JPS62111481A - Light emitting diode - Google Patents

Abstract

PURPOSE:To obtain sufficiently large coupling efficiency even if a distance from the surface of the lens of a light emitting diode to the end surface of an optical fiber is made large, by adopting a composite lens system comprising two lenses, and optimizing the design. CONSTITUTION:A first lens 2 of a light emitting diode is a spherical glass lens made of Na2O-CaO-SiO2 which has a refractive index of 1.5 and a diameter of 200mum. A second lens 5 is a glass convex lens made of Na2O-CaO-SiO2 which has a radium of curvature of 0.8mm for both an incident surface and an output surface, a thickness of 1mm and a refractive index of 1.5. The lenses 2 and 5 are fixed with an interval of 0.8mm being provided. Light comes into a graded index type optical fiber, which has a core diameter of 50mum and an angular aperture of 0.2. A ratio between the power of the incident light and the power of total light emitted from the surface of an LED chip 1 is determined. The relation between said ratio and a distance between the output surface of the second lens and the end surface of the optical fiber is determined from an experiment and computer simulation. Then relative coupling efficiency of about 42%, which is equal to the conventional value, is determined at a position, which is separated from the surface of a cap by about 1.5mm.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (a) Field of Industrial Application The present invention relates to a light emitting diode used in optical fiber communications.

(b) Conventional Technology Conventionally, as a method for improving the coupling efficiency between a surface-emitting light emitting diode used as a light source for optical fiber communication and a multimode optical fiber, a semiconductor chip with a refractive index of 1.8 to 2.0 is coated on the surface of a semiconductor chip. A fixed ball lens with a diameter of about 100 to 300 μm (for example, S, Horiuchi
, K., Ikeda, T., Tanaka and~
V, 5usaki, “A New LED
5structure with a Self
-Aligned 5phere-Lens for
Efficient Coupling to 0pti
cal Fibers, “IEEE Trans, E
electron.

Devices ED-24, p986-990 (19
77)), a fixed lens with a part of a spherical surface cut out, or a semiconductor chip whose surface is carved into a spherical shape (e.g. O, Wada, S, Yamakos)
hi, FIIL Abe.

Y, N15hitani, and T, 5akura
i, ” High RadianceInGaAsP
/InP Lensed LED's for O
Physical Communication System
m at 1.2-1.3 μm ″ I EEEJ,
Quantum Electron, QE-17, p
174-178 (1981)) have been devised and used.

if, = refractive index 1.8 ~ as a system using multiple lenses
2.0, a ball lens with a diameter of 400-600 μm and a refractive index of 1
．． A lens using a left-handed lens with a radius of curvature of about 4 to 1.6 mm and a radius of curvature of about 0.7 to 0.8 mm has been reported. (For example, light emitting diode LN193 manufactured by Matsushita Electronics Co., Ltd.) (C) Problems to be solved by the invention In the conventional method of coupling a light emitting diode and an optical fiber, as shown in FIG.
Since the optimum distance from the surface of the lens 2 fixed to the lens 2 to the end face 4 of the optical fiber is as short as 50 to 500 μm, it has been difficult to align the optical fiber. If the optical fibers were moved away to facilitate alignment, sufficient coupling efficiency could not be obtained.

Furthermore, even when attaching a cap 6 as shown in FIG. 4 in order to improve the reliability of the light emitting diode and make it easier to handle, the distance from the lens 2 to the end face 4 of the optical fiber is long, so that sufficient coupling is required. It is difficult to obtain efficiency, and for example, as shown in FIG. It had to have a good structure.

When combining multiple lenses, the number of design parameters increases, making it extremely difficult to optimally design the entire lens system. Even in the conventional technology mentioned above, the coupling efficiency is 2-3% because the lens system is not optimized.
The optimum distance between the lens surface and one end of the optical fiber is 300 to 500.
There were many problems such as the short length of μm.

(d) Purpose of the Invention In order to eliminate these drawbacks, the present invention employs a compound lens system consisting of two lenses, and by optimizing its design, the distance from the lens surface to one end face of the optical fiber can be reduced. Even if the coupling efficiency is increased, a sufficiently large coupling efficiency can be obtained.

Structure of the invention (e) Means for solving the problems FIG. 1 shows one embodiment of the invention,
■ is a semiconductor chip, 2 is a first lens, 3 is a header for fixing the semiconductor chip, t is one end surface of an optical fiber, 5 is a second lens, 6 is a metal for fixing the second lens It's a cap.

FIG. 2 is an enlarged view of the lens part, and the light generated in the light emitting region 9 is changed in direction by the first lens 2 as shown in 10, and is further focused on the end face 4 of the optical fiber by the second lens 5. Ru.

In this system, by changing the parameters of each component,
As a result of repeated computer simulations and prototype experiments using the ray tracing method, it was found that light emitted from a semiconductor chip with a refractive index of 32, a thickness of 50 μm from the active layer to the surface, and a diameter of the light emitting region of 25 μm was converted into a gray light with a core diameter of 50 μm and a numerical aperture of 0.2. When coupled to a Did-index optical fiber, the diameter of the first lens 2 is 150 to 250 μm1, the refractive index is 1.45 to 1.55, and the distance between the first lens 2 and the second lens 5 is 0.6 ~0.9mm, second lens 5
The radius of curvature 13°14 of the entrance surface 11 and exit surface 12 is both 0.7 to 0.9 mm, and the thickness 15 of the lens is 0.8 mm.
~1 mm, and it was found that the optimum oil contact ratio was selected in the range of 1.45 to 1.55.

