JPS61107206A - Optical coupler - Google Patents

Abstract

PURPOSE:To very efficiently make light of a light source incident on an optical fiber and to ease parts assembling works, by constituting an optical coupler with a lens which is composed of a transparent cylindrical body having a specific refractive index n(r) at a distance (r) from its optical axis and satisfies special conditions. CONSTITUTION:Rays diffusedly coming out from a light source 1 of light emission diode semiconductor laser, etc., are made incident on a self-focusing type lens 2 and, after they are condensed, further made incident on an optical transmission fiber 3. The lens 2 is composed of a transparent cylinder having the maximum refractive index n0 at its center axis and a refractive index n(r) with the refractive index distribution expressed by formula (1) at a distance (r) from the center axis in the radial direction, and has parallel planes at both end faces which are normal to the optical axis. Special conditions required by the lens 2 are as follows: (1) C1=0, (2) C2=0, (3) 2.69l1Sf-4.0<m<0.5l1Sf-1.7 within a range of 0<=l1Sf<=0.4, (4) 2.69l1SF-4.0<=m<=1.67l1Sf-2.168 within a range of 0.4<=l1Sf<=0.65, (5) 1.15l1 Sf-2.9975<=m<=1.67l1Sf-2.168 within a range of 0.65<=l1Sf, and (6) -4<=m<=-1. However, the C1 and C2 respectively represent the curvatures of the incident end face and outgoing end face and the lambda1 is the back focus on the light source side. The Sf is equal to g/0.3 (Sf=g/0.3) and the (m) is the paraxial lateral magnification. Moreover, the n0 is the refractive index at the center axis and the (g), h4, and h6 are distribution constants.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical coupler for efficiently inputting light from a light emitting element such as a light emitting diode or a semiconductor laser to an optical transmission 7-aiper.

[Explanation of Kairai technology]

The diffused light flux from the light source as described above is efficiently transmitted into the core of the optical transmission fiber via the optical coupler.

In order to achieve this, it is necessary to sufficiently reduce the axial aberrations and off-axis aberrations of the lenses that make up the coupler so that not only axial incident light but also off-axis incident light due to assembly errors etc. enters the fiber core without leaking. It is necessary to correct it.

Further, the coupler is required to be small, lightweight, and inexpensive. Conventionally, as this type of optical coupler, one using a self-focusing lens whose end surfaces are parallel planes and whose lens length is //II with the meandering period of the light ray is known.

However, in the case of a self-focusing lens with parallel planes on both end surfaces as described above, although axial aberrations can generally be corrected, off-axis aberrations, especially comatic aberrations, are large, so for example, if the light source is away from the lens optical axis. When the shift occurs, the light rays emitted from the light source are 1
The light will no longer be focused on a point. It is also known that one end surface or both end surfaces of a self-focusing lens are polished into a spherical surface, but in this case, the drawback is that polishing requires many man-hours and is expensive.

[Means for solving interlayer points]

The coupler of the present invention solves the problems of the prior art described above.
The refractive index n(r) at a distance r from the optical axis is n2(r)-no" (/-(gr)2+h4(gr)
'+h6(gr)6+---), (2) C2=0 (2.69 l in the range of 310<11・Sf<0.4)
I 5f-LO<m<, 0. ! ; 11sf-/, 7(
4) 2 in the range of 0.11<l l Sf<0.65
, ≦91ISf-LO<m<8471.15f-2,/
4za (5) In the range of 0.63 x 11sf /, /
! ; 11sf-2,9wa 76km/, 6711Sf
-2, /61+6) -4'<m<-/ It is constituted by a lens that satisfies the condition.

However, C1+02 is the curvature of the entrance end face and exit end face, JL is the back 7 orcus on the light source side, Sf-glo, 3, m is the paraxial lateral magnification, no is the refractive index on the central axis, grh4+h6 is the distribution constant, and (1) to Among the conditions in (6), the condition (xJ
(2) indicates that both end surfaces of the lens are flat, and since both ends of the coupler lens of the present invention are flat, polishing is extremely easy. Conditions (3) to (5) indicate the range in which the absolute value of the amount of unsatisfactory sine condition is 1% or less.When 0m is larger than the range of conditions (3) to (5), the amount of unsatisfied sine condition is 1% or more. shows that when it is small, the amount of dissatisfaction of the sine condition is −1% or less −
There is. The lower limit of condition (6) is determined by conditions (3) to (5), and the upper limit is determined by the normal magnification of the lens used for coupling with the optical fiber.

