CN-114787621-B - Ultrasonic sensing and imaging based on Whispering Gallery Mode (WGM) micro-electrostatic resonator

CN114787621BCN 114787621 BCN114787621 BCN 114787621BCN-114787621-B

Abstract

An acoustic sensor based on an optical Whispering Gallery Mode (WGM) resonator, an imaging system employing the acoustic sensor, and a method of detecting ultrasound waves using the acoustic sensor are disclosed.

Inventors

L.Yang
G.Zhao
X.Jiang
Y.LI

Assignees

华盛顿大学

Dates

Publication Date: 20260512
Application Date: 20200918
Priority Date: 20190918

Claims (17)

1. An acoustic sensor, comprising: An optical whispering gallery mode resonator; a coupling waveguide for optical coupling to the resonator, the coupling waveguide being separated from the resonator by a gap, and A polymer encapsulating a portion of the coupling waveguide and the resonator and filling the gap, the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator, wherein the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator includes an upper boundary of the polymer being a convex upper boundary; Wherein each of the resonator and the coupling waveguide has a refractive index higher than that of the polymer, Wherein the gap spacing is selected such that the acoustic sensor operates at an operating condition or maximum load factor of critical coupling of the resonator and the coupling waveguide when the polymer fills the gap spacing.
2. The acoustic sensor of claim 1, wherein the resonator comprises a diameter ranging from 50 μιη to 200 μιη.
3. The acoustic sensor of claim 1, wherein the separation gap ranges from 0.6 μιη to 0.8 μιη.
4. The acoustic sensor of claim 1, wherein the separation gap results in a maximum load factor during operation of the acoustic sensor.
5. The acoustic sensor of claim 1, wherein the coupling waveguide is a tapered optical fiber having a minimum tapered diameter of less than 1.5 μιη.
6. The acoustic sensor of claim 1, wherein the acoustic sensor encodes pressure fluctuations as fluctuations in transmission amplitude through the resonator.
7. The acoustic sensor of claim 1, wherein the polymer is a UV cured polymer having a refractive index of 1.33.
8. An acoustic sensing system comprising: An optical whispering gallery mode resonator; A coupling waveguide for optical coupling to the resonator, the coupling waveguide having a first end and a second end opposite the first end, the coupling waveguide being separated from the resonator by a gap, and A polymer encapsulating a portion of the coupling waveguide and the resonator and filling the gap, the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator, wherein the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator includes an upper boundary of the polymer being a convex upper boundary; A light source coupled to the first end of the coupling waveguide and protruding from the polymer, and A photodetector coupled to the second end of the coupling waveguide and protruding from the polymer; Wherein each of the resonator and the coupling waveguide has a refractive index higher than that of the polymer, Wherein the gap spacing is selected such that the acoustic sensing system operates under operating conditions or maximum load factor of critical coupling of the resonator and the coupling waveguide when the polymer fills the gap spacing.
9. The acoustic sensing system of claim 8, further comprising a drive system having a computing device with a processor, the drive system being operably coupled to the light source and the light detector, wherein the drive system is configured to: Obtaining a transmission spectrum by operating the light source in a wavelength range and receiving a plurality of detector signals from the light detector, the detector signals encoding transmission of light from the light source through a coupling fiber coupled to the resonator; selecting an operating wavelength for detecting pressure fluctuations based on the transmission spectrum, and Selecting the spacing gaps based on at least one transmission spectrum, and Pressure fluctuations are detected by operating the light source at the operating wavelength and receiving a second plurality of signals from the light detector.
10. The acoustic sensing system of claim 9, wherein the acoustic sensor encodes pressure fluctuations as fluctuations in transmission amplitude through an optical whispering gallery mode resonator.
