JPS60112005A - Optical demultiplexer - Google Patents

Abstract

PURPOSE:To obtain a low-loss optical demultiplexer by passing light beams through compound lenses corresponding to respective optical fibers of a bundle of input optical fibers, converging them through a condenser lens, and outputting the converged light beams to plural optical fibers through compound lenses respectively. CONSTITUTION:Plural optical fibers are bundled into an input optical fiber 1, compound lenses 2 as many as optical fibers are provided in front of the input optical fiber group 1 corresponding to input optical fibers, and the condenser lens 3 is provided in front of the lenses 2 to converge light beams from input optical fiber ends on one point. Further, an optical fiber 4 for luminous flux conversion 4 has an end surface at the convergence point of light, and a distribution lens 5 is arranged in front of the other end of the fiber 4; and similar compound lenses 6 are provided and an output optical fiber group 7 is formed by bundling optical fibers having end surfaces at convergence points of the compound lenses 6 by as many as the compound lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Technical Field The present invention relates to an optical distributor 1 necessary for optical communication (j'f, etc.).

An optical splitter equally distributes light from one transmission line to multiple transmission lines. This is necessary when α wants to simultaneously transmit the same signal to multiple receivers.

(a) Prior art and its problems An optical splitter as shown in FIG. 5 has been proposed.

Optical fiber J!Y30, which bundles many optical cores,
A slab-shaped waveguide 32 is interposed between the fiber groups '31. - In the example, 100 optical fibers are made on the input side and 100 optical fibers on the output side.

It is desirable that the large number of optical fibers on the exit side be bundled as closely as possible, so the optical fiber is in the form fg consisting of a core and a cladding.Moreover, the core diameter is large and the cladding diameter is extremely large. , For example, if the core diameter is 50μ
η2, the thickness of the cladding layer is about 5 μm/12 mm.

This is because if there is a vinyl coating or the like, the ratio of light rays emitted from the slab-like path 32 and incident on the core will be small. The reason for sowing crud is the same. The refractive index difference between the core and the cladding is, for example, about 1%.

The slab waveguide 32 is a thin, flat rectangular plate. Since it is a slab waveguide, the light in this waveguide is TE wave, Ti
It becomes a Vl wave. The traveling direction is taken as two axes, the normal direction of the slab is taken as the y-axis, and the parallel direction of the optical fiber groups 30 and 31 is taken as the x-axis.

Light propagating through any one optical fiber in the input-side optical fiber group 30 spreads conically into the slug waveguide 32 from the end face and enters the slug waveguide 32 .

When the traveling direction of light has an X-direction component, this light is repeatedly totally reflected at iI'Ili below 1 and travels in two directions.

When the traveling direction of light has an X-direction component, this light spreads in the X-direction.

Therefore, if the length of the waveguide in two directions is sufficient, light will propagate equally to all output side optical fibers.

The same thing happens when light passes through it. Only the input and output sides are reversed.

Such an optical splitter is effective in transmitting the same information to a large number of terminals because the number of fibers in the fiber/fiber groups on the input side and the output side can be significantly increased.

In addition, manufacturing is easy because it is only necessary to wire the optical fiber, polish the end face, and bond it to the end face of the slab waveguide.

However, since it passes through the slab waveguide 32, it does not necessarily come out corresponding to the core part of the optical fiber /( on the output side. All the light Q that goes out to parts other than the core will be lost. It's about to happen.

At the base of the slab waveguide 32 is a guide layer 33 with a refractive index of '::5. The path of the light beam r1 is restricted within the guide layer 33.

If the guide layer 33 satisfies A'X < I and the cladding of the optical fiber is made thin, the relative amount of light incident on the core on the output side can be increased.

Furthermore, inside the nine fibers, the electric and magnetic fields have a cylindrically symmetrical distribution. However, in the slab line, 6 is cylindrically symmetrical (not d) and has an independent distribution in the X direction and the X direction.

In this way, the electric field and magnetic field modes are completely different between an optical fiber and a slab line. Therefore, a large amount of mode coupling loss occurs at the coupling portion between the optical fiber and the slab waveguide.

For this reason, the optical splitter Q shown in FIG. 5 cannot be a low-loss optical splitter.

Other optical distributors have also been proposed.

For example, it has been proposed to bundle a large number of optical fibers, heat and melt a part of this, twist the light 71475 bundle in this part many times, then pull it thinly, cool it blindly, and solidify it to make an optical distributor. has been done.

