Estimate of the limitations in data transmission imposed on digitally modulated laser diodes by the bit pattern
In this paper, the cut-off bit-pattern phenomenon of a digitally-modulated semiconductor laser diode (LD) is calculated. The cut-off bit-pattern \(\left( {Q_{\textit{off}}^{\textit{cut}\text{- }\textit{off}} }\, \right) \) is defined as the number of 0 bits (i.e., OFF pulses) preceding the considered 1 bit (i.e., ON pulse) above which an LD cannot respond normally to an injected data pattern and will consequently shutdown or become inoperable. The latter case occurs when the turn-on time delay of an LD exceeds the bit-time interval of the injected current pulse. An analytical calculation for an LDs cut-off bit-pattern is derived in terms of laser cavity parameters, bit rate, modulation and dc-bias currents. This calculation can be used to predetermine, based on typical values for an LD, accurate dc-bias and modulation current values that should be utilized to ensure an LD is operational for high-speed optical communications applications.
digital modulation laser diode cut-off bit-pattern theoretical analysis