Optical microresonator array device for ultrasound sensing

Abstract

An apparatus can include one or more optical fibers, one or more optical waveguides, and a plurality of resonator nodes arranged in an array of sensing locations. Each resonator node can include an optical coupling between an optical waveguide and an optical fiber having a set of resonant frequencies at a respective sensing location. Each resonator node can be further configured to transmit a set of signals corresponding to a displacement of at least one of the set of resonant frequencies in the optical fiber at the respective sensing location.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Patent Application No. 63 / 001,738, filed on March 30, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure generally relates to the field of ultrasound, and more particularly to methods and apparatus for ultrasonic sensing using an optical microresonator array. Background Technology

[0004] Due to its many advantages, ultrasound sensing is used in various industries that include medical imaging. For example, ultrasound sensing utilizes ultrasound signals with significant penetration depth. Furthermore, ultrasound imaging is known to be an advantageous form of non-invasive imaging because it is based on non-ionizing radiation.

[0005] Conventional ultrasonic sensing utilizes piezoelectric materials such as lead zirconate titanate (PZT), thick polymer films (PTF), and polyvinylidene fluoride (PVDF). However, some challenges associated with the piezoelectric properties of these materials include high operating voltage requirements, high electric field requirements (which can lead to breakdown and failure), nonlinear responses with high hysteresis, and limited detection angles. Therefore, new and improved devices and methods are needed for ultrasonic sensing. Summary of the Invention

[0006] Generally, in some embodiments, an apparatus may include one or more (e.g., multiple) optical fibers, one or more optical waveguides, and multiple resonator nodes arranged in an array of sensing locations. Each resonator node may include optical coupling between the optical waveguide and an optical fiber having a set of resonant frequencies at the corresponding sensing location. Each resonator node may be further configured to transmit a set of signals corresponding to a shift in the set of resonant frequencies in the optical fiber at the corresponding sensing location. In some embodiments, each optical fiber may have the same or substantially similar cross-sectional geometry and / or material homogeneity, such that the optical fibers may have the same or substantially similar set of resonant frequencies. By utilizing such homogeneous material properties (e.g., using mass-produced optical fibers), ultrasonic sensing systems incorporating such apparatus can be more easily mass-produced in a cost-effective and consistent manner, and have more consistent and predictable performance.

[0007] In some embodiments, the one or more optical fibers may be configured to receive a plurality of ultrasonic echoes. Furthermore, the one or more optical fibers may be configured to undergo the shift in the set of resonant frequencies in response to the plurality of ultrasonic echoes. In some embodiments, the one or more optical waveguides are configured to propagate a set of signals corresponding to the at least one shift in the set of resonant frequencies to an optical detector.

[0008] In some embodiments, the one or more optical waveguides may comprise one or more tapered optical fibers or one or more integrated photonic waveguides (e.g., silicon photonic waveguides). The one or more tapered optical fibers may be in a polymer structure.

[0009] The one or more optical fibers may be arranged perpendicular to the one or more optical waveguides. For example, in some embodiments, the one or more optical fibers may be arranged linearly at predetermined equal distances from each other and perpendicular to the one or more tapered optical fibers. Furthermore, the one or more optical fibers and the one or more optical waveguides may be arranged in a rectangular grid.

[0010] In some embodiments, the one or more optical waveguides may be coupled to a light source, and the light source may propagate light within the one or more optical waveguides. For example, the light source may comprise a broadband light source or a tunable laser source.

[0011] The one or more optical fibers and the one or more optical waveguides can be arranged in any suitable manner to enable optical coupling at each resonator node. For example, in some embodiments, the optical fiber may be in physical contact with the optical waveguide at the resonator node. Alternatively, in embodiments, a short separation gap (e.g., about 1 μm or less) may exist between the optical fiber and the optical waveguide at the resonator node. Furthermore, the optical waveguide and the optical fiber can be spaced apart in any suitable manner. For example, in some embodiments, the distance between the optical waveguides of the one or more optical waveguides may be at least about 20 times the wavelength of the light from the light source. In some embodiments, the distance between the optical fibers of the one or more optical fibers may be less than about 3 times the wavelength of the light.

[0012] Generally, in some embodiments, a method for ultrasonic sensing may include receiving a first set of signals at one or more optical waveguides via a plurality of (e.g., more than one) resonator nodes, corresponding to a first set of whispering-gallery patterns propagating circumferentially along one or more optical fibers. The method may further include receiving a second set of signals at the one or more optical waveguides via the plurality of resonator nodes, corresponding to a second set of whispering-gallery patterns propagating circumferentially along each optical fiber. In some embodiments, the second set of whispering-gallery patterns may propagate in response to the reception of multiple ultrasonic echoes by the one or more optical fibers. The method may further include detecting a set of differences between the first set of signals and the second set of signals. The method may further include calculating a magnitude of each ultrasonic echo at each resonator node based at least in part on the first set of signals, the second set of signals, and / or the set of differences. The method may further include associating the magnitude of each ultrasonic echo with a sensing location of each resonator node. In some embodiments, the method may further include transmitting multiple ultrasonic signals using a plurality of piezoelectric elements. The method may further include receiving the plurality of ultrasonic echoes corresponding to the plurality of ultrasonic signals at the one or more optical fibers, wherein the plurality of resonator nodes may be configured to perform synthetic aperture (SA) operation or compressed sensing (CS) operation.

[0013] In some embodiments, the one or more optical fibers may comprise multiple fibers having the same or substantially similar cross-sectional geometry and materials to have the same or substantially similar sets of resonant frequencies. In some embodiments, the one or more optical fibers may be perpendicular to the one or more optical waveguides. In some embodiments, the one or more optical waveguides may comprise one or more tapered optical fibers and / or one or more integrated photonic waveguides, or another suitable waveguide that may be coupled to a light source to propagate light from the light source. In some embodiments, the one or more optical fibers and / or the one or more optical waveguides may be in a polymer structure.

[0014] The one or more optical fibers and the one or more optical waveguides can be arranged in any suitable manner to enable optical coupling at each resonator node. For example, in some embodiments, the optical fiber may be in physical contact with the optical waveguide at the resonator node. Alternatively, in embodiments, a short separation gap (e.g., about 1 μm or less) may exist between the optical fiber and the optical waveguide at the resonator node. Furthermore, the optical waveguide and the optical fiber can be spaced apart in any suitable manner. For example, in some embodiments, the distance between the optical waveguides of the one or more optical waveguides may be at least about 20 times the wavelength of the light from the light source. In some embodiments, the distance between the optical fibers of the one or more optical fibers may be less than about 3 times the wavelength of the light.

[0015] Generally, in some embodiments, an apparatus may include one or more optical fibers and one or more optical waveguides optically coupled to the one or more optical fibers at multiple resonator nodes. The circumference of each optical fiber may be configured to propagate a first set of whispering-gallery modes. In some embodiments, the one or more optical fibers transmit a first set of signals corresponding to the first set of whispering-gallery modes to the one or more optical waveguides. The one or more optical waveguides may be configured to propagate the first set of signals to at least one optical detector.

[0016] In some embodiments, the one or more optical fibers may comprise multiple fibers having the same or substantially similar cross-sectional geometry and materials to have the same or substantially similar sets of resonant frequencies. In some embodiments, the one or more optical fibers may be perpendicular to the one or more optical waveguides. In some embodiments, the one or more optical waveguides may comprise one or more tapered optical fibers and / or one or more integrated photonic waveguides, or another suitable waveguide that may be coupled to a light source to propagate light from the light source. In some embodiments, the one or more optical fibers and / or the one or more optical waveguides may be in a polymer structure.

[0017] The one or more optical fibers and the one or more optical waveguides can be arranged in any suitable manner to enable optical coupling at each resonator node. For example, in some embodiments, the optical fiber may be in physical contact with the optical waveguide at the resonator node. Alternatively, in embodiments, a short separation gap (e.g., about 1 μm or less) may exist between the optical fiber and the optical waveguide at the resonator node. Furthermore, the optical waveguide and the optical fiber can be spaced apart in any suitable manner. For example, in some embodiments, the distance between the optical waveguides of the one or more optical waveguides may be at least about 20 times the wavelength of the light from the light source. In some embodiments, the distance between the optical fibers of the one or more optical fibers may be less than about 3 times the wavelength of the light.

