CA1313071C - Isotopic fiberoptics - Google Patents
Isotopic fiberopticsInfo
- Publication number
- CA1313071C CA1313071C CA 594392 CA594392A CA1313071C CA 1313071 C CA1313071 C CA 1313071C CA 594392 CA594392 CA 594392 CA 594392 A CA594392 A CA 594392A CA 1313071 C CA1313071 C CA 1313071C
- Authority
- CA
- Canada
- Prior art keywords
- cladding
- core
- amorphous silicon
- chamber
- gaseous mixture
- 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 - Fee Related
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/24—Deposition of silicon only
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01807—Reactant delivery systems, e.g. reactant deposition burners
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C13/00—Fibre or filament compositions
- C03C13/04—Fibre optics, e.g. core and clad fibre compositions
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C13/00—Fibre or filament compositions
- C03C13/04—Fibre optics, e.g. core and clad fibre compositions
- C03C13/045—Silica-containing oxide glass compositions
- C03C13/047—Silica-containing oxide glass compositions containing deuterium
-
- 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
- G02B6/02—Optical fibres with cladding with or without a coating
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
- C03B2201/22—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with deuterium
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Optics & Photonics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Inorganic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- General Physics & Mathematics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Chemical Vapour Deposition (AREA)
Abstract
ABSTRACT
An optical fiber in which chemical non-uniformities leading to optical losses at the core and cladding interface are minimized by selecting materials for the core and the cladding which are chemically substantially identical, at least one element in the core being the isotope of the corresponding element in the cladding and selected to impart a refractive index in the core which exceeds the refractive index in cladding.
An optical fiber in which chemical non-uniformities leading to optical losses at the core and cladding interface are minimized by selecting materials for the core and the cladding which are chemically substantially identical, at least one element in the core being the isotope of the corresponding element in the cladding and selected to impart a refractive index in the core which exceeds the refractive index in cladding.
Description
3~3~
ISOTOPIC FIBEROPTICS
This invention relates to the production of an optical fiber in which the number of imperfections between the core and the cladding is substantially reduced so as to minimize attenuation of electromagnetic radiation or light travelling ; 5 through the fiber and maximize total internal reflectlon.
Attenuation of light in an optical fiber i5 partly due to intrinsic factors and also to extrinsic factors. The intrinsic factors are inherent to the component materials comprising a fiber and are generally recognized to include electronic and vibrational absorption, and Rayleigh scattering.
Current developments in optical fiber research include the selection of new materials which are selected on the basis of their intrinsic low attenuation properties.
The attenuation of light in an optical fiber may also be ascribed to extrinsic losses resulting from contamination and improper processing. In particular, in silica-based material, an important absorbing species is the hydroxyl radical (OH-) which is formed when hydrogen is present in the fiber material.
One approach for reducing the hydroxyl caused attenuation, has been to replace the hydrogen with deuterium so as to shift the vibration mode of the radical impurity to a longer wavelength outside the region of interest.
While the substitution of deuterium for hydrogen in silica-based optical fibers has had the desired effect, and the non-silica-based fiber materials, the so-called second generation fiber materials including halide-containing crystals, , . ~;
:
. ~ ' ~3~ 3~7~
chalcogenide glasses and heavy-metal fluoride glasses are attractive because of their intrinsically low attenuation properties, these approaches do not address physical attenuation factors which necessarily arise at the interface between materials of different chemical composition.
It is the object of this invention to provide an optical fiber in which the opportunity for the attenuation of light at the interface between the cladding and core materials is substantially minimized.
In accordance with this invention, there is provided an optical fiber comprising a core and a cladding in which the core material and the cladding material include at least one common constituent element, the common element in the core being an isotope of the element in the cladding.
Preferably, the core material and cladding material will have the same chemical composition, so that the interface between the core and cladding will be chemically coherent. The , material composing the core and cladding are selected so that at ~¦ least one element in the core material is an isotope of the element in the cladding material and the resulting refractive index in the core exceeds the refractive index in the cladding.
