Recent Advances in Telecommunications Avalanche Photodiodes

For high-bit-rate long-haul fiber optic communications, the avalanche photodiode (APD) is frequently the photodetector of choice owing to its internal gain, which provides a sensitivity margin relative to PIN photodiodes. APDs can achieve 5-10-dB better sensitivity than PINs, provided that the multiplication noise is low and the gain-bandwidth product is sufficiently high. In the past decade, the performance of APDs for optical fiber communication systems has improved as a result of improvements in materials and the development of advanced device structures. This paper presents a brief review of APD fundamentals and describes some of the significant advances

I. Introduction

Over the past five decades, avalanche photodiodes (APDs) have been utilized for a wide range of commercial, military, and research applications. In recent years, the primary driving force for research and development of APDs has been the optical communications. It is well known that the internal gain of APDs provides a higher sensitivity in optical receivers than PIN photodiodes [1]–[4], however, at the cost of more complex epitaxial wafer structures and bias circuits. The APDs have been successfully deployed in optical receivers that operate up to 10 Gb/s, and research on materials and device structures that will extend to higher bit rate applications is ongoing.