[0018] In some embodiments, the one or more optical fibers are configured to receive a plurality of ultrasonic echoes and propagate a second set of whispering-gallery modes in response to the plurality of ultrasonic echoes. The one or more optical fibers are configured to transmit a second set of signals corresponding to the second set of whispering-gallery modes to the one or more optical waveguides. In some embodiments, the one or more optical waveguides are configured to propagate the second set of signals to the at least one optical detector.

[0019] In some embodiments, the one or more optical fibers may be configured to transmit a set of signals corresponding to the difference between the first set of whispering wall modes and the second set of whispering wall modes to the one or more optical waveguides via the plurality of resonator nodes. For example, the difference between the first set of whispering wall modes and the second set of whispering wall modes includes at least one of the following: a shift in at least one of the resonant frequencies of the optical fibers and / or attenuation of the resonances of the one or more optical fibers. Attached Figure Description

[0020] Figure 1A This is a schematic description of an exemplary optical microresonator array.

[0021] Figure 1B This is a schematic description of an exemplary optical microresonator array.

[0022] Figure 1C This is a schematic description of an exemplary optical microresonator array.

[0023] Figure 1D This is a schematic description of an exemplary optical microresonator array.

[0024] Figure 2A This is a schematic description of an exemplary method for packaging optical microresonator arrays.

[0025] Figure 2B This is a schematic description of an exemplary method for packaging optical microresonator arrays.

[0026] Figure 3A This is a schematic description of an exemplary optical microresonator array.

[0027] Figure 3B This is a schematic description of an exemplary optical microresonator array.

[0028] Figure 3C This is a schematic description of an exemplary optical microresonator array.

[0029] Figure 4 This is a schematic description of an exemplary method for sensing a set of ultrasonic echoes using an optical microresonator array device.

[0030] Figure 5 This is a schematic description of an exemplary method for measuring the optical response of an optical microresonator array device.

[0031] Figure 6 This is a schematic description of an exemplary method for measuring the optical response of an optical microresonator array device.

[0032] Figure 7 and Figure 8 This is a schematic description of an exemplary ultrasound probe. Detailed Implementation

[0033] Non-limiting examples of various aspects and variations of the invention are described herein and illustrated in the accompanying drawings.

[0034] This paper describes an exemplary optical microresonator array and its fabrication method. Furthermore, as described herein, such optical microresonator arrays can be combined to form optical microresonator arrays with high quality factors and various other beneficial features as described below, for use in applications such as ultrasonic sensing and / or ultrasonic imaging.

[0035] Optical microresonator array

[0036] This paper describes optical microresonator arrays suitable for high-sensitivity applications involving high-sensitivity acousto-optic sensing systems. For example, such as... Figure 1A As shown, an exemplary optical microresonator array 100A may include a set (e.g., multiple) of optical fibers 103A, a set (e.g., multiple) of optical waveguides 102A, and multiple resonator nodes 104A arranged in a sensing position array. Each resonator node 104A may include optical coupling between the optical waveguide and the optical fiber at a corresponding sensing position. Each optical fiber may have a set of resonant frequencies, and each resonator node 104A may be further configured to transmit a set of signals corresponding to a shift of at least one of the set of resonant frequencies in the optical fiber at the corresponding sensing position. At each resonator node, the cross-section of the optical fiber may act as an optical microresonator (e.g., a whispering-gallery mode microresonator), which is configured to transmit a set of signals corresponding to a shift of at least one of the set of resonant frequencies in the optical fiber. These signals are associated with a corresponding sensing position for the resonator node.

[0037] Each optical microresonator in an optical microresonator array comprises a closed loop of transparent medium, which allows light of certain permitted frequencies to propagate continuously within the closed loop and stores the optical energy of the permitted frequencies within the closed loop. Therefore, permitted propagation occurs around the optical microresonator, with whispering-gallery modes (WGMs) corresponding to the permitted frequencies circulating around the circumference of the optical microresonator. Each mode from the WGM may, for example, correspond to the propagation of light at a certain frequency from the permitted frequencies.

[0038] The optical microresonator array described herein exhibits high sensitivity, at least in part, due to its high quality factor, as it advantageously allows light of the permitted frequency to remain within the closed loop of the optical microresonator array for an extended period. The permitted frequency of light and the quality factor of the optical microresonator array described herein are at least partially based on the geometric parameters of the optical microresonator array, the refractive index of the transparent medium, and the refractive index of the environment surrounding the optical microresonator array.

[0039] As further described herein, optical microresonator arrays can be configured to receive light, transmit light, and are useful in practice (e.g., for ultrasonic imaging or other sensing applications in acousto-optic systems). Acousto-optic systems based on optical microresonator arrays can directly measure ultrasound via photoelastic effects and / or physical deformation of the optical microresonator array in response to ultrasound waves (e.g., ultrasonic echoes). For example, in the presence of ultrasonic (or any pressure) waves, the WGM propagating from the optical microresonator array can undergo one or more spectral shifts caused by changes in the refractive index and / or shape of the optical microresonator array. Spectral changes can be easily monitored and analyzed in the spectral domain and in the light transmission intensity entering and leaving the optical microresonator array. Additional spatial and other information can be derived by monitoring and analyzing the shifted WGMs in multiple optical microresonator arrays.

[0040] In some embodiments, the optical microresonator array may comprise optical fibers along its length and / or having the same or substantially similar cross-sectional characteristics (e.g., cross-sectional geometry and / or material properties) relative to each other, as further described herein. Thus, the availability of mass-producible optical fibers can be utilized to fabricate the optical microresonator array in an efficient and highly reproducible manner suitable for large-scale production. Furthermore, the use of such similar mass-produced optical fibers (and / or optical waveguides) in the optical microresonator array can produce more consistent and reliable performance in ultrasonic sensing. Therefore, the optical microresonator arrays described herein offer several advantages over microresonator arrays formed by conventional techniques, where individual microresonators must be painstakingly formed individually before being assembled into an array, and may exhibit inconsistent or unreliable performance due to variability within the individual microresonators and / or require complex micron or nanometer fabrication techniques to adjust the resonant wavelength of each microresonator. Furthermore, for embodiments of optical microresonator arrays with optical fibers having the same or very close WGM resonance conditions and resonant frequencies, it is possible to use a single-frequency laser or other single-frequency light source to simultaneously detect or excite all WGMs in the optical microresonator array, thereby simplifying the operation of the sensing microresonator array.

[0041] Alternatively, in some embodiments, at least some optical fibers may have varying known cross-sectional characteristics (e.g., different radii, different material distributions), thus exhibiting different resonant frequencies during analysis of signals obtained due to the shifted WGM.

[0042] Fiber optics and optical waveguides

[0043] The set of optical fibers 103A in the optical microresonator array may be made of a material (e.g., glass, polymer, crystal, etc.) that is transparent to light propagating within the set of optical fibers at a certain frequency. The set of optical fibers 103A may comprise, for example, one or more single-mode fibers, one or more multimode fibers, one or more graded-index fibers, one or more abrupt-index fibers, one or more polarization-maintaining fibers, and / or any fiber suitable for supporting whispering-gallery modes at its circumference. In some embodiments, the set of optical fibers may comprise commercially available fibers, for example, those that share the same or significantly similar properties in terms of size, refractive index, and / or resonant wavelength. For example, the set of single-mode fibers may have a very uniform material index of 1.5 and a diameter of 125 μm across any vertical cross-section of the set of single-mode fibers.

[0044] In some embodiments, the set of optical fibers 103A may be selected and / or etched to have a small radius. The small radius of the set of optical fibers results in a larger free spectral range for the set of resonant frequencies. As a result, the spectral density of the resonant modes supported by the radius of the set of optical fibers 103A is reduced, which can improve the dynamic range of the sensing performance of the optical microresonator array 100A.

