Hideki Maruyama

Simultaneous measurement of the phase and group indices and the thickness of transparent plates by low-coherence interferometry

We propose and demonstrate a novel technique for simultaneous measurement of the phase index, n(p) , the group index, n(g) , and the thickness, t , of transparent plates by use of a low-coherence interferometer. The output light from a superluminescent diode is focused upon the front plane of a transparent plate that is used as the sample. The sample stage is subsequently moved until the light is focused upon the rear plane of the plate. Measurement of the stage movement distance and the corresponding optical path difference allows us to determine both n(p) and n(g) . By placing the sample between two glass plates, we measured n(p) , n(g) , and t simultaneously, with an error of 0.3% or less, for nearly 1-mm-thick transparent plates, including glass and electro-optic crystals.

Low-coherence interferometer system for the simultaneous measurement of refractive index and thickness

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(p) and group index n(g) can be determined automatically in a wide thickness range of from 10 microm to a few millimeters. Two unique techniques are presented to measure n(p), n(g), and t simultaneously. One allows us to determine n(p), n(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 delta n of index is approximately expressed as a function of (n(p) - 1) on the basis of measured values of n(p) and n(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 microm. The measurement time is also 3 min or more.

TE-TM mode splitter using directional coupling between heterogeneous waveguides in LiNbO/sub 3/

We propose and demonstrate a novel passive TE-TM mode splitter using an anomalous directional coupler consisting of Ti-diffused and annealed, proton-exchanged waveguides in LiNbO/sub 3/. The extraordinary wave was successfully power-transferred to the cross output with the extinction ratio of >12 dB in both X- and Z-cut LiNbO/sub 3/. The ordinary wave experienced no power transfer without any excess loss due to side-way diffusion of Ti or proton. The coupler length was only >

Low coherence interferometry for simultaneous measurement of refractive index and thickness

Low coherence interferometry has been used for optical ranging with an accuracy comparable to the coherence length of the light source of the interferometer. This technique has been extended to optical imaging for clinical diagnosis. Very recently, we developed a practical interferometer system which allowed us to measure automatically the refractive index (n) and thickness (t) in a wide thickness range of 20 /spl mu/m to a few mm. This low coherence interferometer is shown. The light source is a superluminescent diode (SLD) having a coherence length 12 /spl mu/m at the center wavelength of 850 nm. The developed system will be widely used in practice for precise measurement or monitoring of index and thickness of all optical materials including crystals, glass, polymer, epoxy, and so on. In addition, our method is applicable for determination of the refractive index and geometric dimension of biological tissue.

Practical measurement system for determination of refractive index and thickness using low-coherence interferometry

Very recently, we developed a computer-controlled low- coherence interferometer system with precise translation stages for simultaneous measurement of refractive index and thickness. Both phase and group indices can be determined automatically in a wide thickness range of 20 micrometer to a few mm. This paper presents the system configuration and the measurement principle accompanied with typical examples of automatic measurement.