JPH0468601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improvement in an optical isolator for preventing noise generation due to reflected light from an optical device in an optical communication system.

(Prior Art) Rutile (TiO ₂ ) single crystal is mainly used as a polarizer and analyzer material for optical isolators. The method for manufacturing rutile single crystals involves dropping raw material powder into an oxyhydrogen flame, melting it, and growing it on top of the seed crystals below.
It is produced in large quantities using the so-called Bernoulli method. Recently, the floating zone method has begun to be used, in which a raw material rod and a seed crystal are arranged vertically, a molten envelope is formed by concentrated infrared heating, and a single crystal is grown by moving the molten envelope. However, since the crystal size that can be grown is determined by the relationship between the weight of the melt and the surface tension, it was not possible to grow large crystals.

Therefore, wafers approximately 10-odd millimeters in size were used to manufacture isolators.

(Problem to be solved by the invention) Optical isolators used in optical communications etc. use a polarizer in the direction in which light enters and a polarizing element called an analyzer in the direction in which light passes. It is made by bonding them together as a rotating element. The size is usually 1 to several millimeters square, but it is convenient for manufacturing to bond large wafers together and then cut them into pieces later. This is a common method when manufacturing small devices, but in the case of isolators, it is necessary to strictly set the crystal orientation when bonding, which is a time-consuming process, so it is recommended to manufacture from as large a wafer as possible. It is desired.

By the way, as mentioned above, the maximum diameter of rutile wafers is currently limited to 12 to 15 mm due to the manufacturing method, whereas bismuth garnet thick film wafers are manufactured in large diameters of 35 to 50 mm. Therefore, the small diameter of the rutile wafer
It was a problem. There were also problems with optical quality, and the yield rate was as low as about 50%.

(Means for Solving the Problems) In order to solve the above problems, the present invention uses a YVO ₄ (yttrium vanadate) single crystal grown by a pulling method as a polarizer and analyzer material. YVO ₄ can grow high-quality, large-sized single crystals using general pulling equipment.

(Function) The properties of YVO ₄ as a polarizing material were not clear, but as a result of growing and measuring high quality large crystals, the present inventors found that the separation of ordinary light and extraordinary light, degree of extinction of polarized light, weather resistance, etc. It was found that the quality of rutile is almost the same as that of high quality rutile.

(Example) YVO ₄ single crystal growth was performed using a general pulling device and a high frequency induction heating method. For raw materials
Using powder with YVO ₄ composition, diameter 50mm, depth 50mm,
Fill an iridium crucible with a wall thickness of 1.5 mm with 500 g of raw material, and use a seed crystal in the c-axis orientation to
It was pulled up at a speed of mm. During this period, the melt temperature is changed every hour.
The temperature continued to decrease at a rate of 20-25°C. After raising the crystal for about 10 hours, the grown crystal is separated from the melt and the crucible temperature reaches
Cool slowly at a rate of 50 to 70°C per hour until it reaches 800°C.
After that, it was left to cool. The crystals recovered from the growth furnace have a diameter of 25
This crystal, which was 35 mm in length and 35 mm in length, was fixed on a sample stage of a slicing device and tilted at 45 degrees from the c-axis to the a-axis direction to produce a wafer with a thickness of 1.3 to 1.4 mm.

Both sides of the wafer were optically polished to a thickness of 1.2 mm, and evaluated as a polarizing material for optical isolators. The measurement items were the separation distance of ordinary light and extraordinary light, insertion loss, and extinction ratio, all of which were equivalent to good quality rutile.

Furthermore, after coating both sides of the yttrium vanadate wafer with an anti-reflection film for a wavelength of 1.3 μm, a thick bismuth garnet film was bonded to form an optical isolator, and the isolator function was measured. demonstrated performance.

Note that in this example, a crystal wafer produced in a crucible with a diameter of 50 mm was used, but it is possible to obtain a large crystal wafer by using a larger crucible.

(Effects of the Invention) In the present invention, a YVO ₄ single crystal wafer is used, but unlike conventional rutile, this yttrium vanadate is obtained by a pulling growth method, so a high quality product can be obtained at a low cost. In addition, since it is easy to increase the size, production efficiency can be particularly improved when an isolator is manufactured by bonding it with a large-sized Faraday rotary element wafer, contributing to a reduction in price.

Claims (1)

[Claims] 1. An optical isolator comprising a polarizer, a Faraday rotator, and an analyzer, characterized in that a YVO ₄ (yttrium vanadate) single crystal wafer is used for the polarizer and the analyzer.