[0045] In some embodiments, the set of optical waveguides 102A may comprise a set of integrated photonic waveguides made of glass, silicon, silicon nitride, and / or any material transparent to light propagating at a certain frequency within the set of optical fibers. For example, the set of optical waveguides 102A may comprise a set of strip waveguides, slot waveguides, planar waveguides, strip-loaded slot waveguides, photonic crystal waveguides, and / or any integrated photonic waveguide suitable for supporting light propagation across the length of an optical microresonator array.

[0046] Alternatively or alternatively, the set of optical waveguides 102A may comprise a set of tapered optical fibers made of optical fibers. For example, at least a portion of the set of optical waveguides 102A may be made of a set of single-mode optical fibers, multimode optical fibers, graded-type optical fibers, abrupt-change optical fibers, polarization-maintaining optical fibers, etc. Generally, in some embodiments, the set of tapered optical fibers can be produced by gently stretching the optical fibers while heating them. In doing so, the optical fibers become thinner over a certain length. Alternatively or alternatively, in some embodiments, at least a portion of the set of tapered optical fibers can be produced by completely or partially etching (e.g., using wet etching) the fiber cladding.

[0047] In some embodiments, the set of optical fibers and / or the set of tapered optical fibers may be etched to reduce their size. For example, a chemical solution (e.g., hydrochloric acid) may be used to etch the set of optical fibers and / or the set of tapered optical fibers to reduce their length and / or radius. A predetermined portion of the set of optical fibers and / or the set of tapered optical fibers may be exposed to the chemical solution, thereby etching only the portions exposed to the chemical solution.

[0048] The system may further include one or more light sources. For example, the set of optical waveguides 102A may be coupled to one or more light sources such that light 101A from the set of light sources is input into the set of optical waveguides 102A and into optically coupled optical fibers 103A. The light then propagates along the azimuth of each fiber to excite the WGM of the resonator node, as further described herein. Additionally, light may be further coupled out from optical fiber 103A and returned to optical waveguide 102A.

[0049] One or more light sources may comprise broadband light sources, tunable laser sources, optical frequency comb (OFC) laser sources using digital modulation methods or Kerr four-wave mixing (FWM) methods, and / or any other light source suitable for the operating frequency band of the optical microresonator array 100A. In some embodiments, the group of one or more light sources may comprise a single-frequency light source configured to propagate light 101A having the same spectral characteristics into the group of optical waveguides 102A. In some embodiments, at least one light source may comprise a fiber laser source that directly emits input light 101A into the group of optical fibers, which may couple the input light 101A into a group of integrated photonic waveguides. In some embodiments, the group of light sources may comprise a group of chip-based laser sources that directly emit the group of input light 101A into the group of integrated photonic waveguides. The group of integrated photonic waveguides may then be configured to couple the group of input light into a group of tapered optical fibers. Furthermore, in some embodiments, one or more light sources may be coupled into a planar or planar waveguide, as described in further detail below.

[0050] Optical fibers and optical waveguides can be arranged in any of a variety of suitable ways. For example, such as... Figure 1A As shown, the optical microresonator array 100A may include a tapered optical fiber (used as an optical waveguide 102A) superimposed on the optical fiber 103A to form a plurality of resonator nodes 104A. Alternatively, as described in further detail below, at least a portion of the optical fiber 103A may be superimposed on the tapered optical fiber (waveguide 102A).

[0051] As another example, one or more optical fibers may be arranged on, for example, a silicon photonics platform, a silicon nitride platform, and / or such as... Figures 1B to 1D The platform shown in the image is located above the integrated photonic waveguide platform. Figure 1BThis is a schematic description of an exemplary integrated photonic waveguide array 100B. In some embodiments, the integrated photonic platform may include a substrate 107B (e.g., silicon, silica, silicon nitride, etc.), an embedded oxide layer 106B, and other integrated photonic components. The waveguide array 100B may be coupled to a group of one or more light sources. In some embodiments, the group of light sources may be fiber-coupled light sources or other light sources that emit light 101B into an optical fiber vertically aligned with an on-chip grating coupler 102B. The grating coupler 102B, combined with other integrated photonic components (e.g., a multimode interferometer 103B), may couple light into the waveguide array 100B having one or more optical waveguides 108B. For example, such as Figure 1B As shown, input light from a single light source can be coupled into multiple optical waveguides 108B via a partitioned or branched pattern. In some embodiments, at least a portion of the optical waveguide array 100B may be coated with an encapsulation layer 105B (e.g., spin-coated with a matching polymer), while other portions of the optical waveguide array 100B may remain uncoated with the encapsulation layer 105B (e.g., by selectively etching the encapsulation layer).

[0052] Figure 1C This is a schematic description of another exemplary optical microresonator array 100C, in which multiple resonator nodes 104C are positioned at a set of sensing locations. The optical microresonator array 100C may include an optical waveguide array 102C having multiple optical waveguides 108C arranged in an integrated planar optical platform (similar to the above description). Figure 1B The description includes an optical waveguide array 100B and a set of optical fibers 103C optically coupled to the optical waveguide array 102C at the set of sensing locations to establish a plurality of resonator nodes 104C. Each resonator node may have a predetermined position relative to other resonator nodes for determining the location of the acoustic echo detected by the resonator node. Similar to the above description... Figure 1B As described, the optical waveguide array 102C may comprise an integrated photonic waveguide fabricated on a substrate 105C. In some embodiments, the optical waveguide array may comprise a plurality of light sources coupled to an input waveguide 101C, each of which may be connected to a plurality of optical waveguides 108C (e.g., via a beam splitter or fiber coupler). Figure 1CThe embodiment shown herein includes a single optical input for three optical waveguides; however, it should be understood that other embodiments may include any suitable ratio of optical input to optical waveguide 108C (e.g., about 1:2, 1:3, 1:4, etc.). Each optical waveguide 108C in the optical waveguide array 102C may be perpendicular to a set of optical fibers 103C to generate multiple resonator nodes 104C. As further described herein, the multiple resonator nodes 104C may couple light into the set of optical fibers 103C to propagate a set of WGMs and generate a set of optical signals in the optical waveguide array 102C. The optical waveguide array may be connected to a set of photodetectors and a multichannel spectrometer to characterize the set of optical signals for ultrasonic sensing.

[0053] Figure 1D This is a schematic description of another optical microresonator array 100D, in which a set of resonator nodes 104D are positioned at a set of sensing locations. The optical microresonator array 100D may include an optical waveguide array 102D having multiple optical waveguides 108D arranged in an integrated planar optical platform (similar to the above description). Figure 1B The description includes an optical waveguide array 100B and a set of optical fibers 103D optically coupled to the optical waveguide array 102D at the set of sensing locations to establish a plurality of resonator nodes 104D. Each resonator node may have a predetermined position relative to other resonator nodes for determining the location of the acoustic echo detected by the resonator node. Figure 1D As shown, each optical waveguide 108D from the optical waveguide array 102D can be optically coupled to a corresponding optical input 101D (each optical input can be coupled to a corresponding light source, for example, or at least some optical inputs can obtain light from a common light source). In other words, the ratio of optical input to optical waveguide 108D can be 1:1. Each optical waveguide 108D in the optical waveguide array 102D can be perpendicular to a set of optical fibers 103D to generate multiple resonator nodes 104D. As further described herein, the multiple resonator nodes 104D can couple light into the set of optical fibers 103D to propagate a set of WGMs and generate a set of optical signals into the optical waveguide array 102D. The optical waveguide array can be connected to a set of photodetectors and a multichannel spectrometer to characterize the set of optical signals for ultrasonic sensing.

[0054] Resonator node

[0055] The system can consist of a set of resonator nodes at various sensing locations where the optical waveguide and fiber optics are coupled. For example, Figure 1A This is a schematic illustration of an optical microresonator array 100A, where resonator nodes 104A are located at sensing positions where optical fiber 103A and optical waveguide 102A are optically coupled. Each resonator node may have a predetermined position relative to other optical microresonators for determining the location of detected acoustic echoes.

