Could you use a laser beam as a modulated carrier wave for radio signal? Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern) 2019 Moderator Election Q&A - Question CollectionCan you use a laser to measure the speed of light with a rotating mirror?I'm looking for a formal definition of 'scintillations' in laser beam propagationIs circular masking a laser beam an acceptable way to get the beam diameter you require?About quantization of EM energy for amplitude-modulated waveHow can beam divergence be corrected for in a CO2 laser cutter?What medium could I use for a laser pointer to hit and illuminate an entire area behind it?How do you make a spherical radio wave?How do we write the state of a continuous-wave laser beam?What is the scientific explanation for radio waves bending around the Earth?Is it possible for smaller laser beams to merge into one large beam - I.E, the Death Star?
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Could you use a laser beam as a modulated carrier wave for radio signal?
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)
2019 Moderator Election Q&A - Question CollectionCan you use a laser to measure the speed of light with a rotating mirror?I'm looking for a formal definition of 'scintillations' in laser beam propagationIs circular masking a laser beam an acceptable way to get the beam diameter you require?About quantization of EM energy for amplitude-modulated waveHow can beam divergence be corrected for in a CO2 laser cutter?What medium could I use for a laser pointer to hit and illuminate an entire area behind it?How do you make a spherical radio wave?How do we write the state of a continuous-wave laser beam?What is the scientific explanation for radio waves bending around the Earth?Is it possible for smaller laser beams to merge into one large beam - I.E, the Death Star?
$begingroup$
There have been successful experiments in modulating sound over a carrier ultrasound wave. Not so long ago, I've even seen an DIY implementation on Hackaday.
I also encountered and tested a program that would modulate FM wave over a high-frequency PWM signal.
I don't remember much of the background math but my layman observation is that if you could draw a sinusoidal wave over a signal, then for all purposes the wave is there.
My question is then if you could do the same thing with a completely normal laser beam. That is, change the beam intensity as to form a FM wave over the visible light wave.
This picture kinda illustrates what I mean, not to scale:
The purple line is the frequency of the laser beam (as I said, it's not to scale) and the red line is the intended signal transmission, which is driven by some circuit powering the laser.
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
If this isn't possible, and I think so, why exactly does it work with ultrasound but not a laser?
electromagnetism laser radio-frequency
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
$endgroup$
add a comment |
$begingroup$
There have been successful experiments in modulating sound over a carrier ultrasound wave. Not so long ago, I've even seen an DIY implementation on Hackaday.
I also encountered and tested a program that would modulate FM wave over a high-frequency PWM signal.
I don't remember much of the background math but my layman observation is that if you could draw a sinusoidal wave over a signal, then for all purposes the wave is there.
My question is then if you could do the same thing with a completely normal laser beam. That is, change the beam intensity as to form a FM wave over the visible light wave.
This picture kinda illustrates what I mean, not to scale:
The purple line is the frequency of the laser beam (as I said, it's not to scale) and the red line is the intended signal transmission, which is driven by some circuit powering the laser.
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
If this isn't possible, and I think so, why exactly does it work with ultrasound but not a laser?
electromagnetism laser radio-frequency
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
$endgroup$
1
$begingroup$
Not that they use this specific FM scheme (they tend to use pulse amplitude modulation and quadrature amplitude modulation schemes), but how do you think optical-fibre telecommunications links work?
$endgroup$
– Emilio Pisanty
Apr 1 at 18:20
2
$begingroup$
Side note: I believe your example looks more like AM (Amplitude Modulation) over a constant-frequency carrier. FM works in a different way. Check the animated picture: at en.wikipedia.org/wiki/Frequency_modulation .
$endgroup$
– jjmontes
Apr 1 at 19:46
1
$begingroup$
Look up "RF over Glass"
$endgroup$
– immibis
Apr 1 at 21:11
$begingroup$
Also look up "radio over fiber" which is the industry term for "RF over glass"
$endgroup$
– slebetman
Apr 2 at 4:43
$begingroup$
@EmilioPisanty with digital signal you don't need to modulate - you just turn your LED's on or off. But carrier-grade fiber gear do use modulation especially multimode systems.
