Optomechanical system for monitoring the mechanics of a solid-state, liquid of soft matter sample

Abstract

The invention relates to an optomechanical system for monitoring the mechanics of a sample, comprising: a photonic crystal (1, 2) with a substrate (1) and an array of transversally extending nanopillars (2) defining at least one row (3); a nanopillar cavity (4) for confining light and acting as a sensor for the sample; and a mirror region (5) formed in the array of nanopillars (2), the cavity (4) and the mirror region (5) being configured to prevent the propagation of light with Transverse-Magnetic (TM) polarization; the nanopillars (2) being spatially arranged to create a gradient of effective refractive index along the cavity (4), the maximum value of the effective refractive index inside the cavity (4) being lower than the effective refractive index of the mirror region (5).

Description

[0001] DESCRIPTION

[0002] OPTOMECHANICAL SYSTEM FOR MONITORING THE MECHANICS OF A SOLID-STATE, LIQUID OF SOFT MATTER SAMPLE

[0003] TECHNICAL FIELD

[0004] The present invention belongs to the technical field of nanophotonic detectors.

[0005] More particularly, the invention refers to an optomechanical system comprising at least one array of nanopillars defining a nanopillar cavity, that acts as a photonic crystal for monitoring the mechanics of solid-state, liquid or soft-matter, for example and without being limitative, the ex vivo monitoring of tissue mechanics.

[0006] This project, which led to this application, has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 964808.

[0007] STATE OF THE ART

[0008] In the last years there has been a growing interest in nanophotonics, a branch of optics intended to study the behavior of light on the nanometer scale, as well as the interaction of nanometer scale objects with light.

[0009] Nanophotonics has given rise to new promising applications in different technical fields, such as, photolithography techniques (which are frequently employed, for example, in the fabrication of integrated circuits), improvement of the storage capability of disk drives, miniaturization of optoelectronic devices and most notably, the development of new photodetectors intended to measure physical and / or chemical properties of different materials. The present invention refers mainly to this last application.

[0010] Nevertheless, most of current nanophotonic detectors are unable to monitor and quantify mechanical or frictional parameters of materials, so still there is room for improvement in this area. One of the few existing exceptions is document CN1047645521 , which discloses a nanophotonic detector capable of acting as an optomechanical system, since it is provided with a periodic array of nanopillars, disposed on a silicon substrate, and which is used in a micro-vibration detection method. Thanks to these features, the resulting micro-vibration detection method has an increased sensitivity and better detection limits.

[0011] On the other hand, document US20162460000A1 discloses an optomechanical device with mechanical elements and optical filters for actuating and / or detecting movement of the elements, including a support, and an array of mechanical elements anchored to the support and configured to move with respect thereto, and an actuating and / or detection device actuating the elements and / or detecting movement of the elements or frequency variations of the movement.

[0012] Despite these progresses, it would be preferred to develop an optomechanical system capable of measuring mechanical or frictional properties of materials at multiple scales, while also allowing for the quantification of their mass and dimensional parameters.

[0013] On the other hand, most of already known optomechanical systems are typically fabricated using semiconductor-on-insulator wafers, which are associated with high production costs.

[0014] BRIEF EXPLANATION OF THE INVENTION

[0015] In order to address the problems and disadvantages mentioned above, the present invention refers to an optomechanical system for monitoring the mechanics of a solid-state, liquid or soft-matter sample, said system comprising: a photonic crystal with a substrate and an array of nanopillars extending transversally to the substrate; the array of nanopillars comprising at least one row; the system also comprising a nanopillar cavity and a mirror region formed in the array of nanopillars, the cavity configured to confine light and act as a sensor for a sample placed on it, and the mirror region configured to prevent the propagation of light with Transverse-Magnetic (TM) polarization; where the nanopillars of the cavity are spatially arranged to create a gradient of effective refractive index along the cavity, the maximum value of the effective refractive index inside the cavity being lower than the effective refractive index of the mirror region.

[0016] These nanopillars can have any form and as such can have any cross-section shape and / or area. Preferably, the mentioned nanopillars are solids of revolution and / or polyhedrons, most preferably the nanopillars are cylindrical.

