Megahertz scan rates enabled by optical sampling by repetition-rate tuning

Repetition frequency tunability and stability of BH InAs/InP QD and InGaAsP/InP QW two-section mode-locked laser diodes

Ultra-high repetition rate (UHRR) mode-locked laser diodes (MLLD) have shown promising results for applications based on optical sampling such as asynchronous optical sampling (ASOPS), optical sampling by repetition-rate tuning (OSBERT), and optical ranging. Important metrics to consider are the repetition frequency (RF) and the RF linewidth. Here, we compare two monolithically integrated MLLDs. A quantum dot (QD) MLLD with an RF of approx. 50.1 GHz and a quantum well (QW) MLLD with an RF of approx. 51.4 GHz. The tunability of the RF is characterized by sweeping the lasers pump current, temperature, and saturable absorber (SA) reverse voltage. The QW MLLD has a tuning range of 31 MHz with an average RF linewidth of 53 kHz, while the QD MLLD has a smaller tuning range of 26 MHz with a higher average RF linewidth of 172 kHz.

Modelling two-laser asynchronous optical sampling using a single 2-section semiconductor mode-locked laser diode

We present a theoretical overview and a proposed methodology which demonstrates SLASOPS (single laser asynchronous optical sampling) as a single-laser alternative to the conventional two-laser ASOPS technique. We propose the optical and electronic setup in which SLASOPS may be achieved experimentally with a single 2-section mode-locked laser diode as the pulsed-laser source and simulate how asynchronous optical sampling is generated and detected theoretically. We highlight the technique's ability to provide customizable scan ranges, scan rates and scan resolutions through variation of the imbalance in the interferometer arms and by tuning the repetition rate of the pulsed-laser source, which we present as optical cross-correlations between pulse pairs. We incorporate jitter into the system mathematically to assess the limitations on resolving both intensity and interferometric cross-correlation traces and to investigate the effects of averaging such traces in real-time. Analysis is then carried out on cross-correlation trace amplitude, width, and temporal positioning in order to discuss the technique's ability for deployment in typical optical sampling applications. In particular we note SLASOPS' ability to conduct asynchronous optical sampling using only a single laser, halving both the expense and technical requirements, doing so at megahertz scan rates, and within a spatial precision of just a few microns.