US 20220413135A1 

INI 

( 19 ) United States 

( 12 ) Patent Application Publication ( 10 ) Pub . No .: US 2022/0413135 A1 

Gorman et al . ( 43 ) Pub . Date : Dec. 29 , 2022 

( 54 ) OPTOMECHANICAL ULTRASOUND Publication Classification 

DETECTOR AND PERFORMING 

ULTRASOUND IMAGING 

( 71 ) Applicant : Government of the United States of 

America , as represented by the 

Secretary of Commerce , Gaithersburg , MD ( US ) 

( 72 ) Inventors : Jason John Gorman , Silver Spring , MD ( US ) ; Thomas Warren LeBrun , Washington , DC ( US ) ; David 

Alexander Long , Bethesda , MD ( US ) 

( 51 ) Int . Ci . GOIS 15/89 ( 2006.01 ) 

GOIS 7/52 ( 2006.01 ) 

( 52 ) U.S. CI . CPC GOIS 15/8968 ( 2013.01 ) ; GOIS 15/8915 

( 2013.01 ) ; GOIS 7/52023 ( 2013.01 ) ; GOIS 

7752079 ( 2013.01 ) 

( 57 ) ABSTRACT 

An optomechanical ultrasound detector includes : a micro 

mirror substrate ; a mechanical resonator that receives ultra sound waves , oscillates at resonator frequency f , changes cavity length Lc and produces intra - cavity light ; and an 

optical microcavity between the micromirror substrate and 

the mechanical resonator with cavity length Lc and cavity 

resonance frequency f , formed by the mechanical resonator 

and the micromirror substrate , such that the micromirror 

substrate produces vity output light from the intra - cavity light , wherein the cavity output light optically encodes 

information about the ultrasound waves received by the 

mechanical resonator . 

( 21 ) Appl . No .: 17 / 853,106 

( 22 ) Filed : Jun . 29 9 , 2022 

Related U.S. Application Data 

( 60 ) Provisional application No. 63 / 216,079 , filed on Jun . 29 , 2021 . 

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US 2022/0413135 A1 Dec. 29 , 2022 

1 

OPTOMECHANICAL ULTRASOUND 

DETECTOR AND PERFORMING 

ULTRASOUND IMAGING 

CROSS REFERENCE TO RELATED 

APPLICATIONS 

[ 0001 ] This application claims the benefit of U.S. Provi 

sional Patent Application Ser . No. 63 / 216,079 ( filed Jun . 29 , 2021 ) , which is herein incorporated by reference in its 

entirety . 

changing the cavity length Le of the optical microcavity 

based on oscillation of the mechanical resonator at resonator frequency f ; communicating initial laser light from the 

micromirror substrate to the mechanical resonator ; receiv 

ing , by the mechanical resonator , initial laser light from the 

micromirror substrate ; producing , by the mechanical reso 

nator , intra - cavity light from the initial laser light ;optically encoding , by the mechanical resonator , in the cavity output light information about the ultrasound waves received by the 

mechanical resonator ; repeatedly communicating the intra cavity light between the micromirror substrate and the 

mechanical resonator across the cavity length Le when the 

intra - cavity light is resonant with the cavity resonance frequency f ; and communicating the intra - cavity light from 

the mechanical resonator to the micromirror substrate ; and producing , by the micromirror substrate , cavity output light from the intra - cavity light to perform ultrasound imaging . 

STATEMENT REGARDING FEDERALLY 

SPONSORED RESEARCH 

[ 0002 ] This invention was made with United States Gov 

ernment support from the National Institute of Standards and 

Technology ( NIST ) , an agency of the United States Depart 

ment of Commerce . The Government has certain rights in 

this invention . BRIEF DESCRIPTION OF THE DRAWINGS 

BRIEF DESCRIPTION 

? 

[ 0003 ] Disclosed is an optomechanical ultrasound detector for performing ultrasound imaging , the optomechanical ultrasound detector comprising : a micromirror substrate ; a 

mechanical resonator disposed on the micromirror substrate , in optical communication with the micromirror substrate , spaced apart from the micromirror substrate at a cavity length Lc , and that : receives ultrasound waves ; oscillates at 

a resonator frequency f , in response to receipt of the ultra 

sound waves , changes the cavity length Le based on oscil 

lation of the mechanical resonator at resonator frequency fu ; 

receives initial laser light from the micromirror substrate ; 

and produces intra - cavity light from the initial laser light ;

and an optical microcavity optically interposed between the 

micromirror substrate and the mechanical resonator and 

comprising the cavity length Le with cavity resonance fre 

quency fc formed by optically opposing surfaces of the 

mechanical resonator and the micromirror substrate and that : 

when the intra - cavity light is resonant with the cavity 

resonance frequency fc , repeatedly communicates the intra 

cavity light between the micromirror substrate and the 

mechanical resonator across the cavity length Lc ; and when 

the intra - cavity light is non - resonant with the cavity reso 

nance frequency fc communicates the intra - cavity light from the mechanical resonator to the micromirror substrate , such that the micromirror substrate produces cavity output light from the intra - cavity light ,wherein the cavity output light optically encodes information about the ultrasound 

waves received by the mechanical resonator . [ 0004 ] A process for performing ultrasound imaging with 

a optomechanical ultrasound detector , the process compris ing : receiving ultrasound waves by a mechanical resonator 

of a optomechanical ultrasound detector , the optomechani cal ultrasound detector comprising : a micromirror substrate ; 

a mechanical resonator disposed on the micromirror sub 

strate , in optical communication with the micromirror sub 

strate , spaced apart from the micromirror substrate at a cavity length Le and an optical microcavity optically inter 

posed between the micromirror substrate and the mechanical 

resonator and comprising the cavity length Le with cavity 

resonance frequency f , formed by optically opposing sur 

faces of the mechanical resonator and the micromirror 

substrate ; oscillating the mechanical resonator at a resonator 

frequency f , in response to receiving the ultrasound waves ; 

