APPARATUS AND METHOD FOR TAPERING OPTICAL FIBERS TO CONFORM TO A DESIRED RADIAL PROFILE

• US 20090320527A1
• Filed: 06/30/2008
• Published: 12/31/2009
• Est. Priority Date: 06/30/2008
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Dimmick, Timothy Eugene, Norwood, Timothy Joseph, Harper, Kevin Randolph
• Granted Patent: US 8,056,368 B2
• Time in Patent Office: Days
• US Class Current: 65/381
• CPC Class Codes: C03B 37/15 with heat application, e.g. for making optical fibres fusion-splicing of light guides G02B6/255; treatment of light guides to shape optical elements G02B6/2835, G02B6/2856
• CPC Class Codes: G02B 6/02052 comprising optical elements other than gratings, e.g. filters comprising gratings G02B6/02057
• CPC Class Codes: G02B 6/2552 reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends
• CPC Class Codes: G02B 6/2835 formed or shaped by thermal treatment, e.g. couplers

Abstract

An apparatus and method for tapering an optical fiber segment having an initial radial profile to substantially conform to a pre-specifiable desired radial profile for controlling mutually coordinated elongation and softening of different axial portions of the segment according to control parameters derivable based on a normalized axial coordinate reference by which points of the initial profile map to corresponding points of the desired profile. The softening and/or elongation may progress substantially in either a step-wise, time-discrete manner or time-continuously. The invention is useful for forming tapered fused couplers as well as for tapering individual fibers.

Claims

1. A method of tapering a segment of an optical fiber from one having an initial radial profile into one having a desired radial profile, said method comprising the steps of:

softening the segment to form at least one softened portion, each said softened portion being located at a respective axial position;

elongating said at least one softened portion axially, and

said softening step and said elongating step being controlled in accordance with at least one parameter which is related to a normalized axial coordinate reference by which points of the initial radial profile map to corresponding points of the desired radial profile.

2. A method as claimed in claim 1 wherein said softened portion is repositionable from at least one said axial position to another said axial position and said softened portion has a respective repositioning speed at each respective said axial position and wherein said elongating step comprises the step of elongating said softened portion, at a respective elongation rate and by a respective elongation distance, at each said respective said axial position and wherein said at least one parameter comprises a plurality of parameters and said axial position, said repositioning speed, said elongation rate and said elongation distance are each parameters which are included among said plurality of parameters.

3. A method as claimed in claim 2 wherein the value of at least one of said plurality of parameters is changed in a substantially stepwise, time-discrete manner during at least a portion of the time during which the method is carried out.

4. A method as claimed in claim 2 wherein the value of at least one of said plurality of parameters is changed in a substantially time-continuous manner during at least a portion of the time the method is being carried out.

5. A method as claimed in claim 1 wherein said softening step and said elongating step are carried out to successively form and elongate each of a plurality of said softened portions each said softened portion being located at a different respective said axial position, each respective one of said plurality of softened portions being formed and elongated at one of said axial positions before a different one of said softened portions is formed and elongated at a different one of said axial positions.

6. A method as claimed in claim 1 wherein said normalized axial coordinate reference is a coordinate reference by which said points of the initial radial profile map to said corresponding points of the desired radial profile according to a substantially isovolumetric relationship between the initial radial profile and the desired radial profile.

7. A method as claimed in claim 6 wherein said relationship can be expressed by an equation substantially of the form:

$\begin{array}{cc}{\int <br><br>}_{-1}^{z_n}<br><br>r_i^2<br><br>\left(z_n^{\mathrm{\prime <br><br>}}\right)<br><br><br><br><br><br>z_n^{\mathrm{\prime <br><br>}}={\int <br><br>}_{z_{f<br><br><br><br>1}}^{z_f}<br><br>r_f^2<br><br>\left(z_f^{\mathrm{\prime <br><br>}}\right)<br><br><br><br><br><br>z_f^{\mathrm{\prime <br><br>}}& \mathrm{Equation}<br><br><br><br>3\end{array}$

where;

z_n and z_f represent the normalized axial domain and the actual domain of the desired radial profile, respectively;

z_f1 represents an axial endpoint of the desired radial profile;

r_i represents the initial radial profile; and

r_f represents the final radial profile.

