Multiple beam redirection device comprising plasmonic optical nanoantennas

Abstract

The present invention relates to a multiple beam redirection device comprising plasmonic optical nanoantennas comprising M>=2 plasmonic nanoantennas located at a distance from each other. Each nanoantenna is formed by a row of N plasmonic nanostructures, the angle θi of each nanoantenna with respect to an axis being coplanar to the nanoantenna and to the propagation vector of the electromagnetic field and perpendicular to the latter, wherein λi is a beam wavelength and D is the distance between nanostructures of a nanoantenna.

Description

[0001] MULTI-BEAM REDIRECTOR DEVICE BASED ON PLASMONIC OPTICAL NANOANTENNA

[0002] DESCRIPTION

[0003] TECHNICAL SECTOR

[0004] The invention belongs to the field of optics, more specifically to devices capable of controlling the direction of an electromagnetic radiation beam without the need to physically move the emitting source.

[0005] STATE OF THE ART

[0006] Beam steering is a technique used to control the direction of an electromagnetic radiation beam, such as light or radio waves. It involves directing the beam to a specific target without physically moving the source. Among the existing methods for beam steering is the mechanical method, which is based on physically controlling the beam's direction, generally through the mechanical rotation of an element irradiated by the beam and acting as a guide. This element can be a mirror, a lens, an antenna, or any other device that can be mechanically moved to change the beam's direction. The mechanical component that moves this element can be a motor or a microelectronic structure (MEMS). When a motor is used, the light beam is directed at the element, and then the element is rotated.These types of devices are usually bulky / expensive, and the motor can also generate noise. If a MEMS structure is used, the device's viewing angle is limited.

[0007] These mechanical devices also have a response speed limited by the maximum speed at which the mechanical component can be moved; an accuracy limited by the precision of the movement mechanism, which can be affected by mechanical stability problems or vibrations; mechanical wear due to the repeated movement of the mechanical component, which requires frequent and potentially costly maintenance; and high energy consumption, because the mechanical component has to be powered.

[0008] There are non-mechanical devices based on the use of an optical phased array (OPA). Instead of relying on mechanical components to direct the beam, these devices use phase modulation in multiple individual optical elements to electronically control the beam's direction. In an OPA, each optical element can be an electro-optical modulator, a piezoelectric element, or some other similar device. These elements can independently and rapidly adjust the phase of the light passing through them. By properly adjusting the phases in each element of the array, a constructive interference pattern can be generated that directs the optical beam in the desired direction.For example, there are methods that take advantage of the interference of a set of beams in the form of a waveguide, but a drive pixel must be provided for each waveguide for electrical or thermal drive, which complicates the required circuitry and increases the price of the device.

[0009] Implementing an optical phase array (OPA) requires sophisticated and precise optical and electronic devices, which can increase the complexity of the design and manufacturing, and therefore the cost. Furthermore, due to the nature of multiple elements working together, precise calibration and alignment are required to ensure optimal system performance, which is complex and requires specialized and expensive equipment. On the other hand, although this method does not involve mechanical movement, it requires energy to power the electronic devices that control the array elements and modulate the light phase, so energy consumption can also be significant.

[0010] Finally, there is another non-mechanical beam redirection method based on the use of photonic crystals. In this method, the beam direction is controlled by manipulating the properties of the photonic crystal, such as dielectric constant, refraction, or dispersion, through various mechanisms, including the application of electric fields, temperature changes, or the incidence of external light. However, the fabrication of these devices is complex, their cost is high, and their effectiveness can be sensitive to changes in ambient temperature, humidity, or radiation, which may require additional measures to stabilize the system.

