Optical fiber sensor system for ultrasound sensing and imaging

Abstract

The present disclosure relates to optical fiber sensor systems for ultrasonic sensing and imaging. Provided herein are optical fiber-based acoustic sensors. The optical fiber-based acoustic sensors described herein include an acoustically responsive optical structure configured to detect and receive acoustic signals, including ultrasonic signals, and provide an associated optical signal to a system for processing and interpretation, thereby implementing tracking, localization, and imaging capabilities. The optical fiber-based sensors provided herein can be disposed at an end of an optical fiber or along an optical fiber length. The optical fiber-based sensors can be included within various devices, including, for example, medical devices.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 510,079, titled “FIBER-OPTIC SENSOR SYSTEM FOR ULTRASOUND SENSING AND IMAGING,” and filed on June 23, 2023, which is incorporated by reference herein. This application is further related to U.S. Provisional Application No. 63 / 522,793, titled “OPTICAL FIBER WITH AN ACOUSTICALLY SENSITIVE FIBER BRAGG GRATING AND ULTRASOUND SENSOR INCLUDING THE SAME,” and filed on June 23, 2023, which is incorporated by reference herein. This application is further related to U.S. Provisional Application No. 63 / 522,994, titled “TRANSPONDER TRACKING AND ULTRASOUND IMAGE ENHANCEMENT,” and filed on June 23, 2023, which is incorporated by reference herein. This application is further related to U.S. Patent Application titled “Transponder Tracking and Ultrasound Image Enhancement,” having attorney docket number 109835-1394978, and filed concurrently on October 23, 2023, which is incorporated by reference herein. This application is further incorporated by reference U.S. Provisional Patent Application titled “Miniature Mixed Array Imaging Probe,” filed on October 23, 2023, filed on October 23, 2023, and having attorney docket number 109835-1386207, which is incorporated by reference herein. TECHNICAL FIELD

[0003] The present invention relates generally to the field of ultrasound sensing and imaging. BACKGROUND

[0004] Acoustic imaging is used in various industries, including medical imaging. Acoustic imaging technology can be used to visualize and provide internal imaging of a patient's body. Further, acoustic imaging technology can be used to visualize and track objects (e.g., needles, catheters, guide wires, endoscopes, etc.) for medical applications such as diagnostic or therapeutic clinical procedures, including but not limited to biopsy, fluid aspiration, delivery of therapeutic agents such as drugs, nerve blocks / anesthetics, or biologies, catheterization, needle guidance, needle placement, deep vein cannulation, injection, IV, PIC line placement, device implantation, minimally invasive surgery, etc. Using acoustic imaging for medical applications provides several advantages. For example, acoustic imaging such as ultrasound imaging is a non-invasive form of imaging. Additionally, ultrasound imaging uses ultrasound signals that are known to have significant penetration depth.

[0005] In non-medical applications, ultrasound is used for industrial applications such as defect detection, non-destructive testing, structural testing, and microparticle sorting, geological applications including mining and drilling operations, and underwater marine applications.

[0006] Some existing imaging technology uses acoustic energy generation (AEG) materials for transducers to visualize and track medical objects and generate images during diagnostic or therapeutic medical procedures. Commonly used AEG materials include piezoelectric materials such as lead zirconate titanate (PZT), ceramics, piezoelectric single crystals (e.g., PIN-PT, PIN-PMN-PT), and polyvinylidene fluoride (PVDF), among many others known to those skilled in the art. AEG transducers have limitations. The echogenicity of the objects being tracked and / or the anatomy being visualized affects the image quality of the objects being tracked and the tissue being imaged. In certain medical procedures, a small form factor is required, and small AEG transducers typically have low to minimal signal output. Thus, using AEG transducers for medical applications requiring a small form factor can be challenging due to size constraints (e.g., physical size).

[0007] Accordingly, there is a need for new and improved compact technology with high sensitivity to visualize and track objects and provide anatomical imaging, particularly in medical applications. SUMMARY

[0008] Systems, devices, and methods for ultrasound sensing and imaging are presented herein. In particular, the systems, devices, and methods described herein can include fiber optic microsensor devices and systems and methods of use.

[0009] In an embodiment, a device is provided that includes a sensor fiber. The sensor fiber can include an optical waveguide including a core and cladding structure; an optical sensor structure coupled to a first end of the optical waveguide and including at least one of an optical resonator, an optical interferometer, and a polarization sensitive structure, the optical sensor structure configured to: detect an acoustic signal, and provide an optical signal corresponding to the acoustic signal to the optical waveguide. The sensor fiber can further include an encapsulation structure configured with a first portion surrounding the optical waveguide and a second portion at least partially surrounding the optical sensor structure.

[0010] In some aspects, the apparatus described herein relates to a device including: a sensor fiber including: an optical waveguide including a core and cladding structure; an optical sensor structure coupled to a first end of the optical waveguide and including at least one of an optical resonator, an optical interferometer, a facet end microstructure, and a polarization sensitive structure, the optical sensor structure configured to: detect an acoustic signal, and provide an optical signal corresponding to the acoustic signal to the optical waveguide. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, which are incorporated herein to form a part of the specification, illustrate embodiments of systems, methods, and apparatuses for ultrasound sensing and imaging. Together with the specification, the drawings further serve to explain the principles of the methods, systems, and apparatuses described herein and to enable a person skilled in the relevant art to make and use the methods, systems, and apparatuses described herein. The drawings are provided to illustrate various features of the embodiments described herein and are not necessarily drawn to scale. In the drawings, like reference numerals indicate like or functionally similar elements.

[0012] Figure 1 An optical sensor system for use with a fiber optic optical sensor is shown in accordance with an embodiment of the present application.

[0013] Figure 2 An optical sensor system for use with a fiber optic sensor is shown in accordance with an embodiment of the present application.

[0014] Figure 3A A sensor fiber including a fiber optic sensor and an associated fiber optic is shown.

[0015] Figure 3B A sensor fiber including an optical waveguide and an optical resonator structure having a Fabry-Perot resonator as an optical sensor is shown.

[0016] Figures 4A-4E Several variations of an optical resonator structure in accordance with an embodiment of the present application are shown.

[0017] Figure 5A and 5B Examples of optical sensor systems and optical fiber sensors according to embodiments of the application are shown.

[0018] Figure 5C and 5D Examples of optical sensor systems and optical fiber sensors according to embodiments of the application are shown.

[0019] Figure 5E and 5F Examples of microfacets structures according to embodiments of the application are shown.

[0020] Figures 6A-6E Examples of optical sensor systems and optical fiber sensors according to embodiments of the application are shown.

[0021] Figure 6F and 6G Examples of optical sensor systems and optical fiber sensors according to embodiments of the application are shown.

[0022] Figure 6H and 6I Examples of optical sensor systems and optical fiber sensors according to embodiments of the application are shown.

[0023] Figures 7A-7D Examples of manufacturing techniques that can be used to shape or machine the end of an optical waveguide are provided.

[0024] Figures 8A-8D Examples of manufacturing techniques that can be used to manufacture optical resonator structures at the end of an optical waveguide are provided.

[0025] Figures 9A-9B Methods of applying thermal tuning to a sensor fiber are shown.

[0026] Figure 10 Embodiments of sensor fibers containing multi-core optical waveguides are shown.

[0027] Figure 11A and Figure 11B Comparisons between sensor fibers arranged with forward optical sensors and lateral optical sensors are shown.

[0028] Figure 12 Embodiments of sensor fibers providing rear acoustic detection capability according to embodiments of the application are shown.

[0029] Figure 13 Embodiments of sensor fibers providing improved rear acoustic detection capability according to embodiments of the application are shown.

[0030] Figure 14Directional range of optical resonant structures according to embodiments of the application is shown.

[0031] Figure 15 Optical resonator structures comprising fiber Bragg gratings according to embodiments of the application are shown.

[0032] Figure 16 Methods of operating fiber-based optical sensors according to embodiments of the application are shown.

[0033] Figures 17A-17B Needles configured with sensor optical fibers according to embodiments herein are shown.

[0034] Figures 18A-18D Needles configured with sensor optical fibers according to embodiments herein are shown.

[0035] Figure 19 Acoustic signals incident on sensor optical fibers from lateral directions are shown.

[0036] Figures 20A-20B Close-up view of a needle with integrated sensor optical fiber according to embodiments of the application is provided.

[0037] Figures 20C-20D Needles with sensor optical fibers incorporated therein according to embodiments of the application are shown.

[0038] Figure 21 Medical devices distal ends incorporating catheter-delivered needles according to embodiments of the application are shown.

[0039] Figure 22 Use of fiber-based optical sensors in needle guidance or positioning is shown.

[0040] Figures 23A-23B Catheter-delivered needles incorporating fiber-based optical sensors are shown. DETAILED DESCRIPTION

[0041] Non-limiting examples of various aspects and variations of the present disclosure are described herein and illustrated in the accompanying drawings. The following detailed description is merely illustrative in nature and is not intended to limit the disclosure or the application and uses of the disclosure. Although the description of the present disclosure is in the context of fiber optic microsensor systems, methods, and devices for ultrasound imaging and sensing, the present disclosure should not be considered limited to this. For example, although methods can be discussed herein with respect to various medical procedures, embodiments of the present disclosure can be suitable for other medical procedures, as well as other procedures or methods in other industries that can benefit from the sensing and imaging techniques described herein. In addition, various systems and devices incorporating fiber optic microsensors are described. It should be understood that fiber optic microsensors, as described herein, can be integrated into and / or used with various systems and devices not described herein. Modifications can be made to the embodiments described herein without departing from the spirit and scope of the disclosure. Accordingly, the following detailed description is not intended to be limiting. Moreover, it is not intended that the disclosure be limited by any expressly or implied theory of operation described in prior art, background, summary or the following detailed description.

[0042] Structures are described herein in terms of their geometric properties. As discussed herein, all structures so described can differ from the described shape according to tolerances of known manufacturing techniques. Unless otherwise specified, features described with the term “substantially” should be understood to be within 5% of precision. For example, features described as “substantially parallel” can deviate from true parallel by 5%.

[0043] Systems, devices, and methods for ultrasound sensing and imaging by using fiber optic microsensors or fiber optic sensor devices are disclosed. In particular, the techniques described herein can track, visualize, and monitor (e.g., sense) objects during medical procedures, as well as generate ultrasound images. The fiber optic microsensor devices described herein incorporate optical devices disposed at the end of a fiber or at a specified location along its length and configured for detecting acoustic signals, including ultrasound signals. As described herein, a sensor fiber includes an optical waveguide (e.g., optical fiber) having a fiber optic microsensor device coupled at its end. As used herein, the term optical waveguide can refer to an optical fiber, a core, a photonic integrated waveguide, a planar waveguide, etc., based on a material system such as fused glass, polymer, semiconductor / dielectric wafer, nanoimprinted / 3D printed polymer on different substrates, or any other optical signal channel.

[0044] The technology described herein is compact in size and has high sensitivity, making it suitable for a variety of industrial applications as well as therapeutic and diagnostic medical applications. In non-medical applications, ultrasound is used for industrial applications such as defect detection, non-destructive testing, structural testing, and microparticle sorting, geological applications including mining and drilling operations, and underwater marine applications. Such applications are consistent with the embodiments described herein. Therapeutic and diagnostic medical applications include ultrasound imaging as well as sensing (tracking, visualization, guidance, and monitoring) of objects (e.g., needles, catheters, guide wires, etc.) during needle access, biopsy, aspiration, drug, biologic, anesthetic or other therapeutic agent delivery, catheter insertion, minimally invasive surgery, ablation, cauterization, object placement or movement, tissue, cutting and / or slicing, and other medical procedures. Procedures and applications in the following disciplines are examples of diagnostic and therapeutic procedures that use ultrasound extensively and require precise guidance and imaging: anesthesiology, cardiology, critical care, dermatology, emergency medicine, endocrinology, gastroenterology, gynecology, hepatology, infectious disease, interventional radiology, musculoskeletal medicine, nephrology, neurology, oncology, orthopedics, pain management, pediatrics, plastic and reconstructive surgery, urology, and vascular access.

[0045] Object visualization, tracking, guidance, and position determination in medical applications can be an important aspect of performing medical procedures in a safe and reliable manner. Objects used for tracking, visualization, and position determination can include any type of medical device that travels or is positioned within a subject. For example, a physician visualizes and tracks a needle tip while performing a biopsy to ensure safety. In this case, precise needle tip visualization or tracking can help prevent or reduce unintended blood vessel, nerve, tissue, or internal organ damage. Similarly, visualization, tracking, or positioning of a needle, endoscope, cannula, laparoscopic tool, or other medical device tool can be helpful when performing a medical procedure such as, but not limited to, fluid aspiration; injection of joints, tendons, and nerves with drugs or biologies; biopsy of fluid or soft tissue masses; aspiration and lavage of calcifications; removal of tissue, organs, or foreign bodies, placement of stents, filters, valves, permanent, temporary, or biodegradable implants, shunts, or drains, anesthetic injection, insertion of vascular access devices for infusion therapy, ablation procedures, performing Seldinger technique or catheterization for safe access to blood vessels and / or other organs. Visualization and tracking are advantageous in laparoscopic surgery, minimally invasive surgery, and open surgical procedures, especially when visualization of an area is difficult due to restricted access, intervening tissue or organs, blood, or other fluids.

[0046] Some existing technologies use ultrasound imaging for guidance during medical procedures to visualize the anatomy of interest, as well as to visualize, locate, and track inserted medical devices, particularly the distal and / or working portion of the device. However, there are several drawbacks associated with traditional ultrasound imaging technology for medical applications. Traditional technology uses an imaging probe that emits ultrasound waves. Since needles and other inserted medical devices have smooth surfaces, the incident ultrasound waves that reflect off the surface can be directed away from the receiving direction. This can make the reflected waves too weak to be easily detected, making it difficult to determine the location of the device during a procedure. In some technologies, the medical device can have a roughened surface, such as a dimpled, etched, or coated surface, to increase visibility in ultrasound by increasing the echogenicity of the medical device. However, even with these efforts, there are still limitations. Ultrasound guidance tools can also be limited by their dependence on a specific angle of incidence, which limits their ability to provide accurate visualization, particularly for deeply placed devices. Because of this limitation, ultrasound guidance tools can be placed at surface locations, which limits their utility, adoption, and cost-effectiveness as a deployable solution.

[0047] At least two key acoustic performance limitations exist in existing AEG transducers (such as, but not limited to, lead zirconate titanate (PZT), ceramic, piezoelectric single crystals (such as PIN-PT, PIN-PMN-PT), and polyvinylidene fluoride (PVDF)) compared to the proposed optical sensing technology. First, achieving very high sensitivity requires transducers fabricated from specific AEG materials or specific acoustic designs, but such transducers can only provide a relatively narrow acoustic response bandwidth. Second, as the electrical element size is reduced relative to its resonant frequency, the acoustic response of AEG transducers can be limited due to electrical impedance mismatch. Thus, for applications requiring small form factors (e.g., intravascular or intracardiac ultrasound, endoscopy, needle tracking, lung biopsy, sensing and monitoring, etc.), the signal-to-noise ratio (SNR) and bandwidth of small AEG transducers are reduced. And in certain applications, a highly directional response can also be presented. Additionally, some AEG transducers and systems can be affected by electromagnetic interference, such as that caused by ablation tools, cauterization tools, or any other procedure or technology that applies electrical energy to tissue. Furthermore, the use of electromechanical transducers at the distal end would entail electrically conductive wires and associated components that require additional design and safety requirements and challenges.

[0048] In contrast, the optical fiber sensors according to the present disclosure are capable of providing an ultrasonic receiver with high sensitivity, wide bandwidth, and wide acceptance angle, and without the need for electrical components required for electromechanical transducers. With these characteristics, the optical fiber sensors will be able to sense harmonic or scattered signals that are not possible with the prior art. Moreover, the optical fiber sensors consistent with the present disclosure can be compact, low cost, and can contribute to scalable sensor systems. Embodiments of the present invention include optical fiber sensors configured to detect acoustic signals. Such optical fiber sensors can be disposed at the end of an optical fiber, in the vicinity of the end of the optical fiber, or at a diagnostic or treatment related location on a medical device to create a sensor fiber. The optical fiber sensors include resonant structures including, but not limited to, Fabry-Perot (FP) resonators, optical cavity resonators, whispering gallery mode resonators, and photonic crystal resonators; optical interferometers including, but not limited to, MZIs, phase-shifted coherent interferometers, self-mixing interferometers; acoustically responsive fiber end faces; and acoustically induced birefringent polarization sensors.

