hello zulkarnain,,,
the various types of modulation schemes are external modulation (which include two techniques electro absorbtion modulation and electro opto modulator)..
another technique isDirect Current Modulation of ssemiconductor laser.
moreover you can refer the links
http://www.ijcem.org/papers72011/72011_17.pdf
http://www-ee.stanford.edu/~jmk/pubs/mod.and.det.tech.COTA.6-06.pdf
regards