JPS6333705A - Production of refractive index distribution type plastic optical fiber - Google Patents

Abstract

PURPOSE:To continuously produce a GI type optical fiber made of a thermoplastic resin such as polymethyl methacrylate (PMMA) by condensing the laser light of a YAG laser from the direction of the side face to the center part of a core, which is produced by continuous extrusion and consists of the thermoplastic resin, to optically process the core. CONSTITUTION:The emitted beams of the YAG laser is divided into 16 by the combination of a beam splitter and a total reflection mirror after being expanded through a beam expander, and one of divided beams is used for power monitor, and every three beams of 15 beams of the rest are gathered into one irradiation unit. Individual irradiation units are condensed on the center part of the core at the angles of 120 deg. in a plane perpendicular to the PMMA core, and each beam 3 has the energy linearly concentrated in the lengthwise direction of the center part of a core 1 by a cylindrical lens 2. Thirty irradiation units are arranged on a PMMA extrusion line, and the PMMA core is extruded, and pulses of the YAG laser are projected at intervals of a certain length. Thus, the refractive index in the center part is made higher than that in the peripheral part to obtain the GI type plastic optical fiber.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to a core wire of a thermoplastic resin such as polymethyl methacrylate (hereinafter abbreviated as PMMA), which is continuously produced by an extrusion method, and is exposed to a YAG laser from a side direction. By irradiating the PMMA core with a laser beam, a refractive index distribution is created in the core wire radial direction due to the thermal strain effect of the laser beam, thereby eliminating the need for chemical diffusion effects such as ion exchange. This makes it possible to manufacture graded index plastic optical fibers.

[Conventional technology]

Optical fibers for optical communication are of the step-index type (hereinafter referred to as SI type), in which the refractive index distribution between the core and cladding is on a discontinuous staircase, and in the step-index type (hereinafter referred to as SI type), where the refractive index distribution between the core and the cladding is discontinuous, and the other is the step-index type (hereinafter referred to as SI type), in which the refractive index distribution between the core and the cladding is discontinuous, and the optical fiber has a substantially parabolic shape extending from the central axis to the outer circumference. It is roughly classified into a graded index type (hereinafter referred to as GI type) having a refractive index distribution.

Among these, the GI type is better for optical communication purposes because it has less mode dispersion during transmission and can provide a wider transmission band. As a manufacturing method for this GI type optical fiber, techniques such as the vapor phase shafting method have been established for silica fiber, and have already been commercialized.

[Problem that the invention seeks to solve]

However, the manufacturing method for plastic optical fibers is basically an extrusion method, which is fundamentally different from that for silica-based optical fibers, which mainly use a base material method, so it is not possible to apply the same technology as for silica-based optical fibers. Can not. Therefore, at present, the type of plastic optical fiber is limited to SIW, and GI type plastic optical fiber is not manufactured.

[Means for solving problems]

The present invention was completed based on the discovery that it is possible to continuously manufacture GII optical fibers made of thermoplastic resin such as PMMA by applying the thermal strain effect of thermoplastic resin such as PMMA using a YAG laser.

The GI type plastic optical fiber of the present invention can be manufactured as follows. For example, a method for manufacturing a gradient index optical fiber by irradiating a PMMA core wire (diameter 1 tx) with pulsed light from a YAG laser will be explained with reference to the drawings.

FIG. 1(a) is a plan view showing the manufacturing process of the GII optical fiber of the present invention, and FIG. 1(a) is a side view thereof.

After expanding the emitted beam of a YAG laser (LAY-603, manufactured by Toshiba) into a Gaussian distributed beam with a diameter of 10 m through a beam expander, it is divided into 16 beams using a combination of a beam splinter and a total reflection mirror, and one beam is divided into 16 beams with a power This will be used for monitoring, and the remaining 15 beams will be grouped into 3 beams each to form one irradiation site. As shown in Figure 1, each irradiation site is set so that the three beams form an angle of 120° to each other in a plane perpendicular to the PMMA core and are focused on the center of the core. Each beam (3) is focused on the core wire (1) by a cylindrical lens (2) placed just before focusing on the core wire.
The energy is concentrated linearly in the longitudinal direction of the center.

In addition, since the linearly concentrated energy distribution is a Gaussian-like non-uniform distribution in the longitudinal direction of the core wire, the arrangement of the cylindrical lenses is as shown in Figure 1 (b).
As shown in the figure, the irradiation parts are arranged so that half of them overlap each other, so that the energy irradiation distribution is approximately uniform.

A total of 30 such irradiation units were placed on the PMMA extrusion line, and the PMMA core wire was extruded at a speed of 5 n/sec to generate a YAG laser beam (pulse width 9 m5ec).
By irradiating at 0.5 second intervals, each part of the core wire receives a total of 30 pulses at 0.5 second intervals, and as a result, the refractive index of the center increases compared to the surrounding area. 0.1%
The degree of improvement improved, and we were able to manufacture GI type plastic optical fiber.

[Brief explanation of drawings]

FIG. 1 is a process diagram for making a GI type plastic lens of the present invention. I2IW engraving (Naiku; 21st edition) Supplementary procedural device (method) October 73, 1985

Claims (1)

[Claims] A method for manufacturing a gradient index plastic optical fiber, which is characterized by focusing laser light from a YAG laser from the side toward the center of a core wire of thermoplastic resin manufactured by a continuous extrusion method, and optically processing the core wire. .