CN113381277B - Circular polarization laser of chiral metamaterial - Google Patents

Abstract

The invention provides a circularly polarized laser of a chiral metamaterial, which belongs to the field of laser and electromagnetic metamaterials. Includes gain medium and resonant cavity. The gain medium is solid and located in the resonant cavity; the resonant cavity includes two chiral polarization-maintaining metasurface mirrors, and the chiral polarization-maintaining mirror is a chiral metamaterial composed of a metal base plate, a dielectric substrate and a metal array, and the metal The array structure covers the dielectric substrate. The linearly polarized pump light enters the resonator backwards from a chiral polarization-maintaining metasurface mirror. With the circular polarization selection characteristics of the chiral polarization-maintaining metasurface mirror, only a single circularly polarized light can pass between the two chiral mirrors. The coherent enhancement of circularly polarized light is realized through the gain medium, and the circularly polarized laser is output after exceeding the threshold of the gain medium.

Description

Circularly Polarized Lasers Based on Chiral Metamaterials

technical field

The invention relates to the field of lasers and electromagnetic metamaterials, in particular to a circularly polarized laser of chiral metamaterials.

Background technique

Due to its unique advantages of high work efficiency, high brightness, high monochromaticity and high directivity, laser plays an important role in material processing, measurement control, medical diagnosis and other applications, and has become a research hotspot. Solid-state lasers, liquid lasers, gas lasers, and tunable lasers are widely used in communication, ranging and other aspects. Circularly polarized lasers have attracted the attention of researchers because circularly polarized light has rotational symmetry and is almost unchanged during system transmission, and is suitable for the field of communication. In the current polarized laser, the polarized laser is mainly realized by using a resonant cavity, a gain medium, and a pump source, but the resonant cavity has defects such as large size, low efficiency, bulky volume and difficult operation. Therefore, there is an increasing demand for high-efficiency, small-volume, and highly-integrated polarization lasers.

Metasurface is a two-dimensional form of metamaterials arranged by artificially designed resonant units, which can be used to control the transmission characteristics of electromagnetic waves. With the precise design of artificially designed resonant units, metasurfaces can generate many novel optical phenomena, such as vortex light, circular dichroism, spin Hall effect, surface waves, etc. When the structure of the resonant unit is changed, the transmission, dispersion, and coupling effects of the metasurface will have significant changes. Metasurfaces interact with light fields to enable active manipulation of light propagation. Metasurfaces have obvious advantages in the development of miniaturized multifunctional photonic devices, and thus have attracted more and more attention from researchers.

The usual meaning of chirality means that the mirror image of an object cannot coincide with the object through simple translation and rotation. It exists widely in nature, such as molecules, proteins, crystals, etc. In the field of metamaterials, the characteristic of chirality can cause special phenomena such as strong optical rotation and circular dichroism. In recent years, chiral metamaterials have attracted extensive attention due to their stronger chiral optical interactions than natural materials. Therefore, researchers have a lot of research on realizing broadband circular polarizers, asymmetric transmission, and transmission-type spin-selective absorbers.

In recent years, polarized lasers have been widely used in sensing and measurement. At present, spin-selective mirrors based on chiral metamaterials have been realized in the microwave segment (App. Phys. Lett., 2017, 110(23): 231103). The chiral metamaterial reflector can realize high reflection of right-handed circularly polarized light and high absorption of left-handed circularly polarized light. In addition, scientists have studied circularly polarized light beam shaping based on metamaterials, (Adv.Opt.Mater., 2014, 2, 978-982), and experimentally realized an ultra-thin, broadband beam for visible light and near-infrared light Shaping device.

In 2008, Prof. Zheludev's research group at the University of Southampton in the UK proposed to use two-dimensionally arranged coherent metamaterials to achieve plasmon gain amplification, as shown in Figure 9. The device consists of a gain dielectric plate, periodically arranged asymmetric metal split ring resonators. The asymmetric metal split ring can be excited to produce an antisymmetric current distribution, and the radiation of electric and magnetic dipoles generated by this current distribution will cancel in space, so the two-dimensional array metamaterial can support high-Q value Electromagnetic resonance, with coherence, can generate spatially and temporally coherent surface plasmon radiation in a gain medium.

