Mid-infrared materials and devices on a Si platform for optical sensing

Abstract

In this article, we review our recent work on mid-infrared (mid-IR) photonic materials and devices fabricated on silicon for on-chip sensing applications. Pedestal waveguides based on silicon are demonstrated as broadband mid-IR sensors. Our low-loss mid-IR directional couplers demonstrated in SiNx waveguides are useful in differential sensing applications. Photonic crystal cavities and microdisk resonators based on chalcogenide glasses for high sensitivity are also demonstrated as effective mid-IR sensors. Polymer-based functionalization layers, to enhance the sensitivity and selectivity of our sensor devices, are also presented. We discuss the design of mid-IR chalcogenide waveguides integrated with polycrystalline PbTe detectors on a monolithic silicon platform for optical sensing, wherein the use of a low-index spacer layer enables the evanescent coupling of mid-IR light from the waveguides to the detector. Finally, we show the successful fabrication processing of our first prototype mid-IR waveguide-integrated detectors.

Mid-infrared integrated photonics on silicon: a perspective

“…One strategy involves replacing the lossy silicon oxide cladding with other materials exemplified by silicon-on-nitride ( Figure 3A-B) [10] and germanium-on-nitride [17] or with air cladding in pedestal [11,18,19] or suspended silicon structures [12][13][14][20][21][22][23] (Figure 3C-H). Another option is Ge-on-Si (or SiGeon-Si), which claims the advantage of compatibility with Si CMOS processing, as high-quality Ge can be epitaxially grown on Si ( Figure 3I-J) [15,17,[24][25][26][27][28].…”

“…In all these cases, the accessible wavelength is bound by the Si material absorption at approximately 7-8 μm. For photonic devices operating at even longer wavelengths, alternative materials other than Reprinted with permission from [11], (D, E) schematic view and top-view SEM image of suspended Si mid-IR micro-ring resonators [12] (© 2013 Optical Society of America), the waveguides assume a ridge geometry and an undercut etch removes the silicon dioxide cladding through access holes on the slab layer, (F, G) SEM micrographs of a suspended mid-IR Si photonic crystal cavity [13] (© 2011 Optical Society of America), (H) suspended mid-IR Si waveguides with sub-wavelength grating (SWG) claddings [14] (© 2016 Optical Society of America); here the SWG provides both lateral optical confinement as well as access to the oxide under cladding during wet etch structure release; the arrows indicate light propagation direction in the suspended core. (I, J) Ge-on-Si [15] (© 2015 IEEE): (I) a mid-IR Ge-on-Si ridge waveguide; (J) TEM cross-sectional image of the Ge-on-Si film showing that the dislocations are confined at the Si/Ge interface.…”

Multilayer Black Phosphorus as a Versatile Mid-Infrared Electro-optic Material

“…As such, integrated photonic solutions that can operate between λ = 2-10 µm are of great technological importance. In particular, progress has been made in components such as broadband source and frequency comb with on-chip form-factor [3,4], Si 3 N 4 and SiGebased low-loss optical waveguides, and photodetectors utilizing low-bandgap materials [5]. However, the realization of MIR optical modulators, which require material platforms with versatile opto-electronic properties, remain challenging.…”

On-chip infrared sensors: redefining the benefits of scaling

“…Traditional on-chip microcavity absorption spectrometers measure the change in complex refractive index, the sensitivity of which is largely limited by scattering loss from cavity sidewall roughness [27][28][29][30][31][32] . In order to achieve sensitivities comparable to state-of-the-art benchtop spectroscopy instruments, on-chip sensors must exploit unique properties of their reduced size and waveguiding materials.…”