JP2000019569A - Optical circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical circuit capable of regulating the power of optical channels at need by decreasing inter-channel crosstalks. SOLUTION: Optical switches (gates) 3 to 6 of one input one output capable of varying transmittance are disposed between the switches 1, 2 (first stage) and switches 7, 8 (third stage) of matrix optical switches composed of a tree structure network. As a result, the transmittance of the gates may be varied, by which the inter-channel crosstalks may be decreased and the regulation of the power of the optical channels is made possible at need.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit, and more particularly to a waveguide type optical circuit which controls switching of an optical path using an optical waveguide provided in a substrate.

[0002]

2. Description of the Related Art In recent years, as optical communication systems have been put into practical use, optical communication systems having higher capacity and higher functions have been desired. In particular, in order to operate many optical transmission lines more stably and efficiently, it is necessary to appropriately reconfigure the optical transmission lines in response to a failure of the transmission line or traffic. Also, it has become necessary to reconfigure the optical path in the optical transmission apparatus in response to a failure of the optical device or the like.

In order to meet these requirements, for example, an optical switch using a diffusion type optical waveguide in which an electro-optic crystal typified by lithium niobate (LN) is doped with titanium or the like from the substrate surface by thermal diffusion is used. Have been reported.

[0004] This optical switch is described in "Large-scale waveguide type optical matrix switch" [Hideaki Okayama, Masato Kawahara,
Technical techniques, TECHNICAL REPORT OF
TEICE SSE94-214, OCS94-95
(1995-02), pp67-72], or "St.
movies on a 128-Line Photo
nic Space-Division Switch
ing Network Using LiNbO ₃
Switch Matrices and Optic
al Amplifiers "(C. Burke, M .;
Fujiwara, M .; Yamaguchi, H .; Ni
Shimoto, H .; Honmon, OSA Proc
eating on photonic switch
ing, 1991, Vol. 8, pp2-6).

A matrix optical switch in which these optical switches are integrated is described in "Polarizati."
on Independent-DC Drift F
ree Ti: LiNbO ₃ 4x4 Matrix
Optical Switch "[Y. Nakabay
ashi, J .; Ushioda, M .; Kitamur
a, 2nd Optoelectronics Com
communicationsConference (OEC
C'97) Technical Digest, Jul
y 1997, Seoul, KOREA, 9C5-3.
pp 202-203].

There is also a matrix optical switch that utilizes a change in the refractive index of an optical waveguide caused by a thermo-optic effect using a heater provided in a part of a quartz or polymer optical waveguide. About this optical switch, “DC-drift
Free Polarization independence
dent Ti: LiNbO ₃ 8x8 Optica
l Matrix Switch "[Y. Nakaba
yashi, M .; Kitamura, T, Sawan
o, 22nd European Conference
e on Optical Communicatio
n-ECOC '96, Oslo, ThD. 2.4,4.
157-4.160].

Here, a single element having an optical path switching function is called an optical switch, and a device or an optical circuit that enables more input / multiple output path switching by combining a plurality of optical switches is a matrix. The combination of the optical switches in the matrix optical switch is called an optical switch, and the network is called a network.

[0008]

In the matrix optical switch used for the conventional transmission path switching described above, it is required to reduce the amount of crosstalk to approximately -40 dB or less in order to ensure transmission quality.

Also, when a matrix optical switch is used for path switching within the apparatus, it is desirable that the amount of crosstalk be as small as possible. However, it is difficult for many of the optical switches reported so far to satisfy such a low crosstalk amount as the performance of the optical switch itself.

Further, EDFA (Erbium Dop)
It is known that in a multi-wavelength communication system or the like using an ed Fiber Amplifier, the optical power of each wavelength channel becomes non-uniform due to the wavelength dependence of the optical amplification factor of the EDFA, which limits the transmission distance. Have been. Therefore, a relay device in a multi-wavelength communication system or the like using an EDFA is required to have a function of eliminating optical power non-uniformity between wavelength channels.

A matrix optical switch for reconfiguring an optical transmission line is generally incorporated in a repeater of a multi-wavelength communication system. Therefore, the matrix optical switch itself has a function of adjusting the power of each optical channel. This is also desirable from the viewpoint of miniaturization of the relay device.

Accordingly, an object of the present invention is to solve the above problems and reduce crosstalk between channels.
An object of the present invention is to provide an optical circuit that can adjust the power of an optical channel as needed.

