In a second step, the laser optical power is adjusted so that the measured power is PTX = −6.5 dBm at the end of the patchcord. After performing any of these references, the patch cords must remain connected to the measurement units or an IL variation will occur upon reconnection. In addition to the LB reference procedure, ORL link measurements require knowledge of the zero-offset ORL power, or the measured power P0, due to the return loss of the unit. Figure 1c shows how to perform the zero-offset ORL reference. Connecting the patch cord J1 between the unit and a non-reflective termination ensures a very low return loss. During the zero-offset ORL reference, the laser emits as the power meter on the same port measures the reflected optical power, P0, which is linked to the directivity of the 3-dB coupler inside the measurement unit and to the return loss of the mated connectors at the unit output.
After completing the reference procedures, perform the link measurement step shown in Figure 2. Connect each of the units and their associated patch cord to either side of the link under test. IL and/or ORL measurements can then be performed on one or both units during the same test. The measured data is then displayed on both units. IL should be 40 dB or less, so that the two measurement units can communicate correctly with each other.