Digitally controlled optical fiber delay line

• US 7,283,708 B2
• Filed: 12/30/2003
• Issued: 10/16/2007
• Est. Priority Date: 12/30/2003
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Efimov, Oleg M.
• Primary Examiner(s): PAK, SUNG H
• Application Number:
  US10/749,187
• Publication Number:
  US 20050141814A1
• Time in Patent Office: 1,386 Days
• Field of Search: None
• US Class Current: 385/39
• 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

Abstract

An optical fiber delay line includes: multiple differential delay lines; and multiple switchers connecting the differential delay lines in pairs. Using, for example, N+1 differential delay lines numbered by k from 0 to N, the k-th differential delay line delays an input optical signal by an amount of time (t^k_A−t^k_B)=2^k τ, so that the electronically controlled switchers allow digitally controlling the delay over a range from 0 to (2^N+1−1)τ with a time resolution of τ. The delay line can also be used simultaneously as a phase modulator, enabling a system of synchronization that can be realized entirely electronically and may be very useful in the case of large fiber arrays comprising a number of fiber modules such as beam splitters, fiber amplifiers, connectors, and collimators. The delay line can also be used as a commutator, for controlled switching of optical signals between channels.

Claims

1. An optical delay line comprising:

a plurality of optical fiber differential delay lines, each comprising a long A optical fiber and a short B optical fiber; and

a plurality of phase actuated switchers connecting said plurality of optical fiber differential delay lines, wherein;

each of said plurality of phase actuated switchers is configured to switch an input signal to the long A optical fiber or the short B optical fiber of its respective optical fiber differential delay line; and

wherein at least one of said phase actuated switchers includes;

a fiber coupler connected to at least one of said plurality of optical fiber differential delay lines; and

a spatial light modulator that reflects an input signal from said fiber coupler.

2. The optical delay line of claim 1 wherein for each of said plurality of optical fiber differential delay lines:

said long A optical fiber is connected to a first one and a second one of said plurality of phase actuated switchers; and

said short B optical fiber is connected to said first one and said second one of said plurality of phase actuated switchers.

4. The optical delay line of claim 1 wherein at least one of said plurality of optical fiber differential delay lines comprises:

a short B optical fiber having a length L^k_B;

a long A optical fiber having a length L^k_A wherein said differential delay line delays an input optical signal by an amount of time proportional to (L^k_A−

L^k_B).

5. The optical delay line of claim 1 wherein at least one of said plurality of optical fiber differential delay lines comprises:

a short B optical fiber having a length L^k_B;

a long A optical fiber having a length L^k_A wherein;

said differential delay line delays an input optical signal by an amount of time (t_A−

t_B) proportional to (L^k_A−

L^k_B); and

(t_A−

t_B)=2^kτ

, for some integer value of k≧

0, where τ

is a time resolution of the optical delay line.

6. The optical delay line of claim 5 wherein:

said plurality of phase actuated switchers connect said plurality of differential delay lines in pairs between an input and an output of the optical delay line so that a differential delay Δ

t between an input and an output of the optical delay line is the sum of the differential delays of each of the plurality of differential delay lines; and

$\mathrm{\Delta <br><br>}<br><br><br><br>t=\mathrm{\tau <br><br>}<br><br>\underset{i=1}{\overset{M}{\sum <br><br>}}<br><br><br><br>2^{k_1},$

where {k₁, . . . , k_M} is a set differential delay lines with an A optical fiber selected.

3. An optical delay line comprising:

a plurality of optical fiber differential delay lines, each comprising a long A optical fiber and a short B optical fiber; and

a plurality of phase actuated switchers connecting said plurality of optical fiber differential delay lines, wherein;

each of said plurality of phase actuated switchers is configured to switch an input signal to the long A optical fiber or the short B optical fiber of its respective optical fiber differential delay line; and

wherein at least one of said phase actuated switchers includes;

a fiber coupler connected to at least one of said plurality of optical fiber differential delay lines;

at least one switch fiber connected to said fiber coupler; and

a piezoelectric-stretcher attached to said switch fiber.

7. An optical communication system comprising:

a plurality of optical fiber differential delay lines; and

a plurality of phase actuated switchers connecting said plurality of optical fiber differential delay lines in pairs wherein at least one of said phase actuated switchers includes;

a fiber coupler connected to at least one of said plurality of optical fiber differential delay lines;

at least one switch fiber connected to said fiber coupler;

a collimator at an end of said switch fiber; and

a mirror of an electronically controlled spatial light modulator that reflects an input signal from said collimator back into said collimator; and

wherein;

at least one of said plurality of optical fiber differential delay lines comprises;

a long A optical fiber wherein said long A optical fiber is connected to a first one and a second one of said plurality of phase actuated switchers; and

a short B optical fiber wherein said short B optical fiber is connected to said first one and said second one of said plurality of phase actuated switchers.

8. The system of claim 7 wherein at least one of said phase actuated switchers includes:

a fiber coupler connected to at least one of said plurality of optical fiber differential delay lines;

at least one switch fiber connected to said fiber coupler; and

an electronically controlled electro-optical modulator that adjusts the phase of an input signal in said switch fiber.

9. The system of claim 7 wherein at least one of said phase actuated switchers includes:

a fiber coupler connected to at least one of said plurality of optical fiber differential delay lines;

at least one switch fiber connected to said fiber coupler;

a collimator at an end of said switch fiber;

a stationary mirror; and

an electronically controlled bi-refringent crystal disposed between said collimator and said stationary mirror.

