Visible-light silicon nitride waveguide devices and implantable neurophotonic probes on thinned 200 mm silicon wafers

Abstract

We present passive, visible light silicon nitride waveguides fabricated on ≈ 100 µm thick 200 mm silicon wafers using deep ultraviolet lithography. The best-case propagation losses of single-mode waveguides were ≤ 2.8 dB/cm and ≤ 1.9 dB/cm over continuous wavelength ranges of 466-550 nm and 552-648 nm, respectively. In-plane waveguide crossings and multimode interference power splitters are also demonstrated. Using this platform, we realize a proof-ofconcept implantable neurophotonic probe for optogenetic stimulation of rodent brains. The probe has grating coupler emitters defined on a 4 mm long, 92 µm thick shank and operates over a wide wavelength range of 430-645 nm covering the excitation spectra of multiple opsins and fluorophores used for brain stimulation and imaging.

Implantable photonic neural probes for light-sheet fluorescence brain imaging

“…For example, the sheet density may be increased by integrating multiple photonic layers [40]. Also, the optical transmission of the probes can be increased by roughly an order of magnitude with efficient fiber-to-chip edge couplers [41] and optimized low-loss components; the fiber-to-chip coupling efficiency of the edge couplers in this work was limited to ≈ 14% with optimal alignment [34]. Optimized packaging solutions can also mitigate transmission variations amongst light sheets and improve the thermal stability of the packaged probes.…”

“…S1 in the Supplementary Materials. The photonic components were designed for a wavelength of 488 nm to enable excitation of common fluorophores such as green fluorescent protein (GFP) and green calcium dyes; however, these components can also be designed for green, yellow, and red wavelengths, as we show in [34] To rapidly switch between different sheets, we used a spatial addressing approach similar to [35] and as illustrated in Fig. 2(a).…”

“…Chemical mechanical planarization (CMP) was used for layer planarization during the fabrication. The fabrication process and waveguide characteristics are described in more detail in [34].…”

High coupling efficiency, passive alignment setup for visible-range fiber-to-waveguide edge coupling

“…This growing interest is moving beyond telecommunication and data center sectors in the infrared wavelength, onto applications such as biosensing, optogenetics, and medical imaging in the visible wavelengths. 1,2 For optogenetics, visible light is used to modulate neurons using light-activated proteins [3][4][5][6] and to expose different engineered cell lines to release therapeutic protein or drugs in vivo. [7][8][9] In addition, visible photonic platform can facilitate lab-on-chip spectroscopy, super-resolution microscopy, miniature endoscopy, and cytometry.…”

Strain-enabled ultra-broadband Ge-based photonic devices for low-cost integration in PICs

“…Furthermore, the Si composition can be increased to 4% to shift the entire broad operating range to ~1,300 nm, while Sn can also be alloyed into Ge for an operating coverage beyond 1,700 nm. The mature SiN x -based process 36,37 makes this approach readily accessible in the state-of-the-art foundries. Compared to other Ge strain engineering techniques 38,39,40 , the recessed SiN x stressor maintains both CMOS-compatibility and small device footprint for compact integration.…”