Thermally-shaped optical fiber and a method for forming the optical fiber
A thermally-shaped optical fiber and a method for forming the same so as to minimize the presence of optical artifacts in the optical fiber that contributes to insertion loss.
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The present application is a divisional of U.S. patent application Ser. No. 10/167,071, filed on Jun. 11, 2002, entitled “A Thermally-Shaped Optical Fiber and a Method for Forming the Optical Fiber,” which is incorporated by reference herein.
BACKGROUND OF THE INVENTIONThe present invention relates to optical waveguides. More particularly, the present invention is directed toward forming optical waveguides from optical fibers, which are suitable for use in data communication.
To minimize insertion loss, the loss of optical energy when coupling data links in fiber-optic communication systems, it is important to correctly match the aperture through which optical energy is transmitted with the aperture through which optical energy is detected. As a result, the areas of the apertures must be correctly sized and aligned.
The ideal interconnection of one fiber to another would have two fibers that are optically and physically identical and held by a connector that aligns the fibers so that the interconnection does not exhibit any influence on light propagation therethrough. Formation of the ideal interconnect is difficult for several reasons. These include variations in fiber properties, tolerances in the connector, as well as in cost and ease of use.
Commercially available interconnection devices have typical insertion losses from between 0.2 dB to 4 dB. This range of insertion loss results from several factors that may be divided into those related to fibers and those related to interconnection devices. Fibers intrinsically contribute loss to an interconnection and any fiber has variations that are produced during manufacture. These variations exist not only among different lots of fibers, but also within a length of a single fiber, as well. The main variations in these cases are in the core and cladding diameters and fiber numerical aperture (NA). The core ellipticity, cladding ellipticity, and core-to-cladding eccentricity exacerbate the problems associated with variations in the core and cladding diameters. Losses caused by diameter variations, NA variations, eccentricity, and ellipticity are intrinsic to the fiber and the total loss contributed by these intrinsic factors can range from less than 0.2 dB to over 2 dB, depending on how well two fibers match.
Connector-related losses may also arise even when there are no intrinsic variations in the fibers. These types of losses arise when two fibers are not aligned on their center axes and lateral or axial displacement can be, and usually is, the greatest cause of loss in the connection. For example, a 0.5 dB loss that is due to a displacement, equal to 10% of the core diameter, will require tolerances to be maintained on each connector (fiber) that is within 2.5 μm. Tolerances of this magnitude are difficult to achieve. Add to this, the losses that are also induced due to angular misalignment, and the total tolerances that must be maintained in the termination process, proper fiber and/or connector end preparation becomes problematic.
The considerations discussed above with respect to fiber-to-fiber interconnections apply equally to fiber-source and fiber-detector interconnections, as well. The result is that the requirements that should be achieved to provide efficient optical coupling necessitate end-finishing or termination processes that strives to provide lossless propagation of optical energy. To that end, it is desired to provide the end of a fiber that functions as either a transmission or reception aperture with a smooth end finish free of such defects that may change the geometrical propagation patterns of optical energy passing therethrough. These defects include hackles, burrs, fractures, bubbles and other contaminants.
Preparation of conventional glass optical fibers employs score-and-break techniques or mechanical polishing techniques. The score-and-break technique provides an optical fiber with an arc that is scored. Tension is applied to that optical fiber so that the score propagates across the width of the optical fiber, segmenting the same. This technique is capable of producing an excellent cleaved end. Repeatability, however, it is difficult, lowering yields and increasing the cost of the finished optical fibers. In addition, a great amount of skill is required to properly control both the depth of the scoring and the amount of tension during breaking. The aforementioned control may be frustrated by intrinsic fiber variations. Finally, the difficulty in controlling both the depth of scoring and breaking tension increases as the length of the optical fiber becomes shorter.
Polishing, compared to scoring-and-breaking, has the advantage of consistent results, but is a much more costly technique. Polishing is typically performed after a connector, or ferrule, has been attached to the optical fiber. Polishing a bare optical fiber is impractical. Usually, a polishing fixture is provided that controls the polishing to a fixed dimension, e.g., usually within 0.3 μm.
Polymer-based optical fibers may be segmented with a sharp, and preferably hot, blade. As with the polishing technique mentioned above with respect to glass optical fibers, segmenting is performed on polymer-based optical fibers after a connector has been attached. Polymer-based optical fibers may also be polished, but it is very difficult to achieve the performance of a glass or quartz optical fiber.
In addition to providing a smooth end finish, the preparation procedure should provide the optical fiber with a cleaved end, i.e., the end of the optical fiber is typically planar and lies in a plane with the longitudinal axis of the optical fiber extending orthogonally thereto. Otherwise, an angle may exist between the axes of juxtaposed fibers and fiber-devices, referred to as tilting. Tilting can cause additional, and sometimes quite severe, losses in addition to those mentioned previously. While tilting loss can be controlled to some degree by proper end preparation and positioning of adjacent fiber ends, it should not be completely ignored. Often alignment mechanisms are employed to reduce the effects of tilting. Such alignment mechanisms include lenses that may be effectively coupled and aligned, (with minimum loss to the end of the optical fiber).
