JPS58220103A - Single polarization fiber for ultralong wavelength - Google Patents

Abstract

PURPOSE:To decrease the loss of light in the ultralong wavelength range of a single polarization fiber and to improve the characteristic for maintaining polarization by providing stress applying parts on both sides of a core of a chalcogen compd. CONSTITUTION:The compsns. of glass for a core 1 and a clad 2 of a chalcogen compd. which has a low loss at 2-10mum wavelength range are made respectively AsxS1-y, AsyS1-y, and the relation of the equation I is satisfied, whereby the formation of a fiber is made possible. If the equation II is satsified, the refractive index of the core can be made larger than the refractive index of the clad, and a waveguide construction can be formed. If As-Ge-S-Ge is used as the glass material in stress applying parts 3 to be provided on both sides of the core, the difference DELTAbeta in the constant of propagation between an HE<x>11 mode and HE<y>11 mode is larger as the double refractive index B of the mode in the core is larger as shown by the equation III. The loss of light is thus decreased at the large DELTAbeta without receiving the influence of disturbance such as bending and the characteristic for maintaining polarization is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single polarization fiber that maintains the polarization state of incident light and has low loss in the wavelength range of 2 to IO μm.

The mode degeneracy in the optical fiber is defined as MtkHE, -Fl-
- By increasing the difference in propagation constant between mode, HE□, and y mode, H
Conventionally, G60. Or a core with P2O5 added to SiO□, a cladding of Sin, and B
A quartz-based single-polarization fiber consisting of a stress-applying portion in which O is added to Sin is known. However, in silica-based optical fibers, the loss for light with a wavelength of 2 μm or more is extremely large, so it has been difficult to propagate light with a wavelength of 2 μm or more. On the other hand, a calfgenated Th,4 optical fiber composed of AE and S has low loss in the wavelength range of 2 to 10 μm, and is therefore useful as an optical fiber for light in this wavelength range.

However, in conventional chalcogenide fibers, H
The propagation constants for the E mode and the HE mode and the y mode are either the same or very small, so if a disturbance such as bending or pressure is applied to the fiber, mode coupling will easily occur, and the HE mode or It was difficult to propagate only the HE□, y mode.

The purpose of the present invention is to solve these drawbacks by providing four stress-applying parts on both sides of the core of the fluoride yarn fiber.
The object of the present invention is to provide a single-polarization fiber for ultra-long wavelengths that has low loss and good polarization bz retention characteristics in the 2 to 10 μm band. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a diagram showing one embodiment of the present invention, in which 1 is a core, 2 is a cladding, and 8 is a stressed portion. Chalcogenization'I!
The range in which the 7I fiber can be made into a fiber is as follows: The composition of the chalcogenide glass is A3X50-8 or AsyS,
, is expressed as p, 8＠ M kick x Mata Tri y
No 11! We know that i must satisfy the relation. When X and y are 42 or more, crystallization occurs, and when x and y are zO or less, drawing is difficult. (References: Hyperactivity, rA, -8
“Preparation of system optical fiber” 29th Society of Applied Physics Society T-Makishu 2p-
W-I P 102,] 982) Figure 2 is A
FIG. 3 is a diagram showing the relationship between the content Mx of A8 in sx5□-8 glass and the refractive index (provided that the wavelength λ is 1.15 μm). As shown in Figure 2, the larger X is, the more ASX" 1
-X The refractive index of the glass increases.

However, the composition of the core glass is ASX$1-8, and the composition of the cladding glass is AS'! /51-y, then
If the relationship X>y (2) is satisfied, the refractive index of the core can be made larger than the refractive index of the cladding, and a waveguide structure can be formed.

In the embodiment of the present invention, A84 is used as the core glass.
The glass used for the cladding was A388S62. At this time, the 111 rating, photoelastic constant, thermal expansion coefficient, and glass transition temperature of the core and cladding are as shown in Table 4.

Next, the material composition of the stress applying portion will be described. .

The four stressed parts are required to have (1) a coefficient of thermal expansion different from that of the cladding, and (11) a refractive index that is the same as or smaller than that of the cladding. Condition (1) is a condition for producing thermal stress in the core, and condition (11) is for preventing light from being guided to the four stressed parts. As a material that satisfies the above two conditions, As
-Go-S -86 was found to be suitable. In the embodiment of the present invention, the material of the stressed 4 part was A8□7Ge16''48''e19 as a composition satisfying the fiberization iJ ability condition of this material and the above two conditions. At this time, the refractive index of the 4 stressed parts is η-2,40, and the thermal expansion coefficient is α-
It was 21×10 (/'.).

Moreover, the glass transition temperature is 260°C. the said core;
In a single polarization fiber consisting of a cladding and a stress applying part, the core radius a -2,2μm N Ilb force 4
The inner and outer radius of the part are r, -5a, r, -10a, respectively.
Then, analysis using the finite element method shows that the stress difference in the X and y directions generated in the core GM (Jy is σ - σ
−−1,29(groan/fight”) (+])y It was found that the difference in the photoelastic constant of the core is 0□−
0,--5,328X 10-' (tm”/9)
r, so B+ηX−ηy−((El−0,)・(
σX−σy)−7X10″″B (4). where, η, η9 are the propagation constants β8. for light polarized in the X and y directions, respectively. β, divided by the light wave 111, is expressed as (k-2π/λ, where λ is the wavelength of the light). From equation (4) * f5), the propagation constant difference Δβ between the HE,,” mode and the HE,,y mode is Δβ
-mu βy -kB (61) It can be seen that the larger B is, the better.For example, when an optical fiber is bent to a bending radius of about 1 cm, the mode birefringence that occurs in the core due to bending stress is B -IX
It is about IO. Therefore, the propagation constant difference of the single polarization fiber of the embodiment of the present invention is sufficiently large and hardly affected by disturbances such as bending, so that HE, or HEo, y
Only the mode can be stably propagated.

As is clear from the above explanation, the ultra-long wavelength single-polarization fiber of the present invention has low loss in the wavelength range of 2 to 10 μm.
In addition, it can be used as a single-polarization fiber for ultra-long wavelengths with high polarization maintaining properties, so it has great advantages as a coherent optical polarization type optical fiber sensor in the 2 to 10 μm band.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the present invention, and FIG. 2 is a diagram showing the relationship between the content of A8 and the refractive index of A8xS1-x glass. 1... Core 2... Clad 3...
Stress applying part

Claims (1)

[Claims] 1., A3X5 i -x (x is 0<X<100
(7) real number) and A8yS1-y (y is O
A cladding having a refractive index smaller than the refractive index of the core, and stress applying parts having a different coefficient of thermal expansion from the cladding are arranged in parts of the cladding located at both ends of the core. A single-polarization fiber for ultra-long wavelengths. λSpecial Wl' In the ultra-long wavelength single-polarization fiber according to claim 1, one axis of A single-polarization fiber for ultra-long wavelengths, characterized in that one diagonal of -(74
In the wave fiber, the glass material forming the stress applying part is A
A single-polarization fiber for ultra-long wavelengths, characterized in that it is s-G, -S-Se.