11. An ultrasound imaging apparatus comprising: An acoustic sensor, comprising: An optical whispering gallery mode resonator; A coupling waveguide for optical coupling to the resonator, the coupling waveguide having a first end and a second end opposite the first end, the coupling waveguide being separated from the resonator by a gap; A polymer encapsulating a portion of the coupling waveguide and the resonator and filling the gap, the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator, wherein the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator includes an upper boundary of the polymer being a convex upper boundary; A light source coupled to the first end of the coupling waveguide and protruding from the polymer, and A photodetector coupled to the second end of the coupling waveguide and protruding from the polymer; Wherein each of the resonator and the coupling waveguide has a refractive index higher than that of the polymer, Wherein the gap spacing is selected such that the acoustic sensor operates at an operating condition or maximum load factor of critical coupling of the resonator and the coupling waveguide when the polymer fills the gap spacing.
12. The ultrasound imaging apparatus of claim 11, wherein the acoustic sensor encodes pressure fluctuations as fluctuations in transmission amplitude through the resonator.
13. The ultrasound imaging device of claim 11, wherein the acoustic sensor is configured to detect ultrasound pulses generated within a region of interest in response to excitatory ultrasound pulses directed into the region of interest by an ultrasound transducer.
14. A photoacoustic imaging apparatus comprising: An acoustic sensor, comprising: An optical whispering gallery mode resonator; A coupling waveguide for optical coupling to the resonator, the coupling waveguide having a first end and a second end opposite the first end, the coupling waveguide being separated from the resonator by a gap; A polymer encapsulating a portion of the coupling waveguide and the resonator and filling the gap, the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator, wherein the polymer having dimensions designed to enhance acoustic focusing on the optical whispering gallery mode resonator includes an upper boundary of the polymer being a convex upper boundary; a transducer light source coupled to the first end of the coupling waveguide and protruding from the polymer; a transducer photodetector coupled to the second end of the coupling waveguide opposite the first end and protruding from the polymer, and A photoacoustic light source; Wherein the resonator and the coupling waveguide each have a refractive index that is higher than a refractive index of the polymer, and the gap is selected such that the acoustic sensor operates at an operating condition or maximum load factor of critical coupling of the resonator and the coupling waveguide when the polymer fills the gap spacing.
15. The photoacoustic imaging apparatus of claim 14, wherein the acoustic sensor encodes pressure fluctuations as fluctuations in transmission amplitude through the resonator.
16. The photoacoustic imaging apparatus of claim 14, wherein the acoustic sensor is configured to detect a photoacoustic signal generated within the region of interest in response to illumination of a laser pulse generated by the photoacoustic light source.
17. A method for detecting ultrasound, the method comprising: providing an acoustic sensing system comprising: An optical whispering gallery mode resonator; a coupling waveguide optically coupled to the resonator, the coupling waveguide having a first end and a second end opposite the first end, the coupling waveguide being separated from the resonator by a gap; A polymer encapsulating a portion of the coupling waveguide and the resonator and filling the gap, the polymer further forming a sample contact surface, the polymer having a size designed to enhance acoustic focusing on the optical whispering gallery mode resonator, wherein the polymer having a size designed to enhance acoustic focusing on the optical whispering gallery mode resonator includes an upper boundary of the polymer being a convex upper boundary; A light source for coupling to the first end of the coupling waveguide and protruding from the polymer, and A photodetector for coupling to the second end of the coupling waveguide and protruding from the polymer; Wherein the resonator and the coupling waveguide each have a refractive index that is higher than a refractive index of the polymer, and the gap is selected such that the acoustic sensing system operates at an operating condition or maximum load factor of critical coupling of the resonator and the coupling waveguide when the polymer fills the gap spacing; acoustically coupling the sample contact surface with a sample such that ultrasonic waves emitted from within the sample are conducted through the polymer to the resonator and the portion of the coupling waveguide; Introducing light generated by the light source into the first end of the coupling waveguide; converting light from the second end of the coupling waveguide detected by the photodetector into a detector signal encoding an amplitude of the detected light, and The detector signal is converted to pressure using a predetermined calibration rule.