[0013]

An optical circuit according to the present invention comprises:
The output ports of m (m is a positive integer) 1-input n-output optical switches (n is a positive integer) and the input ports of n m-input 1-output optical switches are the m1th (m1 is a positive integer) Branch-select in the form of connecting the n1st (n1 is a positive integer) output port of the output port of the 1-input, n-output optical switch and the m1-th input port of the n1-th m-input, 1-output optical switch In a matrix optical switch circuit forming a type network, the 1-input n-output optical switch and the m-input 1-output optical switch are optical circuits made of a material having an electro-optical characteristic whose refractive index changes by application of an electric field, wherein A gate member is provided between the output port of the optical switch having n inputs and n outputs and the input port of the optical switch having m inputs and one output, and has a variable transmittance.

That is, in the optical circuit of the present invention, in a matrix optical switch constituted by a branch-selection type network, a one-input one-input unit having a variable transmittance at a central stage thereof.
An output optical switch (gate) is provided.

First, the operation in the case of an optical switch having the simplest configuration of two inputs and two outputs (hereinafter referred to as 2 × 2) will be described. In the case of a 2 × 2 matrix optical switch, this network has a so-called TREE (tree) configuration when only the first and third stages are viewed, and a gate is inserted in the second stage, which is the center stage.

Thus, by changing the transmittance of the gate, crosstalk between channels can be reduced in a waveguide type optical switch in which optical path switching control is performed using an optical waveguide provided in a substrate. And the power of the optical channel can be adjusted as needed.

In general, in the case of an m × n matrix optical switch, there are m 1 × n switches at the input stage,
There are n mx1 switches in the output stage. In this configuration, a matrix optical switch with low crosstalk is configured by installing mxn gates in the center stage, and the output power from each channel can be adjusted by adjusting the transmittance of the appropriate gate. Become.

Therefore, in a waveguide-type optical switch that performs optical path switching control using an optical waveguide provided in a substrate, crosstalk between channels can be reduced, and the power of the optical channel can be reduced as necessary. Can be adjusted.

[0019]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a network configuration of an optical circuit according to one embodiment of the present invention. FIG.
FIG. 3 is a network diagram for explaining an operation principle according to an embodiment of the present invention in the case of a 2 × 2 matrix optical switch.

This network has a so-called TREE (tree) configuration when only the first and third stages are viewed. In one embodiment of the present invention, a gate is inserted in the second stage, which is the center stage. I have. That is, optical switches (gates) 3 to 6 whose transmittance is adjustable between switches 1 and 2 connected to inputs # 1 and # 2 and switches 7 and 8 connected to outputs # 1 and # 2 are connected. Inserted.

First, input a 2 × 2 matrix switch #
To set the connection from 1 to the output # 1 and from the input # 2 to the output # 2, adjust each switch so that the light from the input # 1 is guided to the switch 1 → gate 3 → switch 7 → output # 1. I do. Therefore, the gate 3 is set in a state where light is transmitted.

At this time, the crosstalk light generated from the switch 1 is guided to the gate 3. Therefore, by closing the gate 3, the crosstalk light generated from the switch 1 is attenuated by the extinction ratio of the gate 3.

The switch 8 is set from the gate 6 to the output # 2 to guide the light from the input # 2 to the output # 2. Therefore, the attenuated crosstalk light guided from the gate 5 is further attenuated by the switch 8.

As described above, when the extinction ratio of each optical switch and gate is, for example, 20 dB, the amount of crosstalk in the matrix optical switch using the present network is-
It is reduced to 60 dB. By adjusting the transmittance of the gate 1 and the gate 4 in this state, the optical power output from the output 1 and the output 2 can be adjusted.

FIG. 2 is a diagram showing another example of the network configuration of the optical circuit according to one embodiment of the present invention. Figure 2 shows mxn
FIG. 4 is a network diagram for explaining an operation principle according to an embodiment of the present invention in the case of a matrix optical switch (m and n are positive integers).

The input stage has m 1 × n switches 11-1.
-11-m, and n mx1 switches 1 in the output stage.
There are 2-1 to 12-n. Mxn gates 1 in the center
By installing the three, a matrix optical switch with low crosstalk is configured. Further, by adjusting the transmittance of an appropriate gate, the output power from each channel can be adjusted.