[0017] In the state of the art there exist various ways of preventing the propagation of light with TM polarization. One of them is described in the non-patent literature documents by Parag B. Deotare et al., “High quality factor photonic crystal nanobeam cavities,” Appl. Phys. Lett. 94 (12): 121106, 2009, and M. Notomi et al., "Ultrahigh-Q Nanocavity with 1 D Photonic Gap," Opt. Express 16, 11095- 11102, 2008, and involves the construction of one-dimensional photonic crystals by embedding an optical cavity region within at least one mirror region. In these works, the mirror region — designed for Transverse Electric (TE) polarization — is created by periodically repeating a unit cell, forming a band-gap of forbidden photon energies around the energy of the optical mode supported by the cavity, thereby preventing light from escaping. We adopt this strategy in our case, tailoring it for TM polarization by constructing a mirror region that confines TM- polarized light through a periodic arrangement of nanopillars, and more specifically, in such a way that the nanopillars in the mirror region are arranged with a fixed separation between contiguous nanopillars. This periodic structuring creates a band-gap of forbidden photon energies, effectively preventing the propagation of TM-polarized light.

[0018] The technical feature of creating a gradient of effective refractive index along the cavity, makes possible for the optomechanical system according to the present invention, to produce a differentiated, position-dependent response. This is advantageous since it allows measuring mechanical or frictional properties of materials at multiple scales, while also allowing for the quantification of their mass and dimensional parameters.

[0019] Thus, the present invention is able to meet the following two requirements at the same time: on the one hand, it is able to achieve a large mechanical displacement response to applied forces in nanopillars (as it was the case, for example, of the nanophotonic detectors disclosed by CN1047645521 ) while, on the other hand, allows a great sensitivity, low detection limit and large responsivity of the detection mechanism (i.e. , monitoring of the spectral shift of optical resonances due to geometrical deformation of a mechanical element) to applied forces. In fact, the system according to the present invention allows a much better spatial localization of the perturbing element and a better responsivity and minimum sensitivity, as compared to the nanophotonic detectors disclosed by CN1047645521. This is because the present invention relies on the deformation of the nanopillars composing the photonic cavity, which involves a small portion of the whole device. Conversely, the sensing principle of invention CN1047645521 involves the nanopillar array as a whole.

[0020] Unlike the optomechanical devices disclosed by US20162460000A1 , in the present invention, the mechanical and photonic elements are the same (i.e., the nanopillars), resulting in a more compact alternative platform which improves the integration. In fact, the manufacturing of devices according to US20162460000A1 is way more complex, since it requires the bonding of two wafers that should be perfectly aligned with each other, to align the optical filters with the mechanical elements. Moreover, in invention under US20162460000A1 , the mechanical elements must be actuated externally. In the system of the present invention, it is possible to detect the thermally activated mechanical modes of the pillars (i.e., not external actuation is required).

[0021] Moreover, devices according to US20162460000A1 seem hardly applicable to the monitoring of the mechanics of solid-state, liquid or soft-matter, for example and without being limitative, for the ex vivo monitoring of tissue mechanics. In fact, optomechanical devices according to US20162460000A1 would be sensible to forces perpendicular to the plane of the sample substrate, while the system of the present invention is sensible to forces in the plane of the sample substrate (i.e. parallel to the top surface of the pillars).

[0022] In the systems according to the present invention, the optomechanical readout is carried out at a location that is physically separated from the measurement region, formed by the nanopillar cavity. The test sample is positioned over the measurement region, and a waveguide can be used to separate the optomechanical readout and measurement regions. The working principle of the optomechanical system of the present invention is based on the deformation and variations in the mechanical motion of nanopillars in the cavity region and the optical readout of such deformations. Individually, each nanopillar in the cavity region acts as a mechanical resonator that vibrates at a specific mechanical resonance frequency different from the others, caused by the existence of a gradient of effective refractive index along said cavity.

[0023] It is important to point out that, throughout the present description, expression "effective refractive index", refers to the refractive index experienced by light of a given wavelength when propagating within a photonic crystal of an optomechanical system according to the present invention, constructed by repeating in space a unit cell comprising a single nanopillar and a volume of the surrounding medium.

[0024] In one embodiment of the present invention, the nanopillars of the cavity are arranged with a variable separation (or pitch) between contiguous nanopillars, from an outer edge of the photonic crystal to a centre of the photonic crystal, and / or the cross-section areas of the nanopillars vary from the outer edge of the photonic crystal to the centre of the photonic crystal.

