JPH07123073A - Optical time division multiplex - Google Patents

Abstract

PURPOSE:To simplify the multiplex processing by applying intensity modulation to a continuous light or a predetermined pulse light with an input digital signal of each channel and arranging the resulting signals on a time basis. CONSTITUTION:A continuous light (e) from a light source 11 is demultiplexed by an optical demultiplexer circuit 62 and the demultiplexed lights are inputted to optical intensity modulators 631-634 respectively, in which the lights are intensity-modulated by input digital signals b1-b4. Signal lights f1-f4 subject to intensity modulation are inputted to an optical signal compression section 12, in which the lights are compressed on a time basis. A different delay is provided respectively to compressed lights g1-g4 by delay circuits 641-644 so that they are not overlapped on a time basis, they are multiplexed by an optical multiplexer circuit 65, from which an output is provided. Moreover, plural bits of the input digital signals are modulated in the lump.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical time division multiplexer for converting a plurality of digital signals into one high speed optical digital signal.

[0002]

2. Description of the Related Art A conventional optical time division multiplexer first multiplexes a plurality of low-speed digital signals at the electrical signal stage,
This multiplexed signal is converted into a high-speed optical digital signal by electrical / optical conversion. That is, in this configuration, the signal speed of the multiplexed electric signal becomes the signal speed of the optical digital signal. However, since it is difficult to realize a signal speed exceeding 10 Gb / s by multiplexing electrical signals, it was not possible to make full use of the high speed of optical signals.

Therefore, an optical time division multiplexer for generating an ultrahigh-speed optical digital signal of several tens to 100 Gb / s by modulating a short optical pulse train with a plurality of digital signals and closely arranging them on the time axis is provided. Invented. Currently,
By using the gain switching of the semiconductor laser or the mode-locking method, a short optical pulse train having a pulse width of about several picoseconds can be obtained relatively easily.

FIG. 6 shows the configuration of a conventional optical time division multiplexer using a short optical pulse train. In the figure, a short light pulse train generation unit 61 outputs a short light pulse train a having a pulse width t _P having a constant pulse interval t _S. The short optical pulse train a is branched by the optical branching circuit 62 and input to the light intensity modulators 63 _{1 to} 63 ₄ . Each light intensity modulator 63 ₁ ~
63 ₄ intensity-modulates the input light with the input digital signals b _{1 to} b ₄ . Each signal light c _{1 to} c after intensity modulation
₄ is a delay circuit 64 so that they do not overlap each other on the time axis.
_{1-64 4} different delays respectively given, is output after being multiplexed by the optical multiplexing circuit 65.

The maximum signal speed of the multiplexed signal light d obtained by such an optical time division multiplexer is about 1 / t _P (b / s). The signal speed of the input digital signals b _{1 to} b ₄ is 1 / t _S (b / s). For example, t _P = 10 ps, t
_{If S} = 100 ps, the maximum signal speed that can be obtained is about 100
It becomes Gb / s, and the signal speed of the input digital signal is 10 Gb / s.
s.

As described above, in the optical time division multiplexer shown in FIG. 6, by combining the short optical pulse train and the delay circuit and multiplexing the optical signal as it is, it is possible to perform ultra-high-speed multiplexing which is difficult for an electric circuit. It has become.

[0007]

By the way, in future communication networks in which information forms are diversified, a plurality of bits (for example, 1 byte) of each input digital signal are collectively multiplexed in an optical time division multiplexer. Also, the ability to multiplex input digital signals of different signal rates is required.

However, in the configuration of the optical time division multiplexer shown in FIG. 6, the signal speed of the input digital signal is determined by the pulse interval and pulse width of the short optical pulse train. Therefore,
When the signal speed of the input digital signal is different for each channel, it is necessary to make the signal speed of the input digital signal uniform at the stage of the electric signal. Further, in order to collectively multiplex a plurality of bits, it was necessary to parallelize the input digital signals at the stage of electric signals and input each parallelized signal to the optical time division multiplexer.

As described above, in the conventional optical time division multiplexer, when a plurality of bits of each input digital signal are collectively multiplexed or when input digital signals of different signal speeds are multiplexed, an electric circuit is used. Pretreatment with is required. For this reason, the entire apparatus has become complicated and large-scaled. There is also a problem that the signal speed of the input digital signal is limited by the processing speed of the electric circuit.

