JPS5826219B2 - Hikari Tsushin Souchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical communication device using an acousto-optic filter, which multiplexes audio, video, computer information, etc. by using a plurality of light flux lines color-separated for each wavelength of light. The purpose is to transmit.

The idea of using light rays as a signal transmission medium similar to radio waves has been around for a long time, and has been attracting attention since early on for applications such as infrared communications.

In recent years, with the advent of lasers, the possibility of transmitting large amounts of information over long distances has increased, and multiplex transmission of audio and TV images is progressing from the laboratory to the practical stage.

In laser transmission, the use of the directivity and coherent properties of lasers has attracted attention, but unfortunately the latter property has not yet reached a technological level that can be fully exploited.

In other words, if light itself could be used as a carrier wave, similar to radio waves, the frequency of microwaves is on the order of 2109 Hz, whereas the frequency of light is on the order of 1014 Hz, so the utilization of that bandwidth would be immeasurable. Will.

However, since this is currently difficult, only the geometrical optical characteristics of the laser beam itself are used.

Therefore, since laser light is originally monochromatic light, the amount of information carried by one laser beam is determined by the performance of the means for electrically modulating it.

Therefore, if you want to transmit more information, consider using multiple laser beams, or splitting something like a white light source into multiple beams with different wavelengths and carrying different signals on each beam. However, in this case, the problem is the electrical means to separate the light beams.

For light other than laser light, there are communication devices that use light emitting diodes, for example.

It uses an element such as GaAs or GaP to directly modulate the current of the element itself, and a parabolic reflecting mirror is used as the optical system.

This is suitable for short-distance communication because the emitted energy of the element itself is weak, but since the device is simple, it is noteworthy as a means of communication under special conditions.

An example of the above concrete example is shown in FIG.

Figure 1a shows an example of a communication device using a laser beam, with 100
101 is a lens system, and 102 is an optical modulator (for example, L i Nb
03Y plate and glass acousto-optic modulator), 103
104 is a transmission optical system, 104 is a transmission signal source, 105 is an electrical modulation device, 106 is an optical transmission path in the atmosphere, 107 is a reception optical system, 108 is a light receiving element (for example, a phototube), 109 is a demodulation device, and 110 is a This is the regenerated received signal.

The output beam of laser light source 100 is optically modulated by the electrical output of modulator 105 as it passes through optical modulator 102 .

If a modulated signal subjected to AM or FM modulation is supplied to the signal source 104 as the output of the modulator 105, the light beam emitted into the optical transmission path 106 via the transmission optical system 103 will contain the information of the signal source 104. It will be transported.

At the reception point, the light is received by a reception optical system 107 (for example, a parabolic concave mirror), subjected to photoelectric conversion by a light receiving element 108, and detected by a demodulator 109 to reproduce the original signal.

Figure 1 shows an example of a communication device using light emitting diodes.
1 is a transmission signal source, 112 is a modulator, 113 is a light emitting diode (for example, GaAs), 114 is a transmission optical system, 1
15 is an optical transmission line, 116 is a receiving optical system, 11T is a light receiving diode, 118 is a demodulator, and 119 is a regenerated receiving signal No. 4.

In this example, a light source 113 is directly electrically modulated and transmitted by the output of a modulator 112, and at a receiving point, an optical system 116 and a light receiving diode 11 having the same structure as the transmitting system are used.
This differs from case a in that 7 is used.

All of the above examples are communication forms that use a single beam of a single wavelength as light.

On the other hand, when using incoherent light such as a normal white light source, it is conceivable to divide the light into multiple spectra and use them multiplexed.

However, as the light becomes weaker, the transmission path becomes a problem.

Regarding optical transmission lines, in recent years, the development of high-quality optical fibers with low loss and convergent optical fibers has progressed, and it is becoming possible to transmit long distances even with fairly weak light as transmission cables.

Therefore, by using such an optical cable, signal transmission using the above incoherent light is possible.

In view of the above, the present invention provides a new communication system that performs multiplex communication by electrically performing wavelength decomposition of light at high speed using an acousto-optic filter.

The present invention will be described in detail below based on specific examples.

FIG. 2 is an example of a communication device using an acousto-optic filter.

