Abstract
Micro- and nanoscale photonic structures and devices play important roles in the development of advanced biophotonic systems, in particular, implantable light sources for optogenetic stimulations. In this paper, we numerically investigate silicon (Si) photonics based microprobes that can achieve multi-site, multi-spectral optical excitation in the deep animal brain. On Si substrates, silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) based planar waveguides can deliver visible light in the deep tissue with low losses, and couple to grating emitters diffracting light in targeted brain regions. In our model, we combine near-field wave optic and far-field ray tracing simulations, showing that the designed photonic structures spectrally split blue, green and red photons into different locations in the tissue. Furthermore, by introducing dual grating components, photons at different wavelengths can be spatially separated at different depths. Therefore, these photonic probes can be used to selectively activate or inhibit specific neurons and nuclei, when expressing various corresponding light sensitive opsins. We anticipate that such device strategies can find wide applications in the design of advanced implantable photonic systems for neuroscience and neuroengineering.
Highlights
Optogenetics plays an indispensable role in the field of neuroscience and neuroengineering for decoding neural signals and modulating neural activities, which could enrich understandings in brain functions and help discover novel strategies for neurological disease treatments [1], [2]
As excitation spectra of most opsins typically lie within the visible range, where light penetration is severely limited by the tissue scattering and absorption, advanced waveguides and optoelectronic devices
A source of plane wave from 400 nm to 700 nm in transverse magnetic (TM) mode is coupled to the waveguide
Summary
Optogenetics plays an indispensable role in the field of neuroscience and neuroengineering for decoding neural signals and modulating neural activities, which could enrich understandings in brain functions and help discover novel strategies for neurological disease treatments [1], [2] Such optically based neural interrogation methods employ various light-sensitive microbial opsins that exhibit different excitation spectra and control different ion channels, providing precise control over specific neural activities with light modulations at certain wavelengths [3], [4]. As excitation spectra of most opsins typically lie within the visible range, where light penetration is severely limited by the tissue scattering and absorption, advanced waveguides and optoelectronic devices.
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