Ultrafast electro-optical modulation device and method

Abstract

The present invention relates to the field of information technology, and discloses an ultrafast electro-optical modulation device and method thereof. The device includes a first conductor, a second conductor, and a third conductor. The first conductor and the second conductor form an antenna structure; the antenna structure receives an external modulated electrical signal. The third conductor is located within the antenna structure; the third conductor is a micro-nano structure, and there is a portion on the micro-nano structure with a curvature radius of less than 10 nanometers; the modulation method is that the light to be modulated is enhanced by the antenna structure and then excited at the third conductor to generate a localized spatial light field; the potential difference caused by the modulated electrical signal between the first conductor and the second conductor affects the carrier density distribution in the micro-nano structure; the change in the carrier density distribution changes the properties of the spatial light field, thereby achieving modulation of the input light. The present invention is suitable for modulation of light in the visible and infrared bands, has the advantages of ultrafast modulation speed and ultra-low power consumption, and has a simple structure, which is conducive to secondary design optimization and integrated manufacturing.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to an electro-optical modulation device with ultra-fast modulation speed and ultra-low power consumption, and an electro-optical modulation method based on the device. Background Art

[0002] Optical modulators control certain degrees of freedom of light, including optical intensity modulators, phase modulators, polarization modulators, and spatial direction modulators. Over the past decade, various modulators based on different principles have emerged one after another. Representative examples include: In 2008, a team from Peking University proposed a photonic crystal system containing a strongly nonlinear conductor or semiconductor (C153-doped polystyrene), which can achieve low power consumption and picosecond response speed optical modulation through nonlinear effects (Nature Photonics, vol. 2, pp. 185-189 (2008)). In 2009, a team from Los Alamos National Laboratory proposed using voltage to control the carrier concentration in the depletion layer at the interface between GaAs and a conductor or semiconductor, thereby modulating the absorption of light by metamaterials (Nature Photonics, vol. 3, pp. 148-151 (2009)). In 2016, a team from Northwestern University in the United States used pump light to deform the mechanical structure in an optomechanical system, thereby regulating optical signals. These modulators have a slow response due to the electrical, optical, and mechanical physical processes involved in their principles, reaching a maximum of gigahertz (GHz) levels (Nano Letters, vol. 16, pp. 7690-7695 (2016)). In order to obtain faster modulation speeds, considering that the Dirac cone band structure unique to graphene allows its carrier concentration to be sensitively regulated by voltage, modulation of light absorption can be indirectly achieved. The University of California, Berkeley and Cornell University have both reported graphene optical modulators based on this mechanism, with modulation speeds reaching 10 GHz (Nature, vol. 474, pp. 64-67 (2011)). Furthermore, in 2018, a team from Harvard University in the United States reported optical modulation with a modulation speed of 210 GHz based on the Pockels effect of lithium niobate (Nature, vol. 562, pp. 101-104 (2018)). However, the modulator's size of over 100 microns makes it difficult to integrate it in a high-density manner on a chip, and its modulation speed still does not reach the terahertz (THz) level.

[0003] Due to the inherent fast response speed of plasmons in metallic structures, active optical modulation based on inelastic electron tunneling in metallic nanogap structures has received considerable attention in recent years. The modulation speed of such devices is primarily dependent on three factors: 1. the electron tunneling time, 2. the radiation decay time, and 3. the RC relaxation time of a resistor-capacitor (RC) circuit, τ = RC, where R and C represent the equivalent resistance and capacitance of the circuit, respectively. Electron tunneling and radiation are both femtosecond-scale processes or even faster, and the modulation speed of such modulators is primarily limited by the RC relaxation time. In such devices, because sufficient tunneling current and inelastic tunneling current-induced optical radiation are required, the gap between the metals is often very small (e.g., less than 1 nanometer) and the effective area is large, resulting in a significant capacitance of the metal structure. Furthermore, due to the strong tunneling current, the equivalent resistance R of the entire circuit system is also large. Therefore, the RC relaxation time significantly limits the modulation speed. Taking all factors into consideration, the modulation speeds of these devices can generally only barely reach terahertz levels. For example, a team from ETH Zurich proposed a light modulation scheme based on inelastic electron tunneling through nanogaps (Nature Nanotechnology, vol. 10, pp. 1058-1063 (2015)). Furthermore, due to the presence of tunneling current, these devices consume significant power during operation.

