Laser frequency stabilization

1 . A laser stabilization system, comprising:

a laser configured to produce a laser light signal at a target frequency;

a phase modulator configured to apply a phase modulation to the laser light signal to produce a phase modulated laser light signal;

a stable optical resonator configured to receive the phase modulated laser light signal and return a light signal;

a light detection system configured to receive the light signal from the stable optical resonator and produce an amplitude modulated electrical signal based on the light signal; and

a digital domain circuit configured to generate a control signal based on the amplitude modulated electrical signal, wherein the digital domain circuit comprises:

a signal generator that is phase locked to a system clock of the digital domain circuit;

an analog-to-digital converter between the light detection system and the digital demodulation system;

a digital mixer receiving an output of the analog-to-digital converter and an output signal of a Local Oscillator (LO) of the digital domain circuit;

a low pass filter coupled to an output of the digital mixer;

a servo controller coupled to the output of the low pass filter; and

a digital-to-analog converter between an output of the servo controller and the laser;

wherein the digital domain circuit is configured to perform a control signal generation method comprising:

generating, by the signal generator, a drive signal for the phase modulator to control the phase modulation applied by the phase modulator to the laser light signal, wherein the generating the drive signal for the phase modulator comprises:

generating, by the signal generator, a carrier signal at a first frequency:

phase modulating the carrier signal at a second frequency to produce a modulated carrier signal; and

providing the modulated carrier signal as the drive signal for the phase modulator:

converting, by the analog-to-digital converter, the amplitude modulated electrical signal from the light detection system to a digital time series,

mixing, by the digital mixer, the digital time series with the output signal of the LO to obtain a demodulated digital time series;

filtering, by the low pass filter, the demodulated digital time series to obtain a digital error signal;

conditioning the digital error signal by the servo controller to obtain a digital control signal; and

converting, by the digital-to-analog converter, the digital control signal to the control signal for controlling the laser to produce the laser light signal at the target frequency.

2 . The laser stabilization system of claim 1 , wherein the signal generator is a Direct Digital Synthesizer (DDS).

3 . The laser stabilization system of claim 1 , wherein the digital domain circuit further comprises a numerically controlled oscillator (NCO) configured to provide the output signal of the LO of the digital domain circuit.

4 . The laser stabilization system of claim 3 , wherein the output signal of the LO of the digital domain circuit is a time-series signal.

5 . The laser stabilization system of claim 1 , wherein the digital domain circuit is implemented on a single integrated circuit chip.

6 . The laser stabilization system of claim 1 , wherein the digital domain circuit is a Field Programmable Gate Array (FPGA).

7 . The laser stabilization system of claim 1 , wherein the phase modulator is an Electro-Optic Phase Modulator (EOM).

8 . A digital domain circuit configured to generate a control signal for tuning a laser light output frequency of a laser to a target frequency, the digital domain circuit comprising:

a signal generator that is phase locked to a system clock of the digital domain circuit wherein the signal generator is configured to:

generate a carrier signal at a first frequency;

phase modulate the carrier signal at a second frequency to produce a modulated carrier signal; and

provide the modulated carrier signal as the drive signal for a phase modulator configured to control a phase modulation applied by the phase modulator to a laser light output of the laser;

an analog-to-digital converter configured to receive an electrical signal from a light detection system;

a digital mixer receiving an output of the analog-to-digital converter and an output signal of a Local Oscillator (LO) of the digital domain circuit;

a low pass filter coupled to an output of the digital mixer;

a servo controller coupled to the output of the low pass filter; and

a digital-to-analog converter between an output of the low pass filter and the laser.

9 . The digital domain circuit of claim 8 , wherein the digital domain circuit is configured to perform an error signal generation method comprising:

converting, by the analog-to-digital converter, the electrical signal from the light detection system to a digital time series;

mixing, by the digital mixer, the digital time series with the output signal of the LO to obtain a demodulated digital time series;

filtering, by the low pass filter, the demodulated digital time series to obtain a digital error signal;

conditioning the digital error signal by the servo controller to obtain a digital control signal; and

converting, by the digital-to-analog converter, the digital control signal to the control signal for controlling the laser to produce the laser light signal at the target frequency.

10 . The digital domain circuit of claim 8 , wherein the signal generator is a Direct Digital Synthesizer (DDS).

11 . The digital domain circuit of claim 8 , further comprising a numerically controlled oscillator (NCO) configured to provide the output signal of the LO of the digital domain circuit as a time series signal.

12 . The digital domain circuit of claim 8 , wherein the digital domain circuit is implemented on a single integrated circuit chip.

13 . The digital domain circuit of claim 8 , wherein the digital domain circuit is a Field Programmable Gate Array (FPGA).

14 . A control signal generation method performed by a digital domain circuit configured to generate a control signal for tuning a laser light output of a laser to a target frequency, the control signal generation method comprising:

generating a drive signal for a phase modulator to control a phase modulation applied by the phase modulator to the laser light output, wherein the generating the drive signal for the phase modulator comprises:

generating a carrier signal at a first frequency;

phase modulating the carrier signal at a second frequency to produce a modulated carrier signal; and

providing the modulated carrier signal as the drive signal for the phase modulator;

receiving an electrical signal from a light detection system;

analog-to-digital converting the amplitude modulated electrical signal from the light detection system to a digital time series;

mixing the digital time series with an output signal of a Local Oscillator (LO) of the digital domain circuit to obtain a demodulated digital time series;

low pass filtering the demodulated digital time series to obtain a digital error signal;

conditioning the digital error signal by a servo controller to obtain a digital control signal; and

digital-to-analog converting the digital control signal to the control signal for tuning the laser light output of the laser to the target frequency

wherein the output of the servo controller is provided to the laser via a digital port.