Ichiro Fujima

High-resolution distance meter using optical intensity modulation at 28 GHz

A high-resolution distance meter was fabricated using optical waveguide modulators. An optical intensity modulation frequency of 28 GHz was utilized for the displacement measurement when the driving frequencies to the optical modulators were around 14 GHz. The distance meter was evaluated in the National Research Laboratory of Metrology (NRLM) tunnel, which is a semi-underground tunnel. The measurement resolution is 1 and for a distance of 5 and 100 m, respectively, in one standard deviation after correction of the cyclic error. Furthermore, cyclic errors are examined for 28 GHz optical intensity modulation.

A two-color heterodyne interferometer for measuring the refractive index of air using an optical diffraction grating

A new two-color heterodyne interferometer using an optical grating was proposed for measuring the refractive index of air. The heterodyne modulation is realized by moving the diffraction grating. The method allows us to measure the refractive index with high accuracy by using a 1:06 lm YAG laser and its second-harmonic wave because two beams (the fundamental and the second-harmonic wave) are in common path completely. Moreover, good signal-to-noise ratio (SNR) can be obtained by the heterodyne interference. Using the refractive index calculated by Edl e equation as a reference, that measured by present method was experimentally evaluated having an accuracy of about 1 � 10 � 6 within a distance of 100 mm. 2002 Elsevier Science B.V. All rights reserved.

Laser interferometer for calibration of a line scale module with analog output

NMIJ line standard interferometer has been modified for measurement of a linear scale module with analog output. The interferometer was developed for line standard calibration. The light source is a stabilized He-Ne laser. Before the modification, a line standard can be calibrated with an uncertainty of about 0.2 micrometer for the total length of 500 mm (k=2). After the modification, a linear scale module can be calibrated as well as a line standard. A linear scale is set in a support on a moving carriage. The displacement of the moving carriage is measured by the interferometer with a sampling frequency of 30 kHz to 300 kHz while the electronic output of the linear scale module is sampled with the same timing. The analog output of the line scale module is used instead of digital output because it is important to assure the simultaneous sampling of the displacement and the scale output.

APMP.L-K1: Calibration of gauge blocks by interferometry: Final Report

The results of the APMP key comparison on calibration of gauge blocks by interferometry (APMP.L-K1) are reported. The comparison involved the measurement, by ten participating institutes, of eight steel gauge blocks and ten ceramic gauge blocks ranging from 0.5 mm to 100 mm in length using techniques based on interferometry. The results are analysed using En values with weighted mean values as the reference values. Some measurement results had to be excluded by application of the En-criterion for the steel and ceramic gauges. Investigations of the reasons for the deviations have already been started by the respective institutes, including follow-up gauge block comparison, APMP.L-K1.1 with the same pilot laboratory as APMP.L-K1. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Precise measurement of the difference of the air-refractive indices between visible and near-infrared wavelengths using two-color interferometer

Optical measurement technique is widely used in length measurement, such as laser interferometers and electronic distance meters. The correction of air refractive index is necessary because the optical path length should be converted to the geometrical length in most vases. In order to obtain an average refractive index through the optical path, Edlens formulae have been widely used with environmental measurements of air temperature, pressure, humidity and carbon dioxide concentration. In recent days, more precise formulae for calculating a refractive index of air have been desired in IR region. However, the measurement accuracy for near IR region is not sufficient.

High-resolution distance meter using optical modulators at 3.5 GHz

A high resolution distance meter has been made using optical wave-guide modulators. The modulation frequencies for the optical modulators are around 3.5 GHz, while the modulation frequencies of optical intensity are around 7 GHz because the modulation bias voltages are set to peak points of the electro-optic characteristic. The distance meter was evaluated in the NRLM tunnel. The measurement resolution is 15 micrometers of a standard deviation for a distance range of 0.5 m to 5 m after a correction of a cyclic error.

Ghz Traveling-Wave Optical Modulator For Precision Distance Measurement

Traveling-wave type optical modulators using LiTa03 crystals have been designed and fabricated for high resolution distance measurement. The modulation property of the modulator is characterized at GHz frequencies. The distance measuring-system is constructed using two of these optical modulators and is preliminarily tested. The modulators were driven by slightly different frequencies in the GHz region in order to measure the phase of the modulated signal using the heterodyne method. The displacement of a target was measured with a resolution of 15pm and with a linearity of 0.2%.

Measurements of long gauge blocks using a fringe-counting interferometer and subgauge blocks with lines

A new method for measuring long gauge blocks using a fringe-counting interferometer with a 633 nm wavelength-stabilized He-Ne laser is described. Two subgauge blocks, which have V-type graduation lines covered with glass plates, are optically contacted with both sides of a long gauge block. They are handled with bare hands and the surfaces of the glass plates are wiped with a paper towel after the optical wringing procedure. Using the National Research Laboratory of Metrology 2 m line standard automatic measuring machine, several gauge blocks up to 1 m long are measured with a repeatability less than 0,1 µm in standard deviation. A comparison between the lengths of gauge blocks measured by the new method and by the conventional excess fractions method is made. The results show that the length of gauge blocks up to 1 m can be determined with an expanded uncertainty U = 0,3 µm, corresponding to a level of confidence of about 95 %.

Correction of cyclic error in optical waveguide distance meter

Sinusoidal modulation method is utilized in optical distance meters. In this method, the phase delay of the returned beam is measured with high resolution. One of the dominant error factors in the phase measurement is cyclic error. We have already reported on a cyclic error compensation of an optical waveguide distance meter using a preliminary phase measurement with mechanical displacement. In this paper, a new technique of the cyclic error compensation is described, which is based on the modulation frequency scanning of the waveguide distance meter around 14 GHz. We have compared two types of cyclic error curves; one was obtained from the data during the displacement of the target and the other was obtained from the data during the scanning of the modulation frequency. The curve fitting technique was used to determine the amplitude and the phase of the cyclic error component for the two curves. We have obtained almost the same values for both parameters of the amplitude and the phase for the two cyclic error curves. Therefore, the cyclic error curve obtained from the data of frequency scanning can be utilized for the cyclic error compensation instead of the displacement of the target.

Outdoor laser-tracking system

A laser tracking system has been developed to trace a moving target for outdoor measurements of 3D position. Beam direction of a 670 nm laser diode is controlled with two mirrors mounted on Galvano scanners, for horizontal ((phi) ) and vertical ((theta) ) directions, respectively, in order to trace a target made of reflection sheet. The beam reflected by a the target is detected at a quadrant photodiode to estimate the position of the target. The distance D between the apparatus and the target was measured with a range finder of 830 nm LED, the light beam from which is superposed on the beam for tracking by a beam combiner. Finally 3D position of the target is estimated from two azimuth angles of the 2 scanners and the measured distance. The whole system was set on a crane to measure the position of a weight suspended by the cranes arm. Up to about 100 m, this system traced the target and detected the distance. The 3D position of the target is measured with a resolution of 10 mm.