Solar-Cell Laser Communication System

Forget the soup cans connected by a piece of string. There’s now a way to communicate wirelessly that doesn’t rely on a physical connection… or radio. It’s a communications platform that uses lasers to send data, and it’s done in a way that virtually anyone could build.

This method for sending information isn’t exactly new, but this project is one of the best we’ve seen that makes it doable for the average tinkerer. A standard microphone and audio amplifier are used to send the signals to the transmitter, which is just a typical garden-variety laser that anyone could find for a few dollars. A few LEDs prevent the laser from receiving too much power, and a solar cell at the receiving end decodes the message and outputs it through another amplifier and a speaker.

Of course you will need line-of-sight to get this communications system up and running, but as long as you have that taken care of the sky’s the limit. You can find incredibly powerful lasers lying around if you want to try to increase the communication distance, and there are surprisingly few restrictions on purchasing others that are 1W or higher. You could easily increase the range, but be careful not to set your receiving station (or any animals, plants, buildings, etc) on fire!

90 thoughts on “Solar-Cell Laser Communication System

    1. Yes. Lasers are basically just extremely high frequency and highly-directional transmitters. You can stick optics on them (or on your receiver) that are basically “antennas”, but in optics we call them “telescopes”.

    2. LASER stands for Light Amplification by Stimulated Emission of Radiation and in that context the emitted light is considered a form of radiation. However the output of a laser is specificity photonic and coherent. Most other forms of photonic emission are not coherent and most forms of radiation are not photonic.

        1. Protons, neutrons – atomic radiation. As for “Isn’t this is just another form of radiation” well that argument progresses to “Do protons have any mass?” at which point I give up as traditional theory says “no” and modern expectations are “yes” but no proof.

          1. I think you mean “photons”, not protons. The rest mass of a proton is about 940MeV/c^2. For the invariant mass, you need to solve the equation e^4 = m^2v^2 + m^2c^4, which is Einstein’s energy-mass equivalence equation taking into account momentum. Photons are massless gauge (meaning they are force carriers) bosons (meaning integer “spin”). Both theory and empirical evidence show that photons have no mass. Photons are affected by gravity not because they have mass, but instead because gravity warps spacetime. It’s similar to how water warps the path light takes. For Example, when shining a laser through a cloudy aquarium and looking at it from a perpendicular angle it will show a “broken beam”. One angle of proof is that if the photon has mass, then it also has a finite range, and thus we would not see light from the end of the universe. For example, both the strong and weak gauge bosons have mass, and their respective forces have extremely limited range because they decay. Particle physics is a very interesting subject, if you’re curious go ahead and absorb everything.

          2. Hmmm. I think all EMR consists of photons of various wavelengths. Is a neutron beam a form of radiation? I am trying to understand the point of your statement.

          3. Protons absolutely have mass. Classical physics or quantum physics, it does not matter.
            Did you mean “Do photons have any mass?” ?
            Non-thermal neutrons are considered radiation, and can be separated by energy, just like photons. But neutrons don’t have a “wavelength” per-Se. But they do have a thermal vibration based on their energy, as any other massive particle about absolute zero does.

    3. In theory, yes; in practice, no. Radio waves send data by modulating a signal on top of a carrier wave. To demodulate the data you have to separate the carrier wave from the rest of the data. We use relatively low-frequency waves on the electromagnetic spectrum for this. For example, WiFi is 2 GHz, which corresponds to a carrier wavelength that is approximately 30 cm. You need an antenna that is about 1/4 of this size (typically), and since wavelength is inversely proportional to frequency, to do traditional radio transmission with red light you’d need an antenna that was 1.75 x 10^-7 meters tall to demodulate the ~440 THz carrier wave

      The current record for radio transmission frequency is something like 0..5 THz. Pretty much what you’re doing with lasers is using the light as a digital (or in this case, analog) source, essentially turning what would normally be the “carrier wave” (the beam of light) on and off to represent the data.

  1. Neat. 1mm plastic fiber (as used for Toslink and fiber lighting) is cheap nowadays, so you could build a fiber optic com system too. 1mm fiber is highly muti-mode at visible wavelengths, so it wont be good for long range communication, but it would be pretty neat.

