(in reverse chronological order)

alt text 

High-frequency, resonant acousto-optic modulators fabricated in a MEMS foundry platform
Stefano Valle and Krishna C. Balram
Optics Letters (2019)
Summary: We report the design and characterization of high-frequency, resonant acousto-optic modulators (AOMs) in a micro-electro-mechanical systems (MEMS) foundry process. The doubly resonant cavity design, with short acoustic and optical cavity lengths, allows us to measure acousto-optic modulation at GHz frequencies with high modulation efficiency. In contrast to traditional AOMs, these devices rely on the perturbation induced by the displacement of cavity boundaries, which can be significantly enhanced in a suspended geometry.

alt text 

The 2019 surface acoustic waves roadmap: Cavity optomechanics with surface acoustic waves
Kartik Srinivasan, Marcelo Wu and and Krishna C. Balram
Journal of Physics D: Applied Physics (2019)
Summary: We summarize the opportunities and potential roadblocks presented by the adoption of piezoelectric material platforms for cavity optomechanics.

alt text 

Tuning and stabilization of optomechanical crystal cavities through NEMS integration
Karen E. Grutter, Marcelo I. Davanco, Krishna C. Balram, and Kartik Srinivasan
APL Photonics (2018)
Summary: We demonstrate the electrostatic tuning and stabilization of optomechanical devices, by integrating a Si3N4 slot-mode optomechanical crystal cavity with a nanoelectromechanical systems element, which controls the displacement of an additional “tuning” beam within the optical near-field of the optomechanical cavity.

alt text 

Acousto-Optic Modulation and Optoacoustic Gating in Piezo-Optomechanical Circuits
Krishna C. Balram, Marcelo I. Davanço, B. Robert Ilic, Ji-Hoon Kyhm, Jin Dong Song, and Kartik Srinivasan
Phys. Rev. Applied (2017)
Summary: We extend our prior work on piezo-optomechanical circuits by studying dynamical effects in these circuits. We demonstrate acousto-optic modulation and optoacoustic gating (the inverse effect), in which the application of modulated optical pulses interferometrically gates the transmission of propagating acoustic pulses.

alt text 

Efficient fiber-coupled single-photon source based on quantum dots in a photonic-crystal waveguide
Raphaël S. Daveau, Krishna C. Balram, et al.
Optica (2017)
Summary: We demonstrate an efficient fiber-coupled photonic-crystal waveguide (PCWG) based single-photon source by optimizing the evanescent coupling of the light field between the tapered waveguide and a tapered optical fiber. The coupling is robust, stable, and broadband.

alt text 

The Nanolithography Toolbox
Krishna C. Balram, et al.
Journal of Research of the National Institute of Standards and Technology (NIST) (2016)
Summary: We introduce a platform-independent software package for scripted lithography pattern layout generation.

alt text 

Coherent coupling between radiofrequency, optical and acoustic waves in piezo-optomechanical circuits
Krishna C. Balram, Marcelo I. Davanço, Jin Dong Song, and Kartik Srinivasan
Nature Photonics (2016)
Summary: We develop a platform for nanoscale cavity optomechanical circuits in which optomechanical cavities supporting co-localized 1,550 nm photons and 2.4 GHz phonons are combined with photonic and phononic waveguides.

alt text 

Moving boundary and photoelastic coupling in GaAs optomechanical resonators
Krishna C. Balram, Marcelo I. Davanço, Ju Young Lim, Jin Dong Song, and Kartik Srinivasan
Optica (2014)
Summary: We develop GaAs optomechanical resonators and investigate the moving dielectric boundary and photoelastic contributions to the optomechanical coupling rate.

alt text 

Surface-Normal Ge-SiGe Asymmetric Fabry–Perot Optical Modulators Fabricated on Silicon Substrates
Ross M. Audet, Elizabeth H. Edwards, Krishna C. Balram et al.
IEEE Journal of Lightwave Technology (2013)
Summary: We demonstrate the first vertical-incidence Ge-SiGe quantum well reflection modulators fabricated entirely on standard silicon substrates. These modulators could help enable massively parallel, free-space optical interconnects to silicon chips.

alt text 

Nanoscale resonant-cavity-enhanced germanium photodetectors with lithographically defined spectral response for improved performance at telecommunications wavelengths
Krishna C. Balram, Ross M. Audet, and David A. B. Miller
Optics Express (2013)
Summary: We demonstrate the use of a subwavelength planar metal-dielectric resonant cavity to enhance the absorption of germanium photodetectors at wavelengths beyond the material’s direct absorption edge, enabling high responsivity across the entire telecommunications C and L bands.

alt text 

Selective area growth of germanium and germanium-silicon-germanium quantum wells in silicon waveguides for on-chip optical interconnect applications
S. A. Claussen, Krishna. C. Balram, E. T. Fei, T. I. Kamins, J. S. Harris, and D. A. B. Miller
Optical Materials Express (2012)
Summary: We propose a robust fabrication process for growing Ge and Ge-based heterostructures in growth windows with Si sidewalls which can be applied to growth in thick Si optical waveguides.

alt text 

Self-aligned silicon fins in metallic slits as a platform for planar wavelength-selective nanoscale resonant photodetectors
Krishna C. Balram, and David A. B. Miller
Optics Express (2012)
Summary: We propose and demonstrate a novel nanoscale resonant metal-semiconductor-metal (MSM) photodetector structure based on silicon fins self-aligned to metallic slits. This geometry allows the center wavelength of the photodetector’s spectral response to be controlled by the silicon fin width, allowing multiple detectors, each sensitive to a different wavelength, to be fabricated in a single-step process.

alt text 

Routing and photodetection in subwavelength plasmonic slot waveguides
Dany-Sebastien Ly-Gagnon, Krishna C. Balram, et al.
Nanophotonics (2012)
Summary: We demonstrate a photodetector linked to a two conductor metallic slot waveguide that supports a mode with a minute cross-sectional area of λ^2/100 and propagation lengths of 10λ (λ = 850 nm).

alt text 

Strained germanium thin film membrane on silicon substrate for optoelectronics
Donguk Nam, Devanand Sukhdeo, Arunanshu Roy, Krishna C. Balram, et al.
Optics Express (2011)
Summary: We present a novel method to introduce a sustainable biaxial tensile strain larger than 1% in a thin Ge membrane using a stressor layer integrated on a Si substrate.

alt text 

Tensile-strained germanium-on-insulator substrate fabrication for silicon-compatible optoelectronics
J. Raja Jain, Dany-Sebastien Ly-Gagnon, Krishna C. Balram, et al.
Optical Materials Express (2011)
Summary: We present a method to fabricate tensile-strained germanium-on-insulator (GOI) substrates using heteroepitaxy and layer transfer techniques

alt text 

Multiple-Wavelength Focusing of Surface Plasmons with a Nonperiodic Nanoslit Coupler
Takuo Tanemura, Krishna C. Balram, et al.
Nano Letters (2011)
Summary: An array of nanoslits patterned on a thin metal film is used to couple free-space light into surface plasmon polaritons (SPPs) and simultaneously focus different-wavelength SPPs into arbitrary predefined locations in the two-dimensional plane.