The invention has a theoretical basis which is described below and supplemented by experimental results with reference to the accompanying drawings in which:
Fig. l is a schematic representation of the apparatus used for plasma enhanced chemical vapour deposition (PCVD) of isotopic layers according to the invention;
;,, ' ! 2 ~,' ,, ' ~ :
,, Fig 2 is a graphical representation of the opti..eal bandgap (ev) on the ordinate axis and layer thiekness (~ m) on the abscissa for specimens of deuterated and hydrogenated amorphous silicon produced by PCVD with the apparatus of Fig. 1;
and Fig. 3 is a graphieal representation of the ratio of the refraetive indiees minus 1 (~-1) on the ordinate axis and the thiekness of the hydrated assoeiated amorpho~s silieon layer on the abseissa for the speeimens of Fig 2.
The expeeted variations in lattice constant d for isotopically different materials, for typical transparent crystalline solids, may be represented as follows:
d ~ 10 3 to 10 4 d in accordance with Matthew, J.A.D., 1968. Journal of Physics C, vol. 1, p. 1768.
Based on the first order approximation by the Clausius-Mosotti relationship for refraetive index (Blakemore, 2Q J.S., 1985. "Solid State Physics", Cambridge University Press), the relation between lattiee eonstant d and refraetive index n may be represented as follows:
~n ~ 3c . ~d n d . .
where c is a dimensionless ad~ustment faetor of the order of unity.
1~3~
It follows that a minimum expected ratio of the refractive indices at a typical isotopic interface will range between 3 x 10 3 and 3 x 10 4 or = nl/n2 = 1.003 1.0003.
From the Snell law of light refraction (Sin ~2/Sin ~1 =
nl/n2), applicable to small angles, the following expression for the ray bending angle ~ at which light ~ravels through a refractiYe boundary may be deduced:
10~ = ~ arcsin (nl/n2 sin B) where B is the angle between the falling ray and normal to the interface. For a sliding ray in which ~ ~ 90, the control ;~ case for light confinement in fibers, one obtains a ray bending angle ~ of 1.5 to 4.5 degrees, sufficient for confining light.
j The following experiments were conducted to determine the ratio of the refractive indices ~ in isotopically different materials. The materials under investigation were hydrogenated amorphous silicon and deuterated amorphous silicon. Sandwiches of varying thickness were produced, with hydrogenated layers deposited on a silicon substrate and deuterated layers deposited over the hydrogenated layers and vice versa.
Deposition was effected by plasma enhanced chemical vapour deposition (PCVD) in a reaction chamber schematically ,j ~i 25 illustrated in Fig. 1 and generally indicated by the numeral 20. The chamber made of Pyrex (TM), is generally cylindrical in shape and has a length of 65 cms with an internal diameter of 5.5 cms.
"
.: ;
~ . ' ', ' '", , :
..
~3~3~1 The chamber 20 has a gas inlet port 22 at one end and a gas outlet port 24 at the other end which, in use, is operatively connected to a pump (not shown). An anode 26 and a cathode 28 are provided at opposite ends of the chamber 20 and spaced 43 cms from each other. The anode 26 and cathode 28 are electrically connected to apply a high voltage discharge of 500 - 3000V across the chamber and create a chemically re~ctive plasma in the chamber ~or enhancing deposition. A plurality of electrostatic probes 32 for monitoring plasma parameters such as electron temperature and plasma density are spaced along the length of the chamber 20 at 70 cm intervals between the anode 26 and the cathode 28.
Silicon substrates, which oxidize very easily, were carefully prepared prior to introduction into the chamber where they were supported on a glass boat 30 placed inside the chamber 20 at the cathode end. The substrates, measuring 1.3 x 1.3 cms, were immersed in a trichloroethylene solution where they were cleaned ultrasonically for five minutes. The trichloroethylene solution was subsequently heated to boiling and the substrates rinsed in distilled water.
The substrates were then introduced into a sulphuric acid and hydrogen peroxide solution (1:1) heated to 80C for a period o~ ten ~inutes. The substrates were then washed with water and placed in a solution of hydrofluoric acid and water (1:5~ for five minutes to remove any silicon oxide and washed agaln.
After placing the substrates into the chamber 20 on the glass boat 30, the chamber was evacuated to a pressure of 10 3 :~
~3:~3~
Torr to minimize contamination and pre-heated to a temperature of 120C for twelve hours so as to remove any remaining water from the substrates.
The chamber 20 was then purged with argon gas and fed a gaseous mixture comprising 95% argon, 2.5% silane (SiH4) and 2.5% deuterium or 97% argon and 3% silane according to whether `~ the first deposit~d layer was to be deuterated amorphous silicon or hydrogenated amorphous silicon, respectively.
