JPS60156023A - Optical coupling device between light emitting element and optical fiber - Google Patents

Abstract

PURPOSE:To eliminate preliminarily the light, which should be in the clad mode (CM), in an optical coupling part by coating completely an optical waveguide, which couples optically the front end part of an optical fiber and a light emitting, with a CM eliminating resin. CONSTITUTION:An optical fiber 8 to be connected to a light emitting element 6 has a primary coating layer 3 (refractive index n3) and a secondary coating layer 7 removed in the front end part and is coupled to the light emitting element 6 (n6) through an optical waveguide 4 (n4) for optical coupling. The optical waveguide 4 is formed to a sandglass shape, and the diameter is shortest in the center part. A CM eliminating resin 5 (n5) is packed in a frame 13. If relations between respective refractive indexes are selected to satisfy n3<=n5 and n4>=n5, the light, which has such radiation angle that it is propagated as CM, is leaked into the resin 5, and therefore, generation of CM in the optical fiber 8 is prevented. It is more desirable than n6>n4>n1 is satisfied.

Description

Detailed Description of the Invention Background of the Invention The present invention relates to an optical coupling device between a light emitting element and an optical fiber, and in particular, the present invention relates to an optical coupling device between a light emitting element and an optical fiber. Optical coupling device suitable for use of small optical fibers
Regarding this.

The biggest challenge in optical coupling devices that input light from a light emitting element to an optical fiber is how much light from the light emitting element can be input to the optical fiber, and various efforts have been made to date. One of the conventional optical coupling devices is
There are methods in which a light converging lens is provided between the light emitting element and the optical fiber to be optically coupled, or the light emitting element or the optical fiber is provided with a lens effect.

In all of these optical coupling devices, the light emitting element and the optical fiber are opposed to each other with a space between them, so air is present between them, increasing Fresnel loss and making it impossible to obtain sufficient coupling efficiency. When did you have a problem? Therefore, there has been an attempt to simultaneously achieve optical coupling and mechanical fixation by arranging a light emitting element and an optical fiber facing each other and filling the space between them with transparent resin. However, in this optical coupling device, the light emitted from the light emitting element is diffused, and a portion of the light is not guided to the optical fiber and is lost, so the coupling efficiency is still insufficient.

The conventional approach to optical coupling is to make as much light as possible enter the optical fiber as mentioned above, and the only problem is to determine in what mode the light that enters the optical fiber propagates. It was not considered at all. As is well known, the step green fiber type fiber is composed of a central core and a cladding layer surrounding it, and the periphery of the wire is covered with a primary coating layer, and A secondary coating layer is provided. The refractive index n1 of the core is naturally larger than the refractive index n2 of the cladding layer, and therefore, light is totally reflected at the interface between the core and the cladding layer and propagates within the core (usually per second). The refractive index n3 of the primary coating layer varies depending on the optical fiber, and some are larger than the refractive index n2 of the cladding layer, while others are smaller. In an optical fiber in which the refractive index n3 of the primary coating layer is smaller than the refractive index n2 of the cladding layer, the normal mode described above is totally reflected at the interface between the cladding layer and the primary coating layer. A so-called cladding mode is generated in which light propagates. The existence of this clad fist mode makes the apparent numerical aperture of the optical fiber abnormally large, and the apparent optical coupling efficiency increases abnormally. This is particularly noticeable in multi-component glass fibers.

For example, in an optical fiber in which the core refractive index nl is 1.614 and the cladding layer refractive index n2 is 1.518, the upper numerical aperture is as high as 0.69, and approximately 35% of the light propagates as the cladding working mode. It turns out. If the strands of the optical fiber are in contact with air at the optical coupling part, an even larger Rad mode is generated.

Light propagating in such a Tallarado mode causes a phenomenon in which connector coupling efficiency is significantly reduced when a connector is coupled in the middle of an optical fiber, which is a very serious problem in practice. For example, when the coating of the connecting portion of an optical fiber is removed and the strands to be connected are fixed to a ferrule with an adhesive in a state where they face each other, the adhesive is applied around the crack and rad layers. If the adhesive has a high refractive index, cladding mode light is no longer totally reflected, causing light leakage. This leakage amount is generally 1 (IB or more) for epoxy adhesives. Even if an apparent amount of light enters the optical fiber and propagates at the joint between the light emitting element and the optical fiber, If there is a large optical loss due to connector coupling, and the presence or absence of loss and the amount of loss differ depending on the optical fiber used, it is very difficult to actually design and implement it.This is due to the existence of cladding modes. This loss occurs when the optical fiber is cut and processed, so it may occur during unexpected cutting or processing, or if the fiber is placed at a distance of 100 m from the light emitting element for several months. 1, and it is difficult to deal with it.Furthermore, there is also the problem that cladding modes tend to include higher-order modes, which greatly affects practical performance.Therefore, it is also important to increase optical coupling efficiency. In practice, it is an extremely important issue to eliminate the occurrence of cladding modes in advance at the coupling position between the light emitting element and the optical fiber.This also applies to graded index optical fibers. Mr. □.

