. Note that an arbitrary retardation can be set by adjusting the film thickness of the retardation film 12b.

[0028] The protective film 12c suppresses the intrusion of moisture into the retardation film 12b and stabilizes the optical properties. The material constituting the protective film 12c is not particularly limited, and examples thereof include dielectric materials such as SiO 2 and the like. The film thickness of the protective film 12c is not particularly limited, and is, for example, 30 nm or more and 3 μm or less. The method for forming the protective film 12c is not particularly limited, and examples thereof include chemical vapor deposition, plasma assist method, and sputtering method.

[0029] The shape of the pattern of the pattern layer 12 is set according to the use of the wave plate 10. For example, when the wave plate 10 is applied to a wavelength selection switch, the shape of the pattern of the pattern layer 12 is not particularly limited as long as it rotates the polarization direction of one polarized light component separated from the incident light by 90° and does not change the polarization direction of the other polarized light component.

[0030] The transparent substrates 11 and 15 are not particularly limited as long as they can retain the function as a wave plate with respect to the light in the used band. The transmittance of the light in the used band of the transparent substrates 11 and 15 is, for example, 92% or more. The wavelength of the light in the used band is not particularly limited, and is, for example, 250 nm or more and 1700 nm or less. The light in the used band is preferably infrared light. The refractive index of the transparent substrates 11 and 15 is not particularly limited, and is, for example, 1.1 or more and 2.2 or less. The material constituting the transparent substrates 11 and 15 is not particularly limited, and examples thereof include glasses such as quartz glass and white plate glass. The average thickness of the transparent substrates 11 and 15 is not particularly limited, and is, for example, 0.1 mm or more and 1.0 mm.

[0031] The curable resin constituting the curable resin layer 13 is a material transparent to the wavelength of the light in the above-mentioned used band, and preferably has the same refractive index as the transparent substrates 11 and 15. The curable resin layer 13 is formed, for example, by curing a photocurable resin or a thermosetting resin. Thereby, the mechanical properties of the retardation film 12b are improved. Examples of commercially available ultraviolet curable resins include optical adhesive NOA61 (manufactured by Norland) having a refractive index of 1.56 (typical value) for the cured product.

[0032] The antireflection films 12a, 14, 16, and 17 are formed, for example, by alternately laminating two types of dielectric materials having different refractive indices. The dielectric material is not particularly limited, and examples thereof include TiO 2 , SiO 2 , Ta 2 O 5 , Al 2 O 3 , CeO 2 , ZrO 2 , ZrO, Nb 2 O 5 , HfO 2 . Among these, combinations of SiO 2 and Nb 2 O 5 , and combinations of TiO 2 and SiO 2 are preferable. The number of layers of the antireflection films 12a, 14, 16, and 17 is not particularly limited, and is, for example, 2 or more and 40 or less.

[0033] Next, a method for manufacturing the wave plate 10 will be described.

[0034] First, after cleaning the transparent substrate 11, an antireflection film 12a and a retardation film 12b, which are precursors of the pattern layer 12, are sequentially formed on the transparent substrate 11 (see Fig. 2(a)). At this time, in order to evaporate the moisture present in the voids of the retardation film 12b, annealing treatment may be performed at a temperature of 100°C or higher. Next, the antireflection film 12a and the retardation film 12b are laser processed to form a recess 21 having a rectangular shape in top view, thereby forming a pattern on the antireflection film 12a and the retardation film 12b (see Figs. 2(b) and 3). At this time, since the degree of freedom of processing is high and the thermal influence on the workpiece is small, it is preferable to use an ultrashort pulse laser. Next, a protective film 12c is formed on the surfaces of the laser-processed antireflection film 12a and retardation film 12b to obtain the pattern layer 12 (see Fig. 2(c)). Thereby, the intrusion of moisture into the voids of the retardation film 12b is suppressed. Next, a photocurable resin or a thermosetting resin 13A is filled into the recess 21 (see Fig. 4(a)). Further, after bonding a transparent substrate 15 on which an antireflection film 14 has been previously formed to the photocurable resin or the thermosetting resin 13A, the photocurable resin or the thermosetting resin 13A is cured to form a cured resin layer 13 (see Fig. 4(b)). At this time, the surfaces of the transparent substrates 11 and 15 may be polished to adjust the thicknesses of the transparent substrates 11 and 15. Next, antireflection films 16 and 17 are formed on the surfaces of the transparent substrates 11 and 15 (see Fig. 4(c)).

