Hirofumi Yoshida

Bio: Hirofumi Yoshida is an academic researcher from Shizuoka University. The author has contributed to research in topics: Signal & Optical fiber. The author has an hindex of 15, co-authored 124 publications receiving 1001 citations. Previous affiliations of Hirofumi Yoshida include Chiba Institute of Technology.

Compact and high-precision range finder with wide dynamic range and its application

Abstract: Described is a new range finder using a self-mixing laser diode (SM-LD). The range finder has a high accuracy of +or-0.15% and a wide dynamic range of 0.2-1 m using only one sensor head. Compared to ultrasonic range finders, the light beam of this laser range finder can be focused and scanned. The feasibility study shows a possible application of the range finder to a visual sensor of a robot. The proposed range finder has been successfully applied as an infrared (IR) active type range finder of a single-lens reflex camera. >

Laser speckle velocimeter using self-mixing laser diode

Abstract: We have built a novel laser speckle velocimeter using a self-mixing laser diode (SM-LD). The speckle signal obtained by the measurement system has a waveform independent of the target velocity when the same path on the target surface is iteratively measured. The mean frequency of the speckle signal is directly proportional to the target velocity when the laser beam spot diameter is kept constant, and greater than 0.36 mm. The mean speckle signal frequency is automatically measured by using a computer. Its measurement error is inversely proportional to the scanned length, and is 2% for 100 mm. It is possible to detect velocity of the target transversely moving across the laser light beam using this compact measuring system.

Self-mixing laser speckle velocimeter for blood flow measurement

Abstract: A velocimeter using speckle phenomena in self-mixing laser diodes (SM-LDs) is used to evaluate the blood flow noninvasively. The mean frequency of the speckle signal obtained from the self-mixing laser diode reflects the activity of the blood flow in a certain probing area. The experimental results show that this new type of speckle velocimeter can be useful for the relative evaluation of blood flow in human tissues.

Compact and versatile self-mixing type semiconductor laser Doppler velocimeters with direction-discrimination circuit

Abstract: A compact vector-velocimeter is described which uses a self-mixing type laser Doppler velocimeter (SM-LDV). It electrically identifies features of the sawtooth-like Doppler beat signal waveform to determine the direction of target motion within a velocity range of 23 mm/s-23 m/s. The range of velocity measured is 0.2 mm/s-34 m/s. The measured vector velocity of a reciprocally moving target as well as a rotating target agrees well with the theoretical value. >

Microprocessor control signal transmission through optical fiber

Abstract: The authors describe an optical fiber control signal transmission system in which multiples frequency signals are used as an 8b control signal for a CPU control system consisting of Z80 data processors, motion control devices, and position sensors. Four control terminals are connected to the control center. Motion control devices are connected to the data processor installed in each control terminal. Frequencies at 100 kHz, 200 kHz, 300 kHz, and 400 kHz are used as series signals to specify the current operating states of the motion control devices, and the frequencies at 500 kHz, 600 kHz, 700 kHz, and 800 kHz are used as parallel signals to specify the four control terminals. The initial step in implementing the transmission system, including the function of the control bus and the configuration of the transmission system for the 8b parallel control signals, is discussed. >

Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging

Abstract: Laser Doppler velocimetry uses the frequency shift produced by the Doppler effect to measure velocity. It can be used to monitor blood flow or other tissue movement in the body. Laser speckle is a random interference effect that gives a grainy appearance to objects illuminated by laser light. If the object consists of individual moving scatterers (such as blood cells), the speckle pattern fluctuates. These fluctuations provide information about the velocity distribution of the scatterers. It can be shown that the speckle and Doppler approaches are different ways of looking at the same phenomenon. Both these techniques measure at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. This has been done for both time-varying speckle and laser Doppler. However, with the speckle technique it is also possible to devise a full-field technique that gives an instantaneous map of velocities in real time. This review article presents the theory and practice of these techniques using a tutorial approach and compares the relative merits of the scanning and full-field approaches to velocity map imaging. The article concludes with a review of reported applications of these techniques to blood perfusion mapping and imaging.

Laser diode self-mixing technique for sensing applications

Abstract: The laser diode self-mixing (or feedback) interferometric technique is reviewed as a general tool for remote sensing applications. The operating principle is outlined, and the attainable performance is compared to conventional coherent detection. Applications to metrology and to new sensing schemes are described, experimental results are reported and the overall performance of the sensors are assessed.

Laser diode feedback interferometer for measurement of displacements without ambiguity

Abstract: We report what, to our knowledge, is the first example of laser feedback interferometer capable of measuring displacements of arbitrary form using a single interferometric channel. With a GaAlAs laser diode we can measure 1.2-m displacements, with interferometric resolution, simply by means of the backreflection from the surface (reflective or diffusive) under test. The operation is performed at moderate (i.e., not very weak) levels of feedback, such that a two-level hysteresis is found in the amplitude modulated signal. This is shown to allow the recovery of displacement without sign ambiguity from a single interferometric signal. Experimental results are reported, which are found to be in good agreement with the underlying theory. Performances of the developed feedback interferometer are finally presented. >

Laser feedback interferometry: a tutorial on the self-mixing effect for coherent sensing

Abstract: This tutorial presents a guided tour of laser feedback interferometry, from its origin and early development through its implementation to a slew of sensing applications, including displacement, distance, velocity, flow, refractive index, and laser linewidth measurement Along the way, we provide a step-by-step derivation of the basic rate equations for a laser experiencing optical feedback starting from the standard Lang and Kobayashi model and detail their subsequent reduction in steady state to the excess-phase equation We construct a simple framework for interferometric sensing applications built around the laser under optical feedback and illustrate how this results in a series of straightforward models for many signals arising in laser feedback interferometry Finally, we indicate promising directions for future work that harnesses the self-mixing effect for sensing applications

Global network computers

Abstract: This invention generally relates to one or more computer networks having computers like personal computers or network servers with microprocessors linked by broadband transmission means and having hardware, software, firmware, and other means such that at least one parallel processing operation occurs that involve at least two computers in the network. More particularly, this invention relates to one or more large networks composed of smaller networks and large numbers of computers connected, like the Internet, wherein more than one separate parallel processing operation involving more than one different set of computers occurs simultaneously and wherein ongoing processing linkages can be established between virtually any microprocessors of separate computers connected to the network. Still more particularly, this invention relates to business arrangements enabling the shared used of network microprocessors for parallel and other processing, wherein personal computer owners provide microprocessor processing power to a network, preferably for parallel processing, in exchange for network linkage to other personal and other computers supplied by network providers, including linkage to other microprocessors for parallel or other processing; the basis of the exchange between owners and providers being whatever terms to which the parties agree, subject to governing laws, regulations, or rules, including payment from either party to the other based on periodic measurement of net use or provision of processing power.