WO2000052452A1

WO2000052452A1 - All fiber optic module for an optical chemical sensing system

Info

Publication number: WO2000052452A1
Application number: PCT/US2000/005839
Authority: WO
Inventors: Jamie N. Lussier
Original assignee: Yellow Springs Optical Sensor Co. Pll
Priority date: 1999-03-05
Filing date: 2000-03-03
Publication date: 2000-09-08
Also published as: EP1076815A1; CA2330769A1; JP2002538460A

Abstract

An optical chemical sensor comprising a sensor element (12), a distal optical fiber (14) communicating with the element (12), and a plurality of proximal optical fibers (16, 18, 20) having distal ends fused to a proximal end of the distal optical fiber (14).

Description

ALL FIBER OPTIC MODULE FOR AN OPTICAL CHEMICAL SENSING SYSTEM

Field of the Invention The present application is directed to an optical chemical sensing system and. more particularly, to a sensor system using the optical absorption or fluorescence of a fluid dye material to measure the concentration of a dissolved analyte.

Background of the Invention

Various forms of analyte measuring instruments have been designed and developed for use in numerous medical, industrial and environmental applications. Among these devices are those that rely on optical properties of a sensing element containing a dye material which is responsive to a particular analyte. When the dye material and the analyte interact, optical characteristics of the dye material, such as the absorption or fluorescence spectrum, change to a degree related to the concentration of the analyte in the surrounding medium. Thus, one may determine the concentration of the analyte in a medium from measurements of light reflected or fluoresced from the dye material when the dye material is exposed to the analyte-containing medium.

For example, certain prior art devices trap an aqueous dye solution in a sensor element or probe between an exposed analyte-permeable membrane and a distal end of at least one optical fiber. When the probe is exposed to an analyte- containing medium, analyte molecules diffuse through the membrane and interact with the dye solution. Light at one or more selected frequencies illuminates the dye solution. The optical fiber gathers reflected or fluoresced light from the dye solution and conducts the reflected or fluoresced light to one or more transducers. The one or more transducers provide a measure of the intensity of the reflected or fluoresced light corresponding to the one or more selected illumination frequencies which correlate, in turn, with the concentration of the analyte in the medium.

In particular, it is known to form pH sensors using mildly acidic dyes which are capable of dissociating to form conjugate bases having absorption and fluorescence spectra different from the corresponding spectra of the dyes themselves. It is also known to form dissolved carbon dioxide sensors by associating an aqueous sodium bicarbonate solution with such an acidic dye material, separated by a hydrogen ion-permeable membrane. In the latter sensors, dissolved carbon dioxide interacts with the sodium bicarbonate solution to produce dissolved hydrogen ion. which suppresses the dissociation of the dye and alters the optical properties of the dye solution.

When it has been desired to illuminate the dye solution with more than one frequency of light, or to measure reflected or fluoresced light at more than one frequency, expensive optical elements such as dichroic mirrors have been used. Dichroic mirrors comprise materials or coatings which reflect certain frequencies of light and transmit others. When one or more dichroic mirrors are arranged along a path, they can be used to direct light of different frequencies along different paths so that separate intensity measurements can be made at different frequencies.

Dichroic mirrors are expensive to prepare and contribute significantly to the cost of the sensor system. They tend to be bulky and require some care to avoid breakage. Beyond this, free standing optical elements such as dichroic mirrors must be carefully aligned so that the disparate elements communicate optically with each other. This alignment further increases the cost of such systems.

Therefore, there remains a need in the art for an optical chemical sensing system which overcomes these drawbacks of systems using dichroic mirrors.

Summary of the Invention The present invention is directed to an optical chemical sensing system using an all fiber optic module to illuminate a sensor element or probe and to conduct reflected or fluoresced light back to one or more measuring photodetectors. More particularly, a preferred sensor system includes a sensor element or probe; a distal optical fiber communicating with the probe; and a plurality of proximal optical fibers having distal ends fused to a proximal end of the distal optical fiber so as to conduct light between the distal optical fiber and the plurality of proximal optical fibers.

