JP3184358B2 - Star coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an N.times.N star coupler, and is particularly useful as an optical component essential for optical signal distribution in a large-capacity LAN (Local Area Network) system.

[0002]

2. Description of the Related Art Conventionally, an N × N star coupler having a structure as shown in FIG. 4 has been known as an N × N star coupler for uniformly branching an optical signal incident on an arbitrary input optical waveguide into N output optical waveguides. Had been. The star coupler shown in FIG. 1 connects one between N = 8 input optical waveguides 4 and N = 8 output optical waveguides 6.
The structure is such that two 3 dB directional couplers 5 are connected.

In a star coupler having such a structure, 3d
The number M of the B-direction couplers 5 requires M = (N / 2) log ₂ N (1).

[0004]

In the above-mentioned prior art, for example, in the case of a large-capacity LAN system with N = 128, the number becomes M = 448. Therefore, the size of the star coupler is very large, and the production yield is low and the cost is high. Also, the coupling ratio of the 3 dB directional coupler 5 is usually
The star coupler having the conventional structure also has a drawback that it can be used only at a specific wavelength because it changes depending on the wavelength of light.

SUMMARY OF THE INVENTION In view of the above prior art, an object of the present invention is to provide an N × N star coupler which has a uniform signal branching ratio and is suitable for large scale.

[0006]

To achieve the above object, the present invention comprises a slab optical waveguide having no lateral light confinement structure and N slab optical waveguides disposed opposite to both ends of the slab optical waveguide. (N is an integer) and an input optical waveguide and N output optical waveguides, splitting the optical power incident on any one in the input waveguide to the output optical waveguide the N N × N
In a star coupler, the input optical waveguide and the output
Each of the optical waveguides has a core width and
The core thickness is constant and the input optical waveguide and
In each of the output optical waveguides, the core width or the core thickness is smaller as the bending radius is larger .

[0007]

According to the present invention having the above-described structure, the optical power incident on any one input optical waveguide is uniformly branched into N output optical waveguides.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, an input optical waveguide array I
Is an aggregate of many (in this example, N = 16) input optical waveguides 1. The output optical waveguide array II is an aggregate of the same number of output optical waveguides 2 as the input optical waveguides 1. These input / output optical waveguides 1 and 2 have a core width W in this embodiment.
(Usually, the core thickness T = W), a core of refractive index n ₁ refractive index n
It is composed of a rectangular optical waveguide covered with a cladding of ₀ , and is disposed opposite to both ends of the slab optical waveguide 3. The slab optical waveguide 3 is an optical waveguide having no light confinement structure in the lateral direction.

The detailed structure near the slab optical waveguide of the star coupler is described in JP-A-4-96007 and JP-A-4-204508.

The relative refractive index difference between the core and the clad is ク ラ ッ ド = (n ₁
−n ₀ ) / n ₁ = 0.75% and W = T = 6 μm, the minimum bending radius of the input / output optical waveguides 1 and 2 (the bending loss is 0.1d)
B or less) is R = 5 mm. Therefore, the minimum bending radius of the outermost input / output optical waveguides 1 and 2 of the slab optical waveguide 3 is 5 mm, and the bending radius of the input / output optical waveguides 1 and 2 at the center of the slab optical waveguide 3 is larger.

Normally, when light enters the optical waveguide, unnecessary modes of light are excited in addition to the intrinsic mode propagating in the optical waveguide. In the input / output optical waveguides 1 and 2 closer to the peripheral portion of the slab optical waveguide 3, the bending radius is small,
Since the light in these unnecessary modes is discarded outside the input / output optical waveguides 1 and 2, it does not adversely affect the characteristics of the star coupler. On the other hand, in the input / output optical waveguides 1 and 2 at the center, the excited unnecessary mode propagates as it is because the bending radius is large and close to a straight line. For this reason, the light pattern when light is emitted from the input optical waveguide array I to the slab optical waveguide 3 is disturbed, and a uniform light distribution cannot be obtained.

This situation is shown in FIGS. 2 (a) and 2 (b). FIGS. 2A and 2B show the input / output optical waveguide arrays I and II in a 64 × 64 star coupler having the same core width W, in which (a) light is input to the outermost input optical waveguide 1 and (b) input at the center. It is a result of measuring a light distribution of the output optical waveguide 2 when light is input to the optical waveguide 2. Here, the bending radius of the outermost input / output optical waveguides 1 and 2 is R = 5 mm, and the bending radius of the central input / output optical waveguides 1 and 2 is R = 120 mm.
It is. In FIG. 2A, since the bending radius is small, the light in the unnecessary mode is discarded outside the waveguide, and good light branching characteristics are obtained. On the other hand, in FIG. 2B, it can be seen that the unnecessary mode propagates through the optical waveguide as it is because the bending radius is large, so that the light branching characteristic is greatly deteriorated.

