Fiber-optical sensor system for ultrasound sensing and imaging

Abstract

To provide new and improved compact technology with high sensitivity to visualize and track objects and provide anatomical imaging, in medical applications.SOLUTION: Optical fiber based acoustic sensors include acoustically responsive optical structures configured to detect and receive acoustic signals, including ultrasound signals, and provide associated optical signals to a system for processing and interpretation so as to implement tracking, location and imaging capabilities. The optical fiber based sensors are disposed at ends of or along the length of optical fibers. The optical fiber based sensors are included in various devices, including, for example, medical devices.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Related Applications This application claims priority to U.S. Provisional Application No. 63 / 510,079, filed June 23, 2023, entitled FIBER-OPTICAL SENSOR SYSTEM FOR ULTRASOUND SENSING AND IMAGING, which is incorporated herein by reference. This application is further related to U.S. Provisional Application No. 63 / 522,793, filed June 23, 2023, entitled OPTICAL FIBER WITH AN ACOUSTICALLY SENSITIVE FIBER BRAGG GRATING AND ULTRASOUND SENSOR INCLUDING THE SAME, which is incorporated herein by reference. This application is further related to U.S. Provisional Application No. 63 / 522,994, filed June 23, 2023, entitled "TRANSPONDER TRACKING AND ULTRASOUND IMAGE ENHANCEMENT," which is incorporated herein by reference. This application is further related to U.S. patent application having Attorney Docket No. 109835-1394978, entitled Transponder Tracking and Ultrasound Image Enhancement, filed on October 23, 2023, which is incorporated herein by reference. This application further incorporates by reference U.S. provisional patent application having Attorney Docket No. 109835-1386207, entitled Miniature Mixed Array Imaging Probe, filed on October 23, 2023, which is incorporated herein by reference.

[0002] The present invention relates generally to the field of ultrasonic sensing and imaging. [Background technology]

[0003] Acoustic imaging is used in a variety of industries, including medical imaging. Acoustic imaging techniques may be used to visualize and provide internal imaging of a patient's body. Additionally, acoustic imaging techniques may be used to visualize and track objects (e.g., needles, catheters, guidewires, endoscopes, etc.) used in medical applications such as diagnostic or therapeutic clinical procedures, including, but not limited to, biopsies, fluid aspiration, delivery of therapeutic agents such as drugs / nerve blocks / anesthesia or biologics, catheter insertion, needle guidance, needle placement, deep vein cannulation, injections, IV placement, PIC lines, device implants, minimally invasive surgical procedures, etc. The use of acoustic imaging in medical applications offers several advantages. Acoustic imaging, such as ultrasound imaging, is a non-invasive form of imaging. In addition, ultrasound imaging uses ultrasound signals, which are known to have a significant penetration depth.

[0004] In non-medical applications, ultrasound is used in industrial applications for defect detection, non-destructive testing, structural testing, and particulate particle sorting, as well as in geological applications including mining and drilling operations and underwater marine applications, among other applications.

[0005] Some existing imaging technologies use acoustic energy generating (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 other materials known to those skilled in the art. AEG transducers have limitations. The echogenicity of the tracked object and / or the visualized anatomical structure can affect the image quality of the tracked object and the imaged tissue. Certain medical procedures require a small form factor, and small AEG transducers generally have a low to minimum signal output. Therefore, due to size limitations (e.g., physical size), it can be difficult to use AEG transducers in medical applications that require a small form factor.

[0006] Therefore, there is a need for new and improved compact techniques with high sensitivity for visualizing and tracking objects to provide anatomical imaging, especially in medical applications. Summary of the Invention

[0007] Presented herein are systems, devices, and methods for ultrasonic sensing and imaging. In particular, the systems, devices, and methods described herein may include fiber microsensor devices, systems, and methods of use.

[0008] In one embodiment, an apparatus is provided that includes a sensor fiber. The sensor fiber may include an optical waveguide having a core and a cladding structure, and an optical sensor structure coupled to a first end of the optical waveguide, the optical sensor structure including at least one of an optical resonator, an optical interferometer, and a polarization sensing 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 may 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.

[0009] In some aspects, devices described herein relate to an apparatus that includes a sensor fiber that includes an optical waveguide that includes a core and cladding structure, and an optical sensor structure coupled to a first end of the optical waveguide that includes at least one of an optical resonator, an optical interferometer, a facet end microstructure, and a polarization sensing structure, where the optical sensor structure is configured to detect an acoustic signal and provide an optical signal corresponding to the acoustic signal to the optical waveguide. [Brief description of the drawings]

[0010] The accompanying figures incorporated herein form a part of the specification and illustrate embodiments of systems, methods, and devices for ultrasound sensing and imaging. Together with the description, the drawings enable one skilled in the art to explain the principles of the methods, systems, and devices described herein and to make and use the methods, systems, and devices 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 numbers indicate identical or functionally similar elements.

[0011] [Figure 1] 1 illustrates an optical sensor system for use with a fiber optic sensor according to embodiments herein. [Diagram 2] 1 illustrates an optical sensor system for use with a fiber optic sensor according to embodiments herein. [Figure 3A] 1 illustrates a sensor fiber including a fiber optic sensor and an associated optical fiber. [Figure 3B] 1 shows a sensor fiber including an optical waveguide and an optical resonator structure having a Fabry-Perot resonator as an optical sensor. [Figure 4A-4E] 1 illustrates several variations of optical resonator structures according to embodiments herein. [Figure 5A-5B] 1 illustrates an example of an optical sensor system and a fiber optic sensor according to embodiments herein. [Fig. 5C-5D] 1 illustrates an example of an optical sensor system and a fiber optic sensor according to embodiments herein. [Fig. 5E-5F] 1 illustrates an example of a microfaceted structure according to an embodiment of the present disclosure. [Fig. 6A-6DD] 1 illustrates an example of an optical sensor system and a fiber optic sensor according to embodiments herein. [Figure 6E-6F] 1 illustrates an example of an optical sensor system and a fiber optic sensor according to embodiments herein. [Figure 6G-6H] 1 illustrates an example of an optical sensor system and a fiber optic sensor according to embodiments herein. [Figure 7A-7D] Examples of manufacturing techniques that may be used to shape or machine the ends of the optical waveguides are provided. [Figure 8A-8D] We provide examples of fabrication techniques that may be used to fabricate optical resonator structures at the ends of optical waveguides. [Figure 9A-9B] A method of thermal conditioning applied to a sensor fiber is shown. [Figure 10] 1 illustrates an embodiment of a sensor fiber including a multi-core optical waveguide. [Figure 11A-11B] 13 shows a comparison between a sensor fiber arranged with a forward-facing light sensor and a sensor fiber arranged with a sideways-facing light sensor. [Figure 12] 1 illustrates an embodiment of a sensor fiber that provides rear-facing acoustic detection capability, according to embodiments herein. [Figure 13]1 illustrates an embodiment of a sensor fiber that provides increased rearward acoustic detection capabilities, according to embodiments herein. [Figure 14] 1 illustrates a range of directions for an optically resonant structure according to an embodiment herein. [Figure 15] 1 illustrates an optical resonator structure including an in-fiber Bragg grating according to an embodiment herein. [Figure 16] 1 illustrates a method of operating a fiber-based optical sensor according to an embodiment herein. [Figure 17A-17B] 1 illustrates a needle configured with a sensor fiber, according to an embodiment of the present disclosure. [Figures 18A-18D] 1 illustrates a needle configured with a sensor fiber, according to an embodiment of the present disclosure. [Figure 19] 1 shows an acoustic signal entering the sensor fiber from the side. [Figure 20A-20B] 1 provides a close-up view of a needle with an integrated sensor fiber, according to embodiments herein. [Fig. 20C-20D] 1 illustrates a needle having a sensor fiber contained therein, according to an embodiment of the present disclosure. [Figure 21] 1 illustrates a distal end of a medical device incorporating a catheter delivery needle, according to an embodiment of the present disclosure. [Figure 22] 1 illustrates the use of fiber optic sensors in needle guidance or needle location. [Figure 23A-23B] 1 shows a catheter delivery needle incorporating a fiber optic optical sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Non-limiting examples of various aspects and variations of the present invention are described herein and illustrated in the accompanying drawings. The following detailed description is merely exemplary in nature and is not intended to limit the present invention or the application and uses of the present invention. Although the detailed description of the present invention is in the context of fiber optic microsensor systems, methods, and devices for ultrasound imaging and sensing, the disclosure should not be considered as so limiting. For example, while the methods may be discussed herein with respect to various medical procedures, the embodiments herein may be suitable for other medical procedures, as well as other procedures or methods in other industries that may benefit from the sensing and imaging techniques described herein. Additionally, various systems and devices incorporating fiber microsensors are described. It is understood that fiber microsensors as described herein may be integrated into and / or used with a variety of systems and devices not described herein. Modifications can be made to the embodiments described herein without departing from the spirit and scope of the present invention. Accordingly, the following detailed description is not meant to be limiting. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.

[0013] Various structures are described herein according to their geometric characteristics. As discussed herein, all structures described as such may vary from the described shapes according to the tolerances of known manufacturing techniques. Unless otherwise specified, features described with the term "substantially" are understood to be accurate to within 5%. For example, features described as "substantially parallel" may deviate from true parallel by 5%.

[0014] Systems, devices, and methods are disclosed for ultrasonic sensing and imaging through the use of fiber microsensors or fiber sensor devices. In particular, the techniques described herein may track, visualize, and monitor (e.g., sense) objects during medical procedures as well as generate ultrasonic images. The fiber microsensor devices described herein incorporate optical devices disposed at the end of an optical fiber or at designated locations along its length and configured for detection of acoustic signals, including ultrasonic signals. A sensor fiber as described herein includes an optical waveguide (such as an optical fiber) having a fiber microsensor device coupled to its end. As used herein, the term optical waveguide may refer to optical fibers, optical fiber cores, photonic integrated waveguides, planar waveguides, etc., based on material systems such as fused glass, polymers, semiconductor / dielectric wafers, nanoimprinted / 3D printed polymers on various substrates, or any other optical signal channel.

[0015] The technology described herein is compact in size and has high sensitivity, making it viable for a variety of industrial applications, as well as therapeutic and diagnostic medical applications. In non-medical applications, ultrasound is used in industrial applications for defect detection, non-destructive testing, structural testing, and particulate particle sorting, geological applications including mining and drilling operations, and underwater marine applications, among other applications. Such applications are consistent with the embodiments described herein. Therapeutic and diagnostic medical applications include ultrasound imaging and sensing (tracking, visualization, guidance, and monitoring) of objects (e.g., needles, catheters, guidewires, etc.) during needle access, biopsy, aspiration, delivery of drugs, biologics, anesthesia, or other therapeutic agents, catheter insertion, minimally invasive procedures, ablation, cauterization, placement or movement, cutting and / or sectioning of objects and tissues, and other medical procedures. Procedures and applications in the following fields are examples of the widespread use and need for precise guidance and imaging during diagnostic and therapeutic procedures: anesthesia, cardiology, critical care, dermatology, emergency medicine, endocrinology, gastroenterology, gynecology and obstetrics, hepatology, infectious diseases, interventional radiology, musculoskeletal medicine, nephrology, neurology, oncology, orthopedics, pain management, pediatrics, plastic and reconstructive surgery, urology, and vascular access.

[0016] Visualization, tracking, guidance, and location of objects in medical applications can be important aspects for performing medical procedures in a safe and reliable manner. Objects for tracking, visualization, and location determination can include any type of medical device moving or located within a subject's body. For example, a physician visualizes and tracks a needle tip while performing a biopsy to ensure safety. In such cases, accurate needle tip visualization or tracking can help prevent or reduce unintended blood vessel, nerve, tissue, or organ damage. Similarly, it may be useful to visualize, track, or localize needles, endoscopes, cannulas, laparoscopic tools, or other medical device tools when performing medical procedures such as, but not limited to, aspirating fluids, injecting joints, tendons, and nerves with drugs or biologics, biopsying fluid or soft tissue masses, aspirating and irrigating calcifications, removing tissue, organs, or foreign bodies, placing stents, filters, valves, permanent, temporary, or biodegradable implants, shunts, or drains, injecting for anesthesia, inserting vascular access devices used for infusion therapy, ablation procedures, performing the Seldinger technique or catheterization to gain access to blood vessels and / or other organs in a safe manner. Visualization and tracking may be advantageous in both minimally invasive laparoscopic procedures and open surgical procedures, especially when areas are difficult to visualize due to limited access, blood or other fluids in the intervening tissues or organs.

[0017] Some existing techniques use ultrasound imaging for guidance during medical procedures to visualize anatomical structures of interest as well as to visualize, localize, and track inserted medical devices, particularly the distal and / or working portion of the device. However, there are several drawbacks associated with conventional ultrasound imaging techniques for medical applications. Legacy techniques use imaging probes that emit ultrasound waves. Due to the smooth surfaces of needles and other inserted medical devices, incident ultrasound waves reflected from the surface may be steered away from the direction of reception. This can make the reflected waves too weak to be detected, making it difficult to determine the location of the device during the procedure. In some techniques, the medical device may have a rough surface, such as a recessed, etched, or coated surface, to increase ultrasound visibility by increasing the echogenicity of the medical device. However, even with such efforts, limitations remain. Ultrasonic guidance tools may also be constrained by their reliance on a specific angle of incidence, which limits their ability to provide accurate visualization, especially for deeply placed devices. Due to this constraint, ultrasonic guidance tools may be relegated to superficial locations that limit their usefulness, adoption, and cost-effectiveness as a deployable solution.

[0018] Compared to the proposed optical sensing technique, current state-of-the-art AEG transducers (including but not limited to lead zirconate titanate (PZT), ceramics, piezoelectric single crystals (e.g., PIN-PT, PIN-PMN-PT), and polyvinylidene fluoride (PVDF)) have at least two major acoustic performance limitations. First, to achieve very high sensitivity, transducers fabricated from specific AEG materials or specific acoustic designs are required, but such transducers may provide only a relatively narrow bandwidth in acoustic response. Second, the acoustic response of AEG transducers may be limited due to electrical impedance mismatch when the electrical element size becomes small relative to the resonant frequency of the AEG transducer. As a result, for applications requiring a small form factor (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, they may exhibit high directional response. In addition, some AEG transducers and systems may be affected by electromagnetic interference, such as that caused by ablation tools, cauterization tools, or any other procedure or technique that applies electrical energy to tissue. Furthermore, the use of electromechanical transducers at the distal end involves conductive wires and associated components that require additional design and safety requirements and challenges.

[0019] In contrast, fiber optic sensors according to the present disclosure can provide ultrasonic receivers with high sensitivity, wide bandwidth, and wide reception angles, without the need for electrical components required for electromechanical transducers. These properties allow fiber optic sensors to sense harmonic or scattered signals that existing technologies cannot sense. Furthermore, fiber optic sensors according to the present disclosure can be compact, low cost, and contribute to scalable sensor systems. Embodiments herein include fiber optic sensors configured to detect acoustic signals. Such fiber optic sensors can be disposed at the end of an optical fiber, adjacent to the end of an optical fiber, or at diagnostic or therapeutically relevant locations on a medical device to create a sensor fiber. Fiber optic 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-shifting coherent interferometers, self-mixing interferometers, acoustically responsive fiber end facets, and acoustically induced birefringence polarization sensors.

