JPS6181099A - Time-division light switchboard - Google Patents

Abstract

PURPOSE:To reduce the number of switches by dividing inputted light signals by a light branching circuit, projecting it on a bistable semiconductor laser, and making writing and memory operation controlling injection current of above-mentioned laser according to the time in which signals are to be written and other time. CONSTITUTION:An injection current i to the bistable semiconductor laser 340 is changed by a current driving circuit 345 as shown in the figure 410 in the first period in the first time slot of a light signal 100. Consequently, the quantity of outgoing light Pout of the laser 340 is changed as shown in the figure 440 according to an injection current pulse 410. In the second period of the signal 100, a current is kept at ib1, and the quantity of outgoing light 440 changes as shown in the figure 440 according to the quantity of incident light. After this, information P11 or P01 is held in the laser 340. Reading of information A thus written is made as follows. A figure 450 shows a controlling voltage by a light switch driving circuit 331. Supposing that a light switch 330 connects waveguide paths 342 and 380 only when a voltage 450 is V1, a light signal obtained by extracting outgoing light 440 of the laser 340 by the voltage 450 is obtained in the waveguide path 380 as shown in the figure 460.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a time-division optical switch that performs exchange control of time-division optical signals.

(Prior art and its problems) Optical communication systems using optical fibers as transmission paths are capable of high-speed, large-capacity signal transmission, and various transmission methods have been put into practical use. One of the most important methods is the time-division transmission method for digital flight numbers, which takes advantage of its high speed. In optical communication systems currently in practical use, optical signals are simply transmitted through optical fibers, and the signals are exchanged after being converted into electrical signals. As mentioned above, in the method of converting optical signals into electrical signals and exchanging them, when transmitting the exchanged signals again, it is necessary to convert the electrical signals back into optical signals, which increases the complexity of the equipment and costs. The disadvantage is that it is expensive. Another drawback is that it is difficult to exchange high-speed signals of 100 megabits per second or more using conventional time-division switching equipment for electrical signals.

As a means to solve this drawback, an optical switch that exchanges time-division optical signals as optical signals has been proposed. This optical switch was described in Japanese Patent Application Laid-Open No. 53-117311 and
, NXM input/output terminals are connected by a group of optical fibers having mutually different lengths, that is, the optical fibers are used as delay lines.

Basically, time-division optical signals input to an optical switch are distributed to different fibers for each time slot, delayed by different times, and then combined in the next optical switch to change the time order of the signals. It is. However, in optical switching equipment that uses such optical fiber delay lines, the delay time is determined by the length K of the optical fiber, and long optical fibers are required to exchange signals with a long frame period. There were drawbacks such as the large size of the device.

In addition, since time-division exchange is performed simply by selecting the delay time of the optical transmission path, loss occurs at the connection between the optical switch and the optical fiber, and the output optical signal level decreases significantly compared to the input optical signal level. It also had the disadvantage of doing so.

To eliminate this drawback, a semiconductor exhibiting bistable operation between a circular writing optical switch with 11 input terminals and multiple output terminals and a reading optical switch with multiple input terminals and one output terminal. The inventor of the present application proposed a time-division optical switch having a structure in which a laser is inserted in Japanese Patent Laid-Open No. 59-107675. Its configuration is such that the input time-division optical signal is sequentially written into a different optical memory, that is, a bistable semiconductor laser, for each time slot by a writing optical switch, and the input signal is held, and each signal is output by a reading optical switch. It selectively cuts out time slots and performs time-division optical exchange. This configuration has the advantage that the length of the frame period to be replaced can be set arbitrarily, the device can be easily miniaturized, and a high output optical signal level can be easily obtained. The write and read optical switches constituting this time-division optical exchange require high-speed performance, so waveguide type optical switches are used. However, as the number of channels in a waveguide optical switch increases, it becomes large in size and requires a large number of manufacturing steps, making it very expensive. Therefore, there 2
This time-division optical switching system using multiple optical switches has the drawbacks of being bulky and expensive.

(Object of the Invention) An object of the present invention is to provide a time-division optical switching system which eliminates the conventional drawbacks, requires fewer optical switches, is small in size, and is inexpensive.

