JPH06273629A - Optical star coupler - Google Patents

Abstract

PURPOSE:To provide the optical star coupler which uniformly distributes and outputs light coming in both directions with a small loss and a small distribution deviation. CONSTITUTION:The optical star coupler where plural input optical waveguides 1 and plural output optical waveguides 5 are optically coupled and input and output optical waveguides 1 and 5 are connected to a slab optical waveguide 4 to uniformly distribute the optical power inputted to arbitrary one of input optical waveguides 1 to respective output optical waveguides 5 and input and output optical waveguides 1 and 5 are arranged and connected in a fan shape is characterized by providing the connection parts between input and output optical waveguides 1 and 5 and the slab optical waveguide 4 with taper optical waveguide parts 10 and 13 whose core width is increased after being reduced toward the slab optical waveguide 4 like tapers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical star coupler, and more particularly to an optical star that evenly distributes optical power input to an arbitrary optical waveguide among a plurality of input optical waveguides to a plurality of output optical waveguides. Regarding the coupler.

[0002]

2. Description of the Related Art In signal distribution in a large-scale LAN (local area network) system or the like, a plurality (N) of light input to any one of a plurality (N) of input optical waveguides is output. An N × N star coupler is used as an optical component that is uniformly distributed to an optical waveguide.

FIG. 5 is a schematic view of a conventional N × N star coupler.

As shown in FIG. 1, the N × N star coupler has an input optical waveguide array 32 in which N input optical waveguides 30 are arranged in a fan shape, and a fan shape facing the input optical waveguide array 32. Output optical waveguide array 33 composed of N output optical waveguides 31 and both optical waveguide arrays 32, 33
And a slab optical waveguide 34 that propagates light in the direction along the surface.

The input optical waveguide 30 and the output optical waveguide 31 are composed of tapered optical waveguides 35 and 36 whose core width is gradually reduced, curved optical waveguides 37 and 38, and linear optical waveguides 39 and 40 ( Japanese Patent Application No. 4-204508
Issue).

FIG. 6 is an enlarged view of the slab optical waveguide and the tapered optical waveguide of the N × N star coupler shown in FIG.

In the figure, the tapered optical waveguide 35 (or 36) gradually decreases in a tapered shape toward the slab optical waveguide 34, and the connecting portion 4 with the slab optical waveguide 34 is formed.
It becomes the minimum at 1 (42).

The curved optical waveguide 37 (38) has an inflection point 43 (4) in the input optical waveguide 30 (or the output optical waveguide 31).
4), and the central axes are smoothly connected at the inflection point 43 (44) without discontinuity. Further, the tapered optical waveguide 35 (36) and the curved optical waveguide 37 (38)
The central axis is not discontinuous but is smoothly connected also in the connection portion 45 (46) with and the connection portion 47 (48) with the curved optical waveguide 37 (38) and the linear optical waveguide 39 (40).

[0009]

However, in the above-described conventional optical star coupler, the core widths of the input optical waveguide 30 and the output optical waveguide 31 are made gentle in the connecting portion 41 (42) of the slab optical waveguide 34 and its vicinity. Since the taper is reduced, the connecting portion 41 (4
In 2), the optical power mode mismatch between the input optical waveguide 30, the output optical waveguide 31, and the slab optical waveguide 34 is large, and a large coupling loss occurs when the slab optical waveguide 34 is input and output (bidirectionally). Will occur.

Further, the input optical waveguide 30 and the output optical waveguide 3
1 and the connecting portion 41 (4) of the tapered optical waveguide 35 (36)
In 2), since the central axes are connected smoothly without correction, the mode mismatch of the guided light occurs at the connection portion 41 (42), resulting in a large connection loss.

Further, when light is input to the optical waveguide on one end side of the input optical waveguide array 32, the light becomes asymmetrical with respect to the central axis of the tapered optical waveguide, so that in the input optical waveguide array 32. The optical power becomes asymmetrical, which causes a large variation in the output optical power.

Therefore, an object of the present invention is to solve the above problems and to provide an optical star coupler capable of evenly distributing and outputting light from both directions with low loss and low distribution deviation.

[0013]

In order to achieve the above object, the present invention optically couples a plurality of input optical waveguides with a plurality of output optical waveguides and inputs them to any one of the input optical waveguides. In order to evenly distribute the optical power to each output optical waveguide, the input / output optical waveguides are connected by slab optical waveguides, and the input / output optical waveguides are arranged in a fan shape. A tapered optical waveguide whose core width is tapered toward the slab optical waveguide and then expanded in a tapered shape is provided at a connection portion with the optical waveguide.

