Photonic devices using cavity differential techniques

Abstract

The photonic device has one or more optical resonators having a first resonant frequency response to temperature and a different second resonant frequency response to temperature. In at least one embodiment, a first waveguide optically couples input light having a first frequency to the first optical resonator, and a second waveguide optically couples input light having a second frequency to the second optical resonator. The optical outputs from the one or more optical resonators are combined. The temperature of the photonic device can be determined from a beat frequency in the composite optical output. One or more optical detectors can convert the composite optical output to an electrical signal, and the detected frequency in the electrical signal indicates the beat frequency of the composite optical output. The beat frequency is correlated to the temperature of the photonic device. In one embodiment, one or more multimode optical resonators can be used.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to photonic devices and methods, and more particularly to photonic devices and methods for measuring physical conditions such as temperature. Summary of the Invention [Problem to be solved by the invention]

[0002] Photonic thermometers are a class of temperature measurement systems that detect properties of light within a sensor to obtain temperature measurements. These systems are valued for their size, robustness, accuracy, precision, and range of potential applications. However, these temperature measurement systems suffer from certain drawbacks. The response characteristics of some measurement devices used to detect properties of light can cause the photonic thermometer to drift over time. As a result, operation of the measurement system may require periodic recalibration to obtain consistent performance over time. Some classes of measurement devices used in these systems can be expensive and may have limited resolution. Ambient temperature fluctuations can also significantly affect the operation of these measurement devices, so exposing these measurement devices to temperature fluctuations can introduce uncertainty into the measurements obtained. [Means for solving the problem]

[0003] Disclosed herein are systems and methods in which a photonic device has one or more optical resonators with a first resonant frequency response to temperature and a different second resonant frequency response to temperature, and when the photonic device is implemented in an optical thermometer, the resonant frequency difference generates an output signal having a beat frequency indicative of the temperature of the photonic device.

[0004] In various embodiments, a photonic system of the present disclosure comprises a photonic device including a substrate, a first optical resonator in or on the substrate, the first optical resonator having a first resonant frequency response over temperature, a second optical resonator in or on the substrate, the second optical resonator having a second resonant frequency response over temperature, a first waveguide optically coupled to receive a first optical beam and optically coupled to the first optical resonator, and a second waveguide optically coupled to receive a second optical beam and optically coupled to the second optical resonator. The photonic system further includes a detector configured to convert output light from the photonic device into an electrical signal. The detector may be a photodetector, a wavemeter or frequency meter, or other detection circuit configured to detect an aspect of the output light, such as intensity, wavelength, or frequency. The detector converts the output light into an electrical signal by generating an electrical signal representative of the detected aspect of the output light.

[0005] The photonic system may further comprise an optical combiner configured to combine the first output light from the first waveguide and the second output light from the second waveguide into a composite light, the composite light being the output light of the photonic device, and one or more measurement devices configured to measure a characteristic of the electrical signal that corresponds to or is otherwise indicative of a physical condition of the photonic device, such as a temperature of the photonic device.

[0006] In various embodiments, a method of operating a photonic device may include directing a first light beam into a first waveguide of the photonic device, directing a second light beam into a second waveguide of the photonic device, determining a frequency difference between first output light from the first waveguide and second output light from the second waveguide, and determining a temperature of the photonic device based on the frequency difference. In some cases, the first output light from the first waveguide and the second output light from the second waveguide may be combined into a composite light, and the frequency difference is determined based on the composite light.

[0007] The method includes adjusting the frequency of a first optical beam to a frequency of a first optical cavity in a photonic device. 1st Co Circulation The wavenumber of the second light beam is locked to the photonic device. The second cavity of the second optical cavity in the Circulation and locking to a frequency. The wavenumber difference is the frequency of the first light beam locked to the first resonant frequency and the frequency of the second light beam locked to the The frequency can be determined after it is locked to the second resonant frequency. [Brief explanation of the drawings]

[0008] In the drawings, like elements or functions are identified by the same reference numbers. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes and orientations of various elements are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve drawing clarity. Additionally, the particular shapes of elements as shown are not necessarily intended to convey any information regarding the actual shape of the particular elements, but may simply be selected for ease of recognition in the drawings. [Figure 1A] FIG. 1 is a perspective view of an example of a photonic device that can be used to measure temperature. [Figure 1B] FIG. 1B is a top view of the optical cavity of the photonic device of FIG. 1A. [Figure 2A] 1B is a graph showing the change in refractive index of the photonic device of FIG. 1A with respect to temperature. [Figure 2B] 1B is a graph illustrating the change in resonant response of the photonic device of FIG. 1A with respect to temperature. [Figure 3] FIG. 1 is a schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 4A] 4 is a top view of the first and second optical resonators of the photonic device of FIG. 3. FIG. [Figure 4B]4B is a cross-sectional view of the first optical cavity taken along line AA of FIG. 4A. [Figure 5] 4 is a graph showing the change in optical resonant frequency of the first optical resonator and the second optical resonator of the photonic device of FIG. 3 with respect to temperature. [Figure 6] 4 is a graph showing the change in beat frequency of the photonic device of FIG. 3 with respect to temperature. [Figure 7] 4 is a graph illustrating the variation of the refractive index of the first optical cavity and the second optical cavity of the first photonic device of FIG. 3 with respect to temperature. [Figure 8] 1 is a graph showing the variation of the resonant wavelength of an optical resonator with respect to the mode number and optical path length of a cavity in the optical resonator. [Figure 9] FIG. 4 is a flow diagram illustrating a method for determining the temperature of the photonic thermometer of FIG. 3. [Figure 10] FIG. 1 is another schematic block diagram of a temperature measurement system including a photonic thermometer, in accordance with one or more embodiments of the present disclosure. [Figure 11] FIG. 1 is another schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 12] FIG. 1 is another schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 13] FIG. 1 is another schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 14] FIG. 1 is another schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 15] FIG. 1 is another schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 16] FIG. 1 is another schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 17] FIG. 1 is another schematic block diagram of a measurement system including a photonic device, in accordance with one or more embodiments of the present disclosure. [Figure 18] 1 illustrates an example of an optical resonator that may be implemented in a photonic device of the measurement system described herein. [Figure 19] 1 illustrates exemplary configurations of multiple photonic crystals that may be used to resonate light in the measurement systems described herein. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1A illustrates at least one embodiment of a system 100 including a photonic device 102 that may be used, for example, in a photonic thermometer to measure temperature. The photonic device 102 includes a substrate 108 having an optical resonator 106 and a waveguide 104 proximate to the optical resonator 106. The photonic device 102 can be used to measure temperature based on the resonant frequency of the optical resonator 106 changing due to a thermo-optic effect of the optical resonator 106, such as a change in the refractive index of the material forming the optical resonator 106 in response to a change in temperature of the photonic device 102. The waveguide 104 is a conduit for light that includes a first port 110 and a second port 112 on the substrate 108 for transmitting light into and out of the waveguide 104.

[0010] The substrate 108 supports the optical resonator 106 and the waveguide 104 in a fixed relationship. The substrate 108 (including the waveguide 104 and the optical resonator 106) may be formed of a material having optically transparent properties such that at least a portion of light entering the waveguide 104 is directed into the optical resonator 106 via internal reflection within the waveguide 104. For example, the substrate 108 may be formed from a metal, including, but not limited to, silicon such as silicon dioxide, a silicate (e.g., borosilicate glass, lead glass, aluminum silicate), a carbonate (e.g., sodium carbonate), a glass ceramic, an amorphous metal, or a silica-free glass. The substrate 108 may also be formed of other suitable materials based on the desired application or properties of the photonic device 102. The photonic device 102, including the substrate 108, the waveguide 104, and the optical resonator 106, may be formed using a variety of fabrication methods, such as, but not limited to, lithographic methods (e.g., photolithography, electron beam lithography, embossing, direct pattern writing, 3D printing), film deposition, film spreading, and film etching.

[0011] 2A shows a graph 200 illustrating the relationship between the refractive index and temperature of a substrate 108. More specifically, graph 200 illustrates the relationship between the refractive index n and temperature T of a substrate 108 formed of silicon. As shown, the change in the refractive index n of the substrate 108 is directly proportional to the change in temperature T. For example, the refractive index n of the substrate 108 may vary linearly with the temperature T of the substrate 108. In some embodiments, the substrate 108 may have optical properties that have different response characteristics with respect to temperature.

[0012] 1A , the optical resonator 106, in at least some embodiments, is optically coupled to the waveguide 104. In some embodiments, the waveguide 104 is spaced apart from the optical resonator 106. At least a portion of the light that enters the waveguide 104 via a first port 110 is received within the optical resonator 106. The properties of the light within the optical resonator 106 are modified, and the modified light is coupled back into the waveguide 104. The modified light, along with the original light, overlaps and passes through the remainder of the waveguide 104. The modified light and the original light are output from a second port 112 of the waveguide 104.

[0013] FIG. 1B illustrates an optical path 116 of the optical resonator 106. In particular, the optical resonator 106 has a ring-shaped or toroidal shape. The optical path 116 extends circumferentially through the cross-sectional center of the optical resonator 106. During operation, light coupled into the optical resonator 106 enters the optical resonator 106 at a first point 118 and internally reflects between the inner surfaces of the optical resonator 106 along the optical path 116. The light exits the optical resonator 106 at a second point 120. The properties of the light passing through the optical resonator 106 can be modified relative to the light passing through the waveguide 104. Those skilled in the art will appreciate that there can be different first and second points 118, 120 at which different light rays are coupled into and out of the optical resonator 106, respectively. The modified light is coupled back into the waveguide 104 at the second point 120 and exits the waveguide 104 along with the original light.

[0014] As a result of changes in temperature experienced by photonic device 102 and the resulting change in refractive index n, the effective length of optical path 116 may change. For example, the effective length of optical path 116 may change according to the following equation: L eff (T)=n eff (T)L In the formula, L eff is the effective length of the optical path 116, T is the temperature to which the photonic device 102 is subjected, and n is the refractive index of the substrate 108. As can be seen, the effective length L eff changes with the change in temperature T to which the photonic device 102 is subjected. eff may, for example, increase with a corresponding increase in temperature.

[0015] Effective length L eff A change in temperature results in a corresponding change in the light within the optical resonator 106. Figure 2B shows a graph 202 illustrating changes in the properties of the light output from the second port 112 as a result of temperature changes. For example, the intensity of the modified light may have a first profile 204 versus wavelength at a first temperature and a second profile 206 versus wavelength at a second temperature.

[0016] Existing thermal measurement systems, or photonic thermometers, may include a photonic device 102 and a wavemeter coupled to receive light output from the second port 112 of the photonic device 102. The wavemeter analyzes the wavelength of the light, detects its resonance, and can determine the temperature of the photonic device 102 based on a known relationship between the resonance and temperature of the photonic device 102. However, currently known wavemeters are expensive to procure and maintain. Wavemeters can also experience significant drift over time, adversely affecting the calibration of the overall system. Periodic recalibration of the system may be required to ensure accurate measurements over time. Therefore, significant training and scientific knowledge is required for users of such measurement systems, increasing the cost and complexity associated with operating such systems.

[0017] 3 is a schematic block diagram of a measurement system 300 including a photonic device 302 operating as a photonic thermometer in accordance with one or more embodiments of the present disclosure. The photonic device 302 includes a first waveguide 304 and a first optical resonator 306 in or on a substrate 308, where the first optical resonator 306 is optically coupled to the first waveguide 304. The photonic device 302 also includes a second waveguide 310 and a second optical resonator 312 in or on the substrate 308, where the second optical resonator 312 is optically coupled to the second waveguide 310. The second waveguide 310 is spaced apart from the first waveguide 304 and defines an optical path separate from the first waveguide 304. In some embodiments, the first waveguide 304, the first optical resonator 306, the second waveguide 310, and the second optical resonator 312 are constructed on the same chip.

[0018] Light introduced into the photonic device 302 may pass through a first waveguide 304 between a first port 314 and a second port 316, which may be located or exposed external to the substrate 308. Light introduced into the photonic device 302 may also pass through a second waveguide 310 between a first port 318 and a second port 320, which may also be located or exposed external to the substrate 308. In some embodiments, one or both of the first ports 314, 318 or one or both of the second ports 316, 320 may include one or more grating couplers or other types of couplers configured to couple input light into the first waveguide 304 or the second waveguide 310. In some embodiments, one or both of the first or second waveguides 304, 310 may have a different shape at one or both of the first ports 314, 318 or one or both of the second ports 316, 320 to facilitate efficient coupling of light. In some embodiments, one or both of the first ports 314, 318 or one or both of the second ports 316, 320 may be configured to edge couple light into or out of one or both of the first or second waveguides 304, 310.

