Waveplate, wavelength selection switch, optical branch insertion device, and method for manufacturing waveplate

Abstract

Provided is a waveplate comprising: a transparent substrate; a pattern layer that is patterned on the transparent substrate; a first cured resin layer that is formed on at least a part of the outer periphery of the pattern layer on the transparent substrate; and a second cured resin layer that is formed in a region on the transparent substrate, said region being further to the inner side than the first cured resin layer where the pattern layer is not formed. The pattern layer has a retardation film.

Description

Waveplate, wavelength selective switch, optical add / drop device, and method of manufacturing waveplate

[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.

[0002] In recent years, traffic in data centers and mobile networks has increased dramatically, making high speed, large capacity, long distance, and reliable the optical trunk networks that support them. 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 the optical trunk network configuration poses significant costs, leading to the development of the Reconfigurable Optical Add / Drop Multiplexer (ROADM) (see, for example, Non-Patent Document 1). ROADMs are capable of remotely selecting and switching the optimal transmission path 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 each wavelength and switching the path of optical signals.

[0003] A WSS is a mechanism in which, for example, light incident from an input port is incident on a liquid crystal on silicon (LCOS) switching element (light beam deflector) via multiple optical elements, and the LCOS modulates the phase of the incident light before directing it to any output port. The LCOS, which modulates the phase of the incident light, has polarization dependency, operating only with polarization in a specific direction. Therefore, it is necessary to input polarized light that can be modulated by the LCOS. Therefore, the WSS requires a configuration for compensating for the polarization state. The WSS includes, for example, a polarizing beam splitter that splits the incident light from the port array into two orthogonal linearly polarized lights, a wave plate that rotates the polarization direction of one of the split linearly polarized lights by 90°, and a switching element (light beam deflector) that modulates the phase of the incident light before directing it to any 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.

[0005] Japanese Patent Application Laid-Open No. 2020-12876

[0006] Yuzo Ishii, Naoki Ohba, Akio Sahara, and Koichi Hadama, "WSS Module Technology for High-Performance ROADM," NTT Technical Journal, November 2013, pp. 21-24

[0007] Here, in order to apply the half-wave plate described in Patent Document 1 to a wavelength selective switch, it is possible to consider patterning 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.

[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) A wave plate described in any one of (1) to (3), further comprising a second transparent substrate arranged 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 described in (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.

[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.

[0019] 1 is a cross-sectional view showing a wave plate according to one embodiment of the present invention; FIG. 2 is a cross-sectional view illustrating a method for manufacturing the wave plate of FIG. 1; FIG. 3 is a top view illustrating a method for manufacturing the wave plate of FIG. 1; FIG. 4 is a cross-sectional view illustrating a method for manufacturing the wave plate of FIG. 1; FIG. 5 is a top view illustrating a modified shape of the first recess of FIG. 3; FIG. 6 is a schematic view showing a part of a wavelength selective switch including the wave plate of FIG. 1; FIG. 7 is a top view illustrating a method for manufacturing a test piece used in the examples; FIG. 8 is a cross-sectional view showing a precursor of the test piece used in the examples.

[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 an area of ​​the transparent substrate 11 on which the patterned layer 121 is not formed and on the inner periphery of the first cured resin layer 131. 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 the surface is covered with a protective film 12c. The area on 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 outer periphery of the first cured resin layer 131 on the transparent substrate 11. Like the patterned layer 121, the non-patterned layer 122 has an anti-reflection 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 anti-reflection 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 anti-reflection films 16 and 17 formed on the surfaces of the transparent substrates 11 and 15, respectively, that do not face the anti-reflection 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 gaps 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 is, for example, Ta ２ O ５ , TiO ２ , SiO ２ , Al ２ O ３ , NbO ５ , MaF ２ Among these, Ta, which has a refractive index of 2.25, is preferred. ２ O ５ It is preferable that the thickness of the retardation film 12b is adjusted to set an arbitrary retardation.

[0025] The protective film 12c prevents moisture from penetrating into the retardation film 12b and stabilizes the optical characteristics. The material of the protective film 12c is not particularly limited, but may be, for example, SiO ２ Examples of suitable dielectric materials include the above. The thickness of the protective film 12c is not particularly limited, but is, for example, 30 nm to 3 μm. The method for forming the protective film 12c is not particularly limited, but examples 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 cured 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 by alternately laminating two types of dielectric materials with different refractive indices. The dielectric materials are not particularly limited, but 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 ２Among these, SiO ２ and Nb ２ O ５ and TiO ２ and SiO ２ The number of layers of the antireflection films 12a, 14, 16, and 17 is not particularly limited, but is, for example, 2 or more and 40 or less.

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

[0032] First, the transparent substrate 11 is cleaned, and then 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, are formed. In this process, an ultrashort pulse laser is preferably used 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 or thermosetting resin 13A is filled into the first recess 21 and the second recess 22 (see FIG. 4(a)). At this time, the photocurable or 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 or thermosetting resin 13A, and the photocurable or 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 recess 21 may be formed on a part of the outer periphery of the second recess 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 without bonding the transparent substrate 15 on which the anti-reflection film 14 has been formed in advance, to form the first cured resin layer 131, the second cured resin layer 132, and the third cured resin layer 133. In this case, for example, the anti-reflection 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 portion 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 does not change.

[0039] The two orthogonal linearly polarized light beams separated by the polarizing beam splitter 51 respectively refer to polarized light beams whose electric field oscillations are parallel and perpendicular to the plane of incidence, 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 includes 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 side of the first cured resin layer 131, and the second cured resin layer 132 is not present.

[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 Piece) First, a glass substrate serving as the transparent substrate 11 was cleaned, and then a retardation film 12b (Ta) serving as a precursor of the patterned layer 121 and the non-patterned layer 122 was formed on the transparent substrate 11. ２ O ５ A film) was formed on the retardation film 12b. 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 ２film) was formed to form a patterned layer 121 and a non-patterned layer 122. Next, a photocurable resin was filled into the first recesses 21. At this time, a photocurable resin was also formed on the patterned layer 121 and the non-patterned layer 122. Furthermore, after a glass substrate serving as a transparent substrate 15 was bonded to the photocurable resin, the photocurable resin was 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 (TiO ２ and SiO ２ A layer-by-layer laminate film (layer-by-layer film) was formed 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 the test piece.

[0044] (Cracks in 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 occurred in the retardation film 12b formed on the inner periphery of the first recess 21 where the cured resin layer 13 was formed, but cracks occurred in part of the retardation film 12b formed on the outer periphery of the first recess 21 where the cured resin layer 13 was formed. Furthermore, after dicing the test piece precursor 10A, the retardation film 12b was observed. It was found that no cracks occurred in the retardation film 12b formed on the inner periphery of the cured resin layer 13, but cracks 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.

[0045] REFERENCE SIGNS LIST 10 Wave plate 11, 15 Transparent substrate 121 Patterned layer 122 Non-patterned layer 12a, 14, 16, 17 Anti-reflection film 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 selection switch 51 Polarization beam splitter

Claims

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 that is more inward than the first cured resin layer and where no patterned layer is formed, wherein the patterned 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. The wave plate according to claim 1 or 2, 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 or 2, 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 and second cured resin layers 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 device comprising the wavelength selective switch according to claim 6.

8. A method for producing a waveplate according to claim 1 or 2, 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 that is more inward than the first cured resin layer and where no pattern layer is formed; wherein the retardation film is formed when the precursor of the pattern layer is formed.

9. The method for manufacturing a wave plate according to claim 8, further comprising the steps of: sequentially forming an anti-reflection film and the retardation film when forming a precursor of the pattern layer; 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.

Images