Planar photonic resonant motor structure

Abstract

A photonic motor is here described, comprising a first optical waveguide arrangement adapted to guide at least one optical mode and forming a stator (12), and an electromagnetic interaction arrangement with said optical mode configured for rotating and forming a rotor (14) comprising a plurality of optical resonators or a plurality of reflecting metallic structures or a combination thereof, internally concentric to the first optical waveguide arrangement and separated therefrom by a predetermined lateral interaction distance adapted to establish an evanescent wave coupling of the optical mode with the plurality of second optical resonators or a reflection of the evanescent wave of the optical mode by the plurality of reflecting metallic structures. The rotor includes a circular frame (22) coaxial to a central hub (20) and including a monolithic arrangement of spokes (R) converging towards the central hub, adapted to support regions for housing (24) the plurality of second optical resonators or the plurality of reflecting metallic structures in a peripheral region of the frame. The frame is separated from the central hub and is disposed above a substrate (S), on which it can rest by way of support formations (26) in a non-operational condition, and which it can lift up from in an operational condition wherein the optical mode is guided in the first optical waveguide arrangement of the stator.

Description

[0001] DESCRIPTION

[0002] Planar Photonic Resonant Motor Structure

[0003] The present invention relates to opto-mechanical systems . Speci fically, the present invention relates to a mechanical system that allows to implement a photonic motor in order to obtain mechanical energy from a photon source ( for example, a laser source ) . In particular, the obj ect of the present invention is a photonic motor according to the preamble of claim 1 . International patent application WO 2018 / 087789 discloses a photonic motor suitable for efficiently converting optical power into a mechanical couple, comprising an arrangement of two sets of guided wave photonic resonators , optically coupled with each other and having one and the same axis of rotation, which reciprocally rotate thanks to asymmetrical optical forces generated, which are induced by resonance phenomena . In this motor, a stator plane contains a number of optical ring resonators arranged according to a circular geometry that are simultaneously excited through a primary ring resonator which surrounds them . A rotor plane preferably contains the same number of optical ring resonators disposed in the same way in the stator plane . The rotor and the stator planes are optically coupled with each other through an evanescent coupling between specular ring resonators . At certain input excitation wavelengths , the photonic resonance motor rotates and follows the wavelength of an optical source, thanks to the opto-mechanical couple generated through the force associated with the radiation pressure resulting from the coupling of the stator resonators with the rotor ones . The asymmetrical optical forces associated with the symmetrical and anti-symmetrical resonating modes that excite the rings create working couples onto the rotor .

[0004] Italian patent 102021000007118 discloses a photonic resonance motor of the type mentioned above in a planar configuration, which comprises a first optical waveguide arrangement - for example, a plurality of first optical resonators - forming a static part of the motor, or stator, and a second optical waveguide arrangement - for example, at least one second optical resonator - forming a movable part of the motor, or rotor, which lies in a first and second regions of space of the common plane respectively, separated from each other by a predetermined lateral coupling distance , where the second optical waveguide arrangement is configured for moving in the second region of plane with respect to the first optical waveguide arrangement .

[0005] The lateral coupling distance is adapted to establish an evanescent wave coupling of the optical modes between at least one first optical resonator in the first optical waveguide arrangement and at least one second optical resonator in the second optical waveguide arrangement , in a proximity condition of the first and second optical resonators , hence a condition is created whereby the second optical resonator is attracted to or repelled from the first optical resonator, respectively, which results in the second optical resonator being moved closer to or moved away from the first optical resonator, respectively, according to a pre-determined local movement direction .

[0006] More speci fically, such photonic motor comprises at least one optical radiation input and an arrangement of excitation optical waveguides coupled with a first optical waveguide arrangement at a predetermined optical mode coupling distance with respect to at least one first optical resonator and configured for receiving at least one optical radiation at a predetermined wavelength from the optical radiation input and for optically coupling said optical radiation with at least one first optical resonator . The photonic motor also comprises control means preset to control at least one parameter of the radiation coming from the optical radiation input so as to selectively establish at least one symmetrical and anti-symmetrical mode .

