KR100238167B1 - Optical polarizer and its fabrication method - Google Patents

Abstract

The present invention relates to an optical deflector and a method for manufacturing the same, and more particularly, to a method for manufacturing a LiNbO ₃ optical waveguide.

The present invention the optical deflecting device is LiNbO ₃ Ti diffusion in the waveguide-type AOD with substrates LiNbO ₃ waveguide is the optical path to TIPE waveguide makes use of a lens material, the thickness of the waveguide are each 1μm level, the Ti diffused waveguide is single-mode Δn _max ˜0.01, which is the maximum refractive index change value, and the TIPE waveguide has three modes, and the maximum refractive index change value is Δn _max ˜0.11. The manufacturing method for this is characterized in that the Ti diffusion waveguide has a Ti film thickness of 40 nm, and the diffusion thereof is carried out at 1000 ° C. for 2 hours, and the TIPE waveguide is proton exchanged at 245 ° C. for 30 minutes using benzoic acid. .

This optical deflecting device of the present invention has a high coupling efficiency of 95% or more.

Description

Optical deflector and its manufacturing method

1 is a schematic perspective view of the AOD,

2 to 8 are cross-sectional views showing a general AOD manufacturing process.

9 is a coupling efficiency curve between the Ti diffusion waveguide and the TIPE waveguide according to the waveguide thickness change.

10 is a temperature and atmosphere schedule of a Ti diffusion process.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflecting device and a manufacturing method thereof, and more particularly, to a LiNbO ₃ optical waveguide and a manufacturing method thereof.

Recently, with a large capacity and a large scale of information, a recording medium that meets this demand has been required, and an optical recording method has been adopted and used as a medium capable of satisfying such a demand.

However, an optical recording apparatus, for example, an optical image recording apparatus, which can be used for general home use, has not been developed yet. It is a general view that the optical recording method is most suitable for home use, but the optical head for this purpose is not developed, but a bulk acoustic optical deflector (AOD; Acousto), which has a considerable size. Optic Deflector) is mainly used, and recently, the waveguide type AOD has been studied.

The bulk AOD has the disadvantage that the size of the optical system is large and the manufacturing cost is high because the crystals of the rectangular parallelepiped are used, and in particular, the deflection field angle is small, which is not suitable for large-capacity recording. However, the waveguide-type AOD can easily obtain the required deflection angle because the optical system can be miniaturized and the bandwidth can be adjusted according to the IDT (interdigital transducer) electrode type.

The waveguide-type AOD is being studied as the attention has been focused since the appearance of an optical waveguide and an optical fiber at the end of 1960.

LiNbO ₃ , a representative material for this, has excellent optical properties, and various studies on various characteristics have been attempted. In early 1973, LiNbO ₃ was diffused out of vacuum or gas at 900-1100 ° C. to produce a waveguide. The first internal diffused waveguide diffused high polarity (Poolarizability) Ti ions onto LiNbO ₃ surface in 1974 to satisfy Transverse Electric (TE) and TM (Transverse Magnetic) modes, and increased the normal and abnormal refractive index by 0.01. Was produced. Fabrication of PE (Proton Exchange) waveguides was first discovered in 1982 by ion exchange of LiNbO ₃ using Benzoic Acid (C ₆ H ₅ COOH) at 100-250 ° C. PE waveguide is available only in TE mode, and the abnormal refractive index change is as large as 0.12. The titanium in-diffusion proton exchange (TIPE) method is a relatively new method for fabricating optical waveguides in LiNbO ₃ , and this method may exhibit properties that cannot be obtained using only Ti diffusion method or PE method.

1 schematically shows the overall structure of a waveguide type AOD.

