How this calculator works
Each detected primary photon produces an avalanche charge proportional to gain. Dividing photocurrent by incident optical power gives responsivity. Broadcom's first-order model multiplies primary response by 1 plus the crosstalk and afterpulsing probabilities. It does not describe recursive correlated avalanches, dark-current subtraction, saturation or incomplete cell recovery. Use gain, probabilities and responsivity measured at the same bias and temperature.
Formula
R = [e lambda/(h c)] PDE G (1+Pcross+Pafter). Therefore PDE = R h c/[e lambda G (1+Pcross+Pafter)].
Worked example
At wavelength 1.239841984332 micrometres, h c/(e lambda) is 1. With gain 1000 and no correlated noise, 500 A/W corresponds to 50% PDE; 40% PDE corresponds to 400 A/W.
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Frequently asked questions
Is responsivity the same as PDE?
No. Responsivity includes wavelength, avalanche gain and correlated charge. PDE is the probability of detecting an incident photon as a primary event.
Does this fit the full SiPM response?
No. It implements the cited first-order conversion. High correlated noise, bright light and incomplete recovery need a device-specific response model.
Why can a computed PDE be rejected?
Primary detection probability cannot exceed one. Inconsistent data can arise from units, dark current, gain definitions or mismatched operating points.