A common optical module has a center wavelength of 850 nm, 1310 nm, or 1550 nm, whereas a WDM module has different center wavelengths. That value determines whether the module is designed for multimode fiber (MMF) or single-mode fiber (SMF), how much attenuation the signal will experience, how dispersion behaves over distance, and. WDM modules differ from other types of optical modules in center wavelengths. As the core optoelectronic devices operating at the Physical Layer of the OSI model, their primary function is to perform electro-optical and photo-electric conversion during signal. An optical module is a typically hot-pluggable optical transceiver used in high-bandwidth data communications applications.