[0056] In some embodiments, input light 101A may be coupled to the set of optical fibers 103A such that a set of whispering-gallery modes (WGMs) propagate around the inner circumference of the optical fibers 103A at a plurality of resonator nodes 104A. Each resonator node may have associated sensing coordinates. The plurality of resonator nodes 104A may receive a set of ultrasonic echoes spatially distributed at various intensities across the plurality of resonator nodes 104A of the optical microresonator array. In some embodiments, each resonator node may have a predetermined position relative to other resonator nodes for determining the location of the acoustic echo detected by the resonator node. In some other cases, each resonator node may have a characteristic geometry and / or material refractive index associated with the resonator node that distinguishes the optical response of the resonator node from that of other resonator nodes. Sensing using resonator nodes is described in further detail below.

[0057] Resonator node 104A can be arranged in various suitable arrays and in various suitable ways relative to the set of optical fibers and the set of optical waveguides. In some embodiments, the set of optical fibers 103A can be perpendicular to the optical waveguide 102A to allow light from the optical waveguide 102A to circulate around the cross-section of the optical fiber 130A. For example, the optical fibers can be arranged perpendicular to the optical waveguides using an alignment procedure. The alignment procedure may include propagating a first set of light with a first set of intensities to the set of optical waveguides 102A. The alignment procedure may further include detecting a second set of light with a second set of intensities. The alignment procedure may include adjusting a set of angles between the set of optical fibers 103A and the set of optical waveguides 102A (e.g., by using a high-precision positioning system) to maximize the second set of intensities. In one example, the adjustment of the set of angles is to achieve a perpendicular angle between each optical fiber and the optical waveguide. In some cases, the alignment procedure may create gaps between the optical fibers and the optical waveguides to achieve coupling conditions that generate the highest power coupled into the resonator node. In some other cases, the optical fibers may be in physical contact with the optical waveguides to improve the stability of the coupling conditions. The perpendicular angle between the set of optical fibers 103A and the set of optical waveguides 102A allows light to couple from the set of optical fibers 103A to the set of optical waveguides 102A, and vice versa. In some embodiments, the alignment procedure may include verifying the perpendicularity between the set of optical fibers 103A and the set of optical waveguides 102A by verifying the optical coupling between the optical fibers and the optical waveguides.

[0058] In some embodiments, resonator nodes may be arranged in a grid, such as a rectangular array, formed by optical fibers and waveguides arranged in the grid. For example, the set of waveguides may also be arranged parallel to each other and equidistant from each other, and the optical fibers may be arranged parallel to each other, equidistant from each other, and perpendicular to the set of waveguides. However, in some embodiments, the optical fibers may be irregularly spaced and / or the waveguides may be irregularly spaced.

[0059] Although in some embodiments, the optical microresonator array may include multiple optical waveguides and multiple optical fibers, for example Figure 1A As shown in the figure, it should be understood that multiple resonator nodes can also be formed by a single optical waveguide or a single optical fiber.

[0060] For example, such as Figure 3A As shown, in some embodiments, the optical microresonator array may comprise multiple resonator nodes formed by a single optical waveguide 302A optically coupled to multiple optical fibers 303A and 303A' at multiple sensing locations. In some cases, a set of light having multiple different wavelengths may propagate in a single optical waveguide 302A. In some other cases, a single wavelength of light may propagate in a single optical waveguide 302A. In some other cases, broadband light 301A may propagate in a single optical waveguide 302A. The single optical waveguide 302A may be perpendicular to and optically coupled to optical fibers 303A and 303A' at multiple individual sensing locations along the waveguide length, thereby forming first and second resonator nodes 304A and 304A'. It should be understood that, although Figure 3A Two resonator nodes are shown, but any suitable number of resonator nodes can be formed along a single optical waveguide by coupling any suitable number of optical fibers (e.g., three, four, five, or more, etc.) to the optical waveguide. Optical input 301A can be coupled into and propagate around optical fibers 303A and 303A', respectively, to excite the WGM at resonator nodes 304A and 304A', respectively. Optical signals embodying any shifts in the WGM and WGM can then be coupled into the optical fiber at the resonator node and provided as output light 305A.

[0061] As another example, such as Figure 3BAs shown, in some embodiments, the optical microresonator array may include multiple resonator nodes formed by multiple optical waveguides 302B and 302B' coupled to a single optical fiber 303B at multiple sensing locations. In some cases, a first input light 301B and / or a second input light 301B', each with a different wavelength, may propagate in each optical waveguide. In some other cases, the first single-wavelength light 301B may propagate in one optical waveguide (e.g., optical waveguide 302B), and the second single-wavelength light 301B' may propagate in another optical waveguide (e.g., optical waveguide 302B'). Optical waveguides 302B and 302B' may be perpendicular to and optically coupled to a single optical fiber 303B at multiple individual sensing locations along the fiber length, thereby forming first and second resonator nodes 304B and 304B'. In some embodiments, optical waveguides 302B and 302B' may be identical in radius and material uniformity distribution, and therefore exhibit the same WGM and resonant frequency at a set of resonator nodes 304B and 304B. It should be understood that, although Figure 3B Two resonator nodes are shown, but any suitable number of resonator nodes can be formed along a single optical fiber by coupling any suitable number of optical waveguides (e.g., three, four, five or more, etc.) to the optical fiber.

[0062] Optical inputs 301B and 301B' can be coupled into optical fiber 303B and propagate along it to excite WGM at resonator nodes 304B and 304B', respectively. Optical signals embodying any shifts in WGM and WGM can then be coupled into optical fiber at the resonator nodes and provided as output light 305B and 305B'.

[0063] Sensing at the resonator node

[0064] For simplicity, sensing at the resonator nodes in an optical microresonator array will be discussed below regarding... Figure 3C The single resonator node 304C shown is described herein. A resonator node 304C is formed at a sensing location when the optical waveguide 301C is aligned and positioned for optical coupling to a single optical fiber 303C. On an optical microresonator array, multiple resonator nodes may be located at multiple sensing locations or coordinates. For example, in some embodiments, the sensing location may be located at the intersection of the optical waveguide and the optical fiber.

[0065] Optical waveguide 302C may be located on top of or at the bottom of optical fiber 303C (or at any suitable tangent or laterally offset from the tangent separation gap). Optical waveguide 302C may be optically coupled to optical fiber 303C at any location along the length of a single optical fiber 303C. The longitudinal axis of optical waveguide 302C may be perpendicular to the longitudinal axis of optical fiber 303C. Optical fiber 303C may be characterized by predetermined geometric and material characteristics, such as fiber radius, fiber surface roughness, and / or fiber material refractive index, each of which may affect impedance, scattering loss, and / or absorption loss of the single optical fiber 303C affecting the set of signals provided by the resonator nodes.

[0066] Furthermore, resonator node 304C generally has a set of characteristic resonant frequencies determined by the geometric and material properties of its location at the sensing position. These geometric and material properties at the sensing position can be affected by a set of ultrasonic echoes received at the sensing position, thereby shifting the resonant frequencies and / or attenuating the resonant peaks or dips of said set of resonant frequencies of resonator node 304C. Considering the multiple resonator nodes across the entire optical microresonator array, the received ultrasonic echoes can affect the geometric and / or material properties of multiple resonator nodes with different intensities at different sensing coordinates. Therefore, ultrasonic echoes can shift said set of resonant frequencies and / or attenuate the resonant peaks / dips of said set of resonant frequencies of multiple resonator nodes by various amounts indicating the different intensities of said set of ultrasonic echoes.

[0067] During sensing, optical waveguide 302C can receive and propagate light 301C from a light source. The light can be, for example, single-wavelength light (e.g., a 532 nm laser), broadband light (e.g., an erbium-doped fiber amplifier), and / or multi-wavelength light (e.g., a frequency comb). The light can be coupled to fiber 304C at resonator node 304C to excite a set of waveguide-mode signals (WGMs) propagating azimuthally around the circumference of the fiber. The WGMs can generate a set of signals 305C in optical waveguide 302C. The set of signals can include a set of resonant characteristics as properties of a single resonator node 304C, a single optical waveguide 302C, and / or a single fiber 303C.

