Abstract: By employing a high-repeatability optical switch that transmits input optical power selectively either to the standard or the unit under test (UUT), OPHASE presents a system for performing a rapid, repeatable comparison between the standard and the UUT. Further, the selective routing of beam traveling through one of the two output fibers that are coupled to the switch either to the standard or the UUT enables the elimination of much of the system uncertainty by enabling initial characterization of the ratio, Rp, and inequivalence, Im, between the power outputs of the multiple output fibers coupled to the switch. This characterization is accomplished by using an angled interface which is constructed so as to allow simultaneous coupling of the multiple output fibers to the angled interface and enable the power readout of all the output fibers at the standard. Rp and Im are then used to calculate the correction factor that reduces the total uncertainty level in the subsequent calibration of the unit under test.