Waveguide Experiments in PbTe Thin Films and the Tuning Character of PbTe Diode Lasers
Quarterly technical rept. no. 2, 1 Jul-30 Sep 1973
FORD MOTOR CO DEARBORN MI
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Grating couplers have been fabricated in thin-film PbTe waveguides on BaF2 substrates. The grating spacings are between 1.8 and 2.1 micrometers, which is the appropriate range for coupling into the low order modes of a high index film n 5-6 with a 10.6 micrometer CO2 laser. The gratings are first formed in a photoresist layer on the film using holographic or mask exposure. The pattern is then transferred to the PbTe by etching in a dilute bromic acid and bromine solution. The last step is essential for obtaining high coupling efficiencies. Due to the high index of the film, efficient coupling cannot be achieved with a low index photoresist layer alone. Coupling efficiencies are estimated to be approximately 10. Tuning characteristics of a number of PbTe thin-film lasers are measured. Tuning rates are typically 1.5-0.15 GHzmA depending on diode resistance and thermal impedance. The maximum tuning range observed in a single mode was 70 GHz.
- Lasers and Masers