Compact Phase-Modulated Photonic Structures for On-Chip Multiband Spectroscopy

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Due to the rapid developments of highly-integrated photonics and quantum communication technologies as well as the recent advancements of high-resolution medical imaging techniques, there is currently a compelling need for miniaturized and scalable optical elements that enable simultaneous light focusing and directional control over different spectral bands. Responding to these challenges, this project advances the understanding of optical devices that combine multiple functionalities on the nanoscale. The research team utilizes experimental and computational approaches to help develop novel materials and structures that enable controllable light focusing responses with reduced losses and enhanced efficiency for use in next generation of power-efficient nanophotonics devices, such as on-chip spectrometers, optical sensors, and miniaturized imaging systems that operate over multiple and spectral regions. The project supports one graduate student and encourages the involvement of undergraduate students in the research through a vibrant outreach program aimed at introducing fundamental concepts of optical science and engineering in their academic curricula in partnership with practical laboratory demonstrations and research activities through summer programs at Boston University. An important component of this outreach plan is to attract underrepresented minorities to a career in optical engineering through participation in the project. Finally, the outreach involves the development of a focused teaching module addressing the emerging field of Metaphotonics that will be offered to students (graduate and undergraduate) and practitioners both in industry and academia as part of the photonics outreach programs at Boston University.The primary goal of this proposal is to combine favorable aspects from both meta-optics and diffractive optics technologies in order to design, fabricate, and experimentally characterize high-performance, ultra-compact novel diffractive devices with spatially-modulated phase profiles based on high-index transparent materials and scalable multi-level fabrication. In particular, the researchers will focus on two closely related novel photonic structures: (i) single-element, ultra-compact micro- spectrometers based on achromatic axilenses with engineered phase modulation, and (ii) multi-spectral axilens-based focusing devices that achieve simultaneous focusing of radiation over selected spectral bands. The goals will be accomplished by a comprehensive integration of rigorous Rayleigh-Sommerfeld diffraction theory, device-level Finite Element Method (FEM) numerical design, materials fabrication, and experimental characterization of optical devices with integrated imaging and spectroscopic functionalities across a wide spectral range. While using silicon (Si) and titanium dioxide (TiO2) transparent dielectrics for the visible and near-infrared (NIR) spectral range, the research concepts, methods and design approach can naturally be extended to any wavelength of interest and dielectric materials platforms. The intellectual merit of the proposed research program relies on the development of novel and more powerful avenues for cost-effective, miniaturized, phase-engineered devices that are polarization insensitive, work over a large range of incidence angles, and combine highly-efficient focusing and grating responses that, in addition to optical spectroscopy, also find applications to multi- spectral optical detection, quantum information sources, and on-chip sensing. This project enables a substantial broader impact as it provides the foundation for the next generation of ultra-compact spectroscopic phase-modulated devices for optical imaging, sensing, and spectroscopy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.