JPH0443844Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a polished optical fiber coupler constructed using optical fibers.

<Prior Art> FIG. 4 shows a perspective view of a conventionally used optical fiber coupler. In the figure, reference numeral 1 denotes a pair of substrates made of, for example, fused silica glass, and each substrate is embedded with an optical fiber 2 consisting of a cladding and a core, so that, for example, light incident from the a side is split into predetermined directions to the b and c sides. Branched by ratio.

5a to 5c are diagrams schematically showing the manufacturing process of the optical fiber coupler, in which a groove 8 is formed in the substrate 1 with a radius of curvature r, and the optical fiber 2 is inserted along the curved surface of the groove.
FIG. 2 is a perspective view showing a state in which the Note that the width of the groove 8 is the same as or slightly larger than the outer diameter of the optical fiber 2, and the depth is processed so that the top of the cladding 3 of the optical fiber buried along the groove 8 is slightly lower than the surface of the substrate 1. . b is a perspective view showing a state in which the portion of the surface of the substrate 1 indicated by the dotted line has been polished. Polishing is performed until the distance between the cladding 3 and core 4 of the optical fiber is several μm (note that this distance is difficult to measure in practice, so the final amount of polishing is determined by measuring the amount of transmitted light.c) is the above a,
It is a perspective view which shows the state before fixing the two board|substrates manufactured in the process of b. In this case, the substrates are stacked and fixed so that the portions indicated by e of the polished cladding 3 are in close contact with each other.

According to the above configuration, the two cores are fixed in close proximity to each other within several μm. When the cores approach each other in this way, light does not propagate through each core independently, but propagates while exchanging optical power with each other. Therefore, when light is incident on one core, the light is coupled to the other core. Therefore 2
The required branching ratio can be obtained by adjusting the distance between the book cores and the length of the connecting portion.

<Problems to be solved by the invention> By the way, if the optical fiber coupler with the above configuration is ideally created, the light incident from a will be directed to b and c.
The beam is divided into branches according to a certain branching ratio and emitted. That is, if the optical power from a is Pa, and the optical power of the emitted light from sides b and c is Pb and Pc, respectively, the relationship Pa=Pb+Pc (1) holds between them. However, in reality, irregularities on the polished surface of the substrates and minute foreign matter 5 enter between the substrates as shown in FIG. 6, creating a very thin air layer 6 between the substrates. Reflection and scattering occur at the interface between this air layer and the substrate, resulting in light loss. For this reason
Equation (1) becomes Pa>Pb+Pc...(2). This optical loss is called excess loss Pz, and Pz=-10log {(Pb+Pc)/Pa} (dB)
...It is expressed as (3).

The object of the present invention is to provide an optical fiber coupler that does not have excessive loss in the prior art described above.

<Means for solving the problems> The structure of the present invention to solve the above problems is as follows.
An optical fiber consisting of a cladding and a core portion; an optical fiber consisting of a cladding and a core portion; and a substrate having a groove for embedding the optical fiber formed with a predetermined radius of curvature r in the depth direction of the substrate surface, and the groove has a predetermined curvature radius r. The depth of the groove having radius r is such that when the optical fiber is buried/fixed, the top of the cladding along the curved surface is slightly lower than the surface of the substrate, and the surface on the side where the optical fiber is buried is polished together with the cladding. and remove the core to a few μm before it is exposed, and combine the two substrates into a set,
In an optical fiber coupler in which the clads on the polished sides are fixed in contact with each other, at least one of the substrates has a radius of curvature R larger than the radius of curvature of the groove.
It is characterized by being formed into a convex spherical shape having.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 3 is a sectional view showing the polished state of the substrate, and the process is the same as the conventional example until a groove with a radius of curvature r is formed and the cladding 3 and core 4 are buried/fixed. In the present invention, at least one of the substrates is formed into a spherical shape having a radius R larger than the radius of curvature of the groove, whereas conventionally the surfaces of the substrates were polished horizontally and two substrates were fixed as a set. . In addition,
Spherical processing can be performed using a mold with a spherical concave portion and polished using abrasive grains, similar to general convex lens processing.

FIGS. 1a and 1b are cross-sectional views showing one embodiment of an optical fiber coupler, in which one substrate is polished flat and the other substrate has a spherical surface. In addition, figure b is - of figure a.
FIG.

FIGS. 2a and 2b are sectional views showing another embodiment. Note that, similar to FIG. 1, figure b is a cross-sectional view taken from figure a. In this embodiment, both substrates are processed into spherical shapes. The size of the optical fiber coupler is approximately 10 mm in length and width and 50 mm in length, the radius of curvature r is several mm to several tens of mm, and R is approximately several tens of cm. Generally, when spherical parts are brought into close contact, the contact surface is considered to be a point contact, but the area where the cladding is polished is very small, and the board itself is not completely rigid and has some elasticity. Since the two substrates are held together, when the two substrates are fixed with an adhesive or by the force applied, for example, when they are fixed using bolts, etc., they are deformed and are brought into close contact with each other in a plane state.

<Effects of the invention> As described above in detail with the embodiments, according to the invention, the surface of the substrate is polished into a convex spherical surface and the polished surfaces are brought into close contact, creating a structure in which air layers are difficult to form. Excessive loss due to the presence of the air layer can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention;
The figures are cross-sectional views showing other embodiments, FIG. 3 is a cross-sectional view showing the relationship between the radius of curvature of the groove and the radius of curvature of the spherical surface, and FIG.
The figure is a perspective view showing a conventional example, FIG. 5 is a perspective view showing a conventional general manufacturing process, and FIG. 6 is a diagram showing a conventional example in which minute foreign matter has entered between the substrates. 1... Substrate (fused silica glass, etc.), 2... Optical fiber, 3... Clad, 4... Core, 8...
groove.

Claims (1)

[Scope of utility model registration request] consisting of an optical fiber consisting of a cladding and a core part, and a substrate having a groove for embedding the optical fiber formed with a predetermined radius of curvature r in the depth direction of the substrate surface,
The depth of the groove having the radius of curvature is such that when the optical fiber is buried and fixed, the top of the cladding along the curved surface is slightly lower than the surface of the substrate, and the surface on the side where the optical fiber is buried is polished together with the cladding. At least one of the substrates is connected to the optical fiber in an optical fiber coupler in which the two substrates are assembled into a set and the polished claddings are brought into contact with each other and fixed. An optical fiber coupler characterized by having a convex spherical shape having a radius of curvature R larger than a radius of curvature r of an embedding groove.