[0007] Every first and second optical resonator is adapted to guide a symmetrical resonator mode at a first predetermined wavelength or an antisymmetrical resonator mode at a second predetermined wavelength, depending on the lateral coupling distance , as well as the distance between the first and second optical resonators in the plane . Whenever a symmetrical resonator mode is selectively established, a condition is created whereby the second optical resonator is attracted to the first optical resonator, which, in the second region of space in the plane , generates an approaching movement of the second optical resonator to the first optical resonator according to a predetermined local movement direction . Whenever an anti-symmetrical resonator mode is established, a condition is created whereby the second optical resonator is repelled from the first optical resonator, which, in the second region of space in the plane , generates a condition whereby the second optical resonator is moved away from the first optical resonator according to a predetermined local movement direction .

[0008] The control means are also configured for : synchronously controlling the wavelength of the radiation coming from the optical radiation input in such a way as to selectively switch from a symmetrical resonator mode to an anti-symmetrical resonator mode whenever, along the direction of movement predetermined in the second region of space of the common plane , a second optical resonator is close to the maximum proximity condition, or condition of lateral coupling distance with respect to a first optical resonator in the first region of space of said common plane ; or a symmetrical resonator mode having been set , synchronously controlling the activation of the optical radiation input only during the approaching step while switching it of f whenever, along the predetermined direction of movement in the second region of space of the common plane , the second optical resonator gets closer to the maximum proximity condition, or condition of lateral coupling distance with respect to a first optical resonator in the first region of space of the common plane , and, thanks to the forces of inertia, reaches a subsequent evanescent wave coupling condition with a di f ferent first optical resonator along said predetermined direction of movement ; or once an anti-symmetrical resonator mode is set , synchronously controlling the activation of the optical radiation input only during the moving-away step and switching it on whenever, along the predetermined direction of movement in the second region of space of the common plane , the second optical resonator gets closer to the maximum proximity condition, or condition of coupling lateral distance with respect to a first optical resonator in the first region of space of the common plane , and switching it of f whenever, along the predetermined direction of movement in the second region of space of the common plane , the second optical resonator leaves the coupling condition and, thanks to the forces of inertia , it reaches the subsequent coupling condition with a di f ferent first optical resonator along the predetermined direction of movement .

[0009] A photonic motor of the type described in the present status of the art does not describe a mechanical system solution for supporting and maintaining the rotor in rotation with respect to the stator under lateral coupling conditions .

[0010] An obj ect of the present invention is to provide a planar photonic motor that features a structure suitable for maintaining the rotor in rotation with respect to the stator, by keeping the rotor and stator waveguides in a lateral coupling condition, so as to maintain an opto-mechanical force that is used to allow to keep the rotor in rotation in the common plane .

[0011] A further obj ect of the invention is to implement a planar photonic motor that features a reduced technological complexity in both implementation and operation .

[0012] According to the present invention, these obj ects are achieved by a photonic motor having the characteristics set forth in claim 1 .

[0013] Particular embodiments are described in the dependent claims , whose contents are an integral part of the present disclosure .

[0014] Specifically, the invention relates to a planar photonic motor, comprising a first optical waveguide arrangement - comprising a first optical ring resonator suitable for guiding at least one optical mode - forming a static part of said motor, or stator, in a planar region, o stator plane, and an electromagnetic interaction arrangement with said at least one optical mode , internally concentric to the first optical ring resonator - comprising a plurality of second optical resonators or a plurality of reflecting metallic structures or a combination thereof - forming a movable part of said motor, or rotor, in a planar region, or rotor plane , wherein the stator plane and the rotor plane are co-planar in an operational condition of the motor . The static part and the movable part of the motor are separated from each other by a predetermined lateral interaction distance , whereby the electromagnetic interaction arrangement with the optical mode guided by the first optical ring resonator is configured for rotating in the rotor plane with respect to the first optical waveguide arrangement in the stator plane .

