36 research outputs found
Multi-layer silicon nitride-on-silicon polarization-independent grating couplers
A polarization-independent grating coupler is proposed and demonstrated in a 3-layer silicon nitride-on-silicon photonic platform. Polarization independent coupling was made possible by the supermodes and added degrees of geometric freedom unique to the 3-layer photonic platform. The grating was designed via optimization algorithms, and the simulated peak coupling efficiency was −2.1 dB with a 1 dB polarization dependent loss (PDL) bandwidth of 69 nm. The fabricated grating couplers had a peak coupling efficiency of −4.8 dB with 1 dB PDL bandwidth of over 100 nm
Patterned photostimulation via visible-wavelength photonic probes for deep brain optogenetics
Optogenetic methods developed over the past decade enable unprecedented optical activation and silencing of specific neuronal cell types. However, light scattering in neural tissue precludes illuminating areas deep within the brain via free-space optics; this has impeded employing optogenetics universally. Here, we report an approach surmounting this significant limitation. We realize implantable, ultranarrow, silicon-based photonic probes enabling the delivery of complex illumination patterns deep within brain tissue. Our approach combines methods from integrated nanophotonics and microelectromechanical systems, to yield photonic probes that are robust, scalable, and readily producible en masse. Their minute cross sections minimize tissue displacement upon probe implantation. We functionally validate one probe design in vivo with mice expressing channelrhodopsin-2. Highly local optogenetic neural activation is demonstrated by recording the induced response—both by extracellular electrical recordings in the hippocampus and by two-photon functional imaging in the cortex of mice coexpressing GCaMP6
Multi-layer silicon nitride-on-silicon polarization-independent grating couplers
A polarization-independent grating coupler is proposed and demonstrated in a 3-layer silicon nitride-on-silicon photonic platform. Polarization independent coupling was made possible by the supermodes and added degrees of geometric freedom unique to the 3-layer photonic platform. The grating was designed via optimization algorithms, and the simulated peak coupling efficiency was −2.1 dB with a 1 dB polarization dependent loss (PDL) bandwidth of 69 nm. The fabricated grating couplers had a peak coupling efficiency of −4.8 dB with 1 dB PDL bandwidth of over 100 nm
Monolithically Integrated Multilayer Silicon Nitride-on-Silicon Waveguide Platforms for 3-D Photonic Circuits and Devices
In this paper, we review and provide additional details about our progress on multilayer silicon nitride (SiN)-on-silicon (Si) integrated photonic platforms. In these platforms, one or more SiN waveguide layers are monolithically integrated onto a Si photonic layer. This paper focuses on the development of three-layer platforms for the O- and SCL-bands for very large-scale photonic integrated circuits requiring hundreds or thousands of waveguide crossings. Low-loss interlayer transitions and ultralow-loss waveguide crossings have been demonstrated, along with bilevel and trilevel grating couplers for fiber-to-chip coupling. The SiN and Si passive devices have been monolithically integrated with high-efficiency optical modulators, photodetectors, and thermal tuners in a single photonic platform
Implantable Photonic Neural Probes with 3D-Printed Microfluidics and Applications to Uncaging
Advances in chip-scale photonic-electronic integration are enabling a new
generation of foundry-manufacturable implantable silicon neural probes
incorporating nanophotonic waveguides and microelectrodes for optogenetic
stimulation and electrophysiological recording in neuroscience research.
Further extending neural probe functionalities with integrated microfluidics is
a direct approach to achieve neurochemical injection and sampling capabilities.
In this work, we use two-photon polymerization 3D printing to integrate
microfluidic channels onto photonic neural probes, which include silicon
nitride nanophotonic waveguides and grating emitters. The customizability of 3D
printing enables a unique geometry of microfluidics that conforms to the shape
of each neural probe, enabling integration of microfluidics with a variety of
existing neural probes while avoiding the complexities of monolithic
microfluidics integration. We demonstrate the photonic and fluidic
functionalities of the neural probes via fluorescein injection in agarose gel
and photoloysis of caged fluorescein in solution and in flxed brain tissue
Silicon photonic transmitter for polarization-encoded quantum key distribution
Silicon (Si) photonics is forming a fabless ecosystem, which is enabling low-cost and densely integrated components for optical communications and quantum information. We present a Si optical transmitter for polarization-encoded quantum key distribution (QKD). The chip was fabricated in a standard Si photonic foundry process and integrated together a pulse generator, intensity modulator, variable optical attenuator, and polarization modulator in a 1.3  mm×3  mm1.3  mm×3  mm die area. The devices in the photonic circuit meet the requirements for QKD. The transmitter was used in a proof-of-concept demonstration of the BB84 QKD protocol over a 5 km long fiber link. This work shows the potential of using foundry Si photonics for low-cost, wafer-scale fabricated components for quantum information
Nanophotonic Neural Probes for in vivo Light Sheet Imaging
We present implantable silicon neural probes with nanophotonic waveguide routing networks and grating emitters for light sheet imaging. Fluorescein beam profiles, fluorescent bead imaging, and fluorescence brain imaging in vivo are presented