[0049] The acoustically responsive fiber end face can include a substrate adapted to add various microstructures to enhance the response of the optical fiber sensor to acoustic signals. Such microstructures can be: acoustically responsive structures such as metasurfaces that include a pattern of small elements (e.g., having dimensions smaller than approximately one wavelength of the optical signal) arranged to change the wavefront shape of the acoustic signal and maximize detection of the acoustic signal; acoustically responsive low-dimensional materials with special optomechanical features that are more easily deformed; and plasmonic structures that are patterned to amplify light-matter interactions. In addition to operating as optical sensors, the fiber end face structures can be added to other optical fiber sensors described herein to further enhance the acoustically responsive. For example, a metasurface can include a pattern of small elements arranged to change the wavefront shape of the acoustic signal and maximize the collection of acoustic signals by other types of optical fiber sensors discussed herein to improve the sensitivity of the optical fiber sensor. Adding low-dimensional materials to the fiber end face can also improve sensitivity as such materials are more easily deformed by acoustic waves, which can translate into larger changes in the optical signal. By writing plasmonic patterns on the fiber end face, the optical response to acoustic waves can be enhanced. This enhancement can be achieved by amplifying light-matter interactions with hotspots and resonances generated by these plasmonic patterns. As used herein, a “low-dimensional” or “two-dimensional” feature can refer to a feature having a thickness of less than 1 micrometer.

[0050] The optical structures described above are configured to respond to acoustic signals (e.g., ultrasonic signals). Thus, these optical structures can include acoustically responsive materials and / or acoustically responsive structures. As used herein, acoustically responsive refers to structures or materials that are configured to respond to incident acoustic signals (e.g., ultrasonic acoustic signals) in a manner that adjusts the optical properties of the material or structure. The response to acoustic signals in such resonator, interferometer, or acoustically responsive fiber facet structures can be due to the photoelastic effect and / or physical deformation of the structure. When affected by an acoustic signal, the resonator, interferometer, or acoustically responsive fiber facet structure experiences mechanical stress and / or strain from the alternating pressure of the acoustic signal sound waves. This mechanical stress and / or strain can change the optical properties of the optical sensor structure due to the photoelastic effect and can also induce changes or deformations in the physical structure of the resonator. For polarization-based sensors, when the medium through which the light passes is affected by an acoustic signal, the polarization of the light signal changes. When coupled to a light source (e.g., a laser source, a broadband light source (e.g., a lamp or LED), or other suitable light source) via an optical waveguide (e.g., an optical fiber), the effects of the acoustic signal on the optical sensor structure can be measured due to the changes in the light returned by the optical sensor structure via the optical waveguide. In this disclosure, the light signal and light can be referred to as a response to the acoustic signal. It should be understood that this response is due to the interaction between the acoustic signal and the medium through which the light passes. Thus, as discussed herein, so-called acoustically responsive materials or structures can respond to typical acoustic signals of an ultrasonic environment in a manner that can be measured by a light signal according to embodiments of the present invention by techniques described herein.

[0051] Embodiments of the present invention include systems configured to be used with fiber optic sensors. For example, systems according to the present disclosure can include light sources (e.g., laser sources, broadband light sources (e.g., lamps or LEDs), or other suitable light sources), light receiving devices (e.g., photodetectors, etc.), optical devices (splitters, combiners, circulators, polarization sensitive couplers, polarization analyzers, polarization controllers, frequency shifters, etc.), control devices, computer processing units, and other devices to facilitate the functioning of fiber optic sensors. In addition, such systems according to the present disclosure can include acoustic devices, such as transducers, probes, and hardware / software for control thereof. Systems according to the present disclosure can further include medical systems and devices, including all devices, systems, hardware, and software necessary to perform any medical procedures for which fiber optic sensors are used to facilitate.

[0052] Figure 1An optical sensor system for use with a fiber optic sensor is shown. As used herein, the term "fiber optic sensor" and the term "fiber optic based optical sensor" refer to an optical sensor adapted and / or configured to detect acoustic signals, as described in further detail below. The optical sensor system 100A includes a light source 104, e.g., a laser, a light receiving device 103, e.g., a photodetector, one or more optical waveguides 105, an optical circulator 102, and a fiber optic sensor 101. In operation, the light source 104 supplies an initial light signal 111 to the fiber optic sensor 101 via the optical waveguide 105 and through the optical circulator 102. The supplied initial light signal 111 passes along the optical waveguide 105 through the fiber optic sensor 101 back. The returned light signal 112 travels via the optical waveguide 105 through the optical circulator 102 and is received at the light receiving device 103. As discussed above, acoustic signals incident on the fiber optic sensor 101 alter the optical properties of the fiber optic sensor 101, which can include physical structure as well as optical material properties. Such optical property alterations can be measured from changes in the returned light signal 112, as discussed in further detail below.

[0053] Figure 2 An optoacoustic sensor system for use with a fiber optic sensor is shown. The optoacoustic sensor system 200 includes components, devices, hardware, and software for facilitating use of a fiber optic sensor 101 or a fiber optic sensor array 201, including a plurality of fiber optic sensors 101, as depicted in Figure 2 Figure 2 The use of a single fiber optic sensor 101 can be specifically referred to; however, it should be understood that in additional embodiments, a fiber optic sensor array 201 can be incorporated into the optoacoustic sensor system 200 in conjunction with any of the features discussed below, and any functionality attributed to the fiber optic sensor 101 can be further performed by the fiber optic sensor array 201. In embodiments, for example Figure 2 As shown, the optoacoustic sensor system 200 can include hardware and components for facilitating use of an ultrasonic transducer and / or an ultrasonic probe. The ultrasonic transducer can be used to generate and receive acoustic signals, or to only generate acoustic signals. The optoacoustic sensor system 200 can include a processing system 250, an optical subsystem 215, and an output device 208.

[0054] ​The processing system 250 can include a processing unit 209 and an image reconstruction unit 206. The processing unit 209 can include at least one computer processor, at least one non-transitory computer readable storage medium, and appropriate software instructions. The processing unit 209 is configured to provide control signals to and receive information signals from the light source control unit 207, the light receiving device 203, and the acoustic control unit 222. The processing unit 209 can be in communication with the light source control unit 207 (via control signals and information signals), thereby providing control over the light signals provided to the optical fiber sensor 101. The processing unit 209 can be in communication with the acoustic control unit 222 (via control signals and information signals), thereby providing control over and receiving of acoustic signals via the acoustic probe 245. The processing unit 209 is further configured to be in communication with the light receiving device 203 to receive information signals associated with the light signals received by the light receiving device 203. Thus, the processing unit 209 is used to provide the required control signals and receive the acquired information signals in the photoacoustic sensor system 200.

[0055] The processing unit 209 is also in communication with the image reconstruction unit 206, which is used to generate images based on the data and / or information acquired by the processing unit 209. The image reconstruction unit 206 can generate images based on the data captured by the optical fiber sensor 101 and the acoustic probe 245 related to a medium, such as a human body. The medical device distal end 231 can include one or more of a needle, a catheter, a guidewire, a delivery device, and / or any other device or apparatus configured for use within a patient. The image reconstruction unit 206 can be integrated within the system containing the processing unit 209, and / or can be a separate system including at least one computer processor, at least one non-transitory computer readable storage medium, and appropriate software instructions. The processing system 250 can provide control signals to an output device 208 to provide data output. The output device 208 can include, for example, a display or a device including a display.

[0056] In some embodiments, the output device 208 can further include additional systems, such as a medical procedure system configured to use the data as output. For example, the output device 208 can include an endoscopic system, a laparoscopic system, a robotic surgical system, a neurosurgical system, and additionally can include an ultrasound imaging system that can be interoperable. The output data can include information about the location of the medical device distal end or working portion 231, as well as acquired images of the medium in the area in which the medical device distal end 231 is used / deployed, such as patient anatomy, tissue, other medical tools / devices, etc.

[0057] Optical subsystem 215 includes light source control unit 207, light source 204, optical devices 202A, 202B, 202C, and 202D, and light receiving device 203. The light source control unit is configured to interface with and control light source 204 to control the generation of initial optical signal 211. The light source can generate continuous wave (CW) or pulsed light emission (stimulated emission, spontaneous emission, etc.). Initial optical signal 211 can include coherent light, such as a laser, provided at one or more frequencies in one or more modes. Initial optical signal 211 can have a single frequency / wavelength, a range of frequencies / wavelengths, and / or a broadband light source. Thus, light source 204 can include an array of lasers configured to generate laser light at one or more frequencies in one or more modes. Additionally, the polarization of the supplied light can be controlled as required by the application to optimize the detected signal level. The polarization state of the light can be controlled to be linearly polarized at a specific angle or circularly polarized. Linearly polarized light will respond best to a specific input ultrasound direction, while circularly polarized light will respond to ultrasound in all directions. The polarization of the light can be defined in terms of the laser source output, and the output polarization state can be controlled by an inline fiber polarizer, a paddle fiber polarization controller, an inline fiber polarization controller, or other type of polarization controller. Optical devices 202A, 202B, and 202C can be configured to manipulate or affect initial optical signal 211 received at fiber optic sensors 101. Initial optical signal 211 can be provided at multiple wavelengths or across a spectrum of wavelengths. Optical device 202A can include, for example, a wavelength division multiplexing (WDM) device configured to multiplex multiple frequencies of initial optical signal 211 provided by light source 204 for simultaneous transmission through optical waveguide 205, which directs initial optical signal 211 to fiber optic end optical sensors 101. Optical device 202B can be a circulator having first, second, and third ports, with the first port in optical communication with the light source through wavelength division multiplexing device (WDM) 202A. Initial optical signal 211 can pass through second optical device 202B, which can be, for example, an optical circulator, and is configured to direct initial optical signal 211 to optical device 202C. Optical device 202C can include a WDM device configured to demultiplex initial optical signal 211 provided to fiber optic sensors 101, which can be part of array 201, such that each of the plurality of fiber optic sensors 101 receives and subsequently outputs light of a different wavelength. Optical device 202C is in optical communication with the second port of second optical device 202B to separate initial optical signal into optical signals each having one of the wavelengths associated therewith, and to combine optical signals returned from fiber optic sensors 101, which are then directed to light receiving device 203 through third port and optical device 202D, which can include a WDM device.

[0058] The initial optical signal 211 is received by the optical fiber sensor 101 (or optical sensor 101 of the array of optical fiber sensors 201 in some embodiments) and returned through one or more optical waveguides 205 to the optical device 202C, which can be further configured to multiplex the returned optical signal 212 (if needed) for transmission to the optical receiving device 203. The returned optical signal 212 is directed by the optical device 202C through the optical device 202B and toward the optical device 202D, which can be a WDM device configured to demultiplex the returned optical signal 212 for reception by the optical receiving device 203.

[0059] The optical device 202D can be in optical communication with the third port of the optical device 202B to receive the returned optical signal and split it into individual wavelength components. For example, the optical receiving device 203, which can be an array of photodetectors, can be in optical communication with the optical device 202D to receive the individual wavelength components of the returned optical signal such that the detected phase shift or other change in the individual wavelength components is indicative of the sensed acoustic signal.

[0060] It is to be understood that in embodiments where the initial optical signal 211 and the returned optical signal 212 do not require frequency multiplexing / demultiplexing, optical devices 202A and 202C can not be required. The optical receiving device 203 can include any suitable device configured to detect incident light, including, for example, a photodetector. The optical receiving device 203 can further include, but is not limited to, a photodiode. The optical receiving device 203 can be in optical communication with an optical device 202D (e.g., a wavelength division multiplexing optical splitter) to receive individual wavelength components of the returned optical signal 212 such that phase shifts, polarization changes, or other changes of the individual wavelength components detected are indicative of a sensed acoustic signal. Changes in the returned optical signal 212 can be converted (e.g., by the processing unit 209 and / or by additional optical components, such as polarization sensitive couplers and / or frequency shifters) into data representative of the sensed acoustic signal (e.g., which can be further used to generate a representation of the tissue / anatomy of the medium distal of the medical device distal end 231 in a diagnostic or therapeutic procedure and / or to identify a location of the medical device distal end 231 within the medium). In embodiments, these signals (the initial optical signal 211 and the returned optical signal 212) can be subjected to pre-processing, beamforming, and post-processing as described in the following documents.Various methods for ultrasound beamforming and image processing are disclosed in the following applications: US Application 18 / 032953, filed April 20, 2023, entitled “Image Compounding for Mixed Ultrasound Sensor Array”; US Application 18 / 205081, filed March 7, 2023, entitled “Synthetic Aperture Imaging Systems and Methods Using Mixed Arrays”; US Application 18 / 901073, filed December 29, 2022, entitled “Acoutso-Optic Harmonic Imaging with Optical Sensors”; PCT Application PCT / US2022 / 077762, filed October 7, 2022, entitled “Ultrasound Beacon Visualization with Optical Sensors”; PCT Application PCT / US2022 / 041250, filed August 23, 2022, entitled “Multi-Dimensional Signal Detection with Optical Sensor”; and PCT Application PCT / US2022 / 018515, filed March 2, 2022, entitled “Acoustic Imaging and Measurements Using Windowed Nonlinear Frequency Modulation Chirp”, each of which is incorporated herein by reference. The image and / or data representing the distal end 231 of the medical device (or the fiber optic sensor 101) can then be displayed to a user on an output device 208, which can include a computer display or the like. The image and / or data representing the distal end of the medical device can further include the distal portion of the medical device in the acoustically transparent region.

[0061] As discussed above, the light receiving device 203 is in communication with the processing unit 209. The processing unit 209 receives from the light receiving device 203 an information signal representative of the returned light signal 212 received at the light receiving device 203. The processing unit 209 can also receive from the light control unit 207 an information signal representative of the initial light signal 211 output by the light source 204. The processing unit 209 is used to process the information signal associated with the returned light signal 212 (optionally as compared to the information signal associated with the initial light signal 211) to determine the acoustic environment at the fiber optic sensor 101, as discussed further below. The acoustic environment determination can include detection, identification, and interpretation of acoustic signals incident to one or more fiber optic sensors 101 of the fiber optic sensor array 201. The processing unit 209 can determine the presence and nature of acoustic signals incident to one or more fiber optic sensors 101.

[0062] Thus, the fiber optic sensor 101 can be used to detect and / or receive acoustic signals (e.g., ultrasound signals) and provide, through the optical receiving chain (e.g., optical devices 202C, 202B, 202D), a light signal representative of the acoustic signals and consistent with the acoustic signals to the light receiving device 203, which is configured to detect and / or receive the light signal and provide an electrical signal representative of the light signal and consistent with the light signal to the processing unit 209 for processing and interpretation. Thus, the processing unit 209 can be configured to receive an electrical signal representative of and consistent with the received acoustic signals and process and interpret the electrical signal to reconstruct an image from the acoustic signals. For example, an ultrasound image can be reconstructed using delay-and-sum beamforming principles, a common way of reconstructing ultrasound images. In delay-and-sum beamforming, the spatial distribution of the ultrasound field amplitude in a volume of interest (image region) is reshaped according to the delay between transmission, image pixel, and receiver, and thus the received ultrasound signals are recombined for the purpose of generating an image. In delay-and-sum beamforming, the signals are coherently summed at each image pixel location according to the delay.

[0063] The processing unit 209 can further be in communication with an acoustic control unit 222. The acoustic control unit 222 can be configured to provide control data to and receive signal data from the acoustic probe 245 and / or the acoustic transducer 221. The acoustic probe 245 can be configured for ex vivo or in vivo use and can include an AEG transducer or an AEG transducer array (or any other suitable acoustic transducer) configured to generate and / or receive acoustic signals, such as ultrasound signals. The acoustic probe 245 can also include a hybrid array of both an AEG transducer (or any other suitable acoustic transducer) configured to generate and / or receive acoustic signals and an optical sensor configured to receive an optical sensor, such as disclosed in U.S. Patent Publications US2022 / 0365036, US2023 / 0097639; US2022 / 0350022, and US2023 / 0148869, each of which is incorporated herein by reference. One or more array elements of a first type (e.g., AEG transducers) can be used to form a first image. In parallel, one or more array elements of a second type (e.g., optical sensors) are used to detect acoustic echoes that can be used to form a second image. The second image generated by the highly sensitive broadband optical sensors can be used alone or in combination with the first image to form a further improved image. Due to the high sensitivity and wide bandwidth of the optical sensors, the image produced by the optical sensors can have improved spatial resolution, improved penetration depth, improved signal-to-noise ratio (SNR), improved tissue harmonic imaging, and / or improved Doppler sensitivity.