[0020] The acoustically responsive fiber end facet may comprise a substrate suitable for adding various microstructures to enhance the response of the fiber sensor to acoustic signals. Such microstructures may be acoustically responsive structures such as metasurfaces that include patterns of small elements (e.g., having a size less than approximately one wavelength of an optical signal) arranged to change the wavefront shape of the acoustic signal and maximize the detection of the acoustic signal, acoustically responsive low-dimensional materials with special opto-mechanical characteristics that are more susceptible to deformation, and plasmonic structures patterned to amplify light-matter interactions. In addition to operating as an optical sensor, the fiber end facet structures may be added to other optical fiber sensors described herein to further enhance the acoustic response. For example, a metasurface may include a pattern of small elements arranged to change the wavefront shape of the acoustic signal and maximize the collection of the acoustic signal collected by other types of optical fiber sensors discussed herein, improving the sensitivity of the optical fiber sensor. Adding low-dimensional materials to the fiber end facet may also improve sensitivity as such materials are more susceptible to deformation induced by acoustic waves, which may be translated into larger changes in the optical signal. By writing plasmonic patterns into the fiber end facet, it is possible to enhance the optical response to acoustic waves. This enhancement can be achieved by exploiting the hot spots and resonances created by these plasmonic patterns to amplify light-matter interactions. As used herein, "low-dimensional" or "two-dimensional" features may refer to features having a thickness of less than 1 micron.

[0021] The optical structures described above are configured to respond to acoustic (e.g., ultrasonic) signals. Thus, these optical structures may include acoustically responsive materials and / or structures. As used herein, acoustically responsive refers to a structure or material configured to respond to an incident acoustic signal (e.g., ultrasonic acoustic signal) in a manner that modulates the optical properties of the material or structure. The response to an acoustic signal in such a resonator, interferometer, or acoustically responsive fiber end facet structure may be due to a photoelastic effect and / or physical deformation of the structure. When exposed to an acoustic signal, the resonator, interferometer, or acoustically responsive fiber end facet structure is subjected to mechanical stress and / or strain from the alternating pressure of the acoustic signal sound wave. This mechanical stress and / or strain may change the optical properties of the optical sensor structure due to the photoelastic effect and may also cause a change or deformation of the physical structure of the resonator. In a polarized sensor, the polarization of the optical signal changes when the medium through which the light is passing is exposed to an acoustic signal. When coupled to a light source (e.g., a laser light 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 effect of the acoustic signal on the optical sensor structure can be measured due to changes in the light returned by the optical sensor structure via the optical waveguide. Within this disclosure, the optical signal and the light may be referred to as responsive to the acoustic signal. It is understood that such response is due to an interaction between the acoustic signal and the medium through which the light passes. Thus, as discussed herein, a material or structure that is referred to as acoustically responsive may respond to acoustic signals typical of an ultrasonic environment by the techniques discussed herein in a manner that may be measured by an optical signal according to embodiments herein.

[0022] The embodiments herein include systems configured for use with fiber optic sensors. For example, systems according to the present disclosure may include light sources (e.g., laser light 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 that facilitate the functionality of the fiber optic sensors. Furthermore, such systems according to the present disclosure may include acoustic devices, such as transducers, probes, and hardware / software for their control. Systems according to the present disclosure may further include medical systems and devices, including all devices, systems, hardware, and software necessary to perform any medical procedure that the fiber optic sensors are used to facilitate.

[0023] FIG. 1 illustrates an optical sensor system for use with a fiber optic sensor. As used herein, the terms “fiber optic sensor” and “fiber-based optical sensor” refer to an optical sensor adapted and / or configured to detect an acoustic signal, as described in more detail below. The optical sensor system 100A includes a light source 104, such as a laser, an optical receiving device 103, such as a photodetector, one or more optical waveguides 105, an optical circulator 102, and a fiber optic sensor 101. In operation, the light source 104 provides an initial optical signal 111 to the fiber optic sensor 101 via the optical waveguide 105 and through the optical circulator 102. The provided initial optical signal 111 is returned by the fiber optic sensor 101 along the optical waveguide 105. The return optical signal 112 travels through the optical circulator 102 via the optical waveguide 105 and is received at the optical receiving device 103. As discussed above, an acoustic signal incident on the fiber optic sensor 101 modifies the optical properties (which may include physical structure and optical material properties) of the fiber optic sensor 101. Such optical property modifications may be measured according to changes in the return optical signal 112, as discussed in more detail below.

[0024] FIG. 2 illustrates an optical acoustic sensor system for use with a fiber optic sensor. The optical acoustic sensor system 200 includes components, devices, hardware, and software to facilitate the use of a fiber optic sensor 101 or a fiber optic sensor array 201 (including multiple fiber optic sensors 101 as depicted in FIG. 2). Further reference to FIG. 2 may specifically refer to the use of a single fiber optic sensor 101, but it will be understood that in additional embodiments, a fiber optic sensor array 201 may be incorporated into the optical acoustic sensor system 200 in combination with any of the features discussed below, and any functionality that is an attribute of the fiber optic sensor 101 may further be performed by the fiber optic sensor array 201. In an embodiment, for example, as shown in FIG. 2, the optical acoustic sensor system 200 may include hardware and components to facilitate the use of an ultrasonic transducer and / or an ultrasonic probe. An ultrasonic transducer may be used to generate and receive acoustic signals, or simply generate acoustic signals. The optical acoustic sensor system 200 may include a processing system 250, an optical subsystem 215, and an output device 208.

[0025] The processing system 250 may include a processing unit 209 and an image reconstruction unit 206. The processing unit 209 may include at least one computer processor, at least one non-transitory computer-readable storage medium, and suitable 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 optical receiving device 203, and the acoustic control unit 222. The processing unit 209 may communicate with the light source control unit 207 (via control signals and information signals) to thereby provide control of the optical signals provided to the optical fiber sensor 101. The processing unit 209 may communicate with the acoustic control unit 222 (via control signals and information signals) to thereby provide control and reception of the acoustic signals via the acoustic probe 245. The processing unit 209 is further configured to communicate with the optical receiving device 203 to receive information signals associated with the optical signals received by the optical receiving device 203. Thus, the processing unit 209 operates to provide the necessary control signals and receive the acquired information signals in the optical acoustic sensor system 200 .

[0026] The processing unit 209 further communicates with the image reconstruction unit 206, which operates to generate an image based on data and / or information acquired by the processing unit 209. The image reconstruction unit 206 may generate an image based on data related to a medium, such as a human body, captured by the fiber optic sensor 101 and the acoustic probe 245. The medical device distal end 231 may 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's body. The image reconstruction unit 206 may be integrated within a system including the processing unit 209 and / or may be a separate system including at least one computer processor, at least one non-transitory computer readable storage medium, and suitable software instructions. The processing system 250 may provide control signals to the output device 208 for providing a data output. The output device 208 may include, for example, a display or a device including a display.

[0027] In some embodiments, the output device 208 may further include additional systems, such as medical procedure systems configured to use the output data. For example, the output device 208 may include an endoscopic system, a laparoscopic system, a robotic surgical system, a neurosurgical system, and may additionally include an interoperable ultrasound imaging system. The output data may include information regarding the location of the medical device distal end or working portion 231 and images obtained from media in the area where the medical device distal end 231 is used / deployed, such as the patient's anatomy, tissue, other medical tools / devices, etc.

[0028] The optical subsystem 215 includes a light source control unit 207, a light source 204, optical devices 202A, 202B, 202C, and 202D, and an optical receiving device 203. The light source control unit is configured to interface with and control the light source 204 to control the generation of the initial optical signal 211. The light source may generate continuous wave (CW) or pulsed emission (stimulated emission, spontaneous emission, etc.). The initial optical signal 211 may include coherent light, e.g., laser light, provided in one or more modes and one or more frequencies. The initial optical signal 211 may be a single frequency / wavelength, a selection of frequencies / wavelengths, and / or a broadband light source. Thus, the light source 204 may include a laser array configured to generate laser light in one or more modes and one or more frequencies. Additionally, the polarization of the provided light may be controlled to optimize the detected signal level according to application requirements. The polarization state of the light may be controlled to be linearly polarized at a specific angle or to be circularly polarized. Linear polarization responds optimally to a particular input ultrasound direction, while circular polarization responds to ultrasound from all directions. The polarization of the light may be defined from a laser source output, and the output polarization state may be controlled by an in-line fiber polarizer, a paddle fiber polarization controller, an in-line fiber polarization controller, or other type of polarization controller. The optical devices 202A, 202B, and 202C may be configured to manipulate or affect the initial optical signal 211 received at the optical fiber sensor 101. The initial optical signal 211 may be provided at multiple wavelengths or across a spectrum of wavelengths. The optical device 202A may include, for example, a wavelength division multiplexing (WDM) device configured to multiplex multiple frequencies of the initial optical signal 211 provided by the optical source 204 for simultaneous transmission through the optical waveguide 205 that directs the initial optical signal 211 to the optical fiber end sensor 101. The optical device 202B may be a circulator having first, second and third ports, the first port being in optical communication with the optical source through a wavelength division multiplexing device (WDM) 202A.The initial optical signal 211 may pass through a second optical device 202B, which may be, for example, an optical circulator, and is configured to direct the initial optical signal 211 to an optical device 202C. The optical device 202C may include a WDM device configured to demultiplex the initial optical signal 211 provided to the optical fiber sensor 101, which may be part of an array 201, where each of the optical fiber sensors 101 receives and then outputs different wavelengths of light. The optical device 202C is in optical communication with a second port of the second optical device 202B to split the initial optical signal into optical signals, each having one of the wavelengths associated therewith, and then combine the returned optical signals from the optical fiber sensor 101 that are directed to the optical receiving device 203 through a third port and the optical device 202D, which may include a WDM device.

[0029] The initial optical signal 211 is received by the optical fiber sensor 101 (or some embodiments of the optical sensor 101 of the optical fiber sensor array 201) and returned through one or more optical waveguides 205 to the optical device 202C, which may be further configured to multiplex the return optical signal 212 (if necessary) for transmission to the optical receiving device 203. The return optical signal 212 may be directed by the optical device 202C through the optical device 202B towards the optical device 202D, which may be a WDM device configured to demultiplex the return optical signal 212 for reception by the optical receiving device 203.

[0030] Optical device 202D may be in optical communication with a third port of optical device 202B to receive the returning optical signal and split it into individual wavelength components. Optical receiving device 203, which may be, for example, a photodetector array, may be in optical communication with optical device 202D to receive the individual wavelength components of the returning optical signal, such that a detected phase shift or other change in the individual wavelength components is indicative of a sensed acoustic signal.

[0031] It will be appreciated that in embodiments not requiring frequency multiplexing / demultiplexing of the initial optical signal 211 and the return optical signal 212, the optical devices 202A and 202C may not be required. The optical receiving device 203 may include any suitable device configured to detect incident light, including, for example, a photodetector. The optical receiving device 203 may further include, but is not limited to, a photodiode. The optical receiving device 203 may be in optical communication with the optical device 202D (e.g., a wavelength division multiplexing splitter) to receive the individual wavelength components of the return optical signal 212 such that a detected phase shift, change in polarization, or other change in the individual wavelength components is indicative of a sensed acoustic signal. The changes in the return optical signal 212 may be converted (e.g., by the processing unit 209 and / or by additional optical components, such as a polarization sensitive coupler and / or a frequency shifter) into data representative of the sensed acoustic signal (which may be further used, for example, to generate data representative of the tissue / anatomical structure of the medium in which the medical device distal end 231 is inserted into the area of ​​the diagnostic or therapeutic procedure and / or to identify the location of the medical device distal end 231 within the medium). In an embodiment, the initial optical signal 211 and the return optical signal 212 may undergo pre-processing, beamforming, and post-processing as described in the following documents:No. 18 / 032953, filed April 20, 2023, entitled Image Compounding for Mixed Ultrasound Sensor Array, which discloses various methods for ultrasound beamforming and image processing; U.S. Application No. 18 / 205081, filed March 7, 2023, entitled Synthetic Aperture Imaging Systems and Methods Using Mixed Array; U.S. Application No. 18 / 901073, filed December 29, 2022, entitled Acousto-Optic Harmonic Imaging with Optical Sensors; and PCT Application No. PCT / US2022 / 077762, filed October 7, 2022, entitled Ultrasound Beacon Visualization with Optical Sensors, which discloses various methods for ultrasound beamforming and image processing, each of which is incorporated herein by reference. No. PCT Application No. PCT / US2022 / 041250, filed Aug. 23, 2022, entitled Acoustic Imaging and Measurements Using Windowed Nonlinear Frequency Modulation Chirp Sensor, and PCT Application No. PCT / US2022 / 018515, filed Mar. 2, 2022, entitled Acoustic Imaging and Measurements Using Windowed Nonlinear Frequency Modulation Chirp Sensor. The image and / or data representative of the medical device distal end 231 (or the fiber optic sensor 101) may then be displayed to a user on an output device 208, which may include a computer display or the like. The image and / or data representative of the medical device distal end may further include a distal portion of the medical device in the illuminated area.

[0032] As discussed above, the optical receiving device 203 communicates with the processing unit 209. The processing unit 209 receives from the optical receiving device 203 an information signal representative of the return optical signal 212 received at the optical receiving device 203. The processing unit 209 may also receive from the optical control unit 207 an information signal representative of the initial optical signal 211 output by the light source 204. The processing unit 209 operates to process the information signal associated with the return optical signal 212 (optionally compared with the information signal associated with the initial optical signal 211) to make a determination about the acoustic environment at the optical fiber sensor 101, as discussed further below. The acoustic environment determination may include detection, identification, and interpretation of acoustic signals incident on one or more optical fiber sensors 101 of the optical fiber sensor array 201. The processing unit 209 may determine the presence and nature of acoustic signals incident on the optical fiber sensors 101 of the optical fiber sensor 101.

[0033] Thus, the optical fiber sensor 101 may function to detect and / or receive acoustic (e.g., ultrasound) signals and provide optical signals representative of and according to the acoustic signals through an optical receiving chain (e.g., optical devices 202C, 202B, 202D) to the optical receiving device 203, which is configured to detect and / or receive the optical signals and provide electrical signals representative of and according to the optical signals to the processing unit 209 for processing and interpretation. Thus, the processing unit 209 may be configured to receive electrical signals representative of and according to the received acoustic signals, and process and interpret the electrical signals to reconstruct an image from the acoustic signals. For example, the delay-and-sum beamforming principle (a common method for reconstructing ultrasound images) may be used to reconstruct an ultrasound image. In delay-and-sum beamforming, the spatial distribution of ultrasound field amplitudes in a volume of interest (region of an image) is reshaped according to delay timings between the transmitter, image pixels, and receiver, and as a result, 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 a delay.

[0034] The processing unit 209 may further communicate with an acoustic control unit 222. The acoustic control unit 222 may 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 may be configured for ex vivo or in vivo use and may include an AEG transducer or an array of AEG transducers (or any other suitable acoustic transducers) configured to generate and / or receive acoustic signals, such as ultrasound signals. The acoustic probe 245 may also include a mixed array of both AEG transducers (or any other suitable acoustic transducers) configured to generate and / or receive acoustic signals and optical sensors configured to receive optical signals, as disclosed in U.S. Patent Publication Nos. 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) may be used to form a first image. In parallel, one or more array elements of a second type (e.g., optical sensors) may be used to detect acoustic echoes that may be used to form a second image. The second image generated by the high sensitivity and wide bandwidth optical sensor may be used independently or may be combined with the first image to form a further improved image. Due to the high sensitivity and wide bandwidth of the optical sensor, the image generated by the optical sensor may have improved spatial resolution, improved penetration depth, improved signal-to-noise ratio (SNR), improved tissue harmonic imaging, and / or improved Doppler sensitivity.

