Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2000-08-18
2002-09-03
Palmer, Phan (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
C385S012000, C385S024000, C385S016000, C065S395000
Reexamination Certificate
active
06445861
ABSTRACT:
TECHNICAL FIELD
The invention relates to the field of fiber devices, and in particular, to integrated fiber optic sol-gel sensors and related technology.
BACKGROUND ART
The preparation of single and multicomponent glasses using sol gel processes has been known for about 50 years. Sol gel glasses can be prepared with dopant to modify the physical, electronic or optical properties of the material. Such modifications can include index of refraction, dielectric constant, optical transmission characteristics. Sol-gel materials have been used in combination with optical fibers for many applications, and there is significant R&D activity in the area of combining sol-gel materials with optical fiber for sensing applications. Examples of possible uses include chemical sensing, stress monitoring, pressure sensing, and temperature sensing, in the fields of biomedical monitoring and smart structures, for example.
The fiber optic sensor market has the potential for tremendous growth. To illustrate the potential for fiber optic sensing technologies, consider, for example, chemical sensing. Driven by their increased use in biomedical applications, fiber optic chemical sensors may have accounted for almost 60% of the total fiber optic sensor market in 1998. This corresponds to a revenue of $540 million for all chemical sensors.
As a specific example, there are very sensitive methods for the detection of phosphatases. The advantages of using an optical fiber sensor in such an application include the following: the volume of enzyme and substrate containing fluid solution needed for analysis can be smaller than in the other techniques, which is important because the substrates are very expensive; the sensor itself can be very small; and the sensor can be relatively inexpensive and therefore disposable.
Fiber optic sensors are a rapidly g owing field in other areas as well. Since fiber optics are lightweight, EMI immune, and passive, they are excellent candidates for a variety of newly emerging applications such as smart sensors. Smart sensors are embedded in a structure, e.g. an aircraft fuselage, and can allow for online real time health monitoring of the structure.
Some publications relating to fiber sensors are listed below:
1. “Measurement of Low Oxygen Concentrations by Phosphoescence Lifetime Using Fiber Optic”, Campo, Perez, et. al., IEEE 1998 Instrumentation and Measurement Conference
2. “An Integrated Optical Technology Based on Sol Gel Glasses on Silicon: The Nodes Project”, Yeatman, 1995 SBMO/IEEE MTT-S IMOC '95 Conference Proceedings
3. “Applications of sol-gel films in optical wavelength filters”, Blue, Mauchline, Stewart, Electronics Letters, 3
rd
Mar. 1994, Vol. 30, No. 5, pg 402
4. “Detecting Alpha Radiation by Scintillation in Porous Materials”, Keillor, Burggraf, IEEE Transactions on Nuclear Science, Vol 44, No. 5, Oct. 5, 1997, 1741-1746
5. “A Distributed Fiber Optic Sensor Based on Cladding Fluoresence”, Lieberman, Blyler, Cohen, Journal of Lightwave Technology, Vol. 8, No. 2, Feb. 2, 1990, 212-220
However, the existing technologies involving sol-gel fiber optic sensors have involved evanescent coupling to the fiber optic through sol-gels applied as an external media. Existing sol-gel sensors either have sol-gel as a thin film or deposited material along the outside of the optical fiber, or are in the shape of monoliths with dopants deposited on the surface of the monolith. Such optical seniors are usually engineered either by coating the surface of the optical fiber, or by attaching directly to the fiber, water-soluble systems contained in porous membranes.
The thin film or deposited material types operate through evanescent optical coupling by light being coupled from the outside film or material down to the core of the optical fiber such that the sensor information in the form of an optical signal can be guided down the core of the fiber. However, this method of coupling is disadvantageously optically lossy, allowing very little of the light in the cladding to actually be coupled for guidance in the core.
Another drawback is that the amount of sensor reagent is proportional to the amount of bulk sol-gel material processed due to the solubility limits of the sol-gel, and the amplitude of the sensor signal is directly proportional to the amount of sensor reagent. Therefore, the smaller the sol-gel volume, the smaller the effective volume for the sensing. In thin film applications, the thickness is disadvantageously less than 1 micron, because surface coating limits the thickness of the reagent/sol-gel solution.
In processes where sol-gel monoliths are fabricated, the dopant material is deposited into the pores. of the sol-gel material on the outside surface of the monolith. However, in the prior art, when sol-gel samples are polymerized successfully, they are subjected to high temperatures during the process which can disadvantageously fatigue an optical fiber. The deposition is done in this fashion due to the processing temperature required in the prior art for polymerization (approximately 1000 degrees C.). Also, disadvantageously, when the monolith is exposed to environmental elements, the dopants tend to leach out.
Applicant realized that it would be advantageous to have a fiber sol-gel sensor which overcame the above disadvantages and drawbacks of the prior art. Applicant realized that such a device would be a fiber having a sol-gel core. However, successful polymerization of sol-gel monoliths inside of a hollow core fiber such that the system becomes a functional waveguide was not known.
Therefore, a need existed for a fiber device having a sol-gel core, and a method for manufacturing same, which overcame the drawbacks and disadvantages of the prior art.
STATEMENT OF INVENTION
The invention relates to a process of fabricating fiber devices having a doped sol-gel core, a plurality of fiber device products made by the process, and a plurality of apparatus utilizing a fiber device product made according to the process.
It is, therefore, a principal object of this invention to provide sol-gel core fiber devices, and in particular, to provide an optical fiber sensor using sol-gel processing of monoliths inside a hollow core fiber.
It is another object of the invention to provide methods for producing the sol-gel core fiber devices.
These and other objects of the present invention are accomplished by the invention disclosed herein.
According to an aspect of the invention, the characteristics of sol-gel materials and the sensors made with these materials according to the invention, provide a number of advantages. These characteristics and advantages include their rigidity, their chemical inertness, their high porosity, that they are hydrophilic, their optical transparency, their good dynamic range, and their ease of processing.
The rigidity provides resistance to mechanical deformation. The is chemical inertness provides low chemical interaction with the environment. The high porosity entraps photometric reagents, for example, but leaves them exposed to exogenic analytes, with minimal chemical interaction or interference with the source and emitted light. The characteristic of being hydrophilic provides an increased availability of reagents. An improved dynamic range means that simultaneous measurement of several analytes by co-immobilized sensor reagents at different wavelengths is possible.
Also, since sol-gel changes color in the presence of certain chemicals, chemical monitoring is enhanced.
Further, using sol-gels eliminates the need for other equipment, e.g., signal processors, other sensors, in certain applications.
According to an aspect of the invention, a device is produced having a solid core monolith structure.
According to an aspect of the invention, it is an object to practice a process for manufacturing fiber optic sensors using hollow core optical fiber waveguides and customizable silica sol-gel cores.
According to an exemplary embodiment of the invention, an optical fiber sensor with a solid, monolithic, sol-gel core is produced. This distinguishes the
Manuel Michele V.
Ott Melanie N.
Shaw Harry C.
Palmer Phan
The United States of America as represented by the Administrator
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