Final Examination of Abbas Shiri for the degree of Doctor of Philosophy in Electrical Engineering

Friday, July 1, 2022 1 p.m. to 2:30 p.m.

Dissertation Title: “Space-Time Photonics”


Abstract: Many of the features of photonic devices, including some of the most ubiquitous components such as resonators and waveguides, are usually thought to be intrinsically dependent on their geometry and constitutive materials. As such, the behavior of an optical field interacting with such devices is dictated by the boundary conditions imposed upon the field. For instance, the resonant wavelengths and linewidths of a planar cavity are expected to be set by the mirrors’ reflectivity, cavity length, and refractive index. Henceforth, satisfying a longitudinal phase-matching condition allows for incident light to resonate with the cavity. As another example, consider the planar waveguide; the field is confined along one transverse dimension, but diffracts along the other unbounded dimension. We have recently introduced several strategies for challenging these long-held intuitions that may be collected under the moniker ‘space-time (ST) photonics’, whereby the response of a photonic device is tailored post-fabrication in useful ways by sculpting the spatio-temporal structure of the incident optical field. In fact, introducing a prescribed relationship between the spatial frequencies and the temporal frequencies can help overcome the constraints imposed by the boundary conditions. We refer to such pulsed beam configurations as ST wave packets. In one scenario, introducing carefully designed angular dispersion into a pulsed field allows the realization of omni-resonance: the pulse traverses the cavity without spectral filtering even if the pulse bandwidth is larger than the cavity resonant linewidth after the entire bandwidth resonates with it. A similar strategy enables a new class of planar waveguide modes we refer to as ‘hybrid guided ST modes’ where the field is confined along the unbounded dimension through ST coupling. Crucially, the spatio-temporal structure introduced into the field along the unbounded dimension enables overturning the impact of the boundary conditions along the other dimension. For example, the modal size, index, and dispersion can all be engineered independently of the thickness and refractive index of the planar waveguide; i.e., the impact of the boundary conditions is overturned.


Educational Career:

BS: 2009, Electrical Engineering, Bu-Ali Sina University

MS: 2012, Electrical Engineering, University of Tehran


Committee in Charge: 

Ayman Abouraddy, Chair

Mohammad Assefzadeh

George Atia

Peter Delfyett

Aristide Dogariu


Approved for distribution by Ayman Abouraddy, Committee Chair, on June 16th, 2022.

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