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Athermal silicon nitride angled MMI wavelength division (de)multiplexers for the near-infrared


Wavelength division (de)multiplexing (WDM) devices are important elements required to increase the capacity of data-links and high speed telecommunication photonic systems. The most popular WDM integrated technologies include arrayed waveguide gratings (AWG), planar concave gratings (PCG) and micro-ring resonators (RR). These components usually require sophisticated design processes and complex fabrication steps to achieve low insertion losses and improved spectral responses. More recently, an alternative technology based on dispersive selfimaging in multimode waveguides has also been used to obtain angled multimode interferometers (AMMI) for WDM in the near infra-red (NIR) and mid infra-red (MIR). These AMMI structures have a distinctive ease of fabrication, high tolerance to dimensional errors and low insertion losses compared to other WDM approaches. The vast majority of WDM components have been fabricated on the mature silicon-oninsulator (SOI) platform. However, their transmission characteristics tend to be strongly sensitive to temperature variations due to the relatively high thermo-optic coefficient of Si (1.8×10-4/°C).In fact, the thermal shift produced in the central wavelength of these devices is of the order of 70-100pm/°C in the NIR region. As a result, they require active temperature control or complex compensation techniques to stabilize the wavelength drift in order to preserve their performance at different temperatures.
To tackle this situation, we have demonstrated an AMMI using our silicon nitride platform (SiNx) with low propagation losses and lower thermo-optic coefficient in the O band with a wavelength shift < 10pm/°C .



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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