US Patent 7619744 Movement sensor

In an apparatus for handling sheet material or an optical input device, for example, which employs a relative movement sensor (108) utilizing the so-called “self-mixing” effect of a laser diode, a band pass filter (100) is provided for filtering the electric signal resulting from measurement of the electric signal to reduce or substantially eliminate the effects of both the low frequency carrier signal and the high frequency noise present in such a signal. As a result, the precision of the laser self-mixing translation measurements is significantly improved.