Direct Modulation of Semiconductor Injection Lasers

Narrow stripe geometry double-heterostructure injection lasers for optical communication applications allow direct modulation up into the Gbit/s range. Modulation behavior and influence of modulation on the laser spectrum are discussed. The spectral and modulation properties of gain-guided and index-guided laser types differ significantly. Limitations arise from intensity fluctuations due to intrinsic quantum noise, dynamic instabilities, and reflected optical power, and also, in the case of analog modulation, from harmonic distortion. By coherent injection locking, single mode operation and strongly damped transient response can be achieved. Electronic circuits for Gbit/s direct modulation are discussed.