Optical fibers without cladding

1. A fiber bundle comprising:

a first optical fiber that has a first clad portion and a first exposed fiber core that extends from the first clad portion, wherein the first exposed fiber core is devoid of cladding;

one or more second optical fibers wherein each of the one or more second optical fibers has a second clad portion and a second exposed fiber core that extends from the second clad portion, wherein each second clad portion is arranged substantially parallel to the first clad portion, and wherein each second exposed fiber core is devoid of cladding;

a condensed region in which a first distal end of the first exposed fiber core is arranged substantially parallel to a second distal end of each second exposed fiber core, wherein adjacent distal ends in the condensed region have a first center-to-center spacing, wherein each of the first optical fiber and the one or more second optical fibers is configured to be optically aligned with a transducer of an array of transducers, and wherein two adjacent transducers of the array of transducers are spaced at a nominal pitch substantially equal to the first center-to-center spacing; and

a non-condensed region that includes the first clad portion and the one or more second clad portions, wherein adjacent clad portions in the non-condensed region have a second center-to-center spacing that is greater than the first center-to-center spacing.

2. The fiber bundle of claim 1 , wherein the first center-to-center spacing is less than a diameter of the first clad portion of the first optical fiber.

3. The fiber bundle of claim 1 , wherein the first center-to-center spacing is approximately equal to a core diameter of the first exposed fiber core of the first optical fiber.

4. The fiber bundle of claim 1 , wherein the first center-to-center spacing is between 10 micrometers and 100 micrometers, and the second center-to-center spacing is between 150 micrometers and 500 micrometers.

5. The fiber bundle of claim 4 , wherein the first center-to-center spacing is about 50 micrometers and the second center-to-center spacing is about 250 micrometers.

6. The fiber bundle of claim 1 , wherein a length of each second exposed fiber core depends on a lateral displacement between a center of each corresponding second clad portion and a center of each corresponding second distal end.

7. The fiber bundle of claim 6 , wherein the length of each second exposed fiber core is greater than or equal to 4·R·a sin [0.5(D/R) 1/2 ], where R is a minimum bend radius of the corresponding second optical fiber, a sin is an inverse sine function, and D is the lateral displacement between the center of each corresponding second clad portion and the center of each corresponding second distal end.

8. The fiber bundle of claim 1 , further comprising a ferrule that secures the adjacent distal ends in the condensed region at the first center-to-center spacing.

9. The fiber bundle of claim 1 , wherein:

the first optical fiber further includes a first mode stripper layer that surrounds at least a portion of the first exposed fiber core; and

each of the one or more second optical fibers further includes a second mode stripper layer that surrounds at least a portion of the corresponding second exposed fiber core.

10. The fiber bundle of claim 1 , wherein:

the first optical fiber further includes a first mode-conversion reflector that surrounds at least a portion of the first exposed fiber core; and

each of the one or more second optical fibers further includes a second mode-conversion reflector that surrounds at least a portion of the corresponding second exposed fiber core.

11. The fiber bundle of claim 10 , wherein each of the first mode-conversion reflector and the second mode-conversion reflector comprises a diffuse reflector.

12. The fiber bundle of claim 1 , wherein the array of transducers includes an array of source emitters that are arranged to emit optical signals into the first distal end of the first exposed fiber core and into the second distal end of each second exposed fiber core.

13. The fiber bundle of claim 12 , wherein:

a sum of a diameter of each source emitter in the array of source emitters and a lateral position tolerance of each source emitter is less than a diameter of each of the first exposed fiber core and each second exposed fiber core;

a refractive index of each of the first exposed fiber core and each second exposed fiber core is greater than or equal to 1.34; and

a distance between a light emission surface of each source emitter and a light entrance surface of each corresponding distal end is less than or equal to a threshold distance at which 90% of light emitted by each source emitter is incident on each corresponding light entrance surface of each corresponding distal end.

