CN211554589U - Optical bistable device based on plasma super-surface unit - Google Patents
Optical bistable device based on plasma super-surface unit Download PDFInfo
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- CN211554589U CN211554589U CN202020512318.9U CN202020512318U CN211554589U CN 211554589 U CN211554589 U CN 211554589U CN 202020512318 U CN202020512318 U CN 202020512318U CN 211554589 U CN211554589 U CN 211554589U
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Abstract
The utility model relates to the technical field of plasma super-surface, and discloses an optical bistable device based on plasma super-surface units, which comprises at least one plasma super-surface unit, wherein the at least one plasma super-surface unit is periodically arranged and is spliced seamlessly to form a super-surface; each plasma super-surface unit comprises a metal plate, the metal plate is provided with a sub-wavelength through hole, and a nonlinear medium is embedded in the sub-wavelength through hole; the problem that the optical thickness of the existing resonator is at least the order of magnitude of the working wavelength or the input signal is strong is solved; the utility model discloses can realize the low threshold value of optics bistable state to it is irrelevant with the optics thickness of device, can not restrict the application and the integration of optics bistable device.
Description
Technical Field
The utility model belongs to the technical field of the super surperficial technique of plasma and specifically relates to an optics bistable device based on super surface unit of plasma.
Background
Generally, optical bistability occurs only when the optical thickness of the device or the input optical power is too great. Optical bistability is a nonlinear optical phenomenon with potential applications in optoelectronics and logic elements such as optical switches, optical memories, optical transistors, optical diodes, and optical computing. An optical bistable device is a new type of optical device made by using the nonlinear optical properties of substances, in which the input light has two stable states in the same state, and the optical bistable device is in which one of the two stable states at a certain time depends on the state of the device at the previous time.
Conventional optical bistable devices consist of fabry-perot (FP) resonators filled with a nonlinear medium. In order to be able to maintain the appropriate FP mode to provide the necessary feedback mechanism for amplifying the input signal, the optical thickness of the resonator is at least of the order of the operating wavelength, or the input signal must be strong. Such constraints severely limit the application and integration of optically bistable devices.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing a super surperficial unit's of plasma optics bistable state device based on exists to prior art, can realize optics bistable low threshold value to it is irrelevant with the optical thickness of device, can not restrict optics bistable state device's application and integration.
The above utility model discloses an above-mentioned utility model purpose can realize through following technical scheme:
an optical bistable device based on plasma super-surface units comprises at least one plasma super-surface unit, wherein the at least one plasma super-surface unit is periodically arranged and seamlessly spliced to form a super-surface; each plasma super-surface unit comprises a metal plate, the metal plate is provided with a sub-wavelength through hole, and a nonlinear medium is embedded in the sub-wavelength through hole; the sub-wavelength through holes comprise cross-shaped through holes, each cross-shaped through hole is formed by two first straight-line-shaped through holes which are mutually perpendicular and crossed, four end parts of each cross-shaped through hole are respectively connected with one type of convex through hole, and the four types of convex through holes are arranged in a four-fold rotational symmetry mode by taking the center of each cross-shaped through hole as a rotation center; each convex through hole comprises a second straight-line-shaped through hole, two ends of each second straight-line-shaped through hole are respectively connected with a right-angle-shaped through hole, each right-angle-shaped through hole is connected with the second straight-line-shaped through hole in a right-angle Z shape, and the two right-angle-shaped through holes are axisymmetric by taking the vertical center line of the second straight-line-shaped through hole as a symmetry axis; the end part of the cross-shaped through hole is vertically connected with the center of the second straight-line-shaped through hole.
By adopting the technical scheme, the constraint that the optical thickness of the device is at least the order of magnitude of the working wavelength or the input signal must be very strong is weakened by combining the changed surface plasmon polariton (SP) resonance in the artificial metamaterial with optical nonlinearity, so that the bistable low threshold value is realized, and the optical bistable threshold value is basically independent of the thickness of the metal plate 1; the physical process is determined by the shape resonance of the sub-wavelength structure, strongly enhancing the local field inside the aperture of the embedded nonlinear material.
The present invention may be further configured in a preferred embodiment as: the aperture of the sub-wavelength through hole is 20 μm or 15 μm.
By adopting the technical scheme, the bistable threshold field of the device can be influenced.
The present invention may be further configured in a preferred embodiment as: the nonlinear medium is Kerr nonlinear medium.