[0068] A single resonator node 304C can then receive a set of ultrasonic echoes that mechanically vibrate the optical waveguide 302C, optical fiber 303C, resonator node 304C, and / or the materials inside and / or outside these components. Therefore, the geometry and / or refractive index of the materials inside and / or outside the optical waveguide 302C, optical fiber 303C, resonator node 304C, and / or these components may undergo variations associated with changes in the WGM used for the resonator node. These variations may be small or large compared to the default values ​​for each geometry and / or material refractive index. Even small variations in each geometry and / or material refractive index can significantly affect the resonant characteristics and generate a detectable signal. In an illustrative example, the refractive index of a single optical fiber 303C changes by Δn = 0.01, which is two orders of magnitude smaller than the refractive index n = 1.5 for a single optical fiber 303C. However, this change in refractive index may be sufficient to shift the resonant characteristics by a frequency equivalent to half the full width at which the resonant characteristics reach their maximum value.

[0069] In other words, a set of one or more shifts in the resonant characteristic in response to the received ultrasonic echo can correspond to a shift in the propagation of a set of optical signals (e.g., related to the difference between a first set of WGMs and a second set of WGMs in response to the ultrasonic echo). The set of shifts in the resonant characteristic can be multiple shifts (i.e., consecutive shifts, or shifts at each optical frequency). The optical signals can be transmitted to a photodetector or a spectrometer for characterization. For example, suitable computing devices can be operatively coupled to a photodetector and / or a spectrometer to detect differences in the optical signals before and after the receipt of the ultrasonic echo. In some embodiments, reading out the sensed signals from different optical fibers coupled to the same optical waveguide can be achieved by implementing a timing mechanism that synchronizes physical perturbations at the different optical fibers with the optical readout time at the output of the optical waveguide.

[0070] Furthermore, in some embodiments, if different optical fibers have different cross-sectional properties (e.g., radius, material) and therefore different resonant frequencies, then light of different wavelengths can propagate along the same optical waveguide and be used to detect the WGM in the different optical fibers. The optical signals read at the output of the optical waveguide can be separated according to the transmission wavelength associated with the respective different optical fibers.

[0071] In one example, the optical microresonator array may comprise a set of resonator nodes having a resonant frequency of 193 THz and / or a resonant dip corresponding to 10% of the transmission rate at the resonant frequency. The optical microresonator array can receive an intensity of 0.03 W / cm² at a first sensing coordinate (x = 1, y = 1). 2 The ultrasonic echo and the intensity at the second sensing coordinate (x=3, y=4) are 0.1 W / cm. 2The ultrasonic echo, for example, where x can indicate the position of the optical fiber and y can indicate the position of the optical waveguide. The first resonator node located at the first sensing coordinate (x=1, y=1) can be attributed to an intensity of 0.03 W / cm. 2 The ultrasonic echo shifts the resonant frequency from 193 THz to 194 THz. The second resonator node located at the second sensing coordinate (x = 3, y = 4) can be attributed to an intensity of 0.1 W / cm². 2 The ultrasonic echo shifts the resonant frequency from 193 THz to 198 THz. As demonstrated in this example, the amount of frequency shift for each resonator node can be correlated with the amount of frequency shift in the intensity of the ultrasonic echo. By plotting the amount of resonant shift used for sensing coordinates, ultrasonic imaging can be performed based on the ultrasonic echo.

[0072] The resonator nodes described herein possess high sensitivity, at least in part, due to their high quality factor, as they advantageously allow light of the permitted frequency to remain within the closed loop of the optical microresonator for extended periods. The permitted frequency and quality factor of the optical microresonator described herein can be based, at least in part, on the geometric and material parameters of the set of optical fibers (e.g., extinction coefficient, refractive index, defects, homogeneity), the geometric parameters of the set of waveguides, the refractive indices of the set of optical fibers and the set of waveguides, the refractive index of the surrounding environment of the set of optical fibers and the set of waveguides, and so on.

[0073] Packaged optical microresonator array

[0074] The performance of optical microresonator arrays depends at least in part on the elasticity and elastic optical properties of the materials within the device. Optical microresonator arrays can be encapsulated (e.g., in polymer structures) to further enhance their capabilities, such as... Figure 2A and Figure 2B As shown in the image. Figure 2A This is a schematic description of an exemplary method for encapsulating the set of optical fibers 203A and / or the set of optical waveguides 204A in a structure (e.g., in a polymer structure) to produce an encapsulated optical microresonator array. The structure may include a backing region 202A (e.g., a backing polymer) and / or a matching region 205A (e.g., a matching polymer). In some embodiments, the backing region 202A and / or the matching region 205A may be layers deposited (e.g., spin-coated) on a substrate, as described in further detail below. Furthermore, the mechanical stability of the optical microresonator array can also be improved, at least in part, by encapsulating the optical microresonator array in a material structure such as a soft material having a low refractive index (at least lower than that of the set of optical waveguides 204A and the set of optical fibers 203A).

[0075] Methods for encapsulating an optical microresonator array may include cleaning the surface of a substrate 201A, such as silicon, silica, quartz, plastic, or any other material suitable for serving as an acousto-optic sensor device. In some cases, a substrate with a higher etch rate compared to other materials used in the optical microresonator array may be selected so that the substrate can be etched away after encapsulating the optical microresonator array. Suitable materials serving as the substrate may include damping materials to eliminate residual vibrations and minimize ultrasonic echoes within the sensor structure. Reference Figure 2A The substrate 201A can then be coated with one or more coating materials comprising the backing polymer 202A. The backing polymer 202A may be a damping material, such as a polymer material with a low refractive index, configured to obtain a wide whispering-gallery mode (WGM) frequency response around the circumference of the set of optical fibers 203A, while having high ultrasonic attenuation to prevent reverberation of a set of ultrasonic echoes that the optical microresonator array is designed to sense. In some embodiments, the acoustic impedance of the damping material of the backing polymer may, for example, be matched to the acoustic impedance of the matching polymer layer 205A used to encapsulate the optical microresonator array, as further described below.

[0076] like Figure 2A As shown, the set of optical waveguides 204A, such as tapered optical fibers, can be placed in a backing polymer 202A or a matching polymer 205A. As described above, the set of optical waveguides 204A may comprise a set of tapered optical fibers receiving a set of light from an optically coupled light source, a set of integrated photonic waveguides receiving a set of light from an on-chip light source, a set of integrated photonic waveguides coupled to the set of tapered optical fibers propagating the set of light from the optically coupled light source, or any other suitable medium for propagating a set of light from the light source to a set of resonator nodes optically coupled to the set of optical fibers 203A and the set of optical waveguides 204A. In some embodiments, the set of optical fibers 203A may be placed in the backing polymer 202A before curing the backing polymer 202A. Placing the set of optical fibers 203A on an uncured backing polymer allows the set of optical fibers to be embedded in the backing polymer 202A. After placing the set of optical waveguides 204A, the backing polymer can be cured, for example, by baking the backing polymer at a preset temperature.

[0077] The method of encapsulating an optical microresonator array may further include placing the set of optical waveguides 204A close to the set of optical fibers 203A to optically couple the set of optical fibers to the set of optical waveguides. For example, the set of optical fibers 203A and the set of optical waveguides 204A may be positioned (e.g., using a high-precision positioning system) such that the set of optical waveguides is perpendicular to the optical fiber set (e.g., as described above with respect to FIG. 1). Although the method of encapsulating an optical microresonator array is primarily described as placing the optical fibers before the optical waveguides, it should be understood that in some embodiments, the optical waveguides may be placed before the optical fibers.

[0078] Figure 2B Depicting optical microresonator arrays (e.g., about Figure 1C An exemplary fabrication process for the described optical microresonator array (100C) is presented. The optical microresonator array can be based on an integrated photonic platform and encapsulated (e.g., in a polymer structure) to further enhance the capabilities of the optical microresonator array, such as... Figure 2B As shown in the image. Figure 2B This is a schematic description of an exemplary method for encapsulating the set of optical fibers 203B and / or the set of integrated photonic waveguides 204B in a structure (e.g., in a polymer structure) to produce an array of encapsulated optical microresonators. The structure may include a backing region 202B (e.g., a backing polymer) and / or a matching region 205B (e.g., a matching polymer). In some embodiments, the backing region 202B and / or the matching region 205B may be layers deposited (e.g., spin-coated) on a substrate, as described in further detail below.