[0025] In this particular embodiment of the invention, the gradient of effective refractive index along the cavity is therefore created by varying the separation between contiguous nanopillars and / or the cross-section areas of the nanopillars, from the outer edge of the photonic crystal, to the centre of the photonic crystal.

[0026] This implies that the optomechanical system according to the present invention provides spatial localization in the readouts at different scales, for example, hundreds of nanometres and tens of microns. In this specific case, where the nanopillars are cylindrical, the spatial localization is set by: i) the separation and different radii of the nanopillars (which is in the range of hundreds of nm); and ii) the separation of each measuring element which is determined by the nanopillar cavity length, which is in the tens of pm-range. Each measuring element can be repeated forming an array or matrix composed of many elements spread over a surface, extending over several mm2and even up to cm2.

[0027] This scalability of the optomechanical system according to the present invention is due to its compatibility with Complementary Metal-Oxide-Sem iconductor (CMOS) fabrication techniques. It is noteworthy that each measuring region can be independently read out by, for example, multiplexing the readout signal. This array of measuring regions enables the generation of “time-resolved” maps of the relevant parameters for analysing the dynamics of the test sample and tracking its changes over time.

[0028] Preferably the pitch of the array of nanopillars is from about 250 nm to about 600 nm, more preferably about 350 nm or about 500 nm.

[0029] On the other hand, when the nanopillars are cylindrical, the radii of the nanopillars are preferably from about 70 nm to about 500 nm, and more preferably about 105 nm in the mirror region.

[0030] Finally, the height of the nanopillars is, preferably, up to about 6 pm, more preferably up to about 3 pm.

[0031] In other embodiment of the present invention, which is compatible with all the remaining embodiments of the invention, at least one nanopillar of the cavity comprises a first portion, in contact with the substrate and a second portion, isolated from the substrate, the effective refractive index of the first portion of the nanopillar being different from the effective refractive index of the second portion of the nanopillar.

[0032] In a first alternative of the above-mentioned embodiment of the invention, the difference in the effective refractive index existing between the first portion and the second portion of the nanopillars, is caused by the fact that both portions are made from different materials. Thus, in this case, the first portion of the nanopillar comprises a first material having a refractive index which is different to the refractive index of a second material from which the second portion of the nanopillar is made. Most preferably, the refractive index of the first material is lower than the refractive index of the second material. In a second alternative of the above-mentioned embodiment of the invention, the difference in the effective refractive index existing between the first portion and the second portion of the nanopillar, can also be caused by the fact that the crosssection area of the first portion of the nanopillar is different from the cross-section area of the second portion of the nanopillar. Most preferably, the cross-section area of the first portion of the nanopillar is smaller than the cross-section area of the second portion of the nanopillar.

[0033] Another possibility contemplated by the present invention is that the first portion of the nanopillar comprises a cross-section area reduction, arranged so that the cross-section area decreases as the distance to substrate increases. In this case, the cross-section area reduction of the first portion of the nanopillars is preferably performed by etching.

[0034] Said fabrication technique allows the photonic crystal of the optomechanical system of the invention to be produced on a full semiconductor substrate, like a wafer, using complementary metal-oxide-semiconductor (CMOS) compatible fabrication techniques. To achieve this, the issue of substrate loss in full silicon structures is addressed by confining the light in the third dimension on the nanopillar by performing a cross-section area reduction to the first portion thereof by etching. This is very novel and advantageous since prior art photonic and optomechanical devices are typically fabricated using semiconductor-on- insulator wafers, which are generally much more expensive than bulk silicon wafers due to their complex manufacturing process and the need for high-purity materials.

[0035] In another embodiment of the invention, compatible with all the remaining embodiments of the invention, the array is a two-dimensional array of nanopillars comprising a plurality of rows, arranged in parallel.

[0036] Preferably, in the system according to the present invention, each of the nanopillars are arranged on a vertex of a regular polygon pattern. Thus, more preferably each of the nanopillars are arranged on a vertex of an equilateral triangle pattern or, alternatively, on a vertex of a square pattern. DESCRIPTION OF THE DRAWINGS

[0037] For a better understanding of the invention, the following figures are included, showing a particular embodiment thereof, wherein:

[0038] Figure 1 is a schematic view, in perspective, of an optomechanical system according to a first exemplary embodiment of the present invention;

[0039] Figure 2A shows a first example of nanopillar which forms part of an optomechanical system according to the present invention;

[0040] Figure 2B shows a second example of nanopillar which forms part of an optomechanical system according to the present invention;

[0041] Figure 3 schematically shows, in plan view, a detail of an optomechanical system according to a second exemplary embodiment of the present invention;

[0042] Figure 4a schematically shows, in plan view, an optomechanical system according to a third exemplary embodiment of the present invention; and

[0043] Figure 4b is a photograph, at micrometer scale, of an optomechanical system according to Fig 4a.

