SCRIBE: Subsurface volumetric integration of freeform micro-optical elements for advanced beam shaping and light routing

Richards, Corey Allan

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https://hdl.handle.net/2142/120497 Copy

Description

Title

SCRIBE: Subsurface volumetric integration of freeform micro-optical elements for advanced beam shaping and light routing

Author(s)

Richards, Corey Allan

Issue Date

2023-04-03

Director of Research (if dissertation) or Advisor (if thesis)

Braun, Paul V

Doctoral Committee Chair(s)

Braun, Paul V

Committee Member(s)

• Shim, Moonsub
• Schleife, Andre
• Zhao, Yang

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Optics
• Materials
• 3D Printing
• Photonics

Abstract

Subsurface Controllable Refractive Index via Beam Exposure (SCRIBE) is a new micro-optics fabrication approach developed by the Braun Research Group that combines direct-write multiphoton lithography with porous media like porous silicon and porous silica. Optical elements printed via SCRIBE exhibit unprecedented simultaneous control over geometry, spatial positioning, and refractive index. This advancement has enabled the formation of dispersion engineered achromatic doublets, high aspect ratio optical fibers that traverse 3D space, and gradient refractive index lenses, all of which lie outside the purview of what is readily achievable with traditional direct-write lithography methods. Notably, the world’s smallest Luneburg lens with a 15 μm diameter that focuses visible wavelengths is demonstrated by creating a spherical lens with an internal center-to-edge index profile. Porous silicon and porous silica have been extensively investigated for photonics applications due to their favorable optical properties. Namely, these porous materials exhibit high transparency and ultralow, tunable refractive indices, making them attractive candidates for spectral filters and microcavities. The most significant recent advancements in porous silicon optics were made by the Braun Group, the members of which have shown that the optical properties of porous silicon can be permanently modified by introducing secondary materials into the pores. TiO2 or VO2 are conformally deposited into the void volume via atomic layer deposition to create new high index or thermally tunable composites. This concept is expanded upon by using direct-write lithography to introduce local changes in the optical properties of porous silicon and porous silica instead of bulk changes, forming the basis of SCRIBE-printed micro-optics. With SCRIBE, micro-optical elements are formed by first introducing a photosensitive liquid resin into the void volumes of porous silicon and porous silica. An ultrafast laser is then focused into the volume of these materials, polymerizing the liquid resist via nonlinear absorption. By scanning the laser in the desired pattern, microstructures are 3D printed with submicron resolution. The porous matrix surrounding the printed optics provide mechanical support, enabling the fabrication of stacked optics in configurations not typically possible. Most significantly, polymer diffractive and refractive optics are seamlessly integrated and aligned within the volume of porous silica for hybrid achromatic imaging applications. Hybrid achromatic microlenses presented in this dissertation are highly compact by virtue of the porous host media, with gaps between the diffractive and refractive components as small as 2 μm. Hybrid achromats fabricated with SCRIBE can achieve higher focusing efficiencies, numerical apertures, and chromatic correction than other compact achromats in the literature. In this dissertation, great strives are made to transition SCRIBE optics from laboratory-scaled demonstrations to industry components that can survive a variety of environments. One limitation of porous silicon and porous silica are their susceptibility to high temperatures, water, and basic solutions. Using the industrial grade moisture barrier, parylene C, SCRIBE-printed optics can survive for hundreds of hours in harsh environments with little to no damage. This also allows SCRIBE optics to operate in liquid without loss of index contrast, opening the door to bioimaging applications. The throughput of SCRIBE is also enhanced by adapting this approach to work with state-of-the-art grayscale multiphoton printers capable of printing larger areas at higher speeds than what has been demonstrated thus far.

Graduation Semester

2023-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Corey Richards

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