[Paper Review] Waveguide, Photodetector, and Imaging Applications of Microspherical Photonics

Kenneth W. Allen|arXiv (Cornell University)|Mar 11, 2015

Near-Field Optical Microscopy127 references18 citations

TL;DR

This dissertation investigates microspherical photonics for waveguide integration, photodetection, and imaging by leveraging dielectric microspheres to generate photonic nanojets and support whispering-gallery modes. By assembling multiple spheres into chains, clusters, or arrays and integrating them with waveguides or host materials, the study demonstrates enhanced optical confinement, super-resolution focusing, and improved photodetection efficiency through engineered resonant structures.

ABSTRACT

Dielectric microspheres with diameters on the order of several wavelengths of light have attracted increasing attention from the photonics community due to their ability to produce extraordinarily tightly focused beams termed photonic nanojets, to be used as microlenses for achieving optical super-resolution or to develop sensors based on whispering-gallery mode resonances. In this dissertation, we study the optical properties of more complicated structures formed by multiple spheres which can be assembled as linear chains, clusters or arrays, integrated with waveguides or embedded inside other materials to achieve new optical properties or device functionalities.

Motivation & Objective

• To explore the optical properties of complex microsphere-based structures for advanced photonic device integration.
• To address the need for compact, high-sensitivity optical sensors and imaging systems through microsphere-enhanced light manipulation.
• To develop functional photonic devices by integrating microspheres with waveguides or embedding them in host materials.
• To achieve optical super-resolution and enhanced detection by leveraging photonic nanojets and resonant modes.
• To demonstrate practical applications in imaging and photodetection through scalable microsphere array architectures.

Proposed method

• Design and simulation of linear chains, clusters, and arrays of dielectric microspheres with diameters on the order of optical wavelengths.
• Utilization of photonic nanojets generated by single microspheres for subwavelength focusing and super-resolution imaging.
• Employment of whispering-gallery mode (WGM) resonances in microspheres for high-Q optical sensing and enhanced light-matter interaction.
• Integration of microspherical structures with planar waveguides to enable guided light coupling and on-chip photonic functionality.
• Embedding microspheres within host materials to tailor effective refractive index and enhance optical confinement.
• Application of electromagnetic modeling and FDTD simulations to analyze field distribution, resonance conditions, and device performance.

Experimental results

Research questions

• RQ1 How do microsphere arrays in chain, cluster, or lattice configurations enhance optical field confinement and transmission?
• RQ2 What is the role of photonic nanojets in enabling optical super-resolution beyond the diffraction limit?
• RQ3 How can whispering-gallery mode resonances in microspheres be leveraged for high-sensitivity photodetection?
• RQ4 What are the optimal geometries and arrangements for integrating microspheres with waveguides to maximize coupling efficiency?
• RQ5 How does embedding microspheres in a host medium affect their resonant properties and device performance?

Key findings

• Microsphere arrays generate highly confined photonic nanojets capable of subwavelength focusing, enabling optical super-resolution imaging beyond the diffraction limit.
• Whispering-gallery mode resonances in individual microspheres provide high-quality factors (Q-factors), enhancing sensitivity for label-free optical sensing applications.
• Integration of microspheres with waveguides enables efficient coupling of light into and out of the microsphere structures, supporting on-chip photonic circuits.
• Cluster and chain configurations of microspheres exhibit collective optical modes that can be tuned by inter-sphere spacing and arrangement, enabling reconfigurable optical responses.
• Embedding microspheres in dielectric matrices modifies their effective refractive index and resonance conditions, allowing for tailored optical properties.
• Simulations demonstrate that optimized microsphere configurations can enhance photodetection efficiency by concentrating light into subwavelength volumes, improving signal-to-noise ratios.