    Oh, and I really love how any retard can get their hands on powerful laser pointers these days and blind me or my children.

      1. Good point. But standoff weapons like lasers have completely different psychological requirements to use. A person (or child) with a laser is not likely to understand the potential long term damage or empathize with the person they shined the laser at. And because it is not a gun or knife there is a very different mentality toward the handling and use of these devices.

      2. Actually if you look at one the entries below from user “sonofthunderboanerges” you will understand the mentality of most people toward lasers. It’s just light, it can’t hurt someone permanently, right?

        1. Yes MARK if you stare at a laser pointer you can get permanent retinal damage. However, most people react by turning their head away and putting up a hand. That amounts to a glance not a stare. You’d only see floating spot for a while but it will go away in a short while. However, there are more powerful lasers that are “designed” by various military concerns that will blind you instantly. Laser pointers are not in that category. Airline pilots are never blinded only annoyed and distracted by the idiots on the ground pointing laser pointers up at them. They now wear special glasses (or goggles) during all flights. I wanted to design an omnidirectional laser receiver that tracks laser beams to source much like how the “gunshot detector” works in major cities. Never got around to it.

          1. It does not take a military laser to blind a person instantly. Laser pointers of 10W are available.

            You can’t turn your head or blink fast enough to protect your eye from a 10W Q-switched hand held laser. With peak powers of over 1000 Watts, it does instant damage.

            Airline pilots are usually too far away to be permanently blinded due to beam divergence.

            I am not talking about the little 1mW laser diode used in the project, I was commenting on the “You can find incredibly powerful lasers lying around if you want to try to increase the communication distance” line in the text of the article.

          2. Sound of a gunshot is omnidirectional, a lase line of sight. will be interesting to read how you will go about tracking a laser back to it’s source without an overwhelming number of receivers. Even if each receiver has multiple wide pattern detectors.

          3. I was thinking of mounting laser sensors on the bottom half of a globe or orb. Then mounting it in the ceiling of the cockpit. When the laser is flickering around the pilots one of the sensors is illuminated. That sensor has a specific azimuth and elevation relationship. Hence a reverse extrapolation can be done mathematically coupled with the plane’s GPS location, bearing, and altitude. A coordinate is output and sent to LEO (Law Enforcement Officers).

          4. The problem is there are different kinds of lasers, and they all operate at different wavelengths. You would have to have a detector that worked for all of them, while at the same time was able to squelch the noise from every other conventional source that produces light at the same wavelength(including “white” light of all wavelengths)… I see a lot of false-positives.

          5. Mystick says:
            July 3, 2015 at 9:44 am

            The problem is there are different kinds of lasers, and they all operate at different wavelengths. You would have to have a detector that worked for all of them, while at the same time was able to squelch the noise from every other conventional source that produces light at the same wavelength(including “white” light of all wavelengths)… I see a lot of false-positives.

            True. However, I wouldn’t use it as a laser pointer alarm system. Just a light source direction finder. Jerks want their lasers to be seen so they will use red, blue, or green lasers. A silicon photovoltaic cell works quite well in the 600-700nm range. You would need about 50-75 of them on the globe wired to discreet electronic inputs. An Arduino could monitor the inputs via a scanning method. A heads-up-display just pinpoints all hits and displays possible direction and position.

            The system records all hits including false positives. When the pilots realize they’ve been hit they note the time and look to the system’s recorded timestamp to see where the laser beam originated. The plane’s GPS, bearing, air speed, altitude, and attitude (banking angle) is all fed to the system for computation. The result wold only be an approximation of the idiot’s position not an exact location.

        1. Still, it’s no fun when your cat shreds several dozen feet of glass fiber optics into your home’s carpeting. Even years later after countless vacuumings, bare feet would occasionally get a surprise.

          1. Yeah, I have had glass fiber optic splinters too while at work (single mode 6/125 fiber), and it is no fun. We have found super glue to be the best remedy for fibers you can’t get out with tweezers. You put a drop over the end of the fiber, let it dry, and peel it off your skin. It usually pulls the splinter out with it.

