Linearisation Method of DML-Based Transmitters for Optical Communications Part III: Pulse Amplitude Modulation

Abstract

A new linearization method for optical transmitters based on directly modulated lasers (DMLs), named the Stretched A method, was proposed in Parts I and II of this work. Parts I and II presented the theoretical framework of the method for non-return-to-zero (NRZ) modulation and related detailed simulation and experimental results. Here, we extend the method to pulse amplitude modulation schemes (PAM). Focussing on 4level PAM (PAM-4), we present the theoretical background and discuss implementations options. A simplified variation of the method for the generation of PAM signals with a significantly lower number of sub-currents is proposed. Simulation studies for PAM-4 transmission at 50 GBaud (100 Gb/s) and an experimental proof-of-principle demonstration at 16 GBaud (32 Gb/s) are reported based on 850 nm vertical-cavity surfaceemitting lasers (VCSELs). For PAM-4, products of effective eye diagram areas ( ) of 0.6×10 -5 and 43×10 -5 before and after applying the Stretched A method were measured, demonstrating an improvement ratio of ~72. The sensitivity and tolerances of the method are analyzed using simulation and experiment.

Free Space Optical Communication Networking Technology Based on a Laser Relay Station

“…Further analysis of the performance of various modulation methods, assuming the transmission power of the light source, the transmission bandwidth of OOK, and the channel capacity of OOK, is performed according to the principle of optical communication modulation [41][42][43][44][45][46], and the performance comparison histogram of the average transmission power, transmission bandwidth and channel capacity of various modulation modes when M = 1 is shown in Figure 2. For the data with symbol length M, the average symbol length, average transmit power, transmission bandwidth, channel capacity, and signal synchronization of the above optical communication modulation methods are further summarized according to Figure 2, as shown in Table 1.…”