In 2020, the team of Professor Song Qinghai from Harbin Institute of Technology (Shenzhen) made an important breakthrough in the field of ultrafast modulation microlasers (Science, 2020, 367, 1018-1021). The new principle of all-optical switch proposed is expected to break through ultra-short switching time and ultra-low energy Contradictions between consumption. They studied the optical switching mechanism of topologically protected BICs, which ensured the mutual ultrafast switching of microlasers from radially polarized ring beams to linearly polarized sidelobe light. The extremely high quality factor of BIC can significantly reduce the laser threshold, thereby breaking through the bottleneck of traditional all-optical switches.

Circularly polarized laser is of great significance to the development of optical detection, optical imaging and other fields, and has a good application prospect. However, circularly polarized lasers based on metamaterials are still a technical problem to be solved urgently.

Contents of the invention

The object of the present invention is to provide a chiral metamaterial-based circularly polarized laser with high output light intensity and small volume.

The object of the present invention is achieved like this:

A circularly polarized laser of a chiral metamaterial, comprising a resonant cavity and a gain medium positioned in the resonant cavity, the resonant cavity comprising two opposite chiral polarization-maintaining metasurface mirrors, the chiral polarization-maintaining mirrors being The chiral polarization-maintaining metasurface reflector comprises a metal base plate, a dielectric substrate and a metal array, and the metal array structure is covered on the dielectric substrate. The linearly polarized pump light enters the resonator backwards from a chiral polarization-maintaining metasurface mirror, a single circularly polarized light is reflected multiple times between two chiral polarization-maintaining metasurface mirrors, and the gain medium coheres the circularly polarized light Intensify, and output circularly polarized laser light after exceeding the threshold of the gain medium.

The present invention can also include such features:

1. The geometric shape of the array unit of the metal array is one of similar rectangles, trapezoids, rhombuses, ellipses, split resonant rings, reverse split nested resonant rings, L-like shapes, I-like shapes, double-grating-like shapes, etc. kind.

2. Determine the handedness and/or light intensity of the output circularly polarized light by selecting the geometry and/or spatial layout of the array units of the metal array.

The resonant cavity of the circularly polarized laser of the chiral metamaterial of the present invention includes two opposite chiral polarization-maintaining metasurface mirrors, and a linearly polarized pump source is arranged outside the resonant cavity, and the linearly polarized pump light is obtained from a chiral polarization-maintaining metasurface mirror. The metasurface mirror enters the resonant cavity backwards. With the circular polarization selection characteristics of the chiral polarization-maintaining metasurface mirror, only a single circularly polarized light can be reflected multiple times between the two chiral mirrors, and the circular polarization is realized through the gain medium. The coherence of light is strengthened, and circularly polarized laser light is output after exceeding the threshold of the gain medium.

Compared with prior art, the advantage of the present invention is:

1. The geometric unit shape and spatial distribution of the chiral metasurface can determine the handedness and output light intensity of the circularly polarized laser;

2. The circularly polarized laser of the chiral metamaterial can work in the visible light, near-infrared light or mid-infrared band;

3. The circularly polarized laser is small in size, easy to integrate, and the device is easy to realize. This patent provides a feasible laser design scheme for communication, sensing and other fields;

4. Due to the flexible design of the metasurface, the output characteristics of the circularly polarized laser can be easily adjusted;

5. The output of the circularly polarized laser is only related to the design of the chiral metasurface, and the polarization characteristics are not affected by other factors.