[0064] The acoustic transducer 221 can be one component of a medical device system configured for intracorporeal deployment within a medium in which a diagnostic or therapeutic procedure is being performed or is to be performed. The acoustic transducer 221 can include a luminal or intracavity transducer located on a catheter, cannula, or the like, or can be an intraoperative transducer that allows for positioning of the transducer during minimally invasive surgery, such as on a laparoscopic tool, on the end of a robotic arm, or held by a surgeon, assistant, or any other medical personnel for selective positioning. In embodiments, the acoustic transducer 221 can be disposed on the same medical device as the medical device distal end 231, such as along with the fiber optic sensor 101. In embodiments, the acoustic transducer 221 can be disposed on one or more devices separate from the device of the medical device distal end 231.

[0065] The in-vivo transducer 221 can be positioned on a catheter / endoscope / cannula and transmit sound waves outward that are capable of penetrating a region of interest in the medium, and can be referred to as a forward-looking probe, as known in the art. Alternatively, the acoustic transducer 221 can emit sound waves to the side. For example, the transducer 221 can be part of a side-firing phased array used in IVUS applications. In another example, the transducer 221 can be used in a guide catheter with two side-by-side lumens, one lumen capturing a guidewire and the other working lumen not extending as distally as the guidewire lumen. Further, the transducer 221 can transmit sound waves in a radial pattern. For example, the transducer 221 can be included in an echoendoscope with a radial (or sector), linear, curvilinear (convex array), trapezoidal, or any other image format used in ultrasound imaging. Also linear (convex array) acoustic modes. A radial echoendoscope can provide a circumferential view at right angles to the shaft in the echoendoscope, or in other words, provide an image perpendicular to the insertion tube. Different ultrasound frequencies can be used to provide ultrasound imaging of distal and proximal structures. A radial echoendoscope can provide a 360-degree image of the anatomy, which can be useful for screening, but can be limited to therapeutic applications, such as obtaining tissue samples. Curvilinear, linear, or other appropriate arrays can be used for therapeutic applications, such as tissue sample harvesting, cyst drainage, biopsy of lesions / lymph nodes, and injections for pain management. In embodiments, the transducer 221 can be incorporated in a curvilinear echoendoscope that visualizes within a range depending on the curvilinear radius and allows real-time insertion of a needle / treatment device. In such embodiments, the ultrasound view can be in line or in the same plane as the scope axis. In other embodiments, the transducer 221 can be incorporated in a transverse array and provide an image in a plane perpendicular to the scope axis.

[0066] In other procedures, the movable intraoperative transducer can be positioned on the end of a robotic arm or other tool (such as a bkMedical Rob 12C4), or simply held by a medical professional during surgery. Further, certain cannulas and endoscopes can have forward-firing transducers 221 for causing sound to penetrate the area in front of the cannula, catheter, or scope, such as a craniotomy transducer.

[0067] A typical ex-vivo transducer 221 or probe 245 can be positioned on the skin surface of a patient, such as is typically used for general imaging or for specific procedures, such as needle guidance, needle localization, or needle placement.

[0068] The processing unit 209 is configured to use the information signals received by the fiber optic sensor 101 from the acoustic probe 245 or acoustic transducer 221 (and any other acoustic signal generator that can be connected or in communication with the photoacoustic sensor system 200) to sense, track, and monitor the medical device distal end 231 and generate ultrasound images of the anatomical structures in the surgical region. In embodiments, the fiber optic sensor 101 or sensor array 201 is used to receive / detect acoustic signals generated by the acoustic probe 245 and / or acoustic transducer 221, as well as scattered signals and tissue harmonics. Imaging of the medium can be achieved by the processing unit 209 from the difference between the acoustic signals output or transmitted by the acoustic probe 245 and / or acoustic transducer 221 and the corresponding acoustic signals received and / or detected by the acoustic probe 245 and / or acoustic transducer 221 and the fiber optic sensor 101. The detected signals can include detected scattered signals and tissue harmonics. The portion of the medium through which the acoustic signals generated by the acoustic probe 245 and / or acoustic transducer 221 travel can be imaged from the detected acoustic signals.

[0069] The fiber optic sensor 101 (or sensor array 201) receives acoustic signals transmitted from the acoustic probe 245 and / or acoustic transducer 221. Based on the signals received from the fiber optic sensor 101, the position of the fiber optic sensor 101 (and thus the medical device distal end 231) can be computed through triangulation (e.g., based on receiving one or more acoustic signals transmitted from a known source) and / or through coherent image formation. Further details can be found in: co-pending U.S. Provisional Application No. 63 / 522,994, titled “Transponder Tracking and Ultrasound Image Enhancement” and filed on June 23, 2023; and US Application titled “Transponder Tracking and Ultrasound Image Enhancement” with attorney docket number 109835-1394978 and filed concurrently with this application on October 23, 2023. The position of the fiber optic sensor 101 can be overlaid on the ultrasound images of the anatomical structures to determine the relative position of the fiber optic sensor 101 with respect to the known position of the acoustic probe 245 and / or acoustic transducer 221. Further, the ultrasound images of the surrounding anatomical structures can be coherently reconstructed from the combination of acoustic signals received by the fiber optic sensor 101 and received by one or more of the acoustic probe 245 and / or acoustic transducer 221. Such combination can result in better image quality than images formed using the acoustic probe 245 and / or acoustic transducer 221 alone.

[0070] In embodiments where the location and movement of the medical device distal end 231 is tracked, sensed, and monitored, the photoacoustic sensor system 200 can include a plurality of acoustic probes 245 that are fixed in place or whose locations are tracked. For example, tracking, sensing, determining, and monitoring the location and movement of the medical device distal end 231 can be achieved by identifying timing and / or directional differences between a plurality of acoustic signals detected by the fiber optic sensor 101 and the acoustic transducer 221.

[0071] It is to be understood that the configurations of the photoacoustic sensor system 200 shown are provided by way of example, and that different configurations can be employed without departing from the scope of the present disclosure. Figure 2 The optical devices 202A / B / C / D can be arranged in different arrangements, different numbers and arrangements of fiber optic sensors 101 and fiber optic sensor arrays 201 can be employed. In embodiments, the light source control unit 207 and the acoustic control unit 222 can be incorporated or integrated within the processing system 250. Additional combinations of components of the photoacoustic sensor system 200 can be selected as desired to achieve the functionality described herein.

[0072] Figure 3A Sensor fibers containing fiber optic sensors and associated optical fibers are shown. Figure 3AThe illustrated device can include a sensor optical fiber 301. The sensor optical fiber 301 can be an optical fiber configured with an optical fiber sensor disposed on an end thereof. The sensor optical fiber 301 includes an optical waveguide 311 including a core 312 and a cladding structure 313. The optical waveguide 311 is configured to transmit or carry light therein, e.g., within the core 312. The core 312 is surrounded by and protected by the cladding structure 313. The optical waveguide 311 can be substantially cylindrical along its length, and / or can have another suitable shape. The core 312 can be substantially centered within the cladding structure 313. In embodiments, the optical waveguide 311 can be an optical fiber, and can include any material common to optical fibers. For example, the core 312 can include silica glass, a polymer, or other suitable material. For example, the material of the cladding structure 313 can be selected to be responsive to changes in pressure or strain induced by ultrasound. The pressure or strain induced by ultrasound will introduce a deformation or change in refractive index, resulting in a change in the optical signal passing through the optical fiber. For example, when used as an ultrasound sensor, the greater the change, the higher the sensitivity, and the better the detection limit. The cladding material can have at least one material property associated therewith, where the at least one material property can be a refractive index (RI) that is lower than that of the core 312. Material properties, such as the Young’s modulus and the photoelastic coefficient of the core, cladding material, and encapsulation structure, which can be the same or different materials, can be tailored to the application. A smaller Young’s modulus and a larger photoelastic coefficient can be preferred for improved ultrasound sensitivity and acoustical responsiveness. As used herein, a material that is sensitive or responsive to acoustic signals can refer to a material that has a relatively small Young’s modulus (E), a relatively high photoelastic coefficient, and / or a relatively large refractive index (n) compared to a silica material, for example. As used herein, a relatively small Young’s modulus can refer to a Young’s modulus that is less than 3.0 GPa, less than 2.0 GPa, less than 1.2 GPa, or in a range between 1.2 and 0.8 GPa. A relatively high photoelastic coefficient C (i.e., |C1-C2|) can refer to a photoelastic coefficient that is greater than C = 2*10 -121 / Pa. A relatively large refractive index can refer to a refractive index greater than approximately 1.46 for optical signals in the range of approximately 300 nm - 2000 nm. Such materials can be selected to increase, improve, or optimize the ability of the optical structures discussed herein to detect acoustic signals. Because the optical structures described herein are configured to detect acoustic signals (e.g., ultrasonic signals), the materials from which they are constructed can be selected to maximize or increase the sensitivity of the optical properties of the structures to incident acoustic signals. For example, materials with lower Young's modulus require less stress to deform. In some applications, increased deformation can be undesirable. However, increased deformation in response to an incident acoustic signal can amplify or increase the detectable changes in optical signals that pass through the optical structures that experience greater deformation. Similarly, increased photoelastic effects are desirable in the optical structures described herein, but can be undesirable in different structures configured for different purposes.

[0073] It should be appreciated that the core 312 can be any suitable type of core, such as those made of silica, silicon, optically transparent polymers, and the like. As a non-limiting example, if the core 312 is made of silica (Si02), the cladding material can be MY-133, a low refractive index optical coating manufactured by MY Polymers Ltd. of Israel, or BIO-133, also a low refractive index optical coating manufactured by MY Polymers Ltd. of Israel. As another non-limiting example, if the core is silicon, with a higher RI than silica, the cladding structure 313 can be polyvinylidene fluoride (PVDF), polystyrene (PS), parylene, benzocyclobutene (BCB), MY-133, or BIO-133.

[0074] The optical waveguide 311 can be configured for single mode (SM) transmission or multi-mode (MM) transmission, depending on the form factor and laser and sensor wavelength tuning requirements, as the dimensions of SM optical fibers can be smaller. For example, a single mode optical fiber configured to operate in the 1550 nm band can have a 50 um cladding structure diameter and a core D => 4.2 um. Such an optical fiber can be a polarization maintaining optical fiber. A multi-mode optical fiber configured to operate in the 1550 nm band can have a core D = 50 um - 60.5 um and a cladding diameter of 125 um. In embodiments, polymer optical fibers (e.g., PMMA, polystyrene) can be used. Such optical fibers can have a larger diameter and a larger minimum bend radius than typical glass optical fibers. In other embodiments, photonic crystal optical fibers (with a hollow structure / periodic pattern) can be used.

[0075] Optical resonator structure 321 is disposed at an end of sensor optical fiber 301. Optical resonator structure 321 is coupled to an end of optical waveguide 311 and can include an optical resonator, such as a Fabry-Perot (FP) resonator, a whispering gallery mode resonator, a micro-ring, a microtoroid, a spiral resonator, or a photonic crystal resonator integrated therein. In addition to the optical resonator, optical resonator structure 321 and other optical resonator structures described herein can also include additional structures and components configured to facilitate the functioning of the optical resonator, as described below. The optical resonator is configured to receive a first optical signal (e.g., light) supplied to it via the optical waveguide and return a second optical signal along the optical waveguide. The second optical signal can correspond to and represent an acoustic signal incident to optical resonator structure 321. As discussed above, the incident acoustic signal can cause physical deformation and / or material property alteration of optical resonator structure 321. Thus, the optical signal provided by optical resonator structure along optical waveguide 311 can be altered by, affected by, or otherwise indicative of or representative of the acoustic signal, and can therefore be used to characterize the incident acoustic signal.

[0076] Sensor optical fiber 301 can further include a cladding structure 314, which can include, for example, an outer coating, a shroud, a protective outer layer, and / or a fiber jacket. Cladding structure 314 is configured with a first portion 314A that surrounds optical waveguide 311 and a second portion 314B that at least partially surrounds optical resonator structure 321. Cladding structure 314 can include a polymer, such as parylene, MY-133, BIO-133, or other suitable polymer that is sensitive or responsive to acoustic signals, as discussed above. The acoustic impedance of cladding structure 314 can be selected to match the impedance of optical resonator structure 321 in order to enhance the detection sensitivity of acoustic signals. As used herein, "matching impedance" can refer to selecting materials and / or structures with matching acoustic impedances, as is generally known to those skilled in the art of medical ultrasound, with acoustic impedances that differ from one another by within 20% providing an acceptable match. Closer matching of acoustic impedances results in better transmission of acoustic signals (e.g., less of the acoustic signal is reflected), resulting in higher sensitivity. In embodiments, first portion 314A that surrounds optical waveguide 311 and second portion 314B that at least partially surrounds optical resonator structure 321 can comprise different materials selected for different purposes. For example, first portion 314A can include an acoustically transparent material, for example, with an acoustic impedance selected to increase the match and thereby minimize reflection of acoustic signals. Second portion 314B can include an acoustically responsive / sensitive material, as discussed above, to increase the response to incident acoustic signals in the region of optical resonator structure 321. Unless explicitly stated otherwise, all cladding structures discussed herein can include similar properties to those of cladding structure 314, including first and second portions comprising different materials selected for different purposes.

[0077] An optical resonator structure 321 is disposed at the end of an optical waveguide 311 and can therefore be referred to as an optical fiber end sensor. The cladding structure 313 may have a first diameter, and the optical resonator structure 321 may have a second diameter. The first and second diameters may or may not be substantially the same. Depending on the application, it may be advantageous to have the optical fiber have substantially the same dimensions or to make the sensor significantly larger than the optical fiber, for example, it may also be an asymmetrical bulb-shaped structure. Increased dimensions can further enhance the acoustically sensitive surface area of ​​the sensor, thereby increasing overall sensitivity. As discussed above, considering the need for small form factors in some medical applications, the sensor fiber 301 can be compact, in some examples where the first and / or second diameters are less than 200 micrometers, less than 175 micrometers, less than 150 micrometers, less than 130 micrometers, less than 100 micrometers, or less than 85 micrometers.

[0078] Figure 3B A sensor fiber comprising an optical waveguide and an optical resonator structure is shown, the optical resonator structure having a Fabry-Perot type resonator as an optical sensor. Sensor fiber 351 is an example of sensor fiber 301 and may include any of the features of sensor fiber 301 described above. Sensor fiber 351 comprises an optical waveguide 371 having a core 352 and a cladding structure 353. Core 352 may have a diameter in the range of 7 to 12 micrometers, or approximately 9 micrometers. These dimensions are provided only as examples and do not limit the dimensions and diameters covered by embodiments of this disclosure. Sensor fiber 351 may comprise an encapsulation structure 354 encapsulating the optical waveguide 371 and an optical resonator structure 361 disposed at the end of the optical waveguide 371, the encapsulation structure may, for example, include an outer coating, a protective outer layer, and / or an optical fiber sheath. Encapsulation structure 354 may be a multilayer structure, comprising, for example, an inner layer 355 and an outer layer 356. The inner layer 355 may comprise gold or any suitable reflective material for light waves, while the outer layer 356 may comprise parylene, MY-133, BIO-133, or other suitable acoustically transparent protective layers. The encapsulation structure 354 may comprise a first portion 354A encapsulating or surrounding the optical waveguide 371 and a second portion 354B encapsulating or surrounding the optical resonator structure 361. The encapsulation structure 354 may have features similar to those of the encapsulation structure 314, comprising the first and second portions of different materials. The optical resonator structure 361 may be configured with a Fabry-Perot resonator as an optical resonator 362. The optical resonator 362 includes a distal reflective surface 364 and a proximal reflective surface 363 disposed on either side of the optical cavity 365. The distal reflective surface 364 and the proximal reflective surface 363 may be constructed from any suitable reflective material. Figure 3BAs shown, the distal reflective surface 364 and the proximal reflective surface 363 are formed by and integral with the inner layer 355 of the enclosing structure 354, and thus are formed of gold or other suitable reflective material. As shown in FIG. 3B, the distal reflective surface 364 and the proximal reflective surface 363 can be formed of different materials. As shown in FIG. 3C, the distal reflective surface 364 and the proximal reflective surface 363 can be separate structures from the enclosing structure 354. Figure 3B As shown in FIG. 3A, the distal reflective surface 364 can be curved and the proximal reflective surface 363 can be substantially flat. This arrangement is by way of example only, and the distal and proximal reflective surfaces 364 / 363 can be arranged in different shapes and / or configurations. As shown in FIG. 3B, the distal reflective surface 364 can be substantially flat and the proximal reflective surface 363 can be curved. As shown in FIG. 3C, the distal reflective surface 364 and the proximal reflective surface 363 can be formed of different materials. Figures 4A-4E Some additional examples are provided in FIGS. 4A-4C. In other embodiments, the distal reflective surface 364 and the proximal reflective surface 363 can be formed of different materials, and / or can be separate structures from the enclosing structure 354. An optical cavity 365 is disposed between the distal reflective surface 364 and the proximal reflective surface 363. As used herein, the term "optical cavity" refers to a volume occupied by a material that provides minimal attenuation to light passing therethrough (e.g., having a high Q-factor typically above 1000). The quality (Q) factor is a dimensionless parameter that describes how under-damped an oscillator is. A higher Q-factor corresponds to a more sensitive resonator.

