Synchronization of lasers and RF sources using timing information transfer in the optical domain

• US 7,593,644 B2
• Filed: 05/10/2005
• Issued: 09/22/2009
• Est. Priority Date: 05/12/2004
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Kim, Jung Won, Perrott, Michael, Kaertner, Franz X.
• Primary Examiner(s): Phan; Hanh
• Application Number:
  US11/125,800
• Publication Number:
  US 20050265406A1
• Time in Patent Office: 1,596 Days
• Field of Search: 398/154, 398/98, 398/102, 398/161, 398/173, 398/175, 398/182, 398/183, 398/191, 398/188, 398/186, 398/200, 398/202, 398/203, 398/204, 398/206, 398/207, 356/450, 356/460, 356/483, 356/459, 356/476, 372/18, 372/32, 372/34, 372/38.01, 372/36, 372/30
• US Class Current: 398/154
• CPC Class Codes: G04G 7/02 by radio
• CPC Class Codes: H01S 3/105 by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity lengthH01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/1305 Feedback control systems
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 3/139 by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity length
• CPC Class Codes: H01S 3/1394 by using an active reference, e.g. second laser, klystron or other standard frequency source
• CPC Class Codes: H01S 3/1398 by using a supplementary modulation of the output
• CPC Class Codes: H01S 3/1625 titanium
• CPC Class Codes: H01S 3/1636 Al2O3 (Sapphire)
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

A RF-synchronization system includes a laser that creates pulse trains for synchronization. A modulation means transfers the timing information of the pulse train into an amplitude modulation of an optical or electronic system. A synchronization module changes the driving frequency of the modulation means until it reaches a phase-locked state with the pulse train.

Claims

1. A RF synchronization system comprising:

a laser that creates pulse trains for synchronization;

a modulation means that transfers the timing information of pulse trains from a modelocked laser source with respect to an RF signal to be tightly synchronized to the pulse stream into an amplitude modulated optical signal; and

a synchronization module that changes the driving frequency of the RF-signal and with it of said modulation means until it reaches a phase-locked state with the pulse trains, said synchronization module using a filter that receives an error signal so as to tune the frequency of said timing information until said pulse train arrives to a selective balance point.

2. The RF-synchronization system of claim 1, wherein said modulation means is a phase modulator in a Sagnac loop.

3. The RF-synchronization system of claim 1, wherein said laser comprises a Ti:

sapphire mode-locked laser or a fiber laser.

4. The RF-synchronization system of claim 1, wherein said synchronization module comprises a VCO so as to form a microwave output signal.

5. The RF-synchronization system of claim 4, wherein said synchronization module comprises a balanced detector that generates a difference signal.

6. The RF-synchronization system of claim 5, wherein said synchronization module comprises a passive loop filter that receives said difference signal and performs filtering.

7. The RF-synchronization system of claim 6, wherein said synchronization module comprises a VCO that receives the output of said passive loop filter and drives said modulation means.

8. A method of performing RF-synchronization comprising:

providing pulse trains from a laser source;

transferring the timing information of pulse trains from a modelocked laser source with respect to an RF signal to be tightly synchronized to the pulse stream into an amplitude modulated optical or electrical signal; and

changing the driving frequency of the timing information of the pulse trains until it reaches a phase-locked state with the pulse using a passive filter that receives an error signal so as to tune the frequency of said timing information until said pulse train arrives to a selective balance point.

9. The method of claim 8, wherein said laser source comprises a Ti:

sapphire mode-locked laser or a fiber laser.

10. The method of claim 8, wherein changing the driving frequency comprise producing output signals that includes providing a VCO so as to form a microwave signal.

11. The method of claim 10, wherein producing said output signals comprises generating a difference signal.

12. The method of claim 10, wherein producing said output signals comprises filtering said difference signal.

13. The method of claim 12, wherein producing said output signals comprises driving at least one phase modulator.

14. The method of claim 13 further comprising providing a bandpass filter that receives as input said pulse signal.

15. The method of claim 8, wherein said pulse trains comprise a repetition rate of at least100 MHz.

16. A method of extracting a low jitter microwave signal from a mode-locked laser that serves as the clock work of an optical clock comprising:

providing a laser that creates pulse trains;

transferring the timing information of optical pulse trains from a modelocked laser source with respect to an RF signal to be tightly synchronized to the pulse stream into an amplitude modulated optical signal;

changing the driving frequency of the timing information of the optical pulse trains until it reaches a phase-locked state with the optical pulse train using a filter that receives an error signal so as to tune the frequency of said timing information until said pulse train arrives to a selective balance point.

17. The method of claim 16, wherein changing the driving frequency requires a VCO so as to form a microwave output signal.

18. The method of claim 16, wherein changing the driving frequency requires a balanced detector that generates a difference signal.

19. The method of claim 18, wherein changing the driving frequency requires a passive loop filter that receives said difference signal and performs filtering.

20. The method of claim 16, wherein said pulse trains comprise a repetition rate of at least 100 MHz.

21. An optical synchronization system comprising

a laser that creates pulse trains and

a pair of modulators that uses said pulse trains to formulate timing information that is transferred into an intensity imbalance between two optical beams by sending the pulse signals through said pair of amplitude modulators so as to produce an error signal used by a filter in tuning the frequency of said timing information until said pulse train arrives to a selective balance point.

22. The optical synchronization system of claim 21, wherein said laser comprises a Ti:

sapphire or fiber mode-locked laser.

23. The optical synchronization system of claim 21 further comprising a bandpass filter that receives as input said pulse signal.

24. The optical synchronization system of claim 21, wherein said pulse signals comprise a repetition rate of at least 100 MHz.

25. A method of performing optical synchronization comprising

providing a laser that creates pulse trains and

formulating timing information by using said pulse trains;

and

transferring into an intensity imbalance between two optical beams by sending the pulse signals through a pair of amplitude modulators so as to produce an error signal used by a filter in tuning the frequency of said timing information until said pulse train arrives to a selective balance point.

26. The method of claim 25, wherein said laser comprises a Ti:

sapphire or fiber mode-locked laser.

27. The method of claim 25 further comprising a bandpass filter that receives as input said pulse trains.

28. The method of claim 25, wherein said pulse trains comprise a repetition rate of at least 100 MHz.