11. The system of claim 7 wherein said plurality of optical fiber differential delay lines includes N+1 differential delay lines numbered by k from 0 to N, wherein N is a number greater than or equal to zero, and for each specific value of k, the k-th differential delay line comprises:

a k-th short B optical fiber having a length L^k_B;

a k-th long A optical fiber having a length L^k_A wherein;

said k-th differential delay line delays an input optical signal by an amount of time (t^k_A−

t^k_B) proportional to (L^k<sub>A−

L</sub>^k_B);

(t^k_A−

t^k_B)=2^kτ

, where τ

is a time resolution of the optical delay line;

said N+1 differential delay lines and said plurality of phase actuated switchers allows digitally controlling a differential delay Δ

t over the range from 0 to (2^N+1−

1)τ

with a time resolution of τ

; and

$\mathrm{\Delta <br><br>}<br><br><br><br>t=\mathrm{\tau <br><br>}<br><br>\underset{i=1}{\overset{M}{\sum <br><br>}}<br><br><br><br>2^k,$

where {k₁, . . . , k_M} is a set differential delay lines with an A optical fiber selected.

10. An optical communication system comprising:

a plurality of optical fiber differential delay lines; and

a plurality of phase actuated switchers connecting said plurality of optical fiber differential delay lines in pairs wherein at least one of said phase actuated switchers includes;

a fiber coupler connected to at least one of said plurality of optical fiber differential delay lines;

at least one switch fiber connected to said fiber coupler and terminated with a mirror; and

an electronically controlled piezoelectric-stretcher attached to said switch fiber between said fiber coupler and said mirror; and

wherein;

at least one of said plurality of optical fiber differential delay lines comprises;

a long A optical fiber wherein said long A optical fiber is connected to a first one and a second one of said plurality of phase actuated switchers; and

a short B optical fiber wherein said short B optical fiber is connected to said first one and said second one of said plurality of phase actuated switchers.

12. An optical system comprising:

a plurality of optical fiber differential delay lines; and

a plurality of phase actuated switchers connecting said plurality of optical fiber differential delay lines in pairs wherein;

said plurality of phase actuated switchers comprises a plurality of mirrors of a spatial light modulator;

said spatial light modulator provides equal adjustment of positions for all mirrors simultaneously to phase modulate an input optical signal;

said plurality of optical fiber differential delay lines includes N+1 differential delay lines numbered by k from 0 to N, wherein N is a number greater than or equal to zero, said plurality of phase actuated switchers includes N+2 phase actuated switchers numbered by k from 0 to N+1, and for each specific value of k, the k-th differential delay line comprises;

a k-th short B optical fiber having a length L^k_B and connected between a k-th phase actuated switcher and a (k+1)-th phase actuated switcher of said plurality of phase actuated switchers;

a k-th long A optical fiber having a length L^k_A and connected between said k-th phase actuated switcher and said (k+1)-th phase actuated switcher of said plurality of phase actuated switchers and wherein;

said k-th differential delay line delays said input optical signal by an amount of time (t^k_A−

t^k_B) proportional to (L^k_A−

L^k_B);

(t^k_A−

t^k_B)=2^kτ

, where τ

is a time resolution of the optical delay line;

said N+1 differential delay lines and said plurality of phase actuated switchers allows digitally controlling a differential delay Δ

t over the range from 0 to (2^N+1−

1)τ

with a time resolution of τ

;

$\mathrm{\Delta <br><br>}<br><br><br><br>t=\mathrm{\tau <br><br>}<br><br>\underset{i=1}{\overset{M}{\sum <br><br>}}<br><br><br><br>2^k,$

where {k₁, . . . , k_M}is a set of said N+1 differential delay lines with an A optical fiber selected by one of said plurality of phase actuated switchers.

13. An optical phase modulator comprising:

a plurality of optical fiber differential delay lines; and

a plurality of phase actuated switchers connecting said plurality of optical fiber differential delay lines in pairs, wherein;

each of said phase actuated switchers includes;

a fiber coupler connected to at least one of said plurality of optical fiber differential delay lines; and

a light phase adjustment device that includes a mirror and is connected to said fiber coupler;

at least one of said plurality of optical fiber differential delay lines comprises a long A optical fiber connected to a first one and a second one of said plurality of phase actuated switchers, and a short B optical fiber connected to said first one and said second one of said plurality of phase actuated switchers; and

each of said light phase adjustment devices is simultaneously controlled to equally adjust a phase of an input signal at all mirrors simultaneously so that said optical phase modulator modulates said phase of said input signal.

14. A method for providing a differential delay in an optical signal comprising the steps of:

switching an input signal, either into a long A optical fiber of a differential delay line or else into a short B optical fiber of said differential delay line, to have any delay in a pre-determined dynamic range with time resolution τ

; and

phase modulating the input signal by simultaneously adjusting a phase of the input signal by an equal amount at a plurality of phase actuated switchers.

15. The method of claim 14 wherein said switching step further includes:

switching the input signal among a plurality of differential delay lines so that the input signal is delayed by a sum of delays and said sum of delays includes a combination of long A optical fibers and short B optical fibers of said plurality of differential delay lines.

16. The method of claim 14 wherein said switching step further includes:

providing a first differential delay line with a minimum time delay τ

;

providing at least one second differential delay line with a time delay that is a multiple of time delay τ

; and

providing phase actuated switchers capable of switching the input signal among all possible combinations of long A optical fibers and short B optical fibers of said first and second differential delay lines so that a differential delay of the input signal may sum to any multiple of τ

within a predetermined total range.

17. The method of claim 14 wherein said switching step further includes:

switching the input signal over a variable part of a delay line, wherein said variable part comprises a plurality of differential delay lines allowing digitally controlling a delay over the range from 0 to (2^N+1−

1)τ

with a time resolution of τ

, wherein N is a number greater than or equal to zero and N+1 is the number of said differential delay lines.