[0044] EXPLANATION OF NUMERICAL REFERENCES

[0045] 1 Substrate;

[0046] 2 Nanopillar;

[0047] 2a First portion of the nanopillar;

[0048] 2b Second portion of the nanopillar;

[0049] 3 Row (of nanopillars);

[0050] 4 Nanopillar cavity;

[0051] 5 Mirror region;

[0052] 6 Separation (between two contiguous nanopillars);

[0053] 7a, 7b Outer edges (of the photonic crystal);

[0054] 8 Center (of the photonic crystal);

[0055] 9 Radius of the first portion of the nanopillar;

[0056] 10 Radius of the second portion of the nanopillar; 10a Radius of the second portion of the nanopillar (in the mirror region of the 2D hexagonal embodiment);

[0057] 10b Radius of the nanopillar (in the center of the cavity of the nanopillar of the 2D hexagonal embodiment);

[0058] 10c Radius of the second portion of the nanopillar (of the first neighbors of the cavity of the 2D hexagonal embodiment);

[0059] 11 Incident Light;

[0060] 12 Hexagonal unit cell.

[0061] 13a Lattice constant (of the mirror region in the 2D hexagonal embodiment); and

[0062] 13b Lattice constant (of cavity in the 2D hexagonal embodiment).

[0063] EMBODIMENTS OF THE INVENTION

[0064] Several embodiments of the invention are briefly described below, as illustrative, and non-limiting examples thereof, in accordance with the attached figures. Throughout these figures, identical or similar elements will be designated using the same numerical references.

[0065] Figure 1 corresponds to a first preferred embodiment of an optomechanical system according to the present invention.

[0066] In this particular case, the optomechanical system comprises a photonic crystal, that acts as a sensor system for ex vivo monitoring of tissue mechanics, or any other elastic material or liquid placed on it. Said photonic crystal is formed by a substrate 1 -arranged horizontally- and an array of nanopillars 2, extending transversally to the substrate 1 and forming one single row 3.

[0067] Both the substrate 1 and the nanopillars 2 are made from a bulk silicon wafer using CMOS compatible fabrication techniques. This is advantageous since manufacturing costs are reduced, as compared to the use of semiconductor on insulator wafers, which are generally much more expensive.

[0068] For clarity reasons, only three of the nanopillars 2 have been indicated with their corresponding numerical reference, in Figure 1. In this embodiment, the nanopillars 2 are cylindrical and the area of their cross-sections are defined by radii. A nanopillar cavity 4 is formed in the central part of the nanopillar row 3 (which surrounds the centre 8 of the photonic crystal), while a mirror region 5 is formed in both end parts thereof, each end part including one of the outer edges, 7a and 7b, of the photonic crystal.

[0069] Nanopillar cavity 4 is constructed by introducing a defect (i.e., a gradient of effective refractive index) within this zone of the photonic crystal, which is engineered to create an optical cavity state within the bandgap.

[0070] In this particular case, the variation of the effective refractive index is achieved by decreasing the separation 6 (or pitch) existing between contiguous nanopillars 2, which form part of the cavity 4. In addition, as shown in Fig. 1 , the radius of the nanopillars 2 progressively decrease inside the nanopillar cavity 4. By introducing this geometrical variation, the optical modes are pulled-up of the lower photonic band from the X point (k=rr / a) of the first Brillouin zone, effectively confining the incident light 11 down to the cavity 4 volume within the photonic crystal and thereby creating a high-Q (quality factor) resonance at near infrared and telecom wavelengths. Conversely, both the nanopillar 2 radius and the separation 6 between contiguous nanopillars 2, remains the same within the mirror region 5, since it is merely configured to prevent the propagation of light 11 with Transverse-Magnetic polarization by creating a band-gap of forbidden photon energies.

