U.S. patent application number 11/129489 was filed with the patent office on 2006-10-19 for hollow core photonic band gap infrared fibers.
Invention is credited to Ishwar Aggarwal, Brian Cole, Fred Kung, P. C. Pureza, Jasbinder Sanghera, L. B. Shaw.
Application Number | 20060230792 11/129489 |
Document ID | / |
Family ID | 34104308 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060230792 |
Kind Code |
A1 |
Sanghera; Jasbinder ; et
al. |
October 19, 2006 |
Hollow core photonic band gap infrared fibers
Abstract
This invention pertains to a hollow core photonic band gap
chalcogenide optical glass fiber and to a fabrication method for
making the fiber. The fiber, which is 80-1000 microns in outside
diameter, is characterized by a solid glass circumferential region
and a structured region disposed centrally within the solid region,
the structured region includes a hollow core of 1 micron to several
hundreds of microns in diameter surrounded by a plurality of
parallel hollow capillaries extending parallel to the core, the
core being centrally and longitudinally located within the fiber.
Ratio of open space to glass in the structured region is 30-99%.
The fabrication method includes the steps of providing a mold,
placing chalcogenide micro-tubes around the mold, stacking
chalcogenide micro-canes around the stacked micro-tubes, fusing the
micro-tubes and the micro-canes to form a preform, removing the
mold and drawing the preform to obtain the fiber. In an alternative
fabrication method, the fiber is made by extruding flowing
chalcogenide glass through suitably made plate to form a preform
and then drawing the preform to form the fiber.
Inventors: |
Sanghera; Jasbinder;
(Ashburn, VA) ; Aggarwal; Ishwar; (Fairfax
Station, VA) ; Shaw; L. B.; (Woodbridge, VA) ;
Pureza; P. C.; (Burke, VA) ; Kung; Fred;
(Alexandria, VA) ; Cole; Brian; (Alexandria,
VA) |
Correspondence
Address: |
NAVAL RESEARCH LABORATORY;ASSOCIATE COUNSEL (PATENTS)
CODE 1008.2
4555 OVERLOOK AVENUE, S.W.
WASHINGTON
DC
20375-5320
US
|
Family ID: |
34104308 |
Appl. No.: |
11/129489 |
Filed: |
May 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10632210 |
Aug 1, 2003 |
6993230 |
|
|
11129489 |
May 16, 2005 |
|
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Current U.S.
Class: |
65/389 ; 385/123;
65/393; 65/401; 65/409 |
Current CPC
Class: |
C03B 2203/42 20130101;
C03B 2203/14 20130101; C03B 2203/12 20130101; Y10T 428/2913
20150115; C03B 2201/88 20130101; C03B 37/0122 20130101; Y10T
428/265 20150115; G02B 6/02328 20130101; C03B 37/01274 20130101;
C03B 2203/16 20130101; G02B 6/02347 20130101; C03B 2201/86
20130101; C03C 13/043 20130101; C03C 11/00 20130101 |
Class at
Publication: |
065/389 ;
065/393; 065/401; 385/123; 065/409 |
International
Class: |
G02B 6/02 20060101
G02B006/02; C03C 3/32 20060101 C03C003/32; C03B 37/022 20060101
C03B037/022; C03B 37/02 20060101 C03B037/02; C03B 37/075 20060101
C03B037/075; C03B 37/027 20060101 C03B037/027 |
Claims
1-11. (canceled)
12. Fabrication method for a hollow core photonic band gap optical
fiber comprising the steps of: (a) providing a mold, (b) placing
chalcogenide micro-tubes around the mold, (c) stacking chalcogenide
micro-canes around said micro-tubes, (d) fusing the micro-tubes and
the micro-canes for form a preform, (e) removing the mold, and (f)
drawing the preform to form the hollow core photonic band gap fiber
having outside diameter of 80-1000 .mu.m, hollow core of from 1
micron to hundreds of microns, a structured region to impart
photonic band gap to the fiber aroung the hollow core formed of
plurality of openings arraned in at least three courses around the
core with each opening being 1-12 .mu.m and arranged in a pattern
to yield a photonic band gap, and a solid region 5-500 .mu.m thick
surrounding the microstructured region to provide structural
integrity to the microstructured region.
