Abstract :
In the above-named letter, Chen, et al. presented three structures for low-crosstalk optical add-drop multiplexers. The commentors would like to point out that they published two of these structures seven months earlier, in a paper at OFC??2000 [A.V. Tran, W.D. Zhong, R.S. Tucker, and R. Lauder, "Compact optical add??drop multiplexers with low homodyne crosstalk using a single optical circulator and fiber Bragg gratings," in Proc. OFC??2000, Mar. 2000, Paper WM39, pp. 326??328], which was not cited by Chen, et al.