Optical fibers are typically formed of amorphous, light transmissive materials such as fused silicon. Radial variations in the refractive indices channel light along the lengths of the fibers. Where portions of optical fibers formed of the same material are melted and fused together, such fused joints are homogenous in character and present little impedance to light propagating therethrough.

In accordance with a first especially preferred embodiment, distal ends of first, second and third proximal optical fibers are fused to a proximal end of a single distal optical fiber. Proximal ends of the first and second proximal optical fibers each communicate with monochromatic light sources of different frequencies while a proximal end of the third proximal optical fiber communicates with a frequency-sensitive photodetector system. As a consequence, the first and second proximal optical fibers each conduct light through the fused joint between the proximal and distal optical fibers toward the probe. Output light from the probe (such as reflected or fluoresced light from a dye solution) returns through the distal optical fiber. The output light enters the third proximal optical fiber through the fused joint and propagates toward the frequency-sensitive photodetector system.

In accordance with a second especially preferred embodiment, the first proximal optical fiber communicates with a monochromatic light source while the second and third proximal optical fibers communicate with frequency-sensitive photodetector systems. The monochromatic light propagates through the first proximal optical fiber, the fused joint and the distal optical fiber toward the probe. Output light from the probe returns through the distal optical fiber; divides at the fused joint; and propagates through each of the second and third proximal optical fibers toward the frequency-sensitive photodetector systems.

While in each case the especially preferred embodiments have been described as having three proximal optical fibers, there is no limitation in theory on the number of proximal optical fibers which may be fused to the distal optical fiber. Instead, the number of such proximal fibers used is a matter of design choice depending on the application for which the sensor is to be used.

It should be noted that the fused joints referred to in the foregoing descriptions need not result from direct fusion of the proximal end of the distal optical fiber with the distal ends of the proximal optical fibers. For example, the proximal end of the distal optical fiber and the distal ends of the proximal optical fiber may each be fused to opposite ends of a mixing section of optical fiber rather than directly to each other.

In accordance with a third especially preferred embodiment, a bleed optical fiber fused in parallel with the distal optical fiber communicates with a reference photodetector. The bleed optical fiber has a diameter less than that of the distal optical fiber so that less light flows into the bleed fiber than into the distal fiber. The reference photodetector provides a reference light level which can be used to compensate for variations in the intensities of light produced by the monochromatic light sources.

Therefore, it is one object of the invention to provide an all fiber optic module which eliminates the need for bulky, expensive optical elements such as dichroic mirrors in optical chemical sensor systems. This allows for the encapsulation of the all fiber optic module within a portable housing. Unlike a dichroic-based system, the all fiber optic modules described above may be encapsulated in a moisture-resistant electronic assembly potting compound for use in severe environments. The optical elements need not be carefully aligned because the optical fibers channel light from one element to the next. As a result, the cost of an optical chemical sensor system using the all fiber optic module will likely be less than that of systems using free-standing optical elements.

The invention will be further described in conjunction with the appended drawings and following detailed description.

Brief Description of the Drawings Fig. 1 is a schematic view of a first embodiment of an optical chemical sensor system including an all fiber optic module in accordance with the invention;

Fig. 2 is a schematic disassembled view of a preferred sensor element or probe for use in the optical chemical sensor system of Fig. 1 : and

Fig. 3 is a schematic view of a second embodiment of an optical chemical sensor system including an all fiber optic module in accordance with the invention.

Detailed Description of the Preferred Embodiment As shown in Fig. 1, a first preferred embodiment of an optical chemical sensor system 10. such as a system for measuring dissolved carbon dioxide. includes a sensor element or probe 12, a distal optical fiber 14, a first proximal optical fiber 16. a second proximal optical fiber 18. a third proximal optical fiber 20. a first monochromatic light source 22. a second monochromatic light source 24. a frequency-sensitive photodetector system 26. a bleed optical fiber 28 and a reference photodetector 30.

