Wire grid polarizers and optical isolators

Abstract

We provide a wire grid polarizer capable of reducing infrared reflectivity. [Solution] The wire grid polarizer 10 comprises a transparent substrate 11 and a grid-like protrusion 12 arranged on one surface of the transparent substrate 11 at a pitch of 1 / 2 or less of the wavelength of the incident infrared light and extending in a predetermined direction. The grid-like protrusion 12 has an aluminum layer 12a, and further has a β-FeSi2 layer 12b and an amorphous FeSi2 layer 12c on one side of the aluminum layer 12a.

Description

Technical Field

[0001] The present invention relates to a wire grid polarizer and an optical isolator.

Background Art

[0002] In optical communication using a semiconductor laser that generates infrared light with a wavelength of 1.31 μm or 1.55 μm as a light source and a quartz fiber as a transmission path, an optical isolator is used to achieve a low error rate. The optical isolator transmits forward light and blocks backward light (return light). A polarization-dependent optical isolator includes an incident polarizer, a Faraday rotator, and an exit polarizer.

[0003] As a polarizer for a polarization-dependent optical isolator, polarizing glass is known (see, for example, Patent Document 1). Polarizing glass has metal particles having shape anisotropy oriented and dispersed in the glass. Examples of the metal constituting the metal particles include copper, silver, gold, and platinum. Here, since polarizing glass is made of an inorganic material and has high heat resistance, it is suitable as a polarizer for a polarization-dependent optical isolator.

[0004] On the other hand, as a polarizer made of an inorganic material, a wire grid polarizer that operates in the infrared region is known (see, for example, Patent Document 2). Here, the wire grid polarizer has a first surface on which a plurality of metal wires extending in parallel are formed at a periodic interval equal to or less than the wavelength of the incident light, and a second surface having an antireflection structure having a period equal to or less than the wavelength of the incident light. Examples of the metal constituting the metal wires include gold, silver, aluminum, nickel, chromium, tungsten, tungsten silicide, and copper.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, when the wire grid polarizer described in Patent Document 2 is used as the incident polarizer for a polarization-dependent optical isolator, it is not possible to block the reflected light caused by the reflection of infrared light from the first surface. For this reason, it is desirable to reduce the infrared reflectivity of the wire grid polarizer.

[0007] The present invention aims to provide a wire grid polarizer capable of reducing infrared reflectivity. [Means for solving the problem]

[0008] (1) A wire grid polarizer comprising a transparent substrate and a grid-like protrusion arranged on one surface of the transparent substrate at a pitch of 1 / 2 or less of the wavelength of incident infrared light and extending in a predetermined direction, wherein the grid-like protrusion has an aluminum layer or an aluminum alloy layer, and further has a β-FeSi2 layer and an amorphous FeSi2 layer on one side of the aluminum layer or aluminum alloy layer.

[0009] (2) The wire grid polarizer according to (1), having the β-FeSi2 layer and the amorphous FeSi2 layer in order from the side of the transparent substrate.

[0010] (3) The wire grid polarizer according to (1) or (2), wherein the sum of the thicknesses of the β-FeSi2 layer and the amorphous FeSi2 layer is 30 nm or more and 100 nm or less.

[0011] (4) The wire grid polarizer according to any one of (1) to (3), further comprising an inorganic oxide layer formed on the lattice-like protrusions.

[0012] (5) A wire grid polarizer according to any one of (1) to (4), wherein the wavelength of the infrared radiation is 0.8 μm or more and 2.0 μm or less, and the reflectance of the infrared radiation is 10% or less.

[0013] (6) An optical isolator comprising a wire grid polarizer as described in any one of (1) to (5) and a Faraday rotator.

