Physics

Laser linewidth

Free spectral range

Laser

Resonator

Optics

Semiconductor laser theory

Injection seeder

Optical cavity

Materials science

Laser diode

Longitudinal mode

Diode

Tunable laser

Optoelectronics

Wavelength

Distributed feedback laser

Optics Express

Extending the cavity length of diode lasers with feedback from Bragg structures and ring resonators is highly effective for obtaining ultra-narrow laser linewidths. However, cavity length extension also decreases the free-spectral range of the cavity. This reduces the wavelength range of continuous laser tuning that can be achieved with a given phase shift of an intracavity phase tuning element. We present a method that increases the range of continuous tuning to that of a short equivalent laser cavity, while maintaining the ultra-narrow linewidth of a long cavity. Using a single-frequency hybrid integrated InP-Si3N4 diode laser with 120 nm coverage around 1540 nm, with a maximum output of 24 mW and lowest intrinsic linewidth of 2.2 kHz, we demonstrate a six-fold increased continuous and mode-hop-free tuning range of 0.22 nm (28 GHz) as compared to the free-spectral range of the laser cavity.

Ring resonator enhanced mode-hop-free wavelength tuning of an integrated extended-cavity laser