Box 1: Figures of merit of photodetectors Selection of sensitivity measures: The time it takes the current to increase from 10 to 90% (90 to 10%) of its final value is called the rise (fall) time. Two different laser excitations are distinguished: Steady (a) and non-steady state (b) excitation, as sketched below. In the steady state a square pulse illumination increases the current to the highest possible photocurrent. The non-steady state mimics real data transfer by illumination with a delta shaped impulse and observing the response time. Via the power spectrum, the frequency-based speed measure, the 3dB bandwidth, can be determined, giving the maximal operation frequency at which the initial photocurrent has dropped to 70%. Note that the often-used approximation 𝑡 𝑟𝑖𝑠𝑒 = 0.35 𝑓 3𝑑𝐵 ⁄ can lead to large deviations compared to the much more precise power spectrum, when calculating the bandwidth.