Therefore, in the present embodiment, the core width W of the input / output optical waveguides 1 and 2 at the central portion is made smaller than that at the peripheral portion to reduce the unnecessary mode light which is likely to be generated at the central portion. Is disposed so as to be thrown out of the waveguide.

For example, the core width W of the input / output optical waveguides 1 and 2 having a bending radius R (mm) is

W = W ₀ + (C / R) (μm) The core width W is smaller in the input / output optical waveguides 1 and 2 at the center where the bending radius R is large as shown in (2). . Here, in equation (2), W ₀ is the core width W of the linear optical waveguide (R = ∞), and C (μm · mm) is a constant.

The same effect can be obtained by reducing the core thickness T and the core diameter.

Next, the above-mentioned star coupler is connected to a quartz light guide.
A manufacturing method in the case of manufacturing using a waveguide will be described. Ma
Without using a SiO_TwoLower class
A TiO2 layer and then TiO_TwoOr G_eO_TwoThe
-SiO added as punt_Two Deposit glass core layer
After that, the glass is transparently vitrified in an electric furnace. Then, the expression
The core layer is formed using the mask pattern prepared based on (2).
Etching, predetermined input / output optical waveguide arrays I, II,
And a slab optical waveguide 3 are formed._TwoUpper part
Deposit a cladding layer.

FIG.₀= 4 (μm), C = 10 (μm
・ Mm) 64 × 64 star coupler smell
(A) When light is input to the outermost input optical waveguide 1
(B) Light was input to the input optical waveguide 1 at the center.
It is a result of measuring the light distribution of the output optical waveguide 2 in the case.
Here, the bending radius of the outermost input optical waveguide 1 is R = 5 mm.
(W = 6 μm), and bending of the input optical waveguide 1 at the center portion
The radius is R = 120 mm (W = 4.08 μm). FIG.
In FIG. 2A, since the bending radius is small, the conventional FIG.
As in (a), the light in the unnecessary mode is discarded outside the waveguide.
Good light branching characteristics are obtained. On the other hand, FIG.
Since the core width W is smaller than before, the bending radius
Even if the light is large, the light in the unnecessary mode is discarded outside the waveguide and good.
Optical branching characteristics are obtained, and the unique effects of the present invention are confirmed.
It has been certified. In this measurement, W ₀= 4 (μ
m), C = 10 (μm · mm), but this is only
This is just one example.

[0020]

As described above in detail with the embodiments, the star coupler of the present invention can uniformly branch the optical power incident on any one optical waveguide into N output optical waveguides. This has a great advantage in optical signal distribution in a large-scale LAN system, a wavelength multiplexing system, and the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a star coupler according to an embodiment of the present invention.

FIG. 2 shows the same input / output optical waveguides having the same core width W of 64 ×
In the 64-star coupler, the results of measuring the light distribution of the output optical waveguide when (a) light is input to the outermost input optical waveguide and (b) when light is input to the central input optical waveguide are shown. It is a characteristic diagram.

FIGS. 3A and 3B show (a) a case where light is input to the outermost input optical waveguide and (b) a case where W ₀ = 4 (μm) and C = 10 (μm · mm); FIG. 4 is a characteristic diagram showing a result of measuring a light distribution of an output optical waveguide when light is input to an input optical waveguide in a central part.

FIG. 4 is a diagram showing a structure of a conventional N × N star coupler.

[Explanation of symbols]

 Reference Signs List 1 input optical waveguide 2 output optical waveguide array 3 slab optical waveguide

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/12-6/14 G02B 6/28-6/293

Claims (1)

(57) [Claims] 1. A slab optical waveguide having no lateral light confinement structure, N (N is an integer) input optical waveguides and N output optical waveguides disposed opposite each other at both ends of the slab optical waveguide. and a waveguide, for branching the optical power incident on any one in the input waveguide to the output optical waveguide the N N × N
In the star coupler, each of the input optical waveguide and the output optical waveguide is an optical waveguide.
Core width and core thickness are constant along the waveguide direction of
One, each of said input optical waveguide and the output optical waveguide has a minimum bend the larger radius, star coupler, wherein the core width or the core thickness is small.