Description

Ultrasonic sensing and imaging based on Whispering Gallery Mode (WGM) micro-electrostatic resonator Cross Reference to Related Applications The present application claims priority from U.S. provisional application serial No. 62/901,883 filed on 9, 9 and 18, 2019, the entire contents of which are incorporated herein by reference. Statement regarding federally sponsored research or development The present invention was completed under government support under W911NF1710189 and W911NF1210026 awarded by the army research office. The government has certain rights in this invention. Technical Field The present disclosure relates generally to systems and methods for performing ultrasound imaging using an acoustic transducer including a whispering gallery mode resonator. Background Ultrasound technology has attracted increasing attention in various fields, particularly in non-invasive measurement, telemetry and biomedical imaging. Ultrasound imaging is used in a variety of settings to non-invasively image internal structures of a patient by detecting ultrasound pulses reflected from tissue boundaries within the patient. Ultrasound detectors for imaging applications typically have low Noise Equivalent Pressure (NEP) and operate at high frequencies and wide bandwidths. Currently available piezoelectric-based ultrasound detectors generally meet these requirements. However, for imaging applications that require detectors with smaller dimensions, the use of piezoelectric-based ultrasound detectors is limited by noise, as the reduction in size of piezoelectric-based ultrasound detectors is accompanied by an increase in noise associated with ultrasound detection. In addition, when the resolution of the ultrasonic wave increases due to the application of the acoustic wave of higher frequency, the penetration depth thereof decreases due to the increase in acoustic attenuation. This tradeoff between resolution and penetration depth presents challenges in the context of conventional piezoelectric ultrasonic sensors. Photonic devices (e.g., gratings, etalons, etc.) and optical pressure detection techniques have shown great promise in terms of ultrasonic detection, and have attracted increasing attention as these devices can be fabricated on a micro-scale without sacrificing ultrasonic detection performance or sensitivity. In photonic devices, refractive index modulation and/or shape deformation caused by acoustic wave induced strain is translated into a change in detected light intensity or spectral characteristics of the device. In some existing devices, optical resonators have been used as high sensitivity ultrasound detectors. In these resonators, the arrival of the ultrasonic waves results in a modulation of the resonant frequency or the transmitted light intensity. In general, the performance of an optical resonator is limited by its quality factor Q (i.e., the higher the Q, the lower the optical loss, the smaller the detectable resonant displacement) as well as the acousto-optic and mechanical properties of the resonator fabrication material. Other objects and features will be in part apparent and in part pointed out hereinafter. Disclosure of Invention In one aspect, an acoustic sensor is disclosed that includes an optical whispering gallery mode resonator, a coupling waveguide for optically coupling to the resonator, and a polymer encapsulating a portion of the coupling waveguide and the resonator. The coupling waveguide is separated from the resonator by a gap. The resonator and the coupling waveguide each have a refractive index that is higher than a corresponding refractive index of the polymer. In other aspects, an acoustic sensing system is disclosed that includes an optical whispering gallery mode resonator, a coupling waveguide for optically coupling to the resonator, a polymer encapsulating a portion of the coupling waveguide and the resonator, a light source coupled to a first end of the coupling waveguide and protruding from a low refractive index polymer, and a light detector coupled to the second end of the coupling waveguide and protruding from the low refractive index polymer. The coupling waveguide has the first end and a second end opposite the first end, and the coupling waveguide is separated from the resonator by a gap. The resonator and the coupling waveguide each have a refractive index that is higher than a corresponding refractive index of the polymer. Further, a photoacoustic imaging apparatus is disclosed, which includes an acoustic sensor. The acoustic sensor includes an optical whispering gallery mode resonator, a coupling waveguide for optically coupling to the resonator, a polymer encapsulating a portion of the coupling waveguide and the resonator, a transducer light source coupled to a first end of the coupling waveguide and protruding from a low refractive index polymer, a transducer light detector coupled to a second end of the coupling waveguide opposite the first end and protruding fro