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This invention relates to a dual optical fiber device and is particularly concerned with a device for transmitting elec tromagnetic radiation to a radiation sensitive component and receiving output radiation from said component involving a radiation-transmissible junction of optical fibers which provides a substantially unattenuated output radiation signal. The inven-tion also relates to a method for determining a desired parameter w~lieh is a function of said output radiation using said device.
In a more specific aspect, the invention relates to a multi-channel electromagnetic radiation transmission system and particularly to a system which is adapted to be used in a plurality of modes for the selective determination of two or more substances in a medium. More particularly, the invention relates to a system involving a series of radiation-transmissible junctions of optical fibers, which system provides substantially unattenuated output radiation signals. The invention is also concerned with a method for the determination of two or more parameters each of which is a function of the output radiation of a radiation sensitive com-ponent, utilizing said system.
The measurement of desired parameters in liquids, partieularly in biological systems, is frequently required. For e~ample, the measurement in blood of pH levels and concentration of gases, particularly oxygen and carbon dioxide, is important during surgieal procedures, post-operatively, and during hosital-ization under intensive care and many devices for the measurement of said physiologieal parameters have been suggested in the art.
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~9~ 4680-414 United States Patent No. 4,003,707 disclose a method and an arrangement for measuring the concentration of gases and the pH value of a sample, e.g. blood, involving -the use of a fluores-cent indicator at the end of a light-conducting cable which is sealingly covered by or embedded in a selectively permeable dif-fusion membrane. The radiation transmitted to and emitted -Erom the indicator must be passed through various filtering elements and light elements, including reflectors, beam splitters and ampli-~iers beEore any meaningful measurements can be made.
United States Patent No. 4,041,932 discloses a method whereby blood constituents are monitored by measuring the concen-tration of gases or fluids collected in an - la ~
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enclosed chamber sealingly attached to a skin "window formed by removing the stratum corneum over a small area of the patient's skin. The measurements in the enclosed chamber are made, inter alia, by determining the difference in intensity of light emitted from a fluorescent indicator.
U.S. Patents No. 4,200,110 and 4,476,870 disclose the use of a pH sensitive indicator in conjunction with a fiber optic pH probe. In each of these patents the dye indicator is enclosed within a selectively permeable membrane envelope.
U.S. Patent No~ 4,548,907 discloses a fluorescent-based optical sensor comprising a membrane immobilized fluorophor secured to one end of a bifurcated fiber optic channel for exposure to the sample to be analyzed.
Many fluorescent indicators sensitive to pH, and thereby useful for PCO2 measurements, are known in the art. Examples of useful fluorescent indicators are ~0 disclosed in the above patents and also in "Practical Fluorescence" by George E. Guilbault, (1973) pages 599-600.
Sensor device using fluorescent indicators may be used for in vitro or in vivo determinations of compo-~5 nents in physiological media. For in vitro determina-tions the size of the device is normally of no conse-quence, but for in vivo use, the size of the sensor may be extremely critical and there is an increasing need in the art to miniaturize sensor devices, particularly catheter-type devices, for the in vivo determination of components in physiological media, e.g. blood. However, diminution in size of the components of such devices, particularly in the size of the sensor itself, decreases the strength of the signal emitted by the indicator and consequently presents problems in the detection and ... . . . .. .. .. . . . . ..
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measurement of said si~nal. These problems are aggravated when the detector system re~uires a multiplicity of components, such as filters, beam splitters and reflectors to isolate and measure the emitted energy. Ea~h o~ the said components reduces the emitted signal strength resulting in a sequential loss of ~easurable signal. Consequently, the more componen-ts present in the system, the weaker the final signal strength.
It has now been found that the emission siynal froln radiation-sensitive indicators, particularly fluorescent 1~ indlcators of the type disclosed in the references discussed above, may be received substantially unattenuated in a suitable detector without the necessi~y of filters, beam splitters, reflectors or other light elements used in the prior art if the transmitting optical fiber and emission-receiving optical fiber are coupled in a manner according to the present invention, as described hereinafter.
The elimination of the need for additional optical elements provided by the improved device of the present invention allows greater miniaturization of sensor systems than that attainable in prior art systems wi~hout loss of signal strength.