14. A method of forming an optical fiber, the method comprising:

forming an exposed fiber core and an unexposed fiber core by feeding a core material into a first crucible chamber of a double crucible;

wherein the unexposed fiber core is formed after forming the exposed fiber core, and wherein the unexposed fiber core is formed continuous with the exposed fiber core;

forming a cladding layer by feeding a cladding layer material into a second crucible chamber of the double crucible, wherein the cladding layer surrounds the unexposed fiber core,

wherein the cladding layer and the unexposed fiber core form a clad portion from which the exposed fiber core extends; and

separately controlling the feeding of the core material into the first crucible chamber and the feeding of the cladding layer material into the second crucible chamber to form the exposed fiber core prior to formation of the cladding layer.

15. A fiber bundle comprising:

a first optical fiber that includes a first clad portion and a first exposed fiber core that extends from the first clad portion, wherein the first exposed fiber core has a first distal end; and

second optical fibers arranged around the first optical fiber,

wherein:

each second optical fiber includes a second clad portion and a second exposed fiber core that extends from the second clad portion, and each of the second exposed fiber cores has a corresponding second exposed fiber core length; and

each second exposed fiber core includes a bend region in which the corresponding second exposed fiber core is displaced by a corresponding displacement distance towards the first exposed fiber core, wherein each of the first optical fiber and the one or more second optical fibers is configured to be optically aligned with a transducer of an array of transducers, and wherein two adjacent transducers of the array of transducers are spaced at a nominal pitch substantially equal to a center-to-center spacing, the center-to-center spacing being substantially equal to a spacing between adjacent distal ends within the a region that includes the first distal end of the first optical fiber and a second distal end of each second optical fiber.

16. The fiber bundle of claim 15 , wherein:

each second clad portion is substantially parallel to the first clad portion;

and

the first distal end of the first exposed fiber core is substantially parallel to the second distal end of each second exposed fiber core.

17. The fiber bundle of claim 16 , further comprising a ferrule that secures adjacent ones of the first distal end of the first exposed fiber core and second distal ends of the second exposed fiber core at a center-to-center spacing less than a clad diameter of the first clad portion of the first optical fiber.

18. The fiber bundle of claim 15 , wherein each second exposed fiber core length is greater than or equal to 4·R·a sin [0.5(D/R) 1/2 ], where R is a minimum bend radius of the second optical fiber, a sin is an inverse sine function, and D is the displacement distance.

19. An optical assembly, including:

a plurality of transducers, that has a transducer spacing between a first transducer and a second transducer of the plurality of transducers; and

a fiber bundle which includes a first optical fiber that has a first clad portion and a first exposed fiber core that extends from the first clad portion, and a second optical fiber that has a second clad portion and a second exposed fiber core that extends from the second clad portion, wherein the second clad portion is substantially parallel to the first clad portion,

wherein the fiber bundle includes:

a condensed region in which a first distal end of the first exposed fiber core is arranged substantially parallel to a second distal end of the second exposed fiber core, wherein the first distal end and the second distal end has a first center-to-center spacing, wherein each of the first optical fiber and the one or more second optical fibers is configured to be optically aligned with a transducer of the plurality of transducers; and

a non-condensed region that includes the first clad portion and the second clad portion, wherein the first clad portion and the second clad portion in the non-condensed region have a second center-to-center spacing,

wherein the second center-to-center spacing is greater than the first center-to-center spacing, and the first center-to-center spacing is approximately equal to the transducer spacing.

20. The optical assembly of claim 19 , wherein each of the plurality of transducers is optically coupled to a selected optical fiber of the fiber bundle, wherein the first distal end is optically coupled to the first transducer, and the second distal end is optically coupled to the second transducer.

21. The optical assembly of claim 19 , wherein the plurality of transducers includes a plurality of source emitters.

22. The optical assembly of claim 19 , wherein the plurality of transducers includes a laser.

23. The optical assembly of claim 19 , wherein the plurality of transducers includes an optical detector.