Abstract
Our theoretical study reveals the opportunity to develop an electric field sensor based on the exploitation of the symmetry protected mode (SPM) that we excite within an electro-optical material, namely lithium niobate (LN). The SPM consists of a dark Fano-like resonance that results from the combination of a discrete Bloch mode of a photonic crystal (PhC) with a continuum mode of a membrane, both of them made in LN. The dark character is linked to the structure geometry having a high degree of symmetry. The SPM excitation is then made possible thanks to an illumination under small oblique incidence, which breaks the symmetry of the configuration. This results in several ultra-sensitive and tunable Fano-like resonances with high quality factors up to 105 in the telecoms spectral range. Some of these resonances provide modes with a highly confined electric field inside LN. This confinement allows the enhancement of the electro-optic Pockels effect by a factor up to 5 × 104, thus exacerbating the detection sensitivity of the designed sensor.
Highlights
Today, the world faces a large number of challenges in different disciplines such as health, data processing, energy, information flow and environment
Seeking a configuration exhibiting a resonance with high quality factor, we came across the symmetry protected mode (SPM) [26,27,28]
In order to point out the origin of these resonances, we have studied the optical response of the Photonic Crystal (PhC) and the lithium niobate (LN) membrane separately
Summary
The world faces a large number of challenges in different disciplines such as health, data processing, energy, information flow and environment. Seeking a configuration exhibiting a resonance with high quality factor, we came across the symmetry protected mode (SPM) [26,27,28] This kind of resonance provides an excellent electromagnetic field confinement essential to enhance the LN EO effect surpassing a conventional Fano resonance [21]. As it is well-known [29, 30], SPM generally occurs when a structure with a high degree of symmetry is assumed. This allows a detection sensitivity of 4 pm.m/V, 160000 times greater than the sensitivity obtained through a Mach-Zehnder interferometer design [22] and 1600 times greater than what was predicted with a membrane PhC Fano resonance [21]
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