Supported planar germanium waveguides for infrared evanescent-wave sensing

Abstract

We have fabricated miniature planar IR waveguides with thicknesses of 30-50 mum, consisting of 12-mm long, 2-mm wide strips of Ge supported on ZnS substrates. Evidence for efficient propagation of broadband IR light through these waveguides is provided by the presence of characteristic high- and low-frequency optical cutoffs of Ge; by the observation of an oscillatory interference pattern in the transmittance spectrum, which exhibits a dependence on waveguide thickness and propagation angle that closely matches waveguide theory; and by the detection of strong evanescent-wave absorption from small (2 mm(2)) droplets of liquid, e.g., water, on the waveguide surface. As also predicted by theory, the surface sensitivity (detected light absorbance per unit area of sample-waveguide contact) is shown to increase as a function of incidence or bevel angle.

Mid-infrared transmission properties of amorphous germanium optical fibers

“…Coupling into the core was facilitated by using a pyroelectric Electrophysics PV 320 camera to image the guided output. The losses measured at these two wavelengths were 17.3 dB/cm at 3.39 µm and a much reduced value of 4.8 dB/cm at 10.6 µm, which is significantly lower than previously reported losses for mid-infrared transmission in germanium [15,16]. In order to relate the loss values in this large core fiber with those of the smaller core fiber, measurements were also conducted around 2 µm using the OPO and the results obtained over the entire wavelength range are plotted in Fig.…”

Germanium Mid-Infrared Photonic Devices

“…It has also higher carrier mobility and larger non linear effects than Si. Germanium core fibers [15] and germanium slabs on zinc sulfide substrates [16] were realized before first reports on Ge-on-Si based MIR planar photonic devices. Chang et.al demonstrated Ge-on-Si (GOS) waveguides with losses of 2.5-3.0 dB/cm at λ=5.8 µm [11], which was followed by GOS multiplexers [12,13] at ~5.3 µm, and Mach-Zehnder interferometers and thermo-optic modulators [14] at the same wavelength range.…”

Low-loss germanium strip waveguides on silicon for the mid-infrared

“…Germanium has a broad transparent range in mid-IR and has been made into fibers [11] and planar waveguides on substrates like ZnS and IRTRAN2 [12,13]. It is nontoxic, and has the advantages of biocompatibility and silicon process compatibility.…”