TEMPERATURE MEASUREMENT USING FABRY-PÉROT RESONATOR ON END OF OPTICAL FIBER

A temperature measurement device includes a Fabry-Pérot resonator constructed of an inorganic optical material on an end of an optical fiber. Light in the optical fiber couples into a cavity of the Fabry-Pérot resonator and resonates at a resonance that varies with temperature of the Fabry-Pérot resonator. A detector receives output light from the Fabry-Pérot resonator and produces a signal indicating a detected resonance. Computing circuitry receives the signal, determines a temperature of the Fabry-Pérot resonator based on the detected resonance and a relationship that correlates the detected resonance with the temperature of the Fabry-Pérot resonator, and outputs a temperature measurement. The cavity may include a channel comprised of a material having a different refractive index than surrounding material. The temperature measurement device may include multiple Fabry-Pérot resonators. The inorganic optical material enables the temperature measurement device to output a temperature measurement that extends to at least 900° C.

BACKGROUND

Technical Field

The present disclosure relates to temperature measurement, and in particular, to temperature measurement devices, systems, and methods that measure a temperature based on a resonance of light in an optical resonator.

Description of the Related Art

Temperature measurement is an important part of many technological processes, for example, in operating industrial equipment, conducting manufacturing process control, monitoring environmental conditions, etc. Cost, stability, and accuracy are major considerations in thermometry. Resistance thermometers that use measurements of resistance of a thin metal film or wire, e.g., platinum resistance thermometers, are known and can produce accurate temperature measurements. However, resistance thermometers are typically sensitive to environmental variables such as humidity, material degradation, and mechanical shock, which causes the resistance relative to temperature to drift over time, requiring frequent, expensive, and time-consuming calibration. Resistance thermometers are also limited in the range of temperatures that they can measure and cannot measure higher temperatures exceeding an upper threshold.

Photonic thermometry is an alternative to resistance thermometry. Photonic thermometers rely on temperature-dependent changes in an optical material, typically a combination of thermo-optic effects and thermal expansion, which cause detectable changes in light traversing the optical material. Photonic thermometers constructed on a silicon substrate can provide high temperature sensitivity while being less susceptible to environmental variables, as noted above for resistance thermometers, but photonic thermometers constructed on silicon are also limited in the range of temperatures that they can measure.

BRIEF SUMMARY

Aspects of the present disclosure provide temperature measurement devices, systems, and methods that can accurately measure temperatures across a wide range of temperatures, including higher temperatures at which conventional thermometers fail.

In various embodiments, the present disclosure provides a temperature measurement device that uses a Fabry-Pérot resonator constructed of an inorganic optical material arranged on an end of an optical fiber. Input light that scans across a range of wavelengths is injected into the optical fiber. A portion of the light transmitted by the optical fiber is coupled into the Fabry-Pérot resonator and resonates in a cavity between end mirrors of the Fabry-Pérot resonator. The light in the cavity resonates at a resonance (i.e., a resonant wavelength or frequency) that varies (i.e., shifts) according to the temperature of the Fabry-Pérot resonator, due to thermos-optic effects of the temperature on the material of the resonator. A detector receives output light from the Fabry-Pérot resonator and produces a signal indicating a detected resonance of the light in the Fabry-Pérot resonator. Computing circuitry determines the temperature of the Fabry-Pérot resonator based on the detected resonance and a predetermined relationship that correlates the detected resonance with the temperature of the Fabry-Pérot resonator. The predetermined relationship may be represented by a characteristic curve that is expressed, for example, by a numeric equation or by a data structure such as a lookup table.

In various embodiments, the Fabry-Pérot resonator may be constructed directly on the end of an optical fiber using multilayer deposition techniques. Because the Fabry-Pérot resonator is made of inorganic optical material, the temperature measurement device can measure temperatures that exceed an upper threshold (e.g., above 600° C.) at which conventional thermometers fail.

In various embodiments, the cavity of the Fabry-Pérot resonator may include a channel of material having a different refractive index than material in the cavity surrounding the channel. The channel provides a waveguide for light that is coupled into the cavity of the Fabry-Pérot resonator. This channel, or waveguide, may be constructed using two materials in the cavity of the Fabry-Pérot resonator, that is, one material having a first refractive index in the center of the cavity providing a “core” and another material having a different, second refractive index providing a “cladding” that surrounds the “core”. An advantage of including a waveguide in a Fabry-Pérot resonator cavity is that the resonator achieves a significantly higher quality factor or sharper peak resonance. For a range of wavelengths of light that is input, the resonance of a waveguide Fabry-Pérot resonator as described herein may be 5-10 times sharper/higher quality factor than a single material Fabry-Pérot resonator. In some cases, achieving a sharper peak resonance can translate to higher accuracy temperature measurements.

In various embodiments, a temperature measurement system of the present disclosure includes a temperature measurement device as described above, wherein the Fabry-Pérot resonator is a first Fabry-Pérot resonator, and the detected resonance of the light in the cavity of the first Fabry-Pérot resonator is a first detected resonance. The temperature measurement system further includes a second Fabry-Pérot resonator, also constructed of an inorganic optical material. The second Fabry-Pérot resonator is optically coupled to the first Fabry-Pérot resonator such that output light from the first Fabry-Pérot resonator is coupled into a cavity of the second Fabry-Pérot resonator. The light in the cavity of the second Fabry-Pérot resonator resonates at a resonance that varies (i.e., shifts) according to a temperature of the second Fabry-Pérot resonator.

A detector as previously described, is configured to receive output light from the second Fabry-Pérot resonator, and the signal produced by the detector indicates at least one of the first detected resonance of the first Fabry-Pérot resonator or a second detected resonance of the second Fabry-Pérot resonator. Computing circuitry receives the signal and determines at least one of a first temperature of the first Fabry-Pérot resonator or a second temperature of the second Fabry-Pérot resonator. The first temperature of the first Fabry-Pérot resonator is determined based on the first detected resonance and a first relationship that correlates the first detected resonance with the temperature of the first Fabry-Pérot resonator. The second temperature of the second Fabry-Pérot resonator is determined based on the second detected resonance and a second relationship that correlates the second detected resonance with the second temperature of the second Fabry-Pérot resonator. The computing circuitry outputs a temperature measurement based on at least one of the first temperature of the first Fabry-Pérot resonator or the second temperature of the second Fabry-Pérot resonator.

