Use of Current-Assisted Principles in Optical Receivers

Current-Assistance (CA) was originally used for quickly modulating an electric field in time-gated image sensors (Current-Assisted Photonic Demodulator, or CAPD). Its main application was and still is sampling optical signals. This thesis, however, focuses on optical receivers meant for optical telecommunication applications. Instead of integrating a sampled photocurrent over multiple cycles, we want to use CA for real-time photodetection. Rather than redirecting photocurrent from one point to another, we use CA to gather photogenerated holes and electrons as quickly as possible. Apart from fast electric-field modulation, CA pixels showed interesting properties that can be applied to the domain of optical receivers. We go through the fundamentals of homotype junctions (like the p-type high-low doped junction) which are not often explained in literature but are used extensively in CA-based pixels. We also analyze the PIP photodetector and how it compares to a regular PIN photodiode. We then use these insights to find out what advantages CA can have for optical receivers and come to the Current-Assisted Photodiode (called CAP, as CAPD was already taken) which has a very small (sub-femtofarad) junction capacitance and in some cases even a photo-gain that is not based on avalanching, while not overlooking that it may also have associated disadvantages such as an intrinsic dark current and a reduced bandwidth. We also discuss how exactly these properties can be used to our advantage in optical telecommunication. These structures were fabricated, and then characterized and compared using simulations that are in turn based on our gained understanding of the earlier derived theoretical equations.

Publication year:2020

Keywords:Current-Assistance