By adopting the technical scheme, the Kerr nonlinear medium is embedded into the sub-wavelength through hole, so that the transmission spectrum is strongdThe dependence provides the ability to modulate transmission by input power.
The present invention may be further configured in a preferred embodiment as: the planar shape of the metal plate is square, rectangular, circular, oval or rhombic.
The present invention may be further configured in a preferred embodiment as: the length of the first through hole is 100 mu m.
The present invention may be further configured in a preferred embodiment as: the right-angle through holes are formed by mutually and vertically crossing two third straight-line-shaped through holes, wherein the length of the third straight-line-shaped through hole perpendicular to the second straight-line-shaped through holes is 40 mu m, and the length of the third straight-line-shaped through hole parallel to the second straight-line-shaped through holes is 60 mu m; the length of the second in-line through hole is 40 mu m.
The present invention may be further configured in a preferred embodiment as: the thickness of the metal plate is 60 mu m, and the height of the sub-wavelength through hole is 60 mu m.
The present invention may be further configured in a preferred embodiment as: the metal plate is made of copper.
To sum up, the utility model discloses a following at least one useful technological effect:
1. the bistable low threshold is realized by combining the changed Surface Plasmon (SP) resonance in the artificial metamaterial with optical nonlinearity to weaken the constraint that the optical thickness of the device is at least the order of magnitude of the working wavelength or the input signal must be very strong, and the optical bistable threshold is basically independent of the thickness of the metal plate 1; the physical process is determined by the shape resonance of the sub-wavelength structure, and the local field embedded in the aperture of the nonlinear material is strongly enhanced;
2. by embedding a Kerr nonlinear medium in the sub-wavelength via, the ability to modulate transmission by input power can be provided for the strong dependence of the transmission spectrum.
Drawings
Fig. 1 is a schematic view of an xy plane structure according to an embodiment of the present invention.
Fig. 2 is a schematic xy plane structure diagram of a single plasma super-surface unit in an embodiment of the present invention.
Fig. 3 is a schematic perspective view of a single plasma super-surface unit according to an embodiment of the present invention.
Fig. 4 is a graph of the following calculated by FDTD simulation (circles) and analysis model (solid line) according to an embodiment of the present inventiondA plot of the transmission spectrum of the change.
Fig. 5 is a bistable hysteresis chart of an embodiment of the present invention having a metal plate thickness h of 60 μm and a subwavelength via hole diameter w of 20 μm.
Fig. 6 is a bistable hysteresis diagram of an embodiment of the present invention having a metal plate thickness h of 80 μm and a sub-wavelength via aperture w of 20 μm.
Fig. 7 is a bistable hysteresis chart of an embodiment of the present invention having a metal plate thickness h of 60 μm and a subwavelength through hole diameter w of 15 μm.
Fig. 8 is a graph of threshold field (triangle) and saturation field (circle) as a function of sheet metal thickness in an embodiment of the invention.
Fig. 9 is a graph of threshold field (triangles) and saturation field (circles) in FP plates as a function of metal plate thickness.
Fig. 10 is a graph of bistable threshold field and saturation field at different metal plate thicknesses.
In the figure, 1, a metal plate, 2, a sub-wavelength through hole, 21, a cross-shaped through hole, 22, a convex-like through hole, 221, a second straight-line-shaped through hole, 222, a right-angle-shaped through hole and 3 are plasma super-surface units.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, for the utility model discloses an optical bistable device based on super surface unit of plasma, including at least one super surface unit 3 of plasma, all super surface unit 3 of plasma extend along x axle and y axle on xy plane outward, are periodic arrangement and form super surface by seamless concatenation.
It is noted that fig. 1 shows only one example of a periodic arrangement of 9 plasmonic super surface elements 3 constituting a super surface structure, the number of plasmonic super surface elements 3 being related to the area of the incident electromagnetic wave.
