JPS6084536A - Optical switch - Google Patents

Abstract

PURPOSE:To switch relatively easily wide-band signals at a high speed by switching optionally connections between (l) pcs. of input optical transmission lines and (m) pcs. of output branches. CONSTITUTION:When there are two inputs and two outputs, LEDs 31a-31d are arranged on a semiconductor substrate 21 in front of two input light guides 30a and 30b corresponding to the number of output branches. For example, when connections from the light guide 30a to an output branch 32a and from the light guide 30b to an output branch 32b are made, the LEDs 31a and 31d are only connected to reverse bias circuits 33a and 33b equipped with photodetection systems. A light signal from the light guide 30a is absorbed partially at the part of the LED31a and outputted as a photocurrent 34a to the output branch 32a. A light signal from the light guide 30b propagates almost without being absorbed at the part of the LED31c, and is absorbed by the LED31d and outputted as a photocurrent 34b to the output branch 32b. When the connections are switched, LED reverse biases are only inverted in on-off state, realizing switch operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical switch that arbitrarily switches the connection between an input optical transmission line of 1 m<≧1) and an output branch of m (>2) sea bream.

With the full-scale commercialization of optical communication 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, such optical switches have been widely used as copper loose mechanical ones that move prisms, lenses, or the optical transmission line itself, but they have high switching and switching speeds,
Considering the requirements for operational reliability, multichannelization, etc., it is thought that non-mechanical switches that can be integrated will become mainstream in the future. The following three methods have been proposed to obtain such a switch.

(1) Method using a waveguide light switch (2) Light → electricity, electricity → light conversion method (07B, E1
0 method) (3) Method using photo diode switch These methods will be explained below using the figures.

In the following explanation, for simplicity, two input optical transmission lines and two input optical transmission lines are used.
We will discuss the case of switching the connection between the output branch of the book and the output branch of the book. FIG. 1 is a schematic diagram illustrating the method using the waveguide optical switch (1). Here, as an example, a case is shown in which a directional coupler type optical switch is used as a basic element of a waveguide type optical switch. Input optical transmission lines 3g, 3t, and output optical transmission lines 4m, 4b are directly connected to both ends of the two waveguides 2a, 2b of the directional coupling type. In a directional coupler light switch, the voltage applied to the control electrode (omitted in the figure)
From the connection state of 3a-+41, 3b 4b) (3a→4
b, the connection state is switched from 3b to 4a).

This type of system has the advantage that it is possible to switch and switch the optical signal as it is, and the switching speed is generally high, but on the other hand, the polarization of the light to be switched.

There are restrictions on modes, etc., and it is difficult to obtain sufficient characteristics in terms of p-stoke insertion loss. In addition, the shape is relatively large and there is a problem in multi-channeling. Next (2) 07Fi
The E10 conversion method 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 3h are converted into electrical signals by 0/F converting means (photodiode + amplifier circuit, etc. in body A) 5a and 5b, respectively. This electrical signal is electrically switched by the switch 71 circuit 6 and output to the output branch 8a18b. The output branches 8a, 8bK are connected to B10 conversion means (integrated drive circuit and light emitting element) 7a, 7b, which convert the electric signal into an optical signal again and output it to the output optical transmission lines 4a, 4b. In this method, since the system is a regenerative amplification system, there is no need to consider insertion loss, and it is also possible to correct waveform deterioration. Another advantage is that the properties of the light to be switched are not selective. However, in order to switch high-band optical signals at high speed, the requirements for the intermediate switch 71 circuit 6 are extremely strict, such as the need to eliminate interference between information and control signals. Next, the photodiode switch (3) will be explained.

FIG. 3 is a diagram for explaining the operation of the photodiode switch. The optical signals transmitted through the incident optical transmission line 311.3b are each connected to an optical branch 9a.

9bK branched, each photodiode 10g,
The light is received by 10b, 1lfi, and llb. Here, by switching the bias applied to the photodiodes in accordance with the control signal and operating only the 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 bandwidth of the transmitted signal can be very high, the electric circuit is not too complicated, and crosstalk can be tolerated, but since the light is split, there is a loss of light as the number of channels increases. There is a problem 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 each have their own shortcomings and are not sufficient. An object of the present invention is to eliminate the above-mentioned drawbacks and provide an optical switch that has a relatively simple configuration, can switch wideband signals at high speed, and is suitable for integration. The optical switch according to the present invention has I! formed in parallel on a semiconductor substrate corresponding to one input light transmission path. (≧1) semiconductor optical waveguides and a junction for applying an electric field in the direction of the optical waveguide layer of each of the optical waveguides, and is made of a high-resistance semiconductor material having a composition that absorbs the guided light. (≧2) A photodiode corresponding to the output branch of the sensor, a detection circuit of m1il that puts each of the photodiodes in a reverse bias state and outputs a photocurrent to the corresponding output branch, and the photodiode and the detection circuit. means for opening and closing the connections in response to a control signal, all of the semiconductor layers have an electro-optic effect, and the thickness of the buffer layer is the same as the thickness of the buffer layer when no reverse bias is applied to the photodiode. The semiconductor waveguide is characterized in that it is set to be sufficiently thin so that the guided light propagating through the semiconductor waveguide is hardly absorbed by the light absorption layer of the photodiode. The present invention will be explained in detail below with reference to the drawings.

