JPH04371904A - Optical fiber - Google Patents

Abstract

PURPOSE:To propagate in the core even incident light whose optical axis is deviated from the center axis of a core. CONSTITUTION:The graded index type core 1 constitutes an incidence part which is provided on a constant section on the side of an incidence surface 4. The refractive index distribution of the graded index type core 1 is a nearly square distribution and its core diameter is larger than the core diameter of a single-mode part core 2. The signal-mode type core 2 constitutes an outgoing part provided on the section from an incoming part to an outgoing end surface 5.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to optical fibers, and more particularly to the structure of single mode optical fibers.

0002

2. Description of the Related Art Conventionally, a single mode optical fiber is composed of a single mode core 2 and a cladding 3, as shown in FIG.
The core diameter is the same in all parts.

In such a conventional single mode optical fiber, as shown in FIG. 4, since the core diameter of the single mode portion core 2 is small, the optical axis of the incident light a incident on the input end face 6 is aligned with the single mode portion core. There is a problem in that it is very difficult to align with the central axis of 2. That is, incident light a whose optical axis is aligned with the central axis of the single-mode core 2 propagates through the single-mode core 2, but incident light b whose optical axis is deviated from the central axis of the single-mode core 2 propagates through the cladding. 3, it cannot be propagated through the single mode portion core 2.

0004

OBJECTS OF THE INVENTION The present invention has been made to eliminate the problems of the conventional ones as described above, and is to provide an optical fiber that can propagate through the core even when incident light whose optical axis is deviated from the central axis of the core. For the purpose of providing.

[0005]

[Structure of the Invention] The optical fiber according to the present invention is an optical fiber consisting of a single mode core that propagates input light, has a core diameter larger than the core diameter of the single mode core, and is a graded index type optical fiber. A core member having a refractive index distribution is provided at the input end of the single mode core.

[0006]

[Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention. In the figure, an optical fiber according to an embodiment of the present invention has an input part consisting of a graded index core 1 and a cladding 3 provided in a certain section on the input end face 4 side, and a part from this input part to an output end face 5. It is composed of a transmission section consisting of a single mode section core 2 and a cladding 3 provided in the section. Here, the graded index type core 1 has a refractive index distribution approximately in the form of a square distribution, and its core diameter is larger than the core diameter of the single mode portion core 2.

That is, the input portion has a graded index fiber structure that facilitates alignment of the optical axis of the incident light, and the transmission portion has a single mode fiber structure with low transmission loss.

FIG. 2 is a diagram showing the state of incidence of incident light on the incident end face 4 of FIG. 1. In the figure, incident light a incident near the central axis of the optical fiber passes through the center of a graded index core 1, enters a single mode core 2, and is propagated by the single mode core 2 as it is.

On the other hand, the incident light b that is incident off the central axis of the optical fiber is refracted by the graded index type core 1 in the direction of the central axis of the optical fiber and enters the single mode portion core 2. Propagated by 2.

[0011] In this way, a certain section on the side of the entrance end face 4 is
By using the graded index type core 1 which has a core diameter larger than that of the single mode part core 2, the incident light beams a and b can be adjusted without loss with low precision optical axis alignment.
can be incident. Therefore, even if the incident light b whose optical axis is shifted from the central axis of the optical fiber, the single mode part core 2
It can be propagated inside.

0012

[Effects of the Invention] As explained above, according to the present invention, the core diameter is larger than that of the single mode core,
By providing a core member having a graded index type refractive index distribution at the input end of the single mode core, there is an effect that even incident light whose optical axis is deviated from the central axis of the core can be propagated through the core. .

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing the state of incidence of incident light on the incident end face of FIG. 1;

FIG. 3 is a longitudinal sectional view showing a conventional example.

FIG. 4 is a diagram showing the state of incidence of incident light on the incident end face of FIG. 3;

[Explanation of symbols]

1 Graded index type core 2 Single mode part core 3 Clad 4 Incident end surface

Claims (1)

[Claims] 1. An optical fiber comprising a single mode core that propagates input light, the core member having a core diameter larger than the core diameter of the single mode core and having a graded index type refractive index distribution. An optical fiber characterized in that an optical fiber is provided at the input end of the single mode core.