Localized fluid flow measurements with an He-Ne laser spectrometer

A novel approach for remotely sensing mechanical cardiovascular activity for use as a biometric marker is proposed. Laser Doppler Vibrometry (LDV) is employed to sense vibrations on the surface of the skin above the carotid artery related to arterial wall movements associated with the central blood pressure pulse. Carotid LDV signals are recorded using noncontact methods and the resulting unobtrusiveness is a major benefit of this technique. Several recognition methods are proposed that use the temporal and/or spectral information in the signal to assess biometric performance both on an intrasession basis, and on an intersession basis where LDV measurements were acquired from the same subjects after delays ranging from one week to six months. A waveform decomposition method that utilizes principal component analysis is used to model the signal in the time domain. Authentication testing for this approach produces an equal-error rate of 0.5% for intrasession testing. However, performance degrades substantially for intersession testing, requiring a more robust approach to modeling. Improved performance is obtained using techniques based on time-frequency decomposition, incorporating a method for extracting informative components. Biometric fusion methods including data fusion and information fusion are applied to train models using data from multiple sessions. As currently implemented, this approach yields an intersession equal-error rate of 6.3%.

Laser Doppler Vibrometry Measures of Physiological Function: Evaluation of Biometric Capabilities

In this paper we present our experimental studies on controlling the amplified spontaneous emission (ASE) from Yb3+ ions in Er/Yb co-doped fiber amplifiers. We propose a new method of controlling the Yb-ASE by stimulating a laser emission at 1064 nm in the amplifier, by providing a positive 1 μm signal feedback loop. The results are discussed and compared to a conventional amplifier setup without 1 μm ASE control and to an amplifier with auxiliary 1064 nm seeding. We have shown, that applying a 1064 nm signal loop in an Er/Yb amplifier can increase the output power at 1550 nm and provide stable operation without parasitic lasing at 1 μm.

Controlling the 1 μm spontaneous emission in Er/Yb co-doped fiber amplifiers

This paper describes a digital holographic setup based on in-line holography and a high-speed recording to get a multipoint vibrometer. The use of a high-speed sensor leads to specificities that enable the in-line configuration to be used. The case of transient vibrations is investigated through a full simulation of the holographic process. The simulation shows that the first instants are critical since distortion may occur, resulting in errors in the phase measurement. Experimental results are provided by exciting an aluminum beam with a transient signal. A comparison with the velocity measured by a pointwise vibrometer is provided. Frequency response functions are extracted and the experimental results confirm the ability of the method to provide full-field contactless measurements at the high-speed time scale evolution of the vibration.

Multi-point vibrometer based on high-speed digital in-line holography

Crack identification in composite elements with non-linear geometry using spatial wavelet transform

Laser Doppler vibrometer (LDV) has a potential application prospect in remote sensing. Based on the correlation theories of heterodyne detection, a LDV system with a configuration of all fiber and heterodyne techniques is developed to detect the sound signal through the vibration of glass. Experimental results show that the LDV system has an ability to acquire the real-time speech signal 25 m away through glass. While, the system signal-to-noise ratio (SNR) value decreases with the increase of the glass thickness and the detection distance.

Laser Doppler vibrometer for real-time speech-signal acquirement

A multiplex parallel data acquisition system based on a field programmable gate array is composed of a simulated modulation module, an ADC module, a power module, a press key, USB, an FPGA chip, JTAG, EPCS, an SDRAM memory, an SRAM memory, a Flash memory and an upper computer. The USB realizes the communication between the FPGA chip and the upper computer. The peripheral equipment of the SDRAM memory, the JTAG and the EPCS are respectively connected to an Avalon bus inside the FPGA chip through respective control core and the SRAM memory and the Flash memory are connected to the Avalon bus through a tristate bus line; and the power module supplies power to all the devices above. The system effectively solves the contradiction that CPU resources are occupied for long time in ADC conversion and processing process, and is characterized by simple structure and rapid data reading and storage.

Multipath paralleling data acquisition system based on on-site programmable gate array

In this paper, a 1550 nm all fiber monostatic laser range finder system based on linear chirp modulation and heterodyne detection is presented. The fiber end face signal is used as a range starting indicator. The transmitted laser power is 5 mW with a laser pulse length of 131 micros and a linear chirp bandwidth of 40 MHz. The telescope with an aperture of 3 cm couples the return light into a single mode fiber. Better than 14 cm distance accuracy and 26 dB SNR can be achieved for a wood target at a distance of about 43 m by using the above system setup. Several experiments with different system parameters are conducted. The system performance is tested under variable laser pulse length, linear chirp bandwidth, local oscillator power, and background noise. Finally, an application of the linear chirp modulation heterodyne laser range finder in a spaceborne ranging system is proposed.

Experimental study on the 1550 nm all fiber heterodyne laser range finder.

The invention discloses an underwater acoustic signal sensing method and device through coherent laser remote-sensing detector, which comprises the following steps: dividing the single-frequency laser into detecting light and reference light; transmitting the detected light to the water surface through optical heterodyne; vibrating the water surface through acoustic wave from underwater element; making the frequency and strength of underwater acoustic wave consistent with the vibrating frequency and amplitude; modulating frequency of reflective light of water surface through forced vibrating speed; interfering the reflective light and reference light detected by photoelectric detector; modulating the vibrating speed of water surface through electric heterodyne modulator; obtaining the waveshape of the underwater acoustic wave; realizing the detection of the underwater acoustic signal. The invention has high sensitivity, far distant measurement, flexible optical path and reliable structure, which is easy to modulate.

Method and device for detecting underwater acoustic signal with coherent laser remote sense

A 1550-nm all-fiber monostatic lidar system based on linear chirp amplitude modulation and heterodyne detection for the measurements of range and velocity is presented. The signal processing method is given, after which the relationship between the peak frequency values in the final signal spectrum, the target's range, and the line-of-sight velocity is obtained in the presence of the fiber end-face-reflected signal plaguing many monostatic lidar systems. The range of an electric fan as well as the line-of-sight fan speed of different levels is tested. This proposed system has a potential application for the space-borne landing system.

Jianhua Shang

Papers

Laser Doppler vibrometer for real-time speech-signal acquirement

Multipath paralleling data acquisition system based on on-site programmable gate array

Experimental study on the 1550 nm all fiber heterodyne laser range finder.

Method and device for detecting underwater acoustic signal with coherent laser remote sense

Development of an all-fiber heterodyne lidar for range and velocity measurements