Stabilized microwave-frequency source incorporating a tunable voltage-controlled oscillator

A microwave-frequency source comprising:

• (a) a tunable voltage-controlled electrical oscillator (VCO) arranged so as to generate a VCO output electrical signal at a frequency fM, a first portion of which forms an output electrical signal of the microwave-frequency source, the VCO being tunable over a tuning range for the frequency fM that spans at least ±5% of a nominal microwave frequency, the nominal microwave frequency being between 1 GHz and 100 GHz;
• (b) a dual optical-frequency reference source arranged so as to generate (i) a first optical reference signal at a first optical reference frequency v1 and (ii) a second optical reference signal at a second optical reference frequency v2 that is greater than v1;
• (c) an electrical reference oscillator arranged so as to generate a reference oscillator electrical signal at a reference oscillator frequency δfREF;
• and
• (d) an electro-optic frequency divider (eOFD) structured and connected so as to (i) receive the first and second optical reference signals, a second portion of the VCO output electrical signal, and the reference oscillator electrical signal, (ii) generate from the first and second optical reference signals and the second portion of the VCO output electrical signal an eOFD electrical signal at a frequency δf=|v2−v1−n·fM| where n is an integer, (iii) generating a loop-filtered electrical error signal dependent on relative phase of the reference oscillator and eOFD electrical signals, and (iv) applying the loop-filtered electrical error signal to the VCO to couple the VCO and the eOFD in a negative feedback arrangement so as to function as a phase-locked loop to stabilize the frequency fM.