Optical sensing system

Abstract

To provide a sensing system including optical fibers.SOLUTION: A set of wavelength shift sensors are inscribed in an optical fiber. The set of wavelength shift sensors includes at least one first wavelength shift sensor configured to reflect a first wavelength band of input light as a first optical output signal. The first wavelength shift sensor has a first value of an optical characteristic that changes intensity of the first optical output signal. At least one second wavelength shift sensor is configured to reflect a second wavelength band of the input light as a second optical output signal. The second wavelength shift sensor has a second value of the optical characteristic that changes intensity of the second optical output signal, in which the second value is different from the first value.SELECTED DRAWING: Figure 2A

Description

Background Art

[0001] Broadband light is used as input light in many optical sensing applications. In a wavelength multiplexing sensing system, broadband light can be used as input light to many optical fiber sensors arranged along a single optical fiber. For example, a number of fiber Bragg grating (FBG) sensors can be arranged at different positions of the optical fiber, and each FBG sensor reflects a different wavelength band. Each FBG sensor reflects a different spectral portion of the broadband input light as output light from the sensor. The output light of each of the plurality of FBG sensors can be spectrally decomposed, enabling the acquisition of sensing information from each sensor. This technology is often referred to as wavelength multiplexing optical sensing.

Summary of the Invention

[0002] Embodiments described herein include a sensor system including an optical fiber. A set of wavelength shift sensors is inscribed on the optical fiber. The set of wavelength shift sensors includes at least one first wavelength shift sensor configured to reflect a first wavelength band of input light as a first optical output signal. The first wavelength shift sensor has a first value of an optical property that changes the intensity of the first optical output signal. At least one second wavelength shift sensor is configured to reflect a second wavelength band of input light as a second optical output signal. The second wavelength shift sensor has a second value of an optical property that changes the intensity of the second optical output signal, and the second value is different from the first value.

[0003] Embodiments include a method for manufacturing a sensor system comprising etching a pair of wavelength shift sensors onto an optical fiber. The pair of wavelength shift sensors includes at least one first wavelength shift sensor configured to reflect a first wavelength band of input light as a first optical output signal. The first wavelength shift sensor has a first value of an optical property that affects the intensity of the first optical output signal. At least one second wavelength shift sensor is configured to reflect a second wavelength band of input light as a second optical output signal. The second wavelength shift sensor has a second value of an optical property that affects the intensity of the second optical output signal, the first value being different from the second value.

[0004] The method includes generating input light for a sensor system. The sensor system includes an optical fiber. A pair of wavelength shift sensors is engraved on the optical fiber. The pair of wavelength shift sensors includes at least one first wavelength shift sensor having a first value of optical properties. At least one second wavelength shift sensor has a second value of optical properties that is different from the first value. A first wavelength band of the input light is reflected as a first optical output signal. The first value of optical properties affects the intensity of the first optical output signal. A second wavelength band of the input light is reflected as a second optical output signal. The second value of optical properties affects the intensity of the second optical output signal. [Brief explanation of the drawing]

