An optical module includes a first ferrule, a second ferrule that is aligned with the first ferrule via a positioning pin, a housing including a support part that supports the second ferrule, and a ferrule clip that is fastened to the housing and presses the first ferrule toward the second ferrule. In one aspect, a method is provide that includes rotating a machine readable medium, and detecting a spiral on the machine readable medium. In either case, by detecting the widths of the servo windows and detecting signal amplitude as a servo head passes relative to the servo track, servo tracking can be achieved without the use or need for additional synchronization marks in the servo pattern. The input transducers have the same polarity and the output transducers have opposite polarities.