Optical locking based on optical resonators with high quality factors

1. A device, comprising:

a laser that produces a laser output beam at a laser frequency;

an optical interferometer located in an optical path of the laser output beam and comprising a first optical path that receives a first portion of the laser output beam, a second optical path that receives a second portion of the laser output beam, and an optical combiner where the first and second optical paths meet each other and terminate, the optical combiner (1) transmitting a part of light from the first optical path and reflecting a part of light from the second optical path to produce a first combined optical output, and (2) transmitting a part of the light from the second optical path and reflecting a part of the light from the first optical path to produce a second combined optical output;

an optical resonator optically coupled in the first optical path to filter light in the first optical path;

a detection module that detects the first and the second combined optical outputs to produce an error signal representing a frequency difference between the laser frequency and a resonance of the optical resonator; and

a feedback control mechanism that receives the error signal and tunes, one of (1) the laser and (2) the optical resonator, in response to the frequency difference of the error signal to lock the laser and the optical resonator with respect to each other.

2. The device as in claim 1 , wherein:

the feedback control mechanism tunes the laser to lock the laser relative to the resonance of the optical resonator.

3. The device as in claim 1 , wherein:

the feedback control mechanism tunes the optical resonator to lock the resonance of the optical resonator to the laser.

4. The device as in claim 1 , wherein:

the detection module comprises a differential amplifier that produces a differential signal of power levels of the first and the second combined optical outputs as the error signal.

5. The device as in claim 1 , wherein:

the detection module comprises:

a first signal processing unit that shifts a phase of the first combined optical output to produce a first signal;

a second signal processing unit that performs a time derivative of the second combined optical output to produce a second signal; and

a signal multiplier that multiplies the first signal and the second signal to produce a multiplied signal,

wherein the detection module uses the multiplied signal to generate the error signal indicating the frequency difference.

6. The device as in claim 5 , wherein:

the detection module uses a DC component of the multiplied signal to generate the error signal.

7. The device as in claim 5 , comprising:

a second detection module that comprises a differential amplifier that receives a portion of the first combined optical output and a portion of the second combined optical output to produce a differential signal of power levels of the received portions of the first and the second combined optical outputs as a second error signal representing the frequency difference between the laser frequency and the resonance of the optical resonator,

wherein the feedback control mechanism uses both the error signal and the second error signal to lock the laser and the optical resonator with respect to each other.

8. The device as in claim 7 , comprising:

a second differential amplifier that receives the error signal and the second error signal to produce a different output signal, wherein the feedback control mechanism responds to the different output signal to lock the laser and the optical resonator with respect to each other.

9. The device as in claim 1 , wherein:

the optical resonator is a narrow-band whispering gallery mode optical resonator.

10. A method for locking a laser and an optical resonator to each other, comprising:

operating a laser to produce a laser output beam at a laser frequency without modulating the laser beam;

directing laser light of the laser output beam into an optical interferometer which includes a first optical path and a second optical path that intersect to produce optical interference between light in the first and second optical paths;

optically coupling an optical resonator in the first optical path to filter light in the first optical path;

using two optical outputs of the optical interferometer to produce an error signal representing a frequency difference between the laser frequency of the laser and a resonance of the optical resonator; and

tuning one of (1) the laser and (2) the optical resonator, in response to the frequency difference of the error signal, to lock the laser and the optical resonator with respect to each other.

11. The method as in claim 10 , comprising:

producing a differential signal of power levels of the two optical outputs of the optical interferometer as the error signal.

12. The method as in claim 10 , comprising:

shifting a phase of one of the two optical outputs of the optical interferometer by 90 degrees to produce a first signal;

performing a time derivative of the other of the two optical outputs of the optical interferometer to produce a second signal; and

multiplying the first signal and the second signal to produce a multiplied signal to generate the error signal indicating the frequency difference.

13. The method as in claim 12 , comprising:

using a DC component of the multiplied signal to generate the error signal.

14. The method as in claim 12 , comprising:

producing a differential signal of power levels of the two optical outputs of the optical interferometer as a second error signal representing the frequency difference between the laser frequency and the resonance of the optical resonator; and

using both the error signal and the second error signal to lock the laser and the optical resonator with respect to each other.