According to the present invention, the input / output optical waveguide is composed of a tapered optical waveguide, two curved optical waveguides and a straight optical waveguide, and the central axes of the cores are aligned with each other so as to align with the center of light at their respective connecting portions. It is slightly shifted laterally with respect to the traveling direction of light.

[0015]

According to the above construction, since the light input to the input optical waveguide is reduced by the tapered optical waveguide and then expanded and input to the slab optical waveguide, the light propagates radially in the slab optical waveguide. And are uniformly input into each output optical waveguide.
Therefore, the optical coupling state in the input optical waveguide array and the output optical waveguide array can be controlled to the optimum state, and the mode mismatch of the optical power in the connection portion with the slab optical waveguide can be reduced and the efficiency can be improved efficiently. The optical power can be distributed. In addition, the central axes of the cores are transverse to the traveling direction of the light in order to align the center of the light at each connection portion of the tapered optical waveguide, the two curved optical waveguides, and the linear optical waveguide that constitute the input / output optical waveguide. Since there is a step at each connection, a part of the light with a biased optical power is blocked by this step and the optical power always propagates on the central axis of the core. Is prevented from shifting to the left and right, and the variation in branch power is greatly reduced.

[0016]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic view of an embodiment of the optical star coupler of the present invention.

In the figure, the optical star coupler has an input optical waveguide 1, dummy optical waveguides 2, 3, 6, and 7, a slab optical waveguide 4, and an output optical waveguide 5. Each of these optical waveguides 1 to 7 is formed of a core having a thickness t and a refractive index n ₁ , covered with a clad having a refractive index slightly lower than the refractive index of the core, and formed on a substrate (not shown). .

FIG. 2 is an enlarged view near the slab optical waveguide of the optical star coupler shown in FIG.

As shown in the figure, the input optical waveguide 1 and the dummy optical waveguides 2 and 3 are arranged in a fan shape near the slab optical waveguide 4 to form an input optical waveguide array 8. The output optical waveguide 5 and the dummy optical waveguides 6 and 7 are arranged in a fan shape to form an output optical waveguide array 9. The input optical waveguide array 8 and the output optical waveguide array 9 are arranged to face each other and are connected by the slab optical waveguide 4.

The slab optical waveguide 4 is composed of a layered medium having a single-layer or multi-layer structure, and is adapted to propagate light in the direction along the plane, and the input optical waveguide array 8 and the output optical waveguide arranged opposite to each other. In the intermediate portion with the array 9, no light confining structure is provided in the lateral direction with respect to the traveling direction of light.

The input optical waveguide 1 is a tapered optical waveguide portion 1
0, a curved optical waveguide portion 11 and a linear optical waveguide portion 12. Slab optical waveguide 4 and tapered optical waveguide 10
Are connected by a connecting portion 16, the tapered optical waveguide portion 10 and the curved optical waveguide portion 11 are connected by a connecting portion 17, and the curved optical waveguide portion 11 and the linear optical waveguide portion 12 are connected by a connecting portion 18. There is. Similarly, the output optical waveguide 5 also has a tapered optical waveguide portion 13, a curved optical waveguide portion 14, and a linear optical waveguide portion 15.
And are connected by connecting portions 19 to 21, respectively.

The tapered optical waveguide portion 10 of the input optical waveguide 1
Indicates that the core width gradually decreases from the connection portion 17 toward the slab optical waveguide 4 in a taper shape, the core width becomes a minimum in the minimum portion 22, and then gradually increases again in a taper shape. It is connected to the waveguide 4. Similarly, in the tapered optical waveguide portion 13 of the output optical waveguide 5, after the core width gradually decreases from the connection portion 20 toward the slab optical waveguide 4, the core width becomes the minimum at the minimum portion 23, and then the tapered optical waveguide portion 13 gradually becomes tapered again. The number is increased and the connection portion 19 is connected to the slab optical waveguide 4.

The curved optical waveguide portion 11 of the input optical waveguide 1 is
The curved optical waveguides 24 and 25 have different curvature centers, and the curved optical waveguide portion 14 of the output optical waveguide 5 also has two curved optical waveguides 26 and 27 having different curvature centers.

FIG. 3 is an enlarged view of the vicinity of the connecting portion of the curved optical waveguide portion shown in FIG.

