JP2003318863A - Variable delay optical buffer circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable delay optical buffer circuit for optionally controlling delay of optical signals for realizing an optical buffer circuit essential for realizing a superspeed optical network in the next generation and afterward. <P>SOLUTION: The variable delay optical buffer circuit is provided with an S/P conversion part for converting a serial optical signal into a parallel optical signal, a photoelectric converting part for converting the optical signal from the S/P conversion part into an electric signal and for holding a peak value in prescribed time and an output part for converting the electric signal from the photoelectric converting part into the optical signal at the prescribed timing, for simultaneously converting it into a serial signal and for outputting the serial signal. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable delay type optical buffer circuit which can freely change the delay of an optical signal and is optimal for an ultra high speed optical network.

[0002]

2. Description of the Related Art An input optical signal is temporarily stored,
The buffer function of reading the accumulated optical signal at the timing of signal processing is an essential function for optical signal processing. A conventional buffer circuit using an electronic circuit has a limitation in speeding up due to the speed of the electronic circuit itself.

As an alternative to such a buffer circuit using an electronic circuit, there is an optical buffer circuit capable of speeding up. In the optical buffer circuit, as shown in FIG. 7, the lengths of the optical fiber cables 101 to 10n are adjusted at equal intervals, as shown in FIG.
An array of a plurality (n) of these is used. This is based on the principle that the optical transmission speed of an optical fiber cable is about 20 cm at 1 ns, and the optical signal cable transmission time differs depending on the cable length. Therefore, the optical signal delay time is controlled by adjusting the cable length. it can.

[0004]

However, when the delay time is controlled by adjusting the cable length, the buffer time becomes discrete, and the longer the buffer time, the longer the optical fiber cable length (for example, 500 ns).
There is a problem that it is not realistic.

As another example, a bistable laser utilizing the saturable absorption characteristic of a semiconductor can operate as an optical memory element, but the characteristic largely depends on the wavelength of input light, and the operating speed depends on the relaxation oscillation frequency. Since it is rate-controlled, it is difficult to operate at more than 10 Gbps.

The present invention has been made under the above circumstances, and an object of the present invention is to realize an optical buffer circuit which is indispensable for realizing an ultrahigh-speed optical network for the next generation and beyond. An object of the present invention is to provide a variable delay type optical buffer circuit capable of arbitrarily controlling signal delay.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a variable delay type optical buffer circuit, and an object of the present invention is to provide an S / P converter for converting a serial optical signal into a parallel optical signal, and the S / P converter.
A photoelectric conversion unit that converts an optical signal from the / P conversion unit into an electric signal and holds a peak value at a predetermined time, and an electric signal from the photoelectric conversion unit at a predetermined timing into an optical signal and a serial signal It is achieved by providing an output section for outputting the output.

The above object of the present invention is to provide the S / P converter,
The present invention is more effectively achieved by providing a control unit that controls the photoelectric conversion unit and the output unit. Further, the present invention relates to a variable delay type optical buffer circuit. A first optical fiber cable or an optical waveguide having a different length, and a first optical gate that operates based on a first optical gate pulse inserted in each of the optical fiber cables or the optical waveguide, A photoelectric conversion element for converting an optical signal output from each of the optical fiber cables or the optical waveguide via the first optical gate into an electric signal, and each peak value of the electric signal output from each of the photoelectric conversion elements at a predetermined time. And a second optical gate that operates on the basis of the second optical gate pulse while receiving the output signals of the respective peak hold circuits. The by transmitting in different second optical fiber cable or optical waveguide lengths optical multiplexes, it is achieved by providing an optical multiplexing section that outputs a serial optical signal.

The above object of the present invention is to determine the length of the first optical fiber cable or optical waveguide and the length of the second optical fiber cable or optical waveguide from the bit interval of the serial optical signal and the optical transmission speed, respectively. Alternatively, the delay time of the serial optical signal is arbitrarily set by detecting the input of the serial optical signal and outputting the first optical gate pulse, or by controlling the generation of the second optical gate pulse. Is achieved more effectively.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The configuration of the variable delay type optical buffer circuit of the present invention holds optical information not as light but as an ON / OFF (open / close) state of an optical gate. Regeneration of the optical pulse train can be realized by sending a single optical pulse (serial optical signal) to each gate and passing it through a delay line and a multiplexer corresponding to the time interval (bit interval) of the pulse. That is, since the pulse width is determined by the output of the reproducing semiconductor laser or another light source, the degree of freedom is high. The pulse interval can be easily changed by changing the delay width of the delay line. On the other hand, when only the input / output unit is composed of a semiconductor laser and a photodetector and the buffer is composed of an electronic circuit, it is difficult to perform high-speed processing with an optical pulse width of several ps and a pulse interval of 10 ps or less. In particular, the portion that converts serial data into parallel data is an area where high-speed operation of the optical element is effective.

