Optik 150 (2017) 22–28 Contents lists available at ScienceDirect Optik j o ur nal ho me pa ge: www.elsevier.de/ijleo Original research article Full field retardation measurement of birefringent samples Santa Sircar, Ipsita Chakraborty, Suvanwit Roy, K. Bhattacharya ∗ Department of Applied Optics and Photonics, University of Calcutta, JD-2, Sector 3, Salt Lake City, Kolkata 700106, India a r t i c l e i n f o Article history: Received 7 June 2017 Accepted 22 September 2017 Keywords: Full field retardation measurement Identification of fast axis Analysis of retardation plates and birefringent wedges a b s t r a c t This work aims to characterize the retardation of birefringent samples such as wave-plates and birefringent wedges where the principal axis is uniform over the sample zone. The in-line procedure described and implemented for the purpose uses four frames of intensity data that are digitally recorded and combined to characterize the sample in terms of its retardance from 0 to 2 as also to uniquely identify the direction of its fast axis. Simulated and experimental results presented are in good agreement with the proposed theory. © 2017 Elsevier GmbH. All rights reserved. 1. Introduction Measurement of optical birefringence have wide applicability in many fields involving polarized light [1] such as electro- optic and magneto-optic modulators, liquid crystal displays, laser resonator configurations and non-linear optics. As such, the accurate measurement of phase retardation due to birefringence and the orientation of fast axis assumes importance in the manufacturing and testing process of the birefringent retarder and its practical application [2,3]. Accurate calibration of a retardation plate is therefore an important area of research and considerable scientific literature is devoted to this topic. Reference [4] gives a comprehensive and comparative review of the existing methods available for phase retardation measurements. Analysis of retardance essentially indicates quantitative measurement of the phase difference between the components of the amplitudes emerging from the specimen along its principal directions as well as identifying the direction of the fast axis with respect to a reference coordinate system. The former is referred to as the magnitude of retardance and the latter as the direction of birefringence. While it is relatively easy to identify the principal directions of a retarder by placing it between two crossed polarizers, identification of the fast axis calls for advanced procedures [5]. According to the basic principles and operating characteristics, the existing methods characterization of retardation can be roughly classified into polarization rotation method, interference method, spectroscopy method, nonlinear optical method, time-domain method, intracavity polarization method and phase comparison method. In polarization rotation methods the light beam passes successively through the polarizer, the compensator, the measured element and the analyzer. By measuring the rotation angle of the analyzer or polarizer, or by measuring the change of light intensity or other derivative physical quantities, the phase retardation of the measured element can be obtained. According to the specific implementations and detecting objects, this technique may be divided into rotating extinction method [6,7], ellipsiometry method [8], half-shade method [9,10], light-intensity measurement method [11,12], phase shifting method [13,14], modulation compensation method, including electro-optical modulation [15,16], magneto-optical modulation [17] and photoelastic modulation [18]. ∗ Corresponding author. E-mail addresses: kbaop@caluniv.ac.in, khattacharya@gmail.com (K. Bhattacharya). https://doi.org/10.1016/j.ijleo.2017.09.083 0030-4026/© 2017 Elsevier GmbH. All rights reserved.