Tunable oscillator with low phase noise

A radio frequency (RF) oscillator system comprising:

• a housing;
• a photonic subsystem disposed within the housing, the photonic subsystem including a laser diode, a crystalline microresonator, and photonic circuitry configured to produce a clock signal based on light emitted by the laser diode;
• laser control circuitry disposed within the housing, the laser control circuitry including a Pound-Drever-Hall control loop configured to lock a frequency of the light emitted by the laser diode to a quiet point of the microresonator;
• and
• a direct digital synthesizer disposed within the housing and configured to produce an oscillator output signal based on the clock signal, a frequency of the oscillator output signal being tunable over an output frequency range.

An RF oscillator system comprising:

• a housing having an internal volume of less than 50 cubic centimeters;
• a laser diode disposed within the housing and configured to emit laser light;
• a photonic integrated circuit (PIC) disposed within the housing, the PIC including an optical waveguide network and configured to generate a clock signal based on the laser light;
• a crystalline microresonator disposed within the housing;
• a photonic wirebond configured to couple the laser light between the optical waveguide network and the crystalline microresonator via evanescent coupling;
• laser control circuitry disposed within the housing and configured to lock a frequency of the light emitted by the laser diode to a quiet point of the microresonator, and
• a direct digital synthesizer disposed within the housing and configured to produce a tunable oscillator output signal based on the clock signal.