(Structure of the Invention) The time-division optical exchanger of the present invention includes an optical branching circuit having one input end and a plurality of output ends, and a light branching circuit having an output end such that light emitted from the output end enters from one end of a laser resonator. A plurality of semiconductor lasers exhibiting bistable operation are installed corresponding to each output end, and a plurality of input ends and one a readout optical switch having an output end, and a current drive circuit that drives each of the semiconductor lasers, respectively;
The device includes an optical switch driving circuit that drives the reading moonlight switch, and a central control device that controls the timing of each of the current driving and optical switch driving circuits.

(Operation of the Invention) In the present invention, an input time-division optical signal is divided by an optical branching circuit and made to simultaneously enter all the bistable semiconductor lasers, and the injected current of each bistable semiconductor laser is written as a signal. The current value is increased to a state that can be triggered by the input optical signal only during the desired time slot, and the current value is kept low enough that the written state is maintained and the input optical signal does not trigger the current value for the rest of the time. Write operations and optical memory operations are performed by

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a time division optical switch according to the present invention. In FIG. 1, an input optical waveguide 310 for inputting a first time-division optical signal 100 consisting of four time slots carrying different information, and a second
output optical waveguide 3 for outputting a time-division optical signal 190 of
A semiconductor laser 340 exhibiting bistable operation has an input terminal connected to the input optical waveguide 310 and an output terminal connected to the input optical waveguide 80.
Optical waveguide 3 guided to the input end of 350, 360° 370
41, 351, 361° 371, respectively, and optical waveguides 342, 352, 362, 372 guided to the emission end of the bistable semiconductor laser.
A readout 4×1 optical switch 330 whose input terminal is connected to the output optical waveguide 380 and whose output terminal is connected to the output optical waveguide 380.
is installed. An optical switch drive circuit 331 is connected to this optical switch 330, and current drive circuits 345, 355 for injecting bias current into bistable semiconductor lasers 340, 350, 360, and 370, respectively.
, 365°375 are connected. Optical switch drive circuit 331 and current drive circuits 345, 355, 365, 3
75 is connected to a central control unit (not shown). This central control device is composed of a timing extraction circuit, a mesh circuit, etc., and generates control signals for controlling the optical switch drive circuit and the current drive circuit.

Each current drive circuit is a device that generates three-value current according to commands from a central controller, and a simple example thereof is shown in the circuit diagram of FIG.

This current drive circuit consists of two transistors TripTr.
2 and two resistors. The collectors of these transistors T rl + T r 2 are connected to the bistable semiconductor laser LD1. Each errata has a resistance R
1 and R2 are connected to the power source 1, and the base terminal serves as an input terminal for a control signal. In this figure, if the pace voltage of transistor Tri,T,2 is smaller than V, then transistor TrllT,! Since both are off, the bistable semiconductor laser LD inserted in series on the collector side
No current flows through .

On the other hand, the voltage V (V
When V) is applied, the transistor T r 1 is turned on, and the current 1 of the bistable semiconductor laser LD1 becomes i-i (Vl-V)/R1. Similarly, when voltage v1 is added to '1', o pace, iwi, x(Vl-V)/
It becomes R2. Also, voltage ■1 is applied to both T and □+'T'r2.
When is applied, a current of 1=i3-i+12 flows through the bistable semiconductor laser. In this way, the circuit shown in FIG. 2 allows a three-value current to flow through the LD □ which is a bistable semiconductor υ in response to an external signal.

Here, a specific example of the 4×1 optical switch for readout and the optical branch circuit of this embodiment, a bistable semiconductor laser 340°350.3
A specific example of 60,370 will be explained.

First, FIG. 3 111 shows a plan view of an example of a directional coupling type optical switch that can be used as a 4×1 optical switch 330 for reading. Ferroelectric crystal or semiconductor crystal substrate 20
Ninety-four directional coupling type optical switches 21 and 22 are formed above.
, 23.30. For example, an optical waveguide is created by diffusing titanium onto a lithium niobate crystal.
The above-mentioned directional coupling type optical switch can be obtained by placing electrodes on optical waveguides close to each other. The directional coupling type switch 30 is a switch for cutting off optical signals passing through the optical waveguide 24. When the optical waveguide 24 is used for output and the optical waveguides 25, 26, 27, and 28 are used for input, it can be used as a 4×1 optical switch for reading.