[0005] Throughout this specification, refer to the attached drawings. [Figure 1] This shows the power output of broadband light sources, including superluminescent light-emitting diodes (SLEDs). [Figure 2A] A sensing system, according to one embodiment, is shown, which includes an optical fiber and a compensated array of multiple FBG sensors engraved along the optical fiber. [Figure 2B] One embodiment of the sensing system is shown, which includes an optical fiber and a compensated array of FBG sensors engraved along the optical fiber having one or more bends. [Figure 3] The system, according to some embodiments, includes an optical fiber having a compensated sensor array, which includes first and second FBG sensors engraved on the top, having different reflectances due to refractive index modulation. [Figure 4] Figure 3 shows graphs illustrating the refractive index modulation of the first and second FBG sensors. [Figure 5] One embodiment shows a sensor system including an optical fiber having a compensated sensor array including a first FBG sensor and a second FBG sensor engraved on the top, wherein the first and second sensors have different reflectances due to different sensor lengths. [Figure 6] This figure shows a system, according to some embodiments, that includes an optical fiber having a compensated array of first and second FBG sensors engraved on the top, where each sensor has a different attenuation at the sensor's center wavelength or wavelength band. [Figure 7A] A comparison graph is provided showing the reflected light from multiple sensors in a system including an uncompensated sensor array (Figure 7A) and the reflected light from multiple sensors in a system including a compensated sensor array system (Figure 7B), where the sensors have different reflectances to compensate for spectral non-uniformity of the light source. [Figure 7B] A comparison graph is provided showing the reflected light from multiple sensors in a system including an uncompensated sensor array (Figure 7A) and the reflected light from multiple sensors in a system including a compensated sensor array system (Figure 7B), where the sensors have different reflectances to compensate for spectral non-uniformity of the light source. [Figure 8] This describes a wavelength-multiplexed sensor system, including a compensated array of multiple FBG sensors arranged on a single optical fiber, according to some embodiments. [Figure 9] This is an ideal representation of light reflected from an FBG sensor deployed on a single-mode optical fiber cable. [Figure 10A] This block diagram shows a demultiplexer output, a wavelength shift detector, and a portion of an analyzer according to some embodiments. [Figure 10B] A wavelength shift detector according to some embodiments is shown in more detail.

[0006] Drawings are not necessarily to scale. Similar numbers used in drawings refer to similar components. However, it should be understood that the use of numbers to refer to components in a given drawing is not intended to limit components in another drawing labeled with the same number. [Modes for carrying out the invention]

[0007] The power output of broadband light sources is typically non-uniform with respect to wavelength. Figure 1 shows the power intensity of broadband light sources, including superluminescent light-emitting diodes (SLEDs). As shown in Figure 1, the intensity of a broadband light source varies with wavelength across the entire spectrum of the light source.

[0008] Broadband light sources are useful for wavelength-multiplexed optical sensing because they can be used as input light for many FBG sensors that are arranged on a single optical fiber and reflect light in many different wavelength bands. If the intensity (or optical power) of the input light is non-uniform with respect to wavelength, and the sensors have substantially the same response in those wavelength bands, then the intensity (or optical power) of the light reflected by the FBG sensors arranged along the optical fiber will also be non-uniform. Referring again to Figure 1, in an uncompensated sensor array, FBG sensors with wavelength bands corresponding to wavelengths close to the peak of the intensity-versus-wavelength curve of the input light will reflect light of higher intensity. These FBG sensors with wavelength bands corresponding to wavelengths close to the edge of the intensity-versus-wavelength curve of the input light will reflect light of lower intensity. Systems that acquire information from FBG sensors often use a minimum intensity threshold to isolate the received signal from noise. If the measured signals from all FBG sensors are significantly greater than the minimum intensity threshold, the noise characteristics of the system are improved. Therefore, it may be useful to use the compensated FBG sensor array described herein, as the intensity of the reflected light from the sensors is more uniform. While the embodiments described herein use an FBG sensor as an example of a wavelength shift sensor, it should be understood that the sensor may include any other type of wavelength shift sensor (e.g., a Fabry-Perot sensor).

[0009] Some embodiments described herein relate to systems and methods for compensating for spectral non-uniformity of input light to a plurality of FBG sensors engraved along an optical fiber. Figure 2A shows a sensing system 201 according to some embodiments, which includes an optical fiber 275 and a compensated array including a plurality of FBG sensors 210-260 engraved at various positions along the optical fiber 275. Each FBG sensor 210-260 is configured to receive input light from a light source 290 and reflect a portion of the input light in the wavelength band of the FBG sensors 210-260.

[0010] The compensated sensor array of system 201 includes at least a first FBG sensor 210 having a first value of optical properties. The first FBG sensor 210 is configured to reflect a first wavelength band as a first optical output signal from the first FBG sensor 210. The compensated sensor array of system 201 includes at least a second FBG sensor 220 having a second value of optical properties. The second FBG sensor 220 is configured to reflect a second wavelength band of input light as a second optical output signal from the second FBG sensor 220. The optical properties affect the intensity of the light reflected by sensors 210, 220. The difference between the first and second values ​​of optical properties is configured to reduce the difference between the intensity of the first optical output signal of the first FBG sensor 210 and the intensity of the second optical output signal of the second FBG sensor 220.