A waveguide layer 11 is provided on the surface of a LiNbO ₃ substrate (generally referred to as a Y-cutting substrate: 10) in which a plane perpendicular to the Y axis is cut, and light passing through the waveguide layer 11 is collected at the center thereof. A triangular prism 30 for injecting incident light 60 in the X-axis direction of the waveguide layer 11 is provided on one side of the middle portion of the substrate 10, and a mode indexed lens layer 20 to which the right side is provided. The ultrasonic generator 50 having an IDT electrode for generating ultrasonic waves in the Z direction is provided by the drive 40.

In the above structure, the mode indexed lens layer is one of the two waveguide layers used in the AOD, and serves as a lens by having an effective refractive index different from that of the other waveguide layer, that is, the Ti diffusion waveguide layer. do.

The general manufacturing process of the conventional AOD having such a mode indexed lens is as follows.

First, in summary, a substrate of LiNbO ₃ is first prepared in a direction orthogonal to the Y axis of the crystal, and Ti ions are diffused to form a waveguide layer on the surface of the substrate, and a lens layer (in the middle of the waveguide layer) 20) and IDT floor.

2 to 9 show the processing state of the substrate 10 during the manufacturing step of the AOD.

1. Prepare the substrate 10 as shown in FIG.

2. As shown in FIG. 3, the Ti layer 11 'is formed on the surface of the substrate 10 by electron beam deposition.

3. As shown in FIG. 4, heat treatment is performed at high temperature to diffuse the Ti into the surface layer of the substrate to form the Ti diffusion layer 11.

4. As shown in FIG. 5, an intermediate metal layer 21 is formed on the surface of the diffusion layer 11, on which a photoresist of a predetermined pattern is opened with an opening 221 for the lens layer. Form layer 22.

5. As shown in FIG. 6, the photoresist layer 22 is removed after etching a part of the intermediate metal layer 21 exposed through the opening 221 of the photoresist layer.

6. As shown in FIG. 7, proton exchange was performed for about 10 minutes in benzoic acid at about 245 ° C. to form a TIPE waveguide layer, that is, a lens layer 20 on a part of the Ti diffusion layer. do.

7. Then, the IDT layer is prepared on the substrate 10 through a subsequent process.

Through the above process, the substrate 10 as shown in FIG. 1 having the Ti diffusion waveguide layer, the TIPE waveguide layer, and the IDT layer is obtained.

In developing AOD (Acousto Optic Deflector) for recording and reproducing an image signal using the optical head as described above, a LiNbO ₃ optical waveguide is essential. To date, LiNbO ₃ optical waveguide fabrication has been actively studied by various methods, and the Ti diffusion and PE methods described above are representative methods. In this AOD, Ti diffusion and TIPE waveguides coexist.Because the coupling efficiency of two waveguides having different refractive indices depends on the number of modes and thickness of the waveguide, two waveguides are required to fabricate an AOD having high coupling efficiency. The optimal condition of the liver should be determined, but the results of the study are insufficient.

The present invention provides fabrication conditions for determining the thickness, refractive index, and number of modes of a Ti diffusion waveguide and a TIPE waveguide to have a high coupling efficiency of 95% or more in the fabrication of a waveguide for use as an AOD.

Therefore, in the waveguide type AOD using a LiNbO ₃ substrate, the TI diffused LiNbO ₃ waveguide is used as an optical transmission path and the TIPE waveguide as a lens material. The waveguide has a thickness of about 1 μm, a single mode, and a maximum refractive index change Δn _max. The characteristic is that it is -0.01.

In the manufacturing method of the present invention, in manufacturing an acoustic optical deflecting device in which a Ti diffusion LiNbO ₃ waveguide and a TIPE LiNbO ₃ waveguide are provided in a Y-cut single crystal LiNbO ₃ single crystal, the refractive index change is about 0.01, The condition for obtaining a Ti diffusion waveguide with a waveguide thickness of about 1 μm is a Ti film thickness of 40 nm, and its diffusion is characterized by being carried out at 1000 ° C. for 2 hours.

In addition, the PE manufacturing process is characterized in that it is made for 30 minutes at 245 ℃.

