Design and Fabrication of Microscale, Thin-Film Silicon Solid Immersion Lenses for Mid-Infrared Application

Abstract

Lens-based optical microscopes cannot resolve the sub-wavelength objects overpass diffraction limit. Recently, research on super-resolution imaging has been conducted to overcome this limitation in visible wavelength using solid immersion lenses. However, IR imaging, which is useful for chemical imaging, bio-imaging, and thermal imaging, has not been studied much in optical super-resolution by solid immersion lens owing to material limitations. Herein, we present the design and fabrication schemes of microscale silicon solid immersion lenses (µ-SIL) based on thin-film geometry for mid-infrared (MIR) applications. Compared with geometrical optics, a rigorous finite-difference time-domain (FDTD) calculation of proposed silicon microlenses at MIR wavelengths shows that the outstanding short focal lengths result in enhanced magnification, which allows resolving objects beyond the diffraction limit. In addition, the theoretical analyses evaluate the influences of various structural parameters, such as radius of curvature (RoC), refractive index, and substrate thickness, in µ-SIL. In particular, the high refractive index of µ-SIL is beneficial to implement the outstanding near-field focusing, which corresponds to a high numerical aperture. On the basis of this theoretical background, novel methods are developed for the fabrication of a printable, thin-film silicon microlens array and its integration with a specimen substrate. From the result, we provide a physical understanding of near-field focusing phenomena and offer a promising tool for super-resolution far-field imaging in the MIR range.

Photonic lenses with whispering gallery waves at Janus particles

“…The truncated particle presents a solid immersion lens (SIL) which can overcome diffraction limit 13 . It could be noted that physical principles of truncated spherical SIL, for which aberration free focusing occurs and also known as Weierstrass SIL, is based on compressing the emitted light into a small NA by decreasing of the refraction angle of the transmitted light, measured from the optical axis.…”

“…New phenomena arise in particles in which a segment of a sphere or cylinder is removed (Janus particles [11,12]). It is a typical design of solid immersion lens [13,14]. It is known that parameters of a photon jet from a hemisphere (or hemicylinder) can be very different from the parameters of a jet formed by a whole sphere [15] or cylinder [16].…”

Photonic Nanojet Generation Using Integrated Silicon Photonic Chip with Hemispherical Structures

“…Therefore, further studies were carried out with a substrate thickness of 3.5𝜆. Since both the substrate and spherical dome are made of Si, such structure/device can be fabricated using standard CMOS microfabrication [23,24] and could be integrated with other photonic devices/components and microfluidics for sensing and imaging in a fluidic environment.…”

“…The on-chip CMOS compatible structure that we are proposing consists of a silicon hemispherical dome on a silicon substrate (Figure 2a). Such structure can be mass-produced using standard lithography and dry etching [23,24] and much easier to align in an optical setup. Figure 2b shows the simulated electric field intensity distribution of this structure when illuminated with a plane wave of λ = 1550 nm through the substrate.…”

“…Here we demonstrate an on-chip PNJ using silicon, which is the most appropriate device platform for most of the applications mentioned above. Due to the simplicity of design, it can be fabricated using standardized silicon micro-/nano-fabrication techniques [23,24] and the structure can be easily aligned in any optical setup and PNJs can be excited using plane waves.…”