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EP-4739984-A1 - ULTRASOUND TRANSDUCER

EP4739984A1EP 4739984 A1EP4739984 A1EP 4739984A1EP-4739984-A1

Abstract

The present relates to an on-chip opto-acoustic transducer element for converting an acoustic pressure wave into a modulation of a property of light and to an ultrasound receiver and imager assembly comprising said transducer element. The transducer comprises a membrane (5); a waveguide layer structure (4) comprising a waveguide (1) having a first portion (1a), a second waveguide portion (1b), and coupler (8) disposed between the first and the second portions, wherein the first and the second portion are comprised in a first respective a second sublayer (4a,4b) of the waveguide layer structure, and wherein the coupler comprises end sections of the first and second portion (1a,1b) that co-propagate with respect to each other forming an overlap thereby optically coupling the first and the second waveguide portions.

Inventors

  • HARMSMA, PETER JOHAN
  • Quesson, Benoit André Jacques
  • van Neer, Paul Louis Maria Joseph
  • van der Heiden, Maurits Sebastiaan
  • ALTMANN, Robert Karl

Assignees

  • Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk Onderzoek TNO

Dates

Publication Date
20260513
Application Date
20240705

Claims (15)

  1. 1. On-chip opto-acoustic transducer element (10) for converting an acoustic pressure wave (P) into a modulation of a property of light (L), the transducer element comprising: a membrane (5) extending over an aperture (6) or recess in a surface of a carrier substrate (9); a waveguide layer structure (4) disposed at the membrane, the waveguide layer structure comprising a waveguide (1) providing a light path extending between an input (20) and an output (30), the waveguide comprising: a first waveguide portion (la), a second waveguide portion (lb), and a waveguide coupler (8) disposed between the first and the second waveguide portions, wherein the first waveguide portion (la) is comprised in a first sublayer (4a) of the waveguide layer structure and the second waveguide portion is comprised in a second sublayer (4b) of the waveguide layer structure, and wherein the coupler comprises a section of the first waveguide portion (la) and a section of the second waveguide portion (lb), whereby the sections co-propagate with respect to each other forming an overlap thereby optically coupling the first and the second waveguide portion.
  2. 2. The transducer element according to claim 1, wherein the first waveguide portion provides a forward portion of the light path from the input towards the coupler, wherein the second waveguide portion provides a return portion of the light path from the coupler towards the output, and wherein first sublayer and the second sublayer are disposed on a same side of the membrane (5).
  3. 3. The transducer element according to any of claim 1 - 2, wherein the first and the second waveguide portion (la, lb) form a first and a second spiral portion (la-s, Ib-s) that respectively spiral about the waveguide coupler (8) .
  4. 4. The transducer element according to any of the preceding claims, wherein the waveguide (1) further comprises a chirality inversion section (9), said chirality inversion section disposed between the waveguide coupler (8) and one of the first and the second waveguide portion (la, lb), so that the first and the second waveguide portion counter propagate about the chirality inversion section.
  5. 5. The transducer element according to claim 4, wherein the chirality inversion section (9) comprises a first curved waveguide section (1c) and a second curved waveguide section (2c), wherein the first curved waveguide section (1c) continues into the second curved waveguide section (2c) under an abrupt angle (0) forming a merged interconnect (12), the interconnect terminating at a mirror element (11) configured to reflect light (L) traveling along one of the first and the second section to the other, wherein the mirror element is an upstanding sidewall (Iw) of the waveguide, and wherein the angle (0) is larger than two times a critical angle of incidence (0c) for total internal reflection.
  6. 6. An on-chip opto-acoustic transducer element (10) for converting an acoustic pressure wave (P) into a modulation of a property of light (L), the transducer element (10) comprising: a membrane (5) extending over an aperture (6) or recess in a surface of the carrier substrate (9); a waveguide layer structure (4) disposed at the membrane, the waveguide layer structure comprising a waveguide (1) providing a light path extending between an input (20) and an output (30), the waveguide comprising: a first curved waveguide section (1c), a second curved waveguide section (2c), and wherein an end of the first curved waveguide section continues into an end of the second curved waveguide section under an abrupt angle (0) forming a merged interconnect (12), the interconnect terminating at a mirror element (11) configured to reflect light traveling along one of the first and the second section to the other.
  7. 7. The transducer element (10) according to claim 5 or according to claim 6, wherein the mirror element (11) is an upstanding sidewall (Iw) of the waveguide and wherein the angle (0) is larger than two times a critical angle of incidence (0c) for total internal reflection.
  8. 8. The transducer element according to any of the preceding claims 5 - 7, wherein the merged interconnect is provided at a central position of the membrane, and wherein both the first waveguide section and the second waveguide section, each comprise a spiral portion.
  9. 9. The transducer element according to any of the preceding claims 5 - 7, wherein the waveguide layer comprises a plurality of: the first curved waveguide section, the second curved waveguide section, and the merged interconnect, wherein the first waveguide section and the second waveguide section have a radius of curvature > a radius of curvature of the membrane, and whereby individual ones of the plurality of merged interconnects are provided alternatingly across opposing ends of the aperture or recess to interconnect respective ones of the plurality of the first waveguide section and the second waveguide section in a zig-zag fashion.
  10. 10. The transducer element according to claim 8, wherein the spiral portions of the first and the second waveguide section co-propagate along the membrane with the same handedness and wherein the number of overlaps (XI) between the spiral portions is less than a number of full revolutions about the merged interconnect, preferably whereby wherein an angle between the first and the second spiral at each of the overlaps (XI) is no less than 30 degrees.
  11. 11. The transducer element according to any of claims 5 - 10, wherein the merged interconnect comprising at least two upstanding mirror elements, preferably is a prism element, combinedly configured to reflect light traveling along one of the first and the second light path portion to the other.
  12. 12. The transducer element according to claim 11, wherein the first and the second curved waveguide section are a single curved waveguide section and whereby the merged interconnect is a multimode interference reflector, the multimode interference reflector comprising the at least two upstanding mirror elements at a terminal end combinedly configured to reflect light traveling from single curved waveguide section back into the single curved waveguide section.
  13. 13. The sensor element according to any of the preceding claims, wherein at least the waveguide (1) is cladded by a polymer.
  14. 14. The transducer element according to any of the preceding claims, further comprising a reference waveguide layer structure (2) extending at least in part along a second side of the membrane opposite the first side across a natural bending plane (N) of the membrane.
  15. 15. An ultrasound imager assembly (200) comprising: the on-chip transducer element (10) to any of claims 1 - 14, an ultrasound transmitter (150) a light source (110) operably configured for injecting fight into the input (20), readout circuitry (40) including: one or more light detector (41) operably connected to the one or more output (30) and configured to provide as, electrical signals, an output (S) based on a detected fight intensity and/or phase shift; a processing unit (120) configured for processing the output.