[0011] An optical nanoantenna is an optical device that receives light and can manipulate, control, and concentrate it. Typically, nanoantennas operate at a single wavelength, which limits their tuning capabilities. Some nanoantennas can be electronically tuned to change the direction of the radiation beam they emit or receive, for example, using Ag nanopillars and an Ag substrate and inserting a barium titanate (BTO) substrate as a dielectric in between [L. Bibbó et al., “Radiation-direction steerable nanoantennae,” SN Appl. Sc., vol. 1, no. 8, p. 844, Jul. 2019, doi: 10.1007 / s42452-019-0882-9], There are also patents such as US11211761 B1 that describe devices with a layer whose refractive index changes, with several antennas arranged on it, a wavelength selection layer below the index-changing layer, and a drive unit that applies an electrical signal to the refractive-index-changing layer.Other devices propose tunable optical nanoantennas using several layers, one of which is a wavelength-tunable layer that can be controlled electrically, optically, or thermally, as described in US9904077B2. Finally, a plurality of transmission-type optical modulation devices has been proposed, each containing a phase modulator with a nanoantenna. These devices allow two-dimensional control of the incident beam by applying electrical signals to the nanostructures, which changes the phase of the light. Combining these devices can direct the beam in two dimensions. However, they are only capable of generating a single beam, emitting in only one direction, although this direction is controllable. Furthermore, they require electronic tuning, thus needing a power supply for these electronic components, increasing energy consumption.

[0012] SUMMARY OF THE INVENTION

[0013] The present invention solves the technical problems described above by means of a multi-beam redirection device based on plasmonic optical nanoantennas comprising M plasmonic nanoantennas, with M>=2, where each nanoantenna is formed by a row of N plasmonic nanostructures of radius ry and height ha a distance D from each other, the angle θ of each nanoantenna being with respect to an axis coplanar to the nanoantenna and to the propagation vector of the electromagnetic field and perpendicular to the latter = arcsin - 1 , where A¡ is a wavelength of the beam.

[0014] The nanostructures suitable for the invention are those with plasmonic resonance, such as those of Ag, Au, Cu, Pd, Pt, and Al, and the possible substrates SiO2, Si, InP, GaAs, SiN, or some aqueous medium. The radiation source must emit at least two wavelengths Ai. By adding photovoltaic power converters, the invention can be used as a transistor switch. By establishing a wireless optical link between each nanoantenna and a transducer rectenna, the invention can be used as an activator for a rectenna system. By associating each nanoantenna with an optical fiber, the invention can be used as a demultiplexer or as a fiber aligner. If a source is available that allows the selection of one or more wavelengths (for example, by using configurable wavelength-selective switches or filters), the invention can be used as a spatial optical switch.

[0015] BRIEF DESCRIPTION OF THE FIGURES

[0016] To aid in a better understanding of the characteristics of the invention and to complement this description, the following figures are included as an integral part thereof, the nature of which is illustrative and not limiting:

[0017] Figures 1a and 1b show the basic elements of a nanoantenna formed by nanocylinders placed on the same axis and the orientation of said axis with respect to a “y” axis coplanar to the nanoantenna and to the propagation vector of the electromagnetic field and perpendicular to the latter.

[0018] Figure 2 shows a vertical cross-section of a nanoantenna and the nanocylinders that form it.

[0019] Figure 3 is a representation of a device according to the invention comprising M nanoantennas separated by a distance d from each other. Figure 4 shows a top view of Figure 3. The arrangement of the M rows can be clearly seen in it.

[0020] Figures 5a and 5b show the emission from the device in different directions when illuminated with different wavelengths.

[0021] Figure 6 is a graph of the incident wavelength versus the angle at which resonance occurs, in an example wavelength range of between 400 nm and 900 nm, and for an example device with 51 Au nanocylinders with D=300 nm, r=30 nm and h=58 nm located on a SiO2 substrate.

[0022] Figures 7a and 7b show the effect illustrated in Figures 5a and 5b, for the particular case of 2 rows, with 51 gold nanocylinders each, with D=300 nm, r=30 nm and h=58 nm located on a SiO2 substrate.

[0023] Figure 8 is a representation of the use of the invention to activate a series of transistors by incorporating photovoltaic power converters.

[0024] Figure 9 shows the selective activation of an array of rectennas using the invention.

[0025] Figure 10 shows a demultiplexer using the invention and an array of optical fibers.

