JPH02230203A - Polarizer - Google Patents

Abstract

PURPOSE:To obtain the polarizer which allows relatively easy production, has excellent mass productivity and has high quality by providing a substrate with a grating having parallel groove parts and embedding a transparent material having the refractive index of an ordinary ray or extraordinary ray in the grooves. CONSTITUTION:The surface of a single crystal substrate consisting of lithium tetraborate has the grating 2 disposed with the plural grooves in parallel at specified intervals. The transparent material 3 having the refractive index n0 of the ordinary ray of the substrate is embedded in the grooves of the grating 2 when the direction of the grooves is the direction orthogonal with the c axis and the transparent material 3 having the refractive index ne of the extraordinary ray of the substrate is embedded therein when the direction of the grooves is in the direction parallel with the c axis. The difference DELTAn between the refractive index n0 of the ordinary ray and the refractive index ne of the extraordinary ray in the lithium tetraborate exhibits a value as large as >=0.05 near visible ray and, therefore, the sepn. of the ordinary ray 7 and the extraordinary ray 8, 8' is efficiently execute. The high-quality polarizer which is simple in constitution, allows the relatively easy production and has the excellent mass productivity is obtd. in this way.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a polarizer that separates ordinary rays and extraordinary rays, and in particular to a thin plate-shaped polarizer that has a simple configuration and is easy to manufacture. It is related to. [Prior Art] A polarizer is an element that selectively transmits light polarized in a specific direction, and is widely used in various optical devices. A variety of conventional polarizers are used, ranging from high-quality ones that combine calcite prisms such as Nicol prisms or Glan-Thompson prisms to simple structures that have a birefringent plate sandwiched between glass plates or transparent plastic plates. It is being done. [Problem to be solved by the invention] The former Glan-Thompson prism is often used in cases where high quality is required, such as in optical measurement or optical communication equipment, but it requires high processing precision. Moreover, it is difficult to mass produce, and furthermore, it is extremely expensive due to the limited supply of calcite. Furthermore, since the structure is a combination of two prisms, there is also the problem that the element size becomes large.

In contrast, recently, lithium niobate plates (LiN
A method has been proposed in which the refractive index for extraordinary light is spatially modulated by performing proton exchange processing on the (bOs). However, although this method has the potential for mass production compared to conventional prism-shaped polarizers such as Glan-Thompson prisms, there are limitations in reproducibility associated with a type of thermal diffusion process called proton exchange, and Because it is difficult to form fine patterns due to the need for a compensation film for ordinary light, it does not have sufficient characteristics as a polarizer for use with small diameter light beams, and it is not necessarily sufficient in terms of mass production. There wasn't. In view of the above-mentioned problems, the present invention has sufficient characteristics even for small diameter light beams7, is relatively easy to manufacture, and has excellent mass productivity. Another object of the present invention is to provide a high-quality polarizer that can be supplied at a low cost.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a substrate made of a lithium tetraborate single crystal plate cut so that the crystal cutting direction is perpendicular to the C axis, and a surface of the substrate. The grating has a groove portion on which a plurality of grooves are arranged in parallel at regular intervals in a direction perpendicular to the C-axis or parallel to the C-axis, and the grooves of the grating have grooves whose direction is C In the direction perpendicular to the axis, the refractive index n of the ordinary ray of the substrate. embedding a transparent material with a refractive index equal to
When the direction of the groove is parallel to the C-axis, the refractive index of the extraordinary ray of the substrate n. Further, in one aspect of the present invention, the groove portion of the grating is composed of a plurality of portions having groove depths different from each other. shall be.

Furthermore, the present invention is characterized in that, as another aspect, a retention film that also serves as an antireflection film is formed on the surface of the substrate.

Furthermore, as a preferred embodiment of the present invention, when the depth of the grating groove is d, the wavelength of the incident light beam incident on the substrate is λ, Δn = I no-nal and 0
Let Jo be the next Bessel function, Jo=(2π△nd/λ
The groove depth d is determined so that the conditional expression )=0 is satisfied.

