Multiple mode couplings in waveguide array for broadband near-zero dispersion and supercontinuum generation



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Photonic chips can enhance the light-matter interaction by confining light within a submicron-scale waveguide cross-section and have advanced many nonlinear optical processes, such as supercontinuum and Kerr frequency comb generations. These nonlinear frequency conversion processes rely on the phase-matching of an optical system, which can be achieved by engineering the dispersion of the photonic waveguides. A typical dispersion engineering method, however, is bounded by the material dispersions, limiting the spectral bandwidth and efficiency of many nonlinear processes. Moreover, it causes certain fabrication challenges; for example, a thick silicon nitride film is required for anomalous dispersion, which is easy to crack due to high film-stress and incompatible with the complementary metal-oxide-semiconductor (CMOS) foundry. Thus, to develop fully CMOS compatible on-chip photonic devices, further advanced dispersion engineering is required. This work presents a coupled waveguide array scheme that introduces multiple mode couplings at different wavelengths and achieves a near-zero dispersion profile at near-infrared. A broadband near-zero dispersion profile, spanning over the spectral range of 1350-1900 nm within ±140 ps/nm/km, is obtained on a 300 nm-thick silicon nitride film, which is compatible with the CMOS process but shows high normal dispersion unless otherwise engineered. Using this engineered dispersion profile, an octave-spanning supercontinuum is numerically generated by pumping near the spectral regions of the mode couplings. The concept of utilizing multiple mode couplings to achieve broadband near-zero dispersion can be applied to other spectral regimes and material platforms as well, by engineering the structural parameters to shift the positions of the zero-dispersion-wavelengths. This CMOS compatible waveguide array design would allow mass production in supercontinuum generating chips, which can then be used in molecular sensing and spectroscopic applications.



Dispersion Engineering, Integrated Optics, Supercontinuum Generation