Inverse photonic design of functional elements that focus Bloch surface waves

Abstract

Bloch surface waves (BSWs) are sustained at the interface of a suitably designed one-dimensional (1D) dielectric photonic crystal and an ambient material. The elements that control the propagation of BSWs are defined by a spatially structured device layer on top of the 1D photonic crystal that locally changes the effective index of the BSW. An example of such an element is a focusing device that squeezes an incident BSW into a tiny space. However, the ability to focus BSWs is limited since the index contrast achievable with the device layer is usually only on the order of Δn≈0.1 for practical reasons. Conventional elements, e.g., discs or triangles, which rely on a photonic nanojet to focus BSWs, operate insufficiently at such a low index contrast. To solve this problem, we utilize an inverse photonic design strategy to attain functional elements that focus BSWs efficiently into spatial domains slightly smaller than half the wavelength. Selected examples of such functional elements are fabricated. Their ability to focus BSWs is experimentally verified by measuring the field distributions with a scanning near-field optical microscope. Our focusing elements are promising ingredients for a future generation of integrated photonic devices that rely on BSWs, e.g., to carry information, or lab-on-chip devices for specific sensing applications.

Laser-Inscribed Stress-Induced Birefringence of Sapphire

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Inverse Design of Nanophotonic Devices with Structural Integrity

“…in a small square with an area of 60 nm × 60 nm, has been shown to lead to tight focal spots in inverse design problems. 42 We assume that the structure is mechanically held in place on the left and right edges of the domain. This could be realized by placing e.g.…”

Centimeter‐Scale Propagation of Optical Surface Waves at Visible Wavelengths

“…The authors reported, through a rough experimental determination, an extinction coefficient smaller than 10 −2 cm −1 for the fundamental surface mode, [1] thus making optical surface waves relevant candidates for on-chip optical information transportation. Over the past 40 years, many studies have explored the possibilities offered by Bloch surface waves (BSWs), from the near-UV to mid-infrared wavelengths, [22][23][24][25][26][27][28][29][30] particularly for sensing applications. [31][32][33][34][35][36] Still, only very few works have discussed their propagation properties [37,38] and even fewer have made reports of experimentally measured propagation lengths.…”