All-microwave stabilization of microresonator-based optical frequency combs
Systems and methods in accordance with embodiments of the invention implement all-microwave stabilized microresonator-based optical frequency comb. In one embodiment, an all-microwave stabilized microresonator-based optical frequency comb includes: an optical pump configured to generate pulses of light; a microresonator including an input configured to receive pulses generated by an optical pump and an output configured to generate an optical frequency comb signal characterized by frep and ξ; where frep describes spacing of frequency components in the optical frequency comb; where the optical frequency comb includes a primary comb and a plurality of subcombs and ξ is a frequency offset between subcombs; and two phase locked loops that phase lock frep and ξ to low noise microwave oscillators by modulating output power and pump frequency of the optical pump.
1. An all-microwave stabilized microresonator-based optical frequency comb, comprising:
an optical pump configured to generate pulses of light:
a microresonator including an input configured to receive pulses generated by an optical pump and an output configured to generate an optical frequency comb signal characterized by f rep and ξ, where:
f rep describes spacing of frequency components in the optical frequency comb, and
the optical frequency comb includes a primary comb and a plurality of subcombs and ξ is a frequency offset between subcombs; and
two phase locked loops that phase lock f rep and ξ to low noise microwave oscillators by modulating output power and pump frequency of the optical pump.
2. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein optical pump output power is modulated using an electro-optical modulator.
3. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein the optical pump comprises an external cavity diode laser (ECDL).
4. The all-microwave stabilized microresonator-based optical frequency comb of claim 3 , wherein the pump frequency is controlled via a diode current of the ECDL.
5. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein respective intrinsic offset frequencies ξ are uniquely defined and resemble corresponding carrier envelope offset frequencies, f ceo after the stabilization of respective repetition frequencies, f rep .
6. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein pump power P p and pump frequency f p are implemented such that only a single set of respective primary comb lines is generated, resulting in the unique definition of a respective intrinsic offset frequency, ξ.
7. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein the offset frequency ξ is in the RF domain.
8. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein the primary comb lines are separated by Δ and a secondary comb line is spaced by f rep , wherein Δ is not an integer multiple of f rep and the frequency comb exhibits a single intrinsic offset frequency, ξ.
9. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , further comprising using additional slow feedback through the gain of an erbium-doped fiber amplifier (EDFA) and a piezoelectric transducer (PZT) of an ECDL to extend the stable operation time of the phase-locked loops.
10. The all-microwave stabilized microresonator-based optical frequency comb of claim 9 , wherein the control units of the slow feedback loops are the EDFA gain and the PZT.
11. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , further comprising utilizing PI 2 D control servos for feedback in the f rep and ξ phase lock loops.
12. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein to isolate the microresonator from ambient thermal fluctuations, the chip is mounted on a temperature-controlled chip-holder and enclosed in an acrylic chamber.
13. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein the offset frequency, ξ, is linked with the primary comb line spacing, Δ, by the constitutive relation
ξ
=
Δ
-
⌊
Δ
f
rep
⌋
f
rep
.
14. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein a proportional integral corner frequency is set lower than that of the f rep stabilization loop to reduce the crosstalk between the two phase-locked loops.
15. The all-microwave stabilized microresonator-based optical frequency comb of claim 1 , wherein multiple mode-spaced combs are formed comprising several subcomb families with incommensurate spacing between them.
16. The all-microwave stabilized microresonator-based optical frequency comb of claim 15 , wherein a first set of primary comb lines are formed at an offset of Δ 1 from the pump and a second set are formed at an offset of Δ 2 from the pump, wherein Δ 2 is not a multiple of Δ 1 and neither Δ 2 nor Δ 1 are integral multiples of f rep , and two offset beats ξ 1 and ξ are generated by beating of subcombs with each other.
17. The all-microwave stabilized microresonator-based optical frequency comb of claim 16 , wherein only the first set of primary comb lines is formed due to modulation instability via the pump, and all other primary comb lines are generated via cascaded four-wave mixing between the pump and the first set of primary comb lines, which allows for a single offset ξ throughout the comb.