JPS61179403A - Polarization plane maintaining optical fiber and its manufacture - Google Patents

Abstract

PURPOSE:To hold the direction of the optical main axis of a maintaining optical fiber constant by making the coating layer of the optical fiber not circular, but, for example, elliptic. CONSTITUTION:A clad layer 2 is formed around a core 1 and its periphery is coated with an elliptic jacket layer 3 and a substrate 5 to form the polarization plane maintaining optical fiber, which is covered with the coating layer 4 which has flat section. In this case, there are two main axes, which are installed in the lengthwise direction of the coating layer 4 as shown in figure (a) and figure (b). In either case, the optical fiber is wound invariably as shown in figure (c) to uniform the main shaft in the invariably constant direction.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to the cross-sectional shape of a coating layer of an optical fiber, and in particular, to an optical fiber that guides polarized light, the optical axis can be set in any direction or in a fixed direction. The present invention relates to the shape of an optical fiber coating and its manufacturing method.

[Summary of the invention]

In the coating layer of a polarization maintaining optical fiber, this invention provides:
An NFC optical fiber designed to form a coating layer with a non-circular cross section, capable of maintaining the optical axis of the optical fiber in an arbitrary or fixed direction, and capable of maintaining the plane of polarization. Demeru.

[Conventional technology]

A conventional polarization-maintaining optical fiber has a circular cross section as shown in FIG. By making the jacket layer 8 completely circular, etc., polarization maintaining optical fibers can be used. Kon
By making the core 1, cladding layer 2, or jacket layer 3 elliptical and applying different order strains in the axial direction of direct firing, a birefringence effect occurs, and this effect maintains the plane of polarization of the incident polarized light. Ideally, when light polarized in the direction of the principal axis is incident, it will not combine with the polarization component perpendicular to the main axis, so the light energy will always remain as the incident polarization component. It is called propagation.

Generally, optical fibers are coated with plastics such as silicone, polyurethane, epoxy resin, polybutadiene, etc. during the drawing process to make the original fiber from the preform, in order to completely prevent the brittle characteristics from breaking. However, in the conventional polarization-maintaining optical fiber, the coating layer 4 has a circular cross section, so when the optical fiber is wound until it is bent, The optical fiber is bent in any direction with respect to the main axis direction, and the main axis of the optical fiber is not always constant. In this case, part of the optical energy propagating in the optical fiber transfers to other polarization components, resulting in an increase in polarization dispersion, phase disturbance, and further energy in the optical fiber being released to the outside. There was a problem that optical loss occurred.

Therefore, in order to solve these conventional drawbacks, this invention aims to maintain the principal axis of the polarization-maintaining optical fiber in automatic fishing, so that the main axis direction of the polarization-maintaining optical fiber remains constant in any state, and to obtain an optical fiber with excellent polarization maintenance. It is an object.

[Means to solve all problems]

In order to solve the above-mentioned problems, the present invention proposes to make the coating layer of the polarization-maintaining optical fiber not circular but having a non-circular cross section such as an elongate circle or a crescent shape. We designed a method that can keep the distance constant throughout. That is,
If the cross section of the coating layer is flattened and then rolled and bent according to its jL, the principal axes will naturally align in a certain direction, making it possible to always match the polarization. The polarization-maintaining optical fiber according to the present invention can provide better polarization characteristics in communications, optical measurements, etc. that utilize polarized light.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

The polarization-maintaining optical fiber in FIG. It is covered with a flat covering layer 4. At this time, there are two main axes, one for installing the optical fiber in the long axis direction of the coating layer 4 as shown in Fig.
There are cases where it is done as shown in the figure). In the case of Izun, the fourth
If you wind it as shown in the diagram, you can always align the main axis in a certain direction.

Basically, the object of the present invention will be achieved if the covering layer 4 has a flat cross section, but in order to absorb the tension during winding and changes in tension due to temperature changes, it may be made as follows. The shape of the coating is also misleading. That is, in Figure 5),
(6) If the shape is a skewered dumpling shape as shown in (c) or a similar shape, or a crescent or half-moon shape, the voids can absorb the tension. Also, the type of glasses shown in Figure 6 is
When accommodating multiple optical fibers, it is difficult to match the characteristics. The central neck n acts as a cushion that absorbs tension.

Next, a method for forming a coating layer of a polarization maintaining optical fiber according to the present invention will be explained with reference to FIG. A bare optical fiber 6 consisting of a core 1, a cladding layer 2, a jacket layer 3, and a substrate 5 is passed through a funnel 9 filled with a liquid polymeric monomer such as plastic, which is the material of the coating layer 4. The shape of the exit port 8 of the funnel 9 is set to the cross-sectional shape of the coating layer 4, and this is polymerized and solidified in the cutting edge thermal furnace 10 to form a polarization-maintaining optical fiber 7 that covers the entire stock layer 4 having a flat cross section. can be easily manufactured.

