Ultra-Low Phase Noise Measurement of Microwave Sources Using Carrier Suppression Enabled by a Photonic Delay Line

We propose and demonstrate a photonic delay line based carrier suppression interferometer system for measuring the phase noise of microwave sources. We show both theoretically and experimentally for the first time that carrier suppression is capable of suppressing the effects of the residual phase noise of the microwave amplifiers and the relative intensity noise of light in the system by up to 70 dB, and therefore effectively eliminates the contributions of these noise sources to the noise floor of the phase noise measurement system. Using a 2-km photonic delay line, we achieved phase noise measurement floors of -126 dBc/Hz at 1 kHz and -152 dBc/Hz at 10 kHz around a 10 GHz carrier, respectively, which are 15 and 20 dB lower than those of a frequency discriminator based phase noise measurement system using the same length of fiber delay and the same optical and microwave components. The noise floor of -152 dBc/Hz at 10 kHz is also 8 dB and 17 dB lower than those of a Keysight E5052B phase noise measurement system with 100-times cross-correlation and without cross-correlation, respectively. Even lower phase noise floors are expected for such a carrier suppression system if microwave phase shifters with lower residual phase noise or a longer photonics delay line are used.