JPH0510653B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides e (≧1) input transmission lines and m (≧1) input transmission lines.
2) relates to an optical switch that arbitrarily switches connections between output branches.

With the full-scale commercialization of optical signal systems in recent years, systems that provide new functions and services not previously available are being considered. An example of a device required in such a system is an optical switch that switches connections between a large number of optical transmission lines at high speed. Conventionally, so-called mechanical type optical switches that move prisms, lenses, or the optical transmission line themselves have been widely used as such optical switches, but demands such as high switching speed, operational reliability, and multichannelization Considering this, it is thought that non-mechanical switches that can be integrated will become mainstream in the future. The following three methods have been proposed so far to obtain such a switching system.

(1) Method using waveguide type optical switch (2) Light → electricity, electricity → light conversion method (O/E, E/
(3) Method using photo diode switch These methods will be explained below using the figures.

In the following description, for the sake of simplicity, a case will be described in which connections between two input optical transmission lines and two output branches are switched.

FIG. 1 is a diagram for explaining the method (1) using a waveguide type optical switch. Here, as an example, a case is shown in which a directional coupler type optical switch is used as the basic element of a waveguide type optical switch.

Two waveguides 2 of directional coupler type optical switch 1
Direct input optical transmission lines 3a, 3b at both ends of a, 2b,
Output optical transmission lines 4a and 4b are connected. For directional coupler type optical switches, control electrode (omitted in the diagram)
By the voltage applied to (3a → 4a, 3b → 4b)
The connection state of (3a→4b, 3b→4a) is switched. This type of system has the advantage that it is possible to switch the optical signal as it is, and the switching speed is generally fast.
On the other hand, there are restrictions on the polarization, mode, etc. of the light that can be switched.
It is also difficult to obtain sufficient characteristics in terms of crosstalk insertion loss. Moreover, the shape is relatively large, and there is a problem in multi-channeling.

Next, the O/E and E/O conversion method (2) will be explained.

FIG. 2 is a diagram for explaining the operation of a switch according to this method. The optical signals on the input optical transmission lines 3a and 3b are converted into electrical signals by O/E conversion means (specifically, photodiodes + amplifier circuits, etc.) 5a and 5b, respectively. This electrical signal is electrically switched by switching circuit b to output branch 8.
It is output to a and 8b. Output branches 8a, 8b
are connected to E/O conversion means 7a, 7b (integrated drive circuit and light emitting element), which convert electrical signals back into optical signals and output optical transmission lines 4a, 4.
Output to b. In this method, the system is a regenerative amplification system, so there is no need to consider insertion loss.
It is also possible to correct waveform deterioration. Another advantage is that the properties of the light to be switched are not selective. but,
In order to switch high-band optical signals at high speed, information,
When it is necessary to eliminate interference between control signals, the demands on the intermediate switching circuit 6 become very strict.

Next, the photodiode switch (3) will be explained.

FIG. 3 is a diagram for explaining the operation of the photodiode switch. Incident light transmission lines 3a, 3b
The optical signals transmitted by the optical branches 9a and
The light is branched by 9b and received by photodiodes 10a, 10b, 11a, and 11b, respectively.

Here, by switching the bias applied to the photodiodes in accordance with the control signal and operating only desired photodiodes, it is possible to switch the electrical signals output to the output branches 8a and 8b. This method has the advantage that the band of the transmitted signal can be very high, the electrical circuit is not too complicated, and crosstalk is also good, but since the light is split, there is a loss of light as the number of channels increases. There is a problem in that it is difficult to integrate multiple channels due to the increase in the number of channels.

As described above, the optical switching methods that have been proposed so far have their own shortcomings and are not sufficient.

An object of the present invention is to provide an optical switch which has a relatively simple structure, can switch wideband signals at high speed, and is suitable for integration, except for the above-mentioned drawbacks.

The optical switch according to the invention has m (≧2) corresponding to the number of output branches with p-n junctions of semiconductor material separated from each other and optically cascaded.
e (≧1) optical circuits each consisting of active waveguides;
e optical circuits that input optical information signals from the e input optical transmission lines to the e optical circuits; a drive circuit that drives each of the active optical waveguides in a forward bias state; and each of the active waveguides. a detection circuit that outputs an electrical signal according to the optical information signal to a corresponding output branch with the signal in a reverse bias state, and each of the active waveguides is selectively connected to the drive circuit and the circuit according to a control signal. It is characterized by having a means.

