LOW-LOSS LAMINATED POLARIZATION SPLITTERS FOR WAVELENGTHS LONGER THAN1.3 MU-M PREPARED BY PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION

We have decreased remarkably the insertion loss of a laminated polariz ation splitter (LPS) designed for wavelengths longer than 1.3 mu m, wh ich consists of a-SiC:H/SiO2 multilayers prepared by plasma enhanced c hemical vapor deposition. Previously fabricated LPSs have the problem of a large scattering loss because the surface of the multilayer film is not sufficiently flat; this is especially remarkable in the SiO2 fi lm. The flatness of the SiO2 film is improved by optimization of the s ubstrate temperature and flow rate of the source gases. The a-SiC:H fi lm with a high refractive index and low absorption is obtained by opti mizing the mixing of source gases at fixed substrate temperature. The total loss of a multilayer film at normal incidence is decreased from 1.22x10(-2) dB mu m(-1) (previous work) to 1.4x10(-3) dB mu m(-1). The insertion loss of the LPS is also decreased from 5.2 x 10(-2) dB mu m (-1) (previous work) to 7 x 10(-3) dB mu m(-1).