JPH0682847A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To obtain the optical switch which has small crosstalk without requiring high machining precision. CONSTITUTION:Input terminals 21 and 31 of 2nd and 3rd optical switches 20 and 30 are connected to two output terminals 13 and 14 of a 1st optical switch 10. Then when signal light which is made incident from an input terminal 11 is projected from an output terminal 32, the optical switches 10, 20, and 30 are switched and controlled into a cross state, a through state, and a cross state respectively; and then leak light projected to the output terminal 13 by the optical switch 10 is scattered by the optical switch 20 without being outputted to an output terminal 22 and signal light which is projected by the optical switch 10 to the output terminal 14 is outputted by the optical switch 30 to the output terminal 21 as it is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch used in an optical communication system and an optical switching system, and more particularly to a waveguide type optical switch having good crosstalk characteristics.

[0002]

2. Description of the Related Art A typical example of a conventional waveguide type optical switch of this type is, for example, a directional coupler type disclosed in "Optical Integrated Circuit" by Hiroshi Nishihara et al. (Ohm Co., p.304). There is a switch.

FIG. 2 shows the most basic structure of the switch, which includes two optical waveguides 1 and 2 arranged close to each other.
It is composed of electrodes 3 and 4 provided to change the propagation state of light propagating through the optical waveguides 1 and 2 through the electro-optic effect of the waveguide medium by an applied voltage.

In the directional coupler type switch, in order that the light input to the optical waveguide 1 is completely transferred to the optical waveguide 2, the element length l of the coupler is a complete coupling length L, that is, an integer of L = π / 2X. It is necessary to satisfy the condition of being doubled, where X (= (β _e −β _o ) / 2) is the propagation constant difference between the even and odd modes of the optical waveguide.

When a voltage is applied to such a directional coupler type switch, the propagation constant of the optical waveguide to which the voltage is applied changes, resulting in a propagation constant difference Δβ, that is, Δβ = β _A -β _B. Where β _A is the propagation constant of the optical waveguide 1, β _B
Is the propagation constant of the optical waveguide 2.

The propagation constant difference Δβ determines whether the input light travels from the optical waveguide 1 to the optical waveguide 2 (cross state) or proceeds as it is (through state) to perform switching. In an actual switch, the electrode 3 is used. , 4 controls the difference in the propagation constants.

FIG. 3 illustrates the conditions of the switching operation in the above-mentioned directional coupler type switch. In the figure, the vertical axis represents the element length l expressed as a ratio to the complete coupling length L,
The horizontal axis is the propagation constant difference Δβ expressed by multiplying the element length 1 and dividing by π.

In FIG. 3, "x" indicates a cross state,
“=” Indicates the locus of the through state, and 5 indicates the locus of the through state. In order to output the light input to the optical waveguide 1 from the same optical waveguide 1 (through state), the propagation constant difference Δβ, that is, the voltage applied to the electrodes. Should be adjusted. On the contrary,
In order for the light input to the optical waveguide 1 to be output from the optical waveguide 2 (cross state), the element length 1 is previously set to the complete coupling length L.
Must be set to an integer multiple of. If the element length l is deviated from an integral multiple of the complete coupling length L, the light transfer is not completely performed, and leaked light remains in one optical waveguide to deteriorate the crosstalk characteristics.

[0009]

However, in the production of an actual optical switch, the element length l is changed to the complete coupling length L.
Is difficult to process to an integral multiple of, and its crosstalk becomes a problem. In particular, in a directional coupler type switch using a semiconductor, the width and interval of the optical waveguide are 2 μm due to the single mode condition of guided light determined by the refractive index of the semiconductor.
However, there is a problem in that it is difficult to secure the processing accuracy and only about -10 dB to -15 dB can be realized as crosstalk.

In view of the above-mentioned conventional problems, it is an object of the present invention to realize an optical switch with less crosstalk without requiring high processing accuracy.

[0011]

FIG. 1 shows an outline of a waveguide type optical switch of the present invention, in which 10, 20, 3 are shown.
Reference numeral 0 denotes an optical switch, which has two optical waveguides 10a, 10b, 20a, 20b, 30a, and 30b, respectively, and which propagates in the optical waveguide by controlling the propagation state of light in the optical waveguide. The optical path of is switched.

The optical switch 10 includes optical waveguides 10a and 10a.
It is provided with two input terminals 11 and 12 formed at one end of b and two output terminals 13 and 14 formed at the other ends of the optical waveguides 10a and 10b. Also, the optical switch 20
Is composed of one end of the optical waveguide 20b and is the optical switch 10
One input terminal 21 connected to one output terminal 13
And one output terminal 22 formed at one end of the optical waveguide 20a. Further, the optical switch 30 includes one input terminal 31 configured at one end of the optical waveguide 30a and connected to the other output terminal 14 of the optical switch 10, and one output terminal 32 configured at one end of the optical waveguide 30b. Is equipped with.