13. Method of claim 12 wherein the micro-tubes have thickness of
50-200 .mu.m, internal diameter of 500-2000 .mu.m, and length of
2-100 cm; and micro-canes are solid with outside diameter of
600-2400 .mu.m and length of 2-100 cm and the hollow core is
circular 2-200 .mu.m in diameter.
14. Method of claim 12 wherein the micro-tubes have thickness of
100-150 .mu.m, and length of 5-20 cm; and the micro-canes are solid
with outside diameter of 1000-2000 .mu.m and length of 5-20 cm.
15. Method of claim 13 wherein the micro-tubes are disposed in a
glass tube.
16. Method of claim 13 wherein said step of fusing is carried out
in an inert atmosphere in the glass transition temperature.
17. Method of claim 12 wherein the chalcogenide glass in the
micro-tubes and micro-canes has loss of 0.5 dB/m and lower.
18. Method of making hollow core photonic band gap optical
chalcogenide fiber comprising the steps of: (a) extruding through a
plate having a central opening, a region corresponding to a
structured region with a plurality of openings arranged in a
periodic pattern in at least three courses around the central
opening, and a solid region around the region corresponding to the
structured region to form a preform, and (b) drawing the preform to
obtain the fiber.
19. Method of claim 18 including the step of cooling the drawn
fiber to room temperature.
20. Method o claim 18 including the step of heating chalcogenide
glass having loss of 0.5 dB/m or lower to a temperature high enough
to render it flowable.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention pertains to hollow core photonic band gap
chalcogenide fibers and to the method of making same.
[0003] 2. Description of Related Art
[0004] Practically every molecular species possesses a
characteristic vibrational spectrum in the infrared wavelength
region between about 2 and 12 .mu.m. Consequently, chemicals can be
clearly and definitely identified based on their unique infrared
absorption spectra. In fact, this is called the "fingerprint
region." Detection and identification can be performed on liquids,
gases and solids using traditional infrared (IR) spectrometers and
Fourier Transform Infrared spectrometers. The chemicals can be
detected using various modes including absorption and reflectance
spectroscopy.
[0005] Fiber optic based sensors have been developed using
chalcogenide glass fibers. Chalcogenide fibers transmit in the
fingerprint region and can be coupled to an IR spectrometer. In
this case, the evanescent field propagating outside the core can be
accessed by removal of the cladding via etching or by reducing the
diameter of the fiber by stretching. The evanescent field on the
outside surface of the fiber, can interact with the surrounding
analyte and provide definitive chemical identification even in
mixtures. The advantage of the fiber approach is that the sensing
can now be done remotely but one drawback of the evanescent
spectroscopy is that the technique has limited sensitivity since
only a small fraction, i.e., a few percent, of the light propagates
in the evanescent field. Furthermore, the field decays
exponentially from the surface of the fiber and so only analyte at
the surface will interact with the evanescent field. Therefore,
while IR spectroscopy is a very powerful tool for definitive
chemical identification, there is a need to improve the sensitivity
so that it will find widespread use.
[0006] Hollow core silica fibers with a structured region providing
a photonic band gap have been known since about 1999. Photonic band
gap fibers have been recently demonstrated using silica glass with
a minimum loss of 13 dB/km at 1.5 .mu.m. It would be obvious use
hollow core photonic band gap silica fiber to transmit wavelengths
longer than 1.5 .mu.m since it was believed that the light was
guided in the hollow core and therefore 2-12 .mu.m light can be
used to perform fingerprint IR spectroscopy. However, it turns out
that hollow core PBG silica fibers do not transmit well beyond
about 2 .mu.m since several percent of the light propagates in the
microstructured region and this light is highly attenuated through
multiphonon absorption in silica. Hence, it is not possible to use
silica PBG fibers to perform fingerprint spectroscopy in the IR
beyond a wavelength of about 2 .mu.m.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
[0007] An object of this invention is a hollow core photonic band
gap chalcogenide glass fiber.