With the configuration of the present invention, 100 Gbps is applied to the optical pulse.
High speed is required (pulse interval 10 ps or less), but the existing response speed can be used as an electronic circuit, and the buffer time can be set freely by adjusting the time timing of sending the reproduction optical pulse. The feature is that you can do it.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a basic configuration of the present invention. An optical signal (a 4-bit serial signal in this example) PS1 is input to an optical branching unit 1 and is branched and the optical fiber cables 2A to 2A ... It is transmitted in 2D. The optical signal PS1 is
Control unit 2 via photodiode 11 and smoothing circuit 12
0 is also input, and the input of the optical signal PS1 is detected. Each optical fiber cable 2A-2D has
Optical gates 3A to 3D that are on / off controlled by an optical gate pulse PG1 from a laser diode 4 operating under the control of the control unit 20 are respectively inserted, and the control unit 20 inputs the optical signal PS1 to the optical gate pulse PG1. The signal is output at the detected predetermined timing t ₀ .
The optical gate pulse is input to the optical gate through an optical multiplexer installed between the optical gate and the optical fiber cable or the optical waveguide. The optical gates 3A to 3D are
It is turned on when the optical gate pulse PG1 is input from the laser diode 4 controlled by the controller 20, and the serial signal is converted into a parallel signal.

The outputs of the optical fiber cables 2A to 2D are photodiodes PD1 to PD4 as photoelectric conversion elements.
Is converted into an electric signal respectively, and each electric signal holds a peak value for a predetermined time.
Input to PH4. Each peak hold circuit PH1-P
The output of H4 is on / off controlled by the laser diode 5 whose emission is controlled by a control signal from the control unit 20,
It is input to the optical gates 6A to 6D that convert electric signals into optical signals. Each of the peak hold circuits PH1 to PH4 is reset by the reset pulse RS from the control unit 20 when a predetermined time has elapsed. The optical signals from the respective optical gates 6A to 6D are transmitted through the optical fiber cables 7A to 7D having different lengths, combined by the combining unit 8 and converted into the serial signal PS2 for output.

In FIG. 1, thin lines indicate electric signals and thick lines indicate optical signals.

When the input optical signal PS1 allocates time t ₁ (ns) to _one digital bit as shown in FIG. 2, the lengths of the optical fiber cables 2A to 2D connected to the optical branching unit 1 are long. It is determined and adjusted according to the following formula (1). However, the transmission speed of light in the optical fiber cable is X cm / ns.

X × t ₁ (cm) (1) Therefore, assuming that the length of the optical fiber cable 2D is L (cm), the lengths of the optical fiber cables 2C to 2A are the following (2) to (5), respectively. ).

2D: L (2) 2C: L + X × t ₁ (3) 2B: L + 2 × X × t ₁ (4) 2A: L + 3 × X × t ₁ (5) Optical fiber cable or optical waveguide The same applies to 7A to 7D. That is, when the length of the optical fiber cable 7A is M (cm), the optical fiber cable 7A to
The length of 7D is set as shown in (6) to (9) below.

7A: M (6) 7B: M + X × t ₁ (7) 7C: M + 2 × X × t ₁ (8) 7D: M + 3 × X × t ₁ (9) As described above, the optical fiber By adjusting the lengths of the cables 2A to 2D, the optical signal reaching the optical gate 3D becomes as shown in FIG. 3 (A), and the optical signal reaching the optical gate 3C becomes as shown in FIG. 3 (B). , The optical signal reaching the optical gate 3B becomes as shown in FIG.
The optical signal that reaches the point is as shown in FIG. Therefore, the control unit 20 causes the optical gate pulse PG at the timing t _0.
By outputting 1, the signals of FIGS. 3A to 3D can be simultaneously output. As a result, a parallel signal (4 bits in this example) is obtained.

