Photonic local oscillator for SIS mixers

This paper presents the development of a new type of millimeter-wave oscillator, which is called a photomixer, based on nonlinear optical frequency conversion, or photomixing, in a uni-traveling-carrier photodiode (UTC-PD). This study demonstrates that the photomixer can produce a millimeter wave at 100 GHz with output power as high as 2 mW, when the photodiode is optically-pumped by two 1.55-μm lasers with input power of ∼100 mW each. This work has used the photomixer as an LO source for superconductor-insulator-superconductor (SIS) mixers at 100-GHz band. The photomixer output and an RF signal are combined by a cross-guide coupler with a coupling efficiency of ∼-25 dB placed on the 4-K stage in a dewar and then coupled into the SIS mixer. This LO coupling scheme is popularly used in low-noise receivers at millimeter wavelengths. It is demonstrated that the photomixer can provide sufficient LO power required for optimum operation of the SIS mixer in the frequency band from 85 to 110 GHz.