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Zachariah
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Hi, i have a question about the optical interference, supposing we have two LEDs which spectra are partially overlapped, can we have interferences?? is there any chance to have a partial coherence between the two lights??
Zachariah said:I agree, in this case we cannot visualize the pattern, and even if we take an image of it with the camera, we will get the mean intensity which is the sum of the individual intensities, but in my case, the result intensity is always below that sum, that pushed me to suppose the existence of destructive interference, even if i cannot visualize it. would that be true?
Yes, the detector is linear with respect to the incident power.Tom.G said:Is you detector linear with respect to the incident power?
If you are measuring the sum of the LEDs with an optical fiber are their angles equally off-axis from the fiber entrance angle?
To be sure i don't have a measurement error i tried several configurations:SlowThinker said:Still must be a measurement error. Either the power source is shared for both LEDs and cannot supply both at high power, or there's a problem measuring the light intensity.
You can't have interference from two independent sources of light.
Still it has to be an error somewhere. It definitely is not interference. All optical phenomena are linear, at least at the intensities a mere mortal can access (I know that very strong lasers use nonlinear mirrors).Zachariah said:To be sure i don't have a measurement error i tried several configurations
The imager was not saturated in any of those measurements, i worked with moderated powers.SlowThinker said:Still it has to be an error somewhere. It definitely is not interference. All optical phenomena are linear, at least at the intensities a mere mortal can access (I know that very strong lasers use nonlinear mirrors).
This sounds like the detector can't take light that is too intense.
What happens if you switch one light source on and off at say 1 Watt (or whatever typical value it has) and increase the other from 0 to 10 Watts? Is the step the same at first then flattens out? Or is it 10% less throughout the range? Also what is the accuracy of the detector, can you actually perform this experiment?
If you have enough equipment around, you can try to split the light in two using a piece of glass at around 45 degrees, measure the two images (straight and reflected) and add the intensities.
Ok i will try this, i keep u tuned.Tom.G said:Since the usual problems have been largely addressed, here is another track to follow.
The LEDs could be pumping each other when their spectrums overlap. There is a known similar problem with LASER diodes. A possible way to test this would be:
- Place an 90%/10% beamsplitter in front of each LED. 90% beam going to your present integrating sphere & detector
- Monitor each of the 10% beams with additional detectors and readouts
- If the individual, 10%, detectors track with the power anomaly in your main setup, then the LEDs are talkin' to each other... either optically, thru a common power supply, or thermally.
LEDs need 3V and consume some milliamperes, the power supply output is 3V/1Asophiecentaur said:IS it possible that the two LEDs are sharing a power supply and its output power is limited?
Edit - sorry, that's be thought of already.
OK but is there any common series resistance in the circuit? Power supplies and lack of decoupling are very common faults. Sometimes they are very subtle.Zachariah said:LEDs need 3V and consume some milliamperes, the power supply output is 3V/1A
Zachariah said:Is this protocol has an appellation so i can read more about it? Link?
Well actually i don't say this is definitely an interference, i encountered this phenomena and i tried to know why it occurs and i did not find any other explanation but the possibility of having an optical interaction. Same electrical circuit is used in all other combination i experimented and gave good results. The existence of the interference does not imply that we must have a pattern of it, in case of partial coherence we will have a blurred screen instead of fringes.sophiecentaur said:OK but is there any common series resistance in the circuit? Power supplies and lack of decoupling are very common faults. Sometimes they are very subtle.
I don't see the cause as being due to interference because you would have to expect fringe patterns that would move about as the equipment is physically distorted. You would need a fantastic level of alignment to see partial cancellation all across the field of view. This is in addition to the other reasons from other people, above.
A diagram (complete) would be an advantage in chasing something as odd as this.
Thank you very much, i hope this will help.Tom.G said:Here is one that's along the same lines as, but not exactly identical to, the optical crosstalk conjecture. When the spectrums of the two LEDs overlap, that could be similar to a 3-mirror optical cavity when used with a LASER source.
Quote from: http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=2195791
"The power spectrum of the laser changes due to interaction between the lasing field and the small backscattered field, which re-enters the laser cavity with results described by Eq. (1)."
Agreed. But the mean value that the blurred screen shows would be the sum of the two powers - conservation of energy demands that.Zachariah said:in case of partial coherence we will have a blurred screen instead of fringes
Can the optical components (Lenses..) be responsible for such aberration?Charles Link said:Experimentally, there are so many factors that could give an erroneous experimental result. One of them is in coupling to the fiber (this is unlikely, but possible), the heating of the entrance of the fiber is causing its acceptance area to increase. In any case, it is extremely unlikely that any kind of optical interference is occurring between 2 LED's. The optics and interference principles all say "no" to any interference phenomena of this kind. Along the lines of what Tom G. said, perhaps light from one LED is reflecting off the fiber and/or around it and into the other LED, perhaps heating it or otherwise disrupting its performance.
The set up is so simple: Two lights are mixed in an integrant sphere which is coupled with an optical fiber, at the end of the optical fiber i placed a camera for readout.sophiecentaur said:A diagram is easy to produce with a drawing package and it can be attached with no effort
Zachariah said:at the end of the optical fiber i placed a camera for readout.
basler scout sca640-70gm lens mounted.Drakkith said:What kind of camera?
Charles Link said:I would not rule out something such as the solid state photosensor getting slightly saturated at a particular wavelength and thereby behaving slightly non-linearly.
There must be something about the setup that is not as simple as you think. If it were simple then you would not have this mysterious result. Unless the World is about to end and all our Physics is wrong, there must be a practical reason for this. In the absence of more details, I can only suggest changing one parameter / component at a time and seeing which change makes the Physics come right again.Zachariah said:The set up is so simple:
Optical interference is a phenomenon that occurs when two or more light waves interact with each other, resulting in either constructive or destructive interference. This can produce a variety of effects, such as bright and dark fringes, changes in color, or even complete cancellation of light.
LEDs, or light-emitting diodes, use optical interference to produce light. When an electric current is applied to the LED, it excites electrons in the material, causing them to emit photons. These photons then interact with the material's structure, resulting in optical interference and the production of light.
Coherence refers to the relationship between two or more light waves. In order for optical interference to occur, the waves must be coherent, meaning they have the same frequency, wavelength, and phase. This allows them to interact and produce interference patterns.
Optical interference is used in a variety of technologies, such as optical coatings, holography, and interferometry. It is also a key principle in the development of advanced optical devices, such as lasers and fiber optics, which are used in telecommunications, medical imaging, and many other fields.
One common application of optical interference is in anti-reflective coatings on eyeglasses and camera lenses. These coatings use destructive interference to reduce glare and improve visibility. Optical interference is also used in the production of thin-film coatings for solar panels, as well as in the creation of colorful iridescent materials, such as butterfly wings and soap bubbles.