Influence of deposition parameters in the fabrication of a large-area narrow band-pass filter of bandwidth on subnanometer scale

A narrow band-pass filter of subnanometer bandwidth is extremely sensitive to errors in the layer thickness and the optical constant of composite layers. For a filter made by vacuum deposition, such an error may be due to small fluctuations in deposition parameters. The distribution and deposition rate of the evaporating species, the distribution of ion current density and the ion voltage of the ion beam, the vacuum conditions, the wobbling of rotating substrate and the substrate temperature are all important parameters when fabricating such delicate filters. This work analyzes the role of these parameters in fabricating a large-area narrow band-pass filter of bandwidth on a subnanometer scale. The technique of shaping tooling factor (STF) was then applied to enlarge the useful coating area. Filters for dense wavelength division multiplexing (DWDM) systems with useful coated areas of larger than 1800mm² (for 100GHz filters) and 300mm² (for 50GHz filters) were fabricated. Experimental results indicate that the pass bandwidths at -0.3dB exceeded 0.5 and 0.25nm for 100 and 50GHz filters, respectively, and the stop bandwidths at -25dB were less than 1.1 and 0.6nm, respectively. Moreover, the ripple of all these filters was less than 0.2dB.