Dual-Wavelength Light Source Assisted Frequency Response Measurement Method of Photodetectors

Dual-wavelength light source assisted frequency response measurement of photodetectors based on double-sideband suppressed-carrier modulation is proposed in this letter. In this method, a directly modulated laser with a modulation frequency of f
₁
combined with an optical tunable filter is used to generate a dual-wavelength carrier, which can be highly stable since only one light source is introduced. The dual-wavelength carrier generates two pairs of first-order sidebands under double-sideband suppressed-carrier modulation of the Mach-Zehnder modulator at frequency f
_m
. Afterwards, the modulated signal is injected into the photodetector under test, and the frequency response of the photodetector can be extracted by recording the electric power at specific frequencies. Based on this method, we used a 35-GHz modulator to measure the frequency response of photodetectors with bandwidth of 15 GHz and 43.5 GHz respectively. Moreover, a comparison of the results is performed between our method, the swept frequency method, and electro-absorption modulator deduction method. The results show that the new method extends the frequency response measurement range from f
_m
to f
₁
+2f
_m
, and the influence of the modulator on the frequency response measurement results is reduced simultaneously.