The present invention relates to evanescent field optical fiber devices, including optical fiber sensors.
Evanescence based fiber optic sensors have received considerable attention in the past years due to their widespread applications in various parameter measurements such as temperatures, pressures and of biological and chemical materials that may be present in an environment or sample of interest.
Various techniques, well known in the art, have been developed to access the evanescent field in an optical fiber. For example, an optical fiber may be tapered by stretching it while it is heated, e.g. over a flame. Another technique is by polished coupler in a glass block to protect the optical fiber during the grinding and polishing steps. A third technique entails removal of a portion of the cladding by mechanical or chemical means. However, when a portion of the cladding of an optical fiber is removed to access the evanescent field, the fiber already of minute diameter is increasingly more fragile and delicate. Although the third technique may be carried out in very specialized circumstances such as in a laboratory, it is very difficult to manufacture and difficult to use.
Therefore, there is a need for improved techniques for use of optical fibers as components of optical sensors and such sensors that have good mechanical resistance and, of course, that are easy to use and to manufacture. Such a need also exists for improved techniques for use of optical fibers in components of systems using optical fibers, such as optical fiber communications systems, including couplers, splitters, repeaters, switchers, amplifiers, attenuators, isolators and the like.
One approach for optical sensors is described in U.S. patent application 2004/0179765 in which an optical fiber is coupled or connected to a larger optical waveguide in which a portion of the cladding, and optionally the core, has been removed using any suitable known techniques in the art, to permit access to the evanescent field. However, to be put into practice, this type of sensing device requires an alignment or axial coupling of two or more optical fibers with a separate optical waveguide of far larger diameter. This step is not only complex but also requires very precise alignment in order to minimize the loss of light energy.
Thus, it is desired to improve on evanescence based fiber optic sensors, having a good mechanical resistance with improved durability and ease of assembly and use.
The present invention reduces the difficulties and the disadvantages of the prior art by reinforcing an optical fiber itself without, for example, the need of connecting the latter to another optical waveguide.
The present invention relates to an evanescent field optical fiber device comprising one or more optical fibers wherein a portion of said one or more fibers is without coating, and a support which provides for the mechanical integrity of the one or more optical fiber and for access of the evanescent field without impairing the optical fiber.
More particularly, the present invention provides an evanescence based optical fiber device comprising one or more optical fibers as above and a support which assures mechanical strength of the optical fiber wherein one or more grooves has been machined in the support and in a cladding portion of the one or more optical fibers in order to gain access to the evanescent field.
In a further embodiment, the present invention relates to the use of a support in the mechanical or chemical removal of cladding from an optical fiber for use in an evanescence based fiber optic device.
Another embodiment is the method of using the support for the mechanical or chemical removal of cladding from an optical fiber for use in an evanescence based fiber optic device.
A further embodiment of the present invention is such a support for one or more optical fibers or such optical devices, comprised of shape memory material.
In order that the invention may be more readily understood, currently preferred embodiments will now be further described by way of example with reference to the accompanying drawings in which:
The present invention is based on a particular use of devices as a support for optical fibers in optical fiber devices, such as optical fiber sensors, couplers, splitters, repeaters, switchers, amplifiers, attenuators, isolators and the like. Such devices are of the type as described in U.S. Patent Nos. 7,066,656 and 7,121,731, and WO 2005/040876 published May 6, 2005. A skilled person would understand that the optical fiber will generally comprises at least one core, a cladding and a protective coating layer. For simplicity, we refer herein to cladding only, but it will be understood that when discussing the removal of cladding for the purpose of practicing the present invention, this will include the removal of any other coating on an optical fiber, as may be necessary.
The present invention is herein described in more detail in an embodiment relating to optical fiber sensors, although a skilled person will readily appreciate and be able to put into practice other embodiments of the invention as described herein and based on the following teachings.
Referring to
The support of the present invention may be made of any of several materials depending on its use and on the particular environment in which the support is used. For example, the support of the present invention may be made from a shape memory material. For the purposes of the present application, with respect to shape memory material (SMM), reference may be made to AFNOR Standard “Alliages à mémore de former—Vocabulaire et Mesures” A 51080-1990.
Materials, which are suitable for the support of the present invention, will illustrate a very low Young's modulus (elastic modulus) and/or pseudo elastic effect. Pseudo elastic effect is encountered in SMM. Concerning the shape memory effect, when the material is below a temperature (MF), which is a property dependent on the particular SMM, it is possible to strain (deform) the material from about some tenths of a percent to more than about eight percent, depending on the particular SMM used. When the SMM is heated above a second temperature (AF), which is also dependent on the particular SMM as well as the applied stress, the SMM will tend to recover its assigned shape. If unstresses, the SMM will tend toward total recovery of its original shape. If a stress is maintained, the SMM will tend to particularly recover its original shape. Concerning the pseudo elastic effect, when the SMM is at a temperature greater than its (AF), it may be strained at particularly higher rates, that is exhibiting non-used elasticity, arising from the shape MEMORY properties. Initially, in the SMM when stressed the strain will increase linearly, as in a used elastic material. However, at an amount of stress, which is dependent on the particular SMM and temperature, the ratio of strain to stress is no longer linear, strain increases at a higher rate as stress is increasing at a lower rate. At a particular higher level of stress, the increase in strain will tend to become smaller. This non-linear effect exhibited by SMM a temperature above (AF) may manifest itself as a hysteresis like effect, wherein on the release or reduction of stress the reduction in strain will follow a different curve from the one manifest as stress was increased, in the manner of a hysteresis like loop.
