JPH04204508A - Tapered star coupler - Google Patents

Abstract

PURPOSE:To obtain a star coupler which is suitable for large-scale use and with which light can be uniformly distributed by contracting each core width of the input and output light guide passages in a gentle tapered form in a joint part between the input or output light guide passage and a slab light guide passage and in the vicinity. CONSTITUTION:Since the light inputted into an arbitrary input light guide passage 1 is not confined in the lateral direction with respect to the light advance direction in a slab light guide passage 4, the light spreads in the lateral direction. Since an input light guide passage array 8 and an output light guide passage array 9 arrange the guide passage in a sector form, the spread light is uniformly branched into an output light guide passage 5. In particular, at the joint part between the input light guide passage 1 or the output light guide passage 5 and a slab light guide passage 4 and in the vicinity, when each core width of the input light guide passage 1 and the output light guide passage 5 gently contracts in a tapered form, the light joint state between the guide passages can be controlled to an optimum state, and the uniformity of the light branching ratio can be improved, and the excessive loss can be reduced favorably. Accordingly, a star coupler which is suitable for a large-scale use can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to large-capacity LAN (Local Aero
This invention relates to an NXN star coupler, which is an essential optical component for optical signal distribution in network systems, optical switching systems, and the like.

<Prior art> Conventionally, an NXN star coupler that uniformly branches the optical power incident on any one of N input optical waveguides to N output optical waveguides has the structure shown in Fig. 6. It has been known. The star coupler shown in the figure is of N28. That is, it has eight input optical waveguides 11 and eight output optical waveguides 12, and from these input optical waveguides 11 to output optical waveguides 12, there is a 3 dB directional coupler 1.
They are connected in three stages via 3.

Therefore, the optical power incident on any one of the eight input optical waveguides 11 is divided stepwise and equally into 1/2.1/4.1/8 by the 3 dB directional coupler 13. It is branched into all eight output optical waveguides 12. Therefore, in this example, twelve 3 dB directional couplers 13 are required.

<Problems to be Solved by the Invention> In the star coupler of the conventional structure described above, although it is possible to equally split the optical power incident on any input optical waveguide 1 to a plurality of output optical waveguides 12, the following equation There is a problem in that a large number of 3 dB directional couplers 13 are required as shown in FIG.

M = (N / 2) A o g 2N...
-(1) However, M is the number of necessary 3clB directional couplers 13.

For example, in the case of a large-capacity LAN system with N=128, the number will be an enormous number of M=448.

Therefore, not only does the size of the star coupler become very large, but also the production yield is poor and it becomes expensive.

The present invention has been made in view of the above-mentioned prior art,
By reducing the core width of the input and output optical waveguides to a gentle taper at and near the junction between the input or output optical waveguide and the slab optical waveguide, it is suitable for large scale applications where light can be distributed uniformly. The purpose of the present invention is to provide a star coupler that has the following characteristics.

<Means for Solving the Problems> The configuration of the present invention to achieve the above object uniformly branches the optical power incident on any one of one or more input optical waveguides to two or more output optical waveguides. In the star coupler, an input optical waveguide array in which the input optical waveguides are arranged in a fan shape and an output optical waveguide array in which the output optical waveguides are arranged in a fan shape are installed facing each other, and the input optical waveguide The array and the output optical waveguide array are laterally coupled by a slab guided waveguide having no optical confinement structure, and the input optical waveguide is connected to the input optical waveguide or at the junction between the output optical waveguide and the slab guided waveguide and in the vicinity thereof. A feature is that the core widths of the optical waveguide and the output optical waveguide are reduced in a gentle taper shape.

<Operation> The light incident on any input optical waveguide is not confined in the transverse direction with respect to the traveling direction of the light in the slab optical waveguide, and therefore spreads in the transverse direction. Since the waveguides of the input optical waveguide array and the output optical waveguide array are arranged in a fan shape, the spread light is uniformly branched to the output optical waveguide.

In particular, when the core widths of the input optical waveguide and the output optical waveguide are reduced to a gentle taper at and near the junction between the input optical waveguide or the output optical waveguide and the slab optical waveguide, the optical coupling state between the waveguides is optimized. Since it can be controlled to
This is suitable for improving the uniformity of the light branching ratio and reducing excessive loss.

