Optimizing the linearity in high-speed photodiodes

TL;DR

This paper demonstrates that by externally manipulating circuit impedance, high-power, high-linearity photodiodes can achieve unprecedented linearity in ultrashort optical pulse detection, significantly reducing distortion and extending microwave power capabilities.

Contribution

The study introduces a method to enhance photodiode linearity by circuit impedance control, surpassing previous limits and eliminating the need for precise tuning of operating parameters.

Findings

Over 50 dB rejection of amplitude-to-phase conversion.

Photodiode linearity extended to photocurrents of 40 mA.

Achieved 1000-fold improvement over state-of-the-art photodiodes.

Abstract

Analog photonic links require high-fidelity, high-speed optical-to-electrical conversion for applications such as radio-over-fiber, synchronization at kilometer-scale facilities, and low-noise electronic signal generation. Photodetector nonlinearity is a particularly vexing problem, causing signal distortion and excess noise, especially in systems utilizing ultrashort optical pulses. Here we show that photodetectors designed for high power handling and high linearity can perform optical-to-electrical conversion of ultrashort optical pulses with unprecedented linearity over a large photocurrent range. We also show that the broadband, complex impedance of the circuit following the photodiode modifies the linearity significantly. By externally manipulating the circuit impedance, we extend the detector's linear range to higher photocurrents, with over 50 dB rejection of amplitude-to-phase conversion for photocurrents up to 40 mA. This represents a 1000-fold improvement over state-of-the-art photodiodes and significantly extends the attainable microwave power by a factor of four. As such, we eliminate the long-standing requirement in ultrashort pulse detection of precise tuning of the photodiode's operating parameters (average photocurrent, bias voltage or temperature) to coincide with a nonlinearity minimum. These results should also apply more generally to reduce nonlinear distortion in a range of other microwave photonics applications.