[0079] Methods for encapsulating optical microresonator arrays may include cleaning (e.g., using a piranha solution) the surface of a substrate 201B, such as silicon, silica, quartz, plastic, or any other material suitable for serving as an acousto-optic sensor device. In some cases, a substrate with a higher etch rate than other materials used in the optical microresonator array may be selected, allowing the substrate to be etched away to release the optical microresonator array. Suitable materials serving as substrates may include damping materials to eliminate residual vibrations and minimize ultrasonic echoes within the sensor structure. Reference Figure 2B The substrate 201B can then be coated with one or more coating materials comprising the backing polymer 202B. The backing polymer 202B may be a damping material, such as a polymer material with a low refractive index, configured to obtain a wide whispering-gallery mode (WGM) frequency response around the circumference of the set of optical fibers 203B, while having high ultrasonic attenuation to prevent reverberation of a set of ultrasonic echoes that the optical microresonator array is designed to sense. In some embodiments, the acoustic impedance of the damping material of the backing polymer may, for example, be matched to the acoustic impedance of the matching polymer layer 205B used to encapsulate the optical microresonator array, as further described below.

[0080] like Figure 2B As shown, the set of optical waveguides 204B, such as a set of integrated photonic waveguides, can be fabricated on top of substrate 201B. In some embodiments, the set of optical waveguides 204B can be fabricated from a computer-aided design (CAD) pattern using photolithography. The material of the set of optical waveguides 204B on the integrated photonic platform can include silicon, silicon oxide, silicon nitride, or any material suitable for reliably and efficiently guiding optical signals. The set of optical waveguides 204B on the integrated photonic platform can receive a set of light from an on-chip light source or an optically coupled light source. Furthermore, the set of optical waveguides 204B can be configured to couple to other sets of integrated photonic components (e.g., beam splitters, interferometers, multimode interferometers, etc.).

[0081] In one example, the set of light sources may be single-wavelength fiber-coupled sources that emit single-wavelength light into an optical fiber vertically aligned with an on-chip grating coupler. The grating coupler alters the wave vector of the single-wavelength light and guides it to an integrated photonic waveguide. The integrated photonic waveguide propagates the single-wavelength light to a multimode interferometer, which splits the single-wavelength light into multiple integrated photonic waveguides. The multiple integrated photonic waveguides couple the single-wavelength light into the set of optical fibers 203B to propagate a set of WGMs within their circumference and generate a set of optical signals in the multiple integrated photonic waveguides.

[0082] In some embodiments, the set of optical waveguides 204B may be deposited or coated with an encapsulation layer 206B, which may, for example, improve the mechanical stability of the optical microresonator array. Generally, in some embodiments, the encapsulation layer 206B may be the same material as the backing polymer 202B or the matching polymer 205B. The method of encapsulating the optical microresonator array may further include placing the set of optical fibers 203B close to the set of optical waveguides 204B to optically couple the set of optical fibers 203B to the set of optical waveguides 204B. For example, the set of optical fibers 203B and the set of optical waveguides 204B may be positioned (e.g., using a high-precision positioning system) such that the set of optical waveguides is aligned perpendicular to the optical fiber set (e.g., as described above with respect to FIG. 1). Although the method of encapsulating the optical microresonator array is primarily described as placing the optical waveguides before the optical fibers, it should be understood that in some embodiments, the optical fibers may be placed before the optical waveguides.

[0083] Example

[0084] Optical microresonator arrays, such as those described in this article, can be used in ultrasonic sensor devices, such as acousto-optic sensor devices. Figure 4This is a schematic description of using an acousto-optic sensor device 403 to sense ultrasonic echoes. The acousto-optic sensor device 403 includes an optical microresonator array comprising a plurality of resonator nodes 410. Although a set of optical waveguides and a set of optical fibers of the optical microresonator array are shown arranged linearly at predetermined distances from each other, it should be understood that in some embodiments, at least some of the optical waveguides and / or optical fibers may be arranged at different distances from each other. However, generally, the set of optical waveguides and the set of optical fibers may be arranged in a rectangular grid.

[0085] As described above, the set of optical waveguides propagating light from one or more light sources can be optically coupled to the set of optical fibers at resonator nodes at various sensing locations. Each optical fiber and each optical waveguide in the optical microresonator array can be characterized by a specific cross-sectional geometry, material homogeneity, a specific refractive index of the material used to fabricate the optical fiber or waveguide, and the refractive index of the encapsulation material, as described above regarding... Figure 2A and Figure 2B Further detailed description. The light source can be a single-wavelength light source, a broadband light source, a tunable laser source, an optical frequency comb (OFC) laser source using digital modulation methods or Kerr four-wave mixing (FWM) methods, or any other light source suitable for the operating frequency band of the acousto-optic sensor device 403. Light can be coupled to an array of optical microresonators to propagate a first set of whispering-gallery modes (WGMs) around the circumference of the set of optical fibers at a set of resonator nodes 410 where the set of optical fibers and the set of optical waveguides are optically coupled (e.g., intersecting). The propagation of the first set of WGMs causes the generation of a first set of optical signals corresponding to the first set of resonant frequencies of the WGMs. In some cases, the distance between the set of optical waveguides is greater than five times the wavelength of the light. In some other cases, the distance between the set of optical fibers is greater than three times the wavelength of the light.

[0086] In use, the acousto-optic sensor device 403 can be configured to receive a set of ultrasonic echoes 402 generated and / or reflected from an object 401. The set of ultrasonic echoes may have different propagation times (t1, t2, t3, etc.) for individual resonator nodes. That is, ultrasonic echoes from the same object will arrive at each sensor in the array at slightly different times. The known distance between each sensor and these measured slight delays allow for a better calculation of the object's location (e.g., better spatial resolution). The set of ultrasonic echoes can induce a set of variations in geometry, material homogeneity, the refractive index of the material used to fabricate the optical fiber or waveguide, and / or the refractive index of the encapsulation material. These variations can introduce changes in WGMs, such as a second set of WGMs, propagating around the walls of the set of optical fibers at the set of resonator nodes in the optical microresonator array. The propagation of the second set of WGMs prompts the generation of a second set of optical signals corresponding to a second set of resonant frequencies of the WGMs. The first and second sets of optical signals can be configured to propagate in the set of optical waveguides to a set of optical detectors and / or a set of spectrometers. An optical detector can be connected to a computing device to detect the difference between a first set of optical signals and a second set of optical signals. In some embodiments, the difference between the first set of optical signals and the second set of optical signals may enable the measurement of changes in one or more resonant frequencies of the set of resonator nodes. In some other embodiments, the difference between the first set of optical signals and the second set of optical signals may additionally or alternatively enable the measurement of changes in the resonant amplitude of the resonant frequencies of the set of resonator nodes.

[0087] In some embodiments, the acousto-optic sensor device 403 may be configured to receive continuous ultrasonic echoes 402 generated and / or reflected from an object 401. The continuous ultrasonic echoes may induce continuous variations in geometry, material homogeneity, and / or the refractive index of the material used to fabricate the optical fiber or waveguide and / or the refractive index of the encapsulation material. These continuous variations may introduce continuous waveguide-mass resonators (WGMs) propagating around the walls of the set of optical fibers at the set of resonator nodes of the optical microresonator array (e.g., a second set of WGMs, a third set of WGMs, a fourth set of WGMs, etc.). The propagation of the continuous WGMs leads to the generation of continuous optical signals corresponding to the continuous resonant frequencies of the WGMs. The continuous optical signals may be configured to propagate in the set of optical waveguides to a set of optical detectors and / or a set of spectrometers. The optical detectors may be connected to a computing device to detect continuous differences between each pair of optical signals from the continuous optical signals. These continuous differences enable the measurement of continuous variations in the resonant amplitude of the resonant frequencies of the set of resonator nodes.