[ 0005 ] The following description cannot be considered limiting in any way . Various objectives , features , and advan 

tages of the disclosed subject matter can be more fully appreciated with reference to the following detailed descrip tion of the disclosed subject matter when considered in connection with the following drawings , in which like 

reference numerals identify like elements . [ 0006 ] FIG . 1 shows an optomechanical ultrasound detec 

tor , according to some embodiments . [ 0007 ] FIG . 2 shows an optomechanical ultrasound detec 

tor , according to some embodiments . [ 0008 ] FIG . 3 shows an optomechanical ultrasound detec 

tor , according to some embodiments . [ 0009 ] FIG . 4 shows an optomechanical ultrasound detec 

tor , according to some embodiments . [ 0010 ] FIG . 5 shows an optomechanical ultrasound detec 

tor , according to some embodiments . [ 0011 ] FIG . 6 shows plan views for a resonator substrate , micromirror substrate , and nanophotonic waveguide on a 

dielectric layer , according to some embodiments . [ 0012 ] FIG . 7 shows an optomechanical ultrasound detec 

tor , according to some embodiments . [ 0013 ] FIG . 8 shows an optomechanical ultrasound detec 

tor for transmission mode ultrasound detection and reflec 

tion mode ultrasound detection , according to some embodi 

ments . 

DETAILED DESCRIPTION 

[ 0014 ] A detailed description of one or more embodiments is presented herein by way of exemplification and not 

limitation . 

[ 0015 ] Conventional ultrasound transducers for medical imaging and structural diagnostics have limited resolution 

due to stiffness and low sensitivity of piezoelectric elements 

in such conventional ultrasound transducers . As a result , detecting small changes in material properties and imaging through highly reflective materials has been challenging , if 

not impossible , with conventional technology . Accordingly , certain conventional technologies have limited use for ultra sound imaging . The optomechanical ultrasound detector 100 

described herein overcome these limitations . [ 0016 ] It has been discovered that a optomechanical ultra 

sound detector 100 described herein ultra - sensitively and 

optomechanically detects ultrasound waves for ultrasound 

? 
US 2022/0413135 A1 Dec. 29 , 2022 

2 

imaging . Advantageously , the sensitivity of optomechanical 

ultrasound detector 100 can be at least two orders of magnitude better than conventional technology and suffi 

cient for novel medical imaging modalities , including ultra 

sound whole brain imaging . Optomechanical ultrasound detector 100 can include a Fabry - Perot optical cavity with a 

mechanical resonator so that when the mechanical resonator 

moves under the influence of ultrasound , ultra - sensitive 

readout of the motion is achieved using the optical cavity and laser light . In addition to sensitivity , the optomechanical ultrasound detector 100 provides greater safety during imag ing than conventional devices due to lower ultrasound power that can be used while yielding higher resolution imaging . Performing ultrasound imaging with optomechanical ultra 

sound detector 100 can be applied for acoustic detection as 

well as photoacoustic measurements . [ 0017 ] Optomechanical ultrasound detector 100 performs ultrasound imaging . In an embodiment , with reference to 

FIG . 1 , FIG . 2 , FIG . 3 , FIG . 4 , FIG . 5 , FIG . 6 , FIG . 7 , and 

FIG . 8 , optomechanical ultrasound detector includes : a 

micromirror substrate 110 ; a mechanical resonator 104 dis 

posed on the micromirror substrate 110 , in optical commu nication with the micromirror substrate 110 , spaced apart from the micromirror substrate 110 at a cavity length Lc , and 

that : receives ultrasound waves 103 ; oscillates at a resonator frequency fr in response to receipt of the ultrasound waves 

103 ; changes the cavity length Lc based on oscillation of the 

mechanical resonator 104 at resonator frequency fr ; receives 

initial laser light 124 from the micromirror substrate 110 ; and produces intra - cavity light 111 from the initial laser light 124 ; and an optical microcavity 118 optically interposed between the micromirror substrate 110 and the mechanical 

resonator 104 and including the cavity length Lc with cavity 

resonance frequency fc formed by optically opposing sur 

faces of the mechanical resonator 104 and the micromirror 

substrate 110 and that : when the intra - cavity light 111 is 

resonant with the cavity resonance frequency fc , repeatedly communicates the intra - cavity light 111 between the micro 

mirror substrate 110 and the mechanical resonator 104 

across the cavity length Lc ; and when the intra - cavity light 111 is non - resonant with the cavity resonance frequency fc , communicates the intra - cavity light 111 from the mechanical 

resonator 104 to the micromirror substrate 110 , such that the micromirror substrate 110 produces cavity output light 125 

from the intra - cavity light 111 , wherein the cavity output light 125 optically encodes information about the ultrasound 

waves 103 received by the mechanical resonator 104 . [ 0018 ] In an embodiment , optomechanical ultrasound 

detector 100 includes resonator substrate 102 disposed on 

the micromirror substrate 110 and on which the mechanical 

resonator 104 is disposed . [ 0019 ] In an embodiment , optomechanical ultrasound 

detector 100 includes anti - reflective member 108 disposed 

on an ultrasound surface 107 of the mechanical resonator 

104 and that receives the ultrasound waves 103 . 

[ 0020 ] In an embodiment ,optomechanical ultrasound 

detector 100 includes resonator optical reflector 106 dis 

posed on a reflector surface 105 of the mechanical resonator 

104 and that receives the initial laser light 124 from the 

micromirror substrate 110 and reflects the initial laser light 124 as the intra - cavity light 111 . [ 0021 ] In an embodiment ,optomechanical ultrasound 

detector 100 includes mirror anti - reflective member 116 

disposed on an optical coupling surface 109 of the micro 

mirror substrate 110 and that receives the initial laser light 124 , communicates the initial laser light 124 to the mechani 

cal resonator 104 via the optical microcavity 118 , receives 

the intra - cavity light 111 from the optical microcavity 118 , and produces the cavity output light 125 from the intra cavity light 111 . [ 0022 ] In an embodiment , optomechanical ultrasound 

detector 100 includes concave micromirror 112 disposed on 

an optical coupling surface 109 of the micromirror substrate 

110 , such that the concave micromirror 112 is arranged to be optically concave with respect to the optical microcavity 

118 . 