[0019] The photonic device 302, including the substrate 308, the first optical cavity 306, and the second optical cavity 312, can be fabricated using a variety of materials. Non-limiting examples of such materials include silicon, silicon nitride, silicon dioxide (also known as silica, oxide, quartz, fused silica), gallium arsenide, sapphire (alumina, aluminum oxide), germanium, fluoride materials, bromide materials, and chloride materials. The photonic device 302, including the substrate 308, the first optical cavity 306, and the second optical cavity 312, can be formed using a variety of fabrication methods, including, but not limited to, lithography methods (e.g., photolithography, electron beam lithography, embossing, direct pattern writing, 3D printing), film deposition, film expansion, and film etching.

[0020] The second optical resonator 312 is spaced apart from the first optical resonator 306. The first optical resonator 306 and the second optical resonator 312 are optically isolated from each other so that light from one of the optical resonators is not coupled into the other optical resonator. In some embodiments, the first optical resonator 306 and the second optical resonator 312 are the same type of optical resonator. However, one or more aspects of the second optical resonator 312 are different from the first optical resonator 306. As a result, the second optical resonator 312 has a different resonant frequency response over a temperature range than the first optical resonator 306.

[0021] There are many ways to create a difference in resonant frequency response between the first optical resonator 306 and the second optical resonator 312. For example, one or more thin film regions may be positioned around one of the first optical resonator 306 or the second optical resonator 312 and not the other, or thin film regions of different size or composition may be positioned around both the first optical resonator 306 and the second optical resonator 312. The mechanical stress on or around the first optical resonator 306 may be different from the mechanical stress on or around the second optical resonator 312. Different temperatures may be applied to each of the first optical resonator 306 and the second optical resonator 312 using passive thermal mechanisms (e.g., chip design) or by active thermal mechanisms (e.g., microheaters). As a further example, the refractive index of the first optical resonator 306 may differ from the refractive index of the second optical resonator 312 using active or passive refractive index variations, such as varying the type or concentration of the dopant(s) used to create the first optical resonator 306 and the second optical resonator 312. Those skilled in the art will appreciate that there are myriad ways in which differences in resonant frequency response between the first optical resonator 306 and the second optical resonator 312 may be implemented without departing from the scope of the present disclosure.

[0022] The different resonant frequency response of the second optical resonator 312 relative to the first optical resonator 306 may be due to one or more differences in the size of the second optical resonator 312 relative to the first optical resonator 306. For example, the first optical resonator 306 and the second optical resonator 312 may have different values in one or more dimensions. For example, the first optical resonator 306 and the second optical resonator 312 may have different optical path lengths (circumferential direction C shown in FIG. 3 ), different thicknesses (axial direction A shown in FIG. 3 ), or different widths (radial direction R shown in FIG. 3 ). As a non-limiting example, the first optical resonator 306 may have an optical path length of 186.572 μm, and the second optical resonator 312 may have an optical path length of 186.800 μm. As another non-limiting example, the first optical resonator 306 may have a width of 533 nm, and the second optical resonator 312 may have a width of 530 nm. Therefore, the first optical resonator 306 and the second optical resonator 312 may have different optical resonant frequencies with respect to temperature due to the dimensional difference.

[0023] The different resonant frequency response of the second optical resonator 312 relative to the first optical resonator 306 may be due to one or more differences in the material of the second optical resonator 312 relative to the first optical resonator 306. The second optical resonator 312 may, for example, include a different material than the first optical resonator 306. The second optical resonator 312 may include an additional layer of cladding not included in the first optical resonator 306. As a specific, non-limiting example, the first optical resonator 306 may be formed on a layer of silicon oxide (SiO). The second optical resonator 312 may include an additional material, such as a layer of aluminum oxide (AlO) formed on the silicon oxide layer, while the first optical resonator 306 does not include an aluminum oxide layer or has an aluminum oxide layer of a different thickness.

[0024] The difference in material can be between the material of the core of the first optical resonator 306 and the material of the core of the second optical resonator 312. The difference in material can be between the material of the cladding of the first optical resonator 306 and the material of the cladding of the second optical resonator 312. The difference between the core or cladding of the first optical resonator 306 and the second optical resonator 312 can be a difference in material type or composition, optical properties of the material, concentration of the material, or other difference.

[0025] The resonant wavelengths of the first optical resonator 306 and the second optical resonator 312 can be calculated using the following equations:

[0026]

number

[0027] The slopes of the curves representing the change in resonant wavelength with respect to temperature for the first optical resonator 306 and the second optical resonator 312 may vary with respect to temperature. In particular, the change in slope of the resonant wavelength curves for the first optical resonator 306 and the second optical resonator 312 is represented by the following equation:

[0028]

number

[0029]

number

[0030]

number

[0031] The different resonant frequency response of the second optical resonator 312 relative to the first optical resonator 306 may be due to one or more differences in the structure of the second optical resonator 312 relative to the first optical resonator 306. As an example, Figure 4A shows a top view of the first optical resonator 402 and the second optical resonator 404, where the first optical resonator 402 has structural features that are not present in the second optical resonator 404. In particular, the first optical resonator 402 has a section 406 on or within the optical path of the first optical resonator 402.

[0032] FIG. 4B shows a cross-sectional view of first optical resonator 402 taken along line AA in FIG. 4A. First optical resonator 402 is formed on a substrate 408. Section 406 is formed on or within a portion of the optical path of first optical resonator 402. First optical resonator 402 may have a width W1 and a thickness T1. Section 406 shown in FIGS. 4A and 4B has one or more attributes that differ from the remainder of first optical resonator 402. The differences may be differences in dimension or size, material in or around section 406, mechanical stress, or other attributes discussed above with respect to FIG. 3 that change the resonant frequency of first optical resonator 402 relative to an optical resonator without section 406.

[0033] For example, in FIG. 4B , section 406 has a width W2 that is different from the width W1 of the remainder of first optical resonator 402. The difference in dimension may include a difference in thickness T1. In other cases, other dimensions of first optical resonator 402 and second optical resonator 404 may be the same. In some embodiments, section 406 may be formed on first optical resonator 402, or between first optical resonator 402 and substrate 408, or formed widthwise outward on or near a side of first optical resonator 402. In some embodiments, section 406 may have a cross-sectional shape that is different from the rest of first optical resonator 402. For example, section 406 may have a circular cross-sectional shape, while the rest of first optical resonator 402 may have a rectangular cross-sectional shape.

[0034] 3 , measurement system 300 includes an input portion 322 coupled to first ports 314 and 318 and an output portion 324 coupled to second ports 316 and 320. Input portion 322 includes a light source 328 that generates light 326. Light source 328 may be a tunable light source that is controllable to tune the frequency of light 326. For example, light 326 may initially have a first frequency f1, and light source 328 may be operated a second time to tune light 326 to have a second frequency f2.

[0035] In some embodiments, light source 328 is a laser light source that generates laser light. The laser light source may be, by way of non-limiting example, a telecom C-band laser that generates laser light in the wavelength range of 1530 nm to 1565 nm. Light source 328 may generate light in other spectrums, including, by way of non-limiting example, the visible spectrum, near-infrared, mid-infrared, and far-infrared, the X-ray spectrum, and the ultraviolet spectrum. In some embodiments, a high-frequency electromagnetic source may be used. Light source 328 may be a continuous-wave narrowband laser source, a frequency comb source, a broadband source, a pulsed source, a coherent source, an incoherent source, or any other type of light source operable to generate light compatible with the optical resonance of photonic device 302.

[0036] The light 326 is directed into an optical element 330 that splits the light 326 into a first input light 332 and an auxiliary light 334. The optical element 330 may be a beam splitter that splits the beam into two light beams, the first input light 332 and the auxiliary light 334, having the same optical properties. The auxiliary light 334 is directed into an optical shifter 336 that shifts the frequency of the auxiliary light 334 by a fixed frequency amount f S The optical shifter 336, in some embodiments, may shift the phase of the assist light 334. The optical shifter 336 outputs a second input light 338 having a third frequency f3 that is different from the second frequency f2 of the first input light 332. The optical shifter 336, in some embodiments, may include one or more passive devices, including optical elements that do not consume power to achieve the shift in the characteristics of the assist light 334. The optical shifter 336 may, for example, include a material with a crystalline structure that changes the frequency of the light passing therethrough. In some embodiments, the optical shifter 336 includes an active device (e.g., a frequency modulator) that consumes power to achieve the shift in characteristics. In such embodiments, the optical shifter 336 may be controlled to tune the frequency of the second input light 338 to the resonant frequency of the second optical resonator 312.

[0037] The frequency of light 326 from light source 328 may be tuned from a first frequency f1 to a second frequency f2, which may be the resonant frequency of the first optical resonator, and split by optical element 330 to provide first input light 332. The frequency of first input light 332 is locked to second frequency f2, which is the resonant frequency of first optical resonator 306 for a particular temperature and mode number (e.g., mode number 300 at a temperature of -200°C). The frequency of second input light 338 is tuned and locked to third frequency f3, which is the resonant frequency of second optical resonator 312 for the same particular temperature and mode number (e.g., mode number 300 at a temperature of -200°C). In some embodiments, optical shifter 336 controls the amount by which the frequency of assist light 334 is shifted, f s In some embodiments, the optical shifter 336 is selectively controllable to vary a fixed frequency amount f s In such an embodiment, the resonant frequencies of the first optical resonator 306 and the second optical resonator 312 can be determined separately at the output of the photonic device 302. A frequency difference between the first output light from the first waveguide 304 and the second output light from the second waveguide 310 can be determined, and based on the frequency difference, a physical condition of the photonic device 302, such as temperature, can be determined.

[0038] During operation, the frequency of the light source 328 may be swept or varied from a first frequency f to a second frequency f over a period of time. For example, the light source 328 may be controlled so that the emitted light 326 initially has a first frequency f. The light source 328 is controlled to increase or decrease the frequency of the emitted light 326 over a period of time until the light 326 has a second frequency f, which is the resonant frequency of the first optical resonator 306 at the current temperature of the photonic device 302.

[0039] Because both the fill light 334 and the first input light 332 are split from the light source 326, the frequency of the fill light 334 varies with the frequency of the first input light 332. The light shifter 336 shifts the frequency of the second input light 338 relative to the fill light 334 by a frequency amount f sThe frequency of the light 326 may be varied continuously or stepwise in defined increments. As described herein, the output of the photonic device 302 is evaluated to identify the resonant frequencies of the first optical resonator 306 and the second optical resonator 312, and the resonant frequencies are used to determine the temperature of the photonic device 302. The input section 322 may include an optical frequency locked loop that controls the frequency of the second optical input 338 relative to the frequency of the first input light 332.

[0040] The temperature of the photonic device 302 may be determined by accessing temperature correspondence data stored in memory. In some embodiments, the temperature of the photonic device 302 is determined based on the resonant frequencies of the first optical resonator 306 and the second optical resonator 312. In some embodiments, the temperature is determined based on the correspondence between the frequency difference of the resonant frequencies and the temperature, as reflected in the temperature correspondence data. The temperature correspondence data may include a lookup table and / or a function (i.e., a formula or equation) that represents the correspondence between the resonant frequency (or an aspect, combination, or difference thereof) and the temperature of the photonic device 302.

[0041] In some embodiments, measurement system 300 may include a second light source (not shown) that generates second input light 338. In such embodiments, measurement system 300 may exclude optical element 330 and optical shifter 336. For example, first light source and second light source may be separate or separately operable laser light sources, each generating laser light. Second input light 338 generated by the second light source is directed into second waveguide 310 via first port 318. First input light 332 is generated by light source 328 and directed into first waveguide 304 via first port 314. Light source 328 and second light source are independently controlled to adjust the frequencies of first input light 332 and second input light 338. In particular, the frequency of the first input light 332 is locked to the resonant frequency of the first optical resonator 306, and the frequency of the second input light 338 is locked to the resonant frequency of the second optical resonator 312. The second light source may be substantially similar to the light source 328, and therefore further description thereof will be omitted.

