Picosecond Gain Switching Semiconductor Laser Seed Source

Comparing with common mode-locking and Q-switching lasers, gain-switchinglaser diodes have superior advantages in structural compactness, performance stability,parameters tunability and high repetition frequency. But the development ofgain-switching laser diodes as pulsed laser source has been limited by the drawbackssuch as broad pulse duration, low power and spectral instability. This dissertationfocuses on the methods to obtain high quality, high repetition frequency, picosecondlaser with gain-switching laser diode along with injection-locking technique, pulsecompression technique and other relevant techniques. The aim is to construct a suitableseed laser for the high power fiber pulsed laser amplification system, which canchallenge prevalent mode locked laser sources.The dissertation begins with a thorough review of important advances relating withthe gain-switching laser diode in the last decade. A scheme of generating high qualitypulsed laser with gain-switching laser diode system, which is composed of pulsegenerating, injection locking, pulse compressing and reshaping and pulse amplification,is proposed.Firstly, the influences of stimulating current parameters and laser diodecharacteristics on the pulse waveform of gain-switching laser diode are numericallysimulated and analyzed based on the basic principle of gain switching and rate equationtheory. Furthermore, based on the calculation the proper parameters of current signaland laser diode are chose to obtain high quality picosecond pulse with high peak power,narrow pulse width and small pulse tail.Experimentally, semiconductor laser with Fabry-Pérot cavity at1.06μmmodulated by high-frequency sinusoid electrical signal is used to produce stableshort-pulse laser trains with changeable pulse width around100ps, repetition frequencycontinuously tunable in the range of500MHz~1500MHz and peak power100~300mW.The effects of the variation of modulation current on the output performance of the laserdiode are experimentally analyzed.The injection locking of single frequency laser to the gain-switching laser diode isstudied experimentally, which has improved the spectral performance of output pulse bysuppressing the extra longitude modes. A side mode suppression ratio of43.4dB isobtained when raising injection power. Furthermore, the effects of wavelength driftcaused by temperature change on injection locking are studied.A pulse compressing&shaping scheme is designed based on the theory and thecharacteristics of pulses from gain-switching laser diode. The numerical simulationpredicts a compression of100ps hyperbolic secant pulse to454fs, keeping a favorablepulse shape. The pulse laser from gain-switching laser diode is amplified in power, obtaining anoutput power of22.7W and light-to-light conversion rate of66.7%while retaininggood spectrum and pulse shape.