A time-delay-free chaotic laser array generation system based on metasurface coupling

Abstract

The utility model discloses a kind of no time-delay chaotic laser array generation systems based on super-structure surface coupling, including laser line reflector, gain medium, first lens, diaphragm, second lens, super-structure surface and partial reflector;The laser line reflector and partial reflector constitute laser resonant cavity, for extending the working length of gain medium;First lens and second lens constitute self-imaging system, for improving the working area of gain medium;The rear focal plane of first lens and the front focal plane of second lens coincide and constitute common focal plane, the diaphragm is placed at common focal plane, and the diaphragm is used as angular selector, so that system becomes mode number adjustable self-imaging cavity;The super-structure surface is used as beam deflection device, for realizing laser array generation and mode coupling.The utility model utilizes the arbitrary wavefront regulation and control characteristics of super-structure surface and the multiple transverse mode degenerate characteristics of degenerate cavity, constructs laser array from spatial dimension and regulates and controls the efficient coupling between mode, realizes the parallel output of chaotic light signal, with good practicability.

Description

Technical Field

[0001] This utility model belongs to the field of optoelectronic technology, specifically relating to a time-delay-free chaotic laser array generation system based on metasurface coupling. Background Technology

[0002] Laser chaos, as a nonlinear dynamic process, exhibits sensitivity to initial conditions and noise-like characteristics. Therefore, chaotic lasers can be used as physical entropy sources to extract random signals from time series, applicable to fields such as random number generation, secure communication, lidar, and optical computing. However, traditional methods employ external cavity feedback, utilizing the relaxation oscillation frequency and external cavity mode beat frequency to generate laser chaos. The resulting chaotic signals are difficult to output independently in parallel, and the autocorrelation curves contain significant time delays, failing to meet the high throughput and security requirements of future information systems. Therefore, to meet the practical application needs of parallel random number generators, MIMO secure communication systems, and other applications, there is an urgent need to develop chaotic laser arrays.

[0003] Currently, the main methods for obtaining parallel chaotic signals include frequency division multiplexing (FDM), mutual coupling, and optical feedback. For example, the research team at Peking University proposed and verified a scheme using chaotic microcavity optical combs as large-scale parallel chaotic sources based on FDM. By using a continuous-wave laser to pump the optical microcavity, a chaotic microcavity optical comb can be generated, with each comb tooth carrying a chaotic signal. However, the overall system requires a high-precision processing platform, with harsh production conditions and complex processes (Nature Communications, 2023, 14(1): 4590). The research team at Southwest University can obtain two chaotic signals by injecting two mutually coupled semiconductor lasers. This scheme requires a laser at the transmitter of each signal, which greatly increases the device deployment cost (Laser Physics, 2012, 22: 1476-1480). The research team at the University of Electronic Science and Technology of China introduced optoelectronic hybrid feedback and parallel filtering on the basis of optical feedback, and generated three chaotic signals simultaneously in the experiment. However, the number of output channels of this method is limited and cannot meet the needs of real-world scenarios for the scalability of the number of parallel chaotic signals (Journal of Lightwave Technology, 2021, 40(3): 751-761.).

[0004] On the other hand, the main approach to eliminating time delay labels is to use the nonlinear effects of optical devices to eliminate time delay characteristics. For example, the research team at the University of Ottawa in Canada proposed a random grating feedback scheme, which uses a large number of randomly spaced external cavity modes in the feedback light to suppress time delay characteristics. The research team at Taiyuan University of Technology used the time delay dispersion characteristics of chirped fiber gratings to suppress time delay features (Optics Express, 2017, 25(10): 10911-10924.); the research team at the University of Valles in Spain used Faraday rotators to suppress time delay features (Optics letters, 2011, 36(23):4632-4634); the research team at City University of Hong Kong used the self-phase modulation effect in optical fibers to suppress the time delay label of laser signal output, but long-distance optical fibers are required to achieve a significant time delay suppression effect (Optics Letters, 2018, 43(19): 4751-4754.); the research team at the Free University of Brussels used phase-controlled dual-optical feedback to suppress time delay features (Optics Continuum, 2022, 1(10):2127-2134). However, the above solutions can only use relevant optical means to process the signal to achieve time delay suppression, and cannot eliminate the time delay characteristics from the laser itself. Utility Model Content

[0005] The purpose of this invention is to provide a time-delay-free chaotic laser array generation system based on metasurface coupling, which aims to utilize the arbitrary wavefront modulation characteristics of metasurfaces and the multi-mode characteristics of degenerate cavities to achieve parallel output of chaotic optical signals.