$endgroup$
– slebetman
Apr 2 at 4:45
add a comment |
$begingroup$
There have been successful experiments in modulating sound over a carrier ultrasound wave. Not so long ago, I've even seen an DIY implementation on Hackaday.
I also encountered and tested a program that would modulate FM wave over a high-frequency PWM signal.
I don't remember much of the background math but my layman observation is that if you could draw a sinusoidal wave over a signal, then for all purposes the wave is there.
My question is then if you could do the same thing with a completely normal laser beam. That is, change the beam intensity as to form a FM wave over the visible light wave.
This picture kinda illustrates what I mean, not to scale:
The purple line is the frequency of the laser beam (as I said, it's not to scale) and the red line is the intended signal transmission, which is driven by some circuit powering the laser.
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
If this isn't possible, and I think so, why exactly does it work with ultrasound but not a laser?
electromagnetism laser radio-frequency
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
$endgroup$
There have been successful experiments in modulating sound over a carrier ultrasound wave. Not so long ago, I've even seen an DIY implementation on Hackaday.
I also encountered and tested a program that would modulate FM wave over a high-frequency PWM signal.
I don't remember much of the background math but my layman observation is that if you could draw a sinusoidal wave over a signal, then for all purposes the wave is there.
My question is then if you could do the same thing with a completely normal laser beam. That is, change the beam intensity as to form a FM wave over the visible light wave.
This picture kinda illustrates what I mean, not to scale:
The purple line is the frequency of the laser beam (as I said, it's not to scale) and the red line is the intended signal transmission, which is driven by some circuit powering the laser.
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
If this isn't possible, and I think so, why exactly does it work with ultrasound but not a laser?
electromagnetism laser radio-frequency
electromagnetism laser radio-frequency
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
asked Apr 1 at 12:42
Tomáš ZatoTomáš Zato
1,11931529
1,11931529
1
$begingroup$
Not that they use this specific FM scheme (they tend to use pulse amplitude modulation and quadrature amplitude modulation schemes), but how do you think optical-fibre telecommunications links work?
$endgroup$
– Emilio Pisanty
Apr 1 at 18:20
2
$begingroup$
Side note: I believe your example looks more like AM (Amplitude Modulation) over a constant-frequency carrier. FM works in a different way. Check the animated picture: at en.wikipedia.org/wiki/Frequency_modulation .
$endgroup$
– jjmontes
Apr 1 at 19:46
1
$begingroup$
Look up "RF over Glass"
$endgroup$
– immibis
Apr 1 at 21:11
$begingroup$
Also look up "radio over fiber" which is the industry term for "RF over glass"
$endgroup$
– slebetman
Apr 2 at 4:43
$begingroup$
@EmilioPisanty with digital signal you don't need to modulate - you just turn your LED's on or off. But carrier-grade fiber gear do use modulation especially multimode systems.
$endgroup$
– slebetman
Apr 2 at 4:45
add a comment |
1
$begingroup$
Not that they use this specific FM scheme (they tend to use pulse amplitude modulation and quadrature amplitude modulation schemes), but how do you think optical-fibre telecommunications links work?
$endgroup$
– Emilio Pisanty
Apr 1 at 18:20
2
$begingroup$
Side note: I believe your example looks more like AM (Amplitude Modulation) over a constant-frequency carrier. FM works in a different way. Check the animated picture: at en.wikipedia.org/wiki/Frequency_modulation .
$endgroup$
– jjmontes
Apr 1 at 19:46
1
$begingroup$
Look up "RF over Glass"
$endgroup$
– immibis
Apr 1 at 21:11
$begingroup$
Also look up "radio over fiber" which is the industry term for "RF over glass"
$endgroup$
– slebetman
Apr 2 at 4:43
$begingroup$
@EmilioPisanty with digital signal you don't need to modulate - you just turn your LED's on or off. But carrier-grade fiber gear do use modulation especially multimode systems.