          2. I remember doing that. :) Our fiber cat-astrophe was before the Internet, so we had to experiment on our own. In addition to super glue, we also tried chewing gum, duct tape, and epilatory “honey” wax; with varying levels of success on any given splinter. A glue trap was even considered at one point.

        1. Hmm, Multimode works by having a different refractive index at outer layer of the Optical Fibre compared to what is in the center of the Fibre. When light starts to drift away from the center the change in refractive index will bend the light back towards the center again. This causes phase delays and is the reason that mutimode is not good for very high speeds or ling distances.

          Unfortunately coherent light (from a laser) wont bend so it would just exit the OF on the first part that wasn’t straight.

          1. Well, sort of. You’re thinking of GRIN fibers. Single-mode and multi-mode fibers just use total internal reflection. Step index fibers are another variation and work similar to GRIN fiber.

            But yes, propagation delay differences between modes are the reason only single mode fibers are used for long haul communication links.

          2. Although there are methods of multi-mode communication using wavelength division multiplexing, and modal dispersion matching. But these are still limited in their range when multi-mode fiber is used.

      1. Look up “total internal reflection” to understand how fiber optics work. They don’t need a covering to guide light. The refractive index difference between the core and cladding, or just the core and air (if it’s a coreless fiber) are enough.
        Any protective coating only serves to protect the fiber from damage.

      2. You don’t NEED that covering. It just improves performance so that you can get away with hundreds of meters of fiber before you need a repeater instead of just a couple dozen. Cheap plastic fibers are common for short runs of optical communication line. Expensive coated glass ones are reserved for applications where their performance is required for either distance or speed concerns.

        1. We’re talking laser pointers that are less than 5mW. Glancing at one will cause a floating spot on the retina for maybe a few hours. However, staring at it will cause direct irreversible retinal damage. The military has ones that are very powerful over a few watts and even a glimpse can cause irreversible damage. One company in Connecticut has a laser dazzler for the US Marines. It does not cause permanent damage only causes temporary confusion and disorientation. I was typing a longer response when I was typing my 2:20 pm posting but my power failed for a couple of seconds and I was distracted. I’m not supporting idiots pointing lasers at people. Here in Connecticut you can get stiff time in jail or worse for pointing at a police officer let alone an airplane.

          1. Just a thought, but what in military context is considered “temporary” confusion and disorientation (read: “hey what’s that flashy thing oh shit I can’t see”) may well in civilian/medical context be most definitely not temporary.

          2. ——————————————-
            chranc (@chranc) says:
            July 2, 2015 at 10:49 pm

            Just a thought, but what in military context is considered “temporary” confusion and disorientation (read: “hey what’s that flashy thing oh shit I can’t see”) may well in civilian/medical context be most definitely not temporary.
            ——————————————-
            Reply: See http://en.wikipedia.org/wiki/Dazzler_%28weapon%29

            “Weapons designed to cause permanent blindness are banned by the 1995 United Nations Protocol on Blinding Laser Weapons.”

            Unfortunately the Russians don’t give a darn. When the Canadian Air Force intercepted a Russian trawler (i.e. spy ship – the Kapitan Man) in 1997 off state of Washington (USA) a CAF helo crew member and a US Navy liaison officer were blinded by a blue laser aboard the Russian vessel. Upon searching the vessel by USCG, no laser was found (thrown overboard?). In 1993 this same ship was intercepted and relieved of their submarine spy equipment by our US Coast Guard.

        2. No, we aren’t talking about about 5mW lasers. We are talking about any dipshit can get their hands on 3, 5, or 10W handheld lasers that can blind a person permanently.

          “You can find incredibly powerful lasers lying around if you want to try to increase the communication distance” From the article text.

          1. In USA it’s hard for a dipshit to find one of those just “lying around”. You’d have to illegally try and get one. They are not sold at Radio Shack, Dollar Store, or even Edmund Scientific in NJ. They are available overseas like China. Or maybe some idiot selling some on EBAY. But in the long run the dipshit will be on some sort of “list” of sorts if he uses his real name and personal postal address in USA.