FIG. 3 is a view showing an optical waveguide and electrode structure of a Mach-Zehnder (MZ) type optical switch on an LN (lithium niobate) substrate used in one embodiment of the present invention. In the figure, an optical switch according to an embodiment of the present invention is a polarization independent switch in which an operating voltage or the like does not change due to input polarization by using an X-cut LN crystal and making the propagation direction of the waveguide coincide with the Z axis. ing.

The waveguide is manufactured by a Ti diffusion method on an ordinary LN substrate. This polarization independent switch includes electrodes 21 to 23, a switch 24, and a power supply 25.

FIG. 4 is a diagram showing operating characteristics obtained by a Mach-Zehnder (MZ) optical switch on an LN substrate used in one embodiment of the present invention. FIG. 4 shows the operating characteristics normally obtained with this optical switch when one signal electrode and a ground electrode are formed so as to surround the MZ-type optical interference system.

When the lengths of the electrodes 21 to 23 are set to about 6 mm, typically, the operating voltage of about 50 V changes the cross state from the input # 1 to the output # 2 and from the input # 2 to the output # 1. Move to the opposite bar state.

FIG. 5 is a diagram showing a waveguide layout of a 2 × 2 matrix optical switch constituted by the MZ type optical switch shown in FIG. In the figure, inputs # 1 and # 2
The gates 33 to 36 disposed between the switches 31 and 32 connected to the switches # 1 and # 37 and the switches 37 and 38 connected to the outputs # 1 and # 2, that is, the gates 33 to 36 are also MZ optical switches.

When the voltage applied to all the switches 31, 32, 37 and 38 and the gates 33 to 36 is set to zero volt, the operating characteristics of the switches 31, 32, 37 and 38 are as shown in FIG.
By following this, a cross state from input # 1 to output # 2 and input # 2 to output # 1 was obtained as a 2 × 2 matrix switch. The crosstalk level at this time was typically −60 dB. Gate 3 in this state
5 is adjusted according to the output characteristic curve to the cross port of the operating characteristics shown in FIG.
The output power to 2 could be adjusted.

Further, all the switches 31, 32, 37,
By applying 50V to the gate 38 and the gates 33 to 36,
Input # 1 to output # 1 as 2x2 matrix switch
A so-called bar state, which guides light to the light, was obtained.

The crosstalk level at this time is typically −
60 dB was obtained. By adjusting the applied voltage to the gate 33 and the gate 35 in this state, the output power to the outputs # 1 and # 2 could be adjusted.

FIG. 6 is a diagram showing a waveguide layout of a 4 × 4 matrix optical switch constituted by the MZ type optical switch shown in FIG. In the figure, four 1 × 4 switches 41 connected to inputs # 1 to # 4 and outputs # 1 to # 4
The MZ type optical switch is also used between the four 4 × 1 switches 43 connected to the gate stage, that is, the gate stage 42 installed at the center stage.

The state setting for connecting each input from input # 1 to input # 4 to which output port is substantially the same as that of the 2 × 2 matrix switch shown in FIG. The crosstalk level at this time was typically −60 dB. Also, by adjusting the voltage applied to the gate of the appropriate gate stage in each state setting, the insertion loss of the present matrix switch could be arbitrarily adjusted from 7 dB to 25 dB.

One embodiment of the present invention describes in detail the case where an MZ type optical switch on an X-cut LN crystal substrate is used for an optical switch and a gate. As is apparent from the above description, the optical path switching circuit according to the embodiment of the present invention does not depend on the type of the optical element used for the optical switch and the gate.

For example, it is possible to use a semiconductor optical amplifier gate in the gate stage used in the center. As is well known, a semiconductor optical amplifier gate is an element that absorbs light when there is no current injection and has an optical amplification function by appropriate current injection. Therefore, when the semiconductor optical amplifier gate is used as the gate switch in one embodiment of the present invention, the insertion loss of the 1 × N switch installed in the preceding and subsequent stages can be compensated, and a lower-loss matrix can be formed. .

Further, by changing the refractive index of a directional coupler formed as an optical waveguide made of, for example, an electro-optic crystal by a 1 × N switch or gate by electric field change, an optical output is actually obtained from a plurality of output optical waveguides. It is also possible to apply a directional coupler type optical switch having a function of selecting a waveguide to be used.

