The operating wavelength of single-mode optical modules is generally 1310nm or 1550nm. Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. These modules vary in core size, transmission distance, speed, cost, and application. This guide breaks down practical differences—core geometry, wavelengths, connector types, performance limits, cost trade-offs, and ideal use-cases—so you can pick the right optical modules with. How to Distinguish Single-Mode and Multi-Mode Optical Modules by Wavelength? First, we can look at the wavelength parameters of the optical module.