Quantum devices have the potential to revolutionize applications in computing, communications, and sensing; however, current state-of-art resources must operate at extremely low temperatures. There is an increasing interest in optical fiber transduction to microwave link with superconducting and Si qubits. The quality depends strongly on the characteristics of the photodiode, specifically uni-traveling carrier photodiodes (UTC-PDs) for high-frequency operation, yet most do not have the high-speed and high-linearity performance or the ability to handle ultracold temperatures. To address these low-temperature and high-frequency problems, an RF photonic microwave transducer is used to measure the frequency response and investigate the linearity dependence on frequency, bias voltage, and temperature. An electro-optical microwave transducer is created using the heterodyning beat method. A high-speed MUTC photodiode designed for cryogenic temperatures is tested as the transducer and characterized with a spectrum analyzer. The linearity of the device is also tested at bias voltages of 0 V and −5 V, frequencies of 3 GHz and 10 GHz, and temperatures of 300 K and 77 K. With a low bias voltage, the frequency response shows a decrease in power due to the increase of harmonic noise. The results show that the linearity does depend on frequency, bias voltage, and temperature. A higher reverse bias voltage showed the highest 1-dB compression point, while a bias voltage of 0 V and a frequency of 10 GHz showed the lowest power and the lowest 1-dB compression point. Our results should help contribute to the future design of highly linear cryogenic quantum links.