JPH08288948A - Optical atm switch - Google Patents

Abstract

PURPOSE: To attain high speed processing by providing an input buffer circuit, an electrooptic cell conversion circuit, an optical wayeguide, an optical star coupler, an optical cell selection circuit, an optoelectric cell conversion circuit and an output buffer circuit. CONSTITUTION: An electric ATM cell outputted from input buffer circuits 2-1-2-n is given to electrooptic cell conversion circuits 3-1-3-n. The circuits 3-1-3-n modulate an optical short pulse train whose pulse width is Δτr and whose period is 1/N(s) by an electric ATM and converts the pulse train into an optical signal. An optical ATM cell of each channel is given to an optical star coupler 5 via optical waveguides 4-1-4-n having a relative time delay Δt between adjacent channels, the optical ATM cell is outputted from the coupler 5 while being subject to bit multiplexing for each Δt. At the output of the coupler 5, each optical switch of optical selection circuits 6-1-1-6-n-N selects a desired cell. Each optical ATM cell is converted by optoelectric cell conversion circuits 7-1-7-n, the converted cell is subject to contention avoidance control by corresponding output buffer circuits 8-1-8-n and the result is sent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed and large-capacity optical A capable of not only one-to-one communication but also multicasting.
Regarding the TM switch.

[0002]

2. Description of the Related Art FIG. 11 shows the structure of a conventional time division type optical ATM switch. In the figure, a cell signal string in which the number of bits of one cell is L and the time length of one cell is T is input from input signal lines 91-1 to 91-n having a signal speed V (bit / s). . Cell coder 92-1 corresponding to each input signal line
92-n are optical short pulse trains with a repetition period 1 / V (s) supplied from the short pulse light source 93 through the optical coupler 94, which are modulated by the electric cells of the respective input signal lines to be converted into optical signals.
Further, it is converted into a high-speed optical cell and output. These high-speed optical cells are time-division multiplexed by the optical star coupler 95 to generate high-speed optical highways and distribute them to each outgoing line.

For each outgoing line, the cell selectors 96-1 to 96-n for selecting a desired optical cell, the cell buffers 97-1 to 97-n for controlling outgoing line conflict avoidance, and the high-speed optical cell are used as original sources. Cell decoders 98-1 to 98- for converting to low-speed electric cells
n are connected in order. The address information is the cell coder 92.
From the cell selector 9
Address determination is performed at 6 to control the cell selector 96 and the cell buffer 97. The cell buffer 97 is 1 × m
It consists of an optical tree type switch, an optical fiber delay line and an optical coupler.

[0004]

The conventional optical ATM switch shown in FIG. 11 is called an output buffer type optical ATM switch and has a simple structure and a small number of internal blocks. The advantage is that the effects of disability are less likely to occur. However, there are problems such as a large optical power loss when generating a high-speed optical cell, difficulty in realizing an optical cell memory in a cell buffer, and difficulty in synchronizing when detecting an optical cell.

It is an object of the present invention to provide an optical ATM switch which has a high speed and a large capacity, and which can reduce optical power loss and can easily synchronize optical signals as compared with a conventional optical ATM switch.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a plurality of input buffer circuits for buffering electric ATM cells respectively input from a plurality of input lines, and an optical short circuit having a repetition period corresponding to the signal speed of the electric ATM cells. Electric pulse A
A plurality of electric / optical cell conversion circuits for intensity-modulating by a TM cell and converting into optical ATM cells, and a plurality of optical circuits for giving a relative time delay to the optical ATM cells of the respective channels output from the plurality of electric / optical cell conversion circuits. A waveguide, an optical star coupler for bit-multiplexing and outputting an optical ATM cell of each channel that has passed through a plurality of optical waveguides, and a plurality of cascaded connections for a plurality of output lines, respectively, and bit multiplexing by an optical star coupler A plurality of optical cell selection circuits that select and output optical ATM cells of a predetermined channel from the optical ATM cells, and a plurality of optical cell selection circuits that convert the optical ATM cells of each channel selected by the plurality of optical cell selection circuits into electrical ATM cells Of the optical / electrical cell conversion circuit and the plurality of output lines are arranged to buffer the electrical ATM cells of each channel output from the plurality of optical / electrical cell conversion circuits. A plurality of output buffer circuits, based on the destination address of each electric ATM cell notified from the input buffer circuit, a conflict avoidance control of the input buffer circuit,
A control device that performs channel selection of each optical cell selection circuit and contention avoidance control of the output buffer circuit is provided.

