Sculpting Angular Tolerance to Reshape Mid-InfraredNonlocal Guided Resonances

Photonic crystal guided resonances (PCGRs) are an essential class of nonlocal resonant elements that drive various nanophotonic applications. Their <i>Q</i>-factor and efficiency are believed to be limited by highly dynamic dispersion, especially when a significant angular beam spread is inevitable, as in mid-infrared (MIR) spectroscopy. Here, we discover that the high-index slab’s thickness, along with the associated group index, provides a tuning knob not only for well-known optical confinement effects but also for the angular tolerance of the PCGR. With this new approach, we theoretically and experimentally demonstrate a ∼ 3-fold reduction in the angular sensitivity of the PCGR across a wide bandwidth, matching or even surpassing the performance of other state-of-the-art high-<i>Q</i> nonlocal metaresonators. This optimal angular tolerance enables a series of high-efficiency, angle-multiplexed PCGRs throughout a broad section of the MIR fingerprint region. This study overcomes the primary barrier to using PCGRs, setting the stage for future advancements in surface-enhanced MIR spectroscopy and numerous applications.