The present invention is an optical time division multiplexer capable of implementing a process of collectively multiplexing a plurality of bits of an input digital signal or a process of multiplexing input digital signals of different signal speeds with a simple configuration. The purpose is to provide.

[0011]

According to a first aspect of the present invention, there is provided means for generating a plurality of continuous lights corresponding to respective channels, and light for intensity-modulating the continuous lights by an input digital signal of each channel. An intensity modulator, an optical signal compression unit that compresses the intensity-modulated signal light corresponding to each channel at a predetermined compression ratio, a delay circuit that gives a different delay to each compressed signal light, and each delay And an optical multiplexing circuit for arranging the obtained signal lights on a time axis.

According to a second aspect of the invention, in the optical time division multiplexing apparatus according to the first aspect, there is provided means for cutting out continuous light into pulsed light having a predetermined pulse width and pulse interval, and the pulsed light is used. This is a configuration applied to the optical intensity modulator corresponding to each channel.

The invention described in claim 3 is provided with a means for generating a plurality of short optical pulse trains having a pulse interval corresponding to the signal speed of each channel, instead of the means for generating continuous light.

According to a fourth aspect of the present invention, an optical signal compressing section for compressing a plurality of multiplexed signal lights time-division multiplexed at a predetermined signal rate at a predetermined compression rate, and each compressed multiplexing. A delay circuit that gives different delays to the signal light,
And an optical multiplexing circuit for arranging the multiplexed signal lights given each delay on the time axis.

[0015]

In the optical time division multiplexing apparatus of the present invention, the intensity of a plurality of bits is collectively modulated by intensity-modulating continuous light or predetermined pulsed light with the input digital signal of each channel. This intensity-modulated light is compressed at a predetermined compression rate for each channel, and this compressed light is arranged on the time axis via a delay circuit and an optical multiplexing circuit, so that multiple bits of each channel are collectively multiplexed. be able to. Further, by setting the compression rate for each channel, it is possible to handle a plurality of input digital signals having different signal rates.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the invention described in claim 1. In the figure, the light source 11 outputs continuous light e. The continuous light e is branched by the optical branching circuit 62 are inputted into the optical intensity modulator 63 _{1-63 4.} Each optical intensity modulator 63 _{1-63 4,} the input digital signal b ₁ ~b
_The input light is intensity-modulated by ₄ . The signal lights f _{1 to} f ₄ after the intensity modulation are input to the optical signal compression unit 12 and compressed on the time axis. The compressed lights g _{1 to} g ₄ are given different delays by the delay circuits 64 ₁ to 64 ₄ so that they do not overlap each other on the time axis, and are combined by the optical combining circuit 65 and output. h is the multiplexed signal light in this embodiment.

Since the continuous light is intensity-modulated by the input digital signal in this embodiment, a plurality of bits of the input digital signal are collectively modulated. In this embodiment, each channel has a configuration in which 2 bits are collectively multiplexed.

FIG. 2 shows a configuration example of the optical signal compression section 12. In the figure, an optical signal compression unit 12 includes a first dispersion adding unit 21, an optical phase modulator 22 that causes a linear frequency displacement in signal light by a phase modulation signal given from the outside,
The second dispersion adding unit 23 is connected in cascade. The optical phase modulator 22 includes a material having an electro-optical effect (for example,
A waveguide type made of LiNbO ₃ ) can be used. An optical fiber or a diffraction grating pair that functions as a normal dispersion medium (or an abnormal dispersion medium) for the input light wavelength can be used for the dispersion adding units 21 and 23.

In such a configuration, the first dispersion-adding unit 21 has the conditions for reproducing the time waveform of the input light of the first dispersion-adding unit 21 at the output end of the second dispersion-adding unit 23. The group velocity dispersion amount at B ₁ and the second dispersion addition unit 2
3, the group velocity dispersion amount is B ₂ , the phase modulation angular frequency is ω _m ,
When the phase modulation degree is α, the relationship of (1 / B ₁ ) + (1 / B ₂ ) = α · ω _m ² (1) holds.

Here, assuming that F _t = 1 / (αω _m ² ),
The formula (1) has the same form as the formula (1 / s ₁ ) + (1 / s ₂ ) = 1 / f (2) of the imaging system using the lens. Note that s ₁ , s ₂ , and f represent the distance from the object plane to the lens, the distance from the lens to the image plane, and the focal length of the lens, respectively.

