JPS6355501A - Diffraction grating type polarizing plate - Google Patents

Abstract

PURPOSE:To obtain a thin and small-sized polarizing element by forming an optical diffraction grating having ion exchange regions periodically to the main plane of a lithium niobate crystal plate. CONSTITUTION:The proton ion exchange regions 2 are periodically formed on the lithium niobate crystal plate 1. The grating constituted of the ion exchange regions 2 having periods in the z-axis direction and the non-exchange regions is formed on the lithium niobate crystal plate 1 of an x-axis. The refractive index (no) to ordinary rays does not change and the refractive index (ne) to extraordinary light increases by about 0.13 to the refractive index approximately equal to (ne) if the lithium niobate is subjected to a proton ion exchange. The similar effect; i.e., optical isolation effect or optical circulation effect is obtainable by using the grating type polarizing element formed in the above- mentioned manner in the same manner as heretofore; i.e., by combining the same with a quarter-wave plate. Since this grating type polarizing element is formable by using the thin lithium niobate crystal plate, compact and thin polarizing element is obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a birefringent polarizing plate used in various optical devices using a semi-integrated laser, and a grating type polarizing plate having diffraction efficiency that differs depending on the polarization direction. (Prior art) A polarizing element, particularly a polarizing beam splitter, is an element that changes the propagation direction of light between orthogonal polarized lights, and is used to reflect light from crystals with large birefringence, such as Glantomnon prisms, B, Kuyon prisms, etc. A dielectric multilayer film is provided on the reflective surface of a total reflection prism made of an isotropic optical medium such as glass. Many are used that completely reflect or transmit light by utilizing the difference in refractive index due to polarization of the multilayer film.

These are used as components for optical isolators and optical circulators in optical fiber communication light source modules, optical discs, and other devices.

For example, in a light source module for optical 7-eye μ communication, the Faraday effect 'Y + lJ of a photomagnetic material is used as an optical isolator to prevent reflected light from an optical fiber connector etc. from re-entering the semiconductor laser that is the light source. It is used in combination with a polarization rotator (Faraday rotator) that rotates the light by 45 degrees. In addition, when transmitting light for optical disks, the information signal from the optical disk substrate is not returned to the light source, making it more efficient.
17 as an optical circulator element leading to the receiving optical system.
It is used in combination with a 4-wavelength plate.

(Problems to be Solved by the Invention) These conventional polarization splitting elements have the disadvantage of being large, regardless of whether they are polarizing elements using zero-light anisotropic crystals or dielectric thin film type polarizing elements. Since it has a reflective boundary surface obliquely arranged at 45 degrees or more with respect to the optical axis, it becomes a regular cube with a diameter at least 5 times the diameter of the transmitted beam. Since the transmitted beam is large when used for optical disk heads, particularly those of a reproducing-only type that can record without a word, the conventional polarizing element has a cubic shape with sides of 8 to 10 mm. This is one of the reasons why the size of the light for optical discs is increasing.The purpose of the present invention is to
The object of the present invention is to provide an extremely thin grating-type optical polarizing plate that eliminates the electrical point of the conventional polarizing element.

(Means for Solving the Problems) The structure of the diffraction grating type light polarizing plate of the present invention is such that one of the H ion exchange regions having a period on the main surface of the lithium niobate crystal plate.
It is characterized by forming a mechanical diffraction grating.

(Example) An example of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a perspective view of a diffraction grating type light polarizing plate according to an embodiment of the present invention, in which 1 is a lithium niobate crystal plate, 2 is a protonoion exchange region, and this exchange region is formed periodically. It is.

In a non-example, a lattice consisting of an ion exchange region and a non-exchange region having a period in the Z-axis direction is formed on a lithium niobate crystal plate on the X-axis. To configure this cycle,
This may be performed using a commonly used photolithography technique or the like. When lithium niobate is subjected to proton ion exchange, the refractive index noG2 for ordinary rays does not change, and the refractive index ne for extraordinary rays increases by about 0.13, making it almost ne;n
It becomes o.

