Stabilized microwave-frequency source

Patent metadata

Field	Value
Publication number	US-9450673-B2
Application number	US-201514605977-A
Country	US
Kind code	B2
Filing date	Jan 26, 2015
Priority date	Jan 24, 2014
Publication date	Sep 20, 2016
Grant date	Sep 20, 2016

Abstract

A microwave-frequency source at frequency f M comprises: a dual optical-frequency reference source, an electro-optic sideband generator, an optical bandpass filter, an optical detector, a reference oscillator, an electrical circuit, and a voltage-controlled oscillator (VCO). The sideband generator modulates dual optical reference signals at v 2 and v 1 to generate sideband signals at v 1 ±n 1 f M and v 2 ±n 2 f M . The bandpass filter transmits sideband signals at v 1 +N 1 f M and v 2 −N 2 f M . The optical detector generates a beat note at (v 2 −N 2 f M )−(v 1 +N 1 f M ). The beat note and a reference oscillator signal are processed by the circuit to generate a loop-filtered error signal to input to the VCO. Output of the VCO at f M drives the sideband generator and forms the microwave-frequency output signal. The resultant frequency division results in reduced phase noise on the microwave-frequency signal.

First claim

What is claimed is:

1. A microwave-frequency source for generating an output electrical signal at an output frequency f M , the microwave-frequency source comprising:
(a) a dual optical-frequency reference source arranged so as to generate (i) a first optical reference signal at a first optical reference frequency v 1 and (ii) a second optical reference signal at a second optical reference frequency v 2 >v 1 ;
(b) an electro-optic sideband generator arranged so as to (i) receive the first and second optical reference signals and a sideband generator input electrical signal at the frequency f M and (ii) generate therefrom multiple sideband optical signals at respective sideband optical frequencies of the form v 1 ±n 1 f M and v 2 ±n 2 f M , wherein n 1 and n 2 are integers;
(c) an optical bandpass filter arranged so as to transmit a subset of the multiple sideband optical signals including the sideband optical signal at a frequency v 1 +N 1 f M and the sideband optical signal at a frequency v 2 −N 2 f M , wherein N 1 and N 2 are integers;
(d) an optical detector arranged so as to (i) receive the transmitted sideband optical signals and (ii) generate an optical detector electrical signal at a beat frequency f BEAT =(v 2 −N 2 f M )−(v 1 +N 1 f M );
(e) a reference oscillator arranged so as to generate a reference oscillator electrical signal at a reference oscillator frequency f R ;
(f) an electrical circuit arranged so as to (i) receive the optical detector electrical signal and the reference oscillator electrical signal, (ii) generate therefrom, using a comparator portion of the electrical circuit, an electrical error signal dependent on relative phase of the optical detector and reference oscillator electrical signals, and (iii) process the electrical error signal using a loop-filter portion of the electrical circuit; and
(g) a voltage-controlled electrical oscillator arranged so as to (i) receive the loop-filtered electrical error signal as a VCO input electrical signal and (ii) generate a VCO output electrical signal at the frequency f M , wherein a first portion of the VCO output electrical signal is received by the electro-optic sideband generator as the sideband generator input electrical signal and a second portion of the VCO output electrical signal forms the output electrical signal of the microwave-frequency source,
(h) wherein reception of the first portion of the VCO output electrical signal by the electro-optic sideband generator as the sideband generator input electrical signal results in the electrical circuit and the voltage-controlled oscillator being coupled in a negative feedback arrangement so as to function as a phase-locked loop.

2. The microwave-frequency source of claim 1 wherein phase noise of the output electrical signal of the microwave-frequency source is reduced by a factor of about (N 1 +N 2 ) 2 relative to phase noise of a reference difference frequency signal at a reference difference frequency v 2 −v 1 of the dual optical-frequency reference source.

3. The microwave-frequency source of claim 1 wherein the output frequency f M is between about 0.3 GHz and about 300 GHz.

4. The microwave-frequency source of claim 1 wherein the output frequency f M is between about 1 GHz and about 100 GHz.

5. The microwave-frequency source of claim 1 wherein the reference oscillator frequency and the beat frequency are between about 1 MHz and about 500 MHz.