8. A method as claimed in claim 7 further comprising the steps of forming the segment into a first intermediate radial profile which more closely conforms to the desired profile than does the initial radial profile conform to the desired radial profile.

9. A method as claimed in claim 8 further comprising the steps of softening and elongating the segment from said first intermediate radial profile into a subsequent radial profile.

10. A method as claimed in claim 9 wherein said subsequent radial profile comprises a second intermediate radial profile which conforms more closely to the desired radial profile than does said first intermediate radial profile conform to the desired radial profile.

11. A method as claimed in claim 9 wherein said subsequent radial profile substantially conforms to the desired radial profile.

12. A method of tapering an axial segment of a plurality of adjacent optical fibers which together have initial radial profile, to form a tapered, fused optical device having a desired radial profile, said method comprising the steps of:

softening the segment to form at least one softened portion, each said softened portion being located at a respective axial position;

elongating said at least one softened portion axially,

said softening step and said elongating step being controlled in accordance with at least one parameter which is related to a normalized axial coordinate reference by which points of the initial radial profile map to corresponding points of the desired radial profile, where said initial radial profile is specified by an initial effective radius and an initial degree of fusion and said desired radial profile is specified by a desired effective radius and a desired degree of fusion.

13. A method as claimed in claim 12 wherein said softened portion is repositionable from at least one said axial position to another said axial position and said softened portion has a respective repositioning speed at each respective said axial position and wherein said elongating step comprises the step of elongating said softened portion at a respective elongation rate and by a respective elongation distance at each respective said axial position and wherein said at least one parameter comprises a plurality of parameters and said axial position, said repositioning speed, said elongation rate and said elongation distance are each parameters which are included in said plurality of parameters.

14. A method as claimed in claim 13 wherein the value of at least one of said plurality of parameters is changed in a substantially stepwise, time-discrete manner during at least a portion of the time during which the method is carried out.

15. A method as claimed in claim 13 wherein the value of at least one of said plurality of parameters is changed in a substantially time-continuous manner during at least a portion of the time the method is being carried out.

16. A method as claimed in claim 12 wherein said softening step and said elongating step are carried out to successively form and elongate each of a plurality of said softened portions each said softened portion being located at a different respective said axial position, each respective one of said plurality of softened portions being formed and elongated at one said axial position before a different one of said softened portions is formed and elongated at a said different said axial position.

17. A method of tapering a segment of an optical fiber from one having an initial radial profile into one having a desired radial profile, said method comprising the steps of:

softening the segment to form a softened portion at an axial position whose time rate if change is a repositioning speed;

elongating said softened portion axially by an elongation distance at an elongation rate; and

controlling said axial distance, said repositioning speed, said elongation distance and said elongation rate in accordance with a relationship which can be expressed by;

$x<br><br>\left(z_n\right)=x_0+2<br><br>{\int <br><br>}_{-1}^{z_n}<br><br>\left(\frac{<br><br>z_f}{<br><br>z_n^{\mathrm{\prime <br><br>}}}-\frac{<br><br>z_i}{<br><br>z_n^{\mathrm{\prime <br><br>}}}\right)<br><br><br><br><br><br>z_n^{\mathrm{\prime <br><br>}}$ $\mathrm{and},<br><br>y<br><br>\left(z_n\right)=y_0+{\int <br><br>}_{-1}^{z_n}<br><br>\left(\frac{<br><br>z_f}{<br><br>z_n^{\mathrm{\prime <br><br>}}}+\frac{<br><br>z_i}{<br><br>z_n^{\mathrm{\prime <br><br>}}}\right)<br><br><br><br><br><br>z_n^{\mathrm{\prime <br><br>}}$ $\mathrm{and},<br><br>y<br><br>\left(x\right)=y<br><br>\left(z_n<br><br>\left(x\right)\right)$ $\mathrm{and},<br><br>\frac{v}{u}=\frac{<br><br>y}{<br><br>x}$ $\mathrm{and},$

where;

x(z_n) represents normalized axial location;

x₀ represents any initial said elongation distance;

x_i represents the actual domain of the initial radial profile of the segment;

x_f represents the actual domain of the desired radial profile of the segment;

v represents said repositioning speed;

u represents said elongation rate; and

$\frac{<br><br>y}{<br><br>x}$

is a differential quantity which represents a rate of change of said axial position with respect to said elongation distance.

