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Developing coupled cavity living laser for biological cell analysis

Binti Sapingi, Husni Hani 2016. Developing coupled cavity living laser for biological cell analysis. PhD Thesis, Cardiff University.
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The development of a prototype of a coupled cavity living laser that is aimed to be used for cell analysis is described. Quantum well and quantum dot material is characterized as the potential active medium. Quantum dot material has the beneficial qualities of a low internal optical loss ai of 2±1 cm-1, broader gain spectrum with reduced peak gain magnitude as well as larger spectral peak gain shift with increasing current density. However, the maximum gain available with quantum dot at 300 K is smaller (15 cm-1 compared to 37 cm-1), which might limit the device performance where the etched mirror loss was large. The quantum well active medium material is therefore used for the fabrication of the prototype. The recipe for the fabrication of etched facets has been investigated since the monolithic design of the coupled cavity living laser doesn’t allow cleaving of the inner facets. A nickel mask is found to be a suitable mask for inductively coupled plasma etching of semiconductor crystal here as unlike silicon oxide the metal doesn’t have any significant interaction with the etchant during the etching process. Oxide stripe lasers with cleaved – etched facets show decreasing threshold current density and increasing external and internal quantum efficiency as an increasing exposure dose factor and short development time is applied. The electron beam lithography process for mask patterning requires a high exposure dose factor which is 1.5 and short development time, which is 40 seconds to produce etched facet with minimum striations and the best reflectivity achieved is 0.24. This level of total losses, where a mirror reflectivity of 0.24 is achieved, coupled with the measured ai means that quantum dot material could be used for future iterations.The prototype of a coupled cavity living laser is fabricated with the developed processing procedure. The laser devices function as individual laser cavities with threshold current of 538 mA for laser 1 and 588 mA for laser 2. The vertical far field divergence of 25O along with the channel width of 125 μm means that only 0.004 of the emitted electric field profile overlaps with the second cavity. The fabricated prototype of a coupled cavity living laser also operates in a source – detector mode. Laser 1 and 2 appear to give iv threshold current of 421 mA and 446 mA respectively when they are operating as a source and signal is measured using the other device operating as a detector. The apparent reduction compared to the externally measured threshold is likely to be due to the changing fraction of light coupled from one section to the other as the near field and consequently the far field changes around threshold and the influence this has on the determination of the threshold from the slope characteristic. When both sections are operated as lasers a negligible effect is seen on the threshold current of one due to contributions from the other and this may be due to the very small fraction of light coupled from one to the other.

Item Type: Thesis (PhD)
Date Type: Publication
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: coupled cavity laser system, etched facet, quantum well, quantum dot.
Date of First Compliant Deposit: 12 May 2016
Last Modified: 15 Nov 2016 05:51

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