Fig. 1.

Si₃N₄ microresonators for soliton frequency comb generation in the NIR. a Set-up schematic used for dissipative Kerr soliton generation and characterisation: a tunable external-cavity diode laser with a centre wavelength of 1050 nm is used as a seed, YDFA – ytterbium-doped fibre amplifier, FPC – fibre polarisation controller, VNA – vector network analyser, EOM – electro-optical phase modulator, PD – photodiode, OSC – oscilloscope, ESA – electrical spectrum analyser, OSA – optical spectrum analyser. b Left: optical microscope image of the 1-THz microring resonator (highlighted in red) with a pulley-style bus waveguide (blue). Right: scanning electron microscope images of the resonator and bus waveguide cross sections obtained via focused ion beam cuts at different positions (A–C) marked on the left image. c Simulated integrated dispersion profiles (D_int/2π) for TM₀₀ mode of resonator waveguides having different heights of 0.70, 0.74 and 0.78 μm, widths of 1.2, 1.3 and 1.4 μm and fixed sidewall angle of 77° (see more details on dispersion engineering in Supplementary Note 1). d Transmission trace of the 1-THz microresonator shown in (b). The two fundamental mode families (TE₀₀ and TM₀₀) can be distinguished based on their free spectral ranges (0.992 THz for TM₀₀ and 1.001 THz for TE₀₀), and are marked with red and blue shapes correspondingly. Other resonances correspond to higher order modes with comparably lower Q-factors. e Linewidth measurements of the fundamental mode families. The frequency axis was calibrated using a fibre-loop cavity. Typical loaded linewidth of the modes is ~400 MHz for TE₀₀ and ~500 MHz for TM₀₀