A. Satpathi

Bio: A. Satpathi is an academic researcher from University of Calcutta. The author has an hindex of 1, co-authored 1 publication(s) receiving 14 citation(s).

The Generalised Lau Effect

Abstract: It has been shown that the process of coded imaging of incoherently illuminated extended objects by self-imaging structures (SIS) naturally leads to the formation of Lau-type fringes at finite conjugates. The object grating and the grating representing the SIS need not be of the same period. The generalised Lau fringes are obtained under a conjugate relation characteristic of the SIS imaging and a general matching condition involving the periods and frequencies of the two periodic structures. The classical Lau fringes and the so-called finite conjugate classical Lau fringes are formed under special imaging conditions. Useful applications have been mentioned.

Metrological errors in optical encoders

Abstract: Optical encoders are commonly used for high accuracy position measurement, both linear and angular. In order to determine the position, the optical encoder generates two electrical signals that are combined using the arctangent algorithm. There are a number of situations, optical, mechanical and electronic, that affect these signals and produce an error in the position measurement. In this work, we analyze the error produced in optical encoders when the electrical signals vary from their nominal values. By using a linear expansion, simple expressions for the error estimation are obtained which can be used to improve the design of the optical encoders. In addition, an experimental verification of the theoretical results is performed.

Apparatus for producing patterned illumination including at least one array of light sources and at least one array of microlenses

Abstract: An apparatus for producing structured light comprises a first optical arrangement which comprises a microlens array comprising a multitude of transmissive or reflective microlenses which are regularly arranged at a lens pitch P and an illumination unit for illuminating the microlens array. The illumination unit comprises an array of light sources for emitting light of a wavelength L each and having an aperture each, wherein the apertures are located in a common emission plane which is located at a distance D from the microlens array. For the lens pitch P, the distance D and the wavelength L, the following equation applies P 2=2LD/N, wherein N is an integer with N≧1. High-contrast high-intensity light patterns can be produced.

Collimation method using a double grating system.

Abstract: We present a collimation technique based on a double grating system to locate with high accuracy an emitter in the focal plane of a lens. Talbot self-images are projected onto the second grating producing moire interferences. By means of two photodetectors positioned just behind the second grating, it is possible to determine the optimal position of the light source for collimation by measuring the phase shift between the signals over the two photodetectors. We obtain mathematical expressions of the signal in terms of defocus. This allows us to perform an automated technique for collimation. In addition, a simple and accurate visual criterion for collimating a light source using a lens is proposed. Experimental results that corroborate the proposed technique are also presented.

Double grating systems with one steel tape grating

Abstract: Steel tape gratings are used in different metrology applications. As the period of these gratings was large (around 100μm,), its analytical study has been performed, up to date, using a geometrical approach. Nowadays, steel tape gratings can be manufactured with lower periods, around 20–40 μm, and diffractive effects must be taken into account. Also, due to the roughness of the surface, statistical techniques need to be considered to analyze their behavior. In this work, an analysis of the pseudo-imaging formation in a double grating system including one steel tape grating is performed. In particular Moire and Lau configurations are analyzed. We have found that roughness significantly affects to Moire configuration. However, its effect is negligible in Lau configuration. Generalized grating imaging configuration is also studied in depth. It is shown that roughness does not affect to the contrast of pseudoimages, but it modifies their depth of focus.

Invariant grating pseudoimaging using polychromatic light and a finite extension source

Abstract: The Talbot effect is a well studied phenomenon by which grating pseudoimages appear at certain periodic distances when monochromatic light is used Recently, numerical simulations have shown a new phenomenon; when a polychromatic light beam is used in a double grating system, the intensity of the pseudoimages presents a transverse-profile that remains unaffected over a wide range of propagation distances This effect can be used to increase the tolerances of gratings based optical devices, such as displacement measurement systems, interferometers, and spectrometers The pseudoimages formation with a polychromatic and finite extension light source is analytically and experimentally demonstrated Relatively simple analytical expressions for the intensity and the contrast allow us to predict when pseudoimages present a constant contrast and when they disappear Furthermore, we experimentally obtain the pseudoimages using the proposed configuration, corroborating the theoretical predictions