JPH0695664B2 - High-speed optical pulse multiplexer / demultiplexer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for multiplexing or demultiplexing high-speed optical pulses used for high-speed signal transmission.

(Prior art and its problems) Since the commercialization of a semiconductor laser capable of performing direct modulation with high efficiency with high efficiency, the field of application of optical communication using a semiconductor laser as a light source is rapidly expanding. However, in the direct modulation of a semiconductor laser, the upper limit of the modulation speed is limited by the injected carrier lifetime, and it is currently up to about 4 Gb / s. By driving with a narrow current pulse, an optical pulse with a narrow pulse width of about 50 ps can be obtained. However, in this case also, due to the influence of a large injected carrier lifetime, a change in response due to the pulse pattern, a so-called pattern effect occurs, so that the speed corresponding to the minimum pulse width, for example, at 20 Gb / s for a 50 ps width, It was difficult to carry optical signals. On the other hand, a method using a high-speed external modulator has also been proposed, but in order to drive a modulator by amplifying a high-speed random pulse signal, in addition to a wide-band pulse amplifier, the frequency characteristics of the modulator have wide-band flatness. However, there is a drawback that it is practically difficult to operate at several Gb / s or more. As another conventional example, there has been known a system in which a plurality of independent optical signal sources having a low pulse width but a narrow pulse width are coupled in parallel by an optical multiplexer to obtain a high-speed optical pulse signal. However, this method has a drawback that it is difficult to increase the speed by causing interference between adjacent pulses unless the synchronization jitter between the optical signal sources is suppressed small, and the upper limit of the signal speed is
There is a drawback that it is limited by the pulse width of the light source. Further, when the optical waveguide is a single mode system, there is a drawback that the multiplexing loss tends to increase.

(Object of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks, and to perform high-speed optical pulse multiplexing / demultiplexing that enables multiplexing or demultiplexing of ultra-high-speed optical pulse signals
To provide a separating device.

(Structure of the Invention) According to the present invention, in a high-speed optical pulse multiplexer / demultiplexer configured to include a plurality of cross-type optical switches connected in series, adjacent optical switches of the optical switches are arranged between the optical switches. Controlled by an opening / closing control pulse signal having a pulse delay time different from the optical pulse propagation time, and the width of the opening / closing control pulse signal is smaller than the difference between the optical pulse propagation time and the pulse delay time. An optical pulse multiplexer / demultiplexer can be obtained.

(Example) Next, this invention is demonstrated in detail with reference to drawings.

FIG. 1 is a diagram showing the configuration of a first embodiment according to the present invention. This embodiment is a cross-type optical switch connected in series.
41, 42, 43, output optical waveguide 20 connecting them, and input optical waveguides 11, 12, 1 respectively connected to optical switches 41, 42, 43
3. The control line 30 for transmitting the opening / closing control pulse signal of the optical switches 41, 42, 43. Optical switch 41,4
As 2,43, a directional coupling type optical switch or the like formed on a LiNbO ₃ electro-optic crystal is used. The electrical signal controls the coupling state between the input optical waveguides 11, 12, 13 and the output optical waveguide 20. The optical switches 41, 42, and the output optical waveguide 20 connecting the optical switches 42, 43 is composed of an optical fiber whose length is adjusted so that the optical pulse propagation time between the optical switches is 1 ns. The control line 30 is configured to include delay lines 31 and 32 for giving a constant delay to an electric signal, and is designed to give a pulse delay time of 1.833 ns between adjacent optical switches. The repetition cycle of the open / close control pulse signal is 2.5 ns and the pulse width is 0.4 / ns. Input optical waveguide 11,12,1
Optical pulse signal given to 3 (input signal # 1, # 2, #
In 3), each part of the optical switches 41, 42 and 43 is almost synchronized with the opening / closing control pulse signal and the pulse width thereof is about 0.5 ns. FIG. 3 is an operation diagram of this embodiment. Each input signal is multiplexed so that the difference between the optical pulse propagation time and the delay time of the switching control pulse signal is an interval.

