Field of the Invention

[0001] The present invention relates generally to optical devices for measuring chemical components, and more particularly to a quasi-distributed optical fiber sensor and system for measuring chemical components, particularly the dissolved oxygen.

Background of the Invention

[0002] Among the important water quality factors in aquaculture is dissolved oxygen. The de facto standard for measuring dissolved oxygen concentrations in aqueous environment is using Clark sensor which involves the use of chemical analytes that need to be changed from time to time, and the membrane of the sensor is susceptible to punctures due to aquatic insects, improper handling and waterborne debris. Also, due to the limited length of electrical wiring that can be extended to the sensor head, the measurement can only be taken at the surface of the pond, which does not reflect the overall oxygen concentration in the aquatic pond.

[0003] Measurement of oxygen concentration at different locations in an aquatic pond can be achieved by adopting optical fiber sensor with quasi distributed arrangement. Dissolved oxygen sensing based on optical fiber can be realized using the principle of photo luminescent principle whereby a luminescent material such as Ruthenium is being excited by blue light which in turn emits energy in the red electromagnetic spectrum. If the excited Ruthenium material encounters an oxygen molecule, the excess energy is transferred to the oxygen molecule in a non-radiative manner. This decreases the fluorescence signal and the degree of decreasing fluorescence correlates to the partial pressure of oxygen around the sensing material. Such arrangement works for a single point sensor where the oxygen sensitive material is coated at one end of an optical fiber with blue light (acting as excitation source) is injected at the other end. To achieve quasi distributed sensing scheme, multiple sensing region need to be created along the optical fiber line. Hence, the oxygen sensitive material needs to be coated on various locations on the optical fiber. Interrogation of each oxygen sensitive material can be done by measuring the time delay between a short excitation blue light pulse propagating in the optical fiber to the sensor point and the subsequent sensor luminescence pulse returning to the front end of the optical fiber. Measurement of the oxygen concentration is achieved through luminescence lifetime detection which requires sophisticated opto-electronics setup. Alternatively, changes of luminescence intensity can also be observed for oxygen sensing. Interrogation of different sensor point along the continuous stretch of the optical fiber can be achieved by using different oxygen sensitive material coated on the sensing region which upon excitation, responds to different spectral wavelength unique for each material.

Summary of the Invention [0004] One aspect of the present invention provides a quasi-distributed optical fiber sensor for measuring a chemical component. In one embodiment, the quasi-distributed optical fiber sensor comprises a linear launching optical fiber at center; and a probe optical fiber enclosing the linear launching optical fiber; wherein the probe optical fiber contains a plurality of sensor elements sequentially located at its distal stretch, and wherein each sensor element contains a chemical component sensitive nano-material and is formed by etching the cladding first and then coating with the chemical component sensitive nano- material.

[0005] In another embodiment of the quasi-distributed optical fiber sensor, the chemical component is oxygen, and the chemical component sensitive nano-materials are oxygen sensitive nano-materials. In a further embodiment of the quasi-distributed optical fiber sensor, the oxygen sensitive nano-materials include Tris(4,7-diphenyl-l,10- phenanthroline)ruthenium(II), Platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-entafluorphenyl) - porphyrin, and Palladium(II)-5,10,l 5,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin. In yet another further embodiment of the quasi-distributed optical fiber sensor, the oxygen sensitive nano-materials are entrapped in an oxygen permeable and optically clear sol gel matrix for coating.

[0006] Another aspect of the present invention provides a quasi distributed optical fiber sensor system for measuring a chemical component. In one embodiment, the quasi distributed optical fiber sensor system comprises an excitation light source for providing an excitation light, a quasi-distributed optical fiber sensor optically coupled with the excitation light source, with a proximity end coupled to the excitation light source and a distal stretch with sequentially disposed chemical component sensitive nano-materials for emitting excited fluorescence lightwaves when encountered with the chemical component, a wavelength selection module optically coupled with the quasi-distributed optical fiber sensor for blocking the excited fluorescence lightwaves back to the excitation light source and filtering the excited fluorescence lightwaves, an optical switch optically coupled with the wavelength selection module for allowing the excited fluorescence lightwaves to pass for measurement, a spectrometer optically coupled with the optical switch for measuring the fluorescence intensities of the excited fluorescent lightwaves; and a microprocessor electronically coupled with the spectrometer, wherein the microprocessor is embedded with an algorithm for translating the measured fluorescent intensities into the concentration of the chemical component.