[0015] The optical mode guided by the first optical waveguide arrangement is provided by at least one excitation optical waveguide coupled with the first optical waveguide arrangement at a predetermined optical mode coupling distance, configured for receiving at least one optical radiation at a predetermined wavelength from at least one optical radiation input, which is at least one coherent radiation source or is coupled with at least one coherent radiation source .

[0016] In a presently preferred embodiment, the first optical ring resonator and the second optical resonators , as well as the excitation optical waveguide, are implemented by optical guides integrated on a dielectric substrate, and the excitation optical waveguide is co-planar with the first optical waveguide arrangement .

[0017] The lateral interaction distance is adapted to establish an evanescent wave coupling of said at least one optical mode between the first optical resonator and said plurality of second optical resonators or a reflection of the evanescent wave of said at least one optical mode of said first optical resonator by said plurality of reflecting metallic structures . The evanescent wave optical coupling determines a trans fer of part of the optical power from the waveguide of the stator to the second optical resonators of the rotor . Conversely, the reflection of the evanescent wave results in an exchange of momentum, hence a radiation pressure , which generates a torque which is exerted onto the rotor .

[0018] In order to keep the lateral interaction distance stable and to enable the rotor to rotate with respect to the stator, an innovative configuration of a mechanical rotor system is proposed .

[0019] The rotor is formed of a circular frame, in the form of a wheel , which includes a monolithic arrangement of spokes converging toward a central hub, coaxial to the axis of rotation of the rotor, which are suitable for peripherically supporting regions for housing the plurality of second optical resonators or the plurality of reflecting metallic structures . The second optical resonators or the reflecting metallic structures are uniformly distributed along the circumferential peripheral region of the rotor frame . In the mechanical rotor system, the central hub is separated from the frame , and the frame is disposed above a substrate, on which it can rest by way of support formations integral with the frame or connected thereto and orthogonally proj ecting with respect thereto in the half-plane facing the substrate, free of moving on the substrate . The height of the support formations is determined in such a way as to maintain the rotor frame at a predetermined lift-up distance from the substrate , so as to bring it a little bit below the level of the stator plane and, in an operational condition wherein an optical mode is excited and guided in the first optical waveguide arrangement of the stator, to excite an attractive opto-mechanical force between the rotor and the stator, which results in lifting the rotor up until reaching an alignment condition with the stator plane . The rotor being lifted up advantageously reduces the static and dynamic frictions and the adhesive forces between the rotor and the substrate, in that it suppresses or strongly reduces the areas of the support formations intended for contacting with the substrate through a total or partial levitation of the rotor .

[0020] The area of the support formations intended for contacting with the substrate is in any case as small as possible, in order to reduce the adhesive and contact forces acting between them and the substrate .

[0021] The central hub is secured to the substrate, which lies under the wheel and is configured for forming a j oint of the mechanical rotor system and allowing a rotary movement of the rotor in the frame plane , while limiting the degrees of freedom in other directions of the space and preventing the rotor from separating during rotation .

[0022] Advantageously, such mechanical structure prevents movements of the rotor in a plane perpendicular to the plane of rotation, such as movements whereby it raises up with respect thereto or lowers and rests on the substrate , thus optimizing couples and reducing the static friction forces and the adhesive forces which microscopically act between the rotor plane and its respective support substrate .

[0023] Further characteristics and advantages of the invention will be discussed in more detail in the following description of one preferred embodiment, which is provided for exemplary, non-limitative purposes , with reference to the attached drawings , wherein : figure la is an exemplary planar view of the planar photonic resonance motor according to the present invention in a first embodiment ; figure lb is an exemplary planar view of the planar photonic resonance motor according to the present invention in a second embodiment ; figures 2a and 2b are two exemplary cross- sectional views I la- I Ia and I lb-I Ib respectively of the planar photonic resonance motor according to the present invention, in an operational condition; figure 2c is an exemplary view of the planar photonic resonance motor in the cross-sectional view of figure 2b, in a non-operational condition; figure 3a is an enlarged view of a portion of the rotor of the photonic resonance motor according to the invention; and figure 3b is a cross-sectional view of figure 3a according to line I l lb-I I Ib .