Assuming the former, a direct current power supply of 0.6 KW was applied to establish a discharge current between the ; anode 26 and the cathode 28 of 10 - 100 mA for a selected period of time sufficient to deposit a predetermined thickness of deuterated amorphous silicon on the silicon substrates.
With the power off, the chamber 20 was purged with argon gas and subsequently fed with the 97% argon and 3% silane (SiH4) gaseous mixture and the power was reactivated to produce a discharge current of 10 - 100 mA and create an argon silane gas plasma between the anode 26 and the cathode 28. The power was sustained until the desired thickness of hydrogenated amorphous silicon was deposited on the inner layer of deuterated amorphous silicon.
he procedure was reversed, first feeding the 97%
~` argon, 3% silane (Si~I4~ gaseous mixture and subsequently feeding the 95% argon, 2.5% silane ~SiH4) and 2.5% deuterium gaseous mixture to coat silicon substrates with a first inner layer of hydrogenated amorphous silicon and a second outer layer of deuterated amorphous silicon.
;:
::, '' ,, , :
: ;
. ` . ''.~ .
: ' , -"` 13~ 3~7:~
Optical bandgap values (Eg) for the deuterated amorphous silicon layers and hydrogenated amorphous silicon layers were measured using standard optical techni~ues and the results are graphically illustrated in Fig. 2 where the optical bandgap lies on the ordinate a~is and the thickness of the respective amorphous silicon layer lies on the abscissa.
At comparable thicknesses o~ one rnicrometer, the bandgap values for the deuterated amorphous silicon and hydrogenated amorphous silicon diEfer significantly, being 2.0Q
eV and 1.75 e~ respectively.
; Bandgap values are related to the refractive index in accordance with the Moss relationship (Pankove, J.I., 1971.
"Optical Processes in Semiconductors", Dover Publications, N.Y., p. 89.) as follows:
Eg n4~- constant Substituting the experimentally determined values of the band-gap Eg for deuterated amorphous silicon (a - Si : D/H) and hydrogenated amorphous silicon ta - Si:~) at a thickness of 1 micrometer, the ratio of their respective refractive indices is calculated as follows:
= nl/n2 = ~Eg2/Egl] / = ~2.00/1.75] / = 1.034 improving on the theoretically expected ratio by one order of 2S magnitude.
It will be understood by those skilled in the art that an acceptable range of ratios of the refractive indices for the core to the cladding is 1.001 - 1.01 and that the above ratio ~, : ' .
.
~ 13~3~7~
represents a 3% difference in the refractive indices of the core and cladding thereby providing a light confinement angle of several degrees.
In Fig. 3, solid curves were plotted for specimens in which the inner layer is deuterated and the outer layer is hydrogenated. Dashed curves were plotted for specimens in which the inner layer is hydrogenated and the outer layer is deuterated. Each curve joins points having a common deuterated amorphous silicon layer thickness.
For the specimens in which the outer layer is hydrogenated, it will be seen that the ratio of the refractive indices of the deuterated layer to the hydrogenated amorphous silicon layer increases as the thickness of the hydrogenated layer increases to reach a maximum peak and decreases for further increases in the thickness of the hydrogenated layer.
For specimens in which the outer layer is deuterated, the ratio of the refractive indices increases for increases in the thickness of the hydrogenated layer.
It will thus be appreciated that a variation of the ratio of the thicknesses of the isotopic layers, and the order of the hydrogenated and deuterated layers, are two parameters whereby one can control the refractive index change required for a particular application.
It will be understood that several variations may be made to the above described procedure for producing isotopic layers on a suitable substrate. It will be apparent to those skilled in the art that conventional methods of chemical vapour deposition (CVD) or oE plasma enhanced chemical vapour , .. . ... ~ . , ! ~
. . .
`~
~, , .
'.
~3 3L~71 deposition (PCVD) may be easily adapted to produce an optical fiber preform wherein the material of the core and the cladding are selected so that their compositions are substantially identical and at least one element in the core is an isotope of the corresponding element in the cladding.