[0014] (7) The optical isolator according to (6), wherein the wire grid polarizer is formed on the Faraday rotor. [Effects of the Invention]

[0015] According to the present invention, a wire grid polarizer capable of reducing infrared reflectivity can be provided. [Brief explanation of the drawing]

[0016] [Figure 1] This is a cross-sectional view showing a wire grid polarizer according to one embodiment of the present invention. [Figure 2] Figure 1 is a top view showing a wire grid polarizer. [Figure 3] This is the XRD spectrum of β-FeSi2. [Figure 4] A cross-sectional view showing a wire grid polarizer according to another embodiment of the present invention. [Figure 5] This is a schematic diagram showing an optical isolator relating to one embodiment of the present invention. [Figure 6] This is the infrared reflectance spectrum of the test specimen of Comparative Example 1. [Figure 7] This is the infrared reflectance spectrum of the test specimen from Example 1. [Figure 8] This graph shows the optical admittance trajectory of the laminate in Example 1. [Figure 9] This graph shows the optical admittance trajectory of the laminate in Example 2. [Figure 10] This graph shows the optical admittance trajectory of the laminate in Example 3. [Figure 11] Cross-sectional SEM image of the wire grid polarizer of Example 4. [Figure 12] Graph showing the polarization characteristics of the wire grid polarizer of Example 4.

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments for carrying out the present invention will be described.

[0018] [Wire Grid Polarizer] FIG. 1 shows a wire grid polarizer according to an embodiment of the present invention.

[0019] The wire grid polarizer 10 includes a transparent substrate 11 and grid-like convex portions 12 that are arranged on one surface of the transparent substrate 11 at a pitch of 1 / 2 or less of the wavelength of the incident infrared rays and extend in the depth direction in the figure. The wire grid polarizer 10 transmits a polarized light wave (TM wave) whose electric field direction is perpendicular to the direction in which the grid-like convex portions 12 extend, and reflects or absorbs a polarized light wave (TE wave) whose electric field direction is parallel (see FIG. 2). Here, the grid-like convex portions 12 have an aluminum layer 12a, and further have a β-FeSi2 layer 12b and an amorphous FeSi2 layer 12c on the lower side with respect to the aluminum layer 12a. Therefore, as shown in FIG. 1, when infrared rays are incident from the side where the grid-like convex portions 12 of the wire grid polarizer 10 are not formed, that is, from the side where the aluminum layer 12a of the grid-like convex portions 12 is not formed, the infrared reflectance of the wire grid polarizer 10 is reduced. At this time, the TE wave is reflected by the aluminum layer 12a after passing through the β-FeSi2 layer 12b and the amorphous FeSi2 layer 12c, but the TE wave reflected by the aluminum layer 12a interferes and attenuates when passing through the amorphous FeSi2 layer 12c and the β-FeSi2 layer 12b.

[0020] In contrast, a wire grid polarizer having a lattice-like protrusion on one side of the aluminum layer 12a that does not further have a β-FeSi2 layer 12b and / or amorphous FeSi2 layer 12c has a high infrared reflectivity. When such a wire grid polarizer is used as the incident polarizer of an optical isolator for optical communication, it is not possible to block the reflected light to the light source (e.g., a semiconductor laser) due to the reflection of infrared light.

[0021] The wire grid polarizer 10 may have an aluminum alloy layer instead of the aluminum layer 12a. Examples of elements other than aluminum that make up the aluminum alloy layer include copper and silicon, and two or more of these may be used in combination.

[0022] The order in which the β-FeSi2 layer 12b and amorphous FeSi2 layer 12c are stacked is not particularly limited, but from the viewpoint of ease of manufacturing, it is preferable that the lattice-shaped protrusions 12 have the β-FeSi2 layer 12b and amorphous FeSi2 layer 12c in that order from the side of the transparent substrate 11.

[0023] Figure 3 shows the XRD spectrum of β-FeSi2.

[0024] The sum of the thicknesses of the β-FeSi2 layer 12b and the amorphous FeSi2 layer 12c is preferably 30 nm to 100 nm, and more preferably 30 nm to 80 nm. When the sum of the thicknesses of the β-FeSi2 layer 12b and the amorphous FeSi2 layer 12c is 30 nm to 100 nm, the infrared reflectivity of the wire grid polarizer 10 is reduced.