[0079] In optics, the Q-factor of a resonant cavity is given by:

[0080]

[0081] where f0is the resonant frequency, E is the energy stored in the cavity, and is the power dissipated. The optical Q-factor is equal to the ratio of the resonant frequency to the bandwidth of the cavity resonance. The average lifetime of a resonant photon in the cavity is proportional to the Q-factor of the cavity. Thus, a high Q-factor indicates low damping, and photons within the cavity have a high lifetime.

[0082] The Q-factor, as well as any other measure of sensitivity and responsiveness, is ultimately limited by the choice of material used for the core. Conventional Fabry-Perot interferometers can be uniformly formed of a single material, such as silica throughout the structure. For example, while silica has excellent optical transmission capabilities, it does not have equally excellent acoustic sensitivity. While many materials with excellent acoustic sensitivity are known, these materials can not be suitable replacements for the silica or the like of the core by themselves. The present invention employs a resonant actuator to take advantage of the acoustic sensitivity found in other materials.

[0083] The optical cavity 365 can be composed of a suitable material, e.g. a polymer. A polymer material with high acoustic transmissivity, such as MY-133 or BIO-133, can be used to enhance the sensitivity of the optical resonator structure, as discussed above. The optical resonator structure 361 can be configured to detect acoustic signals. Acoustic signals incident to the optical resonator structure, e.g. to the distal reflective surface 364, the proximal reflective surface 363 and / or the optical cavity 365, can cause these structures to vibrate and / or other physical deformations, which can alter or affect their optical properties. Furthermore, due to the photoelastic effect, the material properties of these structures can be altered, and thus further change the optical properties. Accordingly, the return light signal provided by the optical resonator structure 361 to the optical waveguide 371 (e.g. in response to the light signal supplied via the optical waveguide 371) can be indicative of or representative of the acoustic signal incident to the optical resonator structure 361. More specifically, the phase shift of the light in the detected sensor beam is indicative of the sensed acoustic signal. With a polarization-based sensor, the polarization analyzer will interpret the phase shift / delay between the different polarization components in order to generate a signal indicative of the sensed acoustic signal.

[0084] Figures 4A-4E Several variations of the optical resonator structure 361 according to embodiments of the application are shown. Figure 4A An optical resonator structure 361 is shown, having a proximal reflective surface 363 and a distal reflective surface 364, which are substantially flat and substantially parallel at either end of a substantially cylindrical optical cavity 365. Figure 4B An optical resonator structure 361 is shown, having a proximal reflective surface 363 which is substantially flat and substantially square with respect to the optical waveguide 371, and a distal reflective surface 364 which is concave with respect to the optical cavity 365. Figure 4C An optical resonator structure 361 is shown, having a proximal reflective surface 363 which is convex with respect to the optical cavity 365, and a distal reflective surface 364 which is concave with respect to the optical cavity. Figure 4D An optical resonator structure 361 is shown, having a proximal reflective surface 363 which is concave with respect to the optical cavity 365, and a distal reflective surface 364 which is substantially flat and substantially square with respect to the optical waveguide 371. Figure 4E An optical resonator structure 361 is shown, having a proximal reflective surface 363 and a distal reflective surface 364, which are both concave with respect to the optical cavity 365.

[0085] Figure 5A An optical sensor system 100B according to embodiments herein is configured for use with an interferometer-based optical fiber sensor 101B, as shown in Figure 5B An interferometer-based optical sensor according to embodiments herein is shown. Figure 5A An optical sensor system 100B according to embodiments herein is configured for use with an interferometer-based optical fiber sensor 101B, as shown inFigure 5B As shown.

[0086] Fiber optic sensor 101B can include a fiber optic end sensor having an interferometer-based acoustic sensor. Fiber optic sensor 101B can include a sensor fiber 301A having an interferometer-based fiber optic end sensor structure 321A disposed at an end thereof, e.g., at an end of optical waveguide 311A. In addition to what is mentioned, sensor fiber 301A can include features and structures consistent with those of sensor fiber 301. Interferometer-based fiber optic end sensor structure 321A can include, e.g., a Mach-Zehnder (MZ) type interferometer. Interferometer-based fiber optic end sensor structure 321A is coupled to an end of optical waveguide 311A. Interferometer-based fiber optic end sensor structure 321A can include additional structures and components configured to facilitate the functioning of the interferometer-based fiber optic end sensor, as described below. The interferometer-based fiber optic end sensor is configured to receive a first optical signal (e.g., light) supplied to it via optical waveguide 311A, and return a second optical signal along optical waveguide 311A. The second optical signal can correspond to and represent an acoustic signal incident to interferometer-based fiber optic end sensor structure 321A. The incident acoustic signal can cause physical deformation and / or material property alteration of interferometer-based fiber optic end sensor structure 321A. Thus, the optical signal provided by interferometer-based fiber optic end sensor structure 321A along optical waveguide 311A can be altered by, affected by, or otherwise indicative of or representative of the acoustic signal, and thus can be used to characterize the incident acoustic signal.

[0087] Interferometer-based fiber optic end sensor structure 321A can include an acoustically responsive polymer portion 317A including parylene or other suitable polymer sensitive to acoustic signals. The acoustic impedance of polymer portion 317A can be selected to match the acoustic impedance of the cladding structure of sensor fiber 301A (e.g., within 1%, 5%, 10%, or 20% difference) to enhance the sensitivity of fiber optic end sensor structure 321A, as described above. A distal reflective surface 364A is disposed at the distal end of fiber optic end sensor structure 321A, and can be constructed of any suitable material, e.g., gold. As shown, distal reflective surface 364A is formed of gold and is integral with polymer portion 317A. Figure 5B

[0088] ​The optical fiber end sensor structure 321A is disposed at the end of the optical waveguide 311A and can thus be referred to as an optical fiber end sensor. The optical waveguide 311A can have a first diameter and the optical fiber end sensor structure 321A can have a second diameter. The first diameter and the second diameter can be substantially the same, and / or can have a ratio in the range between 1.05 and 0.95, a ratio in the range between 1.02 and 0.98, or a ratio in the range between 1.01 and 0.99. As discussed above, the sensor optical fiber 301A can be compact, e.g., where the first diameter and / or the second diameter is less than 200 microns, less than 175 microns, less than 150 microns, less than 130 microns, less than 100 microns, or less than 85 microns.

[0089] The optical sensor system 100B is configured for use with an interferometer-based optical fiber sensor 101B. The optical sensor system 100B can include a light source 104, e.g., a laser, a light receiving device 103, e.g., a photodetector, one or more optical waveguides 105, an optical circulator 102, one or more frequency shifters 106, and one or more couplers 107. In operation, the light source 104 supplies an initial light signal 111A to the optical fiber sensor 101 via the optical waveguide 105, through the coupler / decoupler 107A and through the optical circulator 102. The supplied initial light signal 111A is returned through the optical fiber sensor 101 along the optical waveguide 105. The returned light signal 112 travels via the optical waveguide 105 through the optical circulator 102 and the coupler / decoupler 107B and is received at the light receiving device 103. The coupler / decoupler 107A is used to direct a portion of the initial light signal 111A as a reference light signal 111B through the frequency shifter 106 to the coupler / decoupler 107B, where it can be combined with the returned light signal 112 for detection and comparison at the light receiving device 103. As discussed above, an acoustic signal incident on the optical fiber sensor 101 alters the optical properties of the optical fiber sensor 101, including the physical structure as well as the optical material properties. Such optical property alterations can be measured from changes in the returned light signal 112 compared to the reference light signal 111B.

[0090] Figure 5C and 5DEmbodiments of fiber optic sensors are shown that include fiber end faces configured to provide or enhance acoustic detection capabilities. Fiber optic sensor 101C and fiber optic sensor 101D each include at least optical waveguide 311, core 312, cladding structure 313, and cladding structure 314. Fiber optic sensor 101C includes optical sensor structure 329C that includes acoustically responsive polymer portion 397 and face substrate 398A at a distal end thereof. Fiber optic sensor 101D includes optical sensor structure 329D that includes acoustically responsive polymer portion 397, face substrate 398B disposed between polymer portion 397 and core 312 and cladding structure 313, and distal end reflective surface 394 disposed at a distal end of polymer portion 397.

[0091] In fiber optic sensor 101C, face substrate 398A is disposed at a distal end of fiber optic sensor 101C. Optical sensor structure 329C is formed by polymer portion 397 and face substrate 398A. Face substrate 398A includes one or more face structures 399A, as shown in the cross-sectional view. Face structures 399A can include acoustically responsive microstructures, such as metasurfaces that include a pattern of small elements arranged to change the wavefront shape of an acoustic signal and maximize detection of the acoustic signal, acoustically responsive low-dimensional materials that have optomechanical features selected to optimize acoustic response, such as features that are more easily deformed upon receiving an acoustic signal, exhibit a greater material response to an acoustic signal, and plasmonic structures that are patterned to amplify light-matter interactions, as described herein. The plasmonic structures can locally amplify incident light due to their plasmonic resonances. Face structures 399A operate as optical sensors as described herein. During operation, supplied optical signal 1111 is reflected from face substrate 398A and returned to the system as returned optical signal 1121. Because face structures 399A are acoustically responsive, returned optical signal 1121 is modified by changes in face structures 399A caused by an incident acoustic signal. In embodiments, plasmonic resonances induced in plasmonic metasurfaces acting as face structures 399A or Mie resonances induced in dielectric metasurfaces acting as face structures 399A can be altered (e.g., shifted) by the incident acoustic signal, such that the modification of returned optical signal 1121 is detectable. Returned optical signal 1121 can then be interpreted by any of the systems described herein.

[0092] In the fiber optic sensor 101D, a face substrate 398B is disposed between the polymer portion 397 and the core 312 and cladding structure 313. The optical sensor structure 329D is formed by the polymer portion 397, the face substrate 398B, and the distal reflective surface 394. The face substrate 398B includes one or more face structures 399B, as shown in the cross-sectional view. The face structures 399B can include acoustically responsive microstructures, similar to those described above with respect to the face structures 399A. The face structures 399B function to enhance, improve, or otherwise modify the acoustical response of the optical sensor structure 329D. During operation, the supplied optical signal 1111 is reflected from the distal reflective surface 394 and returned to the system as the returned optical signal 1121. The polymer portion 397 and the distal reflective surface 394 are acoustically responsive, and the returned optical signal 1121 is modified in accordance with the acoustic signal incident to these structures. Because the face structures 399B are acoustically responsive and both the supplied optical signal 1111 and the returned optical signal 1121 pass through the face substrate 398B, the returned optical signal 1121 is further modified by the changes to the face structures 399B caused by the incident acoustic signal. In embodiments, the face structures 399B can be designed and / or selected to optimize coupling (e.g., reduce signal loss) and / or achieve critical coupling (e.g., eliminate signal loss) for the optical sensor structure 329D. Increased coupling in the optical sensor structure 329D functions to increase the amplitude of the optical signal responsive to the incident acoustic signal. Thus, the returned optical signal 1121 can exhibit a higher signal-to-noise ratio. In addition, the incident acoustic signal that deforms the face structures 399B can also be used to alter the extent to which the face structures 399B modify the coupling in the optical sensor structure 329D, thereby providing another aspect of the returned optical signal 1121 that is altered by the incident acoustic signal for interpretation. The returned optical signal 1121 can then be interpreted by any of the systems described herein. Thus, the face substrate 399B can function to enhance, improve, or otherwise modify the acoustical response of the optical sensor structure 329D.

[0093] The face structures 399A and 399B are shown incorporated into the fiber optic sensors 101C and 101D, respectively. Figure 5C and 5D Such face substrates are not limited to use with interferometer-based optical sensors having the structure and operation of the fiber optic sensors 101C and 101D, and can be incorporated into any of the fiber optic sensors discussed herein.

[0094] Figure 5E An example of a plasmonic metasurface is shown, and Figure 5F An example of a dielectric metasurface is shown. As Figure 5EAs shown in FIG. 5, optical fiber 500 can include plasmonic metasurface 511 disposed at an end of optical waveguide 502 having core 501. Plasmonic metasurface 511 can be disposed within an area defined by core 501 on the end of optical fiber 500. As shown, for example, plasmonic metasurface 511 can be disposed in a square pattern, or can also be disposed in any other suitable pattern. Plasmonic metasurface 511 can exhibit plasmonic resonances when impinged by a light signal from core 501. Distortions caused by an incident acoustic signal alter the plasmonic resonances and allow detection and decoding of the acoustic signal, as discussed herein. Plasmonic metasurface 511 can include various metals, particularly noble metals such as gold. Additionally, plasmonic metasurface 511 can be a thin film surface, having a height of less than 50 microns, less than 40 microns, less than 30 microns, less than 20 microns, or less than 10 microns. In other embodiments, plasmonic metasurface 511 can be a low-dimensional or two-dimensional surface, having a height of less than 1 micron. In lateral dimensions, features of plasmonic metasurface 511 can be small, having lateral dimensions D (e.g., width and / or length) that are less than a wavelength of the light signal used by the sensor (e.g., less than 600 nanometers, less than 400 nanometers, less than 200 nanometers, etc.). The lateral dimensions of the features of plasmonic metasurface 511 can also refer to the spacing between features. Figure 5F A dielectric metasurface 512 is shown, which can be disposed in a similar manner within an area of core 501 at an end of optical waveguide 502 of optical fiber 550. Dielectric metasurface 512 can be arranged in a strip or rectangle, as shown in FIG. 5, or arranged in any other suitable shape. Dielectric metasurface 512 can be configured to exhibit Mie resonances when impinged by a light signal. The Mie resonances can be altered by an incident acoustic signal, thereby permitting detection and decoding of the acoustic signal. In embodiments, dielectric metasurface 512 can include a dielectric material, such as silicon, titanium oxide, etc. In embodiments, dielectric metasurface 512 can be dimensioned in a similar manner to plasmonic metasurface 512, as discussed above. Figure 5F

[0095] Figure 6A An optical sensor system for use with an optical fiber sensor according to embodiments herein is shown. Figure 6B ​A polarization-based optical sensor according to embodiments herein is shown. Optical sensor system 100B is configured for use with polarization-based fiber optic sensor 101C. Fiber optic sensor 101C can include a fiber optic end sensor having a polarization-based acoustic sensor. Fiber optic sensor 101C can include sensor optical fiber 301B having polarization-based fiber optic end sensor structure 321B disposed at an end thereof, e.g., at an end of optical waveguide 311B. In other embodiments, as discussed below, polarization-based fiber optic end sensor structure 321B can be disposed at any location along sensor optical fiber 301B. In addition to what is mentioned, sensor optical fiber 301B can include features and structures consistent with those of sensor optical fiber 301. Sensor optical fiber 301B includes cladding structure 314C, which can include, e.g., an outer coating, a protective outer layer, and / or a fiber jacket. Cladding structure 314C can include a material selected to have a relatively high acoustic impedance mismatch with the cladding structure of sensor optical fiber 301B. Thus, locations where sensor optical fiber 301B is covered by cladding structure 314C can reflect incident acoustic signals. Polarization-based fiber optic end sensor structure 321B can be exposed through window 320B defined by the lack of cladding structure 314C, and can include polymer portion 317B comprising an acoustically responsive polymer and distal reflective surface 364B configured to reflect initial optical signal 111 as reflected optical signal 112. Polarization-based fiber optic end sensor structure 321B is configured to receive a first optical signal (e.g., light) supplied to it via optical waveguide 311B, and return a second optical signal along optical waveguide 311B. The second optical signal can correspond to and represent an acoustic signal incident to polarization-based fiber optic end sensor structure 321B. The incident acoustic signal can cause physical deformation and / or material property alteration of polarization-based fiber optic end sensor structure 321B. Thus, the optical signal provided by polarization-based fiber optic end sensor structure 321B along optical waveguide 311B can be altered, affected, or otherwise indicative or representative of the acoustic signal by the acoustic signal, and thus can be used to characterize the incident acoustic signal. In polarization-based fiber optic end sensor structure 321B, the incident acoustic signal induces a stress in polymer portion 317B that causes one or more of birefringence and rotation of the polarization of light passing through polymer portion 317B, thereby changing the polarization of light carried by optical waveguide 311B, which can be detected and analyzed by optical sensor system 100B, as discussed below.