As best shown in Fig. 2, a preferred probe 12 for use in a dissolved carbon dioxide sensor comprises a sensor capsule 40 housed between a sensor housing 42 and a sensor cap 44. The sensor capsule 40 includes an outer housing 46; an insert member 48: a perforated metal disc 50: a C0₂-permeable silicone membrane 52: and a light-transmissive polytetrafluoroethylene ("PTFE") membrane

54. The outer housing 46 and the insert member 48 snap together around the perforated disc 50 and the membranes 52. 54 to form a unitary capsule 40 which may be easily removed and replaced without sacrificing the entire probe 12.

A pool 56 of a aqueous solution of a weakly acidic dye and carbonate ion is trapped in the preferred probe 12 between the silicone membrane 52 and the

PTFE membrane 54. A distal end 58 of the distal optical fiber 14 (Fig. 1) extends through the sensor housing 42 into optical communication with the aqueous dye solution 56 through the PTFE membrane 54. The PTFE membrane 54 separates and protects the distal end 58 of the distal optical fiber 14 (Fig. 1) from aqueous dye solution 56.

The preferred probe 12 is described in more detail in co-pending U.S. Provisional Patent Application No. 60/106.528. filed October 31. 1998, the disclosure of which is incorporated herein by reference. Returning to Fig. 1. the optical fibers 14. 16. 18, 20 are each preferably formed of an amorphous, light transmissive material such as fused silicon. formulated in radial layers so as to channel the flow of light along their respective lengths. Distal ends 60. 62 and 64 of the proximal optical fibers 16. 18, 20 are fused to a proximal end 66 of the distal optical fiber 14 and encapsulated to form a fused coupling 68 with minimal impedance to the frequencies at which the dye solution (not shown) is to be illuminated and at which intensity measurements are to be taken. The monochromatic light sources 22. 24 each comprise a light source 80. such as a bulb or a light emitting diode, and a band-pass filter 82 to isolate a frequency at which the aqueous dye solution (not shown) is to be illuminated. The light source and the band-pass filter are of conventional construction. The monochromatic light sources 22. 24 communicate with proximal ends 84. 86 of the first and second proximal optical fibers 16. 18 to permit the first and second proximal optical fibers 16, 18 to transmit monochromatic light from the monochromatic light sources 22, 24 toward the distal optical fiber 14.

The frequency-sensitive photodetector system 26 includes a band-pass filter 90 in optical communication with a measuring photodetector 92. The bandpass filter 90 and the measuring photodetector 92 are of conventional construction. The band-pass filter 90 communicates optically with a proximal end 94 of the third proximal optical fiber 20. The frequency-sensitive photodetector system 26 measures the intensity of a component of light returning through the third proximal optical fiber 20 within a narrow energy range surrounding a selected frequency.

The bleed optical fiber 28 is fused to the distal optical fiber 14 so that it directs a portion of the light propagating through the distal optical fiber 14 toward the reference photodetector 30. It preferably is formed of an amorphous, light transmissive material such as fused silicon and has a diameter much less than a diameter of the distal optical fiber 14 so that the portion of light directed through the bleed optical fiber 28 toward the reference photodetector 30 is much less than the portion directed through the distal optical fiber 14 toward the probe 12. This permits the reference photodetector 30 to monitor the intensity of light output by the two monochromatic light sources 22. 24 so as to provide a reference level to correct for the effects of variations in the intensity of light produced by the sources 22. 24 on the intensity measured by the frequency-sensitive photodetector system 26.

Most preferably, the monochromatic light sources 22. 24; the photodetector 26: and the reference photodetector 30 each communicate electronically with a controller, such as a microprocessor (not shown). The controller modulates the light illuminating the aqueous dye solution (not shown) in the probe 12. It also processes intensity measurements reported by the photodetector 26 and the reference photodetector 30 to derive analyte concentration measurements. In the case of a dissolved carbon dioxide sensor, one preferred aqueous dye solution (not shown) for use in the optical chemical sensor system 10 of Fig. 1 is 8-hydroxypyrene-1.3,6-trisulfonic acid (HPTS). buffered with carbonic acid. As described in more detail in U.S. Provisional Patent Application No. 60/085.366. filed May 13. 1998, the disclosure of which is incorporated herein by reference. HPTS is a weak acid which decomposes to form dissolved hydrogen ion and a conjugate base. Dissolved carbon dioxide interacts with water in the dye solution to increase the supply of carbonic acid, which suppresses the dissociation of the HPTS into its conjugate base.