[0071] In the example of the invention shown in Fig. 1 the nanopillars 2 which make up the cavity 4 have radii in the range of 100 nm and up to 3 pm height, with a pitch 6 that varies from about 300 nm to 600 nm. These dimensions also enable enhanced optomechanical interaction. Light and mechanical motion are coupled in a confined space in the nanopillar optomechanical cavity 2, and thus changes in the mechanical position of the nanopillars 2 affect the optical field. Their mechanical vibrations induce a modulation in the optical intensity which enables the transduction of the mechanical modes into the light readout. Thus, small mechanical displacements (of the order of picometers) can be measured by monitoring changes in the optical field. Moreover, if the tested sample exerts mechanical forces on the pillars in the cavity 4 inducing a deformation, consequently, the optical resonance shifts with a magnitude that exceeds the linewidth of the optical resonance, providing a second channel for sensing. Thus, the nano optomechanical system provides spatial localization in the readout set by the separation of the nanopillars 2 (from 300 to 600nm) and different radii as it is based on the deformation and mechanical motion of individual or collective nanopillars 2 forming the cavity 4.

[0072] Figure 2A shows a first example of a nanopillar 2, which forms part of the optomechanical system shown in Figi .

[0073] In this case, nanopillar 2 has two clearly differentiated portions: a first portion 2a, in contact with the substrate 1 and a second portion 2b, isolated from the substrate 1 and located above the first portion 2a. Moreover, radius 9 of the first portion 2a of the nanopillar 2, is smaller than radius 10, of the second portion 2b of the nanopillar 2.

[0074] This difference in radius, solves the issue of substrate 1 loss in full silicon structures. In fact, it makes possible to confine incident light 11 in the second portion 2b of the nanopillar 2, successfully isolating spatially the supported optical modes from the substrate 1 . Moreover, it also enables greater lateral deformations of the nanopillars 2.

[0075] Figure 2B shows a second example of a nanopillar which makes part of an optomechanical system according to the present invention. In this embodiment, the radius 9 of the first portion 2a of the nanopillar 2 is exactly the same, as the radius 10 of the second portion 2b thereof. Nevertheless, both portions 2a and 2b are made from different materials, having different refractive indexes. More particularly the first portion 2a is made from silicon dioxide, while the second portion 2b is made from silicon. Thanks to the use of said different material, the same isolation effect from the substrate 1 is achieved also in this case.

[0076] Figure 3, shows an optomechanical system according to a second exemplary embodiment of the present invention. In this case the array of nanopillars 2, also comprises forming one single row 3.

[0077] Thanks to the plan view, it can be clearly seen that, in the embodiment of the invention shown in Fig. 3, both the radius 10 and the separation 6 between contiguous nanopillars 2, remains the same within the mirror region 5. On the contrary, the separation 6 and the radius 10 of the nanopillars 2 progressively decrease inside the nanopillar cavity 4.

[0078] Figure 4a schematically shows, in plan view, a detail of a third exemplary embodiment of the present invention, in which the array of nanopillars 2 define a two-dimensional (2D) optomechanical system. In fact, the array of nanopillars 2 defines, in this case, a 2D structure formed by the repetition along a horizontal plane of a hexagonal unit cell 12. The dimensions are very similar to the ones used in the embodiment of Fig.1 (in which the nanopillar cavity 4 was 1 D, one dimensional) and the operating principle is the same, but the way the cavity 4 is constructed is slightly modified to confine spatially the optical mode in the central region of the photonic crystal. Thus, inside cavity 4 the separation between contiguous nanopillars 2 (pitch) and the radius 10 of the second portion of the nanopillars progressively decrease, as compared with the first neighbours, in order to minimize the mode volume and obtain spatial resolution.

[0079] More particularly the characteristic parameters of the embodiment shown in Figure 4a, in the case where nanopillars are cylindrical, are the following: in the mirror region 5: o a lattice constant 13a is 500 nm; and o a radius 10a of the second portion of the nanopillars is 10Onm; in the cavity 4: o the lattice constant 13b is 480 nm (i.e., 0,96 times the lattice constant 13a of the mirror region 5; o the radius 10b of the central nanopillar is 85nm (i.e., 0,85 times the radius 10a of the second portion of the nanopillars of the mirror region 5; and o the radius 10c of the first neighbour nanopillars is 92,5nm (i.e., 0,925 times the radius 10a of the second portion of the nanopillars of the mirror region 5; where the lattice constants 13a, 13b are defined as the distance from the geometric centre of each nanopillar 2 with respect to the geometric centre of contiguous nanopillars 2 contained within the same zone, namely, within the mirror region 5 or cavity 4. When the nanopillars 2 are cylindrical, as is the case in the embodiment shown in Figure 4a, the value of lattice constants 13a, 13b is calculated as the distance between centres of contiguous nanopillar 2 radii contained within a same zone.