According to this embodiment, in each optical switch unit, the switch is in the open state while the optical pulse signal pushed in by the preceding optical switch is passing, and is output to the output optical waveguide 20 as it is,
Further, mutual interference between the passing optical pulse signal and the optical pulse signal inserted by the optical switch section does not occur. The interval between the optical pulse signals inserted and multiplexed in the adjacent optical switch is very stable because it is determined by the difference between the optical pulse propagation time and the pulse delay time of the switching control pulse signal, and the relative jitter associated with multiplexing is It is possible to prevent an increase in the amount. Since the optical pulse signal width after multiplexing is determined by the switching control pulse signal, it contributes to the reduction of mutual jitter at the same time as the waveform shaping of each input signal. According to this embodiment, three input signals having a bit rate of 400 Mb / s are multiplexed and a 1.2 Gb / s signal is obtained.

Although the optical pulse propagation time between the optical switches is shorter than the pulse delay time of the opening / closing control pulse signal in this embodiment, on the contrary, the optical pulse propagation time between the optical switches is the opening / closing control pulse. It may be configured to be longer than the pulse delay time of the signal. However, even in this case,
The width of the switching control pulse signal must be set smaller than the difference between the optical pulse propagation time between the optical switches and the pulse delay time of the switching control pulse signal. When the optical pulse propagation time between the optical switches is set to be longer than the pulse delay time of the opening / closing control pulse signal, the input signals # 1, # 2, and # 3 on the multiplexed optical pulse signal are 3, #
2 and # 1 will be arranged in this order.

FIG. 2 is a diagram showing a second embodiment according to the present invention.

This embodiment is the same as the first embodiment except that it is constructed in a form integrated on a GaAs semiconductor substrate. N-type Al _0.3 Ga _0.7 As (1
× 10 ¹⁷ cm ^-3 Si-doped, thickness 2 μm, n-type GaAs (1
× 10 ¹⁵ cm ^-3 Si-doped, thickness 0.1 μm), p-type Al _0.3 Ga
_0.7 As (2 × 10 ¹⁵ cm ^-3 Be-doped, thickness 1 μm) was sequentially epitaxially grown, and the p-type Al _0.3 Ga _0.7 As layer was patterned into a ridge waveguide type to form an input optical waveguide.
11, 12, 13, output optical waveguide 20, and optical switches 41, 42, 43 are formed. The width of the ridge waveguide is 2 μm, the waveguide spacing in the optical switch is 1 μm, the coupling length is 1 mm, the spacing between the optical switches 41, 42 and 43 is 10 mm (optical pulse propagation time about 100 p
s). The control line 30 is on the p-type Al _0.3 Ga _0.7 As layer,
Parts other than the optical switch section are formed of Au wiring via SiO ₂ . By inserting the delay lines 31 and 32 between the optical switches 41 and 42 and between the optical switches 42 and 43, a pulse delay time of about 200 ps, which is 100 ps longer than the optical pulse propagation time, is obtained.

In this embodiment, as the input signals # 1, # 2, and # 3, signals having a wavelength of 1.3 μm and a bit rate of 2 Gb / s were input, and a pulse having a repetition rate of 500 ps and a width of 50 ps was used as the opening / closing control pulse signal. As a result, a 6 Gb / s multiplexed optical pulse signal can be obtained. With the configuration of this embodiment, it is possible to increase the number of input terminals to 5 and up to 10 Gb / s. Since the optical switch parts, which are the insertion points of the optical pulse signals, are connected in series, there is little bending of the optical waveguide part during integration as in the present embodiment, and there is a problem in using an optical multiplexer when the number of multiplexing is large. The advantage is that there is little multiplexing loss.

By the way, in each of the above-described embodiments, the configuration having the optical multiplexing function is described. However, if the opening / closing control pulse signal having the inverted input / output and synchronized with the input optical pulse signal is used, the optical signals separated by each optical switch unit are used. It goes without saying that a pulse signal can be obtained.