[0042] A first input light 332 is directed or introduced into the first waveguide 304, and a second input light 338 is directed or introduced into the second waveguide 310. When the first input light 332 has a frequency corresponding to the resonant frequency of the first optical resonator 306, the first optical resonator 306 resonates at least a portion of the first input light 332, causing a corresponding change in the characteristics (e.g., amplitude) of the first output light 340 output from the second port 316. When the second input light 338 has a frequency corresponding to the resonant frequency of the second optical resonator 312, the second optical resonator 312 resonates at least a portion of the second input light 338, causing a corresponding change in the characteristics (e.g., amplitude) of the second output light 342 output from the second port 320. The first optical resonator 306 is optically isolated from the second optical resonator 312 such that the first optical resonator 306 and the second optical resonator 312 do not exchange light through the substrate 308 or otherwise.

[0043] In some embodiments, the output section 324 includes an optical combiner 344 that combines or mixes the first output light 340 (“Output 1”) and the second output light 342 (“Output 2”) into a composite light 346. The optical combiner 344 is an optical element, such as a beam combiner or a dichroic mirror, that combines the first output light 340 and the second output light 342 into a single light beam, i.e., the composite light 346. In embodiments in which the optical combiner 344 is not used, the resonant wavelength of each optical resonator 306, 312 can be determined separately from the first output light 340 and the second output light 342 (e.g., by generating separate electrical signals representative of the detected resonant wavelengths of the respective optical resonators 306, 312), and the wavelength (frequency) difference between the two optical resonators 306, 312 is used to determine the temperature of the photonic device 302.

[0044] The composite light 346 has a beat frequency f , which corresponds to the frequency difference between the first output light 340 and the second output light 342 due to constructive and destructive interference between the first output light 340 and the second output light 342. beat Output section 324 includes a photodetector 348 that generates an electrical signal 350 corresponding to one or more properties of composite light 346. In particular, electrical signal 350 corresponds to the beat frequency f of composite light 346. beat The frequency range of electrical signal 350 may have a known or ascertainable relationship to a physical condition of photonic device 302, such as a temperature range of photonic device 302, such that the frequency of electrical signal 350 is indicative of the temperature of photonic device 302. In other embodiments, for example, the physical condition of photonic device 302 may be stress, strain, stretching, or compression of the material forming the photonic device, which causes a change in the resonant frequency of first optical resonator 306 and second optical resonator 312, producing a corresponding change in electrical signal 350. In such a case, for example, the frequency of electrical signal 350 may be indicative of the stress, strain, stretching, or compression experienced by photonic device 302.

[0045] The output portion 324 includes one or more electrical measurement devices 352 that measure one or more characteristics of the electrical signal 350. Such characteristic(s) of the electrical signal 350 are indicative of the physical condition of the photonic device 302. The one or more electrical measurement devices 352 may include, by way of non-limiting example, a measurement device that measures the frequency of the electrical signal 350, such as a frequency counter, or a measurement device that measures the energy distribution in the frequency spectrum of the electrical signal 350, such as a spectrum analyzer. The measurement device(s) 352 generate an output 354, such as a visual representation (e.g., on a display) of data or numerical values that represent the one or more characteristics measured in the electrical signal 350. The measurement device(s) 352 may determine other characteristics of the electrical signal 350, such as amplitude. The one or more measurement devices 352 may be used to determine one characteristic relative to another characteristic in the electrical signal 350, such as amplitude relative to frequency of the electrical signal 350, or the change in one characteristic relative to another characteristic in the electrical signal 350, such as amplitude change relative to frequency of the electrical signal 350. Embodiments that include a spectrum analyzer may analyze the energy distribution in the frequency spectrum of the electrical signal and measure the magnitude of the energy distribution in the frequency spectrum versus frequency in the frequency spectrum.

[0046] In some embodiments, the output portion 324 is a signal representing the beat frequency f represented by the electrical signal 350 as measured by the measurement device(s) 352. beat The computer system 356 may include a computer system 356 configured to determine a temperature corresponding to the frequency measurement of the photonic device 302. The computer system 356 may include one or more processors coupled to a memory that stores instructions that, when executed by the one or more processors, cause the computer system 356 to determine the temperature of the photonic device 302. The memory of the computer system 356 may store information indicative of a relationship between the frequency measurement and the temperature of the photonic device 302. In some embodiments, the computer system 356 may be a specially designed system that includes one or more features of the input portion 322 and the output portion 324.

[0047] In some embodiments, photonic device 302 may include one or more light sources, such as light source 328, that internally generate first input light 332 and second input light 338. The one or more light sources internal to photonic device 302 may be controllable by an external device, such as computer system 356, to adjust the frequency of first input light 332 and the frequency of second input light 338. Photonic device 302 may include one or more optical shifters or optical frequency locked loops controllable to adjust the frequency of second input light 338 relative to first input light 332.

[0048] In some embodiments, photonic device 302 may include a photodetector 348. In such embodiments, photonic device 302 may include an optical combiner 344, where first output light 340 and second output light 342 may be combined into a composite light 346 within photonic device 302. Composite light 346 is directed onto or into a photodetector 348 within photonic device 302 to generate an electrical signal 350, which is output from photonic device 302 instead of or in addition to composite light 346.

[0049] 5 is a graph 500 illustrating an example of the change in optical resonant frequency with temperature of an optical resonator of a photonic device, in accordance with one or more embodiments of the present disclosure. Graph 500 includes a trend line 502 of the resonant frequency response of a first optical resonator, such as first optical resonator 306. Graph 500 also includes a trend line 504 of the resonant frequency response of a second optical resonator, such as second optical resonator 312. Trend lines 502 and 504 demonstrate that the resonant frequency of the first optical resonator and the resonant frequency of the second optical resonator change based on changes in temperature. For example, the resonant frequency responses of the first and second optical resonators may be inversely proportional to temperature, such that the optical resonators have higher resonant frequencies at lower temperatures and lower resonant frequencies at higher temperatures.

[0050] The trend line 502 for the first optical resonator is different from the trend line 504 for the second optical resonator. The slope of the trend line 502, for example, is different from the slope of the trend line 504. In some embodiments, the shape of the trend line 502 may be different from the shape of the trend line 504. Thus, the difference between the optical resonant frequencies of the first and second optical resonators varies with temperature. For example, at temperature 508, a first difference 510 exists between the optical resonant frequencies of the first and second optical resonators. At another temperature 512, a second difference 514 exists between the optical resonant frequencies of the first and second optical resonators, where the second difference 514 is different from the first difference 510.

[0051] The resonant frequency response of the optical resonators may drift over time. Trend lines 502 and 504 may, for example, drift upward or downward along the optical resonant frequency axis over time. However, the optical resonant frequency trend lines 502 and 504 will drift together. As a result, even if the resonant frequency responses of first optical resonator 306 and second optical resonator 312 drift over time, temperature measurements using photonic device 302 can be continuously obtained accurately and precisely based on the difference between the resonant frequencies of the optical resonators without recalibrating measurement system 300. In contrast, if optical resonator 106 of photonic device 102 of FIG. 1A experiences a drift in its resonant frequency response, recalibration of the measurement system implementing photonic device 102 may be required to continuously obtain accurate and precise temperature measurements.

[0052] Furthermore, measurement system 300 is less expensive and more reliable than measurement systems that implement photonic device 102. In measurement systems used to determine the temperature of photonic device 102, a wavemeter may be used to detect the wavelength of light output by photonic device 102. However, ambient temperature may have a significant effect on the operation of such a wavemeter, reducing the reliability of temperature measurements obtained using such a device. Some characteristics of wavemeters are also prone to drift over time, making periodic calibration appropriate to maintain sufficient accuracy and precision of the system.

[0053] Due to the design of photonic device 302, the temperature of photonic device 302 may be determined without the use of a wavemeter by detecting the difference in the resonant frequencies of first optical resonator 306 and second optical resonator 312. As a result, measurement system 300 may have improved accuracy and precision over a longer period of time, may be less expensive to manufacture and operate, and may require less maintenance (e.g., calibration) for measurement systems implementing photonic device 102 of FIG. 1A. Potential advantages or improvements of measurement system 300 include improved resolution, reduced cost, improved robustness to ambient temperature fluctuations, and reduced calibration frequency.

[0054] FIG. 6 shows a graph 600 of a beat frequency curve 602 of the composite light 346 over a temperature range of the photonic device 302, in accordance with one or more embodiments. As described herein, the beat frequency of the composite light 346 is equal to the difference between the resonant frequencies of the first output light 340 and the second output light 342. Referring to FIG. 5 , the beat frequency curve 602 corresponds to the difference between the trend lines 502 and 504 over the temperature range. The photodetector 348 may, for example, output an electrical signal 350 having a frequency response corresponding to the beat frequency curve 602 over the temperature range. The computer system 356 may store temperature correspondence data indicating a correspondence between the output 354 of the measurement device 352 and the temperature of the photonic device 302. The memory of the computer system 356 may store, for example, a lookup table or other data structure in which beat frequency values of the beat frequency curve 602 are associated with corresponding temperature values. Alternatively, or in addition, the temperature correspondence data may include a function (i.e., a formula or equation) representing the beat frequency curve 602. The computer system 356 may provide output (eg, as data on a display) based on the received output 354 using temperature-related data stored in memory.

[0055] One or more sources of uncertainty in differential photonic resonance temperature measurements may be present in the framework described herein. Such sources potentially include laser lock frequency uncertainty and frequency counter uncertainty. However, the level of uncertainty is significantly better and more stable over time than uncertainties associated with other measurement systems, such as systems implementing photonic device 102.

[0056] 7 shows a graph 700 illustrating the variation in refractive index of the first optical resonator 306 and the second optical resonator 312 with respect to temperature. Graph 700 shows a first refractive index 702 of the first optical resonator 306 over a range of temperatures. Graph 700 also shows a second refractive index 704 of the second optical resonator 312 over a range of temperatures. As shown, the effective refractive index of the first optical resonator 306 and the second optical resonator 312 changes with changes in temperature experienced by the photonic device 302. In this example, the first refractive index 702 and the second refractive index 704 have the same slope and may drift at the same rate over time.

[0057] 8 shows a graph 800 illustrating the variation of resonant wavelength λ with respect to mode number m and optical path length l for an optical resonator described herein. There may be multiple resonant wavelengths λ of the optical resonator (e.g., 1300 nm to 1650 nm) represented by lines in graph 800. Thus, different resonant optical wavelengths λ i is the optical path length l i and optical mode number m i Other considerations described herein also contribute to the resonant wavelength λ of the light output by the optical resonators herein.

[0058] 9 illustrates a method 900 of operating a measurement system including a photonic device (in this case, a photonic thermometer) having two or more optical resonators with different resonant frequency responses, such as measurement system 300, in accordance with one or more embodiments of the present disclosure. Method 900 includes controlling 902 light source 328 to emit light 326. Controlling 902 may include controlling light source 328 to emit light having a particular frequency and luminous flux. In some embodiments, controlling 902 may include adjusting a characteristic of light 326 from a first value to a second value over a period of time. For example, light source 328 may be controlled to initially emit light 326 having a first frequency f1, and then the frequency of light 326 is adjusted (e.g., increased, decreased) over a period of time until light 326 has a second frequency f2 that matches the resonant frequency of first optical resonator 306. The resonant frequency of the first optical resonator 306 may be determined by detecting a change in the amplitude of the first output light 340 or a change in the amplitude of the electrical signal 350. For example, the amplitude of the first output light 340 or the electrical signal 350 may change significantly (e.g., increase in amplitude, decrease in amplitude) when the frequency of the first input light 332 is adjusted to match the resonant frequency of the first optical resonator 306. The change in the frequency of the light 326 may be continuous or in steps or in increments.

[0059] The method 900 includes splitting (904) the light 326 into a first light beam, such as an auxiliary light 334, and a second light beam, such as a first input light 332. The first light beam and the second light beam have the same frequency and phase. Splitting (904) the light 326 includes introducing the light 326 into an optical element 330 or other such optical element.

[0060] The method 900 may include shifting 906 a characteristic of the second light beam. The shifting 906 may include introducing or directing the second light beam (auxiliary light 334) into an optical shifter 336. In some embodiments, the shifting 906 includes shifting the frequency of the second input light 338 relative to the first input light 332. The shifting 906 may also include adjusting the frequency of the second input light 338 relative to the frequency of the first input light 332 using an optical frequency locked loop.

[0061] The shifting (906), in some embodiments, is performed as a result of determining that the frequency of the first input light 332 is locked to the resonant frequency of the first optical resonator 306. The optical shifter 336 may be selectively controlled to shift the frequency of the second input light 338 relative to the first input light 332 until the frequency of the second input light 338 matches the resonant frequency of the second optical resonator 312. The resonant frequency of the second optical resonator 312 may be determined by detecting a change in the amplitude of the second output light 342 or a change in the amplitude of the electrical signal 350. For example, the amplitude of the second output light 342 or the electrical signal 350 may change significantly (e.g., increase in amplitude, decrease in amplitude) when the frequency of the second input light 338 is adjusted to match the resonant frequency of the second optical resonator 312.

