A method for reducing the size and cost of optical system for precision measurement based on the Levitation Mass Method (LMM) is proposed. In the LMM, a mass levitated using a pneumatic linear bearing with sufficiently small friction is made to collide with the object being tested. The velocity and acceleration of the mass are measured using a compact optical interferometer. The size of the optical system can be drastically reduced by using a planar lightwave circuit (PLC), in which several optical elements are arranged on a planar surface of a silica or semiconductor substrate. Several applications of the PLC to precision measurement will be discussed.