Generation and Detection of Short Optical Pulses Using Semiconductor Devices

Karkhanehchi, Mohammad Mehdi (1997) Generation and Detection of Short Optical Pulses Using Semiconductor Devices. PhD thesis, University of Glasgow.

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The design, fabrication and characterisation of semiconductor waveguide autocorrelator, as a device for use in the analysis of ultra-short pulses, are described. The initial experiments carried out, using an AlGaAs optical waveguide, to detect the interferometric autocorrelation trace of light from a mode-locked Nd+3:YAG laser. Both intensity and interferometric autocorrelation traces of pulses from a mode-locked Nd+3:YLF laser were then successfully obtained for the first time using the same device. The autocorrelation trace gives the full width at half maximum of the mode-locked pulses from the Nd+3:YLF laser to be approximately 17.7 ps. The complete polarisation dependence of the two photon absorption coefficient, beta, has been obtained by measuring the orientational dependence and the contrast ratio of the photocurrent in the device at an optical frequency far above that of the half-bandgap. Measurements of the pulse width dependence of the two-photon absorption photocurrent in GaAs p-i-n waveguide photodetector using subpicosecond optical pulses at 1.5 mum are reported. For a fixed pulse energy, the photocurrent is observed to depend linearly on the inverse of the optical pulse width. A subnanosecond electrical response is also observed. The propagation loss and the single photon absorption coefficients are measured as a function of wavelength in a device with an Al0.2Ga0.8As waveguide core. The propagation loss was as low as 1.37 cm-l at a wavelength of 904 nm. Using a photocurrent technique, band-to-band absorption was measured for photon energies well below that of the bandgap. It was demonstrated that, although the band-to-band absorption coefficient is small (~10-2 cm-1 at a wavelength of 1 mum), it is responsible for reducing the contrast ratio of the waveguide autocorrelator. Two-section lasers were fabricated in strained layer InGaAs/GaAs double quantum well material with intracavity saturable absorbers. Passive Q-switching was demonstrate in these lasers. Self-pulsation is seen at frequencies up to 12.5 GHz with a full width at half maximum of 20 ps.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: John Marsh
Keywords: Electrical engineering
Date of Award: 1997
Depositing User: Enlighten Team
Unique ID: glathesis:1997-75293
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 21:18
Last Modified: 19 Nov 2019 21:18

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