Optical low coherence interferometers (OLCI's) are useful for absolute measurements of thickness and refractive index of optical samples, and characterizations of optical waveguides and fibers such as distributed measurements of backscattering and mode coupling coefficients.
We constructed an OLCI with a SuperLuminescent Diode (SLD) as a broadband source and a single-mode fiber Michelson interferometer. The spectrum of SLD was centered at 824 nm with 20.6-nm width. Optical path-length scan was provided by a moving retro-reflector with a maximum scan range of 40 cm and a resolution of 0.4㎛.
Using the OLCI, we simultaneously measured the thickness and group index of a fused quartz block. The measured thickness and group index were 6.38±0.06 mm and 1.463±0.008, respectively, which agreed well with actual values of 6.37 mm and 1.466. From the 4% reflection on the surface of the block, the minimum reflection sensitivity of OLCI was determined to be -67dB. We also applied the OLCI to distributed measurements of polarizaztion cross-coupling points in a polarization maintaining fiber spool of 129.4-m long. The minimum detectable crosstalk was -79dB. The spool length could be accurately determined to be 129±2.6 m by using the OLCI.