In FIG. 2, 200 is a light source containing a broad spectrum, 201 is a collimating lens system, 202 is a collimated input light beam, 203 is an acousto-optic filter,
204 is a diffracted light, 205 is a non-diffracted transmitted light, 206 is a condensing lens system, 207 is an optical fiber optical transmission line, 208
is a transmission signal source group to be transmitted, 209 is a multiplexer,
210 is an amplifier, 211 is an ultrasonic modulator, 212 is a sweep signal generator, 213 is a synchronization signal generator, and the above is the configuration of the transmitting side.

On the other hand, 214 to 225 indicate the receiving side, 214 is a collimating lens system, 216 is a collimated received light beam,
211 is a diffracted light, 218 is a condensing lens system, 219 is a photoelectric converter, 220 is an amplifier, 221 is an ultrasonic signal generator, 222 is a sweep signal generator, 223 is a synchronization signal generator,
224 is a demultiplexer, 225 is a filter circuit group, 22
6 is a group of received signals that have been reproduced.

It is assumed that the light source 200 has a wide spectral distribution characteristic over a certain wavelength region in intensity with respect to the wavelength λ as shown in FIG. 3e, for example.

Such a light beam 202 is made to enter an acousto-optic filter 203, and an ultrasonic wave whose frequency f changes with time t as shown in FIG. 3 is propagated into the filter medium via an ultrasonic transducer. When this is done, diffracted light whose wavelength λ is selected in a specific direction is generated according to the frequency of the ultrasonic wave as shown in FIG. 3C.

For example, a TeO2 crystal is used as the acousto-optic filter 203, and incident light is allowed to travel within the crystal so as to be tilted in the 110 direction by 10 or more, for example 20, from the 110 axis.
On the other hand, if the transducer is configured to have a displacement in 110 directions and propagate transverse ultrasonic waves in 110 directions, then f will be 5.
When changing from 0 MHz to 80 MHz, 4500 lights from 650 OA of light wavelength are selected accordingly.

The half-value width of the wavelength of the selected light can be set to 1.0λ or less, so that the light in the visible range can be divided into 200 or more parts for use.

Utilizing such characteristics, for example, in FIG. 3, for each time slot tltt2+..., tN, an N-channel signal source s1°S2t that changes independently
......, when the intensity of the ultrasonic sweep signal that changes from fl to fN is amplitude-modulated according to each amplitude signal from 51 to SN with SN corresponding, the diffracted light that is selected correspondingly is as follows. , whose intensity is for each λ1. λ2.・・・・・・For λN, each of the above s1. s2.・・・・・・、S
The signal is modulated by N.

λ1. λ2. ......, depending on the characteristics of the light source and the acousto-optic element, the optical signal corresponding to λN is output as the amplitude of the original signal multiplied by a certain coefficient, as shown in Figure 3d, for example. , this is not important.

Each time slot 11, 12. ......, the wavelength of light λ1 for tN. λ2. .

At this time, λ1. λ2... Light with wavelengths other than λN is transmitted in the direction 205 as undiffracted light.

FIG. 4 shows signal waveforms when multiplex communication is performed using the configuration shown in FIG. 2 using this principle.

Signal outputs at major locations in FIG. 2 are indicated by symbols a-1.

Transmission number 4 of the 1 to N signal sources 208 is transmitted at time t1... by the sampling clock e of the synchronization signal generator 213.
t2. ..., signal S□ corresponding to tN.

s2. ..., SNs are sampled one after another.

sl. S2. ......, SN is multiplexer 20
9 is combined into one signal line (waveform a), and the modulator 21
1 amplitude modulation AM input terminal.

Since the above sampling is repeated with a period T, and each signal source is therefore sampled every T time, the sampling theorem limits the band of signals that can be co-transmitted on each channel by KT.

On the other hand, in synchronization with this T, the sweep signal generator 212 generates a sawtooth wave (waveform b) for sweeping, and leads this to the frequency modulation FM terminal 211.

The ultrasonic signal output of 211 is therefore at times 11 and 12.
．． ......, the frequencies are fl, f2 for tN.
..., fN is taken and the amplitudes are sl, s2.・・・・・・
...It becomes an FM-AM wave proportional to SN.