[0007] In another embodiment of the quasi-distributed optical fiber sensor system, the wavelength selection module comprises a wavelength selective coupler; and a plurality of filter ports; wherein the wavelength selection module allows the excitation light to pass, acts as an isolator to block the excited fluorescence lightwaves from entering back to the launching optical fiber and hence the excitation light source, and directs the excited fluorescence lightwaves to the plurality of filter ports; and wherein the plurality of filter ports correspond to the exact wavelength of the excited fluorescence lightwaves, so that each of the filter ports allows one fluorescence lightwave to pass through.

[0008] The objectives and advantages of the invention will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawings.

Brief Description of the Drawings

[0009] Preferred embodiments according to the present invention will now be described with reference to the Figures, in which like reference numerals denote like elements.

[0010] FIG 1 shows a schematic block diagram of a quasi distributed optical fiber sensor system for determining the oxygen partial pressures at three different locations in accordance with one embodiment of the present invention. Detailed Description of the Invention

[0011] The present invention may be understood more readily by reference to the following detailed description of certain embodiments of the invention.

[0012] Throughout this application, where publications are referenced, the disclosures of these publications are hereby incorporated by reference, in their entireties, into this application in order to more fully describe the state of art to which this invention pertains.

[0013] The present invention provides a quasi-distributed optical fiber sensor for measuring a chemical component at different locations or depths. In principle, the quasi- distributed optical fiber sensor is linear, and cladding etched at sequential locations and coated with a plurality of chemical sensitive nano-materials forming a quasi-distributed configuration. The chemical sensitive nano-materials can be luminescent. Thus, the quasi- distributed optical fiber sensor can measure a chemical component at different locations if horizontally disposed and at different depths if vertically disposed. The present invention also provides a system comprising the quasi-distributed optical fiber sensor for measuring a chemical component.

[0014] For the purpose of illustration, the measurement of dissolved oxygen employing the quasi-distributed optical fiber sensor and system of the present invention is described in detail hereinbelow.

[0015] Referring now to FIG 1, there is provided a schematic block diagram of a quasi distributed optical fiber sensor system for determining the oxygen partial pressures at three different locations in accordance with one embodiment of the present invention. As shown in FIG 1 , the quasi distributed optical fiber sensor system 1 comprises an excitation light source 2 for providing an excitation light, a quasi-distributed optical fiber sensor 3, a wavelength selection module 4, an optical switch 5, a spectrometer 6, and a microprocessor (e.g., computer) (not shown).

[0016] The quasi-distributed optical fiber sensor 3 comprises a linear launching optical fiber 31 at the center and a probe optical fiber 32 enclosing the linear launching optical fiber 3. The quasi distributed optical fiber sensor 3 has a proximity end coupled to the excitation light source 2 and a distal stretch. The probe optical fiber 32 contains three sensor elements 33, 34, 35 sequentially located at the distal stretch; each sensor element is formed by etching the cladding first and then coating with an oxygen sensitive nano- material; in one embodiment, the oxygen sensitive nano-materials are referred as oxygen sensitive nano-material 1, oxygen sensitive nano-material 2, and oxygen sensitive nano- material 3 respectively. In one embodiment, the oxygen sensitive nano-material is luminescent including Ruthenium, Platinum and Palladium. The exemplary oxygen sensitive nano-materials include Tris(4,7-diphenyl-l,10-phenanthroline)ruthenium(II), Platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluo henyl)-porphyrin, Palladium(II)- 5,10,15,20-tetrakis-(2,3,4,5,6-pentafiuorphenyl)-porphyrin. Upon excitation from a blue light source (450 nm), the three oxygen sensitive luminescent nano-materials (Ruthenium, Platinum, Palladium) emit fluorescences at roughly three different wavelengths, 620 nm, 650 nm and 670 nm respectively. In one embodiment, the oxygen sensitive nano-material is entrapped in an oxygen permeable and optically clear sol gel matrix for coating.