[0008] It is another object of this invention to sense molecular
species in the fingerprint region of the vibrational spectrum of
about 2 to 12 .mu.m at levels of parts per billion (ppb).
[0009] It is another object of this invention to increase
sensitivity of sensing molecular species over evanescent technique
by hundreds of times.
[0010] It is another object of this invention to use the hollow
core fiber of this invention for transmission of higher power
sources, exceeding power density of 10 GW/cm.sup.2 pulse power for
pulsed lasers and exceeding power of about 10 W for continuous wave
lasers.
[0011] It is another object of this invention to fabricate hollow
core photonic band gap glass fibers from chalcogenide glass.
[0012] These and other objects of this invention can be
accomplished by a hollow core photonic band gap fiber made totally
from chalcogenide glass that can sense molecular species in the
spectrographic region of about 2-12 .mu.m and that can transmit
ultrahigh power light signals, the glass fiber having a hollow core
for passing a light signal therethrough, a microstructured region
surrounding the hollow core, and a solid circumferential region
surrounding the microstructured region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic illustration in cross-section of a
hollow core photonic band gap chalcogenide fiber showing the hollow
core, the microstructured region concentrically surrounding the
hollow core and a solid glass circumferential region surrounding
the microstructured region.
[0014] FIG. 2 is an exemplary graph of the molecular specie of
acetone in the 6-8 .mu.m wavelength region which is sensed by the
fiber of this invention.
[0015] FIG. 3 is a schematic illustration of the use of the hollow
core photonic band gap fiber of this invention to sense presence of
lower levels of a molecular specie.
DETAILED DESCRIPTION OF THE INVENTION
[0016] This invention pertains to a hollow core photonic band gap
chalcogenide optical fiber and to a fabrication method for making
the fiber.
[0017] An illustration of a typical hollow core photonic band gap
infrared fiber in cross-section is shown in FIG. 1 where the fiber
100 includes hollow core 102, microstructured region in hexagonal
or honeycomb or any other shape 104, and circumferential region
106. The fiber is typically made from chalcogenide glasses but can
also be made from chalcohalide glasses and other infrared
transmitting glasses. The fiber 100 is typically circular in
cross-section although it can be of any other shape and its outside
diameter is typically in the range of 80-1000 .mu.m. Hollow core
102 can be hexagonal in cross-sectional shape, circular or any
other shape, although, typically, it is circular. The hollow core
diameter is typically from 1 .mu.m to several 100 s .mu.m, more
typically 2-200 .mu.m. Openings 108 in the microstructured region
104 are typically circular in cross-section although they can be of
any other shape. The diameter of the openings are typically from a
fraction of a micron to about 10 .mu.m in diameter with a
center-to-center spacing or periodicity of 1-12 .mu.m. In the
microstructured region of the fiber, air fill fraction should be
30-99%, preferably 40-70%. The purpose of the openings is to create
the photonic band gap which channels light into the hollow core. In
absence of the microstructured region, which imparts photonic band
gap to the fiber, the light passing through the hollow core would
be scattered or lost and the fiber would not be functional for the
intended purpose. It is believed that at least three courses i.e.,
layers around the center hollow core 102, of the openings disposed
in a particular arrangement are needed to create the photonic band.
The arrangement of the openings can be in hexagonal or honeycomb
structure or in any other periodic or non-periodic way that
produces the photonic band gap. Openings 108 are typically arranged
in hexagonal pattern and typically there are 4-5 courses of the
openings in the microstructured region 104 disposed concentrically
around the hollow core 102 although, there may be fewer than four
or more than four courses.
[0018] Thickness of the solid region 106 is typically 5-500 .mu.m,
and more typically 50-300 .mu.m, although it will depend on the
glass composition and other parameters to provide physical
integrity to the microstructured region 104. Thiskness of the
microstructured region is 5-500 .mu.m, preferably 20-300 .mu.m.