[Function] The polarizer of the present invention has a lithium tetraborate single crystal plate (
The grating is formed by machining parallel grooves on the substrate (substrate),
A transparent material having a refractive index matching the refractive index of the ordinary ray or extraordinary ray of lithium tetraborate is embedded in the grooves of this grating. The difference between the refractive index no of the ordinary ray and the refractive index n of the extraordinary ray in lithium tetraborate shows a large value of 0.05 or more in the vicinity of visible light, so it is possible to efficiently separate the ordinary and extraordinary rays. It can be carried out. In addition, the above-mentioned parallel groove processing can be easily performed by, for example, either the tri-edging method or the wet etching method, and it is also possible to fill the groove portion with a transparent material using a flattening film forming technique used in semiconductors, etc. This can be done relatively easily using . Therefore, according to the present invention, a high-quality polarizer with excellent mass productivity can be easily provided.

[Actual Travel Example] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Figure 1 shows the configuration of a polarizer according to the first embodiment of the present invention, this figure (^) shows the external appearance of the element, and the zero figure (B) shows its longitudinal section. . Here, 1 is a substrate using a single crystal of lithium tetraborate (chemical formula: Li2B407-hereinafter abbreviated as 14BO), 2 is a grating consisting of a plurality of parallel grooves at regular intervals formed on the surface of the LBO single crystal substrate 1, 3 is a transparent dielectric film embedded in the grooves of grating 2; 4 and 5 are protective films with anti-reflection films provided on both sides of substrate 1; 6 is incident light to the element; 7, 8, and 8' is the polarized output light.

The above LBO substrate 1 has its surface normal (crystal cutting direction) set in the crystal a@ direction. Also, the groove of grating 2 is L
The grooves are formed on the surface of the BO substrate 1 so as to be parallel to the crystal b-axis which is perpendicular to the crystal C-axis, and the groove portions are provided so that the irregularities are repeated along the crystal C-axis direction. Assuming that the width of this groove portion, that is, the recessed portion and the width of the convex portion are equal, and the dimension of the width is W, the grating period p is equal to two stomachs. A transparent dielectric film 3 is formed in the recess by a manufacturing method such as sputtering to form a so-called buried structure. Next, the operation of this embodiment will be explained below.

The lithium tetraborate of the substrate 1 is a uniaxially anisotropic crystal with the C-axis as the optical axis, and the refractive index of extraordinary rays, that is, the light vibrating in the C-axis direction (extraordinary ray refractive index), is n. The refractive index (ordinary ray refractive index) of the ordinary ray, that is, the light vibrating in the direction perpendicular to the C-axis, is set to 00. Further, the refractive index of the transparent dielectric 3 embedded in the groove portion of the grating 2 is denoted as nd, and when the dielectric material is appropriately selected, nd is the ordinary ray refractive index n mentioned above. shall be equal to

Under the above conditions, the element having the structure shown in FIG. 1 acts merely as a flat transparent plate for ordinary light, that is, incident light polarized in the b-axis direction.

On the other hand, for the extraordinary ray, that is, the incident light polarized in the C@ direction, the refractive index of the convex part of the grating 2 and the refractive index of the grooved part change periodically in the C-axis direction. 2 acts as a so-called phase grating, the extraordinary rays undergo diffraction in the C-axis direction.

Therefore, for the incidence of ordinary rays, arrow 7 in Figure 1
As shown in , the output light 7 is obtained in the same direction as the input light 6. On the other hand, the extraordinary ray can be separated from the ordinary ray 7 because it is diffracted in the C-axis direction as shown by arrow 8.8' in FIG.

As a further preferred embodiment, by setting the depth of the grooves of the grating 2 according to the wavelength λ of the incident light 6 under the conditions described below, the ordinary ray and the extraordinary ray can be completely separated using the {i photons of the embodiment. Can be separated. Next, conditions for complete separation will be explained.

