Optical Transmission Modulation Methods Advance

By Robert Huntley, EETimes Europe (November 21, 2024)

With our society’s instantiable appetite for consuming vast amounts of data, it is no surprise that the back-end data networks must constantly evolve. Most high-throughput data networks rely on optical transmission methods to transfer data, with two dominant modulation techniques: 4-level pulse amplitude modulation (PAM4) and coherent modulation. PAM4, where each amplitude level represents two bits, is a bandwidth-efficient modulation technique that suits short-range (< 10km) applications. Coherent modulation, which involves the modulation of a coherent light source’s amplitude, phase and polarization, is more suited to high-speed, long-distance (>10km) transmission. Both modulation techniques are in demand as the race is on to achieve transfer rates of up to 800 Gbps. There are signs that as each technique evolves, the differences in cost, simplicity and power consumption between them will reduce.

EE Times Europe spoke with Tony Chan Carusone, chief technology officer of Alphawave Semi (London, U.K.), to discover the underlying applications driving bandwidth demand and to find out if PAM4 and coherent modulation techniques are ever likely to converge.

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