TOSA is the component inside the transmit side of SFP ports which is responsible for converting the electrical signal into an optical signal and then transmitting it over the optical fiber strand connected to it. OSAs generally fall into three main categories: TOSA, ROSA, and BOSA. Now, ETU-LINK will introduce to you the components of the optical module— TOSA. Optoelectronic devices are generally located in the visible and near-infrared (NIR) regions of the electromagnetic spectrum.