In other embodiments, a temperature measurement system of the present disclosure includes a temperature measurement device as previously described, wherein the Fabry-Pérot resonator is a first Fabry-Pérot resonator, and the detected resonance of the first Fabry-Pérot resonator is a first detected resonance. The temperature measurement system further includes a second Fabry-Pérot resonator constructed of an inorganic optical material on the end of the optical fiber. Light in the optical fiber is coupled into both the cavity of the first Fabry-Pérot resonator and a cavity of the second Fabry-Pérot resonator. Light in the cavity of the second Fabry-Pérot resonator resonates at a resonance that varies according to the temperature of the second Fabry-Pérot resonator. The detector, as previously described, receives output light from both the first Fabry-Pérot resonator and the second Fabry-Pérot resonator, and the signal produced by the detector indicates at least one of the first detected resonance of the first Fabry-Pérot resonator or a second detected resonance of the second Fabry-Pérot resonator.

The computing circuitry receives the signal indicating at least one of the first detected resonance or the second detected resonance, and determines at least one of a first temperature of the first Fabry-Pérot resonator or a second temperature of the second Fabry-Pérot resonator. As with previous embodiments, the first temperature of the first Fabry-Pérot resonator is determined based on the first detected resonance and a first relationship that correlates the first detected resonance with the temperature of the first Fabry-Pérot resonator, and the second temperature of the second Fabry-Pérot resonator is determined based on the second detected resonance and a second relationship that correlates the second detected resonance with the second temperature of the second Fabry-Pérot resonator. The computing circuitry outputs a temperature measurement based on at least one of the first temperature of the first Fabry-Pérot resonator or the second temperature of the second Fabry-Pérot resonator.

In yet other embodiments, a temperature measurement system of the present disclosure similarly includes a temperature measurement device as previously described. The optical fiber as previously described is a first optical fiber, the Fabry-Pérot resonator is a first Fabry-Pérot resonator on the end of the first optical fiber, the detector is a first detector configured to receive the output light from the first Fabry-Pérot resonator, and the signal is a first signal from the first detector indicating a first detected resonance of the light in the first Fabry-Pérot resonator. The temperature measurement system further includes a second Fabry-Pérot resonator and a second detector. The second Fabry-Pérot resonator is constructed of an inorganic optical material on an end of a second optical fiber, wherein light in the second optical fiber is coupled into a cavity of the second Fabry-Pérot resonator. Light in the cavity of the second Fabry-Pérot resonator resonates at a resonance that varies according to the temperature of the second Fabry-Pérot resonator. The second detector receives output light from the second Fabry-Pérot resonator and produces a second signal indicating a second detected resonance of the light in the second Fabry-Pérot resonator.

The computing circuitry receives at least one of the first signal that indicates the first detected resonance or the second signal that indicates the second detected resonance. The computing circuitry determines at least one of a first temperature of the first Fabry-Pérot resonator based on the first detected resonance and a first relationship that correlates the first detected resonance with the temperature of the first Fabry-Pérot resonator, or a second temperature of the second Fabry-Pérot resonator based on the second detected resonance and a second relationship that correlates the second detected resonance with the second temperature of the second Fabry-Pérot resonator. The computing circuitry outputs a temperature measurement based on at least one of the first temperature of the first Fabry-Pérot resonator or the second temperature of the second Fabry-Pérot resonator.

Also described herein are methods for temperature measurement that employ any of the temperature measurement devices or systems described herein. By way of one example, a method for temperature measurement includes injecting light into an optical fiber from a light source that emits light over a range of wavelengths or frequencies, and detecting a resonance of light in a Fabry-Pérot resonator constructed of an inorganic optical material on an end of the optical fiber. Light in the optical fiber is coupled into a cavity of the Fabry-Pérot resonator and resonates at a resonance that varies according to a temperature of the Fabry-Pérot resonator. The method includes determining a temperature of the Fabry-Pérot resonator based on the resonance of the light in the Fabry-Pérot resonator and a relationship that correlates the resonance of the light in the Fabry-Pérot resonator with the temperature of the Fabry-Pérot resonator. The method further includes outputting a temperature measurement based on the temperature of the Fabry-Pérot resonator. A waveguide may be constructed in the cavity of the Fabry-Pérot resonator, as described herein.

DETAILED DESCRIPTION

In contrast to conventional thermometers that are limited in the range of temperatures they can measure, embodiments of the present disclosure provide a photonic temperature measurement device, system, and method that can measure temperature across a wider range of temperatures, including temperatures in a higher temperature range at which conventional thermometers fail. In particular, the present disclosure uses a Fabry-Pérot (FP) resonator constructed of an inorganic optical material on an end of an optical fiber. The inorganic optical material enables the Fabry-Pérot resonator to operate at temperatures that exceed an upper threshold at which conventional thermometers fail, thus enabling temperature measurements at higher temperatures.

As will be described herein, a portion of the light conducted by the optical fiber is coupled into a cavity of the FP resonator on the end of the optical fiber. The light in the cavity resonates at a resonance (resonant wavelength or frequency) that varies with the temperature of the FP resonator. A detector receiving output light from the FP resonator detects the resonance of the light in the FP resonator. The detector outputs a signal indicating the detected resonance to computing circuitry, which determines the temperature of the FP resonator based on the detected resonance and a relationship correlating the detected resonance with the temperature of the FP resonator.

In various embodiments, the material in the cavity of the FP resonator may include a channel of material having a different refractive index than the material in the cavity surrounding the channel. This dual material arrangement provides a waveguide for the light that is coupled into the cavity of the FP resonator. The waveguide is preferably arranged in the middle of the cavity. With a waveguide, the FP resonator is able to achieve a higher quality factor and large extinction ratio for the resonance of the light in the cavity.

Because the FP resonator is constructed of inorganic optical material on the end of an optical fiber, the temperature measurement device is able to operate in a high-temperature range, e.g., above 600° C. and even in a range of 900° C. to 2000° C. or more. Furthermore, constructing an FP resonator directly on the end of an optical fiber eliminates the need for photonic bonding to couple light from the optical fiber into the FP resonator. This reduces uncertainty in the temperature measurement, including in higher temperature applications as described. The channel of material forming a waveguide in the FP resonator cavity also provides a higher-quality resonance of the light in the cavity.

Also, as described herein, a temperature measurement system may include multiple FP resonators arranged either in parallel or in series on the end of the optical fiber. The multiple FP resonators may each be constructed with different optical properties (e.g., length of cavity, refractive index or indices of material in the cavity) so as to resonate at different resonances according to the temperature of the FP resonators. In this manner, for example, the multiple FP resonators may be arranged to individually resonate within a shorter range of input light wavelengths (or frequencies) for different ranges of temperatures, and collectively provide a temperature measurement system capable of temperature measurement across a broad range of temperatures, including temperatures in a high-temperature range.

