Showing 2 results for Olyaee
S. Olyaee, Sh. Mohammad-Nejad,
Volume 3, Issue 3 (October 2007)
Abstract
A new heterodyne nano-displacement with error reduction is presented. The
main errors affecting the displacement accuracy of the nano-displacement measurement
system including intermodulation distortion error, cross-talk error, cross-polarization error
and phase detection error are calculated. In the designed system, a He-Ne laser having
three-longitudinal-mode is considered as the stabilized source. The free spectral range of
the 35cm laser cavity is about 435-MHz at 632.8-nm wavelength, which a secondary beat
frequency equal to 300-kHz is produced by combining the reference and measurement
beams. The resolution of the displacement measurement resulting from intermodulation
distortion, cross-talk and cross-polarization errors is limited to 18-pm. Also, the phase
detection uncertainty causes an error of only 5.9-pm in the displacement measurement.
Furthermore, frequency-path models of two- and three-longitudinal-mode laser
interferometers are modeled as the ac interference, ac reference, dc interference and optical
power terms. A comparison study between two- and three-longitudinal-mode laser
interferometers confirms that the performance of the designed system is considerably
improved.
Shahram Mohammad Nejad, Saeed Olyaee,
Volume 5, Issue 2 (June 2009)
Abstract
In this paper, we present a high accuracy laser range finder and velocimeter using ultra-fast time-to-digital converter (TDC). The system operation is based on the measuring the round-trip time of a narrow laser pulse. A low-dark current high-speed PIN photodiode is used to detect the triggered laser beam and to produce start signal. The pulsed laser diode generates 45W optical power at 30ns duration time and 905nm wavelength. A high-responsivity avalanche photodiode (APD) detects the reflected beam from the target. An optical head including beam splitter, lenses and optical filters is also designed and implemented. The signal conditioner of the system includes pre- and post-amplifiers, comparator, opto-isolators and monostable. By using a 3MV/W reach-through structure avalanche photodiode and a wideband pre-amplifier, the pre-amplifier output reaches 15.9mV, resulting from the minimum detectable optical power. The APD temperature and as a result its responsivity is controlled by a thermoelectric controller unit. The start and stop signals from PIN and APD are led to the time-to-digital converter to count the round-trip time of the laser beam. The system is tested by a retro-reflector as a target for 30-1200m distances. The resolutions of the distance and velocity measurement are limited to 18.75mm and 1.2m/s, respectively. In the worst condition, the minimum reflected optical power is limited to about 5.3nW in 1.2km distance.