Such a method could, for example, use a tubular silicon substrate adapted to receive a first gaseous mixture of, for example, argon and silane to coat the interior of the silicon tube, and subsequently a second gaseous mixture of argon, silane and deuterium to coat the previously deposited layer of hydrogenated amorphous silicon (a - Si:H) with a layer of deuterated amorphous silicon (a - Si:D/H). The resultant cylinder would then be heated in conventional fashion to consolidate the core of deuterated amorphous silicon and collapse the hydrogenated amorphous silicon and silicon around it into a solid preform for drawing into a Eiber in conventional manner.
A similar procedure could also be adopted to make a ~' preform in which the core is hydrogenated and the cladding is deuterated by making suitable adjustments to the relative thicknesses of the core and the cladding.
It will of course be understood that several variations may be made to the above described method o~ fabricating a preform and will include substituting the noble gas helium for argon as is well known in the art and that various materials may be selected, within the scope of this invention, to produce the core and cladding.
~, _ 9 _
ISOTOPIC FIBEROPTICS
This invention relates to the production of an optical fiber in which the number of imperfections between the core and the cladding is substantially reduced so as to minimize attenuation of electromagnetic radiation or light travelling ; 5 through the fiber and maximize total internal reflectlon.
Attenuation of light in an optical fiber i5 partly due to intrinsic factors and also to extrinsic factors. The intrinsic factors are inherent to the component materials comprising a fiber and are generally recognized to include electronic and vibrational absorption, and Rayleigh scattering.
Current developments in optical fiber research include the selection of new materials which are selected on the basis of their intrinsic low attenuation properties.
The attenuation of light in an optical fiber may also be ascribed to extrinsic losses resulting from contamination and improper processing. In particular, in silica-based material, an important absorbing species is the hydroxyl radical (OH-) which is formed when hydrogen is present in the fiber material.
One approach for reducing the hydroxyl caused attenuation, has been to replace the hydrogen with deuterium so as to shift the vibration mode of the radical impurity to a longer wavelength outside the region of interest.
While the substitution of deuterium for hydrogen in silica-based optical fibers has had the desired effect, and the non-silica-based fiber materials, the so-called second generation fiber materials including halide-containing crystals, , . ~;
:
. ~ ' ~3~ 3~7~
chalcogenide glasses and heavy-metal fluoride glasses are attractive because of their intrinsically low attenuation properties, these approaches do not address physical attenuation factors which necessarily arise at the interface between materials of different chemical composition.
It is the object of this invention to provide an optical fiber in which the opportunity for the attenuation of light at the interface between the cladding and core materials is substantially minimized.
In accordance with this invention, there is provided an optical fiber comprising a core and a cladding in which the core material and the cladding material include at least one common constituent element, the common element in the core being an isotope of the element in the cladding.
Preferably, the core material and cladding material will have the same chemical composition, so that the interface between the core and cladding will be chemically coherent. The , material composing the core and cladding are selected so that at ~¦ least one element in the core material is an isotope of the element in the cladding material and the resulting refractive index in the core exceeds the refractive index in the cladding.
The invention has a theoretical basis which is described below and supplemented by experimental results with reference to the accompanying drawings in which:
Fig. l is a schematic representation of the apparatus used for plasma enhanced chemical vapour deposition (PCVD) of isotopic layers according to the invention;
;,, ' ! 2 ~,' ,, ' ~ :
,, Fig 2 is a graphical representation of the opti..eal bandgap (ev) on the ordinate axis and layer thiekness (~ m) on the abscissa for specimens of deuterated and hydrogenated amorphous silicon produced by PCVD with the apparatus of Fig. 1;
and Fig. 3 is a graphieal representation of the ratio of the refraetive indiees minus 1 (~-1) on the ordinate axis and the thiekness of the hydrated assoeiated amorpho~s silieon layer on the abseissa for the speeimens of Fig 2.
The expeeted variations in lattice constant d for isotopically different materials, for typical transparent crystalline solids, may be represented as follows:
d ~ 10 3 to 10 4 d in accordance with Matthew, J.A.D., 1968. Journal of Physics C, vol. 1, p. 1768.
Based on the first order approximation by the Clausius-Mosotti relationship for refraetive index (Blakemore, 2Q J.S., 1985. "Solid State Physics", Cambridge University Press), the relation between lattiee eonstant d and refraetive index n may be represented as follows:
~n ~ 3c . ~d n d . .
where c is a dimensionless ad~ustment faetor of the order of unity.