[0017] The wavelength selection module 4 comprises a wavelength selective coupler 41 and three filter ports 42,43,44, where the wavelength selection module 4 is optically coupled with quasi-distributed optical fiber sensor 3 and disposed between the proximity end and the first sensor element 33 from the proximity end. The wavelength selective coupler 41 allows the excitation light to pass and at the same time acts as an isolator to block the fluorescence lightwaves from the sensor elements 33,34 5 from entering back to the launching optical fiber 3 and hence the excitation light source 2. The wavelength selective coupler 41 directs the fluorescence lightwaves to the filter ports 42,43,44, where the three filter ports 42,43,44 corresponds to the exact wavelength of the 600 nm, 650 nm and 670 nm respectively, so that each of the filter ports allows one fluorescence lightwave to pass through.

[0018] The optical switch 5 is optically coupled with the three filter ports 42,43,44, and allows the filtered fluorescence lightwaves to alternately pass to the spectrometer 6 being optically coupled with the optical switch 5. The spectrometer 6 comprises a photodetector 61, where the photodetector 61 measures the fluorescence intensities of the fluorescence lightwaves one at a time based on the switching rate of the optical switch 5.

The florescence intensity from the spectrometer 6 is then outputted to the microprocessor. The microprocessor relates the fluorescence intensities to the partial pressure of oxygen via an embedded algorithm that translates the intensity measurement into oxygen values.

[0019] It is to be noted that all optical and electronic components for the present invention are conventional unless otherwise indicated.

[0020] The operation of the quasi distributed optical fiber sensor system shown in FIG 1 is briefly described herein. The excitation light source 2 sends an excitation light with a wavelength at roughly 475 nm to the launching optical fiber 31, and the excitation light passes through the wavelength selective coupler 41 and the probe optical fiber 32. The 457 nm excitation lightwave at the sensor element 33 then encounters and excites the first oxygen sensitive luminescent nano-material, Tris(4,7-diphenyl-l,10- phenanthroline)ruthenium(II), where the excited Tris(4,7-diphenyl-l,10- phenanthroline)ruthenium(II) emits a fluorescence lightwave at roughly 600 nm. The same 475 nm excitation lightwave further travels over the sensor elements 34,35 and sequentially excites the second and third oxygen sensitive luminescent nano-materials, Platinum(II)-5, 10, 15,20-tetrakis-(2,3 ,4,5,6-pentafluorphenyl)-porphyrin, and Palladium(II)-5, 10, 15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin, where the excited Platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6- entafluo henyl)-porphyrin and Palladium(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluo henyl)-porphyrin emits fluorescence lightwaves at roughly 650 nm and 670 nm respectively.

[0021] When the excited oxygen sensitive nano-materials encounter oxygen molecules around the sensor elements 33,34,35, the excess energy will be transferred to the oxygen molecules, resulting in the decrease of the fluorescence intensities of the fluorescence lightwaves. The decrease of the fluorescence intensities correlates to the partial oxygen pressure at the sensor elements 33,34,35. The fluorescence lightwaves then travel back to the wavelength selective coupler 41 and are directed to the filter ports 42,43,44 which corresponds to the exact wavelength of the 600 nm, 650 nm and 670 nm.

[0022] The filtered fluorescence lightwaves are then alternately being allowed to pass the optical switch 5 which is coupled into the spectrometer 6. The fluorescence intensities of the fluorescence lightwaves are being measured by the spectrometer 6 one at a time based on the switching rate of the optical switch 5. The florescence intensity from the spectrometer 6 is then relates to the partial pressure of oxygen via an algorithm that translates the intensity measurement into oxygen values.

[0023] While the present invention has been described with reference to particular embodiments, it will be understood that the embodiments are illustrative and that the invention scope is not so limited. Alternative embodiments of the present invention will become apparent to those having ordinary skill in the art to which the present invention pertains. Such alternate embodiments are considered to be encompassed within the scope of the present invention. Accordingly, the scope of the present invention is defined by the appended claims and is supported by the foregoing description.