[0004] As mentioned above, to date, although the modulation speed of the modulator can theoretically reach the terahertz level, in practice factors such as the large RC time constant limit the response speed of the modulator. Modulation devices with terahertz modulation speeds are rarely reported, and the modulation process is generally accompanied by high power consumption. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to propose an electro-optical modulation method based on carrier density distribution control in a conductive material and its supporting device, aiming to achieve electro-optical modulation with ultrafast response and ultra-low power consumption.

[0006] The present invention first proposes an ultrafast electro-optical modulation device. The device comprises a first conductor, a second conductor, and a third conductor. The first conductor and the second conductor form an antenna structure for enhancing light scattering and absorption. The gap between the first conductor and the second conductor is less than 100 nanometers, with the minimum distance of the gap ensuring that no current is conducted between them. The third conductor is located within the gap and conducts electricity with one of the first and second conductors, but not with the other. The third conductor is a micro-nanostructure with a portion having a curvature radius of less than 10 nanometers. The antenna structure receives an external modulated electrical signal.

[0007] Furthermore, part or all of the external environment of the first conductor and the second conductor is a vacuum or other insulating material.

[0008] Preferably, the gap between the first conductor and the second conductor is a vacuum or other insulating material.

[0009] Further preferably, the first conductor, the second conductor, and the third conductor are made of the same conductive material, or different conductive materials.

[0010] The source of the modulated electrical signal is a bias voltage applied between the first conductor and the second conductor, or a background electric field applied to the entire electro-optical modulation device.

[0011] The present invention also proposes an electro-optical modulation method based on the ultrafast electro-optical modulation device, comprising the following steps:

[0012] Step i, irradiating the light to be modulated onto the conductor 1 and the antenna structure composed of the conductor;

[0013] Step ii, the input light to be modulated is enhanced by the antenna structure and then excited at three locations on the conductor to generate a localized spatial light field;

[0014] Step iii: Under the action of the source of the modulated electrical signal, a local electric field is generated between the first conductor and the second conductor, and the local electric field changes the carrier density distribution in the third conductor;

[0015] Step iv, the carrier density changes so that the spatial light field is modulated;

[0016] Step v: The modulated spatial light field is radiated to the far field under the enhancement effect of the antenna structure, forming an output light signal that can be detected by an external detection device.

[0017] Preferably, the light to be modulated is visible light or infrared light.

[0018] The basic principle of this invention is that Conductor 3, a micro-nanostructured conductor, includes a portion with a curvature radius less than 10 nanometers, making its carrier density distribution sensitive to the external environment. This also enables Conductor 3 to generate a localized spatial light field distribution when excited by incident light to be modulated, and its properties are significantly dependent on this carrier density distribution. The local electric field between Conductor 1 and Conductor 2 modulates the carrier density distribution in Conductor 3; this change in carrier density changes the spatial light field distribution, modulating the spatial light field. Ultimately, certain properties of the modulated light, such as intensity or phase, change in response to the applied modulation signal.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] First, the device of the present invention has very small equivalent capacitance and equivalent resistance, thereby providing a response speed exceeding terahertz or even tens of terahertz.

[0021] Secondly, the present invention modulates the spatial light field by achieving changes in carrier density distribution, while the existing technology relies on conduction or tunneling current. Therefore, compared with existing modulators that require conduction or tunneling current, the present invention has lower power consumption.

[0022] Thirdly, the modulation device of the present invention has a simple structure and is easy to be redesigned to add or change some structures to achieve a better modulation effect.

