Risto A. Myllylae

Binary logic operations using a beam-scanning laser diode

A beam-scanning binary logic (BSBL) and its implementation using a beam-scanning laser diode (BSLD) are proposed. The BSBL is categorized as spatial coding information processing, which operates with spatially coded light signals. A basic BSBL unit consists of two photodetectors, two amplifiers, a light source, and a beam scanner. A unit with three output photodetectors can execute eight types of binary two-inputs/one-output optical logic operations with small modifications: FALSE, AND, XOR, OR, NOR, XNOR, NAND, and TRUE.

Comparison of continuous-wave and pulsed time-of-flight laser range-finding techniques

Time-of-flight laser rangefinders based on the propagation speed of light and direct detection may be roughly divided into two classes depending on whether their light emission is continuous or pulsed. In the modulated continuous wave (CW) rangefinding technique an amplitude modulated light carrier is emitted and the distance information is extracted from the received signal by comparing its modulation phase to that of the emitted signal. In the pulsed time-of-flight (TOF) rangefinding method the distance is obtained by measuring the time interval between the transmitted and received light pulses. A comparison is made in this paper between the TOF and CW techniques in terms of the range measurement resolution achievable. The basis for comparison is that the actual measurement or averaging time is the same with both techniques. Comparison is made in the case where the average optical power level used is the same and also in that in which an unambiguous measurement distance is set for both techniques. With an equal average optical power level and a noise contribution dominated by the signal itself, it is shown that the ratio of achievable range resolution between the TOF and CW techniques is directly proportional to the ratio of the modulation frequency of the CW method to the receiver bandwidth of the TOF method. When the average optical power level is reduced and the photon-noise limited condition is not achieved, the TOF mode rangefinder gains an advantage over the CW mode because the resolution is directly proportional to the optical power level and the available energy in the TOF technique can be concentrated at the moment of timing. This enables a TOF rangefinder to be much faster than a similar CW rangefinder in many practical applications.

Laser radar-based measuring systems for large scale assembly applications

Long term research on pulsed time-of-flight laser distance measurement has opened new dimensions in measurement applications, from large scale assembly in shipbuilding to precast concrete element production, leading to improved quality control and more efficient manufacturing. The ACMAN 3-D coordinate meters measure the coordinate values of a point in terms of radial distance and two angles directly from natural surfaces. The accuracy of coordinate values is 1 mm (1-sigma) in the measurement range of 3 - 30 m. The functions of the automatic ACMAN 200 include pointing with a red beam, automatic searching and measuring of marked target points and shape measurement by scanning. Coaxial optics of measuring, pointing and aiming provide the optimal measurement geometry. ACMAN 3-D coordinate meters are integrated into the ACMAN 1000 and ACMAN 2000 series dimension control systems.

Photoacoustic determination of glucose concentration in whole blood by a near-infrared laser diode

The near-infrared photoacoustic technique is recognized as a potential method for the non-invasive determination of human glucose, because near-infrared light can incident a few millimeters into human tissue, where it produces an acoustic wave capable of carrying information about the composition of the tissue. This paper demonstrates a photoacoustic glucose measurement in a blood sample as a step toward a non-invasive measurement. The experimental apparatus consists of a near-infrared laser diode operating with 4 micro joules pulse energy at 905 nm, a roller pump connected to a silicon plastic tube and a cuvette for circulating the blood sample. In addition, the apparatus comprises a PZT piezoelectric transducer integrated with a battery-powered preamplifier to receive the photoacoustic signal. During the experiment, a glucose solution is mixed into a human blood sample to change its concentration. Although the absorption coefficient of glucose is much smaller than that of blood in the near-infrared region, the osmotic and hydrophilic properties of glucose decrease the reduced scattering coefficient of blood caused by the dissolved glucose surrounding the blood cells. This changes the distribution of the absorbed optical energy in blood, which, in turn, produces a change in the photoacoustic signal. Our experiment demonstrates that signal amplitudes in fresh and stored blood samples in crease about 7% and 10%, respectively, when the glucose concentration reaches the upper limit of the physiological region (500 mg/dl).