FIG.1illustrates a side cross-sectional schematic view of an optical fiber100having Fabry-Pérot (FP) resonator108constructed on end thereof106in accordance with aspects of the present disclosure. The optical fiber100may include an outer cladding102that surrounds a central optical core104. The optical fiber100may be a single mode or multimode optical fiber as is known in the art, and may be constructed of materials known for withstanding high temperature such as sapphire.

In operation, a light source injects input light into the optical fiber100at a first end of the optical fiber100. The input light is communicated through the optical fiber100toward a second end106, where the FP resonator108is constructed. The FP resonator108is useable to measure temperature based on a detected resonant wavelength or frequency of light resonating in a cavity110of the FP resonator108. The resonance of the FP resonator108varies with the temperature of the FP resonator due to characteristics such as thermal expansion and thermo-optic effects that are temperature dependent.

Advantageously, the FP resonator108is formed of an inorganic optical material that maintains functional integrity at higher temperatures. This differs from polymer-based materials that are used in FP resonators for other applications. Examples of an inorganic optical material that may be used in various embodiments of the present disclosure include silicon nitride, titanium dioxide, and gallium arsenide, all of which are part of a class of inorganic dielectric material suitable for use at higher temperatures. In various embodiments, the inorganic optical material maintains integrity at temperatures above 600° C. In some cases, temperature measurement devices using a FP resonator as described herein are operable to measure temperatures to at least 900° C., or even higher to 2000° C.

In the example shown inFIG.1, the FP resonator108includes a first reflective surface112and a second reflective surface114with a cavity (or etalon)110arranged therebetween. The first reflective surface112is constructed directly on the end106of the optical fiber100. At least a portion of the light traversing the optical fiber100passes through the reflective surface112and is coupled into the cavity110. Light may resonate within the cavity110between the first and second reflective surfaces112,114, and be output from the FP resonator108through either (or both) the first reflective surface112and/or the second reflective surface114.

Output light passing through the second reflective surface114may be received by a detector310, as illustrated inFIG.3. Output light from the FP resonator passing through the first reflective surface112back into the optical fiber100may travel in superposition with incoming input light and be redirected to a detector412, as illustrated inFIG.4.

The first and second reflective surfaces112,114, as well as the cavity110therebetween, may be constructed using multilayer deposition techniques such as sputtering, electron beam evaporation, or other types of deposition processes. The first reflective surface112and/or the second reflective surface114may each be constructed of multiple layers of material, as illustrated inFIG.1. Each layer of material in the reflective surface may have a refractive index that is different than the refractive index of at least one adjacent layer of material. The combination of layers forming the first and second reflective surfaces112,114form a mirror that partially reflects light within the cavity110between the reflective surfaces. Depending on the wavelength of the light in the cavity110and the temperature of the FP resonator, the light reflected between the first and second reflective surfaces112,114may constructively resonate within the cavity110and produce a detectable difference in intensity of output light that passes out of the cavity110through the reflective surfaces112,114. As will be described herein, this difference in intensity of the output light is detectable by a detector that receives the output light from the FP resonator108.

Additionally, the cavity110may include a channel116arranged in a direction between the first reflective surface112and the second reflective surface114. The channel116has a width W and is comprised of a material having a different refractive index than material118in the cavity surrounding the channel116. The channel116thus forms a waveguide within the cavity110of the FP resonator108. Patterning techniques known in the art may be used to deposit such materials having different refractive indices within the cavity110and the channel116in the cavity110.

The material in the channel116may have a refractive index profile that varies across the width W of the channel116. In some cases, the material in the channel116may have a single refractive index that differs in a stepwise manner (i.e., a step refractive index) from the refractive index of the material118surrounding the channel. In other cases, the material in the channel116may have a refractive index profile that varies continuously (i.e., a gradient refractive index) across the width W of the channel. In yet other cases, multiple materials with different refractive indices may be used in the channel116.

FIG.2Ais an example diagram200depicting a relationship between a refractive index of material forming the FP resonator108ofFIG.1and the temperature of the FP resonator108. The FP resonator108may be constructed of a material having a refractive index n that changes according to changes in the temperature T of the FP resonator108. The diagram200depicts a relationship between a refractive index, ni, and the temperature, Ti, of the FP resonator108. At a temperature T1, the material in the FP resonator108has a refractive index of n1, and at a different temperature T2, the material in the FP resonator108has a different refractive index n2. In this example, the change in the refractive index n of the material forming the FP resonator108is directly proportional to the change in temperature T of the FP resonator108, e.g., the refractive index n changes linearly relative to the temperature T of the FP resonator108. In other implementations, the relationship of the refractive index n and the temperature T may be nonlinear.

FIG.2Bis an example diagram202illustrating a change in resonance of an FP resonator, such as the FP resonator108ofFIG.1, relative to the temperature of the FP resonator108. In particular,FIG.2Bdepicts two intensity profiles204,206showing a shift in peak intensity of output light emitted from the FP resonator108as a result of a change in temperature of the FP resonator108. For instance, the intensity (or power) of the output light may have a first profile204relative to wavelengths of the input light at a first temperature T1of the FP resonator108. The intensity of the output light may have a different, second profile206relative to wavelength of the input light at a second temperature T2of the FP resonator108. The first profile204and the second profile206depict a shift in the detectable peak resonance (resonant wavelength) of the light in the FP resonator108, resulting from a change in the temperature of the FP resonator.

The profiles204,206indicate the resonance of the light in the FP resonator108with respect different wavelengths of the input light. In some cases as described herein, a detector receiving output light from the FP resonator108may detect maximum or minimum intensities of the output light received from the FP resonator108to detect the resonance of the FP resonator108. In some cases, the detector may evaluate changes in the slope of profiles204,206to identify inflection points indicative of maximum or minimum intensities of the output light and thus detect the resonance of the FP resonator108. As the temperature T of the FP resonator108progresses from temperature T1to T2, the resonance of the FP resonator108shifts from a first detectable resonant wavelength to a second detectable resonant wavelength. Because the detected resonant wavelength of the FP resonator is correlated with the temperature of the FP resonator108, a temperature measurement device may determine the temperature of the FP resonator108from the detected resonant wavelength of the FP resonator108.

FIG.3is a schematic block diagram of at least one embodiment of a temperature measurement device300with a single FP resonator306constructed in accordance with the present disclosure. A light source (e.g., a tunable laser)302is configured to emit light having a wavelength that, over a period of time, changes or scans across a range of wavelengths. In some cases, the light source302may be coupled to a current ramp (not shown) that controls the light emitted by the light source302and causes the emitted light to change wavelength over a range of wavelengths. Under control of the current ramp in this example, the light source302emits light at increasing or decreasing wavelengths. In some cases, the light source302may be controlled to emit light across the range of wavelengths at a relatively constant rate of change of wavelength. In other cases, the light source302may be controlled to emit light at different wavelengths at a variable rate of change.