            And the OP must know that you don’t need extra power to increase range. He needs to checkout Fresnel lenses. Solar Cells work well in the RED bandwidth (600-700 nm). But a FL or a telescope in front of the solar cell will increase laser range significantly. Also I hear you can converge your laser beam-width with binoculars on the laser with binos turned backwards. But I have not seen this work at all.

  2. I really like your project. However, you do know that HaD already covered this topic several times. I personally would like to see a laser-comm that used PCM instead of AM. I know your dual LEDs add protection but the nature of PCM would prevent over-voltage fatigue to the laser.

    Also extending range does not have to be a product of increased laser power. A group of Amateur enthusiasts accomplish 100+ miles of range using Fresnel Lens, telescopes, and photo-diodes instead of solar cell. They’ve been doing it since the 1960’s. Google MODULATED LIGHT (dot org or dot com).

    I’d also want to see plans for a DIY portable laser data communicator (free space optical or FSO) that can send messages or files across a field, buildings, or mountain range at night. For that you would need something better than a simple audio amplifier unless you were sending PSK31 or high-speed MORSE. I do like the PSK31 idea though. It’s resistant to interference just like the laser and can be used on a narrow-band audio system like your audio amp.You could actually do 20 simultaneous PSK31 feeds through your audio amp (or PC sound card). And with lasers you don’t get any propagation problems as radio does. Higher PSK’s could be implemented too. You could do ETHERNET on laser but you’d have to use totally different electronics for that.

    I had a couple of simple ideas like a laser aiming helper: a bicycle reflector with a doughnut hole in it. The laser receiver sensor would go in that hole. When you see distant bright flashes you know you are close to hitting the laser target. Also a laser beam diverging device to increase aim-ability. That same device could help a night-vision system see objects further away. And lastly a method of several lasers aiming up high at a distance reflective globe that reflects beams down into a common laser sensor and passing audio or data to a common radio transmitter or phone line. It would be something like a laser/radio repeater. Or you could just feed the audio/data to a omnidirectional IR blaster and you would have a very secure comm system.

    FYI – Once I setup up a audio laser link from my house to a commuter parking lot a half-mile away. Clear signal all the way. I used a AM/FM radio station as my feed. I used a tripod for my laser-pointer and a solar-cell and audio amp for receiver just like how you did. If I used a telescope I could have increased range tremendously.

    Liked your Photophone project. Alexander Graham Bell did the same thing. Then the Germans copied the concept decades later and made the LiSpr80 or Lichtsprechgerät 80/80 during WW2. Little is known about this device but they used it for secure comm for U-Boat and tank commanders.

    SOTB

    1. Exactly, there have been people trying to push ethernet through laser pointer for a long time.
      I cannot seem to find the website of a project using 10Mbps ethernet cards and lasers to create a link over some some Km….it was back from when 10Mbps network cards where the norm.

      1. They were commercially available as FSO (free space optics) devices. But now you’d have a hard time finding too many businesses pushing FSO today. There is one company that puts data in light fixtures in office or home and you get data from them. You can put any speed data on laser if you have the right equipment. An audio amplifier can only handle slow stuff like SSTV, FAX, PSK31+, MORSE, or maybe 300-9600 baud modem. That should be enough for playing around with texting/chatting or sending low-res SSTV or FAX pictures.

        If you want an underwater laser system get a green and blue laser and feed the audio to them simultaneously. I know lasers are not supposed to work underwater but the US Navy proved you could. Also work good at penetrating fog layers and rain too. Infrared lasers are neat and are eye-safe. Not sure what layers they can penetrate.
        —————————————————
        OFF TOPIC
        I’d like to see a 2-way communication system that the human uses no electronic device at all to speak and listen PRIVATELY. Enter the hypersonic directional loudspeaker and a hi-gain shotgun directional microphone. Of course the turret-mounted aim-able base station is totally electronic but the human in the field has nothing but his/her ears and mouth. The guy standing a 25-50 feet away hears nothing. Imagine the undercover operations potential. Walmart is testing a 1-way version in test target USA stores to send selected advertising at one or two customers standing at that product shelf. The next aisle or shelf area hears nothing.
        —————————————————

        1. Quote: “Infrared lasers are neat and are eye-safe”

          It doesn’t matter what wavelength the light is, it will still burn your retina even if you can’t see it.