HPTS achieves peak fluorescent emission when excited at a wavelength of approximately 405 nm while its conjugate base achieves peak fluorescent emission at a wavelength of approximately 460 nm. Both HPTS and its conjugate base have fluorescent emission frequencies of approximately 515 nm.

If the probe 12 containing the buffered aqueous solution of HPTS is exposed to a medium (not shown) so as to allow carbon dioxide from the medium to diffuse into the HPTS solution; if the HPTS solution is sequentially illuminated with monochromatic light having components with wavelengths of approximately 405 nm and 460 nm; and if the intensity of the fluorescent emission from the HPTS solution at a wavelength of approximately 515 nm is measured for each wavelength of illuminating light, a correlation exists between the partial pressure of dissolved carbon dioxide in the medium and the measured intensities of the fluorescent emission.

More specifically, in an especially preferred optical chemical sensor system 10 using a buffered aqueous solution of HPTS (not shown) to measure the partial pressure of dissolved carbon dioxide ["pCO,"]. the monochromatic light sources 22. 24 supply light at frequencies in the vicinity of 405 nm and 460 nm. respectively. Light from the two monochromatic light sources 22. 24 propagates through the first and second proximal optical fibers 16, 18: through the fused coupling 68: and through the distal optical fiber 14 toward the probe 12. A controller, such as a microprocessor-based controller (shown schematically at 100). may be used to turn the monochromatic light sources 22. 24 ON and OFF to modulate the light illuminating the HPTS solution in the probe 12. Fluorescent emission from the HPTS solution (not shown) returns through the distal optical fiber 14. the fused coupling 68 and the third proximal optical fiber 20 toward the frequency-sensitive photodetector system 26. The frequency-sensitive photodetector system 26 measures the intensity of the fluorescent emission within a range of frequencies in the vicinity of 515 nm. Meanwhile, the reference photodetector 30 provides a reference illumination level which may be used to normalize the intensities measured by the frequency-sensitive photodetector system 26.

These intensities are related to the pCO_: of the medium (not shown) as follows:

E _λ, = 405 nm / ' Λ_λ = 405 nm _ K ^^KH_t π I == 440055 m nm» ' P λ = 405 nm) _pH _.₃ pCO

*^* _λ = 4₆0 _nm ' "λ = 460 n_m H C>₃ J \ _{λ = 460 mχ} I P_{χ = 4ω nm}J_{pH =}

X λ = 405 nm ' "λ = 405 m -- ₁₂ ( λ = 460 nm ' " λ = 460 nm) _{pH = 12} where "F_{λ = 405 nm} ^" is the measured emission intensity of the dye due to excitation by the 405 nm light during exposure to the medium of interest; "F_λ---_{460 n}-_τ-'^' is the measured emission intensity of the dye due to excitation by the 460 nm light during exposure to the medium of interest; "P_{λ = 405 nm} ^" and "P_{i =460 lιm}" are the intensities of the illuminating light at 405 nm and 460 nm, respectively, measured by the reference photodetector 30; "(F_{λ = 405 nm} / P_λ --._{405 nm}) _pΗ= '^* is a reference value for the normalized emission intensity of the dye. measured while the dye was exposed to a reference solution of pH 3 and illuminated at 405 nm; "(F_λ--_{405 nm} / Px _{= 4}o_{5 nm}) _H=i₂ ^{" an}^ "(F_{λ = 460 nm} / P_{λ = 460 nm}) _H=ι₂" ^are reference values for the normalized emission intensities of the dye. measured while the dye was exposed to a reference solution of pH 12 and illuminated at 405 nm and 460 nm, respectively; "K^" is the net dissociation constant for the dissociation of the buffered dye solution; and "K_H ^" is the Henry^'s law ratio between the concentration of dissolved C0₂ gas and the pCO_:. Reference values are measured at pH 3 and pH 12 because the concentration of the HPTS molecular species is negligible at pH 12 and the concentration of the PTS^~ conjugate base ion is negligible at pH 3. Where optical chemical sensor system 10 includes a microprocessor-based controller 100. the values at pH 3 and pH 12 may be tabulated, and the pCO_: value may be calculated, within the system 10.

