Abstract
Generation of ultra short pulses is of great importance for applications in optical signal processing, communications, highspeed electronics, and time resolved study of many physical, chemical and biological processes. However, it is desirable to be able to generate these pulses at an arbitrary repetition rate with high stability. The pulse instability in figure-eight fiber lasers can be removed by introducing intentional twist in the fiber, which provides a controllable birefringence-induced phase-bias. The proposed theory has been verified experimentally. The stabilized laser can generate very stable pulses with the wavelengths tunable by simply adjusting the polarization controllers in the two loops of a figure-eight laser. The stability of the laser has been analyzed quantitatively by using RF spectrum analysis of the mode-locked pulse train. Fluctuations in pulse repetition time and in pulse energy as well as jitter in pulse width occur simultaneously. All these types of noise have been characterized quantitatively by examining the higher harmonics of the RF spectrum. By optimizing the total dispersion and cavity length of the laser, it was found by measurement that a peak to peak stability of 99.2% and a timing jitter of 5.59 psec for 2.31 MHz pulse train were obtained. However, it is observed that the variation of cavity parameters results in increased timing jitter and peak pulse instability.