Quantum dash frequency comb laser stabilisation by optical self‐injection provided by an all‐fibre based delay‐controlled passive external cavity

The intermode beat frequency stability of a 1 mm long quantum dash self mode‐locked semiconductor laser emitting optical frequency combs centred at 1535 nm is improved by single‐cavity optical self‐injection. A novel all‐fibre based cavity employing a piezo‐stretchable fibre spool provides both macroscopic optical path cavity length of 76 m and microscopic fine‐delay fibre length control. The maximum achieved intermode beat frequency tuning is 2 MHz. The intermode beat frequency line width indicating the optical frequency comb stability is improved from 67 kHz to below 900 Hz constituting an improvement by a factor of 74. An independent free‐space stabilisation experiment and stochastic time‐domain modelling confirm the demonstrated intermode beat frequency tuning range.