there are many Phase modulation methods.. & i was able to only these.. checkout these links...
1) h**p://www.gdpspace.com/Telemetry_pdf/Wide%20Deviation%20Phase%20Modulator.PDF
2) h**p://crca.ucsd.edu/~msp/techniques/latest/book-html/node82.html
3) h**p://www.fiber-optics.info/articles/external-mod.htm
cheers...