Transducing electromagnetic waves with soft phonon polaritons

Efficiently transducing microwave signals into optical signals is one of the major demands in modem telecommunication. Electro-optical crystals hosting optical whispering gallery modes incorporated in a properly designed microwave cavity emerge as a promising candidate towards much more efficient microwave-to-light transducer [1, 2]. Here, we propose to use a ferroelectric crystal close to its paraelectric-ferroelectric phase transition temperature to take advantage of its large relative permittivity due to the softened optical phonon mode, which may further enhance the electro-optic coupling.