[0011] One potential cause of spectral non-uniformity in the input light to the multiple FBG sensors 210-260 is the spectral non-uniform intensity output of the input light source 290, as previously mentioned in relation to Figure 1. Another potential cause of non-uniformity in the input light to the multiple FBG sensors 210-260 is scattering loss in the optical fiber 275. For example, the first FBG sensor 210, located closer to the light source 290, can receive higher intensity input light, while the second FBG sensor 220, located further away from the light source 290, can receive relatively lower intensity input light due to scattering loss that occurs as the input light travels along the optical fiber 275. In these situations, the difference between the first and second values ​​of the optical properties may be based on the distance between the sensors.

[0012] As shown in Figure 2B, in some configurations of the sensing system 202, the optical fiber 275 may be configured to include one or more bends 285. The bends 285 increase scattering loss, allowing FBG sensors 210-230 positioned between the light source 290 and the bends 285 to receive higher intensity input light compared to lower intensity input light received by FBG sensors 240-260 positioned behind the bends 285.

[0013] For example, to compensate for variations in input light due to distance between sensors, scattering loss, bending of optical fibers, spectral non-uniformity of the input light source, and / or other sources of variation, at least one of the FBG sensors 210 arranged along the optical fiber 275 may have one or more optical characteristic values ​​that differ from one or more optical characteristic values ​​of at least one other FBG sensor 220. The difference in the one or more optical characteristic values ​​of the first and second FBG sensors 210, 220 is configured to reduce the difference between the first optical output signal of the first FBG sensor 210 and the second optical output signal of the second FBG sensor 220. For example, in some embodiments, the compensated FBG sensor array can make the intensities of the first and second optical output signals substantially equal, or within 10% of each other, or within 20% of each other. For example, the difference in intensity between the first and second optical signals may be reduced by 5%, 25%, or even 50% when compared to a system where the value of one or more optical properties of the first sensor in the first wavelength band is substantially equal to the value of the optical properties of the second sensor in the second wavelength band.

[0014] In some embodiments, the adaptive optics characteristic having different values ​​for the first and second FBG sensors is reflectance. Figure 3 shows a system 300, according to some embodiments, that includes an optical fiber 375 having a compensated sensor array including first and second FBG sensors 310, 320 having different reflectances, engraved on the top. It should be noted that although the sensing system 300 in Figure 3 shows two FBG sensors 310, 320, more FBG sensors may be arranged on the optical fiber 375. The first FBG sensor 310 reflects a first wavelength band, and the second FBG sensor 320 reflects a second wavelength band different from the first wavelength band. The first sensor 310 can receive input light of relatively low intensity in the first wavelength band and has a relatively high reflectance in the first wavelength band. The second sensor 320 can receive input light of relatively high intensity in the second wavelength band and has a relatively low reflectance in the second wavelength band. In this configuration, the difference in reflectivity between the first FBG sensor 310 and the second FBG sensor 320 in their respective wavelength bands reduces the difference between the intensity of the first optical output signal of the first FBG sensor 310 and the intensity of the second optical output signal of the second FBG sensor 320.

[0015] An FBG sensor may be configured as a portion of an optical fiber that reflects wavelengths near the Bragg wavelength associated with the FBG sensor as output light and transmits other wavelengths. An FBG sensor can be formed by periodically changing the refractive index along the length of the optical fiber core. The reflected wavelength is called the Bragg wavelength λ. B ,teeth, λ B =2η eff Equivalent to Λ, In the formula, η eff Λ is the effective refractive index of the sensor, and Λ is the period of the sensor.

