Monolithic, tunable, single frequency, narrow linewidth lasers using quantum well intermixing

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Jia, Zhengkai
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University College Cork
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With the development of Internet technology, the number of Internet users and Internet traffic has increased exponentially every year, and there is a large-scale demand for photonic components at the core of optical communication networks. Semiconductor lasers are the heart of photonic devices which are attractive for their low form factor, mass producibility and compatibility with photonic integrated circuits (PICs). Quantum well intermixing (QWI) is one of the important monolithic techniques used in the integration of PICs. QWI is a post-growth technique, which is used in the preparation of integrated devices and creates a modified energy band gap of a quantum well without any regrowth. QWI in Indium phosphide (InP) based AlGaInAs multiple quantum well active regions was demonstrated in this dissertation by applying QWI to monolithic tunable single frequency narrow linewidth lasers. This design reduces both the potential cost and power consumption of the devices. This work has been focused on creating small size coherent optical laser sources, making them attractive devices to satisfy the rising demand for photonic components. This work investigates the development of components that can be simply fabricated without requiring any epitaxial regrowth. A regrowth-free monolithic InP-based laser / photonic integrated circuit (PIC) was demonstrated with tunable single-frequency operation in the C + L bands and a sub 10 kHz linewidth. The laser PIC integrates a gain section with a 1×2 multimode interferometer (MMI), a linear curvature ring reflector on one side and a slotted mirror on the other. The MMI and ring reflector were made transparent to the gain wavelength using the impurity-free vacancy disordering (IFVD) quantum well intermixing technique to extend the cavity for narrow linewidth. The slotted mirror acts as higher order distributed Bragg reflector (DBR) to select the lasing mode. The laser was fabricated using the typical Fabry Perot (FP) laser process used in the Integrated Photonics Group, with a self-aligned technique for achieving two etch depths. The fabricated laser demonstrated single longitudinal mode tunability over a 39 nm range with a side mode suppression ratio (SMSR) of greater than 35 dB and a 3.79 kHz linewidth at room temperature with 87 mA current injection on the gain section and 115 mA on the slotted mirror section.
Tunable single frequency lasers , Quantum well intermixing , Narrow linewidth lasers
Jia, Z. 2022. Monolithic, tunable, single frequency, narrow linewidth lasers using quantum well intermixing. MResThesis, University College Cork.
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