[0080] Finally, Figure 4b is a photograph, at micrometer scale, of an optomechanical system according to Fig 4a in which the hexagonal unit cell 12, corresponding to the center of the nanopillar cavity, is shown.

Claims

CLAIMS1 . An optomechanical system for monitoring the mechanics of a solid-state, liquid or soft-matter sample, the system comprising: a photonic crystal (1 ,2) with a substrate (1 ) and an array of nanopillars (2) extending transversally to the substrate; the array of nanopillars (2) comprising at least one row (3); the system also comprising a nanopillar cavity (4) and a mirror region (5) formed in the array of nanopillars (2), the cavity (4) configured to confine light and act as a sensor for a sample placed on it, and the mirror region (5) configured to prevent the propagation of light (11 ) with Transverse-Magnetic polarization, characterized in that the nanopillars (2) of the cavity (4) are spatially arranged to create a gradient of effective refractive index along the cavity (4), the maximum value of the effective refractive index inside the cavity (4) being lower than the effective refractive index of the mirror region (5).

2. The optomechanical system according to claim 1 , wherein the nanopillars (2) of the cavity (4) are arranged with a variable separation (6) between contiguous nanopillars (2), from an outer edge (7a, 7b) of the photonic crystal (1 ,2) to a centre (8) of the photonic crystal (1 ,2); and / or the cross-section areas of the nanopillars (2) vary from the outer edge (7a, 7b) of the photonic crystal (1 ,2) to the centre of the photonic crystal.

3. The optomechanical system according to any of the previous claims, wherein at least one nanopillar (2) of the cavity comprises a first portion (2a), in contact with the substrate (1 ) and a second portion (2b), isolated from the substrate (1 ), the effective refractive index of the first portion (2a) of the nanopillar (2) being different from the effective refractive index of the second portion (2b) of the nanopillar (2).

4. The optomechanical system according to claim 3, wherein the first portion (2a)of the nanopillar (2) comprises a first material having a refractive index which is different to the refractive index of a second material from which the second portion (2b) of the nanopillar (2) is made.

5. The optomechanical system according to claim 4, wherein the refractive index of the first material is lower than the refractive index of the second material.

6. The optomechanical system according to claim 3, wherein the cross-section area (9) of the first portion (2a) of the nanopillar (2) is different from the crosssection area (10, 10a, 10b, 10c) of the second portion (2b) of the nanopillar (2).

7. The optomechanical system according to claim 6, wherein the cross-section area (9) of the first portion (2a) of the nanopillar (2) is smaller than the crosssection area (10, 10a, 10b, 10c) of the second portion (2b) of the nanopillar (2).

8. The optomechanical system according to claim 3, wherein the first portion (2a) of the nanopillar comprises a cross-section area reduction, arranged so that the cross-section area (9) decreases as the distance to substrate (1 ) increases.

9. The optomechanical system according to claim 8, wherein the cross-section area reduction of the first portion (2a) of the nanopillars (2) is performed by etching.

10. The optomechanical system according to any of the previous claims, wherein the array is a two-dimensional array of nanopillars comprising a plurality of rows (3), arranged in parallel.11 . The optomechanical system according to the previous claims, wherein the nanopillars (2) are arranged each on a vertex of a regular polygon pattern.

12. The optomechanical system according to claim 11 , wherein the nanopillars (2) are arranged each on a vertex of an equilateral triangle pattern or, alternatively, on a vertex of a square pattern.

13. The optomechanical system according to any of the previous claims, wherein the separation (6) between the centres of contiguous nanopillars (2) of the array is from about 250 nm to about 600 nm, preferably about 350 nm.

14. The optomechanical system according to any of the previous claims, wherein the nanopillars (2) are cylindrical.

15. The optomechanical system according to claim 14, wherein the radii (9, 10) of the nanopillars (2) are from about 70 nm to about 500 nm.

16. The optomechanical system according to any of the previous claims, wherein the height of the nanopillars (2) is up to about 6 pm, preferably up to about 3 pm.

17. The optomechanical system according to any of the previous claims, wherein the nanopillars in the mirror region (5) are arranged with a fixed separation between contiguous nanopillars.

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