<Examples> The present invention will be described in detail below with reference to examples shown in the drawings.

FIG. 1 shows an embodiment of the present invention. This embodiment relates to an NXN star coupler.

That is, as shown in the figure, the star coupler of this embodiment is
It has an input optical waveguide 1, dummy waveguides 2 and 3, a slab optical waveguide 4, an output optical waveguide 5, and dummy waveguides 6 and 7. The input optical waveguide 1 has a core having a refractive index n1 and a core having a refractive index n1.

The width of the core is 2a and the thickness is 2t.
are usually designed to be equal. The output optical waveguide 5 and the dummy waveguides 2, 3, 6.7 also have the same configuration as the input optical waveguide 1.

The input optical waveguide 1 and dummy waveguides 2 and 3 are arranged in a fan shape to form an input optical waveguide array 8, and the output optical waveguide 5 and dummy waveguides 6 and 7 are also arranged in a fan shape to form an output optical waveguide array. The input optical waveguide array 8 and the output optical waveguide array 9 are arranged to face each other,
They are coupled via a slab leading waveguide 4. As shown in an enlarged view of FIG. 2, the slab leading waveguide 4 is located at an intermediate portion between an input waveguide array and an output waveguide array that are arranged in a fan shape facing each other, and is transverse to the direction of light propagation. It does not have an optical confinement structure in the direction. In the joint portions of the input optical waveguide 1, the output optical waveguide 5, and the slab optical waveguide 4, and in the vicinity thereof, the core widths of the input optical waveguide 4 and the output optical waveguide 5 are reduced in a gentle taper shape. In FIG. 2, N , , a is the input optical waveguide array 8 (
or the dummy waveguide 2 in the output optical waveguide array 9),
3 (or 6°7), 0 is the center of curvature of the input optical waveguide array 8 arranged in a fan shape, O' is the center of curvature of the output optical waveguide array 9 arranged in a fan shape, and Lo is the center of curvature of the output optical waveguide array 9 arranged in a fan shape. The distance between the centers of curvature 00', RS is the radius of curvature when N a + r a optical waveguides are lined up without any gaps, (Rs
1q+) is the radius of curvature of the actual fan-shaped optical waveguide array. Here, qI≧0. Note that R3 is the radius of curvature when waveguides of uniform width are arranged in a fan shape without gaps.

The tapered star coupler was designed using the beam propagation method (M, D, Felt et al., Light
propagation in graded-ind.
ex opticalf 1bers”, Appl,
Opt, Vol. 17. no, 24.
pp. 3990-3998 (1978). Figure 3 shows the simulation results of light propagation for a star coupler of order N = 8. The parameters of the star coupler are N, . (3 each), L c” 1690 μm, R5 ~ 890 μm
m, qI=390μm, Ys=870μm,
The wavelength of light λ=1.55 μm. FIG. 3(a) shows that when light is incident on the center input optical waveguide l (seventh from the left), and FIG. 3(b) shows that the leftmost input optical waveguide 1
This is the light propagation intensity distribution when the light is incident (fourth from the left). As shown in the figure, light input from an arbitrary input optical waveguide 1 spreads laterally in the slab optical waveguide 4 and is evenly dispersed, regardless of the position of the incident light.
It can be seen that the optical power is uniformly branched to the eight output optical waveguides 5.

FIG. 4 shows the simulation results of FIG. 3 as optical propagation waveforms. Figure (a) shows when light is incident on the central input optical waveguide (seventh from the left), and Figure (b) shows the leftmost input optical waveguide (fourth from the left). This is the propagation waveform of light when light is incident on .

Looking at the optical waveform at the boundary between the input optical waveguide array 8 and the slab optical waveguide 4, the light is coupled to several adjacent waveguides, and this side lobe is coupled between the slab optical waveguide 4 and the output optical waveguide array 9. It is confirmed that the boundaries between the two areas are extremely important in achieving an even distribution of light.

Therefore, in the present invention, in order to effectively utilize this side lobe, the input waveguide array 8 and the output waveguide array 9, which are arranged opposite to each other on both sides of the slab optical waveguide 4, are not only formed in a fan shape, but also The core widths of the input optical waveguide 5 and the output optical waveguide 6 are formed into a gentle taper shape.