[0016] The reflectivity of the FBG sensor depends on one or both of the length (number of periods) of the sensor and the intensity of the refractive index modulation of the FBG sensor. FIG. 4 is a graph showing the refractive index modulation of the first and second FBG sensors 310 and 320. The refractive index modulation is the difference between two refractive index values of the modulation. The refractive index modulation 411, n2 - n1 of the first sensor 310 generates a first reflectivity value in the first wavelength band of the first FBG sensor 310. The refractive index modulation 421, n3 - n1 of the second sensor 320 generates a second reflectivity value in the second wavelength band of the second FBG sensor 320. For example, the difference between the reflectivity of the first sensor 310 and the reflectivity of the second sensor 320 may be, for example, 5% to 95%.

[0017] In some embodiments, the reflectivity of the FBG sensor can depend on the length of the FBG sensor that is a function of the number of periods of the refractive index modulation of the FBG sensor. FIG. 5 shows a sensor system including an optical fiber 575 having a compensated sensor array including a first FBG sensor 510 and a second FBG sensor 520 engraved on the top, and the first sensor 510 and the second 520 have different reflectivities depending on the sensor length. The respective lengths of the sensors 510, 520 can be, for example, in the range of about 0.5 μm to about 10 mm. The first FBG sensor 510 has a relatively small number of periods N1 of the refractive index modulation, and correspondingly, the reflectivity in the wavelength band of the first sensor 510 is lower. Compared with the first FBG sensor 510, the second FBG sensor 520 has a relatively large number of periods N2 of the refractive index modulation, and correspondingly, the reflectivity in the wavelength band of the second sensor 520 is higher. For example, the first FBG sensor 510 may have a period Λ1 and a number of periods N1 for the total length N1Λ1. The second FBG sensor 520 may have a period Λ2 and a number of periods N2 for the total length N2Λ2, where N1 < N2 and / or N1Λ1 < N2Λ2.

[0018] In some embodiments, the compensating optical characteristic having different values for the first and second FBG sensors is optical attenuation. FIG. 6 shows a system 600 including an optical fiber 675 having a compensated sensor array including first and second FBG sensors 610, 620 etched on the top. Although the sensing system 600 of FIG. 6 shows two FBG sensors 610, 620, it should be noted that more FBG sensors can be arranged on the optical fiber 675. The first FBG sensor 610 operates in a first wavelength band, and the second FBG sensor 620 operates in a second wavelength band different from the first wavelength band. The first sensor 610 can receive input light with a relatively low intensity in the first wavelength band and has a lower optical attenuation in the first wavelength band. The second sensor 620 can receive input light with a relatively high intensity in the second wavelength band and may have a relatively high attenuation in the second wavelength band compared to the first FBG sensor 610. In this configuration, the difference in the attenuation values of the first and second FBG sensors 610, 620 in each wavelength band reduces the difference between the intensity of the first optical output signal of the first FBG sensor 610 and the intensity of the second optical output signal of the second FBG sensor 620.

[0019] Optical attenuation can be the result of many processes such as, for example, scattering, reflection, deflection, absorption, and / or diffraction. Materials can be selected to be used over long distances considering low attenuation, and / or materials such as those within an optical fiber attenuator can be selected considering high attenuation, which absorbs light. Discontinuities in the optical path can also introduce scattering and attenuate light. Discontinuities can be introduced, for example, by doping of materials, defects in the waveguide structure, and / or transitions of materials (optical fiber connectors).

[0020] According to the various embodiments described herein, there are several examples of attenuation of input light. Attenuation loss may be inherent to the fiber optic cable material. Over shorter distances, this loss can be negligible, but when traversing hundreds or thousands of kilometers, it becomes significant, for example, due to scattering and / or absorption. Attenuation loss may be inherent to the maximum bending radius of the fiber optic cable. For example, sharp bends in a fiber optic cable allow light to scatter from the waveguide. In some cases, attenuation loss may be due to discontinuities in the optical path. For example, fiber optic connectors (i.e., LC / APC, FC / APC, etc.) introduce loss into the system due to incomplete coupling of light between two connecting waveguides. According to various embodiments, loss may be due to an optical splitter. Fiber optic splitters are used to split input light into multiple output waveguides, which may result in the output light having a lower signal than the input light. In some embodiments, loss may be due to an optical attenuator. Fiber optic attenuators can be used to intentionally attenuate the intensity of light in a waveguide. This component is often used to absorb light, thereby reducing the power of the transmitted light. This is particularly useful, for example, when the readout sensor is in a saturated state.