As shown in Fig. 3. a second preferred embodiment of an optical chemical sensor system 110, such as a system for measuring dissolved carbon dioxide, includes a sensor element or probe 112. a distal optical fiber 1 14, a first proximal optical fiber 116. a second proximal optical fiber 1 18. a third proximal optical fiber 120, a monochromatic light source 122. a first frequency-sensitive photodetector system 124. a second frequency-sensitive photodetector system 126. a bleed optical fiber 128 and a reference photodetector 130. The preferred probe 112 (including the sensor housing 142 and the sensor cap 144) is similar in structure to the preferred probe 12 of Fig. 1, although the system 110 of Fig. 3 is likely to use different dye solutions than the system 10 of Fig. 1. Likewise, the preferred optical fibers 114. 116. 118, 120. 128 are similar in structure to the optical fibers 14, 16, 18, 20, 28 of Fig. 1. The preferred monochromatic light source 122; the preferred frequency-sensitive photodetector systems 124. 126; and the reference photodetector 130 of Fig. 3 are similar in structure to the monochromatic light sources 22. 24: the frequency-sensitive photodetector system 26: and the reference photodetector 30 of Fig. 1. respectively, although the corresponding components of the two systems are likely to be set to different frequencies corresponding to the peak excitation and emission frequencies of the dye solutions used. Distal ends 160, 162 and 164 of the proximal optical fibers 116. 1 18, 120 are fused to a proximal end 166 of the distal optical fiber 114 and encapsulated to form a fused coupling 168 with minimal impedance to the frequencies at which the dye solution (not shown) is to be illuminated and at which intensity measurements are to be taken.

The fusing of optical fibers 14, 16. 18. 20 and 1 14. 116. 118, 120 in the optical chemical sensor systems 10 and 110 is accomplished via a laser fusion process. Specifically, the fibers to be fused together, such as proximal optical fibers 16. 18 and 20 as shown in Fig. 1 , are fixtured in a chuck (not shown), and then rotated in the path of a focused 125 watt Carbon Dioxide laser beam (wavelength of 9.4 to 10.4 micrometers) (not shown). The energy of the C0₂ laser beam heats up the three optical fibers to a temperature at which fusion occurs. A similar process is performed with the distal optical fiber 14 and bleed fiber 28. The region of fusion no longer contains an outer cladding layer, but is of sufficiently short distance that the optical losses are minimized and at an acceptable level.

After fusion of proximal optical fibers 16, 18 and 20 into one fused fiber unit, and distal optical fibers 14 and bleed fiber 28 into one another, the two fused fiber units 16, 18. 20 and 14, 28 are then joined by a butt-end fusion via a laser fusion process. To accomplish the fusion, both fused fiber units are mounted in rotating chucks (not shown) and the fused fiber unit ends are brought together in the focused beam path of the laser. In some situations, it may be desirable to incorporate a mixing section of optical fiber (not shown). To do this, a section of optical fiber is butt-end fused to both fused fiber units, such that the mixing section is located in between the two fused fiber units. In the case of a dissolved carbon dioxide sensor, another preferred aqueous dye solution (not shown) for use in the optical chemical sensor system 10 is an aqueous solution of carboxy-seminapthofluorescein (c-SNAFL), buffered with carbonic acid. As described in more detail in U.S. Provisional Patent Application No. 60/085.366. filed May 13. 1998, the disclosure of which is incorporated herein by reference, the buffered c-SNAFL solution indicates the partial pressure of dissolved carbon dioxide in a manner analogous to the buffered HPTS solution described earlier.

Both c-SNAFL itself and its conjugate base achieve peak fluorescent emission when excited by light at a wavelength of approximately 480 nm. When illuminated by light at approximately 480 nm, c-SNAFL fluoresces at a wavelength of approximately 540 nm while its conjugate base fluoresces at a wavelength of approximately 630 nm.