$endgroup$
– slebetman
Apr 2 at 4:45
1
1
$begingroup$
Not that they use this specific FM scheme (they tend to use pulse amplitude modulation and quadrature amplitude modulation schemes), but how do you think optical-fibre telecommunications links work?
$endgroup$
– Emilio Pisanty
Apr 1 at 18:20
$begingroup$
Not that they use this specific FM scheme (they tend to use pulse amplitude modulation and quadrature amplitude modulation schemes), but how do you think optical-fibre telecommunications links work?
$endgroup$
– Emilio Pisanty
Apr 1 at 18:20
2
2
$begingroup$
Side note: I believe your example looks more like AM (Amplitude Modulation) over a constant-frequency carrier. FM works in a different way. Check the animated picture: at en.wikipedia.org/wiki/Frequency_modulation .
$endgroup$
– jjmontes
Apr 1 at 19:46
$begingroup$
Side note: I believe your example looks more like AM (Amplitude Modulation) over a constant-frequency carrier. FM works in a different way. Check the animated picture: at en.wikipedia.org/wiki/Frequency_modulation .
$endgroup$
– jjmontes
Apr 1 at 19:46
1
1
$begingroup$
Look up "RF over Glass"
$endgroup$
– immibis
Apr 1 at 21:11
$begingroup$
Look up "RF over Glass"
$endgroup$
– immibis
Apr 1 at 21:11
$begingroup$
Also look up "radio over fiber" which is the industry term for "RF over glass"
$endgroup$
– slebetman
Apr 2 at 4:43
$begingroup$
Also look up "radio over fiber" which is the industry term for "RF over glass"
$endgroup$
– slebetman
Apr 2 at 4:43
$begingroup$
@EmilioPisanty with digital signal you don't need to modulate - you just turn your LED's on or off. But carrier-grade fiber gear do use modulation especially multimode systems.
$endgroup$
– slebetman
Apr 2 at 4:45
$begingroup$
@EmilioPisanty with digital signal you don't need to modulate - you just turn your LED's on or off. But carrier-grade fiber gear do use modulation especially multimode systems.
$endgroup$
– slebetman
Apr 2 at 4:45
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
It's definitely possible to modulate a laser beam to carry radio frequency signals, using any of several different methods. Amplitude modulation, frequency modulation, and phase modulation are all easy. An Acousto-Optic modulator can be used to modulate either amplitude or frequency at radio frequencies. Many decades ago I designed (and a friend built) a laser transmitter-receiver system that simply bounced a collimated laser beam off an aluminized Mylar film stretched across a small speaker cone. An audio signal fed to the speaker caused a "drumhead" deflection of the film, which distorted the reflected wavefront, causing slight deviations from collimation. At a distance, this resulted in amplitude modulation of the beam's brightness- easily detected using a photodiode.
The frequency of a laser is directly related to its cavity length, defined by the distance between its two mirrors. A piezoelectric crystal is easily used to drive one of the mirrors and thereby modulate the laser frequency.
The most direct way to modulate a laser beam at radio frequencies might be an electro-optic modulator. A Pockels cell can modulate at up to about 100 kHz. A Kerr cell can modulate at up to about 10 GHz. An acousto-optic modulator can modulate at up to about 200 MHz.
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
$endgroup$
$begingroup$
Perhaps Kerr cells are not desirable for this purpose as they are nonlinear?
$endgroup$
– IamAStudent
Apr 1 at 19:20
$begingroup$
Their nonlinearity isn't really much of an issue, since there are ways to work around nonlinearities. More to the point is that the Kerr effect is normally relatively weak, requiring high voltages.
$endgroup$
– S. McGrew
Apr 1 at 19:40
add a comment |
$begingroup$
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
It is possible to do this, but is substantially more complicated and expensive for many use cases than using amplitude modulation (AM). To learn more, you can google the term coherent optical communication.
Using optical phase or frequency modulation does give a small advantage in the distance that can be spanned on a single fiber-optic link, so it is most often used in long distance links (particularly undersea links) where minimizing the number of amplifiers and repeaters (and the expense of accessing them for maintenance and repairs in the event of failure) is at a premium. It's also starting to be used in shorter links when maximizing the total data capacity of the fiber is required (i.e. when the the capacity target is measured in 100's of gigabits or terabits per second).