The electric / optical cell conversion circuit is an electric AT.
A short pulse light source that generates a short optical pulse train having a repeating period corresponding to the signal speed of the M cell and an intensity modulator that intensity-modulates the short optical pulse train by an electric ATM cell are provided. The optical cell selection circuit includes an optical branching device that branches an optical ATM cell that is bit-multiplexed and that is input, and one branched optical ATM cell.
Optical ATM of the channel which inputs the cell and responds to the control pulse
Optical switch for selecting cell and other branched optical AT
An optical synchronization circuit for inputting M cells to perform bit synchronization of the control pulse and an optical switch drive circuit for controlling the phase of the control pulse having the bit synchronization according to the selected channel are provided.

[0008]

In the optical ATM switch of the present invention, the optical cell generation,
Functions such as bit multiplexing, optical cell selection, and synchronization are realized by optical signal processing technology using optical short pulse trains, and buffering processing is realized by electrical technology. This allows, for example, electrical processing time of sub-nanosecond and light pulse width of 10
With picoseconds, the signal speed of the conventional ATM switch using electric signals can be increased, and the switch capacity can be increased accordingly. In addition, the optical power loss is reduced as compared with the conventional optical ATM switch,
It has a configuration that makes it easy to synchronize optical signals.

Further, a plurality of optical cell selection circuits are connected in cascade for each output line, and after the selected optical cells are converted into electric signals, conflict avoidance control is performed by the output buffer circuit. As a result, the switch throughput on the output side can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an optical ATM switch according to the present invention. In the figure, 1-1 to 1-n are electric ATMs
Cell input lines, 2-1 to 2-n are input buffer circuits, 3-
1 to 3-n are electric / optical cell conversion circuits, 4-1 to 4-n are optical waveguides that give appropriate relative time delays between the optical paths, 5 is an optical star coupler, and 6-1-1 to 6-1. -N, 6-2-1
6-2-N, ..., 6-n-1 to 6-n-N are photocell selection circuits connected in cascade, and 7-1 to 7-n are optical / electrical cell conversion circuits (photodetectors). ), 8-1 to 8-n are output buffer circuits, 9-1 to 9-n are optical ATM cell output lines, 100 is input buffer circuits 2-1 to 2-n, and optical cell selection circuit 6-1-1. To 6-n-N, output buffer circuit 8
It is a control device which controls -1 to 8-n.

The electrical / optical cell conversion circuit 3 is composed of a short pulse light source 10 and an intensity modulator 11 as shown in FIG. The optical cell selection circuit 6 includes an optical branching device 1 as shown in FIG.
2, an optical synchronization circuit 13, an optical switch 14, and an optical switch drive circuit 15. Hereinafter, an operation example of this embodiment will be described. The electric ATM cells having the signal speed V (bit / s) are input from the electric ATM cell input lines 1-1 to 1-n to the corresponding input buffer circuits 2-1 to 2-n. Each input buffer circuit sends the destination address of the cell at the head of the cell memory to the control device 100. The control device 100 controls transmission of cells from the cell memory on the basis of each address so that cell competition does not occur on the input side. The control of the input buffer circuit can be handled by a known control algorithm. The number of cells that can be output to the same outgoing line at one time is
It is the number M of photocell selection circuits connected in cascade.

The electric ATM cells output from the input buffer circuits 2-1 to 2-n are electric / optical cell conversion circuits 3-1.
To 3-n intensity modulators 11 are input. The intensity modulator 11 has a pulse width Δ supplied from the short pulse light source 10.
A short optical pulse train with τ and repetition period 1 / V (s)
It is modulated by the TM cell and converted into an optical signal. The optical ATM cell of each channel has a relative time delay Δt between adjacent channels.
Since the light is input to the optical star coupler 5 via the optical waveguides 4-1 to 4-n having, the bits are multiplexed for each Δt and output from the optical star coupler 5.

FIG. 4 shows a pulse operation at the input / output of the electric / optical cell conversion circuit 3 and the optical star coupler 5 when n = 3. In the figure, is an electric ATM cell input to the electric / optical cell conversion circuits 3-1 to 3-3, and is a channel 1 converted by the electric / optical cell conversion circuit 3-1 and output from the optical waveguide 4-1. The optical ATM cell is converted by the electric / optical cell conversion circuit 3-2 and output from the optical waveguide 4-2. The optical ATM cell of the channel 2 is converted by the electric / optical cell conversion circuit 3-3 and the optical waveguide 4-. The optical ATM cell of channel 3 output from the optical fiber 3 is a bit-multiplexed optical ATM cell output from the optical star coupler 5.

On the output side of the optical star coupler 5, a desired cell is selected by each optical switch 14 of the optical cell selection circuits 6-1-1 to 6-n-N connected in cascade. The selected optical ATM cells are the optical / electrical cell conversion circuits 7-1 to 7-1.
7-n, it is converted into an electric ATM cell, and the corresponding output buffer circuits 8-1 to 8-n are subjected to conflict avoidance control and sent to the respective optical ATM cell output lines 9-1 to 9-n.

