The influence of a predefined threshold value on high reflectivity measurement in an optical feedback cavity ring-down technique (OF-CRD) is investigated. The strong optical feedback from the front cavity mirror of a linear ring-down cavity is re-injected into the oscillator cavity of the diode laser and causes line-width reduction of diode laser. The narrowed laser line is occasionally in resonance with one or more ring-down cavity modes and large resonant peaks are observed in the ring-down cavity output signals. The diode laser is switched off at the negative step of the square-wave modulation signal. If the amplitude at the negative step exceeds the pre-defined threshold value, an exponential decay signal is recorded to fit the cavity decay time. The reflectivity of the cavity mirror is determined statistically to be 99.9907±0.0002% and 99.9899±0.0004% with threshold values of 350mV and 50mV, respectively. All reflectivities measured at six cavity lengths with a higher threshold are more precise than that measured with the lower threshold. A method to determine the threshold value is proposed for accurate high reflectivity measurement.

Date Published: 20 May 2009
PDF: 6 pages
Proc. SPIE 7283, 4th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment, 72830U (20 May 2009); doi: 10.1117/12.828618

Published in SPIE Proceedings Vol. 7283:
4th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment
Yudong Zhang; James C. Wyant; Robert A. Smythe; Hexin Wang, Editor(s)