In addition, the optical switch drive circuits 321 and 331 are centrally controlled
fi#F1 Tips k a-A/V? h4-xλ
,, 4-2 'J n 4'+ Generates an electrical signal for performing the translation I Nl.

For example, if the optical switch 330 is the optical switch shown in FIG. 3 111, it has the function of supplying voltages with different z values to the directional coupling type optical switches 21, 22, 23, and 30, respectively. When each of these directional coupling type optical switches 21, 22, 23.30 has an applied voltage of O, a light wave incident on one of the optical waveguides passes through the incident optical waveguide as it is, and when the voltage is set to V, the incident light approaches When moving to the other optical waveguide, the optical switch drive circuit 331 can most simply be configured with a circuit using one transistor for each directional coupling type optical switch.

For example, a voltage V is applied to the collector of a transistor through a resistor R.
It is constructed by connecting the device to the power supply of the machine, grounding the emitter, using the base as the input terminal for control signals, and outputting the output voltage terminal from the collector. In this circuit, when the voltage of the control signal is 00, the output voltage is v1, and when the control signal voltage is positive, the output voltage is O.

FIG. 3 (bl shows an optical fiber branching circuit as a specific example of the optical branching circuit 320. 40 is an input optical fiber, 42° 43,
44.45 is an output optical fiber. This branch circuit consists of 4
It can be manufactured by bundling optical fibers together and heat-sealing the bundled portion 41. Also, Figure 3 f
A waveguide-type optical branch circuit can also be constructed using an optical waveguide provided on a substrate similar to AT.

FIG. 4 is a sectional view showing a specific example of a bistable semiconductor laser 340, 350, 360°, 370. The structure is almost the same as a commonly used current injection type semiconductor laser, for example, GaAIAa/GaAs or InGaAaP/InP.
This is a laser with a double heterojunction structure made of . However, it differs from a normal semiconductor laser in that the electrodes are not uniform and there are some parts into which current is not injected. Since this current non-injection region acts as a saturable absorber, this bistable semiconductor laser can have bistable characteristics in the injection current versus optical output characteristics. In addition to making the electrode non-uniform, it is also possible to create similar bistable characteristics by making the active layer, which is the light emitting region, less uniform, and by providing a saturable absorption region in a part. I can do it.

In these bistable semiconductor lasers, by appropriately selecting the injection current 1t, bistable characteristics can also be obtained in the characteristics of the emitted light with respect to the externally injected light. Details of such bistable semiconductor lasers can be found in the literature Electronics Letters (El
electronics I, 6tter) Volume 17, 741
Page and in the 1985 IEICE Optical-Radio Division National Conference Lecture Proceedings (Volume 2) No. 272.

Fig. 5 (al, (bl, (C1) is a characteristic diagram explaining the operation of the bistable semiconductor laser shown in Fig. 4. In other words, when the injection current is increased from Lt-16, the output light amount Pout increases rapidly at t-i, and conversely, when the injection current i is decreased from it, the output light amount Pout increases from t-i. The light amount pout exhibits a hysteresis characteristic such that it rapidly decreases at i-1°, and has two stable points A1 and B1 of the output light amount Pot and P □ at a current value of 1m1b which is slightly larger than 1c. , larger than l & slightly smaller than current value 1=i
Similarly, b1 has two stable points A2 and B2 of the output light amount Po2 and P□2.

Figure 5 (bl is the injection current 1 = -1 in Figure 5 fa+)
, 1 is a diagram showing the relationship between the incident light amount pin and the output light amount pout. That is, the output light amount Pout = -p
O.

If the input light amount Pin is increased from 0 when it is at the stable point A of @1, the output light amount pout will be Pin = P1□
When the incident light quantity pin m pt increases rapidly and is thereafter decreased from the incident light quantity pin m pt □, the output light quantity pout hardly decreases and moves to the second stable point B of the output light quantity pout x P □. Points A and B1 in FIG. 5 (bl) represent the same points as points A1 and B1 in FIG. 5 (alK), respectively.