As shown in FIG.
The central axes of the two curved optical waveguides 24 and 25 are connected in such a manner that they are slightly deviated from each other in the lateral direction with respect to the traveling direction of light by a predetermined amount. Similarly, the two curved optical waveguides 2 of the curved optical waveguide unit 14 are
The central axes of the reference numerals 6 and 27 are also slightly displaced from each other, and are connected by the connecting portion 29 (see FIG. 1). In addition, the tapered optical waveguide unit 10
Connection part 17 between (13) and curved optical waveguide part 11 (14)
(20), also in the connecting portion 18 (21) of the curved optical waveguide portion 11 (14) and the straight optical waveguide portion 12 (15), the central axis of the optical waveguide is laterally smaller than the traveling direction of light by a predetermined amount. It is connected in the wrong position.

Next, the operation of the embodiment will be described.

The core width of the input optical waveguide 1 and the core width of the output optical waveguide 5 are respectively the connecting portion 1 with the slab optical waveguide 4.
Since the light is gradually tapered toward the slab optical waveguide 4 at 7 and 20 and in the vicinity of the slab optical waveguide 4 and then expanded to the gentle tapered shape again, the light input from the tapered optical waveguide portion 10 into the slab optical waveguide 4 is reduced. The power propagates radially and is uniformly input to each output optical waveguide 5, and the input optical waveguide array 8
Also, the optical coupling state in the output optical waveguide array 9 can be controlled to an optimum state, and the mode mismatch of the optical power in the connecting portions 16 and 19 with the slab optical waveguide 4 is reduced, so that the optical power can be efficiently output. Can be distributed.

The input optical waveguide 1 comprises a tapered optical waveguide portion 10, a curved optical waveguide portion 11 and a linear optical waveguide portion 12, and the output optical waveguide 5 comprises a tapered optical waveguide portion 13, a curved optical waveguide portion 14 and a straight line. The optical waveguide portion 15 is formed, and the central axes of the cores of the connecting portions 17 to 21 are slightly deviated from each other in the lateral direction with respect to the traveling direction of light. Occurs. When optical power that is asymmetric with respect to the central axis of the tapered optical waveguide unit 10 is input, a part of the power of the light that is biased by the step generated in each of the connection units 17 to 21 is blocked, and the optical power is always the center of the core. The optical power is prevented from shifting on the axis and the optical power is prevented from shifting to the left and right, and the dispersion of the branch power is greatly reduced.

The above-described optical star coupler has been described in the case where the light is input through the input optical waveguide 1 and output through the output optical waveguide 5, but the present invention is not limited to this, and the light is output through the output optical waveguide 5. It goes without saying that it may be inputted and outputted from the input optical waveguide 1.

Next, the optical star coupler of the present embodiment will be described with reference to numerical values, but the present invention is not limited to this.

In FIG. 2, N _array represents the total number of waveguides including the dummy optical waveguides 2, 3 (or 6, 7) in the input optical waveguide array 8 (or the output optical waveguide array 9), and O ₁ is a fan shape. Represents the center of curvature of the input optical waveguide array 8 and the O ₂ represents the center of curvature of the output optical waveguide array 9 arranged in a fan shape. Lc is the center of curvature O ₁ O
₂ represents the distance between the _two , R ₁ represents the radius of curvature of the fan-shaped optical waveguide array, and θ represents the spread angle of the fan-shaped optical waveguide array.

Input optical waveguide 1 (or output optical waveguide 5)
In the above, w ₀ represents the core width of the linear optical waveguide portion 12 (15) and the curved optical waveguide portion 11 (14), and w ₁ is the core width of the minimum portion 22 (23) of the core width of the tapered optical waveguide portion 10. , W ₂ are the tapered optical waveguide portion 10 in the connecting portion 16 between the tapered optical waveguide portion 10 and the slab optical waveguide 4.
Represents the core width of.

In FIG. 3, d ₁ is the central axis of the core of the curved optical waveguide and the central axis of the core of the curved optical waveguide in the connecting portion 28 of the two curved optical waveguides constituting the curved optical waveguide portion 11 of the input optical waveguide 1. Represents the amount of deviation from. Similarly,
d ₂ represents the amount of deviation of the central axes of both cores at the connecting portion 17 between the tapered optical waveguide portion 10 and the curved optical waveguide portion 11,
d ₃ represents the amount of deviation from the central axes of both cores at the connecting portion 18 between the curved optical waveguide portion 11 and the linear optical waveguide portion 12.

