  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.

Instrumentation and Detectors;Optics