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; and a cured resin layer that is formed in a region on the transparent substrate where the pattern layer is not formed. The pattern layer has a retardation film. When the main refractive index of the retardation film is Nx, Ny, and the refractive index of the cured resin layer is Nr, formula Nx > Nr > Ny is satisfied.

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 conceivable to pattern the optically anisotropic layer, but it is desirable to adjust and reduce the optical path difference between transmitted light that has passed through an area where the optically anisotropic layer is formed and transmitted light that has passed through an area where the optically anisotropic layer is not formed. In this case, it is conceivable to insert another optical element to correct the optical path difference, but this would add a new component, which would increase costs.

[0008] The present invention aims to provide a wave plate that can adjust the optical path difference between transmitted light that has passed through an area where a pattern layer is formed and transmitted light that has passed through an area where a pattern layer is not formed.

[0009] (1) A wave plate comprising: a transparent substrate; a patterned layer formed on the transparent substrate; and a cured resin layer formed in an area of ​​the transparent substrate where the patterned layer is not formed, wherein the patterned layer has a retardation film, and where Nx and Ny are the principal refractive indices of the retardation film and Nr is the refractive index of the cured resin layer, the wave plate satisfies the formula Nx>Nr>Ny.

[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 cured resin layer from the transparent substrate.

[0013] (5) The wave plate according to (4), further comprising an anti-reflection film disposed between the 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 cured resin layer in an area on the transparent substrate where the pattern layer is not 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 cured resin layer from the transparent substrate; and forming an anti-reflection film between the cured resin layer and the second transparent substrate.

[0018] According to the present invention, a wave plate can be provided that can adjust the optical path difference between transmitted light that has passed through an area where a pattern layer is formed and transmitted light that has passed through an area where a pattern layer is not formed.

[0019] 1 is a cross-sectional view illustrating a wave plate according to an 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; and FIG. 4 is a cross-sectional view illustrating a method for manufacturing the wave plate of FIG. 1. It is a schematic diagram illustrating a part of a wavelength selective switch including the wave plate of FIG.

[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 12 formed on the transparent substrate 11, and a cured resin layer 13 formed in an area of ​​the transparent substrate 11 where the patterned layer 12 is not formed. The cured resin layer 13 is also formed on the patterned layer 12. The patterned layer 12 includes an antireflection film 12a and a retardation film 12b, which are sequentially stacked on the transparent substrate 11, and a protective film 12c covering the surface. The area of ​​the transparent substrate 11 where the patterned layer 12 is not formed is also covered with the protective film 12c. The wave plate 10 includes an antireflection film 14 and a transparent substrate 15, which are sequentially stacked on the cured resin layer 13. The wave plate 10 also includes antireflection films 16 and 17 formed on the surfaces of the transparent substrates 11 and 15 opposite the antireflection films 12a and 14, respectively. This improves the transmittance of light in the wavelength band of the wave plate 10.

[0023] In this case, 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 following equation is satisfied: Nx>Nr>Ny. Therefore, the wave plate 10 can adjust the optical path difference (hereinafter referred to as the optical path difference) between transmitted light that has passed through the region where the pattern layer 12 is formed and transmitted light that has passed through the region where the pattern layer 12 is not formed.

[0024] For example, if Nx = 1.608, Ny = 1.492, Nr = 1.541, and the thickness of the retardation film 12b is 6 μm, the optical path difference for ordinary light corresponding to the slow axis (Nx axis) is (1.608 - 1.541) x 6 = 0.402 [μm], and the optical path difference for extraordinary light corresponding to the fast axis (Ny axis) is (1.541 - 1.492) x 6 = 0.294 [μm]. Therefore, the optical path difference for ordinary light and extraordinary light is small.

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

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

[0027] 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.

[0028] 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.

[0029] The shape of the pattern of the pattern layer 12 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 12 is not particularly limited as long as it rotates the polarization direction of one polarized component separated from the incident light by 90° and does not change the polarization direction of the other polarized component.

[0030] 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.

[0031] The curable resin constituting the curable resin layer 13 is a material that is transparent to the wavelengths of light in the aforementioned band of use, and preferably has a refractive index equivalent to that of the transparent substrates 11 and 15. The curable resin layer 13 is 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.

[0032] 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 , HfO２ Among 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.

[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 are sequentially formed on the transparent substrate 11 as precursors of the pattern layer 12 (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 rectangular recesses 21 in a top view, thereby patterning the antireflection film 12a and the retardation film 12b (see FIGS. 2(b) and 3). In this process, an ultrashort pulse laser is preferably used because of its high processing flexibility and 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 the pattern layer 12 (see FIG. 2(c)). This prevents moisture from penetrating the voids of the retardation film 12b. Next, photocurable resin or thermosetting resin 13A is filled into recess 21 (see FIG. 4(a)). Furthermore, a transparent substrate 15, on which an anti-reflection film 14 has been formed in advance, is bonded to photocurable resin or thermosetting resin 13A, and then photocurable resin or thermosetting resin 13A is cured to form cured resin layer 13 (see FIG. 4(b)). At this time, the surfaces of transparent substrates 11 and 15 may be polished to adjust the thickness of transparent substrates 11 and 15. Next, anti-reflection films 16 and 17 are formed on the surfaces of transparent substrates 11 and 15 (see FIG. 4(c)).

[0035] After filling the recesses 21 with the photocurable resin or thermosetting resin 13A, the photocurable resin or thermosetting resin 13A may be cured to form the cured resin layer 13 without bonding the transparent substrate 15 on which the anti-reflection film 14 has been formed in advance. In this case, for example, the anti-reflection film 14 is formed on the cured resin layer 13, and then the transparent substrate 15 is bonded to the cured resin layer 13.

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

[0037] FIG. 5 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 present invention has been described above with reference to the preferred embodiment, the present invention is not limited to the preferred embodiment and may be modified as appropriate within the spirit and scope of the present invention. For example, at least a portion of the anti-reflection films 12 a, 14, 16, and 17 and the protective film 12 c may be omitted.

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

Claims

1. A wave plate comprising: a transparent substrate; a patterned layer formed on the transparent substrate; and a cured resin layer formed in an area of ​​the transparent substrate where the patterned layer is not formed, wherein the patterned layer has a retardation film, and where the principal refractive indices of the retardation film are Nx and Ny and the refractive index of the cured resin layer is Nr, the wave plate satisfies the formula Nx>Nr>Ny.

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 cured resin layer from the transparent substrate.

5. The waveplate of claim 4, further comprising an anti-reflective coating disposed between said cured resin layer and said 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 cured resin layer in an area of ​​the transparent substrate where the pattern layer is not formed, wherein the retardation film is formed when the precursor of the pattern layer is formed.

9. A method for manufacturing a wave plate as described in claim 8, further comprising the steps of: forming an anti-reflection film and the phase difference film sequentially when forming a precursor of the pattern layer; arranging a second transparent substrate on the opposite side of the cured resin layer to the transparent substrate; and forming an anti-reflection film between the cured resin layer and the second transparent substrate.

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