Summary of the Invention The present invention provides an optical coupling device between a light emitting element and an optical fiber, which enables stable optical coupling that does not generate cladding modes and can substantially increase coupling efficiency.◇ This invention An optical coupling device between a light emitting element and an optical fiber according to the present invention is an optical fiber consisting of a core at the center, a cladding layer covering the outer periphery of the core, and a primary coating layer covering the outer periphery of the cladding layer. The coating layer is removed, and the tip of the optical fiber and the light-emitting element are placed facing each other, and an optical waveguide for optical coupling is provided between them. The surrounding area is coated with a cladding mode eliminating resin, and the refractive index n3 of the primary coating layer of the optical fiber, the refractive index n4 of the optical coupling guide waveguide, and the refractive index n5 of the cladding mode eliminating resin coating is between. It is characterized in that the relationships n4)n5 and n3≦n5 hold true.

Due to the presence of the cladding mode removing resin coating, the light that should become the cladding mode is removed in advance at the optical coupling part, and the light that propagates within the optical fiber becomes only the above-mentioned normal mode. Therefore, even if the optical fiber is cut or processed in the middle, significant loss will not occur at that part as in the conventional case, and design and implementation become easier. Furthermore, since there is an optical waveguide for optical coupling, Fresnel loss and scattering loss, which are conventional, are reduced, and the light from the light emitting element is input into the optical fiber with high coupling efficiency.

This invention is effective for optical fibers in which the refractive index of the primary coating layer is smaller than the refractive index of the cladding layer.

The present invention is applicable not only to step-index optical fibers but also to graded-index optical fibers. In a grrated index type optical fiber, the peripheral portion of the strand of fiber having a small refractive index can be considered to be the cladding layer.

Description of Examples In FIG. 1, a light emitting element (chip) (6) has a stem (
10), and the central portion of the light emitting element (6) serves as a light emitting surface (6a). A terminal (11) is connected to the light emitting element (6) by wire bonding (12.Terminal 01) is connected to the stem Q via an insulator (151).
It is fixed at O). A frame body (case) (13) is placed over the stem a, and the upper end of this frame body αJ is open.

The optical fiber (8) to be connected to the light emitting element (6) is inserted into the frame Q3 from the upper end opening of the frame 03, and one optical fiber WIFM is inserted at the tip located inside the frame (131).
(3) and the secondary coating layer ((7)) are removed to expose the cladding layer (2). The tip end surface of the exposed wire consisting of the cladding layer (2) and the core (1) inside the cladding layer (2) is cut flat and faces the light emitting surface (6a) of the light emitting element (6) at an appropriate distance. It is arranged like this.

The optical coupling optical waveguide (4) is made of, for example, a transparent photocurable resin, and is formed between the tip surface of the strand of the optical fiber (8) and the surface including the light emitting surface (6a) of the light emitting element (6). It is set up to connect these. The optical waveguide (4) is shaped like a drum, and has the smallest diameter at its center. The transparent rad mode removal resin (5) is attached to the frame (
131, and part of the light emitting element (6), optical waveguide (4), and optical fiber (8) (exposed wires and M layer +31 +71 are embedded in this resin (5). It has a rounded shape.

The refractive indexes of the core (1), cladding layer (2), and one cladding ffi J'2F +31 of the optical fiber (8) are respectively nl, n2, and n3. The refractive index of the optical waveguide (4) is n4, the refractive index of the cladding mode removal resin (5) is n5, and the refractive index of the light emitting element (6) is n6. These refractive indices C′! , n, :3 (n5 and n4) n5. It is preferable that n5 has a value as close to n3 as possible. Also n 6) n 4) n 1
It is desirable that It is true that nl>n2.

According to the above configuration, the light emitted from the light emitting element (6) is transmitted through the optical waveguide (4) to the optical fiber (8) even if its radiation angle is slightly larger than the aperture angle of the optical core (8). The coupling efficiency increases because the propagation occurs within the aperture angle of the optical fiber (5).
When the light is incident on the optical waveguide (4) and the optical fiber (
Since it leaks into the resin (5) without propagating through the wire portion of 1), cladding mode is prevented from occurring within the optical fiber (8).