[0035] The acoustic transducer 221 may be a component of a medical device system configured for in vivo deployment in a medium in which a diagnostic or therapeutic procedure is being or will be performed. The acoustic transducer 221 may include an intraluminal or intracavity transducer located on a catheter, cannula, or the like, or may be an intraoperative transducer that may enable transducer positioning during minimally invasive procedures, such as with a laparoscopic tool located at the end of a robotic arm or held by a surgeon, assistant, or any other medical personnel for selective positioning. In an embodiment, the acoustic transducer 221 may be disposed on the same medical device as the medical device distal end 231, for example with the fiber optic sensor 101. In an embodiment, the acoustic transducer 221 may be disposed on one or more devices separate from the device of the medical device distal end 231.

[0036] The in-vivo transducer 221 may be positioned on a catheter / endoscope / cannula as known in the art and transmit acoustic waves outwardly illuminating an area of ​​interest in the medium, and may be referred to as a forward looking probe. Alternatively, the acoustic transducer 221 may emit acoustic waves to the side. For example, the transducer 221 may be part of a side-emitting phased array used in IVUS applications. In another example, the transducer 221 may be used in a guide catheter with two parallel lumens, one to capture the guidewire and one working lumen that does not extend as distally as the guidewire lumen. Additionally, the transducer 221 may transmit acoustic waves radially. For example, the transducer 221 may be included in an echo endoscope with radial (or sector), linear, curved linear (convex array), trapezoidal, or any other image format used in ultrasound imaging. and linear (convex array) acoustic patterns. A radial echo endoscope may provide a circumferential view perpendicular to the shaft of the echo endoscope, i.e., an image perpendicular to the insertion tube. Different ultrasound frequencies may be used to provide ultrasound imaging of distal and proximal structures. A radial echo endoscope may provide a 360 degree image of anatomy that may be used for screening, but may be limited to therapeutic applications such as obtaining tissue samples. A curved linear, linear, or other suitable array may be used for therapeutic applications such as tissue sample collection, cyst drainage, lesion / lymph node biopsy, and injection for pain management. In an embodiment, the transducer 221 may be incorporated into a curved linear endoscope that provides visualization to a range dependent on the curve radius and allows real-time insertion of needles / therapeutic devices. In such an embodiment, the ultrasound view may be in the same line or plane as the scope shaft. In a further embodiment, the transducer 221 may be incorporated into a transverse array to provide an image in a plane perpendicular to the shaft of the scope.

[0037] In further procedures, a mobile intraoperative transducer may be positioned on the end of a robotic arm or other tool (such as, for example, the bk Medical Rob12C4) or may simply be held by the medical professional during the procedure. Additionally, certain cannulas and endoscopes may have a front-emitting transducer 221 for illuminating the area in front of the cannula, catheter, or scope, such as a craniotomy transducer.

[0038] A typical ex vivo transducer 221 or probe 245 may be positioned on the patient's skin surface, such as those commonly used for general imaging or for specific procedures such as needle guidance, needle positioning, or needle placement.

[0039] The processing unit 209 is configured to use the information signals from the acoustic probe 245 or acoustic transducer 221 (and any other acoustic signal generators that may be connected to or in communication with the optical acoustic sensor system 200) received by the optical fiber sensor 101 to sense, track, and monitor the medical device distal end 231 and generate an ultrasound image of the anatomical structure in the area of ​​treatment. In an embodiment, the optical fiber sensor 101 or the sensor array 201 operates to receive / detect the acoustic signals generated by the acoustic probe 245 and / or acoustic transducer 221 along with the scattering signals and tissue harmonics. The imaging of the medium may be achieved by the processing unit 209 according to 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 optical fiber sensor 101. The detected signals may include the detected scattering signals and tissue harmonics. A portion of the medium through which the acoustic signals generated by the acoustic probe 245 and / or acoustic transducer 221 travel may be imaged according to the detected acoustic signals.

[0040] 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 location of the fiber optic sensor 101 (and thus the location of the medical device distal end 231) can be calculated either by triangulation (e.g., based on receiving one or more acoustic signals transmitted from a known origin) and / or by coherent imaging. Further details can be found in co-pending U.S. Provisional Application No. 63 / 522,994, entitled Transponder Tracking and Ultrasound Image Enhancement, filed June 23, 2023, and U.S. application entitled Transponder Tracking and Ultrasound Image Enhancement, having Attorney Docket No. 109835-1394978, filed concurrently herewith on October 23, 2023. The location of the fiber optic sensor 101 may be overlaid on an ultrasound image of the anatomical structure to determine the relative location of the fiber optic sensor 101 to the known locations of the acoustic probe 245 and / or acoustic transducer 221. Furthermore, an ultrasound image of the surrounding anatomical structure may be coherently reconstructed according to a combination of acoustic signals received by the fiber optic sensor 101 and by one or more of the acoustic probe 245 and / or acoustic transducer 221. Such a combination may produce better image quality than an image formed using the acoustic probe 245 and / or acoustic transducer 221 alone.

[0041] In an embodiment for tracking, sensing, and monitoring the medical device distal end 231, the optical acoustic sensor system 200 may include multiple acoustic probes 245 that are either fixed in position or tracked in location. Tracking, sensing, determining, and monitoring the location and movement of the medical device distal end 231 may be accomplished, for example, by identifying timing and / or direction differences between multiple acoustic signals detected by the fiber optic sensor 101 and the acoustic transducer 221.

[0042] It will be understood that the configuration of the optical acoustic sensor system 200 as shown in FIG. 2 is provided as an example. Different configurations may be employed without departing from the scope of the present disclosure. For example, different arrangements of the optical devices 202A / B / C / D, different numbers and arrangements of the optical fiber sensors 101 and the optical fiber sensor array 201 may be employed. In an embodiment, the light source control unit 207 and the acoustic control unit 222 may be incorporated or integrated within the processing system 250. Additional combinations of the components of the optical acoustic sensor system 200 may be selected as appropriate to achieve the functionality as described herein.

[0043] FIG. 3A illustrates a sensor fiber including a fiber optic sensor and an associated optical fiber. As shown in FIG. 3A, the device may include a sensor fiber 301. The sensor fiber 301 may be an optical fiber configured with a fiber optic sensor disposed at an end. The sensor fiber 301 includes an optical waveguide 311 with a core 312 and a cladding structure 313. The optical waveguide 311 is configured to transmit or carry light in the optical waveguide 311, for example within the core 312. The core 312 is surrounded and protected by the cladding structure 313. The optical waveguide 311 may be substantially cylindrical along the length of the optical waveguide 311 and / or may be another suitable shape. The core 312 may be substantially centered in the cladding structure 313. In an embodiment, the optical waveguide 311 may be an optical fiber and may include any material common to optical fibers. For example, the core 312 may include silica glass, a polymer, or other suitable material. The cladding structure 313 material may be selected to be responsive to, for example, ultrasonically induced pressure or strain changes. The pressure or strain induced by ultrasonic waves introduces deformation or refractive index changes, leading to variations in the optical signal passing through the optical fiber. For example, when used as an ultrasonic sensor, the larger the variations, the higher the sensitivity and improved detection limit. The cladding material may have at least one material property associated with it, which may be a lower refractive index than the refractive index (RI) of the optical fiber core 312. The material properties, such as Young's modulus and photoelastic coefficient, of the fiber core, cladding material, and encapsulation structure may be the same or different materials and may be tailored for the application. A smaller Young's modulus and a larger photoelastic coefficient may be preferred for increased ultrasonic sensitivity and acoustic responsiveness. As used herein, being sensitive or responsive to acoustic signals may refer to a material having a relatively small Young's modulus (E), a relatively high photoelastic coefficient, and / or a relatively large refractive index (n), for example, as compared to a silica material. As used herein, a relatively low Young's modulus can refer to a Young's modulus less than 3.0 GPa, less than 2.0 GPa, less than 1.2 GPa, or in the range of 1.2 to 0.8 GPa.The relatively high photoelastic coefficient C (i.e., |C1-C2|) is C=2*10. -12 A relatively large refractive index may refer to a photoelastic coefficient greater than 1 / Pa. A relatively large refractive index may refer to a refractive index greater than approximately 1.46 for optical signals in the range of approximately 300 nm to 2000 nm. Such materials may 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 may be selected to maximize or increase the sensitivity of the optical properties of the structures to the incident acoustic signals. For example, a material with a lower Young's modulus requires less stress to deform. In some applications, the increased deformation may be undesirable. However, the increased deformation in response to an incident acoustic signal may amplify or increase the detectable change in an optical signal passing through an optical structure that undergoes a larger deformation. Similarly, an increased photoelastic effect may be desirable in an optical structure as described herein, but may not be desirable in a different structure configured for a different purpose.

[0044] It should be appreciated that the optical fiber core 312 can be any suitable type of optical fiber core, such as made from silica, silicon, an optically transparent polymer, etc. As a non-limiting example, if the optical fiber core 312 is made from silica (SiO2), the cladding material can be MY-133, a low refractive index optical coating manufactured by MY Polymers Ltd. of Israel, or BIO-133, a low refractive index optical coating manufactured by MY Polymers Ltd. of Israel. As a further non-limiting example, if the core is silicon, which has a higher RI than silica, the cladding structure 313 can be polyvinylidene fluoride (PVDF), polystyrene (PS), parylene, benzocyclobutene (BCB), MY-133, or BIO-133.

[0045] The optical waveguide 311 may be configured for single mode (SM) or multimode (MM) transmission depending on the form factor and laser and sensor wavelength tuning requirements, where SM fiber would be smaller in size. For example, a single mode fiber configured to operate in the 1550 nm band may have a cladding structure diameter of 50 um and a core D≧4.2 um. Such a fiber may be a polarization maintaining fiber. A multimode fiber configured to operate in the 1550 nm band may have a core D=50 um-60.5 um and a cladding diameter of 125 um. In an embodiment, a polymer fiber (e.g. PMMA, polystyrene) may be used. Such a fiber may have a larger diameter and a larger minimum bend radius than a typical glass optical fiber. In another embodiment, a photonic crystal fiber (with a hollow structure / periodic pattern) may be used.

[0046] An optical resonator structure 321 is disposed at the end of the sensor fiber 301. The optical resonator structure 321 is coupled to the end of the optical waveguide 311 and may include an optical resonator, such as a Fabry-Perot (FP) resonator, a whispering gallery mode resonator, a microring, a microtoroid, a spiral resonator, or a photonic crystal resonator, integrated within the optical resonator structure 321. The optical resonator structure 321 and other optical resonator structures described herein may include additional structures and components in addition to the optical resonator configured to facilitate the functionality of the optical resonator, as described below. The optical resonator is configured to receive a first optical signal (e.g., light) that is provided to the optical resonator via an optical waveguide and provide a second optical signal that returns along the optical waveguide. The second optical signal may correspond to and represent an acoustic signal incident on the optical resonator structure 321. As discussed above, the incident acoustic signal may cause physical deformation and / or alteration of material properties of the optical resonator structure 321. Thus, the optical signal provided along the optical waveguide 311 by the optical resonator structure may be modified, affected by, or otherwise indicative of or representative of the acoustic signal, and therefore may be used to characterize the incident acoustic signal.

[0047] The sensor fiber 301 may further include an encapsulation structure 314, which may include, for example, an outer coating, a shield, a protective outer layer, and / or a fiber jacket. The encapsulation structure 314 is configured with a first portion 314A surrounding the optical waveguide 311 and a second portion 314B at least partially surrounding the optical resonator structure 321. The encapsulation structure 314 may include a polymer, such as parylene, MY-133, BIO-133, or other suitable polymers that are sensitive or responsive to acoustic signals, as discussed above. The acoustic impedance of the encapsulation structure 314 may be selected to match the impedance of the optical resonator structure 321 to enhance the sensitivity of the detection of the acoustic signal. As used herein, "impedance matching" may refer to selecting materials and / or structures with matching acoustic impedances, generally providing an acceptable match for acoustic impedances within 20% of each other is well known to those skilled in the art of medical ultrasound. A closer match of acoustic impedances leads to better transmission of the acoustic signal (e.g., a smaller portion of the acoustic signal is reflected) and therefore higher sensitivity. In an embodiment, the first portion 314A surrounding the optical waveguide 311 and the second portion 314B surrounding at least partially the optical resonator structure 321 may include different materials selected for different purposes. For example, the first portion 314A may include an acoustically transparent material, e.g., having an acoustic impedance selected to improve matching and thereby minimize reflection of the acoustic signal. The second portion 314B may include an acoustically responsive / sensitive material, as discussed above, to increase the response to an incident acoustic signal in this region of the optical resonator structure 321. Unless otherwise stated, all encapsulation structures discussed herein may include similar properties to those of the encapsulation structure 314, including first and second portions including different materials selected for different purposes.

[0048] The optical resonator structure 321 is disposed at the end of the optical waveguide 311 and may therefore be referred to as a 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 a fiber of substantially the same size or to have a sensor that is significantly larger than the fiber, such as a bulb-like structure that may or may not be symmetrical. The increased size may further increase the acoustic sensitive surface area of ​​the sensor and increase the overall sensitivity. As discussed above, the sensor fiber 301 may be as compact as necessary, in some instances, given the small form factor required for certain medical applications, with the first and / or second diameters being 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.

[0049] FIG. 3B illustrates a sensor fiber including an optical waveguide and an optical resonator structure having a Fabry-Perot resonator as an optical sensor. The sensor fiber 351 is an example of the sensor fiber 301 and may include any of the features of the sensor fiber 301 as described above. The sensor fiber 351 includes an optical waveguide 371 having a core 352 and a cladding structure 353. The core 352 may have a diameter in the range of 7-12 microns, or a diameter of approximately 9 microns. These dimensions are provided by way of example only and do not limit the sizes and diameters encompassed by the embodiments of the present disclosure. The sensor fiber 351 may include an encapsulation structure 354, which may include, for example, an outer coating, protective outer layer, and / or fiber jacket that encapsulates both the optical waveguide 371 and the optical resonator structure 361 disposed at the end of the optical waveguide 371. The encapsulation structure 354 may be a multi-layer structure including, for example, an inner layer 355 and an outer layer 356. The inner layer 355 may include gold or any suitable reflective material layer for light waves, while the outer layer 356 may include parylene, MY-133, BIO-133, or other suitable protective layer that may be acoustically transparent. The encapsulation structure 354 may include a first portion 354A that encapsulates or surrounds the optical waveguide 371 and a second portion 354B that encapsulates or surrounds the optical resonator structure 361. The encapsulation structure 354 may have similar features to those of the encapsulation structure 314, including first and second portions of different materials. The optical resonator structure 361 may be configured with a Fabry-Perot resonator as the optical resonator 362. The optical resonator 362 includes a distal reflective surface 364 and a proximal reflective surface 363 disposed on either side of an optical cavity 365. The distal reflective surface 364 and the proximal reflective surface 363 may be configured of any suitable reflective material. As shown in Figure 3B, distal reflective surface 364 and proximal reflective surface 363 are formed from and are integral with inner layer 355 of encapsulation structure 354, and thus are formed of gold or other suitable reflective material. As shown in Figure 3B, distal reflective surface 364 may be curved and proximal reflective surface 363 may be substantially flat. This arrangement is by way of example only, and distal and proximal reflective surfaces 364 / 363 may be arranged in different shapes and / or configurations.Some additional examples are provided in Figures 4A-4E. In other embodiments, the distal reflective surface 364 and the proximal reflective surface 363 may be formed from different materials and / or may be structures separate from the encapsulation 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., typically has a Q factor greater than 1000). The quality (Q) factor is a dimensionless parameter that describes the amount of attenuation in a resonator. A higher Q factor corresponds to a more sensitive resonator.