In some cases, the light source302may be controlled so as to produce light in a subrange of wavelengths that is smaller than the maximum output wavelength range of the light source. It may be sufficient to inject light into the temperature measurement device300in a short range of wavelengths to obtain a detectable resonant wavelength that corresponds to a temperature of the FP resonator306. Using a subrange of wavelengths for the light that is input to the FP resonator306is advantageous in that, by only needing to scan a shorter subrange of wavelengths, a shorter time for delivery of the input light may result in faster detection of the resonant wavelength of the FP resonator306, and quicker determination of the temperature of the FP resonator306.

Light emitted by the light source302is coupled into an optical fiber304at a first end of the optical fiber304. The light traverses the optical fiber304and at least a portion thereof is coupled into the FP resonator306constructed on a second end of the optical fiber304. As previously described, the FP resonator306is constructed of an inorganic optical material that can withstand higher temperatures, e.g., exceeding 600° C.

As the light from the light source302scans across a range of wavelengths and a portion of the light in the optical fiber304is coupled into the FP resonator306, the light at a particular wavelength may resonate in the cavity of the FP resonator306depending on the temperature of the FP resonator306. A portion of the light in the FP resonator306is output from the FP resonator306as output light308. The output light308is received by a detector310and a resonance in the output light308is detected by the detector310.

In some cases, the detector310may be a photodetector configured to produce an electric signal312that is indicative of a detected resonance of the light in the FP resonator306. Computing circuitry314receives the signal312and determines the resonance of the FP resonator306based on the intensity or power of the output light308as indicated in the signal312.

The computing circuitry314is comprised of one or more processors with associated memory in which programmed instructions cause the one or more processors to evaluate the signal312and determine the resonance of the FP resonator306. In some cases, the programmed instructions cause the one or more processors to determine the wavelength at which the optical intensity or power of the output light308from the FP resonator306peaks (maximum or minimum), thus indicating a peak resonance (resonant wavelength or frequency) of the light in the FP resonator306. Other ways for determining the resonance of the FP resonator306may also be used. For example, the computing circuitry may use components that provide frequency locking, which tracks the wavelength of the output light308and reports a detected peak wavelength. In some cases, as will be described below with respect to the embodiments shown inFIGS.5-9where multiple FP resonators are used, the computing circuitry314may be programmed to detect two or more peaks in the optical intensity or power of the output light, and thus determine two or more resonant wavelengths in the output light.

Upon detecting a resonance (e.g., resonant wavelength or frequency) of the FP resonator306in the signal312, the computing circuitry314is configured to determine a temperature of the FP resonator306based on the detected resonance and a predetermined relationship known or obtainable by the computing circuitry314that correlates the detected resonance of the FP resonator306with the temperature of the FP resonator306. The predetermined relationship may correlate a range of resonances with a range of temperatures of the FP resonator. In some cases, the relationship is a calibrated characteristic curve that relates resonances to temperatures.

The relationship between a detected resonance and the temperature of an FP resonator may be determined by a calibration process and represented by, for example, a mathematical model or equation that provides a continuous correlation between resonance wavelengths and temperatures of the FP resonator. In other cases, the relationship may be represented by a lookup table that provides discrete correlations between resonance wavelengths and temperatures of the FP resonator. If needed, the computing circuitry314may interpolate between discrete resonance wavelengths and corresponding temperature values in the lookup table to determine the temperature of the FP resonator based on a detected resonance in the signal312.

In the embodiment illustrated inFIG.3, the computing circuitry314is communicatively coupled to a temperature measurement output316. The temperature measurement output316may be, for example, a display (such as an LCD or LED display) that outputs a temperature reading representing the temperature detected by the temperature measurement device300. In some cases, the temperature measurement output316may be a networking node in which a value representing the temperature measurement is communicated to one or more remote computing devices coupled to a network. The temperature measurement that is output by the temperature measurement device300is based on the temperature of the FP resonator306. In some cases, the temperature measurement output316reports a temperature measurement that equals the determined temperature of the FP resonator306. In other cases, a calibration may be used to correlate the temperature of the FP resonator306to the reported output temperature measurement for the environment in which the temperature measurement device300is deployed.

FIG.4is an alternative schematic block diagram of a temperature measurement device400constructed in accordance with aspects of the present disclosure. The temperature measurement device400includes a light source402, an FP resonator408, a detector412, computing circuitry418, and a temperature measurement output420that operate similar to the light source302, FP resonator306, detector310, computing circuitry314, and temperature measurement output316described above with respect toFIG.3. The temperature measurement device400differs from the temperature measurement device300in that an optical circulator406is arranged along an optical fiber404that receives input light from the light source402. The optical circulator406is configured to direct light emitted from the light source402toward the FP resonator408, and to direct output light received from the FP resonator408toward the detector412.

The FP resonator408is constructed of inorganic optical material on an end of the optical fiber404. Light emitted by the light source402and directed by the optical circulator406is carried by the optical fiber404to the FP resonator408. A portion of the light in the optical fiber404is coupled into the cavity of the FP resonator408, and the light in the cavity of the FP resonator408resonates at different wavelengths depending on the temperature of the FP resonator408.

Output light from the FP resonator408may pass through a reflective surface (e.g., first reflective surface112shown inFIG.1) back into the optical fiber404and travel in superposition with input light from the light source402that is also traversing the optical fiber404. The optical circulator406redirects the output light410to the detector412. The detector412(which may be constructed similar to the detector310) produces a signal416that is received by the computing circuitry418. The signal416is indicative of detected optical intensity or power of the output light410and thus indicative of a detected resonance of the light in the FP resonator408.

The computing circuitry418is configured to evaluate the signal416and determine the resonance of the FP resonator408, e.g., by determining a peak resonance (resonant wavelength or frequency) of the FP resonator408as indicated in the signal416. The computing circuitry418determines a temperature of the FP resonator408based on the detected resonance and a predetermined relationship, as previously described, that correlates the detected resonance of the FP resonator408with the temperature of the FP resonator408. The temperature measurement determined by the computing circuitry418is communicated to the temperature measurement output420for local display for example, or for communication to one or more remote computing devices.

