CA1105705A - Method of producing optical fiber access coupler - Google Patents
Method of producing optical fiber access couplerInfo
- Publication number
- CA1105705A CA1105705A CA350,117A CA350117A CA1105705A CA 1105705 A CA1105705 A CA 1105705A CA 350117 A CA350117 A CA 350117A CA 1105705 A CA1105705 A CA 1105705A
- Authority
- CA
- Canada
- Prior art keywords
- fibers
- twisted
- access
- coupler
- biconical
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Abstract
T I T L E
METHOD OF PRODUCING OPTICAL
FIBER ACCESS COUPLER
I N V E N T O R S
BRIAN S. KAWASAKI
KENNETH O. HILL
DERWYN C. JOHNSON
ABSTRACT OF DISCLOSURE
The low loss access coupler includes two multi-mode optic fibers, each having a biconical taper section. The biconical taper sections of the fibers are fused together to provide optical coupling between the fibers. The fused fibers may also be twisted around one another to enhance mode mixing.
The access couplers may be produced by fusing two fibers together along a small length, then heating the fused length and pulling the fibers to form the biconical tapers; or by twisting a portion of each of the fibers around-one another, applying a tensile force to the twisted portions of the fibers and heating a region of the twisted fibers to soften and fuse a predetermined length of twisted fibers. If the fibers already have biconical taper sections, the access coupler may be produced by twisting the fibers together along their taper sections and heating a region of the taper sections to fuse them together.
METHOD OF PRODUCING OPTICAL
FIBER ACCESS COUPLER
I N V E N T O R S
BRIAN S. KAWASAKI
KENNETH O. HILL
DERWYN C. JOHNSON
ABSTRACT OF DISCLOSURE
The low loss access coupler includes two multi-mode optic fibers, each having a biconical taper section. The biconical taper sections of the fibers are fused together to provide optical coupling between the fibers. The fused fibers may also be twisted around one another to enhance mode mixing.
The access couplers may be produced by fusing two fibers together along a small length, then heating the fused length and pulling the fibers to form the biconical tapers; or by twisting a portion of each of the fibers around-one another, applying a tensile force to the twisted portions of the fibers and heating a region of the twisted fibers to soften and fuse a predetermined length of twisted fibers. If the fibers already have biconical taper sections, the access coupler may be produced by twisting the fibers together along their taper sections and heating a region of the taper sections to fuse them together.
Description
BACK~RoUND OF THE INYENTION
ThiS invention is directed to fiber op-tic couplers and in part.icular to low loss access couplers for multi-mode optial fibers and a method o~ produci~g these couplers.
An ernbodirnent o.E an inventi.o:n disclos~d in th.is application is c:laimed in co-pend..ing ~anadian ~ppl~.cation 350,118, filed April 1, 1980 by B.S. Kawasaki et al.
The two main network topology systems for the distribution of optical communication signals using single-strand multimode fiber are the tree distribution system and thestar system. For networks with.many terminals the tree dis-tribution scheme provides advantages o~ flexibility in the number and location of the distribution paths or drops and : minimizes the amount of ~iber used in comparison to a star system~ However, a tree network can suffer from an ineffective utilization of the total optical power launched in the trunk feeder.if there are.many lossy access junctions along the trunk which are encoun~ered in series. The tree scheme can be efect-ively utiliz'ed only if the excess loss above furcation loss at each access junction is made su~ficiently small.
Recently two methods for producing low loss access couplers for multimode fibers have been demonstratedO In t~e fi.rst which is described in a publication by Takesh.i Oæeki and Brian S. Kawasakl entitled "Optical direc-tional coupler using tapered sections in multimode fibers", -- Applied Physics Letters, ~olO 28, No~.9, May 1, 1976 - pa~es 528 and 529, twin biconlcal tapered sections o~ multimode optical ~ibe~ axe ~oi~ed by an optical epoxy to produce a directlonal coupler.
.~ In the second which is described in a publication b~ M.K~ Barnoski and H~R. Friedrich entitled "Fabrication of an access coupler ~ith single strand multi-mode fiber waveguides", - Applied Optics, ~cl. lS, No. llt November 1976, pages 2629 - 2630, t:wo sections of multimode fiber are fused side-by-side to form a low loss junction.
In both of these structures, the excess loss is iII the order of 1 ctB.
SU~ RY OF THE INVENTION
It is t~erefore an object of this in~ention to provide an access coupler having highly efficient coupling action.
It is a further object of this inven~ion to provide an access coupler in which considerable mode mixing and mode coupling occurs.
It is another object o~ this invention to provide an access coupler which is directional.
It is a urther object of this invention to provide an access coupler which has isolation of the uncoupled port~
It is another object Qf this invention to pro~ide simple and inexpensive methods of producin~ low loss access eouplersO
These and other objects are achieved in an access -coupler comprising a fixst and a second multimode fiber, each of the fibers having a biconical taper section~ the biconical taper sections of the fibers being twisted around one another and fused together along a predetermined length.
One method of producing an access coupler for coupling optic energy between a first and a ~econd multimode fiber, comprises fusing thP first and the second fiber together along a predetermined length, applying a tensile force to the length of fused fibars, and heating the fused length of fibers to form biconical taper sections in the fused fibers.
Another method of producing an access coupler for coupling optic energy between a first and a second multimode
ThiS invention is directed to fiber op-tic couplers and in part.icular to low loss access couplers for multi-mode optial fibers and a method o~ produci~g these couplers.
An ernbodirnent o.E an inventi.o:n disclos~d in th.is application is c:laimed in co-pend..ing ~anadian ~ppl~.cation 350,118, filed April 1, 1980 by B.S. Kawasaki et al.
The two main network topology systems for the distribution of optical communication signals using single-strand multimode fiber are the tree distribution system and thestar system. For networks with.many terminals the tree dis-tribution scheme provides advantages o~ flexibility in the number and location of the distribution paths or drops and : minimizes the amount of ~iber used in comparison to a star system~ However, a tree network can suffer from an ineffective utilization of the total optical power launched in the trunk feeder.if there are.many lossy access junctions along the trunk which are encoun~ered in series. The tree scheme can be efect-ively utiliz'ed only if the excess loss above furcation loss at each access junction is made su~ficiently small.
Recently two methods for producing low loss access couplers for multimode fibers have been demonstratedO In t~e fi.rst which is described in a publication by Takesh.i Oæeki and Brian S. Kawasakl entitled "Optical direc-tional coupler using tapered sections in multimode fibers", -- Applied Physics Letters, ~olO 28, No~.9, May 1, 1976 - pa~es 528 and 529, twin biconlcal tapered sections o~ multimode optical ~ibe~ axe ~oi~ed by an optical epoxy to produce a directlonal coupler.
.~ In the second which is described in a publication b~ M.K~ Barnoski and H~R. Friedrich entitled "Fabrication of an access coupler ~ith single strand multi-mode fiber waveguides", - Applied Optics, ~cl. lS, No. llt November 1976, pages 2629 - 2630, t:wo sections of multimode fiber are fused side-by-side to form a low loss junction.
In both of these structures, the excess loss is iII the order of 1 ctB.
SU~ RY OF THE INVENTION
It is t~erefore an object of this in~ention to provide an access coupler having highly efficient coupling action.
It is a further object of this inven~ion to provide an access coupler in which considerable mode mixing and mode coupling occurs.
It is another object o~ this invention to provide an access coupler which is directional.
It is a urther object of this invention to provide an access coupler which has isolation of the uncoupled port~
It is another object Qf this invention to pro~ide simple and inexpensive methods of producin~ low loss access eouplersO
These and other objects are achieved in an access -coupler comprising a fixst and a second multimode fiber, each of the fibers having a biconical taper section~ the biconical taper sections of the fibers being twisted around one another and fused together along a predetermined length.
One method of producing an access coupler for coupling optic energy between a first and a ~econd multimode fiber, comprises fusing thP first and the second fiber together along a predetermined length, applying a tensile force to the length of fused fibars, and heating the fused length of fibers to form biconical taper sections in the fused fibers.
Another method of producing an access coupler for coupling optic energy between a first and a second multimode
-2-~f~St7 fiber comprises twisting a portion of each o~ the fibers around one another, applying a tensile force to the twisted porkions of the ~ibers and heating a region of the twisted fibers to soEten the fibers forming biconical taper sections and to ~use a predetermined length o e the twisted fibers together.
When the fibers already have biconical taper sections, the access coupler may be produced by twisting the fibers together along their taper sections and heating a region of the taper sections to fuse them together.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Figure 1 illustrates an access coupler in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 illustrakes an access coupler 1 in accordance with the present invention. The access coupler 1 consisks of a first fiber 2 with ends or ports Pl and P2 and a second fiber 3 with ends or ports P3 and P4. Each fiber 2,3 may be a gradea index mulkimode ~iber or a stepped index multimod~ fiber havlng an optical core 4 and a cladding 5. Each ~iber 2,3 also has a biconical tapered section 6 in which the diameter of the fiber 2,3 narrows and then widens to the normal fiber cliameter. Within the tapered section 6, the fibers 2,3 are fused to~ether along a predetermined length Q which may be greaker than the entire length of section 6. In addikion r within this fused length Q, the fibers 2 and 3 may be twisted around one another as shown in ~igure 1.
Generally, fibers 2 and 3 have similar diameters, : :
7~5 however, fibers of different diameters may be used in an access coupler 1 in which it is desired to have preferential coupling. If fiber 3 has a greater diameter ~han fiber 2 optical energy will .be preferentially coupled to fiber 3 from fiber 2, that is to the larger diameter fiber. Optical energy can thus be efficiently coupled into a trunk line .: using a coupler 1 in which the larger diameter fiber is connected into the line and optical energy is coupled into the line via the smaller diameter fiber.
The access coupler 1 may be produced by fusing a predetermined length of the fibers 2 and 3 together. Once fused, the fibers are pulled by a tensile force and the fused length is heated to soften t~e f:ibers 2 and3 ~uch that they may be drawn to form biconical taper sections 6.
Another method by which couplers 1 may be produced consists of taking two fibers 2 and 3, twisting or winding the fibers 2 and 3 around one ariother and applying a tensile force to the fîbers 2 and 3, as by putting them under spxing tension in a clamping jig~ A desired region of the twisted fibers 2 and 3 is then heated sufficiently to soften and fuse the fibers 2 and 3~ The spring tension causes th fibers 2 and 3 to be elongated in the softened ragion forming the biconical tapers, and the twist in the fibers ~ and 3 causes the fibers 2 and 3 to stay together and to fuse during the pulling process. The heating of the fibers 2 and 3 in the desired region may be accomplish~d by an oxy-butane microtorch flameO
However, when the two fibexs already have biconical taper sections 6, the access coupler 1 may be produced by twisting the two fibers 2 and 3 together along their taper sections and heatirlg a xegion of the twisted biconical taper ' .. . .
sections to fuse the fibers 2 and 3 together along a preae-termined length Q o~ the taper section~. T~ese me~hods o~ producing access couplers may be used to produce the couplers in a plant or may be usecl in the field to produce couplers direc-tly on a multimode fiber bus.
Some examples o~ twis-ted access couplers 1 fabricated using the second process describecl, are tabulatea i~ table 1 below. The couplexs 1 wexe made ~rom Cornin~ *
sil.ica step-index fiber having an 85 Imicron core di~meter, .0 a 20 micron cladding thickness and a numerical aper~ure of 0.175. The biconical section 6 was appxoximately 1 cm. long.
The access couplexs 1 were evaluated by illuminating poxt P1 with a HeN~ beam coupled into port Pl o iber 2 w;~h ~
xS0 microscope objecti~e. Oil ba~h cladding mode strippers were mounted on ports Pl, P2 and P4 and the power coupled ! from ports P2 and P~ was measured. The input power to the coupler 1 through port Pl was measuxed by breaking the fiber 2 at a point located downstream ~rom the mode s~rippex and upstream from section 6.
. TABLE 1 Coupler ._ . P2 P4 Couplingl Excess Insertion~Loss .
. Ratio P P4 . (m~) ~mW) (mW3 4/Pl 10 log 2 (dB~:
~ ... . ~ . ~ . .. . _ . .
a 7.05 6.53 0.27 0O038 ~0.16 -. b 5.92 6.00 0.58 0.084 -0.22 c 6.30 5.~1 0.74 ~ -0.11 d 7.20 6012 0.87 0.12: -0.13 e 6.92 4.40 1.65 '~~ ~-* Trademark .~
: ~5~
~, ~ ' ,.
., . .. : . . . .
. . . .
.. . . . . . . ... .
~35~
Table 1 shows the measured power levels and the calculated excess insertion loss for several couplers with various values of the coupling ratio P4/Pl where Pl represents the optical power in coupler port Pl. This coupling ratio increases wit.h an increase of the ratio of the diameter of the fiber to the diameter of th~ narrowest portion of each taper. The coupling ratio can vary from near zero with no taper section, to 50% with very high values of diameter ratio, i.e. ~ 10:1. Generally, increasing values for coupling ratios lead to increased insertion losses. The values of excess insertion loss are very low with the better couplers having values between 0.1 and 0.2 dB. This efficient coupling action is the result of the operation of the access coupler in accordance with the present invention.
As the light in port Pl enters the narrowing tapexed section 6, the higher order modes are forced to radiate out of the core 4 area to be guided as cladding modes. The llght can cross the fused boundary between the two biconical sections and is therefore guided in the overall structure.
As the ligh~ pxopagates beyond to the region of increasing tapers associated with ports P2 and P4, the cladding modes propagate at gradually decreasing angles to the fibex axis and ar~ recaptured by the tapered core section to again become core modes in the untapered portions of the fibers.
The coupling action is much ]ess lossy in this type of -structure than in the structure described by Ozeki and Kawasaki because of the high optical quality of the air-cladding interface. In the~present access couplerr i is difficult to discern the coupling region from a cursory examination of the scat~ered light alone~ The coupling action is also more efficient than in the coupler described by sarnoski and Friedrich because of the increasing -taper section 6. In this region of the device, light which is propa~ating in the cladding region can be recaptured by the core because the effect of an increasing taper is to r~duce the propagation angle of the light. It is .important that the l.ight propagating in the taperecl sections 6 be totally xeflected at the interface between the surace of the tapers 6 and the surroundiny medium. Therefore, the biconical taper sections 6 should be long and shallow and without sharp angles.
Another significant characteristi~ of the present device is that considerable mode mixing occurs. Though the low order modes are predominantly in port P~ rather than port P4 as expected, a fairly uniform filling of the modes is observed in port P4. The mode mixing is enhanced due to the twist asymmetry in the access coupler 1. This result, ~ thought unexpected is particularly advanta~eous when these ; couplers are used in series as a part of a tree distribution network.
It is also noted that a high degree of directionality or isolation is observed in the a~cess coupler 1 in accordance with this inventionL For exampl~, when port P
lS illuminated, the light propagates in one direction appearing at ports P2 and P4 with an excess insertion loss of 0.1 to 0.2 dB loss and with virtually no light appearing at port P3. Isolations in the order of -60 dB (10 ln P3/Pl) have been measured for access coupler 1.
: ....
, ., .. . - .
. : . - , , : , - .
When the fibers already have biconical taper sections, the access coupler may be produced by twisting the fibers together along their taper sections and heating a region of the taper sections to fuse them together.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Figure 1 illustrates an access coupler in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 illustrakes an access coupler 1 in accordance with the present invention. The access coupler 1 consisks of a first fiber 2 with ends or ports Pl and P2 and a second fiber 3 with ends or ports P3 and P4. Each fiber 2,3 may be a gradea index mulkimode ~iber or a stepped index multimod~ fiber havlng an optical core 4 and a cladding 5. Each ~iber 2,3 also has a biconical tapered section 6 in which the diameter of the fiber 2,3 narrows and then widens to the normal fiber cliameter. Within the tapered section 6, the fibers 2,3 are fused to~ether along a predetermined length Q which may be greaker than the entire length of section 6. In addikion r within this fused length Q, the fibers 2 and 3 may be twisted around one another as shown in ~igure 1.
Generally, fibers 2 and 3 have similar diameters, : :
7~5 however, fibers of different diameters may be used in an access coupler 1 in which it is desired to have preferential coupling. If fiber 3 has a greater diameter ~han fiber 2 optical energy will .be preferentially coupled to fiber 3 from fiber 2, that is to the larger diameter fiber. Optical energy can thus be efficiently coupled into a trunk line .: using a coupler 1 in which the larger diameter fiber is connected into the line and optical energy is coupled into the line via the smaller diameter fiber.
The access coupler 1 may be produced by fusing a predetermined length of the fibers 2 and 3 together. Once fused, the fibers are pulled by a tensile force and the fused length is heated to soften t~e f:ibers 2 and3 ~uch that they may be drawn to form biconical taper sections 6.
Another method by which couplers 1 may be produced consists of taking two fibers 2 and 3, twisting or winding the fibers 2 and 3 around one ariother and applying a tensile force to the fîbers 2 and 3, as by putting them under spxing tension in a clamping jig~ A desired region of the twisted fibers 2 and 3 is then heated sufficiently to soften and fuse the fibers 2 and 3~ The spring tension causes th fibers 2 and 3 to be elongated in the softened ragion forming the biconical tapers, and the twist in the fibers ~ and 3 causes the fibers 2 and 3 to stay together and to fuse during the pulling process. The heating of the fibers 2 and 3 in the desired region may be accomplish~d by an oxy-butane microtorch flameO
However, when the two fibexs already have biconical taper sections 6, the access coupler 1 may be produced by twisting the two fibers 2 and 3 together along their taper sections and heatirlg a xegion of the twisted biconical taper ' .. . .
sections to fuse the fibers 2 and 3 together along a preae-termined length Q o~ the taper section~. T~ese me~hods o~ producing access couplers may be used to produce the couplers in a plant or may be usecl in the field to produce couplers direc-tly on a multimode fiber bus.
Some examples o~ twis-ted access couplers 1 fabricated using the second process describecl, are tabulatea i~ table 1 below. The couplexs 1 wexe made ~rom Cornin~ *
sil.ica step-index fiber having an 85 Imicron core di~meter, .0 a 20 micron cladding thickness and a numerical aper~ure of 0.175. The biconical section 6 was appxoximately 1 cm. long.
The access couplexs 1 were evaluated by illuminating poxt P1 with a HeN~ beam coupled into port Pl o iber 2 w;~h ~
xS0 microscope objecti~e. Oil ba~h cladding mode strippers were mounted on ports Pl, P2 and P4 and the power coupled ! from ports P2 and P~ was measured. The input power to the coupler 1 through port Pl was measuxed by breaking the fiber 2 at a point located downstream ~rom the mode s~rippex and upstream from section 6.
. TABLE 1 Coupler ._ . P2 P4 Couplingl Excess Insertion~Loss .
. Ratio P P4 . (m~) ~mW) (mW3 4/Pl 10 log 2 (dB~:
~ ... . ~ . ~ . .. . _ . .
a 7.05 6.53 0.27 0O038 ~0.16 -. b 5.92 6.00 0.58 0.084 -0.22 c 6.30 5.~1 0.74 ~ -0.11 d 7.20 6012 0.87 0.12: -0.13 e 6.92 4.40 1.65 '~~ ~-* Trademark .~
: ~5~
~, ~ ' ,.
., . .. : . . . .
. . . .
.. . . . . . . ... .
~35~
Table 1 shows the measured power levels and the calculated excess insertion loss for several couplers with various values of the coupling ratio P4/Pl where Pl represents the optical power in coupler port Pl. This coupling ratio increases wit.h an increase of the ratio of the diameter of the fiber to the diameter of th~ narrowest portion of each taper. The coupling ratio can vary from near zero with no taper section, to 50% with very high values of diameter ratio, i.e. ~ 10:1. Generally, increasing values for coupling ratios lead to increased insertion losses. The values of excess insertion loss are very low with the better couplers having values between 0.1 and 0.2 dB. This efficient coupling action is the result of the operation of the access coupler in accordance with the present invention.
As the light in port Pl enters the narrowing tapexed section 6, the higher order modes are forced to radiate out of the core 4 area to be guided as cladding modes. The llght can cross the fused boundary between the two biconical sections and is therefore guided in the overall structure.
As the ligh~ pxopagates beyond to the region of increasing tapers associated with ports P2 and P4, the cladding modes propagate at gradually decreasing angles to the fibex axis and ar~ recaptured by the tapered core section to again become core modes in the untapered portions of the fibers.
The coupling action is much ]ess lossy in this type of -structure than in the structure described by Ozeki and Kawasaki because of the high optical quality of the air-cladding interface. In the~present access couplerr i is difficult to discern the coupling region from a cursory examination of the scat~ered light alone~ The coupling action is also more efficient than in the coupler described by sarnoski and Friedrich because of the increasing -taper section 6. In this region of the device, light which is propa~ating in the cladding region can be recaptured by the core because the effect of an increasing taper is to r~duce the propagation angle of the light. It is .important that the l.ight propagating in the taperecl sections 6 be totally xeflected at the interface between the surace of the tapers 6 and the surroundiny medium. Therefore, the biconical taper sections 6 should be long and shallow and without sharp angles.
Another significant characteristi~ of the present device is that considerable mode mixing occurs. Though the low order modes are predominantly in port P~ rather than port P4 as expected, a fairly uniform filling of the modes is observed in port P4. The mode mixing is enhanced due to the twist asymmetry in the access coupler 1. This result, ~ thought unexpected is particularly advanta~eous when these ; couplers are used in series as a part of a tree distribution network.
It is also noted that a high degree of directionality or isolation is observed in the a~cess coupler 1 in accordance with this inventionL For exampl~, when port P
lS illuminated, the light propagates in one direction appearing at ports P2 and P4 with an excess insertion loss of 0.1 to 0.2 dB loss and with virtually no light appearing at port P3. Isolations in the order of -60 dB (10 ln P3/Pl) have been measured for access coupler 1.
: ....
, ., .. . - .
. : . - , , : , - .
Claims (3)
1. A method of producing an access coupler for coupling optical energy from a first multimode optic fiber to a second multimode optic fiber comprising:
- twisting a portion of each of the first and second optic fibers around one another;
- applying a tensile force to the twisted portion of the first and second fibers;
- heating a region of the twisted fibers to soften the fibers in the region thereby elongating the region of twisted fibers into biconical taper sections and to fuse together a predetermined length of the biconical taper sections.
- twisting a portion of each of the first and second optic fibers around one another;
- applying a tensile force to the twisted portion of the first and second fibers;
- heating a region of the twisted fibers to soften the fibers in the region thereby elongating the region of twisted fibers into biconical taper sections and to fuse together a predetermined length of the biconical taper sections.
2. A method as claimed in claim 1 wherein the heating is provided by an oxy-butane microtorch flame.
3. A method as claimed in claim 2 wherein the tensile force is applied by clamping the fibers in a spring tensioned jig.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA350,117A CA1105705A (en) | 1977-06-13 | 1980-04-01 | Method of producing optical fiber access coupler |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US805,865 | 1977-06-13 | ||
| US05/805,865 US4291940A (en) | 1977-06-13 | 1977-06-13 | Low loss access coupler for multimode optical fiber distribution systems |
| CA000300298A CA1119860A (en) | 1977-06-13 | 1978-04-03 | Low loss access coupler for multimode optical fiber distribution systems |
| CA350,117A CA1105705A (en) | 1977-06-13 | 1980-04-01 | Method of producing optical fiber access coupler |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105705A true CA1105705A (en) | 1981-07-28 |
Family
ID=27165597
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA350,117A Expired CA1105705A (en) | 1977-06-13 | 1980-04-01 | Method of producing optical fiber access coupler |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1105705A (en) |
-
1980
- 1980-04-01 CA CA350,117A patent/CA1105705A/en not_active Expired
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