FTTx/xPON Optical Network Unit A FTTx/xPON Optical Network Unit (ONU) terminates optical signals transmitted via fiber to electrical signals for voice and data distribution. These electrical signals are then sent to individual subscribers over twisted copper pairs to an ONT. ONUs are commonly used in fiber-to-the-building (FTTB) or fiber-to-the-curb/node (FTTC) applications. Silicon Labs' proven SLIC and Timing IC solutions offer a one stop shop for FTTx solutions. Silicon Labs also provides several microcontrollers (MCUs) ideal for optical modules.