[ 0023 ] In an embodiment , optomechanical ultrasound 

detector 100 includes mirror reflective member 114 disposed 

on a cavity surface 101 of the micromirror substrate 110 and 

that receives the initial laser light 124 from the micromirror 

substrate 110 and is an intra - cavity mirror for the optical microcavity 118 , such that the mirror reflective member 114 : 

reflects the intra - cavity light 111 when the intra - cavity light 111 is resonant with the cavity resonance frequency f ; and communicates the intra - cavity light 111 to the micromirror 

substrate 110 when the intra - cavity light 111 is non - resonant with the cavity resonance frequency fe . [ 0024 ] In an embodiment ,optomechanical ultrasound detector 100 includes optical fiber 120 in optical commu 

nication with the micromirror substrate 110 and that com 

municates the initial laser light 124 to the micromirror 

substrate 110 and receives the cavity output light 125 from 

the micromirror substrate 110. In an embodiment , optom echanical ultrasound detector 100 includes coupling lens 

122 in optical communication with the micromirror sub 

strate 110 and that receives the initial laser light 124 , communicates the initial laser light 124 to the micromirror 

substrate 110 , and receives the cavity output light 125 from 

the micromirror substrate 110 , wherein the micromirror 

substrate 110 is interposed between coupling lens 122 and 

the optical microcavity 118. The coupling lens 122 can be 

disposed on the micromirror substrate 110. In an embodi 

ment , mirror anti - reflective member 116 is disposed on the coupling lens 122 , wherein the coupling lens 122 is inter 

posed between the mirror anti - reflective member 116 and the 

micromirror substrate 110 . [ 0025 ] In an embodiment , optomechanical ultrasound detector 100 includes nanophotonic waveguide 144 in opti 

cal communication with the micromirror substrate 110 and 

that receives the initial laser light 124 , communicates the 

initial laser light 124 to the micromirror substrate 110 , and 

receives the cavity output light 125 from the micromirror 

substrate 110. The micromirror substrate 110 can be inter 

posed between nanophotonic waveguide 144 and the optical microcavity 118. In an embodiment , nanophotonic wave 

guide 144 includes nanophotonic coupling member 146 in 

optical communication with the micromirror substrate 110 

and that receives the initial laser light 124 , communicates 

the initial laser light 124 to the micromirror substrate 110 , and receives the cavity output light 125 from the micromir 

ror substrate 110. The micromirror substrate 110 can be interposed between nanophotonic coupling member 146 and 

the optical microcavity 118. In an embodiment , optom echanical ultrasound detector 100 includes nanophotonic substrate 142 on which the nanophotonic waveguide 144 is disposed . In an embodiment , optomechanical ultrasound 

detector 100 includes a dielectric layer 140 disposed on the 

nanophotonic substrate 142 such that the dielectric layer 140 a 
US 2022/0413135 A1 Dec. 29 , 2022 

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a 

is interposed between the nanophotonic substrate 142 and the nanophotonic waveguide 144 . [ 0026 ] In an embodiment , optomechanical ultrasound 

detector 100 includes meta - optic 127 disposed on the micro 

mirror substrate 110 in optical communication with the 

micromirror substrate 110 and that receives the initial laser 

light 124 , communicates the initial laser light 124 to the 

micromirror substrate 110 , and receives the cavity output light 125 from the micromirror substrate 110. The micro 

mirror substrate 110 can be interposed between the meta optic 127 and the optical microcavity 118 . [ 0027 ] When ultrasound waves 103 impinge mechanical 

resonator 104 , mechanical resonator 104 displaces periodi cally due to the pressure wave generated by ultrasound 

waves 103. The optical microcavity 118 transduces motion 

of ultrasound waves 103. Various optical readout configu rations and processes can be included to determine how cavity length Le of optical microcavity 118 changes as a 

function of time and to determining the motion of mechani 

cal resonator 104. The motion of mechanical resonator 104 

detects presence of ultrasound waves 103 , e.g. , as ultrasound reflections during imaging . Such reflections are used to 

construct images of a sample under inspection . Due to a high displacement sensitivity provided by this optical microcav 

ity readout , the optomechanical ultrasound detector 100 has higher sensitivity to ultrasound waves 103 than conventional 

detectors . [ 0028 ] The optomechanical ultrasound detector 100 

includes optical fiber 120 and coupling lens 122 to send initial laser light 124 into optical microcavity 118 and to 

collect cavity output light 125 reflected from mechanical 

resonator 104 and output from optical microcavity 118. The 

initial laser light 124 can be communicated into optical microcavity 118 in various ways and configurations , such as 

with integrated lens 122 , e.g. , as shown in FIG . 2. The 

optomechanical ultrasound detector 100 can include com 

munication of initial laser light 124 via nanophotonic struc 

tures such as nanophotonic waveguide 144. The optom echanical ultrasound detector 100 with integrated lens 122 

can include optical fiber 120 , and initial laser light 124 can be coupled into optical microcavity 118 by coupling lens 

122 disposed on micromirror substrate 110 , which can 

provide a reduction in size of optomechanical ultrasound 

detector 100. The optomechanical ultrasound detector 100 with nanophotonic light delivery 144 further can reduce the 

size of optomechanical ultrasound detector 100 by replacing the optical fiber 120 with a nanophotonic substrate 142 and 

nanophotonic coupling member 146. The nanophotonic sub 

strate 142 couples light from a nanophotonic waveguide 144 , through a nanophotonic coupling member 146 , passing initial laser light 124 through integrated lens 122 , and into optical microcavity 118 so that optomechanical ultrasound 

detector 100 can be formed by stacked substrates that can be 

aligned and bonded in an absence of laborious manual assembly . 

