Abstract
We demonstrate for the first time a 300nm thick, 300μm × 300μm 2D dielectric photonic crystal slab membrane with a quality factor of 10,600 by coupling light to slightly perturbed dark modes through alternating nano-hole sizes. The newly created fundamental guided resonances greatly reduce nano-fabrication accuracy requirements. Moreover, we created a new layer architecture resulting in electric field enhancement at the interface between the slab and sensing regions, and spectral sensitivity of >800 nm/RIU, that is, >0.8 of the single-mode theoretical upper limit of spectral sensitivity.
Highlights
Optical detection techniques are useful in evaluating different materials without altering the observed objects’ structure or characteristics
In this work we designed, fabricated and characterized a novel checkerboard photonic crystal slab (CPCS) with superior sensitivity, STM = 832nm/RIU, and higher quality factor, QTM = 10643, than regular homogeneous PCS (HPCS) in a relatively small mesa size )300μm ! 300μm. These results present an increase in Q values by a factor >2 for TM- and >2.5 for TE-like modes in CPCS design with respect to HPCS
The high-Q values are attributed to coupling to previously dark guided modes (GM) of HPCS, which due to CPCS lattice geometry, are band-folded to become bright
Summary
Optical detection techniques are useful in evaluating different materials without altering the observed objects’ structure or characteristics. Typical localized photonic crystal cavities and optical resonators can achieve very high Q values ranging from 104 to 106 [2], but show a small field overlap with the analyte, and a low detection volume [12], resulting in a low spectral sensitivity and limited usability in medical practice. Special structural designs of PCSs enable access to their ‘dark’ modes, i.e. modes that lie outside the light-cone This turns these modes to lower order GRs with higher Q values as compared to the original fundamental modes [26,30]. Breaking the HPCS symmetry and accessing higher order modes while obtaining relatively high Q values, ~104, with large area PCS lattices was demonstrated by perturbing the HPCS structure [31] or tilting the incident light angle away from normal incidence [36].
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