An example of such above material would be a shape memory alloy (SMA). Examples concerning activation of the shape memory element in a SMA include D.E. Muntges et al., “Proceedings of SPIE”, Volume 4327 (2001), pages 193-200 and Byong-Ho Park et al., “Proceedings of SPIE”, Volume 4327 (2001), pages 79-87. Miniaturized components of SMA may be manufactured by laser radiation processing. See for example, H. Hafer Kamp et al., “Laser Zentrum Hannover e.v.”, Hannover, Germany [publication].
The support of the present invention may, for example, be made from a polymeric material such as isostatic polybutene, shape ceramics such as zirconium with some addition of Cerium, Beryllium or Molybdenum, copper alloys including binary and ternary alloys, such as Copper-Aluminum alloys, Copper-Zinc alloys, Copper-Aluminum-Beryllium alloys, Copper-Aluminum-Zinc alloys and Copper-Aluminum-Nickel alloys, Nickel alloys such as Nickel-Titanium alloys and Nickel-Titanium-Cobalt alloys, Iron alloys such as Iron-Manganese alloys, Iron-Manganese-Silicon alloys, Iron-Chromium-Manganese alloys and Iron-Chromium-Silicon alloys, Aluminum alloys, and high elasticity composites which may optionally have metallic or polymeric reinforcement.
In use, the fiber conduit is enlarged by deforming the support of the present invention in any suitable way. Without limitation, an optical fiber may be inserted into and positioned in the support in any manner as described in the aforementioned U.S. Patent Nos. 7,066,656 and 7,121,731, and WO 2005/040876 published May 6, 2005, for the purpose of practicing the present invention. For example and generally, a constraint is applied to the support which will induce an expansion of the fiber conduit for insertion of an optical fiber. Removal of the constraint will allow retention of the optical fiber within the fiber conduit of the support which then applies a uniform radial pressure along the fiber. At this stage, a portion of the cladding of the optical fiber can be safely removed for accessing the evanescent field by any known techniques in the art as, for example, mechanically or by chemical means, the mechanical resistance of the optical fiber being now adequately secured.
There are several manners to use the support of the present invention in relation with an optical fiber in order to have access to the evanescent field, for use an evanescent field optical sensor and for the making of such evanescent field optical sensor. For example, as shown in
Furthermore, in order to obtain a high-quality sensor, the portion removed from the cladding of the optical fiber maintained by the support may be further polished by any suitable techniques known in the art as, for example, by the use of a CO2 laser as described in Nowak (Nowak, K. M. (2006) .
After polishing the exposed cladding portion of the optical fiber, it is possible to apply a substrate in a manner known in the art on the polished surface of the optical fiber which shows a substantial variation of its refractive index in relation with the parameter to measure (temperature, pressure, shear, concentration of a particular chemical, presence and concentration of an agent, etc). This is well demonstrated in
In order to increase the absorption of the substrate and improve the precision of the sensor, one could add a thin layer of metal (few nanometers of thickness) over the polished surface of the exposed cladding before applying the substrate. This is clearly shown in
In a further aspect of this invention illustrated in
Referring now to
Furthermore, one would understand that it is possible to apply the same principle as described above to an optical fiber having a multitude of cores. For example, if an optical fiber has two cores, the dilation and the modification of the refractive index of the substrate would alter the coupling between the four cores.
In a further embodiment illustrates in
Turning now to
Firstly, for the design based on reflection (
Secondly, regarding the design based on transmission, it is possible to connect several evanescent field optical fiber sensors in series along a single optical fiber to obtain different information from each of the sensors.
Moreover, the addition of Bragg grating within the fiber before and after the active zone allows a significant augmentation of the sensitivity of the device in order to obtain usable values. The Bragg grating reflects particular wavelengths of light and transmits all others. This is clearly illustrated in
Polychromatic light travels within an optical fiber as an excitation signal. The variation in absorption of the evanescent wave is generated by the variation of the studied parameter. This absorption strongly depends from the excitation signal wavelength, i.e. the detection of a certain parameter is related to a specific wavelength while the detection of another parameter requires another wavelength. The Bragg grating allows the desired wavelength to be reflected according to the Bragg conditions while allowing the other wavelength to continue as transmitted in the fiber including to other sensors. The value of interest to be measured by each individual sensor is captured and recovered by analysis of the wavelength corresponding to the value associate with a particular sensor.
In a further embodiment, a device such as shown in
Furthermore, in order to rapidly and easily control the transmitted power within an optical fiber, it would be appreciated that the device of the present application could also be used as an attenuator in order to attenuate the signal travelling within the fiber. Similarly, it could also be used as a commutator.
It will be understood by the skilled person, that number of the grooves, the dimension and sizing of the grooves and the spatial orientation and the spacing between the grooves from each other can all be accomplished by known mechanical or chemical means. The skilled person would know how to select the appropriate components (optical fibers, substrate, Bragg grating, wavelength, support material, etc) for the purpose of putting the present invention into practice as described herein.
It will also be appreciate that these types of evanescence based optical fiber sensors comprising of a support with optical fiber all as described herein can be fabricated to have utility in extreme conditions such as a harsh fluid stream or under other harsh physical conditions, for example in measurement of fractional streams in petroleum or chemical processing; or extractions; aeronautic and aerospace applications and military applications including in detection of dangerous chemical and biological agents.
Further, it will be appreciated from the above description that the present invention may include all kinds of optical fibers devices such as couplers, splitters, repeaters, switchers, amplifiers, attenuators, isolators and the like.
While the above description constitutes the preferred embodiments, it will be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning of the accompanying claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CA2008/001652 | 9/18/2008 | WO | 00 | 8/10/2010 |
Number | Date | Country | |
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60973264 | Sep 2007 | US |