Referenced Frequency Ruler for the Phase Noise Analysis of Oscillators in the High GHz Range

In this paper we present a system for generating a comb of low phase noise microwave signals. Each of the comb's teeth can be used as a reference signal for converting the output signal of a GHz-oscillator into an intermediate signal in the MHz range. This allows the oscillator's phase noise to be measurable with conventional phase noise analyzers and exploits the high sensitivity of the analyzer at low frequencies. The microwave comb is generated by means of a femtosecond laser and spans up to several 100 GHz with the comb teeth spaced about 250 MHz apart. We will show that by phase locking the repetition rate of the laser to an RF reference signal, the phase noise of the RF reference is transferred to each tooth of the microwave comb.