Monolithic high power mode locked GaAs/AlGaAs quantum well lasers

Tandoi, Giuseppe (2011) Monolithic high power mode locked GaAs/AlGaAs quantum well lasers. PhD thesis, University of Glasgow.

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In this thesis, approaches for increasing the output power in monolithically integrated semiconductor mode locked (ML) lasers were investigated. The wavelength range considered
is the range of operation of low temperature grown GaAs photomixers, devices commonly used for THz generation. In particular, two GaAs/AlGaAs quantum well laser epistructures (operating at 830 nm and 795 nm) were considered, both with reduced optical confinement and elongated vertical optical mode size. In this work, such
laser epistructures, commonly used by high power semiconductor laser manufacturers,
were successfully employed, for the first time, for producing passively ML devices. Improved average powers (up to 48 mW) under ML operation were demonstrated, around
ten times higher than values previously reported in monolithic GaAs/AlGaAs ML lasers.
In continuous wave operation, the output power was limited by the catastrophic damage of the laser facets at around 50 mW. For this reason, facet passivation techniques were investigated, allowing for powers up to 124 mW to be achieved. In ML regime, the output power was instead limited by the catastrophic damage of the reverse biased section of the laser. This failure mechanism was investigated and explained considering thermal
effects on the reverse biased section. Such effects limited the output power to around 27 mW in 830 nm devices, which was then improved by 70% in 795 nm devices with
a 70% larger optical mode area. The larger mode size, combined to a small duty-cycle laser geometry, enabled a record peak power of 9.8 W to be achieved at 6.83 GHz. This
particular repetition rate was specifically designed for coherent population trapping experiments
in 87Rb vapors. Sub-picosecond transform limited pulses were achieved in both the laser materials considered, with a minimum duration of 0.43 ps at 126 GHz.
With the values of peak power achieved, the developed devices may also be directly used for two-photon microscopy applications.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Semiconductor laser, quantum well laser, GaAs/GlGaAs laser, mode locked laser, high power laser, ridge waveguide laser, optical pulse source, quantum well intermixing, two photon absorption autocorrelation, gain measurements, absorption measurements, catastrophic optical mirror damage, non absorbing mirrors, protective facet coatings, saturable absorber failure, transform limited pulse, coherent population trapping
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Ironside, Prof. C.N. and Bryce, Prof. A.C.
Date of Award: 2011
Depositing User: Dr Giuseppe Tandoi
Unique ID: glathesis:2011-2721
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Jun 2011
Last Modified: 10 Dec 2012 13:59

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