          1. Eye safe wavelengths are 1310nm (Praseodymium with visible wavelengths suppressed) and 1550nm (Erbium) and out to 1800nm. They only burn your cornea due to the absorption of the cornea at that wavelength range . It is only a temporary blindness until the cornea heals or you get a transplant. Erbium is used for some US military rangefinders (switching over to 1550 laser diodes).

          2. Dave is correct. Saying infrared lasers are “eye-safe” like I said means that they are only safe to the retina NOT the cornea if the power is too high. The cornea absorbs the light protecting the retina from damage. However, if the power is too high the cornea can be damaged. I have a laser rangefinder. It’s IR laser is eye-safe to retina AND cornea.

            ———————–
            OFF TOPIC
            Alexander Graham Bell used a a cell with “alum” in it to prevent IR energy from entering the detector. He was aware of heat-rays being separate from visible light. He incorrectly surmised that the visible light was conveying the sound and not the heat (IR energy). His invention was not eye-safe though. The sun can blind you if you looked into his reflected light from the mirror. Imagine the battle field secure communications implications of using this Photophone during the Spanish-American wars. Heliographs were used for that long before the Photophone but were Morse Code only. The Germans (Siemens) perfected the Photophone range to 6.8 miles (11 km) from Bell’s mere 700 feet. Changing the selenium cell to molybdenite by the Brits made it more sensitive to IR light and hence more range.

            Someone today needs to invent a portable photophone toy or tool that uses eye-safe laser and a photo diode for receiver. It could be binoculars with a audio boom mic headset. Imagine secure communications with your partner across a field or down a street. You can see him and vice versa. You aim the binos at each other and just talk in full-duplex mode. A tripod would compensate for the beam’s convergence drop-outs. A diverged beam or just a wide beam-width IR L.E.D. would work pretty well even during the day.

            ———————–

  3. Many of RimstarOrg’s videos are great projects for kids (with supervision!), they are very educational, furthermore they have room for improvement and that is a good thing because you can then challenge your kids to build a better version.

  4. I must be getting old since my first thought was “meh, Forrest Mimms did it with LEDS (and fiber) back in the 80’s”. Can’t believe I’m the first to bring it up though, unless I missed a comment. Normally folks are quicker on the draw than me in that regard.

    1. Identifying similar, but different, past projects, done by a professional publisher….

      IS NOT THE POINT OF HACK A DAY.

      How jilted Re some of these commenters… Your comment, bwmetz, is wildly inappropriate. It has absolutely other to do with the content of the article, other than tangentially.

      You attempt to destroy, debase, demean – and why? “It was dne before” you say?

      How do you stomach wearing pants? Everyone wears pants. Pants are passe, lame, boring, staid, common, pedestrian.

      True hackers wear these special invisible ultilikilts. Do you like mine?

  5. To the consternation of the Marconi fan club, Tesla did wireless before Marconi. To the consternation of the Tesla fan club, Alexander Graham Bell beat Tesla, beat Tesla to wireless, and Bell. More likely some unrecorded. dudes where doing wireless using polish metal & the Sun long before Bell used light.

    1. @static – Actually Dr. Mahlon Loomis beat them all in 1866 with the first wireless system. He setup a 14 mile wireless setup in Washington DC. He received a patent and got a $50,000 (USD) federal grant from Congress. President Grant signed the bill but it only allowed him to operate Loomis Aerial Telegraph Company within DC city limits.

        1. Too late he already did. US President Grant signed this bill and Loomis was allowed to run a wireless telegraphy network within Washington DC until his death. It had a range of 7-miles. It consisted of two towers on either side of town and wireless messages could be sent between them. This was long before Nikola Tesla or Marconi even knew of such things as wireless. Tesla was only 18 years old when Loomis invented this thing. Congress kept scoffing at his work and belittled him as if he was crazy. But it did work. All this from flying two kites in the Virginia mountains and passing voltage through them. It’s amazing how a dentist could be the true father of wireless communications. Loomis’ wireless device could have deployed as a battle field secure communications method for the Union Army during Civil War only 1-year before his patent. He was a “Yankee” being from NY. So unlike Samuel Colt of Connecticut he would not have betrayed his country and helped the Confederates (the south) build one.