[0021] The approach described above provides a system having a compensated sensor array in which the sensor output signal is compensated for differences in input light intensity. These systems reduce the difference in intensity of reflected light from FBG sensors. Figures 7A and 7B are graphs comparing the reflected output signals from multiple sensors in an uncompensated system with the reflected output signals from multiple sensors in a compensated array. In Figure 7A, the sensors in the uncompensated array are not compensated for differences in input light intensity. In Figure 7B, each sensor in the compensated array has a reflectivity that compensates for differences in input light intensity due to spectral non-uniformity of the light source. From Figures 7A and 7B, it can be seen that the difference in intensity of reflected light from sensors in the compensated array (Figure 7B) is reduced compared to the difference in intensity of reflected light from sensors in the uncompensated array (Figure 7A).

[0022] As previously discussed and shown here in Figure 8, the wavelength multiplexing system 800 can use a compensated sensor array including a plurality of FBG sensors 821, 822, 823 arranged on a single optical fiber 811. Sensors 821-823 can be configured to sense parameters including, for example, one or more of temperature, strain, and / or vibration. As shown in Figure 8, the input light is provided by a light source 810, which includes, or may include, a light-emitting diode (LED) or a superluminescent laser diode (SLD). The spectral characteristics (intensity vs. wavelength) of the broadband light are shown by inset 891. The intensity is highest near the center of the spectrum and decreases at the edges of the spectrum. Sensors 821, 822, 823 include compensation, e.g., one or more of different reflectances and different attenuations, to reduce the difference in intensity of the output signal light reflected by the sensors, thereby compensating for input light whose intensity is non-uniform due to, for example, spectral non-uniformity of the light source and / or scattering loss in the optical fiber. The input light is transmitted to the first FBG sensor 821 via the optical fiber (FO) cable 811. The first FBG sensor 821 reflects a portion of the light in a first wavelength band having a center wavelength λ1. Light with wavelengths outside the first wavelength band is transmitted through the first FBG sensor 821 to the second FBG sensor 822. The spectral characteristics of the light transmitted to the second FBG sensor 822 are shown in inset graph 892, which shows a notch 881 in the first wavelength band centered at λ1, indicating that light in this wavelength band is reflected by the first sensor 821.

[0023] The second FBG sensor 822 reflects a portion of light in a second wavelength band having a central wavelength λ2. Light not reflected by the second FBG sensor 822 is transmitted through the second FBG sensor 822 to the third FBG sensor 823. The spectral characteristics of the light transmitted to the third FBG sensor 823 are shown in inset graph 893, and include notches 881 and 882 centered on λ1 and λ2.

[0024] The third FBG sensor 823 reflects a portion of light in a third wavelength band having a center wavelength or peak wavelength λ3. Light not reflected by the third FBG sensor 823 is transmitted through the third FBG sensor 823. The spectral characteristics of the light transmitted through the third FBG sensor 823 are shown in inset graph 894 and include notches 881, 882, and 883 centered on λ1, λ2, and λ3.

[0025] Light from wavelength bands 861, 862, and 863, having central wavelengths λ1, λ2, and λ3 (shown in inset 895), is reflected to the optical wavelength demultiplexer 850 by the first, second, or third FBG sensors 821, 822, and 823, respectively, along FO cables 811 and 811'. The compensated input characteristics of sensors 821, 822, and 823 reduce the difference in intensity peaks of light 861, 862, and 863 compared to the intensity peaks from the uncompensated sensor array.

[0026] From the wavelength demultiplexer 850, the sensor light 861, 862, and 863 may be sent to the wavelength shift detector 855, which generates an electrical signal in response to the shift of the central wavelength λ1, λ2, λ3 and / or wavelength band of the sensor light. The wavelength shift detector 855 receives the reflected light from each of the sensors and generates a corresponding electrical signal in response to the shift of the central wavelength λ1, λ2, and λ3 or wavelength band of the light reflected by the sensors 821-823. The analyzer 856 can compare the shift with a characteristic fundamental wavelength (known wavelength) to determine whether a change has occurred in the value of the parameter sensed by the sensors 821-823. The analyzer 856 can determine that one or more values ​​of the sensed parameters have changed based on the wavelength shift analysis and can calculate relative or absolute measurements of the change.

