Fogale Nanotech presents the fiber-optic LISE (low-coherence interferometric sensor) as a metrology tool for optics manufacturing.

Applications include the center-thickness measurement of single optical components, and the "global"' on-axis metrology of completely mounted optical systems where all lens thicknesses and airgaps along the optical axis are measured without touching or disassembling the optical system.

The system works as a comparator of optical group delays. The group delay along the optical axis of the probe interferometer arm containing an object -- a lens assembly, for example -- is compared with the group delay of the reference arm containing a movable delay line. The light source is a superluminescent diode emitting at typically 1310 nm with a coherence length of typically 25 µm.

Thanks to the limited temporal coherence of the source, multiple surfaces of the object can be detected during a single scan of the delay line. Measurement ranges are between a few millimeters up to 600 mm (optical thickness). The measurement zone can be placed at a working distance of up to several meters away from the instrument's exit. The absolute accuracy is between +-1 µm (for the standard system) and +-200 nm ( for the second generation, high-accuracy system).

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