Long-Range Coherent Emission of Propagating Exciton–Polaritons from a Mach–Zehnder Interferometer

Long-range coherence of the part-matter, part-light exciton–polariton has potential applications in all-optical logic that combine the large nonlinearity of the matter component with the delocalization by the light component. A polariton condensate has been shown to have long-range coherence, although the formation of a condensate requires complex device fabrication and well-defined operation conditions. In this work, we demonstrate a Mach–Zehnder interferometer that exhibits room-temperature, long-range coherent propagation of Bloch surface wave polaritons (BSWPs) that does not depend on the formation of a condensate. Due to strong coupling of the organic exciton and the delocalized BSW supported by a distributed Bragg reflector (DBR), the hybrid light–matter states sustain coherence over distances of ∼50 μm, giving rise to wavelength-dependent interference patterns within the devices. Our results show that the BSWP represents a promising platform for room-temperature coherent polaritonic devices, thus enabling integrated photonic circuits that operate under ambient conditions.