METHOD AND APPARATUS FOR REPETITION RATE SYNCHRONISATION OF MODE-LOCKED LASERS

摘要

A method and apparatus for passively synchronising the repetition rate of two or more mode-locked lasers is described. The method and apparatus involve forming a first synchronising optical field (6) by separating a portion of an output field of a first mode-locked laser (2) and thereafter redirecting this synchronising optical field to form a driving signal for a second mode-locked laser (3). Employing these techniques results in systems with timing jitter of less than 1 fs. The method is independent of the wavelength and polarisation at which the mode-locked lasers operate and so is not limited to use with any particular type of mode-locked laser. Since the technique is passive it does not require the employment of electronics, variable time delay paths or additional non-linear optical crystals. Therefore, the method and apparatus are significantly less complex than those known in the art and are not power limited by additional non-linear optical processes. Part of the output (7) of the first mode-locked laser (2) is redirected via a beam splitter (9) and beam steering mirrors (11,12) and a half-wave plate (15) to a polariser (13) in the the beam line of the second mode-locked laser (3). The seeding and synchronising signal from the first mode-locked laser (2) may be perpendicularly polarized with respect to the polarization of the second mode-locked laser (3) and may have a different wavelength.