[0019] Glass fiber 100 in FIG. 1 is made of chalcogenide glass,
which is a vitreous material composed of the chalcogen elements of
Group VI of the Periodic Table. These elements are usually mixed
with elements of Groups IV and V to form the familiar compound
glasses. More particularly, chalcogenide glasses are made from
mixtures containing at least one of sulfur, selenium, and
tellurium. Other elements can be added. Examples of other elements
that can be combined with at least one chalcogen element include
germanium, arsenic, and antimony.
[0020] Chalcogenide glass typically contains at least about 25 mole
percent, and generally at least 50 mole percent, of one or more of
the three chalcogen elements. The presence of tellurium in the
glass composition has been found to increase the transmission in
the infrared region. While sulphide fibers, such as
As.sub.2S.sub.3, transmit from about 1-6 .mu.m, the transmission
window is increased to beyond 10 .mu.m by including the heavier
chalcogenide element tellurium. Glasses containing high levels of
tellurium typically transmit in the 3-12 .mu.m region.
[0021] The use of chalcogenide fibers is advantageous not only for
wide transmittance range but also for chemical durability. Although
chalcogenide glass cannot be used in strongly basic environments
because it undergoes chemical attack, there are numerous
environments where chalcogenide fibers can be used. For instance,
chalcogenide glass does not react with water, unlike fluoride
glass, and can, therefore, be used in aqueous non-basic
environments. Additionally, chalcogenide glass can be used in
acidic and organic environments.
[0022] The fiber of this invention can also be made from mixtures
of halide and chalcogenide glass components. Halide glasses, such
as ZBLAN (53ZrF.sub.6-20BaF.sub.2-4LaF3-3AlF.sub.3-20NaF by mole
percent) with more than about 5% of a halide, such as bromine or
fluorine, have relatively poor chemical durability and low glass
transition temperatures, especially the non-fluoride glasses,
whereas chalcogenide glasses are well known for their chemical
durability but their relatively high refractive indices give rise
to high reflectivities from the glass surface. Chalcohalides
contain both halides and chalcogens and have some beneficial
characteristics of both glasses. The structural aspect of these
glasses is interesting from a fundamental viewpoint since
chalcogenide glasses are predominantly covalent and halide glasses
are predominantly ionic in character. As used herein, the term
"chalcogenide" includes "chalcohalide."
[0023] The photonic band gap hollow fibers of this invention can
have a polymeric material cladding, or a cladding of any other
material, on the outside of the fiber 100, although such cladding
is not required. The cladding is provided on the fiber to
facilitate handling thereof. The cladding material can be
hydrophobic or hydrophilic, typically it is hydrophobic for obvious
reasons. Some hydrophobic polymeric materials in an aqueous
environment containing a hydrophobic analyte will repel water but
will preferably solubilize the hydrophobic analyte. Specific
exampes of the polymeric materials include low density polyethylene
and polydimethylsiloxane. There are other polymeric materials which
do not allow species to penetrate them.
[0024] The periodic layered structure of holes and glass in the
microstructured region of the hollow core fiber of this invention,
shown in cross-section in FIG. 1, creates a photonic band gap that
prevents light from propagating in the microstructured region,
analogous to a 2 D grating, and so light is confined to the hollow
core. Typically, the periodicity of the holes is on the scale of
the wavelength of light and the outer glass or the circumferential
glass region is used for providing mechanical integrity to the
fiber. The fact that light travels in the hollow core also means
that the losses will be lower so longer path lengths can be used.
Since light is guided in the hollow core, an analyte disposed
therein will have maximum interaction with light, unlike the prior
art evanescent sensors.
[0025] FIG. 2 shows the spectrum of acetone recorded in the 6-8
.mu.m wavelength region using the photonic band gap hollow core
chalcogenide fiber of this invention with the set-up shown in FIG.
3. These bands are associated with the characteristic bending
vibrations of acetone and were used to definitely identify acetone.
This is not possible in hollow silica PBG fibers due to
attenuation.