FIG.5is a schematic block diagram of at least one embodiment of a temperature measurement system500with multiple FP resonators506,508constructed in accordance with the present disclosure. The temperature measurement system500includes a temperature measurement device having components as shown inFIG.3, including a light source502, a first FP resonator508, a detector512, computing circuitry516, and a temperature measurement output518, that operate similar to the light source302, FP resonator306, detector310, computing circuitry314, and temperature measurement output316of the temperature measurement device300inFIG.3. The temperature measurement system500differs in that the temperature measurement system500includes a second FP resonator508that is constructed and arranged in series with the first FP resonator506.

The light source502emits light across a range of wavelengths and this light is injected into an optical fiber504. The first FP resonator506is constructed of an inorganic optical material on an end of the optical fiber504. A portion of the light carried by the optical fiber504is coupled into the cavity of the first FP resonator506, which produces an output light as previously described with respect to the FP resonator306shown inFIG.3. InFIG.4, the output light from the first FP resonator506is coupled into the second FP resonator508.

The second FP resonator508is constructed on an end of the first FP resonator506opposite to the end of the first FP resonator506that is on the end of the optical fiber504. The second FP resonator508may be constructed using similar techniques as described above with respect to the FP resonator306inFIG.3, e.g., by depositing layers of material having different refractive indices forming first and second reflective surfaces as well as the material forming a cavity in the FP resonator508, possibly with a channel having a different refractive index and forming a waveguide, as described with respect toFIG.3.

Output light from the first FP resonator506is coupled into the cavity of the second FP resonator508and resonates in the second FP resonator508at a resonance that varies with temperature of the second FP resonator508. A portion of the light in the second FP resonator508is output as output light510from the second FP resonator508. This output light510is received by The detector512is arranged to receive the output light510from second FP resonator508, and produce a signal514indicative of detected intensities of the output light510. The output light510may include resonant peaks indicative of a resonance of light in the first FP resonator506and/or a resonance of light in the second FP resonator508.

The signal514indicates a resonance in the output light510, e.g., by indicating detected maximum or minimum intensities (peaks) of the output light510that the computing circuitry516can use to determine the resonance of the first and/or second FP resonators506,508. In this manner, the signal514produced by the detector512indicates at least one of a first detected resonance of the light in the first FP resonator506or a second detected resonance of the light in the second FP resonator508.

The computing circuitry516is configured to receive the signal514indicating the first detected resonance or the second detected resonance and based thereon, determine at least one of a first temperature of the first FP resonator506or a second temperature of the second FP resonator508(which can include determining both first and second temperatures of the first and second FP resonators506,508). The computing circuitry516is configured to determine the first temperature of the first FP resonator506based on the first detected resonance in the signal514, and similarly, the computing circuitry516is configured to determine the second temperature of the second FP resonator508based on the second detected resonance in the signal514. The computing circuitry516uses the first detected resonance and/or the second detected resonance in conjunction with a predetermined first and/or second relationship that respectively correlates the first and/or second detected resonance with the temperature of the first and/or second FP resonators506,508. The computing circuitry516thereafter outputs a temperature measurement to the temperature measurement output518based on at least one of the first temperature of the first FP resonator506or the second temperature of the second FP resonator508(which can include outputting both the first and second temperatures). In some cases, the computing circuitry516may output multiple temperature measurements to the temperature measurement output518, corresponding to temperature measurements obtained from multiple FP resonators in the temperature measurement system500.

Using multiple FP resonators in a temperature measurement system can provide several advantages. For example, in at least one implementation, the overall range of temperatures that the temperature measurement system500can measure may be divided into multiple subranges of temperatures. The first FP resonator506may be sized and constructed of optical materials that are selected to detect a temperature in a first subrange of temperatures, while the second FP resonator508may be sized and constructed of optical materials that are selected to detect a temperature in a second subrange of temperatures that is different than the first subrange of temperatures. Collectively, the first and second temperature subranges may cover an overall range of temperatures to be measured by the temperature measurement system500. The temperature measurement system500achieves accurate temperature measurements over a wide range of temperatures by taking advantage of different sizing and/or optical materials in the multiple FP resonators which, at a given temperature, cause light to resonate in at least one of the FP resonators506,508, at a wavelength within the same range of wavelengths emitted by the light source502(which may be a short range of wavelengths) and injected into the optical fiber504.

An advantage of dividing the overall temperature range of the temperature measurement system500into multiple temperature subranges is that each FP resonator in the temperature measurement system500may be tuned to detect a temperature in a respective temperature subrange using the same range of wavelengths of light emitted by the light source502. In other words, instead of requiring the light source502to be tunable to emit light over a wide range of wavelengths (which can be very expensive), implementations of the temperature measurement system500may use a light source that emits light over a shorter range of wavelengths (which can significantly decrease the complexity and cost of the temperature measurement system500). For a given temperature of the first and second FP resonators506,508, within the (shorter) range of wavelengths emitted by the light source502, at least one of the first or second FP resonators506,508is configured to produce a resonance that is detectable by the detector512and output in the signal514to the computing circuitry516.

The computing circuitry516may be configured to determine which FP resonator of the first or second FP resonators506,508produced the resonance that is detected by the detector512, and using the detected resonance, determine the temperature of the respective first or second FP resonator based on the detected resonance and a relationship associated with the respective first or second FP resonator that correlates the detected resonance with the temperature of the respective first or second FP resonator. For example, with the temperature measurement system500shown inFIG.5, a resonant peak intensity produced by the first FP resonator506may be diminished in value before it is detected by the detector512because the output light of the first FP resonator506(which includes the resonant peak intensity of the first FP resonator) must first traverse the second FP resonator508before the output light is detected by the detector512. Consequently, a resonant peak intensity of the second FP resonator508would be expected to have an intensity that exceeds the intensity of a resonant peak intensity produced by the first FP resonator506. The computing circuitry516is able to determine the temperature of the first or second FP resonator506,508by selecting and applying a predetermined relationship that is associated with the respective first or second FP resonator, to correlate the detected resonance of the respective first or second FP resonator with the temperature of the respective first or second FP resonator. In other cases, the computing circuitry516may distinguish whether a detected peak intensity in the output light510derives from resonance in the first FP resonator506or the second FP resonator508by recognizing the wavelengths at which the first and second FP resonators are expected to resonate in the temperature range that the temperature measurement system500is operating.

In another implementation of the temperature measurement system500, both the first and second FP resonators506,508may be constructed of materials and tuned to produce a detectable resonance over similar temperature ranges. For example, in at least one implementation, the first FP resonator506may be tuned to produce a coarse (or rough) temperature determination having a broader range of error, while the second FP resonator508may be tuned to produce a finer, more precise determination of temperature. When the first and second FP resonators506,508are operating correctly, the finer temperature measurement produced by the second FP resonator508should fall within the measured temperature range produced by the first FP resonator506. In other words, the coarse temperature determination obtained using the first FP resonator506can be used to verify that the finer determination obtained using the second FP resonator508is correct.

