Tunable linear-optical phase amplification

Abstract

We combine lossless, phase-only transformations with fully-transmitting linear-optical scatterers to define the principle of linear-optical phase amplification. This enables a physical phase shift $\ddot{I}•$ to be nonlinearly mapped to a new space ${\hat{I}}^3(\ddot{I}•)$ using linear optics, resulting in a completely general and enhanced phase shifter that can replace any standard one. A particular phase amplifier is experimentally realized, allowing the phase enhancement parameter $d{\hat{I}}^3/d\ddot{I}•$ to be continuously tuned. Placing this enhanced phase shifter in one arm of a Mach-Zehnder interferometer led to an intensity-phase slope more than twenty times steeper than what can be obtained with its unamplified counterpart.