Ion beam sputtered (SiO_2)x(Si_3N_4)_1−x antireflection coatings on laser facets produced using O_2–N_2 discharges

The chemical composition of a (SiO(2))(x)(Si(3)N(4))(1-x) film produced by ion beam sputtering was precisely controlled by the ratio of O(2) and N(2) flow rates under a discharge current kept constant to within an accuracy of +/-0.05 A. The reproducibility of the refractive index was improved to +/-0.01. This film was applied to form antireflection coatings with extremely low reflectivity on facets of 830-nm AlGaAs double heterostructure lasers. The minimum reflectivity was 6.8 x 10(-5), and a reflectivity of 1 x 10(-4) was achieved reproducibly. Experimental studies show that antireflection coatings are effective for suppressing the interferometric light output variation of composite cavity lasers.