1~3~
It follows that a minimum expected ratio of the refractive indices at a typical isotopic interface will range between 3 x 10 3 and 3 x 10 4 or = nl/n2 = 1.003 1.0003.
From the Snell law of light refraction (Sin ~2/Sin ~1 =
nl/n2), applicable to small angles, the following expression for the ray bending angle ~ at which light ~ravels through a refractiYe boundary may be deduced:
10~ = ~ arcsin (nl/n2 sin B) where B is the angle between the falling ray and normal to the interface. For a sliding ray in which ~ ~ 90, the control ;~ case for light confinement in fibers, one obtains a ray bending angle ~ of 1.5 to 4.5 degrees, sufficient for confining light.
j The following experiments were conducted to determine the ratio of the refractive indices ~ in isotopically different materials. The materials under investigation were hydrogenated amorphous silicon and deuterated amorphous silicon. Sandwiches of varying thickness were produced, with hydrogenated layers deposited on a silicon substrate and deuterated layers deposited over the hydrogenated layers and vice versa.
Deposition was effected by plasma enhanced chemical vapour deposition (PCVD) in a reaction chamber schematically ,j ~i 25 illustrated in Fig. 1 and generally indicated by the numeral 20. The chamber made of Pyrex (TM), is generally cylindrical in shape and has a length of 65 cms with an internal diameter of 5.5 cms.
"
.: ;
~ . ' ', ' '", , :
..
~3~3~1 The chamber 20 has a gas inlet port 22 at one end and a gas outlet port 24 at the other end which, in use, is operatively connected to a pump (not shown). An anode 26 and a cathode 28 are provided at opposite ends of the chamber 20 and spaced 43 cms from each other. The anode 26 and cathode 28 are electrically connected to apply a high voltage discharge of 500 - 3000V across the chamber and create a chemically re~ctive plasma in the chamber ~or enhancing deposition. A plurality of electrostatic probes 32 for monitoring plasma parameters such as electron temperature and plasma density are spaced along the length of the chamber 20 at 70 cm intervals between the anode 26 and the cathode 28.
Silicon substrates, which oxidize very easily, were carefully prepared prior to introduction into the chamber where they were supported on a glass boat 30 placed inside the chamber 20 at the cathode end. The substrates, measuring 1.3 x 1.3 cms, were immersed in a trichloroethylene solution where they were cleaned ultrasonically for five minutes. The trichloroethylene solution was subsequently heated to boiling and the substrates rinsed in distilled water.
The substrates were then introduced into a sulphuric acid and hydrogen peroxide solution (1:1) heated to 80C for a period o~ ten ~inutes. The substrates were then washed with water and placed in a solution of hydrofluoric acid and water (1:5~ for five minutes to remove any silicon oxide and washed agaln.
After placing the substrates into the chamber 20 on the glass boat 30, the chamber was evacuated to a pressure of 10 3 :~
~3:~3~
Torr to minimize contamination and pre-heated to a temperature of 120C for twelve hours so as to remove any remaining water from the substrates.
The chamber 20 was then purged with argon gas and fed a gaseous mixture comprising 95% argon, 2.5% silane (SiH4) and 2.5% deuterium or 97% argon and 3% silane according to whether `~ the first deposit~d layer was to be deuterated amorphous silicon or hydrogenated amorphous silicon, respectively.
Assuming the former, a direct current power supply of 0.6 KW was applied to establish a discharge current between the ; anode 26 and the cathode 28 of 10 - 100 mA for a selected period of time sufficient to deposit a predetermined thickness of deuterated amorphous silicon on the silicon substrates.
With the power off, the chamber 20 was purged with argon gas and subsequently fed with the 97% argon and 3% silane (SiH4) gaseous mixture and the power was reactivated to produce a discharge current of 10 - 100 mA and create an argon silane gas plasma between the anode 26 and the cathode 28. The power was sustained until the desired thickness of hydrogenated amorphous silicon was deposited on the inner layer of deuterated amorphous silicon.
he procedure was reversed, first feeding the 97%
~` argon, 3% silane (Si~I4~ gaseous mixture and subsequently feeding the 95% argon, 2.5% silane ~SiH4) and 2.5% deuterium gaseous mixture to coat silicon substrates with a first inner layer of hydrogenated amorphous silicon and a second outer layer of deuterated amorphous silicon.