This output is propagated through the transducer into an acousto-optic filter medium, and the light ray 202 that has received mutual interference with the ultrasound wave becomes a diffracted light 204 and is guided to a transmission path 207.

204 is tl, t2. ......, the wavelength is λ1 for tN. λ2. ......, λN1 intensity is Sl, S
2t..., a time-division multispectral optical signal that changes depending on the SN.

This optical signal is guided to the receiving point via the optical transmission line 207 and enters the acousto-optic filter 215 again.

Here, a synchronization pulse is generated from the synchronization signal generator 223 at the same timing as the synchronization signal generator 213, and a sweep waveform f having the same period T as that of the sweep signal generator 212 is generated from the sweep signal generator 222 to the ultrasonic signal generator. 2210 frequency sweep terminal.

Then, the received light 216 receives tl, t2 .・
..., λ□, λ22.corresponding to tN.・・・１
．． Since the light of λ is diffracted in a specific direction, if the timing pulses of transmission and reception are synchronized, all of the 216 lights become the diffracted light 21
It becomes 7.

11.12. ......, for tN, the ultrasonic frequency f1. f2. ..., fN that do not correspond, the diffracted light at that time cannot be obtained in the direction 217.

Therefore, after the diffracted light 217 is photoelectrically converted by the photoelectric converter 219, the electrical signal output is sent to the demultiplexer 224.
using fl, f2. When distributed by the time pulse g + h t l t, which corresponds to fN, at time tl, the signal for wavelength λ1, that is, the signal wave corresponding to sl at the transmitting end, is distributed. appear.

Similarly 12, 13. ......, tN, the corresponding transmitting end signal 52tS3+..., SN
will appear.

These are PAM waves (pulse amplitude modulated waves) sampled at a period T as shown in Fig. 4 j and l, so
By passing through the low-pass filter 225, the desired receiving mother liquor R1,
R2, . . . , RN can be obtained.

As shown in the above embodiment, in this case, there is only one optical transmission path, and by modulating the frequency and amplitude of the ultrasonic driving source of the acousto-optic filter, multiple channels can be multiplexed and transmitted simultaneously. can.

In this case, by selecting the required number of ultrasonic frequencies on the receiving side, it is also possible to selectively receive only a specific channel.

In the above example, since synchronous detection is performed for each wavelength of light, the influence of noise caused by external light can be reduced.

FIG. 5 shows another embodiment.

The transmitting side is exactly the same as the example in Figure 2, with 50 components.
0 to 513 correspond to 200 to 213 in FIG. 2, respectively.

On the receiving side, 514, 515, 516 are 21 in FIG.
4,215,216, but here the ultrasonic signal source 521 merely needs to continuously supply ultrasonic waves of constant frequency and constant amplitude into the acoustic filter 515.

As before, the received light 516 has time t1. t2゜...
..., the wavelength of light λ1.corresponding to tN. λ2.・・・・・・
..., λN is the transmission number s1. s2. ......,SN
λ1. λ2. . . . are dispersed discretely in different directions corresponding to λN.

The direction of this dispersion is an angle that satisfies the conditions for Bragg diffraction at each wavelength with respect to the coarse and dense gratings in which the ultrasonic waves are generated in the medium.

The light rays 517 separated in this manner are guided to corresponding light receiving element groups 518, respectively.

The outputs of 518 are clearly sl, S2 .・・・・・・
..., carries the information of SN, and the waveform j in Fig. 4
, , l . . . are the separated received waves corresponding to .

When this is filtered by the low-pass filter group 519, the same received signals R1°R2, . . . , RN as before can be obtained.

In this embodiment, the configuration on the receiving side is clearly simpler than the example shown in FIG. 2.

That is, simply by continuously applying single-frequency ultrasound from the ultrasound signal source 521, channel signals can be separated.

In this case, if the light receiving element group 518 is in the form of a diode array, it is possible to increase the density.

FIG. 6 shows yet another embodiment.

In this example, the receiving side is exactly the same as the example of FIG. 5, and components 614-621 correspond to 514-521.