Under the conditions of optical diffraction by a phase grating, that is, Raman Nass diffraction, incident light is generally separated into ±m-order (m is an integer) diffracted light beams, and the diffraction angle θ,1 is tanθ.

=λ/mp=λ/2+aw. Moreover, the intensity 1G' of the undiffracted light (m=o) is Io' = Io,
It is given by Io (2kd). Here, I0 is the intensity of the incident light, d is the depth of the groove, and Jo is the O-order Bessel function. Also, k is given by the following equation (1). k: π△n/λ (1) where △n = l n. -n. I
(2).

Jo(2kd) When =O, the intensity of undiffracted light! . ' becomes zero. That is, when taking a value such as , the zero-order Hetzsell function, 1o, becomes ÷. Therefore, the ordinary ray and extraordinary ray of the emitted light at this time can be completely separated, and the best polarizer characteristics can be obtained.

Further, the refractive index of the LBO of the substrate 1 is no=1.608 n,=1.552 Δlow0.056 in the wavelength band of 0.6 μm. Specific numerical examples of polarizers are shown below. When w = 10/7ts λ = 0.63μm, the condition for the annihilation of the undiffracted light of the extraordinary light is as follows by substituting it into the above equation (3): d = 4.3μs, or 9.9μm, or 15.5
Values such as μw can be obtained. Any of these groove depth d values can be achieved relatively easily by chemical etching, sputter etching, or the like.

On the other hand, the condition for Raman Nass diffraction is Q=yr・λ−d/2−W2(4)? Q defined
It is necessary that the value of is sufficiently smaller than 1. For the above value of d, even when d = 15.5 μl, Q =
Since it is 0.154, it satisfies the conditions for Raman Nass diffraction.

The transparent dielectric film 3 embedded in the recess of the grating 2 of the substrate 1 is made of, for example, quartz (SiO) and tantalum pentoxide (T).
aJs) and sputtering the mixture. If this mixing ratio is selected appropriately, nd-00 can be achieved.
Further, the buried formation of the transparent conductive film 3 can be realized using a flattening film forming technique used in semiconductors and the like.

The protective films 4 and 5 are provided to ensure moisture resistance since the LBO of the substrate 1 is water-soluble, although very slightly, but they are not necessarily necessary to obtain polarizer operation.
There are no particular restrictions on the material of the protective film 4.5 as long as it is transparent and stable, but if a material with a refractive index different from the ordinary ray refractive index no of the substrate 1 is used, the thickness can be set to an appropriate value. By doing so, it can also serve as an antireflection film.

In the above explanation, the case where grooves are provided parallel to the b-axis of the substrate 1 has been described, but periodic grooves are provided parallel to the c-axis of the substrate 1, and the refractive index n, of the embedded transparent dielectric film 3 is adjusted to reflect the extraordinary light. It is clear that even if the refractive index is made equal to n6, a polarizer having the same effect as described above can be obtained. In addition, in a lithium tetraborate crystal, the a-axis and b@ are optically equivalent, so any substrate that has a crystal cutting direction perpendicular to the C-axis is sufficient. Therefore, the crystal cutting direction is not limited to the a-axis, but is However, a substrate between the a@ and b axes may also be used.

B. Embodiment 2 Figure 2 shows the configuration of a second embodiment of the present invention. In this embodiment, the grating 2 is divided into a plurality of groups, and the depth d of the grooves in each group is made different.

As is clear from the above equation (3), the depth d of the groove at which the undiffracted light disappears is wavelength dependent. In this example, the depth d of the grooves differs from group to group. Now, as described below, a polarizer that can be used in a wide range of wavelengths can be realized.

