Comparative Study of Passive Modelocking Configurations in Semiconductor Lasers

[摘要] This thesis is concerned with the investigation of different configurations of semiconductor lasers to generate short optical pulses through passive modelocking, and the analysis of the possible uses for these optical pulse generators. Three different modelocking configurations have been studied to generate optical pulses at frequencies between 1 and 15 GHz; two of them monolithic configurations, namely all active cavity mode-locked lasers and extended cavity mode-locked lasers and the third one being an external cavity configuration. The all active cavity mode-locked lasers have the advantage of having the easiest and most reliable fabrication process, but exhibited high threshold, around 100 mA for 5 mm long laser, broad pulses, around 10 ps, and high timing jitter levels, up to 22 ps (1 kHz-l0MHz). The extended cavity mode-locked lasers, which incorporate active and passive sections, are also easy to fabricate, but the reliability of the fabrication process depends on the reliability of the technique to fabricate the passive section of the device. They are excellent short pulse generators with very low threshold current, around 25 mA for a 5 mm long laser, pulses as narrow as 3.5 ps and jitter levels as low as 9 ps (1 kHz- 10MHz), which indicates a high stability in the pulse generation. With the external cavity configuration the pulse generation frequency can be reduced to values as low as hundreds of MHz. The drawback with this type of laser is their mechanical instability, which makes them a difficult device to work with. An important application for these optical pulse generators is that of all-optical clock recovery. The locking range of the monolithic configurations, under external periodic excitation, was studied. The all active cavity lasers showed a locking range wider than 0.15% of the free running modelocking frequency, whilst the extended cavity lasers locking range was around 0.03% of the free running modelocking frequency.

[发布机构] University:University of Glasgow

[关键词] Electrical engineering