Here, the optical paths in the optical switches 10, 20, 30 are set so that the light inputted from the input terminal 11 in the optical switch 10 is outputted to the output terminal 13, that is, when the optical switch 20 is switched to the through state. In the optical switch 30, the light input from the input terminal 21 is output from the output terminal 22, that is, in the cross state, and the light input from the input terminal 31 in the optical switch 30 is not output to the output terminal 32, that is, in the through state. When the light input from the input terminal 11 of the optical switch 10 is output to the output terminal 14, that is, when the cross state is switched, the input terminal 2 of the optical switch 20 is switched.
Switching control is performed so that the light input from the optical switch 1 is not output from the output terminal 22, that is, in the through state, and the light input from the input terminal 31 in the optical switch 30 is output to the output terminal 32, that is, in the cross state. I came to do it.

[0014]

By using the optical switch of the present invention, the crosstalk characteristic of the switch can be improved.

For example, by inputting the signal light having the power P1 to one input terminal 11 of the optical switch 10 and switching the signal light, the signal light having the power P1 'is output to the output terminal 14 and to the output terminal 13. It is assumed that the leaked light of power P2 'is output. At this time, if the signal transmissibility α = P1 ′ / P1 crosstalk transmissivity γ = P2 ′ / P1, the switch performance when this optical switch is used alone is as follows: Crosstalk (Cross) alone = 10log (P1 / P
2 ') =-10 logγ extinction ratio (S / N) simple substance = 10 log (P1' / P2 ') = 10 l
It becomes og (α / γ).

On the other hand, two output terminals 1 of the optical switch 10
When the two optical switches 20 and 30 are connected to 3 and 14, respectively, as described above, the input light power P1
Respect, the power P1 of the signal light output from the optical switch 30 "P1arufa ^2, power P2 of the leakage light output from the optical switch 20 'becomes P1γ ^2. Therefore, cross-talk (Cross) = 10log (P1 / P1γ 2)
= 2 × (Cross) alone extinction ratio (S / N) = 10log ( P1α 2 / P1γ 2) = 2 ×
(S / N) is a single unit, and in each case, it is possible to improve the performance by a factor of two.
Therefore, if the optical switch requires a crosstalk of -20 dB, the performance of each optical switch constituting the optical switch is -10.
dB is sufficient.

[0017]

FIG. 4 shows a first embodiment of a waveguide type optical switch according to the present invention. In the figure, reference numeral 41 denotes a first optical switch, which is a directivity composed of two adjacent optical waveguides. It is a combiner. Reference numerals 42 and 43 denote second and third optical switches, which are directional couplers in which the output waveguide of the optical switch 41 is an optical waveguide on one side. In this embodiment, the output waveguide is terminated, and the light propagating through this optical waveguide is finally dissipated. The other optical waveguide is an optical waveguide connected to the output end, and the light transferred to this optical waveguide is emitted from the switch. Each directional coupler is processed to a size close to the complete coupling length, and in a voltage-off state, light is in a cross state in which it is transferred to an adjacent optical waveguide.

In the waveguide type optical switch, the input A
When the signal light entering from the output B is emitted from the output B, the optical switch 41 may be in a voltage-OFF cross state, the optical switch 42 may be in a voltage-ON through state, and the optical switch 43 may be in a voltage-OFF cross state. At this time, the power of the signal light output from the output B is P1 with respect to the signal light of power P1.
The power of the light leaked from α ² and the output A is P ¹ γ ² , and the crosstalk twice as much as the single switch can be obtained.

On the other hand, the signal light incident from the input A is output A
For more emission, the optical switch 41 may be in a voltage-on through state, the optical switch 42 may be in a voltage-off cross state, and the optical switch 43 may be in a voltage-on through state.

FIG. 5 shows a second embodiment of the waveguide type optical switch of the present invention.
In the figure, reference numeral 51 denotes a first optical switch, which is a directional coupler composed of two optical waveguides arranged close to each other. Further, 52 and 53 are second and third optical switches, which are directional couplers in which the output waveguide of the optical switch 51 is a waveguide on one side. The other optical waveguide is a dummy waveguide that is not connected to other elements, and the light propagating through this optical waveguide is radiated from the end face and dissipated. Each directional coupler is processed to a size close to the complete coupling length, and in a voltage-off state, light is in a cross state in which it is transferred to an adjacent optical waveguide.

