A spectrally efficient equalization technique for optical sources with direct modulation

In this Letter, a novel equalization method for directly modulated optical sources is introduced. Conventional source equalization methods balance the low- and high-frequency responses of the source by cutting down the low-frequency components in any drive signal. Typically, this ensures a flat frequency and linear signal response up to some predetermined upper-frequency limit. It is conventionally done under a fixed linear dynamic range. However, in this Letter, it is found that the source's dynamic range varies by frequency. We describe a novel method that determines the limit of signal linearity at each frequency and uses this to create the enhanced equalizer response. This leads to an improved source bandwidth and, in practice, allows greater transmitted signal energy. Experimental results for a resonant-cavity LED transmitter show date-rate improvement of ∼40% and, to the best of our knowledge, a record date rate of 8.76 Gb/s with a bit-error-rate less than 3.8×10^-3.