In accorclance with the present invention there is provided a device for transmitting electromagnetic radiation to a radiation sensitive component, receiving output radiation from said component and transmitting said output radiation substantially unattenuated to a radiation measuring, transducing, recording or retransmitting component, which device comprises a first cladded optical fiber having a proximal end and a distal end, said proxlmal end being adapted to receive source radiation and said distal end having an exposed tip which touches but is not integrally joined to an exposed intermediate portion of a second cladded optical fiber having a proximal end and a distal end, the touch contact between said tip and the exposed portion of said second optical fiber forming a highly directional radiation-transmissible junction, the proximal end of said second optical fiber being adapted ~o be a~tached to a radiation sensitive component such that the output radiation from said radiation '.
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6~680-414 sensitive component passes substantially unattenuated along said second optical fiber and through said junction to said radiation measuxing, transducing, recording or retransmittinCJ component, said junction being encased in an opaque, radiation reflective jacket.
~ he invention also provides a method for determining a desired parameter which is a function of the output radiation of a radiation-sensitive co~ponent, which comprises ~ransmitting electromagnetic radiation from a source into a device comprising a first cladded optical fiber having a proximal end and a distal end with an exposed tip which substan~ially contacts an exposed intermediate portion of a second cladded optical fiber having a proximal end and a distal end, said contact forming a radiation-transmissible junction which is encased in an opaque, radiation reflective jacket, said radiation entering the device through the proximal end of said first optical fiber, passing along said first optical fiber and through said junction into said second optical fiber towards the distal end thereof, a major proportion of any radiation not directly passing into said second optical fiber ~0 being internally reflected thereinto by the reflective jacket, impinging upon said radiation-sensitive component attached to -the distal end of said second optical fiber, causing said component to emit a signal haviny at least one characteristic dependent upon the parameter to be measured, and said signal passing substantially unattenuated through said second optical fiber toward the proximal end thereof whereby the desired determination is made with the aid of a radiation-detector attached to the proximal end of said second optical fiber.
According to another aspect, the invention provides a multi-channel electromagnetic radiation transmission system comprising a plurality of first cladded optical fibers each having a proximal end and a distal end, said proximal end being adapted to receive radiation from a source and said distal end having an exposed tip with touches but is not integrally joined to an exposed intermediate portion of a second cladded optical fiber havin0 a proximal end and a distal end, the touch contact between -6~6~0-414 said tip and the exposed portion of said se~on~ optical fiber ~ormin~ a highly directiona:l radiation-transmissible junction which is encased in an opaque, radiation reflective jacket, said second cladded optical fiber being either a single fiber having a plurality of said ~unctions corresponding to the number of first optical fibers located sequentially alony its length or one of a plurality of fibers each having at least one of said junctions, wherein the total number of said junctions corresponds to the number of first optical fibers, the proximal end of said single second optical fiber or of each of said plurality of second optical fibers being adapted to be attached to a radiation measuring, transducing, recording or retransmitting component and the distal end thereof being attached to a radiation sensitive componen~, whereby the output radiation from said radiation sensitive component passes substantially unattenuated along said second optical fiber and through its associated junction toward the proximal end of said second optical fiber for determination by said radiation measuring, transducing, :recording or retransmitting component.
The present invention also provides a method for selectively determining a plurality of parameters each of which is a function of the output radiation of a radiation sensitive component, which comprises transmitting electromagnetic radiation from a .
- 6 - ~ ~9~ 4680-4141 source into a system comprising a plurality of first cladded opti-cal fibers each having a proximal end and a distal end, said proximal end being adapted to receive said radiation and said distal end having an exposed tip which substantially contacts an exposed intermediate portion of a second cladded optical fiber having a proximal end and a distal end, the contact between said tip and said second optical fiber forming a radiation-transmissible junction which is encased in an opaque, radiation reflective jacket, said second cladded optical fiber being either a single fiber having 1~ a plurality of said junctions corresponding to the number of first optical fibers located sequentially along its length or one of a plurality of fibers each having at least one of said junctions, wherein the total number of said junctions corresponds to the num-ber of first optical fibers, said source radiation entering the system through the proxima-l end of each of said plurality of first optical fibers, passing along each of said first optical fibers and through each of said junctions into said second optical fiber towards the distal end thereof, a major portion of any radiation not passing directly into said second optical fiber being internal-ly reflected thereinto by its associated reflective jacket, im-pinging upon said radiation sensitive component attached to the distal end of said second optical fiber, causing said component to emit a signal having at least one characteristic dependent upon at least one of the parameters to be determined, and said signal passing substantially unattenuated through said second optical fiber toward the proximal end thereof whereby the desired deter-~z~
~ 680-4141 mination is made with th~ aid of a radiation detector attached to the proximal end of said second optical fiber.