When formed in a lattice shape as shown in Fig. 1, for the polarized light component vibrating in the y-axis direction of the incident light 3, that is, the ordinary light component,
Even if a grating is formed by ion exchange, the refractive index is uniform at one in-plane pressure and there is no effect of an optical diffraction grating, so the O-order light 4 is transmitted straight through the crystal plate 1. on the other hand,
For the polarized light component vibrating in the biaxial directions of the incident light 3, that is, the extraordinary light component, the proto/ion exchange region 2 is ne+Q.
, 33° Since the non-exchanged region is incident on an optical diffraction grating in which the refractive index of ne periodically differs, the niobic acid in the ion-exchanged region 2 becomes diffracted light 5 and 6 and is also emitted from the crystal plate 1. When the depth into the lithium crystal is shallow, that is, the diffraction efficiency of the 0th order diffracted light by an optically thin diffraction grating is given by JO (2 to T).

Here, =πΔn/λO9Δn is the difference in refractive index between the exchange region and the non-exchange region, which is 0. 】3, JO is the wavelength in vacuum, and T is the thickness of the grating, that is, the depth of the exchange region. T)=0°, that is, 2 to T; 2.
4, and for a light wavelength of 0.8 .mu.m, T, that is, the wall thickness of the exchange region, may be set to about 2.3 .mu.m, and for a light wavelength of 1.3 .mu.m, to about 3.8 .mu.m.

By performing proton ion exchange on lithium niobate crystals,
The method of forming the light guide is well known;
When TECUMU crystals containing lyopic acid are immersed in benzoic acid heated to about 17° C. for about 6 hours, ion exchange to a depth of about 2.3 μm is achieved. Furthermore, if the time is increased, the exchange depth can be increased by 4 μmait.

By using the lattice polarized element produced by the above manufacturing method in the same manner as before, that is, in combination with a 174-wave plate, it is possible to obtain the same effect, that is, the original isolation effect or the original isolation effect. . Since this lattice type polarizing element can be formed using the thin lithium niobate crystal 8j, a small and thin polarizing element can be obtained.

Furthermore, the accuracy of the ion exchange time described above does not require very high accuracy. This is because even if the ion exchange time is insufficiently set and Jo (2kT) = 0 is slightly off, it is necessary to install multiple diffraction gratings, that is, to provide diffraction gratings on both sides of the lithium niobate crystal ( By using it for l number of plates tR, it is possible to make the rigidity of the transmission 0 kyu to be extremely small δ.

In the above example, the case of 1Q ton ion exchange was described, but the same effect can be obtained by immersing silver ion exchange in silver nitrate or talicum nitrate.

It has been confirmed that cream ion exchange occurs and the refractive index increases by about 0.13 in the extraordinary refractive index.

(Effects of the Invention) As described in detail above, according to the present invention, a thin and compact polarizing element can be obtained, and furthermore.

Since it is manufactured using the niobic acid crystal wafer 1 as a material, it is possible to produce a polarizing element in large quantities and at low cost by using a badate process.

[Brief explanation of drawings]

FIG. 1 shows the fl of a diffraction grating type light polarizing plate according to an embodiment of the invention.
+ View parent plan. 1... Lithium niobate crystal plate, 2...
・Ion exchange region, 3...Incoming light, 4-6...
・・・・Regeneration analysis source. Agent Patent Attorney Oto Uchihara.・-/. Vol. 1 (Volunteer to write procedural amendments) 5 62.7. -6 Showa year month/day 61, Indication of the case 1988 Patent Application No. 201039 2, Title of the invention
Diffraction grating type light polarizing plate 3, relationship with the case of the person making the amendment
5-33-1 Shiba, Minato-ku, Tokyo Name (423)
) NEC Corporation Representative: Tadahiro Sekimoto 4, Agent Address: 5-37-8 Shiba, Minato-ku, Tokyo 108 Sumitomo Sanda and Lumi Denwa Tokyo (03) 456-3111 (Main Representative) (
(Contact address: Patent Department, NEC Corporation), Claims column of the specification to be amended, Contents of the amendment (1) The scope of claims will be amended as shown in the attached sheet.

Claims (1)

[Claims] A diffraction grating type optical polarizing plate, characterized in that an optical diffraction grating of periodic H^+ ion exchange regions is formed on the main surface of a lithium niobate crystal plate.