Description of drawings

Figure 1 is a flow chart of the implementation of circularly polarized lasers based on chiral metasurfaces;

Figure 2 is based on the schematic diagram of the implementation of the circularly polarized laser on the chiral metasurface (output left-handed circularly polarized laser);

Figure 3(a) is a schematic diagram of polarization conversion of left-handed circularly polarized light realized by a chiral polarization-maintaining metasurface;

Figure 3(b) is a schematic diagram of the polarization conversion of right-handed circularly polarized light realized by the chiral polarization-maintaining metasurface;

Figure 4 is a structural design effect diagram of a right-handed circularly polarized laser based on chiral metamaterials;

Figure 5 is an effect diagram of another structural design of a left-handed circularly polarized laser based on chiral metamaterials;

Fig. 6 (a) is the shape diagram of the quasi-rectangular array unit of the chiral metasurface metal array;

Figure 6(b) is a shape diagram of the split resonator ring array unit of the chiral metasurface metal array;

Fig. 6 (c) is the shape diagram of the trapezoidal array unit of the chiral metasurface metal array;

Figure 6(d) is a shape diagram of the I-shaped array unit of the chiral metasurface metal array;

Fig. 6 (e) is the shape diagram of the reverse opening nested resonant ring array unit of the chiral metasurface metal array;

Fig. 6 (f) is the shape diagram of the quasi-double grating array unit of the chiral metasurface metal array;

Fig. 6 (g) is the diamond-like array unit shape diagram of the chiral metasurface metal array;

Figure 6(h) is a shape diagram of the L-like array unit of the chiral metasurface metal array;

Fig. 6 (i) is the shape diagram of the elliptical array unit of the chiral metasurface metal array;

Figure 7(a) is a diagram of a chiral metasurface composed of rectangular array units with irregular spatial distribution;

Figure 7(b) is a diagram of a C4 structure chiral metasurface composed of L-shaped array units;

Figure 7(c) is a diagram of a G-shaped chiral metasurface composed of rhombic array units;

Figure 7(d) is a chiral metasurface diagram composed of two split resonator ring array units;

Figure 7(e) is a chiral metasurface diagram composed of two I-shaped array units;

Figure 7(f) is a chiral metasurface diagram composed of three elliptical array units;

Figure 8(a) is a metasurface diagram of circularly polarized light in the optical band;

Fig. 8 (b) is the reflectance diagram of the optical band circularly polarized light metasurface;

Figure 9 is a two-dimensional arrangement of coherent metamaterials to realize the gain amplifier of plasmons.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

With reference to Fig. 2, the first embodiment of the present invention comprises a resonant cavity and a gain medium 4 located in the resonant cavity, the resonant cavity comprises two opposite chiral polarization-maintaining metasurface mirrors, the first chiral polarization-maintaining mirror is It includes a first metal base plate 3-1, a first dielectric substrate 1-1, and a first metal array 2-1, and the second chiral polarization-maintaining mirror includes a second metal base plate 3-2, a second dielectric substrate 1 -2 and the first metal array 2-2, the metal array is covered on the dielectric substrate, the geometric shape of the array unit of the metal array is a rectangle, and 12 rectangular metal array units are uniformly and regularly arranged in 4×3 on the dielectric substrate to form a hand The material of the dielectric substrate is one of silicon, silicon dioxide, etc., the material of the metal array is one of copper, gold, aluminum, etc., and the gain medium is a bandgap semiconductor, laser glass, ceramics, laser dye, etc. one of a kind. The linearly polarized pump light enters the resonator backward from the first chiral polarization-maintaining metasurface mirror, the single circularly polarized light is reflected multiple times between the two chiral polarization-maintaining metasurface mirrors, and the circularly polarized light is processed by the gain medium. The coherence is strengthened, and the left-handed circularly polarized laser is output after exceeding the threshold of the gain medium.

Referring to Fig. 4, the second embodiment of the present invention is based on the first embodiment, the geometric shape of the array unit of the metal array is changed to a rhombus, and 11 diamond-shaped metal array units are arranged irregularly on the dielectric substrate. Chiral metasurface, the linearly polarized pump light enters the resonator backward from the first chiral polarization-maintaining metasurface mirror, the single circularly polarized light is reflected multiple times between the two chiral polarization-maintaining metasurface mirrors, the gain medium Coherence enhancement is performed on the circularly polarized light, and the right-handed circularly polarized laser is output after exceeding the threshold of the gain medium.