First, the operation of the waveguide photodetector used in the present invention will be explained. FIG. 4 shows an embodiment of a waveguide and a photodiode used in the present invention. Here, for convenience of explanation, InGaAs)' with InP as the substrate,
This figure shows a case where InGaAs-based materials are used.

An n-InGaAsP waveguide layer 22 having a refractive index greater than InP and an n-InP buffer layer 23 are formed on an n-InP substrate or a buffer layer 21, and an n-InGaAsP layer 24 and a p-layer are formed thereon. ”-1, G, A, layer 2
A mesa type photodiode consisting of 5 is formed.

The ohmic electrode 2 is connected to the p-1nGaAs layer 25 through a contact hole formed in a passivation film 26 made of an insulator provided to stabilize the mesa interface.
Similarly, an ohmic electrode 28 is formed on the n-InP substrate 21. Here the upper and lower In
The n-IHGBABP layer 22 sandwiched between P layers has a high refractive index, so it functions as a waveguide. At this time, the thickness of the n InP buffer layer 230 at the bottom of the mesa is set to be sufficiently thin within a range where the guided light is sufficiently attenuated. In this state, n-InG1
Light propagating through the AsP waveguide layer 22 can be propagated uniformly regardless of whether the upper photodiode is grown or not. next,
Consider a case where a reverse bias is applied to the photodiode and it is operated while light is propagating in the n InGaAsP waveguide layer 22 in this manner. At this time, the depletion layer changes from the pn junction in InGaAs to the n-
It extends towards the InP substrate. An electric field is effectively applied within the depletion layer of , and in this state light is generated at a wavelength within the absorption band. This depletion layer is an n-InGaAs layer 24,
By making the ar9 concentration of the n-InP layer 23 sufficiently low, the n-InP layer 23 and the n-In(laAsP waveguide layer 22 can be easily formed with a low reverse bias).
It is possible to reach up to. On the other hand, InGaAsP,
Semiconductor materials such as InP are known to exhibit an electro-optic effect in which their refractive index changes in response to an applied electric field. Therefore, the depletion layer generated by applying a reverse bias to the photodiode is
When it extends to the point where it overlaps with the field distribution of light propagating in the waveguide layer 22, the waveguide state of the light is affected by the electro-optic effect at the overlapping portion. In a crystal such as InP, which is used for a school of fish 43m, when a waveguide in the <011> direction is formed on a (100) substrate, an electric field in the <100> direction causes i'E- through the primary electro-optic effect. The refractive index increases for t-does. In other words, in the configuration shown in FIG. 4, the refractive index of the n--InP fiber layer 23 increases, and the guided light leaks upward. Therefore, when no reverse bias is applied, the light that propagates in the waveguide layer 22 regardless of the presence of the upper photodiode leaks upward at the shifted diode part due to the application of a reverse bias. A portion of it will be absorbed into the InGaAs layer. By applying a reverse bias, part of the guided light can be detected by the upper photodiode. This means that if a photodiode is partially formed on a waveguide made of a semiconductor that has an electro-optic effect, a reverse bias can be applied to the photodiode when necessary, and the signal carried on the guided light can be detected. can be extracted from the photodiode. Furthermore, when no reverse bias is applied, the light propagates through the waveguide as it is, so it does not suffer any additional loss. Furthermore, the photodiode shown in FIG. 4 has a very fast response in principle, and can be expected to have a relatively fast switching speed by turning on and off the reverse bias.

Furthermore, since the method of guiding light to the photodiode does not require a long interaction length like directional coupling, it is extremely compact, and it is easy to connect many waveguides in tandem along the length of the waveguide. It is possible. Such a system is 1
Optical switch for switching connections between one optical transmission line and a large number of output branches;

I'll explain about this. FIG. 5 is a diagram for explaining the operation of the optical switch of the present invention. Two input optical waveguides 3
In front of 0a and 30b, there is a photodiode (31a#) formed on the semiconductor substrate 21 as shown in FIG.
3 l b ) (31 d + 31 m) are arranged corresponding to the number of output branches (two in this case) K.

Here, as an example, between the input optical transmission klA 30a, 30b and the output branches 32a, 32b, aO,→32. ,3
Let us consider the case where the connection 01)→32b is made.

