MIT Lincoln Laboratory

Inverse design of optical components based on adjoint sensitivity analysis has the potential to address the most challenging photonic engineering problems. However, existing inverse design tools based on finite-difference-time-domain (FDTD) models are poorly suited for optimizing waveguide modes for adiabatic transformation or perturbative coupling, which lies at the heart of many important photonic devices. Among these, dispersion engineering of optical waveguides is especially challenging in ultrafast and nonlinear optical applications involving broad optical bandwidths and frequency-dependent anisotropic dielectric material response. In this talk I will describe gradient back-propagation through a general-purpose electromagnetic eigenmode solver and demonstrate its use for waveguide dispersion optimization for second harmonic generation with maximized phase-matching bandwidth[1]. I will show that the computational cost of gradient back-propagation is independent of the number of parameters, as required for optimization of complex geometries. Finally, I will discuss how this technique enables practical inverse design for a broad range of previously intractable photonic devices.

[1] D Gray, G N West and R J Ram. "Inverse design for waveguide dispersion with a differentiable mode solver." Optics Express 32.17 (2024)

Biography:

Dr. Dodd Gray is a member of the technical staff in the Integrated RF and Photonics Group at MIT Lincoln Laboratory. His research is focused on the physics of photonic and optoelectronic waveguide devices and roughly falls into three categories: (1) waveguide nonlinear optics for wavelength conversion, (2) integrated pulsed lasers for compact optical frequency combs and optical atomic clocks, and (3) instrumentation for scalable manufacturing and characterization of integrated photonics.

Prior to joining Lincoln Laboratory in April 2023, Dodd worked as a Photonic Design Engineer at Ayar Labs and briefly as a Research Scientist at Physical Sciences Inc. in 2022. From 2019-2022 Dodd was Postdoctoral Fellow in the Physical Optics and Electronics (POE) Group at MIT led by Prof Rajeev Ram. There Dodd developed the first differentiable fully vectorial mode solver for dispersion optimization of nonlinear optical waveguides and a novel high-contrast SHG microscope for imaging ferroelectric domain patterns in poled nonlinear optical films. Dodd completed his Ph.D. under the supervision of Prof. Hideo Mabuchi in the Applied Physics department at Stanford (2012-2019). There he developed a scanning confocal Raman microscope to characterize ferroelastic domain patterns in cryogenic SrTiO₃ and studied wavelength conversion in CMOS-fabricated silicon waveguide devices. Dodd previously worked in the POE group as an undergrad and master's student at MIT, developing modeling and experiment tools to study thermoelectric effects in light-emitting diodes.

Dodd earned degrees in Electrical Engineering from Stanford University, Ph.D. '19, and MIT, B.S. '10 and M.Eng. '11