[0050] In optics, the quality factor of a resonant cavity is

number

number

[0051] The Q factor, and any other determination of sensitivity and responsivity, is ultimately limited by the choice of material used for the optical fiber core. A conventional Fabry-Perot interferometer may be made uniformly from a single material, such as silica, throughout the entire structure. Silica, for example, has excellent optical transmission capabilities, but does not have exceptional acoustic sensitivity as well. Many materials are known that have excellent acoustic sensitivity, but such materials, alone, may not be suitable replacements for silica, etc., for optical fiber cores. The present invention adapts resonant actuators to take advantage of the acoustic sensitivity found in other materials.

[0052] The optical cavity 365 may be constructed of a suitable material, such as a polymer. Polymeric materials, such as MY-133 or BIO-133, with high acoustic transmission, may be employed to enhance the sensitivity of the optical resonator structure, as discussed above. The optical resonator structure 361 may be configured to detect an acoustic signal. An acoustic signal incident on the optical resonator structure, for example on the distal reflective surface 364, the proximal reflective surface 363, and / or the optical cavity 365, may cause vibration and / or other physical deformation of these structures, which may modify or affect their optical properties. Furthermore, due to the photoelastic effect, the material properties of these structures may be modified, thus further changing the optical properties. Thus, the return optical signal provided by the optical resonator structure 361 to the optical waveguide 371 (e.g., in response to an optical signal provided via the optical waveguide 371) may be indicative of or representative of the acoustic signal incident on the optical resonator structure 361. More specifically, the detected phase shift of the light in the sensor beam is indicative of the sensed acoustic signal. Using a polarized sensor, a polarization analyzer interprets the phase shift / delay between the different polarization components to generate a signal indicative of the sensed acoustic signal.

[0053] 4A-4E illustrate several variations of optical resonator structures 361 according to embodiments herein. FIG. 4A illustrates an optical resonator structure 361 having a proximal reflective surface 363 and a distal reflective surface 364 that are substantially flat and substantially parallel at opposite ends of a substantially cylindrical optical cavity 365. FIG. 4B illustrates an optical resonator structure 361 having a proximal reflective surface 363 that is substantially flat and substantially square with respect to the optical waveguide 371 and a distal reflective surface 364 that is concave with respect to the optical cavity 365. FIG. 4C illustrates an optical resonator structure 361 having a proximal reflective surface 363 that is convex with respect to the optical cavity 365 and a distal reflective surface 364 that is concave with respect to the optical cavity 365. FIG. 4D illustrates an optical resonator structure 361 having a proximal reflective surface 363 that is concave with respect to the optical cavity 365 and a distal reflective surface 364 that is substantially flat and substantially square with respect to the optical waveguide 371. FIG. 4E shows an optical resonator structure 361 having a proximal reflective surface 363 and a distal reflective surface 364 that are both concave with respect to an optical cavity 365 .

[0054] FIGURE 5A illustrates an optical sensor system for use with a fiber optic sensor according to an embodiment of the present disclosure. FIGURE 5B illustrates an interferometric optical sensor according to an embodiment of the present disclosure. The optical sensor system 100B of FIGURE 5A is configured for use with an interferometric fiber optic sensor 101B as shown in FIGURE 5B.

[0055] The optical fiber sensor 101B may include a fiber end sensor having an interferometric acoustic sensor. The optical fiber sensor 101B may include a sensor fiber 301A having an interferometric fiber end sensor structure 321A disposed at an end of the optical fiber sensor 101B, for example, at the end of the optical waveguide 311A. Except where noted, the sensor fiber 301A may include features and structures consistent with the features and structures of the sensor fiber 301. The interferometric fiber end sensor structure 321A may include, for example, a Mach-Zehnder (MZ) type interferometer. The interferometric fiber end sensor structure 321A is coupled to the end of the optical waveguide 311A. The interferometric fiber end sensor structure 321A may include additional structures and components configured to facilitate the functionality of the interferometric fiber end sensor, as described below. The interferometric fiber end sensor is configured to receive a first optical signal (e.g., light) provided to the interferometric fiber end sensor via the optical waveguide 311A ​​and provide a second optical signal returning along the optical waveguide 311A. The second optical signal may correspond to and represent an acoustic signal incident on the interferometric fiber end sensor structure 321A. The incident acoustic signal may cause physical deformation and / or alteration of material properties of the interferometric fiber end sensor structure 321A. Thus, the optical signal provided along the optical waveguide 311A ​​by the interferometric fiber end sensor structure 321A may be altered, affected, or otherwise indicative of or representative of the acoustic signal, and thus may be used to characterize the incident acoustic signal.

[0056] The interferometric fiber-end sensor structure 321A may include an acoustically responsive polymer portion 317A, including parylene or other suitable polymers that are sensitive to acoustic signals. The acoustic impedance of the polymer portion 317A may be selected to match (e.g., within 1%, 5%, 10%, or 20%) the acoustic impedance of the encapsulation structure of the sensor fiber 301A to enhance the sensitivity of the fiber-end sensor structure 321A, as described above. The distal reflective surface 364A is disposed at the distal end of the fiber-end sensor structure 321A and may be composed of any suitable material, such as gold. As shown in FIG. 5B, the distal reflective surface 364A is formed from gold and is integral with the polymer portion 317A.

[0057] The fiber end sensor structure 321A is disposed at the end of the optical waveguide 311A ​​and may therefore be referred to as a fiber end sensor. The optical waveguide 311A ​​may have a first diameter and the fiber end sensor structure 321A may have a second diameter. The first diameter and the second diameter may be substantially the same and / or may have a ratio in the range of 1.05 to 0.95, a ratio in the range of 1.02 to 0.98, or a ratio in the range of 1.01 to 0.99. As discussed above, the sensor fiber 301A may be compact, e.g., the first diameter and / or the second diameter are 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.

[0058] The optical sensor system 100B is configured for use with an interferometric optical fiber sensor 101B. The optical sensor system 100B may include an optical source 104, such as a laser, an optical receiving device 103, such as 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 optical source 104 provides an initial optical signal 111A to the optical fiber sensor 101 via the optical waveguide 105, via the coupler / decoupler 107A, and through the optical circulator 102. The provided initial optical signal 111A is returned by the optical fiber sensor 101 along the optical waveguide 105. The return optical signal 112 travels through the optical circulator 102 and the coupler / decoupler 107B via the optical waveguide 105 and is received at the optical receiving device 103. The coupler / decoupler 107A functions to direct a portion of the initial optical signal 111A through the frequency shifter 106 to the coupler / decoupler 107B as a reference optical signal 111B, which may be combined with the return optical signal 112 for detection and comparison at the optical receiving device 103. As discussed above, the acoustic signal incident on the optical fiber sensor 101 modifies the optical properties (including the physical structure and optical material properties) of the optical fiber sensor 101. Such optical property modifications may be measured according to changes in the return optical signal 112 compared to the reference optical signal 111B.

[0059] 5C and 5D show embodiments of fiber optic sensors including fiber end facets configured to provide or enhance acoustic detection capabilities. Fiber optic sensor 101C and fiber optic sensor 101D each include at least an optical waveguide 311, a fiber core 312, a cladding structure 313, and an encapsulation structure 314. Fiber optic sensor 101C includes an optical sensor structure 329C including an acoustically responsive polymer portion 397 and a facet substrate 398A located at a distal end of the acoustically responsive polymer portion 397. Fiber optic sensor 101D includes an optical sensor structure 329D including an acoustically responsive polymer portion 397, a facet substrate 398B disposed between the polymer portion 397 and the core 312 and the cladding structure 313, and a distal end reflective surface 394 disposed at a distal end of the polymer portion 397.

[0060] In the optical fiber sensor 101C, a facet substrate 398A is disposed at the distal end of the optical fiber sensor 101C. The optical sensor structure 329C is formed by the polymer portion 397 and the facet substrate 398A. The facet substrate 398A includes one or more facet structures 399A, as shown in a cross-sectional view. The facet structures 399A may include acoustically responsive microstructures, such as metasurfaces including patterns of small elements arranged to change the wavefront shape of the acoustic signal and maximize detection of the acoustic signal, acoustically responsive low-dimensional materials with opto-mechanical characteristics selected to optimize the acoustic response, such as features that are more deformable when receiving an acoustic signal and exhibit a larger material response to the acoustic signal, and plasmonic structures patterned to amplify light-matter interactions, as described herein. The plasmonic structures may locally amplify incident light due to plasmonic resonance of the plasmonic structures. The facet structures 399A operate as optical sensors as described herein. In operation, the provided optical signal 1111 reflects off the facet substrate 398A and is returned to the system as a return optical signal 1121. Because the facet structure 399A is acoustically responsive, the return optical signal 1121 is modified by changes in the facet structure 399A caused by the incident acoustic signal. In an embodiment, the plasmonic resonance induced in the plasmonic metasurface acting as the facet structure 399A or the Mie resonance induced in the dielectric metasurface acting as the facet structure 399A may be altered (e.g., shifted) by the incident acoustic signal to provide a detectable modification to the return optical signal 1121. The return optical signal 1121 may then be interpreted by any of the systems described herein.

[0061] In the optical fiber sensor 101D, the facet 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 facet substrate 398B, and the distal reflective surface 394. The facet substrate 398B includes one or more facet structures 399B, as shown in cross-section. The facet structures 399B may include acoustically responsive microstructures similar to those described above with respect to the facet structures 399A. The facet structures 399B operate to enhance, improve, or otherwise modify the acoustic response of the optical sensor structure 329D. In operation, the provided optical signal 1111 reflects from the distal reflective surface 394 and is returned to the system as a return optical signal 1121. The polymer portion 397 and the distal reflective surface 394 are acoustically responsive, and the return optical signal 1121 is modified according to the acoustic signal incident on these structures. Because the facet structure 399B is acoustically responsive and both the supplied optical signal 1111 and the returned optical signal 1121 pass through the facet substrate 398B, the returned optical signal 1121 is further modified by changes in the facet structure 399B caused by the incident acoustic signal. In an embodiment, the facet structure 399B may be designed and / or selected to optimize the coupling (e.g., reduce signal loss) and / or achieve critical coupling (e.g., eliminate signal loss) of the optical sensor structure 329D. The increased coupling at the optical sensor structure 329D serves to increase the amplitude of the optical signal responsive to the incident acoustic signal. Thus, the returned optical signal 1121 may exhibit a higher signal-to-noise ratio. Furthermore, the incident acoustic signal causing a deformation in the facet structure 399B may also be a server to modify the degree to which the facet structure 399B modifies the coupling at the optical sensor structure 329D, thus providing another aspect of the returned optical signal 1121 modified by the incident acoustic signal for interpretation. The return optical signal 1121 may then be interpreted by any of the systems described herein. Thus, the facetted substrate 399B may function to enhance, improve, or otherwise modify the acoustic response of the optical sensor structure 329D.

[0062] Facet structures 399A and 399B are shown in Figures 5C and 5D as being incorporated into fiber optic sensors 101C and 101D. Such facet substrates are not limited to use with optical sensors having interferometric structures and operation of fiber optic sensors 101C and 101D, but may be incorporated into any of the fiber optic sensors described herein.

[0063] FIG. 5E illustrates an example of a plasmonic metasurface, and FIG. 5F illustrates an example of a dielectric metasurface. As shown in FIG. 5E, a fiber 500 can include a plasmonic metasurface 511 disposed at the end of an optical waveguide 502 having a core 501. The plasmonic metasurface 511 can be disposed at the end of the fiber 500 within a region defined by the core 501. As shown, the plasmonic metasurface 511 can be disposed in, for example, a square pattern, or any other suitable pattern. The plasmonic metasurface 511 can exhibit a plasmonic resonance when struck by an optical signal from the core 501. Deformations caused by an incident acoustic signal modify the plasmonic resonance, allowing for detection and decoding of the acoustic signal, as discussed herein. The plasmonic metasurface 511 can include various metals, particularly noble metals such as gold. Furthermore, the plasmonic metasurface 511 may 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 further embodiments, the plasmonic metasurface 511 may be a low-dimensional or two-dimensional surface having a height of less than 1 micron. In the lateral dimension, the features of the plasmonic metasurface 511 may be small and have a lateral dimension D (e.g., width and / or length) less than the wavelength of the optical signal used by the sensor (e.g., less than 600 nanometers, less than 400 nanometers, less than 200 nanometers, etc.). The lateral dimension of the features of the plasmonic metasurface 511 may also refer to the spacing between the features. FIG. 5F shows a dielectric metasurface 512 that may also be disposed in a region of the fiber core 501 at the end of the optical waveguide 502 of the fiber 550. The dielectric metasurface 512 may be arranged in strips or rectangles, as shown in FIG. 5F, or in any other suitable shape. The dielectric metasurface 512 can be configured to exhibit a Mie resonance when impinged by an optical signal. The Mie resonance can be modified by an incident acoustic signal, thereby enabling detection and decoding of the acoustic signal. In an embodiment, the dielectric metasurface 512 can include a dielectric material, such as silicon, titanium oxide, etc. In an embodiment, the dielectric metasurface 512 can be a similar size to the plasmonic metasurface 512, as discussed above.

[0064] FIG. 6A illustrates an optical sensor system for use with a fiber optic sensor according to an embodiment herein. FIG. 6B illustrates a polarized optical sensor according to an embodiment herein. The optical sensor system 100B is configured for use with a polarized fiber optic sensor 101C. The fiber optic sensor 101C may include an optical fiber end sensor having a polarized acoustic sensor. The fiber optic sensor 101C may include a sensor fiber 301B having a polarized fiber end sensor structure 321B disposed at an end of the fiber optic sensor 101C, for example, at an end of the optical waveguide 311B. In further embodiments, the polarized fiber end sensor structure 321B may be disposed anywhere along the sensor fiber 301B, as discussed below. Except as noted, the sensor fiber 301B may include features and structure consistent with the features and structure of the sensor fiber 301. The sensor fiber 301B includes an encapsulation structure 314C, which may include, for example, an outer coating, a protective outer layer, and / or a fiber jacket. The encapsulation structure 314C may include a material selected to have a high acoustic impedance mismatch relative to the cladding structure of the sensor fiber 301B. Thus, when the sensor fiber 301B is covered by the encapsulation structure 314C, an incident acoustic signal may be reflected. The polarized fiber end sensor structure 321B may include a polymer portion 317B that may be exposed by a window 320B defined by the absence of the encapsulation structure 314C and that includes an acoustically responsive polymer and a distal reflective surface 364B configured to reflect the initial optical signal 111 as a reflected optical signal 112. The polarized fiber end sensor structure 321B is configured to receive a first optical signal (e.g., light) provided to the polarized fiber end sensor structure 321B via the optical waveguide 311B and provide a second optical signal that returns along the optical waveguide 311B. The second optical signal may correspond to and represent the acoustic signal incident on the polarized fiber end sensor structure 321B. The incident acoustic signal may cause physical deformation and / or alteration of material properties of the polarized fiber end sensor structure 321B.Thus, the optical signal provided along the optical waveguide 311B by the polarized fiber end sensor structure 321B may be modified, affected, or otherwise indicative of or representative of the acoustic signal, and thus may be used to characterize the incident acoustic signal. In the polarized fiber end sensor structure 321B, the incident acoustic signal induces stress in the polymer portion 317B, which results in one or more double refractions and rotations of the polarization of the light passing through the polymer portion 317B and a change in the polarization of the light carried by the optical waveguide 311B, which may be detected and analyzed by the optical sensor system 100B, as discussed below.

