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SEQUENCE:1
X-APPLE-TRAVEL-ADVISORY-BEHAVIOR:AUTOMATIC
UID:237731
DTSTAMP:20260616T145241Z
DTSTART;TZID=America/New_York:20260622T100000
DTEND;TZID=America/New_York:20260622T110000
URL;TYPE=URI:https://www.wpi.edu/news/calendar/events/applied-physics-phd-d
 efense-peter-hedlesky
SUMMARY:Applied Physics PhD Defense of Peter Hedlesky
DESCRIPTION:ABSTRACT\n"Physics-Based Design Methods for Adiabatic Mode Tran
 sformation in Integrated Photonics"\n\n\nImage\n  \n\n\n\nIntegrated photo
 nics is a growing field of Applied Physics, and photonic integrated circui
 ts (PICs) have reached very-large-scale integration (VLSI), with more than
  105 components demonstrated today. This growth is also reflected by the e
 xpanding PIC market, which has been reported to have a Compound Annual Gro
 wth Rate (CAGR) of approximately 10.8%. However, as the scaling andapplica
 tions of PICs continue to grow, so will the limitations of current design 
 methodologies. The Integrated Photonic Systems Roadmap–International (IPSR
 -I) outlines several challenges and scaling gaps between laboratory protot
 ypes and ready-to-use commercial systems. Several of these challenges are 
 linked to mode transformation theory, including the efficient transfer of 
 optical power between fibers, waveguides, layers, materials, and guided mo
 des.\nLinear inverse tapers are widely used as a baseline because they are
  simple and robust. More advanced adiabatic profiles can provide enhanced 
 performance, but their usefulness depends on how well the design method ca
 ptures the local physics of modal evolution. Many current approaches to th
 is challenge avoids physics-driven design by usingsimple geometric profile
 s, empirical optimization, or full-wave simulation sweeps. Simulation-heav
 y approaches such as FDTD are powerful but can be expensive for routine de
 sign generation, while some semi-analytic or local design methods can fail
  when their local assumptions break down. Therefore, there is a need for d
 esign workflows that connect taper geometry directly to the physics of mod
 e coupling and radiation loss, rather than treating the taper shape only a
 s a geometric or numerical optimization variable.\nThis dissertation devel
 ops and compares four design methods foradiabatic mode trans-formation, us
 ing silicon-nitride Si3N4 edgecouplers as the testing platform and a stand
 ard linear edge coupler as the reference design. Two of these methods are 
 numerical and provide direct optimization or validation references. These 
 are the Numerical Adiabatic Mode Evolution Structure (NAMES) and the finit
 e-difference time-domain (FDTD)-derived optimization. NAMES uses sectional
  EME loss minimization and is historically important as a proof-of-concept
  design method. The FDTD-derived method is developed in this work as a pro
 pagation-based optimization and refinement approach for thetaper. The othe
 r two methods are physics-based design methods: the monotonic mode-trackin
 g, or Mono, approach and the coupledlocal-mode theory (CMT) method. Mono u
 ses local overlap sensitivity to develop a local adiabaticity, or loss, te
 rm for its design rule, while CMT models coupling from the target TE00 mod
 e to the radiationcontinuum. The CMT method is the main physics-driven con
 tribution of this dissertation. Together, these workflows are evaluated us
 ing theory, Lumerical simulations, fabricated devices, and experimental me
 asurements.\nAcross the studied platforms, the adiabatic taper designs are
  evaluated against linear references using both simulation and experimenta
 lmeasurement. The AIM platforms provide the strongest validation cases for
  the physics-based workflows, showing that adiabatic tapering can improve 
 simulated performance and provide useful design guidance when the fabricat
 ed device and launch conditions are close to the simulation assumptions. T
 he Applied Nanotools comparison shows a more complicated case, where simul
 ations predicted improvement from the adiabatic profiles, but the measured
  results showedsubstantial disagreement with the models. This result is no
 t interpreted as a failure of CMT, but as evidence that lossless models ca
 n be incomplete when taper-region loss, launch distortion, or polished-fac
 et quality differ from the assumed model. Among the methods studied, CMT i
 s identified as the most promising future workflow because it directly con
 nects the taper shape to coupling between the target mode and the radiatio
 n continuum. More broadly, this work provides a physics-based design and c
 omparison framework for adiabatic modetransformers beyond edge couplers, i
 ncluding transitions between waveguide dimensions, material platforms, lay
 ers, and guided-mode families.\nAdvisor: Doug Petkie\nCommittee members: J
 ames Eakin, Raisa Trubko, Lyubov Titova and Sathwik Bharadwaj\nZoom link:h
 ttps://wpi.zoom.us/j/91527422389\n\n
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