JPS59162502A - Single-mode optical fiber of circular polarization maintainability and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a long-sized optical fiber with small loss by providing a linear glass layer of glass composition which is slightly different in refractive index from core glass or clad glass near a core lengthwise in the core glass or clad glass. CONSTITUTION:The linear glass layer 2 of glass composition which is slightly different in refractive index from the core glass of a core part 1 or the clad glass of a clad layer 2 near the core part 1 is provided in the core glass or clad glass. Said linear glass layer 2 is formed linearly in the clad layer 3 contacting the core 1 while turned once per 1cm length of the fiber. The difference in refractive index between the core glass and linear glass layer is 0.1%. When laser light of clockwise circular polarization is made incident to this single-mode optical fiber of circular polarization maintainability, the combination with a counterclockwise circular polarized wave due to a dispersion of pulses is extremly small and the state of clockwise circular polarization is maintained very excellently. Consequently, the manufacture is simplified and the long-sized, small- loss fiber is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single mode optical fiber having circular polarization preserving properties and a method for manufacturing the same.

The fundamental mode propagating in a single mode optical fiber is composed of two circularly polarized modes rotating in opposite directions. In normally manufactured fibers, minute structural disturbances (for example, the deviation of the core from a perfect circle) cause a propagation time difference between these two circularly polarized modes, so long-distance optical transmission systems are not possible. , which causes the time division of the optical pulse.

Therefore, in order to reduce the pulse broadening due to the propagation time difference of this circularly polarized wave mode, a single mode optical fiber having circular polarization preserving property is required, and one form thereof is:
A twisted single-mode optical fiber (hereinafter abbreviated as 1-twisted fiber J) has been devised, in which a twist is added to every fixed length in the longitudinal direction of the fiber. In this twisted fiber, birefringence occurs due to torsional stress, and this birefringence is distributed in a twisted state in the longitudinal direction of the fiber, so that the circularly polarized wave mode is preserved and propagated. Therefore, if only a polarization mode that rotates in one direction is incident, the circular polarization state is preserved and transmission can be performed without causing pulse broadening.

However, since the above-mentioned twisted fiber requires periodic twisting in the longitudinal direction, there are problems such as a complicated manufacturing process and difficulty in achieving low loss.

In order to solve these drawbacks, the present invention provides a linear glass layer consisting of a glass composition having a slightly different refractive index from the core glass or clad glass in the longitudinal direction within the core glass or within the clad glass near the core. The purpose of this invention is to develop a low-loss single-mode optical fiber with excellent circular polarization preservation and its manufacturing method. The purpose is to provide a method.

Figure 1 shows an embodiment of the single mode optical fiber with circular polarization preserving properties according to the present invention [(a) is a cross-sectional view in the diameter direction of the fiber, and (b'') is a cross-sectional view in the longitudinal direction of the fiber]. 1 is a core portion, 2 is a spiral glass layer made of a glass composition with a slightly different i refractive index from the core glass or clad glass, 3 is a clad layer, and 4 is a jacket layer.For example, FIG. In the circularly polarized wave preserving single mode optical fiber of the present invention, Si 02-G is used as the core glass material.
eO2 (3 mol%), Si02-Ge02 (2 mol%) as the glass material for the spiral glass layer 2, SiO2 as the glass material for the cladding layer 3, Si02' (quartz tube or Synthetic quartz) is used, and a linear glass layer 2 is formed in a spiral (clockwise) manner in the cladding layer 3 in contact with the core 1, with one mark per fiber length. Create polarization preserving single mode fiber. The relative refractive index difference between the core glass and the spiral glass layer in this fiber is 0.1%. When we input a right-handed circularly polarized laser beam into the circularly polarized, single-mode optical fiber we created, we found that the coupling (coupling, energy transfer) to the left-handed circularly polarized wave, which causes pulse broadening, was It was extremely small, and the right-handed circular polarization state was extremely well preserved.