[Multiple lights] "The diameter of the fiber wire becomes thinner at the melting point, and
, 7: Since the VCs are close to each other, adjacent cores are optically coupled to each other. Even if the diameter is reduced, the refractive index distribution of the core and cladding remains. Since the cladding is thin, light energy is propagated and transferred from core to core.

In this way, light entering one of the optical fibers at one end is split into all the optical fibers at the other end.

However, in such an optical splitter, it is expected that all optical fibers will not be equally coupled to each other, and that the distributed PsoC energy will vary significantly.

(i) Purpose of the Invention The object of the present invention is to provide a low-loss optical distributor that is free from mode coupling loss and loss due to light entering the cladding.

(1) Structure of the invention FIG. 1 is a diagram showing the configuration of the optical system of the optical distributor of the present invention.

The input optical fiber group 1 is a set of a plurality of optical fibers. It may be a solo fiber wire consisting of a core and a cladding, or it may be in the form of a core wire with a coating. There is no requirement that adjacent optical fibers be in close contact.

Therefore, there is sufficient cross-sectional area for each optical fiber.

A compound lens 2 is provided on each optical axis of the input optical fiber 1. In this figure, the end face of the optical fiber coincides with the focal point of the compound lens 2. However, this does not necessarily have to be the case.

Compound lens 2 is an equivalent lens whose optical axis is parallel and overlaps the normal to the end face of the corresponding optical fiber.

The number of compound lenses is equal to the number M of optical fibers.

One collective lens 3 is provided in front of the compound lens 2. This has the effect of converging the light rays emitted from all the compound lenses 2 at the end face of the light flux converting fiber 4 (().

The light flux conversion fiber 4 may be straight or curved, and may have any length.

A distribution lens 5 is provided on the optical axis at the other end of the light flux conversion fiber 4.

In this figure, the optical fiber 4 for light flux conversion is positioned at the focal point of the distribution lens 5, so that the light beam passing through the distribution lens 5 becomes parallel light.

In front of the distribution lens 5, compound lenses 6 are arranged in rows and columns on the same plane.

The light Q focused by the compound lens 6 is converged on the end face of the output optical fiber group 7. Output]'r The number N of fibers in the IPA group and the number of compound lenses 6 are equal.

The number M of input optical fibers and the number N of output -16 funnels are not necessarily equal.

The distance between the Mfm plane of input optical fiber group 1 and compound lens 2 is fl, the distance m in front of compound lens 2 and collective lens 3 is β1,
The same distance between the )71i planes of the collective lens 3 and the light flux converting optical fiber 4 is +2.

The distance between the other end face of the optical fiber for light flux conversion and the splitting lens 5 is +3, the distance in front of the splitting lens 5 and the splitting lens 5 is 42,
The distance between the compound lens 6 and the 11jiJ plane of the output optical fiber group is +4.

Let the focal lengths of the compound lens 2.6 be Fl and F4.

Let the focal lengths of the collective lens 3 and the distributing lens 5 be F2 and F3.

The illustrated feed ((in f,=F,,+2:F2,f
3-F 3,f,=F4. Tsuriri Hikari 7-
The opposing end surfaces of the 7' fibers are the focal points of the opposing lenses.

The light becomes parallel between the compound lens 2 and the collective lens 3. The light is also parallel between the distribution lens 5 and the compound lens 6. In this case, there is no restriction on 41.12.

In this example, the input light] "The light that exits the fiber 1 has a numerical aperture N A = sin θC determined by the refractive index of the core and cladding.
It spreads within a conical surface whose apex angle is twice the angle θC determined by .

Regarding the spread of the circular button or shape of light, the same relationship holds even when it is emitted to both ends of the solo fiber for light flux conversion and to the end face of the output optical fiber.

These b ° giant filly: about tc, generally f
What is necessary is to make Ik F l hold true. In this case, the central axis of the input optical fiber 1 and the optical axis of the compound lens 2 do not match. If the distance from the basic central axis of each optical fiber 1 is (t, +72), then the optical axis of the compound lens (l,
It should be a short distance m from the center of the end face of the optical fiber and as close as δ to the basic central axis m. However, it is. The constraint conditions are (1) and (2) between fl, 11, and +2.
). This is .

The same holds true on the output side of the optical fiber 4 for light flux conversion. In this case, fl, name, f2 in formula ++] ~ (5)
f4. It is sufficient to replace it with β2 and f3.

