Abstract
We present a simple theory explaining the extraordinary features of high-contrast optical gratings in the near-wavelength regime, particularly the very broadband high reflectivity (>99%) and the ultra-high quality factor resonances (Q>10(7)). We present, for the first time, an intuitive explanation for both features using a simple phase selection rule, and reveal the anti-crossing and crossing effects between the grating modes. Our analytical results agree well with simulations and the experimental data obtained from vertical cavity surface emitting lasers incorporating a high contrast grating as top reflector.
Highlights
Optical gratings are among the most fundamental building blocks in optics. They are well understood in two regimes: the diffraction regime, where the grating period (Λ) is greater than the wavelength (λ) [1] and the deep-subwavelength regime, where the grating period is much less than the wavelength [2]
With the advent of nanofabrication technologies, near-wavelength gratings have been explored for high reflectivity diffractive elements (85%–90%) [3,4], optical isolator [5], resonant grating waveguides as optical modulators or switches [6], and optical filters [7]
We discovered a novel near-wavelength grating structure where the high index grating is completely surrounded by low index materials, referred as high-contrast gratings (HCG) [8]
Summary
Optical gratings are among the most fundamental building blocks in optics. They are well understood in two regimes: the diffraction regime, where the grating period (Λ) is greater than the wavelength (λ) [1] and the deep-subwavelength regime, where the grating period is much less than the wavelength [2]. With the advent of nanofabrication technologies, near-wavelength gratings have been explored for high reflectivity diffractive elements (85%–90%) [3,4], optical isolator [5], resonant grating waveguides as optical modulators or switches [6], and optical filters [7] In all these cases, the gratings were typically etched into the substrate with a large index contrast with the medium on top, from which light incident. One main difference from ordinary slab waveguides stands-out: HCG has a discrete set of modes below the air light line, i.e. β
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