JPS63133108A - Photodetector - Google Patents

Abstract

PURPOSE:To improve the light condensing efficiency by providing a supporting member which bends and fixes an optical fiber and an optical waveguide which has one end closely brought into contact with the surface of the bending part of the optical fiber and has the other end formed into an exit end. CONSTITUTION:A substrate 2 used for production of an optical element is used as the means which bends an optical fiber 1 with a prescribed radius of curvature and supports it. A groove 2a formed into a desired optical fiber shape is provided on the substrate 2 with the width approximately equal to the diameter of the optical fiber 1. An optical waveguide 3 having a width approximately equal to that of the groove 2a is formed in the substrate 2. One end of the optical waveguide 3 is exposed near the apex of bend of the groove 2a, and the other is exposed to the side face of the substrate 2. Since the light radiated from the bent optical fiber 1 is very efficiently acquired, light is detected by a relatively large radius of curvature of the optical fiber 1 and a general detecting system.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a photodetector used for extracting a portion of an optical signal propagating through an optical fiber from an optical fiber. More specifically, the present invention provides an optical fiber that is a transmission path for optical signals, without physically cutting the optical fiber, without applying mechanical stress, and without causing loss due to radiation or the like. The present invention relates to a novel photodetector configuration that is capable of detecting a portion of an optical signal at a desired branching ratio without causing any problems. Note that the photodetector according to the present invention can be advantageously used in fields such as optical communication, but is not limited thereto.

BACKGROUND OF THE INVENTION Due to advances in optical communication related technology, optical communication is being applied to relatively small-scale systems such as optical LANs and various monitoring systems. In such a system, an element is essential for extracting optical signals propagating through an optical fiber, which is a transmission path, to various processing devices.

Conventionally, optical fiber couplers, optical waveguide type splitters, and the like have been used as such photodetecting elements.

An optical fiber coupler is made by fusing two optical fibers at the sides and then stretching them, and is characterized by being able to form a splitter with any branching ratio by changing the length of the fused part. . However, the process of fusing and stretching is difficult to automate, making it unsuitable for mass production.

On the other hand, an optical waveguide type splitter using a 7-shaped optical waveguide formed on a substrate can be mass-produced by applying semiconductor element manufacturing technology. However, this type of optical splitter can only obtain a splitting ratio of 1:1 or a value close to it. However, in the case of a system in which a plurality of nodes are connected to one optical fiber bus, for example, if the branching ratio is small, the attenuation of the optical signal propagating on the bus side becomes large. Therefore, when an optical waveguide type splitter is used, only a very small-scale system (about 5 to 10 nodes) can be constructed.

In addition, in the case of a leading wave type splitter, an element made of a material different from the optical fiber is connected to the optical fiber.
It is known that large coupling losses occur due to mismatching of refractive index distribution, etc.

Problems to be Solved by the Invention In recent years, a type of photodetector called an optical tap has appeared as a new photodetector that can overcome the problems of the various conventional photodetectors as described above. This means that when the optical fiber is bent,
This method takes advantage of the fact that the radiation mode increases in the light propagating through the optical fiber, and a portion of the propagating light leaks to the outside of the optical fiber.

As shown in FIG. 4, the optical tap condenses and processes the light leaking from the bent optical fiber 10 using an optical system 20 or by adding a photoelectric conversion element 30. .

The feature of this method is that the optical signal can be detected without cutting the optical fiber through which the signal to be detected propagates, so there is little coupling loss, and it can be configured to be detachable. Furthermore, it has many practical advantages, such as being able to easily obtain a large branching ratio and having relatively little insertion loss as an element.

However, with conventionally known optical taps, it is difficult to efficiently collect the light emitted from a bent optical fiber, and it is necessary to use a high-quality, expensive optical system or a highly sensitive light-receiving element. There is a problem. On the other hand, if you try to obtain sufficient emitted light by bending the optical fiber strongly, you will force the optical fiber to bend strongly (1 to 2 mm or less), and in severe cases, there is a risk that the optical fiber may break. .

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to develop an optical tap type photodetector, which basically has a number of advantageous features, into a practical device by improving the collection efficiency of light emitted from a bent optical fiber. It is about completion.