Similarly, FIG. 5 fcl shows the relationship between the incident light amount Pin and the output light amount pout when s'-'b2 is shown in FIG. 5 tal. In this case, the point Pt2 where the amount of emitted light increases rapidly is smaller than Ptt.

Table 1 below shows the operation of the bistable semiconductor laser with respect to the injection current i and the incident light Pin.

That is, when the injected current i is ib and the incident light Pin is O, the bistable semiconductor laser has two stable points A□ and B in Figure 5+al according to the previously written data.
1, and the output light amount P0□ or P
□, maintain. In FIG. 5 fat, when the bistable semiconductor laser maintains one stable point B (output light amount P□□) t-, the injection current it-once i.

Then, when it returns to tbt again, the output light amount P out becomes B1→D
→ A1, and then the other stable point A1 (output light amount P
. □) t-Hold, ie the bistable semiconductor laser is reset. In addition, the current is set to 1-ib2, and Fig. 5 (C1
, the bistable semiconductor laser reaches stable point A2 (output light amount P
. 2) While holding t-, if the input light amount is set to P and then returned to O-, the output light amount Pout changes from A2 to E4B2 and maintains the stable point B2 (output light amount P12), that is, it is a bistable semiconductor. Laser hissected. In this state, if the current is set to 1 = il, the stable point will be shifted to B and maintained. In the state of i=i>1, even if Pin=Pt1 is input, there is a danger that it will be set. When the injection current t is 10 and the incident light amount Pin is Ptl, the output light amount Pout shows a value P2 which is similar to the characteristics of a bistable semiconductor laser, but this light amount is not directly used in the present invention, so a description thereof will be omitted.

FIG. 6 shows the bistable semiconductor laser 3 of the embodiment shown in FIG.
40 is a time chart for explaining write and read operations. Referring to FIGS. 5 and 6, the time-division optical signal 100 is guided to the optical waveguide 310 shown in FIG. The optical signal 400 in FIG. 6 is a time-division optical signal 100.
Each of the information A, B, C, and D is converted into 1-bit NRZ
A specific example when used as a signal is shown below. Here, the light quantities o and pt1t- shown in FIG. 5 are respectively required as a signal of 0.1. In FIG. 1, bistable semiconductor lasers 340, 350,
360 and 370 have current drive circuits 345 and 35, respectively.
5,365,375, the current value i shown in FIG.
A current of b is injected. When using the current drive circuit shown in FIG. 2, in this state the transistor T r
Only 1 is on. The optical waveguide 380 is always connected to the optical waveguides 342, 352, 362, . . . by the optical switch 330.
It has been separated from 372. The optical switch 330 is the third
♀ (In the case of the configuration shown in al., at this time, the voltage v1 is applied to the directional coupling type optical switch 30 by the optical switch drive circuit 331, and the directional coupling type optical switch 3
0 is in a blocked state.

In FIG. 1, writing of the time-division optical signal 100 into the bistable semiconductor laser 340 is performed as follows. That is, first, in the first period in the first time slot of the time-division optical signal 100, the current lt injected into the bistable semiconductor laser 340 is once reduced to 10 as shown in FIG. 6 410, and then changed to ibz.

This can be accomplished, for example, by turning off transistor T r l of FIG. 2 and then turning on transistors T, T, and T, 2 simultaneously. As a result, the bistable semiconductor laser 34
Even if the light intensity P1□ was previously maintained at the output light intensity Pout of 0 as shown in FIG. 6 440, the injection current pulse 4
It is reset to Po0 at the falling leading edge 411 of 10. Then, in a second period following said first period within a first time slot of time-divided optical signal 100, the current ib
It is kept at z. As a result, the bistable semiconductor laser 340
When the incident light amount is Pt2, the output light amount 440 is P1□ at the rising edge 431 of the current pulse 410.
and P when the incident light amount 430 is 0.

It becomes 2.