[0065] The optical sensor system 100B includes a light source 104, such as a laser, an optical receiving device 103, such as a photodetector, one or more optical waveguides 105, an optical circulator 102, and an optical fiber sensor 101B. In operation, the light source 104 provides an initial optical signal 111 to the optical fiber sensor 101B via the optical waveguide 105 and through the optical circulator 102. The provided initial optical signal 111 is returned by the optical fiber sensor 101B along the optical waveguide 105. The return optical signal 112 travels through the optical circulator 102 via the optical waveguide 105, through the polarization analyzer 108, and is received at the optical receiving device 103. The use of the polarization analyzer 108 allows for the determination of a polarization difference between the initial optical signal 111 and the return optical signal 112. As discussed above, the acoustic signal incident on the optical fiber sensor 101B modifies the optical properties (including the physical structure and optical material properties) of the optical fiber sensor 101B, causing a modification of the polarization of the return optical signal 112. Such a polarization change can be measured according to the difference between the return optical signal 112 and the initial optical signal 111, as determined according to the photodetector.

[0066] In an embodiment, the angular sensitivity of the polarized fiber end sensor structure 321B may be subject to differences in the polarization of the initial optical signal 111. Depending on the polarization of the initial optical signal 111, the angle of the incoming acoustic signal to which the polarized fiber end sensor structure 321B is most sensitive may be altered, as shown in FIG. 6C. Thus, in an embodiment, the control system associated with the optical sensor system 100B may be configured to adjust or optimize the polarization of the initial optical signal 111, such as from input polarization state 1 to input polarization state 2, to increase the acoustic sensitivity. These polarization states are provided by way of example only and may be altered or configured according to operational needs, as discussed below. FIG. 6C illustrates the directions in which input polarization state 1 and input polarization state 2 are most sensitive to the input acoustic signal. The solid arrow corresponds to the direction in which input polarization state 1 is most sensitive, and the dashed arrow corresponds to input polarization state 2. Thus, the lobe of the polarization state provides the highest acoustic sensitivity. Thus, the input polarization states may be selected and implemented to align with the expected direction of the acoustic signal, or the direction in which acoustic sensitivity is most desired. This may enable the optical sensor system 100B to optimize the performance of the fiber end sensor structure 321B according to the incident direction of the acoustic signal. The angular sensitivity of the polarized fiber end sensor structure 321B does not depend on the structure of the fiber end sensor structure 321B. In an embodiment, a polarization-maintaining fiber may be used. After the polarization state is selected and implemented, the polarization state is maintained by the optical signal. In an embodiment, an adjustable fiber component may be used to provide an adjustable polarization state. In an embodiment, the polarization state may be adjusted during use to account for changing conditions (movement of the acoustic transducer 221 that generates the acoustic signal and / or movement, rotation, etc. of the fiber end sensor structure 321B). Further advantages of the polarized fiber end sensor structure 321B may include simplified sensor structure and wavelength locking requirements.

[0067] FIG. 6D illustrates a further embodiment of a fiber-based optical sensor according to embodiments herein. The sensor fiber 301C may be an optical fiber configured similarly to the sensor fiber 301, including an optical waveguide with a core and cladding structure as described herein. The sensor fiber 301C may have a fiber end sensor structure 321C disposed at the end of the sensor fiber 301C. The fiber end sensor structure 321C may include any of the fiber end sensor structures discussed herein, including an optical resonator structure, an interferometer structure, an acoustically responsive fiber end facet structure, and a polarized structure. The sensor fiber 301C may further include an encapsulation structure 314C configured to reflect an incident acoustic signal, and a window 320C representing a gap or exposed area lacking the encapsulation structure 314C. The window 320C may expose a polarized optical sensor structure 322C, for example, as discussed with respect to FIG. 6B. In an embodiment, the polarized optical sensor structure 322C is formed from the cladding structure and core of the fiber of which it is a part. That is, the polarized optical sensor structure 322C may be defined by its exposure to the incident acoustic signal created by the lack of acoustic shielding at the window 320C, rather than any additional structure in the fiber. The sensor fiber 301C may include any number of windows 320C and polarized optical sensor structures 322C disposed along the length of the sensor fiber 301C. Thus, the sensor fiber 301C may include multiple optical acoustic sensor structures, including both fiber end sensor structures 321C and polarized optical sensor structures 322C configured for mid-fiber locations. In a further embodiment, the window 320C may be sufficiently sized along the length of the fiber such that the window 320C operates as a line sensor, as opposed to a point sensor, as discussed in more detail below. The line sensor may be a linear sensor or a curvilinear receiver. In further embodiments, the sensor fiber 301C does not include a fiber-end sensor structure 321C, but may be configured with one or more polarized optical sensor structures 322C disposed along the length of the sensor fiber 301C.

[0068] Each of the fiber end sensor structure 321C and the polarized optical sensor structure 322C may be used to facilitate both imaging and tracking, as described herein. In an embodiment, the polarized optical sensor 322C may be configured to facilitate imaging, tracking, or both, for example, by size / shape. For example, a longer polarized optical sensor structure 322C may function as a line sensor to improve image quality, and the line may be straight or curved. In another example, multiple polarized optical sensor structures 322C may be used to facilitate tracking methods (e.g., multiple sensors along a device may aid in direction determination).

[0069] In some embodiments, the polarizing window portion may also function as a fiber optic sensor to detect scattered acoustic signals and / or tissue harmonics. When the fiber optic sensor is positioned within the imaging region of interest, it may receive weak harmonics or scattered acoustic signals that cannot propagate very far. The optical fiber may transmit optical signals corresponding to the received acoustic signals to a system processor (e.g., processing unit 209). The system processor may use the received optical signals to reconstruct an ultrasound image of the anatomical structures surrounding the sensor using a delay and add beamforming method or other suitable image reconstruction method, as discussed in detail in corresponding U.S. Provisional Application No. 63 / 522,994, entitled Transponder Tracking and Ultrasound Image Enhancement, filed June 23, 2023, and U.S. application entitled Transponder Tracking and Ultrasound Image Enhancement, having attorney docket number 109835-1394978, filed concurrently on October 23, 2023. Using this data, the system processor may generate better quality images than those generated based solely on pulses emitted and received by the acoustic probe. In embodiments, the system processor may construct an image based solely on optical signals received from one or more fiber optic sensors. In embodiments, optical signals received from one or more fiber optic sensors may be used in conjunction with acoustic signals received by a traditional ultrasound probe.

[0070] This principle is illustrated in more detail in FIG. 6DD. As shown in FIG. 6DD, an acoustic probe 601 may be used to transmit an acoustic signal 620 to a region of interest. The acoustic probe 601 may function as a traditional acoustic probe to detect reflections of the acoustic signal 620 for imaging purposes. These images may be enhanced with additional information acquired by one or more fiber optic sensors. The fiber optic sensor 612 of the sensor fiber 602 may correspond to any of the fiber end optical sensor configurations discussed herein and may receive an acoustic signal 622. The acoustic signal 622 may result from reflection, scattering, and / or tissue harmonics. As shown in FIG. 6DD, the acoustic signal 622 is generated from a point 621 within the region of interest. The fiber optic sensor 612 may be configured to receive the acoustic signal 622 from any direction, as discussed herein. The sensor fiber 603 may be configured to function as a polarized optical sensor, as discussed herein, and may receive the acoustic signal 622 from a direction transverse to the axis of the sensor fiber 603. As used herein, "lateral" refers to any direction that is not parallel to the axis of the sensor fiber 603. As shown in FIG. 6DD, the acoustic signal 622 may be received by the sensor fiber 602 from any direction at any exposed portion along the length of the sensor fiber 602, as discussed with respect to FIG. 6D. Additionally, as discussed with respect to and shown in FIG. 6C, the polarization of the sensor fiber 602 may be selected or adjusted to match an expected or desired radial angle of incidence of the acoustic signal 622. FIG. 6DD further illustrates the sensor fiber 604, which may be curved within the region of imaging interest. Similar to the sensor fiber 603, the sensor fiber 604 may detect the incident acoustic signal 622 laterally, substantially laterally, or from any direction relative to the axis of the sensor fiber 604. Detection of the transverse signal at multiple points along the length of the sensor fiber 604 may enhance the ability to track and / or localize the sensor fiber 604 when the sensor fiber 604 is disposed within a medium (e.g., within the human body during a medical procedure).For example, as shown in Fig. 6DD(b), multiple signals incident along the length of the sensor fiber 604 may enhance the ability to determine the location of different portions of the sensor fiber 604 along the length of the sensor fiber 604, and thus identify the location of the entire sensor fiber 604, and not just the tip region. For example, as shown in Fig. 6DD(c), multiple signals incident along the length of the sensor fiber 604 may enhance the ability to determine the location of different portions of the sensor fiber 604, and thus identify the curvature of the sensor fiber 604 with greater accuracy.

[0071] 6E and 6F show optical sensor systems for use with optical fiber sensors according to embodiments herein. FIG 6F shows an optical resonator-based optical sensor configured for use with a multi-core optical fiber according to embodiments herein. The optical sensor system 100D of FIG 6E is configured for use with a multi-core optical resonator-based optical fiber sensor 101D as shown in FIG 6F. In further embodiments, other optical sensors discussed herein may be employed in a multi-core optical fiber-based system, including, for example, an interferometric sensor.

[0072] The optical fiber sensor 101D may include a fiber end sensor having an optical resonator acoustic sensor as described herein. The optical fiber sensor 101D may include a sensor fiber 301D having an optical resonator fiber end sensor structure 321D disposed at an end of the optical fiber sensor 101D, for example at an end of an optical waveguide 311D. Except where noted, the sensor fiber 301D may include features and structures consistent with the features and structures of the sensor fibers 301 and 351. The optical resonator fiber end sensor structure 321D is coupled to the end of the optical waveguide 311D. The optical resonator fiber end sensor structure 321D may include an optical resonator sensor 322D in addition to additional structures and components configured to facilitate the functionality of the optical resonator sensor 322D, as described below. The optical resonator fiber end sensor 322D, as shown diagrammatically in FIG. 6F, may be waveguide-coupled to be configured to receive an initial optical signal 111 (e.g., light) provided to the optical resonator fiber end sensor 322D via a first optical core 313D of the sensor fiber 301D and provide a return optical signal 112 returning along a second optical core 312D of the sensor fiber 301D. The second optical signal may correspond to and represent an acoustic signal incident on the optical resonator fiber end sensor structure 321D. The incident acoustic signal may cause physical deformation and / or alteration of material properties of the optical resonator fiber end sensor structure 321D. Thus, the optical signal provided by the optical resonator fiber end sensor structure 321D along the second optical core 312D may be altered, affected, or otherwise indicative or representative of the acoustic signal, and thus may be used to characterize the incident acoustic signal.

[0073] The optical resonator fiber-end sensor structure 321D may include an acoustically responsive polymer portion 317D, including parylene or other suitable polymers that are sensitive to acoustic signals. The acoustic impedance of the polymer portion 317D may be selected to match (e.g., within 1%, 5%, 10%, or 20%) the acoustic impedance of the encapsulation or cladding structure 314D of the sensor fiber 301D to enhance the sensitivity of the optical resonator fiber-end sensor structure 321D, as described above.

[0074] The fiber end sensor structure 321D is disposed at the end of the optical waveguide 311D and may therefore be referred to as a fiber end sensor. The encapsulation or cladding structure 314D may have a first diameter and the fiber end sensor structure 321D may have a second diameter. The first and second diameters may be substantially the same and / or may have a ratio in the range of 1.05 to 0.95, a ratio in the range of 1.02 to 0.98, or a ratio in the range of 1.01 to 0.99. As discussed above, the sensor fiber 301D may be compact, e.g., the first and / or second diameters are 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. With very small fiber diameters, increasing the diameter of the fiber sensor end may further increase acoustic sensitivity.

[0075] The optical sensor system 100D is configured for use with the resonator-based optical fiber sensor 101D. The optical sensor system 100D may include an optical source 104, such as a laser, an optical receiving device 103, such as a photodetector, one or more optical waveguides 105, and a multi-core fiber fan-out coupler 109. In operation, the optical source 104 provides an initial optical signal 111 through the multi-core fiber fan-out coupler 109 and via the optical waveguide 105 to the optical fiber sensor 101D. The provided initial optical signal 111 travels through the first optical core 313D to the optical resonator-based fiber end sensor structure 321D, may be affected by an incident acoustic signal, and is then returned as a return optical signal 112 by the second optical core 312D. The return optical signal 112 travels through the optical waveguide 105 through the fan-out coupler 109 to be received at the optical receiving device 103. As discussed above, the acoustic signal incident on the optical fiber sensor 101D modifies the optical properties (including physical structure as well as optical material properties) of the optical fiber sensor 101D. Such optical property modifications can be measured from the return optical signal 112 to measure attributes and characteristics of the incident acoustic signal. In the embodiment of FIG. 6E, for example, it is not necessary to provide the initial optical signal 111 to the optical receiving device 103 to measure the optical property modifications, since the parameters of the initial optical signal 111 are known by the system.

[0076] The multi-core fiber fan-out coupler 109 functions to couple the single-core optical waveguide 105 to the multi-core optical waveguide 311D. Thus, the initial optical signal 111 and the return optical signal 112 may travel in separate optical cores in the multi-core optical waveguide 311D. Compared to the optical sensor system 100B, the use of the multi-core fiber fan-out coupler 109 and the multi-core optical waveguide 311D in the optical sensor system 100D may eliminate the need for an optical circulator. Such a design may be advantageous for several reasons. For example, the multi-core fiber fan-out coupler 109 of the optical sensor system 100D may be smaller, lighter, and / or less expensive than an optical circulator, which may allow for greater flexibility when incorporating the optical fiber sensor 101D into a device or apparatus. In an embodiment, other suitable optical couplers configured to couple a single-core optical fiber to a multi-core optical fiber may be substituted for the multi-core fiber fan-out coupler 109.

[0077] Figures 6G and 6H show optical sensor systems for use with optical fiber sensors according to embodiments herein. Figure 6H shows an optical resonator optical sensor configured for use with a single core optical fiber according to embodiments herein. The optical sensor system 100E of Figure 6G is configured for use with a dual optical fiber resonator sensor 101E as shown in Figure 6H. In further embodiments, other optical sensors discussed herein may be employed in a dual optical fiber system, including, for example, an interferometric sensor.

[0078] The optical fiber sensor 101E may include a fiber end sensor having an optical resonator-based acoustic sensor as described herein. The optical fiber sensor 101E may include a sensor fiber 301E having an optical resonator-based fiber end sensor structure 321D disposed at the end of the optical fiber sensor 101E. Except where noted, the sensor fiber 301E may include features and structure consistent with the features and structure of the sensor fibers 301 and 351.

[0079] The optical fiber sensor 101E may include a dual optical fiber structure. The optical fiber sensor 101E may include a first optical waveguide 311E having a first optical fiber core 313E and a second optical waveguide 315E having a second optical fiber core 312E. Each of the first optical waveguide 311E and the second optical waveguide 315E may be an individual optical fiber and each may have a separate cladding structure 314E. The first optical waveguide 311E and the second optical waveguide 315E may be integrally coupled. For example, the first optical waveguide 311E and the second optical waveguide 315E may be coupled via an adhesive or other adhesive.