In conjunction with Fig. 5, the third embodiment of the present invention is based on the first embodiment, the geometric shape of the array unit of the metal array is changed to a trapezoid, and 9 trapezoidal metal array units are 3×3 uniform on the dielectric substrate. Regularly arranged chiral metasurfaces, the linearly polarized pump light enters the resonator backward from the first chiral polarization-maintaining metasurface mirror, and the single circularly polarized light is reflected multiple times between the two chiral polarization-maintaining metasurface mirrors , the gain medium strengthens the coherence of the circularly polarized light, and outputs a left-handed circularly polarized laser light after exceeding the threshold of the gain medium.

In the above examples, the coherence enhancement of circularly polarized light can be realized at the same time.

Combining Figure 6(a) to Figure 6(i), the geometry of the metal array unit constituting the chiral metasurface can also be selected as: quasi-rectangular, split resonant ring, trapezoid-like, I-like, reverse slot nested resonance Ring, double-grating-like, rhombus-like, L-like, oval, etc.

In combination with Fig. 7(a) to Fig. 7(f), the arrangement of the metal array units on the dielectric substrate can also be selected as follows: irregular spatial distribution composed of rectangular metal array units, regular C4 composed of L-shaped metal array units Spatial distribution, G-shaped spatial distribution composed of diamond-shaped metal array units, spatial distribution composed of two split resonant ring metal array units, spatial distribution composed of two split resonant ring metal array units, composed of two I-shaped metal array units Spatial distribution of array units, spatial distribution of three elliptical metal array units.

The working principle of the reflector substrate of the present invention is as follows:

There are different metasurface structures on the mirror substrate, and the incident linearly polarized pump light enters the chiral metasurface for polarization conversion. Due to the characteristics of polarization selection and high reflectivity of chiral metasurfaces, after two linearly polarized pump lights pass through chiral polarization-maintaining metasurfaces, different chiral metasurface structures can convert their polarizations into circular polarizations with different handedness. Light. The circularly polarized light obtained by polarization conversion is continuously reflected and amplified between the two chiral metasurfaces. Chiral metasurfaces with different spatial distributions and unit shapes can determine circularly polarized light with different handedness. Figure 3(a) and Figure 3(b) provide a schematic diagram of the conversion of linearly polarized light incident to circularly polarized light. FIG. 3( a ) is a schematic diagram of left-handed circularly polarized light obtained after polarization conversion, and FIG. 3( b ) is a schematic diagram of right-handed circularly polarized light obtained after polarization conversion. FIG. 4 is a schematic diagram of realizing a right-handed circularly polarized laser, and FIG. 5 is a schematic diagram of realizing a left-handed circularly polarized laser. Fig. 8(a) and Fig. 8(b) are schematic diagrams of realization of a left-handed circularly polarized laser with light intensity I1.

Combined with Fig. 6(a) to Fig. 6(i), the array unit shapes of several chiral metasurfaces with different unit shapes are provided. The geometric shape of the array unit here is: a quasi-rectangle formed by merging three rectangles of different sizes; a split resonant ring; an inverted trapezoid; a quasi-I shape formed by merging three rectangles of different lengths; two rectangles of different lengths arranged in parallel A similar double grating shape; a rhombus-like shape formed by simplifying two circles in the middle of a rhombus; an L-like shape formed by merging three rectangles of different sizes; an ellipse. In practical applications, the geometry of the array unit is not limited to the above-mentioned ones, and the structure can be changed and optimized according to specific requirements.