[0062] In some embodiments, the optical shifter 336 is configured to shift the frequency of the second input light 338 by a fixed amount. As a result of shifting (906) the second light beam, the second input light 338 is obtained from the output of the optical shifter 336, where the characteristics of the second input light 338 differ from the characteristics of the second light beam (i.e., the fill light 334). In some embodiments, the method 900 may include controlling the second light beam generated by the second light source, as described previously herein. In particular, the method 900 may include controlling the second light source to emit light having a frequency that is locked to the resonant frequency of the second optical resonator 312. In such embodiments, other operations of the method 900 may be omitted or adapted as necessary to accommodate the use of the first and second light sources.

[0063] The method 900 further includes directing 908 the first input light 332 and the second input light 338 into the first waveguide 304 and the second waveguide 310, respectively, of the substrate 308. First output light 340 and second output light 342 are then received 910 from the first waveguide 304 and the second waveguide 310, respectively. Receiving 910 the first output light 340 and the second output light 342 may include detecting the amplitude of the first output light 340 or the second output light 342. For example, in connection with adjusting the frequency of the first input light 332, the amplitude of the first output light 340 may be monitored to determine when the frequency of the first input light 332 matches the resonant frequency of the first optical resonator 306. As another example, in connection with adjusting the frequency of the second input light 338, the amplitude of the second output light 342 may be monitored to determine when the frequency of the second input light 338 matches the resonant frequency of the second optical resonator 312.

[0064] Method 900 optionally includes combining 912 the first output light 340 and the second output light 342 into a composite light 346. As described with respect to measurement system 300, combining 912 the first output light 340 and the second output light 342 may include introducing or directing the first output light 340 and the second output light 342 into an optical combiner 344. The composite light 346 has a beat frequency f corresponding to the frequency difference between the first output light 340 and the second output light 342. beat The method 900 also includes converting 914 the composite light 346 into an electrical signal 350. Converting 914 the composite light 346 includes directing or introducing the composite light 346 onto or into a photodetector 348.

[0065] The method 900 includes detecting (916) one or more characteristics of the electrical signal 350 using one or more measurement devices 352. The electrical signal 350 may be monitored to determine when the frequency of the first input light 332 matches the resonant frequency of the first optical resonator 306 or when the frequency of the second input light 338 matches the resonant frequency of the second optical resonator 312. For example, in conjunction with adjusting the frequencies of the first input light 332 and the second input light 338, the amplitude of the electrical signal 350 may be monitored, and the frequencies of the first input light 332 and the second input light 338 may be locked to the resonant frequencies of the first optical resonator 306 and the second optical resonator 312, respectively, in response to changes in the amplitude of the electrical signal 350.

[0066] Detecting at 916 may include obtaining the frequency of the electrical signal 350 after determining that the frequencies of the first input light 332 and the second input light 338 are locked to the resonant frequencies of the first optical resonator 306 and the second optical resonator 312, respectively. beat may be determined based on the frequency of the electrical signal 350. In some implementations, the beat frequency f beat and the frequency of the electrical signal 350 may be the same. In some implementations, a beat frequency f beatThere may be a defined relationship between the frequency of the electrical signal 350 and the frequency of the electrical signal 350 .

[0067] The method 900 further includes determining 918 the temperature of the photonic device based on the detected characteristic 916 of the electrical signal 350. As described with respect to FIG. beat indicates a particular temperature of the photonic device 302. Thus, determining 918 the temperature is beat This may involve, for example, using computer system 356, accessing a data structure in which beat frequency values of beat frequency curve 602 are associated with corresponding temperature values. Data or a visual representation indicative of the temperature determined in 918 may be output or presented to a user (e.g., on a display, over a network).

[0068] The computer system 356 may be configured to automatically perform one or more operations of the method 900. In some embodiments, the computer system 356 may be operably coupled to the light source 328, for example, via a set of control lines 358. The computer system 356 may be configured to control one or more optical properties (e.g., frequency, amplitude) of the light 326. In some embodiments, the computer system 356 may be operably coupled to the optical shifter 336 and configured to control one or more optical properties (e.g., frequency, amplitude) of the second input light 338. The measurement system 300 in such embodiments may include a feedback loop in which the computer system 356 locks the frequencies of the first input light 332 and the second input light 338 to the resonant frequencies of the first optical resonator 306 and the second optical resonator 312 based on the detected properties of the electrical signal 350. The computer system 356 may lock the frequency of the first input light 332 or the frequency of the second input light 338, for example, in response to detecting a change in the amplitude of the electrical signal 350.

[0069] 10 illustrates a measurement system 1000 including a photonic device 1002 according to one or more embodiments. The photonic device 1002 includes a substrate 1004, a waveguide 1006, and multiple optical resonators 1022a, 1022b, ... 1022N. The measurement system 1000 includes a light source 1008 configured to generate light 1010. The measurement system 1000 also includes a photodetector 1012 configured to convert output light 1014 from the waveguide 1006 into an electrical signal 1016, one or more measurement devices 1018 configured to detect one or more characteristics of the electrical signal 1016, and a computer system 1020 configured to determine a temperature of the photonic device 1002 based on the characteristics of the electrical signal 1016. The one or more measurement devices 1018 may include, for example, a frequency counter configured to detect the frequency of the electrical signal 1016.

[0070] The multiple optical resonators of the photonic device 1002 include multiple optical resonators 1022a, 1022b, ... 1022N positioned adjacent to the waveguide 1006. Each of the multiple optical resonators 1022a, 1022b, ... 1022N has a different resonant frequency response to light over temperature, as described with respect to FIG. 3 and elsewhere herein. The multiple optical resonators 1022a, 1022b, ... 1022N are configured such that each optical resonator has a different resonant frequency response than one or more of the other optical resonators 1022a, 1022b, ... 1022N or the remainder of the optical resonators 1022a, 1022b, ... 1022N. Differences in resonant frequency responses may be the result of differences in material composition, size, surrounding structure / stress, etc., as described with respect to the first optical resonator 306 and the second optical resonator 312. In some embodiments, the plurality of optical resonators 1022a, 1022b, ... 1022N includes three or more optical resonators. In some embodiments, the plurality of optical resonators 1022a, 1022b, ... 1022N are optically isolated from one another so that light from one optical resonator is not coupled into another optical resonator, such as an adjacent optical resonator.

[0071] measurementSystem 1000 includes multiple optical resonators 1022a, 1022b, ... 1022N for determining the temperature of photonic device 1002. In some embodiments, the optical resonators 1022a, 1022b, ... 1022N may be associated in pairs, such that a first pair of optical resonators, e.g., resonators 1022a and 1022b, is associated with a first temperature range and another pair of resonators in the multiple optical resonators 1022a, 1022b, ... 1022N is associated with a second temperature range.

[0072] In some embodiments, the measurement system 1000 may include a plurality of optical switches 1024 and an optical shifter 1026 coupled to the light source 1008. The measurement system 1000 may include a beam combiner and a beam splitter. The light source 1008 is controllable to emit light having a selected frequency. The plurality of optical switches are operable to optically couple the light source 1008 to the waveguide 1006, optically couple the light source 1008 to the optical shifter 1026, optically couple the optical shifter 1026 to the waveguide 1006, or a combination of the foregoing. The optical switch 1024 may be controllable to optically couple the beam combiner to the waveguide 1006 to combine light from the light source 1008 and the optical shifter 1026. The optical switch 1024 may be controllable to split the first light 1028 from the light source 1008 into two beams.

[0073] In a first mode of operation, the optical switch 1024 may be controlled to optically couple the light source 1008 to the waveguide 1006 and optically decouple the optical shifter 1026 from the waveguide 1006, such that the input light 1010 entering the waveguide 1006 is the first light 1028 emitted from the light source 1008. In a second mode of operation, the optical switch 1024 may be controlled to optically decouple the light source 1008 from the waveguide 1006, optically couple the light source 1008 to the optical shifter 1026, and optically couple the optical shifter 1026 to the waveguide 1006. In the second mode of operation, the input light 1010 entering the waveguide 1006 is the second light 1030 from the optical shifter 1026. In the third mode of operation, the optical switch 1024 may be controlled to optically couple the light source 1008 to the beam splitter and split the first light 1028 into two beams, one beam directed to the optical shifter 1026 and the other beam directed to the beam combiner. In the third mode of operation, the optical switch 1024 is also controlled to optically couple the second light 1030 from the optical shifter 1026 to the beam combiner. Thus, the first light 1028 and the second light 1030 are combined when the input light 1010 enters the waveguide 1006 in the third mode of operation. The measurement system 1000 may include an optical frequency-locked loop that controls or locks the frequency of the second light 1030 to the frequency of the first light 1028.

[0074] To determine the temperature of the photonic device 1002, the optical switch 1024 is first controlled to operate the measurement system 1000 in a first mode of operation. In the first mode of operation, the frequency of the light source 1008 is controlled to emit light having a first frequency f1 corresponding to the resonant frequency of a first optical resonator of the plurality of optical resonators 1022a, 1022b, ... 1022N. The optical switch 1024 is secondly controlled to operate the measurement system 1000 in a second mode of operation. In the second mode of operation, the light source 1008 is controlled to emit light having the first frequency f1, and the optical shifter 1026 is controlled to generate light having a second frequency f2 corresponding to the resonant frequency of a second optical resonator of the plurality of optical resonators 1022a, 1022b, ... 1022N. The resonant frequencies of individual optical resonators of the plurality of optical resonators 1022a, 1022b, . . . 1022N may be determined as described with respect to method 900, measurement system 300, and elsewhere herein.

[0075] Then, a third time, the optical switch 1024 is controlled to operate the measurement system 1000 in a third mode of operation. In the third mode of operation, the light source 1008 is controlled to emit a first light 1028 having a first frequency f1, and the optical shifter 1026 is controlled to generate light having a second frequency f2 (in phase with the first light 1028). The output light 1014 exiting the waveguide 1006 is directed onto or into the photodetector 1012. The output light 1014 is at a first resonant frequency f1 of the optical resonator. R1 and the second resonant frequency f R2 The beat frequency f corresponds to the difference between beat Although the input light 1010 cannot resonate in any of the multiple optical resonators 1022a, 1022b, ... 1022N due to the superposition of the first frequency f1 and the second frequency f2, the output light 1014 still has the first resonant frequency f R1 and the second resonant frequency f R2 The beat frequency f is equal to the difference between beatThe one or more measurement devices 1018 measure the beat frequency f of the output light 1014 based on the electrical signal 1016. beat The temperature of the photonic device 1002 is then measured at a beat frequency f as described with respect to FIGS. 3, 5, 9, and elsewhere herein. beat It can be determined based on:

[0076] The computer system 1020 may be operatively coupled to the light source 1008 and the optical shifter 1026 via control signals on a first connection 1032. The computer system 1020 may be configured to control optical properties of the light 1028 and 1030 emitted from the light source 1008 and the optical shifter 1026 via the first connection 1032. The computer system 1020 may be operatively coupled to a plurality of optical switches via control signals on the first connection 1032 and configured to control switching of individual optical switches among the plurality of optical switches. The computer system 1020 may be configured to receive measurements from one or more measurement devices 1018. The computer system 1020, in some embodiments, is configured to perform one or more of the features described herein, such as by selectively controlling the operation of the light source 1008 and the optical shifter 1026 to determine the resonant frequencies of the plurality of optical resonators 1022a, 1022b, ... 1022N.

[0077] In some embodiments, the photonic device 1002 may include a plurality of optical switches (not shown) operable to couple individual optical resonators of the plurality of optical resonators 1022 a, 1022 b, ... 1022 N to the waveguide 1006. The photonic device 1002 may include one or more terminals 1034 for receiving control signals to control the switching states of individual optical switches of the plurality of optical switches in the photonic device 1002. In some embodiments, the plurality of optical switches may be controlled to optically couple a group of the plurality of optical resonators 1022 a, 1022 b, ... 1022 N to the waveguide 1006. For example, a pair of optical resonators of the plurality of optical resonators 1022 a, 1022 b, ... 1022 N may be optically coupled to the waveguide 1006, and the remaining optical resonators of the plurality of optical resonators 1022 a, 1022 b, ... 1022 N may be optically isolated from the waveguide 1006. The frequency of the input light 1010 can be controlled to the resonant frequency of the pair of coupled optical resonators, and the beat frequency f of the output light 1014 can be controlled to beat may be determined as described herein. The computer system 1020 may be coupled to one or more terminals 1034 via a second connection 1036 to control the switching states of the plurality of optical switches of the photonic device 1002.