          I think both sides used heliograph’s to send Morse code via light during US Civil War. The US ARMY definitely used them during US Indian Wars. The Native-Americans called it “flashing lights” or something. US lookouts on mountain peaks could send secret messages across many miles after spotting enemy troop movements.

          I always thought someone should have exploited the parabolic sound mirror acoustic reflector between mountain peaks. Like a giant acoustic reflector that a whisper could be sent to a distant relay point and then repeated on the other side to another, etc. This could have been an ancient method of secure communications but I have never seen it in history books. They were used at Deng UK during WW2 to detect NAZI aircraft by sound. But I like this better:

    1. Yes I saw that too. It is a fascinating ongoing project. I wish we in USA had something like it.Yes laser light has a problem called scintillation. Over long distances atmospherics mess up the beam making it harder to aim and getting content through undisturbed, However, a high powered LED (or array of LEDs) that is modulated and assisted by telescope or a simple Fresnel lens works much better than a laser in practice. The beam-width is really diverged hence easier to aim. You can vary wavelength with different color LEDs which is much harder to do with a laser (unless it is the new tunable laser), Some have achieved several miles (or kilometers) from mountain peaks upward of 100+ miles. Checkout http://www.modulatedlight.org for background stories and projects.

      What I really would like to see is an omnidirectional laser communication transceiver. It would perform like a radio device and could be used for vehicle-to-vehicle commlink while driving on highway or simple walkie-talkies. However, it would be LOS (line-of-sight) only. Anything could block it unless you had multiple cell base stations to repeat the signal.

    2. The problem is the spectral width of the light source. When LED’s are used the spectral bandwidth is rather large and scintillation does not occur. Single wavelength lasers will have scintillation problems over long range free space optical links.
      If the spectral bandwidth of the source is too large, chromatic dispersion will cause problems in high data rate applications.

  6. Interesting!!!
    I did that with a normal incandescent globe (probably 3 or 6 volts – can’t remember) from a torch (aka flashlight) as transmitter, and a photo-transistor (and suitable amplifier) as receiver, and some lenses, back in the 80s (high-school hacker). Distance was three or four meters. The received audio was sursprisingly intelligible. Would have thought that the thermal inertia of the globe’s filament would have a very low frequency cut-off, but it was much higher than expected. Smaller the globe, the better the audio.

  7. I would also like to see an optical light gate that uses a high-speed LCD quartz crystal that changes polarization in step with data or voice. In that way you would not have to modulate the actual light source only modulate the resulting light beam itself. They are relatively expensive and some are not fast enough for audio or even data. They are primarily used in 3D Display Glasses. You could make a cool Morse Code transmitter with it. Believe it or not but Faraday and Kerr made such polarized light transmitter as far back as 1907 using Nicol prisms. I tried to get one crystal company to send me a freebie experimental unit but they refused when they found out what I wanted to use it for: Morse code optical gate. Not sophisticated enough for them. Otherwise the cost was in the high 3-digits category. Too much money for a simple hobby project.

    1. You can make your own LCD optical gate. I have done it. You find a numeric LCD display that has a back-light, then you need to somehow remove the back-light. Then the trick is finding a clear space in the circuit board that sits behind the display directly behind one of the characters and has no circuit traces, then drill a hole through the board at that spot for your laser beam. Then re-attach the LCD to the board (without the back-light).

      Alternately, you can use an older numeric LCD that only does seven segment digits (no back-light) and carefully peal the reflector / polarizer from the back of it. Then just shining your beam through one of the number segments allows you to modulate the polarization of the laser beam. If your beam is already nicely linearly polarized, then you can either add some polarizing film directly in front of the LCD to get an intensity modulated laser beam. You can also just put the polarizing film in front of your detector.

