Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Kelvin H. Wagner

Second Advisor

Daniel Feldkhun

Third Advisor

Steven T. Cundiff

Abstract

As optical imaging in scattering medium is emerging as a promising imaging modality, several challenges arise against deeper imaging due to the multiple-scattering caused by the inhomogeneous distribution of refractive index. To obtain high quality images through active structured light illumination and polarization imaging, an polarized, tunable and intense broadband light source is highly desirable to perform coherence gating for enhancing ballistic photons in a highly scattering medium. This thesis describes the challenges of optical imaging, polarization imaging in scattering medium, the experimental investigations of a dynamic structured illumination microscope (DSIM), and the development of a versatile broadband supercontinuum light source generated using ultra fast nonlinear optics for enabling new optical imaging modalities in scattering medium. The DSIM was demonstrated as a Fourier synthesis and polarization-sensitive imaging method using a moving illumination pattern requiring only a single pixel camera or a photodiode detector. To increase penetration depth in a scattering medium, it is suggested that a broadband supercontinuum laser can be used as a powerful and tunable fiber-based light source for coherence gating to enhance ballistic photons. Therefore, an octave-spanning broadband supercontinuum light laser is experimentally demonstrated using an ultrafast femtosecond Ti:Sapphire seed laser and a highly nonlinear micro-structured photonics crystal fiber. During the experiment, the broadband supercontinuum output is demonstrated to be polarization-dependent, thus a detailed numerical simulation is developed using vectorized generalized nonlinear Schr¨odinger equations (GNLSE) for both isotropic and anisotropic fiber mediums. The polarization trajectories of Raman solitons in the supercontinuum generation visualized on the Poincar´e sphere reveals rich polarization dynamics, including a polarization separatrix for light propagation in the birefringent fiber. While most of the previous works were focused on polarization dynamics for light propagation in linearly birefringent fiber, I investigated the case of circularly birefringent fiber and found a simplified polarization evolution that leads to a motivation for developing twisted fibers for single polarization broadband light sources. The versatile and stable circularly polarized broadband supercontinuum can be potentially one of the most attractive light source to improve optical imaging in scattering medium.

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