〔Effect of the invention〕

As is clear from the examples, the light source and optical fiber coupler according to the present invention have very small spherical aberration and comatic aberration, and can make the light source light enter the 7-eyeper very efficiently. In addition, because aberrations, especially co and ma aberrations, are small, even if the light source is slightly deviated from the lens optical axis due to assembly errors, the wave light loss is small, and the tolerance range for alignment is relatively expanded. The work of assembling parts becomes easier.

Furthermore, since both end surfaces of the lens according to the present invention are flat, a large number of lenses can be flat-polished at once, and the polishing process is easy and can be mass-produced at low cost.

In FIG. 1, a light beam having a diffusion ratio q·1 from a light source 1 such as a light emitting diode or a semiconductor laser enters a self-focusing lens 2, is condensed, and enters an optical transmission fiber 3. Here, lens 2 has the maximum refractive index n□ on the central axis, and the refractive index n(r) at a distance r in the radial direction from the central axis is n2(r), n02(/=(gr)2+b4(gr)'
It consists of a transparent cylindrical body with a refractive index distribution expressed as +h6(gr)60ha(gr)8), and both end surfaces of the lens are parallel planes perpendicular to the optical axis.

In the above light source and optical fiber coupler, 11 is the light source side pack 7 orcus, Sf-glo, 3, m is the paraxial lateral magnification, and Jl, Sf and m are selected from within the shaded range in Fig. 2. As a result, the absolute value of the amount of dissatisfaction of the sine condition is set to 1
% or less.

Next, specific numerical examples of the present invention will be shown.

Example 1 11, -0.3'If, n□-Muro! ; , g-0,3
rh4-c+, gg.

h6-0. /3. hB--/,! ;77 fiber side back 7 Orcus 12-3J61. Lens length Z-A, 3g! ;
, m −2 is shown in FIG. 3.

Example 2 11- to 201. n□-Yaoto j 1g-(7-2r h
4-0.720+h6--0.29. hB--803 12-3. I'l/, Z-9,299,m--/J
The aberration diagram of the lens is shown in Fig.

[Brief explanation of drawings]

Figure 1 is a side view showing an example of the coupler of the present invention. Figure 2 is a graph showing the range of 11.Sf and m in the coupler of the present invention. However, 11 is the focus on the light source side, and distribution of g. When 1ffl&, Sf=g/(7,J, mG is paraxial magnification, Fig. 3 and Fig. 1C are examples of the present invention/, and spherical aberration (solid line) and sinusoidal aberrations for example λ. Dissatisfaction amount (
7, which represents the broken line). /, Light source 2 Self-focusing lens 3 Fiber Figure 1 Figure 2 Figure 2 11 Sf Figure 3 Figure 4

Claims (1)

[Claims] The refractive index n(r) at a distance r from the optical axis is n^2(r
)=n_0^2[1-(gr)^2+h_4(gr)^
4+h_6(gr)^6+...] A light source, light, fiber coupler (1) C_1=0 (2 ) C_2=0 (3) 2.69l_1Sf-4.0≦m≦0.5l_1Sf- in the range of 0≦l_1Sf≦0.4
1.7(4) 2 in the range of 0.4≦l_1Sf≦0.65
．． 69l_1Sf-4.0≦m≦1.67l_1Sf-
2.168(5) 1.15l_1Sf in the range of 0.65≦l_1Sf-2.9975≦m≦1.67l_
1Sf-2.168(6)-4≦m≦-1 where C_1 and C_2 are the curvatures of the entrance end face and the output end face, respectively, l_1 is the back focus on the light source side, and Sf=g
/0.3, m is paraxial lateral magnification, n_0 is central axial refractive index,
g, h_4, h_6 are distribution constants.