JPS6225707A - Fiber polarizer - Google Patents

Abstract

PURPOSE:To make mass production of an inline fiber type polarizer with high precision by using a fiber holding block made of silicon in order to polish the side face of an optical fiber. CONSTITUTION:An optical fiber 20 is held to the fiber holding block 10 made of silicon and a fiber clad 21 near the front layer of a fiber core 22 is polished for each of the holding block 10 so that only the top surface part is removed. A thin CaF2 film layer 40 and a thin aluminum metallic film 30 are formed on the polished surface of the optical fiber 20 by sputtering. The thin film layer 40 is thereby improved in the extinction ratio of a polarizer. Anisotropic etching of silicon is used to manufacture the holding block 10. More specifically, the etching progresses at about 54.74 deg. angle with the substrate surface in the direction parallel with or perpendicular to the <100> plane in the stage of etching the silicon wafer having the surface on the <100> plane by an alkaline soln. A fiber holding groove is precisely made to an arc shape by using such phenomenon. The mass production of the polarizer at a low cost with high precision is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a polarizer (polarizer) for controlling the polarization of light, and particularly to an in-line fiber polarizer suitable for an optical fiber system.

[Background of the invention]

Fiber sensors and optical fiber communication systems using single mode fibers often require a polarizer to control the polarization state of light in order to achieve stable operation. In these two cases, the conventionally used bulk type polarizer using a prism connects optically with the single mode fiber through a circular layer, so an inline type fiber polarizer that is processed from the single mode fiber itself is required. ing. For example, it is disclosed in Japanese Patent Application Laid-open No. 60-2902 and Japanese Patent Application Laid-Open No. 59-7305.

In such a fiber polarizer, a single mode optical fiber having a length of about 50 cm is embedded in an aluminum metal block having a groove with curvature in the depth direction, and then bonded. The length of the embedded part of the fiber is approximately 30 mm, and the curvature of the groove in the aluminum block is approximately 101 mm.Next, the optical fiber embedded in the aluminum block is polished on the side surface of the aluminum block, and the fiber is polished to near the surface layer of the fiber core. Remove crud. Thereafter, a thin film of metal such as aluminum is formed on the polished surface of the fiber by vacuum evaporation.

As described above, in an optical fiber loaded with a metal film near the core, the TE
The propagation loss is larger than that of the mode. Therefore, an element that removes one of the orthogonal polarized lights, that is, a polarizer is obtained.

In such an in-line fiber polarizer, the distance between the fiber core and the metal film is important for performance. In other words, the removal thickness of the fiber cladding is a problem, and therefore the shape and depth of the groove in which the optical fiber is buried greatly influences the performance. Since the fiber is polished at the same time as the block holding the optical fiber (made of aluminum in the example of the above-mentioned document), the shape of the fiber held in the block is important.

When polishing the fiber side surface, the removal thickness of the cladding can be calculated from the grinding depth of the fiber holding block. However, for this purpose, it is necessary that the fiber holding groove be precisely machined. Further, the groove shape needs to be arcuate in order to prevent fiber breakage during polishing, and from the viewpoint of polarizer design and analysis, it is desirable to have a simple curve like a circular arc.

Although the operation and principle manufacturing method of such in-line fiber polarizers have been clarified in literature, it is unclear what manufacturing method is suitable for mass production to achieve high precision and low cost. Met.

[Purpose of the invention]

An object of the present invention is to provide a means for manufacturing an in-line fiber type polarizer with high precision and a method suitable for mass production.

[Summary of the invention]

In the present invention, as a manufacturing method for an in-line type fiber polarizer, we focused on semiconductor processes, adopted silicon as the fiber holding block material, and created the fiber holding groove using anisotropic etching.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an example of an in-line fiber type polarizer according to the present invention. Figure 2 shows its cross-sectional structure. The optical fiber 20 is held in a silicon fiber holding block 10, and the fiber cladding 2 is held close to the surface layer of the fiber core 22.
1, the entire fiber holding block 20 was polished to remove only the upper surface.

