Here are links of some papers you may refer to:
http://www.photonics.com/Article.aspx?AID=19690
http://link.springer.com/article/10.1007/s10297-004-0026-9#/page-1
http://esatjournals.net/ijret/2014v03/i07/IJRET20140307086.pdf
http://www.optical-waveguides-modeling.net/Litchinitser/publ-files/JP1_JLT_1997_DC.pdf
http://www.ijarcce.com/upload/2015/october-15/IJARCCE%2047.pdf
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.512.5937&rep=rep1&type=pdf
I hope this will be helpful to you.
Thanks