Combining Figure 7(a) to Figure 7(f), chiral metasurfaces with different spatial distributions. The chiral metasurfaces listed here are: chiral metasurfaces composed of rectangular array units of metal arrays with irregular spatial distribution; chiral metasurfaces with C4 structure composed of four L-shaped metal array array units; rhombic metal arrays The G-shaped chiral metasurface composed of the array units of the resonant ring metal array; the chiral metasurface composed of the array units of the resonant ring metal arrays with different sizes and different opening angles; two work with different sizes and handedness A chiral metasurface composed of array units of zigzag metal arrays; a chiral metasurface composed of array units of three elliptical metal arrays with different hand directions. In practical applications, under the premise of ensuring that the metasurface is chiral, the spatial distribution of the array units of the metal array is not limited to the above-mentioned ones, and can be changed and optimized according to specific requirements.

Referring to Fig. 8(a) to Fig. 8(b), in the light band 120-160THz of the present invention, the chiral metasurface reflector is made of gold as a reflector, silicon dioxide is used as a spacer layer, and a gold array is used as a metasurface. Among them, gold is constructed by the Drude model, in which the plasma frequency is 1.367×10 ¹⁶ rad/s, the collision frequency is 6.478×10 ¹³ /s, and the refractive index of silicon dioxide is 1.47. The thickness of the gold reflector is 20nm, the thickness of silicon dioxide is 1000nm, and the thickness of the gold array is 50nm. Figure 8(a) is a schematic diagram of the unit structure, and Figure 8(b) is the reflection coefficient of circularly polarized light. Using CST for simulation, the simulated reflection spectrum is shown in Figure 8(b), where r ₊₊ represents the reflection coefficient of right-handed polarized light, r _+- represents the circular cross-polarization reflection coefficient, and r _-+ represents the circular cross-polarization reflection Coefficient, r _-- represents the left-handed circular polarization reflection coefficient. Observing Figure 8(b), it can be found that the reflection curves of circular cross-polarized waves always coincide, while left-handed and right-handed polarized waves have a large reflection difference at 138THz. It shows that the polarization selection effect of the proposed chiral metasurface structure is the best at 138THz.

The structure of the metasurface in the embodiment is only a schematic diagram, and does not limit the size, shape and orientation of the nanounits.

Claims (8)

1. A circular polarization laser of chiral metamaterial comprises a resonant cavity and a gain medium positioned in the resonant cavity, and is characterized in that: the resonant cavity comprises two opposite chiral polarization maintaining super-surface reflectors, each chiral polarization maintaining super-surface reflector comprises a metal bottom plate, a medium substrate and a metal array, the metal array structure covers the medium substrate, linear polarization pump light enters the resonant cavity from one chiral polarization maintaining super-surface reflector, single circular polarization light is reflected for multiple times between the two chiral polarization maintaining super-surface reflectors, the gain medium performs coherent enhancement on the circular polarization light, and circular polarization laser is output after the threshold value of the gain medium is exceeded.

2. A circularly polarized laser of chiral metamaterial according to claim 1, wherein: the geometric shape of the array unit of the metal array is one of a rectangle-like shape, a trapezoid-like shape, a rhombus-like shape, an ellipse-like shape, an open resonant ring, a reverse open nested resonant ring, an L-like shape, an I-like shape and a double grating-like shape.

3. A circularly polarized laser of chiral metamaterial according to claim 2, wherein: the handedness of the circularly polarized light is determined by the choice of the array cell geometry of the metal array.

4. The circularly polarized laser of chiral metamaterial according to claim 2, wherein: the rotation direction of the output circularly polarized light is determined by selecting the spatial layout of the metal array.

5. The circularly polarized laser of chiral metamaterial according to claim 2, wherein: the handedness of the output circularly polarized light is determined by selecting the array unit geometry and the spatial layout of the metal array.

6. A circularly polarized laser of chiral metamaterial according to claim 2, wherein: the light intensity of the output circularly polarized light is determined by selecting the array unit geometry of the metal array.

7. The circularly polarized laser of chiral metamaterial according to claim 2, wherein: the light intensity of the output circularly polarized light is determined by selecting the spatial layout of the metal array.

8. The circularly polarized laser of chiral metamaterial according to claim 2, wherein: the geometrical shape and the spatial layout of the array unit of the metal array are selected to determine the light intensity of the output circularly polarized light.

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