[0096] The optical sensor system 100B includes a light source 104, e.g., a laser, a light receiving device 103, e.g., a photodetector, one or more optical waveguides 105, an optical circulator 102, and an optical fiber sensor 101B. In operation, the light source 104 supplies an initial optical signal 111 to the optical fiber sensor 101B via the optical waveguide 105 and through the optical circulator 102. The supplied initial optical signal 111 is returned through the optical fiber sensor 101B along the optical waveguide 105. The returned optical signal 112 travels via the optical waveguide 105 through the optical circulator 102, through the polarization analyzer 108, and is received at the light receiving device 103. The use of the polarization analyzer 108 allows for the determination of the polarization difference between the initial optical signal 111 and the returned optical signal 112. As discussed above, an acoustic signal incident on the optical fiber sensor 101B alters the optical properties of the optical fiber sensor 101B, including the physical structure as well as the optical material properties, and causes an alteration in the polarization of the returned optical signal 112. Such polarization changes can be measured from the difference in the returned optical signal 112 and the initial optical signal 111 as determined by the photodetector.

[0097] In embodiments, the angular sensitivity of the polarization-based fiber end sensor structure 321B can be affected by the difference in polarization of the initial optical signal 111. Depending on the polarization of the initial optical signal 111, the angle of the incident acoustic signal for which the polarization-based fiber end sensor structure 321B is most sensitive can be altered, as shown. Thus, in embodiments, a control system associated with the optical sensor system 100B can be configured to adjust or optimize the polarization of the initial optical signal 111, e.g., from an input polarization state 1 to an input polarization state 2 to increase the acoustic sensitivity. These polarization states are provided as examples only and can be altered or configured as needed for operation, as discussed below. Figure 6C Figure 6C ​The input polarization states 1 and 2 are shown to be most sensitive to the direction of the incoming acoustic signal. The solid arrow corresponds to the direction to which input polarization state 1 is most sensitive, and the dashed arrow corresponds to input polarization state 2. Thus, the lobe of polarization states provides the highest acoustic sensitivity. Accordingly, the input polarization states can be selected and implemented to align with the expected direction of the acoustic signal or the direction in which acoustic sensitivity is highest. This can enable the optical sensor system 100B to optimize the performance of the fiber-end sensor structure 321B according to the incoming direction of the acoustic signal. The angular sensitivity of the polarization-based fiber-end sensor structure 321B does not depend on the structure of the fiber-end sensor structure 321B. In embodiments, a polarization maintaining fiber can be used. After the polarization states are selected and implemented, they are maintained by the optical signal. In embodiments, adjustable fiber components can be used to provide adjustable polarization states. In embodiments, the polarization states can be adjusted during use, taking into account changes in conditions (e.g., movement and / or rotation of the acoustic transducer 221 generating the acoustic signal, movement of the fiber-end sensor structure 321B, etc.). Other benefits of the polarization-based fiber-end sensor structure 321B can include a simplified sensor structure and no wavelength locking requirements.

[0098] Figure 6D Another embodiment of a fiber-based optical sensor according to embodiments of the application is shown. The sensor fiber 301C can be a fiber configured in a similar manner to the sensor fiber 301, including an optical waveguide comprising a core and cladding structure, as described herein. The sensor fiber 301C can have a fiber-end sensor structure 321C disposed on an end thereof. The fiber-end sensor structure 321C can include any of the fiber-end sensor structures discussed herein, including optical resonator structures, interferometer structures, acoustically responsive fiber end face structures, and polarization-based structures. The sensor fiber 301C can further include a cladding structure 314C configured to reflect an incident acoustic signal and a window 320C representing a gap or exposed region without the cladding structure 314C. The window 320C can expose a polarization-based optical sensor structure 322C, such as with respect to Figure 6Bdiscussed. In embodiments, the polarization-based optical sensor structure 322C is formed from the cladding structure and core of the optical fiber and is part of the optical fiber. That is, the polarization-based optical sensor structure 322C can be defined by exposure to incident acoustic signals that are generated because of the lack of an acoustic shroud at the window 320C, rather than any additional structure within the optical fiber. The sensor optical fiber 301C can include any number of windows 320C and polarization-based optical sensor structures 322C disposed along its length. Thus, the sensor optical fiber 301C can include multiple optical-based acoustic sensor structures, including both the fiber end sensor structure 321C and the polarization-based optical sensor structure 322C configured for an intermediate fiber location. In other embodiments, the window 320C can have sufficient dimensions along the length of the optical fiber such that it will operate as a line sensor rather than a point sensor, as will be discussed in greater detail below. The line sensor can be a straight line sensor or a curved line receiver. In other embodiments, the sensor optical fiber 301C can be configured with one or more polarization-based optical sensor structures 322C disposed along its length, but does not include any fiber end sensor structure 321C.

[0099] Each of the fiber end sensor structure 321C and the polarization-based optical sensor structure 322C can be used to facilitate both imaging and tracking, as described herein. In embodiments, for example, the polarization-based optical sensor 322C can be configured in terms of size / shape to facilitate imaging, tracking, or both. For example, a longer polarization-based optical sensor structure 322C can act as a line sensor to increase image quality, and the line can be a straight line or a curved line. In another example, multiple polarization-based optical sensor structures 322C can be used to facilitate a tracking approach (e.g., multiple sensors along a device can aid in orientation determination).

[0100] In some embodiments, the polarizing window portion can also act as a fiber optic sensor that detects scattered acoustic signals and / or tissue harmonics. When the fiber optic sensor is positioned within an imaging region of interest, it can receive weak harmonics or scattered acoustic signals that cannot propagate far. The fiber optic can convey an optical signal corresponding to the received acoustic signal to a system processor (e.g., processing unit 209). The system processor can use the received optical signal to reconstruct an ultrasound image of the anatomy surrounding the sensor using a delay-and- sum beamforming method or other suitable image reconstruction method, as discussed in more detail in corresponding U.S. Provisional Application No. 63 / 522,994, filed June 23, 2023, entitled “Transponder Tracking and Ultrasound Image Enhancement,” and U.S. Application entitled “Transponder Tracking and Ultrasound Image Enhancement,” having attorney docket number 109835-1394978, and filed concurrently on October 23, 2023. With this data, the system processor can generate an image of better quality than an image generated based only on pulses emitted and received by the acoustic probe. In embodiments, the system processor can construct an image based only on the optical signals received from the one or more fiber optic sensors. In embodiments, the optical signals received from the one or more fiber optic sensors can be used in conjunction with acoustic signals received by a traditional ultrasound probe.

[0101] This principle is shown in more detail in Figure 6E . As shown in Figure 6E , an acoustic probe 601 can be used to transmit acoustic signals 620 into a region of interest. For imaging purposes, the acoustic probe 601 can be used as a traditional acoustic probe to detect reflections of the acoustic signals 620. These images can be augmented by additional information obtained by one or more fiber optic sensors. A fiber optic sensor 612 of a sensor fiber 602 can correspond to any of the fiber end optical sensor structures discussed herein and can receive acoustic signals 622. The acoustic signals 622 can be produced by reflections, scattering, and / or tissue harmonics. As shown in Figure 6E , the acoustic signals 622 are generated from a point 621 within the region of interest. The fiber optic sensor 612 can be configured to receive acoustic signals 622 from any direction, as discussed herein. A sensor fiber 603 can be configured to act as a polarization-based optical sensor, as discussed herein, and can receive acoustic signals 622 from a direction that is lateral to the axis of the sensor fiber 603. As used herein, “lateral” refers to all directions that are not parallel to the axis of the sensor fiber 603. As shown in Figure 6EAs shown, acoustic signals 622 can be received by sensor fiber 602 from any direction at any exposed portion along its length, as discussed with respect to Figure 6D As discussed with respect to Figure 6C As discussed with respect to Figure 6C As shown, the polarization of sensor fiber 602 can be selected or adjusted to accommodate the expected or desired radial angle of incidence of acoustic signals 622. Figure 6E Further shown is sensor fiber 604, which can be curved within the imaged region of interest. Similar to sensor fiber 603, sensor fiber 604 can detect incident acoustic signals 622 that are lateral to, substantially lateral to, the axis of sensor fiber 604, or from any direction. When sensor fiber 604 is disposed within a medium (e.g., disposed within a human body during a medical procedure), detecting lateral signals at multiple points along the length of sensor fiber 604 can enhance the ability to track and / or locate sensor fiber 604. For example, as shown in (b) of Figure 6E As shown in (b) of Figure 6E As shown in (c) of

[0102] Figure 6F and 6G An optical sensor system for use with a fiber optic sensor according to embodiments herein is shown. Figure 6G An optical resonator-based optical sensor configured for use with a multicore fiber is shown according to embodiments herein. Figure 6F Optical sensor system 100D is configured for use with optical resonator-based multicore fiber sensor 101D, as shown in Figure 6G In other embodiments, other optical sensors discussed herein can be employed in multicore fiber-based systems, including, for example, interferometer-based sensors.

[0103] The optical fiber sensor 101D can include an optical fiber end sensor having an optical resonator-based acoustic sensor, as described herein. The optical fiber sensor 101D can include a sensor optical fiber 301D having an optical resonator-based optical fiber end sensor structure 321D disposed at an end thereof, e.g., at an end of an optical waveguide 311D. In addition to what is mentioned, the sensor optical fiber 301D can include features and structures consistent with those of the sensor optical fibers 301 and 351. The optical resonator-based optical fiber end sensor structure 321D is coupled to an end of the optical waveguide 311D. The optical resonator-based optical fiber end sensor structure 321D can include an optical resonator sensor 322D, also including additional structures and components configured to facilitate the functioning of the optical resonator sensor 322D, as described below. In Figure 6G The optical resonator-based optical fiber end sensor 322D, schematically shown in FIG. 31, can be waveguide-coupled such that it is configured to receive an initial optical signal 111 (e.g., light) supplied to it via a first optical core 313D of the sensor optical fiber 301D, and provide a returned optical signal 112 back along a second optical core 312D of the sensor optical fiber 301D. The second optical signal can correspond to and represent an acoustic signal incident to the optical resonator-based optical fiber end sensor structure 321D. The incident acoustic signal can cause physical deformation and / or material property alteration of the optical resonator-based optical fiber end sensor structure 321D. Thus, the optical signal provided by the optical resonator-based optical fiber end sensor structure 321D along the second optical core 312D can be altered by, affected by, or otherwise indicative of or representative of the acoustic signal, and thus can be used to characterize the incident acoustic signal.

[0104] The optical resonator-based optical fiber end sensor structure 321D can include an acoustically responsive polymer portion 317D, including parylene or other suitable polymer sensitive to acoustic signals. The acoustic impedance of the polymer portion 317D can be selected to match the acoustic impedance of the cladding structure or cladding structure 314D of the sensor optical fiber 301D (e.g., within 1%, 5%, 10%, or 20% difference), to enhance the sensitivity of the optical resonator-based optical fiber end sensor structure 321D, as described above.

[0105] The optical fiber end sensor structure 321D is disposed at the end of the optical waveguide 311D and can thus be referred to as an optical fiber end sensor. The cladding or cladding structure 314D can have a first diameter and the optical fiber end sensor structure 321D can have a second diameter. The first diameter and the second diameter can be substantially the same and / or can have a ratio in the range between 1.05 and 0.95, a ratio in the range between 1.02 and 0.98, or a ratio in the range between 1.01 and 0.99. As discussed above, the sensor optical fiber 301D can be compact, e.g., where the first diameter and / or the second diameter is less than 200 microns, less than 175 microns, less than 150 microns, less than 130 microns, less than 100 microns, or less than 85 microns. If the fiber diameter is extremely small, increasing the diameter of the fiber sensor end can further enhance acoustic sensitivity.

[0106] The optical sensor system 100D is configured for use with a resonator-based optical fiber sensor 101D. The optical sensor system 100D can include a light source 104, e.g., a laser, a light receiving device 103, e.g., a photodetector, one or more optical waveguides 105, and a multi-core fiber fan-out coupler 109. In operation, the light source 104 supplies an initial light signal 111 to the optical fiber sensor 101D via the optical waveguide 105 and through the multi-core fiber fan-out coupler 109. The supplied initial light signal 111 travels via the first optical core 313D to the optical resonator-based fiber end sensor structure 321D, where it can be affected by an incident acoustic signal, and then back by the second optical core 312D as a returned light signal 112. The returned light signal 112 travels via the optical waveguide 105 through the fan-out coupler 109 to be received at the light receiving device 103. As discussed above, the acoustic signal incident on the optical fiber sensor 101D alters the optical properties of the optical fiber sensor 101D, including the physical structure as well as the optical material properties. Such optical property alterations can be measured from the returned light signal 112 to measure the properties and characteristics of the incident acoustic signal. In Figure 6F In embodiments, e.g., it is not necessary to provide the initial light signal 111 to the light receiving device 103 to measure the optical property alterations, as the parameters of the initial light signal 111 are known by the system.

[0107] The multicore fiber fan-out coupler 109 is used to couple the single-core optical waveguide 105 to a multicore optical waveguide 311D. Thus, the initial optical signal 111 and the returned optical signal 112 can travel in separate optical cores in the multicore optical waveguide 311D. In contrast to the optical sensor system 100B, the use of the multicore fiber fan-out coupler 109 and the multicore optical waveguide 311D in the optical sensor system 100D can not require an optical circulator. Such a design can be advantageous for some reasons. For example, the multicore fiber fan-out coupler 109 of the optical sensor system 100D can be smaller, lighter, and / or cheaper than an optical circulator, which can enable greater flexibility in incorporating the fiber optic sensor 101D into a device or apparatus. In embodiments, other suitable configurations of optical couplers for coupling single-core optical fibers to multicore optical fibers can be substituted for the multicore fiber fan-out coupler 109.

[0108] Figure 6H and 6I An optical sensor system for use with a fiber optic sensor according to embodiments herein is shown. Figure 6I An optical resonator-based optical sensor configured for use with a pair of single-core optical fibers according to embodiments herein is shown. Figure 6H The optical sensor system 100E is configured for use with an optical resonator-based dual-fiber sensor 101E, as shown in Figure 6I In other embodiments, other optical sensors discussed herein can be employed in dual-fiber-based systems, including, for example, interferometer-based sensors.

[0109] The fiber optic sensor 101E can include a fiber end sensor having an optical resonator-based acoustic sensor, as described herein. The fiber optic sensor 101E can include a sensor optical fiber 301E having an optical resonator-based fiber end sensor structure 321D disposed at an end thereof. In addition to what is mentioned, the sensor optical fiber 301E can include features and structures consistent with those of the sensor optical fibers 301 and 351.

[0110] The fiber optic sensor 101E can include a dual-fiber structure. The fiber optic sensor 101E can include a first optical waveguide 311E having a first optical fiber optical core 313E and a second optical waveguide 315E having a second optical fiber optical core 312E. Each of the first optical waveguide 311E and the second optical waveguide 315E can be a separate optical fiber and can each have a separate cladding structure 314E. The first optical waveguide 311E and the second optical waveguide 315E can be coupled together. For example, the first optical waveguide 311E and the second optical waveguide 315E can be coupled via a glue or other adhesive.

[0111] The optical resonator-based fiber end sensor structure 321E is coupled to the end of both the first optical waveguide 311E and the second optical waveguide 315E. The optical resonator-based fiber end sensor structure 321E can include an optical resonator sensor 322E, as well as additional structures and components configured to facilitate the functioning of the optical resonator sensor 322E, as described below. In Figure 6I The optical resonator-based fiber end sensor 322E, schematically illustrated in FIG. 3B, can be waveguide-coupled such that it is configured to receive an initial optical signal 111 (e.g., light) supplied to it via the first optical core 313E of the first optical waveguide 311E, and provide a returned optical signal 112 back along the second optical core 312E of the second optical waveguide 315E. The returned optical signal 112 can correspond to and represent an acoustic signal incident to the optical resonator-based fiber end sensor structure 321E. The incident acoustic signal can cause physical deformation and / or material property alteration of the optical resonator-based fiber end sensor structure 321E. Thus, the optical signal provided by the optical resonator-based fiber end sensor structure 321E along the second optical core 312E can be altered by, affected by, or otherwise indicative of or representative of the acoustic signal, and thus can be used to characterize the incident acoustic signal. Figure 6H In embodiments, for example, it is not necessary to provide the initial optical signal 111 to the light receiving device 103 to measure the optical property alteration, as the parameters of the initial optical signal 111 are known to the system.

[0112] The optical resonator-based fiber end sensor structure 321E can include an acoustically responsive polymer portion 317E, including parylene or other suitable polymer that is sensitive to acoustic signals. The acoustic impedance of the polymer portion 317E can be selected to match the acoustic impedance of the cladding structure (or cladding structure) of the sensor fiber 301E (e.g., within 1%, 5%, 10%, or 20% difference) to enhance the sensitivity of the optical resonator-based fiber end sensor structure 321E, as described above.

