Germanium-based integrated photonics from near- to mid-infrared applications

D Marris-Morini, V Vakarin, JM Ramirez, Q Liu, A Ballabio, J Frigerio, S Serna … 
Nanophotonics 7 (11), 1781-1793. 

Abstract: Germanium (Ge) has played a key role in silicon photonics as an enabling material for datacom applications. Indeed, the unique properties of Ge have been leveraged to develop high performance integrated photodectors, which are now mature devices. Ge is also very useful for the achievement of compact modulators and monolithically integrated laser sources on silicon. Interestingly, research efforts in these domains also put forward the current revolution of mid-IR photonics. Ge and Ge-based alloys also present strong advantages for mid-infrared photonic platform such as the extension of the transparency window for these materials, which can operate at wavelengths beyond 8 μm. Different platforms have been proposed to take benefit from the broad transparency of Ge up to 15 μm, and the main passive building blocks are now being developed. In this review, we will present the most relevant Ge-based. 

C Caër, SF Serna-Otálvaro, W Zhang, X Le Roux, E Cassan
Optics letters 39 (20), 5792-5794

Abstract: We present the realization of an optical sensor based on an infiltrated high-𝑄 slot photonic crystal cavity in a nonfreestanding membrane configuration. Successive infiltrations by liquids with refractive indices ranging from 1.345 to 1.545 yield a sensitivity 𝑆 of 235 nm/RIU (refractive index unit), while the 𝑄-factor is comprised between 8000 and 25,000, giving a sensor figure of merit up to 3700. This sensor has a detection limit of 1.25×10−5. The operation of this device on a silicon-on-insulator (SOI) substrate allows a straightforward integration in the silicon photonics platform, while providing a compliant mechanical stability.

W Zhang, S Serna, X Le Roux, L Vivien, E Cassan
Optics Letters 41 (3), 532-535

Abstract: We experimentally investigate refractive index sensing in silicon slot waveguide ring resonators by the detection of the giant shift of the ring transmission spectrum envelope enabled by the following specific conditions: the slot waveguide cross section as well as the ring couplers have been designed to lead to a V-shaped microring resonator spectrum modulated by the classical frequency comb and exhibiting quality factor peaks of 2000–6000 around  λ=1.5 μm. By tracking the spectrum envelope wavelength shift, sensitivity up to  S=1,300 nm per refraction index unit (RIU) is reported when the slots are filled by liquids with refraction index values close to 1.33.

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