[0024] Figures la and lb show a photonic resonance motor 10 according to the invention, which includes a stator 12 and a rotor 14 . In the embodiment illustrated in figure la, the stator 12 lies in a stator plane and includes a closed optical waveguide 16 ' , such as an optical ring resonator, coupled with an excitation waveguide 18 . In the embodiment shown in figure lb, the stator 12 lies in a stator plane and includes an open optical waveguide 16 ' ' , in the form of an incomplete optical ring resonator, coupled with the excitation waveguide 18 .

[0025] The reference numeral 20 identifies a central hub emerging from a substrate S which supports the motor, said hub being coaxial to the axis of rotation X of the rotor .

[0026] The rotor 14 includes a circular frame 22 coaxial to the central hub 20 , which defines a rotor plane and includes a monolithic arrangement of spokes R converging toward the central hub 20, adapted to support regions 24 for housing a plurality of second optical resonators or a plurality of reflecting metallic structures or combinations thereof ( rotor poles ) in a circumferential peripheral region of the frame . The reflecting metallic structures might be, j ust as an example , small flat metallic platforms , co-planar with the rotor plane .

[0027] A plurality of support formations 26 , integral with the frame or connected thereto and orthogonally proj ecting with respect thereto in the half-plane facing the substrate S , is adapted to maintain the rotor frame at a predetermined lift-up distance from the substrate S ( for example, 1 . 95 microns ) , such as to bring it a little bit below the level of the stator plane in a non-operational condition of the motor ( for example, 50 nm) .

[0028] The frame 22 is free of rotating around the central hub 20 by ef fect of the tangential optomechanical forces acting between the first optical waveguide arrangement and the plurality of second optical resonators or reflecting metallic structures .

[0029] The frame 22 of the rotor is capable of rotating around the central hub 20 by ef fect of the electromagnetic interaction of the optical mode guided by the optical waveguide 16 ' or 16 ' ' with the plurality of second optical resonators or the plurality of reflecting metallic structures housed in the regions 24 . Such electromagnetic interaction is an evanescent wave coupling of said optical mode guided by the optical resonator of the waveguide 16 ' or 16 ' ' and the plurality of second optical resonators , or a reflection of the evanescent wave of said optical mode guided by the optical resonator of the waveguide 16 ' or 16 ' ' by the plurality of reflecting metallic structures .

[0030] With reference to figures 2a, 2b and 2c, the central hub 20 is integral with the substrate S and comprises a first cylindrical portion 20 ' , proximal to the substrate S , having a cross-section with a first radius , and a second cylindrical portion 20 ' ' , distal from the substrate S , having a cross-section with a second radius , greater than the first radius . The frame 22 is slidably coupled around the central hub 20 at the first cylindrical portion, at a predetermined radial separation radial separation therefrom, and the second cylindrical portion partially extends over the frame , at a predetermined buf fer distance in an operational condition, so as to prevent the frame from lifting up beyond a predetermined height above the plane of rotation .

[0031] The radial elongation of the spokes R of the frame is directly proportional to the working couple generated by the tangential opto-mechanical forces , necessary to overcome the friction and the adhesive couple of the support formations on the substrate , which contrast the rotation of the rotor .

