4 ms·
This doesn't have to do with different propagation paths. The Orbital Angular Momentum (OAM) is an inherent wave property, like Wavelength or Frequency. Just l
by henryaym 15y ago
This doesn't have to do with different propagation paths. The Orbital Angular Momentum (OAM) is an inherent wave property, like Wavelength or Frequency. Just like you can listen to radio on different frequencies (eg 660AM, 1010AM), you can think about this technology as "listening" on different OAM channels.
The twist in the wavefront can be thought of as a newly available subset of channels.
This has been a a field of research that has been primarily been developed in Optics, in fact, my PhD research included creating ultrafast (femtosecond), supercontinuum (white light) vortices that are capable of transmitting information over 2^L channels where L is the amount of twist the light has.
- gallamine 15y agoIs this "twist" related to the circular polarization of light?
- henryaym 15y agoQuick Answer: No. Longer Answer: Sorta. Circular polarization of light (or waves in general) corresponds to a spin angular momentum that arises as the polarization of the light is "spinning". This "twist" is the wavefronts phase rotating or being staggered as it travels forward. Think of the wavefront of the twisted wave as looking like a piece of spiral pasta. It is this spiraling that corresponds to orbital angular momentum.
- jpdoctor 15y ago> orbital angular momentum Under what circumstance can you change the OAM in order to exert a torque? (or maybe vice-versa: What is an example of torque exerting a change in OAM on the wave?) TIA.
- henryaym 15y agoIf I understand your question.. You can prepare waves in such a way that forces them into this spiraled waveform state. This can be done in a cavity (in the case of lasers) as there are solutions of the wave equation that give rise to OAM; or this can be done by using diffractive optics, like a hologram, that somewhat force the wave into this state. It is this case that you can think of a torque being exerted onto the waves. Waves too, can exert torque on small particles (micron sized polystyrene spheres for instance). Light with spin or orbital angular momentum can be used to make these small object rotate!
- jpdoctor 15y ago> Light with spin or orbital angular momentum can be used to make these small object rotate! Thank you, that was exactly the effect I was looking for. Any links handy? Fascinating stuff, this from an old microwave-digital guy.
- henryaym 15y agoSure! Here's a research group in Glasgow that has a great site: http://www.physics.gla.ac.uk/Optics/play/photonOAM/ http://www.physics.gla.ac.uk/Optics/play/photonOAM/ And here is the lab where I did my undergrad research (Colgate Univ.): http://departments.colgate.edu/physics/research/optics/oamgp/gp.htm http://departments.colgate.edu/physics/research/optics/oamgp... happy to offer up my phd thesis as well: http://shel.tv/henry_thesis http://shel.tv/henry_thesis
- jpdoctor 15y agoIf you ever find yourself in Santa Monica, the beer is on me.
- femto 15y agoDoes launching a wave with OAM require an antenna with spatial extent, or can it be done by a point source?
- bjornsing 15y agoYou're right that multipath is very different from SAM and OAM from a theoretical point of view. Not so much from a practical point of view though. In current point-to-point systems you often use SAM to give you two "channels" across the link, most often referred to as horizontal and vertical polarity, but you then hook that up to the same MIMO technology that you would use for multipath. I would expect OAM to be exploited in a similar maner for point-to-point. The fact that SAM is very difficult to exploit for capacity in cellular applications makes me think it will be even more difficult to exploit OAM. IF you ever see it implemented my money would be on using MIMO to exploit multipath + SAM + OAM, where multipath would dominate in complex radio environments and SAM + OAM in simple more point-to-point like environments. But that's just an educated guess of course.