| Abstract [eng] |
Characterisation of GaSb Gain Chips in Tunable External Cavity Lasers Optical sensing is a very useful instrument for medical diagnosis. It is important that sensing systems would be non-invasive, real-time measuring and compact to make a process faster and more comfortable. This kind of systems need to measure the change of concentration of important biomolecules like lactate, glucose, albumin, urea or others in the human body. This goal could be achieved by GaSb based gain chips integrated in external cavity system, which is widely tunable single frequency infrared optical source. GaSb based gain chips were modeled for 2 - 2,5 µm range of wavelengths. Waveguide bending method and optical coatings were applied for device performance optimisation. Optimised gain chips were integrated in Littrow configuration based external cavity system. External cavity diode lasers performances were characterised and the widest tuning ranges were found. Epitaxial device structures were grown by molecular beam epitaxy method for 4 different wavelengths. Optimum bending angles of 5,8°, 6,5°, 5,2° and 6,6° were found for 2025 nm, 2250 nm, 2300 nm and 2380 nm devices, respectively. At this work output power and emission spectra were investigated. For estimation of gain chips output facet reflectivities spectral modulation values were obtained. Reflectivities of coated gain chips were calculated: 2 - 8 x 10-5 for 2025 nm, 1 - 5 x 10-4 for 2250 nm and 2380 nm, ~ 1 x 10-5 for 2300 nm devices. Calculated and designed values had a good correlation. Optimised gain chips in external cavity system achieved 35,3 mW, 32 mW and 45,8 mW optical powers for 2025 nm, 2250 nm and 2380 nm, respectively. External cavity diode lasers exhibited single mode laser emission with side-mode-suppression-ratio of 29,9 – 32 dB. Tuning ranges of 80 nm, 170 nm and 150 nm were achieved by employing automated grating rotation for 2025 nm, 2250 nm and 2380 nm, respectively. Experimentally all wavelengths from tuning range were covered by combining current and piezo tunings mode-hop free. |