In order to send an FM signal over a fiber optic link for a short distance (less than 100 km, maybe), you might rather use subcarrier modulation. This means make a radio-frequency signal with your message signal frequency-modulated onto it, and then use that RF signal to amplitude-modulate the optical carrier. You would then use an ordinary optical power detector to recover the RF signal from the optical carrier, followed by a radio demodulation circuit to recover the message signal. This kind of modulation is well known and often used in optical CATV systems, for example.
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
$endgroup$
add a comment |
$begingroup$
Yes you can, and indeed this is done.
Note that this is AM (amplitude modulation) not FM (frequency modulation): you are modulating the amplitude of the carrier (laser here) not its frequency. I don't know if it's easy to modulate the frequency of a laser but I suspect not (edit: see the other answer by S McrGrew: it is in fact). Note also that probably all real applications will be digital: they'll rely on encoding a bit stream into the laser somehow which makes them much more robust to noise & so on.
answered Apr 1 at 12:49
tfbtfb
16.1k43452
$endgroup$
add a comment |
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3 Answers
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active
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3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
It's definitely possible to modulate a laser beam to carry radio frequency signals, using any of several different methods. Amplitude modulation, frequency modulation, and phase modulation are all easy. An Acousto-Optic modulator can be used to modulate either amplitude or frequency at radio frequencies. Many decades ago I designed (and a friend built) a laser transmitter-receiver system that simply bounced a collimated laser beam off an aluminized Mylar film stretched across a small speaker cone. An audio signal fed to the speaker caused a "drumhead" deflection of the film, which distorted the reflected wavefront, causing slight deviations from collimation. At a distance, this resulted in amplitude modulation of the beam's brightness- easily detected using a photodiode.
The frequency of a laser is directly related to its cavity length, defined by the distance between its two mirrors. A piezoelectric crystal is easily used to drive one of the mirrors and thereby modulate the laser frequency.
The most direct way to modulate a laser beam at radio frequencies might be an electro-optic modulator. A Pockels cell can modulate at up to about 100 kHz. A Kerr cell can modulate at up to about 10 GHz. An acousto-optic modulator can modulate at up to about 200 MHz.
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
$endgroup$
$begingroup$
Perhaps Kerr cells are not desirable for this purpose as they are nonlinear?
$endgroup$
– IamAStudent
Apr 1 at 19:20
$begingroup$
Their nonlinearity isn't really much of an issue, since there are ways to work around nonlinearities. More to the point is that the Kerr effect is normally relatively weak, requiring high voltages.
$endgroup$
– S. McGrew
Apr 1 at 19:40
add a comment |
$begingroup$
It's definitely possible to modulate a laser beam to carry radio frequency signals, using any of several different methods. Amplitude modulation, frequency modulation, and phase modulation are all easy. An Acousto-Optic modulator can be used to modulate either amplitude or frequency at radio frequencies. Many decades ago I designed (and a friend built) a laser transmitter-receiver system that simply bounced a collimated laser beam off an aluminized Mylar film stretched across a small speaker cone. An audio signal fed to the speaker caused a "drumhead" deflection of the film, which distorted the reflected wavefront, causing slight deviations from collimation. At a distance, this resulted in amplitude modulation of the beam's brightness- easily detected using a photodiode.
The frequency of a laser is directly related to its cavity length, defined by the distance between its two mirrors. A piezoelectric crystal is easily used to drive one of the mirrors and thereby modulate the laser frequency.
The most direct way to modulate a laser beam at radio frequencies might be an electro-optic modulator. A Pockels cell can modulate at up to about 100 kHz. A Kerr cell can modulate at up to about 10 GHz. An acousto-optic modulator can modulate at up to about 200 MHz.
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
$endgroup$
$begingroup$
Perhaps Kerr cells are not desirable for this purpose as they are nonlinear?