In this optical switch, only the active waveguides corresponding to the output branches to be connected among the e optical circuits are placed in a reverse bias state, and the remaining active waveguides are placed in a forward bias state. An information signal can be output as an electrical signal to the branch to be connected.

Hereinafter, the present invention will be explained in detail using the drawings.

First, the operation of an active waveguide having a pn junction made of a semiconductor material used in the present invention will be explained. The active waveguide is a waveguide made of a material capable of forming population inversion by current injection, and has a pn junction therein. Specifically, it is used as a material for semiconductor lasers.
It can be formed from materials such as GaAlAs/GaAs and InGaAsP/InP.

It is known that such an active waveguide has an amplifying effect on light having a wavelength near the peak of the gain spectrum when the current is biased above a certain threshold value. Attempts to construct optical amplifiers by taking advantage of this fact have already been widely carried out. It is also known that when such an active waveguide is used in a reverse bias state, it functions as a photodiode for light having a wavelength near the peak of the gain spectrum. In fact, one double heterostructure laser is divided into two by etching an end face in the middle.
Attempts have been made to use one as a laser and the other as a monitoring photodiode. This fact shows that one active waveguide can operate as both an amplifier and a photodiode by switching the bias forward or reverse for light at a wavelength near the wavelength that gives the maximum value of its gain spectrum. It shows that it can be done. This point will be further explained using figures.

FIG. 4 is a diagram for explaining the operation of the active waveguide by switching the bias state. When the active waveguide is biased in the forward direction above the threshold value (a), the incident light 21 to the active waveguide 20 is amplified and output as the output light 22. At this time, almost no change due to a change in the incident light 21 appears in the circuit that applies a bias to the active waveguide 20. On the other hand, when using the active waveguide 20 with reverse bias b
The incident light 21 is absorbed within the waveguide and electrically outputted as a photocurrent 23 due to the action of the reverse bias pn junction, which appears as a voltage across the load resistor 24. At this time, most of the components of the incident light 21 that do not contribute to the photocurrent 23 are also absorbed in the active waveguide 20, and almost no light output is obtained from the active waveguide 20.

For these reasons, when a large number of active waveguides are connected in cascade using appropriate optical means, and when each active waveguide is used in a forward bias state, light incident from one end is amplified while passing through the active waveguide. I will move on. Therefore, if the bias state of one of the active waveguides is reverse biased, the optical signal is extracted there as an electrical signal, and the optical signal is not transmitted to the subsequent active waveguides. In other words, in a system in which many active waveguides are connected in series, if each active waveguide is biased in the forward direction, then by changing the bias of one of the active waveguides to a reverse bias state, it is possible to remove electricity from any active waveguide. This means that an optical signal can be extracted as a signal.

In other words, such a system functions as an optical switch that switches connections between one optical transmission line and multiple output branches.

The present invention extends this fact to the case of multiple inputs and multiple outputs. Next, the optical switch of the present invention will be explained using the drawings, taking as an example the case of two inputs and two outputs.

FIG. 5 is a diagram for explaining the operation of the optical switch of the present invention. Two input optical transmission lines 3a,
3b, there are active waveguides 20a, 20c, respectively corresponding to the number of output branches (two in this case).
When the active waveguides 20b and 20d are arranged and all of the active waveguides are biased in the forward direction, the optical signals output from the input optical transmission lines 3a and 3b are amplified by the respective active waveguides and transmitted as light. It's starting to get better. Here, as an example, input optical transmission line 3
3a → between a and 3b and output branches 8a and 8b
Let us consider a case where the connection is 8b, 3b→8a. For that purpose, the corresponding active waveguide 2
0c and 20b are connected to reverse bias circuits 25a and 25b equipped with a photocurrent detection system, and other active waveguides 2
It is sufficient to bias 0a and 20d in the forward direction. In this state, the optical signal from the optical transmission line 3a is amplified by the active waveguide 20a, and the optical signal is amplified by the active waveguide 20c.
is incident on the reverse bias circuit 25 where it is absorbed.
b is output to the output branch 8b as a photocurrent 23a. On the other hand, the optical signal from the optical transmission line 3b is absorbed by the active waveguide 20b, and similarly the photocurrent 23b
The signal is output to the output branch 8a as a signal. To change the connections, the switching operation can be achieved simply by changing the forward and reverse biases of each active waveguide.
This type of optical switch has a light amplification system, so
There is no need to consider light loss and the strokes are essentially very small. The active waveguides are simply connected in cascade, and there is no need for any complicated optical circuits such as optical branches or combiners. The control system simply switches the bias of each active waveguide, and the optical signal is simply amplified and received within the active waveguide, so no complicated electrical signal is required, and optical signal degradation due to passing through an electrical circuit is minimal. It can be kept to a limit. In addition, since the operating mechanism of the active waveguide is similar to that of a normal laser amplifier or photodiode, it has extremely high speed. Furthermore, since the active waveguide, which is a basic component, is very small and can be easily arranged in an matrix, it is easy to integrate it for multi-channel use. Therefore, with this optical switch, it is possible to realize a very small optical switch with excellent performance.

