LOW JITTER RF DISTRIBUTION SYSTEM

• US 20110123200A1
• Filed: 11/24/2009
• Published: 05/26/2011
• Est. Priority Date: 11/24/2009
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Huang, Gang, Doolittle, Lawrence, WILCOX, RUSSELL
• Granted Patent: US 8,270,844 B2
• Time in Patent Office: Days
• US Class Current: 398/154
• CPC Class Codes: H04B 10/2575 Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines
• CPC Class Codes: H04L 7/0075 with photonic or optical means

Abstract

A timing signal distribution system includes an optical frequency stabilized laser signal amplitude modulated at an rf frequency. A transmitter box transmits a first portion of the laser signal and receive a modified optical signal, and outputs a second portion of the laser signal and a portion of the modified optical signal. A first optical fiber carries the first laser signal portion and the modified optical signal, and a second optical fiber carries the second portion of the laser signal and the returned modified optical signal. A receiver box receives the first laser signal portion, shifts the frequency of the first laser signal portion outputs the modified optical signal, and outputs an electrical signal on the basis of the laser signal. A detector at the end of the second optical fiber outputs a signal based on the modified optical signal. An optical delay sensing circuit outputs a data signal based on the detected modified optical signal. An rf phase detect and correct signal circuit outputs a signal corresponding to a phase stabilized rf signal based on the data signal and the frequency received from the receiver box.

Claims

1. A timing signal distribution system comprising:

an optical frequency stabilized laser signal having an optical frequency ω

_op, wherein the laser signal is amplitude modulated at an rf frequency ω

_rf;

a transmitter box (110) temperature controlled to about ±

0.01°

C. having a first optical port (111) to receive the laser signal, a second optical port (112) to transmit a first portion of the laser signal and receive a modified optical signal, and a third optical port (113) to output a second portion of the laser signal and at least a portion of the returned modified optical signal;

a first optical fiber (14) having a first end and a second end, the first end coupled to the first optical port (111) to carry the first portion of the laser signal and the modified optical signal;

a second optical fiber (24) having a first end and a second end, the first end coupled to the third optical port (113) to carry the second portion of the laser signal and the portion of the returned modified optical signal;

a receiver box (130) temperature controlled to about ±

0.01°

C. having an optical receiver port (131) coupled at a second end of the first optical fiber (14) to receive the first portion of the laser signal and output the modified optical signal, a first electrical port (137) to receive an electrical frequency shift signal to shift the frequency of the first portion of the laser signal to provide the modified optical signal, and a second electrical port (139) to output an electrical signal on the basis of the first portion of the laser signal;

a reference detector (234) at a second end of the second optical fiber (24) co-located with the receiver box (130) to output a detector signal on the basis of the modified optical signal carried over the second optical fiber (24);

an optical delay sensing circuit (150) coupled to the reference detector (234) adapted to output a frequency signal to the first electrical port (137) of the receiver box (130) and output a data signal on the basis of the detected phase of the modified optical signal; and

an rf phase detect and correct signal circuit (160) coupled to the receiver box second electrical port (139) and coupled to the optical delay sensing circuit (150) to receive the data signal, the rf phase detect and correct signal circuit (160) adapted to output a signal corresponding to a phase stabilized rf signal at the frequency ω

_rf on the basis of the data signal and the frequency received from the second electrical port (139).

2. The system of claim 1, further comprising:

an optical amplitude modulator (105) to receive the optical signal from the laser (103); and

a radio frequency (rf) source (107) having an rf frequency ω

_rf coupled to the optical amplitude modulator (105) to drive the optical amplitude modulator (105) to amplitude modulate the laser signal at the rf frequency ω

_rf.

3. The system of claim 1, the transmitter box (110) further comprising:

a first optical fiber directional coupler (122) having at least four ports, wherein a first coupler port is coupled to the optical amplitude modulator (105) via the transmitter box (110) first optical port (111), a second coupler port is coupled to a transmitter box second optical port (112), a third coupler port is coupled to a first box third optical port (113), and a fourth coupler port; and

a transmitter reflector (115) coupled to the fourth coupler port.