[0078] In some embodiments, the measurement system 1000 may include a plurality of light sources 1008 that are individually controllable to generate frequencies corresponding to the resonant frequencies of the plurality of optical resonators 1022a, 1022b, ... 1022N. In such embodiments, a plurality of optical switches 1024 may be controllable to selectively couple and decouple one or more of the plurality of light sources 1008 to and from the waveguide.

[0079] In some embodiments, photonic device 1002 may include one or more multimode optical resonators having two or more resonant frequency responses to light. For example, a multimode optical resonator may resonate light at a first frequency and resonate light at a second frequency at a given temperature. Examples of such multimode optical resonators are described elsewhere herein.

[0080] 11 illustrates a measurement system 1100 that includes a photonic device 1102 and, in this example, is configured to detect the temperature of the photonic device 1102. Various aspects of the measurement system 1100 are substantially similar to corresponding features described with respect to measurement system 300, method 900, and elsewhere herein, and therefore further description thereof will be omitted for the sake of brevity. The measurement system 1100 includes a substrate 1104, a plurality of waveguides 1106 a, 1106 b, ... 1106 N, and a plurality of optical resonators 1108 a, 1108 b, ... 1108 N. Each of the plurality of waveguides 1106 a, 1106 b, ... 1106 N is optically coupled to one of the plurality of optical resonators 1108 a, 1108 b, ... 1108 N. Measurement system 1100 includes a light source 1110 configured to generate light and an optical beam splitter 1112 configured to split the light from light source 1110 into a first input light 1113 and an auxiliary light 1114. Measurement system 1100 includes an optical shifter 1116 that shifts an optical property of the auxiliary light 1114 to generate a second input light 1118.

[0081] Measurement system 1100 also includes a beam combiner 1120 configured to combine first output light 1122 and second output light 1124 into a combined light 1126. Photodetector 1128 receives combined light 1126 and converts combined light 1126 into an electrical signal 1130. Electrical signal 1130 is received by one or more measurement devices 1132, and the temperature of photonic device 1102 is determined based on one or more characteristics of electrical signal 1130. Measurement system 1100 may include a computer system 1134 that may determine the temperature of photonic device 1102 and control aspects of measurement system 1100 as described herein.

[0082] The plurality of optical resonators 1108a, 1108b, ... 1108N includes pairs of optical resonators that can be used to measure temperature at specific conditions. The optical resonator pairs, in some embodiments, can be assigned to measure temperatures within a certain temperature range. For example, a first pair of optical resonators 1108a and 1108b can be assigned to measure in a first temperature range, a second pair of optical resonators 1108c and 1108d (not shown) can be assigned to measure in a second temperature range that is different from the first temperature range, and so on.

[0083] Measurement system 1100 may include a first plurality of optical switches 1136 controllable to optically couple first input light 1113 and second input light 1118 to a pair of waveguides among a plurality of waveguides 1106a, 1106b, ... 1106N. For example, for a first temperature range, one or more switches of first plurality of optical switches 1136 couple first input light 1113 to waveguide 1106a and second input light 1118 to waveguide 1106b. For a second temperature range, one or more switches of first plurality of optical switches 1136 couple first input light 1113 to waveguide 1106c (not shown) and second input light 1118 to waveguide 1106d (not shown).

[0084] The measurement system 1100 measures a first wavelength from a pair of waveguides of a plurality of waveguides 1106a, 1106b, ... 1106N. output Light 1122 and the second output The optical fiber 1102 may include a second plurality of optical switches 1138 that are controllable to optically couple light 1124 to beam combiner 1120. For example, for a first temperature range, one or more switches of second plurality of optical switches 1138 couple first output light 1122 from waveguide 1106a and second output light 1124 from waveguide 1106b to beam combiner 1120. For a second temperature range, one or more switches of second plurality of optical switches 1138 couple first output light 1122 from waveguide 1106c (not shown) and second output light 1124 from waveguide 1106d (not shown) to beam combiner 1120.

[0085] The first plurality of switches 1136 and the second plurality of switches 1138 are shown as being external to the photonic device 1102. However, in some embodiments, the first plurality of switches 1136 and the second plurality of switches 1138 may be included in the photonic device 1102. In such embodiments, a first switch of the first plurality of switches 1136 may be coupled to an input port 1140a of the photonic device 1102 to receive the first input light 1113, and a second switch of the first plurality of switches 1136 may be coupled to an input port 1140b to receive the second input light 1118. The first and second switches of the plurality of switches 1136 may be controllable to optically couple the input ports 1140a and 1140b to corresponding pairs of the plurality of waveguides 1106a, 1106b, ... 1106N. Also, in such an embodiment, a first switch of the second plurality of switches 1138 may be coupled to output port 1142a of photonic device 1102 to output first output light 1122, and a second switch of the second plurality of switches 1138 may be coupled to output port 1142b to output second output light 1124. The first and second switches of the second plurality of switches 1138 in photonic device 1102 may be controllable to optically couple corresponding pairs of the plurality of waveguides 1106a, 1106b, ... 1106N to output ports 1142a and 1142b.

[0086] The computer system 1134 may be coupled to control the switching states of the first plurality of switches 1136 and the second plurality of switches 1138. In embodiments in which the substrate 1104 includes the first plurality of switches 1136 and the second plurality of switches 1138, the photonic device 1102 may include one or more terminals 1144 for receiving signals to control the first plurality of switches 1136 and the second plurality of switches 1138. The computer system 1134 may be communicatively coupled to the one or more terminals to control the switching states of the first plurality of switches 1136 and the second plurality of switches 1138.

[0087] 12 illustrates a system 1200 including a photonic device 1202 and configured to detect a temperature of the photonic device 1202. Various aspects of the measurement system 1200 are substantially similar to corresponding features described with respect to measurement system 300, measurement system 1100, method 900, and elsewhere herein, and therefore further description thereof will be omitted for the sake of brevity. The measurement system 1200 includes a substrate 1204, a plurality of input waveguides 1206 a, 1206 b, ... 1206 N, a plurality of optical resonators 1208 a, 1208 b, ... 1208 N, a plurality of output waveguides 1210 a, 1210 b, ... 1210 N, a light source 1212, an optical beam splitter 1214, and an optical beam combiner 1216.

[0088] Each of the plurality of input waveguides 1206a, 1206b, ... 1206N is optically coupled to a corresponding one of the plurality of optical resonators 1208a, 1208b, ... 1208N. Each of the plurality of output waveguides 1210a, 1210b, ... 1210N is optically coupled to a corresponding one of the plurality of optical resonators 1208a, 1208b, ... 1208N. The plurality of input waveguides 1206a, 1206b, ... 1206N are optically isolated from corresponding ones of the plurality of output waveguides 1210a, 1210b, ... 1210N. For example, input waveguide 1206a is optically isolated from output waveguide 1210a so that output waveguide 1210a does not receive input light 1218a directly from input waveguide 1206a, input waveguide 1206b is optically isolated from output waveguide 1210b so that output waveguide 1210b does not receive input light 1218b directly from input waveguide 1206b, and so on.

[0089] Measurement system 1200 includes a broadband light source 1212 configured, in this example, to emit input light 1217 having an optical spectrum S having a spectral range between a first frequency and a second frequency. Input light 1217 is directed or introduced to an optical beam splitter 1214 that splits input light 1217 into beams of input light 1218a, 1218b, ... 1218N. The beams of input light 1218a, 1218b, ... 1218N are directed or introduced into corresponding ones of a plurality of input waveguides 1206a, 1206b, ... 1206N.

[0090] Each of the plurality of optical resonators 1208a, 1208b, ... 1208N is configured to resonate light having a frequency corresponding to the resonant frequency of the respective optical resonator. Each of the plurality of optical resonators 1208a, 1208b, ... 1208N has a different resonant frequency response based on differences between the resonators, for example, as described with respect to Figures 3, 4, and elsewhere herein. As a result of the resonant frequency of one or more of the plurality of optical resonators 1208a, 1208b, ... 1208N corresponding to a frequency included in the optical spectrum S, light having the corresponding frequency is resonated in one or more of the optical resonators from a corresponding one of the plurality of input waveguides 1206a, 1206b, ... 1206N. The resonant light in each of the one or more optical resonators is coupled to a corresponding one of the plurality of output waveguides 1210a, 1210b, ... 1210N and output from the photonic device 1202.

[0091] For example, if the spectrum S is R1 , input light 1218a having the corresponding frequency f is coupled to and resonates within optical resonator 1208a. Resonated light 1220a is coupled from optical resonator 1208a to output waveguide 1210a and output from output waveguide 1210a. As another example, if spectrum S includes a frequency f corresponding to the resonant frequency f of optical resonator 1208b, then input light 1218a having the corresponding frequency f is coupled to and resonates within optical resonator 1208a. Resonated light 1220a is coupled from optical resonator 1208a to output waveguide 1210a and output from output waveguide 1210a. R2 , input light 1218b having the corresponding frequency f is coupled to and resonates within optical resonator 1208b. Resonated light 1220b is coupled from optical resonator 1208b to output waveguide 1210b and output from output waveguide 1210b. Optical combiner 1216 combines lights 1220a and 1220b into composite light 1222, which is converted by photodetector 1225 into electrical signal 1224, which is detected at the beat frequency f of composite light 1222, as described herein. beatThe signal S is analyzed by measurement device 1227 to determine the temperature of photonic device 1202. Measurement system 1200 may include a computer system 1226 configured to control the operation of light source 1212, such as by controlling the frequency range of spectrum S, and to determine the temperature of photonic device 1202 as described herein.

[0092] Spectrum S may exclude frequencies corresponding to the resonant frequencies of other optical resonators of the plurality of optical resonators 1208a, 1208b, ... 1208N. For example, input light 1217 may not include light having a frequency corresponding to the resonant frequency of optical resonator 1208(N-1) or light having a frequency corresponding to the resonant frequency of optical resonator 1208N. As a result, light is not coupled into or exits corresponding output waveguides 1210(N-1) and 1210N. Light source 1212 may be controlled to include a first set of resonant frequencies of the plurality of optical resonators 1208a, 1208b, ... 1208N and exclude a second set of resonant frequencies of the plurality of optical resonators 1208a, 1208b, ... 1208N. As a result, a set of optical resonators from the plurality of optical resonators 1208a, 1208b, ... 1208N can be selected to be used to determine the temperature of the photonic device 1202 without using an optical switch to couple the beams of input light 1218a, 1218b, ... 1218N to the plurality of input waveguides 1206a, 1206b, ... 1206N.

[0093] In some embodiments, measurement system 1200 may include a plurality of optical switches controllable to selectively direct light into selected ones of the plurality of input waveguides 1206 a, 1206 b, ... 1206 N or a plurality of optical switches controllable to selectively direct light from selected ones of the plurality of output waveguides 1210 a, 1210 b, ... 1210 N, as described with respect to measurement system 1100. In such embodiments, the plurality of switches may be internal or external to photonic device 1202.

[0094] 13 illustrates a measurement system 1300 including a photonic device 1302 and configured to detect a temperature of the photonic device 1302. Various aspects of the measurement system 1300 are substantially similar to corresponding features described with respect to measurement system 300, measurement system 1200, method 900, and elsewhere herein, and therefore further description thereof is omitted for brevity. Photonic device 1302 includes a substrate 1304, an input waveguide 1306, a plurality of optical resonators 1308a, 1308b, ... 1308N, and an output waveguide 1310. In this example, measurement system 1300 includes a broadband light source 1312 configured to generate input light 1314 having an optical spectrum S having a spectral range between a first frequency and a second frequency.

[0095] Input waveguide 1306 is optically coupled to a plurality of optical resonators 1308 a, 1308 b, ... 1308 N. Output waveguide 1310 is also optically coupled to a plurality of optical resonators 1308 a, 1308 b, ... 1308 N. Input waveguide 1306 is spaced apart and optically isolated from output waveguide 1310 such that output waveguide 1310 does not receive input light 1314 directly from input waveguide 1306.

