Adaptive stabilized interferometer with laser diode

Applied Optics, 1978

A technique is described for obtaining a linear readout of fringe shift from a high resolution Fabry-Perot interferometer. One mirror of the interferometer is mounted on a piezoelectric crystal driven by a high frequency sinusoidal voltage. A signal proportional to the mirror displacement is displayed on the Y axis of an oscilloscope, while the X axis is swept with time. Each time the interferometer passes through a transmission maximum, a pulse is produced which is fed to the Z axis ofthe oscilloscope, producing an intensified dot. The displacement of the resultant row of dots from its ambient position is linearly proportional to the fringe shift occurring within the interferometer, has no sign of ambiguity, and is independent of the finesse. All the circuits required for producing the readout were realized using the internal circuitry of a standard laboratory oscilloscope.

2005

The combination of several telescopes is appealing from the scientific standpoint due to the more efficient sampling of the spatial frequency plane. Among other basic requirements, the beams are to be brought and retained into a fixed phase relation, against atmospheric piston. The necessary phase measurements (and corrections) are basically linear with the number of telescopes. This suggests the possibility of a convenient modular approach based on current technology. Besides, fringe tracking may benefit from efficient beam combination schemes and technological innovations in detector and optical components for astronomy. "Technology roadmap for future interferometric facilities"; JENAM 2005, held in Liège (Belgium)

Optics & Laser Technology, 2012

A novel photodetection system for a homodyne distance measuring interferometer by means of fringe counting method is presented. The system is based on applying compact size integrated photodetector operating with fringe pattern having fixed, finite period. 13-element integrated photodiode arranged in novel signal processing scheme receives interference fringes movement. Additional lens is used to adjust the fringe period to photoelements' distances. Due to the proposed configuration of the photoelement's signal processing and the applied lens the system has reduced sensitivity to interference fringe period errors caused by the angular misalignment of interfering beams. The theoretical analysis and experimental verification of the system metrological feasibilities are presented. Comparison of performance of examples of standard and novel detection systems is shown finally.

Optik, 2019

We report on a technique for accurately π/2-phase shifting a stabilized interference pattern of light fringes used for building up a map of phase for 2D deformation measurement. This technique is based on the use of low amplitude phase modulation on the setup in order to generate first and second harmonics temporal terms in the pattern of light to operate an actively stabilized setup. Particular features of this stabilization setup allow one to use them for accurate π/2-phase shifting with the practical advantage of operating on an already stabilized pattern of fringes.

Applied Optics, 1988

A two-step self-tuning phase-shifting method is presented. The phase-step between the two interferograms is not known when the experiment is performed. Our demodulating method finds, in a robust way, this unknown phase-step. Once the phase-step is estimated we proceed to phase demodulate the interferograms. Moreover our method only requires the fringe patterns to have a constant unknown phase-shift between them. As a consequence, this technique can be used to demodulate open and closed-fringed patterns without phase-sign ambiguity. The method may be regarded as a self-tuning quadrature filter, which determines the phase-shift between the two fringe patterns and finally estimates the demodulated phase map. The proposed technique has been tested with simulated and real interferograms obtaining satisfactory results.

Optics and Lasers in Engineering, 2007

The phase shifting method for quantitative fringe pattern analysis provides high accuracy if stringent requirements on the component interferogram recording are met. In the paper the issue of detection and identification of error sources in the two-beam interferogram phase shifting experiment is discussed. The phase shift angle histogram and lattice-site representation are applied for that purpose. Special attention is paid to possible nonlinear recording of component interferograms in the presence of linear and nonlinear phase step errors. Four and five step phase shifting algorithms are considered. The superiority of the lattice-site representation is shown. In the case of phase steps equal to p/2, however, the lattice-site representation of shift angles for five frame algorithm does not allow to detect recording nonlinearity. The four frame counterpart shows to be very helpful in this respect. Its properties related to the fringe pattern profile under study, including a defocused Ronchi grating, are discussed. r

Applied Physics B, 2014

Optics Express, 2011

A two-step self-tuning phase-shifting method is presented. The phase-step between the two interferograms is not known when the experiment is performed. Our demodulating method finds, in a robust way, this unknown phase-step. Once the phase-step is estimated we proceed to phase demodulate the interferograms. Moreover our method only requires the fringe patterns to have a constant unknown phase-shift between them. As a consequence, this technique can be used to demodulate open and closed-fringed patterns without phase-sign ambiguity. The method may be regarded as a self-tuning quadrature filter, which determines the phase-shift between the two fringe patterns and finally estimates the demodulated phase map. The proposed technique has been tested with simulated and real interferograms obtaining satisfactory results.

In fact that Laser play a very important role in various modern applications including laser safety informatics, biophotonics, and communications technology, we compute in this work the spatial coherence and contrast characteristic functions of laser He-Ne beam with a wavelength of 632.8 nm using a Sagnac interferometer configured in triangle. The interference images of related z-axis shift in phases are presented in the form of computer-generated pattern. These computed images are obtained by displaying the experimental results representing fringe intensities obtained by a CCD camera. The interferometer provides a superposition of two beams traverse the same optical path but in opposite direction, which gives rise to a system of fringes. The exploitation of the results was done in two ways; one was based on the change in the polarization state and the other in the determination of the contrast. The computed images are compared with experimentally obtained patterns; good agreement is obtained as predicted by the theory.

Optical and Infrared Interferometry IV, 2014

Fringe tracking (FT) is the adaptive optics component of an Optical Long Baseline Interferometer (OLBIN). It is a critical element in particular for high spectral resolution spectro-interferometric observations. The FT must be accurate and stable, which implies high frequency sampling of the optical path differences introduced by the atmosphere and the interferometer vibrations. It must also be as sensitive as possible, which needs to minimize this sampling frequency. The optimum between these contradictory requirements must be maintained through atmospheric and instrument conditions that change very rapidly. We describe a control framework to face this robustness challenge. First, we approximate the sampled-data feedback system as a discrete time feedback system and we show that the closed-loop FT behavior is entirely determined by key closed-loop transfer functions. To fix the closed-loop bandwith in order to limit the loss of vadidity of the discrete time feedback system, we propose a loop shaping control method based on H ∞ optimization. This H ∞ framework allows to bound the frequency response of the key closed-loop transfer function. First numerical experiments are presented showing satisfactory performance when the sampling frequency disminishes. Extensive simulations to demonstate the effectivness of the proposed approach are in progress. Open issues and perspectives of applicative and/or theoretical interests are discussed.