6. The microwave-frequency source of claim 1 wherein the reference oscillator frequency and the beat frequency are between about 5 MHz and about 100 MHz.

7. The microwave-frequency source of claim 1 wherein the reference oscillator frequency and the beat frequency are between about 10 MHz and about 50 MHz.

8. The microwave-frequency source of claim 1 wherein the reference oscillator comprises a crystal oscillator.

9. The microwave-frequency source of claim 1 wherein the reference oscillator comprises an electrical oscillator.

10. The microwave-frequency source of claim 1 wherein a reference difference frequency v 2 −v 1 is greater than about 100 GHz.

11. The microwave-frequency source of claim 1 wherein a reference difference frequency v 2 −v 1 is greater than about 1 THz.

12. The microwave-frequency source of claim 1 wherein a reference difference frequency v 2 −v 1 is greater than about 10 THz.

13. The microwave-frequency source of claim 1 wherein a reference difference frequency v 2 −v 1 is greater than about 100 THz.

14. The microwave-frequency source of claim 1 wherein N 1 +N 2 is greater than or equal to 10.

15. The microwave-frequency source of claim 1 wherein N 1 +N 2 is greater than or equal to 50.

16. The microwave-frequency source of claim 1 wherein N 1 +N 2 is greater than or equal to 100.

17. The microwave-frequency source of claim 1 wherein N 1 +N 2 is greater than or equal to 1000.

18. The microwave-frequency source of claim 1 wherein the first and second optical reference frequencies v 1 and v 2 are each between about 75 THz and about 750 THz.

19. The microwave-frequency source of claim 1 wherein the first and second optical reference frequencies v 1 and v 2 are each between about 120 THz and about 430 THz.

20. The microwave-frequency source of claim 1 wherein the first and second optical reference frequencies v 1 and v 2 are each between about 150 THz and about 300 THz.

21. The microwave-frequency source of claim 1 wherein the dual optical-frequency reference source is stabilized so as to (i) maintain fluctuations of a reference difference frequency v 2 −v 1 within an operationally acceptable optical reference bandwidth or (ii) maintain phase noise of a reference difference frequency signal within an operationally acceptable reference phase noise level.

22. The microwave-frequency source of claim 21 wherein the operationally acceptable reference bandwidth is less than about 100 Hz over about a 1 second timescale.

23. The microwave-frequency source of claim 21 wherein the operationally acceptable reference bandwidth is less than about 1 Hz over about a 1 second timescale.

24. The microwave-frequency source of claim 21 wherein the operationally acceptable reference phase noise level is about −40 dBc/Hz at 100 Hz offset frequency and about −80 dBc/Hz at 10 kHz offset frequency.

25. The microwave-frequency source of claim 21 wherein the operationally acceptable reference phase noise level is about −80 dBc/Hz at 100 Hz offset frequency and about −125 dBc/Hz at 10 kHz offset frequency.

26. The microwave-frequency source of claim 1 wherein (i) the dual optical-frequency reference source comprises first and second pump laser sources and an optical resonator, (ii) a free spectral range of the optical resonator is substantially equal to an integer submultiple of a Brillouin shift frequency of the optical resonator, (iii) each one of the first and second pump laser sources is frequency-locked to a corresponding resonant optical mode of the optical resonator, and (iv) the first and second optical reference signals comprise stimulated Brillouin laser output generated by optical pumping of the optical resonator simultaneously by the first and second pump laser sources, respectively.

27. The microwave-frequency source of claim 26 wherein the free spectral range of the optical resonator is substantially equal to the Brillouin shift frequency of the optical resonato

Assignees

• California Inst Of Techn
• The Us Secretary Of Commerce The Nat Inst Of Standards And Tech

Inventors

• Vahala Kerry
• Diddams Scott
• Li Jiang
• Yi Xu
• Lee Hansuek

Classifications

• H04B10/25891

  Transmission components (H04B10/40 takes precedence) · CPC title

• H03B17/00

  Generation of oscillations using radiation source and detector, e.g. with interposed variable obturator · CPC title

• H03L7/16

  Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop · CPC title

• H04B2210/006

  Devices for generating or processing an RF signal by optical means · CPC title

• H03L7/08 Primary

  Details of the phase-locked loop · CPC title