4. The system of claim 1, where a first embodiment of the receiver box (130) further comprises:

a receiver box optical port (131) coupled to the second end of the first optical fiber (14), a first electrical port (137) and a second electrical port (139);

a second optical fiber directional coupler (132) having at least four coupler ports, wherein

a first coupler port is coupled to the receiver box optical port (131);

a second coupler port is coupled to a first optical detector (134);

a third coupler port coupled to an optical frequency shifter (136), in which the optical frequency shifter (136) shifts an optical signal by a frequency ω

_FS, the optical frequency shifter (136) coupled to the first electrical port (137) to receive an electrical signal corresponding to the frequency ω

_FS; and

a receiver reflector RR (138) coupled to the optical frequency shifter (136) to reflect the frequency shifted optical signal, wherein the reflected optical signal has a net frequency shift of 2ω

_FS.

5. The system of claim 1, where a second embodiment of the receiver box (330) further comprises:

a receiver box optical port (131) coupled to the second end of the first optical fiber (14), a first electrical port (137) and a second electrical port (139);

an optical frequency shifter FS (136) coupled to the optical port (131) and to the first electrical port (137);

a receiver reflector RR (338) coupled to the optical frequency shifter FS (136), where the receiver reflector RR (338) is a partial reflector/partial transmitter of an optical signal; and

a first optical detector (134) coupled to the receiver reflector RR (338), where an electrical output of the first optical detector (134) is coupled to the first electrical port (137).

6. The system of claim 1, further comprising:

a continuous wave laser (103) outputting an optical signal at a frequency of about ω

_op.

7. The system of claim 6, further comprising a vapor phase absorption cell (104) coupled to the continuous wave laser (103) to frequency stabilize the laser signal, the vapor phase absorption cell (104) containing a selected material in the vapor phase.

8. The system of claim 7, wherein the selected material in the vapor phase is at least one of rubidium, acetylene, hydrogen cyanide, and carbon monoxide.

9. The system of claim 1, further comprising:

an optical amplitude modulator (105) receiving the optical signal from the laser (103) and outputting the amplitude modulated laser signal;

a radio frequency (rf) source (107) operable at the rf frequency ω

_rf, the rf source coupled to the optical amplitude modulator (105) to control the optical amplitude modulator (105) to amplitude modulate the laser signal.

10. The system of claim 9, further comprising:

an optical amplifier (109) to receive the amplitude modulated optical signal from the laser (103) and provide an amplified optical signal to the first optical port (111) of the box (110).

11. The system of claim 1, further comprising a phase stabilized rf output generator (170) coupled to the rf phase detect and correcting circuit (160) to output the phase stabilized at the frequency ω

_rf on the basis of the signal output from the rf phase detect and correcting circuit (160).

12. The system of claim 1, wherein the first optical fiber (14) and the second optical fiber (24) transmit single mode optical signals at the optical frequency that is about ω

_op.

13. A method of stabilizing a distributed rf signal, comprising:

providing an optical frequency stabilized laser signal having an optical frequency ω

_op, wherein the laser signal is amplitude modulated at an rf frequency ω

_rf,

providing a transmitter box (110) temperature controlled to about ±

0.01°

C. having a first optical port (111) to receive the laser signal, a second optical port (112) to transmit a first portion of the laser signal and receive a modified optical signal, and a third optical port (113) to output a second portion of the laser signal and at least a portion of the returned modified optical signal;

coupling the first portion of the laser signal and the modified optical signal into a first optical fiber (14) having a first end and a second end, the first end coupled to the second optical port (112);

coupling the second portion of the laser signal and the portion of the returned modified optical signal via the third optical port (113) into a first end of a second optical fiber (24);

outputting the second portion of the laser signal and the portion of the returned modified optical signal at a second end of the second optical fiber (24);

receiving the first portion of the laser signal at an optical receiver port (131) of a receiver box (130) temperature controlled to about ±