[0088] Figure 5An exemplary measurement setup is depicted for processing a set of signals from an acousto-optic sensor device 505 that senses a set of ultrasonic echoes 504 (also referred to herein as “ultrasonic signals”). The measurement setup may include a single-wavelength light source, a broadband light source, or a tunable laser 501 that propagates a set of light in an optical fiber 502, and an optical fiber polarization controller 503 that can be configured to control the polarization of the light. The measurement setup may further include an acousto-optic sensor device 505, which can be configured to generate a first set of optical signals (as described above regarding the propagation of a first set of whispering-gallery modes (WGMs) in a set of resonator nodes included in the acousto-optic device 505). Figure 1A (As described). An acousto-optic sensor device 505 may be configured to receive a set of ultrasonic signals 504 and generate a second set of optical signals based on the propagation of a second set of WGMs in said set of resonator nodes. The acousto-optic sensor device 505 may be further configured to transmit the first set of optical signals and / or the second set of optical signals to an optical fiber 502. The measurement setup may further include a photodetector (also referred to herein as an "optical detector") 506, which receives the first set of optical signals and / or the second set of optical signals and converts them into a first set of electrical signals and / or the second set of electrical signals. The photodetector 506 may be further configured to transmit the first set of electrical signals and / or the second set of electrical signals to an oscilloscope 507, which is operatively connected to a computer device 510 to process and analyze the first set of signals and / or the second set of signals. The oscilloscope 507 may be further configured to transmit a set of analyzed signals to a function generator 508. The function generator may be configured to generate a set of generated signals and transmit them to a broadband light source or a tunable laser 501 to control the propagation of light in the optical fiber 502.

[0089] In another exemplary measurement setup, Figure 5 The function generator 508 can be replaced by a locking system such as a Pound-Drever-Hall (PDH) locking system to set the wavelength of the light source at the resonant slope of the WGM. The photodetector 506 will receive the oscillating optical signal in response to a set of ultrasonic echoes.

[0090] Figure 6An exemplary measurement setup is depicted for processing a set of signals from an acousto-optic sensor device 604 that senses a set of ultrasonic echoes. The measurement setup may include a laser 601, such as an optical frequency comb (OFC) laser source generated using a digital modulation method or a Kerr four-wave mixing (FWM) method, or any other laser suitable for the operating frequency band of the acousto-optic sensor device 604, to generate a laser. The measurement setup may further include a beam splitter 602, such as a 50:50 beam splitter, an 80:20 beam splitter, or any other beam splitter suitable for the measurement setup. The beam splitter may be configured to split the laser into a first laser and a second laser. The measurement setup may be configured to direct the first laser to an electro-optic modulator 603 to generate and transmit the modulated laser. The measurement setup may be further configured to direct the modulated laser to the acousto-optic sensor device 604 to generate a first set of signals corresponding to a first set of whispering gallery modes (WGMs). The acousto-optic sensor device 604 may be configured to receive a set of ultrasonic signals and generate a second set of signals corresponding to a second set of WGMs. The measurement setup can be further configured to direct a first set of signals, a second set of signals, and / or a second laser to a coherent receiver 605 to mix the second laser with the first set of signals and / or the second set of signals to generate an electronic frequency signal. The measurement setup can be configured to transmit the electronic frequency signal to a Fast Fourier Transform (FFT) module 606, operatively connected to a computing device to process and analyze the difference between the first set of signals and the second set of signals. In one example, an OFC laser can generate a set of comb beams, and each comb beam can generate a data point to detect the difference between the first set of signals and the second set of signals. In this example, a set of comb beams can generate a set of data points corresponding to the set of comb beams. In some embodiments, using an OFC laser source can advantageously reduce the sensing time from milliseconds to microseconds.

[0091] While optical microresonator arrays have been used for ultrasonic detection in the examples above, in some embodiments, they can be used for nanoparticle detection, biomolecule detection, and so on. In some cases, the environment surrounding the resonator nodes at the intersection of the set of optical fibers and the set of optical waveguides can be altered by exposing the set of resonator nodes to nanoparticles and / or biomolecules. This change in environment can cause a change in the whispering-gallery modes (WGMs) propagating at the set of resonator nodes and generate a second WGM. The change between a first set of optical signals associated with the first WGM and a second set of optical signals associated with the second WGM can be detected by a photodetector and / or a spectrometer.

[0092] In some embodiments, an optical microresonator array as described herein may be included in an ultrasonic probe (also referred to herein as an “ultrasonic system”). The ultrasonic probe may include at least one optical waveguide for propagating light. The ultrasonic probe may further include a plurality of piezoelectric elements to generate a set of ultrasonic signals. The ultrasonic probe may further include a plurality of piezoelectric elements to receive a set of ultrasonic echoes corresponding to the set of ultrasonic signals. The ultrasonic probe may further include a set of resonator nodes in a polymer structure. Each resonator node has a pre-assigned sensing position at the intersection of the optical waveguide and the optical fiber. Each resonator node is configured to receive a plurality of ultrasonic echoes and propagate a set of whispering-gallery modes (WGMs). The set of optical fibers is coupled to the set of optical waveguides at the set of resonator nodes such that the set of optical fibers is configured to transmit a first set of signals corresponding to a first set of WGMs to the set of optical waveguides.

[0093] For example, Figure 7 This is a schematic description of an ultrasonic probe utilizing an optical microresonator array as described in this article. Figure 8 yes Figure 7 The image depicts a cross-sectional view of the probe. The ultrasonic probe may include an optical microresonator array 801, a matching layer 802, a piezoelectric crystal array 803, an electrical connection array 804, a set of optical fibers 805, a backing material 806, an acoustic insulator 807, and a cable 808 connected to the ultrasonic data acquisition system. The ultrasonic probe may be coupled to a control system and a display to perform operating procedures as further described in detail herein. The backing material may include damping material bonded to the back of the probe package to eliminate residual vibrations in the operating environment, improve portability, and minimize echoes generated within the sensor structure.

[0094] An ultrasonic probe may be configured to propagate light from a light source to the set of optical microresonator arrays 801 to generate a first set of optical signals corresponding to a first set of WGMs propagating in each optical fiber at a resonator node of the optical microresonator array 801. A piezoelectric crystal array 803 may be configured to receive electrical signals from a control system via a cable 808 and an electrical connection array 804 to generate a set of ultrasonic signals toward the object, such that a set of reflected ultrasonic echoes is generated in the direction toward the ultrasonic probe. The ultrasonic probe may be further configured to generate a second set of optical signals corresponding to a second set of WGMs in the optical microresonator array 801 after receiving the set of ultrasonic echoes. The ultrasonic probe may optionally be configured to receive the set of ultrasonic echoes to generate a set of electrical signals. The ultrasonic probe may be further configured to transmit the first set of signals and / or the second set of signals via the set of optical fibers 805, and / or optionally transmit a set of electrical signals via the electrical connection array 804 to a cable 808 connected to an ultrasonic data acquisition, control system, or display.

[0095] In some embodiments, the ultrasonic probe can be configured to repeat the operating procedure while performing a cross-field scan using a phased array of piezoelectric crystal arrays. Doing so will generate a line-by-line image using the piezoelectric crystal array and a low-resolution image in the lateral direction for each resonator node. A high-resolution optical microresonator array sensor image can then be generated using a known synthetic aperture (SA) algorithm.

[0096] Additionally, in some embodiments, one or more of the piezoelectric elements may be configured to receive ultrasonic echoes corresponding to the set of transmitted ultrasonic signals, and to generate sensor signals based on these received ultrasonic echoes. For example, the sensor signals generated by the piezoelectric elements may supplement or combine with the signals transmitted by the resonator nodes in any suitable manner (e.g., to provide a multimodal sensor image).