(f) Function The diameter of the light emitting region of a surface emitting type light emitting diode used for multimode optical fiber communication is usually about 10 to 30 μm. Most of the light emitted from this region is totally reflected at the interface between the semiconductor and the atmosphere, and does not contribute to coupling with the optical fiber. When a semiconductor chip and a multimode optical fiber are directly coupled, the core diameter of the multimode optical fiber is as small as 50 to 1OOμm, and the numerical aperture is 0.2 to 0.
．． 3, so 99% of the light emitted from the chip surface
This cannot be input into the optical fiber.

When using the structure shown in the present invention, the light emitted from the surface of the semiconductor chip is focused by the first lens, which is a ball lens, and at the position of the incident surface of the second lens fixed at the center of the cap, the light emitted from the surface of the semiconductor chip is It becomes a spot of about 0.5 to 1, O1]Im. At this time, if a lens with the above-mentioned curvature is used as the second lens, the influence of spherical aberration can be reduced, and the core diameter is 50 μm.
m, 4-5% of the light emitted from the chip surface for a graded index optical fiber with a numerical aperture of 0.2.
can be made incident. Also, at this time, a spot is formed at a position 1 to 2 marks away from the exit surface of the second lens.

(g) Embodiment In FIG. 1, the active layer material of the semiconductor chip 1 is I
nGaAsP, 50 μm thick (i'
) InP is used, the first lens is a Na 20-CaO-Si02 glass ball lens with a refractive index of 1.5 and a spherical diameter of 200 am, and the second lens is a spherical lens made of Na 20-CaO-Si02 glass with a radius of curvature of 0 for both the entrance and exit surfaces. .8 mm, thickness 1 [n111
1 refractive index 1.5 Na 2 () CaO-S io2
LE of the optical power incident on a graded index type with a core diameter of 50 μm and an aperture angle of 0.2 when lenses made of glass are fixed with an interval of 0.8 marks.
FIG. 6 shows the relationship between the ratio to the total optical power emitted from the D-chip surface and the distance between the second lens exit surface and one end surface of the optical fiber, obtained through experiments and Hikkonbuek simulations.

Curve 16 in FIG. 6 is a value obtained by computer simulation using the ray tracing method, and black circle 17 is a value measured for an actually prototype LED. Curve 18 is a simulation result of a conventional method in which light is focused on one end face of an optical fiber using a ball lens with a diameter of 200 μm and a refractive index of 1.9 fixed on a semiconductor chip. This is the value obtained when an LED was prototyped and measured.

In the conventional method, the maximum relative coupling efficiency of about 4.3% was obtained when the distance between the ball lens and one end face of the optical fiber was about 400 μm, whereas in the embodiment according to the present invention, a cap covering the LED chip was used. A relative coupling efficiency of about 7.2%, which is equivalent to that of the conventional method, was obtained at a position about 1.5 mm away from the surface.

C1 Effects of the invention (l) As described in detail of the invention, by employing the structure shown in the invention, light generated in a semiconductor chip can be efficiently input into an optical fiber. Furthermore, a light emitting diode with a cap can be realized with a simple structure without reducing coupling efficiency, which is advantageous in terms of reliability and ease of handling. Furthermore, since the maximum coupling position is located further away from the surface of the stone lens fixed at the center of the cap than in conventional products, it is easier to align the optical fiber. As described above, the present invention provides a structure suitable as a light emitting diode for a light source in optical fiber communication.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of the device of the present invention, FIG. 2 is a schematic diagram showing how light is collected by the device of the present invention, and FIG. 3 is a schematic diagram of a conventional unit.
Fig. 11 is a cross-sectional view of a device with a conventional cap with a flat window, and Fig. 5 is a cross-sectional view of a device with a conventional cap with a sleeve for fixing optical fibers. The cross-sectional view, FIG. 6, is a diagram comparing the relationship between the distance between the lens surface and the optical fiber and the coupling efficiency between the conventional example and the example of the present invention. In the figure, l is the semiconductor chip part of the light emitting diode, 2 is the first lens, 3 is the chip fixing header, 4 is one end surface of the optical fiber, 5 is the second lens, 6 is the metal cap, 7
1 is a sleeve for fixing an optical fiber, 8 is a flat window, 9 is a light emitting region of a light emitting diode, 10 is one of the light rays emitted from the light emitting region, 11 is an entrance surface of the second lens, 12 is an exit surface, 13 is the radius of curvature of the entrance surface, 14 is the radius of curvature of the exit surface,
15 represents the thickness of the lens.

Claims (3)

[Claims] (1) A light emitting diode semiconductor chip made of a semiconductor material with a refractive index of 3.0 to 3.4 for a desired wavelength and a thickness of 50 to 70 μm from the light emitting region to the surface, and on the chip. Fixed refractive index 1.45~1
．． 55, a spherical first lens with a diameter of 150 to 250 μm, and a top and bottom surface fixed to the center of the metal cap with a space of 0.6 to 0.9 mm from the first lens surface, each with a radius of curvature of 0.7 A light emitting diode comprising a second lens having a convex surface of ~0.9 mm, a thickness of 0.8 to 1.0 mm, and a refractive index of 1.45 to 1.55. (2) The light emitting diode according to claim 1, wherein the light emitting diode semiconductor chip comprises an InGaAsP light emitting layer and an InP cladding layer. (3) The first lens and the second lens are Na_2O-C
The light emitting diode according to claim 1 or 2, characterized in that it is made of aO-SiO_2 glass.