[0027] In some cases, instead of emitting broadband light, the light source can scan a wavelength range to emit light in a narrow wavelength band that various sensors placed on the FO cable are sensitive to. The reflected light is sensed during several sensing periods timed for the emission of narrowband light. For example, consider a scenario where sensors 1, 2, and 3 are placed on the FO cable. Sensor 1 is sensitive to a wavelength band (WB1), sensor 2 is sensitive to a wavelength band WB2, and sensor 3 is sensitive to WB3. The light source may be controlled to emit light with WB1 during period 1 and sense the reflected light during period 1a, which overlaps with period 1. Following period 1a, the light source may emit light with WB2 during period 2 and sense the reflected light during period 2a, which overlaps with period 2. Following period 2a, the light source may emit light with WB3 during period 3 and sense the reflected light during period 3a, which overlaps with period 3. Using this version of time-domain multiplexing, each sensor can be queried during separate periods. When the intensity of a narrowband light source changes, a compensated sensor array, such as those described herein, may be useful for compensating for variations in the light source intensity.

[0028] The FO cable may include a single-mode (SM) FO cable (as shown in Figure 8) or a multi-mode (MM) FO cable. While single-mode fiber optic cables provide a more interpretable signal, multi-mode fibers may be used to achieve broader applicability and lower manufacturing costs. MM fibers may be made of plastic instead of silica, which is typically used in SM fibers. Plastic fibers may have a smaller radius of gyration compared to silica fibers. This can, for example, offer the possibility of curved or flexible configurations. Furthermore, MM fibers can operate with less expensive light sources (e.g., LEDs), in contrast to SM fibers, which may require more precise alignment with superluminescent diodes (SLDs). Therefore, sensing systems based on optical sensors within MM fibers can result in lower-cost systems.

[0029] Figure 9 is an ideal representation of light reflected from an FBG sensor deployed on an SM FO cable. In a characteristic baseline or known state, the FBG sensor reflects light in a relatively narrow wavelength band 910 with a central (or centroid) wavelength λ. After the FBG sensor experiences a change in sensing conditions, such as temperature, strain, or chemical environment, the light reflected by the sensor shifts to a different wavelength band 920 with a central (or centroid) wavelength λs. Wavelength band 920 is similar in width, amplitude, and other morphological features to wavelength band 910, but the wavelength λs of wavelength band 920 is shifted from the wavelength λ of wavelength band 910 by an amount related to the change in sensing conditions 930.

[0030] Figure 10A is a block diagram showing some of the demultiplexer output, wavelength shift detector, and analyzer components available for use in system 800 of Figure 8. The demultiplexer output includes three optical fibers 1045, 1046, and 1047 carrying the demultiplexed reflected light from sensors 821, 822, and 823, respectively. In the compensated system, the intensity of the light carried by each sensor is more uniform compared to a substantially similar system without compensation for the input light. As the values ​​of the sensed parameters change, the center wavelength or centroid wavelength of the light reflected by the first sensor 821 may shift from λ1 to λ1+Δ1, the center wavelength or centroid wavelength of the light reflected by the second sensor 822 may shift from λ2 to λ2+Δ2, and the center wavelength or centroid wavelength of the light reflected by the third sensor 823 may shift from λ3 to λ3+Δ3. The wavelength shift detectors, including elements 1000-1, 1000-2, and 1000-3, each receive demultiplexed reflected light from their corresponding waveguides 1045, 1046, and 1047, respectively, and generate an electrical signal that responds to the shift in the center wavelength or wavelength band of the reflected light. The analyzer can compare the electrical signals from the wavelength shift detector elements 1000-1, 1000-2, and 1000-3, which indicate a shift to a known baseline or previous value, to determine whether a change has occurred in the value of the parameter sensed by the sensor.