Through this structure, this AOD has high efficiency because of high efficiency of utilization between Ti diffusion and TIPE waveguide in addition to optical loss.

Hereinafter, embodiments of the present invention will be described in detail. FIG. 9 is a graph showing the coupling efficiency curve between the Ti diffusion waveguide and the TIPE waveguide in the waveguide thickness change, and FIG. 10 is a temperature and atmosphere schedule diagram of the Ti diffusion process.

First, we approach the AOD of the present invention theoretically.

The coupling efficiency? Between TE modes at the boundary between two different refractive waveguides forming the waveguide layer of the substrate can be expressed by the following equation, which is an integral value of the TE field profile.

In this case, El (x) and Eh (x) are electric field profiles of each guiding mode of the low refractive waveguide and the high refractive waveguide. The electric field profile E (x) of the planar waveguide is obtained by the following relationship.

Where n (x): refractive index profile

n _e = β / k: guide effective refractive index

β: radio wave constant

k = 2π / λ ₀ : Wave Number in Free Space

λ ₀ : wavelength in free space

According to the calculation, the coupling efficiency is good when the electric field distribution of low refractive index is similar to that of high refractive index. FIG. 9 shows the coupling efficiency between the Ti diffusion waveguide and the TIPE diffusion waveguide calculated by the calculation, and shows the greatest efficiency when the thickness of the TIPE waveguide is about 1 μm. Meanwhile, in the case of the Ti diffusion waveguide, a single mode operation is required, and the thickness of the single mode Ti diffusion waveguide is about 1 μm at a maximum refractive index change Δn _max ~ 0.01. Therefore, a TIPE waveguide with a thickness of about 1 μm is needed.

In the present invention, Ti diffusion process and TIPE process conditions for fabricating waveguides satisfying the following two conditions were determined.

1. Fabrication of Ti diffusion waveguide

Δn: ~ 0.01

Waveguide Thickness: ~ 1μm (single mode)

Loss: <0.5dB / cm

2. Fabrication of TIPE Waveguide

Δn: ~ 0.11

Waveguide Thickness: ~ 1μm (3mode)

Loss: <3dB

First, to prepare a Ti diffusion waveguide, an optical grade Y-cut LiNbO ₃ substrate is prepared such that the lengths of the X, Y, and Z axes are 40, 2, and 12 mm, respectively. In this case, Y-cut surface is a plan view of the λ _0/10: mirror-polished to be a (λ ₀ 633nm), and the other surface are polished with a polishing slurry, including GC # 2000.

On the other hand, the variables to be considered in the fabrication of the Ti diffusion waveguide include the thickness of the Ti film, the temperature and time during Ti diffusion, the Ti diffusion atmosphere, and the cooling time after Ti diffusion. The Ti film on the prepared Y-cut LiNbO ₃ substrate is formed by an electron beam evaporation method. At this time, the Ti film thickness deviation is within the range of 30-60 nm.

The Ti deposited LiNbO ₃ substrate was diffused using a furnace with an error of ± 1 ° C. as shown in FIG. 10, wherein the temperature schedule in the furnace over time is as shown in FIG. 10. .

In other words, when passing the sample through a 150 ℃ hot zone, the atmosphere in the furnace is changed from dry Ar to wet Ar (Flow Rate: 6ℓ / min), and at 600 ℃, Purox (Purox: Al ₂ O ₃ ) A sample charged in a boat is pushed into a quartz tube, and Ti is diffused for 2 hours after heating to 1000 ° C. After diffusion, change to a humid O ₂ atmosphere and cooled to room temperature.

Through the above process, the Ti diffusion LiNbO ₃ substrate after the diffusion process was measured by the prism bonding method, and the number of modes, the effective refractive index, and the transmittance were measured. After the edge polishing of the substrate, the waveguide thickness was determined by butt coupling. It was. Table 1 below shows the refractive index and the number of modes measured in each sample according to the change of Ti film thickness, diffusion temperature and time.

