JPH04257131A - Ultrashort optical pulse modulating circuit - Google Patents

Abstract

PURPOSE:To resolve the complication of a system, to reduce the power consumption, and to suppress the optical power loss and the degradation of S/N by reducing the device constitution of an ultrashort optical pulse modulating circuit and suppressing the use of active elements such as an optical switch. CONSTITUTION:An optical pulse train having a period T from a laser oscillator 1 is subjected to on/off modulation in accordance with an electric signal 5A from the external by an external modulator 5, and a modulated optical pulse train 6 is cumulatively multiplexed by 2N in a cascade compressor 18, and only an optical pulse group 24 of 2N pulses whose headers are correctly multiplexed as the first is segmented from an optical pulse train 23 multiplexed in the cascade compressor 18 based on a gate signal 19A having a period 2N.T.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an ultrashort optical pulse modulation circuit that is capable of highly multiplexing optical pulses, and in particular, by reducing the device configuration and refraining from using active elements such as optical switches. This has been improved to eliminate system complexity, reduce power consumption, and suppress optical power loss and deterioration of the S/N ratio.

0002

2. Description of the Related Art First and second prior art techniques for ultrashort optical pulse modulation circuits will be explained with reference to FIGS. 6 and 7.

In the first prior art, as shown in FIG.
The optical pulse train 2 emitted from the laser oscillator 1 is branched into N pulses in parallel by a 1×N type optical splitter 3, and after each optical pulse train 4 is separately modulated by an external modulator 5, each pulse train 6 is split into N long and short pulses. By providing a relative time delay with the optical fiber 7 and merging them with the N×1 type optical coupler 8, N multiplexed optical pulse trains 9 are emitted.

Each of these N external modulators 5 is controlled by the output signal 12 of each stage of the shift register 11 based on the electrical signal 10 inputted from the outside, and modulates the optical pulse train 4 pulse by pulse. .

[0005] Also, the delay amounts of the N optical fibers 7 are t·c/n, 2t·c/n, . . . N·t·c/n, respectively.
is set. Here, t is the optical pulse width, c is the speed of light, and n
is the refractive index of the optical fiber core.

However, the first prior art has the following two problems. (2) N external modulators 5 are required to multiplex optical pulses. (2) Since the circuit is composed of a combination of an N-output optical splitter 3 and an N-input optical coupler 8, the power loss of optical pulses is large.

On the other hand, in the second prior art, as shown in FIG. 7, an optical pulse train 2 with a repetition frequency V emitted from a laser oscillator 1 is intensity-modulated by an external modulator 5, and the modulated optical pulse train 6 is sent to a multiplexer. The module 13 provides power to N stages connected in series.

Here, each multiplexer module 13
consists of a 1×2 type optical switch 14, two optical fibers 15 that provide a relative amount of delay, and a 2×1 type optical coupler 16. Then, in the K-th stage (K=1 to N) multiplexer module 13, the optical switch 14 is switched to V/2K.
The optical pulse train 17 emitted from the N-th stage is driven with a period of 2N It is obtained as a group of book pulses.

[0009] This second conventional technique can reduce the device configuration such as the number of external modulators 5 and reduce the power loss of optical pulses, compared to the first conventional technique described above. It has the advantage of being possible.

However, the second prior art has the following problems (1) and (2). ■ By using a large number of N optical switches 14,
Since it is necessary to set the timing of the switch control signal, etc., the system becomes complicated and the power consumption of the entire system increases. (2) Furthermore, if the insertion loss or deterioration of the S/N ratio in the optical switch 14 is large, the total power loss or waveform deterioration of the optical pulses becomes a problem because there are many switches.

[0011]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the first and second prior art techniques, the present invention reduces the device configuration and further improves the system by refraining from using active elements such as optical switches. It is an object of the present invention to provide an improved ultrashort optical pulse modulation circuit that eliminates complexity, reduces power consumption, and suppresses optical power loss and deterioration of S/N ratio.

0012

[Means for Solving the Problems] The configuration of the ultrashort optical pulse modulation circuit according to the present invention includes a laser oscillator that outputs an optical pulse train with a period T, and an optical pulse train outputted from the laser oscillator using an externally input electrical signal. An external modulator that turns on and off, and a 2x2 type optical coupler that splits the power of the input optical pulse train one to one, and two optical fibers that have a relative time delay between the two outputs of the optical coupler. A cascade compressor connected to the external modulator by connecting N stages through fibers, and an optical switch connected to the cascade compressor and cutting out only a necessary group of optical pulses from the output of the cascade compressor. That is. In this case, if necessary, the first stage optical coupler of the cascade compressor may be a 1x2 type optical coupler instead of a 2x2 type, or the final stage optical coupler may be a 2x1 type optical coupler instead of a 2x2 type. It can be an optical coupler.