(E) Embodiment An example will be given for the case where both IVI and N of the input/output side fibers are 4 trees.

The compound lens has two rows and two columns. For example, there is one lens groove as shown in FIG. The individual l lenses are square and have the same focal length and dimensions.

By gluing the side surfaces of such a square lens together, a compound lens 2.6 can be constructed.

Actually, instead of using an I lens with unevenness, it is also possible to combine a lens with a flat refractive index distribution.

Such lenses are shown in FIGS. 3 and 4.

This is a compound lens made of four flat, square pieces of glass arranged side by side. Figure 3 shows the external appearance, and Figure 4 shows the refractive index equal to 16.
, 1ffiJ edge 12 is the lowest. The refractive index contour lines 13 are distributed in a solid concentric manner.

The refractive index distribution is achieved by distributing impurities in the glass so that they increase (C1 or decrease) from the center to the periphery.

By using such a lens, the optical system can be made smaller and lighter.

An example of the arrangement shown in FIG. 1 will be described.

+1+ Optical fiber 1.4.7 is a multimode fiber with CI English glass core and cladding, core diameter 50μ2〕7 cladding diameter 125μ7〕2 NA 0.2 (2) Likelihood distance between fibers t1 = t 2 = Q, 5 myrr (3) Complex lens (input side) 2 Focal length nL f + =' 1. Q mm vertical and horizontal spread a-1,0 (4) Collective lens 3 focal length nL f2 = 2-3 vtm diameter 2 mm (5) distribution lens 5 focal length f3 = 2.3 mm diameter 2711+ (6) compound lens 6 focal point W large distance f4 = 1.8 Bu I shoulder vertical and horizontal spread a
=1.0ff1m (force) effect +1+ No mode coupling loss.

Like a slab, light core ino and structural sentence 4th person l'lE
This is because different types are not used. The lenses have a one-to-one correspondence with the individual optical fibers, and since the lenses have circular symmetry, the symmetry is the same as that of the optical fibers.

(2) Any single optical fiber on the input side:
The 14 pairs of lights are distributed to all the optical fibers on the output side. The element 1 responsible for the distribution function is the optical fiber 4 for light flux conversion. Since the core diameter is small, even distribution can be achieved even if the distance it is shorter than that of a slab waveguide.

(3) Since light is transmitted from core to core using a lens system, there is no energy that is dissipated by hitting parts other than the core.

Comparable to (1) and (3), an optical splitter with low loss can be realized.

[Brief explanation of the drawing]

FIG. 1 shows the components of an optical system a, showing an example of the optical distributor of the present invention. Figure 2 is a perspective view of a compound lens used in a light distributor. FIG. 3 is a perspective view of another compound lens used in a light distributor. It uses a gradient index lens. FIG. 4 is a refractive index contour map of a gradient index lens. FIG. 5 is a perspective view showing an example of a proposed optical distributor. 1 Manual optical fiber group 2 Compound lens 3 Collective lens 4 Optical fiber for light flux conversion 5 Distribution lens 6 Compound lens 7 Output '6 fiber group 10 Gradient index lens 11 Center 12 Periphery 13 Constant refractive index - Inventor Mitsuru Nishikawa Patent applicant Sumitomo Electric Industries, Ltd. JP-A-112005 (5) Figure 3 Figure 4

Claims (1)

[Claims] an input optical fiber group 1 made up of a bundle of multiple optical fibers;
A composite lens 2 having the same number and the same number as the optical fibers provided in front of the input optical fiber 7 and the optical fiber group 1 corresponding to each of the input optical fibers, and a light emitted from the end face of the input optical fiber provided on the 13fj side of the composite lens 2. one collective lens 3 that converges the light to one point, an optical fiber 4 for light flux conversion provided such that the end faces of the light coincide with the convergence point of the light by the +ffJ force of the collective lens 3, and optical fiber 4 for light flux conversion 4 and other optical fibers 4 for light flux conversion. 1) IJ at the end
One distribution lens 5 provided on the side and distribution lens 5
A point where light emitted from a plurality of equivalent compound lenses 6 provided on the 110 side of the compound lens 6 and the light flux converting optical fiber 4 provided on the 0 side of the compound 6 lens 6 is converged by the distribution lens 5 and the compound lens 6. A light distributor characterized in that it is anodized by a compound lens 6 having an end face and an output optical fiber group 7 which is a bundle of the same number of optical fibers.