0.01°

C., the receiver box (130) further having a first electrical port (137) to receive an electrical frequency signal to modify frequency of the first portion of the laser signal to provide the modified optical signal, and a to output an electrical signal on the basis of the first portion of the laser signal;

receiving, at a reference detector (234) at a second end of the second optical fiber (24) co-located with the receiver box (130), the second portion of the laser signal and the portion of the returned modified optical signal;

outputting from the reference detector (234) to a optical delay sensing circuit (150) an electrical signal on the basis of the returned modified optical signal;

outputting from the optical delay sensing circuit (150) to the first electrical port (137) a frequency signal and outputting a data signal on the basis of the detected phase of the modified optical signal;

receiving at an rf phase detect and correct signal circuit (160) coupled to the receiver box second electrical port (139) the data signal;

receiving at the rf phase detect and correct signal circuit (160) from the second electrical port (139) the electrical signal on the basis of the first portion of the laser signal; and

outputting from the rf phase detect and correct signal circuit (160) a signal corresponding to a phase stabilized rf signal at the frequency w on the basis of the data signal and the frequency received from the second electrical port (139).

14. The method of claim 13, further comprising:

receiving the optical signal from the laser (103) at an optical amplitude modulator (105); and

driving the optical amplitude modulator (105) to amplitude modulate the laser signal at the rf frequency ω

_rf using a radio frequency (rf) source (107) having an rf frequency ω

_rf coupled to the optical amplitude modulator (105).

15. The method of claim 13, wherein the transmitter box (110) comprises:

a first optical fiber directional coupler (122) having at least four ports, wherein a first coupler port is coupled to the optical amplitude modulator (105) via the transmitter box (110) first optical port (111), a second coupler port is coupled to a transmitter box second optical port (112), a third coupler port is coupled to a first box third optical port (113), and a fourth coupler port; and

a transmitter reflector (115) coupled to the fourth coupler port.

16. The method of claim 13, wherein the receiver box (130) comprises:

a receiver box optical port (131) coupled to the second end of the first optical fiber (14), a first electrical port (137) and a second electrical port (139);

a second optical fiber directional coupler (132) having at least four coupler ports, wherein

a first coupler port is coupled to the receiver box optical port (131);

a second coupler port is coupled to a first optical detector (134);

a third coupler port coupled to an optical frequency shifter (136), in which the optical frequency shifter (136) shifts an optical signal by a frequency ω

_FS, the optical frequency shifter (136) coupled to the first electrical port (137) to receive an electrical signal corresponding to the frequency ω

_FS; and

a receiver reflector RR (138) coupled to the optical frequency shifter (136) to reflect the frequency shifted optical signal, wherein the reflected optical signal has a net frequency shift of 2ω

_FS.

17. The method of claim 13, wherein the receiver box (330) comprises:

a receiver box optical port (131) coupled to the second end of the first optical fiber (14), a first electrical port (137) and a second electrical port (139);

an optical frequency shifter FS (136) coupled to the optical port (131) and to the first electrical port (137);

a receiver reflector RR (338) coupled to the optical frequency shifter FS (136), where the receiver reflector RR (338) is a partial reflector/partial transmitter of an optical signal; and

a first optical detector (134) coupled to the receiver reflector RR (338), where an electrical output of the first optical detector (134) is coupled to the first electrical port (137).

18. The method of claim 13, further comprising:

providing a continuous wave laser (103) outputting an optical signal at a frequency of about ω

_op.

19. The method of claim 18, further comprising:

providing a vapor phase absorption cell (104) coupled to the continuous wave laser (103) to frequency stabilize the laser signal, the vapor phase absorption cell (104) containing a selected material in the vapor phase.

20. The method of claim 19, further comprising selecting material in the vapor phase from at least one of rubidium, acetylene, hydrogen cyanide, and carbon monoxide.

21. The method of claim 13, further comprising:

modulating the amplitude of the frequency stabilized laser signal at the rf frequency ω

_rf using an optical amplitude modulator (105) driven by a radio frequency (rf) source (107) operable at the rf frequency ω

_rf.

22. The method of claim 21, further comprising:

amplifying the amplitude modulated optical signal from the optical modulator (105) using an optical amplifier (109); and

providing the amplified modulated optical signal to the first optical port (111) of the box (110).

23. The method of claim 13, further comprising:

coupling a phase stabilized rf output generator (170) to the rf phase detect and correcting circuit (160);

outputting the phase stabilized at the frequency ω

_rf on the basis of the signal output from the rf phase detect and correcting circuit (160).

24. The method of claim 13, wherein the first optical fiber (14) and the second optical fiber (24) transmit single mode optical signals at the optical frequency that is about ω

_op.