For this purpose, a corresponding photodiode 31. ．． 31d
Reverse bias circuit aaa, aab equipped with photocurrent detection system
Just connect K. In this state, a part of the optical signal from the optical transmission line 30m is absorbed by the 7 photodiodes 31a, and the photoelectric signal fi 34. It is output to the output branch 32m by binding. - The optical signal Fi7 from the force sense transmission line 30b propagates through the waveguide with almost no absorption in the photodiode 31c, is absorbed by the photodiode 31d, and similarly generates a photocurrent 3.
4h to the output branch 32b. To change the connection, all you have to do is turn the photodiode reverse bias on and off, and a switch operation can be achieved. With such an original switch, there is almost no additional loss unless a reverse bias is applied to the photodiode, and furthermore, there is essentially no additional loss.
Stoke is small. The control system simply switches on and off the bias of each photodiode, and since light 46 is simply received by the photodiode, a complicated electrical circuit is not required. Signal deterioration can be kept to a minimum. In addition, due to the principle of operation of photodiodes, they are extremely fast. Furthermore, since the photodiode, which is the basic component, is very small and suitable for matrix or box-like arrangement, it is easy to integrate multiple channels on a single substrate. Therefore, with this optical switch, it is possible to realize an optical switch that is extremely compact and has poor performance.

FIG. 6 is a diagram showing an embodiment of the optical switch according to the present invention. Here, optical waveguides 40m, 401) and a photodiode 41a partially formed thereon.

41b, 41c, and 41d are integrated on one semiconductor substrate 21. Here again, for simplicity, the case of two people and two outputs is shown. input source transmission line 30a,
The optical signals from 30b are connected to coupling circuits 42a and 42b, respectively.
Two optical waveguides 4 formed on a semiconductor substrate 21 by
0m, 40b.

41 m of photodiodes corresponding to the number of output branches (2 in this case) are placed on top of each optical waveguide through 77 layers.
, 41b, 41c, and 41d are formed.

These structures have been explained previously using drawings.

Each photodiode is connected to a corresponding reverse bias circuit 33m, 33b including a photocurrent detection system by a control signal.

43m, 43b, 43c, and 43d are arranged in m groups.

In this state, switch 43m according to the desired connection.

When 43b, 43c, and 43d are turned on and off, electrical signals corresponding to the optical signal 1h are switched and output to the output branches 32m and 32b as described above.

Furthermore, electricity → light (Elo
) 13- If the converting means 44a, 44b (specifically, a drive circuit integrated with a semiconductor laser, a light emitting diode, etc.) are connected, the signal after the switch is converted into an optical signal again and output via the optical transmission lines 45a, 45b. Can be transmitted. Here, an InGIAsP/InP-based material is used as the material, but other materials such as klGaks/GaAs can also be used. Since these materials are excellent not only for optical devices but also for high-speed electron transport devices, reverse bias circuits aaa, 33b including switches 43a, 43b, 43c, and 43d and a photocurrent detection system.

The E10 conversion means 44a, 44b, etc. can also be integrated on one substrate. In that case, #'i all the optical switches will be integrated on a single substrate, resulting in excellent reliability and lower costs due to mass production.

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

14-

[Brief explanation of drawings]

1, 2, and 3 are diagrams for explaining the conventional optical switching system, FIGS. 4 and 5 are diagrams for explaining the optical switch 11 according to the present invention, and FIG. 6 is a diagram for explaining the optical switch 11 according to the present invention. 1 is a diagram showing an example of an optical switch according to FIG. In the figure, 1 is a light switch made by Tokuha, 2m, 2b. 9g, 9b, 40m, 40b are light guides; 3. ．． 3b,
4. . 4b, 30a, 30b, 45a, 45b are optical transmission lines; 5
a. 5b is a photo-electric conversion means, 6,431, 43b, 43c
. 43d is an electrical switch, 7a, 7b, 44g, 44b
is the electric-optical conversion hand, 8crow, 8b, 32m, 32b is the output branch, 101, 10b, lla, llb, 41
1.41b. 41c and 41d are photodiodes, 21.22°23
．． 24.25 is a semiconductor, 2'7.28 is an electrode, 26 is an insulating film, 33. ．． 33b is a reverse bias circuit, a4. ．． 34
bFi photocurrent, 42a, 421) is a coupling circuit. Deputy Chief Petty Attorney Susumu 15- Fig. 1 Fig. 2 Fig. 4 u Z + 0 Fig. 5 3ja 31b 0a Convex 01 31C31d 0b Convex φ Fig.

Claims (2)

[Claims] (1) Formed in parallel on the semiconductor substrate corresponding to the input optical transmission line! (≧1>H semiconductor optical waveguides, and on the optical waveguide layer of each of the above-mentioned optical waveguides, a layer made of a high-resistance semiconductor material is formed electrically separated from each other via 77 layers, and inside the optical waveguide, a layer is formed in the vertical direction. having a junction for applying an electric field;
A photodiode of m(≧21H) made of a high-resistance semiconductor material having a composition that absorbs light for guided light, and a detection circuit of m@ that puts each of the photodiodes in a reverse bias state and outputs a photocurrent to a corresponding output branch. means for opening and closing the connection between the photodiode and the detection circuit according to a control signal, all of the semiconductor layers have an electro-optic effect, and the thickness of the buffer layer is such that the photodiode is reverse biased. The optical switch is set to be sufficiently thin in such a range that the guided light propagating in the semiconductor waveguide is hardly absorbed by the light absorption layer of the photodiode when the semiconductor waveguide is not given. (2) The optical switch according to claim 1, characterized in that a B10 conversion means for converting an electrical signal into an optical signal is connected to each outlet branch of the sea bream.