[0026] It is understood that this disclosure pertains to hollow
core photonic band gap fibers made from chalcogenide glasses
including sulfides, selenides, tellurides and their mixtures, as
well as chalcohalide glasses and other infrared transmitting
glasses. It should also be understood that fabrication of the
hollow core photonic band gap chalcogenide fibers using the tube
stacking technique, described hereinafter, is only one example of
fabricating these specially structured fibers.
[0027] Fabrication of the photonic band gap chalcogenide glass
fiber of this invention was initiated by mixing the glass
components in an ampoule using a glove box containing an inert gas,
like nitrogen, with less than 100 ppb moisture and less than 1 ppm
oxygen. The ampoule was evacuated to about 10.sup.-5 Torr and
sealed with an oxygen-methane torch. The ampoule was then placed
within a furnace and the glass batch within was allowed to react
and then to further purify the batch chemicals by
distillation/sublimation. The distillate was re-melted for
homogenization and then spun at a high rate exceeding 1000 rpm
while the batch was still molten inside the ampoule. During cooling
of the molten batch, while still rotating the ampoule, viscosity of
the molten batch increased and a tube was formed in the ampoule,
annealed and removed at room temperature from the ampoule. The tube
was 10 mm.times.16 mm.times.12 cm (ID.times.OD.times.L) was
subsequently drawn into micro-tubes with outside diameter exceeding
several hundreds of microns. Similarly, a solid glass rod was drawn
into micro-canes with the same diameter as the micro-tubes.
[0028] Several courses of the micro-tubes were stacked around a
Teflon.RTM.-coated mold and several of the micro-canes were stacked
around the micro-tubes to provide mechanical integrity.
Alternatively, the micro-tube assembly can be placed in a thick
walled glass tube. The resulting structure was heat treated in the
vicinity of glass transition temperature at an elevated temperature
exceeding 175.degree. C., depending on the glass, in an inert
atmosphere or vacuum to fuse the micro-tubes and micro-canes
together but without leading to deformation of the shape. The inner
Teflon.RTM.-coated mold was then removed and the structured preform
was then drawn into dozens of meters of the photonic band gap glass
fiber in a draw tower located inside a clean room.
[0029] The fiber loss at this point was about 20 dB/m in the
infrared. This high loss is attributed to the use of low precision
diameter tubes and relatively impure glass, which lead to
scattering losses. The losses can be significantly reduced to less
than 0.1 dB/m by using high precision diameter tubes and rods,
higher quality glasses and better control of the fiber drawing
process. The latter would include better control of draw speed and
pressure to control the collapse of the holes around the central
hollow core. This would assist greatly in retaining the geometry
during fiber drawing. Nevertheless, the purpose herein is not to
fabricate the lowest loss infrared fiber based hollow core photonic
band gap fiber but to demonstrate capability to process the
chalcogenide glasses into a hollow core photonic band gap type
structure. This was successfully achieved and can be subsequently
improved with better processing control.
[0030] FIG. 3 is a schematic illustration of the use of a hollow
core photonic band gap chalcogenide glass fiber as a sensor for
quantitative presence of an analyte. Referring to FIG. 3, light 302
enters and passes through fiber 304, enters connector 306 and then
enters the hollow core photonic band gap chalcogenide glass fiber
308 wherefrom the light passes through connector 310 and out
through fiber 312. Analyte 314 enters connector 306 where it is
mixed with the light 302 and then the mixture of light and the
analyte is passed through connector 306 into fiber 308 and thence
into connector 310 where it is separated from the light and exits
the connector 310 through conduit 316. Fibers 304 and 312 can be
solid core chalcogenide fibers or the hollow core photonic band gap
chalcogenide fibers of this invention since they serve merely as
conduits for the light. Fiber 308 is a hollow core photonic band
gap chalcogenide fiber where interaction between the light and the
analyte takes place. Sensitivity of the presence of a substance in
the analyte is expected to be at the ppb level and length of fiber
308 is expected to be on the order of a few millimeters and up to
10 s of feet long.