$endgroup$
– IamAStudent
Apr 1 at 19:20
$begingroup$
Their nonlinearity isn't really much of an issue, since there are ways to work around nonlinearities. More to the point is that the Kerr effect is normally relatively weak, requiring high voltages.
$endgroup$
– S. McGrew
Apr 1 at 19:40
add a comment |
$begingroup$
It's definitely possible to modulate a laser beam to carry radio frequency signals, using any of several different methods. Amplitude modulation, frequency modulation, and phase modulation are all easy. An Acousto-Optic modulator can be used to modulate either amplitude or frequency at radio frequencies. Many decades ago I designed (and a friend built) a laser transmitter-receiver system that simply bounced a collimated laser beam off an aluminized Mylar film stretched across a small speaker cone. An audio signal fed to the speaker caused a "drumhead" deflection of the film, which distorted the reflected wavefront, causing slight deviations from collimation. At a distance, this resulted in amplitude modulation of the beam's brightness- easily detected using a photodiode.
The frequency of a laser is directly related to its cavity length, defined by the distance between its two mirrors. A piezoelectric crystal is easily used to drive one of the mirrors and thereby modulate the laser frequency.
The most direct way to modulate a laser beam at radio frequencies might be an electro-optic modulator. A Pockels cell can modulate at up to about 100 kHz. A Kerr cell can modulate at up to about 10 GHz. An acousto-optic modulator can modulate at up to about 200 MHz.
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
$endgroup$
It's definitely possible to modulate a laser beam to carry radio frequency signals, using any of several different methods. Amplitude modulation, frequency modulation, and phase modulation are all easy. An Acousto-Optic modulator can be used to modulate either amplitude or frequency at radio frequencies. Many decades ago I designed (and a friend built) a laser transmitter-receiver system that simply bounced a collimated laser beam off an aluminized Mylar film stretched across a small speaker cone. An audio signal fed to the speaker caused a "drumhead" deflection of the film, which distorted the reflected wavefront, causing slight deviations from collimation. At a distance, this resulted in amplitude modulation of the beam's brightness- easily detected using a photodiode.
The frequency of a laser is directly related to its cavity length, defined by the distance between its two mirrors. A piezoelectric crystal is easily used to drive one of the mirrors and thereby modulate the laser frequency.
The most direct way to modulate a laser beam at radio frequencies might be an electro-optic modulator. A Pockels cell can modulate at up to about 100 kHz. A Kerr cell can modulate at up to about 10 GHz. An acousto-optic modulator can modulate at up to about 200 MHz.
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
edited Apr 1 at 18:08
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
answered Apr 1 at 14:05
S. McGrewS. McGrew
9,43821237
9,43821237
$begingroup$
Perhaps Kerr cells are not desirable for this purpose as they are nonlinear?
$endgroup$
– IamAStudent
Apr 1 at 19:20
$begingroup$
Their nonlinearity isn't really much of an issue, since there are ways to work around nonlinearities. More to the point is that the Kerr effect is normally relatively weak, requiring high voltages.
$endgroup$
– S. McGrew
Apr 1 at 19:40
add a comment |
$begingroup$
Perhaps Kerr cells are not desirable for this purpose as they are nonlinear?
$endgroup$
– IamAStudent
Apr 1 at 19:20
$begingroup$
Their nonlinearity isn't really much of an issue, since there are ways to work around nonlinearities. More to the point is that the Kerr effect is normally relatively weak, requiring high voltages.
$endgroup$
– S. McGrew
Apr 1 at 19:40
$begingroup$
Perhaps Kerr cells are not desirable for this purpose as they are nonlinear?
$endgroup$
– IamAStudent
Apr 1 at 19:20
$begingroup$
Perhaps Kerr cells are not desirable for this purpose as they are nonlinear?
$endgroup$
– IamAStudent
Apr 1 at 19:20
$begingroup$
Their nonlinearity isn't really much of an issue, since there are ways to work around nonlinearities. More to the point is that the Kerr effect is normally relatively weak, requiring high voltages.
