Sol–gel fabrication of thick multilayers applied to Bragg reflectors and microcavities
Résumé
We discuss attractive potentialities of the sol–gel process applied to planar microcavities with distributed Bragg reflectors (DBRs). This method is well known for its good flexibility and the optical quality of the thin films obtained. The DBRs are composed of alternated TiO2 and SiO2 thin films. One of the main problems of the sol–gel process is the stresses induced during the layers heat treatment leading to defects and cracks in the films. The study of these stresses shows that with the appropriate annealing temperature and duration of the firing process, the stress in the SiO2 layers partially compensates the stress in the TiO2 layers. DBRs and microcavities formed by 60 stacked layers have been elaborated in these conditions. The reflectivity of such sol–gel DBRs reaches 99.7%. The sol–gel DBRs are used to fabricate microcavities containing Eu3+ rare earth ions with a quality factor of approximately 1000.
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