[0026] DETAILED DESCRIPTION

[0027] The present invention relates to a reconfigurable, multi-beam redirection system based on an array of optical nanoantennas, each consisting of a row of plasmonic nanostructures. The device is designed to precisely direct light to closely spaced points, adjusting its direction according to the wavelength of the applied light.

[0028] Referring to Figures 1a and 1b, each of the M nanoantennas (4) is composed of a row of N plasmonic nanostructures, in one particular case plasmonic nanocylinders (5) of radius ry and height h, although they could also be nanospheres or nanoellipsoids, positioned at a distance D from each other. The nanostructures must be made of a material that exhibits plasmonic resonance. The most common materials are Ag and Au, but others such as Cu, Pd, Pt, Al, etc., could also be used.

[0029] The device, as depicted in Figure 2, comprises a substrate with a refractive index n s(2) on a wafer (1). The wafer material depends on the substrate used, which must allow nanofabrication and operate within the design wavelength range. Silicon-based substrates or combinations such as silica (silicon dioxide) on silicon, silicon on an insulator, combinations with silicon nitride, or other active semiconductor materials such as InP and GaAs, or crystals such as lithium niobate, are possible alternatives. Thus, the substrate can be, for example, SiO2, Si, InP, GaAs, SiN, or some aqueous medium. On this substrate are the M nanoantennas (4), formed by rows of nanostructures with the same axis; the center of each nanoantenna is a distance d from the center of the next nanoantenna, as can be seen in Figure 3. Each row will be positioned at a different angle. associated with a different wavelength The angle θ of each nanoantenna with respect to the y-axis is = arcsin - 1 , where D is the distance between nanostructures in a row, as previously mentioned. One or more coating materials (3) are deposited on the nanoantennas, which can partially or completely cover the nanostructures, as shown in Figures 2 and 3. The distance d between the rows is optimally d>ND so that they do not interfere with each other. The range of possible values ​​for the distance between nanostructures in a group of rows (D) depends on the wavelength range to be redirected A e [A_in¡, A_fin] and is given by D e [A_in¡ / (2 ■ n s ), A_fin / n sFor example, for the specific case of wavelengths in the optical range A and [400 nm, 750 nm], the values ​​of D will be in the interval [200 nm, 750 nm] assuming the nanostructures are located in air, and in the interval [134 nm, 503 nm] if the nanostructures are located on a SiO2 substrate. Using multiple integers within this distance range is also feasible, but the coupling between nanostructures will be lower. The specific value of the distance D will depend on the wavelengths to be redirected and the desired redirection angles, as well as the desired size of the final device. In the specific example based on nanocylinders, it must be true that D > 3r, D > 3h, and 2r > h, where r is the radius of the nanocylinders and h is their height. The size of the nanocylinders is kept as large as possible for each particular case, to allow for greater resonance and intensity of the final beam, as well as to facilitate manufacturing.Similarly, for a fixed distance D, the device will operate in a wavelength range A e [D- n. s , 2 D- n s ].

[0030] As can be seen in Figure 4, each of the nanoantennas is positioned at a different angle... 0 M with respect to the y-axis; therefore, it will resonate at a different wavelength X ... M For the device to function as a reconfigurable single-beam redirector, it must be illuminated with a light source that allows the emission wavelength to be modified (at least between two values). The source can be a tunable laser or a broad-spectrum source with a reconfigurable wavelength-selective filter. If illuminated with a wavelength x The beam will emerge in the direction of the row that is positioned at angle 0 l t that resonates for that And if illuminated with A2, it will emit light in the direction of O2. If both directions are to be implemented simultaneously, the radiation source must include at least two wavelengths, and if it is also to be reconfigurable, a switch would be needed to activate and deactivate each wavelength. The source can be a frequency comb so that all waves are in phase, or a combination of different lasers, even with different phases. The operation of the device can be seen in Figures 5a and 5b, and also more realistically in Figures 7a and 7b. Each row operates independently, and the system is capable of selectively redirecting light beams to specific locations, providing precise control over the direction of the emitted light. The predominant direction (or directions) can be selected by manipulating the excitation wavelength.In this way, depending on the wavelengths used to illuminate the device, certain nanoantennas can be activated, or even all of them. Furthermore, depending on the material of the nanostructures and the spacing between them, the activation can be adjusted to the desired wavelength range.