Two-channel fiber optic skin erythema meter

The skin erythema meter is a fiber optic, dual-wavelength reflectance meter that measures the reflectance of the skin on two wavelengths, one the blood/hemoglobin absorption band (555 nm) and another a reference (660 nm). The instrument consists of a fiber optic sensor head, a microprocessor-based control and analysis unit, and a plotter, and it presents the relation between the measured reflectance results in terms of a reflectance index [R(555 nm):R(660 nm)]. The measurement cycle, including printing, takes 5 s. Stability tests on the erythema meter (constant distance, reference object) showed the standard deviation of the reflectance index to be ± 0.1%, whereas that in repeatability tests was less than ± 0.5% for skin and less than ± 0.2% for paper with handheld positioning and repetition. The dynamic change in the reflectance index was about 30% with strong irritation. Results of various irritation test series on human skin are also presented. Finally, the performance and applicability of the skin erythema meter with respect to allergy test procedures, irritancy testing, and measurement of uv-induced erythema are discussed.

Pulsed time-of-flight laser range-finding techniques for industrial applications

Typical construction and performance data for a pulsed time-of-flight laser rangefinding device intended for industrial measurements is presented. It is shown that by using a laser diode transmitter with a peak power of 5 - 15 W, a measurement range of a few tens of meters can be attained with respect to a noncooperative target. The available single shot resolution reaches mm-level in a fraction of a second. Accuracy depends greatly on the construction and adjustment of the device and levels of better than +/- 3 mm can be achieved in the above measurement range. Various construction details and other factors affecting to the available resolution and accuracy are discussed.

Laser range-finding techniques in the sensing of 3-D objects

Three pulsed time-of--flight laser rangefinders have been developed for studying the measurement of the 3-D shape of large objects. A manually scanned system is suggested for manufacturing accuracy measurement and control for ship block assembly. This system can be used to measure distance, plane regularity, angles, spatial forms etc . , within a range from 3 m to 30 m with mm-level accuracy . The two others are automatically scanning based on galvanometer driven mirrors, and a servo-controlled mechanical scanner. These systems are intended for applications where it is important to be able to gather 3-D data automatically and with high speed. The resolutions are also on the mm-level, but the measurement speed is 10 000 points/s at maximum.

Laser-radar-based three-dimensional sensor for teaching robot paths

Implementation and test results of a 3-D sensor based on time-of-flight (TOF) laser radar are presented. A sensor capable of measuring 3-D positions and orientations in a large working space is used for interactive teaching of robot paths and environments. It consists of a pointing device, a laser rangefinder, and a video tracker. The 3-D position and orientation of the pointer are obtained by measuring the distance from two separate points on the pointer arm to a tracking receiver and by using the tracking-camera image for detecting the angle of the pointer on the plane that is perpendicular to the optical axis of the tracking system. The rangefinder uses a new active target operating principle, including fiber-coupled transmitters attached to the pointer arm. The distance and angle measurement accuracies were measured to be better than ± 5 mm and ± 5 deg in the ranges of 2.3 to 4.7 &mum and ± 40 deg, respectively, using ordinary technology. The operating range is likely to be increased and the accuracy enhanced by using the latest state-of-the-art TOF rangefinding technique.

Fiber optic sensors for traffic monitoring applications

A novel fiber optic sensors for traffic monitoring applications are presented. They are useful for monitoring the traffic entering and leaving guarded areas, counting traffic on public roads as well as in determining lane occupancy at traffic lights. When installing sensor arrays, the sensors may also be used to provide additional information: measure the speed, wheel base of a vehicle and also to determine the number of axles and vehicle type. The sensors are based on optical fiber or cable, installed inside the asphalt layer of the road, to measure compression or vibrations near the road surface. Two sensor principles were used. One based on the microbending effect and another that utilizes the speckle phenomenon. In both cases the whole length of the fiber acts as a sensor. The microbending sensor requires a special fiber and special set-up, whereas in the speckle sensor a standard cable may be used. Both sensor types were tested in field applications where the harsh environment, especially the heat, sets great demands on installation. In these experiments, speed and vehicle type measurements were carried out with good results. In the paper, we will discuss the advantages and disadvantages of both sensor types and present some field test results. We will also show the benefits of these particular fiber optic sensors over traditional sensors.

Imaging lidar for space and industrial applications

A new time-of-flight-based imaging lidar was designed to carry out measurements in the 5 to 100-m range. The concept of the device, along with an illustration of the design of a time-to-digital converter for parallel time interval measurements and a presentation of our sensor breadboard is described. Test results showing sensor performance are also presented and discussed. This lidar can be used for shape and profile measurements in space and industrial applications.