Means for Solving the Problems Therefore, according to the present invention, there is provided a support member for bending and fixing an optical fiber, and one end of the optical fiber fixed by the support member so as to capture the propagating light emitted from the bent portion. Provided is a photodetector characterized by comprising an optical waveguide formed in such a way that the optical fiber is in close contact with the surface of the bent portion of the optical fiber, and the other end thereof is an output end.

The main feature of the photodetector according to the present invention is that it efficiently detects light leaking from the optical fiber while retaining the characteristic of conventional optical taps that it detects light without damaging the optical fiber. By focusing the light well, the mechanical load on the optical fiber is removed and its characteristics as a photodetector are improved.

That is, in the conventional optical tap, the light emitted around the bent part of the optical fiber is focused by optical means, but in the photodetector according to the present invention, the light emitted around the bent part of the optical fiber, that is, the emitted light is focused by optical means. An optical waveguide, which serves as a light focusing means, is closely attached to the area to collect light. Therefore, the light leaked from the optical fiber is hardly scattered outside the condensing means, and the light emitted by the optical fiber can be effectively utilized.

In addition, considering from the side of the optical fiber that emits light, almost all of the emitted light is effectively used, so there is no need to bend the optical fiber extremely strongly, and mechanical damage caused by connecting it to the photodetector is eliminated. The burden can be reduced by B.

EXAMPLES The present invention will be described in more detail below with reference to the accompanying drawings, but what is shown below is only one example of the present invention, and does not limit the technical scope of the present invention in any way. isn't it.

FIG. 1 schematically shows the configuration of a photodetector according to the present invention.

As a means for bending and supporting the optical fiber 1 at a predetermined radius of curvature, a substrate 2 used for manufacturing various optical elements was used here. A groove 2a is formed on the substrate 2 and has a width substantially the same as the diameter of the optical fiber 1 and is formed into a desired optical fiber shape. Furthermore, an optical waveguide 3 is formed within this substrate 2 at approximately the same depth as the groove 2a. This optical waveguide 3
One end of the groove 2a is exposed near the bending apex of the groove 2a, and the other end is exposed on the side surface of the substrate 2. As the optical fiber I, a quartz optical fiber with an outer diameter of 250 μm (outer diameter of the resin coating) was used.

For such a photodetector member A, after fitting the optical fiber 1 into the groove 2a and filling the gap between the optical fiber 1 and the substrate 2 with resin, the entire substrate is further covered with the same material as the substrate from above. It is completed by covering with the produced plate-like member B.

Incidentally, the photodetector member Δ as described above was manufactured as follows.

A groove 3a having a depth of 260 μm as shown in FIG. 2(a) is formed on the 3i02 substrate by dry etching. This groove 3a corresponds to the shape of the optical waveguide 3 described above.

Next, as shown in FIG. 2(1)), a melt of 852S3 was poured into the groove 3a as an optical waveguide material. This 52S3 melt is slowly cooled to form an optical waveguide.

Note that the optical waveguide material may be a polymer material or the like.

Finally, a groove 2a for inserting the optical fiber 1 was formed by dry etching. This groove has a width of 300 μm
1 depth was 260 μm, and the radius of curvature of the bent portion was lQmm.

Figure 3 shows a photodetector manufactured with the configuration shown in Figure 1.
FIG. 2 is a cross-sectional view of the optical fiber 1 taken along a plane including the propagation optical axis. Note that the same reference numerals are given to the members already explained in FIG.

Light propagates through the optical fiber 1 in the direction of arrow C===>)S in the figure. This light is connected to the two arrows in the diagram [→
) As shown by K and L, the light becomes emitted light at the bent portion of the optical fiber 1. This emitted light enters the optical waveguide 3 through the resin layer, but at the interface between the surface of the optical fiber 1 and the resin layer, and the interface between the resin layer and the optical fiber 3, all of the incident light is within a certain angle. It is reflected, propagates through the optical waveguide 3, and reaches the end face of the other end of the optical fiber 3. Therefore, another optical fiber may be connected to this end face, or a photoelectric conversion element may be arranged and processed via a suitable optical system.