In the device or system of the invention the disposition of the second optical fiber with respect to the or each first optical fiber in the or each radiation-transmissible junction is such that the output radiation from the radiation sensitive com-ponent attached to the distal end of said second optical fiber passes substantially unattenuated along said second optical fiber and throu~h said junction to said measuring, transducing, record-1~ in~ or retransmitting component.
The preferred configuration is that in which the contactbetween said exposed tip of the or each first optical fiber and said exposed intermediate portion of said second fiber is substan-tially parallel.
Furthermore, in a preferred embodiment the surface of the exposed tip in contact with the second optical fiber is pre-polished to flatness.
The or each junction also provides a splitting of the source radiation into two components. A first, minor, component ~a travels to the proximal end of the second optical fiber and the detector and a second, major, component travels to the distal end of the second optical fiber and the radiation-sensitive component.
This provides a convenient means for source radiation compensation by measuring the ratio of the first component to the output radia-tion or emission signal.
The optical fibers used in the device or system of the -7a - 4680-414 invention may be made of any suitable material which will transmit electromagnetic radiation of the desired waveleng-th. In a prefer-red embodiment said first and second optical fibers are made of fused silica and the cladding is made of silicone. Fused silica is particularly suitable for the transmission of ultraviolet radiation.
Each of said first optical fiber(s) and second optical fiber may consist of a single fiber strand or a multiple fiber bundle. Preferably the exposed portion of said second fiber has a length equivalent to at least one fiber diameter.
The opaque, radiation reflective jacket which encases the radiation transmissible junction of the device according to the invention or each radiation transmissible junction of the system according to the invention effectively serves two functions; namely, to reflect any radiation which might otherwise escape from the junction back into the second optical fiber and to prevent any extraneous, unwanted radiation from entering the device. Thus, the jacket must be not only internally reflective, but also opaque with respect to external radiation. To accomplish this dual objective ~0 it is preferred that said jacket comprises an inner layer and an outer layer, said inner layer being made of a metal foil or a metalized film whose inner surface is coated with a film of reflec-tive material and said outer layer being made of a heat-shrinkable, opaque, non-metallic material.
A praferred metal foil for said inner layer is aluminum foil. A preferred reflective material is barium sulfate.
- lb - ~ 4680-414 Also, to enhance the coupling efficiency, it is desirable to apply a layer of optical coupling gel over the film of reflec-tive material.
Said coupling gel is a standard material in the art having substantially the same refractive index as the material of the optical fibers. A typical example is a silicone gel.
The heat-shrinkable, opaque, non-metallic material pre-fexably used as the outer layer of the jacket may be any material which .i5 opaque to ambient radiation and which may be heat shrunk la around the junction to form a radiation-tight seal. A suitable material is an opaque plastic, such as polyvinyl chloride. Prefer-ably, to form a completely radiation-tight seal, the outer layer extends over and beyond the inner reflective layer and overlaps the cladded portion of each of the optical fibers.
The device according to the invention is particularly suitable for use in a method for determining a desired parameter which is a function of the output radiation of a radiation-sensitive component. A preferred embodiment of the method is one in which the parameter to be determined is the concentration of a substance in a liquid and said radiation-sensitive component includes a 1uorescent indicator whose emission radiation is altered in the presence of said substance.
A typical example of such method is the determination of the concentration of carbon dioxide in blood.
The system of the invention may be arranged in a number of different ways and some of these arrangements will be particular-~ 7c - 4680-414 ly described as preferred embodiments. It is to be understood that numerous other arrangements are possible without departing from the spirit and scope of the invention, with the proviso that in every possible arrangement the signals reaching the detector must be discernible and measurable.
In one preferred embodiment of the inventive system the proximal end of each of said first optical fibers is attached to a separate source of electromagnetic radiation of a given wavelength.