A CaF2 (gravel stone) thin film layer 40 and an aluminum metal film layer 30 were formed on the polished surface of the optical fiber by sputtering. The CaF2 layer 40 improves the extinction ratio of the polarizer.

In the above in-line fiber type polarizer, anisotropic etching of silicon was used to fabricate the silicon fiber holding block. That is, when a silicon wafer having a (100> plane as a surface is etched with an alkaline solution), etching proceeds at an angle of about 54.74° with respect to the silicon substrate surface in a direction parallel or perpendicular to the <110> plane. Using this phenomenon, a groove for holding the fiber was precisely fabricated in an arcuate shape.This method will be explained in detail below.

FIG. 3 shows the state in which the optical fiber is held in the silicon block before polishing. An optical fiber having a diameter of 2a is held in a groove having an arc of curvature R. To create such a groove on a silicon substrate, a silicon oxide film is applied to the surface of the silicon substrate other than the groove opening, and then alkali etching is performed. Thermal oxidation was performed, followed by photo-etching.

Here, the photomask was designed as follows. The X coordinate is the axial direction of the optical fiber. According to the anisotropic etching, the cross section of the fiber holding groove always becomes an isosceles triangle with a base angle θ=54.74°. Therefore, if the groove is given a constant curvature R, the fiber embedding depth (distance from the silicon substrate surface to the fiber center) δ is small at the center of the groove (X=O), and δ is large at both ends of the groove. Similarly, the opening width W of the groove is the smallest at the center of the groove.

In FIG. 3, the relational expression among the fiber embedding depth δ, the groove depth, and the groove opening width W is as follows.

δ=R-JT[to7shia 1-+a (X<:R) (1
) R D =-+ a (1+secθ) (2) R (θ=54.74°) W”2Dcot 〇cot.

= −x”+2a(coto+cosecθ) (x
<R) Based on formulas (1) to (3), in this example, the fiber holding block was created using a silicon wafer with a diameter of 76φ, a thickness of 1 mm, and a plane orientation (100>).
The figure is a basic layout diagram of a cell on a silicon wafer in which this fiber holding block is a unit. In this example, 28 fiber holding blocks were fabricated on one wafer. FIG. 5 is a detailed diagram of each cell. The groove opening is (3
), the quadratic function is expanded according to the formula. In this example, grooves that disappear as markers during polishing are provided around the fiber holding grooves when polishing progresses to 30 μm, 50 μm, and the target depth to facilitate the polishing process.

〔Effect of the invention〕

As described above, according to the present invention, when manufacturing an in-line fiber type polarizer, the fiber holding block can be manufactured precisely and with high productivity, so that polarizers can be mass-produced with high precision and at low cost.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the in-line fiber polarizer according to the present invention, Fig. 2 is a cross-sectional view thereof, and Fig. 3 shows the shapes of the silicon fiber holding block and fiber holding groove before polishing, and the mounting state of the optical fiber. 4 is a layout diagram of the silicon block cell of FIG. 3 on a wafer substrate, and FIG. 5 is a detailed diagram of the cell. 10... Silicon fiber holding block, 20...
- Single mode optical fiber, 30... Aluminum metal thin film, 40... CaF, thin film, 21... Optical fiber cladding, 22... Optical fiber core.

Claims (1)

[Claims] 1. In a polarizing element having a structure in which the side surface of an optical fiber is polished and a metal film is loaded on the side surface of the optical fiber, a silicon fiber holding block is used to polish the side surface of the optical fiber. Features fiber polarizer. 2. The fiber polarizer according to claim 1, wherein a fiber holding groove is provided in the silicon fiber holding block so that the optical fiber is held in an arc. 3. The fiber polarizer according to claim 2, wherein the fiber holding groove is produced by anisotropic etching.