Now, the refractive index of the cladding layer of the optical fiber 1 is N, and the refractive index of the resin filled in the gap between the optical fiber 1 and the substrate is n. ,
The refractive index of the optical waveguide 3 is 711, and the refractive index of the substrate is n2.

Considering that the light leaking from the optical fiber 1 efficiently propagates to the optical waveguide 3, the relationship between the refractive index of each member in the cross section P in FIG. 3 is N≦n.

≦n1. In addition, in view of the function of the optical waveguide 3, 11,
>n2. 'on the other hand,
From the viewpoint that it is preferable that the amount of emitted light be small in areas that are not in contact with the optical waveguide 3, the relationship between the refractive index of each member in the cross section Q is N2H.

It is desirable that ≧n2.

Putting these together, n, ≧no between each refractive index
A relationship such as =N>n2 becomes clear.

Therefore, with emphasis on the coupling efficiency between the synchrotron radiation and the waveguide, and considering the reduction of the radiation loss of the optical waveguide 3, n, = 2.4.
TI2 = 1.5.

In the photodetector manufactured in this way, the substrate 2 and the optical waveguide 3 are
The total reflection angle at the interface with the L
is coupled to the optical waveguide extremely efficiently. In addition, since the waveguide 3 is tapered in the width direction in the radiation coupling part, high-order mode light is converted to low-order mode light, and the light emitted from the waveguide output end is efficiently focused. It will be done.

Therefore, the photodetector according to the present invention exhibited extremely excellent characteristics such as an insertion loss of 0.1 dB and a coupling efficiency of emitted light from the optical fiber to the optical waveguide of 95% for a branching ratio of 100:3.

Effects of the Invention The photodetector of the present invention has many characteristics of optical taps that have been known for a long time, namely, that the optical fiber is not damaged, a large branching ratio can be obtained, and the coupling loss and insertion loss are small. While maintaining the advantages, the mechanical load on the optical fiber is reduced, making it ideal for optical detection.

That is, the photodetector according to the present invention can extremely efficiently capture the light emitted from the bent optical fiber, so that photodetection can be performed using a relatively large radius of curvature of the optical fiber and a general detection system. be able to.

Furthermore, since the photodetector can be constructed without any processing on the optical fiber on the side to be branched, it also has the feature of being detachable, which is not possible with conventional photodetectors.

Furthermore, in its manufacture, semiconductor manufacturing technology can be applied to many members, making it relatively suitable for mass production.

The photodetector according to the present invention, which has these many features, is an extremely effective element for the widespread use of optical LANs, etc., which have been put into practical use significantly in recent years.

[Brief explanation of the drawing]

FIG. 1 schematically shows a suitable configuration of a photodetector according to the present invention, and FIGS. 2(a) to (C) show the method for manufacturing the photodetector shown in FIG. 1 over time. FIG. 3 is a plan view showing in detail the propagation state of light in the photodetector shown in FIG. 1, and FIG. 4 is a diagram schematically showing the configuration of a conventional optical tap. It is. (Main reference numbers) 1.10...Optical fiber, 2...Substrate, 3...Optical waveguide, 20...Lens, 30...Photodiode

Claims (4)

[Claims] (1) a support member for bending and fixing an optical fiber; one end of the optical fiber fixed by the support member is in close contact with the surface of the bent portion of the optical fiber so as to capture propagating light emitted from the bent portion; 1. A photodetector comprising: an optical waveguide formed such that the other end thereof is an output end. (2) The supporting member is a substrate made of a material having a lower refractive index than the cladding layer of the optical fiber, and has a groove formed therein to fit into the bent optical fiber, and the optical waveguide has one end on the inner surface of the groove. The optical waveguide is made of a material having a refractive index higher than or equal to that of the cladding layer of the optical fiber formed in the substrate with the optical fiber being opened and the other end being released outside the side surface of the substrate. The photodetector according to item 1. (3) A resin or a refractive index matching material having the same refractive index as the cladding layer of the optical fiber is filled between the groove formed in the substrate and the optical fiber housed in the groove. A photodetector according to claim 2. (4) The upper surface of the substrate is sealed with a plate made of a material having a refractive index lower than the refractive index of the cladding layer so as to cover at least the groove and the upper surface of the optical waveguide. A photodetector according to claim 2 or 3.