On the sending side, 600.601.602.603 and 6
07,608 is 500,501°502.50 in Figure 5
3, 507, and 508, but differ here in that multifrequency ultrasound is simultaneously supplied into the medium and multiple optical spectra are transmitted at once.

That is, whereas the previous two sides used a time division method, this example uses a simultaneous method.

In FIG. 6, 609 is a transmission signal source S1. S2゜...
..., different carrier frequencies f corresponding to SN
□, f2. . . . is a modulator group with fN.

These different carrier wave groups correspond to signal groups 51tS2t...
....

For example, AM modulation is performed using SN, and these modulated signals are collected in a mixer 610, and an ultrasonic signal wave obtained as the sum thereof is propagated into an acousto-optic filter 603.

Since ultrasonic waves of different frequencies and amplitudes exist simultaneously within 603, the light that mutually interferes with them is fllf21.
..., the wavelength is λ1 in the direction corresponding to fN. λ2.
. . . diffracts as dispersed light of λN.

Then, each of the dispersed lights is a signal group s1. s2.・
..., the signal is subjected to amplitude modulation at SN.

Now, assume that this dispersed light 604 is focused at one point by a lens system 605 and guided to a point 607.

The light propagating through sl, s2.・・・・・・
- Carrying the information group of tsIIJ, it is transmitted as a single light just like the original white light.

Therefore, at the reception point, as in FIG. 5, an ultrasonic wave with a single frequency and a constant amplitude is supplied to the acousto-optic filter 615 to generate dispersed light 617 again, and these are reproduced through each light receiving element. At the same time, received signal groups R1, R2, . . . corresponding to the original N channels are received.

~ can be obtained.

In this case, the filter group 619 may not be necessary.

This embodiment is more effective than the above two in that simultaneous multiplex transmission is possible and channels can be separated without requiring any synchronization between transmission and reception, but there is interference due to the simultaneous presence of multiple ultrasonic frequencies. Care should be taken in frequency selection, as modulation will occur.

Acousto-optic filters are characterized by the fact that they can separate the wavelengths of light at an extremely high speed through electrical control in a stationary state without any mechanically moving parts.

Further, by arbitrarily changing the frequency of the ultrasonic waves continuously or discretely, it is possible to freely select only a desired wavelength range, sometimes coarsely, sometimes finely.

In the present invention, multiplex transmission of information is achieved by selecting the desired wavelength of light and transmitting multiple channels corresponding to each wavelength at a high speed that cannot be achieved with mechanical systems using electrical input. In addition to being able to freely select channels between transmitters and receivers by selecting a set of ultrasonic frequencies, for example, it is possible to transmit necessary information only from a specific transmitting station to a specific receiving station, or as a secret communication. It has the advantage that it can also be used.

In addition, since light can be modulated simultaneously within the acousto-optic filter, a white light source whose intensity does not change can also be used.

[Brief explanation of drawings]

1A and 1B are schematic diagrams of a conventional optical communication device, FIG. 2 is a configuration diagram of an optical communication device according to an embodiment of the present invention, and FIGS. 3 and 4 are waveforms for explaining the operation of FIG. 2. 5 and 6 are configuration diagrams showing other embodiments of the present invention. 200.500,600... Light source, 203°2
15.503,515,603,615... Acousto-optic filter, 207,507,607...
Optical transmission line, 219,518,618... Light receiving element, 225.519,619... Low pass filter circuit, 208°508.608... Transmission signal source,
209.509...Multiplexer, 210,
220,510...Amplifier, 211,511.
...Ultrasonic modulator, 212.222,512.
...Sweep signal generator, 213.223,513.
... Synchronization signal generator, 221 ... Ultrasonic generator, 521.621 ... Ultrasonic signal source, 609 ... Modulator, 610 ... ...Mixer.

Claims (1)

[Claims] 1 comprising a plurality of input signal channels, a generator for generating an ultrasonic signal having a plurality of frequency components, an acousto-optic filter, and one optical transmission line for transmitting light; Alternatively, the light beam having a continuous spectrum is made to travel, and an ultrasonic signal modulated by the input signal is supplied to wavelength-divide the light beam in the acousto-optic filter, and then the light beam is propagated into the optical transmission path. optical communication equipment.