Comment on ´2*2 multiplexing couplers for all-fibre 1.55 mu m amplifiers and lasers´

For the original article see ibid., vol.27, no.1, p.42-3 (1991). In the aforementioned paper by F. Gonthier et al. a fused coupler with a nonsinusoidal spectral response is described and its potential application for pumping fibre amplifiers is noted. The authors wish to point out that couplers with the same nonsinusoidal response have been described previously by Hill et al. (1990). These couplers were used in a demonstration of a novel bimodal fibre tap. Even though the application is different, the coupling ratio of the coupler has the same nonsinusoidal spectral dependence as described by Gonthier et al. The commenters point out that the potential application of these couplers in fibre amplifier pumping was also known. A prototype coupler with the nonsinusoidal spectral response was sent to Bellcore, Red Bank NJ. This coupler was used in a fibre amplifier experiment reported in May 1990 at CLEO 1990 but is is conceded that Gonthier et al. may not have been aware of the type of coupler being used in the fibre amplifier experiment.