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What is needed, therefore, is a technique to thermally shape an optical fiber while reducing formation of artifacts.
SUMMARY OF THE INVENTIONProvided are a thermally-shaped optical fiber and a method for forming the same that features creating a flow of thermal energy between two spaced-apart regions of the optical fiber. The flux of thermal energy in the flow is substantially constant to define a graded index of refraction in a portion of the optical fiber located between said two-spaced apart regions. This minimizes formation of unwanted optical artifacts in the portion. For example, a graded index of refraction is formed in the portion, thereby avoiding abrupt changes in the variation of the index of refraction in the portion. Additionally, the formation of a self-focusing lens in the portion is minimized, if not abrogated. Both of the aforementioned optical artifacts, abrupt changes in indices of refraction and the self-focusing lens, leads to insertion loss. By avoiding formation of these optical artifacts, the insertion loss of the optical fiber is greatly reduced, if not completely absent.
BRIEF DESCRIPTION OF THE DRAWINGS
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Although any type of laser may be employed, the present exemplary system employed laser manufactured by KERN Electronics and Lasers, Inc. Model # KER6X6-10 to provide basic 10 Watt CO2 beam. Beam 52, therefore, comprises of infrared (IR) wavelengths of optical energy of sufficient power to segment optical fibers 54. The beam profile was adjusted dependent upon the segmentation technique employed, discussed more fully below. With this configuration, the dwell time, period of time in which a single fiber element is exposed to beam 52, can then be varied from less than a microsecond to more than a millisecond. In addition, manual, single pulse or continuous wave operation of laser source 34 was also made available.
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In the first step, beam 152 is provided with a sufficient amount of energy to propagate through the optical fiber 54 to segment both the cladding and core of the same. The energy of beam 152 to achieve segmentation was found to be in the range of 20% to 30% of total power available from laser source 34, dependent upon the type of material that beam 152 has to segment. The width “w” of beam 152 is approximately 1.25-1.4 times greater than the core diameter “d”. When exposed to the thermal energy of beam 152, the core of optical fiber 54 underwent a plurality of phase-changes in which the solid core becomes a viscous liquid and a gas. Specifically, as shown in
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Subsequent to segmenting optical fiber 54, the energy in beam 152 is reduced to be 30% or less of the energy employed to segment optical fiber 54, while maintaining the same beam width. Optical fiber 54 is then exposed to the thermal energy of beam 152 so as to minimize the dwell time. This may be achieved by first having optical fiber 54 thermally insulated from beam 152. Then movement between optical fiber 54 and beam 152 in a direction parallel to the {overscore (x)} axis is undertaken. In this manner, the dwell time is on the order of a few microseconds. During the dwell time, end 59 of optical fiber 54 rapidly undergoes two phase-changes before any sag occurs: solid to a viscous liquid and viscous liquid to a solid. This allows the end 59 of optical fiber 54 to reflow, thereby providing a smooth surface, while avoiding the effects of gravity when optical fiber 54 is placed in the molten state for too long a period of time. This results in a fire polish of end 59 with surface anomalies of 50 nm or less, while minimizing curvature. The depth of refractive action within optical fiber 54 itself due to the curvature itself is minimal at less than 1 μm, which is considered as a perpendicular cut and polish.
It should be understood, that the polishing step may be achieved by movement between optical fiber 54 and beam 152 along a direction parallel to the {overscore (y)} axis. In this manner, beam 152 is initially colinear with optical fiber 54, but spaced-apart sufficient distance to be thermally insulated from the optical fiber 54. After, beam 152 and optical fiber 54 are positioned collinearly, rapid movement along the {overscore (y)} axis is facilitated to expose optical fiber 54 to the thermal energy of beam 152, while minimizing dwell time for the reasons discussed above.
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In this arrangement, typically a beam having a narrow waist 352a is employed, as discussed above, with waist 352a of beam 352 being focused proximate to optical fiber 354, shown in
Length, l, was found to be determined on numerous factors, such as the material from which optical fiber 354 was formed, the heat dissipation characteristics of ferrule 304 and the thermal flux transferred to optical fiber 354 from beam 352. Specifically, it was found that by creating a flow of thermal energy between two spaced-apart regions, such as region 358 and region 304a, the flux of which is substantially constant, abrupt changes in the index of refraction over the length, l, of optical fiber 354 may be reduced, if not avoided. The constant flux of thermal energy in the flow results in the formation of a graded index of refraction over length, l, between spaced apart regions 358 and 304a, i.e., the index of refraction changes linearly over length, l. In addition to minimizing formation of abrupt changes in the index of refraction, a self-focusing lens formation is also reduced. Both of the aforementioned optical artifacts exacerbate insertion loss.