[0032] The support formations 26 are configured for maintaining the rotor fixed at a predetermined height over the substrate ( for example , 1 . 95 microns ) and are free of moving on the substrate which lies below the frame 22 and are preferably configured for having contact areas with the substrate as small as possible in order to reduce the adhesive forces that microscopically act between the frame and the substrate . For example, the support formations include axially perforated pins which present a surface, at a distal extremity from the frame, intended for contacting the substrate, having an area smaller than the area of the cross-section of the pins . The rotor li fting up ( for example , by 50 nm) until reaching an alignment condition with the stator plane in an operational condition, by effect of the excitation of an opto-mechanical attractive force between the rotor and the stator resulting from the excitation of an optical mode guided in the first optical waveguide arrangement of the stator, operates as a mechanism used to reduce the static and dynamic frictions and the adhesive forces , in that it suppresses or strongly reduces the contact areas between the support formations 26 and the substrate S , by way of a total or partial levitation of the rotor .

[0033] Preferably, the support formations 26 are arranged at a radial distance from the axis of rotation of the frame as small as possible , i . e . they are disposed as close as possible to the axis of rotation of the rotor, in order to increase the working couple generated by the tangential optomechanical forces contrasting the friction couples , which depend on the static friction and on the adhesive forces , and contrast rotation .

[0034] Finally, figure 3a shows a presently preferred embodiment of a region 24 for housing a plurality of second optical resonators in details .

[0035] Such region comprises a niche 30 obtained by micro-machining ( etching) the frame 22 of the silicon rotor, and an annular optical waveguide 32 is obtained therein by using similar techniques , to form a second optical resonator . The figure also partially shows a portion of the rotor 12 and of its respective waveguide 16' close to the niche 30 and to the outer portion of the waveguide 32 .

[0036] The manufacturing techniques are those typical of the micro-electromechanical devices (MEMS ) and, consequently, those typically used for manufacturing integrated electronic devices ( e . g . , etching, depositions ) . In one configuration of the structure, the wafers used are of the SOI ( Silicon On Insulator) type, the rotor and the stator being implemented on the same silicon layer as the wafer itself , separated from each other by using appropriate etching techniques , whereas the support formations 26 and the hub 20 are obtained by deposition of their respective materials and they are subsequently separated from the substrate via subsequent etching techniques .

[0037] Advantageously, the photonic motor described above can be used in an application wherein the poles of the rotor, by interacting with the stator, acquire dipole moments from opto-mechanical gradient forces and, instead of being stabilized in an energy status as low as possible, are stabili zed in a higher energy status , thanks to the fact that the interference generated by the opto-mechanical forces creates a nonequilibrium system, following a Rayleigh- Jeans thermali zation .

[0038] In an alternative application, the poles of the rotor, by interacting with the stator, behave like a localized multi-body system capable of creating a condensed matter phase , usable to implement sensors and actuators based on multi-body physics and photonic resonance motors , also of an opto-thermal type .

[0039] In a further application, the poles of the rotor, by interacting with the stator, act as a localized multi-body system capable of creating an optomechanical wave which interacts with other similar devices on a large-scale basis , thus allowing to ampli fy the phenomenon on a large scale .

[0040] In a further application, the poles of the rotor, by interacting with the stator, create a dynamic variation of the index of refraction of the stator, thus acting as a time photonic crystal at the ambient temperature and in the absence of vacuum, for sensory, actuation, and quantum computation applications .

[0041] Finally, the poles of the rotor, by interacting with the stator, dynamically modify the index of refraction of the stator over time , thus generating a dynamic Casimir effect , for applications including generation of new light sources and propulsion on a macro-scale basis .

[0042] It goes without saying that, without prej udice to the principle of the invention, the embodiments can be varied with respect to what described above for explanatory, non-limitative purposes only, without leaving the range of protection, as defined by the attached claims .

