Fast variable optical delay

• US 6,356,677 B1
• Filed: 07/27/1999
• Issued: 03/12/2002
• Est. Priority Date: 01/25/1999
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Hall, Katherine L., Moriarty, Daniel T., Hakimi, Farhad, Hakimi, Hosain, Rauschenbach, Kristin A.
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Curtis, Craig
• Application Number:
  US09/362,349
• Time in Patent Office: 959 Days
• Field of Search: 385/15, 385/24, 385/37, 385/42, 385/122, 359/127, 359/130, 359/188, 359/290
• US Class Current: 385/15
• CPC Class Codes: G02B 6/2706 as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters
• CPC Class Codes: G02B 6/274 based on light guide birefringence, e.g. due to coupling between light guides G02B6/105, G02B6/024 take precedence; mechanically induced birefringence G02F1/0134
• CPC Class Codes: G02B 6/2861 using fibre optic delay lines and optical elements associated with them, e.g. for use in signal processing, e.g. filtering delay lines in general H03H, H01P9/00; optical computing devices G06E
• CPC Class Codes: G02B 6/29346 operating by wave or beam interference interferometers for measuring G01B9/02
• CPC Class Codes: G02B 6/29356 Interference cavity within a single light guide, e.g. between two fibre gratings G02B6/29347 - G02B6/2935 take precedence; evanescent coupling to a resonator cavity G02B6/29335
• CPC Class Codes: G02B 6/29374 in an optical light guide G02B6/02214 takes precedence
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35

Abstract

A method introduces variable time offsets into a stream of optical pulses. The method includes receiving a plurality of coherent optical pulses, receiving a plurality of control signals, and forming a coherent pulse array (CPA) from each pulse in response to one of the received control signals. Temporal spacings between pulses of each CPA are responsive to the associated one of the received control signals. For optical control signals, response times can be very short. The method further includes transmitting each pulse through a dispersive optical medium. The act of transmitting makes pulses of each CPA overlap to form an interference pattern.

Claims

1. A variable temporal grating generator (TGG), comprising:

an amplitude splitter to split a received optical pulse into a plurality of pulses;

a plurality of optical waveguides, each waveguide connected to receive one of the pulses from the splitter, at least one of the waveguides comprising a variable path element, the variable path element having a control terminal and an optical path length responsive to control signals received at the control terminal; and

a waveguide coupler connected to receive pulses from the optical waveguides, the coupler having an output terminal to transmit coherent pulse arrays (CPAs) made of the pulses received.

2. The variable TGG of claim 1, wherein the variable path element further comprises:

a nonlinear optical medium coupled to receive pulses traveling through the one of the waveguides; and

wherein the signals received by the control terminal are optical signals and the control terminal is connected to transmit a portion of each optical signal to the nonlinear medium.

3. The variable TGG of claim 2, wherein the variable path element further comprises:

a filter to impede the control signals from propagating to the waveguide coupler.

4. The variable TGG of claim 1, further comprising:

an output optical waveguide coupled to receive the CPAs from the output terminal; and

a high frequency signal generator coupled to send driving signals to a portion of the output optical waveguide, the driving signals to vary the index of refraction of the portion of the output optical waveguide.

5. The variable TGG of claim 4, wherein the signal generator is capable of producing electrical driving signals correlated to separate pulses of said CPAs.

6. The variable TGG of claim 4, wherein the signal generator is capable of producing optical driving signals correlated to separate pulses of said CPAs.

7. A variable optical delay line, comprising:

a length of dispersive medium having two ends; and

a temporal grating generator (TGG) having an optical input terminal, an optical output terminal and a control terminal, one of the optical input terminal and the optical output terminal being coupled to one end of the dispersive medium, the TGG to generate a coherent pulse array (CPA) at the optical output terminal from each pulse received at the optical input terminal, temporal spacings of pulses of each CPA being responsive to signals received at the control terminal, and the dispersive medium to cause each CPA to produce an interference pattern.