[0031] Having described the invention, the following examples are
given as particular embodiments thereof. It is understood that the
examples are given by way of illustration and are not intended to
limit the specification or the claims in any manner.
EXAMPLE 1
[0032] This example describes the method to fabricate a hollow core
photonic band gap fiber from selenide-based chalcogenide glass with
composition of As.sub.39 Se.sub.61.
[0033] The fabrication method included batching arsenic and
selenium in pre-cleaned quartz ampoules using a glass box
containing nitrogen with less than 100 ppb moisture and less than 1
ppm oxygen. The ampoules were evacuated to about 10.sup.-5 Torr and
sealed using an oxygen-methane torch. The ampoules were then placed
in a furnace and heated to about 800.degree. C. and the batch
allowed to react for about 10 hours and then further distilled to
further purify the chemicals. Purification here is based on
experience and purity of glass sought is up to about 0.5 dB/m and
higher. The distillate was remelted for homogenization and then
spun at about 2500 rpm while still molten in the ampoule. During
cooling of the melt, while still rotating in the ampoule, the
viscosity increased and a tube was formed, annealed and removed
from the ampoule at room temperature. The tube, being 10
mm.times.16 mm.times.12 cm (ID.times.OD.times.L), was subsequently
drawn into micro-tubes with outside diameter of about 900 .mu.m.
Similarly, a solid glass rod was drawn into micro-canes with the
same diameter as the micro-tubes.
[0034] The micro-tubes were stacked around a Teflon.RTM.-coated
mold about 2.7 mm in outside diameter while the micro-canes were
stacked around the micro-tubes to provide mechanical integrity.
Thus was formed a preform assembly that was heat-treated at about
180.degree. C. for about 2 hours in an inert atmosphere of nitrogen
gas to fuse the micro-tubes and the micro-canes together but
without leading to deformation of the circular cross-sectioned
glass fiber. After fusion, the inner Teflon.RTM.-coated mold was
removed and the structured preform was then drawn at about
300.degree. C. and at a rate of about 33 m/min into more than 100
meters of hollow core photonic chalcogenide fiber on a draw tower
located inside a class 100 clean room. FIG. 1 shows the
cross-section of the fiber with an OD of 114 .mu.m, hollow core of
24 .mu.m, a microstructure region in the form of a hexagon with
openings of typically 3 .mu.m inside diameter arranged in
center-to-center spacing of typically 4.5 .mu.m in a hexagonal
arrangement. The solid region was 114 .mu.m from a corner of the
hexagon and 106 .mu.m to the side of the hexagon. The fiber loss
was 20 dB/m in the infrared.
EXAMPLE 2
[0035] This example details the method to fabricate the hollow core
photonic band gap fiber from sulfide-based chalcogenide glass with
composition of As.sub.39 S.sub.61 but without the outer solid
region that provides structural integrity to the fiber,
particularly to the microstructured region.
[0036] The fiber was made by fabricating tubes, stretching by
drawing them to micro-tubes, stacking, fusing and redrawing into
fiber of the micro-structured sulfide preform, in a similar manner
to Ex. 1 with the exception that there were no outer rods, i.e.,
micro-canes, used for mechanical integrity. Also, no
Teflon.RTM.-coated mold was used but instead, the sulfide
micro-tubes were stacked around a similar central sulfide
micro-tube to form the preform and this was drawn into 95 .mu.m
outside diameter fiber. Again, high purity glass and high precision
diameter tubes were not used nor was the gas pressure inside the
tubes controlled during fiber drawing. Improvements in controlling
these parameters will lead to low loss based hollow core photonic
band gap fiber based on sulfide glasses as well as other
chalcogenide glasses.
EXAMPLE 3
[0037] This example describes the use of a selenide fiber of this
invention for chemical identification using remote infrared
spectroscopy, using the system generally depicted in FIG. 3 but
without coupling fibers 304 and 312.
[0038] The sensing step includes the steps of directing infrared
light into hollow core of the glass fiber of this invention,
introducing analyte into the core of the fiber, transmitting the
light and the analyte into the core of the fiber, and analyzing the
light emanating from the fiber for presence of the analyte.
