Wavelength plate, wavelength selection switch, optical branch insertion device and wavelength plate manufacturing method

Abstract

To provide a wavelength plate which can suppress occurrence of cracks of a retardation film.SOLUTION: A wavelength plate 10 includes a transparent substrate 11, a pattern layer 121 which is pattern-formed on the transparent substrate 11, a first curable resin layer 131 which is formed on the outer periphery of the pattern layer 121 on the transparent substrate 11, and a second curable resin layer 132 which is formed in a region where the pattern layer 121 is not formed, on the inner peripheral side of the first curable resin layer 131 on the transparent substrate 11. The pattern layer 121 has a retardation film 12b.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wave plate, a wavelength selective switch, an optical add / drop device, and a method for manufacturing a wave plate. [Background technology]

[0002] In recent years, traffic in data centers and mobile networks has increased dramatically, making high speed, large capacity, long distance, and reliable optical trunk networks essential for supporting these networks. To meet these demands, optical communications utilize wavelength division multiplexing (WDM) signals, which allow multiple optical signals to be transmitted over a single optical fiber, thereby enabling increased communication capacity without the need for additional optical fibers. However, reconfiguring optical trunk networks poses significant costs, leading to the development of the ROADM (Road Add / Drop Multiplexer) (see, for example, Non-Patent Document 1). ROADMs enable remote selection and switching of optimal transmission paths for WDM signals, and are used in optical communications as a technology that enables flexible reconfiguration of optical trunk networks. A key device in ROADMs is the wavelength selective switch (WSS), which has the functions of multiplexing and demultiplexing optical signals of various wavelengths and switching the paths of optical signals.

[0003] A WSS is a mechanism in which light incident from an input port passes through multiple optical elements and enters a liquid crystal on silicon (LCOS) switching element (light beam deflector), which then modulates the phase of the incident light and directs it to a desired output port. The LCOS, which modulates the phase of the incident light, is polarization-dependent and operates only with a specific polarization direction. Therefore, the WSS requires a configuration to compensate for the polarization state. A WSS typically includes a polarizing beam splitter that splits the incident light from the port array into two orthogonal linearly polarized beams, a wave plate that rotates the polarization direction of one of the split linearly polarized beams by 90°, and a switching element (light beam deflector) that modulates the phase of the incident light and directs it to a desired 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] Japanese Patent Publication No. 2020-12876 [Non-patent literature]

[0006] [Non-Patent Document 1] Yuzo Ishii, Naoki Ohba, Akio Sahara, and Koichi Hadama, "WSS Module Technology for High-Performance ROADMs," NTT Technical Journal, November 2013, pp. 21-24 Summary of the Invention [Problem to be solved by the invention]

[0007] Here, in order to apply the half-wave plate described in Patent Document 1 to a wavelength selective switch, it is possible to pattern the optically anisotropic layer, but when manufacturing the wave plate, if the surface of the transparent substrate is polished or diced, there is a risk that the birefringent film will absorb moisture and crack.

[0008] An object of the present invention is to provide a wave plate that can suppress the occurrence of cracks in a retardation film. [Means for solving the problem]

[0009] (1) A wave plate comprising: a transparent substrate; a patterned layer formed on the transparent substrate; a first cured resin layer formed on at least a portion of the outer periphery of the patterned layer on the transparent substrate; and a second cured resin layer formed in an area of ​​the transparent substrate on the inner periphery of the first cured resin layer where no patterned layer is formed, wherein the patterned layer has a retardation film.

[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 includes an anti-reflection 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 opposite side of the transparent substrate with respect to the first cured resin layer and the second cured resin layer.

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

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

[0015] (7) An optical add / drop device comprising the wavelength selective switch according to (6).

[0016] (8) A method for producing the wave plate according to any one of (1) to (5), comprising the steps of: 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 first cured resin layer on at least a part of the outer periphery of the transparent substrate, and forming the second cured resin layer in an area of ​​the transparent substrate on the inner side of the first cured resin layer where no pattern layer is formed, wherein the retardation film is formed when the precursor of the pattern layer is formed.