[ 0029 ] It is contemplated that optomechanical ultrasound detector 100 can be a single detector or arranged into 

one - dimensional , two - dimensional , and the like arrays for wide - field ultrasound imaging . [ 0030 ] Optomechanical ultrasound detector 100 can be 

made of various elements and components that are 

assembled , formed , or fabricated in a number of ways , e.g. , microfabrication , wherein mechanical resonator 104 is a 

mechanical resonator that is suspended by resonator sub 

strate 102 proximate to micromirror substrate 110. In this 

manner , resonator substrate 102 supports mechanical reso 

nator 104 , which results in a cavity length Le providing a separation between resonance modes of optical microcavity 118. On a separate microfabricated chip , concave micromir 

ror 112 can be formed in micromirror substrate 110. When 

the chips containing mechanical resonator 104 and concave micromirror 112 are assembled together , they form optical microcavity 118 , wherein opposing surfaces of mechanical 

resonator 104 and concave micromirror 112 have high reflectivity coatings disposed thereon respectively as reso 

nator optical reflector 106 and mirror reflective member 114 . Motion of the mechanical resonator 104 is measured by using analyzer 135 to detect changes in optical resonances of 

optical microcavity 118 through communication of intra cavity light 111 and cavity output light 125 produced from 

ultrasound waves 103 that cause oscillation of mechanical 

resonator 104 relative to micromirror substrate 110. That is , ultrasound waves 103 are transduced into intra - cavity light 111 by mechanical resonator 104 that is coupled into optical microcavity 118 as intra - cavity light 111 and repeatedly 

reflected between mechanical resonator 104 and micromir 

ror substrate 110 at cavity resonance frequency fc before being communicated out of optical microcavity 118 as cavity output light 125 , wherein cavity output light 125 is 

received by analyzer 135. Micromirror substrate 110 pro vides a stable cavity design that can be , e.g. , a hemispherical cavity , and high reflectivity coatings are included to provide high optical finesse that results in high displacement sensi 

tivity of mechanical resonator 104 relative to concave 

micromirror 112. Coatings and materials used for mechani 

cal resonator 104 and concave micromirror 112 can be 

selected for operation with laser wavelengths for micromir 

ror substrate 110 and mirror reflective member 114 that can 

include visible light from 400 nm to 700 nm , near infrared 

light from 700 nm to 1000 nm , or short - wave infrared from 

1000 nm to 3000 nm . Operation with a laser wavelength 

near 1550 nm can provide integration with a large number of fiber optic components designed for telecommunications , making optomechanical ultrasound detector 100 scalable 

and compatible with off - the - shelf optical characterization 

tools . 

[ 0031 ] Elements of optomechanical ultrasound detector 

100 can be various sizes . It is contemplated that materials for 

micromirror substrate 110 and other optical elements can be 

selected based on a resonance frequency desired for optical microcavity 118. The cavity length L of optical microcavity 

118 , e.g. , can be from 1 micrometer ( um ) to 50 millimeters 

( mm ) , specifically from 10 micrometer ( um ) to 5 millimeters 

( mm ) , and more specifically from 100 um to 10 mm , although other suitable cavity lengths can be included . [ 0032 ] Elements of micromirror substrate 110 can be made 

of a material that is physically or chemically resilient in an 

environment in which micromirror substrate 110 is disposed . Exemplary materials include a metal , ceramic , thermoplas tic , glass , semiconductor ,and the like . The elements of 

micromirror substrate 110 can be made of the same or 

different material and can be monolithic in a single physical body or can be separate members that are phsycially joined . Transmission of a selected wavelength of light , e.g. , for 

micromirror substrate 110 , can be provided by the material 

used for such optical elements . For example , tranmission of 

visible light by micromirror substrate 110 or concave micro 

mirror 112 can be provided by fused silica . 
US 2022/0413135 A1 Dec. 29 , 2022 

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7 

a 

[ 0033 ] In an embodiment , mechanical resonator 104 is a 

continuous mechanical structure connected to resonator sub 

strate 102 on all sides and with a resonator frequency f ,, e.g. , from 0.5 MHz to 100 MHz to coincide with the frequencies used in ultrasound imaging , or another frequency that can be 

selected for a chosen application . The shape of the mechani 

cal resonator 104 in the plane of resonator substrate 102 can 

be arbitrary , wherein exemplary shapes include circular or polygonal ( e.g. , square , hexagonal , and the like ) . A planar 

dimension can be , e.g. , from 50 um to 2 mm . The resonator 

optical reflector 106 and anti - reflective member 108 can include a Bragg grating that can include , e.g. , layered dielectric materials , a two - dimensional photonic crystal that 

can be disposed on or into mechanical resonator 104. The 

resonator optical reflector 106 can have reflectivity from 

20 % to 99.999 % that can depend on its design and fabrica 

tion . The anti - reflective member 108 can have a stiffness perpendicular to resonator substrate 102 due to bending stiffness or tension in the material . While not being limited 

to such , exemplary materials for mechanical resonator 104 

include silicon , silicon nitride , silicon dioxide , silicon car 

bide , fused silica , and the like . 

[ 0034 ] The concave micromirror 112 can be semispherical in an area where initial laser light 124 or cavity output light 125 propagate through the mirror , The mirror reflective 

member 114 and mirror anti - reflective member 116 on 

concave micromirror 112 independently can be a Bragg grating that includes , e.g. , layered dielectric materials . The 

mirror reflective member 114 can have a reflectivity from 20 % to 99.999 % , e.g. , based on its design and fabrication . While not limited thereto , exemplary materials for concave 

micromirror 112 include silicon , silicon nitride , silicon diox 

ide , silicon carbide , fused silica , and the like . The radius of 

concave micromirror 112 and the distance between concave 

micromirror 112 and mechanical resonator 104 is selected so 

that optical microcavity 118 is an optically stable microcav 

ity . 

[ 0035 ] Laser light 124 can have a wavelength ranging from 400 nm to 1700 nm depending on the materials 

selected for the detector , e.g. , analyzer 135. A light source 

138 can produce the initial laser light 124 at a fixed or 

tunable frequency . An optical splitter 137 can communicate 

initial laser light 124 from light source 138 to micromirror 

substrate 110 and communicate cavity output light 125 from micromirror substrate 110 to analyzer 135. The optical splitter 137 can include suitable optical and electrical com 

ponents for this operation such as a mirror , beam splitter , motor , mixer , and the like . 

[ 0036 ] The coupling lens 122 has a focal length that provides efficient mode coupling of initial laser light 124 

into optical microcavity 118 and can be made from and include various materials . Exemplary materials for coupling lens 122 include including silicon , silicon nitride , silicon 

dioxide , silicon carbide , fused silica , titanium oxide , alumi 

num oxide , polymer , and the like . The coupling lens 122 can 

be interposed between micromirror substrate 110 and light 

source 138 either spaced apart from micromirror substrate 

110 or disposed on micromirror substrate 110. The coupling lens 122 can have various geometrical shapes and formats 

such as plano - concave for disposal on micromirror substrate 

110 or a meta - optic 127 such as a flat meta - lens , as shown in FIG . 4. The meta - optic 127 can include , e.g. , a periodic nanostructure , nanofabricated Fresnel lens , and the like . 