FIG. 6 is a diagram showing an embodiment of the optical switch according to the present invention. Again, for simplicity, the case of two inputs and two outputs is shown.

Optical signals from the input optical transmission lines 3a and 3b are transmitted to the coupling circuit 3 by coupling circuits 30a and 30b, respectively.
It is efficiently coupled to an optical circuit consisting of two active waveguides 20a, 20c, 20b, 20d connected in series by 1a, 31b. Each active waveguide is connected to a forward bias circuit 35 and a reverse bias circuit 25a, 25b including a photocurrent detection system, respectively, by selecting and connecting the switch 32a, 3 with a control signal.
2b, 32c, and 32d are connected. In this state, switch 32a, 3
When the connections of the optical signals 2b, 32c, and 32d are switched, electric signals corresponding to the optical signals are switched and outputted to the output branches 8a, 8b as described above. Furthermore, electricity → light (E/
O) If the conversion means 33a, 33b (specifically, a drive circuit integrated with a semiconductor laser, a light emitting diode, etc.) are connected, the signal after switching can be transmitted as an optical signal again through the output optical transmission lines 34a, 34b. You can.

With such a configuration, the active waveguides 20a, 20b,
Same as normal semiconductor laser as 20c and 20d
This can be realized using double heterojunctions, multiple quantum well structures, etc. made of materials such as GaAlAs/GaAs and InGaAsP/InP. Of course, the overall optical configuration can be arranged discretely, but the active waveguides 20a, 20b, 20c, 20 on one semiconductor substrate
d and coupling circuits 30a and 30 using passive waveguides.
A structure in which the elements b, 31a, 31b, etc. are integrated is better.

Furthermore, since materials such as GaAs and InP are excellent as materials for high-speed electron transport devices, it is also possible to integrate the switches 32a, 32b, 32c, 32d and the E/O conversion means 33a, 33b on one substrate. It's not impossible.

As explained in detail above, according to the present invention,
An optical switch can be realized that has a relatively simple configuration, can switch wideband signals at high speed, and is suitable for integration.

[Brief explanation of the drawing]

1, 2, and 3 are diagrams for explaining the conventional optical switching system, FIGS. 4 and 5 are diagrams for explaining the optical switch according to the present invention, and FIG. 6 is a diagram for explaining the optical switch according to the present invention.
The figure is a diagram showing one embodiment of the optical switch according to the present invention. In the figure, 1 is a waveguide type optical switch, 2a, 2
b, 9a, 9b are light guides, 3a, 3b, 4a,
4b, 34a, 34b are optical transmission lines, 5a, 5b are optical-to-electrical conversion means, 6 is an electrical system switch, 7a,
7b, 33a, 33b are electrical-to-optical conversion means; 8
a, 8b are output branches, 10a, 10b, 11
a, 11b are photodiodes, 20, 20a,
20b, 20c, 20d are active waveguides, 21, 2
2 is an optical signal, 23, 23a, 23b is a photocurrent, 2
4 is a load resistor, 25a, 25b are reverse bias circuits, 30a, 30b, 31a, 31b are coupling circuits, 32a, 32b, 32c, 32d are switches, and 35 is a forward bias circuit.

Claims (1)

[Scope of Claims] 1. Input consisting of m (≧2) active waveguides corresponding to the number of output branches with p-n junctions of semiconductor material electrically isolated from each other and optically cascaded. 1 (≧1) optical circuits corresponding to the number of optical transmission lines, one coupling circuit that inputs an optical information signal from one input optical transmission line to the one optical circuit, and each of the above-mentioned optical circuits. a drive circuit that drives the active optical waveguide in a forward bias state; a detection circuit that sets each of the active waveguides in a reverse bias state and outputs an electrical signal corresponding to the optical information signal to a corresponding output branch; An optical switch comprising means for selectively connecting a wave path to the drive circuit and the detection circuit in accordance with a control signal. 2. The optical switch according to claim 1, wherein E/O conversion means for converting an electrical signal into an optical signal is connected to each of the 2 m output branches.