Integrated-optics-based external-cavity laser configured for mode-hop-free wavelength tuning

Aspects of the present disclosure describe systems, methods and structures including an integrated-optics-based externa-cavity laser configured for mode-hop-free wavelength tuning having an increased continuous tuning range with an ultra-narrow linewidth by increasing tuning sensitivity. Ultra-narrow linewidth is provided by extending cavity length with a multi-pass resonator based filter that may advantageously include tunable microring resonators that enable single-mode oscillation while contributing to the optical length of the laser with multiple passes of light through the ring(s) per roundtrip in the laser cavity. Further aspects of the present disclosure describe systems, methods, and structures exhibiting an enhanced "tuning sensitivity" - defined by a continuous wavelength shift per induced cavity phase shift by a phase section. Such tuning sensitivity is increased by approximately a factor of 3 for synchronous tuning of phase section and ring resonators as compared to tuning phase section only.