Automatic phase stepping in fiber-optic ESPI by closed-loop gain switching

Author

Martini, Giuseppe ; Facchini, Mauro ; Parisi, Dario

Author_Institution

Dipt. di Elettronica, Pavia Univ., Italy

Volume

49

Issue

4

fYear

2000

fDate

8/1/2000 12:00:00 AM

Firstpage

823

Lastpage

828

Abstract

In this paper, we describe a new technique for automatic phase stepping in fiber-optic Electronic Speckle Pattern Interferometry (ESPI), useful in both single-point and imaging configurations. The proposed technique is based on closed-loop switching of the gain sign in the control loop used to stabilize the reference wavefront phase, with the aid of a Proportional-Integral (P.I.) controller. Simulation and experimental results are compared, showing that by a synchronization signal or by a proper choice of the feedback loop parameters, a sequence of π/2 steps of the reference wavefront phase, all of the same sign, is obtained, The residual fluctuation of each phase step amounts to ±2.5 mr over a bandwidth of 200 Hz. This level of phase stability is well suited for ESPI applications

Keywords

closed loop systems; electro-optical modulation; electronic speckle pattern interferometry; optical fibre telemetry; physical instrumentation control; synchronisation; two-term control; 200 Hz; automatic phase stepping; closed-loop gain switching; closed-loop switching; control loop; electronic speckle pattern interferometry; feedback loop; fiber-optic ESPI; gain sign; phase stability; proportional-integral controller; reference wavefront phase; residual fluctuation; synchronization signal; Automatic control; Displacement measurement; Fluctuations; Optical fibers; Optical imaging; Optical interferometry; Phase modulation; Pi control; Proportional control; Speckle;

fLanguage

English

Journal_Title

Instrumentation and Measurement, IEEE Transactions on

Publisher

ieee

ISSN

0018-9456

Type

jour

DOI

10.1109/19.863932

Filename

863932