[ 0037 ] Nanophotonic substrate 142 can be included in 

optomechanical ultrasound detector 100. In some embodi 

ments , nanophotonic substrate 142 is include instead of optical fiber 120 or coupling lens 122. Nanophotonic wave 

guide 144 receives initial laser light 124 disposed on nano photonic substrate 142. The nanophotonic waveguide 144 

confines laser light ( 124 , 125 ) with low optical attenuation . Dielectric layer 140 constrains light to propagate in nano photonic waveguide 144 without communication into nano 

photonic substrate 142. The nanophotonic waveguide 144 communicates initial laser light 124 to nanophotonic cou 

pling member 146 and receives cavity output light 125 from nanophotonic coupling member 146. The nanophotonic cou 

pling member 146 can include a periodic nanostructure that communicates laser light ( 124 , 125 ) perpendicular to nano 

photonic substrate 142 with a selected numerical aperture and beam width . Non - limiting examples of materials for 

elements disposed on nanophotonic substrate 142 include 

silicon , silicon nitride , silicon dioxide , silicon carbide , fused silica , titanium oxide , aluminum oxide , polymer , and the 

like . When flat meta - lens 127 is disposed on micromirror 

substrate 110 and includes the periodic nanostructure or 

nanofabricated Fresnel lens , resonator substrate 102 , micro 

mirror substrate 110 , and nanophotonic substrate 142 can be 

bonded together to form a monolithic and compact detector 

of ultrasound waves 103 . 

[ 0038 ] In an embodiment , with reference to FIG . 5 , opto mechanical ultrasound detector 100 includes an integrated piezoelectric ultrasound source 155. The integrated piezo electric ultrasound source 155 can include metal layer 151 , piezoelectric material 152 , vibrating membrane 153 , and 

optional air cavity 154. When an electrical pulse is applied to metal layer 151 , piezoelectric material 152 expands and 

deforms vibrating membrane 153. An electrical pulse with a 

selected frequency and power produces an ultrasound wave that propagates from optomechanical ultrasound detector 

100 until incident at an object external to optomechanical ultrasound detector 100. Some energy of this ultrasound 

wave reflects from the object and is detected by optom echanical ultrasound detector 100 . 

[ 0039 ] It should be appreciated that optomechanical ultra 

sound detector 100 includes optical microcavity 118 that is 

an optical cavity that can include a hemispherical micro 

mirror formed in a micromirror substrate 110 that can be 

bonded to resonator substrate 102 having disposed thereon 

mechanical resonator 104 with resonator optical reflector 106 that can be a flat mirror . Beneficially , optomechanical ultrasound detector 100 can fill a volume less than a cubic 

millimeter . Ultrasound waves 103 incident on mechanical 

resonator 104 cause oscillation of mechanical resonator 104 , which shifts the cavity resonance frequency f of optical microcavity 118. The cavity resonance frequency fe can be 

measured continuously to detect the oscillation of mechani cal resonator 104 and amplitude and phase of ultrasound 

waves 103 . 

[ 0040 ] The concave micromirror and mechanical resona 

tor chips can be microfabricated in substrates that can 

include silicon , glass , or other dielectrics or semiconductors , The concave micromirror and mechanical resonator inde pendently can have high reflectivity surfaces for high finesse 

or low optical loss in optical microcavity 118. This increases the sensitivity of optomechanical ultrasound detector 100 . The high reflectivity surfaces could be dielectric Bragg mirror coatings , photonic crystals , or optical meta - surfaces . 
US 2022/0413135 A1 Dec. 29 , 2022 

5 

The backside of the concave mirror chip can have an antireflection coating to minimize parasitic cavities between 

the various surfaces in the bonded chip stack . [ 0041 ] The mechanical resonator 104 can be a plate ( e.g. , material having bending stiffness ) or a membrane ( e , g . , a 

material under tension with minimal bending stiffness ) . The planar geometry of the plate or membrane can be arbitrary , e.g. , circular or square . The thickness and planar dimensions 

of the mechanical resonator 104 can be selected for a 

selected resonance frequency or compliance based on an 

application . Medical ultrasound imaging can occur from 1 

MHz to 20 MHz , and imaging resolution limit set by the 

ultrasound frequency and acoustic velocity of the human 

body can be from 0.1 mm and 1 mm . The mechanical 

resonator 104 provides imaging in view of these character 

istics . When operating at 20 MHz with a circular resonator , the diameter of mechanical resonator 104 can be , e , g . , 0.1 a 

a mm . 

a 

deep reactive ion etching to etch down to the silicon oxide 

layer and forming a planar shape of mechanical resonator 

104 ; separating the mechanical resonators into individual chips , wherein separating can involve using a dicing saw ; 

and forming resonator optical reflector 106 , mirror anti 

reflective member 116 , other reflective elements , or other 

anti - reflective elements with shadow masking and ion beam sputtering for Bragg grating tantalum - pentoxide / silicon 

dioxide coatings . 

[ 0045 ] According to an embodiment , a process for making 

concave micromirror 112 includes : providing a silicon wafer with thickness ranging from 300 um to 900 um ; using photolithography and deep reactive ion etching to etch a 

trench in the top surface of the silicon wafer to form a trench 

that is square and between 0.5 mm and 5 mm wide ; after cleaning the wafer , depositing silicon nitride on both sides of 

the wafer using chemical vapor deposition with a thickness 

between 200 nm and 1000 nm ; using photolithography and 

reactive ion etching to etch a circular aperture through the 

silicon nitride layer located at the center of the square trench ; 

using hydrofluoric acid , nitric acid , and acetic acid at room 

temperature to etch the silicon exposed by the circular 

aperture , resulting in a semispherical concave micromirror ; 

using heated phosphoric acid to remove the silicon nitride 

layer and then clean the wafer ; using a dicing saw to separate the concave micromirrors into chips ; and using shadow masking with ion beam sputtering for Bragg grating tanta 

lum - pentoxide / silicon dioxide coatings to apply the reflec 

tive element and anti - reflective element . 