[0017] (9) The method for manufacturing a wave plate according to (8), further comprising the steps of: forming an anti-reflection film and the retardation film sequentially when forming a precursor of the pattern layer; and arranging a second transparent substrate on the opposite side of the transparent substrate with respect to the first cured resin layer and the second cured resin layer; and forming an anti-reflection film between the first cured resin layer and the second cured resin layer and the second transparent substrate. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a wave plate that can suppress the occurrence of cracks in the retardation film. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing a wave plate according to an embodiment of the present invention. [Figure 2] 2A to 2C are cross-sectional views illustrating a method for manufacturing the wave plate of FIG. [Figure 3] 2A to 2C are top views illustrating a method for manufacturing the wave plate of FIG. [Figure 4] 2A to 2C are cross-sectional views illustrating a method for manufacturing the wave plate of FIG. [Figure 5] 4 is a top view showing a modified example of the shape of the first recess in FIG. 3. FIG. [Figure 6] 4 is a top view showing a modified example of the shape of the first recess in FIG. 3. FIG. [Figure 7] 2 is a schematic diagram showing a part of a wavelength selective switch including the wave plate of FIG. 1. FIG. [Figure 8] FIG. 2 is a top view illustrating a method for manufacturing a test piece used in the examples. [Figure 9] FIG. 2 is a cross-sectional view showing a precursor of a test piece used in the examples. DETAILED DESCRIPTION OF THE INVENTION

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

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

[0022] The wave plate 10 includes a transparent substrate 11, a patterned layer 121 formed on the transparent substrate 11, a first cured resin layer 131 formed on the outer periphery of the patterned layer 121 on the transparent substrate 11, and a second cured resin layer 132 formed on a region of the transparent substrate 11 on the inner periphery of the first cured resin layer 131 where the patterned layer 121 is not formed. The second cured resin layer 132 is also formed on the patterned layer 121. The patterned layer 121 is formed by sequentially stacking an antireflection film 12a and a retardation film 12b on the transparent substrate 11, and its surface is covered with a protective film 12c. The region of the transparent substrate 11 on which the patterned layer 121 is not formed is also covered with the protective film 12c. A non-patterned layer 122 is formed on the transparent substrate 11 on the outer periphery of the first cured resin layer 131. Like the patterned layer 121, the non-patterned layer 122 has an antireflection film 12a and a retardation film 12b sequentially stacked on a transparent substrate 11, and its surface is covered with a protective film 12c. A third cured resin layer 133 is formed on the non-patterned layer 122. The wave plate 10 has an antireflection film 14 and a transparent substrate 15 sequentially stacked on the first cured resin layer 131, the second cured resin layer 132, and the third cured resin layer 133. The wave plate 10 also has antireflection films 16 and 17 formed on the surfaces of the transparent substrates 11 and 15, respectively, that do not face the antireflection films 12a and 14. This improves the transmittance of light in the wavelength band used by the wave plate 10.

[0023] The first cured resin layer 131 may be formed on a part of the outer periphery of the pattern layer 121 on the transparent substrate 11.

[0024] The retardation film 12b has columnar portions and voids between the columnar portions, and is formed by obliquely evaporating 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. The dielectric material is not particularly limited, but examples thereof include Ta2O5, TiO2, SiO2, Al2O3, NbO5, and MaF2, and two or more of them may be used in combination. Among these, Ta2O5, which has a refractive index of 2.25, is preferred. Note that an arbitrary retardation can be set by adjusting the film thickness of the retardation film 12b.

[0025] The protective film 12c prevents moisture from penetrating into the retardation film 12b, stabilizing the optical characteristics. The material constituting the protective film 12c is not particularly limited, but examples thereof include dielectric materials such as SiO2. The thickness of the protective film 12c is not particularly limited, but examples thereof are 30 nm to 3 μm. The method for forming the protective film 12c is not particularly limited, but examples thereof include chemical vapor deposition, plasma-assisted deposition, and sputtering.