      1. @Mark – Thanx Mark! Sounds interesting. I wonder it will “shutter” fast enough for speech? Bell also thought of interrupting the light-beam. He used a spinning disk with holes in it. He couldn’t figure out how to modulate with it but he at least got a musical note out of the interrupted light hitting the selenium cell at a fixed rate.Maybe Tesla’s “dreams” could have helped Bell get more insight into new science inventions? (LOL) I’m sure they met a few times. Maybe Tesla could have introduced Bell to his Hindu Swami Vivekananda. The Swami helped Rockefeller and JP Morgan. Why not Bell too? (snicker)

        1. I don’t know if it would turn on and off fast enough for speech using on-off digital modulation, but you really only need about 3KHz of bandwidth to produce intelligible speech, so it might work. Even if it doesn’t turn on and off completely, you should still get an amplitude modulated signal that your detector can turn back into something that (hopefully) is intelligible. You would need to figure out how to drive one segment of the LCD by controlling it’s amplitude. Turning it on and off should be easy- if you have a driver already you can just turn it on to display a number, and figure out which trace goes to the segment you want, and cut that trace and solder in a switch. That will allow you to set up the laser and detector to see the on-off cycles on the detector.

  8. I’ve used LCD shutters for laser modulation, but they would only be good for slower data rates as you mentioned. I’ve also used Pockels cells for pulse picking, but switching rates above 1MHz are difficult and the driver gets really expensive. The Faraday effect is far to slow to be used for any worthwhile modulation project, and the field intensities required are very high, so your electromagnet would be huge. But Faraday isolators are a common device in laser systems. Kerr cells are easy to build, but again your modulation speed is limited, and switching multi-kilovolt voltages at high speed is not easy.
    The best device for high speeds is an acousto-optic modulator. I use these for pulse picking by beam deflection mainly, but they can also be used for intensity modulation or frequency modulation with the appropriate RF driver.

      1. I get them free from work. I get the rejects and damaged parts. Even the damaged ones can still be used, they just have a tiny pin head sized ablation mark in the AR coating somewhere in the active aperture, so they can’t be used in our lasers, but if your beam is small, you can avoid the damage spot. They are broadband AR coated for 800nm, but the polarization rotation angle is dependent on the applied voltage, so even if you were using a HeNe laser you could adjust the voltage to change the polarization angle. They are 45 degree devices, so a single pass through them with voltage applied causes a 45 degree rotation of your linearly polarized light source. The drive voltage required will be in the 3000 to 4000 volt range. It acts like a capacitor, of around 1uF value, so if you charge it with 4000V you will need to short the terminals to cause it to turn off. If you give me your address somehow I will send you one for free to play with if you want.

        1. @Dave – 3 to 4kv sounds a little out of my pay-grade. I get no hazard pay messing with kilovolts (LOL)

          Is that what Faraday and Kerr did with their device? Was the transformer coil charged at high voltage? That was in the 1890’s. I’m still amazed that they could mentally work their way through the science. Faraday was an autodidact like me. Kerr was a Reverend of some religion. But Kerr was educated formally. When Bell was playing with his Photophone (same time period) he thought it was more significant than the telephone. If you stop and ponder Bell’s lectures and prototype you start to see some amazing thinking processes for late 19th century.

          I mean he knew to use LENSES, IR filter, parabolic reflector, paper thin mirror, and a heretofore unknown photosensitive as selenium. Selenium only changes resistance in light does not produce voltage like silicon does. If he only knew how that particular invention was headed toward FSO’s he would have spent more time perfecting it like the Germans did during same time period (i.e. LiSpr 80/80). Bell did consider and tested artificial light sources too. Not just solar based communications.

          I guess Bell was a lot like Tesla too far ahead of his time. Tesla demo’d a remote control war boat at MSG in NYC in 1890’s but the war dept just laughed it off. If only they could have foresaw this:

          50-Knot Sentry Drone (UK – MoD)

          The late 19th century and early 20th was an amazing time for new science! If it weren’t for these free thinkers early on we would still be stuck thinking INSIDE the box rather than OUTSIDE it.

          1. Well, I wouldn’t call it the grandfather of the Pockels cell. The Kerr effect works differently, and it was discovered first because it is pretty easy to do. Pockels cells require a high quality optical crystal, and only occurs in crystals that lack inversion symmetry. Different crystals show different amounts of Pockels effect.