As shown in FIG. 2, the optical waveguide (4) may also be L-shaped so that the number of optical cores increases. The other configuration is the same as that shown in FIG. 1G.

An example of a method for forming an optical waveguide for optical coupling (4) G Tips (1)
This will be explained with reference to FIG.

First, the primary coating layer (3) and the secondary coating 111N (71) are removed from the tip of the optical fiber (8), and the strand is taken out.Then, the tip of the strand is polished using a polishing device or a diamond cutter. Cut the tip flat with ``!t!(
1311(”)#[3・Following this, this light core ino(
The tip of (8) is held in a jig that is movable in the tertiary direction so that the tip of the wire always remains horizontal, and the fluid resin (4) is adhered to the tip of the wire. Since the resin (4) is in a minute amount, it becomes hemispherical due to surface tension. This resin (
The amount of deposition in step 4) is preferably such that the radius of the hemisphere matches the radius of the cladding (2) of the optical fiber (8) (see FIG. 3(b)).

The distal end surface of the optical fiber (8) to which the resin (4) is attached faces the light emitting surface of the light emitting element (6), and the optical fiber (8) is moved close to the light emitting element (6) to remove the resin (4). is brought into contact with the light emitting element (6). The resin (4) is used as a light emitting element (6)
When the core (1) and the light emitting element (6) are brought into contact over almost the entire surface thereof and the distance between the core (1) and the light emitting element (6) is adjusted, the optical fiber (8)
A tapered leading waveguide (4) can be formed that expands for a while toward the light emitting element (6) (see FIG. 3(C)).

When the optical fiber (8) is pulled upward from this state, the central portion of the optical waveguide (4) becomes thinner (see FIG. 3(d)).

When the optical waveguide (4) has the desired shape, the resin (4)
) can be cured. It is convenient to use a photocurable resin as the resin (4) because it can be easily cured in a short time.

Note that if a transparent material is used as the frame αJ, the cladding and
A photocurable resin can also be used as the mode removal resin (5).

Examples of the light emitting element include a light emitting diode, a semiconductor laser, a light emitting/receiving element, and the like. It is also possible to simply bring the tip end of the optical fiber into contact with the light emitting element without using a special optical coupling guide waveguide as described above.

It will be used as an optical waveguide.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the invention, FIG. 2 is a sectional view showing a modified example, and FIG. 3 is a sectional view showing a process of forming an optical coupling optical waveguide. (1)... Core, (21-... Clad layer, (3)...
・Primary coating layer, (4)・e・Optical waveguide for optical coupling, (5
)...Clad fist mode removal resin, (6)...Light emitting element, (6a)...Light emitting surface, (8)...Optical fiber. 4 people other than the above 8r (d), r8 (C)

Claims (5)

[Claims] (1) A central core, a cladding layer covering the outer periphery of the core,
The optical fiber has a coating layer including a primary coating layer covering the outer periphery of the cladding layer, and the coating layer at the tip of the optical fiber is removed, and the tip of the optical fiber and a light emitting element are disposed facing each other and are disposed between them. An optical waveguide for optical coupling is provided in the optical fiber, and the tip of the optical fiber and the entire periphery of the leading waveguide for optical coupling are coated with a resin for removing cladding mode, and the refractive index of the primary coating layer of the optical fiber is n3. , between the refractive index n4 of the optical coupling guide waveguide and the refractive index n5 of the resin coating for removing Tallard Φ mode, n 4 > n 5 and n 3 ≦ n 5.
An optical coupling device between a light emitting element and an optical fiber in which the following relationship is established. (2) Between the refractive index nl of the core of the optical fiber, the refractive index n4 of the optical coupling optical waveguide, and the refractive index n6 of the light emitting element, n
An optical coupling device between a light emitting element and an optical fiber according to claim (1), wherein a relationship of 1<n 4 <n 6 holds true. (3) The optical coupling device between a light emitting element and an optical fiber according to claim (1), wherein the frame for fixing the optical fiber and the light emitting element is filled with resin for removing cladding mode. 2 (4) The light-emitting element and optical fiber according to claim (1), wherein the optical coupling optical waveguide has an arcuate ring so that its longitudinal cross-sectional shape is narrowest at the center. Optical coupling device with. (5) Claim 1, wherein the diameter of the optical waveguide for optical coupling is formed such that it gradually increases from one side to the other between the light emitting element and the optical fiber. An optical coupling device between a light emitting element and an optical fiber.