[0113] The optical sensor system 100E is configured for use with a resonator-based fiber optic sensor 101E. The optical sensor system 100D can include a light source 104, e.g., a laser, a light receiving device 103, e.g., a photodetector, one or more optical waveguides 105. The one or more optical waveguides 105 can be structurally bound to one another to form a first optical waveguide 311E and a second optical waveguide 315E of a sensor fiber 301E, and can be separated to couple with the light source 104 and the light receiving device 103. In embodiments, a coupler or another device can be used to facilitate this joining. In operation, the light source 104 supplies an initial light signal 111 to the fiber optic sensor 101E via the optical waveguides 105. The supplied initial light signal 111 travels via the first optical waveguide 311E to the optical resonator-based fiber end sensor structure 321E, where it can be affected by an incident acoustic signal, and then back by the second optical waveguide 315E as a returned light signal 112. The returned light signal 112 travels via the optical waveguides 105 to be received at the light receiving device 103. As discussed above, the acoustic signal incident on the fiber optic sensor 101E alters the optical properties of the fiber optic sensor 101E, including the physical structure as well as the optical material properties. Such optical property alterations can be measured from the returned light signal 112.

[0114] The dual fiber design of the sensor fiber 301E eliminates the need for a circulator or multi-core fan-out coupler. Such a design can be advantageous for several reasons. For example, eliminating the multi-core fiber fan-out coupler and optical circulator can provide a smaller, lighter, and / or less expensive system, which can enable greater flexibility when incorporating the fiber optic sensor 101E into a device or apparatus.

[0115] Figures 7A-7D Examples of manufacturing techniques that can be used to shape or machine the end of an optical waveguide are provided. Figure 7A Methods of CO2 laser machining the end of an optical waveguide to achieve a concave proximal reflective surface, e.g., to accommodate a proximal reflective surface that is concave with respect to the optical cavity, are shown. Figure 7B Methods of wet etching the end of an optical waveguide to achieve a concave proximal reflective surface, e.g., to accommodate a proximal reflective surface that is concave with respect to the optical cavity, are shown. Figure 7C Methods of mechanical polishing the end of an optical waveguide to achieve a concave proximal reflective surface, e.g., to accommodate a proximal reflective surface that is concave with respect to the optical cavity, are shown. Figure 7D Methods of CO2 laser machining the end of an optical waveguide to achieve a concave proximal reflective surface, e.g., to accommodate a proximal reflective surface that is concave with respect to the optical cavity, are shown.

[0116] Figures 8A-8D Examples of manufacturing techniques that can be used to manufacture an optical resonator structure at the end of an optical waveguide are provided. Figure 8AA micro-molding process is shown that can be used to form optical resonator structures. Figure 8B A dip coating process is shown that can be used to form optical resonator structures. Figure 8C A conformal coating process is shown that can be used to form optical resonator structures. Figure 8D A dip coating process is shown that can be used to form optical resonator structures.

[0117] Figure 9A A method of applying thermal tuning to a sensor fiber is shown. An interferometer-based fiber optic sensor (or other optical sensor structure according to embodiments of the invention) can benefit from a wavelength tuning mechanism to maintain the interferometer-based fiber optic sensor at an optimal operating point. The optimal operating point can be based on the resonance of the optical sensor structure. In embodiments, the resonance wavelength of the optical sensor structure and the operating wavelength of a laser providing the optical signal can be selected, adjusted, or determined together to optimize or maximize the optical reading. The resonance wavelength of the optical sensor structure and the operating wavelength of the laser can be selected, adjusted, or determined such that the operating wavelength of the laser coincides with a slope of a resonance peak of the optical sensor structure. The particular location on the slope of the resonance peak can vary depending on the sensor design and application-specific requirements. The particular operating location on the slope of the resonance peak affects the dynamic range and sensitivity of the optical sensor structure. In embodiments, the operating location (e.g., wavelength) can be selected so as to have a response amplitude in the range of 10%-90% of the resonance depth, in the range of 10%-30% of the resonance depth, in the range of 30%-50% of the resonance depth, in the range of 50%-70% of the resonance depth, or in the range of 70%-90% of the resonance depth. Thus, wavelength tuning according to embodiments of the invention can involve tuning the operating wavelength of the laser or the resonance wavelength of the optical sensor to achieve this.

[0118] The wavelength tuning mechanism according to embodiments of the invention can involve, for example, heating or tuning the laser or an external tuner configured for tuning by applying mechanical stress and / or electro-thermal heating. While a tunable laser in the backend system can provide tunability, separate tunability at the sensing frontend (local tuning) is also desirable as it can enable (1) cheaper lasers that do not have wavelength tunability and (2) a scalable sensor array that shares the laser. Figure 9AOne method of local tuning using photothermal tuning is shown, which does not require additional cabling. In embodiments, light from the work laser and a heating laser (at different wavelengths) are guided together by an optical fiber. The work laser wavelength can be chosen to optimize sensing performance, and at least one structure on the end of the optical fiber (e.g., optical resonator structure 321, a portion of cladding structure 314, etc.) is absorptive at the heating wavelength. By tuning the power of the heating laser, the local temperature in the optical resonator structure 321 changes, and thus the temperature sensitive optical transmissivity of the fiber optic sensor is tuned to better match the wavelength of the work laser. Thus, the heating laser is operated to adjust the temperature of the optical resonator structure 321 according to the wavelength of the work laser. The heating laser can be continuous wave or pulsed. In embodiments, the sensor fiber 301C can have a dual cladding structure. Any of the sensor fibers 301 / 301A / 301B can incorporate the features of the sensor fiber 301C. The sensor fiber 301C can include an inner cladding structure 313A and an outer cladding structure 313B. The outer cladding structure 313B can be introduced if the heating wavelength is longer than the cutoff wavelength of the core, which is optimized for operation of light transmission.

[0119] In Figure 9B In another method of local tuning shown, an external tuner 902 can be provided to replace the heating laser for tuning the sensor transmission by applying, for example, mechanical stress or electro-thermal heating. Figure 9B A sensor fiber 301, for example with an optical resonator structure 321, is shown. Any suitable sensor fiber and fiber optic sensor can be used with the external tuner 902. The external tuner 902 can include, for example, a piezoelectric and / or electro-thermal element outside of the optical cavity, which can be configured to apply pressure (i.e., squeeze) or heat to the optical resonator structure 321. This can require additional cabling, wires, traces, and / or micro-heater printed flex circuits along the length of the fiber optic sensor to enable the external tuner. The additional structure does not affect the optical properties of the sensor as long as the sensor optical path in the optical resonator structure 321 (within the dashed box 368) is not interrupted.

[0120] In another example, the optical resonator structure 361 can have an operating wavelength that is tuned to more closely align with the wavelength of a light source (e.g., a source laser). When multiple fiber optic sensors are arranged in an array, the ability to individually calibrate and fine tune each fiber optic sensor within the array provides the potential to drive and synchronize the operation of each sensor in the array. This synchronization can also enable a user to drive multiple (>2) fiber optic sensors with one source laser and simultaneously capture signals from multiple sensors. Such a feature is advantageous when constructing a sensor array for imaging. In this process, a feedback loop can be employed to monitor and adjust the heat source or stress to fine tune the operating wavelength of the sensor to ensure its alignment with the source laser. The synchronized operation of a sensor array guarantees robust data interpretation by simultaneously capturing multiple data points or synergistically analyzing complex imaging patterns.

[0121] Figure 10 Embodiments of a sensor optical fiber comprising a multicore optical waveguide are shown. The sensor optical fiber 801 can comprise any or all of the features of the sensor optical fibers 301 and 351, as described above. The sensor optical fiber 801 can comprise an optical waveguide 811 and an optical resonator structure 321. The optical waveguide 811 comprises a plurality of cores 312, e.g., 2, 3, 4, 5, 6, 7, 8, 9, etc., within the cladding structure 313.

[0122] Figure 11A and Figure 11B Comparisons between sensor optical fibers arranged with forward-facing optical sensors and side-facing optical sensors are shown. When incorporating a sensor with a device, it is an important consideration to consider the environment in which the sensor will be used and the direction in which the acoustic beam is transmitted. For example, some use cases for the optical sensors disclosed herein can benefit from a forward-facing arrangement, while other use cases can benefit from a side-facing arrangement.

[0123] Figure 11A A sensor optical fiber 351 with a Fabry-Perot resonator shown as an optical resonator as part of an optical resonator structure is shown in accordance with Figure 3A The sensor optical fiber 351 with a Fabry-Perot resonator shown as an optical resonator as part of an optical resonator structure is shown in accordance with

[0124] Figure 11BA sensor optical fiber 1001 is shown having a Fabry-Perot resonator serving as an optical resonator as part of an optical resonator structure 1021 arranged to laterally capture incident acoustic signals. The sensor optical fiber 1001 can include all the features of the sensor optical fibers 301, 351, 701, and 801 (even if not shown). The sensor optical fiber 1001 can include one or more cores 1012, one or more cladding structures 1013, a cladding structure 1014, and an optical resonator structure 1021. The optical resonator structure 1021 can include a Fabry-Perot resonator, as shown in Figure 11B FIG. 6B, and / or any other type of optical resonator discussed herein. The optical resonator structure 1021 can include a distal reflective surface 1064 and a proximal reflective surface 1063 arranged on either side of an optical cavity 1065. In embodiments, the optical resonator structure 1021 is configured in a lateral configuration. In the lateral configuration, the acoustically responsive face or surface of the optical resonator structure 1021 configured to receive and detect acoustic signals (in the optical resonator 362, this face can be the distal reflective surface 364 or the proximal reflective surface) is arranged such that the acoustically responsive face or surface is oriented in the same direction as the direction in which the sensor optical fiber 351 extends. The sensor optical fiber 351 and the acoustically responsive surface or face can have an axis that is substantially perpendicular to the axis of the sensor optical fiber 1001. In other embodiments, the angle between the axis of the acoustically responsive surface or face and the axis of the sensor optical fiber 1001 can be between 0° and 90° depending on the desired angle of acoustic sensitivity.

[0125] Figure 12 Embodiments of sensor optical fibers providing the ability for acoustic detection from behind the sensor distal end, or proximal detection ability, are shown in accordance with embodiments of the present application. The sensor optical fibers described herein, such as the sensor optical fiber 301, the sensor optical fiber 351, the sensor optical fiber 701, the sensor optical fiber 801, can be provided with improved proximal detection ability. Figure 12A sensor optical fiber 351 is shown having an optical resonator structure 361 with a proximal reflective surface 363 and a distal reflective surface 364 arranged to share an axis with an optical waveguide 371. Both the proximal reflective surface 363 and the distal reflective surface 364 function as acoustic response surfaces. To improve the look-back capability, the cladding structure 353 can include a material selected to minimize acoustic impedance mismatch with the intended medium in which the sensor optical fiber 351 will be used. By minimizing the acoustic impedance mismatch, the critical angle of the boundary between the sensor optical fiber 351 and the medium in which it is disposed increases, enabling the optical resonator structure 361 to receive a greater angular range of acoustic signals. For example, a sensor optical fiber 351 intended for use within a human body can include a cladding structure 353 comprising a polymer selected to optimize detection sensitivity by minimizing any acoustic impedance mismatch. In embodiments, the cladding structure 353 can be selected to have at least one of a Young’s modulus (E) less than that of the core 352, an optoelastic coefficient greater than that of the core 352, and an index of refraction (n) less than that of the core 352. In embodiments, the cladding structure 353 can include benzocyclobutene (BCB) or polydimethylsiloxane (PDMS), each of which has a small Young’s modulus (E), a high optoelastic coefficient, and a small index of refraction (n). Reducing the acoustic impedance mismatch can increase the acoustic signals that pass through the cladding structure 353 and impinge on the proximal reflective surface 363. A smaller Young’s modulus can increase the stress-related deformation of the cladding structure 353, which can increase sensitivity to incident acoustic signals. A higher optoelastic coefficient can also result in greater sensitivity to acoustic signals, as the optical properties of such materials exhibit a larger strain-related change. Other suitable materials for the cladding structure 353 can include ultrasonic enhancing materials such as polyvinylidene fluoride, parylene, polystyrene, and the like.

[0126] Figure 13 An embodiment of a sensor optical fiber providing improved look-back acoustic detection capability is shown in accordance with an embodiment of the present application. The sensor optical fibers described herein, such as sensor optical fiber 301, sensor optical fiber 351, sensor optical fiber 701, sensor optical fiber 801, can be provided with improved look-back detection capability, as shown in Figure 13 Figure 13 ​A sensor optical fiber 1251 is shown having an optical resonator structure 1261. The optical resonator structure 1261 includes an optical resonator defined by a proximal reflective surface 363 and a distal reflective surface 364, both surfaces arranged to share an axis with the optical waveguide 371 (e.g., the optical resonator is disposed in the same manner as the forward configuration described above). An optical cavity 365 is arranged between the proximal reflective surface 363 and the distal reflective surface 364. Both the proximal reflective surface 363 and the distal reflective surface 364 function as acoustic response surfaces. The optical resonator structure 1261 can further include any features of the optical resonators and optical resonator structures discussed herein in any suitable combination. To increase rearview capability, the optical resonator structure 1261 can include a distal portion of the optical waveguide 371 that is specifically configured to increase acoustic sensitivity at the proximal reflective surface 363. The optical resonator structure 1261 can include a cladding structure of the distal end of the optical waveguide 371, which can include a proximal cladding structure portion 353A and a distal cladding structure portion 353B. The distal cladding structure portion 353B is disposed closer to the optical resonator. The distal cladding structure portion 353B can be selected to have a material that reduces or minimizes acoustic impedance mismatch with the intended medium in which the sensor optical fiber 1251 will be used. For example, the distal cladding structure 353B can include a polymer, as discussed above. In embodiments, the distal cladding structure 353B can include benzocyclobutene (BCB) or polydimethylsiloxane (PDMS), each of which has a small Young’s modulus (E), a high photoelastic coefficient, and a small refractive index (n). The distal cladding structure 353B can have a length dimension sufficient to allow acoustic signals from various rearview angles to reach the proximal reflective surface 363 of the optical resonator. The proximal cladding structure portion 353A can include any suitable material for an optical waveguide, including, for example, silica.

[0127] Figure 14 Directional range of optical resonator structures according to embodiments of the application is shown. As discussed above, the optical resonator structure 1261 can be configured to detect acoustic signals over a wide range of incidence. In embodiments, the optical resonator structure 1261 can be configured to detect acoustic signals across a directional range of at least 180 degrees, at least 270 degrees, at least 300 degrees, or at least 330 degrees. In some embodiments, the optical resonator structure 1261 can be configured to detect acoustic signals in an omnidirectional manner, e.g., across a range of 360 degrees. Figure 14A side view of an optical resonator structure 361 according to an embodiment of the application is shown. The circle 1305 represents a 360 range around the optical resonator structure 1261 and has an axis 1306 that is substantially perpendicular to an axis 1307 of the optical resonator structure 1261. The circle 1305 represents a 360 range from which acoustic signals can be incident on the optical resonator structure 1261. The optical resonator structure 1261 can be configured to detect acoustic signals in an acoustic response portion 1303 of the circle 1305 and can have reduced sensitivity or detection capability in a reduced acoustic sensitivity portion that includes a lateral portion 1301 and a core portion 1302. In the lateral portion 1301, incident acoustic signals can be less detectable due to the oblique angle of incidence onto the reflective surface of the optical resonator. In the core portion 1302, acoustic signals can be less detectable due to the blockage from the core of the optical waveguide. The sum of the ranges of the acoustic response portion 1303 can represent the range in which the optical resonator structure 1261 detects acoustic signals. Different arrangements of optical resonator structures (e.g., lateral optical resonator structure 1021) can have differently arranged acoustic response portions 1303 and reduced acoustic sensitivity portions.

[0128] In embodiments, the optical resonator structure 361 is radially symmetric. Thus, the acoustic response range defined by the two-dimensional circle 1305 can be rotated about the axis 1307 to define a three-dimensional acoustic response range of the optical resonator structure 1261. It should be appreciated that further influences on the acoustic response range can be caused by structures around the optical resonator structure 1261, including, for example, the medical device distal end 231.

