Detector zeroes in on front surface

Nov. 1, 2001
TOKYO—Engineers at Olympus Optical Co. Ltd have developed a near-infrared (near-IR) spectral reflectance detector that can be used to directly measure the surface reflectance of near-IR optical devices typically used in optical communications applications.
JAPANWATCH

Incorporating news from O plus E magazine, Tokyo

TOKYO—Engineers at Olympus Optical Co. Ltd have developed a near-infrared (near-IR) spectral reflectance detector that can be used to directly measure the surface reflectance of near-IR optical devices typically used in optical communications applications.

Annular illumination allows the reflectance of the front surface of a small optical element to be measured without interference from rear reflections. An aperture blocks the unwanted rear reflection.
Click here to enlarge image

This detector is a tabletop model and can make measurements directly using a 50-µm spot. Therefore, it can detect the quality of curved and flat surfaces of optical devices such as lenses, filters, and mirrors that have an outer diameter of 1 to 2 mm. The device covers the near-IR range from 1050 to 1650 nm, thus making possible spectral reflectance measurements in the important 1.3- to 1.55-µm range.

By using an optical system with a donut-shaped (annular) illuminating light source, the influence of reflections from the rear surface of an object to be measured can be reduced. The annular illumination causes light reflected from the object to enter the sensor opening while causing light that is reflected off the rear surface to be deflected away from the opening (see figure). This is due to differences in the position of the foci from the two surfaces.

The apparatus is primarily intended for use in evaluating the antireflection coatings of ball lenses, nonspherical lenses, and other lenses, as well as the spectral reflectance of mirrors and filters.

Courtesy O plus E magazine, Tokyo

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