Sumeeta Arora

Abstract

Gain-switching is a technique to generate short-width optical pulses. Its main advantage is that it does not require any change in the circuitry of the laser diode used or employ an external optical modulator. The modulating signal generator used by previous studies of gain-switching is an RF sine wave source or a comb generator. Previous work on gain-switching using comb generators as input source have selected only a single value of temporal period. For the first time, we study of the dependence of the optical pulsewidth and peak power of gain-switched pulses as a function of the temporal period using a comb generator. We find a baseline optical pulse width at large temporal periods, and that this width decreases by approximately 3$% $ as the temporal period is reduced. The width then increases for even shorter temporal periods. To conclude, there is a region of operation in the temporal period range where a minimum gain-switched pulsewidth can be obtained. The dependence of pulsewidth on the magnitude of DC bias and modulating signal applied is also studied. It is seen that the pulsewidth decreases with the increase in the values of both these currents. But there is a drawback of increasing the magnitude of the applied current that is mostly neglected in the scientific literature; at higher values of applied current, ripples are observed in the gain-switched optical pulses. For the first time, we study gain-switched pulses using a non-regular, data-like pattern "1011" as the modulating signal. The width of the input signal is varied to study the impact on the gain-switched pulses. It is seen that for lower width input signals, a higher value of DC bias is required to obtain optical pulses for the whole data pattern. But for higher width input signal, the whole data pattern is obtained as optical pulses at lower values of DC bias. Moreover, the gain-switched pulses are not uniform in terms of peak power, and we explore means to make these power levels uniform. indent For both the comb-generator pulses and the non-regular, data-like "1011" pulse pattern, we study the impact of chromatic dispersion on the optical pulse width and pulse performance. Chromatic dispersion has been used in previous studies as a means of compressing the gain-switched pulses. For comb-generated pulses, we find that an increase in the bias current applied to the laser diode results in a decrease in the magnitude of chromatic dispersion required to compress the gain-switched optical pulse. Also the percentage change in the width of the gain-switched pulse on passing through a dispersion source increases with the increase in bias current even though the applied chromatic dispersion is decreased. The optical pulses generated using data pattern are more uniform in terms of peak power of the optical pulses when chromatic dispersion in a particular range is applied. A reduction in jitter is also seen for that range of dispersion while it increases for higher and lower values of dispersion. During the course of my thesis work, I activated a gain-switched optical pulse source in the Photonic Systems Laboratory at RIT for the first time. This source will be used to support future research projects. I also developed a suite of MATLAB code for study of gain-switching and dispersion compensation.

Library of Congress Subject Headings

Laser pulses, Ultrashort; Pulse generators; Pulse techniques (Electronics)

Publication Date

7-27-2011

Document Type

Thesis

Department, Program, or Center

Electrical, Computer and Telecommunications Engineering Technology (CAST)

Advisor

Maywar, Drew

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: QC689.5.L37 A76 2011

Campus

RIT – Main Campus

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