JPH04291213A - Stray light removing device - Google Patents

Abstract

PURPOSE:To obtain the stray light removing device which can remove light propagated through the clad or covered part of an optical fiber from the optical fiber. CONSTITUTION:A polarization holding optical fiber 1 is composed of a core, clad and covered part, and the refraction factor of the clad is set lower in comparison with that of the core and the covered part. A stray light removing part 2 composed of resin having the refraction factor equal or higher than that of the above-mentioned covered part is arranged around this polarization holding optical fiber 1. The light propagated through the clad or covered part of the optical fiber 1 enters the stray light removing part 2 through the covered part and is removed from the optical fiber 1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is useful for improving the extinction ratio of the output light of a fixed polarization laser diode module, etc., which uses an optical fiber to transmit the light output from a laser diode while preserving its polarization plane. The present invention relates to a suitable stray light removing device.

0002

[Prior art] A constant polarization laser diode module is
It is used in LN (LiNbO3) optical switches, coherent optical communications, optical fiber sensors such as optical fiber gyros, and magnetic sensors.

FIG. 6 is a schematic cross-sectional view showing a constant polarization laser diode module.

A laser diode 11 is mounted on the support member 13.
A predetermined voltage is applied to the laser diode 11 via an electrode 14. A lens system consisting of a ball lens 12 and lenses 15 and 16 is arranged above the laser diode 11. In addition, a polarizer (polarizer) is placed between the lenses 15 and 16.
zer) 17 are arranged. A ferrule 18 and a polarization-maintaining optical fiber 19 fixed to the ferrule 18 are arranged on the lens 16.

The laser diode 11, lens system, etc. are provided in cases 21, 22, and 23, and the optical fiber 19 is led out from the case 21.

FIG. 7 is a schematic cross-sectional view showing the optical fiber 19. The optical fiber 19 includes a core 19a, a cladding 19b disposed around the core 19a, and a covering portion (not shown) disposed around the cladding 19b. Note that the cladding 19b is
The refractive index is set to be lower than that of a. In addition, if the optical fiber 19 is single mode, the core 1
The diameter of 9a is approximately 10 μm.

[0007]

However, devices that transmit linearly polarized light using polarization-maintaining optical fibers, such as the above-mentioned polarization constant laser diode module, have the following problems. That is, the light output from the laser diode 11 and passed through the polarizer 17 (
Alternatively, the output light of a constant polarization laser diode light source) has linear polarization and has a high extinction ratio. When the light output from the laser diode 11 is focused on the end of the polarization-maintaining optical fiber 19 by lenses 12, 15, 16, etc., in a single mode optical fiber, the core 19
Since the diameter of a is small, the laser beam 2
4 becomes larger than the diameter of the core 19a. Therefore, a portion of the laser beam 24 is exposed to the cladding 19b.
incident on .

When the refractive index of the cladding 19b is higher than that of the covering portion, as shown in FIG.
The light incident on b is totally reflected at the interface between the cladding 19b and the covering portion 19c and the interface between the cladding 19b and the core 19a, and propagates through the cladding 19b. On the other hand, the covering portion 19c
If the refractive index of the fiber is higher than that of the cladding 19b and higher than that of the substance surrounding the fiber (for example, the atmosphere), as shown in FIG. 19c. In any case, since the polarization plane of the light is not maintained in the cladding 19b and the covering portion 19c, the extinction ratio of the light propagating through the optical fiber is reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a stray light removing device that can improve the extinction ratio of light propagating through a polarization-maintaining optical fiber.

0010

[Means for Solving the Problems] A stray light removing device according to the present invention includes a core, a cladding arranged around the core and having a lower refractive index than the core, and a cladding arranged around the cladding and having a lower refractive index than the cladding. a polarization-maintaining optical fiber constituted by a coating portion having a high refractive index; and a stray light removing portion disposed around the optical fiber in a part of the optical fiber and having a refractive index equal to or higher than that of the coating portion. It is characterized by having the following.