[0025] The ratio of the thickness of the amorphous FeSi2 layer 12c to the thickness of the β-FeSi2 layer 12b is preferably 0.1 to 1.2, and more preferably 0.1 to 0.3. When the ratio of the thickness of the amorphous FeSi2 layer 12c to the thickness of the β-FeSi2 layer 12b is 0.1 to 1.2, the infrared reflectivity of the wire grid polarizer 10 is reduced.

[0026] The method for forming the β-FeSi2 layer 12b and the amorphous FeSi2 layer 12c is not particularly limited, but examples include vapor deposition and sputtering. Here, if the temperature of the transparent substrate 11 is raised to 350°C or higher, the β-FeSi2 layer 12b is formed, and if the temperature of the transparent substrate 11 is lower than 350°C, the amorphous FeSi2 layer 12c is formed.

[0027] The thickness of the aluminum layer 12a is not particularly limited, but for example, it is between 30 nm and 300 nm. The method for forming the aluminum layer 12a is not particularly limited, but examples include vapor deposition and sputtering.

[0028] The wire grid polarizer 10 may further include an inorganic oxide layer formed on the lattice-like protrusions 12. This improves the reliability of the wire grid polarizer 10. The inorganic oxide constituting the inorganic oxide layer is not particularly limited, but examples include silica and alumina.

[0029] The thickness of the inorganic oxide layer is not particularly limited, but for example, it is between 1 nm and 100 nm. The method for forming the inorganic oxide layer is not particularly limited, but examples include the CVD method and the ALD method.

[0030] The pitch of the grid-like protrusions 12 is not particularly limited as long as it is less than or equal to half the wavelength of the incident infrared light, but from the viewpoint of ease of manufacture and stability of the wire grid polarizer 10, it is preferably, for example, 100 nm to 200 nm. The pitch of the grid-like protrusions 12 can be measured by observation using a scanning electron microscope or a transmission electron microscope. For example, the pitch of any four locations can be measured using a scanning electron microscope or a transmission electron microscope, and the arithmetic mean can be taken as the pitch.

[0031] The material constituting the transparent substrate 11 is not particularly limited as long as it is transparent to incident infrared rays, but glass is one example.

[0032] In this specification and in the claims, “transparent to incident infrared light” does not mean that the transmittance of incident infrared light is 100%, but rather that the transmittance of infrared light is such that it can maintain its function as a wire grid polarizer. The wavelength of the incident infrared light is, for example, 0.8 μm to 2.0 μm.

[0033] The thickness of the transparent substrate 11 is not particularly limited, but for example, it is 0.3 mm or more and 1 mm or less.

[0034] Figure 4 shows a wire grid polarizer according to another embodiment of the present invention.

[0035] The wire grid polarizer 10A is the same as the wire grid polarizer 10, except that instead of the lattice-like protrusions 12A, it has a lattice-like protrusion 12A that further has a β-FeSi2 layer 12b and an amorphous FeSi2 layer 12c on the upper side of the aluminum layer 12a. Therefore, as shown in Figure 3, when infrared light is incident on the wire grid polarizer 10A from the side where the lattice-like protrusions 12A are formed, that is, from the side where the aluminum layer 12a of the lattice-like protrusions 12A is not formed, the reflectivity of infrared light of the wire grid polarizer 10 is reduced.

[0036] [Method for manufacturing wire grid polarizers] The method for manufacturing the wire grid polarizer 10 includes the steps of forming a laminate by stacking a β-FeSi2 layer 12b, an amorphous FeSi2 layer 12c, and an aluminum layer 12a on one side of a transparent substrate 11, and selectively etching the laminate to form a grid-like protrusion 12.

[0037] When selectively etching a laminate, a mask pattern is formed on the laminate using a resist, for example, by photolithography or nanoimprint lithography, and then the areas of the laminate where the mask pattern is not formed are etched.