[0026] The shape of the pattern of the pattern layer 121 is set depending on the application of the wave plate 10. For example, when the wave plate 10 is applied to a wavelength selective switch, the shape of the pattern of the pattern layer 121 is not particularly limited as long as it rotates the polarization direction of one polarized component separated from incident light by 90° and does not change the polarization direction of the other polarized component.

[0027] The transparent substrates 11 and 15 are not particularly limited as long as they can function as wave plates for light in the used band. The transmittance of the transparent substrates 11 and 15 for light in the used band is, for example, 92% or more. The wavelength of the light in the used band is not particularly limited, but is, for example, 250 nm or more and 1700 nm or less. The light in the used band is preferably infrared. The refractive index of the transparent substrates 11 and 15 is not particularly limited, but 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, but examples include glass such as quartz glass and white plate glass. The average thickness of the transparent substrates 11 and 15 is not particularly limited, but is, for example, 0.1 mm or more and 1.0 mm.

[0028] The curable resins constituting the first cured resin layer 131, the second cured resin layer 132, and the third cured resin layer 133 are preferably transparent to the wavelengths of light in the aforementioned band of use and have a refractive index equivalent to that of the transparent substrates 11 and 15. The first cured resin layer 131, the second cured resin layer 132, and the third cured resin layer 133 are formed, for example, by curing a photocurable resin or a thermosetting resin. This improves the mechanical properties of the retardation film 12b. An example of a commercially available ultraviolet curable resin is the optical adhesive NOA61 (manufactured by Norland), which has a refractive index of 1.56 (typical value) when cured.

[0029] The cured resins constituting the first cured resin layer 131, the second cured resin layer 132, and the third cured resin layer 133 may be the same or different.

[0030] The anti-reflection films 12a, 14, 16, and 17 are formed, for example, by alternately stacking two types of dielectric materials with different refractive indices. Examples of dielectric materials include, but are not limited to, TiO2, SiO2, Ta2O5, Al2O3, CeO2, ZrO2, ZrO, Nb2O5, and HfO2. Among these, combinations of SiO2 and Nb2O5 and combinations of TiO2 and SiO2 are preferred. The number of layers in the anti-reflection films 12a, 14, 16, and 17 is, for example, 2 to 40, but is not limited to these.

[0031] Next, a method for manufacturing the wave plate 10 will be described.

[0032] First, after cleaning the transparent substrate 11, an antireflection film 12a and a retardation film 12b are sequentially formed on the transparent substrate 11 as precursors of the patterned layer 121 and the non-patterned layer 122 (see FIG. 2(a)). At this time, an annealing treatment may be performed at a temperature of 100°C or higher to evaporate moisture present in the voids of the retardation film 12b. Next, the antireflection film 12a and the retardation film 12b are laser-processed to form a first recess 21 that is hollow and rectangular in top view and a second recess 22 that is rectangular in top view and located on the inner periphery of the first recess 21, thereby patterning the antireflection film 12a and the retardation film 12b (see FIGS. 2(b) and 3). Here, the first recess 21 and the second recess 22 are regions where the first cured resin layer 131 and the second cured resin layer 132, respectively, will be formed. Here, it is preferable to use an ultrashort pulse laser because it provides a high degree of freedom in processing and has minimal thermal impact on the workpiece. Next, a protective film 12c is formed on the laser-processed surfaces of the antireflection film 12a and the retardation film 12b to form a patterned layer 121 and a non-patterned layer 122 (see FIG. 2(c)). This prevents moisture from penetrating into the voids in the retardation film 12b. Next, a photocurable resin or a thermosetting resin 13A is filled into the first recesses 21 and the second recesses 22 (see FIG. 4(a)). At this time, the photocurable resin or the thermosetting resin 13A is also formed on the patterned layer 121 and the non-patterned layer 122. Furthermore, a transparent substrate 15 on which an antireflection film 14 has been formed in advance is bonded to the photocurable resin or the thermosetting resin 13A, and the photocurable resin or the thermosetting resin 13A is then cured to form a first cured resin layer 131, a second cured resin layer 132, and a third cured resin layer 133 (see FIG. 4(b)). At this time, the surfaces of the transparent substrates 11 and 15 are polished to adjust the thickness of the transparent substrates 11 and 15, but if the first cured resin layer 131 is not formed, the retardation film 12b constituting the pattern layer 121 will absorb moisture and become prone to cracks. Next, antireflection films 16 and 17 are formed on the surfaces of the transparent substrates 11 and 15 (see FIG. 4(c)). Finally, dicing is performed to obtain the wave plate 10, but if the first cured resin layer 131 is not formed, the retardation film 12b constituting the pattern layer 121 will absorb moisture and become prone to cracks.

