Photolithography allows high-Q AlN microresonators for near octave-spanning frequency comb and harmonic generation

Abstract

Single-crystal aluminum nitride (AlN) possessing both strong Pockels and Kerr nonlinear optical effects as well as a very large band gap is a fascinating optical platform for integrated nonlinear optics. In this work, fully etched AlN-on-sapphire microresonators with a high-Q of 2.1 × 106 for the TE00 mode are firstly demonstrated with the standard photolithography technique. A near octave-spanning Kerr frequency comb ranging from 1100 to 2150 nm is generated at an on-chip power of 406 mW for the TM00 mode. Due to the high confinement, the TE10 mode also excites a Kerr comb from 1270 to 1850nm at 316 mW. In addition, frequency conversion to visible light is observed during the frequency comb generation. Our work will lead to a large-scale, low-cost, integrated nonlinear platform based on AlN.

Directly accessing octave-spanning dissipative Kerr soliton frequency combs in an AlN microresonator

“…Figure 1 illustrates the device characterization and the approach taken in this work. Using standard photolithography and inductively coupled plasma etching processes [39], we fabricated the devices in a quarter of a 2 inch wafer, as shown in Fig. 1(b), that consists of a 1.2-μm-thick epitaxial single-crystal AlN film and a sapphire substrate [40].…”

“…Using standard photolithography and inductively coupled plasma etching processes (see in methods), we fabricated devices in a quarter of a 2 inch wafer (Fig. 1b), that consists of a 1.2-μm-thick epitaxial single-crystal AlN film and a sapphire substrate 38,39 . In this work, we employed a microring resonator with a radius of 60 μm, a waveguide width of 2.29 μm (Fig.…”

Effect of Thermal Tuning and Mode Coupling On Soliton Microcombs in AlN Microresonators

“…The TM00 mode has large anomalous dispersion profiles at ~2.3 μm. The desired dispersion of the TE10 and TM00 modes with a short-wavelength DW is achieved for relatively wider resonators, which have been experimentally used for an octave-spanning comb generations [21], [22].…”

Near-octave-spanning breathing soliton crystal in an AlN microresonator

“…The dips near 1350 nm in the comb profiles results from the antiphase-matched frequencies [34] because of the pulley coupling, which was demonstrated to improve the extraction efficiency of the microcombs at short wavelength compared to the straight coupling. Moreover, a wider coupling gap G of 600 nm was utilized to increase the coupling efficiency at longer wavelength [33]. Therefore, the PSCs spectra obtained from resonator 2 are wider than the others presented in this work.…”

“…1(a) shows, the PSCs with various soliton numbers are excited in different AlN MRRs, coupled with straight or pulley waveguide. The MRRs are patterned from an AlN-on-sapphire wafer (AlN thickness1.2 μm) via standard photolithography and inductively coupled plasma etching processes [33]. All the resonators employed in this work have a radius of 60 μm and a cross section of 2.29×1.2 μm 2 (fully etched), which were designed to ensure a low anomalous dispersion (D2/2π = 4.8 MHz) of the target fundamental transverse electrical (TE00) mode [32].…”