[0129] Figure 15An optical resonator structure including a Bragg grating within an optical fiber is shown according to embodiments of the present application. An optical resonator structure 1421 can be provided, as well as any of the sensor optical fibers discussed herein. The optical resonator structure 1421 includes a distal reflective surface 1464, an elongated optical cavity 1465 including a distal cladding structure 1453A and a proximal cladding structure 1453B, and a Bragg grating 1470. As in the optical resonator structure 1261, the distal cladding structure 1453A can include a polymer (e.g., benzocyclobutene (BCB) or polydimethylsiloxane (PDMS)), while the proximal cladding structure 1453B can include, for example, silica glass. The length of the proximal cladding structure 1453B can be greater than the distal cladding structure 1453A, for example, more than 2x, more than 5x, more than 10x, etc. In embodiments, the proximal cladding structure 1453B can be approximately 10 times the length of the distal cladding structure 1453A, for example, the length of the distal cladding structure can be approximately 10 microns, while the length of the proximal cladding structure is approximately 100 microns. In embodiments, the proximal cladding structure 1453B can have a Young’s modulus in the range of 60-80 GPa, while the distal cladding structure 1453A has a Young’s modulus in the range of 0.8-1.2 GPa. In embodiments, the proximal cladding structure 1453B can have photoelastic coefficients C1 = -6*10 -13 1 / Pa and C2 = -4.2*10 -12 1 / Pa, while the distal cladding structure 1453A has photoelastic coefficients C1 = -4.8*10 -11 1 / Pa and C2 = -2.9*10 -111 / Pa. Although these numbers are provided, such photoelastic coefficients are relative numbers that depend on the material chosen. For the distal end, materials with larger C1 or C2 values are preferred to optimize acoustic sensitivity. The Bragg grating 1470 is integrated within the structure of the core 1412 and defines a change in the refractive index of the core 1412, thereby creating a structure that can reflect light of a specific wavelength. The optical resonator structure 1421 operates as a hybrid Fabry-Perot resonator. In this configuration, the distal cladding structure 1453A (e.g., a polymer structure) provides the primary response to acoustic signals. The distal cladding structure 1453A can be directly fabricated via two-photon polymerization (TPP) 3D printing on top of an optical fiber with a fiber-in-fiber Bragg grating reflector. One advantage of the hybrid optical resonator structure 1421 is the combination of wide bandwidth and high sensitivity. In some designs, there is a tradeoff between wide bandwidth and high sensitivity. In this hybrid configuration, the total length of the elongated optical cavity 1465 is longer because it is the sum of the distal cladding structure 1453A and the proximal cladding structure 1453B. For longer cavity lengths, the frequency bandwidth response can be narrower in conventional designs. However, in this hybrid configuration, the effective sensor thickness is still very small since the primary response of the FPI sensor comes from the polymer region, and a wideband response is provided.

[0130] Figure 16 Steps of a method of generating position and imaging information by a fiber-optic based optical sensor are shown. Further details can be found in co-pending U.S. Provisional Application No. 63 / 522,994, titled “Transponder Tracking and Ultrasound Image Enhancement,” filed on June 23, 2023, and U.S. Patent Application titled “Transponder Tracking and Ultrasound Image Enhancement,” having attorney docket number 109835-1394978, and filed concurrently on October 23, 2023.

[0131] The method 2000 can include block 2010, in which a transponder, such as the transponder 102, transmits acoustic pulses into a medium. The transponder can transmit these pulses using various known methods or as described above. Figure 2 The acoustic probe 245, shown, transmits acoustic pulses into the medium. The transponder can transmit these pulses using various known methods or as described above.

[0132] At block 2020, the fiber-optic sensor 101 receives the ultrasound pulses and / or scattered signals or tissue harmonics transmitted from the probe 245. Then, the fiber-optic sensor 101 converts the ultrasound pulses, scattered signals, and / or tissue harmonics into signals that are subsequently transmitted to the processing unit 209.

[0133] At block 2030, processing unit 209 determines the position of the fiber optic sensor at least in part based on signals received from probe 245. For example, processing unit 209 may utilize triangulation or coherent image formation to determine the position of the distal end of the medical device based on multiple signals received from probe 100 and fiber optic sensor 101.

[0134] At box 2040, processing unit 209 and image reconstruction unit 206 generate an ultrasound image based on the signal returned to probe 245 and / or the scattered signal and tissue harmonics sensed by the fiber optic sensor. The ultrasound image can be transmitted to a display and displayed thereon.

[0135] At block 2050, the processing system modifies the ultrasound image based on ultrasound pulses received from fiber optic sensor 101. In an embodiment, the processing system may also generate and display ultrasound images based on ultrasound pulses received by the fiber optic sensor, without requiring information from ultrasound pulses received by probe 245.

[0136] At frame 2060, the processing system 200 overlays the position of the fiber optic sensor 101 onto the ultrasound image. Therefore, when viewed by a user, such as an ultrasound technician, physician, other medical professional, or patient, the fiber optic sensor 101 at the distal end of the medical device is displayed on the same screen as the ultrasound image, indicating the position of the fiber optic sensor 101 at the distal end of the medical device within the medium.

[0137] Figure 17A and 17B A needle configured with sensor fibers according to embodiments herein is shown. Needle 1500A may be an example of a distal end 231 of a medical device and may include one or more sensor fibers 1501 integrated therewith. Sensor fibers 1501 may include any of the sensor fibers described herein (having any of the optical resonator structures), and / or may include any combination of features of the sensor fibers described herein. Needle 1500A may be any type of needle having any suitable size or function. Needle 1500A includes a needle body 1505 having a needle shaft portion 1510 and a needle tip portion 1511. The needle tip portion 1511 may be characterized by a needle polishing angle 1523. Furthermore, needle 1500A includes at least one sensor channel 1512 extending over the needle body 1505 to at least a portion of the length of the needle shaft portion 1510 and the needle tip portion 1511.

[0138] In embodiments, the sensor channel 1512 can include a groove, recess, or channel in the needle body 1505. The sensor channel 1512 can be sized and configured to receive a sensor optical fiber 1501 according to embodiments of the application. For example, in embodiments, the sensor channel 1512 can have a width of approximately 125 to 250 microns to accommodate a sensor optical fiber 1501 having a diameter of 80 microns. The needle 1500A can include a plurality of sensor channels 1512 to accommodate a plurality of sensor optical fibers 1501. For example, the needle 1500A can include 2, 3, 4, or more sensor channels 1512 for accommodating a plurality of sensor optical fibers 1501 arranged around the circumference of the needle 1500A. The sensor optical fiber 1501 is arranged within the sensor channel 1512 such that the distal end of the load optical resonator structure is positioned at or adjacent the distal end. The sensor channel 1512 can be configured with a depth such that the sensor optical fiber 1501 does not extend beyond the outer surface of the needle body 1505.

[0139] In other embodiments, the sensor channel can be created by adding material to the outer surface to form the channel, for example as a guide. In an example, material can be layered on the outside of the needle to form the channel 1512 as a continuous or intermittent structure as a protrusion. In another example, an adhesive material or tape can be wrapped in a spiral configuration with spaces within the spiral to form the sensor channel, or can be selectively positioned along the needle length to form the sensor channel and guide the sensor optical fiber along the length. In yet another example, an extruded needle can include a tubular sensor channel in the form of a lumen running therethrough.

[0140] The sensor channel 1512 allows the sensor optical fiber 1501 to be located within a protected area of the needle body 1505. This serves to protect the sensor optical fiber 1501 and create a smooth needle surface for insertion. The sensor channel 1512 can be disposed on the outer surface of the needle body 1505 (as shown) or on the inner surface of the needle body 1505. Figure 17B

[0141] ​The sensor optical fiber 1501 can be secured to the needle body 1505. In embodiments, the sensor optical fiber 1501 can be secured within the sensor channel 1512 by a potting compound, such as Norland-65 cement, Norland 81 cement, MY-132A polymer, MY-133, BIO-133, DC-133, or any other suitable potting compound. The potting compound can be selected based on its acoustic and mechanical properties, such as speed of sound, acoustic impedance, thermal conductivity, water resistance, etc. In addition to mechanical securing and protection of the sensor, the potting compound can also provide a modification of the acoustic impedance match to the surrounding medium. The potting compound can be used on all or a portion of the sensor channel 1512. In embodiments, the sensor optical fiber 1501 can be secured within the sensor channel 1512 by a sheath 1520. The sheath 1520 is configured to wrap around the needle body 1505. The sheath 1520 can mechanically secure the sensor optical fiber 1501 to the needle body 1505. The sheath can wrap around the needle with the optical fiber inside a groove such that the optical fiber can freely float within the groove. This can allow the needle to bend / have flexibility. In embodiments, the sensor optical fiber 1501 can be secured at least partially by both the sheath 1520 and the potting compound. Such an arrangement can allow for relative movement between the sensor optical fiber 1501 and the needle body 1505, providing potential strain relief in the event of needle bending. The needle 1500A can be made of any suitable material, including, for example, medical grade materials, including metals such as stainless steel or polymers such as PEEK (polyether ketone). In embodiments, the needle 1500 can be manufactured by additive manufacturing techniques, such as 3D printing, injection molding, or extrusion.

[0142] In Figure 18A and 18B Another embodiment of a needle with a fiber optic based optical sensor is shown. The needle 1500B can further include one or more windows 1513. The windows 1513 are openings in the needle body 1505 disposed at the end of the sensor channel 1512. The needle 1500B can include multiple sensor channels 1512 and a corresponding multiple windows 1513 to accommodate multiple sensor optical fibers 1501. The sensor optical fibers 1501 can be arranged within the sensor channel 1512 such that the distal end carrying the optical sensor extends into the window 1513. In this embodiment, the distal end of the sensor optical fiber 1501 can be secured within the window 1513 by a potting compound, while the proximal portion of the sensor optical fiber 1501 can be secured to the needle body 1505 by a sheath 1520. This will allow for relative movement between the sensor optical fiber 1501 and the needle body, providing strain relief in the event of needle bending.

[0143] The window 1513 allows the acoustic signal to reach the fiber optic sensor of the sensor fiber 1501 without being blocked by the needle body 1505. The edges of the window 1513 can create a boundary for acoustic signal diffraction and allow the acoustic signal to bend and propagate around the window edges to reach the fiber optic sensor at the end of the sensor fiber 1501. The diffraction effect has the function of increasing the circular range of acoustic signal detection of the sensor fiber 1501. In addition, the edges of the channel on the needle surface can also have a diffraction effect that helps to detect the needle axis.

[0144] In embodiments, the optical ultrasound sensor according to embodiments of the present application can be integrated with a medical device (e.g., at the distal end 231 of the medical device) and can work with an ultrasound source (array) configured at an ex vivo location to provide location information of the distal end 231 of the medical device and / or provide real-time acoustic monitoring at the target / anatomical region of the procedure. In different application scenarios, the direction of the incoming acoustic signal can be roughly classified into two categories, namely (1) lateral fire; and (2) axial fire, as shown in Figure 18C and 18D .

[0145] Figure 18C and 18D show acoustic signals incident to the sensor fiber disposed within the needle window 1513. For clarity, the sensor fiber is not shown in these figures. Figure 18C shows a lateral acoustic signal 1600, while Figure 18D shows an axial acoustic signal.

[0146] Figure 18C The lateral acoustic signal 1600 of FIG. 16A is a typical case that can occur when using a side-viewing endoscopic ultrasound transducer or an external transducer. The location of the window 1513 close to the needle tip portion 1511 allows the ultrasound field to reach the window (and the fiber end sensor structure located therein) from either side without being blocked by the opposing walls of the needle. The fiber end sensor structure itself can be arranged in a side- or forward-facing manner, and can also be a polarization-based sensor configured to receive side (lateral) signals, depending on the requirements of the application.

[0147] Figure 18D The axial acoustic signal 1601 of FIG. 16B is a typical case that occurs with respect to a forward-viewing endoscopic ultrasound transducer. Due to the smaller footprint of the endoscopic device, the typical angle of incidence can be smaller relative to the needle body. As shown in Figure 18D , when the angle of incidence is smaller than the needle polishing angle 1523 (as shown in Figure 18DAt least a portion of the acoustic signal 1601 can be blocked (shown with thicker cross-hatching) by the needle body when the acoustic signal 1601 is at a low angle (as shown). To address this issue, in an embodiment, an additional window 1513 opposite the sensor window can be included in the needle body 1505 to allow the axial acoustic signal 1601 to pass through and reach the optical resonator structure. In another embodiment, the orientation of the needle 1500A / B can be manipulated to ensure that low angle axial acoustic signals reach from the portion of the needle where the optical resonator structure is not positioned. In another embodiment, the polish angle 1523 can be selected according to the desired angle of acoustic incidence.

[0148] In Figure 19 Another embodiment of a needle with fiber-based optical sensors is shown. Similar to the needles 1500A and 1500B, the needle 1500C includes a needle body 1505 having a needle shaft portion 1510 and a needle tip portion 1511. The needle tip portion 1511 can be characterized by a needle polish angle. In addition, the needle 1500C includes at least one sensor channel 1512 that extends at least a portion of the length of the needle body 1505 for the needle shaft portion 1510 and the needle tip portion 1511. The needle 1500C can include one or more sensor fibers 1501C disposed in one or more of the sensor channels 1512 thereof. The sensor fibers 1501C can be similar to the sensor fibers 301C and thus can include fiber end sensor structures 1521 disposed at the ends thereof and one or more polarization-based sensor structures 1522 disposed along the length thereof. The polarization-based sensor structures 1522 positioned along the length of the needle 1500C can provide enhanced visualization of the needle 1500C as used to track or visualize acoustic signal impingement on the polarization-based sensor structures 1522. Information gathered from the optical signals indicative of the impinging acoustic signals can be employed alone and / or in conjunction with traditional acoustic ultrasound images to provide improved visualization of the needle 1500C. The polarization-based sensor structures 1522 can operate according to the principles discussed above with respect to the polarization-based sensor structures 322C and with respect to the polarization-based sensor structures 422B. Figure 6D and 6E the principles discussed.

[0149] Figure 20A and Figure 20B Another close-up view of the needle 1500 with integrated sensor fibers 1501 is provided. Figure 20A A perspective view from a first side of the needle 1500 where the channels 1512 are located is shown, and Figure 20BA perspective view is shown from a second side of the needle 1500 opposite the first side. The second side of the needle 1500 includes an internal view of the needle 1500 at the tip portion 1511. As shown, the sensor optical fiber 1501 is disposed within a sensor channel 1512 of the needle 1500, extending from the shaft portion 1510 and into the tip portion 1511. A window 1513 is disposed within the tip portion 1511, thereby ensuring that both sides of the window 1513 (and the sensor optical fiber 1501 disposed therein) are exposed to incoming acoustic signals. In addition, Figures 20A-20B A potting compound 1525 is shown securing the sensor optical fiber 1501 within the window 1513.

[0150] In Figure 20C In another embodiment shown, the sensor optical fiber 1501D can be secured to a surface of the needle body 1505D of the needle 1500D that does not have a channel or other optical fiber receiving structure. A suitable polymer or compound 1527 can be used to secure the optical fiber 1501D to the needle 1500D, selected according to acoustic and mechanical properties. The suitable polymer or compound 1527 can be selected according to its acoustic and mechanical properties, such as, for example, speed of sound, acoustic impedance, thermal conductivity, water resistance, etc. In addition to mechanical securing and protection of the sensor on its surface, the suitable polymer or compound 1527 can also provide a modification of acoustic impedance matching to the surrounding medium. Likewise, as Figure 20D shown, a sheath 1520D can be used to secure the sensor optical fiber to the needle body 1505D. The sheath 1520D is configured to wrap around the needle body 1505D. The sheath 1520D can mechanically secure the sensor optical fiber 1501D to the needle body 1505D. The sheath can wrap around the needle in a manner that allows for some movement of the optical fiber within the sheath. This can allow for needle bending / flexibility. In embodiments, the sensor optical fiber 1501D can be secured at least in part by both the sheath 1520D and the polymer or compound 1527. Such an arrangement can allow for relative movement between the sensor optical fiber 1501D and the needle body 1505D, providing potential strain relief in the case of needle bending. This embodiment can further include a window in a manner that other embodiments incorporate a window. A potting compound or polymer can be used to further secure the optical fiber within the window in a manner of the previous embodiments.

[0151] Figure 21A medical device distal end incorporating fiber optic end sensors is shown, according to embodiments of the present application. The medical device distal end 1901 includes a catheter 1902 and a medical tool, such as a needle 1903. The catheter 1902 is configured to carry the needle 1903 to a treatment and / or diagnostic site via a lumen 1904 (e.g., providing access to a lumen through which a needle can be delivered). The catheter 1902 can further include a guidewire lumen 1905 configured to guide the catheter 1902 along a guidewire to the treatment and / or diagnostic site. The needle 1903 is configured to extend from the lumen 1904 of the catheter 1902 upon reaching the treatment and / or diagnostic site (e.g., by an operator, human or robot). In embodiments, the needle 1903 can be configured in a manner similar to the needle 1500, including one or more sensor fibers 1501 disposed thereon or integrated therewith. In embodiments, the catheter 1902 can include one or more sensor fibers disposed thereon or integrated therewith and one or more acoustic transducers. In embodiments, the one or more sensor fibers 1501 can be used to sense, monitor and / or track the position of the needle 1903 (e.g., based on acoustic signals generated by acoustic transducers / probes located outside of the medium in which the catheter 1902 is used). The one or more sensor fibers 1501 and one or more acoustic transducers disposed on the catheter 1902 can be used to generate images, such as through detection of acoustic echoes by the one or more sensor fibers. The one or more acoustic transducers can generate acoustic signals, while the one or more sensor fibers receive echoes or reflections of the acoustic signals based on their interaction with the surrounding medium. The acoustic transducers will also receive reflected or scattered acoustic signals and / or tissue harmonics, which can then be used to create images of the surrounding area that will add tracking information.

