A system and method for detecting and correcting for thermal shifting of the passbands of an input filter of an optical receiver relative to the passbands of an output of an optical device, such as an optical router, where the router and the receiver are operating at remote locations and at different operating temperatures that cause thermal drifting of the passbands. In one implementation RF signals are impressed on optical signals transmitted by a transmitter to the optical router. Different frequency RF signals are impressed on each of the optical signals and the receiver uses the detected RF frequencies to cancel portions of optical signals that have drifted into adjacent passbands at the optical receiver. In another implementation a mechanically adjustable filter is employed at the receiver which is used to achieve a needed degree of shifting of the receiver passbands to compensate for passband misalignment between the router and the receiver. In another implementation multiple receive channels are employed for each router passband. The various described implementations allow for detecting and correcting of thermal misalignment between the router and receiver passband without the need for controlling the temperature of the router.