Therefore, by using the optical signal compression unit 12 having the configuration shown in FIG. 2, the size of the waveform on the time axis can be converted (enlarged or reduced) like a spatial system lens.
Magnification M of the waveform at this time (if M> 1, waveform expansion, 0 <
If M <1, the waveform reduction is M = B ₂ / B ₁ (3) In this embodiment, B ₁ , so that 0 <M < ₁ ,
By selecting B ₂ , it is possible to reduce the signal light input to the optical signal compression unit 12 to a corresponding magnification, that is, to compress it on the time axis. In optical compression using this principle,
It is possible to collectively compress a plurality of pulses of input light.

In the optical time division multiplexer using the optical signal compression unit 12, a plurality of bits of the input digital signals b ₁ to
The signal lights f _{1 to} f ₄ modulated by b ₄ can be collectively compressed. Further, the optical signal compression unit 12
Since the compression rate can be set arbitrarily, the time widths of the compressed lights g _{1 to} g ₄ are made uniform by adjusting the compression rate even if the signal speeds of the respective channels are different, and the delay circuits 64 _{1 to} 6
4 ₄ and the optical multiplexing circuit 65 can perform multiplexing processing.

Further, even when the number of collectively multiplexed bits of each channel is different and the signal speed is different, as shown in FIG. 3, the compression ratios of the optical signal compression units 12 _{1 to} 12 ₄ corresponding to each channel are adjusted. It can be dealt with. It should be noted that FIG. 3 shows the 2-bit input digital signals b ₁ and b ₃
And the 4-bit input digital signals b ₂ and b ₄ are collectively multiplexed. Further, the signal speed of the input digital signals b ₂ and b ₄ is twice as _high as that of the input digital signals b ₁ and b ₃ . However, here, the optical pulse width of the multiplexed signal light k after multiplexing is made uniform.

By the way, when continuous light is used as the light source, in the optical phase modulator 22 of the optical signal compressor 12, the light existing in the time domain where the negative frequency displacement occurs spreads over a wide time domain and becomes the background light. . Therefore, there arises a problem that the signal-to-noise ratio at the output end of the optical signal compression unit 12 becomes small. However, this problem can be solved by using pulsed light in which the light in the time domain in which the negative frequency displacement occurs in the optical phase modulator 22 is blocked instead of the continuous light e.
The configuration of this embodiment is shown in FIG. 4 (claim 2).

In this embodiment, the light intensity modulator 41 is inserted between the light source 11 and the optical branch circuit 62 in the configuration shown in FIG. The light intensity modulator 41 performs intensity modulation so that the light exists only in the time region in which the positive phase displacement occurs in the optical phase modulator 22 of the optical signal compression unit 12. That is, when the phase modulation frequency is f _m , the light intensity modulator 31
Then, the intensity of the continuous light e is modulated so that the optical pulse train has both a pulse interval and a pulse width of 1 / 2f _m .

This description is for the case where the dispersion adding units 21 and 23 of the optical signal compressing unit 12 are normal dispersion media. When the dispersion adding units 21 and 23 are anomalous dispersion media, the light intensity modulator 41 may conversely block light in the time domain in which a positive frequency displacement occurs in the optical phase modulator 22.

Further, in the above-mentioned embodiments, the continuous light is used as the light source, but a short optical pulse train having a pulse interval corresponding to the signal speed of each channel is also used for each channel. An optical time division multiplexer having the same function can be realized (claim 3). That is, instead of the light source 11 and the optical branching circuit 62, a short optical pulse train generator is provided for each channel.

FIG. 5 shows the configuration of an embodiment of the invention described in claim 4. In the figure, optical time division multiplexers 50 _{1 to} 5
0 ₄ may be either a conventional optical time division multiplexer or an optical time division multiplexer according to the present invention. The multiplexed signal lights p _{1 to} p ₄ output from the respective optical time division multiplexers have the same signal speed and are respectively compressed by the optical signal compressors 51 _{1 to} 51 ₄ . Each compression light q ₁ to q ₄ is supplied with different delayed by the delay circuit 52 ₁ to 52 ₄ so as not to overlap each other on the time axis, is output after being multiplexed by the optical multiplexing circuit 53. r is the multiplexed signal light in this embodiment.

