JPH01107206A - Manufacture of diffraction grating type polarizing plate - Google Patents

Abstract

PURPOSE:To eliminate the need for the process of positioning a photomask and an ion exchange area by depositing a dielectric film on a mask for ion exchange, then dissolving the ion exchange mask and removing a dielectric film at an area where the ion exchange is not performed when forming the thick area and thin area of the dielectric film. CONSTITUTION:The ion exchange mask 2 made of titanium having periodic windows is formed on the main surface of a substrate 1 of a lithium niobate X plate or Y plate and then a proton exchange is made by dipping in benzoic acid to form periodic ion exchange areas 3. Then quartz, etc., is sputtered to deposit the dielectric film 4 and the mask 2 for the ion exchange is dissolved to remove the dielectric 4 in the area where the ion exchange is not performed. Consequently, when the thick area and thin area of the dielectric film 4 are formed, the photomask and ion exchange areas 3 need not be positioned.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a diffraction grating type polarizing plate, which uses lithium niobate and has a diffraction efficiency that differs depending on the polarization direction.

[Conventional technology]

A polarizing beam splitter, which is a polarizing element, is an element that obtains a specific polarized light by changing the propagation direction of light between orthogonal polarized lights. This polarizing element is used as a component of optical isolators and optical circulators in light source modules for optical fiber communications, optical heads for optical disks, and the like.

Conventional polarizing beam splitters include Glan-Thompson prisms and Rochon prisms that separate optical paths by utilizing the difference in transmission or total reflection due to polarization on the light reflecting surface of a crystal with large birefringence, or isotropic beam splitters such as glass. A total reflection prism made of a reflective optical medium has a dielectric multilayer film on its reflective surface, and the difference in refractive index due to the polarization of this dielectric multilayer film is used to completely reflect or transmit light. . However, these devices have drawbacks such as large size, low productivity, and high cost.

A diffraction grating type polarizing plate has periodic ion exchange regions on the main surface of a crystal with optical anisotropy, such as lithium niobate, and thick ion exchange regions on the main surface. A thin dielectric film is formed in areas where no polarization is applied, and optical paths are separated by utilizing differences in diffraction efficiency due to polarization. This diffraction grating type polarizing plate has advantages over conventional polarizing elements, such as being smaller, having higher productivity, and being cheaper. For example, when proton exchange is performed around the main surface of an X plate or a Y plate of lithium niobate, the refractive index for extraordinary light increases by about 0.813 in the proton exchanged region, and the refractive index for ordinary light increases by about 0.813. 04 decrease. Therefore, the dielectric film thickness in the proton-exchanged region is made thicker than the dielectric film thickness in the non-proton-exchanged region to offset the decrease in the refractive index for ordinary rays in the proton-exchanged region. By this, it is possible to reduce both the first-order or higher-order diffraction efficiency of ordinary rays and the zero-order diffraction efficiency of extraordinary rays to zero.

Conventionally, when forming this dielectric film, steps such as those shown in FIGS. 2(a) to 3(h) or 3(a) to 3(h) have been used for the ion exchange region. That is, in FIG. 2, an ion exchange mask 2 having periodic windows is formed of titanium or the like on the main surface of an X-plate or Y-plate substrate 1 made of lithium niobate, and is soaked in benzoic acid at about 249°C for several hours. By dipping, a periodic ion exchange region 3 is formed (second
Figure (a)). After that, the ion exchange mask 2 is dissolved and removed using acid or the like (Fig. 2(b)), the dielectric film 4 is deposited by sputtering etc. (Fig. 2(C)), and the photoresist 6 is applied (Fig. 2(d)). ), and after aligning the photomask 7 with the ion exchange region 3, the exposure is performed as shown in FIG.
e)), developing the dielectric film 4 (FIG. 2(f)), etching the dielectric film 4 (FIG. 2(g)), and finally removing the photoresist 6 to obtain a diffraction grating type polarizing plate (FIG. 2(g)). h)).

In addition, in Figure 3, up to Figure 3 (b) is shown in Figure 2 (b).
), but then photoresist 6 is applied, and (
After aligning the photomask 7 with the ion exchange region 3, exposing it to light (FIG. 3(d)) and developing it (FIG. 3(e)), the dielectric film 4 is formed by sputtering or the like. The photoresist 6 is deposited (FIG. 3(f)), the photoresist 6 is dissolved and removed (FIG. 3(g)), and a dielectric film 5 is deposited as necessary to obtain a diffraction grating type polarizer (FIG. 3(g)). h)).

