26 August 2005 High accuracy optoelectronic control system for near field characterization of millimeter long wave guiding structures
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Abstract
We report on a new high accuracy home-made sample holder for near field characterization of millimeter long wave guiding structures (Y junction, Multi Modes Interference coupler). The principle of near field characterization is based on an atomic force microscopy tip that is brought to the surface of the sample (in the near field zone) in order to coupled out a small amount of the light confined inside the wave guiding structures. Due to the size of the components, scans as long as a few millimeters are required to get an entire optical mapping of the structure [1]. With the commonly available equipments such a scan is performed by acquiring step by step more than 100 images for a 2 mm scan. The overlapping of the different images is time consuming and unsatisfactory unless a numerical stitching procedure based on topographical details is used. Effective refractive indexes are typically determined with a precision of 10-3 which could be further improved by increasing the millimeter scan resolution. The reason why successive images do not overlap is mainly due to the mechanical system supporting the sample. Actually, the nonlinearity of the actuator and the thermal expansion of the mechanical part prevent us to reach nanometric scale of repeatability on the positioning for micrometric range of displacements. In order to enable long range scans with nanometric repeatability and accuracy, we develop a specific mechanical system controlled by a heterodyne interferometric apparatus and a home-made high frequency electronic board [2]. The position of the sample is measured in real time with a resolution of 0.3 nm. The servo-loop allows to control the position of the sample with a repeatability of 1 nm (1σ) for a displacement of 1 mm. Furthermore our method is insensitive to the nonlinearity of the actuator.
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L. Chassagne, S. Topcu, Y. Alayli, P. Juncar, G. Lerondel, S. Blaize, A. Bruyant, I. Stefanon, and P. Royer "High accuracy optoelectronic control system for near field characterization of millimeter long wave guiding structures", Proc. SPIE 5858, Nano- and Micro-Metrology, 585806 (26 August 2005); doi: 10.1117/12.611900; https://doi.org/10.1117/12.611900
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