Furthermore, although this is not necessary for normal polarization maintaining optical fibers,
In particular, when precision is required, it can be manufactured under control as shown in FIG. In this case, the optical fiber 7'i is made from the preform [2]. A beam focused by a light source 15 is irradiated from the side onto the bare optical fiber 6 to create a pattern on the screen 13. This pattern is caused by the wavefront of the light received by the strain metal, so the pattern is symmetrical and is controlled by the direction control motor 11 attached to the top of the preform.

A plurality of photodetectors are installed on the screen 13 to signal the symmetry of the pattern, and a television camera 14 also monitors the pattern. Pass this precisely controlled naked optical fiber 6 through the funnel 9 and skin heat furnace 10.
/f1 An optical fiber 7 with excellent polarization preserving characteristics and low transmission loss can be manufactured.

In addition, the knife 1 shown in Figure 9 is
6, the optical fiber 1 has a normal circular cross section.
In addition to scraping off the coating layer 4 of the optical fiber 7, it is also possible to obtain an optical fiber 7 having a coating layer with a desired cross-sectional shape. At this time, if a heating knife is used, no chips of the coating 84 will be produced. If the viscosity of the monomer filled in the funnel 8 is low, the coating layer 4 will automatically become circular due to surface tension, so this device can also be used to form a coating layer with a flat cross section. It is.

Further, a skewer-shaped coating layer can be formed using the apparatus shown in FIG. That is, the optical fiber 17 that has been spun through the entire funnel with a normal circular nozzle is wound on the reels 18 and 19, and the NFC yarn that has already been spun is wrapped around one or two of the same type of material. The optical fiber 7 is guided to a heating polymerization furnace 10 using a guide [20] to produce an optical fiber 7 having a coating layer having a dumpling-shaped cross section.

〔Effect of the invention〕

This invention has been explained above.
fjt: It is possible to keep the optical axis of the optical fiber constant, and even when bending the optical fiber, the principal axis can always be aligned in the same direction, so that the plane of polarization can be preserved *n This has the effect that a polarization maintaining optical fiber can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a polarization-maintaining optical fiber showing an embodiment of the present invention, Fig. 2 is a cross-sectional view of a conventional polarization-maintaining optical fiber, and Fig. 3) is an embodiment of the present invention. 4 is a partial cross-sectional view showing the optical fiber in FIG. 8 in a well-bent state, and FIG. 5 (2) to (C) and FIG. 6 are views showing other embodiments of the present invention. The cross-sectional views of the optical fiber shown in FIGS. 7, 8, 9, and 10 are perspective views showing the method of forming the coating layer of the optical fiber of the present invention. 10. Core 21. Clad 30. Jacket 40. Composite layer 50. Substrate 60. Bare optical fiber 70. Polarization maintaining optical fiber 80 with a non-circular coating layer. Above the nozzle, Sasaki - Original applicant Seiko Electronics Co., Ltd. Agent, Patent Attorney Mogami - Side eaves view showing the upper lip of the optical fiber (Fig. 4, Fig. 5) ((1) Fig. 6, Fig. 7) Figure 8 Figure 9 Figure 10

Claims (8)

[Claims] (1) A polarization-maintaining optical fiber for guiding polarized light, characterized in that the cross-sectional shape of the coating layer of this optical fiber is non-circular. (2) The polarization-maintaining optical fiber according to claim 1, wherein the cross-sectional shape is flat or rhombic. (3) The polarization-maintaining optical fiber according to claim 1, wherein the cross-sectional shape is crescent-shaped or half-moon-shaped. (4) Claim 1 whose cross-sectional shape is a skewer-shaped dumpling
Polarization-maintaining optical fiber described in Section 2. (5) After passing the bare optical fiber after spinning through a funnel filled with a liquid polymer monomer and having a non-circular cross-sectional shape at the exit port, the monomer is polymerized and solidified in a heating furnace. 1. A method for manufacturing a polarization-maintaining optical fiber, comprising forming an optical fiber coating layer. (6) Polarization preserving light characterized by forming a non-circular coating layer by scraping off the coating layer of an optical fiber, which has a coating layer with a normal circular cross section, with a cutting tool or a heating knife. Fiber manufacturing method. (7) After adding one or two threads already spun from similar materials to the optical fiber on which the coating layer has been formed through a funnel with a normal circular exit port, polymerization is carried out in a heating furnace. 1. A method of manufacturing a polarization-maintaining optical fiber, characterized in that a non-circular coating layer is formed by solidification. (8) The method for manufacturing a polarization-maintaining optical fiber according to claim 7, wherein the coating layer has a skewer-shaped cross-section.