[0038] The etching method is not particularly limited, but one example is a dry etching method that uses an etching gas corresponding to the object to be etched.

[0039] The method for manufacturing the wire grid polarizer 10 may further include a step of forming an inorganic oxide layer on the grid-like protrusions 12.

[0040] [Optical Isolator] Figure 5 shows a polarization-dependent optical isolator as an optical isolator according to one embodiment of the present invention. In Figure 5, the polarization-dependent optical isolator is shown in a state where light in the forward direction is transmitted.

[0041] The optical isolator 100 comprises a wire grid polarizer 10 as an incident polarizer, a Faraday rotator 20, and an exit polarizer 30. In this configuration, infrared light generated by the semiconductor laser 200 is incident on the wire grid polarizer 10 from the side where the grid-like protrusions 12 are not formed. As a result, the reflection of infrared light from the wire grid polarizer 10 back to the semiconductor laser 200 is blocked.

[0042] Furthermore, the output polarizer 30 may be a wire grid polarizer 10 or a known polarizer.

[0043] Alternatively, the wire grid polarizer 10 may be formed on the Faraday rotor 20. In this case, since the wire grid polarizer 10 can be manufactured by a wafer process, the wire grid polarizer 10 can be directly formed on the crystal substrate of the Faraday rotor 20. As a result, there is no need to bond the wire grid polarizer 10 to the Faraday rotor 20, which improves reliability and makes it easier to miniaturize.

[0044] Although 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 spirit of the present invention. [Examples]

[0045] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. In these embodiments, a test specimen was used instead of a wire grid polarizer to evaluate the infrared reflectivity.

[0046] [Comparative Example 1] A 200 nm thick aluminum layer was formed on a Corning Eagle XG glass substrate by sputtering at room temperature, resulting in a test specimen with an aluminum layer formed on the glass substrate.

[0047] Using the FTIR method, infrared light was incident from the side where the aluminum layer was not formed, and the infrared reflectance spectrum of the test specimen (see Figure 6) was measured. From Figure 6, it can be seen that the reflectance of infrared light with a wavelength of 1.55 μm, which is used in optical communications, is 90% or more.

[0048] [Example 1] A Corning Eagle XG glass substrate was heated to 390°C, and a 25nm thick β-FeSi2 layer was formed by sputtering. The substrate was then sufficiently cooled. Next, the Corning Eagle XG glass substrate was cooled to room temperature, and a 30nm thick amorphous FeSi2 layer was formed by sputtering. Subsequently, a 200nm thick aluminum layer was formed by sputtering, resulting in a test specimen with a laminate formed on the glass substrate.

[0049] Using the FTIR method, infrared light was incident from the side where the laminate was not formed, and the infrared reflectance spectrum of the test specimen (see Figure 7) was measured. From Figure 7, it can be seen that the reflectance of infrared light, which has a wavelength of 1.55 μm used in optical communications, has been reduced to 3.6%.

[0050] A laminate consisting of a 25 nm thick β-FeSi2 layer, a 30 nm thick amorphous FeSi2 layer, and a 200 nm thick aluminum layer was analyzed using optical admittance trajectories (see Figure 8). From Figure 8, it can be seen that when infrared light with a wavelength of 1.55 μm is incident from the β-FeSi2 layer side, the presence of the 30 nm thick amorphous FeSi2 layer beneath the 200 nm thick aluminum layer reduces the infrared reflectance to around 50%, and the presence of the 30 nm thick β-FeSi2 layer further reduces the infrared reflectance to 1%.

[0051] [Example 2] The laminate formed on a glass substrate when an amorphous FeSi2 layer with a thickness of 11 nm, a β-FeSi2 layer with a thickness of 44 nm, and an aluminum layer with a thickness of 200 nm are sequentially formed on the glass substrate was analyzed using the optical admittance trajectory (see Figure 9). From Figure 9, it can be seen that when infrared light with a wavelength of 1.55 μm is incident from the amorphous FeSi2 layer side, the presence of the 44 nm thick β-FeSi2 layer beneath the 200 nm thick aluminum layer reduces the infrared reflectance to around 40%, and the presence of the 11 nm thick amorphous FeSi2 layer reduces the infrared reflectance to around 0%.

