JPS6350805A - Optical coupler - Google Patents

Abstract

PURPOSE:To couple light from a semiconductor laser with a single-mode optical fiber with high efficiency by making the NA of a 2nd single-mode optical fiber smaller than the NA of a 1st single-mode optical fiber. CONSTITUTION:The 1st single-mode optical fiber 6 which couples with the semiconductor laser 1 is constituted by increasing the specific refractive index difference DELTA and further forming the tip part of the optical fiber 6 as a convex light convergence part 2 so that the numerical aperture (NA) is made large. Consequently, almost 100% coupling efficiency is obtained. The coupling part between the 1st single-mode optical fiber 6 and the 2nd single-mode optical fiber 7 with low DELTA which is normally used is constituted by a directional coupler 8 formed by fusing and drawing the both, and almost 100% coupling efficiency is obtained at the coupling part as well. Consequently, the light from the semiconductor laser is coupled with the single-mode optical fiber with low DELTA efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical coupler that couples light from a semiconductor laser to a single mode optical fiber with high efficiency.

(Prior Art and Problems) FIG. 2 shows an example of a conventional optical coupler. In FIG. 1, l is a semiconductor laser, 2 is a convex condensing part,
3 is a core, 4 is a cladding, and 5 is a single mode optical fiber. Conventionally, the optical fiber 5 has a relative refractive index difference Δ of about 0.3%, and the spread angle of light from the semiconductor laser I is usually about 2θL=30°. On the other hand, since the optical fiber 5 cannot collect all the diffused light from the semiconductor laser 1, the coupling efficiency is at most 50.
%, and there was a drawback that the light of the semiconductor laser could not be used effectively.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical coupler that overcomes these conventional drawbacks and couples light from a semiconductor laser to a single mode optical fiber with high efficiency.

(Means for Solving the Problems) In the present invention, the first single mode optical fiber coupled to the semiconductor laser has a NA (Numerical Ap
In order to increase the relative refractive index difference Δ, the tip of the optical fiber is formed as a convex condensing portion. This results in a coupling efficiency of nearly 100%. Further, the coupling portion between the first single mode optical fiber and the normally used low Δ second single mode optical fiber is configured by a directional coupler in which both are fused and stretched,
This coupling portion also achieves a coupling efficiency of approximately 100%.

With the above configuration, the light from the semiconductor laser can be efficiently coupled to the low Δ single mode optical fiber.

(Function) Generally, the refractive index distribution n (r) of an optical fiber is expressed by the formula (1)
.

It is expressed by equation (2).

n (r) = n + (1-2Δ(r/a)')
"" (1) Δ= (nI"-n,")/2n,
” (2) Here, 1. and mouth are the refractive indices of the core and cladding, a is the core radius, r is the radial coordinate of the optical fiber, and α is the refractive index distribution index. Here, a single mode optical fiber is Of course, a and Δ satisfy the single mode condition.The NA of this optical fiber is expressed by the formula (3
), given by equation (4).

NA = q n lV'T'X (
3) α is the acceptance angle 2θ at which the optical fiber to the numerical aperture N can receive light.

is given by equation (5) (Okoshi, ed., "Optical Fiber", Ohmsha, 1983. p. 37).

NA=sin θL (5) In order for this optical fiber to sufficiently couple with a semiconductor laser whose emitted laser light has a divergence angle of 2θL, the condition of equation (6) is required.

θL×θF (6) Therefore, from equations (3), (5), and (6), the optical fiber must satisfy the conditions of equation (7) or equation (8).

sin θL≦sin θF = qn r v'TX
(7) Δ ≧ (sin θL / q nI)
”/2 (8) (Example) FIG. 1 is a diagram showing an example of the present invention, and the details of the coupling portion between the semiconductor laser 1 and the first single mode optical fiber 6 are the same as in FIG. 2. Here, the first single mode optical fiber 6 is a square distribution type (α=2) optical fiber with Δ=2.9% and core diameter 2a=2.3 μl, and the second single mode optical fiber Fiber 7 has Δ'=0.3%, core diameter 2a'=10μ
m step type (α=oo) optical fiber. Second
Since the first single mode optical fiber 6 has a high Δ compared to the single mode optical fiber 7, the first single mode optical fiber 6 has a small core diameter and satisfies the single mode condition. The directional coupler 8 is the first
．． It is constructed by fusion-splicing and drawing a second single mode optical fiber 6.7.

In this example, the acceptance angle 2θL of the first single-mode optical fiber 6 is 37.0@ as nI = 1.445 from equation (7), and the emitted light divergence angle 2θL of the semiconductor laser I is about 30”. It can be seen that it is fully applicable in the case of .

The outer diameter of the narrow diameter portion of the directional coupler 8 shown in FIG.
0 μm, and the core diameter of the first and second single mode optical fibers 6.7 is about 1710 μm of the original diameter. Therefore, the propagation constant of the first and second single mode optical fibers is is approximately 100 between both optical fibers to be the same.
% optical coupling occurs. Therefore, the light from the semiconductor laser is coupled to the port on the 7-2 side of the second single mode optical fiber 7 with high efficiency.

In this example, α of the first single mode optical fiber is 2.
, but α may be any value between 1 and ooO.

(Effects of the Invention) As explained above, according to the present invention, it is possible to make the light of a semiconductor laser enter a single mode optical fiber with an efficiency of nearly 100%. It has very great advantages in terms of effect generation, etc.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional optical coupler. 1... Semiconductor laser 2... Convex condensing section 3.
... Core 4 ... Clad 5 ... Single mode optical fiber 6 ... First single mode optical fiber 7 ... Second single mode optical fiber 8 ... Directional coupler patent Applicant Nippon Telegraph and Telephone Corporation Representative Patent Attorney Hidetoshi Sugimura Patent Attorney Oki Sugimura Figure 1

Claims (1)

[Claims] 1. One side of the first single mode optical fiber of a directional coupler having a coupling efficiency of approximately 100%, which is constructed by fusion-drawing the first and second single mode optical fibers. an optical coupler in which a convex condensing part is formed at the tip of the fiber, and the condensing part and a semiconductor laser are coupled, wherein the relative refractive index difference Δ of the first single mode optical fiber is Δ≧ The following condition is satisfied: (sinθ_L/qn_1)^2/2, where 2θ_L is the laser beam spread angle of the semiconductor laser, n_1 is the refractive index of the core, and q=1-0.1
78/α, α is a refractive index distribution index, and an optical coupler characterized in that the NA of the second single mode optical fiber is smaller than the NA of the first single mode optical fiber.