Physics / mechanism
Thin-film stacks of alternating high- and low-refractive-index dielectrics (e.g. TiO₂/SiO₂, Ta₂O₅/SiO₂, Nb₂O₅/SiO₂) deposited by IBS, PECVD, or magnetron sputtering. Reflectance is governed by constructive/destructive interference; layer thickness tuned to λ/4 optical path length. Dielectric mirrors routinely achieve R > 99.999% (5-nines) at target wavelength with scatter losses < 1 ppm—critical for laser cavities and ring-resonator Q-factors. Key parameters: laser damage threshold (LIDT, J/cm²), group delay dispersion (GDD, fs²), spectral bandwidth, and environmental stability (humidity, thermal cycling). State of the art: chirped-mirror designs compress few-fs pulses; ion-beam-sputtered coatings dominate precision metrology and gravitational-wave interferometers (LIGO mirror losses ~1 ppm).
Competitive landscape
Competing approaches split by use case. Metallic mirrors (Ag, Au, Al) offer broad bandwidth but absorb ~1–5% and degrade. Photonic crystal reflectors (etched semiconductor slabs) integrate monolithically on-chip but require fab-node lithography and are narrowband. Grating-based reflectors suit specific polarization tasks. For integrated photonics, Bragg reflectors grown epitaxially (GaAs/AlGaAs DBRs) compete directly with deposited dielectrics on III-V platforms.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.