The optical transmitting part is called TOSA, the optical receiving part is called ROSA, combined the two together are called BOSA. Figure 1: Optical Module Structure What is TOSA?In the era of 5G, AI, and high-speed data centers, optical modules serve as the core bridge for converting electrical signals to optical signals (and vice versa), enabling fast, reliable data transmission across networks. Among various optical module form factors, SFP (Small Form-Factor Pluggable). An SFP (Small Form-factor Pluggable) is a compact, hot-pluggable transceiver module that allows networking equipment — including switches, routers, servers, and media converters — to support different physical media, such as optical fiber or copper, without replacing the host hardware. Figure 1-1 shows how an optical module works.