Circularly‐Polarized Laser Equivalent to Two Phase‐Shifted Linearly‐Polarized Sources.

Compact circularly‐polarized (CP) light sources are important for chirality‐based applications at the chip level. The CP light is conventionally generated by passing the linearly‐polarized (LP) one through quarter wave plates which are too thick for packed integrations. In this work, the in‐plane submicron phase shifter substitutes the quarter‐wave plate in the creation of CP light. After the lasing field of a holed microdisk is coupled into the nearby waveguide and phase shifter, it is guided into two grating couplers that output orthogonally LP waves vertically. The two LP waves are phase‐shifted by π/2$\pi /2$ and combine into the coherent CP radiation in the far‐field zone. Experimentally, the fabricated devices exhibit a degree of circular polarization as high as 74%. This device scheme is simple and effective in that it relies on no extrinsic materials, large‐area auxiliary structures, or specialized operation conditions critical for CP radiation. The compatibility issues for integrated photonic systems are of less concern in such schemes. [ABSTRACT FROM AUTHOR]