If we used an active electronically scanned array that emitted and received in the visible spectrum, what would the be advantages and disadvantages?
Would it be possible to make an AESA flashlight as emitter with the human eye or special filter goggles as receivers? If I used an AESA flashlight, could I illuminate someone in low light conditions so that I could see them but they couldn’t see my flashlight?
Has anyone ever built a flashlight or camera in the visible or IR spectrum that was a scanned array, either active or passive?
This isn’t something that I have any expertise in, but the last I heard, some folks had succeeded in creating fairly small optical arrays operating in the infra-red part of the spectrum. The arrays were too small to be of any practical use, but they were very useful as research tools.
The difficult part, as I understand it, is the really small wavelength involved. This requires them to build waveguides and such by growing and etching them onto substrates in the same way that integrated circuits are fabricated.
The advantage of AESA is that you can create arbitrary radiation patterns on the fly. So using the flashlight example, you could modify the beam width, direction, and brightness, and since it is controlled electronically, you could make these changes extremely quickly. You could use your flashlight to draw pictures on a wall, for example.
In the end, though, you are still making light. You are just using the hills and valleys of the array to steer the light beam. Since the end result is still light, it would be just as visible as a conventional light source. Potential applications that I can see are better, faster, and more precise tracking of objects, or cameras that can change their focus, zoom, etc. extremely quickly, reacting as fast (if not faster) than the human eye. I think we’re still a long way from any practical applications, though.
The last ones that I heard about (which admittedly isn’t recent) were very small arrays operating in the IR range. If they have created larger arrays and have managed to push all the way up into the visible part of the spectrum, I haven’t heard about it, but this isn’t something that I keep up with.
True. Couldn’t it also be used to scan something so that all antennae concentrate very narrowly for the first pixel of the image, then the second, then the third etc? Every pixel of the image would get the combined light input of the whole sensor array.
Can scanned arrays (passive or active) create narrower beams than mechanical antennae of the same approximate size and weight?
One of the main advantages of AESA for radars is that the radar emission is difficult to detect aka low probability of intercept (LPI). Why wouldn’t it work the same way for the visible or IR spectrum?
AESAs are LPI for at least 2 reasons if I understand correctly: 1) They can precisely direct a small coherent beam so that possible receivers who aren’t in that narrow direction do not do not see any beam 2) by mixing simultaneous frequencies, they can code their signal and bury it in the noise floor in much the same way as direct-sequence spread spectrum.
Did I miss any reasons why AESAs are LPI?
Why couldn’t this be done in the visible spectrum?
Can you explain why? We already have arrays that emit visible spectrum radiation. You’re looking at one right now. Isn’t everyone of the pixels on your screen emitting light? You must have heard of Li-Fi also.
That can also be done with passive electronically scanned arrays, right?
Or, make it work like a bar code scanner… Its drawing a really bright dot, but since it moves so quick, its not such a bright glow from the scanning being done.
The OP’s idea is then more easily achieved by using a scanning system, send the beam from the laser or LED , in whatever spectrum, and being sent as a dot rather than a “all at once” (like a torch), it can reach a further range… This might be benefit for the use of IR, as it would be invisible to humans, but wouldn’t suffer temperature noise (as the beam strength would be far above the temperature related IR !)
I think the OP was therefore asking is an AESA system capable of working like a invisible or long range night vision system, or for 3d work…
They do use laser (with mechanical aiming) for 3d mapping of a space… In theory it could be done faster by AESA being able to focus more beam at places more beam is required…
One way to think about the capabilities of such a scanned array is to think of them as an active holograph. You could, in principle, create a moving 3D holographic image. The problem you have is that you need to control the phase and amplitude of light with a spacial resolution that is smaller than the wavelength of light. Once you could do this, you could do anything holographic optical systems can, and do it dynamically.
We make some pretty small spatial optical modulators, but they don’t do phase. You find them in digital projection systems - home theatre is a big driver here. They don’t have the spatial resolution to be useful for holographic system yet either. A driver for an active array is work into optical holographic memory. Where you want to be able to steer the beam(s) in 3D inside the storage element. There have been some adventurous claims made about “nearly ready for production” memory systems for a while, but so far, not a lot of actual evidence of real systems.
Beam steering, or any dynamic change in the optical properties is limited by the speed you can change the spatial modulator. Compared to the speeds of pure electronic systems this is currently slow. This is probably a limitation of holographic memory systems that makes it hard to make them price competitive.