The beam propagation method was used to design the optical star coupler (see MD Feit et al. “Light prop-agation in grade
d-index optical fiber '', Appl.Opt., Vol.17, no.24, pp
3990-3998 (1978)).

Here, the input power P _in of the optical star coupler of the order 16 and the nth output optical waveguide (n = 1 to 16)
The relationship with the (branch) output power P _{out · n of}

[0037]

[Equation 1]

The parameter of the optical star coupler is N
_array = 26 (5 dummy optical waveguides on each side), distance Lc = 4100 μm, radius of curvature R ₁ = 3150 μm, thickness t = 8 μm, core width w ₀ = 8 μm, w ₁ = 8 μm,
w ₂ = 5 μm, w ₃ = 11 μm, spread angle θ = 0.08
7 rad, each deviation amount d ₁ = 0.4 μm, d ₂ = 0.
2 μm, d ₃ = 0.2 μm, relative refractive index difference Δ between core and clad Δ = 0.3%, and light wavelength λ = 1.55 μm, the characteristics shown in FIG. 4 were obtained. .

FIG. 4 is a diagram showing the relationship between the input optical waveguide (input port) and its (branch) output power of the optical star coupler of order 16, where the horizontal axis represents the input port and the vertical axis represents the output power. Shows.

From the figure, it can be seen that at the wavelength of 1.55 μm, the input optical power is uniform and efficiently branched.

As described above, according to the present embodiment, since the light input to the input optical waveguide is reduced by the tapered optical waveguide and then expanded and input to the slab optical waveguide, the light is radiated into the slab optical waveguide. And is uniformly input into each output optical waveguide. Therefore, the optical coupling state in the input optical waveguide array and the output optical waveguide array can be controlled to the optimum state, and the mode mismatch of the optical power in the connection portion with the slab optical waveguide can be reduced and the efficiency can be improved efficiently. Optical power can be branched. In addition, the central axes of the cores are transverse to the traveling direction of the light in order to align with the center of the light at each connection portion of the tapered optical waveguide, the two curved optical waveguides, and the linear optical waveguide that constitute the input / output optical waveguide. Since there is a slight step at each connection, a step is created at each connection, and part of the light with a biased optical power is blocked by this step, and the optical power always propagates on the central axis of the core. Is prevented from shifting to the left and right, and the variation in branch power is greatly reduced. Therefore, it is possible to realize an optical star coupler capable of evenly distributing and outputting light from both directions with low loss and low distribution deviation.

[0042]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) It is possible to realize an optical star coupler capable of evenly distributing and outputting bidirectional light with low loss and low distribution deviation.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of an optical star coupler of the present invention.

FIG. 2 is an enlarged view of the vicinity of a slab optical waveguide of the optical star coupler shown in FIG.

FIG. 3 is an enlarged view of the vicinity of a connection portion of the curved optical waveguide section shown in FIG.

FIG. 4 is a diagram showing a relationship between an input optical waveguide (input port) and its (branch) output power of an optical star coupler of order 16.

FIG. 5 is a schematic view of a conventional N × N star coupler.

6 is an enlarged view of the slab optical waveguide and tapered optical waveguide of the N × N star coupler shown in FIG.

[Explanation of symbols]

 1 Input Optical Waveguide 4 Slab Optical Waveguide 5 Output Optical Waveguide 10, 13 Tapered Optical Waveguide Section 16, 19 Connection Section

Claims (2)

[Claims] 1. A method for optically coupling a plurality of input optical waveguides and a plurality of output optical waveguides, and for equally distributing the optical power input to any one of the input optical waveguides to each of the output optical waveguides. In the optical star coupler in which the input / output optical waveguides are connected by slab optical waveguides, and the input / output optical waveguides are arranged and connected in a fan shape, the core width of the input / output optical waveguides is connected to the slab optical waveguides. Is provided with a tapered optical waveguide portion which is tapered toward the slab optical waveguide and then expanded in a tapered shape. 2. The input / output optical waveguide comprises a tapered optical waveguide portion, two curved optical waveguides and a linear optical waveguide, and the central axes of the cores are arranged so that the central axes of the cores are aligned with each other at their connecting portions. The optical star coupler according to claim 1, wherein the optical star coupler is slightly displaced laterally with respect to the traveling direction of the optical star coupler.