[0031] To demonstrate the device's functionality, theoretical simulations were performed. In this specific example, the wavelengths used are in the visible spectrum, but any expert will recognize that the device can be configured for each specific case by modifying the materials, the size of the nanostructures, the distance between them, or the distance between the rows. Only two rows were used, each with 51 gold nanocylinders, on a SiC>2 substrate. The cylinders have a radius of 30 nm and a height of 58 nm and are separated by a distance of 300 nm. The separation between nanoantennas is 15.30 µm. If we analyze the theoretical resonant angle for each wavelength, which is given by the formula arcsin(A / D-1), we obtain the graph in figure 6. If we have a source with two wavelengths, A_1=850nm and A_2=500nm, in order for the rows to resonate at these wavelengths we must place the first row at 63.8° and the second at 6°.1st, see Figure 6. If we illuminate with A_1=850nm, the first row will resonate, as can be seen in Figure 7a; if we illuminate with A_2=500nm, the second row will resonate (see Figure 7b). These figures show the intensity scattered throughout the system. The field accumulation effect can also be observed; that is, the fact that the nanostructures at the end of the row have greater intensity than those at the beginning. The light beam will emerge from this end, as demonstrated by simulations of coupled dipoles in the figure.

[0032] The minimum dimension of the device, considering only the nanostructure system, will be approximately: x h. The total dimension will be larger, since a minimum manufacturing margin around the rows must be considered, which does not have to be very large, and the heights of the substrate and the wafer, which are decided at the time of manufacture according to what is most convenient.

[0033] The invention requires no moving parts, thus avoiding mechanical wear and the associated maintenance, and resulting in a very small device that allows for its implementation in integrated photonic circuits. Furthermore, being light-based, it boasts a high response speed, and thanks to its nanostructures, it can manipulate light at the nanoscale and redirect it with high precision. As a passive system, it requires no external power source, operating solely with a light source, significantly reducing energy consumption. It can also be mass-produced using nanolithography techniques, which significantly reduces its cost. Moreover, by incorporating a nanoantenna array, the invention can not only redirect a single beam but also independently and reconfigurably direct multiple beams of light.To date, proposed nanoantennas emit either a single beam of light, the direction of which may or may not be configurable, or multiple beams, but always in the same direction. No plasmonic nanoantenna currently exists that can generate multiple beams of light, each associated with a different wavelength, in different, configurable directions.

[0034] In summary, this device solves the problem arising from the need for a multi-beam redirection system that is not based on mechanical responses and that is passive, compact, stable, and easy to manufacture.

[0035] The advantages of the invention are, therefore, among others:

[0036] 1. Reconfigurable multi-beam redirection: The system allows the emission of multiple light beams, each associated with a different wavelength, configurable independently.

[0037] 2. Selective directionality: By adjusting the excitation wavelength(s), the system can selectively direct the emitted beams towards the desired locations.

[0038] 3. Compact and integrated design. Very small size: Integrating the nanoantenna system into a compact substrate like Sio2 allows for miniaturization and seamless integration into various optical devices and systems.

[0039] 4. High response speed

[0040] 5. High redirection accuracy

[0041] 6. Low energy consumption, as it does not require an electrical signal to operate. Various applications of the device of the invention include, for example, activating a transistor array, use as antennas / rectenes, a demultiplexer, optical switches, LIDAR, or for performing precise alignment of optical fibers.

[0042] For use as a transistor activator / switch (Figure 8), each antenna is pointed at a photovoltaic converter, which converts the optical signal into an electrical signal. This electrical signal is then applied to the transistor's gate, activating it. As we know, depending on the wavelengths of the incident light, different antennas will be excited, allowing the selection of which transistors to turn on or off within a system of transistors very close to each other. This enables the selective selection of one transistor or another using a single input fiber and an optical source. Using the device of the invention as a switch allows for high communication speeds and provides electrical isolation between the light source and the transistor, which can improve the device's stability and reliability by reducing the risk of electrical interference and damage from overload.