[0013]

[Operation] The optical pulse train of period T emitted from the laser oscillator is transmitted to the external modulator at a bit rate of V (V=1/T
), the signal passes through a cascade compressor in which N stages of optical couplers are connected, and only the necessary pulse group is cut out by an optical switch. Here, in a cascade compressor, the two optical fibers in the first stage provide T-t, the second stage 2(T-t), and the Nth stage 2N.
A relative time delay of (T-t) is applied, and finally, an optical switch is used to cut out only a group of optical pulses whose head is correctly increased in amount of light, with the first pulse as the first pulse. However, t is an arbitrary time smaller than T. As a result, 2N optical pulses are multiplexed at intervals of t and are emitted from the optical switch.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments shown in the drawings.

FIG. 1 shows an ultrashort optical pulse modulation circuit according to an embodiment of the present invention. As shown in the figure, the ultrashort optical pulse modulation circuit 20 of this embodiment is configured by connecting a semiconductor laser oscillator 1, an external modulator 5, a cascade compressor 18, and an optical switch 19 in series in this order. It is something.

The external modulator 5 is an optical intensity modulator that turns on or off the optical pulse train pulse by pulse in a modifiable band based on the input electrical signal 5A. Here, if the period of the ultrashort optical pulse train 2 from the semiconductor laser oscillator 1 is T, then the bit rate V of the electric signal 5A is V=1/T. An optical pulse train 6 emitted from this external modulator 5 is input to a cascade compressor 18 .

As shown in FIG. 2, the cascade compressor 18 includes N 2×2 type optical couplers 21-1, 21-2,
...21-N to N-1 for one delay optical fiber pair 22-
1, 22-2, . . . 22-N-1 are connected one by one. Here, the relative time delay of the optical fiber pair 21-j of the j (j=1, 2, . . . N-1) stage is defined as j (Tt). t is an arbitrary time such that t<T. A 2×2 type optical fiber branches optical pulses from two input ends into two output ends in a one-to-one ratio. Therefore, the optical pulse trains at both output ends are the same. The output end of the external modulator 5 is connected to one input end of a 2×2 type optical coupler 21-1 at the first stage. Further, one output end of the final stage 2×2 type optical coupler 21 -N is connected to the input end of the optical switch 19 .

The optical switch 19 is supplied with a period of 2N from the optical pulse train 23 emitted from the cascade compressor 18.
- At T, a gate signal 19A is applied that selects only one optical pulse group and makes it the output optical pulse train 24.

Therefore, the above-mentioned ultrashort optical pulse modulation circuit 20
Then, modulation is performed as shown in FIG. This will be explained below.

That is, an ultrashort optical pulse train 2 with a period T is emitted from the semiconductor laser oscillator 1, and this optical pulse train 2 is input to the external modulator 5. The external modulator 5 modulates the optical pulse train 2 pulse by pulse in a modifiable band based on the input electrical signal 5A of the beatlet V.

However, in order to make it easier to see the changes after the modulation of the optical pulse train 2, it is assumed here that the modulation is performed with the input electrical signal 5A in which all bits are at a high level (all 1s). Therefore, the optical pulse train 2 input to the external modulator 5 and the optical pulse train 6 output from this end are the same.

After that, as shown in FIG. 3(a), when the optical pulse train 6 with period T is input to the cascade compressor 18, the optical pulse train outputted from the second stage 2×2 optical coupler 21-2 is At either of the two output ends, as shown in FIG. 3(b), every two optical pulses are emitted with a period T, arranged at an interval t. The optical pulse train 23 (output of the cascade compressor 18) emitted from the N-th stage optical coupler 21-N is output from either of the two output ends as shown in FIG.
As shown in (c), the optical pulses arranged at an interval t are 2N
Each book is emitted at a period T. Note that the same optical pulse train as the input end is emitted from the two output ends of the first-stage optical coupler 21-1, but these are connected to the optical fiber pair 2.
2-1 gives a relative delay of Tt, and the signal enters each input terminal of the second stage.

Therefore, the optical switch 19 is provided with a gate signal 19A having a pulse width of t(2N-1) or more and less than T, which selects only one group of optical pulses with a period of 2N·T as shown in FIG. and cut out the optical pulse. As a result, the optical pulse train 24 emitted by the optical switch 19 is only a group of optical pulses correctly multiplexed by 2N, with the leading optical pulse being the first optical pulse, as shown in FIG. 3(e).

[0024] If the time interval between the true light pulse and the dummy light pulse becomes short in the middle of the cascade compressor 18 and the switching speed of the optical switch 19 makes it impossible to extract the light, then By intervening the optical switch and dividing the extraction of optical pulses into two stages, it becomes possible to obtain only the necessary optical pulse group.