After this, the injection current pulse is held at 1, 1, so the bistable semiconductor laser 340 receives 1 information P, or
O's information P. □ is retained.

In this manner, the information of the time-division optical signal 100 is written into the bistable semiconductor laser 340. Similarly, the current drive circuits 355, 365, and 375 control the currents injected into the bistable semiconductor lasers 350, 360, and 370, respectively, thereby controlling the information B, C, and D of the time-division optical signal 100.
t-each bistable semiconductor laser 350°360.37
Write it to 0. Reading of the information written into the bistable semiconductor laser 340 into the time-division optical signal 190 is performed as follows. That is,
For example, in the fourth time slot of the time-division optical signal 190, the optical waveguide 342 is connected to the optical waveguide 380 by the optical switch 330. 450 in FIG. 6 is an optical switch 330
The optical switch drive circuit 33 performs the connection operation.
1 shows the control voltage supplied to the optical switch 330 by 1.

Here, it is assumed that the optical switch 330 connects the optical waveguide 342 and the optical waveguide 380 only when the control voltage 450 is vl. For example, the optical switch in FIG.
When used as , control voltage 450 represents the voltage applied to directionally coupled optical switch 21 , 22 . As a result, an optical signal obtained by extracting the emitted light 440 of the bistable semiconductor laser 340 by the control voltage 450 is obtained in the optical waveguide 380 as shown in FIG. 6 460. Similarly, the optical waveguide 380 is further provided with the first signal of the time-division optical signal 190. Bistable semiconductor laser 370 in each of the 21st and 3rd time slots.
, 360 and 350, C and B are read out.

In the time-division optical signal 190 thus obtained on the optical i-wavepath 380, information A and D and information B and C of the time-division optical signal 100 are exchanged.

(Effects of the Invention) As explained above, in the present invention, the length of the frame cycle of exchanged information can be arbitrarily set by controlling the write and read optical switches, and a long optical fiber is not used. Therefore, it is easy to downsize the device. Furthermore, by using a bistable semiconductor laser with a high level of emitted light, it is possible to increase the amount of light of the second time-division optical signal 100 compared to that of the first time-division optical signal 190. Furthermore, since only one optical switch is used, a time-division optical switch that is smaller and cheaper than the conventional one can be obtained.

Note that the present invention is not limited to the above-described embodiments. For example, in the embodiment shown in FIG. 1, writing to a bistable semiconductor laser is performed periodically and reading is performed in accordance with the information to be exchanged. Exactly the same exchange operation can be obtained by periodically performing reading according to the information to be exchanged. Also, one time slot is n bits (
n≧2), n bistable semiconductor lasers are installed in each of the two bistable semiconductor lasers shown in this example, and n bistable semiconductor lasers are installed in each time slot. By writing and reading metal data in a semiconductor laser, switching between time slots can be achieved. Further, as the readout optical switch, an optical switch having a configuration in which a gate portion for blocking light is provided in each branch of an optical branch circuit can also be used.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a time-division optical switch according to the present invention, FIG. 2 is a circuit diagram of an example of the current drive circuit of the semiconductor laser shown in FIG. 1, and FIG. FIG. 4 is a cross-sectional view of an example of a bistable semiconductor laser, and FIG. 5(a) is a block diagram of an example of a readout optical switch and an optical branch circuit that can be used. A characteristic diagram showing the operation, and FIG. 6 is a time chart explaining the operation of this embodiment. In the figure, 320... optical branch circuit, 330... optical switch for reading, 34
0,350°360.370...Bistable semiconductor laser. −〕＼

Claims (1)

[Claims] An optical branch circuit having one input end and a plurality of output ends, and a bistable operation installed corresponding to each output end so that the light emitted from the output end enters from one end of the laser resonator. a readout optical switch comprising a plurality of input terminals and one output terminal corresponding to each semiconductor laser so that the emitted light from these semiconductor lasers enters, and each of the semiconductor lasers A current drive circuit that drives each of the readout optical switches, an optical switch drive circuit that drives the readout optical switch, and a central control device that controls the timing of each of the current drive circuits and the optical switch drive circuit. Split optical switch.