In yet another implementation, both of the first and second FP resonators506,508may be similarly tuned to detect a temperature in the same temperature range with the same or similar precision. With this implementation, when one of the FP resonators is drifting from calibration more than the other FP resonator, the computing circuitry516may produce a temperature measurement that is still more accurate than if a single (drifting) FP resonator was used. The computing circuitry516may produce a mathematical combination (e.g., compute an average of) the two temperatures determined from the first and second FP resonators506,508. The temperature measurement system500is thus able to provide, over a longer term, more accurate temperature measurements.

FIG.6is an alternative schematic block diagram of a temperature measurement system600with multiple FP resonators608,610constructed in accordance with aspects of the present disclosure. The temperature measurement system600includes a temperature measurement device with components similar to those shown inFIG.3, including a light source602, a first FP resonator608, a detector614, computing circuitry618, and a temperature measurement output620that operate similar to the light source302, FP resonator306, detector310, computing circuitry314, and temperature measurement output316described above with respect to the temperature measurement device300shown inFIG.3.

Similar toFIG.5, the temperature measurement system600differs from the temperature measurement device300in that the temperature measurement system600includes a second FP resonator610that is constructed and arranged in series with the first FP resonator608. Input light that is scanned across a range of wavelengths is injected by the light source602into an optical fiber604. An optical circulator606is arranged along the optical fiber604to direct light emitted from the light source602toward the first and second FP resonators608,610, and to direct reflected output light from the first and second FP resonators608,610toward the detector614.

Similar to the first and second FP resonators506,508shown inFIG.5, the first and second FP resonators608,610shown inFIG.6are constructed of inorganic optical materials. Also, in some cases, both the cavity of the first FP resonator608and the cavity of the second FP resonator610may include a channel comprised of material having a different refractive index than material in the respective cavity surrounding the channel, thus providing a waveguide that can produce a sharper, detectable resonant wavelength peak. The first FP resonator608is constructed on an end of the optical fiber604, while the second FP resonator610is constructed on the end of the first FP resonator608. A portion of the light in the optical fiber604is coupled into the cavity of the first FP resonator608, which produces output light that is coupled into the cavity of the second FP resonator610. In each of the first and second FP resonators608,610, light may resonate at a particular wavelength for a given temperature of the respective first and second FP resonators.

The first and second FP resonators608,610may be constructed using similar techniques as described above. Output light from the second FP resonator610may be reflected back through the first FP resonator608into the optical fiber604and travel in superposition with input light from the light source602that is present in the optical fiber604. The optical circulator606directs the output light612to the detector614, which produces a signal616that is delivered to the computing circuitry618. The computing circuitry618may determine the resonance of the first and/or second FP resonators608,610, e.g., by determining a peak optical intensity in the output light612detected by the detector614as discussed above. The computing circuitry618determines a temperature of at least one (or both) of the FP resonators608,610based on a detected resonance and a predetermined relationship, as previously described, associated with the respective first FP resonator608or second FP resonator610, that correlates the detected resonance with the temperature of the first and/or second FP resonator608,610. The computing circuitry618communicates the determined temperature measurement(s) to the temperature measurement output620for local display or for communication to one or more remote computing devices. In cases where the computing circuitry618determines both a first temperature of the first FP resonator608and a second temperature of the second FP resonator610, the computing circuitry may determine a combination of the first and second temperatures and output a combined temperature measurement620, e.g., as described with respect toFIG.5.

In some implementations, the first FP resonator608may be constructed of a material having different optical properties than the material used to construct the second FP resonator610such that, for a given temperature of the first and second FP resonators608,610, light in the first FP resonator608resonates at a different resonance than light in the second FP resonator610. This may be advantageous in cases where multiple FP resonators are used in a temperature measurement system to detect different temperatures in different temperature subranges based on the same wavelength range of input light injected into the temperature measurement system.

FIG.7is a schematic block diagram of another embodiment of a temperature measurement system700with multiple FP resonators706,708constructed in accordance with the present disclosure. A light source702emits light over a range of wavelengths as previously described, and this light is injected into an optical fiber704. In contrast with the temperature measurement systems500,600shown inFIGS.5and6, where multiple FP resonators are constructed in series, in the temperature measurement system700the multiple FP resonators706,708are constructed in parallel.

In particular, the first FP resonator706and the second FP resonator708are both constructed of an inorganic optical material on an end of the optical fiber704. A portion of the light traversing the optical fiber704is coupled into a cavity of the first FP resonator706, while another portion of the light traversing the optical fiber704is coupled into a cavity of the second FP resonator708. In this manner, light coupled into the respective cavities of the first and second FP resonators706,708may resonate within the respective cavities according to the dimensions and optical characteristics of the material used to construct the respective first and second FP resonators. In both of the first and second FP resonators706,708, light in a respective FP resonator resonates at a resonance that varies with the temperature of the respective FP resonator.

It should be understood that the first and second FP resonators706,708may be constructed with different cavities between different reflective surfaces. Alternatively, the first and second FP resonators706,708may share reflective surfaces, with a shared cavity therebetween, in which each FP resonator706,708is achieved by using a different channel116(seeFIG.1) that extends, e.g., in parallel, from one reflective surface toward the other reflective surface. In other words, the first and second FP resonators706,708may be formed by different waveguides (channels) in a shared FP cavity. The different waveguides (channels) may be formed using different materials and/or have different geometric properties to provide different resonant characteristics.

The embodiment of the temperature measurement system700shown inFIG.7uses a single detector712that is configured to receive output light710from the first FP resonator706as well as output light714from the second FP resonator708. The detector712, for example, may have a single photosensitive substrate where the output light710impinges upon a first portion of the photosensitive substrate while the output light714impinges upon a second portion of the photosensitive substrate. In other cases, the detector712may be a unitary device that includes multiple photosensitive surfaces arranged to receive the respective output light710and714. The detector712produces a signal716that indicates at least one of a first detected resonance of the light in the first FP resonator706or a second detected resonance of the light in the second FP resonator708.

