Measurement of IP3 in p-i-n photodetectors and proposed performance requirements for RF fiber-optic links

The nonlinearities generated by wide-band, high-current photodetectorsare discussed in the context of the performance of an externally modulated analog radio-frequency fiber- optic link. The quantitative impart of the detector's third-order intermodulationproduct intercept (IP3) on the link's spur-free dynamic range is analyzed. Waveguide p-i-n photodiodes were developed to specifically address these stringent IP3 goals. The IP3 was measured using a four laser heterodynesystem resulting in an IP3 of 27 dBm measured at a center frequencyof 20 GHz with 20 mA of de photocurrent. The authors believe that this is the highest photodetectorIP3 reported to date at these operating conditions.