[0097] Alternatively, in some embodiments, the ultrasound probe may be configured to use different modes of excitation, such as using piezoelectric crystal elements or a group of piezoelectric crystals to transmit ultrasound signals, while using all the piezoelectric crystal elements in the piezoelectric crystal array to receive the set of ultrasound echoes, also known as the compressed sensing (CS) method. A general approach to the CS method is to form a linear model (also known as a forward model) representing the process of acquiring signals from an image and solve the linear equations to obtain the image.

[0098] For purposes of explanation, the foregoing description uses specific terminology to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the specific details are not required to practice the invention. Therefore, the foregoing description of specific embodiments of the invention is presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously, many modifications and variations are possible in light of the foregoing teachings. The embodiments were chosen and described in order to explain the principles of the invention and its practical application, thus enabling others skilled in the art to utilize the invention and various embodiments with various modifications suitable for the particular use contemplated. It is intended that the appended claims and their equivalents define the scope of the invention.

Claims

1. An apparatus comprising: One or more optical fibers; One or more optical waveguides; as well as Multiple resonator nodes are arranged in a sensing position array. Each resonator node includes optical coupling between an optical waveguide and an optical fiber. The one or more optical fibers have a set of resonant frequencies at a corresponding sensing position and are configured to transmit one or more optical inputs to one or more light sources in the one or more optical waveguides. The one or more optical inputs are coupled to the one or more optical fibers and excite a set of whispering-gallery modes at the multiple resonator nodes to propagate along a corresponding circumference of the one or more optical fibers. Each resonator node is configured to transmit a set of signals corresponding to at least one shift of a set of resonant frequencies induced by ultrasonic echoes in the optical fiber at the corresponding sensing location.

2. The apparatus of claim 1, wherein the one or more optical fibers comprise a plurality of optical fibers having the same cross-sectional geometry and material.

3. The apparatus of claim 1, wherein the one or more optical fibers are configured to: Receive multiple ultrasonic echoes; and In response to the plurality of ultrasonic echoes, at least one of the set of resonant frequencies is shifted. The one or more optical waveguides are configured to propagate a set of signals corresponding to a shift of at least one of the set of resonant frequencies to an optical detector.

4. The apparatus of claim 1, wherein the one or more optical waveguides comprise tapered optical fibers or integrated photonic waveguides.

5. The apparatus of claim 1, wherein the one or more optical fibers are contained in a polymer structure.

6. The apparatus of claim 1, wherein the one or more optical fibers and the one or more optical waveguides are contained in a polymer structure.

7. The apparatus of claim 1, wherein the one or more optical fibers are perpendicular to the one or more optical waveguides.

8. The apparatus of claim 1, wherein the optical waveguide and the optical fiber are in physical contact at one or more of the plurality of resonator nodes.

9. The apparatus of claim 1, wherein at one or more of the plurality of resonator nodes, the optical waveguide and the optical fiber are offset by a separation gap.

10. The apparatus of claim 9, wherein the one or more optical waveguides comprise a plurality of optical fibers arranged in parallel, and wherein the plurality of optical fibers arranged in parallel are spaced apart by a distance at least 5 times the wavelength of the light.

11. The apparatus of claim 9, wherein the one or more optical fibers comprise a plurality of optical fibers arranged in parallel, and wherein the plurality of optical fibers arranged in parallel are spaced apart by a distance less than three times the wavelength of the light.

12. An ultrasonic sensing method, comprising: One or more optical fibers and one or more optical waveguides are provided to be arranged to form a plurality of resonator nodes, each resonator node including optical coupling between the optical waveguide and the optical fiber; A first set of whispering-gallery modes is excited via one or more optical inputs emitted from one or more light sources into the one or more optical waveguides, the one or more optical inputs being coupled to the one or more optical fibers, and the one or more optical inputs propagating along corresponding circumferences of the one or more optical fibers. A first set of signals corresponding to the first set of whispering-gallery modes propagating circumferentially along the one or more optical fibers are received at one or more optical waveguides via the plurality of resonator nodes. A second set of signals corresponding to a second set of whispering-gallery modes propagating circumferentially along the one or more optical fibers are received at the one or more optical waveguides via the plurality of resonator nodes; the second set of whispering-gallery modes propagating in response to the reception of a plurality of ultrasonic echoes by the one or more optical fibers; and Detect a set of differences between the first set of signals and the second set of signals.

13. The method of claim 12, wherein the one or more optical fibers comprise a plurality of optical fibers having the same or substantially similar cross-sectional geometry and material.

14. The method of claim 12, further comprising: The magnitude of each ultrasonic echo at each resonator node is calculated at least in part based on the difference between the first set of signals and the second set of signals. as well as The magnitude of each ultrasonic echo is associated with the sensing position of each resonator node.

15. The method of claim 12, wherein the one or more optical waveguides are configured to propagate at least one of the first set of signals and the second set of signals to an optical detector.

16. The method of claim 12, further comprising: Transmit multiple ultrasound signals to the target; as well as The plurality of ultrasonic echoes corresponding to the plurality of ultrasonic signals are received from the target at one or more optical fibers, the one or more optical fibers being configured to perform synthetic aperture operation or compressed sensing operation.

17. The method of claim 12, wherein the one or more optical waveguides comprise one or more tapered optical fibers or one or more integrated photonic waveguides.

18. The method of claim 12, wherein the one or more optical fibers are in a polymer structure.

19. The method of claim 18, wherein the one or more optical fibers and the one or more optical waveguides are contained in a polymer structure.

20. The method of claim 12, wherein each optical fiber is perpendicular to each optical waveguide.

21. The method of claim 12, wherein at one or more of the plurality of resonator nodes, the optical waveguide and the optical fiber are in physical contact.

22. The method of claim 12, wherein at one or more of the plurality of resonator nodes, the optical waveguide and optical fiber are offset by a separation gap.

23. The method of claim 12, wherein the one or more optical waveguides are aligned with the one or more optical fibers to excite the first set of whispering-gallery modes or the second set of whispering-gallery modes in the one or more optical fibers.

24. An apparatus comprising: One or more optical fibers, each configured to propagate a set of whispering-gallery modes along the circumference of the respective fiber, and One or more optical waveguides are optically coupled to one or more optical fibers at multiple resonator nodes. One or more optical inputs are emitted into one or more light sources within the one or more optical waveguides. These optical inputs are coupled to the one or more optical fibers and excite a set of whispering-gallery modes at the multiple resonator nodes. The one or more optical fibers transmit a set of signals corresponding to the set of whispering-gallery modes to the one or more optical waveguides. The one or more optical waveguides are configured to propagate the set of signals to at least one optical detector.

25. The apparatus of claim 24, wherein the one or more optical fibers are configured to: Receives multiple ultrasonic echoes; A second set of whispering galvanic modes propagates in response to the plurality of ultrasonic echoes; and The second set of signals corresponding to the second set of whispering galvanic modes is transmitted to the one or more optical waveguides. The one or more optical waveguides are configured to propagate the second set of signals to the at least one optical detector.

26. The apparatus of claim 25, wherein the set of whispering modes is a first set of whispering modes, and wherein one or more optical fibers are configured to transmit a set of signals corresponding to the difference between the first set of whispering modes and the second set of whispering modes to the one or more optical waveguides through the plurality of resonator nodes.

27. The apparatus of claim 26, wherein the difference between the first set of whispering wall modes and the second set of whispering wall modes is at least one of the following: a shift in at least one of the resonant frequencies of the optical fibers and a decrease in the resonance of the one or more optical fibers.

28. The apparatus of claim 24, wherein the one or more optical fibers comprise a plurality of optical fibers having the same cross-sectional geometry and material.

29. The apparatus of claim 24, wherein the one or more optical waveguides comprise one or more tapered optical fibers or one or more integrated photonic waveguides.

30. The apparatus of claim 24, wherein the one or more optical fibers are contained in a polymer structure.

31. The apparatus of claim 30, wherein the one or more optical fibers and the one or more optical waveguides are contained in a polymer structure.

32. The apparatus of claim 30, wherein the one or more optical fibers are perpendicular to the one or more optical waveguides.

33. The apparatus of claim 30, wherein each of the one or more optical waveguides is coupled to a light source such that the one or more optical waveguides propagate light from the light source.

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