[Problem that the invention seeks to solve]

However, each of these manufacturing methods requires a complicated manufacturing process, and in particular requires an alignment process between the photomask 7 and the ion exchange region 3, as shown in FIG. 2(e) or FIG. 3(d). This has caused a decrease in yield and variations in quality of diffraction grating type polarizing plates.

The purpose of the present invention is to solve these problems, simplify the manufacturing process, improve yield, and make it possible to manufacture high-quality diffraction grating type polarizing plates in large quantities at low cost by eliminating the alignment process. An object of the present invention is to provide a method for manufacturing a diffraction grating type polarizing plate.

[Means for solving problems]

The method for manufacturing a diffraction grating type polarizing plate of the present invention includes a first step in which an ion exchange mask is formed on the main surface of a lithium niobate crystal plate to selectively form ion exchange regions in predetermined synchronization.
a second step of forming an ion exchange region on the main surface at the same time; and a second step of forming an ion exchange region on the main surface in a thick manner in the ion exchanged region and a thin dielectric film in the non-ion exchanged region. and a third step of forming a thick region of the dielectric film and a thin region thereof, after depositing the dielectric film on the ion exchange mask, the ion exchange mask is The method is characterized in that it includes a step of dissolving the dielectric film and removing the dielectric film in the area where ion exchange has not been performed.

〔Example〕 Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIGS. 11(a) to 11(e) are cross-sectional views illustrating a method for manufacturing a diffraction grating type polarizing plate according to an embodiment of the present invention in the order of steps.

That is, first, an ion exchange mask 2 having periodic windows made of titanium or the like is created on the main surface of the substrate 1, which is an X plate or a Y plate of lithium niobate, using a normal lift-off method or the like (see Fig. 1). (a)). The film thickness of this mask 2 is
30 to make it thicker than the dielectric film 4 to be formed later.
00 to 4000 people. Thereafter, proton exchange is performed by immersion in benzoic acid at about 249° C. for about 4 hours to form periodic ion exchange regions 3 with a depth of about 4.6 μm (FIG. 1(b)). Thereafter, a dielectric film 4 such as quartz is deposited to a thickness of about 1,270 layers using sputtering or the like (FIG. 1(C)), and a mask 2 for ion exchange is deposited.
The dielectric material 4 in the area where ion exchange has not been performed is removed by dissolving the dielectric material 4 (FIG. 1(d)). Finally, if necessary, a suitable dielectric film 5 is deposited by sputtering or the like (FIG. 1(e)).

This dielectric film 5 can be made into a non-reflective film by appropriately selecting the refractive index and film thickness.

This manufacturing method can reduce the manufacturing steps by about half compared to conventional manufacturing methods, and is particularly effective when forming the thick and thin regions of the dielectric film 4. Since positioning with 3 is no longer necessary, product variations can be reduced, resulting in high yield and low manufacturing cost.

〔Effect of the invention〕

As explained above, according to the present invention, the manufacturing process of a diffraction grating type polarizing plate can be simplified, and high quality polarizing elements can be manufactured in large quantities at low cost.

[Brief explanation of the drawing]

FIGS. 1(a) to (e) are cross-sectional views of an element explaining the manufacturing method of the present invention in the order of steps, FIGS. 2(a) to (h), and FIG.
a) to (h) are cross-sectional views illustrating two sides of a conventional method for manufacturing a diffraction grating type polarizing plate in order of steps; DESCRIPTION OF SYMBOLS 1... Lithium niobate substrate, 2... Ion exchange mask, 3... Ion exchange region, 4... Dielectric film,
5... Dielectric film, 6... Photoresist, 7... Photomask.

Claims (1)

[Claims] A first step of forming an ion exchange mask for selectively forming an ion exchange region in a predetermined synchronization on the main surface of a lithium niobate crystal plate, and forming an ion exchange region on the main surface in the synchronization. and a third step of forming a dielectric film on the main surface to be thick in areas where ion exchange has been performed and thin in areas where ion exchange has not been performed. When forming a thick region and its thin region, after depositing the dielectric film on the ion exchange mask, the ion exchange mask is dissolved to remove the dielectric film in the region where ion exchange is not performed. A method for manufacturing a diffraction grating type polarizing plate, comprising the step of: