Affiliation: | a Department of Physics, St. Paul's C.M. College, 33/1 Raja Rammohan Roy Sarani, Kolkata-700009, India b Department of Physics, Surendranath College, 24-2 M.G. Road, Kolkata-700009, India c Fiber Optics Research Group, Department of Electronic Science, University of Calcutta, 92 A.P.C. Road, Kolkata-700009, India |