[0011]

[Operation] In the present invention, a stray light removing section is arranged around a part of the polarization-maintaining optical fiber. The polarization-maintaining optical fiber includes a core, a cladding, and a coating, and the cladding has a refractive index lower than that of the core and the coating. Further, the refractive index of the stray light removing section is the same as or higher than the refractive index of the covering section. As a result, the light that has propagated through the cladding or coating of the polarization-maintaining optical fiber enters the stray light removal section via the coating and is removed from the optical fiber.

0012

Embodiments Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a plan view showing a stray light removing device according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along line A--A in FIG.

The stray light removing device according to this embodiment is composed of a polarization maintaining optical fiber 1 and a stray light removing section 2 made of resin and disposed surrounding a part of this optical fiber 1. The polarization-maintaining optical fiber 1 is composed of a core, a cladding placed around the core, and a covering portion covering the periphery of the cladding. The refractive index of the cladding is set lower than that of the core and the covering portion. Further, the refractive index of the stray light removing section 2 is set to be equal to or higher than the refractive index of the covering section. In addition,
An absorbing material may be used in the stray light removing section 2 in order to absorb the light removed from the optical fiber.

FIG. 3 is a schematic diagram showing the propagation state of light propagating through the stray light removing device of this embodiment.

The light propagating within the core 3 is also totally reflected at the interface between the core 3 and the cladding 4 in the stray light remover, and is output from the core 3 of the stray light remover. On the other hand, the light that has propagated through the cladding 4 or the coating section 5 enters the stray light removal section via the coating section 5 and is removed from the polarization-maintaining optical fiber. The light removed from the optical fiber is, for example, emitted to the outside from the stray light removing section or absorbed by an absorbing material of the stray light removing section.

As described above, in this embodiment, the light propagating through the cladding 4 or the covering part 5 is removed using the difference in refractive index between the cladding 4, the covering part 5, and the stray light removing part 2. This improves the extinction ratio of light propagating through the core 3.

FIG. 4 is a plan view showing a second embodiment of the present invention, and FIG. 5 is a sectional view taken along line BB in FIG.

In this embodiment, the stray light removing section 8 is formed in an annular shape, and the polarization maintaining optical fiber 7 is embedded in this stray light removing section 8 in a loop shape. The optical fiber 7 is composed of a core, a cladding, and a covering section, as in the first embodiment, and the refractive index of the cladding is set lower than that of the core and covering section. Further, the stray light removing section is made of resin, and its refractive index is set to be equal to or higher than the refractive index of the covering section.

[0020] In this embodiment as well, the same effects as in the first embodiment can be obtained. Further, in this embodiment, since the polarization-maintaining optical fiber 7 is embedded in the stray light removing section 8 in a loop shape, there is an effect that the size can be reduced compared to the first embodiment.

[0021]

As explained above, according to the present invention, the stray light removing section having a refractive index equal to or higher than that of the coating section of the polarization-maintaining optical fiber is disposed surrounding a part of the optical fiber. Light propagating through the cladding or coating can be removed from the optical fiber. This has the effect that, for example, the extinction ratio of output light from a constant polarization laser diode module or the like can be improved.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a stray light removing device according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG. 1;

FIG. 3 is a schematic diagram showing the propagation state of light in the first embodiment of the present invention.

FIG. 4 is a plan view showing a second embodiment of the invention.

FIG. 5 is a sectional view taken along line BB in FIG. 4;

FIG. 6 is a schematic cross-sectional view showing a constant polarization laser diode module.

FIG. 7 is a schematic cross-sectional view showing an optical fiber.

FIG. 8 is a schematic diagram showing an example of the propagation state of light incident on the cladding.

FIG. 9 is a schematic diagram showing another example of the propagation state of light incident on the cladding.

[Explanation of symbols]

1,7,19; optical fiber 2, 8; Stray light removal section 3,19a; core 4,19b; cladding 5; Covering part

Claims (1)

[Claims] 1. A polarizer comprising a core, a cladding arranged around the core and having a lower refractive index than the core, and a covering part arranged around the cladding and having a higher refractive index than the cladding. A stray light removing device comprising: a wave-maintaining optical fiber; and a stray light removing section that is arranged around the optical fiber in a part of the optical fiber and has a refractive index equal to or higher than that of the coating section.