Nanophotonic Zero-Index-Material-Enabled Optical Coherent Interferometry with High Signal-to-Noise Ratio

Optical interferometry enables distance measurement with record-high precision. However, the conventional interference intensity shows fast spatial variations, limiting photodetection to a single spot. The light intensity at this spot is affected by various noises, restricting the signal-to-noise ratio (SNR) of a coherent system. Here, we generate uniform interference patterns based on zero-index metawaveguides, enabling the photodetection of spatially extended intensity through multiple-pixel measurements of a charge-coupled device. Averaging the intensities measured across multiple pixels cancels uncorrelated noise, significantly improving the SNR and allowing the detection of weakly reflected optical power. Experiments show that nanoscale displacements down to 26 nm (λ0/59) can be converted into high-contrast intensity changes over a macroscopic area, leading to an SNR 10+ times higher (11.68 dB) than that of conventional single-spot photodetection. Our nanophotonic zero-index platform can be implemented in any coherent system, possibly leading to a transformative impact in precise measurement of the distance, profile, and spectrum.