18. An apparatus for tapering a segment of an optical fiber from one having an initial radial profile into one having a desired radial profile, said apparatus, comprising:

a softening device for softening a portion of the segment to form a softened portion at any one of a plurality of axial positions;

at least one first actuator for moving said softening device to enable the softening device to form a said softened portion at different ones of said axial positions at different times, said softening device having a respective repositioning speed associated with each respective one of said axial positions;

at least one member coupleable to the fiber, said member being axially movable;

at least one second actuator, said second actuator being operably coupled to said member for moving said member for axially elongating said softened portion according to a respective elongation distance and a respective elongation rate associated with each respective one of said axial positions;

a controller operably coupled to said first actuator and to said second actuator, said controller being adapted to control said axial position, said repositioning speed, said elongation distance and said elongation rate, said axial position, said repositioning speed, said elongation distance and said elongation rate each being parameters which are related to a normalized axial coordinate reference by which points of the initial radial profile map uniquely to corresponding points of the desired radial profile.

19. An apparatus as claimed in claim 18 wherein first actuator is controlled for moving said softened portion from at least one said axial position to another said axial position according to a respective repositioning speed associated with each respective said axial position, and wherein said second actuator is controlled for elongating said softened portion, at a respective elongation rate and by a respective elongation distance, at each said respective said axial position, and wherein said at least one parameter comprises a plurality of parameters and said axial position, said repositioning speed, said elongation rate and said elongation distance are each parameters which are included among said plurality of parameters.

20. An apparatus as claimed in claim 19 wherein the value of at least one of said plurality of parameters is changed under the control of said controller in a substantially stepwise, time-discrete manner during at least a portion of the time during which the segment is being tapered.

21. An apparatus as claimed in claim 19 wherein the value of at least one of said plurality of parameters is changed under the control of said controller in a substantially time-continuous manner during at least a portion of the time the segment is being tapered.

22. An apparatus as claimed in claim 18 wherein said first actuator and said second actuator are controlled so as to successively form and elongate each of a plurality of said softened portions each said softened portion being located at a different respective said axial position, each respective one of said plurality of softened portions being formed and elongated at one of said axial positions before a different one of said softened portions is formed and elongated at a different one of said axial positions.

23. An apparatus as claimed in claim 18 wherein said normalized axial coordinate reference is a coordinate reference by which said points of the initial radial profile map to said corresponding points of the desired radial profile according to a substantially isovolumetric relationship between the initial radial profile and the desired radial profile.

24. An apparatus as claimed in claim 23 wherein said substantially isovolumetric relationship can be expressed by an equation substantially of the form:

$\begin{array}{cc}{\int <br><br>}_{-1}^{z_n}<br><br>r_i^2<br><br>\left(z_n^{\mathrm{\prime <br><br>}}\right)<br><br><br><br><br><br>z_n^{\mathrm{\prime <br><br>}}={\int <br><br>}_{z_{f<br><br><br><br>1}}^{z_f}<br><br>r_f^2<br><br>\left(z_f^{\mathrm{\prime <br><br>}}\right)<br><br><br><br><br><br>z_f^{\mathrm{\prime <br><br>}}& \mathrm{Equation}<br><br><br><br>3\end{array}$

where;

z_n and z_f represent the normalized axial domain and the actual domain of the desired radial profile, respectively;

z_f1 represents an axial endpoint of the desired radial profile;

r_i represents the initial radial profile, and

r_f represents the final radial profile.