[0052] [Example 3] The laminate formed on a glass substrate when a 200 nm thick aluminum layer, a 50 nm thick β-FeSi2 layer, and a 5 nm thick amorphous FeSi2 layer are sequentially formed on the glass substrate was analyzed using the optical admittance trajectory (see Figure 10). From Figure 10, it can be seen that when infrared light with a wavelength of 1.55 μm is incident from the amorphous FeSi2 layer side, the presence of the 50 nm thick β-FeSi2 layer on the 200 nm thick aluminum layer reduces the infrared reflectance to around 10%, and the presence of the 5 nm thick amorphous FeSi2 layer reduces the infrared reflectance to around 0%.

[0053] [Example 4] (Fabrication of wire grid polarizers) A 30.5 nm thick β-FeSi 2 layer was formed on a Corning Eagle XG glass substrate at 390°C by sputtering, and the substrate was then sufficiently cooled. Next, the Corning Eagle XG glass substrate was cooled to room temperature, and a 36.5 nm thick amorphous FeSi 2 layer was formed by sputtering, followed by a 91 nm thick aluminum layer formed by sputtering, creating a laminate on the glass substrate. Then, a 140 nm pitch line and space (L / S) pattern was formed on the laminate by photolithography, and then chlorine gas was used to selectively etch the pattern to form lattice-like protrusions, thereby obtaining a wire grid polarizer.

[0054] Figure 11 shows a cross-sectional SEM image of a wire grid polarizer.

[0055] (Polarization characteristics of wire grid polarizers) Polarized waves (TM waves and TE waves) were incident on the wire grid polarizer from the side where the lattice-like protrusions are not formed, and the transmittance and reflectance were measured (see Figure 12). From Figure 12, it can be seen that the reflectance of the TE wave, which has a wavelength of 1.9 μm, is reduced to approximately 0%, excluding interfacial reflection at the surface of the glass substrate. [Explanation of Symbols]

[0056] 10, 10A Wire Grid Polarizer 11 Transparent substrate 12, 12A Grid-like protrusions 12a Aluminum layer 12b β-FeSi2 layer 12c amorphous FeSi 2 layers 20 Faraday rotor 30 Output polarizer 100 Optical Isolators 200 Semiconductor Lasers

Claims

1. Transparent substrate and One side of the transparent substrate is provided with a grid-like protrusion arranged at a pitch of 1 / 2 or less of the wavelength of the incident infrared light and extending in a predetermined direction. The aforementioned lattice-shaped protrusions have an aluminum layer or an aluminum alloy layer, and on one side of the aluminum layer or aluminum alloy layer, β-FeSi ２ Layers and amorphous FeSi ２ A wire grid polarizer with additional layers.

2. Starting from the side of the transparent substrate, the β-FeSi ２ Layer and the amorphous FeSi ２ A wire grid polarizer according to claim 1, having a layer.

3. The β-FeSi ２ Layer and the amorphous FeSi ２ A wire grid polarizer according to claim 1 or 2, wherein the sum of the layer thicknesses is 30 nm or more and 100 nm or less.

4. The wire grid polarizer according to claim 1 or 2, further comprising an inorganic oxide layer formed on the lattice-like protrusions.

5. The wavelength of the infrared radiation is 0.8 μm or more and 2.0 μm or less. The wire grid polarizer according to claim 1 or 2, wherein the reflectance of the infrared rays is 10% or less.

6. A wire grid polarizer according to claim 1 or 2, An optical isolator equipped with a Faraday rotor.

7. The optical isolator according to claim 6, wherein the wire grid polarizer is formed on the Faraday rotor.

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