[0096] Each of the plurality of optical resonators 1308a, 1308b, ... 1308N is configured to resonate light having a frequency corresponding to the resonant frequency of the respective optical resonator. Each of the plurality of optical resonators 1308a, 1308b, ... 1308N has a different resonant frequency response based on differences between the resonators, for example, as described with respect to Figures 3, 4, and elsewhere herein. Each of the plurality of optical resonators 1308a, 1308b, ... 1308N has a resonant frequency f R, 1308N respectively. The resonant frequencies of one or more of the optical resonators 1308a, 1308b, ..., 1308N correspond to frequencies included in the optical spectrum S, resulting in light having the corresponding frequencies resonating in the one or more optical resonators from the input waveguide 1306. The resonant light 1313a, 1313b, ..., 1313N in the one or more respective optical resonators is coupled into the output waveguide 1310 and output from the photonic device 1302.

[0097] In some embodiments, photonic device 1302 may include a plurality of optical switches controllable to selectively couple and decouple input waveguide 1306 to a plurality of optical resonators 1308 a, 1308 b, ... 1308 N. In such embodiments, the plurality of switches may be internal or external to photonic device 1302. The plurality of optical switches may be internal to photonic device 1302, and photonic device 1302 may include one or more terminals (not shown) for receiving control signals to control the switching states of the plurality of optical switches.

[0098] The output light 1316 output from the output waveguide 1310 includes resonant light 1313 from one or more of the multiple optical resonators 1308a, 1308b, ... 1308N. For example, if the spectrum S is greater than the resonant frequency f R1 If the spectrum S includes a frequency f corresponding to the resonant frequency f of the optical resonator 1308b, light from the input light 1314 having the corresponding frequency f is coupled into the optical resonator 1308a and resonates therein. The resonant light 1313a is coupled from the optical resonator 1308a into the output waveguide 1310 and output from the output waveguide 1310 in the output light 1316. R2If the input light 1314 further includes a frequency f2 corresponding to the first resonant frequency f of each of the optical resonators 1308a and 1308b, then the light from the input light 1314 having the corresponding frequency f2 is coupled to and resonates within the optical resonator 1308b. The resonant light 1313b is coupled from the optical resonator 1308b along the resonant light 1313a to the output waveguide 1310 and output from the output waveguide 1310. In such a case, the output light 1316 includes the resonant light 1313a and the resonant light 1313b superimposed on each other. As a result, the output light 1316 includes the first resonant frequency f of each of the optical resonators 1308a and 1308b. R1 and the second resonant frequency f R2 The beat frequency f corresponds to the difference between beat Photodetector 1318 and measurement device 1320 may be used to measure the beat frequency f of output light 1316, e.g., as described with respect to measurement system 300, method 900, and elsewhere herein. beat , can be detected to determine the temperature of the photonic device 1302. The measurement system 1300 can control the frequency range of the spectrum S of the input light 1314 emitted by the broadband light source 1312, or the beat frequency f beat The measurement system 1300 may include a computer system 1322 configured to control the operation of various aspects of the measurement system 1300, such as by determining the temperature of the photonic device 1302 based on the temperature of the photonic device 1302.

[0099] In some embodiments, photonic device 1302 may include one or more multimode optical resonators having two or more resonant frequency responses to light at a given temperature. For example, a multimode optical resonator may resonate with light having a first frequency and resonate with light having a second frequency at a given temperature, as described by way of example herein.

[0100] 14 illustrates a measurement system 1400 including a photonic device 1402 and configured to detect a temperature of the photonic device 1402. Various aspects of the measurement system 1400 are substantially similar to corresponding features described with respect to measurement system 300, measurement system 1200, method 900, and elsewhere herein, and therefore further description thereof will be omitted for brevity. The photonic device 1402 includes a substrate 1404, an input waveguide 1406, a first optical resonator 1408, a second optical resonator 1410, a first output waveguide 1412, and a second output waveguide 1414. The measurement system 1400 also includes a broadband light source 1416 configured to generate input light 1418 having a broadband optical spectrum S, in this example, having a spectral range between a first frequency and a second frequency.

[0101] Input waveguide 1406 is optically coupled to first optical resonator 1408 and second optical resonator 1410. First output waveguide 1412 is optically coupled to first optical resonator 1408, and second optical resonator 1410 is optically coupled to second output waveguide 1414. Input waveguide 1406 is spaced apart and optically isolated from first output waveguide 1412 and second output waveguide 1414 such that first output waveguide 1412 and second output waveguide 1414 do not receive direct input light 1418 from input waveguide 1406.

[0102] The first optical resonator 1408 has a resonant frequency f R1 The second optical resonator 1410 is configured to resonate light having a frequency f1 corresponding to the resonant frequency f R2 The first optical resonator 1408 is configured to resonate light having a frequency f2 corresponding to the resonant frequency f R1 is the resonant frequency f of the second optical resonator 1410. R2 Furthermore, the first optical resonator 1408 has a different resonant frequency response than the second optical resonator 1410 due to differences between the resonators, as described with respect to Figures 3, 4, and elsewhere herein. The resonant frequency f of the first optical resonator 1408 isR1 and the resonant frequency f of the second optical resonator 1410 R2 varies based on the temperature of the respective optical resonator.

[0103] As a result of the resonant frequencies of the first optical resonator 1408 and the second optical resonator 1410 corresponding to frequencies contained in the optical spectrum S, light having the corresponding frequencies will resonate within the first optical resonator 1408 and the second optical resonator 1410. R1 and f R2 Light of frequencies other than f1 and f2 is not resonated by the first optical resonator 1408 and the second optical resonator 1410. Resonant light 1420 in the first optical resonator 1408 is coupled to and output from a first output waveguide 1412. Resonant light 1422 in the second optical resonator 1410 is coupled to and output from a second output waveguide 1414. Resonant light 1420 has a frequency corresponding to frequency f1, and resonant light 1422 has a frequency corresponding to frequency f2. Resonant lights 1420 and 1422 are directed or introduced into an optical combiner 1424 and combined into composite light 1426, which is provided to an optical detector 1427. Composite light 1426 has a beat frequency f1 corresponding to the frequency difference between first resonant light 1420 and second resonant light 1422. beat and this beat frequency f beat is detectable in the electrical signal provided by photodetector 1427 to measurement device 1430. Measurement device 1430 may be, for example, an RF spectrum analyzer configured to measure the magnitude of the electrical signal versus the frequency of the electrical signal.

[0104] The measurement system 1400 controls the frequency range of the spectrum S of the input light 1418 emitted by the broadband light source 1416, or the beat frequency f detected by the measurement device 1430. beat The measurement system 1400 may include a computer system 1428 configured to control the operation of various aspects of the measurement system 1400, such as by determining the temperature of the photonic device 1402 based on the temperature of the photonic device 1402.

[0105] 15 illustrates a measurement system 1500 including a photonic device 1502 and configured to detect a temperature of the photonic device 1502. Various aspects of the measurement system 1500 are substantially similar to corresponding features described with respect to measurement system 300, method 900, and elsewhere herein, and therefore further description thereof will be omitted for brevity. The photonic device 1502 includes an input waveguide 1504, a first waveguide junction 1506, a first waveguide loop 1508, an optical resonator 1510, a second waveguide loop 1512, a second waveguide junction 1514, and an output waveguide 1516. The measurement system 1500 also includes a light source 1518 configured to generate input light 1520 having a broadband optical spectrum S, in this example, having a spectral range between a first frequency and a second frequency.

[0106] At first waveguide junction 1506, input waveguide 1504 splits into first input waveguide portion 1522 and second input waveguide portion 1524. First waveguide loop 1508 is a continuous waveguide including first input waveguide portion 1522 and second input waveguide portion 1524. Input light 1520 is input The input light 1520 enters the waveguide 1504 and is split at a first waveguide junction 1506 into a first light portion 1526 and a second light portion 1528. The first light portion 1526 and the second light portion 1528 have the same properties as the input light 1520. The input light 1520, in some embodiments, is split equally between the first light portion 1526 and the second light portion 1528.

[0107] The optical resonator 1510 is a bimodal optical resonator including a first resonator portion 1510a and a second resonator portion 1510b. The first resonator portion 1510a is a portion of the optical resonator 1510 having a first resonant response to temperature. The second resonator portion 1510b is a different portion of the optical resonator 1510 having a second resonant response to temperature, the second resonant response being different from the first resonant response. The first resonator portion 1510a may include a first semicircle or half-disk of the optical resonator 1510, and the second resonator portion 1510b may include a second semicircle or half-disk of the optical resonator 1510. In some embodiments, the optical resonator 1510 has a single continuous resonant structure including the first resonator portion 1510a and the second resonator portion 1510b. The different resonant frequency responses of the first and second resonator portions 1510a and 1510b may be due to differences in size, shape, material composition, mechanical stress, additional or different features (e.g., additional cavities), or other differences described herein. Alternatively, or in addition, a feature 1511 positioned adjacent to the optical resonator 1510 acts to break the symmetry of the optical resonator 1510, causing the clockwise and counterclockwise resonant modes of the optical resonator 1510 (discussed below) to have different frequencies.

[0108] In operation, a first optical portion 1526 of the input light 1520 circulates in a first direction (e.g., clockwise) through the first waveguide loop 1508, and a second optical portion 1528 of the input light 1520 circulates in a second direction (e.g., counterclockwise) opposite the first direction through the first waveguide loop 1508. When the first optical portion 1526 reaches the resonant frequency f of the second resonator portion 1510b, R1 As a result, the first optical portion 1526 is coupled to and resonates within the second resonator portion 1510b, having a frequency f1 corresponding to the resonant frequency f of the first resonator portion 1510a. R2 As a result, the second optical portion 1528 is coupled to and resonates within the first resonator portion 1510a, having a frequency f2 corresponding to

[0109] At the second waveguide junction 1514, the output waveguide 1516 splits into a first output waveguide portion 1530 and a second output waveguide portion 1532. The second waveguide loop 1512 is a continuous waveguide including the first output waveguide portion 1530 and the second output waveguide portion 1532. A first resonant light 1534 resonating in the second resonator portion 1510b is coupled to the first output waveguide portion 1530 and travels through the second waveguide loop 1512 in a first direction (e.g., counterclockwise). A second resonant light 1536 resonating in the first resonator portion 1510a is coupled to the second output waveguide portion 1532 and travels through the second waveguide loop 1512 in a second direction opposite the first direction (e.g., clockwise). The first resonant light 1534 and the second resonant light 1536 enter the second waveguide junction 1514 and combine to form output light 1538 that is output from the output waveguide 1516. The output light 1538 has a beat frequency f equal to the difference between the first resonant light 1534 and the second resonant light 1536. beat The beat frequency of the output light 1538 is f beat is determined using a photodetector 1540 and a measurement device 1542 in the manner described herein.

[0110] The measurement system 1500 controls the frequency range of the spectrum S of the input light 1520 emitted by the light source 1518 or the beat frequency f beat The measurement system 1500 may include a computer system 1544 configured to control the operation of various aspects of the measurement system 1500, such as by determining the temperature of the photonic device 1502 based on the temperature of the photonic device 1502.

[0111] 16 illustrates a measurement system 1600 including a photonic device 1602. The measurement system 1600 is configured to detect a temperature of the photonic device 1602. Various aspects of the measurement system 1600 are substantially similar to corresponding features described with respect to the measurement system 300, the method 900, and elsewhere herein, and therefore further description thereof will be omitted for brevity. The photonic device 1602 includes a port 1603, a waveguide 1604, a waveguide junction 1606, a first waveguide 1608, a first optical resonator 1610 (shown enlarged), a second waveguide 1614, and a second optical resonator 1616 (shown enlarged). The measurement system 1600 also includes a light source 1620 configured to generate input light 1622 having a broadband optical spectrum S, in this example, having a spectral range between a first frequency and a second frequency.

[0112] At the waveguide junction 1606, the incident light is split and directed into a first waveguide 1608 and a second waveguide 1614. A first optical resonator 1610 is positioned within the optical path of the first waveguide 1608, and a second optical resonator 1616 is positioned within the optical path of the second waveguide 1614. As discussed herein, the first optical resonator 1610 has a different resonant frequency response than the second optical resonator 1616. The first and second optical resonators 1610 and 1616 may be whispering gallery mode resonators, photonic crystal cavities, ring resonators, Bragg gratings, Fabry-Perot interferometers (e.g., etalons), disk resonators, or any other suitable optical resonators. In some embodiments, the first optical resonator 1610 may be a different type of optical resonator than the second optical resonator 1616.

[0113] Input light 1622 enters waveguide 1604 through port 1603 and is split at waveguide junction 1606 into a first light portion that enters first waveguide 1608 and a second light portion that enters second waveguide 1614. First optical resonator 1610 resonates the first light portion, and second optical resonator 1616 resonates the second light portion. The resonated first light portion returns through waveguide 1604 and is output from port 1603. The resonated second light portion, along with the resonated first light portion, returns through waveguide 1604 and is output from port 1603. Non-resonant light of input light 1622 also returns through first waveguide 1608 and second waveguide 1614 and is combined with the first and second resonated light portions and output from port 1603.

[0114] Light 1624 output from port 1603 may include resonant and non-resonant light. Measurement system 1600 may include an optical isolator 1626 that allows input light 1622 to travel and reflects output light 1624. Measurement system 1600 includes one or more measurement devices 1628 positioned to receive reflected light 1630 from optical isolator 1626. The one or more measurement devices 1628, in at least some embodiments, include a spectrum analyzer 1634 that analyzes the resonant and non-resonant light in the emitted light 1624 detected by photodetector 1632 to detect the resonant frequencies induced by first optical resonator 1610 and second optical resonator 1616. The temperature of photonic device 1602 may be determined based on the difference between the resonant frequencies, for example, by computer system 1636, as discussed herein.

[0115] FIG. 17 illustrates a measurement system 1700 including a photonic device 1702 and configured to detect the temperature of the photonic device 1702. Various aspects of the measurement system 1700, including the light source 1720, the optical isolator 1722, the photodetector 1724, and the measurement system 1726, are substantially similar to corresponding features described with respect to the measurement system 1600, the method 900, and elsewhere herein, and therefore further description thereof is omitted for brevity. The photonic device 1702 includes a waveguide junction 1704, a first waveguide 1706 adjacent to the first optical resonator, and a second optical resonator 1708 adjacent to the second optical resonator. FIG. 17 illustrates an expanded view of the first and second optical resonators, which may include photonic crystals or other types of optical resonators adjacent to the first waveguide 1706 and the second waveguide 1708, respectively.

[0116] First waveguide 1706 includes an optically reflective end 1710, and second waveguide 1708 includes an optically reflective end 1712. A first portion of the light in first waveguide 1706 is reflected from reflective end 1710, and a second portion of the light in second waveguide 1708 is reflected from reflective end 1712. The reflected first and second portions of the light, including light resonated with the first and second optical resonators and non-resonated light, return via first waveguide 1706 and second waveguide 1708, respectively, and are then combined and measured to determine the temperature of photonic device 1702 by photodetector 1724, measurement device 1726, and computer system 1728, which determine the beat frequency of the returned light and correlate the determined beat frequency with temperature, for example, in the manner described with respect to measurement system 1600 and other measurement systems described herein. As an alternative to the reflecting ends 1710, 1712, the first waveguide 1706 and the second waveguide 1708 may each terminate in a waveguide loop in which the respective first and second optical portions travel through the first waveguide 1706 and the second waveguide 1708 and return to the waveguide junction 1704 and an optical isolator 1722, which directs the returning light to a photodetector 1724.

[0117] FIG. 18 illustrates multiple optical resonators that can be implemented in the photonic devices of the measurement systems described herein. The optical resonator includes a Fabry-Perot interferometer 1802 in which multiple offset beams reflected from its surface generate resonant light. The illustrated optical resonator also includes a whispering gallery resonator 1804 that resonates light in the form of whispering gallery modes. The illustrated optical resonator also includes a photonic crystal 1806 with a periodic dielectric structure configured to propagate light within a specific frequency range and block the propagation of light in other frequency ranges. These optical resonators are provided as examples of the myriad types of optical resonators that can be implemented in the measurement systems described herein. In some embodiments, an optical resonator can have two or more resonant modes, e.g., a first resonant mode at a first frequency and a second resonant mode at a second frequency. In such embodiments, the photonic thermometers described herein can include only a single optical resonator with resonant modes at two or more corresponding frequencies. For example, 2D photonic crystals may also provide resonant optical reflection such that a single optical port and a single waveguide may provide both input and output optical paths for input and output light, respectively.

[0118] 19 shows exemplary structures of multiple photonic crystals that can be used to resonate light in the measurement systems described herein. A first type of photonic crystal 1902 has a crystal structure that is periodic in one direction. For example, the first type of photonic crystal 1902 has a crystal atomic arrangement that is periodic (e.g., repeating) along a first direction. A second type of photonic crystal 1904 has a crystal structure that is periodic in two directions (e.g., two mutually orthogonal directions). A third type of photonic crystal 1906 has a crystal structure that is periodic in three mutually orthogonal directions. One or more of these types of photonic crystals can be implemented in the embodiments described herein.

[0119] Various different types of optical resonators can be implemented in the photonic devices described herein. Non-limiting examples of optical resonators that can be implemented in the photonic devices described herein (e.g., photonic device 302) include whispering gallery mode resonators, photonic crystal cavities, ring resonators, Bragg gratings, Fabry-Perot interferometers (e.g., etalons), and disk resonators. A single optical resonator can include a combination of one or more types of optical resonators. A pair of optical resonators (e.g., first optical resonator 306 and second optical resonator 312) having different resonant frequency responses can include a first optical resonator of a first type and a second optical resonator of a second type. In some embodiments, a single optical resonator can be used instead of two separate optical resonators. In such embodiments, a single optical resonator can have two or more optical modes (either transverse or longitudinal) that provide different resonant frequency responses.

[0120] These variations include variations in the optical resonator design, waveguide dimensions, waveguide path, different couplers in the optical path (e.g., directional couplers, multimode interference couplers), different types of coupling to the optical resonator (e.g., in-line, adiabatic), or any type of input or output to the chip (e.g., grating couplers, edge coupling, loop fiber coupling, tapered fiber).

[0121] The above description and the accompanying drawings set forth certain specific details to provide a thorough understanding of various disclosed embodiments. However, those skilled in the art will recognize that the disclosed embodiments may be practiced without one or more of these specific details, or in various combinations with other methods, components, devices, materials, and the like. In other cases, well-known structures or components associated with the disclosed environments, including, but not limited to, communication systems and networks and environments, have not been shown or described to avoid unnecessarily obscuring the description of the embodiments. Additionally, the various embodiments may be methods, systems, media, or devices. Thus, the various embodiments may be entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects.

[0122] Additionally, throughout the specification, claims, and drawings, the following terms adopt the meanings clearly associated therewith unless the content clearly dictates otherwise. The term "herein" refers to the specification, claims, and drawings to which this document pertains. The phrases "in one embodiment," "in another embodiment," "in various embodiments," "in some embodiments," "in other embodiments," and other variations thereof refer to one or more features, structures, functions, limitations, or characteristics of the present disclosure, and are not limited to the same or different embodiments, unless the content clearly dictates otherwise. As used herein, the term "or" is an inclusive "or" and is synonymous with the phrases "A or B, or both" or "A or B or C, or any combination thereof," with lists including additional elements being treated similarly. The term "based on" is not exclusive and allows for additional unrecited features, functions, aspects, or limitations to be based on unless the content clearly dictates otherwise. Additionally, throughout the specification, the meanings of "a," "an," and "the" include both singular and plural referents. As used herein, references to the term "set" (e.g., "set of items") should be construed as a non-empty collection that includes one or more members or instances, unless otherwise stated or contradicted by context.

[0123] Thus, in view of the foregoing disclosure, various examples of photonic devices may include any one or any combination of the following features: a substrate; a substrate having one or more ports; a plurality of optical resonators; a first optical resonator in or on the substrate; the first optical resonator having a first resonant frequency; the first optical resonator having a first resonant frequency response over temperature; a plurality of waveguides; a first waveguide optically coupled to the one or more ports; a first waveguide optically coupled to the first optical resonator; a second optical resonator in or on the substrate; a second optical resonator having a second resonant frequency; the second optical resonator having a second resonant frequency response over temperature; a second resonant frequency response of the second optical resonator that differs from the first resonant frequency response of the first optical resonator; a second waveguide optically coupled to the one or more ports;

[0124] In one or more examples, the first optical resonator has a size that is different from the size of the second optical resonator, and the difference in size affects the difference between the first resonant frequency response and the second resonant frequency response.

[0125] In one or more examples, the first optical resonator has a structural feature that is not present in the second optical resonator, and that structural feature affects the difference between the first and second resonant frequency responses. In some cases, the structural feature is an additional section.

[0126] In one or more examples, the first optical resonator has structural characteristics that differ from the structural characteristics of the second optical resonator, and the structural characteristics affect the difference between the first resonant frequency response and the second resonant frequency response.

[0127] In one or more examples, the first optical resonator includes a material composition that is different from the material composition of the second optical resonator, and the difference in material composition affects the difference between the first resonant frequency response and the second resonant frequency response.

[0128] In one or more examples, the first optical resonator is spaced apart from the first waveguide, the second optical resonator is spaced apart from the second waveguide, and the first optical resonator is spaced apart from the second optical resonator.

[0129] In one or more examples, the first optical resonator and the second optical resonator are ring resonators.

[0130] In one or more examples, a region adjacent to the first optical resonator includes a material composition that differs from the material composition adjacent to a corresponding region adjacent to the second optical resonator, the difference in material composition affecting a difference between the first resonant frequency response and the second resonant frequency response.

[0131] In one or more examples, a first mechanical stress applied to the first optical resonator differs from a second mechanical stress applied to the second optical resonator, the difference in mechanical stress affecting a difference between the first resonant frequency response and the second resonant frequency response.

[0132] In one or more examples, the first optical resonator is optically isolated from the second optical resonator.

[0133] In one or more examples, the first waveguide includes a first port, the second waveguide includes a second port, and the first waveguide is optically isolated from the second waveguide.

[0134] In one or more examples, the photonic device may further include a third waveguide including a third port, the third waveguide being optically isolated from the first waveguide and the second waveguide, and the third waveguide being optically coupled to at least one of the first optical resonator and the second optical resonator.

[0135] In one or more examples, the first waveguide includes a third port and the second waveguide includes a fourth port.

[0136] In one or more examples, the photonic device may further include a third waveguide optically coupled to the first optical resonator, the third waveguide including a third port and optically isolated from the first waveguide; and a fourth waveguide optically coupled to the second optical resonator, the fourth waveguide including a fourth port and optically isolated from the second waveguide.

[0137] In one or more examples, the first waveguide is optically coupled to a second optical resonator, and the second waveguide is optically coupled to the first optical resonator.

[0138] In one or more examples, the photonic device may further include a third optical resonator in or on the substrate, the third resonant frequency response over temperature, the third resonant frequency response being different from the first resonant frequency response and the second resonant frequency response. The third optical resonator may be optically coupled to the first waveguide and the second waveguide. The third waveguide may be optically coupled to the third optical resonator, the third waveguide including a third port.

[0139] In one or more examples, the photonic device may further include a fourth optical resonator in or on the substrate having a fourth resonant frequency response versus temperature, the fourth resonant frequency response being different from the first resonant frequency response, the second resonant frequency response, and the third resonant frequency response.

[0140] In one or more examples, the photonic device may further include a third waveguide optically coupled to the third optical resonator, the third waveguide including a third port, and a fourth waveguide optically coupled to the fourth optical resonator, the fourth waveguide including a fourth port.

[0141] In one or more examples, the photonic device may further include one or more optical switches selectively controllable to optically couple the first waveguide to the second optical resonator.

[0142] In one or more examples, the photonic device may further include a waveguide junction between the first waveguide and the second waveguide, and a third waveguide optically coupled between the waveguide junction and one of the one or more ports.

[0143] In one or more examples, the photonic device may further include a first waveguide loop optically coupled to an end of the first waveguide and a second waveguide loop optically coupled to an end of the second waveguide.

[0144] In one or more examples, the first waveguide includes a first optically reflective end portion and the second waveguide includes a second optically reflective end portion.

[0145] In one or more examples, the first optical resonator is a first type of optical resonator and the second optical resonator is a second type of optical resonator that is different from the first type of optical resonator.

[0146] In one or more examples, the photonic device may further include one or more light sources configured to generate input light directed into the first waveguide or the second waveguide. The one or more light sources may include a first light source configured to emit a first light beam, the first light source being controllable to tune the frequency of the first light beam.

[0147] In one or more examples, the photonic device may further include an optical beam splitter configured to split the first optical beam to form a second optical beam, and an optical shifter configured to receive the second optical beam and adjust a frequency of the second optical beam, wherein the first optical beam is directed into the first waveguide and the second optical beam is directed into the second waveguide.

