Analysis on the laser beam pointing instability induced fringe shift and contrast dilution from different interferometers used for writing fiber Bragg grating

• Published in: Optics communications 2009-06, Vol.282 (11), p.2204-2211
• Main Authors: Mahakud, R., Prakash, O., Dixit, S.K., Mittal, J.K.
• Format: Article
• Language: English
• Subjects: Bi-prism; Exact sciences and technology; Fiber optics; Fundamental areas of phenomenology (including applications); Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Interference fringe; Interferometers; Optical elements, devices, and systems; Optical instruments, equipment and techniques; Optics; Other fiber-optical devices; Phase mask; Phase mask-Talbot interferometer; Physics; Reflectors, beam splitters, and deflectors
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2009.02.041

This paper presents an analysis on the effect of laser beam pointing instability on the fringe shift and hence the contrast dilution of superposed fringes from two beam interferometers. The interferometers analyzed are those commonly used in writing fiber Bragg grating (FBG) such as phase mask, bi-prism and phase mask based Talbot/Holographic type. The beam pointing instability is incorporated as slight change in the angle between two interfering beams. The relative immunity of different interferometers to laser beam pointing is discussed vs location of FBG writing plane from the beam splitter. The effect of the beam pointing was minimum in proximity FBG writing by phase mask. The effect, in terms of fringes contrast dilution, was worst in case of large length interferometers e.g. phase mask based-Talbot interferometer. For intermediate length prism interferometers, the effect was moderate. For a given length interferometer, the fringe shift was directly proportional to beam pointing angle and inversely proportional to fringe separation. Theoretical analysis is verified experimentally by studying the fringe instability of interference pattern formed by a bi-prism of angle 2o with the copper vapour laser (CVL, λ=510nm) beams of different beam pointing instabilities.