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The environmental and mechanical reliability of a planar lightwave circuit (PLC)-type optical splitter modules is investigated with reference to the Bellcore requirements. The module is composed of Y-branching silica-based waveguides on Si connected to optical fiber with UV-curable adhesives and is packaged in a metal case which is filled with humidity-resistant resin. High optical performance such as low loss, low reflection, and thermal stability are obtained through the use of this fiber connection technique. Ten reliability tests including long-term environmental and mechanical tests were carried out for more than ten PLC splitter modules. Under one of the most severe sets of conditions (75OC and 90% RH), all the 19 samples we tested were stable for more than 5000 hours. Other tests confirmed that the PLC splitters offer long-term stability and that their optical characteristics have sufficient mechanical strength. These results indicate that the PLC splitters can be used for practical applications.

Residual stress and its influence on optical characteristics have been investigated for pure-silica (SiO2)-core/fluorine-doped-silica(F-SiO2)-clad single-mode fibers. Theoretical analysis has shown the following: (1) Very high residual stress concentrated at the small-diameter core region is induced by drawing tension because of the viscosity difference between core and cladding. (2) The refractive index in the core is reduced greatly by the residual stress via the photoeleastic effects. (3) The decrease in the refractive index results in the shift of the cutoff wavelength to shorter wavelengths. These characteristic features have been ascertained experimentally in SiO2-core/F-SiO2-clad single-mode fibers drawn at various conditions, indicating the optimum drawing condition and structure for the single-mode fibers.

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