[0080] The optical resonator fiber end sensor structure 321E is coupled to the ends of both the first optical waveguide 311E and the second optical waveguide 315E. The optical resonator fiber end sensor structure 321E may include an optical resonator sensor 322E in addition to additional structures and components configured to facilitate the functionality of the optical resonator sensor 322E, as described below. The optical resonator fiber end sensor 322E, as shown diagrammatically in FIG. 6H, may be waveguide coupled to receive an initial optical signal 111 (e.g., light) provided to the optical resonator fiber end sensor 322E via a first optical core 313E of the first optical waveguide 311E, and configured to provide a return optical signal 112 returning along a second optical core 312E of the second optical waveguide 315E. The return optical signal 112 may correspond to and represent an acoustic signal incident on the optical resonator fiber end sensor structure 321E. The incident acoustic signal may cause physical deformation and / or alteration of material properties of the optical resonator fiber end sensor structure 321E. Thus, the optical signal provided by the optical resonator fiber end sensor structure 321E along the second optical core 312E may be altered, affected, or otherwise indicative or representative of the acoustic signal, and may thus be used to characterize the incident acoustic signal. In the embodiment of FIG. 6G, for example, it is not necessary to provide the initial optical signal 111 to the optical receiving device 103 to measure the alteration of the optical properties, since the parameters of the initial optical signal 111 are known by the system.

[0081] The optical resonator fiber-end sensor structure 321E may include an acoustically responsive polymer portion 317E, including parylene or other suitable polymers that are sensitive to acoustic signals. The acoustic impedance of the polymer portion 317E may be selected to match (e.g., within 1%, 5%, 10%, or 20%) the acoustic impedance of the encapsulation structure (or cladding structure) of the sensor fiber 301E to enhance the sensitivity of the optical resonator fiber-end sensor structure 321E, as described above.

[0082] The optical sensor system 100E is configured for use with the resonator-based optical fiber sensor 101E. The optical sensor system 100D may include a light source 104, such as a laser, an optical receiving device 103, such as a photodetector, and one or more optical waveguides 105. The one or more optical waveguides 105 may be structurally constrained to one another to form a first optical waveguide 311E and a second optical waveguide 315E of the sensor fiber 301E, and may be separated to couple with the light source 104 and the optical receiving device 103. In an embodiment, a coupler or other device may be used to facilitate the splicing. In operation, the light source 104 provides an initial optical signal 111 to the optical fiber sensor 101E via the optical waveguide 105. The provided initial optical signal 111 travels to the optical resonator-based fiber end sensor structure 321E via the first optical waveguide 311E, may be affected by an incident acoustic signal, and then returned as a return optical signal 112 by the second optical waveguide 315E. The return optical signal 112 travels through the optical waveguide 105 and is received at the optical receiving device 103. As discussed above, the acoustic signal incident on the optical fiber sensor 101E modifies the optical properties (including the physical structure as well as the optical material properties) of the optical fiber sensor 101E. Such modifications of the optical properties can be measured from the return optical signal 112.

[0083] The dual-fiber design of the sensor fiber 301E eliminates the need for a circulator or multi-core fan-out coupler. Such a design may be advantageous for several reasons. For example, eliminating multi-core fiber fan-out couplers and optical circulators may provide a smaller, lighter, and / or less expensive system, which may allow for greater flexibility when incorporating the optical fiber sensor 101E into a device or apparatus.

[0084] 7A-7D provide examples of manufacturing techniques that may be used to shape or machine the end of an optical waveguide. FIG. 7A illustrates a method of CO2 laser machining of the end of an optical waveguide, for example to achieve a recess that matches the proximal reflective surface that is concave to the optical cavity. FIG. 7B illustrates a method of wet etching of the end of an optical waveguide, for example to achieve a recess that matches the proximal reflective surface that is concave to the optical cavity. FIG. 7C illustrates a method of mechanical polishing of the end of an optical waveguide, for example to achieve a recess that matches the proximal reflective surface that is concave to the optical cavity. FIG. 7D illustrates a method of CO2 laser machining of the end of an optical waveguide, for example to achieve a recess that matches the proximal reflective surface that is concave to the optical cavity.

[0085] 8A-8D provide examples of fabrication techniques that may be used to fabricate an optical resonator structure at the end of an optical waveguide. FIG. 8A illustrates a method of micromolding that may be used to form the optical resonator structure. FIG. 8B illustrates a method of dip coating that may be used to form the optical resonator structure. FIG. 8C illustrates a method of conformal coating that may be used to form the optical resonator structure. FIG. 8D illustrates a method of dip coating that may be used to form the optical resonator structure.

[0086] FIG. 9A illustrates a method of thermal tuning applied to the sensor fiber. An interferometric fiber sensor (or other optical sensor structures according to embodiments herein) can benefit from a wavelength tuning mechanism to maintain the interferometric fiber sensor at an optimal operating point. The optimal operating point can be based on the resonance of the optical sensor structure. In embodiments, the resonant wavelength of the optical sensor structure and the operating wavelength of the laser providing the optical signal can be selected, adjusted, or determined collectively to optimize or maximize the optical readout. The resonant 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 matches the slope of the resonance peak of the optical sensor structure. The specific location on the slope of the resonance peak can vary according to the design and application specific requirements of the sensor. The specific operating location on the slope of the resonance peak affects the dynamic range and sensitivity of the optical sensor structure. In embodiments, the operating position (e.g., wavelength) may be selected to have a response amplitude within 10% to 90% of the resonance depth, within 10% to 30% of the resonance depth, within 30% to 50% of the resonance depth, within 50% to 70% of the resonance depth, or within 70% to 90% of the resonance depth. Thus, wavelength tuning according to embodiments herein may include tuning either the operating wavelength of the optical sensor or the laser or resonance wavelength to achieve this.

[0087] Wavelength tuning mechanisms according to embodiments herein may include, for example, a heating or tuning laser, or an external regulator configured to tune via application of mechanical stress and / or electrothermal heating. Although a tunable laser in a back-end system may provide tunability, individual tunability (local tuning) at the sensing front-end is also desirable because it may enable (1) cheaper lasers without wavelength tunability, and (2) scalable sensor arrays with shared lasers. FIG. 9A shows one method for local tuning using photothermal tuning that does not require extra cables. In one embodiment, light from a surgical laser (of different wavelengths) and a heating laser are guided collectively by a fiber. The surgical laser wavelength may be selected to optimize sensing performance, and at least one structure at the fiber end (e.g., optical resonator structure 321, part of encapsulation structure 314, etc.) is absorptive at the heating wavelength. By adjusting the power of the heating laser light, the local temperature at the optical resonator structure 321 is altered, and thus the temperature-sensitive optical transmittance of the optical fiber sensor is adjusted to better match the wavelength of the surgical laser. Thus, the heating laser is operated to adjust the temperature of the optical resonator structure 321 according to the wavelength of the surgical laser. The heating laser may be either continuous wave or pulse width modulated. In one embodiment, the sensor fiber 301C may have a dual cladding structure. Any of the sensor fibers 301 / 301A / 301B may incorporate the features of the sensor fiber 301C. The sensor fiber 301C may include an inner cladding structure 313A and an outer cladding structure 313B. If the heating wavelength is longer than the cutoff wavelength of the core optimized for operating optical transmission, the outer cladding structure 313B may be introduced.

[0088] In another local adjustment method shown in FIG. 9B, an external adjuster 902 may be provided to replace the heating laser, for example to adjust the sensor transmittance through application of mechanical stress or electrothermal heating. FIG. 9B shows a sensor fiber 301 with an optical resonator structure 321 as an example. Any suitable sensor fiber and optical fiber sensor may be used with the external adjuster 902. The external adjuster 902 may include, for example, a piezoelectric and / or electrothermal element external to the optical cavity, which may be configured to apply pressure (i.e., compression) or heat to the optical resonator structure 321. This may require additional electrical cables, wires, traces, and / or microheater printed flex circuits along the length of the fiber sensor to enable the external adjuster. The extra structure does not affect the optical properties of the sensor, as long as the sensor optical path (within the dashed box 368) in the optical resonator structure 321 is not interrupted.

[0089] In a further example, the optical resonator structure 361 may have an operating wavelength tuned to more closely align with the wavelength of the light source (e.g., source laser). When multiple fiber optic sensors are arranged in an array, the ability to individually calibrate and fine-tune each fiber optic sensor in the array provides the possibility to drive and synchronize the operation of each sensor in the array. This synchronization may also allow a user to drive multiple (two or more) fiber optic sensors with one source laser and capture signals from multiple sensors simultaneously. Such a feature is advantageous in building sensor arrays for imaging. In this process, a feedback loop may be employed to monitor and adjust heat sources or stresses and fine-tune the operating wavelength of the sensor to ensure alignment of the sensor with the source laser. Through simultaneous capture of multiple data points or joint analysis of sophisticated imaging patterns, the synchronized operation of the sensor array ensures robust data interpretation.

[0090] 10 illustrates an embodiment of a sensor fiber including a multi-core optical waveguide. The sensor fiber 801 may include any or all of the features of the sensor fibers 301 and 351, as described above. The sensor fiber 801 may include an optical waveguide 811 and an optical resonator structure 321. The optical waveguide 811 includes multiple cores 312, e.g., 2, 3, 4, 5, 6, 7, 8, 9, etc., within a cladding structure 313.

[0091] 11A and 11B show a comparison between a sensor fiber arranged with a forward facing optical sensor and a sensor fiber arranged with a sideways optical sensor. When incorporating a sensor into a device, consideration of the environment in which the sensor will be used and the direction of the transmitted acoustic beam are important considerations. For example, some use cases of the optical sensors disclosed herein may benefit from a forward facing arrangement, while other use cases may benefit from a sideways arrangement.

[0092] 11A shows a sensor fiber 351 with a Fabry-Perot cavity that functions as an optical resonator as part of an optical resonator structure, consistent with the sensor fiber shown in FIG. 3A. The optical resonator structure 361 is arranged in a forward-looking configuration. In the forward-looking configuration, the face or surface of the optical resonator structure 361 configured to receive and detect acoustic signals (in optical resonator 362, this face may be the distal reflective surface 364 or the proximal reflective surface 363) is positioned such that the acoustically responsive surface is oriented in the same direction as the sensor fiber 351 extends. The sensor fiber 351 and the acoustically responsive surface or face may share an axis.

[0093] FIG. 11B illustrates a sensor fiber 1001 having a Fabry-Perot resonator functioning as an optical resonator as part of an optical resonator structure 1021 arranged for sideways capture of an incident acoustic signal. The sensor fiber 1001 may include all of the features of the sensor fibers 301, 351, 701, and 801 (even though not shown). The sensor fiber 1001 may include one or more cores 1012, one or more cladding structures 1013, an encapsulation structure 1014, and an optical resonant structure 1021. The optical resonant structure 1021 may include a Fabry-Perot resonator as shown in FIG. 11B and / or any other type of optical resonator discussed herein. The optical resonant structure 1021 may include a distal reflective surface 1064 and a proximal reflective surface 1063 arranged on either side of an optical cavity 1065. In one embodiment, the optical resonant structure 1021 is configured in a sideways configuration. In the landscape configuration, an acoustically responsive face or surface of the optical resonator structure 1021 is 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) and is positioned such that the acoustically responsive face or surface is oriented in the same direction that the sensor fiber 351 extends. The sensor fiber 351 and the acoustically responsive surface or surface can have an axis that is substantially perpendicular to the axis of the sensor fiber 1001. In a further embodiment, the angle between the axis of the acoustically responsive surface or surface and the axis of the sensor fiber 1001 can be 0.1 to 1.5 mm, depending on the desired angle of acoustic sensitivity. ° It can be ~90°.

[0094] FIG. 12 illustrates an embodiment of a sensor fiber that provides acoustic detection capability from a direction behind the distal end of the sensor, or proximal detection capability, and according to embodiments herein. The sensor fibers described herein, such as the sensor fiber 301, the sensor fiber 351, the sensor fiber 701, and the sensor fiber 801, may have increased proximal detection capability. FIG. 12 illustrates the sensor fiber 351 having an optical resonator structure 361 with a proximal reflective surface 363 and a distal reflective surface 364 arranged to share an axis with the optical waveguide 371. Both the proximal reflective surface 363 and the distal reflective surface 364 act as acoustically responsive surfaces. To increase the rearward capability, the cladding structure 353 may include a material selected to minimize the acoustic impedance mismatch with the intended medium in which the sensor fiber 351 will be used. Minimizing the acoustic impedance mismatch increases the critical angle of the boundary between the sensor fiber 351 and the medium in which the sensor fiber 351 is disposed, allowing the optical resonator structure 361 to receive acoustic signals from a larger angular range. For example, a sensor fiber 351 intended for use within the human body may include a cladding structure 353 comprising a polymer selected to optimize detection sensitivity by minimizing any acoustic impedance mismatch. In an embodiment, the cladding structure 353 may be selected to have at least one of a Young's modulus (E) smaller than that of the core 352, a photoelastic coefficient larger than that of the core 352, and a refractive index (n) smaller than that of the core 352. In an embodiment, the cladding structure 353 may 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). Reducing the acoustic impedance mismatch serves to increase the acoustic signal that penetrates the cladding structure 353 and strikes the proximal reflective surface 363. A smaller Young's modulus may increase the stress-related deformation of the cladding structure 353, which may increase sensitivity to incident acoustic signals.A higher photoelastic coefficient may also result in greater sensitivity to acoustic signals, since the optical properties of such materials exhibit greater strain-related changes. Further suitable materials for the cladding structure 353 may include ultrasonically enhanced materials such as polyvinylidene fluoride, parylene, polystyrene, etc.

[0095] FIG. 13 illustrates an embodiment of a sensor fiber that provides increased backward-looking acoustic detection capability according to embodiments herein. The sensor fibers described herein, such as the sensor fiber 301, the sensor fiber 351, the sensor fiber 701, and the sensor fiber 801, may be provided with increased backward-looking detection capability, as illustrated in FIG. 13. FIG. 13 illustrates a sensor fiber 1251 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 arranged to share an axis with the optical waveguide 371 (e.g., the optical resonator is arranged in the same manner as the forward-looking configuration described above). An optical cavity 365 is disposed between the proximal reflective surface 363 and the distal reflective surface 364. Both the proximal reflective surface 363 and the distal reflective surface 364 act as acoustically responsive surfaces. The optical resonator structure 1261 may further include any of the features of the optical resonators and optical resonator structures discussed herein in any suitable combination. To increase the backward facing capability, the optical resonator structure 1261 may include a distal portion of the optical waveguide 371 configured to increase the acoustic sensitivity, specifically at the proximal reflective surface 363. The optical resonator structure 1261 may include a cladding structure at the distal end of the optical waveguide 371, which may include a proximal cladding structure portion 353A and a distal cladding structure portion 353B. The distal cladding structure portion 353B is disposed on the optical resonator side. The distal cladding structure portion 353B may be selected to have a material that reduces or minimizes the acoustic impedance mismatch with the intended medium in which the sensor fiber 1251 will be used. For example, the distal cladding structure 353B may include a polymer, as discussed above. In an embodiment, the distal cladding structure 353B may include benzocyclobutene (BCB) or polydimethylsiloxane (PDMS), each of which have a small Young's modulus (E), a high photoelastic coefficient, and a smaller refractive index (n). The distal cladding structure 353B may have a length dimension sufficient to allow an acoustic signal from a backward angle to reach the proximal reflective surface 363 of the optical resonator.Proximal cladding structure portion 353A may comprise any suitable material for optical waveguides, including, for example, silica.

