The present teachings relate to the field of fiber optic sensor systems. More particularly, the present teachings relate to methods and devices for a single wavelength fiber optic sensor system.
Fiber Bragg gratings (FBGs) change their reflection characteristics when subjected to changes in their environmental conditions. Accordingly, FBGs are widely used as fiber optic sensors to measure changes in environmental conditions (characteristics, parameters), such as, for example, changes in temperature, stress, moisture and chemical composition in the environment.
As known to a person skilled in the art, an FBG is a periodic structure of, that is embedded within an optical fiber path. The periodic structure of the FBG makes a light reflection of the FBG dependent on a wavelength of the light. Accordingly, a spectral response of the FBG can be tailored for different applications and as needed, via specific design of the periodic structure.
Current fiber optic sensor systems using FBGs may include a light source that emits a broad-wavelength spectrum (BWS) or a light source that is wavelength tunable (WT). Such systems measure a change in the spectral response of the FBG due to one or more changes in the environmental conditions. As known to a person skilled in the art, the FBG can be tailored/designed to be more sensitive with respect to changes of a target environmental parameter, and less sensitive with respect to changes of other environmental parameters.
In such systems using BWS or WT light sources, sensing at different locations along an optical fiber can be provided by including a respective FBG at each of the different locations. However, such approach typically may require that each of the FBGs have a unique and different spectral response. In some prior art implementations, expensive and bulky spectrum analyzers may be used to measure the different spectral responses of the FBGs, but these do not lend themselves well for installation in harsh and/or tight environments.
Another prior art approach for sensing an FBG along an optical fiber may include measurement of a change in the FBG reflection amplitude at a single wavelength. Such approach allows use of a simple laser that can be pulsed. However, in order to provide an accurate measurement of a change in characteristic (i.e., reflection amplitude) of the FBG, knowledge of an absolute value of the power (amplitude) of a light pulse transmitted through the optical fiber is required. This can be achieved via a calibration of the laser power (output) prior to the transmitting, or by measurement of a reflection having a known amplitude during use/measurement. However, either one of these two methods for evaluating an absolute value of the power of the transmitted light pulse may be corrupted if, for example, the laser power and/or a loss through the optical fiber change during the measurement. Known in the art implementations for sensing multiple FBGs along an optical fiber based on a simple (single wavelength) laser may build on the single FBG implementation described above with added complexity (and cost) to the fiber optic sensor system, such as, for example, added tunable optical filter elements, optical circulators, and other, to allow differentiation of light reflected from different FBGs from a combined reflected light.
It follows that there is a need for an FBG based fiber optic sensor system that is cost effective, compact and expandable from a single location sensing to multiple locations sensing. The present teachings disclose such system.
According to a first aspect of the present disclosure, a sensor is presented, the sensor comprising: a first fiber Bragg grating (FBG) arranged within an optical fiber path, the first FBG having a first spectral response; a second FBG arranged within the optical fiber path in proximity of the first FBG, the second FBG having a second spectral response; wherein the sensor is configured for sensing of an environmental parameter over a range of values of the environmental parameter, and wherein over said range of values, respective first and second slopes of the first and second spectral responses overlap at a spectral region that includes a measurement wavelength used for sensing of the environmental parameter.
According to a second aspect of the present disclosure, a sensor is presented, the sensor comprising: a first fiber Bragg grating (FBG) arranged within an optical fiber path, the first FBG having a first spectral response; a second FBG arranged within the optical fiber path in proximity of the first FBG, the second FBG having a second spectral response; wherein the sensor is configured for sensing of an environmental parameter over a range of values of the environmental parameter, and wherein over said range of values, the first and second spectral responses overlap at a spectral region that includes a measurement wavelength used for sensing of the environmental parameter.
The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present disclosure and, together with the description of example embodiments, serve to explain the principles and implementations of the disclosure.
Throughout this description, embodiments and variations are described for the purpose of illustrating uses and implementations of the inventive concept. The illustrative description should be understood as presenting examples of the inventive concept, rather than as limiting the scope of the concept as disclosed herein.
The present disclosure describes methods and devices for a single wavelength fiber optic sensor system that is cost effective, compact and able to operate in harsh environments. Such system can be packaged in a light weight, compact manner, and robust to environmental changes, such as, for example, changes in temperature, moisture, shock and vibration.
The single wavelength fiber optic sensor system according to the present teachings can be adapted to use a larger number of FBG sensors embedded within a single optical fiber. Such FBG sensors may be used to monitor/measure changes in environmental conditions, such as, for example, changes in temperature, strain, humidity, etc. For example, the FBG sensors can be packaged and/or designed in a manner to be sensitive to one of the environmental parameters while remaining insensitive to other environmental parameters.
