Publications (36) View all
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Conference Proceeding: Adaptive algorithms for nonlinearity modeling in laser heterodyne interferometer
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ABSTRACT: Laser heterodyne interferometer is one kind of nano-metrology systems which has been widely used in industry for high-accuracy displacement measurements. The accuracy of the nano-metrology systems based on the laser heterodyne interferometers can be effectively limited by the periodic nonlinearity. In this paper, we present the nonlinearity modeling of nano-metrology interferometric system using some classical adaptive filters. The adaptive algorithms consist of the least mean squares (LMS), normalized least mean squares (NLMS), and recursive least square (RLS). It is also shown that the RLS algorithm can obtain optimal modeling parameters of nonlinearity.Communication Systems Networks and Digital Signal Processing (CSNDSP), 2010 7th International Symposium on; 08/2010 -
Conference Proceeding: Adaptive RLS algorithm for nonlinearity modeling in the nanometrology system
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ABSTRACT: The periodic nonlinearity in the nanometrology systems based on the laser heterodyne interferometers mainly arises from imperfect laser source and misalignment of their optical setup. The accuracy of the nanometric displacement measurements can be effectively limited by the periodic nonlinearity. In this paper, we model the periodic nonlinearity in a modified laser heterodyne interferometer by adaptive recursive least square (RLS) algorithm. It is shown that this approach can obtain optimal modeling parameters of the nonlinearity. The results show that the RLS algorithm has faster conversions speed and lower steady state mean square error (MSE) in the nonlinearity modeling, comparing the neural network approach.Electrical Engineering (ICEE), 2010 18th Iranian Conference on; 06/2010 -
Chapter: Nano-Metrology Based on the Laser Interferometers
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ABSTRACT: The optical interferometry is the most frequent technique which has been widely used in metrology systems with subnanometer resolution. In this chapter, first we have discussed an overview of principals of interferometry, interfere phenomenon in the laser interferometers and their applications. A comparison of homodyne interferometers, advantages and disadvantages with heterodyne interferometers was also investigated. The optical setup and electronic sections of two- and three-longitudinal-mode heterodyne interferometers was then described. A frequency-path model of the nano-displacement measurement system based on the laser heterodyne interferometers was presented. This model is described by the AC reference, AC interference, DC interference and optical power components of the multi-mode, multi-path interferometer. The main parameters affecting the displacement measurement accuracy were discussed in the fourth section. The most important errors are related to imperfect alignment of the optical setup and nonideal polarized modes. The periodic nonlinearity is the principal limitation of the laser interferometers involving polarized light. Therefore, we have analyzed and modelled the periodic nonlinearity resulting from ellipticity and nonorthogonality of the polarised modes, deviation angle and unequal transmissionreflection coefficients of the PBS and a rotation angle of polarizer with two main approaches; plane wave and matrix method based on the Jones calculus. Then by using two polarizers oriented under +45º and -45º, a half-wave plate, and another avalanche photodiode, the periodic nonlinearity has been considerably decreased. In addition it was shown that the first-order nonlinearity can be effectively reduced compared to the second-order nonlinearity.04/2010; , ISBN: 978-953-307-061-2 -
Article: Jones matrix analysis of frequency mixing error in three-longitudinal-mode laser heterodyne interferometer
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ABSTRACT: In this study, the authors investigate theoretically a periodic non-linearity effect and its compensation in a three-longitudinal-mode heterodyne interferometer (TLMI). An analytical formula of the frequency mixing error in the TLMI is obtained based on the Jones calculus taking into account experimental parameters. We find that the non-ideal polarisation states and imperfect alignment of the optical setup play the major role to produce four- and eight-cycle non-linearities. The operation of non-linearity compensation system on the four- and eight-cycle non-linear errors is also presented.IET Optoelectronics 11/2009; · 1.03 Impact Factor -
Article: Unified Pulsed Laser Range Finder and Velocimeter using Ultra-Fast Time-To-Digital Converter
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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.Iranian Journal of Electrical & Electronic Engineering. 07/2009; 5.
