Abstract

It this paper, we report a remarkably simple and powerful technique for the characterization of dispersion in broadband tunable passive modelocked lasers^[1]. A CW-pumped passive modelocked laser chooses its cavity roundtrip time independent of the pump laser cavity length, of course. If we simply note that the cavity roundtrip time at any particular frequency is exactly the total group delay of a quasi-monochromatic wave packet at that frequency, then clearly by accurately measuring the cavity repetition rate as a Junction of frequency while tuning the laser, we obtain the group delay as a junction of frequency directly. In a typical laser the cavity frequency is about 100 MHz, corresponding to a 10 ns roundtrip time. If the round-trip group delay changes by 100 fs, the frequency will change by 1 kHz, which is easily measured with a digital frequency counter.

© 1992 IQEC