[0033] The shape of the first recess 21 is not limited to a hollow rectangular shape when viewed from above, and may be, for example, a hollow circular shape when viewed from above, as long as the shape can suppress moisture absorption of the retardation film 12b constituting the pattern layer 121 by the first cured resin layer 131 and can be formed on the outer periphery of the pattern layer 121 (see, for example, Figure 5).

[0034] Furthermore, when the retardation film 12b absorbs moisture only from a specific direction, the first recesses 21 may be formed in part of the outer periphery of the second recesses 22 (see, for example, FIGS. 6(a) to 6(d)).

[0035] Furthermore, after filling the first recess 21 and the second recess 22 with the photocurable resin or thermosetting resin 13A, the photocurable resin or thermosetting resin 13A may be cured to form the first cured resin layer 131, the second cured resin layer 132, and the third cured resin layer 133 without bonding the transparent substrate 15 on which the antireflection film 14 has been formed in advance. In this case, for example, the antireflection film 14 is formed on the first cured resin layer 131, the second cured resin layer 132, and the third cured resin layer 133, and then the transparent substrate 15 is bonded to the photocurable resin or thermosetting resin 13A.

[0036] The wave plate 10 can be applied to, for example, a wavelength selective switch.

[0037] FIG. 7 shows a part of a wavelength selective switch including a waveplate 10.

[0038] The wavelength selective switch 50 includes a polarizing beam splitter 51 that splits the incident light from the optical port array into two orthogonal linearly polarized lights, and a wave plate 10 that rotates the polarization direction of one of the split linearly polarized lights by 90° to convert it into a polarized light that can be modulated by the LCOS. At this time, one of the linearly polarized lights split by the polarizing beam splitter 51 passes through a phase difference film 12b, and the polarization direction of the other polarized light is rotated by 90°. On the other hand, the other polarized light split by the polarizing beam splitter 51 does not pass through the phase difference film 12b, and therefore the polarization direction remains unchanged.

[0039] The two orthogonal linearly polarized light beams separated by the polarizing beam splitter 51 refer to polarized light beams whose electric field oscillations are parallel and perpendicular to the plane of incidence, respectively, and polarized light beams whose electric field oscillations are parallel to the plane of incidence are defined as P-polarized light beams, and polarized light beams whose electric field oscillations are perpendicular to the plane of incidence are defined as S-polarized light beams. Here, the plane of incidence is perpendicular to the plane of reflection and refers to the plane that contains the incident light beam and the reflected light beam.

[0040] The wavelength selective switch 50 can be applied to, for example, an optical add-drop multiplexer.

[0041] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the present invention. For example, at least a portion of the antireflection films 12a, 14, 16, and 17 and the protective film 12c may be omitted. The first cured resin layer 131 can also be applied to a wave plate in which only a pattern layer having a retardation film is present on the inner circumferential side of the first cured resin layer 131, and the second cured resin layer 132 is not present. [Example]

[0042] Examples of the present invention will be described below, but the present invention is not limited to these examples. In these examples, a test piece simulating the wave plate 10 was used to evaluate cracks in the retardation film 12b.

