Distributed sensing interrogator using single-mode fiber for multi-mode fiber interrogation

1. A system, comprising:

a single-mode circulator coupleable to a distributed sensing interrogator for routing a single-mode optical signal from the distributed sensing interrogator through a single-mode optical fiber to a multi-mode optical fiber positionable along a region to be sensed and communicatively coupleable to an optical receiver of the distributed sensing interrogator for routing a reflective optical signal received from the multi-mode optical fiber to the optical receiver; and

an optical amplifier coupled to the single-mode circulator for amplifying the single-mode optical signal, wherein the single-mode circulator comprises:

a first port coupled to an optical fiber for receiving a reflective optical signal from the multi-mode optical fiber;

a second port communicatively coupleable to the distributed sensing interrogator for receiving the single-mode optical signal from the distributed sensing interrogator; and

a third port coupled to the optical amplifier for routing the single-mode optical signal to the optical amplifier.

2. The system of claim 1 , further comprising:

an optical filter coupled to an output of the optical amplifier for filtering one or more noise components from the amplified single-mode optical signal.

3. The system of claim 1 , further comprising a variable optical attenuator coupled to the single-mode circulator for reducing a power level of the single-mode optical signal.

4. The system of claim 3 , wherein the optical amplifier is coupled directly to an output of the variable optical attenuator for amplifying an attenuated single-mode optical signal from the variable optical attenuator.

5. The system of claim 1 , wherein the first port of the single-mode circulator is coupled to receive light from a multimode optical fiber via a mode field adapter.

6. The system of claim 1 , further comprising:

a second single-mode circulator having a first port coupled to an output of the optical amplifier, a second port connected to the multi-mode optical fiber, and a third port for routing backscatter signaling from the second single-mode circulator to the first port of the single-mode circulator.

7. The system of claim 1 , further comprising:

a mode scrambler coupleable to the multi-mode optical fiber for coupling the amplified single-mode optical signal into a plurality of modes of the multi-mode optical fiber.

8. The system of claim 7 , further comprising:

a second single-mode circulator having a first port coupled to an output of the optical amplifier, a second port connected to the mode scrambler that is connected to the multi-mode optical fiber, and a third port for routing backscatter signaling from the second single-mode circulator to a first port of the single-mode circulator.

9. The system of claim 7 , further comprising:

a multi-mode circulator coupleable to an output of the optical amplifier for routing the amplified single-mode optical signal from the optical amplifier to the multi-mode optical fiber and communicatively coupleable to a first port of the single-mode circulator for routing the reflective optical signal received from the multi-mode optical fiber to the first port of the single-mode circulator.

10. The system claim 9 , wherein the multi-mode circulator comprises:

a first port coupled to the mode scrambler for receiving the multi-mode optical signal; a second port communicatively coupleable to the multi-mode optical fiber for routing the multi-mode optical signal to the multi-mode optical fiber and for receiving the reflective optical signal; and

a third port coupled to an optical fiber for routing the reflective optical signal to a first port of the single-mode circulator.

11. The system of claim 1 , wherein the single-mode optical signal and reflective optical signal have a same signal intensity.

12. The system of claim 1 , wherein the optical amplifier amplifies the single-mode optical signal by a predetermined gain based on a signal intensity of the reflective optical signal.

13. A method, comprising:

routing, by a single-mode circulator communicatively coupled to a distributed sensing interrogator, a single-mode optical signal through a single-mode optical fiber positioned in a wellbore;

amplifying, by an optical amplifier coupled to the single-mode circulator, the single-mode optical signal by a predetermined gain;

filtering, by an optical filter coupled to the optical amplifier, the amplified single-mode optical signal to remove one or more noise components from the amplified single-mode optical signal;

coupling, by a mode scrambler into multiple modes of a multi-mode fiber, the amplified single-mode optical signal from the optical amplifier;

receiving, by a multi-mode circulator coupled to the mode scrambler, a reflective optical signal on a multi-mode optical fiber positioned in the wellbore in response to routing the multi-mode optical signal; and

routing, by ti-mode circulator, the reflective optical signal to the single-mode circulator.

14. The method of claim 13 , further comprising:

modifying, by a variable optical attenuator positioned between the single-mode circulator and the optical amplifier, the single-mode optical signal from the single-mode circulator.

15. A system comprising:

a distributed sensing interrogator;

a distributed sensing mode converter; and

a distributed sensing subsystem positionable along a region to be sensed and that includes a multi-mode optical fiber as a communication medium for an interrogation optical signal and a reflective optical signal,

wherein the distributed sensing mode converter comprises:

a first single-mode circulator coupleable to the distributed sensing interrogator for routing a single-mode optical signal from the distributed sensing interrogator through a single-mode optical fiber to the distributed sensing subsystem and communicatively coupleable to an optical receiver of the distributed sensing interrogator for routing a reflective optical signal received from the distributed sensing subsystem to the optical receiver;

an optical amplifier coupled to the first single-mode circulator for amplifying the single-mode optical signal;

an optical filter coupled to the optical amplifier for filtering one or more noise components from the amplified single-mode optical signal; and

a second single-mode circulator coupled to the optical filter for routing the filtered single-mode optical signal to a mode scrambler and coupled to the first single-mode circulator for routing a reflective optical signal received from the mode scrambler to the first single-mode circulator via the single-mode optical fiber.

16. The system of claim 15 , wherein the mode scrambler is coupleable to the multi-mode optical fiber for coupling the amplified single-mode optical signal into a plurality of modes of the multi-mode optical fiber.

17. The system of claim 16 , wherein the second single-mode circulator comprises a first port coupled to an output of the optical amplifier, a second port connected to the mode scrambler that is connected to the multi-mode optical fiber, and a third port for routing backscatter signaling from the second single-mode circulator to a first port of the single-mode circulator.

18. The system of claim 16 , wherein the first single-mode circulator comprises:

a first port coupled to an optical fiber for receiving the reflective optical signal from the multi-mode optical fiber;

a second port communicatively coupleable to the distributed sensing interrogator for receiving the single-mode optical signal from the distributed sensing interrogator; and

a third port coupled to the optical amplifier for routing the single-mode optical signal to the optical amplifier.

19. The system of claim 18 , further comprising:

a multi-mode circulator coupleable to an output of the optical amplifier for routing the amplified single-mode optical signal from the optical amplifier to the multi-mode optical fiber and communicatively coupleable to a first port of the first single-mode circulator for routing the reflective optical signal received from the multi-mode optical fiber to the first port of the single-mode circulator,

wherein the multi-mode circulator comprises:

a first port coupled to the mode scrambler for receiving the multi-mode optical signal;

a second port communicatively coupleable: to the multi-mode optical fiber for routing the multi-mode optical signal to the multi-mode optical fiber and for receiving the reflective optical signal; and

a third port coupled to an optical fiber for routing the reflective optical signal to a first port of the single-mode circulator.