Nondestructive measurement of refractive index profile of optical fiber preforms using moiré technique and phase shift method

Samaneh Ranjbar; Hamid Reza Khalesifard; Saifollah Rasouli

doi:10.1117/12.667094

28 January 2006 Nondestructive measurement of refractive index profile of optical fiber preforms using moire technique and phase shift method

Samaneh Ranjbar, Hamid Reza Khalesifard, Saifollah Rasouli

Author Affiliations +

Proceedings Volume 6025, ICO20: Optical Communication; 602520 (2006) https://doi.org/10.1117/12.667094
Event: ICO20:Optical Devices and Instruments, 2005, Changchun, China

Abstract

The refractive index profile of optical fiber preform is measured by a nondestructive technique based on Talbot interferometry. In this technique the preform is placed between two ronchi ruling gratings of 10 lines/mm and the system is illuminated by an expanded and collimated beam of He-Ne laser. In this arrangement the 2nd grating is positioned in the Talbot image of the 1st grating and the preform axis is parallel to the gratings planes. To eliminate the effect of clad on the light beam deflection during the measurements, the preform is immersed in an index matching liquid. The phase front of the laser light over the 2nd grating can be monitored by analysis of the moire pattern which is formed over there. The analysis is done by means of 4-step phase shift technique. In this technique the second grating is moved in four steps of 1/4 of the grating vector and in each step the intensity profile of the moire pattern is recorded. The phasefront can be specified by using the recorded intensities. The refractive index profile of the preform can be calculated from the changes on phasefront while the preform is placed between the gratings respect to the case when it is absent. The whole procedure is automated and computer controlled by using a CCD camera to record the moire fringes, a stepper motor for linear translation of the 2nd grating and a code in MATLAB to control the system and measurements.

Citation Download Citation

Samaneh Ranjbar, Hamid Reza Khalesifard, and Saifollah Rasouli "Nondestructive measurement of refractive index profile of optical fiber preforms using moire technique and phase shift method", Proc. SPIE 6025, ICO20: Optical Communication, 602520 (28 January 2006); https://doi.org/10.1117/12.667094

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