Furthermore, with respect to the input optical waveguide l at the left end (or right end), a dummy waveguide 2 (or It turns out that it is necessary to provide 3).

Based on the computer simulation of the star coupler described above, a tapered star coupler was fabricated using a quartz optical waveguide.

First, an 8102 lower cladding layer was deposited on the Si substrate by flame deposition method, and then TlO2 or G e O2
SiO added as a dopant.

A core layer of glass was deposited, followed by clear vitrification in an electric=8=furnace. Next, the core layer was etched using a mask pattern prepared based on computer simulation to form a predetermined input/output waveguide array and slab optical waveguide region, and finally a SiO□ upper clutter layer was deposited.

Figure 5 shows N=8, Δ=0.3%, 2a=7μmL
c=1690μm, R,=890μm, q+=39
0 μm, N.

22. This figure shows the results of measuring the optical branching characteristics of the star coupler Ar14 (three dummy waveguides on each side) using light with a wavelength of λ-1 and 55 μm. The horizontal axis is the light incident position m to the array leading waveguide, and since there are three dummy waveguides on each side, m=4 to 11. The vertical axis is
Normalized branch output P. As shown in the equation below, the input power is Plゎ, and the output power of the n-th output waveguide (n-4 to 11) is Po. 1o.

As is clear from this figure, the wavelength is 1.3 μm to 1.55 μm.
It can be confirmed that it is possible to realize a tapered star coupler with a substantially constant light distribution over a wide wavelength range of μm. Note that when P = 1 (for all n), a uniform light distribution with an upper insertion loss can be obtained.

From these Figures 3 and 4, the design of the tapered star coupler by computer simulation (Figures 5 to 7)
The validity of the figures and equations (4) to (7)) was confirmed.

<Effects of the Invention> As explained above in detail based on the embodiments, the star coupler of the present invention can uniformly branch into any single waveguide, and the branching ratio of optical power can be uniformly branched regardless of the wavelength. Since it is substantially constant, it has a great advantage in signal distribution in large-scale LAN systems, wavelength multiplexing systems, etc. In addition, the core widths of the input and output optical waveguides are reduced in a tapered manner at the junction with the slab optical waveguide and in the vicinity thereof, so the optical coupling state between the arrayed waveguides can be optimally controlled and the optical branching ratio This is effective for improving uniformity and reducing excess loss.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a tapered star coupler according to an embodiment of the present invention, FIG. 2 is an enlarged view of a slab optical waveguide, and FIG.
Figures (a) and (b) are explanatory diagrams showing the simulation results of light propagation by changing the incident position for a star coupler with N = 8, respectively, and Figure 4 (a) (bl is each with N = 8
An explanatory diagram showing the simulation results of the optical propagation waveform with different incident positions for the star coupler, 5th V is N=
8, △=0.3%, 2a=7μm, Lc=16
90 μm SR, = 890 μm, q + = 390 μm,
N, , , , = 14 (3 dummy waveguides each on the left and right
The optical branching characteristics of the star coupler of
A graph showing the results of measurement using μm light and FIG. 6 are explanatory diagrams showing the structure of a conventional NXN star coupler. In the drawing, 1.11 is an input optical waveguide, 2.3, 6.7 are dummy waveguides, 4 is a slab guiding waveguide, 5.12 is an output optical waveguide, - I I = 8 is an input optical waveguide array, 9 is an input optical waveguide Output optical waveguide array 13 is a 3 dB directional coupler.

Claims (1)

[Claims] In a star coupler that uniformly branches optical power incident on any one of one or more input optical waveguides into two or more output optical waveguides, the input optical waveguide array is formed by arranging the input optical waveguides in a fan shape. and an output optical waveguide array formed by arranging the output optical waveguides in a fan shape, are installed facing each other, and the input optical waveguide array and the output optical waveguide array are arranged in a slab having no optical confinement structure in the lateral direction. The input optical waveguide and the output optical waveguide are coupled by an optical waveguide, and the core widths of the input optical waveguide and the output optical waveguide are reduced in a gentle taper shape at and in the vicinity of the joint between the input optical waveguide or the output optical waveguide and the slab optical waveguide. Tapered star coupler.