Electro-optical sampling-based frequency response characterization of photodetectors beyond 120  GHz using a fiber-optic frequency comb

With the rapid development of high-speed data transmission and fiber-optic communication, the frequency response range of high-speed photodetectors is gradually moving towards higher frequencies. The electro-optical sampling-based frequency response characterization technique is considered a terahertz-band-oriented characterization technique with the advantages of wide bandwidth, high accuracy, high spatial resolution, and the possibility of simultaneous time-frequency-domain measurements. To further expand the measurement capability and optimize the measurement stability, in this work, electro-optical sampling-based frequency response characterization of high-speed photodetectors at 90, 100, and 145 GHz is conducted using a femtosecond fiber-optic frequency comb and a LiTaO₃ electro-optic crystal coplanar waveguide. The experimental results show that the quasi-all-fiber measurement system has good accuracy and stability and is expected to break through the accurate frequency response metrology beyond 120 GHz.