As described above, the change in the environmental condition may be in view of a change (in value) of any environmental parameter that can affect the environmental condition, such as, for example, a change in temperature, strain, humidity, etc. Furthermore, the structures defining each of the FBGs (e.g., FBG1, FBG2) may be designed to provide a desired shape of the spectral response, including shapes and positions of the slopes (leading and trailing slopes) and width of the peak (top, substantially flat, portion).
As can be seen in
ΔN(T1−T2)=[ΔR(T1)−ΔR(T2)]/[ΔR(T1)+ΔR(T2)],
as the indicator of the relative change in the value of the environmental parameter. For example, if the environmental condition T1 is in view of a temperature value, t1, and the environmental condition T2 is in view of a temperature value, t2, then the teachings according to the present disclosure measure a relative difference (t1−t2) by using the normalized difference, ΔN(T1−T2), given above. As person skilled in the art will appreciate that such normalized difference, ΔN(T1−T2), varies with respect to a change in the environmental condition, but it is insensitive to any change of: a laser power used to provide a light source to the FBGs (FBG1, FBG2); and/or loss though an optical fiber used to guide the light source to the FBGs.
With continued reference to
According to an exemplary embodiment of the present disclosure, FBG1 and FBG2 are designed to maintain overlapping slopes in a range of values of an environmental parameter of interest at the measurement wavelength λm. In other words, over said range of values, respective slopes of the spectral responses overlap at a spectral region that includes the measurement wavelength λm. For example, if the environmental parameter of interest is temperature, and the range of values is 5 degrees Celsius to 85 degrees Celsius, then FBG1 is designed so that for all values of temperatures in that range: the corresponding shift in the spectral response of FBG1 maintains the measurement wavelength λm within the trailing (e.g., falling) slope of FBG1; and the corresponding shift in the spectral response of FBG2 maintains the measurement wavelength λm within the leading (e.g., rising) slope of FBG2. It should be notes that the extent of shift of respective spectral responses of FBG1 and FBG2 responsive to a change in value of the environmental parameter need not necessarily be equal, so long that overlapping slopes can be maintained as discussed above. It should also be noted that the peak values of the spectral responses of FBG1 and FBG2 need not be substantially same as shown in
According to an exemplary embodiment of the present disclosure, FBG1 and FBG2 are designed so that over the range of values of the environmental parameter of interest, a slope of the spectral response of the one of the two FBGs (FBG1 and FBG2) overlaps with the peak region of the spectral response of the other one of the two FBGs, as shown in
Based on the description above with reference to
With continued reference to
As shown in
With continued reference to
With further reference to
Accordingly, in view of the above embodiments, methods and devices have been disclosed that enable a single wavelength fiber optic sensor system including a plurality of FBGs.
It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of applicable approaches. Based upon design preferences, the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order and are not meant to be limited to the specific order or hierarchy presented.
Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. A storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.
The present application claims priority to U.S. Provisional Application No. 63/009,668 filed on Apr. 14, 2020, the contents of which are incorporated herein by reference in their entirety.
Number | Name | Date | Kind |
---|---|---|---|
5442169 | Kunz | Aug 1995 | A |
5848204 | Wanser | Dec 1998 | A |
6024488 | Wu | Feb 2000 | A |
6525308 | Schmidt-Hattenberger | Feb 2003 | B1 |
7697121 | Coroy | Apr 2010 | B1 |
7899105 | Hargis | Mar 2011 | B1 |
20020027944 | Helmig | Mar 2002 | A1 |
20040052444 | Moslehi | Mar 2004 | A1 |
20040067003 | Chliaguine | Apr 2004 | A1 |
20040245444 | MacDougall | Dec 2004 | A1 |
20050111793 | Grattan | May 2005 | A1 |
20060013534 | Bohnert | Jan 2006 | A1 |
20080106745 | Haber | May 2008 | A1 |
20160123715 | Froggatt | May 2016 | A1 |
20170075064 | Docter | Mar 2017 | A1 |
20170238821 | Hayes | Aug 2017 | A1 |
20170334574 | Wilson | Nov 2017 | A1 |
20190285487 | Seeley | Sep 2019 | A1 |
20200271485 | Seeley | Aug 2020 | A1 |
20210231526 | Seeley | Jul 2021 | A1 |
Number | Date | Country | |
---|---|---|---|
20210318183 A1 | Oct 2021 | US |
Number | Date | Country | |
---|---|---|---|
63009668 | Apr 2020 | US |