Characterization of Photodiode Nonlinearities by Output Frequency Analysis

We introduce a new technique for characterizing nonlinear behavior in photodiodes and illustrate its use for second order intermodulation distortion (IMD). For a given operating point (bias voltage and dc current), we construct a frequency-dependent nonlinear coefficient and plot it versus the output frequency of the IMD product. We find that for large ranges of operating points, the nonlinear coefficient falls on the same single curve, regardless of whether it was a sum, high difference, or low difference frequency plan that created the tone. Additionally, we found evidence of scaling: Regions in which changes in the universal curve due to a change in bias voltage can be cancelled by a systematic change in the dc current. That is, the nonlinear coefficients for a family of bias/current pairs fall on the same curve in these regions. This method shows that standard characterization of nonlinearities, such as finding intercept points, can be efficiently organized. Furthermore, it implies that comparison of nonlinear behavior of different photodiodes can be made directly on a uniform basis.