;:
::, '' ,, , :
: ;
. ` . ''.~ .
: ' , -"` 13~ 3~7:~
Optical bandgap values (Eg) for the deuterated amorphous silicon layers and hydrogenated amorphous silicon layers were measured using standard optical techni~ues and the results are graphically illustrated in Fig. 2 where the optical bandgap lies on the ordinate a~is and the thickness of the respective amorphous silicon layer lies on the abscissa.
At comparable thicknesses o~ one rnicrometer, the bandgap values for the deuterated amorphous silicon and hydrogenated amorphous silicon diEfer significantly, being 2.0Q
eV and 1.75 e~ respectively.
; Bandgap values are related to the refractive index in accordance with the Moss relationship (Pankove, J.I., 1971.
"Optical Processes in Semiconductors", Dover Publications, N.Y., p. 89.) as follows:
Eg n4~- constant Substituting the experimentally determined values of the band-gap Eg for deuterated amorphous silicon (a - Si : D/H) and hydrogenated amorphous silicon ta - Si:~) at a thickness of 1 micrometer, the ratio of their respective refractive indices is calculated as follows:
= nl/n2 = ~Eg2/Egl] / = ~2.00/1.75] / = 1.034 improving on the theoretically expected ratio by one order of 2S magnitude.
It will be understood by those skilled in the art that an acceptable range of ratios of the refractive indices for the core to the cladding is 1.001 - 1.01 and that the above ratio ~, : ' .
.
~ 13~3~7~
represents a 3% difference in the refractive indices of the core and cladding thereby providing a light confinement angle of several degrees.
In Fig. 3, solid curves were plotted for specimens in which the inner layer is deuterated and the outer layer is hydrogenated. Dashed curves were plotted for specimens in which the inner layer is hydrogenated and the outer layer is deuterated. Each curve joins points having a common deuterated amorphous silicon layer thickness.
For the specimens in which the outer layer is hydrogenated, it will be seen that the ratio of the refractive indices of the deuterated layer to the hydrogenated amorphous silicon layer increases as the thickness of the hydrogenated layer increases to reach a maximum peak and decreases for further increases in the thickness of the hydrogenated layer.
For specimens in which the outer layer is deuterated, the ratio of the refractive indices increases for increases in the thickness of the hydrogenated layer.
It will thus be appreciated that a variation of the ratio of the thicknesses of the isotopic layers, and the order of the hydrogenated and deuterated layers, are two parameters whereby one can control the refractive index change required for a particular application.
It will be understood that several variations may be made to the above described procedure for producing isotopic layers on a suitable substrate. It will be apparent to those skilled in the art that conventional methods of chemical vapour deposition (CVD) or oE plasma enhanced chemical vapour , .. . ... ~ . , ! ~
. . .
`~
~, , .
'.
~3 3L~71 deposition (PCVD) may be easily adapted to produce an optical fiber preform wherein the material of the core and the cladding are selected so that their compositions are substantially identical and at least one element in the core is an isotope of the corresponding element in the cladding.
Such a method could, for example, use a tubular silicon substrate adapted to receive a first gaseous mixture of, for example, argon and silane to coat the interior of the silicon tube, and subsequently a second gaseous mixture of argon, silane and deuterium to coat the previously deposited layer of hydrogenated amorphous silicon (a - Si:H) with a layer of deuterated amorphous silicon (a - Si:D/H). The resultant cylinder would then be heated in conventional fashion to consolidate the core of deuterated amorphous silicon and collapse the hydrogenated amorphous silicon and silicon around it into a solid preform for drawing into a Eiber in conventional manner.
A similar procedure could also be adopted to make a ~' preform in which the core is hydrogenated and the cladding is deuterated by making suitable adjustments to the relative thicknesses of the core and the cladding.
It will of course be understood that several variations may be made to the above described method o~ fabricating a preform and will include substituting the noble gas helium for argon as is well known in the art and that various materials may be selected, within the scope of this invention, to produce the core and cladding.
~, _ 9 _
Claims (6)
1. An optical fiber comprising a core and a cladding, the core material and the cladding material including at least one common constituent element, said element in the core material being an isotope of the element in the cladding material and selected to impart a refractive index in the core which exceeds the refractive index in the cladding.
