Ultra-low phase noise transfer oscillator microwave reference via phase modulated mode-locked laser feedback

1 . A system comprising:

a mode-locked laser (MLL) configured to:

receive a first radio frequency (RF) reference signal, and

based on the first RF reference signal, generate an optical frequency comb (OFC);

a wavelength conversion medium configured to:

receive the OFC, and

based on the OFC, generate at least one photonic reference signal; and

a transfer oscillator (TO) circuit comprising a plurality of TO channels, the TO circuit configured to:

receive the OFC and the at least one photonic reference signal,

generate, via each TO channel, a respective processed RF signal

based on the OFC and the at least one photonic reference signal, and

coherently sum each respective processed RF signal to generate the first RF reference signal.

2 . The system of claim 1 , wherein the at least one photonic reference signal corresponds with a tooth from the OFC.

3 . The system of claim 1 , further comprising:

at least one reference laser configured to generate a photonic signal; and

a modified uni-traveling carrier photodiode (MUTC PD),

wherein:

the MUTC PD is configured to:

receive a combination of the photonic signal and the OFC; and

generate a first RF signal based on the combination of the photonic signal the OFC;

receiving the OFC by the TO circuit comprises receiving the first RF signal; and

the wavelength conversion medium is a periodically poled lithium niobate waveguide.

4 . The system of claim 3 , wherein the at least one reference laser comprises a plurality of reference lasers, and the photonic signal is generated by coherently combining an output of the plurality of reference lasers.

5 . The system of claim 3 , wherein each TO channel comprises:

an x-band filter configured to:

receive the first RF signal; and

generate a first filtered RF signal;

a plurality of direct digital synthesizers (DDSs), each DDS configured to:

receive one of the at least one photonic reference signal; and

generate an xth RF signal based on the one of the at least one photonic reference signal,

wherein each TO channel is configured to generate the respective processed RF signal based on the first filtered RF signal and each of the xth RF signals.

6 . The system of claim 5 , wherein

the respective processed RF signal from each TO channel corresponds with a particular tooth from the OFC.

7 . The system of claim 3 , wherein:

the MLL comprises:

a lithium niobate crystal, and

a phase modulator (PM); and

generating the OFC comprises modulating the photonic signal with the phase modulator according to the first RF reference signal into the lithium niobate crystal.

8 . A method comprising:

generating, by a mode-locked laser (MLL), an optical frequency comb (OFC);

generating, by a wavelength conversion medium, based on the OFC, at least one photonic reference signal;

generating, by each of a plurality of transfer oscillator (TO) channels of a TO circuit, a respective processed RF signal based on the OFC and the at least one photonic reference signal;

coherently summing each respective processed RF signal to generate a first radio frequency (RF) reference signal; and

modulating a phase of the MLL based on the first RF reference signal.

9 . The method of claim 8 , wherein the at least one photonic reference signal corresponds with a tooth from the OFC.

10 . The method of claim 9 , further comprising:

generating, by at least one reference laser, a photonic signal;

receiving, by a modified uni-traveling carrier photodiode (MUTC PD), a combination of the photonic signal and the OFC; and

generating, by the MUTC PD, based on the combination of the photonic signal the OFC, a first RF signal,

wherein receiving the OFC by the TO circuit comprises receiving the first RF signal, and

the wavelength conversion medium is a periodically poled lithium niobate waveguide.

11 . The method of claim 10 , wherein the at least one reference laser comprises a plurality of reference lasers, and the photonic signal is generated by coherently combining an output of the plurality of reference lasers.

12 . The method of claim 10 , wherein generating, by each of the plurality of TO channels, the respective processed RF signal comprises, for each of the plurality of TO channels:

receiving, by an x-band filter, the first RF signal;

generating, by the x-band filter, a first filtered RF signal;

for each of a plurality of direct digital synthesizers (DDSs):

receiving one of the at least one photonic reference signals; and

generating an xth RF signal based on the one of the at least one photonic reference signal; and

generating the respective processed RF signal based on the first filtered RF signal and each of the xth RF signals.

13 . The method of claim 11 , wherein

the respective processed RF signal from each TO channel corresponds with a particular tooth from the OFC.

14 . The method of claim 10 , wherein generating, by the MLL, the OFC comprises modulating the photonic signal with a phase modulator (PM) according to the first RF reference signal into a lithium niobate crystal.

15 . A transfer oscillator (TO) circuit comprising at least one TO channel, each TO channel comprising:

an x-band filter configured to:

receive a first RF signal; and

generate a first filtered RF signal; and

a plurality of direct digital synthesizers (DDSs), each DDS configured to:

receive a photonic reference signal; and

generate an xth RF signal based on the photonic reference signal,

wherein each TO channel is configured to generate a processed RF signal based on the first filtered RF signal and each of the xth RF signals; and

wherein the TO circuit is configured to:

coherently sum the processed RF signal from each TO channel; and

generate a first RF reference signal based on the coherent sum.

16 . The TO circuit of claim 15 , wherein the first RF signal is generated based on an optical frequency comb (OFC).

17 . The TO circuit of claim 16 , wherein the processed RF signal from each TO channel corresponds with a particular tooth from the OFC.

18 . The TO circuit of claim 16 , wherein the photonic reference signal corresponds with a tooth from the OFC.

19 . The TO circuit of claim 18 , wherein the first RF signal is generated based on the combination of a photonic signal and the OFC.

20 . The TO circuit of claim 16 , wherein the OFC is generated based on the first RF reference signal.