Abstract
A comprehensive study on semiconductor laser characteristics under gigabit-per-second digital modulation is presented. Comparison of the modulation characteristics under both formats of the return to zero (RZ) and non-return to zero (NRZ) bit formats is introduced. The modulation characteristics include the eye diagram, turn-on jitter (TOJ) and frequency chirp. The study elucidates how the laser modulation performance changes with variation of the modulation bit rate relative to the maximum bit rate and the setting bit rate of the relaxation oscillations. The relative contributions of the intrinsic noise of the laser and the pseudorandom bit-pattern effect to the modulation characteristics are differentiated. The results showed that when the bit rate is higher than the setting bit rate, the eye diagram is partially closed and becomes completely closed when the bit rate increases beyond the maximum bit rate. When the bit rate is higher than 2.25Gbps, the TOJ values under NRZ modulation are smaller than those under RZ modulation near the threshold level. Under both RZ and NRZ formats, chirp increases with the bit rate with the chirp under the RZ format being higher than that under the NRZ format. Copyright (c) 2013 John Wiley & Sons, Ltd.