Polarization- and Phase-Sensitive Low-Coherence Interferometry Setup for the Characterization of Integrated Optical Components

A novel phase-sensitive and polarization-sensitive scheme to implement an optical low-coherence interferometry (OLCI) system is presented. With respect to conventional phase-sensitive OLCI, in our system the interference fringes of the coherent light used to recover phase information are conveniently detected by the same photodetector acquiring the low-coherence signal. This strategy guarantees the intrinsic synchronization of the two signals at any acquisition speed, makes measurements more robust against long-term fluctuations in the experimental setup, and reduces the measurement time without affecting phase accuracy. The residual phase error after the phase recovery procedure is less than 0.01 rad, to the authors' knowledge one of the best results reported so far for OLCI measurements. Polarization sensitivity is achieved in the same setup by means of polarization selective retarders (PSRs) employed to couple light into and out of the device under test. This scheme enables to retrieve the time and frequency domain response of an optical device for both the polarization states from a single data acquisition. The presented technique is extremely versatile; it can be implemented by using either fiber or free space optics and applied to the characterization of generic optical devices. Its effectiveness is demonstrated by reporting the measurement of the amplitude and phase response of integrated optical devices based on ring resonators.