2. An optical fiber according to claim 1 in which the core material and cladding material are composed of a single compound whereof at least one element in the core material is an isotope of the corresponding element in the cladding material.
3. An optical fiber according to Claim 1 in which the core material is composed of deuterated amorphous silicon and the cladding material is composed of hydrogenated amorphous silicon.
4. An optical fiber according to Claim 1 in which the core material is composed of hydrogenated amorphous silicon and the cladding material is composed of deuterated amorphous silicon.
5. A method of fabricating an optical fiber preform by plasma enhanced chemical vapour deposition (PCVD), the method comprising:
supplying a first gaseous mixture of an inert carrier gas and silane (SiH4) to a heated evacuated deposition chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said first gaseous mixture and effect deposition of a hydrogenated amorphous silicon (a-Si:H) cladding on the interior of a tubular silicon substrate provided in the chamber;
supplying a second gaseous mixture of said inert gas, silane (SiH4) and deuterium (D2) to said chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said second gaseous mixture and effect deposition of a deuterated amorphous silicon (a-Si:D/H) core inside the hydrogenated amorphous silicon cladding; and applying heat to consolidate the core and to consolidate the cladding and substrate about the core.
supplying a first gaseous mixture of an inert carrier gas and silane (SiH4) to a heated evacuated deposition chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said first gaseous mixture and effect deposition of a hydrogenated amorphous silicon (a-Si:H) cladding on the interior of a tubular silicon substrate provided in the chamber;
supplying a second gaseous mixture of said inert gas, silane (SiH4) and deuterium (D2) to said chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said second gaseous mixture and effect deposition of a deuterated amorphous silicon (a-Si:D/H) core inside the hydrogenated amorphous silicon cladding; and applying heat to consolidate the core and to consolidate the cladding and substrate about the core.
6. A method of fabricating an optical fiber preform by plasma enhanced chemical vapour deposition (PCVD), the method comprising:
supplying a first gaseous mixture of an inert carrier gas, silane (SiH4) and deuterium (D2) to a heated evacuated deposition chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said first gaseous mixture and effect deposition of a deuterated amorphous silicon (a-Si:H/D) cladding on the interior of a tubular silicon substrate provided in the chamber;
supplying a second gaseous mixture of said inert gas and silane (SiH4) to said chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said second gaseous mixture and effect deposition of a hydrogenated amorphous silicon (a-Si:H) core inside the deuterated amorphous silicon cladding; and applying heat to consolidate the core and to consolidate the cladding and substrate about the core.
supplying a first gaseous mixture of an inert carrier gas, silane (SiH4) and deuterium (D2) to a heated evacuated deposition chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said first gaseous mixture and effect deposition of a deuterated amorphous silicon (a-Si:H/D) cladding on the interior of a tubular silicon substrate provided in the chamber;
supplying a second gaseous mixture of said inert gas and silane (SiH4) to said chamber;
applying an electrical current inside the chamber to create a chemically reactive plasma in said second gaseous mixture and effect deposition of a hydrogenated amorphous silicon (a-Si:H) core inside the deuterated amorphous silicon cladding; and applying heat to consolidate the core and to consolidate the cladding and substrate about the core.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 594392 CA1313071C (en) | 1989-03-21 | 1989-03-21 | Isotopic fiberoptics |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 594392 CA1313071C (en) | 1989-03-21 | 1989-03-21 | Isotopic fiberoptics |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1313071C true CA1313071C (en) | 1993-01-26 |
Family
ID=4139796
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 594392 Expired - Fee Related CA1313071C (en) | 1989-03-21 | 1989-03-21 | Isotopic fiberoptics |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1313071C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL1022140C2 (en) * | 2002-12-11 | 2004-06-15 | Draka Fibre Technology Bv | Deposition of glass layers inside tube using reactive gases, useful for preparing optical fibres, comprises treating glass forming compounds with deuterium before deposition |
-
1989
- 1989-03-21 CA CA 594392 patent/CA1313071C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL1022140C2 (en) * | 2002-12-11 | 2004-06-15 | Draka Fibre Technology Bv | Deposition of glass layers inside tube using reactive gases, useful for preparing optical fibres, comprises treating glass forming compounds with deuterium before deposition |
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