Description

Title: ULTRASOUND TRANSDUCER TECHNICAL FIELD AND BACKGROUND The present disclosure relates to an on-chip opto-acoustic transducer element for converting an acoustic pressure wave into a modulation of a property of light. The present disclosure further relates to an ultrasound receiver and imager assembly comprising said transducer element. Ultrasound receivers for medical imaging of soft tissue, e.g. (human) tissue such as organs are known from the art. The basic principle is that one or more acoustic source sends out an ultrasound signal into a sample, e.g. tissue. Ultrasound receivers are used to detect an output signal in the form of amplitude and/or phase, usually in a linear/curved/phased array for example to construct a 2D image. Tomography allows the construction of a three-dimensional image of the tissue. Typically, multiple emitters and/or receivers are used, and advanced signal optimization and processing for optimum results. Opto-acoustic receivers comprising a resonator supporting an optical wave guide for converting an acoustic pressure wave into a modulation of a property of light are known. The mechanical resonance frequency of the receiver is typically matched to the frequency of the ultrasound signal, so that mechanical amplification of the modulation can be obtained. WO2022053712A1 discloses a Mach-Zehnder type interferometer sensor and measurement unit. The sensor comprises a spiraling waveguide that follows a cascading trajectory along multiple resonant membranes. US11320303B2 relates to a ring-resonator based sensor structure for an acoustical pressure sensor and an opto-mechanical sensor and system that may be used for detecting acoustical pressure waves. Embodiments of a sensor structure for an acoustical pressure sensor are described that include a closed-loop optical waveguide resonator and a plurality of sensor elements. WO2021145766A1 relates to a photonic integrated device that comprises a substrate, a plurality of mechanical resonator structures on a surface of the substrate, exposed to receive sound waves from outside the device; a plurality of sensing optical waveguides, each sensing optical waveguide at least partly mechanically coupled to at least one of the mechanical resonator structures, or a sensing optical waveguide that is at least partly mechanically coupled to all of the mechanical resonator structures. While the known devices can provide some benefits there remains a desire for sensors having increased sensitivity and/or reduced dimensions. Reduced dimensions lead to higher mechanical resonance frequencies, and are therefore beneficial for ultrasound imaging at higher acoustic frequencies leading to improved spatial imaging resolution. SUMMARY Aspects of the present disclosure relate to an opto-acoustic transducer element that addresses the above desires. Aspects of the present disclosure further provide an opto-acoustic receiver comprising the transducer element as disclosed herein to an ultrasound imager assembly comprising the transducer element as disclosed herein. Advantageously, the opto-acoustic transducer element and/or the opto-acoustic receiver can be embodied as an on chip device, e.g. a fully integrated on-chip device. The opto-acoustic transducer can be used to advantage for converting an acoustic pressure wave into a modulation of a property of light, e.g. for the detection of ultrasound and/or for the construction of an image, e.g. as in ultrasound imaging devices such as medical ultrasound imagers. The opto-acoustic transducer comprises at least a carrier substrate having a membrane layer extending over an aperture in a surface of the substrate. The aperture may be fully etched through the substrate, or may be a recess. The membrane is configured to deflect in response to an acoustic pressure wave, typically an external acoustic pressure wave. The opto-acoustic transducer further comprises one or more waveguide layer structure(s) that is disposed at the membrane. The waveguide layer structure comprises at least one waveguide which provides a light path that extends between an input and an output of the transducer element. The waveguide is also referred to as the primary sensing waveguide. As discussed herein the waveguide is typically a so-called single mode waveguide. It will be appreciated that the concepts as disclosed herein can be applied to multimode waveguides, unless clear from context or stated to the contrary. The waveguide can physically, or at least conceptually, be considered to comprise a configuration having a first waveguide portion, a second waveguide portion, and a waveguide coupler. The waveguide coupler is disposed between the first and the second waveguide portions and interconnects the portions to provide an extended light path. In this way the two waveguide portions can effectively be interpreted as a continuous elongated waveguide. For example, the waveguide can be embodied as a sensing arm of an interferometric measureme