[ 0046 ] According to an embodiment , a process for making optomechanical ultrasound detector 100 includes : bonding a 

silicon chip including a concave micromirror to a chip containing a mechanical resonator using silicon fusion bond 

ing ; aligning the bonded chip stack to an optical fiber and 

coupling lens that are located in a metal package with a flat 

surface for holding the chip stack ; and using a low - stress 

adhesive to bond the chip stack to the metal package to make optomechanical ultrasound detector 100 . [ 0047 ] Optomechanical ultrasound detector has numerous advantageous and unexpected benefits and uses . In an 

embodiment , a process for performing ultrasound imaging with optomechanical ultrasound detector 100 includes : 

receiving ultrasound waves 103 by a mechanical resonator 

104 of a optomechanical ultrasound detector 100 , oscillating the mechanical resonator 104 at a resonator frequency fr in 

response to receiving the ultrasound waves 103 ; changing the cavity length Lc of the optical microcavity 118 based on 

oscillation of the mechanical resonator 104 at resonator 

frequency fr ; communicating initial laser light 124 from the 

micromirror substrate 110 to the mechanical resonator 104 ; 

receiving , by the mechanical resonator 104 , initial laser light 124 from the micromirror substrate 110 ; producing , by the 

mechanical resonator 104 , intra - cavity light 111 from the initial laser light 124 ; optically encoding , by the mechanical 

resonator 104 , in the cavity output light 125 information 

about the ultrasound waves 103 received by the mechanical 

resonator 104 ; repeatedly communicating the intra - cavity light 111 between the micromirror substrate 110 and the 

mechanical resonator 104 across the cavity length Lc when 

the intra - cavity light 111 is resonant with the cavity reso 

nance frequency fc ; communicating the intra - cavity light 111 from the mechanical resonator 104 to the micromirror 

substrate 110 ; and producing , by the micromirror substrate 

a 

[ 0042 ] Light ( e.g. , 124 , 125 ) is coupled into and out of the 

optical cavity 118 with optical fiber 120 and lens 122. The optical cavity 118 sensitively optically transduces displace 

ment of the mechanical resonator 104. Transduction of the 

displacement with analyzer 135 and a laser 137 can include 

sideband laser locking , Pound - Drever - Hall laser locking , and the like . 

[ 0043 ] Optomechanical ultrasound detector 100 can be 

made in various ways . It should be appreciated that opto mechanical ultrasound detector 100 includes a number of 

optical , electrical , or mechanical components , wherein such 

components can be interconnected and placed in communi 

cation ( e.g. , optical communication , electrical communica 

tion , mechanical communication , and the like ) by physical , chemical , optical , or free - space interconnects . The compo nents can be disposed on mounts that can be disposed on a bulkhead for alignment or physical compartmentalization . As a result , optomechanical ultrasound detector 100 can be 

disposed in a terrestrial environment or space environment . Elements of optomechanical ultrasound detector 100 can be 

formed from silicon , silicon nitride , and the like although other suitable materials , such ceramic , glass , or metal can be 

used . According to an embodiment , the elements of opto mechanical ultrasound detector 100 are formed using micro fabrication processing techniques . It should be appreciated that optomechanical ultrasound detector 100 can be made by additive or subtractive manufacturing . In an embodiment ,elements of optomechanical ultrasound detector 100 are 

selectively etched to remove various different materials 

using different etchants and photolithographic masks and 

procedures . The various layers thus formed can be subjected to joining by bonding to form optomechanical ultrasound 

detector 100 . 

[ 0044 ] According to an embodiment , a process for making mechanical resonator 104 includes : providing a base mate rial , e.g. , a silicon - on - insulator wafer , wherein the wafer can 

include various layers , e.g. , a stack of materials such as a silicon handle wafer ( e.g. , thickness from 300 um to 900 

um ) , a silicon dioxide layer ( e.g. , thickness from 500 nm to 

2 um ) , and a silicon device layer ( e.g. , thickness from 200 

nm to 50 um ) , such that the base member is subjected to modification for forming mechanical resonator 104 ; subject ing device layer of the base material to photolithography and 

to deep reactive ion etching to etch down to the silicon dioxide layer and forming independent mechanical resona 

tors ; subjecting the handle wafer to photolithography and 

a 

a 
US 2022/0413135 A1 Dec. 29 , 2022 

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' 

110 , cavity output light 125 from the intra - cavity light 111 

to perform ultrasound imaging . [ 0048 ] In an embodiment , the process for performing ultrasound imaging includes communicating the cavity out 

put light 125 from the micromirror substrate 110 to an analyzer 135 . [ 0049 ] In an embodiment , the process for performing ultrasound imaging includes , performing by the analyzer 135 : receiving the cavity output light 125 ; analyzing the 

cavity output light 125 ; and determining the information 

about the ultrasound waves 103 from analyzing the cavity output light 125 . [ 0050 ] In an embodiment , a process for performing ultra 

sound imaging includes receiving initial laser light 124 by optomechanical ultrasound detector 100 , wherein the wave 

length of laser light 124 is set so that part of initial laser light 124 is received in optical microcavity 118 , and multiple wavelengths can be used simultaneously . The initial laser 

light 124 entering optical microcavity 118 circulates intra 

cavity light 111 and initial laser light 124 in optical micro 

cavity 118 , reflecting from mirror reflector member ( 106 , 114 ) . Laser light is continuously coupled into and re - emitted 

by the cavity 118. As the mechanical resonator 104 oscillates in response to receipt of ultrasound waves 103 , mechanical 

resonator 104 changes cavity length Le and the intensity or 

frequency in a spectrum of intra - cavity light 111 and initial 

laser light 124 in optical microcavity 118. Some of intra cavity light 111 exits optical microcavity 118 as cavity 

output light 125 through the concave micromirror 112 and 

propagates toward the light routing element 162 ( e.g. , opti cal splitter 137 ) , as shown in FIG . 7. Intensity or frequency of cavity output light 125 communicated from optical micro 

cavity 118 is measured to determine motion of the mechani 

cal resonator 104. The intensity or frequency of initial laser 

light 124 can be changed to enhance detection of cavity output light 125 , including simultaneous use of multiple wavelengths . 