If the probe 112 containing the buffered aqueous solution of c-SNAFL is exposed to a medium (not shown) so as to allow carbon dioxide from the medium to diffuse into the c-SNAFL solution; if the c-SNAFL solution is illuminated with light at a wavelength of approximately 480 nm; and if the intensities of the fluorescent emissions from the c-SNAFL solution at wavelengths of 540 nm and 630 nm are measured, a correlation exists between the partial pressure of dissolved carbon dioxide in the medium and the measured intensities of the fluorescent emission. More specifically, in an especially preferred optical chemical sensor system 110 using a buffered aqueous solution of c-SNAFL (not shown) to measure pCO₂ values, the monochromatic light source 122 supplies light within a narrow range of frequencies in the vicinity of 480 nm. Light from the monochromatic light source 122 propagates through the first proximal optical fiber 116 and the distal optical fiber 114 toward the probe 112. Fluorescent emission from the c-SNAFL solution (not shown) returns through the distal optical fiber 114; divides at the fused coupling 168; and propagates through the second and third proximal optical fibers 118. 120 toward the frequency-sensitive photodetector systems 124, 126. The frequency-sensitive photodetector system 124 measures the intensity of the fluorescent emission within a range of frequencies in the vicinity of 540 nm while the frequency-sensitive photodetector system 126 measures the intensity of the fluorescent emission within a range of frequencies in the vicinity of 630 nm.

These intensities are related to the pC0₂ of the medium (not shown) as follows:

where "F_{λ = 540 nnι}" is the measured emission intensity of the dye at 540 nm during exposure to the medium of interest; "F_{λ = 630 nm} ^" is the measured emission intensity of the dye at 630 nm during exposure to the medium of interest; "(F_{λ = 540 nm}) _{Low pH} ^" and "(F_{λ = 630 nm}) _{LOW PH}" ^are reference values for the emission intensities of the dye, measured at 540 nm and 630 nm. respectively, while the dye was exposed to a reference solution of having a low pH at which the concentration of conjugate base was negligible; "(F_{λ = 540 nm})_pH=I2 ^v and "(F_{λ = 63ϋ nm} / P_{λ = 460 nm}) _pH-,₁₂" are reference values for the emission intensities of the dye. measured at 540 nm and 630 nm. respectively, while the dye was exposed to a reference solution of pH 12 (where the concentration of c-SNAFL molecular species was negligible); "K" is the net dissociation constant for the dissociation of the buffered dye solution; and "K_H" is the Henry's law ratio between the concentration of dissolved C0₂ gas and the pC0₂. Where optical chemical sensor system 110 includes a microprocessor-based controller (shown schematically at 200), the values at low pH and pH 12 may be tabulated, and the pC0₂ value may be calculated, within the system 110.

All components of the systems 10, 1 10 except the probes 12, 112 and the distal optical fibers 14, 1 14 may be encapsulated in a portable, fluid-tight housing (not shown) to provide durable units for making field measurements. Conventional output devices (not shown) may be provided for reading or recording measurements performed by the system 10, 110.

The all fiber optic module may be encapsulated in a common electronic assembly potting compound (not shown), to provide reliable and robust environmental protection for use in applications associated with severe environments. An optical system using dichroics is very susceptible to damage due to humidity and moisture. This concern is eliminated in a potted assembly. Typically, potting of a dichroic-based system is not practical nor economically feasible.

From the foregoing, it is apparent that the optical chemical sensor systems 10. 110 provide all fiber optic modules which eliminate the need for expensive optical elements such as dichroic mirrors. A size reduction in the overall optical system may be realized with the all-fiber optical module approach, that is not practically achievable with the traditional dichroic based design. Furthermore, the optical elements need not be carefully aligned because the optical fibers channel the light from one element to the next. As a result, the cost of optical chemical sensor systems using the all fiber optic module, such as the systems 10, 110, will likely be less than that of systems using free standing optical elements.