[0023] Fourthly, the effective part of the modulation device of the present invention is only on the order of hundreds of nanometers, which is suitable for high-density integration in technology.

[0024] Fifth, the present invention has no special requirements for the wavelength of the light to be modulated and can modulate the light to be modulated from the visible light to the infrared band. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0026] Figure 1 is a schematic diagram of the device of the present invention;

[0027] Figure 2 It is a top view of a first embodiment of the device of the present invention.

[0028] Figure 3 It is a front view of a first embodiment of the device of the present invention.

[0029] Figure 4 It is a front view of a second embodiment of the device of the present invention.

[0030] Figure 5 It is a side view of a second embodiment of the device of the present invention.

[0031] Figure 6 It is a perspective view of a third embodiment of the device of the present invention.

[0032] Figure 7 This is a cross-sectional view of the plane where the axis of symmetry of the third embodiment of the device of the present invention is located.

[0033] Figure 8 These are the scattering cross-section spectra of the third example of the device of the present invention under different external controlled potential differences.

[0034] Figure 9 This is the modulation contrast spectrum of the third embodiment of the device of the present invention under different potential differences.

[0035] Explanation of symbols: ΔV represents the potential difference between different conductive structures due to the applied modulation signal, ΔV=V1-V2, where V1 and V2 are the potentials of conductive structures 1 and 2, respectively. E represents the background electric field. DETAILED DESCRIPTION

[0036] In order to more clearly illustrate the purpose, principle, technical solution and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] like Figure 1 As shown, the present invention first proposes an ultrafast electro-optical modulation device. The device includes a first conductor 1, a second conductor 2, and a third conductor 3. The first conductor 1 and the second conductor 2 form an antenna structure for enhancing light scattering and absorption. The antenna structure receives an external modulated electrical signal.

[0038] A gap 4 exists between conductor 1 and conductor 2, and is smaller than 100 nanometers. The minimum distance of gap 4 ensures that no current flows between conductor 1 and conductor 2. Gap 4 is filled with a vacuum or other insulating material. Conductor 3 is located within gap 4, electrically conductive with conductor 2, but not with conductor 1. Conductor 3 is a micro-nanostructure with a portion having a curvature radius of less than 10 nanometers. In this specific embodiment, conductor 3 is designated as a carrier regulator based on its function.

[0039] Part or all of the external environment of the first conductor 1 and the second conductor 2 is a vacuum or other insulating material. The first conductor 1, the second conductor 2, and the third conductor 3 are made of the same conductive material or different conductive materials.

[0040] The source of the modulated electrical signal is the bias voltage applied between the first conductor and the second conductor, or the background electric field applied to the entire electro-optical modulation device.

[0041] The electro-optical modulation device of the present invention provides an electro-optical modulation method with ultrafast modulation speed and ultra-low power consumption. The steps are as follows: first, light to be modulated, ranging from visible light to infrared wavelengths, is irradiated onto the modulation device; the light to be modulated is amplified by antenna structures 1 and 2, generating a localized spatial light field distribution near a carrier modulator 3; then, an external signal source device, including electrodes or parallel plate capacitors, is used to change the carrier density distribution of the carrier modulator 3 in the device, thereby changing its optical response; the properties of the localized light field are subsequently altered, and the antenna structure enhances the radiation to form output signal light; finally, by controlling the signal amplitude or frequency of the signal source, the intensity or phase of the output light is modulated.

