A Mirror Seam That Tells Light Where to Go
A tiny spinning coin drops into a narrow seam between two ridged guides. The left and right sides are mirror images. Spin the coin one way and it catches on one side, spin it the other way and it takes the other. Because each side has an upper rail and a lower rail, there are four paths waiting.
Light on a chip is harder to tame, especially when it skims along a surface instead of spreading out. People often add extra pieces to shove it into the right lane and other pieces to check where it went. Here, the trick was to let light's own twist do that sorting.
So the seam itself became the launcher. Light with no favored twist fed both mirrored sides, like a coin given a neutral push. Left-twisting light went to one mirrored region, right-twisting light went to the other. In the coin picture, the guides are the patterned regions, the four rails are the four surface lanes, and the coin's spin is the light's twist.
The match runs deeper than left and right. What matters is how the twist turns compared with the direction the energy moves. That is like watching the coin's rim turn as it rolls, not staring at the face stamped on it. The same handed turn survives the handoff and keeps the surface signal's identity clear.
At the far end, rows of tiny silver posts flicked the surface-hugging light back out into open space. One post pattern gave very clean circular light, but not at the strongest exits, so a smaller partner pattern helped. They also checked that the mirrored material was doing the sorting, not just simple grooves.
When the whole layout was cut into silver on glass, it behaved like the route map promised. Straight light fed both sides. Left and right twisting light came out at opposite ports, carrying opposite twists there. Older designs needed extra steering parts. This one lets the mirrored seam do the sorting inside one compact chip.