Abstract
We have fabricated spherical and cylindrical concave micro-mirrors in silicon with dimensions from 20 microm to 100 microm. The fabrication process involves standard photolithography followed by large area ion beam irradiation and electrochemical anodisation in a HF electrolyte. After thermal oxidation the silicon surface roughness is less than 2 nm. We also present a multilayer porous silicon distributed Bragg reflector fabricated on concave silicon surfaces which selectively reflect and focus a band of wavelengths from a parallel beam of incident white light. Development of such low roughness concave microstructures opens up new applications in areas such as silicon photonics and quantum information science.
Highlights
1.1 Concave mirrors and lensesA concave surface profile in the micron regime is of interest because of its ability to focus incoming light into a spot
In the field of micro-electro-mechanical-systems (MEMS) and optoelectronics, it may be used as a variable optical attenuator [3] or to produce an enhanced and localized light signal for parallel low loss optical interconnect systems [4]
This was primarily motivated by applications in quantum information sciences, for the studies of cavity quantum electrodynamics (CQED)
Summary
A concave surface profile in the micron regime is of interest because of its ability to focus incoming light into a spot. In the field of micro-electro-mechanical-systems (MEMS) and optoelectronics, it may be used as a variable optical attenuator [3] or to produce an enhanced and localized light signal for parallel low loss optical interconnect systems [4] From these concave profiles, it is possible to further fabricate concave optical cavities by coupling two such mirrors together or with an optical fiber [5]. The fabrication of concave mirrors in Si is not trivial, it was reported by Trupke in Ref [5] where concave profiles were created by isotropic wet etching of Si through circular apertures in a lithographic mask using a mixture of HF and HNO3 under continuous agitation This was primarily motivated by applications in quantum information sciences, for the studies of cavity quantum electrodynamics (CQED). The use of thermal oxide (SiO2) and low-stress silicon nitride (Si3N4) as a hard mask together with isotropic wet etching of Si in an etch solution containing etch solution consists of HF and HNO3 was used to create concave profiles on Si which were used subsequently as molds to form microlenses on polymers
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