Self-Equalized Intermodulation Stimulus for Measuring High-Speed Photodetectors Up to Sub-THz Frequency Range

A self-equalized electro-optical stimulus method is proposed for measuring high-frequency responses up to the sub-THz frequency range of photodetectors (PDs) based on high-order intermodulation. In the scheme, dual-drive intensity modulation generates multiple pairs of homogeneous upper and lower sidebands with equalized amplitude in the optical domain. After photodetection, heterogeneous upper and lower sidebands will intermodulate with each other, resulting in sum-and-difference frequency components in the electrical domain. The frequency response of the PD is directly obtained from the amplitude difference of the desired pair of sum-and-difference components, free of any extra correction for power variation, and bias drifting of the stimulus. In the experimental demonstration, a commercial PD is measured up to 110 GHz under swept-frequency modulation up to 13.75 GHz. The consistency between our method and the conventional methods verifies the simple but accurate measurement for high-speed PDs up to the sub-THz frequency range based on the self-equalized intermodulation stimulus.