High-Speed Optical Sampling by Dynamic Repetition Rate Tuning of an Optically Injected Mode-Locked Laser Diode

Optical sampling systems have recently enabled a wide range of applications, from precise distance measurements [1] to Fourier transform spectroscopy [2]. At the core of such sampling systems is the generation of pairs of ultrashort pulses with variable time delay. Optical sampling by cavity tuning (OSCAT) is a method to create such pairs of ultrashort pulses, relying on the modulation of the repetition rate (f
rep
) of an ultrafast laser source, combined with a length-imbalanced interferometer [3]. OSCAT has the advantage of requiring only one ultrafast laser, with a scan range determined by the frep tunability range
$(\Delta \mathrm{f})$
and passive delay line (PDL) length, while its scan rate is defined by frep's modulation rate. However, typical implementations of this method suffer from low scan rates, caused by mechanical limitations in modulating frep [1]–[3]. Moreover, long PDLs are required to compensate for the typical low values of
$\Delta \mathrm{f}$
) with typical lengths of the order of hundreds (or even thousands) of metres. As a consequence, complex fibre stabilization schemes are required in such cases [1], [2].