Abstracts

Brillouin fibre-optic gyro with directional sensitivity

Yosuke Tanaka’, Shigejiimi Yamasaki*, Kazuo Hotate’

‘Research Center for Advanced Science and Technology, The University of Tokyo *Opto-electronics Laboratory, Fujikura Ltd

17th Meeting on Lightwave Sensing Technology

The Brillouin fibre-optic gyro is a solid-state laser gyro, made of a fibre ring-resonator with high finesse. It utilizes the counter- propagating lasing of Stokes beams independently produced in the ring-resonator by the stimulated Brillouin scattering process. Accord- ing to the Sagnac effect, the frequency difference between the counter- propagating Stokes beams shows the rotation rate applied to the ring- resonator. The absolute value of this frequency difference is directly obtained as a beat note by coherently combining those two beams. However, the information on the positive or negative is lost in the process, which means no information on the rotation direction. To overcome this problem, we propose a new scheme based on the phase diversity detection, which gives a set of two beat notes with orthogonal polarization. From the phase difference between the beat notes, the rotation direction is easily recognized as well as its rate. Although the demonstrated experimental set-up includes bulk-optic components, they can be replaced by fibre-optic or integrated optic ones.

Measurement of the thickness and refractive indices of multiple layers by a confocal interference microscope using a low coherence source

Taskashi Fukano’, Ichirou Yamaguchi’

‘Optical Engineering Laboratory, The Institute of Physical and Chemical Research (RIKEN), 2-l Hirosawa, Wako City, Saitama, 351 l-01, Japan *Graduate School of Science, Science University of Tokyo (SUT), 1-2, Kagurazaka, Shinjiku-ku, Tokyo, 162, Japan

17th Meeting on Lightwave Sensing Technology

We propose a novel technique for simultaneous measurement of layer thickness and refractive indices of multiple layers. It is based on a combination of a confocal microscope and low coherence interfero- metry. We derive an expression for geometrical thickness and refractive indices of each layer by both tracing a marginal ray accepted by a microscope objective and optical path matching conditions. Experimental verification of this method is presented by several samples having 13 layers maximum. The geometrical thickness and refractive indices derived agree well with those measured by a micrometer or those cited from literature.

Simultaneous measurement of refractive index and thickness of transparent plates by low coherence interferometry: measure- ment principle and experimental verification

Hideyuki Tajiri’, Takehisa Shiraishi’, Masato Ohmi’.

Masamitsu Haruna’

‘Faculty of Medicine, Osaka Unversity, ’ Faculty of Engineering, Osaka University, l-20, Machikaneyama, Toyo- naka, Osaka 560, Japan

17th Meeting on Lightwave Sensing Technology

We recently proposed and demonstrated a novel technique for simultaneous measurement of the refractive index n and thickness t of transparent plates used as a measured object by low coherence interferometry, in which either a measured object or a focusing lens is scanned with a precise translation stage. An illuminating light is focused on the front and rear plane of the object by moving the object

(or lens). The moving distance and the corresponding optical path difference yield desirable values of n and c with short calculation. The measurement accuracy of ,< 0.1% is essentially obtained with 1 urn step-’ stages, when t 2 1 mm. The use of a more precise stage with a 0.1 urn step-’ should provide an accuracy of 0.1% even if I = 100 urn. The proposed method was experimentally verified using popular optical materials such as quartz, sapphire and so on, where the accuracy of 2 0.3% was achieved for the plate thickness I of nearly 1 mm. Our method is also applicable for determination of the index of biological tissue which can provide basic data in the field of biomedical optics. The measurement principle and the experimental verification are presented, as well as biomedical applications.

Measurement of the distance between cars from a stereo image using liquid crystal displays

Kenichi Sakata, Osami Sasaki, Takamasa Suzuki

Faculty of Engineering, Niigata University, 8050 Ikarashi 2, Niigata 950-21, Japan

17th Meeting on Lightwave Sensing Technology

We propose a new method for detecting the displacement of an object between two different images. These two images are displayed on two liquid crystal displays (LCDs), respectively, which are placed at a constant distance. Several plane waves of different propagating directions are illuminated on to the LCDs. We can obtain the displacement of the object by detecting which plane wave transmitted through the LCDs is strongest. The method is applied to measuring distance between cars from stereo images of the car.

Image processing by artificial retina chips

Kazuo Kyuma

Mitsubishi Electric Corporation, Advanced Technology R&D Center, 8-l-l Tsukaguchi-Honmachi, Amagasaki, Hyogo 661, Japan

17th Meeting on Lightwave Sensing Technology

We have developed a novel type of image sensor called an ‘artificial retina chip’ which combines the functions of a video camera and image processor. The device structure, fundamental performance, operation principle of image sensing/processing, processing functions and applications are described.

Lightwave sensing of a colour image

Satoru Toyooka

Department of Environmental Science and Human Engineer- ing, Saitama University, 225 Shimo-okubo, Urawa, Saitama 338, Japan

17th Meeting on Lightwave Sensing Technology

Colour information provides quality measures in life. Usually, colour analysis is made using a three-dimensional colour coordinate system such as the RGB- and the Lab-models. However, they can represent only the visible wavelength region and there is a problem of metamerism. The spectral representation of colour requires its own colour space and its own technical implementation. In this paper, a subspace method or KL expansion is introduced to colour image analysis, to construct a colour space characteristic of the objective scene. Optical implementations of the inner product of a basis vector and objective spectrum are shown. Spectral reconstruction, classitica- tion and parameter estimation are shown.

Optics & Laser Technology

Vol29 No 2 1997