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Waveguides are the technique Magic Leap (and others) have used in their developer unit, after making a lot of noise a couple of years back about using Fibre Scanning Display. As Karl notes, to achieve a good resolution by spinning a length of optical fibre in a spiral to cover the field of view (akin to how a cathode ray scans back and forth to cover an area) would have said fibre exceeding the sound barrier, if you want a decent refresh rate.