Three-Octave Supercontinuum Generation in Thick Crystalline Aluminum Nitride Waveguides

Abstract

We report an efficient extension of supercontinuum generation through dispersion engineering of crystalline aluminum nitride (AlN)-on-sapphire waveguides. Using a tailored epitaxial regrowth of AlN epilayers and an optimized fabrication protocol, the dispersion sensitivity to the waveguide cross-section was enhanced allowing for a significant reach extension of both short and long dispersive wave with optimized pumping conditions, reaching down to 550 nm in the visible and up to 4.5 μm in the mid-infrared.

Figures (4)

• Figure 1: (a, b) Simulated group-velocity dispersion ($D$) and integrated dispersion ($\beta_\text{int}$) for a 1 µm-thick WG pumped at 1.56 µm (TM), and (c, d) for a 1.3 µm-thick WG pumped at 2.1 µm (TM). Insets in (a, c) show normalized mode profiles at the pump wavelength for 2.5 µm width; the 0.3 µm regrown layer is indicated by a dashed line in (c) inset. Normal (anomalous) dispersion is shown in blue (red); out-of-range values appear in gray. Dashed lines: pump position used for $\beta_\text{int}$; black arrows: LWDW shift with WG width.
• Figure 2: (a) False-color SEM image of an AlN WG facet from a regrown epilayer with silica cladding. (b) TM resonances at 1550 nm from microrings fabricated on 1.0 µm- and 1.3 µm-thick epilayers. The corresponding $Q_\text{i}$ are indicated.
• Figure 3: OSA SC spectra from a 2.5 µm $\times$ 1 µm WG with a TM 1.56 µm pump (a) and from a 2.5 µm $\times$ 1.3 µm WG with a TM 2.1 µm pump (b). Dashed line: pump position. Simulated $\beta_\text{int}$ shown below, with SWDW and LWDW positions indicated by yellow dots. In (b), an FT-OSA with a -40 dBm/nm noise floor is used beyond 3.3 µm (dotted line).
• Figure 4: Surface plots of measured SC spectra from WGs of different widths and 1 µm (a) and 1.3 µm (b) thickness, pumped with TM polarization at 1.56 µm and 2.1 µm, respectively. DWs are indicated by the dotted lines; SHG and THG peaks by arrows. (c) PSD at short wavelengths for the 1 µm$\times$1 µm (left) and 2.5 µm$\times$1.3 µm (right) WGs, with arrows indicating the SWDW (black), SHG (red), THG (blue) and 4$^\mathrm{th}$ harmonic (green). (d) Simulated SC spectrum (top) and pulse spectral broadening along the propagation direction (bottom) for the 2.5 µm $\times$ 1.3 µm WG pumped at 2.1 µm.