[0031] Figure 10B shows a wavelength shift detector 1000 in more detail according to one embodiment. Optionally, the wavelength shift detector 1000 includes a diffusion element 1005 configured to collimate and / or diffuse light from the output waveguide 1040 of the demultiplexer across the input surface of a linearly variable transmission structure (LVTS) 1010 or other spatially dispersed optical element. The diffusion element 1005 may not be used in arrangements where sufficient diffusion of light from the output waveguide 1040 occurs. The LVTS 1010 includes a dispersion element such as a prism or a linearly variable filter. The LVTS 1010 receives light 1091 from the waveguide 1040 and (optionally) the diffusion element 1005 at its input surface 1010a and transmits light from its output surface 1010b to a photodetector pair 1020. At the output surface 1010b of the LVTS 1010, the wavelength of the light changes with distance along the output surface 1010b.

[0032] The photodetector pair 1020 is positioned relative to the LVTS 1010 such that light 1092 transmitted through the LVTS 1010 is incident on the photodetector pair 1020. For example, light 1092 with wavelength λ1 may mainly be incident on photodetector 1021, and light 1092 with wavelength λ1+Δ1 may mainly be incident on photodetector 1022. Photodetector 1021 generates a signal I1 in response to light incident on its photosensitive surface, and photodetector 1022 generates a signal I2 in response to light incident on its photosensitive surface. Signals I1 and I2 contain information about the sensed parameter, and a change in the ratio of I1 and I2 indicates a change in the sensed parameter. Equation

[0033]

number

[0034] In some embodiments, the system includes first and second electrical signals corresponding to first and second sensors. The first electrical signal responds to a shift in a parameter sensed by the first sensor, and the second electrical signal responds to a shift in a parameter sensed by the second sensor. Compensation of the first and second sensors for input light reduces the difference between the intensity of the first optical output signal of the first sensor and the intensity of the second optical output signal of the second sensor. Reducing the difference between the intensity of the first output signal and the intensity of the second output signal reduces, in turn, the difference between the amplitude of the first electrical signal and the amplitude of the second electrical signal.

[0035] While the subject matter is described in a language specific to structural features and / or methodological actions, it should be understood that the subject matter as defined in the attached claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are disclosed as representative forms of implementing the claims.

Claims

1. 1. A sensor system comprising: An optical fiber; a set of wavelength-shifting sensors inscribed on the optical fiber, the set of wavelength-shifting sensors comprising: at least one first wavelength-shift sensor configured to reflect a first wavelength band of input light as a first optical output signal, the at least one first wavelength-shift sensor having a first value of an optical property that modifies an intensity of the first wavelength band of input light; and at least one second wavelength-shift sensor configured to reflect a second wavelength band of the input light as a second optical output signal, the at least one second wavelength-shift sensor having a second value of the optical property that alters an intensity of the second wavelength band of the input light, the second value being different from the first value.

2. 2. The sensor system of claim 1, wherein the difference between the first value and the second value is configured to reduce a difference between an intensity of the first optical output signal and an intensity of the second optical output signal.

3. 2. The sensor system of claim 1, wherein a difference between the first value and the second value is configured to reduce a difference in at least one of a first signal-to-noise ratio (SNR) of the first optical output signal and a second SNR of the second optical output signal.

4. 2. The sensor system of claim 1, wherein the difference between the first value and the second value is configured such that a strength of the first optical output signal and a strength of the second optical output signal are substantially equal.

5. 2. The sensor system of claim 1, wherein the optical property includes a reflectance, and a difference between the first and second values ​​of reflectance is a function of a difference between a first amplitude of a refractive index modulation of the first wavelength-shifting sensor and a second amplitude of a refractive index modulation of the second wavelength-shifting sensor.

6. 2. The sensor system of claim 1, wherein the optical property includes a reflectivity, and a difference between the first and second values ​​of reflectivity is a function of a difference between a first number of periods of a Bragg wavelength of the first wavelength-shifting sensor inscribed on the optical fiber and a second number of periods of a Bragg wavelength of the second wavelength-shifting sensor inscribed on the optical fiber.

