Optical Waveguides for stopping light

Almost twenty years ago the light was slowed 10 million times less than its vacuum speed in a cloud of ultracold atoms of sodium. Upon a sudden turn-off of the coupling laser, a slow light pulse can be imprinted on cold atoms such that it can be read out and converted into photon again. In this process, the light is stopped by absorbing it and storing its shape within the atomic ensemble. Alternatively, the light can be stopped at the band edge in photonic-crystal waveguides, where the group speed vanishes. Here we extend the phenomenon of stopped light to the new field of parity-time (PT) symmetric systems. Researchers show that zero group speed in PT symmetric optical waveguides can be achieved if the system is prepared at an exceptional point, where two optical modes coalesce. This effect can be tuned for optical pulses in a wide range of frequencies and bandwidths, as we demonstrate in a system of coupled waveguides with gain and loss.

The researchers conclude that this effect can be engineered in a PT-symmetric system of two waveguide channels. This approach is not limited only to light but can be extended, e.g., to acoustic waves or other fields in physics related to the PT-symmetry.