Pursuant to the sensing method, hollow core photonic band gap fiber
of Ex. 1 was coupled at one end to a source from an Analect Diamond
20 FTIR spectrometer. The distal end of the fiber was coupled to a
liquid nitrogen HgCdTe detector. A small quantity of acetone was
drawn into the hollow core through capillary action. The periodic
holes were blocked-off with wax prior to this step. The infrared
spectrum of acetone was recorded and the relative transmission
compared with the same fiber without acetone in the hollow core.
FIG. 2 shows the spectrum of acetone recorded in the 6-8 .mu.m
wavelength region using the fiber of Ex. 1 of this invention. These
bends are associated with the characteristic bending vibrations of
acetone and were used to definitely identify acetone. An optimized
fiber in terms of low loss (.ltoreq.0.5 dB) and long length (10
meters) would possess ppb detection limit.
[0039] The fiber of this invention is an infrared transmitting
fiber of a chalcogenide glass that has capability to detect
significantly lower concentrations of analyte than conventional IR
fiber sensors. This is due to the fact that all the light is guided
in the hollow core and furthermore, the analyte disposed therein,
leads to the greatest interaction with the light over considerably
long lengths. In a typical evanescent-based fiber sensors, about 1%
of the light can interact with the analyte over lengths on the
order of 10 cm resulting in sensitivities of a few 100 ppm. For a
hollow core photonic band gap fiber sensor, all the light can
interact with the analyte over lengths of tens of meters. This
results in a sensitivity increase on the order of 10.sup.5 and
allows detection of the analyte at levels of a few ppb. This is a
significantly better than state-of-the-art today.
[0040] The fiber of this invention can be coupled to existing solid
core chalcogenide fibers, or other coupling fibers including the
fibers of this invention, to create an absorption cell using
specialized connectors. This can be used for gas and liquid
analysis. Obviously, particulate filters can be used in-line to
keep the inside of the fibers of this invention clean. An
appropriate means for delivery of analyte would include pressure,
vacuum or their combination. Also, lenses and/or mirrors can be
used for focusing the light into and out of the fibers of this
invention. Also, the holes creating the photonic band gap can be
plugged with wax, glass, glue or other material, or simply
fused/melted shut to prevent contamination and interference from
the analyte. Furthermore, the light source can be a laser, i.e.,
narrow band, broadband, tunable, high power, low power, or other
bright source, such as a glow bar. The dimensions of the coupling
fiber, i.e., core diameter, outer diameter, divergence, spacing,
and the fiber of this invention, can be optimized for efficient
coupling.
[0041] The fiber sensors of this invention will have an impact in
both the military and the commercial sectors. For example, they can
be used in facility clean up; biomedical analysis, such as glucose,
blood, breath, etc.; chemical, biological warfare agent detection;
toxic and hazardous chemical detection; and environmental pollution
monitoring and process control. In addition to chemical sensing,
the fibers of this invention can be used for very high laser power
delivery since the light is predominantly guided in the hollow
core, unlike in traditional fibers which possess a solid core that
will be damaged at high powers. Furthermore, the commercial sector
will also benefit from the fibers of this invention since they
reduce system complexity, weight and cost as well as enabling
remoting of high power IR lasers for cutting, welding and
meteorology, as well as laser surgery, cancer removal and glaucoma
treatment. Infrared lasers for biomedical application include
CO.sub.2 lasers where powers of 10 to 50 watts and higher are
needed and cannot be transmitted using current solid core fibers
where power limit is about 10 watts.
[0042] The laser light delivery system includes a laser light
source, the fiber of this invention, a coupler for coupling light
from the laser light source to the fiber, and a coupler for
coupling the laser light out of the fiber.
[0043] While presently preferred embodiments have been shown of the
novel hollow core photonic band gap chalcogenide fibers, their
fabrication and of the several embodiments discussed, persons
skilled in this art will readily appreciate that various additional
changes and modifications may be made without departing from the
spirit of the invention as defined and differentiated by the
following claims.
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