7. The sensor system of claim 1 , wherein the optical characteristic comprises an attenuation of input light.

8. the first wavelength-shift sensor is disposed at a first location on the optical fiber; the second wavelength-shift sensor is disposed at a second location on the optical fiber; The sensor system of claim 1 , wherein the difference between the first value and the second value is based on a distance between the first location and the second location.

9. the optical fiber is configured such that optical scattering losses occur along the optical fiber; The sensor system of claim 1 , wherein the difference between the first value and the second value is based on the scattering loss.

10. The sensor system of claim 9 , wherein at least a portion of the scattering loss is due to bends in the optical fiber.

11. optically coupled to the optical fiber; receiving the first and second optical output signals from the first and second wavelength-shift sensors; Detecting a wavelength shift in the first wavelength band and a wavelength shift in the second wavelength band; and 2. The sensor system of claim 1, further comprising a wavelength shift detector configured to generate a first electrical signal responsive to the wavelength shift in the first wavelength band and a second electrical signal responsive to the wavelength shift in the second wavelength band, wherein a difference between an amplitude of the first electrical signal and an amplitude of the second electrical signal is responsive to a difference between an intensity of the first optical output signal and an intensity of the second optical output signal.

12. The sensor system of claim 1 , wherein the wavelength-shifting sensor comprises one or more of a Fiber Bragg Grating (FBG) sensor and a Fabry-Perot sensor.

13. 1. A method of manufacturing a sensor system comprising inscribing a set of wavelength-shifting sensors into an optical fiber, the set of wavelength-shifting sensors comprising: at least one first wavelength-shift sensor configured to reflect a first wavelength band of input light as a first optical output signal, the at least one first wavelength-shift sensor having a first value of an optical property that affects an intensity of the first optical output signal; and at least one second wavelength-shift sensor configured to reflect a second wavelength band of the input light as a second optical output signal, the at least one second wavelength-shift sensor having a second value of an optical property affecting an intensity of the second optical output signal, the first value being different from the second value.

14. 14. The method of claim 13, wherein a difference between the first and second values ​​of the optical property is configured to reduce a difference between an intensity of the first optical output signal and an intensity of the second optical output signal.

15. Inscribing the set of wavelength-shifting sensors into the optical fiber comprises: inscribing the first wavelength-shifting sensor with a first amplitude of refractive index modulation; inscribing the second wavelength-shifting sensor with a second amplitude of refractive index modulation, a difference between the first value and the second value being a function of a difference between the first amplitude and the second amplitude.

16. Inscribing the set of wavelength-shifting sensors into the optical fiber comprises: inscribing a first number of periods of a Bragg wavelength of the first wavelength-shifting sensor; and stepping a second number of periods of a Bragg wavelength of the second wavelength-shifting sensor, wherein a difference between the first value and the second value is a function of a difference between the first number and the second number.

17. The method of claim 13 , wherein the optical property comprises an attenuation of input light.

18. 1. A method comprising: generating input light for a sensor system, the sensor system comprising: An optical fiber; a set of wavelength-shifting sensors inscribed on the optical fiber, the set of wavelength-shifting sensors comprising: at least one first wavelength-shift sensor having a first value of an optical property; at least one second wavelength-shift sensor having a second value of the optical property different from the first value; reflecting a first wavelength band of the input light as a first optical output signal, the first value of the optical property affecting an intensity of the first optical output signal; reflecting a second wavelength band of the input light as a second optical output signal, the second value of the optical property affecting an intensity of the second optical output signal.

19. 20. The method of claim 18, wherein a difference between the first value and the second value is configured to reduce a difference in a signal-to-noise ratio (SNR) of at least one of the first optical output signal and the second optical output signal.

20. detecting a shift in the first wavelength band and generating a first electrical signal in response to the shift; 20. The method of claim 18, further comprising detecting a shift in the second wavelength band and generating a second electrical signal in response to the shift, wherein a difference between an amplitude of the first electrical signal and an amplitude of the second electrical signal is responsive to the difference between an intensity of the first optical output signal and an intensity of the second optical output signal.

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