PROCEEDINGS ARTICLE | May 23, 2018
Proc. SPIE. 10686, Silicon Photonics: From Fundamental Research to Manufacturing
KEYWORDS: Mid-IR, Waveguides, Molecules, Germanium, Silicon, Photonics, Supercontinuum sources, Supercontinuum generation, Pollution detection, Absorption
Since many important molecules have strong “fingerprints” in the mid-infrared (mid-IR, between 3μm and 15μm), this wavelength spectrum is currently gaining significant attention for applications ranging from pollution detection, quality control in the food industry, early cancer diagnosis, security and safety [1, 2]. Molecular sensing devices in the mid-IR are currently being developed and are in the process of commercialization. An appealing approach is to create molecular sensing devices in the mid-IR based on low cost integrated mid-IR chips. A key building block is a high brightness integrated broadband light source that would allow the detection of several molecules characterized by distinct absorption lines in parallel. Such an integrated broadband source, referred to as a supercontinuum source, has been already demonstrated in the mid-IR on a chalcogenide chip [3]. However, demonstrating mid-IR supercontinuum on group IV materials, in order to exploit the advantages of reliable CMOS fabrication technology, remains a challenge. So far, numerous CMOS-compatible supercontinuum sources have been demonstrated in silicon nitride-on-insulator [4, 5], silicon-on-insulator [6, 7], silicon germanium-on-insulator [8] and silicon-on-sapphire platforms [9]. However, these sources are limited up to 3.5µm and 6µm due to the absorption in the silica and sapphire substrate, respectively. More recently, the silicon germanium-on-silicon platform [10, 11], emerged as an attractive platform for mid-IR photonics, with transparency potentially extending up to 15μm depending on the Ge content [12].
Here we report experimentally the first octave spanning supercontinuum generation from a SiGe waveguide in the actual mid-IR with 5mW on-chip power exceeding that produced so far in any other Si-based platform (0.15mW in SiGe/SiO2 [8] and ~1mW in silicon-on-sapphire [9]). Our 4.25µm x 2.70µm cross-section air-clad SiGe-on-Si waveguide has been designed and manufactured to achieve single mode operation at 4µm, low anomalous dispersion and strong fundamental TE mode confinement in the core nonlinear material (~96% at 4μm). Losses as low as 0.4dB/cm were measured between 3.8 and 5µm. The achieved supercontinuum covered more than an octave between 2.95 and 6.0µm was generated by pumping a 7cm long waveguide with ~ 200fs pulses at 4.15µm and 63MHz repetition rate, as delivered by a Miropa-fs optical parameter amplifier. These results were supported by simulations and the related generation of a high brightness supercontinuum establishes silicon germanium-on-silicon as a promising platform for integrated nonlinear photonics in the mid-IR, with the potential to extend the operating range to beyond 8μm.
References
[1] R. Soref, Nature Photonics, 4, 495-497, (2010).
[2] B. Mizaikoff, 42, 8683-99, (2013).
[3] Y. Yu, et al., Opt Lett, 41, 958-61, (2016).
[4] J. M. Chavez Boggio, et al., JOSA B, 31, 2846-2857, (2014).
[5] A. R. Johnson, et al., Opt Lett, 40, 5117-20, (2015).
[6] B. Kuyken, et al., Opt Express, 19, 20172-81, (2011).
[7] R. K. W. Lau, et al., Optics letters, 39, 4518-4521, (2014).
[8] M. A. Ettabib, et al., Optics letters, 40, 4118-4121, (2015).
[9] N. Singh, et al., Optica, 2, 797-802, (2015).
[10] L. Carletti, et al., Opt Express, 23, 8261-71, (2015).
[11] L. Carletti, et al., Opt Express, 23, 32202-14, (2015).
[12] J. M. Ramirez, et al., Opt Lett, 42, 105-108, (2017).
