1 May 2015 A subwavelength structured multimode interference coupler for the 3-4 micrometers mid-infrared band
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The mid-infrared is attracting increasing attention since many molecules, including potentially hazardous gases such as methane and carbon dioxide, exhibit very specific absorption spectra in this wavelength region. Integrated silicon photonics circuits are envisioned to enable compact and low-cost measurement solutions for these molecules. Multimode interference couplers (MMIs) are basic building blocks for photonic circuits and a broad operational bandwidth is key if flexible operation is to be achieved, e.g. to detect different gases. Here we overcome the bandwidth limitations found in classical MMIs by segmenting the multimode region at a sub-wavelength pitch to engineer its refractive index and dispersion. We achieve less than 0:5 dB imbalance and excess loss in the complete 3 ̶ 4 µm wavelength range. The sub-wavelength MMI not only exhibits nearly threefold improvement in bandwidth, but is also about three times shorter than the conventional device.
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Alejandro Sánchez-Postigo, Alejandro Sánchez-Postigo, Juan Gonzalo Wangüemert-Pérez, Juan Gonzalo Wangüemert-Pérez, Robert Halir, Robert Halir, Alejandro Ortega-Moñux, Alejandro Ortega-Moñux, Carlos A. Alonso-Ramos, Carlos A. Alonso-Ramos, Íñigo Molina-Fernández, Íñigo Molina-Fernández, Jordi Soler Penadés, Jordi Soler Penadés, Milos Nedeljkovic, Milos Nedeljkovic, Goran Z. Mashanovich, Goran Z. Mashanovich, Pavel Cheben, Pavel Cheben, "A subwavelength structured multimode interference coupler for the 3-4 micrometers mid-infrared band", Proc. SPIE 9516, Integrated Optics: Physics and Simulations II, 95160L (1 May 2015); doi: 10.1117/12.2179454; https://doi.org/10.1117/12.2179454

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