As shown in fig. 2, each plasma super-surface unit 3 comprises a metal plate 1, the metal plate 1 is provided with a sub-wavelength through hole 2, and a nonlinear medium is embedded in the sub-wavelength through hole 2; the sub-wavelength through holes 2 comprise cross-shaped through holes 21, the cross-shaped through holes 21 are formed by mutually and vertically crossing two first straight-line-shaped through holes, four end parts of the cross-shaped through holes 21 are respectively connected with one type of convex through holes 22, and the four types of convex through holes 22 are arranged in a quadruple rotational symmetry mode by taking the center of the cross-shaped through holes 21 as a rotation center; each similar convex through hole 22 comprises a second straight through hole 221, two ends of the second straight through hole 221 are respectively connected with a right-angle through hole 222, each right-angle through hole 222 is connected with the second straight through hole 221 in a right-angle Z shape, and the two right-angle through holes 222 are axisymmetric by taking the vertical center line of the second straight through hole 221 as a symmetry axis; the end of the cross-shaped through-hole 21 is vertically connected to the center of the second in-line through-hole 221.
In this embodiment, the centers of the two first through holes are overlapped and have a length l1Is 100 μm.
Alternatively, as shown in fig. 2, the right-angled through hole 222 is formed by two third straight-line through holes perpendicularly crossing each other. As shown in fig. 3, a length l of the third in-line via perpendicular to the second in-line via 2213A length l of the third in-line via parallel to the second in-line via 221 of 40 μm4Is 60 mu m; length l of second in-line via 2212And 40 μm.
As shown in FIG. 3, the aperture w of the sub-wavelength through-hole 2 is 20 μm or 15 μm, and the height thereof is 60 μm, corresponding to the thickness h of the metal plate 1.
Alternatively, the planar shape of the metal plate 1 is a square, rectangle, circle, ellipse or rhombus, for example, if the metal plate 1 is a square, the side length d is 240 μm (as shown in fig. 3). The material of the metal plate 1 may be copper.
Optionally, the nonlinear medium has a dielectric constant ofdThe Kerr nonlinear medium of (2) is not particularly limited to this embodiment.
Operating the optically bistable device in the THz frequency band, metal can be considered an ideal electrical conductor since the skin depth of metal is negligible. It is emphasized that the non-linear behavior can be kept constant in quality by appropriate optimization of the geometry of the device at frequencies where metal losses and dispersion have to be taken into account.
The incident light polarization is along the x-axis, but it can be noted that the optical properties of the device are independent of polarization, since the structure has a four-fold rotational symmetry in the xy-plane. The numerical result shows that the structure has a perfect transmission peak at a specific frequency whendThe transmission peak is red-shifted when increased, and this transparency is caused by artificial SPs in subwavelength structured metal systems.
The following is a simple analytical model to predict the optical bistable behavior of the optical bistable device described in this embodiment. For the structures shown in fig. 1-3, the sub-wavelength via 2 can be considered as a metal waveguide supporting a series of eigenmodes, and the wave scattering problem associated with such structures can be solved strictly within the framework of general mode expansion.
Fig. 4 shows a graph of transmission spectra as a function of changes calculated by an FDTD simulation and analysis model according to an embodiment of the present invention. The linear transmission spectrum calculated by the model is shown as a solid line, and the FDTD simulation result is shown as a circled curve. It was found by FDTD simulation that S is equal to 15 μm for w and 20 μm for w00.22 and 0.25, respectively. As shown in fig. 4, the linear transmission spectrum calculated using the model has excellent agreement with the FDTD results. Due to the change ofdWave guide cut-off frequency wcModulated and therefore the transmission peak is shifted accordingly.
Fig. 5 to 7 plot bistable hysteresis of devices with varying thickness h and line width w as calculated by FDTD, with arrows indicating the direction of change of input power, lines with coils indicating the results obtained by non-linear FDTD calculation, and solid lines indicating the results obtained by model calculation. The working frequency is f-0.2 THz; dielectric constant of Kerr dielectricd＝2.25+χ(3)|E|2Therein x(3)＝1×10-18m2/V2. As shown in fig. 5 and 6, bistability may occur for a device having a thickness h of only 60 μm (i.e., 1/25 at the operating wavelength), and the bistable threshold field is substantially independent of thickness h, but depends largely on the aperture w (as shown in fig. 5 and 7).
To further demonstrate the ultra-low threshold behavior, FDTD simulations were used to study the dependence of the threshold/saturation field on the thickness h for the controlled case of the optical bistable device described in this example and a Kerr dielectric slab of the same thickness. Since the nonlinear medium is embedded in the sub-wavelength via hole 2, changing the thickness h of the metal plate 1 is equivalent to changing the thickness of the nonlinear medium. Fig. 8 and 9 clearly show that the threshold value of the ultra-thin optical bistable device is smaller than that of the FP system by several orders of magnitude. Furthermore, the optical bistable threshold/saturation field of the optical bistable device described in this embodiment behaves qualitatively differently, which indicates that there may be an abnormal control mechanism compared to a conventional FP plate.
