Study on the Effect of Reflected Lights on Mode Partition Characteristics of Dynamic Single-Mode Laser Diodes

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In this research, the mode partition characteristics of distributed feedback laser diodes (DFB LD's)are experimentally evaluated, and the noise generation mechanisms are investigated by a computer simulation. The following results are obtained.1.By observing the transient spectra of DFB LD's with the time resolving spectroscopic method, it is made clear that DFB LD's oscillate in single longitudinal mode even if they are directly modulated at Gb/s.2.The mode partition noise induced by incoherent reflections is found to increase with the DC bias current. The origin of this noise increase is attributed to the modulation of the threshold of the main mode due to the interference between the reflected light and the light inside of the LD.3.An experimental setup to control the amplitude and the phase of the coherently reflected light is established. In the spectra of directly modulated DFB LD's, it is found that the short wavelength components are enhanced by the coherent reflections. The measurements and the computer simulations are in progress.