Rugate filter manufacturing by electron cyclotron resonance plasma-enhanced chemical vapor deposition of SiNx

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Abstract
Electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) is used to deposit thin films of SiNx of different composition from mixtures of N2 and 30% SiH4 in Ar onto different substrates. Measured values of the complex refractive index over the wavelength range of interest are used in the design and computer-controlled fabrication of one- and two-band rugate optical interference filters. The excursion of the continuously varying refractive index is chosen to be between 0.8 and 1.2, and window functions and matching layers at both sides are employed for sidelobe suppression. Measured reflection patterns of filters agreed well with simulated results. Filters designed for a center wavelength of 1000 nm and a total thickness of 2.1 μm, have a reflectance of 97% in the stopband and a bandwidth of typically 240 nm. The two-band filter is designed for stopbands at 1000 and 770 nm with reflectance of 98 and 96% and bandwidths of 150 and 120 nm, respectively. The total thickness of this filter is 3.33 μm. Filters are successfully deposited on optical fiber ends using one of the fibers for in situ monitoring of the deposition process. © 1997 Society of Photo-Optical Instrumentation Engineers.

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