Introduction Due to the trend towards higher port densities in high-capacity communication systems, Small Form Factor (SFF) Transceivers are becomingpopular. Originally, SFF transceivers were designed to address short reach (2km) and intermediate reach (15km) applications using PIN receivers. We have developed SFF transceivers for the high-end SONET/SDH space (2.5Gb/s speed for 40km and 80km reach). This part of the SONET/SDH space is unique due to the need for Avalanche Photo Diode (APD) based receiver within a SFF footprint, and still maintaining a good transceiver performance is a real challenge. Introductionally to Stroke towards higher port densities in high-capacity communication systems, Small Form Factor (SFF) Transceivers are becomingpopular. Originally, SFF transceivers were designed to address short reach (2km) and intermediate reach (15km) applications using PIN receivers. We have developed SFF transceivers for the high-end SONET / SDH space (2.5Gb / s speed for 40km and 80km reach). This part of the SONET / SDH space is unique due to the need for Avalanche Photo Diode (APD) based receiver within a SFF footprint, and still maintaining a good transceiver performance is a real challenge.