A method for calibrating a preferred disposition for a moveable first mirror of an optical switch core of a photonic crossconnect device relative to a second mirror thereof, the method comprising the steps of determining approximate geometric coordinates of the first mirror relative to the second mirror, effecting a laser light crossconnection between the first and second mirrors to produce data from which to provide first order corrections to refine the geometric coordinates, and effecting a further laser light crossconnection between the first mirror and a third mirror, to produce data from which to provide second order corrections to further refine the geometric coordinates, whereby to calibrate the first mirror such that upon initiation of a laser light crossconnection involving the first mirror, a switching element detects deviation of the first mirror from the preferred disposition thereof and effects corrective changes.