In such an embodiment, it is also preferred that each of said first optical fibers is coupled through a said junction to a single second optical fiber, the distal end of which is attached to a single radiation sensitive indicator and the proximal end of which is attached to a detector adapted to disperse and measure the output radiation emitted by said indicator.
In another preferred embodiment of the multi-channel sys-tem the proximal ends of said plurality of first optical fibers are attached to a single source of electromagnetic radiation. In this embodiment it is also preferred that the distal end of each of said plurality of first optical fibers is coupled through a said 2~ junction to each of plurality of said second optical fibers, the distal end of each of said second optical fibers is attached to a separate radiation sensitive indicator and the proximal ends there-of are attached to a radiation dispersing and measuring device.
Said radiation dispersing and measuring device preferably comprises a grating and a two dimensional array of radiation detectors. This type of device will be described in more detail , .. ;
~ 7~ ~ 4680-414 hereinafter with reference to the accompanying drawings.
In a preferred embodiment of the inventive system the radiation sensitive component attached to the distal end of the second optical fiber is at least one fluorescent indicator.
It is particularly preferred that the radiation sensitive component comprises a plurality of indicators each of which fluo-resces upon excitation by the source radiation and each of which emits radiation of a different distinguishable wavelength, the intensity of each emitted signal being dependent upon the concen-l~ tration of a substance under investigation.
A preferred source of radiation to be used with thesystem of the invention is a laser which produces controlled mono-chromatic or polychromatic radiation.
A further preferred embodiment is a system in which each of said first optical fibers is attached to a single polychromatic source of radiation and each of said fibers is associated with an optical filter which selects the wavelength and an optical relay which selects the timing of the radiation of a desired wavelength to said fiber. Preferably said optical relay comprises a component within said first optical fiber which controls the passage of excitation source radiation into said second optical fiber, which then acts as excitation radiation for an indicator species included in the radiation sensitive component attached to the distal end of said second optical fiber. The resulting system also preferably includes means for sequentially selecting one or more excitation radiation sources transmitted through said optical relays.
- 7e - 4680-414 The system of the invention is particularly suitable for use in a method for selectively determining a plurality of para-meters each of which is a function of the output radiation of a radiation sensitive component. A preferred embodiment of the method is one in which the parameters to be determined are the concentra-tions of at least two substances in at least one medium and said radiation sensitive component includes at least one fluorescent indicator whose emission radiation is dependent upon the presence o~ said substances. In such embodiment, preferably the signal la emitted from each radiation sensitive component is dispersed and measured in a device comprising a grating and a two dimensional array of radiation detectors.
The invention will be more particularly described with reference to preferred embodiments of the system as illustrated in the accompanying drawings in which:
Figure 1 is a schematic side elevation, partly in section, of a dual optical fiber device according to the invention compris-ing a radiation transmissible junction encased in an opaque, radiation reflective jacket;
~a Figure 2 is a schematic representation of one embodiment of a multi-channel system of the invention comprising three first optical fibers coupled to a single second optical fiber through three junctions located sequentially along the length of the second optical fiber;
Figure 3 is a schematic representation of another em-bodiment of the invention comprising three first optical fibers 4~
~ 7f ~ 4680-414 coupled through junctions to three second optical fibers;
Figure 4 is a schematic representation of a preferred radiation dispersing and measuring device comprising a grating and a two dimensional array of radiation detectors; and Figure 5 illustrates the two dimensional array of Figure 4.
Referring to Figure l, the device comprises a first cladded optical. fiber l having an exposed tip 2. The core of the fiber is made of fused silica and the cladding 3 is made of l~ radiation~opaque silicone.
The exposed tip of said first optical fiber is in sub-stantially parallel contact with an exposed intermediate portion 4 of a second cladded optical fiber 5 made of the same materials as said first optical fiber.
The contact between said tip and said second optical fiber forms a radiation-transmissible junction which is encased in an opaque, radiation reflective jacket comprising an inner layer made of aluminum foil and illustrated schematically by dashed line 6 and an outer layer 7 made of a heat-shrinkable opaque non-metallic material, for example polyvinyl chloride. The maximum internal diameter of the opaque heat-shrinkable tubing is about 0.01 inch (.025 mmJ when used with a standard fused silica optical fiber of about 400~m.
diameter. Said outer layer extends beyond the inner metal foil and is heat shrunk onto both the inner layer 1~ and the cladding of the optical fibers to form a radiation-tight seal around the junction.
