There are two common methods for encoding a signal onto an optical beam: either directly modulate the optical source, or externally modulate a continuous wave optical source. Direct modulation is the most widespread method of modulation today, but it introduces demanding constraints on the semiconductor lasers. For example, it is difficult to directly modulate a semiconductor laser at frequencies above a few GHz. Furthermore, it is difficult to maintain single mode operation of these pulsed lasers. Non-single-mode lasers have a larger spectral bandwidth which leads to increased pulse spreading due to dispersion. External modulators offer several advantages over direct modulation. First, one can use a relatively simple and inexpensive continuous wave laser as the primary optical source. Second, since a modulator can encode information based on a number of externally controlled effects, it is not compromised by the need to maintain a population inversion or single mode control. Finally, direct phase modulation (for FM or PM systems) is possible in external modulators, but is nearly impossible to achieve in a laser.
KeywordsInsertion Loss Optical Beam Free Spectral Range Electrooptic Effect Single Mode Waveguide
Unable to display preview. Download preview PDF.
- R. W. Wood, Physical Optics, 3rd ed., Optical Society of America, 1988, USAGoogle Scholar
- A. Yariv and P. Yeh, Optical Waves in Crystals,Wiley Interscience,1984, USAGoogle Scholar
- A. Yariv, Quantum Electronics, 3rd ed., Ch. 5, John Wiley and Sons, 1989, USAGoogle Scholar
- S. G. Lipson and H. Lipson, Optical Physics, 2nd ed.,Cambridge University Press, USA, 1981Google Scholar
- R. J. Pressey, ed. CRC Handbook of Lasers, Chemical Rubber Co., Cleveland, Ohio, (1971)Google Scholar
- A. Yariv, Optical Electronics, 4th ed. Ch. 9, Holt, Rinehart, and Winston, New York (1991)Google Scholar
- A. Yariv, Quantum Electronics, 3rd ed., John Wiley and Sons, USA (1989)Google Scholar
- R. G. Hunsperger, Integrated Optics: Theory and Technology, Vol. 33 Springer Series in Optical Sciences, Berlin (1982)Google Scholar
- A. A. Oliner, editor, Topics in Applied Physics, Vol. 24: Acoustic Surface Waves, Springer, Berlin (1978)Google Scholar
- J. M. Hammer, “Modulation and switching of light in dielectric waveguides,” in Integrated Optics, edited by T. Tamir, Topics in Applied Physics, Vol. 7Google Scholar
- D. Mergerian and E. C. Malarkey, Microwave Journal, 23, pp. 37 (1980)Google Scholar