Simple method for frequency response measurement of photodetectors based on wavelength-to-time mapping

A simple method is proposed for measuring frequency responses of photodetectors (PDs) based on wavelength-to-time mapping in this paper. The proposed method is an all-optical scheme, which is simple, fast, accurate and free from any extra calibration. Optical pulses emitted from a mode-locked laser are firstly pre-chirped by a spool of dispersive compensation fiber. In this way, the frequency spectrum of the pulses is mapped into time domain. Then, the pre-chirped pulses beat with a reference continuous wave laser with a fixed wavelength in the PD under test and generate a linearly chirped microwave signal. The frequency response information of the PD can be decoded by analyzing the generated linearly chirped microwave signal. Experimental results show that the frequency response of the PD with 3-dB bandwidth of ∼15GHz has been accurately measured with a resolution of ∼390MHz. The measurement result agrees well with the one measured by the commercial lightwave component analyzer.