[0148] In one or more examples, the one or more light sources include a second light source configured to emit a second light beam, the second light source being controllable to adjust the frequency of the second light beam. The first light source may be a first laser light source and the second light source may be a second laser light source. In one or more examples, the first and second laser light sources are independently controllable to adjust the frequencies of the first and second light beams, respectively.

[0149] In view of the foregoing disclosure, various examples of methods of operating a measurement system including a photonic device may include any one or any combination of the following features: directing a first light beam into a first waveguide of the photonic device; directing a second light beam into a second waveguide of the photonic device; combining first output light received from the first waveguide and second output light received from the second waveguide into a composite light; determining a frequency difference between the first output light and the second output light based on the composite light; and, if the measurement system is a temperature measurement system, determining a temperature of the photonic device based on the frequency difference.

[0150] In one or more examples, the method may further include locking a frequency of the first optical beam to a first resonant frequency of a first optical resonator in the photonic device and locking a frequency of the second optical beam to a second resonant frequency of a second optical resonator in the photonic device, wherein the frequency difference is determined after the frequency of the first optical beam is locked to the first resonant frequency and the frequency of the second optical beam is locked to the second resonant frequency.

[0151] In one or more examples, the method may further include, prior to splitting the light beam into a first light beam and a second light beam and directing the second light beam into the second waveguide, shifting an optical property of the second light beam relative to the first light beam. The optical property may be a frequency of the second light beam that is shifted relative to a frequency of the first light beam.

[0152] In one or more examples, the method may further include converting the composite light into an electrical signal and detecting a beat frequency of the composite light based on the electrical signal.

[0153] In one or more examples, the method may further include accessing temperature correspondence data stored in the memory and determining a temperature of the photonic device based on a correspondence between the frequency difference and the temperature in the temperature correspondence data.

[0154] In one or more examples, the method may further include controlling the first light source to tune a frequency of the first light beam from a first frequency to a second frequency, the second frequency corresponding to a first resonant frequency of a first optical resonator optically coupled to the first waveguide.

[0155] In one or more examples, the method may further include controlling the optical frequency shifter to tune the frequency of the second optical beam to a third frequency, the third frequency corresponding to a second resonant frequency of a second optical resonator optically coupled to the second waveguide.

[0156] In one or more examples, the method may further include controlling the second light source to tune a frequency of the second light beam to a third frequency, the third frequency corresponding to a second resonant frequency of a second optical resonator optically coupled to the second waveguide. Thus, the methods described herein may relate to methods of detecting temperature, methods of detecting temperature using a photonic device, methods of operating a measurement system, methods of operating a temperature measurement system, and methods of operating a measurement system including a photonic device.

[0157] In view of the disclosure herein, various examples of photonic systems include a photonic device, a photonic device including a substrate, a plurality of optical resonators, a first optical resonator in or on the substrate, the first optical resonator having a first resonant frequency response, the first optical resonator having a first resonant frequency response versus temperature, a second optical resonator in or on the substrate, a second optical resonator having a second resonant frequency response, and a second optical resonator having a second resonant frequency response versus temperature, and an optical resonator configured to receive a first light beam. a first waveguide optically coupled to the first optical resonator; a first waveguide optically coupled to the first optical resonator; a second waveguide optically coupled to receive the second light beam; a second waveguide optically coupled to the second optical resonator; an optical combiner configured to combine the first output light from the first waveguide and the second output light from the second waveguide into a composite light; and a photodetector configured to convert the composite light from the optical combiner into an electrical signal.

[0158] In one or more examples, the photonic system may further comprise one or more measurement devices configured to measure a characteristic of the electrical signal, which may be indicative of a temperature of the photonic device.

[0159] In one or more examples, the one or more measurement devices include a frequency counter configured to measure the frequency of the electrical signal.

[0160] In one or more examples, the one or more measurement devices include a spectrum analyzer configured to analyze the energy distribution in the frequency spectrum of the electrical signal and measure the magnitude of the energy distribution in the frequency spectrum versus the frequencies within the frequency spectrum.

[0161] In one or more examples, the photonic system may further include an optical shifter configured to receive the second optical beam and shift an optical property of the second optical beam before the second waveguide receives the second optical beam. The optical property may be a frequency of the second optical beam.

[0162] In one or more examples, the photonic system may further comprise an optical frequency locked loop configured to control the frequency of the second optical beam relative to the frequency of the first optical beam.

[0163] In one or more examples, the photonic system may further comprise an optical beam splitter configured to split the light emitted by the light source into a first light beam and a second light beam.

[0164] In one or more examples, the photonic system may further include a first light source configured to emit a first light beam. The first light source may be controllable to adjust the frequency of the first light beam. In one or more examples, the photonic system may further include a second light source configured to emit a second light beam. The second light source may be controllable to adjust the frequency of the second light beam.

[0165] In one or more examples, the first light source and the second light source are first and second independently controllable laser light sources.

[0166] In one or more examples, the photonic system may include a broadband light source configured to emit broadband light having a frequency spectrum between a first frequency and a second frequency, and the broadband light source may provide the first light beam and / or the second light beam.

[0167] In light of the disclosure herein, additional examples of photonic devices may include any one or any combination of the features of: a multimode optical resonator; a first waveguide optically coupled to receive input light; the first waveguide optically coupled to the multimode optical resonator; the multimode optical resonator configured to resonate light having a first frequency and to resonate light having a second frequency; and a measurement device configured to determine a temperature of the photonic device based on the beat frequency of the light output from the first waveguide.

[0168] In one or more examples, the multimode optical resonator is a bimodal optical ring resonator having a first portion that resonates light having a first frequency and a second portion that resonates light having a second frequency.

[0169] In one or more examples, the photonic device may further include a first waveguide loop optically coupling the first waveguide to the multimode optical resonator.

[0170] In one or more examples, the photonic device may further include a second waveguide optically coupled to receive the input light and a second waveguide loop optically coupling the second waveguide to the multimode optical resonator.

[0171] In one or more examples, the first portion of the multimode optical resonator has a different material composition than the second portion of the multimode optical resonator.

[0172] In one or more examples, the first portion of the multimode optical resonator has a different size than the second portion of the multimode optical resonator.

[0173] In one or more examples, the first portion of the multimode optical resonator has a different shape than the second portion of the multimode optical resonator.

[0174] In one or more examples, a first portion of the multimode optical resonator is mechanically stressed differently than a second portion of the multimode optical resonator.

[0175] In one or more examples, the multimode optical resonator is a photonic crystal having a periodic crystal structure in two or more directions.

[0176] In one or more examples, the photonic device may further include a first light source configured to emit light that is received by the first waveguide as input light.

[0177] In one or more examples, the first light source is a broadband light source configured to emit broadband light having a spectrum between the first frequency and the second frequency.

[0178] In one or more examples, the first light source is configured to emit light at a first frequency locked to a first resonant frequency of the multi-mode resonator. The photonic device may further include a second light source configured to emit light at a second frequency locked to a second resonant frequency of the same multi-mode resonator.

[0179] In one or more examples, the photonic device may further include one or more photodetectors configured to convert the light output from the first waveguide into an electrical signal, and the measurement device configured to determine a beat frequency of the light based on a frequency detected in the electrical signal.

[0180] In view of the foregoing disclosure, various examples of methods of operating a photonic device may include any one or any combination of the following features: directing broadband light into a photonic device having a resonant frequency; generating output light by the photonic device; converting the output light into an electrical signal; determining a beat frequency of the output light based on the electrical signal; and determining a temperature of the photonic device based on the determined beat frequency.

[0181] In one or more examples, the photonic device has a plurality of resonant frequencies including at least a first resonant frequency corresponding to a first frequency of light in the broadband light and a second resonant frequency corresponding to a second frequency of light in the broadband light, and the method includes generating output light including combining light of at least the first and second frequencies traversed the photonic device.

[0182] The various embodiments and examples described above can be combined to provide further embodiments and examples. These and other changes can be made to the embodiments and examples in light of the above Detailed Description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments or examples disclosed herein, but should be construed to encompass all possible embodiments along with the full range of equivalents to which such claims are entitled. Accordingly, the scope of the claims is not limited by this disclosure.

Claims

1. 1. A photonic system comprising: a photonic device, the photonic device comprising: A substrate; a first optical resonator in or on the substrate, the first optical resonator having a first resonant frequency response versus temperature; a second optical resonator in or on the substrate, the second optical resonator having a second resonant frequency response versus temperature; a first waveguide optically coupled to the first optical resonator and configured to receive a first optical beam; an optical shifter configured to receive a second optical beam, shift the frequency of the second optical beam, and emit a frequency-shifted second optical beam; a second waveguide optically coupled to the second optical resonator and configured to receive the frequency-shifted second optical beam, wherein output light from the photonic device includes light from the first waveguide and light from the second waveguide; a detector configured to convert the output light from the photonic device into an electrical signal, the electrical signal having a characteristic indicative of a physical condition of the photonic device.

2. an optical combiner configured to combine a first output light from the first waveguide and a second output light from the second waveguide into a composite light, the composite light being the output light from the photonic device; and one or more measurement devices configured to measure the characteristic of the electrical signal, the characteristic of the electrical signal indicative of a temperature of the photonic device; The photonic system of claim 1 further comprising:

3. The photonic system of claim 2 , wherein the characteristic of the electrical signal is a frequency of the electrical signal, and the one or more measurement devices include a frequency counter configured to measure the frequency of the electrical signal.

4. 3. The photonic system of claim 2, wherein the characteristic of the electrical signal is an energy distribution in a frequency spectrum of the electrical signal, and the one or more measurement devices include a spectrum analyzer configured to analyze the energy distribution and measure a magnitude of the energy distribution in the frequency spectrum versus a frequency within the frequency spectrum.

5. an optical frequency locked loop configured to control the frequency of the second optical beam relative to the frequency of the first optical beam; The photonic system according to any one of claims 1 to 4.

6. a first light source configured to emit the first light beam, the first light source being controllable to adjust a frequency of the first light beam; a second light source configured to emit the second light beam, the second light source being controllable to adjust the frequency of the second light beam; The photonic system according to any one of claims 1 to 5, further comprising:

7. 7. The photonic system of claim 1, further comprising a broadband light source configured to emit the first light beam having a frequency spectrum between a first frequency and a second frequency.

8. 1. A method of operating a measurement system, comprising: directing a first optical beam into a first waveguide of a photonic device and optically coupling the first optical beam from the first waveguide to a first optical resonator; shifting the frequency of the second light beam and emitting the frequency-shifted second light beam; directing the frequency-shifted second optical beam into a second waveguide of the photonic device and coupling the frequency-shifted second optical beam from the second waveguide into a second optical resonator; determining a frequency difference between a first output light from the first waveguide and a second output light from the second waveguide; and determining a temperature of the photonic device based on the frequency difference.

9. controlling a first light source to tune a frequency of the first light beam to a first resonant frequency of the first optical resonator optically coupled to the first waveguide; The method of operating a measurement system of claim 8 further comprising:

10. controlling an optical frequency shifter to shift the frequency of the second optical beam to a second resonant frequency of the second optical resonator optically coupled to the second waveguide; 10. A method of operating a measurement system according to claim 8 or 9, further comprising:

11. controlling a second light source to shift the frequency of the second light beam to a second resonant frequency of the second optical resonator optically coupled to the second waveguide; 10. A method of operating a measurement system according to claim 8 or 9, further comprising:

12. locking a frequency of the first optical beam to a first resonant frequency of a first optical resonator within the photonic device; locking a frequency of the second optical beam to a second resonant frequency of a second optical resonator in the photonic device, wherein the frequency difference is determined after locking the frequency of the first optical beam to the first resonant frequency and locking the frequency of the second optical beam to the second resonant frequency. A method for operating a measurement system according to any one of claims 8 to 11.

13. A method of operating a measurement system according to any one of claims 8 to 12, wherein the frequency of the second light beam is shifted relative to the frequency of the first light beam.

14. combining the first output light from the first waveguide and the second output light from the second waveguide into a composite light; converting the composite light into an electrical signal; detecting a beat frequency of the composite light based on the electrical signal, the beat frequency indicating the frequency difference between the first output light and the second output light; determining a temperature of the photonic device based on the beat frequency; and A method of operating a measurement system according to any one of claims 8 to 12, further comprising:

15. accessing temperature-related data stored in a memory; determining the temperature of the photonic device based on a correspondence between the frequency difference and the temperature in the temperature correspondence data; A method of operating a measurement system according to any one of claims 8 to 14, further comprising:

Images