Investigations on 4x4 polymer couplers for airborne environment

Due to the potential of high data rates up to several Gb/s, low electromagnetic interference sensitivity and weight reduction capabilities, in future, optical data transmission will become standard in airplanes. The requirements on the necessary optical components that have to be operated in airborne environment in general are extremely high. In addition, airframe manufacturers are interested in low cost components. An example for such an optical component is a star coupler for data distribution, in particular, a device made on base of polymers. The applicability of such 4x4 polymer star couplers under extreme environmental conditions was investigated. The investigations were made at temperatures from -40 to +80 degreesC and up to 98 % humidity. Different types of housings were tested (polymer, metal, ceramic). It was found that housing of the polymer couplers is required necessarily, since non-housed components exhibit a large insertion loss increase of up to 0.5 dB during temperature variation. Best results were achieved with metal or ceramic housings exhibiting a maximum insertion loss increase of approximately 0.1 dB. However, due to a large difference of thermal expansion coefficients of filling and housing material, respectively, ceramic housings mechanically failed (crack formation) and thus metal housings are first choice. The results were also compared to those achieved for commercial 4x4 multimode couplers made of glass and based on fused bi-conical taper technology.