The preceding description and accompanying drawings are intended to be illustrative of the invention and not limited. Various other modifications and applications will be apparent to one skilled in the art without departing from the true spirit and scope of the invention as defined by the following claims.

Claims

-CLAIMS-

1. An optical chemical sensor system for measuring an analyte, said optical chemical sensor system comprising a probe communicating with a dye material having an optical characteristic dependent on a concentration of the analyte: a distal optical fiber having a proximal end portion and a distal end portion, said distal end portion of said distal optical fiber being in optical communication with said probe; and at least three proximal optical fibers, each of said at least three proximal optical fibers having a proximal end portion and a distal end portion; said distal end portions of said at least three proximal optical fibers being fused to said proximal end portion of said distal optical fiber.

2. An optical chemical sensor system as recited in claim 1 wherein at least one of said proximal end portions of said at least three proximal optical fibers communicates with a monochromatic light source and at least another of said proximal end portions of said at least three proximal optical fibers communicates with a frequency-sensitive photodetector system.

3. An optical chemical sensor system as recited in claim 1 wherein said dye material includes an aqueous solution of carboxy-seminapthofluorescein; at least one of said proximal end portions of said at least three proximal optical fibers communicates with monochromatic light sources; and at least two of said proximal end portions of said at least three proximal optical fibers communicate with a frequency-sensitive photodetector system.

4. An optical chemical sensor system as recited in claim 1 wherein said dye material includes an aqueous solution of 8-hydroxypyrene-l,3,6-trisulfonic acid; at least two of said proximal end portions of said at least three proximal optical fibers communicate with a monochromatic light source: and at least one of said proximal end portions of said at least three proximal optical fibers communicates with frequency-sensitive photodetector systems.

5. An optical chemical sensor system as recited in claim 2 further comprising a reference photodetector and a bleed optical fiber connected to said reference photodetector and communicating with said distal optical fiber.

6. An optical chemical sensor system as recited in claim 5 wherein said bleed optical fiber is fused to said distal optical fiber; and said bleed optical fiber has a diameter less than a diameter of said distal optical fiber.

7. An optical dissolved carbon dioxide sensor system comprising: a) a probe supporting an aqueous solution containing carboxy- seminapthofluorescein and carbonate ion; b) a distal optical fiber having a proximal end portion and a distal end portion, said distal end portion of said distal optical fiber being in optical communication with said buffered solution of carboxy-seminapthofluorescein; c) first, second and third proximal optical fibers, each of said first, second and third proximal optical fibers having a proximal end portion and a distal end portion such that said distal end portions of said at least three proximal optical fibers are fused to said proximal end portion of said distal optical fiber; d) a monochromatic light source in optical communication with said proximal end portion of said first proximal optical fiber; e) first and second frequency-sensitive photodetector systems, said first frequency-sensitive photodetector system being in optical communication with said proximal end portion of said second proximal optical fiber and said second frequency-sensitive photodetector system being in optical communication with said proximal end portion of said third proximal optical fiber; f) a bleed optical fiber fused to said distal optical fiber, said bleed optical fiber having a diameter less than a diameter of said distal optical fiber; g) reference photodetector in optical communication with said bleed optical fiber; and h) a controller including a microprocessor in electrical communication with said first frequency-sensitive photodetector, said second frequency-sensitive photodetector and said reference photodetector.

. An optical chemical sensor system for measuring an analyte, said optical chemical sensor system comprising a probe communicating with a dye material having an optical characteristic dependent on a concentration of the analyte: a distal optical fiber having a proximal end portion and a distal end portion, said distal end portion of said distal optical fiber being in optical communication with said probe; at least three proximal optical fibers, each of said at least three proximal optical fibers having a proximal end portion and a distal end portion; said distal end portions of said at least three proximal optical fibers being fused to said proximal end portion of said distal optical fiber: at least one monochromatic light source communicating with said proximal end portion of one of said at least three proximal optical fibers; and at least one frequency-sensitive photodetector system including a photodetector and a band-pass filter communicating between said proximal end portion of another of said at least three proximal optical fibers and said photodetector.