[0042] The physical mechanism behind this modulation method is that, by designing the geometry of the conductive material structure and selecting its constituent materials, the local carrier density of the carrier modulator 3 in the device can undergo significant changes in response to the modulating electrical signal. Specifically, by embedding the carrier modulator 3 within a preferred insulating material structure 4, the insulating material's affinity allows carriers to overflow more beyond the geometric boundaries of the conductive material, enhancing the responsiveness of the carrier distribution at the interface to the applied modulating signal. Furthermore, under the excitation of the modulated light, the carrier modulator 3 supports a localized spatial light field distribution, concentrating over 90% of the light field energy within a volume less than 1000 cubic nanometers. Consequently, the properties of the light field are directly dependent on the local carrier density distribution within the carrier modulator 3. When the carrier density distribution of the conductive material within this spatial region undergoes significant changes under bias or background electric field conditions, the properties of the light field undergo corresponding and significant changes, ultimately leading to observable changes in the output light signal. Furthermore, the designed structures 1 and 2 can serve as radiating antennas to enhance the ability of the aforementioned local light field to radiate to the far field, thereby enabling the modulated local light field to be detected by an external detector.

[0043] Example 1: An electro-optic modulator with ultrafast modulation speed, one of the structures is a flat two-dimensional structure, and its composition is as follows Figure 2 and Figure 3 As shown, the device comprises a conductor 1, another conductor 2, and a nanoscale conductor 3 seamlessly electrically connected to conductor 2. Conductors 1, 2, and 3 are all located on a dielectric substrate 5. A modulation signal is applied using an external instrument, such as an external electrode, to create a potential difference of ΔV between conductors 1 and 2. By controlling the potential difference ΔV, the carrier density distribution within the nanoscale conductive structure 3 undergoes significant changes, resulting in changes in the properties of the localized spatial light field near the surface of structure 3. This localized near-field remains undetectable by external detectors. Furthermore, the materials and geometric parameters of conductors 1 and 2 are designed so that the conductive structures 1 and 2 form a highly efficient radiating antenna, capable of radiating the localized light field near the conductive nanostructure 3 to the far field, where it can be detected by external detectors. This is reflected in significant changes in the absorption and scattering of the modulated light by the modulator as a whole. Ultimately, the output optical signal intensity varies with changes in the modulation signal ΔV, achieving an electro-optical modulation effect.

[0044] Example 2: An electro-optic modulator with ultra-fast modulation speed, one of which only requires a single conductor. Its front view and side view are shown below. Figure 4 and Figure 5As shown, conductors 1 and 3 are seamlessly electrically connected. Based on the same principle as in Example 1, a background electric field generated by a modulation signal source in the area surrounded by the dotted line acts as a modulation signal to influence the carrier density distribution of micro-nano conductive structure 3, thereby affecting the properties of the output light, ultimately achieving a modulation effect.

[0045] Example 3: An electro-optic modulator with ultrafast modulation speed, wherein another structure is a three-dimensional rotationally symmetric structure, such as Figure 6 As shown, the cross-section of the plane where the symmetry axis is located is as follows Figure 7 , comprising a conductor 1, another conductor 2, a nanometer-scale conductive material structure 3 seamlessly electrically connected to conductor 2, and an insulating medium 4 filling the gap between the conductors. Using the same principles and operating steps as Example 1, this device structure can also achieve electro-optical modulation.

[0046] In order to clearly demonstrate the modulation effect and response speed of the modulator device designed based on the modulation method of the present invention, we conducted numerical simulations on Example 3 and estimated its modulation contrast and response time. The modulation contrast can be calculated based on the scattering cross section σ given by the modulated light signal. s (λ) definition, when the modulation voltage ΔV changes in the interval [–U, U] and the operating wavelength is λ, the modulation contrast is (σ s,–U –σ s,U ) / σ s,U From a theoretical perspective, the simulation must accurately describe the variations in carrier density distribution within the nanoscale conductive material structure 3, while ensuring that the computational effort required to simulate the entire structure, including 1, 2, and 3, is manageable. Therefore, a two-dimensional rotationally symmetric finite element method was employed, based on a quantum fluid model calibrated with (time-domain) density functional theory.