Further, the 1 × N switch and the gate are each provided with an optical waveguide made of, for example, an electro-optic crystal.
A function of selecting a waveguide from which light output is actually obtained from a plurality of output optical waveguides by changing the refractive index of each of a plurality of output optical waveguides connected to one input optical waveguide in a Y-branch shape by an electric field change. It is also possible to apply a digital type optical switch having. In addition, as described above,
The method in which the transmittance is varied by the electro-optic effect has the advantages of reducing power consumption and increasing the operating speed as compared with the method using the thermo-optic effect.

As described above, by providing the one-input / one-output optical switch (gate) capable of changing the transmittance at the center stage of the matrix constituted by the TREE structure network, the low crosstalk level required in optical communication can be reduced. This can be easily achieved, and the light intensity level output from each output port can be adjusted. From these points, its industrial value is great.

[0042]

As described above, according to the present invention, m
(M is a positive integer) 1-port n-output (n is a positive integer) optical switch output port and n m-input 1-output optical switch input ports are m1-th (m1 is a positive integer) ) 1
The n1st (n1) of the output ports of the optical switch with input n output
Is a positive integer) and an n1-th m-input / 1-output optical switch connected to the m1-th input port of the optical switch including a matrix optical switch circuit forming a branch-selection network. Is provided between the output port of the 1-input, n-output optical switch and the input port of the m-input, 1-output optical switch, by providing one of the variable input 1-output optical attenuator and the variable optical amplifier. Crosstalk between channels can be reduced,
There is an effect that the power of the optical channel can be adjusted as needed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a network configuration of an optical circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing another example of the network configuration of the optical circuit according to one embodiment of the present invention.

FIG. 3 is a view showing an optical waveguide and an electrode structure of a Mach-Zehnder optical switch on a lithium niobate substrate used in one embodiment of the present invention.

FIG. 4 is a diagram showing operating characteristics obtained by a Mach-Zehnder optical switch on a lithium niobate substrate used in an example of the present invention.

FIG. 5 is a diagram showing a waveguide layout of a 2 × 2 matrix optical switch constituted by the Mach-Zehnder type optical switch shown in FIG. 1;

FIG. 6 is a diagram showing a waveguide layout of a 4 × 4 matrix optical switch constituted by the Mach-Zehnder type optical switch shown in FIG.

[Explanation of symbols]

 1, 2, 7, 8, 31, 32, 37, 38 switch 3 to 6, 33 to 36 gate 11-1 to 11-m 1xn switch 12-1 to 12-n mx1 switch 13 mxn gates 21 to 23 Electrode 24 Switch 25 Power supply 41 Four 1x4 switches 42 Gate stage 43 Four 4x1 switches

Claims (7)

[Claims] 1. The output ports of m (m is a positive integer) 1-input n-output optical switches (n is a positive integer) and the input ports of n m-input, 1-output optical switches are set to the m1-th (m1 Is a positive integer) n of the output port of the 1-input n-output optical switch
1st (n1 is a positive integer) output port and n1st m
In a matrix optical switch circuit which forms a branch-selection type network by connecting an m1 input port of an input 1 output optical switch, the 1-input n-output optical switch and the m-input 1-output optical switch are connected by an electric field. An optical circuit made of a material having an electro-optical characteristic whose refractive index changes, provided between an output port of the 1-input / n-output optical switch and an input port of the m-input / 1-output optical switch, respectively. An optical circuit comprising a gate member having a variable transmittance. 2. The optical circuit according to claim 1, wherein said gate member comprises one of a one-input one-output variable optical attenuator and a variable optical amplifier. 3. The optical circuit according to claim 2, wherein one of said optical switch and said variable optical attenuator for forming said branch-selection type network comprises a Mach-Zehnder interference system. 4. The optical circuit according to claim 2, wherein one of said optical switch and said variable optical attenuator for forming said branch-selection type network comprises a directional coupler. 5. A plurality of output optical waveguides each having one of the optical switch and the variable optical attenuator connected to one input optical waveguide in a Y-branch for forming the branch-selection type network. 3. The optical circuit according to claim 2, comprising a digital type optical switch having a function of selecting a waveguide from which a light output is actually obtained from a plurality of output optical waveguides by changing a rate by an electric field change. 6. The optical circuit according to claim 2, wherein one of said variable optical attenuator and said variable optical amplifier comprises a semiconductor optical amplifier gate. 7. The matrix optical switch circuit comprises an optical waveguide formed in a crystal material having an electro-optic effect, and performs one of switching of an optical path and adjustment of transmittance by a voltage applied to the optical waveguide. The optical circuit according to any one of claims 2 to 4, wherein: