CA2413050A1 - Digital fibre microlens shaper - Google Patents
Digital fibre microlens shaper Download PDFInfo
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- CA2413050A1 CA2413050A1 CA 2413050 CA2413050A CA2413050A1 CA 2413050 A1 CA2413050 A1 CA 2413050A1 CA 2413050 CA2413050 CA 2413050 CA 2413050 A CA2413050 A CA 2413050A CA 2413050 A1 CA2413050 A1 CA 2413050A1
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- 239000000835 fiber Substances 0.000 title claims abstract description 78
- 238000000034 method Methods 0.000 claims abstract description 56
- 239000013307 optical fiber Substances 0.000 claims abstract description 39
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- 238000010168 coupling process Methods 0.000 claims abstract description 37
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- 238000011282 treatment Methods 0.000 claims description 24
- 238000012986 modification Methods 0.000 claims description 17
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- 238000010438 heat treatment Methods 0.000 claims description 7
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 6
- 230000005855 radiation Effects 0.000 claims description 5
- 238000001465 metallisation Methods 0.000 claims description 4
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 3
- 239000001569 carbon dioxide Substances 0.000 claims description 3
- 238000011065 in-situ storage Methods 0.000 claims description 2
- 239000004065 semiconductor Substances 0.000 description 10
- 238000002310 reflectometry Methods 0.000 description 7
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- 238000004519 manufacturing process Methods 0.000 description 3
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- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000013459 approach Methods 0.000 description 2
- 238000005253 cladding Methods 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
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- 238000003486 chemical etching Methods 0.000 description 1
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- 229910002804 graphite Inorganic materials 0.000 description 1
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- 238000000608 laser ablation Methods 0.000 description 1
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- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000005459 micromachining Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
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- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/255—Splicing of light guides, e.g. by fusion or bonding
- G02B6/2552—Splicing of light guides, e.g. by fusion or bonding reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Couplings Of Light Guides (AREA)
- Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
Abstract
This invention relates to the microshaping of a tensed optical fibre such that the coupling of light from a source of laser light into the optical fibre, or between the optical fibre and another optical component, is optimized and, particularly, to the microshaping of such tensed fibres in a digital process whereby the coupling of light into or from the fibre is used directly to control the microshaping process.
Description
PHOTONOVA INC.
December 19, 2002 DIGITAL FIBRE MICROLENS SHAPER
Fedor Timofeev and Raman Kashyap DISCLOSURE
BACKGROUND OF THE INVENTION
The efficient coupling of light to and from optical devices such as laser diode sources, planar optical waveguides, semiconductor optical gain devices, photodiodes or bulk spatial optics into cylindrical optical fibres is of great conunercial importance. The coupling is often compromised by differences in the spatial optical field shapes and spot sizes between the devices being connected, for example coupling of elliptical optical field shapes from a semiconductor light-emitting source to the circular geometry of an optical fibre.
Further, lenses manufactured on optical fibres or waveguides typically result in non-uniformities in the optical field of the lenses due to stresses, scratches, deformations, contaminants or other types of defects.
It is well known that the coupling of light from a source can be improved by using either bulk lenses or lenses integrated on the tips of optical fibres or waveguides, and many designs and mounting arrangements for such lenses have been described (see for example U.S. Patent No.
5,764,838).
Practical methods of improving the coupling of laser light into optical fibres have been developed based on forming microlenses on the ends of the fibres into which the light is to be coupled. U.5. Patent No. 5,455,879 describes use of a wedge-shaped lens to improve the coupling of light from an elliptical shaped radiation source such as a laser diode into a Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada cylindrically symmetrical optical fibre. Such integrated lens designs have the additional benefit that reflectivity is reduced, further improving coupling. The degree of coupling efficiency that can be achieved in this approach is seriously limited, however, as the field that would be efficiently coupled into a wedge-shaped lens would be bi-modal owing to the geometrical ray paths, while the field of the source is typically elliptical.
Variants of the wedge-shaped design have been described, for example in U.S.
Patents Nos.
6,317,550, 6,301,406, 5,845,024, 5,256,851 and 5,101,457. In U.S. Patents Nos.
6,317,550 and 6,301,406, it is disclosed that a small flat section at the tip of a wedge-shaped lens can sharply improve the efficiency of coupling of light from an elliptical laser source into a leased optical fibre, with the improvement being most marked when this flat section has dimensions on the order of a few microns. With such a flattened lens tip, however, back-reflection by the lens is seriously increased and can be as much as 4% or higher. This can have a deleterious effect on the operation of a laser source. In U.S. Patent No. 5,256,851, a method is disclosed for micromachining of the tip of a leased fibre by laser ablation. However, in this method the laser energy penetrates deeply into the lens, and it is very difficult to control introduction of defects into the glass. U.5. Patent No. 5,845,024 discloses a method of mechanical grinding of the tip of a wedge-shaped lens integrated on an optical fibre, to provide a roughly circular profile. This has the disadvantage of being mechanically complex and diffcult to control, while in addition grinding leaves fine markings on the lens which reduce coupling efficiency, increasing scattering losses and back reflection. U.S. Patent No. 5,101,457 discloses a method of microshaping of a lens on the tip of an optical fibre by chemical etching. This process, however, is complex and difficult to control. Further, it and cannot be used in-situ and can result in introduction of contamination into the glass, adversely affecting coupling.
December 19, 2002 DIGITAL FIBRE MICROLENS SHAPER
Fedor Timofeev and Raman Kashyap DISCLOSURE
BACKGROUND OF THE INVENTION
The efficient coupling of light to and from optical devices such as laser diode sources, planar optical waveguides, semiconductor optical gain devices, photodiodes or bulk spatial optics into cylindrical optical fibres is of great conunercial importance. The coupling is often compromised by differences in the spatial optical field shapes and spot sizes between the devices being connected, for example coupling of elliptical optical field shapes from a semiconductor light-emitting source to the circular geometry of an optical fibre.
Further, lenses manufactured on optical fibres or waveguides typically result in non-uniformities in the optical field of the lenses due to stresses, scratches, deformations, contaminants or other types of defects.
It is well known that the coupling of light from a source can be improved by using either bulk lenses or lenses integrated on the tips of optical fibres or waveguides, and many designs and mounting arrangements for such lenses have been described (see for example U.S. Patent No.
5,764,838).
Practical methods of improving the coupling of laser light into optical fibres have been developed based on forming microlenses on the ends of the fibres into which the light is to be coupled. U.5. Patent No. 5,455,879 describes use of a wedge-shaped lens to improve the coupling of light from an elliptical shaped radiation source such as a laser diode into a Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada cylindrically symmetrical optical fibre. Such integrated lens designs have the additional benefit that reflectivity is reduced, further improving coupling. The degree of coupling efficiency that can be achieved in this approach is seriously limited, however, as the field that would be efficiently coupled into a wedge-shaped lens would be bi-modal owing to the geometrical ray paths, while the field of the source is typically elliptical.
Variants of the wedge-shaped design have been described, for example in U.S.
Patents Nos.
6,317,550, 6,301,406, 5,845,024, 5,256,851 and 5,101,457. In U.S. Patents Nos.
6,317,550 and 6,301,406, it is disclosed that a small flat section at the tip of a wedge-shaped lens can sharply improve the efficiency of coupling of light from an elliptical laser source into a leased optical fibre, with the improvement being most marked when this flat section has dimensions on the order of a few microns. With such a flattened lens tip, however, back-reflection by the lens is seriously increased and can be as much as 4% or higher. This can have a deleterious effect on the operation of a laser source. In U.S. Patent No. 5,256,851, a method is disclosed for micromachining of the tip of a leased fibre by laser ablation. However, in this method the laser energy penetrates deeply into the lens, and it is very difficult to control introduction of defects into the glass. U.5. Patent No. 5,845,024 discloses a method of mechanical grinding of the tip of a wedge-shaped lens integrated on an optical fibre, to provide a roughly circular profile. This has the disadvantage of being mechanically complex and diffcult to control, while in addition grinding leaves fine markings on the lens which reduce coupling efficiency, increasing scattering losses and back reflection. U.S. Patent No. 5,101,457 discloses a method of microshaping of a lens on the tip of an optical fibre by chemical etching. This process, however, is complex and difficult to control. Further, it and cannot be used in-situ and can result in introduction of contamination into the glass, adversely affecting coupling.
Property of PhotoNova Ino.,108 Astoria Avenue, Polnte Claire, Quebec H9S 5A8, Canada While such approaches do improve coupling of laser light into a tensed fibre, they are severely restricted since no two semiconductor light sources are identical, and forniing of the microlens tip to optimize light coupling is difficult. Further, the methods of the prior art do not provide means for actively monitoring the optical field of a fibre microlens while it is being shaped, with the consequence that efficient fabrication of microlenses having high coupling efficiency is not possible. Also, most prior art methods are complex and costly, while providing limited coupling efficiency due to limitations of design or to contamination or defects resulting from the fabrication process.
SUMMARY OF THE INVENTION
The present invention provides a novel method of modifying a tensed fibre to maximize the coupling of laser light into the fibre. This is accomplished by applying localized heating to the tip of the lens. This may be applied, for example, by a series of weak electrical discharges or, alternatively, by pulses of light from a tightly focussed laser beam. Such modification can be carried out in a controlled manner so as to allow precise maximization of the coupling of light from the source into the fibre. The method can also be used to modify a Tensed fibre to optimize the coupling of light leaving the fibre to enter another fibre or device. An apparatus is described that can accomplish such microlens modifications.
The object of the invention may be achieved by applying a controlled electrical discharge or laser light to the tip of the Tensed fibre, while monitoring the coupling of light from the light source into the fibre. In a preferred embodiment of the invention, the discharge or laser light treatment is applied digitally, in short pulses that allow the change in coupling efficiency to be precisely controlled.
SUMMARY OF THE INVENTION
The present invention provides a novel method of modifying a tensed fibre to maximize the coupling of laser light into the fibre. This is accomplished by applying localized heating to the tip of the lens. This may be applied, for example, by a series of weak electrical discharges or, alternatively, by pulses of light from a tightly focussed laser beam. Such modification can be carried out in a controlled manner so as to allow precise maximization of the coupling of light from the source into the fibre. The method can also be used to modify a Tensed fibre to optimize the coupling of light leaving the fibre to enter another fibre or device. An apparatus is described that can accomplish such microlens modifications.
The object of the invention may be achieved by applying a controlled electrical discharge or laser light to the tip of the Tensed fibre, while monitoring the coupling of light from the light source into the fibre. In a preferred embodiment of the invention, the discharge or laser light treatment is applied digitally, in short pulses that allow the change in coupling efficiency to be precisely controlled.
Property of PhotoNova Inc., 108 Astoria Avenue, Points Claire, Quebec H9S 5A8, Canada In an alternative embodiment, the near- and/or the far-field distribution of light from the light source is mapped, and the fibre lens is then modified such that the distribution of light leaving the lensed fibre precisely matches this near- and/or far-field distribution map.
In a further embodiment of the invention, the reflection of light launched into the fibre from the microlens is monitored during treatment, and this reflection is calibrated against the change in the optical field of the lens such that its value can be used to control the microshaping of the lens.
In another embodiment, the invention may be used to minimize or eliminate the non-uniformities in the optical field of lensed optical fibres due to stresses, scratches, deformations, contaminants or other types of defects.
DESCRIPTION OF THE DRAWINGS
Fig. la is a graphical representation of the far-field optical power intensity of laser light at 1500 nm emitted from a fibre having an integrated wedge-shaped lens. The wedge has a 63 degree angle and is polished to a 0.1 micrometer finish.
Fig. 1 b is a graphical representation of the angular distribution of optical power emitted at 980 nm from a lensed fibre having a 51 degree single wedge, in which power is measured as a fimction of angle from the centreline of the fibre, perpendicular and parallel to the flat of the wedge.
Fig. 2a is a schematic representation of a typical arrangement used for microlens shaping using an electrical discharge by the method of this invention.
Fig. 2b is a schematic representation of a typical arrangement used for microlens shaping using a focussed laser beam by the method of this invention.
In a further embodiment of the invention, the reflection of light launched into the fibre from the microlens is monitored during treatment, and this reflection is calibrated against the change in the optical field of the lens such that its value can be used to control the microshaping of the lens.
In another embodiment, the invention may be used to minimize or eliminate the non-uniformities in the optical field of lensed optical fibres due to stresses, scratches, deformations, contaminants or other types of defects.
DESCRIPTION OF THE DRAWINGS
Fig. la is a graphical representation of the far-field optical power intensity of laser light at 1500 nm emitted from a fibre having an integrated wedge-shaped lens. The wedge has a 63 degree angle and is polished to a 0.1 micrometer finish.
Fig. 1 b is a graphical representation of the angular distribution of optical power emitted at 980 nm from a lensed fibre having a 51 degree single wedge, in which power is measured as a fimction of angle from the centreline of the fibre, perpendicular and parallel to the flat of the wedge.
Fig. 2a is a schematic representation of a typical arrangement used for microlens shaping using an electrical discharge by the method of this invention.
Fig. 2b is a schematic representation of a typical arrangement used for microlens shaping using a focussed laser beam by the method of this invention.
Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada Fig. 3 is a schematic representation of the tip of a Tensed fibre, indicating for this embodiment the area in which microlens shaping occurs.
Fig. 4a is a graphical representation of the far-field optical power intensity of laser light at 1500 nm emitted from the fibre of Fig. la, following treatment of the integrated wedge-shaped lens by the method of this invention.
Fig. 4b is a graphical representation of the angular distribution of optical power from a Tensed fibre at 980 nm, in which power is measured as a function of angle from the centreline of the fibre, perpendicular and parallel to the flat of the wedge following treatment with 76 discharge pulses by the method of this invention.
Fig. 5 is a graphical representation of the angular distribution of optical power from a semiconductor laser source in comparison with the far-field distribution of light emerging from a Tensed fibre in which the lens has been modified by the method of this invention to match the two profiles.
Fig. 6 is a graphical representation of the variation of the reflectivity of light launched into the Tensed fibre of Fig. 5, and reflected from the internal surface of the lens, as a function of the number of discharges applied during modification of the lens.
Fig. 7 is a graphical representation of the variation of the losses in coupling of light that has been launched into a Tensed fibre, as it exits through the lens and is reflected back to couple into the fibre, as a function of the distance of the mirror from the tip of the fibre lens.
Fig. 8 is a graphical representation of the logarithmic amplitude of the optical field of light emerging from a conical pulled lens on the tip of an optical fibre, before treatment and following two discharge treatments by the method of this invention.
_5 Property of PhotoNova Inc.,108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada DETAILED DESCRIPTION OF THE INVENTION
Figs. 1 a and 1 b present measurements obtained with a single wedge-shaped lens that has been fabricated on the end of an optical fibre. Such lenses are produced, for example, by polishing as described in U.S. Patent No. 5,455,879. In Figs. la and lb, the light-coupling characteristics of such lenses are characterized by passing laser light through the optical fibre such that it exits through the wedge-shaped lens. Fig. la shows the far-field distribution of optical intensity of laser light having a wavelength of 1500 nm emerging from such a lens; this distribution shows a dark spot at its centre. The distribution clearly has two lobes. Thus, coupling of light into an optical fibre through such a lens would be inherently inefficient, as no practical laser light sources or other waveguiding devices have such a two-lobed distribution of output light intensity.
Fig. lb shows the optical power measured in a similar test using light having a wavelength of 980 nm passed through a fibre having a single 51 degree wedge at the end.
Angular distribution of power measured horizontal to the flat surfaces of the lens (curve 1) is symmetrically distributed about the centerline of the fibre. However, optical power measured perpendicular to the flat surfaces of the lens (curve 2) shows a strong minimum at the centerline.
While it is known that modification of the tip of a fibre having a wedge-shaped lens over a dimension of a few microns from the centerline can improve coupling to a semiconductor laser light source, as disclosed for example in U.S. Patents Nos. 5,845,024 and 6,301,406, the fabrication of such geometries requires precise and costly procedures and optimization of coupling of light from the source to the optical fibre is difficult.
The present invention discloses a method of modifying a Tensed fibre in a controlled manner such that it provides optimal coupling of light between an optical fibre and a laser source. In one Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada embodiment, the near- and/or far-field distribution of light from the semiconductor laser source is measured, and the Tensed fibre is then modified to have a matching near-and/or far-field light distribution. Alternatively, back reflection of light launched into the fibre may be monitored as a method of controlling the microshaping of the fibre lens. The invention allows shaping to be carried out on metallized fibres without previous demetallizing or cleaning, as the fibre in the immediate vicinity of the lens, within for example 5 to 20 microns, may be demetallized and/or cleaned in the first few cycles of the treatment.
Fig. 2a is a schematic representation of one embodiment of the arrangement used to realize the lens modification of this invention. An optical fibre (3) which may have a core (4) has an integral single wedge-shaped lens (5). The core (4) could for example have a diameter of 2 to 10 microns, while the fibre could have an overall diameter on the order of 125 microns. The cladding could be a single layer, or could be fabricated with two or more layers and both the core and the cladding could have refractive indices which are graded in the radial direction. The optical fibre (3) may be encapsulated in a protective glass or polymer or other coating, and it may be metallized for soldering or other purposes. The lens (5) by which the fibre is terminated could be fabricated by polishing, etching, drawing, or any other known method, and it could be wedge-shaped or of any other shape suited to the application for which it is intended.
In the embodiment of the invention of Fig. 2a, an electrical discharge is established between two electrodes positioned near the lensed tip of the fibre ( 1 ). The electrodes (6a and 6b) may be of tungsten, graphite or any other suitable material capable of sustaining a repeated electrical discharge. Representative dimensions are shown in Fig. 2a, but these could be adjusted by a person skilled in the art, combined with selection of the electrical parameters of the process, as required to provide the required degree of processing. The electrical pulses causing the electrical Property of PhotoNova Inc., 108 Astoria Avenue, Polnte Claire, Quebec H9S 5A8, Canada discharge between the electrodes (6a and 6b) may be of any suitable intensity and duration, with the geometry selected, for giving a stepwise change in the dimensions of the tip of the lensed fibre and thus of the coupling characteristics of the lens. For example, pulses could be in the form of a square wave or any other shape having typically an amplitude between one and 500 milliamperes and duration on the order of 1 to 100 microseconds or more. Time between pulses is typically on the order of one tenth of a second but may be several seconds or longer, and this time may be controlled either automatically or by manually triggering the treatment pulses.
Different types of materials used to make the optical fibre may require either shorter or longer duration discharges as well as greater or smaller discharge currents. It will be evident to a person skilled in the art that the precise geometrical and electrical parameters necessary to achieve the desired result will depend on humidity, atmospheric pressure, sharpness of the lens shape, fibre size, fibre type, ambient temperature and many other parameters. Any combination of suitable geometric and electrical parameters that achieves the objects of this invention falls within its scope.
Fig. 2b is a schematic representation of a second embodiment of the arrangement used to realize the lens modification of this invention. A laser beam (7) is focussed by a lens or system of lenses (8) such that the focussed beam (9) is incident on the tip of the lens that is to be modified. As for the embodiment of Fig. 2a, the laser light may be pulsed with pulses of any suitable intensity and duration suitable, with the geometry selected, for giving a stepwise change in the dimensions of the tip of the lensed fibre and thus of the coupling characteristics of the lens.
Pulses could have a duration on the order of 1 to 100 microseconds or more, and time between pulses may be on the order of one tenth of a second or longer and may be controlled either automatically or by manually triggering the treatment pulses. Different types of materials used Property of PhotoNova Inc., 108 Astoria Avenue, Points Claire, Quebec H9S 5A8, Canada to make the optical fibre may require either shorter or longer duration pulses as well as greater or smaller intensity of the treatment light. A carbon dioxide laser is well suited to this application.
It will be evident to a person skilled in the art that the precise geometrical and laser parameters necessary to achieve the desired result will depend on humidity, atmospheric pressure, sharpness of the lens shape, fibre size, fibre type, ambient temperature and many other parameters. Any combination of suitable geometric and laser parameters that achieves the objects of this invention falls within its scope Fig. 3 shows schematically the tip of a Tensed fibre at which shaping to be carried out by the method of this invention. The fibre may have a metallization coating (10).
This metallization may for example be an electrolytically-deposited coating of a few microns of nickel and a thin flash of gold (less than 1 micron). Alternatively, it may be a vacuum deposited coating such as, for example, 50 nm of titanium, 100 nm of platinum and 200 nm of gold. All such metallization coatings in the region of the fibre tip can be removed precisely and locally with application of a single or a few electrical discharges or light pulses by the method of this invention. The power level is such that a first single or several discharges or light pulses do not measurably affect the glass of the fibre, but volatilize the thin metal coating. The first discharge or light pulse, whether or not the fibre is metallized, also serves to clean the surface of the lens tip. Continuing application of discharge or light pulses results in progressive modification to the tip of the fibre lens, for example in the region (11). This process of change is monitored and controlled by monitoring either the distribution of laser light exiting the Tensed fibre, or the efficiency of coupling of laser light into the fibre. The reflectivity of the microlens to light launched into the fibre may be used as a surrogate parameter to monitor the process.
_g_ Property of PhotoNova Inc.,108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada Fig. 4 illustrates the effect of this invention on the fibres used to obtain the light distribution results presented in Fig. 1. In Fig. 4a, the far-field distribution of 1500 nm laser light is seen to have changed after application of consecutive discharge pulses, eliminating completely the two-lobed distribution and giving an elliptical distribution which is typical of the light distribution from many commercial semiconductor laser sources.
In Fig. 4b, curve ( 12) is the angular distribution of optical power measured horizontal to the flat surfaces of the lens while curve (13) is the angular distribution of optical power measured perpendicular to the flat surfaces, both measured with laser light at a wavelength of 980 nm following treatment with 76 discharge pulses by the method of this invention.
Curve (13) may be compared with curve (2) of Fig lb. The two-lobed distribution of far optical field intensity about the centerline of the fibre has been completely eliminated by the treatment of the lens.
Fig. 5 illustrates graphically the application of the method of this invention to matching the coupling of a semiconductor laser to a tensed fibre. The curve ( 14) in this figure is the normalized far-field optical power distribution of a 980 nm semiconductor laser source, measured perpendicular to the long axis of the source. The curve (15) is the far-field optical power distribution of 980 nm wavelength light emerging from a Tensed fibre which has been modified by the method of this invention. The fibre in this case was a Flexcore fibre having a single wedge-shaped lens with a 51 degree interior half angle. Successive discharges were applied until the best match with the optical power distribution of the semiconductor laser source was obtained. The match is close, and the efficiency of coupling of light from this laser into the treated fibre is very high.
During modification of a tensed fibre by the method of this invention, it is useful to monitor the back reflection of light, which has been launched into the fibre, reflecting from the internal Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada surface of the lens. This reflectivity is a sensitive indicator of the degree of modification of the lens, and it changes continuously during the modification process, increasing with the number of discharges applied. Fig. 6 presents an example, for treatment of the Tensed fibre of Fig. 5. The reflectivity remains low, below 0.2%, during the treatment. It stays relatively constant during the initial discharge treatments, as fibre cleaning takes place and microscopic distortions of the lens tip are eliminated. Subsequently, the reflectivity increases monotonically with the number of discharges. The precise reflectivity values provide a useful and reproducible indicator of the degree of modification of the lens that has been achieved, and they can be used for control purposes in the application of the method of this invention.
The method of this invention can also be used to achieve a controlled variation of the focal length of a fibre microlens. Fig. 7 shows the variation of the coupling loss for laser light launched into a Tensed fibre and coupled back into the fibre following reflection from a plane mirror located in front of the lens. This coupling loss is plotted as a function of the distance of the reflecting mirror from the lens, so that the peak of the curve corresponds to the focal length of the microlens. The figure shows that the focal length of the lens can be altered as the microlens is treated by the method of this invention. Curve ( 16) shows the focal length after 30 discharge treatments to be approximately 9 microns. After 38 discharge treatments (curve 17) the focal length is decreased to approximately 6.5 microns. In fact, the method of this invention may be used to modify a fibre microlens to have a desired focal length.
This invention may be used to clean and smooth the lenses of Tensed fibres or wave guides, to eliminate the non-uniformities in the optical field of a lens which are inherently present in fibre lenses manufactured by most practical processes. Such non-uniformities could be due to stresses, scratches, deformations, contaminants or other types of defects.
Fig. 8 is a graphical _11_ Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada representation of the far optical field distribution of light emitted from a conical lens which has been formed by drawing the fibre to a point, for example as described in U.S.
Patent No.
4,589,897. Lenses of this type are widely available commercially. In this case; the conical lens was approximately 125 microns in diameter at its base and 300 microns in length. Due to the stresses and imperfections inherent in the drawing process, the optical distribution prior to treatment (curve 18 in Fig. 8) had marked side lobes together with (not shown) a very noisy background. Following treatment with two discharge pulses by the method of this invention (curve 19 in Fig. 8), the side lobes were effectively eliminated and the optical distribution was largely symmetrical. In addition, the noisiness of the background optical signal was almost entirely eliminated.
It should be understood that this invention is not limited to the specific embodiments described above but that various modifications obvious to those skilled in the art, including the use of the method with leased fibres fabricated from polymer or from different glass compositions, may be made therein without departing from the scope of the following claims.
_ 72 _ Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada
Fig. 4a is a graphical representation of the far-field optical power intensity of laser light at 1500 nm emitted from the fibre of Fig. la, following treatment of the integrated wedge-shaped lens by the method of this invention.
Fig. 4b is a graphical representation of the angular distribution of optical power from a Tensed fibre at 980 nm, in which power is measured as a function of angle from the centreline of the fibre, perpendicular and parallel to the flat of the wedge following treatment with 76 discharge pulses by the method of this invention.
Fig. 5 is a graphical representation of the angular distribution of optical power from a semiconductor laser source in comparison with the far-field distribution of light emerging from a Tensed fibre in which the lens has been modified by the method of this invention to match the two profiles.
Fig. 6 is a graphical representation of the variation of the reflectivity of light launched into the Tensed fibre of Fig. 5, and reflected from the internal surface of the lens, as a function of the number of discharges applied during modification of the lens.
Fig. 7 is a graphical representation of the variation of the losses in coupling of light that has been launched into a Tensed fibre, as it exits through the lens and is reflected back to couple into the fibre, as a function of the distance of the mirror from the tip of the fibre lens.
Fig. 8 is a graphical representation of the logarithmic amplitude of the optical field of light emerging from a conical pulled lens on the tip of an optical fibre, before treatment and following two discharge treatments by the method of this invention.
_5 Property of PhotoNova Inc.,108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada DETAILED DESCRIPTION OF THE INVENTION
Figs. 1 a and 1 b present measurements obtained with a single wedge-shaped lens that has been fabricated on the end of an optical fibre. Such lenses are produced, for example, by polishing as described in U.S. Patent No. 5,455,879. In Figs. la and lb, the light-coupling characteristics of such lenses are characterized by passing laser light through the optical fibre such that it exits through the wedge-shaped lens. Fig. la shows the far-field distribution of optical intensity of laser light having a wavelength of 1500 nm emerging from such a lens; this distribution shows a dark spot at its centre. The distribution clearly has two lobes. Thus, coupling of light into an optical fibre through such a lens would be inherently inefficient, as no practical laser light sources or other waveguiding devices have such a two-lobed distribution of output light intensity.
Fig. lb shows the optical power measured in a similar test using light having a wavelength of 980 nm passed through a fibre having a single 51 degree wedge at the end.
Angular distribution of power measured horizontal to the flat surfaces of the lens (curve 1) is symmetrically distributed about the centerline of the fibre. However, optical power measured perpendicular to the flat surfaces of the lens (curve 2) shows a strong minimum at the centerline.
While it is known that modification of the tip of a fibre having a wedge-shaped lens over a dimension of a few microns from the centerline can improve coupling to a semiconductor laser light source, as disclosed for example in U.S. Patents Nos. 5,845,024 and 6,301,406, the fabrication of such geometries requires precise and costly procedures and optimization of coupling of light from the source to the optical fibre is difficult.
The present invention discloses a method of modifying a Tensed fibre in a controlled manner such that it provides optimal coupling of light between an optical fibre and a laser source. In one Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada embodiment, the near- and/or far-field distribution of light from the semiconductor laser source is measured, and the Tensed fibre is then modified to have a matching near-and/or far-field light distribution. Alternatively, back reflection of light launched into the fibre may be monitored as a method of controlling the microshaping of the fibre lens. The invention allows shaping to be carried out on metallized fibres without previous demetallizing or cleaning, as the fibre in the immediate vicinity of the lens, within for example 5 to 20 microns, may be demetallized and/or cleaned in the first few cycles of the treatment.
Fig. 2a is a schematic representation of one embodiment of the arrangement used to realize the lens modification of this invention. An optical fibre (3) which may have a core (4) has an integral single wedge-shaped lens (5). The core (4) could for example have a diameter of 2 to 10 microns, while the fibre could have an overall diameter on the order of 125 microns. The cladding could be a single layer, or could be fabricated with two or more layers and both the core and the cladding could have refractive indices which are graded in the radial direction. The optical fibre (3) may be encapsulated in a protective glass or polymer or other coating, and it may be metallized for soldering or other purposes. The lens (5) by which the fibre is terminated could be fabricated by polishing, etching, drawing, or any other known method, and it could be wedge-shaped or of any other shape suited to the application for which it is intended.
In the embodiment of the invention of Fig. 2a, an electrical discharge is established between two electrodes positioned near the lensed tip of the fibre ( 1 ). The electrodes (6a and 6b) may be of tungsten, graphite or any other suitable material capable of sustaining a repeated electrical discharge. Representative dimensions are shown in Fig. 2a, but these could be adjusted by a person skilled in the art, combined with selection of the electrical parameters of the process, as required to provide the required degree of processing. The electrical pulses causing the electrical Property of PhotoNova Inc., 108 Astoria Avenue, Polnte Claire, Quebec H9S 5A8, Canada discharge between the electrodes (6a and 6b) may be of any suitable intensity and duration, with the geometry selected, for giving a stepwise change in the dimensions of the tip of the lensed fibre and thus of the coupling characteristics of the lens. For example, pulses could be in the form of a square wave or any other shape having typically an amplitude between one and 500 milliamperes and duration on the order of 1 to 100 microseconds or more. Time between pulses is typically on the order of one tenth of a second but may be several seconds or longer, and this time may be controlled either automatically or by manually triggering the treatment pulses.
Different types of materials used to make the optical fibre may require either shorter or longer duration discharges as well as greater or smaller discharge currents. It will be evident to a person skilled in the art that the precise geometrical and electrical parameters necessary to achieve the desired result will depend on humidity, atmospheric pressure, sharpness of the lens shape, fibre size, fibre type, ambient temperature and many other parameters. Any combination of suitable geometric and electrical parameters that achieves the objects of this invention falls within its scope.
Fig. 2b is a schematic representation of a second embodiment of the arrangement used to realize the lens modification of this invention. A laser beam (7) is focussed by a lens or system of lenses (8) such that the focussed beam (9) is incident on the tip of the lens that is to be modified. As for the embodiment of Fig. 2a, the laser light may be pulsed with pulses of any suitable intensity and duration suitable, with the geometry selected, for giving a stepwise change in the dimensions of the tip of the lensed fibre and thus of the coupling characteristics of the lens.
Pulses could have a duration on the order of 1 to 100 microseconds or more, and time between pulses may be on the order of one tenth of a second or longer and may be controlled either automatically or by manually triggering the treatment pulses. Different types of materials used Property of PhotoNova Inc., 108 Astoria Avenue, Points Claire, Quebec H9S 5A8, Canada to make the optical fibre may require either shorter or longer duration pulses as well as greater or smaller intensity of the treatment light. A carbon dioxide laser is well suited to this application.
It will be evident to a person skilled in the art that the precise geometrical and laser parameters necessary to achieve the desired result will depend on humidity, atmospheric pressure, sharpness of the lens shape, fibre size, fibre type, ambient temperature and many other parameters. Any combination of suitable geometric and laser parameters that achieves the objects of this invention falls within its scope Fig. 3 shows schematically the tip of a Tensed fibre at which shaping to be carried out by the method of this invention. The fibre may have a metallization coating (10).
This metallization may for example be an electrolytically-deposited coating of a few microns of nickel and a thin flash of gold (less than 1 micron). Alternatively, it may be a vacuum deposited coating such as, for example, 50 nm of titanium, 100 nm of platinum and 200 nm of gold. All such metallization coatings in the region of the fibre tip can be removed precisely and locally with application of a single or a few electrical discharges or light pulses by the method of this invention. The power level is such that a first single or several discharges or light pulses do not measurably affect the glass of the fibre, but volatilize the thin metal coating. The first discharge or light pulse, whether or not the fibre is metallized, also serves to clean the surface of the lens tip. Continuing application of discharge or light pulses results in progressive modification to the tip of the fibre lens, for example in the region (11). This process of change is monitored and controlled by monitoring either the distribution of laser light exiting the Tensed fibre, or the efficiency of coupling of laser light into the fibre. The reflectivity of the microlens to light launched into the fibre may be used as a surrogate parameter to monitor the process.
_g_ Property of PhotoNova Inc.,108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada Fig. 4 illustrates the effect of this invention on the fibres used to obtain the light distribution results presented in Fig. 1. In Fig. 4a, the far-field distribution of 1500 nm laser light is seen to have changed after application of consecutive discharge pulses, eliminating completely the two-lobed distribution and giving an elliptical distribution which is typical of the light distribution from many commercial semiconductor laser sources.
In Fig. 4b, curve ( 12) is the angular distribution of optical power measured horizontal to the flat surfaces of the lens while curve (13) is the angular distribution of optical power measured perpendicular to the flat surfaces, both measured with laser light at a wavelength of 980 nm following treatment with 76 discharge pulses by the method of this invention.
Curve (13) may be compared with curve (2) of Fig lb. The two-lobed distribution of far optical field intensity about the centerline of the fibre has been completely eliminated by the treatment of the lens.
Fig. 5 illustrates graphically the application of the method of this invention to matching the coupling of a semiconductor laser to a tensed fibre. The curve ( 14) in this figure is the normalized far-field optical power distribution of a 980 nm semiconductor laser source, measured perpendicular to the long axis of the source. The curve (15) is the far-field optical power distribution of 980 nm wavelength light emerging from a Tensed fibre which has been modified by the method of this invention. The fibre in this case was a Flexcore fibre having a single wedge-shaped lens with a 51 degree interior half angle. Successive discharges were applied until the best match with the optical power distribution of the semiconductor laser source was obtained. The match is close, and the efficiency of coupling of light from this laser into the treated fibre is very high.
During modification of a tensed fibre by the method of this invention, it is useful to monitor the back reflection of light, which has been launched into the fibre, reflecting from the internal Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada surface of the lens. This reflectivity is a sensitive indicator of the degree of modification of the lens, and it changes continuously during the modification process, increasing with the number of discharges applied. Fig. 6 presents an example, for treatment of the Tensed fibre of Fig. 5. The reflectivity remains low, below 0.2%, during the treatment. It stays relatively constant during the initial discharge treatments, as fibre cleaning takes place and microscopic distortions of the lens tip are eliminated. Subsequently, the reflectivity increases monotonically with the number of discharges. The precise reflectivity values provide a useful and reproducible indicator of the degree of modification of the lens that has been achieved, and they can be used for control purposes in the application of the method of this invention.
The method of this invention can also be used to achieve a controlled variation of the focal length of a fibre microlens. Fig. 7 shows the variation of the coupling loss for laser light launched into a Tensed fibre and coupled back into the fibre following reflection from a plane mirror located in front of the lens. This coupling loss is plotted as a function of the distance of the reflecting mirror from the lens, so that the peak of the curve corresponds to the focal length of the microlens. The figure shows that the focal length of the lens can be altered as the microlens is treated by the method of this invention. Curve ( 16) shows the focal length after 30 discharge treatments to be approximately 9 microns. After 38 discharge treatments (curve 17) the focal length is decreased to approximately 6.5 microns. In fact, the method of this invention may be used to modify a fibre microlens to have a desired focal length.
This invention may be used to clean and smooth the lenses of Tensed fibres or wave guides, to eliminate the non-uniformities in the optical field of a lens which are inherently present in fibre lenses manufactured by most practical processes. Such non-uniformities could be due to stresses, scratches, deformations, contaminants or other types of defects.
Fig. 8 is a graphical _11_ Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada representation of the far optical field distribution of light emitted from a conical lens which has been formed by drawing the fibre to a point, for example as described in U.S.
Patent No.
4,589,897. Lenses of this type are widely available commercially. In this case; the conical lens was approximately 125 microns in diameter at its base and 300 microns in length. Due to the stresses and imperfections inherent in the drawing process, the optical distribution prior to treatment (curve 18 in Fig. 8) had marked side lobes together with (not shown) a very noisy background. Following treatment with two discharge pulses by the method of this invention (curve 19 in Fig. 8), the side lobes were effectively eliminated and the optical distribution was largely symmetrical. In addition, the noisiness of the background optical signal was almost entirely eliminated.
It should be understood that this invention is not limited to the specific embodiments described above but that various modifications obvious to those skilled in the art, including the use of the method with leased fibres fabricated from polymer or from different glass compositions, may be made therein without departing from the scope of the following claims.
_ 72 _ Property of PhotoNova Inc., 108 Astoria Avenue, Pointe Claire, Quebec H9S 5A8, Canada
Claims (19)
1. ~A method for modifying the shape and finish of the lens of a lensed optical fibre or waveguide by precise and localized application of heat to the tip of the lens.
2. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claim 1, in which localized heating is applied using an electrical discharge between two or more electrodes located in proximity to the lens.
3. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claim 1, in which localized heating is applied using focussed laser radiation.
4. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claims 1 and 3, in which the laser providing localized heating is a carbon dioxide laser.
5. ~A method for modifying the lens of a leased optical fibre or waveguide as in claims 1 to 4, in which the electrical discharge or laser radiation is pulsed such that the treatment of the lens tip proceeds in controlled steps, with pulse durations of 1 to 100 microseconds and intervals of 1 microsecond to several seconds between treatment pulses.
6. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claims 1, 2 and 5, in which the electrical discharge has an amplitude of between 1 and to milliamperes.
7. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claims 1 to 6, in which light coupled to the optical fibre is monitored while the modification is in process and the monitored light is used to control the degree of lens modification.
8. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claim 7, in which the near-field or the far-field distribution of light emerging from the fibre is monitored and modification of the lens is continued until such distribution matches the distribution of light from the source to which the leased fibre or waveguide is to be coupled.
9. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claim 7, in which light reflected internally into the leased fibre or waveguide is monitored as a surrogate for the optical distribution of the lens, to allow control of the degree of modification of the lens.
10. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claims 1 to 6, in which the focal length of the fibre lens is adjusted to a desired length.
11. ~A method for modifying the lens of a leased optical fibre or waveguide as in claims 1 to 6, in which the lens is smoothed or finished so as to reduce side lobes of radiation and background noise in the optical field.
12. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claims 1 to 6, in which metallization of the fibre is removed in the first cycles of treatment of the lensed fibre or waveguide.
13. ~A method for modifying the lens of a lensed optical fibre or waveguide as in claims 1 to 7, in which the modification process is carried out in-situ to maximize coupling between the leased optical fibre or waveguide and the device to or from which light is being coupled.
14. ~An apparatus for modifying the lens of a lensed optical fibre or waveguide in which heat is applied precisely and locally using a controlled electrical discharge the vicinity of the tip of the lens such that the lens is modified in a controlled manner to optimize coupling between the lensed fibre or waveguide and a light source or other optical component or device.
15. ~An apparatus for modifying the lens of a lensed optical fibre or waveguide as in claim 14, in which localized heating is applied using a controlled electrical discharge in the vicinity of the tip of the lens.
16. ~An apparatus for modifying the lens of a lensed optical fibre or waveguide as in claim 14, in which localized heating is applied using focussed laser radiation.
17. ~An apparatus for modifying the lens of a leased optical fibre or waveguide as in claim 16, in which the laser providing localized heating is a carbon dioxide laser.
18. ~An apparatus for modifying the lens of a lensed optical fibre or waveguide as in claim 15 or 16, in which the electrical discharge or laser light is pulsed such that the treatment of the lens tip proceeds in controlled steps, with pulse durations of 1 to 100 microseconds and intervals of 1 microsecond to several seconds between treatment pulses.
19. ~An apparatus for modifying the lens of a lensed optical fibre or waveguide as in claims 15 and 18, in which the electrical discharge has an amplitude of between 1 and milliamperes.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2413050 CA2413050A1 (en) | 2002-12-23 | 2002-12-23 | Digital fibre microlens shaper |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2413050 CA2413050A1 (en) | 2002-12-23 | 2002-12-23 | Digital fibre microlens shaper |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2413050A1 true CA2413050A1 (en) | 2004-06-23 |
Family
ID=32514043
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2413050 Abandoned CA2413050A1 (en) | 2002-12-23 | 2002-12-23 | Digital fibre microlens shaper |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2413050A1 (en) |
-
2002
- 2002-12-23 CA CA 2413050 patent/CA2413050A1/en not_active Abandoned
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