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The manner in which it was determined that a graded index of refraction was produced and, therefore, that the flux of thermal energy between spaced-apart regions 358 and 304a occurred, was by use of Optical Frequency Domain Reflectometry (OFDR). Specifically, an Optical Frequency Domain Reflectometer of the type available from the Group of Applied Physics University of Geneva, Geneva, Switzerland [hereinafter referred to as GAP-Optique] was employed to measure the optical power propagating along optical fiber 354. Optical Frequency Domain Reflectometry measures back reflections from optical fibers and provides the advantages in that greater spatial resolution and sensitivity is provided than that provided by the standard Optical Time Domain Reflectometry (OTDR).
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It is seen that shaping of optical fibers in accordance with the present invention, facilitates concurrently segmenting, polishing and lensing of the optical fiber while avoiding unwanted optical artifacts. Thus, the optical fibers may be quickly and easily shaped to minimize insertion loss.
Moreover, there are other arrangements that may be employed that would fall within the scope of the present invention. As stated above, virtually any type of thermal beam source may be employed, e.g., an Ultra Violet laser such as an Excimer may be employed. Therefore, the scope of the invention should not be based upon the foregoing description. Rather, the scope of the invention should be determined based upon the claims recited herein, including the full scope of equivalents thereof.
Claims
1. A method for forming an optical waveguide from an optical fiber having a longitudinal axis, said method comprising:
- exposing a first region of said optical fiber to thermal energy, with a portion of said thermal energy being transferred to said optical fiber, defining transferred energy;
- dissipating said transferred energy at a second region of said optical fiber, with said first and second regions being spaced-apart, with thermal energy passing between said first and second spaced-apart regions forming a flow; and
- maintaining, in said flow, a constant rate of thermal transfer between said first and second spaced-apart regions, thereby providing a graded index of refraction in a portion of said optical fiber located between said first and second spaced-apart regions.
2. The method as recited in claim 1 wherein dissipating further includes removing said transferred energy from said optical fiber in a direction that extends radially with respect to said longitudinal axis.
3. The method as recited in claim 1 wherein dissipating further includes transferring said transferred energy away from said optical fiber radially symmetrically about said longitudinal axis.
4. The method as recited in claim 1 wherein said index of refraction changes approximately 4% between said first and second spaced-apart regions.
5. The method as recited in claim 1 wherein maintaining further includes avoiding variances in said thermal energy being transferred to said optical fiber proximate to said first region and avoiding variances in a rate of dissipation of said transferred thermal energy.
6. The method as recited in claim 1 further including segmenting said optical fiber proximate to said first region.
7. The method as recited in claim 6 wherein segmenting said optical fiber further includes forming a lens proximate to said first region, with said portion extending from said second region, toward said first region, terminating in a lens.
8. The method as recited in claim 1 wherein exposing said optical fiber further includes impinging a beam of infrared energy upon said optical fiber from a first direction and reflecting a subportion of said infrared energy to impinge upon said optical fiber from a second direction, with said second direction disposed opposite to said first direction.
9. The method as recited in claim 8 wherein a said subportion has a magnitude associated therewith, which is dependent upon a mode associated with said optical fiber.
10. A method for controlling optical properties of an optical fiber having a longitudinal axis, said method comprising:
- creating a flow of thermal energy between two spaced-apart regions of said optical fiber, with a flux of said thermal energy in said flow being substantially constant to define a graded index of refraction in a portion of said optical fiber located between said two-spaced apart regions.
11. The method as recited in claim 10 wherein said creating further includes exposing said first region of said optical fiber to said thermal energy, with a portion of said thermal energy being transferred to said optical fiber, defining transferred energy and dissipating said transferred energy at a second region of said optical fiber.
12. The method as recited in claim 11 wherein dissipating further includes transferring said transferred energy radially symmetrically away from said optical fiber.
13. The method as recited in claim 12 wherein exposing said optical fiber further includes impinging a beam of infrared energy upon said optical fiber from a first direction and reflecting a subportion of said infrared energy to impinge upon said optical fiber from a second direction, with said second direction disposed opposite to said first direction.
14. The method as recited in claim 13 wherein said subportion has a magnitude associated therewith, which is dependent upon a mode associated with said optical fiber.
15. The method as recited in claim 1 further including segmenting said optical fiber proximate to said first region to form a lens, with said portion extending from said second region, toward said first region, terminating in said lens.
16. An optical waveguide, comprising:
- an optical fiber having an interface region and an end region; and
- a lens integrally formed to said interace region, with said interface region being disposed between said end region and said lens, said end region and said lens each having a constant index of refraction and said interface region defining a graded index of refraction.
17. The optical waveguide as recited in claim 16 wherein said graded index of refraction has a maximum value at said lens and a minimum value at said end region.
18. The optical waveguide as recited in claim 17 wherein said graded index of refraction has a median value, with said maximum value being approximately 2% greater than said median value and said minimum value being approximately 2% less than said median value.
19. The optical waveguide as recited in claim 16 wherein said lens is a convex lens.
Type: Application
Filed: Apr 15, 2004
Publication Date: Jan 13, 2005
Applicant: Megladon Manufacturing Group (Austin, TX)
Inventors: John Culbert (Round Rock, TX), Robert Mays (Austin, TX)
Application Number: 10/824,774