Claims

CLAIMS1 . A photonic motor ( 10 ) , comprising : at least one optical radiation input ; a first optical waveguide arrangement adapted to guide at least one optical mode , comprising a first optical ring resonator ( 16 ' ; 16 ' ' ) forming a static part, stator ( 12 ) , of said motor ( 10 ) in a stator plane ; at least one optical excitation waveguide ( 18 ) coupled to said first optical waveguide arrangement at a predetermined optical mode coupling distance and configured to receive at least one optical radiation of a predetermined wavelength from said at least one optical radiation input and to optically couple said optical radiation to said first optical waveguide arrangement ; an electromagnetic interaction arrangement with said at least one optical mode , comprising a plurality of second optical resonators ( 32 ) or a plurality of reflective metallic structures or a combination thereof , internally concentric to said first optical waveguide arrangement and separated therefrom by a predetermined lateral interaction distance adapted to establish an evanescent wave coupling of said at least one optical mode between said first optical resonator(16'; 16' ') and said plurality of second optical resonators (32) or a reflection of the evanescent wave of said at least one optical mode of said first optical resonator (16'; 16' ') by said plurality of reflecting metallic structures, which is configured to rotate with respect to said first optical waveguide arrangement about an axis of rotation (X) according to at least one predetermined direction of rotation, so as to form a movable part, rotor (14) , of said motor (10) in a rotor plane, a central hub (20) emerging from a substrate (S) , coaxial to the axis (X) of rotation of the rotor (14) ; in which said rotor (14) includes: a circular frame (22) coaxial to said central hub (20) and including a monolithic arrangement of spokes (R) converging towards said central hub (20) , the spokes being adapted to support regions (24) for housing the plurality of second optical resonators (32) or the plurality of reflecting metallic structures in a circumferential peripheral region of the frame (22) ; a plurality of support formations (26) integral with the frame (22) and projecting orthogonally thereto, wherein the frame (22) is separated from saidcentral hub (20) and disposed above said substrate (S) , upon which it is capable to rest through said support formations (26) in a non-operational condition, and from which it is capable to lift up in an operational condition in which an optical mode is excited and guided in the first optical waveguide arrangement of the stator (12) , the height of said plurality of support formations (26) being such as to maintain said frame (22) in the non-operational condition at a predetermined lift-off distance from the substrate (S) whereby the rotor plane lies inferiorly and in proximity to the stator plane.

2. The photonic motor (10) according to claim 1, wherein said central hub (20) is integral with said substrate (S) and comprises a first cylindrical portion (20' ) proximal to said substrate (S) , having a cross-section with a first radius, and a second cylindrical portion (20' ' ) distal from said substrate (S) , having a cross-section with a second radius, which is greater than said first radius, the circular frame (22) being slidably coupled around said central hub (20) at said first cylindrical portion (20') at a predetermined radial separation distance from said central hub, said second cylindrical portion (20' ' ) partially extending over said frame (22) so asto avoid a lifting of said frame (22) beyond a predetermined height above the rotation plane.

3. The photonic motor (10) according to any one of the preceding claims, wherein said support formations (26) include axially perforated pins having at one end distal from the frame (22) a surface intended for contact with the substrate (S) having an area less than the cross-sectional area of the pins .

4. The photonic motor (10) according to any one of the preceding claims, wherein said support formations (26) are arranged at the shortest possible radial distance from the axis of rotation (X) of the frame (22) of the rotor (14) .

5. The photonic motor (10) according to any one of the preceding claims, wherein said first waveguide arrangement comprises a closed-loop optical resonator (16') .

6. The photonic motor (10) according to any one of claims 1 to 4, wherein said first waveguide arrangement comprises an open-loop optical resonator (16’ ' ) .

7. The photonic motor (10) according to any one of the preceding claims, wherein said second optical resonators (32) or said reflecting metallicstructures are uniformly distributed along the circumferential peripheral region of the frame (22) of the rotor (14) .

8. The photonic motor (10) according to any one of the preceding claims, wherein said excitation optical waveguide (18) is coplanar to said first optical waveguide arrangement .

9. The photonic motor (10) according to any one of the preceding claims, wherein said optical radiation input is at least one source of coherent radiation or is coupled to at least one source of coherent radiation .

10. The photonic motor (10) according to any one of the preceding claims, wherein the first (16'; 16' ' ) and second optical resonators (32) and said excitation optical waveguide arrangement (18) are formed by optical guides integrated on a dielectric substrate.

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