[ 0051 ] In an embodiment , with reference to FIG . 7 , opto mechanical ultrasound detector 100 can include laser source 

161 that introduces light into the detection system . The laser 

source can produce light with variable frequency or at multiple wavelengths . Light routing element 162 sends laser 

light 124 to the ultrasound detector so that light re - emitted 

by the detector 125 can be analyzed . An analyzer 163 

converts the light re - emitted by the detector into an elec tronic signal representing the representing the instantaneous 

ultrasound amplitude as measured by the motion of the 

detector element under the influence of the ultrasound 

waves . An ultrasound demodulation element 164 demodu 

lates and analyzes the electronic signal from the analyzer to 

yield ultrasound measurements and images . [ 0052 ] Measurement with the optomechanical ultrasound detector can be configured in various ways . In an embodi 

ment , an ultrasound signal ( an acoustic wave or pulse at ultrasonic frequencies ) is produced by a source . The source 

may be separate from the detector 171 or integrated with it 

155. In an embodiment , the signal interacts with an object under test that scatters it ( including absorption , transmission , and reflection , possibly accompanied by changes in ampli tude or frequency ) . In an embodiment , some of the scattered signal 103 impinges on the detector where it causes a 

mechanical element 104 to vibrate . In an embodiment , the vibration of mechanical resonator 104 changes the optical spectrum of the detector by changing the length of the cavity 

118. Accordingly , optomechanical ultrasound detector 100 

measures the change in the optical spectrum to track the 

motion of the mechanical element 104 and measure the 

ultrasound waves 103 . 

[ 0053 ] Optomechanical ultrasound detector 100 and pro 

cesses disclosed herein have numerous beneficial uses . Advantageously , optomechanical ultrasound detector 100 is 

more sensitive than conventional detectors . For example , optomechanical ultrasound detector 100 can be approxi mately two orders of magnitude more sensitive than piezo electric detectors and can detect very weak signals that are 

transmitted through a cranium for neuroimaging , which can 

be used in treatment of head trauma , e.g. , in emergency medicine . [ 0054 ] While one or more embodiments have been shown 

and described , modifications and substitutions may be made 

thereto without departing from the spirit and scope of the 

invention . Accordingly , it is to be understood that the present invention has been described by way of illustrations and not 

limitation . Embodiments herein can be used independently 

or can be combined . [ 0055 ] All ranges disclosed herein are inclusive of the endpoints , and the endpoints are independently combinable 

with each other . The ranges are continuous and thus contain 

every value and subset thereof in the range . Unless other wise stated or contextually inapplicable , all percentages , when expressing a quantity , are weight percentages . The 

suffix ( s ) as used herein is intended to include both the 

singular and the plural of the term that it modifies , thereby including at least one of that term ( e.g. , the colorant ( s ) includes at least one colorants ) . Option , optional , or option ally means that the subsequently described event or circum 

stance can or cannot occur , and that the description includes 

instances where the event occurs and instances where it does 

not . As used herein , combination is inclusive of blends , mixtures , alloys , reaction products , collection of elements , and the like . 

[ 0056 ] As used herein , a combination thereof refers to a 

combination comprising at least one of the named constitu 

ents , components , compounds , or elements , optionally together with one or more of the same class of constituents , components , compounds , or elements . [ 0057 ] All references are incorporated herein by reference . [ 0058 ] The use of the terms “ a , ” “ an , ” and “ the ” and 

similar referents in the context of describing the invention 

( especially in the context of the following claims ) are to be 

construed to cover both the singular and the plural , unless 

otherwise indicated herein or clearly contradicted by con 

text . It can further be noted that the terms first , second , primary , secondary , and the like herein do not denote any order , quantity , or importance , but rather are used to distin 

guish one element from another . It will also be understood 

that , although the terms first , second , etc. are , in some 

instances , used herein to describe various elements , these 

elements should not be limited by these terms . For example , a first current could be termed a second current , and , similarly , a second current could be termed a first current , without departing from the scope of the various described 

embodiments . The first current and the second current are 

both currents , but they are not the same condition unless explicitly stated as such . [ 0059 ] The modifier about used in connection with a 

quantity is inclusive of the stated value and has the meaning dictated by the context ( e.g. , it includes the degree of error 

. 
US 2022/0413135 A1 Dec. 29 , 2022 

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7 

associated with measurement of the particular quantity ) . The conjunction or is used to link objects of a list or alternatives 

and is not disjunctive ; rather the elements can be used 

separately or can be combined together under appropriate 

circumstances . What is claimed is : 

1. An optomechanical ultrasound detector for performing ultrasound imaging , the optomechanical ultrasound detector comprising : 

a micromirror substrate ; 

a mechanical resonator disposed on the micromirror sub 

strate , in optical communication with the micromirror 

substrate , spaced apart from the micromirror substrate 

at a cavity length Lc , and that : 

receives ultrasound waves ; oscillates at a resonator frequency f , in response to 

receipt of the ultrasound waves ; 

changes the cavity length Le based on oscillation of the 

mechanical resonator at resonator frequency f . , ; 

receives initial laser light from the micromirror sub 

strate ; and 

produces intra - cavity light from the initial laser light ; 

and 

an optical microcavity optically interposed between the 

micromirror substrate and the mechanical resonator 

and comprising the cavity length Le with cavity reso 

nance frequency f , formed by optically opposing sur 

faces of the mechanical resonator and the micromirror 

substrate and that : 

when the intra - cavity light is resonant with the cavity 

resonance frequency fc , repeatedly communicates 

the intra - cavity light between the micromirror sub 

strate and the mechanical resonator across the cavity length Lc ; and 

when the intra - cavity light is non - resonant with the cavity resonance frequency f . , communicates the 

intra - cavity light from the mechanical resonator to 

the micromirror substrate , such that the micromirror substrate produces cavity output light from the intra cavity light , wherein the cavity output light optically encodes infor 

mation about the ultrasound waves received by the 

mechanical resonator . 2. The optomechanical ultrasound detector of claim 1 , further comprising a resonator substrate disposed on the 

micromirror substrate and on which the mechanical resona 

tor is disposed . 3. The optomechanical ultrasound detector of claim 1 , further comprising an anti - reflective member disposed on an 

ultrasound surface of the mechanical resonator and that 

receives the ultrasound waves . 4. The optomechanical ultrasound detector of claim 1 , further comprising a resonator optical reflector disposed on 

a reflector surface of the mechanical resonator and that 

receives the initial laser light from the micromirror substrate 

and reflects the initial laser light as the intra - cavity light . 5. The optomechanical ultrasound detector of claim 1 , further comprising a mirror anti - reflective member disposed 

on an optical coupling surface of the micromirror substrate 

and that receives the initial laser light , communicates the 

initial laser light to the mechanical resonator via the optical microcavity , receives the intra - cavity light from the optical microcavity , and produces the cavity output light from the 

intra - cavity light . 

