Design considerations and experimental investigations on fiber ball lens systems for optical metrology

Abstract

Optical fibers play an important role in general and, in particular, in the field of sensors. As part of a sensor system, quite often fibers are coupled by a ball lens. For efficient usage, the fiber ball lens systems (FBLSs) have to be optimized. The present work presents analytic expressions for the design parameters of such systems. FBLSs comprise sections of a single-mode optical fiber, a coreless fiber (CLF) and a ball lens. Their geometric dimensions have to be optimized for their use in different applications in optical metrology. The derived expressions facilitate the optimum parameter choice, which is usually done by expensive numerical simulations. For comparison and validation of the results by experiments, FBLSs with different ball lens radii and CLF sections have been prepared by a fusion splicer technique. Their characteristics were investigated in the optical spectral ranges at 630 nm and 1550 nm. Experimental methods comprising far-field, near-field and reflection/transmission measurements with optical fibers validate the theoretical considerations. To our knowledge, this is the first time that simple analytic approaches have been applied to the fabrication of FBLSs. This facilitates and quickens their general design for different applications in optical metrology significantly.

Keywords

• fiber optical sensor
• optical fiber probe
• fiber design and fabrication
• optical fiber sensing and imaging
• optical fiber coupling