In the waveguide type optical switch, the input A
When the signal light entering from the output B is emitted from the output B, the optical switch 51 may be in the voltage-OFF cross state, the optical switch 52 may be in the voltage-OFF cross state, and the optical switch 53 may be in the voltage-ON through state. At this time, the power of the signal light output from the output B is P1 with respect to the signal light of power P1.
The power of the light leaked from α ² and the output A is P ¹ γ ² , and the crosstalk twice as much as the single switch can be obtained. Other switching states can be easily realized by controlling the cross state and the through state of each directional coupler.

The present optical switch may be composed of a switch other than the directional coupler, such as a Mach-Zehnder interferometer or a Y-branch switch. Furthermore, it can be applied not only as a 2 × 2 switch but also as a constituent element of an N × N large-scale optical switch.

FIG. 6 shows a third embodiment of the waveguide type optical switch of the present invention.
In this example, a 4 × 4 scale optical switch network including the optical switch described in the first or second embodiment as a constituent element is shown. In the figure, 60-1 to 60-12 are the waveguide optical switches described in the first or second embodiment, and
Reference numerals 70-1 to 70-4 are ordinary single 2 × 2 switches.

This switch network is a construction method called a Dilated Benes network. In this case, the extinction ratio (S / N) 4 × 4 of the signal light output from the final stage is approximately (S / N). 4 × 4 = 2 {(S / N) simple substance + 10logα}
-4.8-20log γ where α is the power transfer rate of the single switch composing this switch, and γ is the crosstalk transmissivity of the single switch composing this switch.

Crosstalk of a single switch is -10d
Assuming B and the power transfer rate to be 50%, an extinction ratio of (S / N) 4 × 4 = 35.2 dB is obtained. Since it is 15.2 dB when it is configured with only a single switch, it is possible to improve it by 20 dB by adopting the optical switch of the present invention. Needless to say, this improvement effect is effective not only in the 4 × 4 switch but also in a larger-scale switch network.

[0026]

As described above, according to the present invention, the leakage light due to the switching failure in the first optical switch is removed by the second and third optical switches in the subsequent stage,
Crosstalk can be improved. That is, when all the optical switches are composed of the optical switches having the same characteristics, the crosstalk and the extinction ratio are twice as high as those of the single element. Therefore, according to the optical switch of the present invention, highly precise microfabrication for adjusting to the complete coupling length is reduced, and it is particularly effective for manufacturing an optical switch using a semiconductor material, which has a small waveguide dimension of about 2 μm. .

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a waveguide type optical switch of the present invention.

FIG. 2 is a configuration diagram showing an example of a conventional directional coupler switch.

FIG. 3 is an explanatory diagram of a switching operation in the directional coupler type switch of FIG.

FIG. 4 is a configuration diagram showing a first embodiment of a waveguide type optical switch of the present invention.

FIG. 5 is a configuration diagram showing a second embodiment of the waveguide type optical switch of the present invention.

FIG. 6 is a configuration diagram showing a third embodiment of the waveguide type optical switch of the present invention.

[Explanation of symbols]

10, 41, 51 ... First optical switch, 20, 42, 5
2 ... 2nd optical switch, 30, 43, 53 ... 3rd optical switch.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Hiroaki Takeuchi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Mitsuaki Yanagibashi 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (72) Inventor Naoto Yoshimoto 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (72) Masaki Shintoku 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corp. (72) Inventor Satoshi Sekine 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (1)

[Claims] 1. At least two optical waveguides are provided, and the optical path of light propagating in the optical waveguides is switched by controlling the propagation state of light in the optical waveguides.
The first optical switch includes at least one input terminal and two output terminals, which are formed at both ends of one optical waveguide and one end of the other optical waveguide, and the second optical switch is 1 composed of one end of an optical waveguide and connected to one output terminal of the first optical switch 1
One input terminal and one output terminal configured at the other end of the one optical waveguide or at one end of the other optical waveguide, and the third optical switch is configured at one end of the one optical waveguide and 1 connected to the other output terminal of the optical switch 1
One input terminal and one output terminal configured at the other end of the one optical waveguide or one end of the other optical waveguide, and the optical path in the first optical switch is one When the output path is switched to the output terminal of the second optical switch, the optical path in the second optical switch is changed so that the light input from the input terminal is output from the output terminal, and the optical path in the third optical switch is input to the optical path. When the light input from the terminal is switched so as not to be output to the output terminal, and the light path in the first optical switch is switched to output the light input from the input terminal to the other output terminal, the second In the optical path of the optical switch, the light input from its input terminal is not output from the output terminal,
Further, the waveguide type optical switch is characterized in that the optical path of the third optical switch is controlled so that the light inputted from the input terminal is outputted to the output terminal.