Estimate of the limitations in data transmission imposed on digitally modulated laser diodes by the bit pattern

Abstract

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 LD’s 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.