InAlGaAs-InP laterally coupled DBR and DFB lasers for microwave generation

Pozzi, Francesca (2007) InAlGaAs-InP laterally coupled DBR and DFB lasers for microwave generation. PhD thesis, University of Glasgow.

Abstract

The work reported in this thesis is concerned with the fabrication and characterisation of laterally coupled (LC) distributed feedback (DFB) lasers, both single-and dual-mode, based on InAlGaAs-InP material emitting at 1.35 mum. The aim of the research is to realise a compact device, able to emit two wavelengths simultaneously, to be used for the generation of gigahertz (GHZ) and terahertz (THz) signals by photo-mixing. The motivation comes from the need for portable sources of radiation in the so-called THz region. The first part of the work involved the implementation of a laterally coupled grating that is intended to become a building block for the dual-wavelength device. To prove the effectiveness of the grating structure, single-mode DFBs and distributed Bragg reflector (DBH) lasers were designed and fabricated in the InAlGaAs-InP material, aiming to optimise the necessary technological processing. Assessment of these devices showed excellent performance: stable single-mode emission, with low threshold currents of about 55 mA and high sidemode suppression ratio (SMSR) over 40 dB, were demonstrated. Ridge-waveguide lasers (RWGL) were also fabricated alongside the single-mode devices, to allow comparison of the operating characteristics. The second part of the work was concerned with the implementation of a novel dual-wavelength laser, based on the lateral grating structure. The final device realised was a DFB laser having two different grating periods, one on each sidewall, fabricated in the InAlGaAs-InP material using the technology previously implemented. This source was thoroughly assessed in terms of lasing characteristics, mode behaviour, and suitability to generate microwave signals. Stable dual-mode operation, with low threshold currents around 50 mA and SMSR approaching 30 dB, was successfully demonstrated in continuous wave (CW) operating mode, at room temperature. The dual-mode behaviour was characterised by inspection of the modal transverse distribution and by injection locking experiments. Generation of microwave signals by photo-mixing was performed at about 23 GHz, and the linewidths of each of the individual modes and of the beat mode were measured as a function of the injection current. It was observed that, while the linewidth of the separate modes has a modest dependence on the injection level, the linewidth of the beat mode experiences a strong decrease as the injected current increases.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Marc Sorel
• Keywords: Electrical engineering
• Date of Award: 2007
• Depositing User: Enlighten Team
• Unique ID: glathesis:2007-74009
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 23 Sep 2019 15:33
• Last Modified: 23 Sep 2019 15:33
• URI: https://theses.gla.ac.uk/id/eprint/74009