Optical coherence tomography with graded index fiber for biological imaging

1. A system for optical coherence tomography, comprising:

a source of optical radiation;

an optical fiber;

a graded index fiber attached to a distal end of the optical fiber, wherein the optical fiber and the graded index fiber are together configured to provide a common path for optical radiation reflected from a reference interface at a distal end of the graded index fiber and from a target;

receiving electronics configured to receive the optical radiation reflected from the reference interface and the target; and

a processor to generate an image of the target based upon the optical radiation received by the receiving electronics.

2. The system of claim 1 , wherein a secondary reflection of optical radiation from an interface between the optical fiber and the graded index fiber is less than −60 dB.

3. The system of claim 1 , wherein the reference interface provides a reference reflection of between −28 and −42 dB.

4. The system of claim 1 , further comprising an interface medium at the reference interface and in optical contact with the graded index fiber.

5. The system of claim 4 , wherein a refractive index of the graded index fiber and a refractive index of the reference medium are mismatched such that the receiving electronics operate in a total noise range that is within 5 dB of the shot noise limit.

6. The system of claim 4 , wherein the reference interface is angled with respect to a longitudinal axis of the graded index fiber such the receiving electronics operate in a total noise range that is within 5 dB of the shot noise limit.

7. The system of claim 4 , wherein a surface of the interface medium that is closest to the target is concave.

8. The system of claim 4 , wherein the interface medium is an adhesive.

9. The system of claim 1 , wherein an outer diameter of the graded index fiber and a protective coating around the graded index fiber is less than 0.01 inches.

10. A system for optical coherence tomography, comprising:

a source of optical radiation;

an optical fiber;

a graded index fiber attached to a distal end of the optical fiber, wherein the optical fiber and the graded index fiber are together configured to provide a common path for optical radiation reflected from a reference interface at a distal end of the graded index fiber and from a target;

receiving electronics configured to receive the optical radiation reflected from the reference interface and the target; and

a processor to generate an image of the target based upon the optical radiation received by the receiving electronics;

wherein a secondary reflection of optical radiation from an interface between the optical fiber and the graded index fiber is less than −60 dB.

11. The system of claim 10 , wherein the reference interface provides a reference reflection of between −28 and −42 dB.

12. The system of claim 10 , further comprising an interface medium at the reference interface and in optical contact with the graded index fiber.

13. The system of claim 12 , wherein a refractive index of the graded index fiber and a refractive index of the reference medium are mismatched such that the receiving electronics operate in a total noise range that is within 5 dB of the shot noise limit.

14. The system of claim 12 , wherein the reference interface is angled with respect to a longitudinal axis of the graded index fiber such the receiving electronics operate in a total noise range that is within 5 dB of the shot noise limit.

15. The system of claim 12 , wherein a surface of the interface medium that is closest to the target is concave.

16. The system of claim 12 , wherein the interface medium is an adhesive.

17. The system of claim 10 , wherein an outer diameter of the graded index fiber and a protective coating around the graded index fiber is less than 0.01 inches.