[0047] After partial optimization, the conductive materials structures 1, 2, and 3 are made of silver, and the insulating material structure 4 is made of boron nitride; structure 1 is cylindrical, with a height of 105 nanometers and a diameter of 80 nanometers; structure 2 is also cylindrical, with a diameter of 20 nanometers and a height of 90 nanometers; structure 3 is conical, with a base diameter of 8 nanometers, a height of 8 nanometers, and a tip curvature radius of 1 nanometer; the distance from the tip of structure 3 to structure 2 is 8 nanometers. The scattering cross section and modulation contrast spectrum of the modulation device obtained by simulation calculation under different bias voltages are shown as follows: Figure 7 and Figure 8 As shown in the figure, the modulation contrast reaches its maximum value of 150% near 944 nm. Similar modulation effects can be achieved at other operating wavelengths through structural design to meet different application requirements.

[0048] The modulation response time of Example 3 can be estimated based on the method described in the literature Nature Nanotechnology, vol. 10, pp. 1058-1063 (2015) and its supplementary materials. Since the present invention only utilizes the change in the carrier density distribution near the surface of the conductor and does not rely on inelastic electron tunneling, that is, there is no tunneling current between the conductors, the present invention will have a faster modulation response speed in principle. Using the estimation method of the above literature, Figure 6 The cutoff frequency corresponding to the third example shown is

[0049]

[0050] Since the external circuit resistance is much larger than the device resistance, the total effective circuit resistance can be replaced by the commonly used external circuit resistance R = 50Ω (this parameter is taken from the supplementary material of Nature Nanotechnology, vol. 10, pp. 1058-1063 (2015)). Through quantum fluid model simulation, it can be obtained that the capacitance of the device example 3 of the present invention is C = Q / ΔV ≈ 8.9×10 -18 F, where Q and ΔV are the net charge on a single metal and the potential difference between two metals, respectively. Therefore, f can be estimated c ≈358THz. The modulation speed of the electro-optic modulator device designed based on the present invention is the fastest reported, and the estimated power consumption during the change of the potential difference from –2V to 2V is C(2ΔV) 2 / 2≈71×10 -18 J, reaching below 1 femtojoule, which is also far smaller than the existing reported level.

[0051] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An ultrafast electro-optical modulation device, characterized in that: The antenna structure comprises a first conductor, a second conductor and a third conductor, wherein the first conductor and the second conductor form an antenna structure, and a gap between the first conductor and the second conductor is less than 100 nanometers. The third conductor is located in the gap, is electrically connected to one of the first conductor and the second conductor, and is not electrically connected to the other conductor; The third conductor is a micro-nano structure, and the micro-nano structure has a portion with a curvature radius of less than 10 nanometers; The antenna structure receives an external modulated electrical signal.

2. The ultrafast electro-optical modulation device according to claim 1, wherein: Part or all of the external environment of the first conductor and the second conductor is a vacuum or other insulating material.

3. The ultrafast electro-optical modulation device according to claim 1, wherein: The gap between the first conductor and the second conductor is a vacuum or other insulating material.

4. The ultrafast electro-optical modulation device according to claim 1, wherein: The first conductor, the second conductor, and the third conductor are made of the same conductive material or different conductive materials.

5. The electro-optical modulation device according to claim 1, wherein: The source of the modulated electrical signal is a bias voltage applied between the first conductor and the second conductor, or a background electric field applied to the entire electro-optical modulation device.

6. An electro-optical modulation method for the ultrafast electro-optical modulation device according to claim 1, characterized in that: The following steps are involved: Step i, irradiating the light to be modulated onto the antenna structure composed of the first conductor and the second conductor; Step ii, the input light to be modulated is enhanced by the antenna structure and then excited at three locations on the conductor to generate a localized spatial light field; Step iii: Under the action of the source of the modulated electrical signal, a local electric field is generated between the first conductor and the second conductor, and the local electric field changes the carrier density distribution in the third conductor; Step iv, the carrier density changes so that the spatial light field is modulated; Step v: The modulated spatial light field is radiated to the far field under the enhancement effect of the antenna structure, forming an output light signal that can be detected by an external detection device.

7. The electro-optical modulation method according to claim 6, wherein: The light to be modulated is visible light or infrared light.

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