$endgroup$
– S. McGrew
Apr 1 at 19:40
$begingroup$
Their nonlinearity isn't really much of an issue, since there are ways to work around nonlinearities. More to the point is that the Kerr effect is normally relatively weak, requiring high voltages.
$endgroup$
– S. McGrew
Apr 1 at 19:40
add a comment |
$begingroup$
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
It is possible to do this, but is substantially more complicated and expensive for many use cases than using amplitude modulation (AM). To learn more, you can google the term coherent optical communication.
Using optical phase or frequency modulation does give a small advantage in the distance that can be spanned on a single fiber-optic link, so it is most often used in long distance links (particularly undersea links) where minimizing the number of amplifiers and repeaters (and the expense of accessing them for maintenance and repairs in the event of failure) is at a premium. It's also starting to be used in shorter links when maximizing the total data capacity of the fiber is required (i.e. when the the capacity target is measured in 100's of gigabits or terabits per second).
In order to send an FM signal over a fiber optic link for a short distance (less than 100 km, maybe), you might rather use subcarrier modulation. This means make a radio-frequency signal with your message signal frequency-modulated onto it, and then use that RF signal to amplitude-modulate the optical carrier. You would then use an ordinary optical power detector to recover the RF signal from the optical carrier, followed by a radio demodulation circuit to recover the message signal. This kind of modulation is well known and often used in optical CATV systems, for example.
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
$endgroup$
add a comment |
$begingroup$
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
It is possible to do this, but is substantially more complicated and expensive for many use cases than using amplitude modulation (AM). To learn more, you can google the term coherent optical communication.
Using optical phase or frequency modulation does give a small advantage in the distance that can be spanned on a single fiber-optic link, so it is most often used in long distance links (particularly undersea links) where minimizing the number of amplifiers and repeaters (and the expense of accessing them for maintenance and repairs in the event of failure) is at a premium. It's also starting to be used in shorter links when maximizing the total data capacity of the fiber is required (i.e. when the the capacity target is measured in 100's of gigabits or terabits per second).
In order to send an FM signal over a fiber optic link for a short distance (less than 100 km, maybe), you might rather use subcarrier modulation. This means make a radio-frequency signal with your message signal frequency-modulated onto it, and then use that RF signal to amplitude-modulate the optical carrier. You would then use an ordinary optical power detector to recover the RF signal from the optical carrier, followed by a radio demodulation circuit to recover the message signal. This kind of modulation is well known and often used in optical CATV systems, for example.
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
$endgroup$
add a comment |
$begingroup$
The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
It is possible to do this, but is substantially more complicated and expensive for many use cases than using amplitude modulation (AM). To learn more, you can google the term coherent optical communication.
Using optical phase or frequency modulation does give a small advantage in the distance that can be spanned on a single fiber-optic link, so it is most often used in long distance links (particularly undersea links) where minimizing the number of amplifiers and repeaters (and the expense of accessing them for maintenance and repairs in the event of failure) is at a premium. It's also starting to be used in shorter links when maximizing the total data capacity of the fiber is required (i.e. when the the capacity target is measured in 100's of gigabits or terabits per second).
In order to send an FM signal over a fiber optic link for a short distance (less than 100 km, maybe), you might rather use subcarrier modulation. This means make a radio-frequency signal with your message signal frequency-modulated onto it, and then use that RF signal to amplitude-modulate the optical carrier. You would then use an ordinary optical power detector to recover the RF signal from the optical carrier, followed by a radio demodulation circuit to recover the message signal. This kind of modulation is well known and often used in optical CATV systems, for example.
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
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The idea the is that the laser beam should demodulate into the FM signal on the target. But I can't really imagine that happening at all.
It is possible to do this, but is substantially more complicated and expensive for many use cases than using amplitude modulation (AM). To learn more, you can google the term coherent optical communication.
Using optical phase or frequency modulation does give a small advantage in the distance that can be spanned on a single fiber-optic link, so it is most often used in long distance links (particularly undersea links) where minimizing the number of amplifiers and repeaters (and the expense of accessing them for maintenance and repairs in the event of failure) is at a premium. It's also starting to be used in shorter links when maximizing the total data capacity of the fiber is required (i.e. when the the capacity target is measured in 100's of gigabits or terabits per second).