Note that it is sufficient to connect the output end of the external modulator 5 to only one of the two input ends of the first-stage optical coupler 21-1 of the cascade compressor 18. Therefore, it is possible to use a 1x2 type optical coupler instead of a 2x2 type optical coupler as the first stage optical coupler.

Similarly, the input end of the optical switch 19 connects to the optical coupler 2 at the final stage (Nth stage) of the cascade compressor 18.
It is sufficient to connect only one of the two output terminals 1-N. Therefore, it is also possible to use a 2×1 type optical coupler instead of a 2×2 type optical coupler as the final stage optical coupler.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment uses a plurality of m ultrashort optical pulse modulation circuits 20 shown in FIG. 1 described above.

That is, as shown in FIG. 4, m ultrashort optical pulse modulation circuits 20-1, 20-2, .
-1, 25-2, ...25-(m-1) in parallel,
It is connected to an m×1 type optical coupler 26. Each ultrashort optical pulse modulation circuit emits an optical pulse train 25 shown in FIG. 3(e). In addition, each optical fiber 25-1, 25
-2,...25-(m-1) are respectively 2N ・t, 2
It has a delay amount of N.t.2,...2N.t.(m-1). However, 2N·t is the time width of a group of 2N optical pulses.

Therefore, each ultrashort optical pulse modulation circuit 20-1
, 20-2, . . . 20-m, the optical pulse train 24 is emitted from each optical fiber 25-1, 25-2, . . . 25-(m-1)
The optical pulse train 24, 24-1, 24-2, ... 24-(m-1) is delayed as it passes through the time series as shown in FIG.
When they are combined at the m×1 type optical coupler 26 and emitted, a continuous optical pulse train 27 shown in FIG. 5 is obtained.

That is, in the embodiment shown in FIG. 4, within the blank time width of the optical pulse train 24 emitted by a certain ultrashort optical pulse modulation circuit, the optical pulses emitted from other ultrashort optical pulse modulation circuits are By multiplexing the groups, in principle, an ultra-high-speed optical highway with an information speed comparable to the reciprocal of the optical pulse width can be realized. Note that the degree of multiplexing is preferably determined by adjusting the amount of delay, the number of ultrashort optical pulse modulation circuits 20, etc. so that the optical pulse trains do not overlap.

[0031]

As described above in detail based on the embodiments, in the present invention multiplexing is performed cumulatively using a cascade compressor. Therefore, compared to parallel multiplexing like the first conventional technique, the device configuration such as an external modulator can be significantly reduced, and the overall size can be reduced. Furthermore, compared to the same serial processing multiplexing method as in the second prior art, the use of active elements such as optical switches is minimized, which reduces the complexity of the system required for timing settings, etc. This can reduce the power consumption of the entire system. Moreover, since power loss of optical pulses and deterioration of the S/N ratio in the optical switch can be suppressed, insertion loss and waveform deterioration of the entire system are reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an ultrashort optical pulse modulation circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a cascade compressor.

FIG. 3 is a diagram showing the relationship between each optical pulse and a gate signal to an optical switch.

FIG. 4 is a diagram showing another embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the optical pulse train emitted from each ultrashort optical pulse modulation circuit and the optical pulse train emitted from the m×1 type optical coupler.

FIG. 6 is a diagram showing a first conventional technique.

FIG. 7 is a diagram showing a second conventional technique.

[Explanation of symbols]

1 Laser oscillator 5 External modulator 5A Electric signal 18 Cascade compressor 19 Optical switch 19A Gate signal 20, 20-1 to 20-m Ultrashort optical pulse modulation circuit 2
1-1~21-N 2x2 type optical coupler 22-1~22
-(N-1) Optical fiber (delay line) 25-1 to 25
-(m-1) Optical fiber (delay line) 26 m x 1
type optical coupler

Claims (3)

[Claims] 1. A laser oscillator that outputs an optical pulse train with a period T, an external modulator that turns on and off the optical pulse train output from the laser oscillator using an externally input electrical signal, and a pair of input optical pulse trains. Power branch to 1 2
×2 type optical couplers are connected in N stages by two optical fibers that provide a relative time delay between the two outputs of the optical couplers, and the cascade compressor connected to the external modulator and the An ultrashort optical pulse modulation circuit characterized by comprising an optical switch connected to a cascade compressor and for cutting out only a necessary group of optical pulses from the output of the cascade compressor. 2. The ultrashort optical pulse modulation circuit according to claim 1, wherein the first-stage optical coupler of the cascade compressor is a 1×2 type optical coupler instead of a 2×2 type optical coupler. 3. The ultrashort optical pulse modulation circuit according to claim 1, wherein the final stage optical coupler of the cascade compressor is a 2×1 type optical coupler instead of a 2×2 type optical coupler.