Chirality refers to a geometric phenomenon in which objects are not superimposable on their mirror image. 1 Structures made of nano-scale chiral elements can display chiroptical effects, such as dichroism for left-and right-handed circularly polarized light, which makes them of high interest for applications ranging from quantum information processing and quantum optics 2,3 to circular dichroism spectroscopy and molecular recognition. 4 At the same time, strong chiroptical effects have been challenging to achieve even in synthetic optical media and chiroptical effects for light with normal incidence has been speculated to be prohibited in lossless, thin, quasi-twodimensional structures. 5-8 Here, we report on our experimental realization of a giant chiroptical effect in a thin monolithic photonic crystal mirror. Unlike conventional mirrors, our structure selectively reflects only one spin state of light, while preserving its handedness, with a near unity level of circular dichroism. The operational principle of the photonic-crystal mirror relies on Guided Mode Resonance (GMR) with 1 arXiv:1911.09227v1 [physics.optics] 21 Nov 2019 simultaneous excitation of leaky TE and TM Bloch modes in the photonic crystal slab.Such modes are not reliant on the suppression of their radiative losses through the long-range destructive interference and even small areas of the photonic-crystal exhibit robust circular dichroism. Despite its simplicity, the mirror strongly surpasses the performance of earlier reported structures and, contrary to a prevailed notion, demonstrates that near unity reflectivity contrast for the opposite helicities is achievable in a quasi-two-dimensional structure.

We demonstrate a fiber-integrated Fabry-Pérot cavity formed by attaching a pair of dielectric metasurfaces to the ends of a hollow-core photonic-crystal fiber segment.The metasurfaces consist of perforated membranes designed as photonic-crystal slabs that act as planar mirrors but can potentially allow injection of gases through their holes into the hollow core of the fiber. We have so far observed cavities with finesse of ∼ 11 and Q factors of ∼ 4.5 × 10 5 but much higher values should be achievable with improved fabrication procedures. We expect this device to enable development of new fiber lasers, enhanced gas spectroscopy, and studies of fundamental light-matter interactions and non-linear optics.

We present a lithographically defined, ultra-high vacuum (UHV) compatible on-chip structure acting as a mechanical splicer that allows efficient injection of light from a conventional solid-core (SC) fiber to a hollow-core photonic crystal fiber (HCPCF) and vice versa. We report the observed coupling efficiencies for an assortment of solid-core fibers and a HCPCF with maximum efficiency between solid-core fiber and HCPCF of 93%.

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