Shigenobu Shinohara

Laser Doppler velocimeter using the self-mixing effect of a semiconductor laser diode

A laser Doppler velocimeter (LDV) using a semiconductor laser diode (LD) with its self-mixing effect has been developed. A Doppler signal, caused by mixing a returned wave with an originally existing wave inside the LD, is detected with a photodetector in the LD package; it is also picked up from the variation of the LD driving voltage. When the returned light is weak enough, it confirms that there is no change in the single-mode oscillation and its spectral width of the LD. A LDV of this type is compact enough for many applications.

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

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

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

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.

Microprocessor control signal transmission through optical fiber

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.<<ETX>>

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

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. >

A Comparative Study for the Assessment on Blood Flow Measurement Using Self-Mixing Laser Speckle Interferometer

We study a self-mixing laser diode (SM-LD) as a low-cost compact optical sensor for noninvasive blood flow measurement over the surface of the skin. We compare the SM-LD system with a commercially available Doppler flowmeter to assess the accuracy and feasibility of the SM-LD sensors for such applications. For the SM-LD flowmeter, we apply two different signal processing methods: (1) the counting method, i.e., counting the intensity fluctuations of the signal to obtain a frequency value, and (2) the autocorrelation method, i.e., measuring the autocorrelation time of the signal. In vitro measurements show good agreement with the commercially available flowmeter. In vivo measurements performed on test subjects revealed that the autocorrelation technique shows much better results. The results of in vitro and in vivo studies and the comparison with the commercial flowmeter confirm the applicability of the SM-LD flowmeter.

Noninvasive blood flow measurement using speckle signals from a self-mixing laser diode: in vitro and in vivo experiments

A semiconductor laser speckle velocimeter that uses the self- mixing effect is studied for noninvasive relative blood flow measure- ments. The random modulation of intensity and spectra of the laser di- ode caused by the backcoupling of the scattered light from the red blood cells into the laser cavity is detected as a speckle signal with a photodi- ode inside the laser package. The autocorrelation of this self-mixing speckle signal gives information on the flow velocity of the blood. The proposed method is elucidated with in vitro and in vivo experiments. The results of these measurements are given together with a discussion of dependence of speckle signal of a self-mixing laser diode (SMLD) on various parameters such as velocity, hematocrit level of blood, and back- ground reflectance of blood suspension.

Compact optical instrument for surface classification using self-mixing interference in a laser diode

A compact and noncontact sensor using the self-mixing interference inside a semiconductor laser is designed to classify moving surfaces. An artificial neural network is employed for the data processing. The results indicate more than 92% correct classification for eight different surfaces of different materials, different manufacturing methods and different surface roughnesses. The accuracy of the system is restricted by the localized irregularities on the surface and the mechanical instabilities of the carrying stage over which the surfaces are placed.

Addressed audio and video signal transmission through optical fibers

Describes an addressed audio and video signal transmission system in which audio and video signals together with their address consisting of up to 8 frequencies can simultaneously be sent from the sender to the designated receivers through the optical fibers. The received audio signal covered the frequency range of 10 Hz to 20 kHz with a distortion factor of less than 0.5% and with an SNR of 60 dB (62 dB without addresses). The received video signal covered the frequency range of 100 Hz to 4.2 MHz with a differential gain (DG) of less than 1.0% and with a differential phase (DP) of less than 2.5 degrees. >