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We have developed a low-coherence interferometer system used for the simultaneous measurement of refractive index n and thickness t of transparent plates. Both the phase index [n.sub.p] and group index [n.sub.g] can be determined automatically in a wide thickness range of from 10 [micro]m to a few millimeters. Two unique techniques are presented to measure [n.sub.p], [n.sub.g], and t simultaneously. One allows us to determine [n.sub.p], [n.sub.g], and t accurately by using a special sample holder, in which the measurement accuracy is 0.3% for the thickness t above 0.1 mm. In the other technique the chromatic dispersion 8n of index is approximately expressed as a function of ([n.sub.p] - 1) on the basis of measured values Of [n.sub.p] and [n.sub.g] for a variety of materials, and then the simultaneous measurement is performed with a normal sample holder. In addition, a measurement accuracy of less than 1% is achieved even when the sample is as thin as 20 [micro]m. The measurement time is also 3 rain or more. OCIS codes: 120.3180, 120.4820, 120.5710.

A new laser beam (LB) writing technique that can provide dot lines of a nearly 10-micrometers period in photoresist, with a period fluctuation of less than 4 nm, is proposed and demonstrated. The dot period is also controllable with an accuracy of the order of a nanometer. The so-called LB periodic-dot writing has been successfully applied for definition of interdigital electrodes required for TE-TM mode conversion in Ti:LiNbO3 waveguide wavelength filters, in which the electrode period was nearly 10 micrometers at the center wavelength of the filter around 0.8 micrometer. The fabricated filter with a 5-mm-long LB-written interdigital electrode exhibited a filter bandwidth of 1.1 nm, which was in good agreement with the theoretical value. Eight filters with a period difference of 80 nm were then integrated on a LiNbO3 chip; as a result, the center-wavelength spacing between the adjacent filters was measured to be 5.4 + or - 0.6 nm, as expected. Such fine control of the electrode period has thus become possible by the LB periodic-dot writing that was demonstrated. The writing accuracy is also discussed in detail along with the system description.

We proposed and demonstrated in vitro simultaneous measurement of refractive index and thickness of biological tissue. The technique is based on the low coherence interferometry combined with precise translation stages. Refractive indices were determined with the accuracy of less than 1% for tissue samples of a few hundred micron thickness, including chicken tissue, human tooth and nail. Simultaneous measurement of refractive index and thickness of multilayer tissue are also demonstrated. Index Terms--In vitro measurement, low coherence interferometry, opto-mechatronics, simultaneous measurement of refractive index and thickness.