In order to send an FM signal over a fiber optic link for a short distance (less than 100 km, maybe), you might rather use subcarrier modulation. This means make a radio-frequency signal with your message signal frequency-modulated onto it, and then use that RF signal to amplitude-modulate the optical carrier. You would then use an ordinary optical power detector to recover the RF signal from the optical carrier, followed by a radio demodulation circuit to recover the message signal. This kind of modulation is well known and often used in optical CATV systems, for example.
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
answered Apr 1 at 17:33
The PhotonThe Photon
9,86411933
9,86411933
add a comment |
add a comment |
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Yes you can, and indeed this is done.
Note that this is AM (amplitude modulation) not FM (frequency modulation): you are modulating the amplitude of the carrier (laser here) not its frequency. I don't know if it's easy to modulate the frequency of a laser but I suspect not (edit: see the other answer by S McrGrew: it is in fact). Note also that probably all real applications will be digital: they'll rely on encoding a bit stream into the laser somehow which makes them much more robust to noise & so on.
answered Apr 1 at 12:49
tfbtfb
16.1k43452
$endgroup$
add a comment |
$begingroup$
Yes you can, and indeed this is done.
Note that this is AM (amplitude modulation) not FM (frequency modulation): you are modulating the amplitude of the carrier (laser here) not its frequency. I don't know if it's easy to modulate the frequency of a laser but I suspect not (edit: see the other answer by S McrGrew: it is in fact). Note also that probably all real applications will be digital: they'll rely on encoding a bit stream into the laser somehow which makes them much more robust to noise & so on.
answered Apr 1 at 12:49
tfbtfb
16.1k43452
$endgroup$
add a comment |
$begingroup$
Yes you can, and indeed this is done.
Note that this is AM (amplitude modulation) not FM (frequency modulation): you are modulating the amplitude of the carrier (laser here) not its frequency. I don't know if it's easy to modulate the frequency of a laser but I suspect not (edit: see the other answer by S McrGrew: it is in fact). Note also that probably all real applications will be digital: they'll rely on encoding a bit stream into the laser somehow which makes them much more robust to noise & so on.
answered Apr 1 at 12:49
tfbtfb
16.1k43452
$endgroup$
Yes you can, and indeed this is done.
Note that this is AM (amplitude modulation) not FM (frequency modulation): you are modulating the amplitude of the carrier (laser here) not its frequency. I don't know if it's easy to modulate the frequency of a laser but I suspect not (edit: see the other answer by S McrGrew: it is in fact). Note also that probably all real applications will be digital: they'll rely on encoding a bit stream into the laser somehow which makes them much more robust to noise & so on.
answered Apr 1 at 12:49
tfbtfb
16.1k43452
edited Apr 1 at 14:31
answered Apr 1 at 12:49
tfbtfb
16.1k43452
answered Apr 1 at 12:49
tfbtfb
16.1k43452
answered Apr 1 at 12:49
tfbtfb
16.1k43452
16.1k43452
add a comment |
add a comment |
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Not that they use this specific FM scheme (they tend to use pulse amplitude modulation and quadrature amplitude modulation schemes), but how do you think optical-fibre telecommunications links work?
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– Emilio Pisanty
Apr 1 at 18:20
2
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Side note: I believe your example looks more like AM (Amplitude Modulation) over a constant-frequency carrier. FM works in a different way. Check the animated picture: at en.wikipedia.org/wiki/Frequency_modulation .
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– jjmontes
Apr 1 at 19:46
1
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Look up "RF over Glass"
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– immibis
Apr 1 at 21:11
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Also look up "radio over fiber" which is the industry term for "RF over glass"
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– slebetman
Apr 2 at 4:43
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@EmilioPisanty with digital signal you don't need to modulate - you just turn your LED's on or off. But carrier-grade fiber gear do use modulation especially multimode systems.
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– slebetman
Apr 2 at 4:45