A calibration system is described for the scanning and staring time-of-flight lidars under development for 3D imaging for autonomous driving and similar applications. These lidars must provide distances to objects in the scene with accuracies of a few centimeters while the received light energies span five orders of magnitude. They must operate reliably when exposed to temperature extremes. They must monitor at several dozen frames per second a wide field of view. To fulfill these requirements many lidar designs must incorporate non-linear electronic and optical systems that introduce systematic range-to-target errors that must be compensated by calibration. The calibration system’s alignment stages couple the transmitted laser pulses into a fiber loop which simulates laser propagation in free space for up to one kilometer while retaining a compact, practical device. Optical switches and a variable optical attenuator vary the simulated distance to target and the received pulse amplitude. High stability and repeatability are achieved. Tests of the calibration system will be described that measure the distortion of the laser pulse produced by propagating the laser beam through its fiber optic cables. The ability of the system to calibrate over temperature variations will be discussed.
Several experiments have demonstrated the potential of Laser Doppler Vibrometry, in conjunction with acoustic-toseismic coupling or mechanical shakers, for the detection of buried landmines. For example, experiments conducted by The University Of Mississippi and MetroLaser, Inc. have shown the ability to scan a one square meter area in less than 20 seconds with a 16-beam multi-beam LDV (MB-LDV), and find the landmines under a variety of soil conditions. Some critical requirements for this technology are to reduce the measurement time, increase the spatial resolution, and reduce the size of the systems. In this paper, MetroLaser presents data from three optical systems that help achieve these requirements: 1) A Compact MB-LDV, 2) A two dimensional, or Matrix Laser Doppler Vibrometer (MX-LDV), and 3) A Whole-field Digital Vibrometer (WDV). The compact MB-LDV produces a 1-D array of beams, which may be scanned over the target surface with a scanning mirror. The size of the new, compact MB-LDV system has been reduced to approximately 17" x 11" x 9", thus enhancing its capability for field applications. The MX-LDV, to be developed in 2006, produces a 16x16 array of beams over a one meter area, allowing the ground velocity of the entire area to be measured in a single measurement. The WDV uses a camera-based interferometry system to take a snapshot of the ground vibration over a one meter square area with very high spatial resolution. Field tests for this system are scheduled for mid-2006.
The fundamental principles and characteristics of wavelength distribution optical fiber sensors are described. An optical fiber sensor is used to count railway tickets. This sensor adapts line array optical fiber receivers and two-wavelength difference measurements, thereby greatly decreasing the requirement on light source brightness and steadiness. The system's sensibility and anti-interference ability have been improved at the same time. Compared with traditional inductive touch--needle counter techniques, it has more reliability and high-frequency counting response, and the measurement is contactless.
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