The spectral position of the transmission peak is insensitive to the film thickness h, since high transmission is mainly caused by the waveguide mode that is cut off in the hole; the essence of this mode is to produce lateral resonance in the xy plane. As a result, the optical bistable threshold is also almost independent of h as long as the lateral structure (aperture) is unchanged. On the other hand, the saturation field is more dependent on h because the transmission peak narrows as h increases (as shown in fig. 10).
The constraint that the optical thickness of the device is at least the order of the working wavelength or the input signal must be very strong is weakened by combining the changed surface plasmon polariton (SP) resonance in the artificial metamaterial with optical nonlinearity, the working frequency is 0.2THz, and the device consists of a lambda/25 thick metal plate 1 with sub-wavelength through holes 2 and is filled with nonlinear media. Finite Difference Time Domain (FDTD) simulations indicate that optical bistability may occur in such a device at 3500 times lower excitation power than when using FP resonators of the same thickness, and that the optical bistability threshold is substantially independent of the thickness of the metal plate 1. The physical process is determined by the shape resonance of the sub-wavelength structure, strongly enhancing the local field inside the aperture of the embedded nonlinear material.
The embodiment of this specific implementation mode is the preferred embodiment of the present invention, not limit according to this the utility model discloses a protection scope, so: all equivalent changes made according to the structure, shape and principle of the utility model are covered within the protection scope of the utility model.
Claims (8)
1. An optical bistable device based on plasma super-surface units is characterized by comprising at least one plasma super-surface unit (3), wherein the at least one plasma super-surface unit (3) is periodically arranged and seamlessly spliced to form a super-surface; each plasma super-surface unit (3) comprises a metal plate (1), the metal plate (1) is provided with a sub-wavelength through hole (2), and a nonlinear medium is embedded in the sub-wavelength through hole (2); the sub-wavelength through holes (2) comprise cross-shaped through holes (21), the cross-shaped through holes (21) are formed by two first straight-line-shaped through holes which are mutually perpendicular and crossed, four ends of each cross-shaped through hole (21) are respectively connected with one type of convex through holes (22), and the four types of convex through holes (22) are arranged in a quadruple rotational symmetry mode by taking the center of the cross-shaped through hole (21) as a rotation center; each convex through hole (22) comprises a second straight-line-shaped through hole (221), two ends of each second straight-line-shaped through hole (221) are respectively connected with a right-angle-shaped through hole (222), each right-angle-shaped through hole (222) is connected with the second straight-line-shaped through hole (221) in a right-angle Z shape, and the two right-angle-shaped through holes (222) are axisymmetric by taking the vertical center line of the second straight-line-shaped through hole (221) as a symmetry axis; the end part of the cross-shaped through hole (21) is vertically connected with the center of the second straight-line-shaped through hole (221).
2. A plasmonic super surface unit based optical bistable device according to claim 1, characterized in that the aperture of the sub-wavelength via (2) is 20 μ ι η or 15 μ ι η.
3. A plasmonic super surface unit based optical bistable device of claim 2, wherein said nonlinear medium is a Kerr nonlinear medium.
4. A plasmonic super surface unit based optical bistable device according to claim 2 or 3, characterized in that the planar shape of the metal plate (1) is square, rectangular, circular, elliptical or rhomboid.
5. The plasmonic super surface unit based optical bistable device of claim 4, wherein the length of said first through hole is 100 μm.
6. A plasmonic super-surface unit based optical bistable device according to claim 5, characterized in that the right-angled through hole (222) is composed of two in-line through holes intersecting perpendicularly with each other, wherein the length of the in-line through hole perpendicular to the second in-line through hole (221) is 40 μm and the length of the in-line through hole parallel to the second in-line through hole (221) is 60 μm; the length of the second in-line through hole (221) is 40 μm.
7. A plasmonic super-surface unit based optical bistable device according to any of claims 1 to 3, 5, 6, characterized in that the metal plates (1) are all 60 μm thick and the height of the sub-wavelength via (2) is 60 μm.
8. A plasmonic super-surface unit based optical bistable device according to any of claims 1 to 3, 5, 6, characterized in that the metal plate (1) is made of copper.
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