JPH03231203A - Ion exchange method - Google Patents

Abstract

PURPOSE:To stabilize temp. and to improve the controllability and reproducibility of ion exchange depth by immersing a substrate in a soln. at a temp. close to the b.p. of the soln. under constant vapor pressure and carrying out ion exchange. CONSTITUTION:The region of a substrate 1 not to be subjected to ion exchange is coated with a film 2 of a metal, oxide, nitride, etc., and the substrate 1 is immersed in a soln. 3 as an ion source. This soln. 3 is heated to a temp. close to the b.p. of the soln. 3 with a heater 4 and vapor pressure is kept constant. When the pressure of a vapor phase generated from the soln. is relieved to atmospheric pressure, it can be made constant within a range in which atmospheric pressure varies. Temp. is stabilized, the controllability and reproducibility of ion exchange depth are improved and an optical element is simply obtd. by ion exchange.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an optical element, particularly a polarizing element, using ion exchange.

(Prior Art) A polarizing element, particularly a polarizing beam splitter, is an element that obtains a specific polarized light by changing the propagation direction of light between orthogonal polarized lights. Such elements are used as parts constituting optical isolators and optical circulators in light source modules for optical fiber communications, optical heads for optical discs, and the like.

Conventionally, polarizing beam splitters are those 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, such as a Glan-Thompson prism or Rossicon prism, 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.

On the other hand, there is a multilayer diffraction polarizer that is small, highly productive, and inexpensive. A birefringent grating polarizer has periodic ion exchange regions on the main surface parallel to the optical axis of an optically anisotropic crystal, and the ion exchange region on the main surface has a thick ion exchange region. A thin dielectric film is formed in the area where no exchange is performed, and optical paths are separated by utilizing differences in diffraction efficiency due to polarization. For example, when proton exchange is performed periodically on the main surface of an X plate or a Y plate of lithium niobate, the refractive index for extraordinary rays with a wavelength of 1.3 pm increases by 0.09 in the proton exchanged region, and the refractive index for ordinary rays increases by 0.09. The refractive index decreases by about 0.04.

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 doing so, both the first-order diffraction efficiency of ordinary rays and the zero-order diffraction efficiency of extraordinary rays can be made zero, and the polarizer becomes a polarizer.

(Problems to be Solved by the Invention) In this birefringent grating type polarizer, the extinction ratio or insertion loss deteriorates unless the depth of ion exchange is accurately controlled. For example, if the ion exchange depth deviates from the optimum value by 1%, the extinction ratio will be limited to 20 dB or less. On the other hand, if the temperature during ion exchange shifts by 1 degree, the diffusion depth shifts by about 1.5%. Therefore, in order to create a birefringent grating polarizer with a high extinction ratio, it is necessary to control the ion exchange temperature with high accuracy.

Conventionally, normal temperature control devices have been used to control the temperature of ion exchange, but it has been difficult to obtain sufficient temperature control accuracy with the conventional temperature control devices.

The purpose of the present invention is to stabilize the temperature during ion exchange,
The objective is to provide a simple technique that improves the controllability and reproducibility of ion exchange depth.

(Means for Solving the Problems) The ion exchange method of the present invention is a method of ion exchange by immersing a substrate in a solution serving as an ion source, in which the vapor pressure of the solution is kept constant. It is characterized by ion exchange by immersing the substrate in the solution at a temperature near the boiling point.

(Function) The boiling point of a substance takes a constant value when the pressure is constant. Therefore, by heating a solution serving as an ion source to its boiling point and keeping the pressure of the gas phase constant, the temperature of the solution can be stabilized at that boiling point. Generally, the change in boiling point with respect to a change in pressure is small, so by keeping the pressure constant, the temperature can be stabilized more easily and accurately than by controlling the temperature itself.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of an embodiment of an ion exchange region forming apparatus according to the present invention. A substrate 1 with a film 2 of metal, oxide, nitride, etc. covered on areas that are not desired to undergo ion exchange is immersed in a solution 3 that serves as an ion source, and this solution 3 is heated using a heater 4 or the like. Adjust to near boiling point. This solution 3 is made to have a constant vapor pressure. The embodiment shown in FIG. 1 is an example in which the gas phase of the solution is released to atmospheric pressure. In this case, the pressure can be kept constant within a range of atmospheric pressure fluctuations. In addition, when the ion exchange takes a long time, in order to prevent the solution 3 of the ion source from vaporizing and reducing the amount of the solution 3, a container 5 for holding the solution 3 is installed as shown in FIG.
It is best to put a lid 6 on it. By providing the lid 6 with appropriate airtightness, it is possible to prevent the solution 3 from decreasing and maintain a constant pressure.

Furthermore, as shown in FIG. 3, if a device for keeping the pressure constant, such as a pressure valve 7, is attached to the container 5 or the paper 6, even more stable temperature control can be achieved. Also, by keeping the pressure higher than atmospheric pressure, the boiling point can be raised.
Ion exchange can be performed in a short time.

Note that the ion exchange method of the present invention is effective not only for producing a multilayer diffraction type polarizer but also for other optical elements.

(Effects of the Invention) As described above, according to the present invention, the temperature of ion exchange can be stabilized, the controllability and reproducibility of ion exchange depth can be improved, and ion exchange can be easily performed. element can be manufactured. Furthermore, by keeping the pressure of the solution higher than atmospheric pressure, ion exchangers are shown in FIG. It is a diagram.

1... Crystal substrate with optical anisotropy, 2... Ion exchange mask, 3. ... Ion source solution, 4... Heater, 5... Container, 6... Lid, 7... Pressure valve.

Claims (1)

[Claims] When forming an ion exchange region on the surface of a substrate, the vapor pressure of the solution serving as an ion source is kept constant, the temperature of the solution is brought to a temperature near the boiling point of the solution, and the substrate is immersed in the solution to perform ion exchange. An ion exchange method characterized by: