James Hendrie

Envelope, group and phase velocities in a nested frequency comb

Fabry–Perot etalons have been traditionally used in a laser cavity to tune the optical frequency. In this work we present the generation of interwoven frequency combs with insertion of an intracavity Fabry–Perot in a mode-locked laser. A high frequency comb is generated by insertion of an uncoated (low finesse) Fabry–Perot inside the laser cavity. The intracavity Fabry–Perot acquires a high finesse from the laser cavity and the velocity of the pulses in the Fabry–Perot is affected by the laser cavity length, gain and losses, with the dielectric group velocity dk/dΩ playing only a minor role. The output characteristics are explained by the condition that the radiation is simultaneously resonant with the etalon and the laser cavity.

Impact of resonant dispersion on the sensitivity of intracavity phase interferometry and laser gyros.

Intracavity phase interferometry is a phase sensing technique using mode-locked lasers in which two intracavity pulses circulate. The beat frequency between the two output frequency combs is proportional to a phase shift to be measured. A laser gyro is a particular implementation of this device. The demonstrated sensitivity of 10-8 of these devices could be manipulated by applying a giant dispersion to each tooth of the comb. It is shown that the resonant dispersion of a Fabry-Perot inserted in the cavity couples to the modes of the frequency comb, resulting in a large change in phase response.

Nested Fabry-Perot in mode-locked lasers to monitor minute changes of index

An uncoated glass etalon inserted in a mode-locked laser results generating two nested frequency combs. The ratio of their frequencies, insensitive to external parameters, is an accurate measure of the optical path in the etalon.