As we read the paper by Jianqi Zhang and Huan Xu, Pramana – J. Phys. 72, 547 (2009), two issues became clear, that warranted writing this comment. First, the switch, which is the main building block of the devices, and which is used to route the signal, does not work as explained in Section 4.1. Accordingly, the optical router does not work as explained, either. In addition, the half adder does not work as explained and a completely different Truth Table is obtained. The full adder is left to the reader as an exercise. Secondly, the previously published work, which is closely related to the work reported, was not referenced or discussed. In the following paragraphs we discuss each issue in some detail to give the authors the opportunity to better explain their work and clear such issues.