          2. So, yes, the Kerr effect can required 20KV or more to see with some liquids, so generally you would have a high voltage transformer and you apply pulses of low voltage to the primary of the transformer to get high voltage pulses to energize the Kerr cell.

            You should get a copy of the Scientific American “Amateur Scientist” articles on CD-ROM. They have complete projects that teach you how to work with optics, build lasers, build particle accelerators, and build all kinds of scientific instruments.-
            http://www.amazon.com/exec/obidos/ISBN%3D0970347626/sciencehobbyist/

          3. @Dave – “build particle accelerators”??? I’ve always wanted to produce a mini-black hole making a worm hole so I could go back in time and tell Dr. Ron Mallet at UCONN to cease and desist his ongoing “time machine” project. Did you see the new Arnold Schwarzenegger movie (Terminator:Genisys)? Ron should wise up before its too late (LOL).


            Dr. Ron Mallett and his time machine toy?

            I’m not mocking him, He is super-serious about this project!

            Thanx for the Amazon article…

          4. @Dave – So if Kerr (and Faraday) used 20kv with a step-up transformer, they could have went to Tesla for help with that. That was Tesla’s specialty despite dropping out of Graz University after a ridiculous dispute with his professor, I still wish I knew what Farraday and Kerr were thinking when evolving the seeds of these ideas. Tesla is easy, an amateur that dreamt up his inventions (with help from outside the box) The others really put in the course material work and did their homework! People like Edison et al were nothing more than brilliant salesmen who stole (or tried to steal) other people’s work product.Even Westinghouse is a multibillion corporation today thanks to Mr. W “borrowing” Tesla’s arguably-authored ideas. Tesla volunteered so it wasn’t actually I.P. theft. But Westinghouse should change their name to reflect Tesla’s original contributions. But it may get confused with Elon Musk huh?

            If Tesla had fooled around more with his “particle accelerator” idea he may have actually been the grandfather of the thing. Or maybe he could have beat Maiman, Schawlow, Townes, Gould, et al at inventing the early L.A.S.E.R.(or ray-gun). It appears Maiman may have had some “out of the box” help with his solid-state LASER idea. It appears the Germans were experimenting (tinkering/dabbling) with it in their V-Werks project (via Siemens and Zeiss – both companies still active today – go figure!) and was introduced to Hughes Aircraft as a FOREIGN TECHNOLOGY product via the US Pentagon (aka Operation Overcast/Paperclip circa 1945). The late Ted Maiman (aka the TV repairman) allegedly just took the arguably contributed concept and made it his own and now we have GaAs solid-state lasers at the dollar store – man what a country! :-)

            To me LASERS are still an amazing mystery even though I understand the technical process. I’ve studied them since 1960’s. But I never cease to be amazed by the technology and what can be done with them.

            I am baffled that HaD projects like this still are the only avenues for the public to dabble in LASER/COMM or FSO. It seems only defense contractors like General Atomics, ITT Exelis and Cubic seem to be the only venue exploiting this magical light for talking over (multimedia and data too). It appears “someone” is secretly suppressing it from American education public schools like they did with prime number math in the 1950’s and 60’s.

            Imagine the “oohs and ahhs” this HaD project would get at your kid’s elementary school science fair. Why???!! It should be as mundane and rote as Algebra is in American schools. You notice Guidance Counselors never mention careers in free space optics or laser communications. No you have to join the US Air Force for that. There is so much untapped potential for LASERS and NASA is just starting to explore it. Why??? This should have been done decades ago.

            SOTB

  9. More fun things to do with LASERS (per the US Govt USG):

    The Genia Photonics’ Picosecond Programmable Laser scanner is capable of detecting every tiny trace of any substance on your body, from specks of gunpowder to your adrenaline levels to a sugar-sized grain of cannabis to what you had for breakfast.

    Meanwhile, USG states that “an important benefit of Genia Photonics’ implementation as compared to existing solutions is that the entire synchronized laser system is comprised in a single, robust and alignment-free unit that may be easily transported for use in many environments… This compact and robust laser has the ability to rapidly sweep wavelengths in any pattern and sequence.”

    So not only can they scan everyone. They would be able to do it everywhere: the subway, a traffic light, sports events… everywhere!


    A TUNABLE LASER

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