6. The optomechanical ultrasound detector of claim 1 , further comprising a concave micromirror disposed on an optical coupling surface of the micromirror substrate , such 

that the concave micromirror is arranged to be optically 

concave with respect to the optical microcavity . 7. The optomechanical ultrasound detector of claim 6 , further comprising a mirror reflective member disposed on 

a cavity surface of the micromirror substrate and that 

receives the initial laser light from the micromirror substrate and is an intra - cavity mirror for the optical microcavity , such 

that the mirror reflective member : 

reflects the intra - cavity light when the intra - cavity light is 

resonant with the cavity resonance frequency fc ; and 

communicates the intra - cavity light to the micromirror 

substrate when the intra - cavity light is non - resonant with the cavity resonance frequency fc . 8. The optomechanical ultrasound detector of claim 1 , further comprising an optical fiber in optical communication 

with the micromirror substrate and that communicates the 

initial laser fight to the micromirror substrate and receives 

the cavity output light from the micromirror substrate . 9. The optomechanical ultrasound detector of claim 1 , further comprising a coupling lens in optical communication 

with the micromirror substrate and that receives the initial 

laser light , communicates the initial laser light to the micro 

mirror substrate , and receives the cavity output light from 

the micromirror substrate , wherein the micromirror substrate is interposed between coupling lens and the optical microcavity . 10. The optomechanical ultrasound detector of claim 9 , wherein the coupling lens is disposed on the micromirror 

substrate . 

11. The optomechanical ultrasound detector of claim 10 , further comprising an mirror anti - reflective member dis 

posed on the coupling lens , wherein the coupling lens is 

interposed between the mirror anti - reflective member dis 

posed and the micromirror substrate . 12. The optomechanical ultrasound detector of claim 1 , further comprising a nanophotonic waveguide in optical 

communication with the micromirror substrate and that 

receives the initial laser light , communicates the initial laser 

light to the micromirror substrate , and receives the cavity output light from the micromirror substrate , wherein the micromirror substrate is interposed between nanophotonic waveguide and the optical microcavity . 13. The optomechanical ultrasound detector of claim 12 , wherein the nanophotonic waveguide comprises a nanopho tonic coupling member in optical communication with the 

micromirror substrate and that receives the initial laser light , communicates the initial laser light to the micromirror 

substrate , and receives the cavity output light from the 

micromirror substrate , wherein the micromirror substrate is interposed between nanophotonic coupling member and the optical micro 

cavity . 14. The optomechanical ultrasound detector of claim 13 , further comprising a nanophotonic substrate on which the nanophotonic waveguide is disposed . 15. The optomechanical ultrasound detector of claim 14 , further comprising a dielectric layer disposed on the nano photonic substrate such that the dielectric layer is interposed between the nanophotonic substrate and the nanophotonic waveguide . 
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7 

16. The optomechanical ultrasound detector of claim 1 , further comprising a meta - optic disposed on the micromirror 

substrate in optical communication with the micromirror 

substrate and that receives the initial laser light ,communi 

cates the initial laser light to the micromirror substrate , and receives the cavity output light from the micromirror sub 

strate , wherein the micromirror substrate is interposed between 

the meta - optic and the optical microcavity . 17. The optomechanical ultrasound detector of claim 1 , further comprising a piezoelectric ultrasound source dis 

posed on a resonator substrate on which the mechanical 

resonator is disposed and that produces a probe ultrasound 

wave that is communicated from the optomechanical ultra 

sound detector to an object , such that the objects reflects the 

probe ultrasound wave as the ultrasound waves received by the mechanical resonator . 

18. A process for performing ultrasound imaging with a optomechnical ultrasound detector , the process comprising : 

receiving ultrasound waves by a mechanical resonator of 

a optomechanical ultrasound detector , the optom echanical ultrasound detector comprising : 

a micromirror substrate ; 

a mechanical resonator disposed on the micromirror 

substrate , in optical communication with the micro 

mirror substrate , spaced apart from the micromirror 

substrate at a cavity length Lc ; and 

an optical microcavity optically interposed between the 

micromirror substrate and the mechanical resonator 

and comprising the cavity length Lc with cavity 

resonance frequency f , formed by optically opposing 

surfaces of the mechanical resonator and the micro 

mirror substrate ; 

oscillating the mechanical resonator at a resonator fre 

quency f , in response to receiving the ultrasound 

waves ; changing the cavity length Le of the optical microcavity 

based on oscillation of the mechanical resonator at 

resonator frequency fq ; 

communicating initial laser light from the micromirror 

substrate to the mechanical resonator ; 

receiving , by the mechanical resonator , initial laser light from the micromirror substrate ; 

producing , by the mechanical resonator , intra - cavity light from the initial laser light ; 

optically encoding , by the mechanical resonator , in the cavity output light information about the ultrasound 

waves received by the mechanical resonator ; repeatedly communicating the intra - cavity light between 

the micromirror substrate and the mechanical resonator 

across the cavity length Le when the intra - cavity light is resonant with the cavity resonance frequency fo ; 

communicating the intra - cavity light from the mechanical 

resonator to the micromirror substrate ; and 

producing , by the micromirror substrate , cavity output light from the intra - cavity light to perform ultrasound imaging . 19. The process for performing ultrasound imaging of claim 18 , further comprising communicating the cavity output light from the micromirror substrate to an analyzer . 20. The process for performing ultrasound imaging of 

claim 19 , further comprising , performing by the analyzer ; 

receiving the cavity output light ; 

analyzing the cavity output light ; and 

determining the information about the ultrasound waves from analyzing the cavity output light . c 

* * *