The control of the optical switch 14 is performed by the control device 100.
Via the optical switch drive circuit 15 based on the routing information received from each input buffer circuit. Since the number of optical cell selection circuits connected in cascade is M, the number of cells that can be selected at a time is M. The larger this M, the higher the switch throughput (TTLee, et al., "A
broadband optical multicast switch ", ISS'90, Post
er Session 2, 1990).

Here, when a desired optical cell is selected from a high-speed optical signal train exceeding 100 Gbit / s, the optical / optical processing is effective because the band is extremely difficult to handle electrically. Is. Specifically, optical / optical switching using an optical nonlinear effect, an optical PLL circuit, or the like is used. Figure 5
A configuration example of the optical switch 14 and the optical switch drive circuit 15 is shown.

In the figure, the optical switch drive circuit 15 is
The optical switch control light source 16 and the cell selection timing setting circuit 17 are used. The optical switch 14 includes a multiplexer 18, an optical fiber 19, a demultiplexer 20, and an analyzer 21.
It consists of. Here, an operation example of the optical switch 14 using the optical nonlinear effect will be described with reference to FIG.
The signal light of wavelength λ ₁ and the control pulse of wavelength λ ₂ are combined by the multiplexer 18
Are multiplexed and input to the optical fiber 19. By giving an appropriate power to the control pulse, the optical fiber 19 has 3
The following optical nonlinear effect (optical Kerr effect) occurs and the refractive index changes. As a result, in the signal light whose timing coincides with that of the control pulse, a phase difference occurs between the orthogonal polarizations, and the direction of the linear polarization rotates 90 degrees when the phase difference deviates by just π.
Therefore, the signal light corresponding to the control pulse can be selected by adjusting the analyzer 21 on the output side to the polarization direction of the switching pulse. The control pulse is separated from the signal light by the demultiplexer 20. The optical fiber 19 may be an ordinary one, or an optical waveguide (eg, chalcogenide optical fiber) doped with a substance having a large nonlinear constant may be used. As another configuration of the optical switch 14 using the optical nonlinear effect, for example, one using four-wave mixing or one using a nonlinear Sagnac interferometer can be used.

In the present invention, it is necessary to switch the selected bit string for each cell cycle. Therefore, the optical switch drive circuit 15 causes the optical switch control light source 16 to output an optical pulse having a predetermined cycle according to the output of the optical synchronization circuit 13, and the cell selection timing setting circuit 17 outputs control information provided from the control device 100. The phase of the light pulse is controlled in accordance with the above, and is supplied to the light switch 14 as a control pulse.

The optical synchronizing circuit 13 for bit-synchronizing the control pulse and the signal light detects the correlation between the signal light pulse and the clock pulse by modulating the gain of a traveling wave type semiconductor laser amplifier with a clock, for example. This can be realized by an optical phase-locked loop that feeds back the phase error output to the clock and synchronizes the frequency of the clock pulse with the repetition frequency of the signal light pulse (Kawanishi, et al. "Ultrafast optical pulse synchronization technology using all-optical correlation detection" , NTT R & D, vol.42, N
o.5, pp.679-688, 1993).

FIG. 7 shows a cell selection timing setting circuit 17
A configuration example of is shown. In the figure, the cell selection timing setting circuit 17 alternately connects the 2 × 2 optical switches 22-1 to 22-m and the optical delay line pairs 23-1 to 23-m, and finally 2
In this configuration, a × 1 optical coupler 24 is connected. The first optical delay line pair 23-1 has a relative time difference of Δt, the second optical delay line pair 23-2 has a relative time difference of 2Δt, ..., The mth optical delay line pair 23-m has a relative time difference of 2t. ^m-1 Δt. Two
The control signal of the × 2 optical switch 22 is given from the control device 100.

Here, an operation example in the case of 4-channel multiplexing will be described with reference to FIG. In this case two 2
The x2 optical switches 22-1 and 22-2 are controlled. It is assumed that the 2 × 2 optical switches 22-1 and 22-2 are in the through state when 0 is given as a control signal and in the cross state when 1 is given. The control signals of the 2 × 2 optical switches 22-1 and 22-2 are 2 bits, and the control signal (1,0) that sets the delay 0 when channel 1 is selected, and the delay when the channel 2 is selected. Control signal (0, 1) for setting 1; control signal (1, 1) for setting delay 2 when channel 3 is selected; channel 4
Control signal (0,
0) is used.

Further, the cell selection timing setting circuit 17 is replaced with the 2 × 2 optical switch 22 and, as shown in FIG.
The two optical coupler 24 and the optical gate switch 25 can also be used. It is assumed that the two optical gate switches 25 arranged on the two outgoing lines of the 2 × 2 optical coupler 24 perform complementary operations. Further, the cell selection timing setting circuit 17 can also be configured by a 1 × N optical switch 26, N kinds of optical delay lines 27, and an N × 1 optical switch 28 as shown in FIG. A delay corresponding to the route set by the 1 × N optical switch 26 and the N × 1 optical switch 28 can be obtained.