The optical time division multiplexers 50 ₁ to 50 ₃
In the multiplexed signal lights p _{1 to} p ₃ of 4 optical signals are multiplexed, and the multiplexed signal lights p ₂ and p ₃ are each multiplexed in 2 bits. On the other hand, the optical time division multiplexer 50
Multiplexed signal light p ₄ of ₄ multiplexes the two optical signals. In this case, each time slot of the multiplexed signal light r has a part in which four optical signals are multiplexed and a part in which two optical signals are multiplexed.

As described above, the optical time division multiplexers 50 ₁ to
About 50 ₄ of each multiplexed signal light, further optical signal compression unit 51, by using the delay circuit 52 and the optical multiplexing circuit 53, may be multiplexed similarly to the time axis.

[0031]

As described above, according to the optical time division multiplexing apparatus of the present invention, continuous light or predetermined pulsed light is intensity-modulated by the input digital signal of each channel to compress the signal light at a predetermined compression rate. To do. By this compression operation and the operation of arranging the compressed lights of the respective channels so as not to overlap on the time axis, it is possible to collectively multiplex the input digital signals of a plurality of bits of the respective channels. Further, by setting the compression rate for each channel, a plurality of input digital signals having different signal rates can be multiplexed.

Further, in the configuration of the present invention, since all the operations can be performed with the optical signal as it is, it is possible to realize an optical time division multiplexing apparatus having a simple configuration and supporting an ultra high speed signal.

Further, by configuring the processing units for compressing and multiplexing in multiple stages, it is possible to group multiplexed optical signals having the same signal rate, respectively, and efficiently and easily configure a large-scale multiplexer. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the invention described in claim 1.

FIG. 2 is a block diagram showing a configuration example of an optical signal compression unit 12.

FIG. 3 is a diagram showing another operation example in the embodiment of the invention described in claim 1;

FIG. 4 is a block diagram showing the configuration of an embodiment of the invention described in claim 2.

FIG. 5 is a block diagram showing the configuration of an embodiment of the invention described in claim 4.

FIG. 6 is a block diagram showing a configuration of a conventional optical time division multiplexing device using a short optical pulse train.

[Explanation of symbols]

 11 Light Source 12,51 Optical Signal Compressor 21 First Dispersion Adder 22 Optical Phase Modulator 23 Second Dispersion Adder 41,63 Light Intensity Modulator 50 Optical Time Division Multiplexer 52,64 Delay Circuit 53,65 Optical multiplexing circuit 61 Short optical pulse train generator 62 Optical branch circuit

Claims (4)

[Claims] 1. A means for generating a plurality of continuous lights corresponding to each channel, an optical intensity modulator for intensity-modulating the plurality of continuous lights by an input digital signal of each channel, and intensity-modulated corresponding channels Optical signal compression unit that compresses each signal light at a predetermined compression ratio, a delay circuit that gives different delays to each compressed signal light, and an optical multiplexer that arranges each delayed signal light on the time axis And an optical time division multiplexing device. 2. The optical time division multiplexing apparatus according to claim 1, further comprising means for cutting out pulsed light having a predetermined pulse width and a pulse interval from continuous light, and the pulsed light is modulated in optical intensity corresponding to each channel. An optical time division multiplexing device characterized in that the optical time division multiplexing device is configured to be provided to a receiver. 3. A means for generating a plurality of short optical pulse trains having a pulse interval corresponding to a signal speed of each channel, and an optical intensity modulator for intensity-modulating each of the plurality of short optical pulse trains by an input digital signal of each channel. , An optical signal compression unit that compresses the intensity-modulated signal light corresponding to each channel at a predetermined compression ratio, a delay circuit that gives different delays to each compressed signal light, and a signal given each delay An optical time division multiplexing device comprising: an optical multiplexing circuit that arranges light on a time axis. 4. An optical signal compressing unit for compressing a plurality of multiplexed signal lights time-division multiplexed at a predetermined signal speed at a predetermined compression rate, and different delays for each compressed multiplexed signal light. An optical time division multiplexing apparatus comprising: a delay circuit for giving a delay signal; and an optical multiplexing circuit for arranging multiplexed signal lights given respective delays on a time axis.