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

[摘要] 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.

[发布机构] University:University of Glasgow

[关键词] Electrical engineering