FIG. 2 shows an embodiment of the method of manufacturing a preform for a single mode optical fiber having circular polarization maintaining property according to the present invention. In FIG. 2, 21 is a synthetic torch for forming a core porous body, 22 is a synthetic torch for forming a spiral porous glass layer 26 having a slightly different refractive index from the core glass or clad glass, and 23 24 is a synthetic torch for forming a cladding porous layer, 25 is a core porous body, and 26 is a spiral wire having a slightly different refractive index from the core glass or cladding glass. 27 is a cladding porous layer, and 28 is a jacket porous layer. In the example of the manufacturing method shown in FIG.
A glass raw material of CJ2q-GeCJ2+ (2 mol%) was supplied to the synthesis torch 22 at a rate of 10 cc per minute, 5iCn< was supplied to the synthesis torch 23 at a rate of 200 cc per minute, 3i Cf
24 were respectively supplied to the synthesis torch 24 at a rate of 500 cc per minute.
After creating a porous base material by pulling it up while rotating at m,
A transparent base material was obtained by heating and sintering, and a single mode optical fiber with an outer diameter of 125 μm was manufactured using a high-temperature electric furnace.

When the polarization characteristics of the single mode optical fiber obtained in this way were investigated, the fiber showed good circular polarization characteristics,
Even in a pulse transmission test in which only right-handed circularly polarized light was incident on J3, the pulse spread after 100 kn+ propagation was extremely small. Furthermore, the loss characteristics were investigated and the loss at 1.3 am was as low as 0.5 dB/km.

In the circularly polarized single mode fiber in the above embodiment,
The relative refractive index difference Δ01 between the core glass and the linear glass layer is 0.
．． 1%, and the relative refractive index difference Δn2 between the spiral glass layer and the cladding glass is 0.2%, but these values are of course not absolute, and Δnl.

Together with Δn2, it can be changed in various ways.

Regarding the position of the linear glass layer, in the above embodiment, it was formed on the side surface of the core glass, but it can also be formed inside the core glass or inside the clad glass, which is effective in maintaining circular polarization.

In addition, as for the glass composition of the linear glass layer, Si02-Ge02 was used in the above example, but in addition, Si02-Ge02 was used.
i 02, Ge 02 , B2'05, P2O5, F
, T'i 02.5n02, PbO, and the like can be used.

Furthermore, by adjusting the rotation speed of the porous base material, the helical pitch of the glass layer can be freely controlled.

As explained above, the circularly polarized single mode optical fiber of the present invention has a glass composition that has a refractive index slightly different from that of the core glass or clad glass in the longitudinal direction in the core glass or in the clad glass near the core. Since it has a linear glass layer, it has the advantage that the manufacturing method is simplified and it is easy to obtain a long, low-loss fiber.

Further, if the circularly polarized single mode fiber manufactured by the method of the present invention is applied to an actual optical transmission system, there is an advantage that long-distance, large-capacity transmission becomes possible.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of a single mode optical fiber having circular polarization preserving property according to the present invention, in which (a) is a radial cross-sectional view of the fiber, (b) is a longitudinal cross-sectional view of the fiber, and FIG. FIG. 2 is an embodiment of the method of manufacturing a preform for a single mode optical fiber having circular polarization preserving properties according to the present invention. 1... Core part 2... A linear glass layer made of a glass composition with a slightly different refractive index from the core glass or clad glass
3... Clad layer 4... Jacket layer 21... Synthetic torch 2 for forming the core porous body
2... Synthetic torch for forming a spiral porous glass layer having a slightly different refractive index from the core glass or cladding glass 23... Synthetic torch for forming a cladding porous layer 24... Jacket Synthetic torch 25 for forming a porous layer... Core porous body 26... Spiral porous glass layer 21 having a slightly different refractive index from the core glass or clad glass... Clad porous layer 28 ... Jacket porous layer patent applicant Nippon Telegraph and Telephone Public Corporation Figure 1 (a) (b)

Claims (1)

[Claims] 1. It is characterized by having a spiral glass layer made of a glass composition having a slightly different refractive index from the core glass or clad glass in the longitudinal direction within the core glass or within the Talarado glass near the core. Single mode optical fiber with circular polarization preserving property. 2. In the VAD method, when forming the porous base material for the core or the porous layer for the cladding, from a minute nozzle,
A raw material gas having a glass composition different from that of the glass composition constituting the porous base material for the core or the porous layer for the cladding is ejected into the porous base material for the core or the porous layer for the cladding. After forming a linear glass layer consisting of a glass composition with a slightly different refractive index from the glass materials constituting the porous base material for the core and the porous layer for the cladding, a transparent base material is produced by sintering. A method for manufacturing a single mode optical fiber having circular polarization preservation properties, which further comprises melting the same at high temperature and drawing it to make an optical fiber.