[0043] Similarly, another possible application is a wireless optical link between each antenna and a transducer rectenna, which will convert the transmitted optical energy into a direct current, making it possible to simultaneously turn on several rectennas very close to each other or to choose which ones to activate and which ones not, as can be seen in Figure 9.

[0044] If, instead of a frequency comb or a combination of several lasers, a broadband source is used, in which the input field has multiple wavelengths, the device of the invention can also be used as a demultiplexer when each antenna is connected to an optical fiber or waveguide. This allows for the compact spatial separation of a set of wavelengths from the incident beam, as shown in Figure 10. The demultiplexer function can also be applied to a set of previously multiplexed wavelengths. Furthermore, the system can filter out low levels of coherence, as its performance improves with the coherence of the incident field.If instead of a wide-space source we have an incident light source composed of at least two wavelengths, the device allows the creation of a wavelength-selective optical switch, since if it is illuminated with a wavelength A1, the signal will be transmitted through a first nanoantenna, thus reaching output 1; and if it is illuminated with A2, the signal will be transmitted through antenna 2, reaching output 2. Therefore, by selecting one wavelength or the other, the beam can be redirected to the desired output, thus creating a spatial optical switch.

[0045] This device could also be used to precisely align optical fibers. This would require a light source with as many wavelengths as there are fibers to be aligned, along with our device and the output optical fibers. When the device is illuminated, the corresponding nanoantennas would also be illuminated, and each nanoantenna would be used to align one of the fibers. Once aligned, the device would be removed, leaving the fibers perfectly aligned. The spacing between the fibers is therefore determined by the spacing between the device's nanoantennas. Furthermore, thanks to the invention's ability to concentrate light in extremely small volumes, it could be used in optical trapping applications, to generate high-resolution images, to manufacture highly sensitive sensors or biosensors, or even in novel tumor treatments such as photothermal therapy.

[0046] In view of this description and figures, a person skilled in the art may understand that the invention has been described according to some preferred embodiments thereof, but that multiple variations may be introduced in said preferred embodiments, without exceeding the object of the invention as claimed.

Claims

CLAIMS 1. A multi-beam redirection device based on plasmonic optical nanoantennas (4) comprising M>=2 plasmonic nanoantennas located at a distance d from each other and wherein each nanoantenna is formed by a row of N plasmonic nanocylinders, nanospheres or nanoellipsoids (5), the angle θ of each nanoantenna being with respect to an axis coplanar to the nanoantenna and to the propagation vector of the electromagnetic field and perpendicular to the latter = arcsin - 1 , where A¡ is a wavelength of the beam, D being the distance between nanostructures of a nanoantenna (4).

2. Multiple beam redirection device according to claim 1 characterized in that the nanostructures comprise one or more vapors of the following metals: Au, Ag, Cu, Pd, Pt, Al.

3. Multiple beam redirection device according to claim 1 or 2, characterized in that the nanostructures are placed on a substrate of SiC2, Si, InP, GaAs, SiN, or some aqueous medium.

4. A multi-beam redirection system comprising a device according to any of claims 1-3 and a radiation source having at least two distinct wavelengths Ai that meet the condition = arcsin - 1 .

5. Multibeam redirection system according to claim 4 including means for selecting one or more wavelengths simultaneously 6. A multi-beam redirection system comprising a device according to claim 5, characterized in that the means for selecting one or more wavelengths are a reconfigurable wavelength-selective switch or filter.

7. Multibeam redirection system according to any of claims 5-6 for use as a transistor switch characterized by comprising a photovoltaic power converter associated with each nanoantenna.

8. A multiple beam redirection system according to any of claims 1-4 for use as a demultiplexer or as an optical fiber aligner, characterized in that it comprises an optical fiber or waveguide associated with each nanoantenna.

9. Multibeam redirection system according to claim 6 for use as an optical switch, characterized in that it comprises an optical fiber or waveguide associated with each nanoantenna.

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