25. An apparatus as claimed in claim 24 further comprising the steps of forming the segment into a first intermediate radial profile which more closely conforms to the desired profile than does the initial radial profile conform to the desired radial profile.

26. An apparatus for tapering an axial segment of a plurality of adjacent optical fibers which together have an initial radial profile, to form a tapered, fused optical device having a desired radial profile, said apparatus comprising:

a softening device for softening a portion of the segment to form a softened portion at any one of a plurality of axial positions;

at least one first actuator for moving said softening device to enable the softening device to form a said softened portion at different ones of said axial positions at different times, said softening device having a respective repositioning speed associated with each respective one of said axial positions;

at least one member coupleable to the fiber, said member being axially movable;

at least one second actuator, said second actuator being operably coupled to said member for moving said member for axially elongating said softened portion according to a respective elongation distance and a respective elongation rate associated with each respective one of said axial positions;

a controller operably coupled to said first actuator and to said second actuator, said controller being adapted to control said axial position, said repositioning speed, said elongation distance and said elongation rate, said axial position, said repositioning speed, said elongation distance and said elongation rate each being parameters which are related to a normalized axial coordinate reference by which points of the initial radial profile map uniquely to corresponding points of the desired radial profile, where the initial radial profile is specified by an initial effective radius and an initial degree of fusion and the desired radial profile is specified by a desired effective radius and a desired degree of fusion.

27. An apparatus as claimed in claim 26 wherein said controller causes the value of at least one of said plurality of parameters to change in a substantially stepwise, time-discrete manner.

28. An apparatus as claimed in claim 26 wherein said controller causes the value of at least one of said plurality of parameters to change in a substantially time-continuous manner.

29. An apparatus for tapering a segment of an optical fiber from one having an initial radial profile into one having a desired radial profile, said apparatus comprising:

a softening device for softening a portion of the segment to form a softened portion at any one of a plurality of axial positions;

at least one first actuator for moving said softening device to enable the softening device to form a said softened portion at different ones of said axial positions at different times, said softening device having a respective repositioning speed associated with each respective one of said axial positions;

at least one member coupleable to the fiber, said member being axially movable;

at least one second actuator, said second actuator being operably coupled to said member for moving said member for axially elongating said softened portion according to a respective elongation distance and a respective elongation rate associated with each respective one of said axial positions;

a controller operably coupled to said first actuator and to said second actuator, said controller being adapted for controlling said axial distance, said repositioning speed, said elongation distance and said elongation rate substantially satisfy a relationship which can be expressed by;

$x<br><br>\left(z_n\right)=x_0+2<br><br>{\int <br><br>}_{-1}^{z_n}<br><br>\left(\frac{<br><br>z_f}{<br><br>z_n^{\mathrm{\prime <br><br>}}}-\frac{<br><br>z_i}{<br><br>z_n^{\mathrm{\prime <br><br>}}}\right)<br><br><br><br><br><br>z_n^{\mathrm{\prime <br><br>}}$ $\mathrm{and},<br><br>y<br><br>\left(z_n\right)=y_0+{\int <br><br>}_{-1}^{z_n}<br><br>\left(\frac{<br><br>z_f}{<br><br>z_n^{\mathrm{\prime <br><br>}}}+\frac{<br><br>z_i}{<br><br>z_n^{\mathrm{\prime <br><br>}}}\right)<br><br><br><br><br><br>z_n^{\mathrm{\prime <br><br>}}$ $\mathrm{and},<br><br>y<br><br>\left(x\right)=y<br><br>\left(z_n<br><br>\left(x\right)\right)$ $\mathrm{and},<br><br>\frac{v}{u}=\frac{<br><br>y}{<br><br>x}$

where;

x(z_n) represents normalized axial location;

x₀ represents any initial said elongation distance;

x_i represents the actual domain of the initial radial profile of the segment;

x_f represents the actual domain of the desired radial profile of the segment;

v represents said repositioning speed;

u represents said elongation rate; and

$\frac{<br><br>y}{<br><br>x}$

is a differential quantity which represents a rate of change of said axial position with respect to said elongation distance.