FIG. 2 shows an example of a configuration in which the wavelength region is divided into three wavelength regions. As shown in Fig. 2, along the C axis of the substrate l, the area ■,
Divide into three parts II and III, and set the depth of the groove in each part to a different value, d, d, d, respectively.
shall be. As a result, the wavelengths λ1, λ2, and λ3 at which the undiffracted light disappears in each region differ from each other. Now, for example, λ, = 0.63 μm, λ2 = 0.85 μm, λ
When determining the depth of the continuous groove in the three wavelength bands of s = 1.15 μm, the first zero of the zero-order Bessel spacing number Jo, that is, the right side of the above equation (3) has a value of 2.405. The following values are obtained. dl = 4.3 μm d, = 5.8 μm d3 = 7.9 μm With the above configuration, the incident positions of the incident lights of wavelengths λ1, λ2, and λ3 are set to areas I, I1, and ■, respectively.
A polarizer that completely separates the ordinary and extraordinary rays in each wavelength region can be obtained by adjusting the polarizer. As shown in FIG. 3, the group division to make the depths of the grooves of the grating 2 different may be performed along the b-axis direction of the substrate 1, that is, the direction parallel to the grooves of the grating 2. In this case as well, A polarizer applicable to multiple wavelengths similar to that shown in FIG. 2 can be realized. In addition, by combining the configuration in which groups are divided along the C-axis direction as shown in Figure 2 and the configuration in which groups are divided along the b-axis direction as shown in Figure 3, two-dimensional A configuration in which the area is divided and arranged is also possible.

To actually use a polarizer configured in this way, for example, you can mount the polarizer in a holder with a sliding mechanism and move the holder according to the wavelength of the incident light to obtain the optimal polarization for that wavelength. It can be run as a child.

[Effects of the Invention] As explained above, according to the present invention, the structure is simple, easy to manufacture, and suitable for mass production, and furthermore, the depth of the grating grooves is set based on a predetermined conditional expression. This makes it possible to completely separate the ordinary rays from the extraordinary rays, and by making the depth different for each group, it is possible to provide a polarizer that can operate over a wide wavelength range, which is a remarkable effect. can get.

[Brief explanation of the drawing]

FIG. 1(A) is a perspective view showing the configuration of the first embodiment of the present invention, FIG. 1(B) is a vertical sectional view thereof, and FIG. 2 shows the configuration of the second embodiment of the present invention. FIG. 3 is a perspective view showing a modification of the second embodiment of the present invention. 1... Lithium tetraborate single crystal substrate, 2...
Grating formed on the substrate, 3... Transparent dielectric film, 4.5... Protective film that also serves as an antireflection film, 6... Incident light, 7... Polarized output light (ordinary light), 8.8 ′...Polarized outgoing light (abnormal ray). L.

Claims (1)

[Claims] 1) A substrate made of a lithium tetraborate single crystal plate cut so that the crystal cutting direction is perpendicular to the c-axis, and a substrate formed on the surface of the substrate in a direction perpendicular to the c-axis or along the c-axis. a grating having a groove portion in which a plurality of grooves along parallel directions are arranged in parallel at regular intervals, and when the direction of the grooves is perpendicular to the c-axis, A transparent material having a refractive index equal to the refractive index n_o of the ordinary ray of the substrate is embedded, and when the direction of the groove is parallel to the c-axis, a transparent material having a refractive index equal to the refractive index n_e of the extraordinary ray of the substrate. A polarizer characterized by being configured by embedding. 2) Claim 1, wherein the groove portion of the grating consists of a plurality of portions having different groove depths.
Polarizer described in . 3) The polarizer according to claim 1 or 2, wherein a protective film that also serves as an antireflection film is formed on the surface of the substrate. 4) When the depth of the groove of the grating is d,
The wavelength of the incident light beam incident on the substrate is λ, △n=|n_
o-n_e| and a zero-order Bessel function as J_o, the depth d of the groove is determined so that the conditional expression Jo=(2πΔnd/λ)=0 is established. 3. The polarizer according to any one of 3.