Overcoming Angular Dispersion in Optical Microcavities and Filters by Ultra-Strong Light Matter Coupling

Thin film interference is essential in optoelectronic devices, allowing to manipulate their spectral characteristics such as emission, transmission, and absorption profiles via constructive and destructive interference. However, photonic systems relying on optical thin films face the fundamental challenge of blue shifts at non-normal angles of incidence. We address this issue by utilizing ultra-strong coupling between cavity photons and material excitons, thereby transitioning from a curved photonic to a flat exciton-like dispersion. This technique is especially effective when using organic materials with high oscillator strengths and enables angle-independent, narrowband responses. We demonstrate both narrowband and broadband, angle-independent transmission filters in metallic cavities and are able to generalize this enhanced performance to distributed Bragg reflector-like dielectric stacks [1]. This approach benefits micro-optics, biophotonics, and other fields addressing light collimation challenges, demonstrating the practical utility of strong coupling in enabling spectrally stable optoelectronic devices.