A waveguide loss measurement method based on the reflected interferometric pattern of a Fabry-Perot cavity

We propose a new waveguide loss measurement method based on the reflected interferometric pattern from the waveguide. The loss of the waveguide is obtained by analyzing the fineness of the reflected interferometric pattern from the Fabry-Perot (F-P) cavity formed by the facets of a single-mode waveguide. In this method, a single mode lensed fiber and a circulator is used to direct the tunable laser into the waveguide under test and collect the reflected spectrum pattern through a photodetector. Comparing to the traditional transmission F-P interferometric method relying on double end fiber coupling, the proposed method requires only a single end coupling, considerably simplifying the coupling difficulty and the measurement system complexity. The fineness measurement is also free from the influence of background noise level, and reduces the coupling accuracy requirement. This method is low-cost, easy-to-operate and reliable, which can serve as an alternative method to measure the waveguide loss.