That is, to explain based on the configuration of the first embodiment, the output optical waveguide 20 in the first embodiment is read as an input optical waveguide, and the input optical waveguides 11, 12, and 13 are read as output optical waveguides.
The separated optical input signal is input to the input optical waveguide (20) of the optical switch (43), and the switching control pulse signal is directed from the optical switch (43) to the optical switch (41) on the control line (30). The optical pulse signals separated by applying to each optical switch while delaying are output to the optical waveguide (1
It can be taken out from 3), (12) and (11). Incidentally, it is appropriate that the delay time between the optical switches of the opening / closing control pulse signal is equal to the sum of the pulse time interval of the separated optical input signal and the optical pulse propagation time between the optical switches. .

(Effects of the Invention) Finally, to summarize the effects of the present invention, it is possible to multiplex or demultiplex ultrafast optical pulse signals with less pulse jitter and pulse pattern effects.

[Brief description of drawings]

1 and 2 are diagrams showing the configurations of the first and second embodiments of the present invention, respectively. FIG. 3 is an operation diagram of the first embodiment. In the figure, 11, 12, 13 are input optical waveguides, 20
Is an output optical waveguide, 30 is a control line, and 41, 42, 43 are optical switches.

Claims (2)

[Claims] 1. A cross-type optical switch comprising at least a first and a second cross-type optical switch, and means for applying an opening / closing control pulse signal to the cross-type optical switch, wherein each of the cross-type optical switches has at least two light sources. Input terminal and at least Kotsu 2
One optical output terminal and at least one open / close control pulse signal input terminal, and the open / close control pulse signal outputs the optical input signal of the optical input terminal of A to the optical output terminal of A and the optical input of the optical input terminal of B The state of outputting the signal to the optical output terminal of B and the state of outputting the optical input signal of the optical input terminal of A to the optical output terminal of B and the optical input signal of the optical input terminal of A to the optical output terminal of A The switching control has a function of switching to any one, and one of the optical output terminals of the first crossover optical switch is connected to one of the optical input terminals of the second crossover optical switch, and the opening / closing control is performed. A means for applying a pulse signal is connected to the switching function of the electric signal and the switching control pulse signal input terminals of the first and second crossover optical switches respectively, and first and second outputs for supplying the switching control pulse signal. It has a terminal and The width of the control pulse signal is supplied to the propagation time of the optical signal between the first and second crossover optical switches and to the open / close control pulse signal input terminals of the first and second crossover optical switches, respectively. It is smaller than the difference between the delay times of the switching control pulse signals, and is the first of the optical input terminals of the first crossover optical switch and the optical input terminals of the second crossover optical switch. An optical input terminal that is not connected to the optical output terminal of the crossover optical switch is used as an input terminal for the multiplexed optical signal, and one of the output terminals of the second crossover optical switch is used for the multiplexed optical signal. A high-speed optical pulse multiplexer, which has an output terminal. 2. An optical switch comprising at least first and second crossover optical switches and means for applying an opening / closing control pulse signal to the crossover optical switches, each of the crossover optical switches having at least two optical switches. Input terminal and at least Kotsu 2
One optical output terminal and at least one open / close control pulse signal input terminal, and the open / close control pulse signal outputs the optical input signal of the optical input terminal of A to the optical output terminal of A and the optical input of the optical input terminal of B The state of outputting the signal to the optical output terminal of B and the state of outputting the optical input signal of the optical input terminal of A to the optical output terminal of B and the optical input signal of the optical input terminal of A to the optical output terminal of A The switching control has a function of switching to any one, and one of the optical output terminals of the first crossover optical switch is connected to one of the optical input terminals of the second crossover optical switch, and the opening / closing control is performed. A means for applying a pulse signal is connected to the switching function of the electric signal and the switching control pulse signal input terminals of the first and second crossover optical switches respectively, and first and second outputs for supplying the switching control pulse signal. It has a terminal and The width of the control pulse signal is supplied to the propagation time of the optical signal between the first and second crossover optical switches and to the open / close control pulse signal input terminals of the first and second crossover optical switches, respectively. The first crossover optical switch is smaller than the delay time between the switching control pulse signals and one of the optical input terminals of the first crossover optical switch is the input terminal of the separated optical signal. Optical output terminal not connected to the optical input terminal of the second crossover optical switch, and one output terminal of the second crossover optical switch, the output terminal of the optical signal A high-speed optical pulse separation device characterized by the following.