ORCID

0009-0004-5707-2627

Keywords

Photonic Lantern, Wavefront Sensing, Phase Retrieval, Modal Imaging

Subject Categories

Atomic, Molecular and Optical Physics | Optics | Physics

Abstract

The Rayleigh limit has long defined the angular resolution attainable by conventional intensity-based imaging, which discards the phase of the focal-plane field. By projecting the focal-plane field onto a complete orthonormal spatial mode basis, modal imaging recovers this discarded information and can approach the quantum limit for two-point resolution. A spatial mode sorter such as a Photonic Lantern (PL) is required to achieve improvement in resolution. PLs which are fabricated by adiabatically tapering N single-mode fibers into a multimode core supporting M modes offer a monolithic, broadband, high-throughput alternative to alignment-sensitive free-space converters. Standard PLs scale to large mode counts but mix each input mode across output ports, described by a wavelength-dependent decoding matrix that must be measured, since design alone does not predict real-world device behavior. This dissertation develops a general method for calculating the full complex decoding matrices of an arbitrary lantern across a broad band based on experimental measurements. Using a spatial light modulator to synthesize a large, diverse set of known complex input fields and a dispersive spectrograph to record the wavelength-resolved single-mode-port intensities, we recover the transfer matrix at each wavelength by minimizing the discrepancy between measured and predicted port intensities. Applied to two 19-port lanterns, the procedure confirms that the device behaves as a deterministic broadband linear device. Recovering complex input coefficients from intensity-only measurements is a phase-retrieval problem, fundamentally ill-posed problem when N is approximately close to M. Using wavelength-dependent measurement resolves this: the mode mapping decorrelates rapidly with wavelength, so a single broadband device supplies enough independent measurements to exceed the 4M - 4 injectivity bound, which is a necessary condition for unique recovery. For sources with narrow-band emission, an alternative recovery scheme combines rotation diversity with a second decorrelated wavelength (or orthogonal polarization) to restore injectivity. Finally, two incoherent broadband sources are localized individually; a Cramér–Rao analysis shows the separation variance does not diverge as separation between the two sources shrinks, outperforming direct imaging. These results establish the photonic lantern as a compact platform for sub-diffraction modal imaging and wavefront sensing.

Completion Date

2026

Semester

Summer

Committee Chair

Stephen S. Eikenberry

Degree

Doctor of Philosophy (Ph.D.)

College

College of Optics and Photonics

Format

PDF

Document Type

Dissertation

Language

English

Release Date

8-15-2027

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Available for download on Sunday, August 15, 2027

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