The aluminum foil 6 is coated on its inner surface, i.e. the surface facing the junction of the optical fibers, with a film of radiation reflective material, ~or example barium sulfate. A layer of index matching optical coupling gel, for example silicone gel, is applied over said film of reflective material.
This layer substantially fills the space 8 between the reflective layer and the exposed optical fibers.
~0 Attached to the distal end of the second optical fiber (suitably exposed) is a drop of fluorescent indicator 9. Said fluorescen indicator provides a radiation~s~ensitive component which is excited by radiation ~ entering said first optical fiber from a radiation source (not shown), such as a laser.
In the operation of the device for determining the concentration of a substance in a liquid (not shown) the excitation radiation causes the indicator to fluoresce at a given wavelength. The intensity of the emitted fluorescent radiation is altered by the presence of the substance to be detected and a determination of the concentration of said substance in the liquid under examination may be mada by measuring the intensity of the emitted radiation ~ which passes substantially unattenuated through said second fiber to a detector (not shown).
The following Examples illustrate the invention and the manner in which it may be performed.
Example 1 This Example illustrates the preparation of a preferred device according to the invention.
The tip of a first silicone cladded 400 ~m fused silica optical fiber was stripped of its cladding over 10 a length of about 1 cm. The fiber tip was then polished to flatness with a Buehler fiber optic polisher.
The exposed tip was then washed in acetone to remove residual cladding and polishing grit.
Approximately 1 cm of cladding was stripped from an intermediate portion of a second cladded optical fiber.
Removal of the cladding exposed the fused silica core.
The core was washed in acetone to remove residual cladding.
A strip of aluminum foil approximately 6" x 6" x .0045" was cut.
The surface of the foil was then coated with a commercially available white barium sulfate reflectance coating and dried under mild heat.
~5 A small piece, approximately 1" x 0.5" of the coated foil was cut from the above dried strip.
A thin layer of optical coupling gel was applied over the reflectance coating.
The polished exposed tip of the first optical fiber 3~ was brought into substantially parallel contact with the exposed portion of the second optical fiber. The resulting junction was held in place by taping the cladded portions of the fibers above the junction.
The above prepared foil was rolled into a small 35 cylinder over the barrel of an 18 gauge needle with .. . ..
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the light reflectlve surface on the inslde. This cylinder was then slid over the distal end of the second optical fiber and placed over the junction of the two fibers.
A tube of heat-shrinkable white opaque polyvinyl chloride having an internal diameter of about 0.1"
(2.54 mm) and a length of about 1" (25c4 mm) was slid over the distal end of the second optical fiber and placed over the reflective foil so that it completely overlapped the ends of the foil. The tube was then exposed to heat until it shrunk down over the foil and thus completely sealed the junction from ambient radiation. An added advantage of the heat-shrinkable outer layer is that it not only secured the fibers in place, but also mechanically strengthens the junction.
Example 2 This example illustrates the use of the device of the invention with an oxygen gas sensor.
A nitrogen gas laser emitting substantially ~0 monochromatic radiation having a wavelength of 337 nm.
was coupled to the proximal end of the first optical fiber of the device illustrated in Example 1.
A drop of pyrenebutyric acid, a known fluorescent indicator for oxygen, was attached to the distal end of ~5 the second optical fiber of the device.
A suitable radiation detector was attached to the proximal end of the second optical fiber of the device and readings were taken for the intensity of emission radiation in the presence of ~Tarying concentrations of oxygen gas.
Pyrenebutyric acid, when excited by the above source radiation, emits fluroescent radiation at a wavelength of 396 nm. The intensity of this emitted radiation is quenched in the presence of oxygen and the --ll--reduction of the emitted signal gives a determination of the concentration of oxygen.
The results of the test using the device of the invention were as follows:
Oxygen Relative Concentration Intensity Intensity (0%) (~ = 39fi nm) Ratio Intensity (~ %) 0 137.60 1.0 7 94.95 1.45 21 62.97 2.19 100 21.65 6.36 The above results show the high signal resolution obtained with the device of the invention and the ability to obtain an accurate quantitative determina-tion of the oxygen concentration.
