$Applied Optoelectronics(AAOI)$
The main reason why 6.4T consumes more InP materials is the increase in total lane count and light source volume required to double the bandwidth from 3.2 Terabits per second to 6.4 Tbps.
First, lane count multiplication is needed. To scale up multi-terabit architectures, optical engines rely on multiplying physical lanes or laser wavelengths. A 6.4T engine requires twice the data-carrying capacity of a 3.2T engine. Even when moving to next-generation individual 400G-per-lane speeds, a 6.4T engine requires 16 channels, while a 3.2T engine only needs 8.
Second, laser component volume increases. Whether the architecture uses discrete InP Electro-absorption Modulated Lasers (EMLs) or continuous-wave (CW) InP lasers arrayed to feed a Silicon Photonics (SiPho) engine, the physical number of laser chips or array sizes must scale up to deliver the necessary optical power and channels.
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