Generation of Coherent Multicarrier Signals by Gain Switching of Discrete Mode Lasers

• Published in: IEEE photonics journal Vol. 3; no. 1; pp. 112 - 122
• Main Authors: Anandarajah, P M, Maher, R, Xu, Y Q, Latkowski, S, O'Carroll, J, Murdoch, S G, Phelan, R, O'Gorman, J, Barry, L P
• Format: Journal Article
• Language: English
• Published: IEEE 01.02.2011
• Subjects: Delta modulation; Frequency combs; Gain; injection locked lasers; Laser modes; Laser noise; optical communications; Optical switches; Optical transmitters; pulse compression; Semiconductor lasers
• ISSN: 1943-0655; 1943-0647
• DOI: 10.1109/JPHOT.2011.2105861

The authors demonstrate the generation of a highly coherent multicarrier signal that consists of eight clearly resolved 10.7-GHz coherent sidebands generated within 3 dB of the spectral envelope peak and with an extinction ratio in excess of 45 dB by gain switching a discrete mode (DM) laser. The generated spectral comb displays a corresponding picosecond pulse train at a repetition rate of 10.7 GHz with a pulse duration of 24 ps and a temporal jitter of ~450 fs. The optical spectra and associated pulses of the gain-switched DM laser are subsequently compared with a gain-switched distributed feedback (DFB) laser that generates a spectrum with no discernible sidebands and corresponding pulses with ~3 ps of temporal jitter. By means of external injection, the temporal jitter of the gain-switched DFB laser is then reduced to <; 1 ps, resulting in visible tones on the output spectrum. Finally, a nonlinear scheme is employed and initially tailored to compress the optical pulses, after which, the setup is slightly altered to expand the original frequency comb from the gain-switched DM laser.