Example 3 This Example illustrates the use of the device of the invention with a carbon dioxide sensor in a liquid medium.
In a similar manner to that followed in Example 2, a nitrogen gas laser emitting substantially monochromatic radiation having a wavelength of 337 nm was coupled to the proximal end of the first optical fiber of the device illustrated in Example 1.
~5 A drop of carboxymethyl umbelliferone, a known pH
indicator, was attached to the distal end of the second optical fiber of the device. The indicator was coated with an aqueous gel containing 5 mM sodium bicarbonate and the coated indicator was encased in a carbon dioxide-permeable silicone membrane. The resulting system, when excited by the above source radiation, emits fluorescent radiation at 460 nm and acts as a carbon dioxide sensor.
A suitable radiation detector was attached to the proximal end of the second optical fiber of the device ', ~L r~
and readings were taken for the intensity of emission radiation in the presence of varying concentrations of carbon dioxide in deionized water.
The results of the test when the sensor was immersed in the deionized water were as follo~s:
Carbon Dioxide Relative Concentration Intensity Intensity (0~) ( ~ %) (~ = 460 nm) Ratio Intensity (~ %) 0 99.29 1.0 7 83.63 1.19 100 45.65 2.18 As in Example 2, the above results show the high signal resolution obtained with the device of the invention and the ability to obtain an accurate ~uantitative determination of the concentration of carbon dioxide in a liquid medium.
The device, according to the invention, provides many advantages over prior art optical sensors. Such advantages include:
1~ The use of separate optical fibers for source radiation and output radiation to the detector eliminates the need for dichroic beamsplitters and thus simplifies the radiation measurement system.
~) The splitting of source excitation radiation ~5 at the junction into two components: Component one, the minor component, travelling to the radiation detector, being useful for calibration; and component two, the major component, travelling to the distal end of the second optical fiber for excitation of a fluorescent indicator.
3) Source compensation of fluorescent measurement by using the ratio of component one of the excitation radiation to the fluroescent emission signal.
- 13 - 4680-~14 4) Little or no attenuation of emission radiation at the junction, thus maximizing the signal to the detector.
5) Elimination of additional components as in (1) and sub-stantially no loss of signal strength as in (~) allows optimal miniaturization of the sensor system.
With reference to Figure 2, in one embodiment of the system according to the invention, a first junction Jl which is of the type illustrated in Figure 1 couples a first optical fiber 1 to a second optical fiber 5. Located sequentially along the 1~ second optical fiber are two further junctions J2' J3 which, in like manner, couple the second fiber to additional first optical fibers.
Each of said first optical fibers is adapted to receive radiation from sources Sl, S2, S3.
Attached to the distal end of the second optical fiber is a radiation sensitive component 9. This component contains fluorescent indicators adapted to be excited by radiation of wave-lengths 1, 2 and 3 from sources Sl, S2 and S3, respectively. Upon excitation, said indicators emit fluorescent radiation, the inten-~0 sity of which is dependent upon the concentration of the substances under investigation.
The emission signals from the radiation sensitive compon-ent 9 travel substantially unattenuated along the second optical fiber 5 to the proximal end thereof where they are dispersed and measured by an appropriate detecting device 10 attached to said proximal end.
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The embodiment illustrated in Figure 3 comprises three first optical fibers l adapted to receive radiation from a single source S.
Each of said first optical fibers is coupled through a junction Jl' J2' J3 to a separate second optical fiber 5.
Each second op-tical fiber has a radiation sensitive com-ponent 9 attached to its distal end.
The proximal end of each second optical fiber is attached to a terminal of a radiation dispersing and measuring device 10 which, in this embodiment, comprises a grating and a two dimension-al radiation detector.
As shown in Figure 4, the signal from each second optical fiber is focussed by a concave holographic grating 11 onto a two dimensional array of radiation detectors 12.
Said array comprises, as shown in Figure 5, a series of linear sequences of radiation detectors 13; each linear sequence being adapted to receive and measure the signal from one of said second optical fibers.
Thus each signal provides a visual spectrum which gives ~0 a quantitative determination of the parameter being measured.
The system of the invention provides high signal re-solution and accurate quantitative detexmination of the parameters under investigation.