8. The variable optical delay line of claim 7, wherein the dispersive media is a dispersive optical waveguide.

9. The variable optical delay line of claim 7, wherein the variable TGG further comprises:

an amplitude splitter to split an optical pulse received from the input terminal into a plurality of pulses;

a plurality of optical waveguides, each waveguide connected to receive one of the pulses from the splitter, at least one of the waveguides comprising a variable path element, the variable path element coupling to the control terminal and an optical path length responsive to control signals received at the control terminal; and

a waveguide coupler connected to receive pulses from the optical waveguides, the waveguide coupler having a second output terminal to transmit a portion of the pulses received.

10. The variable optical delay line of claim 8, further comprising:

an optical clock to produce coherent optical clock pulses, the output terminal of the clock being connected to one of an end of the waveguide and the input terminal of the variable TGG.

11. The variable optical delay line of claim 8, further comprising an intensity discriminator connected to receive each interference pattern.

12. The variable optical delay line of claim 8, wherein the control terminal is capable of receiving an optical signal.

13. The variable optical delay line of claim 10, wherein the output terminal of the optical clock is connected to one end of the dispersive waveguide.

14. The variable optical delay line of claim 10, further comprising:

an intensity discriminator connected to receive each interference pattern.

15. The variable optical delay line of claim 11, wherein the intensity discriminator comprises a non-linear optical loop mirror (NOLM).

16. The variable optical delay line of claim 9, wherein the variable path element further comprises:

a nonlinear optical medium coupled to receive pulses traveling through the one of the waveguides; and

wherein the signals received by the control terminal are optical signals and the control terminal is connected to transmit a portion of each optical signal to the nonlinear medium.

17. The variable optical delay line of claim 16, wherein the variable path element further comprises:

a filter to impede the control signals from propagating to the waveguide coupler.

18. An optical phase locked loop, comprising:

an optical switch having first and second input terminals and an output terminal;

an optical clock to produce clock pulses;

a dispersive optical waveguide coupled to the optical clock; and

a variable temporal grating generator (TGG) having a control terminal, being coupled to receive the clock pulses from the dispersive waveguide, and being coupled to transmit interference patterns to the second input terminal of the optical switch, the output terminal of the switch being coupled to the control terminal.

19. The optical phase locked loop of claim 18, wherein the output terminal of the switch is coupled to transmit optical signals to the control terminal.

20. The optical phase locked loop of claim 19, wherein the variable TGG comprises:

an amplitude splitter to split a received clock pulse into a plurality of pulses;

a plurality of connecting optical waveguides, each connecting waveguide connected to receive one of the pulses from the splitter, at least one of the connecting waveguides comprising a variable path element, the variable path element having the control terminal and an optical path length responsive to the optical signals received at the control terminal; and

a waveguide coupler connected to receive pulses from the connecting optical waveguides, the coupler having an output terminal to transmit coherent pulse arrays (CPAs) made of the pulses received.

21. The optical phase locked loop of claim 20, wherein the variable path element further comprises:

a nonlinear optical medium coupled to receive clock pulses traveling in the one of the connecting waveguides; and

wherein the control terminal is connected to transmit a portion of each optical control signal to the nonlinear medium.

22. The optical phase locked loop of claim 20, wherein the variable path element further comprises:

a filter to impede optical control signals from propagating to the waveguide coupler.

23. An antenna array, comprising:

a plurality of remote antennae;

a control system to produce optical control signals;

a plurality of first optical waveguides coupled to receive the optical control signals from the control system;

a plurality of variable temporal grating generators (TGG), each TGG coupled to one of the first optical waveguides; and

a plurality of second optical waveguides, each second optical waveguide connecting one of the TGGs to one of the remote antennae, each second optical waveguide capable of producing an interference pattern from a coherent pulse array (CPA) received from the connected TGG.

24. The antennae array of claim 23, wherein the control system couples to a control terminal of each variable TGG.

25. The antennae array of claim 23, wherein the control system is capable of sending first and second signals to the control terminals of respective first and second ones of the TGGs, the first and second signals to produce CPAs with different pulse spacings.