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Title: Short pulse generation and manipulation in high speed data transmission systems
Author: Chai, Y. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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In this work, an ultrashort optical pulse source, generated through gain-switching of a semiconductor distributed feedback (DFB) laser followed by nonlinear fibre compression scheme, is experimentally demonstrated. Incorporating this with a novel fibre loop mirror, known as the dispersion-imbalanced loop mirror (DILM), simultaneous pulse compression and pedestal suppression are achieved. This generates ultrashort pulses with 350fs full-width half maximum (FWHM) and high quality extinction ratio of 30dB (instrument limited). With such short pulses, timing jitter becomes critical in avoiding signal-to-noise ratio (SNR) degradation. By employing a novel self-seeding scheme with the gain-switched laser, an instrument-limited jitter of 150fs is achieved. This makes the experimentally demonstrated femtosecond pulse source as an ideal candidate for high speed OTDM applications. The performance of the DILM as a noise suppressor is also studied. Interferometric noise, also known as incoherent crosstalk, has been a limiting factor in high-speed multichannel optical communication systems. With the use of the DILM, interferometric noise suppression is achieved with a power penalty improvement of more than 9dB. This is observed to be consistent throughout a wide range of wavelength from 1531-1560nm. This shows that using the DILM as a noise suppressor out-performes any electronic techniques. The combined DILM and self-seeding scheme provides a high quality pulse source which successfully meets the requirements of high capacity data systems. Having achieved this goal, further investigations of next generation sources, such as solid sate lasers for ultrahigh performance system applications are undertaken. A solid state mode-locked laser (CR4+:YAG), which has a 3dB spectral width of 40nm, is demonstrated for spectral slicing using an AWG. A total capacity of 1.36Tb/s (40Gb/s x 32 channels) is achieved. This is the highest capacity ever reported using a single pulse source in the C-band region. The output Q-factor of 8 to 13 demonstrates the feasibility of such innovative approach.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available