[0152] Figure 22 An example use of a fiber optic based optical sensor incorporated into a needle is shown. The illustrated use can incorporate the needle 1500A, 1500B, 1500C, 1500D, or any suitable needle incorporating a fiber optic based optical sensor. As discussed herein, in embodiments of localization / guidance, the fiber optic based optical sensor can receive acoustic signals generated by an external acoustic probe 2245. These acoustic signals can then be used, alone or in combination with reflected acoustic signals captured by the acoustic probe, to determine the position of the needle within a medium 2260 (e.g., a patient's body). Figure 22 As shown, an external acoustic probe 2245 with a needle 1500A / B / C / D incorporating a fiber optic based optical sensor can be employed. As discussed herein, in embodiments of localization / guidance, the fiber optic based optical sensor can receive acoustic signals generated by the external acoustic probe 2245. These acoustic signals can then be used, alone or in combination with reflected acoustic signals captured by the acoustic probe, to determine the position of the needle within a medium 2260 (e.g., a patient's body).

[0153] Figures 23A-23BEmbodiments of fiber-optic based optical sensors incorporated into a catheter- delivered needle are shown. For example, the catheter-delivered needle can be used for a biopsy procedure. The needle 2515 can be delivered to a surgical site via a catheter 2503. The needle 2515 can incorporate a fiber-optic based optical sensor 2501 as described in various embodiments herein. After being delivered to the surgical site via the catheter 2503, the needle 2515 can be extended from a lumen in the catheter 2503 to perform a procedure. The needle 2515 can be monitored, guided, and or positioned by using one or more external acoustic transducers that provide acoustic signals received by the fiber-optic based optical sensor 2501. For example, the acoustic transducers can be associated with an optical sensor system. An optical sensor system, which can be an example of the various optical sensor systems described herein, can provide the processing and signal generation / reception requirements needed to perform the photoacoustic signal sensing methods described herein. In other embodiments, as shown in Figure 23B US Application Publication 20230148869, filed November 18, 2022, entitled “Mixed Ultrasound Transducer Arrays,” and incorporated herein by reference, and US Application Publication US20220350022, filed April 29, 2021, entitled “Modularized Acoustic Probe,” and incorporated herein by reference, disclose various optical sensors that can be used in mixed transducer arrays. The PIC array can be used to detect acoustic signals. Similar to the fiber-optic end sensor discussed herein, the PIC array can be used to detect acoustic signals by measuring or detecting changes in the optical properties of the PIC array caused by acoustic signal incidence. In embodiments, acoustic signal data captured by the fiber-optic based optical sensor 2501, the PIC array, the AEG array, and the external acoustic transducers in different ways can be used by the optical sensor system in any combination to monitor, guide, and position the needle 2515 (and the catheter 2503 that delivers the needle) and to generate images of the medium in which the catheter 2503 is deployed (e.g., the surgical site).

[0154] In other embodiments, the fiber-based optical sensors according to embodiments herein can be used for various additional uses. For example, the fiber-based optical sensors can be used to track a cannula configured with an optical camera and a movable ultrasound transducer for use in vivo during a minimally invasive procedure. In another embodiment, a transcutaneous or percutaneous ultrasound probe can be configured with one or more fiber-based optical sensors according to embodiments of the present disclosure. In another embodiment, a guide wire can be configured with one or more fiber-based optical sensors according to embodiments of the present disclosure.

[0155] In other embodiments, real-time visualization of a device tip containing a fiber-optic sensor can be co-registered with diagnostic ultrasound images, eliminating the need for calibration. This breakthrough enables clinicians to confidently track a device in challenging anatomical regions. A real-time confidence indicator of the device tip intersecting the imaging plane can be provided, with particular consideration to detecting when the device tip exits the imaging plane, which can ensure accurate device tip tracking even during complex procedures. Real-time prospective visualization of the tip trajectory can be provided, providing valuable insights into the predicted path of the device tip and visualization of the device tip trajectory, which can be used to enhance procedure confidence and documentation. Furthermore, a device with the fiber-optic sensors described herein can facilitate displaying anatomical and blood flow images from indwelling sensors co-registered with cross-sectional images, which can enhance diagnostic accuracy and confidence.

[0156] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "includes" and / or "including," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0157] Additional embodiments can include:

[0158] Embodiment 1 is an apparatus comprising: a sensor fiber comprising: an optical waveguide comprising a core and a cladding structure; an optical sensor structure coupled to a first end of the optical waveguide and comprising at least one of an optical resonator, an optical interferometer, a facet microstructure, and a polarization sensitive structure, the optical sensor structure configured for: detecting an acoustic signal, and providing an optical signal corresponding to the acoustic signal to the optical waveguide.

[0159] Example 2 is the apparatus of Example 1, and further includes an encapsulation structure configured with a first portion that surrounds the optical waveguide and a second portion that at least partially surrounds the optical sensor structure.

[0160] Example 3 is the apparatus of any of Examples 1-2, wherein the optical sensor structure is an optical fiber sensor.

[0161] Example 4 is the apparatus of any of Examples 1-3, wherein the optical sensor structure is an optical resonator including a Fabry-Perot resonator, a whispering gallery mode resonator, a microring, a microribbon, a spiral resonator, or a photonic crystal resonator.

[0162] Example 5 is the apparatus of any of Examples 1-3, wherein the optical sensor structure is an optical interferometer including a Mach-Zehnder (MZ) interferometer, a Fabry-Perot interferometer, a phase-shifted coherent interferometer, or a self-mixing interferometer.

[0163] Example 6 is the apparatus of any of Examples 1-3, wherein the optical sensor structure is an optical fiber endface including an acoustically responsive metasurface pattern, an acoustically responsive low-dimensional material, or a plasmonic structure that is patterned to amplify light-matter interactions.

[0164] Example 7 is the apparatus of any of Examples 1-6, wherein the optical sensor structure is configured to cause a change in polarization of transmitted light in response to the acoustic signal.

[0165] Example 8 is the apparatus of any of Examples 1-7, wherein the optical sensor structure is a point sensor or a line sensor.

[0166] Example 9 is the apparatus of any of Examples 1-8, wherein the core or the cladding structure includes a material having at least one of a relatively small Young’s modulus (E) and a relatively high photoelastic coefficient.

[0167] Example 10 is the apparatus of any of Examples 1-9, wherein the cladding structure has a lower refractive index (n) than the core.

[0168] Example 11 is the apparatus of any of Examples 1-10, wherein an acoustic impedance of the encapsulation structure is selected to match an impedance that is within 20% of an optical resonator structure impedance.

[0169] Example 12 is the apparatus of any of Examples 2-11, wherein the encapsulation structure includes a material having a relatively small Young’s modulus (E), a relatively high photoelastic coefficient, and / or a relatively large refractive index (n).

[0170] Example 13 is the apparatus of any of Examples 1-12, wherein an acoustic impedance of the encapsulation structure is selected to match an impedance that is within 20% of an optical resonator structure impedance.

[0171] Example 14 is the apparatus of any of Examples 1-13, further comprising a medical device in which the sensor optical fiber is disposed.

[0172] Example 15 is the apparatus of Example 14, wherein the medical device is one of a needle, an endoscope, a catheter, a cannula, a guide wire, a surgical tool, a diagnostic tool, or a therapeutic tool.

[0173] Example 16 is the apparatus of Example 15, wherein the medical device is a needle including: a shaft portion configured to receive the sensor optical fiber; and a tip portion configured to receive the optical sensor structure.

[0174] Example 17 is the apparatus of Example 16, wherein the needle further includes a window in the shaft portion or the tip portion proximate the optical sensor structure.

[0175] Example 18 is the apparatus of Example 16, wherein the needle further includes a channel disposed in the shaft portion, the sensor optical fiber being disposed within the channel.

[0176] Example 19 is the apparatus of Example 16, wherein the needle further includes a sheath disposed about the needle and configured to house the sensor optical fiber.

[0177] Example 20 is the apparatus of Example 17, wherein the needle further includes a plurality of additional windows in the shaft portion or the tip portion.

[0178] Example 21 is the apparatus of any of Examples 1-20, wherein the optical sensor structure is configured to detect the acoustic signal across a directional range of at least 180 degrees, at least 270 degrees, at least 300 degrees, at least 330 degrees, or 360 degrees.

[0179] Example 22 is the apparatus of any of Examples 1-21, wherein the optical sensor structure is configured for forward detection of the acoustic signal.

[0180] Example 23 is the apparatus of any of Examples 1-22, wherein the optical sensor structure is further configured for rearward detection of the acoustic signal.

[0181] Example 24 is the apparatus of any of Examples 1-23, wherein the optical sensor structure is configured for lateral detection of the acoustic signal.

[0182] Example 25 is the apparatus of any of Examples 1-24, wherein the optical sensor structure includes a distal portion comprising silicon dioxide and a proximal portion comprising a polymer.

[0183] Example 26 is the apparatus of Example 16, wherein the optical sensor structure includes a fiber Bragg grating.

[0184] Example 27 is the apparatus of any of Examples 1-26, wherein the core is included among a plurality of cores in the optical waveguide.

[0185] Example 28 is the apparatus of any of Examples 1-28, further comprising: a light source configured to provide light to the optical sensor structure via the optical waveguide; a photodetector configured to receive the optical signal; and a processing unit configured to: control the light source, receive optical data based on the optical signal from the photodetector, and perform at least one of image generation and position determination based on the optical data.

[0186] Example 29 is the apparatus of any of Examples 1-28, further comprising a wavelength tuning mechanism configured to adjust a resonance of the optical sensor structure via application of at least one of thermal stress and mechanical stress.

[0187] Example 30 is the apparatus of Example 28, wherein the light source is a working laser, and the processing unit is further configured to tune a wavelength of the working laser.

[0188] The above-described examples are illustrative embodiments and are not to be construed as limiting upon the present application. It is to be understood that the various embodiments disclosed herein can be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It is also to be understood that certain actions or events that are described in association with any process or method described herein can be performed in a different order than the order specifically presented in the description and accompanying drawings. Furthermore, although certain features of embodiments of the application can be described as being performed by a single module, unit, or component, it is contemplated that the features and functions described herein can be performed by any combination of units or modules. Thus, various changes and modifications can be made to the various embodiments described herein without departing from the spirit or scope of the application as defined in the appended claims.

Claims

1. An apparatus for processing acoustic signals, the apparatus comprising: Sensor optical fiber, which includes: An optical waveguide, comprising a core and a cladding structure; An optical sensor structure coupled to a first end of the optical waveguide and comprising at least one of an optical resonator, an optical interferometer, a surface microstructure, and a polarization-sensitive structure. The optical sensor structure includes a distal reflective surface, an optical cavity, a distal portion comprising a polymer cladding structure, and a proximal portion comprising a silicon dioxide cladding structure. The optical sensor structure is configured for: Detect sound signals, and An optical signal corresponding to the acoustic signal is provided to the optical waveguide.

2. The device of claim 1, further comprising an encapsulation structure having a first portion surrounding the optical waveguide and a second portion at least partially surrounding the optical sensor structure.

3. The device according to claim 1, wherein the optical sensor structure is a fiber optic sensor.

4. The device according to claim 1, wherein the optical sensor structure is an optical resonator, the optical resonator comprising a Fabry-Perot resonator, a whispering-gallery mode resonator, a microring, a microtoroidal surface, a helical resonator, or a photonic crystal resonator.

5. The device according to claim 1, wherein the optical sensor structure is an optical interferometer, the optical interferometer comprising a Mach-Zehnder (MZ) interferometer, a Fabry-Perot interferometer, a phase-shifting coherent interferometer, or a self-mixing interferometer.

6. The device of claim 1, wherein the optical sensor structure is an optical fiber endface comprising an acoustically responsive metasurface pattern, an acoustically responsive low-dimensional material, or a plasma structure, the plasma structure being patterned to amplify light-matter interactions.

7. The device of claim 1, wherein the optical sensor structure is configured to cause a change in polarization of transmitted light in response to the acoustic signal.

8. The device according to claim 1, wherein the optical sensor structure is a point sensor or a line sensor.

9. The device of claim 1, wherein the core or the cladding structure comprises a material having at least one of a relatively small Young's modulus (E) and a relatively high photoelastic coefficient.

10. The device of claim 2, wherein the cladding structure has a lower refractive index (n) than the core.

11. The device of claim 2, wherein the acoustic impedance of the encapsulation structure is selected to match the impedance of the optical resonator structure within 20%.

12. The device of claim 2, wherein the encapsulation structure comprises a material having a relatively small Young's modulus (E), a relatively high photoelastic coefficient, and / or a relatively large refractive index (n).

13. The device of claim 10, wherein the acoustic impedance of the encapsulation structure is selected to match the impedance of the optical resonator structure within 20%.

14. The device of claim 1, further comprising a medical device in which the sensor optical fiber is disposed.

15. The device of claim 14, wherein the medical device is one of a needle, endoscope, catheter, cannula, guidewire, surgical instrument, diagnostic instrument, or therapeutic instrument.

16. The device of claim 15, wherein the medical device is a needle, the needle comprising: The sensor optical fiber is fixed to the shaft portion; and The tip portion is configured to receive the optical sensor structure.

17. The device of claim 16, wherein the needle further includes a window in the shaft portion or the tip portion near the optical sensor structure.

18. The device of claim 16, wherein the needle further comprises a channel disposed on the exterior of the shaft portion, and the sensor optical fiber is disposed within the channel.

19. The device of claim 16, wherein the needle further comprises a sheath disposed around the needle and configured to receive the sensor optical fiber.

20. The device of claim 17, wherein the needle further includes a plurality of additional windows in the shaft portion or the tip portion.

21. The device of claim 1, wherein the optical sensor structure is configured to detect the acoustic signal across a directional range of at least 270 degrees, at least 300 degrees, at least 330 degrees, or 360 degrees.

22. The device of claim 1, wherein the optical sensor structure is configured for forward detection of the acoustic signal.

23. The device of claim 22, wherein the optical sensor structure is further configured for rear-view detection of acoustic signals.

24. The device of claim 1, wherein the optical sensor structure is configured for lateral detection of the acoustic signal.

25. The apparatus of claim 1, wherein the polymer is selected to reduce impedance mismatch with the operating medium.

26. The device of claim 16, wherein the optical sensor structure comprises an internal Bragg grating in the fiber located near the elongated optical cavity and a near-side reflective surface located far from the internal Bragg grating in the fiber.

27. The device of claim 1, wherein the core is included among a plurality of cores in the optical waveguide.

28. The device according to claim 1, further comprising: A light source configured to provide light via the light waveguide of the optical sensor structure; A photodetector configured to receive the optical signal; as well as The processing unit is configured as follows: Control the light source, Based on the optical signal from the photodetector, optical data is received, and Based on the optical data, at least one of image generation and location determination is performed.

29. The device according to claim 1, further comprising: A wavelength tuning mechanism configured to adjust the resonance of the optical sensor structure by applying at least one of thermal stress and mechanical stress.

30. The apparatus of claim 28, wherein the light source is a working laser, and the processing unit is further configured to tune the wavelength of the working laser.

31. The device according to claim 7, further comprising: A light source configured to provide light via the light waveguide of the optical sensor structure; as well as A polarization analyzer configured to measure the polarization change.

32. The device of claim 7, further comprising an encapsulation structure configured to surround the optical waveguide, wherein the encapsulation structure includes a window at the location of the optical sensor structure to expose the optical sensor structure to incoming acoustic signals.

33. The device of claim 32, wherein the sensor fiber further includes a second optical sensor structure located proximal to the optical sensor structure, and the second optical sensor structure is configured to cause a polarization change in the transmitted light in response to the acoustic signal, and wherein the encapsulation structure includes a window at the location of the second optical sensor structure to expose the second optical sensor structure to the incoming acoustic signal.

34. The device of claim 7, wherein the optical sensor structure is a line sensor comprising a plurality of optical sensor structures spaced apart along the length of a sensor optical fiber.

Images