[0043] (Preparation of test specimens) First, a glass substrate serving as the transparent substrate 11 was cleaned, and then a retardation film 12b (TaO film) serving as a precursor of the patterned layer 121 and the non-patterned layer 122 was formed on the transparent substrate 11. At this time, an annealing treatment was performed at a temperature of 100°C or higher to evaporate moisture present in the voids of the retardation film 12b. Next, the retardation film 12b was laser-processed using an ultrashort pulse laser to form first recesses 21 having a hollow rectangular shape when viewed from above, thereby patterning the retardation film 12b (see FIG. 8). Here, the first recesses 21 are regions where the cured resin layer 13 is to be formed. Next, a protective film 12c (SiO film) was formed on the laser-processed surface of the retardation film 12b to form the patterned layer 121 and the non-patterned layer 122. Next, a photocurable resin was filled into the first recesses 21. At this time, the photocurable resin was also formed on the patterned layer 121 and the non-patterned layer 122. Furthermore, a glass substrate serving as the transparent substrate 15 was bonded to a photocurable resin, and the photocurable resin was then photocured to form a cured resin layer 13. At this time, the surfaces of the transparent substrates 11 and 15 were polished to adjust the thickness of the transparent substrates 11 and 15. Next, antireflection films 16 and 17 (alternately laminated films of TiO2 and SiO2) were formed on the surfaces of the transparent substrates 11 and 15 to obtain a precursor 10A of the test piece (see FIG. 9). Finally, the precursor 10A of the test piece was diced along the dashed lines shown in FIG. 8 to obtain a test piece.

[0044] (Cracks in the retardation film) After polishing the surfaces of the transparent substrates 11 and 15, the retardation film 12b was observed. It was found that no cracks had occurred in the retardation film 12b formed on the inner periphery of the cured resin layer 13, but cracks had occurred in part of the retardation film 12b formed on the outer periphery of the cured resin layer 13. Furthermore, after dicing the test piece precursor 10A, the retardation film 12b was observed. It was found that no cracks had occurred in the retardation film 12b formed on the inner periphery of the cured resin layer 13, but cracks had occurred in part of the retardation film 12b formed on the outer periphery of the cured resin layer 13. From the above, it can be seen that the occurrence of cracks in the retardation film 12b formed on the inner periphery of the cured resin layer 13 was suppressed. [Explanation of symbols]

[0045] 10 wave plate 11, 15 Transparent substrate 121 Pattern Layer 122 Non-patterned layer 12a, 14, 16, 17 Anti-reflective coating 12b Retardation film 12c protective film 131 First cured resin layer 132 Second cured resin layer 133 Third cured resin layer 13A Photocurable resin or thermosetting resin 21 First recess 22 Second recess 50 Wavelength Selective Switch 51 Polarizing beam splitter

Claims

1. A transparent substrate; a pattern layer formed on the transparent substrate; a first cured resin layer formed on at least a part of the outer periphery of the pattern layer on the transparent substrate; a second cured resin layer formed in an area on the transparent substrate where no pattern layer is formed, the area being located more inward than the first cured resin layer; The pattern layer has a retardation film.

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

3. 3. The wave plate according to claim 1, wherein the pattern layer further comprises an anti-reflection film disposed between the retardation film and the transparent substrate.

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

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

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

7. An optical add / drop multiplexer comprising the wavelength selective switch according to claim 6.

8. A method for manufacturing the wave plate according to claim 1 or 2, comprising the steps of: forming a precursor of the pattern layer on the transparent substrate; laser processing a precursor of the pattern layer to form the pattern layer; forming the first cured resin layer on at least a part of the outer periphery of the transparent substrate, and forming the second cured resin layer in an area on the transparent substrate that is inner than the first cured resin layer and where no pattern layer is formed, The method for manufacturing a wave plate includes forming the retardation film when forming a precursor of the pattern layer.

9. When forming a precursor of the pattern layer, an anti-reflection film and the retardation film are formed in sequence; disposing a second transparent substrate on the opposite side of the transparent substrate with respect to the first cured resin layer and the second cured resin layer; The method for manufacturing a wave plate according to claim 8 , further comprising the step of forming an anti-reflection film between the first cured resin layer and the second cured resin layer and the second transparent substrate.

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