[0096] FIG. 14 illustrates a directional range of an optical resonator structure according to an embodiment herein. As discussed above, the optical resonator structure 1261 may be configured to detect acoustic signals over a wide incidence range. In an embodiment, the optical resonator structure 1261 may be configured to detect acoustic signals over 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 may be configured to detect acoustic signals in an omnidirectional manner, for example, over a range of 360 degrees. FIG. 14 illustrates a side view of an optical resonator structure 361 according to an embodiment herein. A circle 1305 represents a range of 360 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 range of 360 where an acoustic signal may be incident on the optical resonator structure 1261. The optical resonator structure 1261 may be configured to detect acoustic signals within the acoustically responsive portions 1303 of the circle 1305 and may have reduced sensitivity or detectability in the reduced acoustic sensitivity portions, including the lateral portions 1301 and the core portion 1302. In the lateral portions 1301, the incident acoustic signal may be less detectable due to the oblique angle of the incident acoustic signal incident on the reflective surface of the optical resonator. In the core portion 1302, the acoustic signal may be less detectable due to blocking from the core of the optical waveguide. The sum of the extents of the acoustically responsive portions 1303 may represent the extent to which the optical resonator structure 1261 detects acoustic signals. Different arrangements of the optical resonator structure (e.g., a lateral optical resonator structure 1021) may have different arrangements of the acoustically responsive portions 1303 and the reduced acoustic sensitivity portions.

[0097] In an embodiment, the optical resonator structure 361 is radially symmetric. Thus, the acoustic responsiveness range defined by the two-dimensional circle 1305 may be rotated about axis 1307 to define a three-dimensional acoustic responsiveness range of the optical resonator structure 1261. It will be appreciated that additional effects on the acoustic responsiveness range may be caused by structures surrounding the optical resonator structure 1261, including, for example, the medical device distal end 231.

[0098] 15 illustrates an optical resonator structure including an in-fiber Bragg grating according to an embodiment herein. The optical resonator structure 1421 may be provided in combination with any of the sensor fibers discussed herein. The optical resonator structure 1421 includes a distal reflective surface 1464, an elongated optical cavity 1465 with 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 may include a polymer (e.g., benzocyclobutene (BCB) or polydimethylsiloxane (PDMS)), while the proximal cladding structure 1453B may include, for example, silica glass. The proximal cladding structure 1453B may be longer than the distal cladding structure 1453A, for example, by more than two times, more than five times, more than ten times, etc. In one embodiment, the proximal cladding structure 1453B may be approximately 10 times the length of the distal cladding structure 1453A, e.g., the distal cladding structure may be approximately 10 microns in length while the proximal cladding structure is approximately 100 microns in length. In an embodiment, the proximal cladding structure 1453B may 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 an embodiment, the proximal cladding structure 1453B has a photoelastic coefficient C1=-6*10 -13 1 / Pa and C2=-4.2*10 -12 1 / Pa, while the distal cladding structure 1453A may have a photoelastic coefficient C1=-4.8*10 -11 1 / Pa and C2=-2.9*10 -111 / Pa. Although these numerical values ​​are provided, such photoelastic coefficients are relative values ​​depending on the material selected. 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 to define a variation in the refractive index of the core 1412, thereby creating a structure that can reflect light of specific wavelengths. 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 of the acoustic signal. The distal cladding structure 1453A can be fabricated via two-photon polymerization (TPP) 3D printing directly on top of the fiber with an 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 trade-off between wide bandwidth and high sensitivity. In this hybrid configuration, the total length of the elongated optical cavity 1465 is longer since the total length is the sum of the distal cladding structure 1453A and the proximal cladding structure 1453B. With a longer cavity length, the frequency bandwidth response may be narrower in a typical design. However, in this hybrid configuration, the effective sensor thickness remains very small, providing a broadband response, since the main response of the FPI sensor comes from the polymer region.

[0099] 16 illustrates method steps for generating location and imaging information with a fiber-optic optical sensor. Further details can be found in U.S. Provisional Application No. 63 / 522,994, filed June 23, 2023, entitled Transponder Tracking and Ultrasound Image Enhancement, and U.S. patent application having attorney docket number 109835-1394978, filed concurrently October 23, 2023, entitled Transponder Tracking and Ultrasound Image Enhancement.

[0100] The method 2000 may include block 2010, where a transponder, for example, the acoustic probe 245 shown in Figure 2, transmits acoustic pulses into the medium. The transponder may transmit these pulses using a variety of known methods or as described above.

[0101] In block 2020, the fiber optic sensor 101 receives the ultrasonic pulses and / or scattered signals or tissue harmonics transmitted from the probe 245. The fiber optic sensor 101 then converts the ultrasonic pulses, scattered signals, and / or tissue harmonics into signals that are then transmitted to the processing unit 209.

[0102] In block 2030, the processing unit 209 determines a location of the fiber sensor based at least in part on the signals received from the probe 245. For example, the processing unit 209 may utilize triangulation or coherent imaging to determine the position of the medical device distal end based on the signals received from the probe 100 and the fiber optic sensor 101.

[0103] In block 2040, the processing unit 209 and the image reconstruction unit 206 generate an ultrasound image based on the signal returned to the probe 245 and / or the scattered signal and tissue harmonics sensed by the fiber sensor. The ultrasound image may be transmitted to a display and displayed on the display.

[0104] At block 2050, the processing system modifies the ultrasound image based on the ultrasound pulses received from the fiber optic sensor 101. In an embodiment, the processing system may also generate and display an ultrasound image based on the ultrasound pulses received by the fiber optic sensor without information from the ultrasound pulses received by the probe 245.

[0105] At block 2060, the processing system 200 overlays the location of the fiber optic sensor 101 on the ultrasound image. Thus, when viewed by a user, such as an ultrasound technician, a doctor, other medical personnel, or a patient, the fiber optic sensor 101 at the distal end of the medical device is shown on the same display as the ultrasound image, showing where in the medium the fiber optic sensor 101 at the distal end of the medical device is located.

[0106] 17A and 17B show needles configured with sensor fibers according to embodiments herein. The needle 1500A may be an example of a medical device distal end 231 and may include one or more sensor fibers 1501 integrated with the needle 1500A. The sensor fiber 1501 may include any of the sensor fibers described herein (having any of the optical resonator structures) and / or any combination of the sensor fiber features described herein. The needle 1500A may be any type of needle of any suitable size or functionality. The needle 1500A comprises 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 sharpening angle 1523. Additionally, the needle 1500A includes at least one sensor channel 1512 extending on the needle body 1505 for at least a portion of the length of the needle shaft portion 1510 and the needle tip portion 1511.

[0107] In an embodiment, the sensor channel 1512 may include a trench, recess, or groove in the needle body 1505. The sensor channel 1512 may be sized and configured to receive the sensor fiber 1501 according to embodiments herein. For example, in an embodiment, the sensor channel 1512 may be approximately 125-250 microns wide to accommodate a sensor fiber 1501 having a diameter of 80 microns. The needle 1500A may include multiple sensor channels 1512 to accommodate multiple sensor fibers 1501. For example, the needle 1500A may include two, three, four, or more sensor channels 1512 to accommodate multiple sensor fibers 1501 arranged around the circumference of the needle 1500A. The sensor fiber 1501 is positioned within the sensor channel 1512 such that a distal end supporting the optical resonator structure is positioned at or adjacent to the distal end. The sensor channel 1512 can be configured with a depth such that the sensor fiber 1501 does not extend beyond the outer surface of the needle body 1505.

[0108] In further embodiments, the sensor channel may be created by adding material to the outer surface to form a channel, for example as a guide. In one example, material may be layered onto the outer surface of the needle to create the channel 1512 as a raised continuous or intermittent structure. In another example, adhesive material or tape may be wrapped in a spiral configuration with spaces within the spiral to form the sensor channel or selectively positioned along the length of the needle to form the sensor channel and guide the sensor fiber along the length. In yet another example, the extrusion needle may include a tubular sensor channel in the form of a lumen through the extrusion needle.

[0109] The sensor channel 1512 allows the sensor fiber 1501 to be placed within a protected area of ​​the needle body 1505. This helps protect the sensor 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 in FIG. 17B) or on the inner surface of the needle body 1505.

[0110] The sensor fiber 1501 may be fixed to the needle body 1505. In an embodiment, the sensor fiber 1501 may be fixed in the sensor channel 1512 by a potting compound, such as Norland-65 adhesive, Norland 81 adhesive, MY-132A polymer, MY-133, BIO-133, DC-133, or any other suitable potting compound. The potting compound may be selected according to the acoustic and mechanical properties of the potting compound, such as sound speed, acoustic impedance, thermal conductivity, waterproofing, etc. The potting compound may also provide a correction of acoustic impedance matching to the surrounding medium in addition to mechanical fixation and protection of the sensor. The potting compound may be employed over the entire or a portion of the sensor channel 1512. In an embodiment, the sensor fiber 1501 may be fixed in the sensor channel 1512 by a sheath 1520. The sheath 1520 is configured to wrap around the needle body 1505. The sheath 1520 may mechanically secure the sensor fiber 1501 to the needle body 1505. The sheath may wrap around the needle with the fiber inside the slot and allow the fiber to float freely within the groove / slot. This may allow bending / flexibility of the needle. In an embodiment, the sensor fiber 1501 may be at least partially secured by both the sheath 1520 and the potting compound. Such an arrangement may allow relative movement between the sensor fiber 1501 and the needle body 1505 and thus provide potential strain relief in case the needle is bent. The needle 1500A may be manufactured of any suitable material including medical grade materials including, for example, metals such as stainless steel or polymers such as PEEK (polyetherketone). In an embodiment, the needle 1500 may be manufactured via additive manufacturing techniques such as 3D printing, injection molding, or extrusion.

[0111] Further embodiments of needles incorporating fiber-based optical sensors are shown in Figures 18A and 18B. The needle 1500B may further include one or more windows 1513. The windows 1513 are openings in the needle body 1505 disposed at the ends of the sensor channels 1512. The needle 1500B may include multiple sensor channels 1512 and corresponding multiple windows 1513 to accommodate multiple sensor fibers 1501. The sensor fibers 1501 may be disposed within the sensor channels 1512 such that the distal ends supporting the optical sensors extend within the windows 1513. In this embodiment, the distal ends of the sensor fibers 1501 may be secured within the windows 1513 by potting compound, while the proximal portions of the sensor fibers 1501 may be secured to the needle body 1505 by the sheath 1520. This allows for relative movement between the sensor fibers 1501 and the needle body, thus providing strain relief in the event the needle is bent.

[0112] 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 may create a boundary for acoustic signal diffraction, allowing the acoustic signal to bend and propagate around the edge of the window to reach the fiber optic sensor at the end of the sensor fiber 1501. The diffraction effect serves to increase the circumferential range of acoustic signal detection of the sensor fiber 1501. In addition, the edges of the channel on the surface of the needle may also have a diffraction effect that aids in needle shaft detection.

[0113] In embodiments, an optical ultrasound sensor according to embodiments herein may be integrated with a medical device (e.g., medical device distal end 231) and may cooperate with an ultrasound source (array) configured at an ex vivo location to provide location information of the medical device distal end 231 and / or provide real-time acoustic monitoring in the area of ​​the treatment target / anatomy. In different application scenarios, the input acoustic signal direction may be broadly classified into two types, namely, (1) transverse fire, and (2) axial fire, as shown in Figures 18C and 18D.

[0114] Figures 18C and 18D show an acoustic signal incident on a sensor fiber disposed in needle window 1513. For purposes of clarity, the sensor fiber is not shown in these figures. Figure 18C shows a transverse acoustic signal 1600 and Figure 18D shows an axial acoustic signal.

[0115] The transverse acoustic signal 1600 in Figure 18C is typical of a situation that may occur when using a side-view endoscopic ultrasound transducer or an external transducer. The location of the window 1513 close to the needle tip portion 1511 allows the ultrasonic field to reach the window (and the fiber end sensor structure located within the window) from either side without being blocked from the opposite wall of the needle. The fiber end sensor structure itself may be positioned in a side-facing or forward-facing fashion and may be a polarized sensor configured to receive a transverse (transverse) signal, depending on the requirements of the application.

[0116] The axial acoustic signal 1601 in FIG. 18D is typical of the situation that occurs with a front-view endoscopic ultrasound transducer. Due to the small footprint of the endoscopic device, the typical angle of incidence may be small relative to the needle body. As shown in FIG. 18D, if the angle of incidence is smaller than the needle sharpening angle 1523 (as shown in FIG. 18D), at least a portion of the acoustic signal 1601 may be blocked by the needle body (shown with thicker crosshatch). To address this, in one embodiment, an additional window 1513 may be included in the needle body 1505 opposite the sensor window 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 may be manipulated to ensure that low angle axial acoustic signals arrive from portions of the needle where the optical resonator structure is not located. In another embodiment, the sharpening angle 1523 may be selected according to the expected acoustic angle of incidence.

[0117] A further embodiment of a needle incorporating a fiber-based optical sensor is shown in Figure 19. Similar to needles 1500A and 1500B, needle 1500C comprises 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 sharpening angle. Additionally, needle 1500C includes at least one sensor channel 1512 extending on needle body 1505 for at least a portion of the length of needle shaft portion 1510 and needle tip portion 1511. Needle 1500C may include one or more sensor fibers 1501C disposed in one or more sensor channels 1512 of needle 1500C. The sensor fiber 1501C may be similar to the sensor fiber 301C and may therefore include a fiber end sensor structure 1521 disposed at the end of the sensor fiber 1501C and one or more polarized sensor structures 1522 disposed along the length of the sensor fiber 1501C. The polarized sensor structure 1522 located along the length of the needle 1500C may provide enhanced visualization of the needle 1500C when an acoustic signal used to track or visualize the needle 1500C strikes the polarized sensor structure 1522. Information gathered from an optical signal indicative of an incident acoustic signal may be employed alone and / or in combination with a traditional acoustic ultrasound image to provide improved visualization of the needle 1500C. The polarized sensor structure 1522 may operate according to the principles discussed above with respect to the polarized sensor structure 322C and with respect to FIGS. 6D and 6DD.

[0118] 20A and 20B provide further close-up views of needle 1500 with integrated sensor fiber 1501. FIG. 20A shows a perspective view from a first side of needle 1500 where channel 1512 is located, and FIG. 20B shows a perspective view from a second side of needle 1500 opposite the first side. The second side of needle 1500 includes a view of the interior of needle 1500 at needle tip portion 1511. As shown, sensor fiber 1501 is disposed within sensor channel 1512 of needle 1500 that extends from needle shaft portion 1510 to needle tip portion 1511. Window 1513 is disposed within needle tip portion 1511, thereby ensuring that both sides of window 1513 (and sensor fiber 1501 disposed within window 1513) are exposed to the input acoustic signal. 20A-20B further show a potting compound 1525 that secures the sensor fiber 1501 within the window 1513. As shown in FIG.

[0119] In a further embodiment shown in FIG. 20C, the sensor fiber 1501D may be fixed to the surface of the needle body 1505D of the needle 1500D without a channel or other fiber receiving structure. A suitable polymer or compound 1527 selected according to its acoustic and mechanical properties may be used to fix the fiber 1501D to the needle 1500D. The suitable polymer or compound 1527 may be selected according to its acoustic and mechanical properties, such as sound speed, acoustic impedance, thermal conductivity, waterproofness, etc. The suitable polymer or compound 1527 may also provide a modification of the acoustic impedance to match the surrounding medium in addition to mechanical fixation and protection of the sensor on its surface. Similarly, as shown in FIG. 20D, a sheath 1520D may be used to fix the sensor fiber to the needle body 1505D. The sheath 1520D is configured to wrap around the needle body 1505D. The sheath 1520D may mechanically secure the sensor fiber 1501D to the needle body 1505D. The sheath may wrap around the needle in a manner that allows some movement of the fiber within the sheath. This may allow bending / flexibility of the needle. In an embodiment, the sensor fiber 1501D may be at least partially secured by both the sheath 1520D and the polymer or compound 1527. Such an arrangement may allow relative movement between the sensor fiber 1501D and the needle body 1505D, thus providing potential strain relief in the event the needle is bent. This embodiment may further include a window in the manner of other embodiments incorporating a window, and a potting compound or polymer may be used to further secure the fiber located within the window in the manner of the previous embodiment.

