Hybrid integration of semiconductor optical amplifiers with frequency-selective feedback circuits, implemented using low-loss Si3N4 waveguides, enables robust chip-sized lasers with outstanding properties. Deploying ring resonators as a tunable feedback filter provides single-mode operation over a wide wavelength range. Moreover, these rings resonantly enhance the cavity length, which results in ultra-narrow intrinsic linewidth, as low as 40 Hz. In this publication the authors present an overview on state-of-the-art developments regarding these lasers. The authors compare linewidth and tuning results for different feedback circuit configurations. Finally, we report on the first demonstration of a hybrid-integrated semiconductor laser that operates in the visible wavelength range.

Read full publication at https://bit.ly/3zWbJpu

25 June 2021

175

In this paper the authors demonstrate a hybrid integrated and widely tunable diode laser with an intrinsic linewidth as narrow as 40 Hz, achieved with a single roundtrip through a low-loss feedback circuit that extends the cavity length to 0.5 meter on a chip. Employing solely dielectrics for single-roundtrip, single-mode resolved feedback filtering enables linewidth narrowing with increasing laser power, without limitations through nonlinear loss. We achieve single-frequency oscillation with up to 23 mW fiber coupled output power, 70-nm wide spectral coverage in the 1.55 µm wavelength range with 3 mW output and obtain more than 60 dB side mode suppression. Such properties and options for further linewidth narrowing render the approach of high interest for direct integration in photonic circuits serving microwave photonics, coherent communications, sensing and metrology with highest resolution.

Read full paper at https://bit.ly/3xIqJoY

22 June 2021

216

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. In this journal 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.

You can read the paper at https://bit.ly/3cSMBGp.

18 June 2021

215

The paper "High-purity microwave generation using a dual-frequency hybrid integrated semiconductor-dielectric waveguide laser" written by Jesse Mak, Albert van Rees, Rob E. M. Lammerink, Dimitri Geskus, Youwen Fan, Peter J. M. van der Slot, Chris G. H. Roeloffzen, Klaus-J. Boller is out!

The paper presents an integrated semiconductor-dielectric hybrid dual-frequency laser operating in the 1.5 μm wavelength range for microwave and terahertz (THz) generation. 

You can read it at https://arxiv.org/abs/2012.07533

15 June 2021

266