  Wang et al. [1] demonstrated different power transmission coefficients for
forward and backward propagation in simulation and experiment. From such a
demonstration, the central claim of their paper is that "the spatial inversion
symmetry breaking diode can construct an optical isolator in no conflict with
any reciprocal principle". Their claim contradicts the Lorentz reciprocity
theorem, from which it is well known that one cannot construct an isolator this
way.