Such parallel optical signals are input to the photodiodes PD1 to PD4 and converted into electric signals,
The peak value of the electric signal is the peak hold circuits PH1 to PH1.
It is held at PH4. Peak hold PH1-PH
The signals held by the four circuits are shown in FIG.
Are adapted to the (D), the optical gate pulse PG2 is output at the timing t ₂ from the control unit 20, a parallel optical signal corresponding thereto is output from the optical gate 6A-6D. The optical signals output from the respective optical gates 6A to 6D are transmitted through the optical fiber cables 7A to 7D, but since the lengths of the respective fiber cables are as shown in the equations (6) to (9), The longer the cable is, the longer the transmission time of the optical signal is delayed, and the signal multiplexed by the multiplexing unit 8 becomes the serial signal PS2 due to the difference in the delay time. Control unit 2
By controlling the output timing of the optical gate pulse PG2 from 0, the buffer time, that is, the signal delay time can be freely changed.

Incidentally, the peak hold circuits PH1 to PH4.
Is reset by the reset signal RS shown in FIG. _4E at the timing tr in FIG.

FIG. 5A shows the relationship between the serial signal and parallel signal of the serial / parallel converter and the optical gate pulse PG1. A parallel pulse is output only when the optical gate pulse PG1 is output. Are taken into the photodiode PD, and an output signal (4 bits) as shown in FIG. 5B is obtained. The output of the photodiode PD is input to the peak hold circuit PH, the maximum value is held and delayed in time as shown in FIG. 5C, and reset every 4 bits by the reset pulse RS.

With such a configuration, the buffer time can be freely adjusted with the upper limit of the time corresponding to the number of bits to be developed in parallel. In addition, it is possible to realize a longer buffer time by increasing the number of bits and adding an information storage mechanism to the peak hold circuit of another stage.

FIG. 6 shows how the reproduction optical gate pulse PG2 is converted from parallel / serial to reproduce the original serial data.

[0025]

As described above, according to the variable delay type optical buffer circuit of the present invention, it is possible to utilize the high speed of the optical element.
It is possible to expand the application of optical signal processing in the area exceeding Gbps. Further, in the optical circuit mainly including the optical element, the element configuration can be made simpler than that of the electronic circuit, so that the number of elements can be reduced by one digit or more and the power consumption can be reduced as compared with the configuration of the conventional electronic circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration example of the present invention.

FIG. 2 is a time chart showing an example of an optical signal.

FIG. 3 is a time chart showing an operation example of serial / parallel conversion.

FIG. 4 is a time chart showing an operation example of a peak hold circuit.

FIG. 5 is a diagram for explaining the operation of the present invention.

FIG. 6 is a diagram for explaining the operation of the present invention.

FIG. 7 is a diagram showing an example of a conventional buffer.

[Explanation of symbols]

1 Optical branch 2A-2D, 7A-7D optical fiber cable 3A-3D optical gate 4, 5 laser diode 6A-6D optical gate 8 Multiplexing section 20 Control unit 101-10n optical fiber cable

Claims (6)

[Claims] 1. An S / P conversion unit for converting a serial optical signal into a parallel optical signal, and a photoelectric conversion unit for converting an optical signal from the S / P conversion unit into an electric signal and holding a peak value at a predetermined time. A variable delay type optical buffer circuit, comprising: an optical signal from the photoelectric conversion unit and an output unit for converting the electric signal into an optical signal at a predetermined timing and converting the electric signal into a serial signal for output. 2. The variable delay type optical buffer circuit according to claim 1, further comprising a control unit for controlling the S / P conversion unit, the photoelectric conversion unit and the output unit. 3. An optical branching section for branching a serial optical signal to a first optical fiber cable or an optical waveguide having a different length, and a first optical fiber cable or an optical waveguide interposed therebetween.
A first optical gate that operates based on an optical gate pulse; a photoelectric conversion element that converts an optical signal output from each of the optical fiber cables or optical waveguides through the first optical gate into an electrical signal; A peak hold circuit that holds each peak value of the electric signal output from the conversion element for a predetermined time, and a second optical gate that receives the output signal of each peak hold circuit and that operates based on the second optical gate pulse A variable delay type optical buffer circuit comprising: a second optical fiber cable or an optical waveguide having a different length for optical multiplexing and optical multiplexing to output a serial optical signal. 4. The length of the first optical fiber cable or optical waveguide and the length of the second optical fiber cable or optical waveguide are determined from the bit interval of the serial optical signal and the optical transmission rate, respectively. Variable delay type optical buffer circuit. 5. The variable delay type optical buffer circuit according to claim 3, wherein the input of the serial optical signal is detected and the first optical gate pulse is output. 6. The variable delay type optical buffer circuit according to claim 3, wherein the generation of the second optical gate pulse is controlled so that the delay time of the serial optical signal can be arbitrarily set.