[0023]

As described above, the optical ATM of the present invention
Since the switch performs high-speed processing using a short optical pulse train having a small pulse width, it is possible to generate a high-speed optical highway having a reciprocal of the pulse width. This makes it possible to realize a large-capacity optical ATM switch capable of multicasting. Further, it is superior to the conventional optical ATM switch in terms of reduction of optical power loss and ease of synchronization. Further, by arranging a plurality of optical cell selection circuits in cascade for each output line, the switch throughput can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical ATM switch according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of an electric / optical cell conversion circuit 3.

FIG. 3 is a block diagram showing a configuration example of an optical cell selection circuit 6.

FIG. 4 is a timing chart explaining the operation of pulses at the input / output of the electric / optical cell conversion circuit 3 and the optical star coupler 5.

FIG. 5 shows an optical switch 14 and an optical switch drive circuit 15.
FIG. 3 is a block diagram showing a configuration example of FIG.

FIG. 6 is a diagram for explaining the operation of the optical switch 14.

FIG. 7 is a block diagram showing a configuration example of a cell selection timing setting circuit 17.

FIG. 8 is a timing chart for explaining the relationship between an input optical cell (4 channel multiplexing) and a control pulse in the optical cell selection circuit 6.

FIG. 9 is a block diagram showing another configuration example of the cell selection timing setting circuit 17.

FIG. 10 is a block diagram showing another configuration example of the cell selection timing setting circuit 17.

FIG. 11 is a block diagram showing a configuration of a conventional time division type optical ATM switch.

[Explanation of symbols]

 1 electric ATM cell input line 2 input buffer circuit 3 electric / optical cell conversion circuit 4 optical waveguide 5 optical star coupler 6 optical cell selection circuit 7 optical / electrical cell conversion circuit (photodetector) 8 output buffer circuit 9 optical ATM cell output Line 10 Short pulse light source 11 Intensity modulator 12 Optical splitter 13 Optical synchronization circuit 14 Optical switch 15 Optical switch drive circuit 16 Optical switch control light source 17 Cell selection timing setting circuit 18 Multiplexer 19 Optical fiber 20 Demultiplexer 21 Detection Photon 22 2 × 2 optical switch 23 Optical delay line pair 24 2 × 2 optical coupler 25 Optical gate switch 26 1 × N optical switch 27 Optical delay line 28 N × 1 optical switch 100 Control device

Claims (3)

[Claims] 1. A plurality of input buffer circuits for buffering electric ATM cells respectively inputted from a plurality of input lines, and an optical short pulse train having a repeating period corresponding to a signal speed of the electric ATM cells in the electric ATM cells. A plurality of electric / optical cell conversion circuits for intensity-modulating and converting into optical ATM cells; and a plurality of optical waveguides for giving a relative time delay to the optical ATM cells of the respective channels output from the plurality of electric / optical cell conversion circuits. , An optical star coupler for bit-multiplexing and outputting the optical ATM cells of the respective channels that have passed through the plurality of optical waveguides, and a plurality of optical star couplers connected in cascade corresponding to a plurality of output lines, and bit-multiplexed by the optical star coupler. A plurality of optical cell selection circuits for selecting and outputting optical ATM cells of respective predetermined channels from the optical ATM cells; A plurality of optical / electrical cell conversion circuits for converting the optical ATM cells of each selected channel into electric ATM cells and a plurality of output lines are arranged corresponding to the optical / electrical cell conversion circuits and output from the plurality of optical / electrical cell conversion circuits. A plurality of output buffer circuits for buffering electrical ATM cells of each channel, contention avoidance control of the input buffer circuits based on the destination address of each electrical ATM cell notified from the input buffer circuit, and each optical cell An optical ATM switch comprising: a control device that performs channel selection of a selection circuit and contention avoidance control of the output buffer circuit. 2. The optical ATM switch according to claim 1, wherein the electric / optical cell conversion circuit generates a short optical pulse train having a repetition period corresponding to a signal speed of the electric ATM cell, and the electric ATM cell. An optical modulator comprising an intensity modulator for intensity-modulating the optical short pulse train in a cell.
TM switch. 3. The optical ATM switch according to claim 1, wherein the optical cell selection circuit is an optical ATM which is input after being bit-multiplexed.
Optical branching device that branches the cell into two and one branched optical AT
Optical AT of channel corresponding to control pulse by inputting M cell
Optical switch for selecting M cell and the other branched light A
An optical synchronizing circuit for inputting a TM cell to bit-synchronize the control pulse, and an optical switch driving circuit for controlling the phase of the control pulse in bit synchronization according to a selected channel. ATM switch.