Design, fabrication, and characterization of semiconductor transverse Bragg resonance lasers
Controlling the spatial modes of a laser cavity is fundamental for improving the beam quality of a laser and achieving highly efficient coupling of power into an optical system. High-power applications are particularly challenging due to the conflicting requirements for large modal volume, to preven...
| Summary: | Controlling the spatial modes of a laser cavity is fundamental for improving the beam quality of a laser and achieving highly efficient coupling of power into an optical system. High-power applications are particularly challenging due to the conflicting requirements for large modal volume, to prevent facet damage by reducing energy density, and narrow width, for single-mode operation of an index-guided waveguide. By replacing traditional index confinement with Bragg reflection in the transverse direction, single-mode operation can be achieved even for large modal volumes. These grating confined structures, transverse Bragg resonance (TBR) waveguides, have the unique ability to support localized modes above the light line. Such modes normally couple to radiation modes of the cladding when the confinement mechanism is total-internal-reflection and are too lossy to be considered guided modes. However, for Bragg resonance confined modes, the modal loss can be designed by careful optical mode engineering to introduce a large loss discrimination that can favor a single spatial, low-loss mode. Semiconductor TBR lasers in an InP/InGaAsP/InGaAs material system were designed, fabricated, and characterized to investigate this property. Two regions of operation are identified for TBR waveguides, and, while transverse mode selection is provided by a grating, longitudinal mode control is found to be also necessary to restrict operation to the region that supports modes above the light line. |
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