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i want to obtain the phase of laser waveform. i know that generally a PLL has a phase detector, so im wondering how to connect it to a laser diode drive circuit.
i want to obtain the phase of laser waveform. i know that generally a PLL has a phase detector, so im wondering how to connect it to a laser diode drive circuit.
i want to obtain the phase of laser waveform. i know that generally a PLL has a phase detector, so im wondering how to connect it to a laser diode drive circuit.
to detect the phase of a laser , y should u connect pll to the drive ckt??
also it is better to use another laser beam derived from the original one , to detect the phase (using interference principle)
oh, i'm using a laser pointer. i just want to sample the difference in phase of the input signal and the transmitted signal. so what shoud i do? i need a splitter to split the laser beam, and maybe two photodetectors? the receiver circuit will be connected to a microcontroller. If i cant find the phase using a pll, then what can i use? i thought a pll has an in-built phase detector? i looked up a few websites and saw some block diagrams that allow sampling lasers using pll. i'm just not sure whether this will work with a 565 pll. there must be other ways.
as audioguru says, there's no way you can directly compare two light signals and find a phase difference using an electronic circuit, which it sounds like you want to do... perhaps you could measure a phase difference between two MODULATED light signals (modulated at some more usable frequency), but considering the speed of light, the phase difference for any distance at which a laser pointer would be effective would probably be almost immeasureable (light travels 1 meter in just over 3 nanoseconds). but you can't hope to directly measure a laser wave... come on... by my quick calculation (someone correct me if i'm wrong) the frequency of a red laser (638nm wavelength) would be c*1/lambda = (3*10^8 )/(638*10^-9) which comes out to be about 470 terahertz... or 470,000 gigahertz :lol: good luck finding a PLL, or even a detector, that could handle that :lol:
If the beam energies are comparable, you can superimpose them on a photodetector that is sensitive to the laser's wavelength. Interference will cause the output of the detector to vary as a function of the phase between the two beams. I think. :roll:
If the beam energies are comparable, you can superimpose them on a photodetector that is sensitive to the laser's wavelength. Interference will cause the output of the detector to vary as a function of the phase between the two beams. I think. :roll:
Ultrasound is easier because sound moves slower than RF or light but sound speed varies with temperature, humidity and barometric pressure, so you would need to calibrate before each measurement.
i know. i would have asked for ultrasonics if i wanted to. it's just a little challenging with light. does anyone know where i can get a readily modulated laser circuit and its receiver online?
I think you are charting new ground here. Most modulators are on-off, not linear. It has been my experience that the light output of an LED is non-linear with applied voltage but perhaps current drive would be more linear. As has been pointed out before, the measurment range will be limited to one cycle of the modulation. The phase detector will probably be an analog to digital conversion, so why not go digital at the beginning?
Last year at my university someone did an audio transmitter that used modulated laser for transmission. If memory serves, they did it by literally cutting apart a normal cheapo laser pointer and connecting their circuit where the batteries would contact... + side to a positive rail, and - side through an NPN or NMOS transistor to ground, then they could modulate the laser by driving the transistor gate. you'd have to experiment with amplitude and biasing point if you're looking to modulate with an analog signal, or if you are going to just modulate with a logic square wave then it's even easier, but either way it shouldn't involve more than a transistor and a few discretes, plus whatever drive circuit you choose.
Yeah, you are right. But what do you mean by "going digital" from the beginning? are they any other easier means to achieve distance measurement by laser? Besides triangulation method, of course. That's rather too simple.
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