In some cases, the detector712is configured to detect in the output light710,714two or more resonances (resonant wavelengths or frequencies) of the first and/or second FP resonators706,708. The computing circuitry718may be programmed to select from the two or more detected resonances at least one resonance that is used to determine a temperature measurement. The at least one resonance may be selected based on which of the two (or more) output lights710,714indicates a resonance of greater intensity. In some cases, a resonance having a greater intensity in one of the output lights710,714is indicative of a wavelength having a stronger correlation to the temperature of the respective FP resonator producing the resonance of greater intensity, and using the wavelength of greater resonance in the temperature correlation processes described herein may yield a more-accurate temperature measurement of the temperature measurement system700. In addition to possibly providing a better temperature correlation, an output light having a wavelength of greater intensity has a larger signal-to-noise ratio, providing greater confidence in the detection of a resonant wavelength in the respective FP resonator.

In some cases, the first FP resonator706may be configured by dimensions or materials to produce a resonant wavelength in a first subrange of temperatures while the second FP resonator708is configured by dimensions or materials to produce a resonant wavelength in a different, second subrange of temperatures, even though the light carried by the optical fiber704from the light source702is scanned across the same range of input light wavelengths. The detector712may discriminate whether a detected resonance is a first detected resonance in the first output light710or a second detected resonance in the second output light714, for example, by determining which portion of the photosensitive substrate of the detector712was impinged by the resonant light.

In some cases, the detector712and/or the computing circuitry718may discriminate whether a detected resonance is produced by the first FP resonator706or the second FP resonator708by receiving a first coarse temperature measurement from a separate thermometer arranged adjacent to the temperature measurement system700. Each of the first FP resonator706and second FP resonator708may be tuned differently to produce a resonant wavelength over different subranges of wavelengths. Depending on the coarse temperature measurement from the separate thermometer, the detector712and/or the computing circuitry718may identify which FP resonator706,708produced the resonance based on knowledge of which temperature subrange includes the coarse temperature measurement.

In any event, the detector712produces a signal716that indicates a detected resonance in at least one of the output light710and/or714, and the signal716is received by the computing circuitry718. The computing circuitry718utilizes a predetermined relationship (embodied, for example, in a mathematical equation or lookup table as previously described) that correlates the detected resonance with the temperature of first or second FP resonator706,708. After receiving the signal716indicating at least one of the first detected resonance or the second detected resonance, the computing circuitry718is configured to determine at least one of a first temperature of the first FP resonator706or a second temperature of the second FP resonator708. The computing circuitry718determines the first temperature of the first FP resonator706based on the first detected resonance in the output light710and a first relationship that correlates the first detected resonance with the temperature of the first FP resonator706. The second temperature of the second FP resonator708may be determined based on the second detected resonance in the output light714and a second relationship that correlates the second detected resonance with the second temperature of the second FP resonator708. Having determined at least one of the first temperature of the first FP resonator706or the second temperature of the second FP resonator708in this manner, the computing circuitry718may output a temperature measurement to the temperature measurement output720based on at least one of the determined first temperature of the first FP resonator706or the determined second temperature of the second FP resonator708.

In some cases, the signal716produced by the detector712indicates both a first detected resonance of the light in the first FP resonator706and a second detected resonance of the light in the second FP resonator708, and the computing circuitry718uses one or both determined resonator temperatures to output a temperature measurement of the system.

In some cases, the optical fiber704is a multicore optical fiber comprising at least a first core and a second core. This may be advantageous in that the first FP resonator706may be situated such that light in the first core is coupled into the cavity of the first FP resonator706, while the second FP resonator708may be situated such that light in the second core is coupled into the cavity of the second FP resonator708. A multicore optical fiber may have any number of cores, e.g, a 3-core, 7-core, 13-core, 19-core optical fiber, etc., coupled with any number of FP resonator(s) on the end of the optical fiber to receive light from the cores.

In some cases, the cavity of the first FP resonator706includes a first channel comprised of a material having a different refractive index than material in the cavity surrounding the first channel. Alternatively or in addition, the cavity of the second FP resonator708includes a second channel comprised of material having a different refractive index than material in the cavity surrounding the second channel. Where the first and second FP resonator706,708are both constructed on the end of the optical fiber704and receive light carried by the optical fiber704, the light in the optical fiber704is coupled into both the first channel of the first FP resonator706and the second channel of the second FP resonator708to produce sharper, detectable resonant peaks in the output light.

FIG.8is an alternative schematic block diagram of a temperature measurement system800with multiple FP resonators812,822constructed in accordance with aspects of the present disclosure. The multiple FP resonators812,822inFIG.8are configured to operate in parallel, similar to the multiple FP resonators706,708shown inFIG.7. Also, as with the temperature measurement system700, the temperature measurement system800includes components similar to the components of the temperature measurement device300shown inFIG.3, including a light source802, a (first) FP resonator812, a (first) detector816, computing circuitry820, and a temperature measurement output830, which may operate similar to the light source302, FP resonator306, detector310, computing circuitry314, and temperature measurement output316shown and described with respect toFIG.3.

However, system800includes a number of differences that structurally distinguish system800from the temperature measurement device300shown inFIG.3and the temperature measurement system700shown inFIG.7. Light emitted by the light source802over a range of wavelengths is injected into an optical fiber804. The input light carried by the optical fiber804is received by a beam splitter806that divides the input light from the light source802and outputs a first portion of the input light to a first optical fiber808and a second portion of the input light into a second optical fiber810.

Constructed on the end of the first optical fiber808is the first FP resonator812, while constructed on the end of the second optical fiber810is the second FP resonator822. Portions of the input light carried by the first optical fiber808and the second optical fiber810are coupled respectively into cavities of the respective first and second FP resonators812,822. Depending on dimensions and materials used to construct the first and second FP resonators812,822, the portions of the input light coupled into the respective first and second FP resonators may resonate at different wavelengths according to the respective temperatures of the first and second FP resonators.

FIG.8also depicts separate first and second to detectors816,826, operating in parallel. The first detector816receives output light814from the first FP resonator812, while the second detector826receives output light824from the second FP resonator822. Each of the first and second detectors816,826may be constructed similar to the detectors previously described herein, including the detector310shown inFIG.3. Each of the first and second detectors816,826outputs respective signals818,828indicative of detected resonances in the respective output light814,824. The signals818,828are received by computing circuitry820, which evaluates the light intensities in the respective signals818,828to determine first and/or second detected resonances of the respective first and/or second FP resonators812,822. The signal818is thus a first signal from the first detector816indicating a first detected resonance of the light in the first FP resonator812. Similarly, the signal828is a second signal from the second detector826indicating a second detected resonance of the light in the second FP resonator822.

Both of the first and second FP resonators are constructed of an inorganic optical material that is capable of retaining functional integrity at higher temperatures, e.g. exceeding 600° C. or higher. Light in the respective cavities of the first and second FP resonators812,822resonates at first and second resonances that vary according to the temperature of the respective first and second FP resonators812,822.