[0035] Note that after filling the photocurable resin or the thermosetting resin 13A into the recess 21, the photocurable resin or the thermosetting resin 13A may be cured to form the cured resin layer 13 without bonding the transparent substrate 15 on which the antireflection film 14 has been previously formed. In this case, for example, after forming the antireflection film 14 on the cured resin layer 13, it is bonded to the transparent substrate 15.

[0036] The waveplate 10 can be applied to, for example, a wavelength selection switch.

[0037] Fig. 5 shows a part of a wavelength selection switch including the waveplate 10.

[0038] The wavelength selection switch 50 includes a polarization beam splitter 51 that separates incident light from the optical port array into two linearly polarized lights that are orthogonal to each other, and a wave plate 10 that rotates the direction of one of the separated linearly polarized lights by 90° and converts it into a polarization that can be modulated by the LCOS. At this time, of the linearly polarized lights separated by the polarization beam splitter 51, one linearly polarized light passes through the retardation film 12b, and the polarization direction rotates by 90°. On the other hand, since the other linearly polarized light separated by the polarization beam splitter 51 does not pass through the retardation film 12b, the polarization direction does not change.

[0039] Note that the two linearly polarized lights that are orthogonal to each other and separated by the polarization beam splitter 51 respectively mean polarized lights in which the vibration of the electric field is parallel and perpendicular to the incident plane. For the incident plane, the polarized light in which the vibration of the electric field is parallel is defined as P-polarized light, and the polarized light in which the vibration of the electric field is perpendicular to the incident plane is defined as S-polarized light. Here, the incident plane is perpendicular to the reflection plane and is the plane including the incident light ray and the reflected light ray.

[0040] The wavelength selection switch 50 can be applied to, for example, an optical branching and insertion device.

[0041] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and the above embodiments may be appropriately changed within the scope of the gist of the present invention. For example, at least a part of the antireflection films 12a, 14, 16, 17 and the protective film 12c may be omitted.

Explanation of Reference Numerals

[0042] 10 Wave plate 11, 15 Transparent substrate 12 Pattern layer 12a, 14, 16, 17 Antireflection film 12b Retardation film 12c Protective film 13 Cured resin layer 13A Photo-curable resin or thermosetting resin 21 Concave portion 50 Wavelength selection switch 51 Beam splitter

Claims

1. A transparent substrate, a pattern layer formed with a pattern on the transparent substrate, and a cured resin layer formed in a region on the transparent substrate where the pattern layer is not formed, and comprising: the pattern layer has a retardation film, when the main refractive indices of the retardation film are Nx and Ny, and the refractive index of the cured resin layer is Nr, the formula Nx > Nr > Ny is satisfied, a wave plate.

2. The wave plate according to claim 1, wherein the surface of the pattern layer is covered with a protective film.

3. The wave plate according to claim 1 or 2, wherein the pattern layer further has an antireflection film disposed between the retardation film and the transparent substrate.

4. The wave plate according to claim 1 or 2, further comprising a second transparent substrate disposed on the side opposite to the transparent substrate with respect to the cured resin layer.

5. The wave plate according to claim 4, further comprising an antireflection film disposed between the cured resin layer and the second transparent substrate.

6. A wavelength selection switch comprising the wave plate according to claim 1 or 2.

7. An optical branching / insertion device comprising the wavelength selection switch according to claim 6.

8. A method for manufacturing the wave plate according to claim 1 or 2, comprising: a step of forming a precursor of the pattern layer on the transparent substrate; a step of laser processing the precursor of the pattern layer to form the pattern layer; and a step of forming the cured resin layer in a region on the transparent substrate where the pattern layer is not formed, and including: forming the retardation film when forming the precursor of the pattern layer, a method for manufacturing a wave plate.

9. When forming the precursor of the pattern layer, sequentially forming an antireflection film and the retardation film, a step of disposing a second transparent substrate on the side opposite to the transparent substrate with respect to the cured resin layer; and a step of forming an antireflection film between the cured resin layer and the second transparent substrate, and further including the method for manufacturing a wave plate according to claim 8.

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