Displacement Sensing Based on Parasitic Cavity Referencing in Optical Circulators

In this letter, we propose a method for utilizing the internal cavities of optical circulator devices—commonly referred to as parasitic cavities—as optical reference cavities. The method involves using an optical circulator operating at 1550 nm, illuminated by a light source at 1330 nm, thereby enhancing the amplitude of the interferometric signals generated by the internal optical cavities. The system was characterized by using both an Optical Spectrum Analyzer (OSA) and the Low-Coherence Interferometry (LCI) technique. Experimental results indicate that the Optical Path Difference (OPD) remains constant with varying aperture sizes, thereby confirming the feasibility of employing the optical circulator as a reference sensor. Finally, its performance as a reference sensor is demonstrated through its integration with an external cavity that functions as a displacement sensor.