[0120] FIG. 21 illustrates a medical device distal end incorporating a fiber end sensor according to an embodiment herein. The medical device distal end 1901 includes a medical tool such as a catheter 1902 and a needle 1903. The catheter 1902 is configured to carry a needle 1903 to a treatment and / or diagnostic site via a lumen 1904 (e.g., provide access through a lumen through which the needle may be conveyed). The catheter 1902 may 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 be extended (e.g., by an operator, human, or robot) from the lumen 1904 of the catheter 1902 upon reaching the treatment and / or diagnostic site. In an embodiment, the needle 1903 is configured similarly to the needle 1500 and may include one or more sensor fibers 1501 disposed with or integrated with the needle 1500. In an embodiment, the catheter 1902 may include one or more sensor fibers and one or more acoustic transducers disposed on or integrated with the catheter 1902. In an embodiment, the one or more sensor fibers 1501 may be used to sense, monitor, and / or track the location of the needle 1903 based on acoustic signals generated by an acoustic transducer / probe located outside the medium in which the catheter 1902 is being used (e.g., the one or more sensor fibers 1501 and the one or more acoustic transducers disposed on the catheter 1902 may be used to generate images, for example, through detection of acoustic echoes by the one or more sensor fibers. The one or more acoustic transducers may generate acoustic signals while the one or more sensor fibers receive echoes or reflections of the acoustic signals based on interaction with the surrounding medium. The acoustic transducers may also receive reflected or scattered acoustic signals and / or tissue harmonics, which may then be used to create an image of the surrounding area to which tracking information is added.

[0121] FIG. 22 illustrates an exemplary use of a fiber-optic optical sensor integrated into a needle. The illustrated use may incorporate needle 1500A, needle 1500B, 1500C, 1500D, or any suitable needle incorporating a fiber-optic optical sensor. As illustrated in FIG. 22, an external acoustic probe 2245 may be employed with needle 1500A / B / C / D incorporating a fiber-optic optical sensor. As discussed herein, in one embodiment for localization / guidance, the fiber-optic optical sensor may receive acoustic signals generated by the external acoustic probe 2245. These acoustic signals may then be used alone or in combination with reflected acoustic signals captured by the acoustic probe to determine the location of the needle within the medium 2260 (e.g., the patient's body).

[0122] 23A-23B show an embodiment of a fiber-optic optical sensor incorporated into a catheter delivery needle. The catheter delivery needle may be used, for example, for a biopsy procedure. The needle 2515 may be delivered to a treatment site via a catheter 2503. The needle 2515 may incorporate a fiber-optic optical sensor 2501, as described in various embodiments herein. Once delivered to a treatment site via the catheter 2503, the needle 2515 may extend from a lumen of the catheter 2503 to perform the procedure. The needle 2515 may be monitored, guided, and / or localized through the use of one or more external acoustic transducers that provide acoustic signals received by the fiber-optic optical sensor 2501. The acoustic transducers may be associated with an optical sensor system, for example. The optical sensor system, which may be one example of various optical sensor systems described herein, may provide the necessary processing and signal generation / reception requirements to perform the optical acoustic signal sensing methods described herein. In a further embodiment, the catheter 2503 may include one or more additional transducers, as shown in FIG. 23B. For example, the catheter may include a mixed acoustic array 2507 including one or more of an AEG (or other suitable acoustic transducer array) array and a PIC (photonic integrated circuit) optical sensor array. U.S. Patent Application Publication No. 20230148869, filed November 18, 2022, entitled Mixed Ultrasound Transducer Arrays, and U.S. Patent Application Publication No. US20220350022, filed April 29, 2021, entitled Modularized Acoustic Probe, and incorporated herein by reference, disclose various optical sensors that may be used in a mixed transducer array. The PIC array may be adapted for detection of acoustic signals. Similar to the fiber end sensor discussed herein, the PIC array may be adapted for detection of acoustic signals by measuring or detecting changes in the optical properties of the PIC array resulting from the incidence of an acoustic signal.In an embodiment, acoustic signal data variously captured by the fiber-optic sensor 2501, the PIC array, the AEG array, and the external acoustic transducer may be used in any combination by the optical sensor system to monitor, guide, and position the needle 2515 (and the catheter 2503 adapted to deliver the needle 2515), as well as to generate an image of the medium (e.g., the treatment site) in which the catheter 2503 is deployed.

[0123] In further embodiments, fiber optic sensors according to embodiments herein may be employed in a variety of additional applications. For example, fiber optic sensors may be used to track a cannula configured with an optical camera and a movable ultrasound transducer for use in vivo during minimally invasive surgery. In another embodiment, a transcutaneous or percutaneous ultrasound probe may be configured with one or more fiber optic sensors according to embodiments herein. In another embodiment, a guidewire may be configured with one or more fiber optic sensors according to embodiments herein.

[0124] In further embodiments, real-time visualization of the device tip including the fiber optic sensor may be co-registered with diagnostic ultrasound images, eliminating the need for calibration. This breakthrough allows clinicians to reliably track devices in difficult anatomical regions. A real-time confidence indicator of where the device tip crosses the imaging plane may be provided, with special consideration to detect when the device tip leaves the imaging plane, thereby ensuring accurate device tip tracking even during complex procedures. A real-time line-of-sight visualization of the tip trajectory may be provided, providing valuable insight into the predicted path of the device tip and visualization of the device tip track, which may be used for enhanced procedure confidence and documentation. Furthermore, devices incorporating fiber optic sensors as described herein may facilitate the display of anatomical and blood flow images from the indwelling sensor co-registered with cross-sectional images, which may increase diagnostic accuracy and confidence.

[0125] The terms used herein are merely for the purpose of describing particular embodiments and are not intended to be limiting of the present invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It is further understood that as used herein, the terms "includes" and / or "including" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0126] Additional embodiments may include the following.

[0127] Embodiment 1 is an apparatus comprising a sensor fiber including an optical waveguide having a core and cladding structure, and an optical sensor structure coupled to a first end of the optical waveguide, the optical sensor structure including at least one of an optical resonator, an optical interferometer, a facet end microstructure, and a polarization sensing structure, the optical sensor structure being configured to detect an acoustic signal and provide an optical signal corresponding to the acoustic signal to the optical waveguide.

[0128] Example 2 is the device of example 1, further comprising an encapsulation structure configured with a first portion surrounding the optical waveguide and a second portion at least partially surrounding the optical sensor structure.

[0129] Example 3 is the device according to example 1 or 2, wherein the optical sensor structure is an optical fiber sensor.

[0130] Embodiment 4 is the device according to any one of embodiments 1 to 3, wherein the optical sensor structure is an optical resonator including a Fabry-Perot resonator, a whispering gallery mode resonator, a microring, a microtoroid, a spiral resonator, or a photonic crystal resonator.

[0131] A fifth embodiment is the device according to any one of the first to third embodiments, in which the optical sensor structure is an optical interferometer including a Mach-Zehnder (MZ) interferometer, a Fabry-Perot interferometer, a phase-shifting coherent interferometer, or a self-mixing interferometer.

[0132] Example 6 is a device according to any one of Examples 1 to 3, wherein the optical sensor structure is a fiber end facet including an acoustically responsive metasurface pattern, an acoustically responsive low dimensional material, or a plasmonic structure patterned to amplify light-matter interactions.

[0133] Example 7 is the device of any one of Examples 1 to 6, wherein the optical sensor structure is configured to induce a change in the polarization of the transmitted light in response to an acoustic signal.

[0134] An eighth embodiment is the device according to any one of the first to seventh embodiments, wherein the optical sensor structure is a point sensor or a line sensor.

[0135] Example 9 is the device of any one of Examples 1-8, wherein the core or cladding structure comprises a material having at least one of a relatively low Young's modulus (E) and a relatively high photoelastic coefficient.

[0136] Embodiment 10 is the device of any one of embodiments 1 to 9, wherein the cladding structure has a lower refractive index (n) than the core.

[0137] An eleventh embodiment is the device of any one of the first to tenth embodiments, wherein the acoustic impedance of the encapsulation structure is selected to match an impedance within 20% of the optical resonator structure impedance.

[0138] Example 12 is the device of any one of Examples 2 to 11, wherein the encapsulation structure comprises a material having a relatively low Young's modulus (E), a relatively high photoelastic coefficient, and / or a relatively high refractive index (n).

[0139] Embodiment 13 is the device of any one of embodiments 1-12, wherein the acoustic impedance of the encapsulation structure is selected to match an impedance within 20% of the optical resonator structure impedance.

[0140] A fourteenth embodiment is the apparatus according to any one of the first to thirteenth embodiments, further comprising a medical device in which the sensor fiber is disposed.

[0141] Embodiment 15 is the apparatus of embodiment 14, wherein the medical device is one of a needle, an endoscope, a catheter, a cannula, a guidewire, a surgical tool, a diagnostic tool, or a therapeutic tool.

[0142] Embodiment 16 is an apparatus described in embodiment 15, wherein the medical device is a needle including a shaft portion configured to receive a sensor fiber and a tip portion configured to receive an optical sensor structure.

[0143] Embodiment 17 is the device of embodiment 16, wherein the needle further comprises a window in the shaft portion or tip portion adjacent to the optical sensor structure.

[0144] Example 18 is the device described in Example 16, wherein the needle further includes a channel disposed in the shaft portion, and the sensor fiber is disposed within the channel.

[0145] Example 19 is the device described in Example 16, wherein the needle further includes a sheath disposed around the needle and configured to contain the sensor fiber.

[0146] Embodiment 20 is the device described in embodiment 17, wherein the needle further comprises a plurality of additional windows in the shaft portion or the tip portion.

[0147] Embodiment 21 is an apparatus described in any one of embodiments 1 to 20, wherein the optical sensor structure is configured to detect acoustic signals over a directional range of at least 180 degrees, at least 270 degrees, at least 300 degrees, at least 330 degrees, or 360 degrees.

[0148] Example 22 is the device of any one of Examples 1 to 21, wherein the optical sensor structure is configured for forward-looking detection of an acoustic signal.

[0149] Example 23 is the device of any one of Examples 1 to 22, wherein the optical sensor structure is further configured for backward detection of acoustic signals.

[0150] Example 24 is the device of any one of Examples 1 to 23, wherein the optical sensor structure is configured for sideways detection of the acoustic signal.

[0151] Example 25 is the device of any one of Examples 1 to 24, wherein the optical sensor structure includes a distal portion including silica and a proximal portion including a polymer.

[0152] Example 26 is the device of example 16, wherein the optical sensor structure comprises an in-fiber Bragg grating.

[0153] Embodiment 27 is the device according to any one of embodiments 1 to 26, wherein the core is included among a plurality of cores in the optical waveguide.

[0154] Embodiment 28 is an apparatus described in any one of embodiments 1 to 28, further comprising a light source configured to provide light to the optical sensor structure via an optical waveguide, an optical detector configured to receive an optical signal, and a processing unit configured to control the light source, receive optical data based on the optical signal from the optical detector, and perform at least one of image generation and location determination based on the optical data.

[0155] Embodiment 29 is an apparatus described in any one of embodiments 1 to 28, further comprising a wavelength tuning mechanism configured to tune the resonance of the optical sensor structure via application of at least one of thermal and mechanical stress.

[0156] Embodiment 30 is the device described in embodiment 28, wherein the light source is a surgical laser, and the processing unit is further configured to adjust the wavelength of the surgical laser.

[0157] The embodiments described above are illustrative examples, and the present invention should not be construed as being limited to these specific embodiments. It should be understood that the various embodiments disclosed herein may be combined in different combinations than those specifically presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain operations or events of any of the processes or methods described herein may be performed in a different order, added, integrated, or omitted entirely (e.g., not all operations or events described may be necessary to perform the method or process). In addition, although certain features of the embodiments herein are described as being performed by a single module, device, or unit for clarity, it should be understood that the features and functions described herein may be performed by any combination of units or modules. Thus, various changes and modifications may be effected by those skilled in the art without departing from the spirit or scope of the present invention, as defined in the appended claims.

Claims

1. An apparatus comprising: A sensor fiber is provided. The sensor fiber includes: an optical waveguide comprising a core and a cladding structure; an optical sensor structure coupled to a first end of the optical waveguide, the optical sensor structure comprising at least one of an optical resonator, an optical interferometer, a facet edge microstructure, and a polarization sensing structure; The optical sensor structure includes: Detecting an acoustic signal; An apparatus configured to provide an optical signal corresponding to the acoustic signal to the optical waveguide.

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

3. The apparatus of claim 1 , wherein the optical sensor structure is a fiber optic sensor.

4. The apparatus of claim 1 , wherein the optical sensor structure is an optical resonator comprising a Fabry-Perot resonator, a whispering gallery mode resonator, a microring, a microtoroid, a spiral resonator, or a photonic crystal resonator.

5. 10. The apparatus of claim 1, wherein the optical sensor structure is an optical interferometer, including a Mach-Zehnder (MZ) interferometer, a Fabry-Perot interferometer, a phase-shifting coherent interferometer, or a self-mixing interferometer.

6. 10. The apparatus of claim 1, wherein the optical sensor structure is a fiber end facet comprising an acoustically responsive metasurface pattern, an acoustically responsive low-dimensional material, or a plasmonic structure patterned to amplify light-matter interaction.

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

8. The apparatus of 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 low 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 apparatus of claim 2 , wherein the acoustic impedance of the encapsulation structure is selected to match an impedance within 20% of an optical resonator structure impedance.

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

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

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

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

16. The medical device comprises: a shaft portion configured to receive the sensor fiber; and a tip portion configured to receive the optical sensor structure.

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

18. The device of claim 16 , wherein the needle further comprises a channel disposed in the shaft portion, the sensor fiber being disposed within the channel.

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

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

21. The apparatus of claim 1 , wherein the optical sensor structure is configured to detect the acoustic signal over a directional range of at least 180 degrees, at least 270 degrees, at least 300 degrees, at least 330 degrees, or 360 degrees.

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

23. The apparatus of claim 1 , wherein the optical sensor structure is further configured for rearward detection of an acoustic signal.

24. The apparatus of claim 1 , wherein the optical sensor structure is configured for side-on detection of the acoustic signal.

25. The device of claim 1 , wherein the optical sensor structure comprises a distal portion comprising silica and a proximal portion comprising a polymer.

26. The apparatus of claim 16 , wherein the optical sensor structure comprises an in-fiber Bragg grating.

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

28. a light source configured to provide light to the optical sensor structure via the optical waveguide; a photodetector configured to receive the optical signal; A processing unit, The processing unit includes: Controlling the light source; receiving optical data based on the optical signal from the optical detector; The apparatus of claim 1 , configured to perform at least one of image generation and location determination based on the light data.

29. The apparatus of claim 1 , further comprising a wavelength tuning mechanism configured to tune a resonance of the optical sensor structure via application of at least one of thermal and mechanical stress.

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

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