High-speed optical coherence domain reflectometry.

Optical coherence domain reflectometry (OCDR) has emerged as an attractive method for obtaining high-spatial-resolution (<10 Am) reflectance measurements of fiber-optic, integrated-optic, and biological structures.` 8 Most previous OCDR systems have achieved high sensitivity and dynamic range by using narrow-band heterodyne detection by piezoelectric path-length modulation and lock-in amplifier techniques. For many applications, present techniques are unacceptably slow. High speed is essential for applications to biological and medical diagnostics, where measurements must be performed rapidly compared with movement of a living subject. Speed is also important for process or assembly line diagnostics, as well as in any application that requires high data acquisition rates. By using a high-speed linear translation stage, OCDR measurements can be performed at high speeds with significant simplifications in system design. In this Letter we demonstrate a new OCDR technique for high-speed optical ranging measurements. Speeds approaching 40 mm/s with a dynamic range of >90 dB and a resolution of -17 ,4m are achieved. The basic schematic of the OCDR setup is shown in Fig. 1. A broadband light source such as a superluminescent diode (SLD) is coupled to a fiber-optic Michelson interferometer. One arm of the interferometer leads to the sample of interest, and the other leads to a reference mirror. Fiber-optic and integrated-optic samples can be directly attached to the sample arm fiber. For bulk-optical or biological samples, a probe module is used to direct the beam onto the sample and to collect the reflected signal. To aid in sample alignment, we use a fiber-coupled visible aiming laser. The reflected light beams are detected at the photodetector. They coherently interfere only when the sample and the reference path lengths are equal to within the source coherence length. Heterodyne detection is performed by takin vivo and the characterization of reflections and