JPS5917518A - Optical coupling device - Google Patents

Abstract

PURPOSE:To couple light from an LED, incandescent lamp, discharge tube, etc., with a transmission line of optical fibers, etc., efficiently, by collimating light from a light source having a light emission part of finite size temporarily and then converging it again. CONSTITUTION:Light from a light emitting element 1 is made incident to the 1st photoconductor 4, which has a refractive index distribution n1(Z)=n0(1+BZ), so light incident to a plane of Z=0 even if slanting to an optical axis becomes parallel at a projection end where Z=l1 (Z; length along the optical axis from point 0 at the terminal of the photoconductor 4). When photoconductors 4a-4d have refractive indexes n1-n4 (n1<...<n4), a light beam P1 at a point S1 is refracted by surfaces I , II, and III to decrease the crossing angle, and a beam P2 is the same; and when Z is a monotonous increase function, nonparallel light is collimated. The parallel light incident to the 2nd photoconductor 5 is converged to one point by a rod lens 3. Light beams at points (a) and (b) of the element 1 travels as shown by a solid and a broken line and are converted to points a' and b' to enter an optical fiber 2.

Description

Detailed Description of the Invention The present invention provides an optical coupling device for efficiently coupling light from a diverging light source with a large light emitting area, such as an LED, an incandescent light bulb, or a discharge tube, to an optical transmission path such as an optical fiber or an optical waveguide. It is related to.

Conventionally, there has been a device shown in FIG. 1 as this type of optical coupling device. In this figure, 1 is a light emitting element such as an LED, 2 is an optical fiber, and 3 is a gradient index Rondo lens (hereinafter simply referred to as a p-Rado lens).

Next, the effect will be explained.

Light emitted from the light emitting element 1 enters the p-rad lens 3. The refractive index distribution within the rod lens 3 is expressed by the following cylinder equation (1).

Here, r is the radial distance from the optical axis, A is a positive constant, and no is the refractive index on the optical axis.

Because of the refractive index distribution, the light emitted from point a of the light emitting element 1 travels like the curve (solid line) in the figure and can be focused at point a' at the end of the optical fiber 2. However, since this optical coupling device focuses light from one point to a single point, it is difficult to focus light with light sources with large light emitting parts such as LEDs and incandescent bulbs.
A sufficient amount of light cannot be coupled into the optical fiber 2.

For example, light from point b in FIG. 1 is focused at point b', and this light does not enter the optical fiber 2.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by converting the light from a light source with a large light emitting area into parallel light and then concentrating it, it can be focused on a single minute point. The object is to provide an optical coupling device that can focus light. Hereinafter, this invention will be explained with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which 4 is a first light guide, 5 is a second light guide, and the same reference numerals as in FIG. 1 indicate the same components.

Next, the effect will be explained.

Light emitted from the light emitting element 1 enters the first light guide 4. The first light guide 4 has a refractive index distribution expressed as, for example, the following equation (2), n+ (Z)=no
(]+BZ)・・・・・・・・・・・・・・・・・・
...(2) Here, 2 is the length from the end 00 point of the first light guide 4 along the optical axis, B is a positive constant, and nQ is 0.
It is the refractive index at a point.

Due to such a refractive index distribution, light incident on the 2=0 plane of the first light guide 4 has a 2=1. At the output end, it is possible to output light as nearly parallel light.

This principle will be explained using FIG.

The first light guide 4 is divided into four parts, each of which is divided into 4a, 4a,
4b, 4c, and 4d, and their refractive indexes are uniform inside each, n, , n2°n3, respectively. n, (
For example, a ray P emitted from the 81st point enters the 1st surface perpendicularly and then enters the 1t, 1 . It passes through the IV plane and exits perpendicularly to the V plane. The ray P, is the 1st °u, i,
■It refracts at the surface, gradually changing the angle of intersection with the optical axis,
At the V-th surface, the light is emitted parallel to the optical axis or at a small angle. Ray p1. Similarly, even if P3 other than p and rays P4 to P6 emitted from 82 points have an angle with respect to the optical axis on the first surface, this angle will be OK on the V surface, or it will be very It becomes small and is emitted.

In this way, when the refractive index is a monotonically increasing function of 2, non-parallel light can be converted into parallel light. As the number of refractive surfaces increases, the refractive index distribution at the final point approaches the shape expressed by equation (2).

Now, in FIG. 2 again, the light emitted by the light emitting element 10 is 2
=l, becomes substantially parallel light at the output end, and enters the second light guide 5. The second light guide 5 only needs to condense the parallel light to one point, and this can be done by using a one-piece lens 3 having a refractive index distribution expressed by equation (11). The light at point a and point b of the light emitting element 1 is represented by a solid line and a solid line, respectively.
Follow the broken line and place points a' and b at the ends of optical fiber 2, respectively.
The light is focused as a point ' and enters the optical fiber 2.

In the above embodiment, the rod lens 3 is used as the second light guide 5, but a spherical lens, an aspherical lens, or the like may be used instead.

As described above, according to the present invention, the light emitted from the light source having a finite size light emitting portion is first converted into parallel light and then condensed again, so that the LED.

It has the advantage that light from incandescent bulbs, discharge tubes, etc. can be efficiently coupled to optical transmission paths such as optical fibers.

[Brief explanation of drawings]

FIG. 1 is a principle diagram of a conventional optical coupling device, FIG. 2 is a principle diagram showing an embodiment of the present invention, and FIG. 3 is a detailed explanatory diagram of the present invention. In the figure, 1 is a light emitting element, 2 is an optical fiber, 3 is a gradient index rod lens, 4 is a first light guide, and 5 is a second light guide. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Shin Kuzuno - (1 other person)

Claims (1)

[Claims] In an optical coupling device for inputting light from a light emitting element into an optical transmission path, the optical coupling device includes a first light guide and a second light guide, the first light guide having a refractive index of a light guide whose distribution is expressed as a monotonically increasing function with respect to its length along its optical axis, the second light guide consisting of a lens having the function of focusing light parallel to the optical axis to a point; Light emitted from a light emitting element made of a conductor and having a size is transmitted to the first. Optical coupling device 0 characterized by having a configuration in which the light enters the optical transmission line through a second light guide.