178 8163A/B, 8164A/B, 8166A/B User’s Guide7 Return Loss MeasurementGetting Started With Return LossWhat is Return Loss?When light passes through an optical component most of it travels in theintended direction, but some light is reflected or scattered. In manyapplications these reflections are unwanted, because they can affect theemission characteristics of any laser in the system. In such applications, itis important to measure the reflections for the components of the system.The reflection factor for a component is a measure of how much light thecomponent reflects. It is a ratio of the power reflected by the device to thepower incident on the device. More normally we talk about the return lossof a component. The return loss has units of dB. Return loss is given by:What is Insertion Loss?Light that is absorbed, scattered, or reflected by a component also affectshow much light a component transmits.The transmission factor for a component is a measure of how much lightthe component transmits. It is a ratio of the power transmitted by thedevice to the power incident on the device. More normally we talk aboutthe Insertion Loss of a component. The insertion loss has units of dB.Insertion Loss is given by:
