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 technique is often referred to as wavelength multiplexing optical sensing.

Summary of the Invention

[0002] Embodiments described herein include a sensor system comprising 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] An embodiment includes a method of manufacturing a sensor system that includes engraving a set of wavelength shift sensors on 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 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, and the first value is different from the second value.

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

Brief Description of the Drawings

[0005] Throughout this specification, reference is made to the accompanying drawings.

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Figure 2A

Figure 2B

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[0006] The drawings are not necessarily to scale. Like numbers used in the drawings refer to like components. However, it will be understood that the use of a number to refer to a component in a given drawing is not intended to limit the component in another drawing labeled with the same number.

DETAILED DESCRIPTION OF THE INVENTION

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

[0008] A broadband light source is useful for wavelength-division multiplexed optical sensing because it can be placed on a single optical fiber and used as the input light for many FBG sensors that 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, 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 FIG. 1, in an uncompensated sensor array, an FBG sensor having a wavelength band corresponding to a wavelength close to the peak of the intensity-versus-wavelength curve of the input light reflects higher-intensity light. These FBG sensors having wavelength bands corresponding to wavelengths near the edge of the intensity-versus-wavelength curve of the input light reflect lower-intensity light. Systems for obtaining information from FBG sensors often use a minimum intensity threshold to separate the received signal from the noise. If the measurement 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, where the intensity of the reflected light from the sensors is more uniform. The embodiments described herein use FBG sensors as an example of wavelength-shift sensors, but it should be understood that the sensors can include any other type of wavelength-shift sensor (e.g., Fabry-Perot sensors).

[0009] Some embodiments described herein are directed to systems and methods for compensating for spectral non-uniformity of input light to a plurality of FBG sensors etched along an optical fiber. FIG. 2A shows a sensing system 201 including an optical fiber 275 and a compensated array including a plurality of FBG sensors 210 - 260 etched at various positions along the optical fiber 275, according to some embodiments. Each of the FBG sensors 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 an optical characteristic. 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 an optical characteristic. The second FBG sensor 220 is configured to reflect a second wavelength band of the input light as a second optical output signal from the second FBG sensor 220. The optical characteristic affects the intensity of the light reflected by the sensors 210, 220. The difference between the first value and the second value of the optical characteristic 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 plurality of FBG sensors 210-260 results from the non-uniform intensity output of the spectral of the input light source 290, as previously described in connection with FIG. 1. Another potential cause of non-uniformity in the input light to the plurality of FBG sensors 210-260 results from scattering losses 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, and the second FBG sensor 220 located farther from the light source 290 can receive relatively lower-intensity input light due to scattering losses that occur as the input light travels along the optical fiber 275. In these situations, the difference between the first value and the second value of the optical characteristic can be based on the distance between the sensors.

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

[0013] For example, to compensate for variations in the input light due to, among other things, the distance between sensors, scattering losses, bends in the optical fiber, spectral non-uniformity of the input light source, and / or other sources of variation, at least one of the FBG sensors 210 disposed along the optical fiber 275 may have one or more optical property values that are different from the one or more optical property values of at least one other FBG sensor 220. The difference in the one or more optical property 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 optical signal and the second optical signal can be reduced by 5%, 25%, or even 50% when compared to a system where the one or more optical property values of the first sensor in the first wavelength band are substantially equal to the optical property values of the second sensor in the second wavelength band.

[0014] In some embodiments, the compensation optical characteristic having different values for the first and second FBG sensors is reflectivity. FIG. 3 shows a system 300 including an optical fiber 375 having a compensated sensor array including first and second FBG sensors 310, 320 with different reflectivities, etched on top, according to some embodiments. Although the sensing system 300 of FIG. 3 shows two FBG sensors 310, 320, it should be noted that more FBG sensors can 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 with a relatively low intensity in the first wavelength band and has a relatively high reflectivity in the first wavelength band. The second sensor 320 can receive input light with a relatively high intensity in the second wavelength band and has a relatively low reflectivity 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 each wavelength band reduces the difference in intensity between the first optical output signal of the first FBG sensor 310 and the second optical output signal of the second FBG sensor 320.

[0015] The FBG sensor may be configured as a portion of an optical fiber that reflects, as output light, a wavelength band near the Bragg wavelength associated with the FBG sensor and transmits other wavelengths. The FBG sensor can be formed by periodically changing the refractive index along the length of the optical fiber core. The reflection wavelength λ, called the Bragg wavelength B , is λ B = 2η eff equal to Λ, where η eff 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 etched on top, where 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 N1 of periods of refractive index modulation, and correspondingly, a lower reflectivity in the wavelength band of the first sensor 510. Compared with the first FBG sensor 510, the second FBG sensor 520 has a relatively large number N2 of periods of refractive index modulation, and correspondingly, a higher reflectivity in the wavelength band of the second sensor 520. For example, the first FBG sensor 510 may have a period Λ1 and of a number N1 with respect to the total length N1Λ1. The second FBG sensor 520 may have a period Λ2 and and circumference a number and number N1 with respect to the total length N2Λ2, where N1 < N2 and / or N1Λ1 < N2Λ2. and circumference a number and number N2, and here N1 < N2 and / or N1Λ1 < N2Λ2.

[0018] In some embodiments, the compensating optical property 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 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 for use over long distances considering low attenuation and / or materials such as those in optical fiber attenuators can be selected considering high attenuation, which absorb 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 various embodiments described herein, there are multiple examples of attenuation of input light. The attenuation loss may be inherent in the fiber cable material. At shorter distances, this loss can be ignored, but when traversing hundreds or thousands of kilometers, this becomes significant, for example, due to scattering and / or absorption. The attenuation loss may be inherent in the maximum bending radius of the fiber cable. For example, sharp bends in the fiber cable can allow light to scatter from the waveguide. In some cases, the attenuation loss may be due to discontinuities in the optical path. For example, optical fiber connectors (i.e., LC / APC, FC / APC, etc.) introduce losses into the system due to imperfect coupling of light between two connected waveguides. According to various embodiments, the loss may be due to an optical splitter. An optical fiber splitter is used to split input light into multiple output waveguides, whereby the output light can have a lower signal than the input light. In some embodiments, the loss may be due to an optical attenuator. An optical fiber attenuator 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 approaches described above provide systems with compensated sensor arrays where the sensor output signal is compensated for differences in input light intensity. These systems reduce the difference in the intensity of the reflected light from FBG sensors. FIGS. 7A and 7B are graphs comparing the reflected output signals from multiple sensors in an uncompensated system and the reflected output signals from multiple sensors in a compensated array. In FIG. 7A, the sensors in the uncompensated array are not compensated for differences in the intensity of the input light. In FIG. 7B, each sensor in the compensated array has a reflectivity that compensates for differences in the intensity of the input light due to spectral non-uniformity of the light source. From FIGS. 7A and 7B, it will be understood that the difference in the intensity of the light reflected from the sensors in the compensated array (FIG. 7B) is reduced when compared to the difference in the intensity of the light reflected from the sensors in the uncompensated array (FIG. 7A).

[0022] As previously discussed and as shown here in FIG. 8, wavelength multiplexing system 800 can use a compensated sensor array that includes a plurality of FBG sensors 821, 822, 823 disposed 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 FIG. 8, input light is provided by a light source 810 that can include, for example, a light emitting diode (LED) or a superluminescent laser diode (SLD), or can be those. The spectral characteristics (intensity versus wavelength) of the broadband light are shown by the inserted graph 891. The intensity is highest near the center of the spectrum and decreases at the edges of the spectrum. Sensors 821, 822, 823 compensate for the difference in intensity of the output signal light reflected by the sensors to compensate for input light that is non-uniform in intensity due to, for example, spectral non-uniformity of the light source and / or scattering losses in the optical fiber, including, for example, one or more of different reflectivities and different attenuations. 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 having a wavelength outside the first wavelength band passes through the first FBG sensor 821 and is transmitted to the second FBG sensor 822. The spectral characteristics of the light transmitted to the second FBG sensor 822 are shown by the inserted graph 892, showing a notch 881 in the first wavelength band centered on λ1, indicating that the light in this wavelength band is reflected by the first sensor 821.

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

[0024] The third FBG sensor 823 reflects a portion of the light in the third wavelength band having a central wavelength or peak wavelength λ3. The light not reflected by the third FBG sensor 823 passes through the third FBG sensor 823. The spectral characteristics of the light that has passed through the third FBG sensor 823 are shown in the inserted graph 894 and include notches 881, 882, 883 centered on λ1, λ2, and λ3.

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

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

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

[0028] The FO cable may include a single mode (SM) FO cable (as shown in FIG. 8) or a multi-mode (MM) FO cable. Single mode optical fiber cables provide more interpretable signals, but multi-mode fibers may be used to achieve broader applicability and lower manufacturing costs. The MM fiber may be made of plastic rather than silica, which is typically used for SM fibers. Plastic fibers may have a smaller radius of curvature compared to that of silica fibers. This can provide, for example, the possibility of a curved or flexible configuration. Further, the MM fiber can operate with a less expensive light source (e.g., an LED), in contrast to SM fibers which may require more precise alignment with a superluminescent diode (SLD). Thus, a sensing system based on optical sensors in MM fibers can produce a lower-cost system.

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

[0030] FIG. 10A is a block diagram showing a portion of the demultiplexer output, wavelength shift detector, and analyzer that can be used in the system 800 of FIG. 8. The demultiplexer output includes three optical fibers 1045, 1046, 1047 that carry the demultiplexed reflected light from the sensors 821, 822, 823, respectively. In a compensated system, the intensity of the light carried by each of the sensors is more uniform when compared to a substantially similar system that does not include compensation for the input light. As the value of the sensed parameter changes, the central or centroid wavelength of the light reflected by the first sensor 821 may shift from λ1 to λ1 + Δ1, the central or centroid wavelength of the light reflected by the second sensor 822 may shift from λ2 to λ2 + Δ2, and the central or centroid wavelength of the light reflected by the third sensor 823 may shift from λ3 to λ3 + Δ3. The wavelength shift detector, including elements 1000-1, 1000-2, 1000-3, receives the demultiplexed reflected light from its corresponding waveguides 1045, 1046, 1047, respectively, and generates an electrical signal in response to a shift in the central wavelength or wavelength band of the reflected light. The analyzer can compare each electrical signal from the wavelength shift detector elements 1000-1, 1000-2, 1000-3, which indicates 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 sensors.

[0031] Figure 10B shows the wavelength shift detector 1000 according to some embodiments in more detail. Optionally, the wavelength shift detector 1000 includes a diffusing component 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 spatial dispersion optical element. In an arrangement where sufficient light diffusion occurs from the output waveguide 1040, the diffusing component 1005 may not be used. The LVTS 1010 includes a dispersive element such as a prism or a linearly variable filter. The LVTS 1010 receives light 1091 from the waveguide 1040 and (optionally) the diffusing component 1005 at its input surface 1010a and transmits the light from its output surface 1010b to the photodetector pair 1020. At the output surface 1010b of the LVTS 1010, the wavelength of the light varies with the distance along the output surface 1010b.

[0032] The photodetector pair 1020 is positioned relative to the LVTS 1010 such that the light 1092 that has passed through the LVTS 1010 is incident on the photodetector pair 1020. For example, light 1092 having a wavelength λ1 may primarily be incident on the photodetector 1021, and light 1092 having a wavelength λ1 + Δ1 may primarily be incident on the photodetector 1022. The photodetector 1021 generates a signal I1 in response to the light incident on its photosensitive surface, and the photodetector 1022 generates a signal I2 in response to the light incident on its photosensitive surface. The signals I1, I2 contain information regarding the sensed parameter, whereby a change in the ratio of I1 to I2 indicates a change in the sensed parameter. Using the equation

[0033]

Equation

[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 the 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 correspondingly reduces the difference between the amplitude of the first electrical signal and the amplitude of the second electrical signal.

[0035] It should be understood that although the subject matter is described in language specific to structural features and / or methodological acts, the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as representative forms for carrying out the claims.

Claims

1. A sensor system, comprising: An optical fiber; and A set of wavelength shift sensors engraved on the optical fiber, wherein 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 at least one first wavelength shift sensor having a first value of an optical property that changes the intensity of the first wavelength band of the input light; and At least one second wavelength shift sensor configured to reflect a second wavelength band of 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 changes the intensity of the second wavelength band of the input light, the second value being different from the first value. The optical property includes reflectivity, and a difference between the first value and the second value of the reflectivity is a function of a difference between a first number of periods of a Bragg wavelength of the first wavelength shift sensor engraved on the optical fiber and a second number of periods of a Bragg wavelength of the second wavelength shift sensor engraved on the optical fiber. Sensor system.

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

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

5. The optical property includes reflectance, and a difference between the first value and the second value of the reflectance is a function of a difference between a first amplitude of refractive index modulation of the first wavelength shift sensor and a second amplitude of refractive index modulation of the second wavelength shift sensor. The sensor system according to claim 1.

6. The optical property includes attenuation of input light. The sensor system according to claim 1.

7. The first wavelength shift sensor is disposed at a first position on the optical fiber. The second wavelength shift sensor is disposed at a second position on the optical fiber. The difference between the first value and the second value is based on a distance between the first position and the second position. The sensor system according to claim 2.

8. The optical fiber is configured such that optical scattering loss occurs along the optical fiber. The difference between the first value and the second value is based on the scattering loss. The sensor system according to claim 1.

9. At least a part of the scattering loss is due to a bent portion of the optical fiber. The sensor system according to claim 8.

10. Optically coupled to the optical fiber, and Receiving the first optical output signal and the second optical output signal from the first wavelength shift sensor and the second wavelength shift sensor, Detecting a wavelength shift in the first wavelength band and a wavelength shift in the second wavelength band, and 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, and a difference between an amplitude of the first electrical signal and an amplitude of the second electrical signal responds to a difference between an intensity of the first optical output signal and an intensity of the second optical output signal. The sensor system according to claim 1.

11. The sensor system according to claim 1, wherein the wavelength shift sensor includes one or more of a fiber Bragg grating (FBG) sensor and a Fabry-Perot sensor.

12. A method, comprising: generating input light for a sensor system, wherein the sensor system includes: an optical fiber; and a set of wavelength shift sensors inscribed on the optical fiber, the set of wavelength shift sensors including: at least one first wavelength shift sensor having a first value of an optical characteristic; and at least one second wavelength shift sensor having a second value of the optical characteristic different from the first value; reflecting a first wavelength band of the input light as a first optical output signal, wherein the first value of the optical characteristic affects an intensity of the first optical output signal; reflecting a second wavelength band of the input light as a second optical output signal, wherein the second value of the optical characteristic affects an intensity of the second optical output signal; wherein the optical characteristic includes reflectivity, and a difference between the first value and the second value of the reflectivity is a function of a difference between a first number of periods of a Bragg wavelength of the first wavelength shift sensor inscribed on the optical fiber and a second number of periods of a Bragg wavelength of the second wavelength shift sensor inscribed on the optical fiber.

13. The method according to claim 12, wherein the difference between the first value and the second value is configured to reduce a difference in signal-to-noise ratio (SNR) of at least one of the first optical output signal and the second optical output signal.

14. detecting a shift of the first wavelength band and generating a first electrical signal in response to the shift; 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 responds to the difference between an intensity of the first optical output signal and an intensity of the second optical output signal, the method according to claim 12.

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