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Ultrahigh-Q photonic crystal cavities in silicon rich nitride,


Two-dimensional Photonic Crystal (PhC) cavities have the ability to strongly confine light in both time and space. Over the last decade, considerable amount of research has been devoted to realizing PhC cavities with ultra-high quality factors (Q) and with low mode volume (V). The unprecedentedly high Q/V values of such cavities offer several benefits for realizing compact optical devices with strong light-matter interaction, which can be orders of magnitude higher than the corresponding bulk medium. High-Q PhC cavities have been exploited for diverse fields of application, such as, in integrated photonics for optical filters, modulators, detectors; for sensing applications; in nonlinear photonics for four-wave mixing and harmonic generation; for optical pulse manipulation; for low-threshold lasers; for cavity quantum electrodynamics and many more. The choice of  material platform has mainly been limited to high refractive index contrast materials, such as silicon (Si) or gallium arsenide (GaAs). However, for many applications that require high optical power, such as nonlinear photonics, silicon imposes a fundamental limitation due to its prohibitively high two-photon absorption(TPA). High-Q cavities just enhance such nonlinear absorption due to strong optical confinement. For example, TPA and associated free carrier absorption (FCA) becomes significant in PhC cavities at an input power level as low as few µWs.
The work demonstrated here and fabricated in Southampton is based on the silicon nitride material that we have developed in house (T. Domínguez Bucio  et al ) and enables the fabrication of Two-dimensional PhC and remove the problems linked to TPA.


The SIN platform development was initiated within the  EPSRC first grant EP/K02423X/1 HERMES: High dEnsity Silicon GeRManium intEgrated photonicS. The platform is currently developped further through  collaboration under the EPSRC  : A Platform Grant EP/N013247/1: Electronic-Photonic Convergence, EP/L021129/1 CORNERSTONE: Capability for OptoelectRoNics, mEtamateRialS, nanoTechnOlogy aNd sEnsing and European project H2020 COSMICC,


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