In view of these results, the conditions for obtaining a Ti diffusion waveguide having a single mode, having a refractive index change of about 0.01, and a waveguide thickness of about 1 μm are 40 nm of a Ti film, and diffusion conditions are 1000 ° C. for 2 hours.

TABLE 1

On the other hand, the proton etching method is known as a very fast and convenient technique for fabricating a LiNbO ₃ waveguide having a large refractive index change.

In the present invention, the Ti diffusion LiNbO ₃ substrate was subjected to a proton etch process using benzoic acid to produce a TIPE waveguide.

Conditions for obtaining a three-mode waveguide having a waveguide of 1 μm equal to the thickness of the Ti diffusion waveguide and having an effective refractive index change Δn of 0.11 and a heat treatment condition of a TIPE optical waveguide with a small decrease in Δn were established.

First, after filling a glass tube with benzoic acid powder, a sample is put into a board | substrate holder, and the glass tube is put into the sealed water PE oven in the state positioned in the middle of the tube.

After heating the oven, turn the metal house over and soak the sample in the benzoic acid solution for the desired time to allow proton icing.

Turn the metal house over again, allow it to cool, remove the sample and clean it with ethanol.

Table 2 shows the thickness of the waveguide and the refractive index mode of Ti diffusion LiNbO ₃ samples measured by changing the time and temperature of the protons.

TABLE 2

In theory, when the Ti diffusion LiNbO ₃ waveguide and the TIPE waveguide have a waveguide thickness of about 1 μm, most of the light energy is coupled, as shown in FIG. At this thickness, the TIPE waveguide is shown in three modes.

The proper condition of the PE process according to the present invention is 245 ℃, 30 minutes, the effective thickness measured at 1.04μm is almost similar to the Ti diffusion waveguide layer.

As a result of the stability test for the sample that passed through the above process, it was confirmed that the sample measured after 23 days of manufacture and the sample mode refractive index change after heat treatment at 200 ° C. for 30 minutes were almost stable.

The following Table 3 shows the characteristic test result data of the AOD of the present invention.

TABLE 3

For AOD, the efficiency of the lens system is limited by the coupling efficiency of the fundamental mode between the Ti diffusion waveguide and the TIPE waveguide. In the waveguide fabricated according to the present invention, the effective thickness of the Ti diffusion and TIPE waveguides is about 1 μm, and each mode has a single mode and three modes. On the other hand, in this case, the coupling efficiency η between the two waveguides is 95% or more, which is advantageous for fabricating the optical head for AOD.

Claims (3)

Y-cut single crystal LiNbO Ti diffusion to ₃ single crystal LiNbO ₃ waveguide and the Ti diffused LiNbO ₃ waveguide In one acoustic optical deflection device to the portion provided with a TIPE LiNbO ₃ waveguide, the Ti diffused LiNbO ₃ waveguide and TIPE LiNbO ₃ waveguide thickness of the Acoustic optical deflector, characterized in that each 1 ± 0.1μm. According as the Y-cut is provided producing an acoustic optical deflector single crystal LiNbO ₃ single crystal Ti diffused LiNbO ₃ waveguide and the Ti diffusion days TIPE LiNbO ₃ waveguide portion of a LiNbO ₃ waveguide, has a single mode, the refractive index change of 0.01 degree and A condition for obtaining a Ti diffusion waveguide having a waveguide thickness of about 1 μm is a Ti film thickness of 40 nm, and the diffusion thereof is performed at 1000 ° C. for 2 hours. The method of claim 2 wherein the step of producing the TIPE has a third mode in a portion of the diffusion LiNbO ₃ waveguide the effective refractive index change of 0.11 or so, the process for the thickness of the waveguide to obtain TIPE LiNbO ₃ waveguide of 1μm degree Method for producing an optical deflecting device, characterized in that the heat treatment for 30 minutes at 245 ℃ using benzoic acid.