The computing circuitry820is configured to receive at least one of the first signal818indicating the first detected resonance of the first FP resonator812or the second signal828indicating the second detected resonance of the second FP resonator822, or both the first and second signals818,828shown inFIG.8. The computing circuitry820is thereafter configured to determine at least one of a first temperature of the first FP resonator812or the second temperature of the second FP resonator822. The computing circuitry820is configured to determine the first temperature of the first FP resonator812based on the first detected resonance and a first relationship that correlates the first detected resonance with the temperature of the first FP resonator812. The computing circuitry820is also configured to determine the second temperature of the second FP resonator822based on the second detected resonance and a second relationship that correlates the second detected resonance with the temperature of the second FP resonator822. One or both of the determined first temperature of the first FP resonator812or the second temperature of the second FP resonator822is (or are) communicated to the temperature measurement output830for local display or communication to one or more remote computing devices.

In cases where the computing circuitry determines both the first temperature of the first FP resonator812and the second temperature of the second FP resonator822, the computing circuitry may be configured to output an overall temperature measurement based on a combination of the first temperature and the second temperature, e.g., as described earlier with respect toFIG.5.

FIG.9is a schematic block diagram of another embodiment of a temperature measurement system900with multiple FP resonators914,926constructed in accordance with the present disclosure. Similar to the temperature measurement system800shown inFIG.8, the temperature measurement900includes a light source902that injects light over a range of wavelengths into an optical fiber904. The light in the optical fiber904is divided by a beam splitter906such that a first portion of the light is carried by a first optical fiber908and a second portion of the light is carried by a second optical fiber910. Similar to the temperature measurement systems400and600shown inFIGS.4and6, the temperature measurement system900inFIG.9includes an optical circulator, namely a first optical circulator912arranged along a length of the first optical fiber908and a second optical circulator924arranged along a length of the second optical fiber910. The first optical circulator912is configured to direct input light carried by the first optical fiber908toward the first FP resonator914, while the second optical circulator924is configured to direct input light carried by the second optical fiber910toward the second FP resonator926. A portion of the light in the respective first and second optical fibers908,910is optically coupled into cavities of the respective first and second FP resonators914,926, and resonates in the respective cavities depending on the temperature of the first and second FP resonators.

Resonant output light reflected by the first and second FP resonators914,926returns along the optical fibers908,910to the first and second optical circulators912,924which respectively direct the output light to first and second detectors918,930. In particular, the first detector918receives output light916from the first optical circulator912, while the second detector938receives output light928from the second optical circulator924. The first detector918produces a first signal920indicative of a resonance in the output light916, while the second detector930produces a second signal932, indicative of a resonance in the output light928.

As illustrated inFIG.9, computing circuitry922is configured to receive both the first signal920and the second signal932and evaluate detected resonances in the first and/or second signals920,932. The computing circuitry is further configured to determine at least one of a first temperature of the first FP resonator914or a second temperature of the second FP resonator926. The first temperature of the first FP resonator914is determined based on the first detected resonance and a first relationship that correlates the first detected resonance with the temperature of the first FP resonator914. Similarly, the second temperature of the second FP resonator926is determined based on the second detected resonance and a second relationship that correlates the second detected resonance with the second temperature of the second FP resonator926. The computing circuitry922outputs one or both of the determined first temperature and/or second temperature to the temperature measurement output934for local display or communication to one or more remote computing devices.

FIG.10is a flow diagram illustrating at least one embodiment of a method1000for temperature measurement in accordance with the present disclosure. All of the embodiments of the temperature measurement devices and systems shown inFIGS.3-9operate according various method steps as previously described. The method1000is an example illustrating the basic steps of a temperature measurement device, e.g., a temperature measurement device300,400as shown inFIG.3or4.

The method1000includes, at step1002, injecting light into an optical fiber from a light source that emits light over a range of wavelengths or frequencies. At step1004, the method includes detecting a resonance of light in a Fabry-Pérot (FP) resonator constructed of an inorganic optical material on an end of the optical fiber. Light in the optical fiber is coupled into a cavity of the FP resonator and resonates at a resonance that varies with temperature of the FP resonator.

At step1006, the method includes determining a temperature of the FP resonator based on the resonance of the light in the FP resonator and a relationship that correlates the resonance of the light in the FP resonator with the temperature of the FP resonator. Lastly, at step1008, the method include outputting a temperature measurement based on the temperature of the FP resonator. In some cases, the method includes detecting the resonance of the light in the FP resonator based on a detected maximum or minimum intensity in output light received from the FP resonator.

In some cases where multiple FP resonators are used, as described herein, the above-indicated FP resonator is a first FP resonator, and the method further includes detecting a resonance of a second FP resonator. The second FP resonator is constructed of an inorganic optical material arranged either on the end of the optical fiber or on the first FP resonator. Similar to light coupled into the cavity of the first FP resonator, which resonates at a resonance that varies with the temperature of the first FP resonator, light coupled into a cavity of the second FP resonator resonates at a resonance that varies with temperature of the second FP resonator.

Similar to the step of measuring temperature using the first FP resonator, the method includes determining a temperature of the second FP resonator based on the resonance of the second FP resonator and a relationship that correlates the resonance of the light in the second FP resonator with the temperature of the second FP resonator. The method then outputs a temperature measurement based on at least one of the temperature of the first FP resonator or the temperature of the second FP resonator, e.g., to a local display or memory or communicated to a remote computing device.

In some cases, the methods described herein may further include constructing the FP resonator on the end of the optical fiber, e.g., by depositing two or more layers of material having different refractive indices to form a first reflective surface directly on the end of the optical fiber, depositing material adjacent to the first reflective surface to form the cavity, and depositing two or more layers of material having different refractive indices on the material forming the cavity to form a second reflective surface, wherein the material forming the cavity separates the first reflective surface from the second reflective surface.

In some cases, depositing material adjacent to the first reflective surface to form the cavity includes depositing a channel of material as a waveguide within the material forming the cavity, the channel of material extending in a direction between the first reflective surface and the second reflective surface, and the channel of material having a refractive index that is different than the material in the cavity around the channel of material.

In some cases, the optical fiber is a multicore optical fiber, and the method includes coupling light from at least a first core of the multicore optical fiber into the cavity of the first FP resonator and coupling light from a second core of the multicore optical fiber into the cavity of the second FP resonator, wherein the first FP resonator operates in parallel with the second FP resonator.

It should be understood that aspects of the various embodiments described above can be individually or collectively combined with each other in yet additional combinations to provide further embodiments. Aspects shown and described with respect to any one of the figures may be combined with aspects of other figures and remain within the scope of the disclosure herein.