[0006] This utility model is mainly achieved through the following technical solutions: A time-delay-free chaotic laser array generation system based on metasurface coupling includes, from front to back, a laser line mirror, a gain medium, a first lens, an aperture, a second lens, a metasurface, and a partial mirror. The laser line mirror and the partial mirror constitute a laser resonant cavity to extend the working length of the gain medium. The first lens and the second lens constitute a self-imaging system to increase the working area of ​​the gain medium. The rear focal plane of the first lens and the front focal plane of the second lens overlap to form a common focal plane. The aperture is placed at the common focal plane and serves as an angular selector, making the system a self-imaging cavity with adjustable mode number. The metasurface serves as a beam deflection device to realize laser array generation and mode coupling.

[0007] To better realize this utility model, further, the distance between the gain medium and the laser line reflector is 10 cm, and the distance between the laser line reflector and the first lens is 20 cm; the front and rear focal lengths of the first lens and the second lens are both 20 cm, and the distances between the aperture stop and the second lens and between the aperture stop and the first lens are both 20 cm; the distance between the metasurface and the partial reflector is 1 mm, and the distance between the partial reflector and the second lens is 20 cm.

[0008] To better realize this utility model, the time-delay-free chaotic laser array generation system is further used to generate a chaotic laser array in a ring distribution. Adjacent array units are coupled to each other in a nearest-neighbor coupling manner to realize the generation of chaos through nonlinear interaction; the beam profile of the array unit of the chaotic laser array is circular.

[0009] To better realize this utility model, further, the distance between the annular center of the chaotic laser array and the array unit is... r= 1.5 mm, the angle between the lines connecting two adjacent array elements and the center of the ring. =45°, the diameter of the array element of the chaotic laser array is 0.75 mm, and the distance between adjacent array elements is... d =1 mm, coupling coefficient is 0.1.

[0010] To better realize this utility model, the metasurface has a transmission efficiency of 80% and a directional ±1st order diffraction efficiency of 10% each, which is used to transmit part of the incident light and reflect part of it directionally into the optical paths of two adjacent modes, thereby realizing mode coupling.

[0011] To better realize this utility model, the outer side of the laser line reflector is coated with a high reflectivity film layer, and the reflectivity of the high reflectivity film layer is >99.9%; the first lens and the second lens are respectively plano-convex lenses or biconvex lenses, and the outer sides of the first lens and the second lens are respectively coated with high transmittance film layers; the beam splitting ratio of the reflection to the transmission of the partial reflector is any one of 7:3, 8:2, and 9:1.

[0012] To better realize this utility model, the diameter of the laser line reflector is 25.4 mm or 50.8 mm; the focal length of the first lens and the second lens is 20 cm or 30 cm, and the diameter is 25.4 mm or 50.8 mm; the diameter of the partial reflector is 25.4 mm or 50.8 mm.

[0013] The beneficial effects of this utility model are as follows: This invention utilizes the arbitrary wavefront modulation characteristics of metasurfaces and the multi-mode characteristics of degenerate cavities to construct laser arrays in a spatial dimension and control the efficient coupling between modes, achieving parallel output of chaotic optical signals. This invention can improve the random number generation rate and realize the construction of multiplexed optical communication links, demonstrating good practicality. Compared with previous solutions, this invention, by employing a degenerate cavity structure, develops a spatially integrated parallel chaotic light source, achieving independent output of multi-mode beams and improving channel capacity in a spatial dimension. Furthermore, this invention leverages the excellent optical field modulation performance of metasurfaces to flexibly control the coupling between modes. This invention abandons the traditional external cavity structure, using mode interactions to generate spontaneous chaos, eliminating external cavity delay tags, increasing the key space at the physical layer, and resulting in high complexity of the chaotic signal, thus demonstrating good practicality. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the time-delay-free chaotic laser array generation system based on metasurface coupling of this invention. Figure 2 This is a schematic diagram of the time-delay-free chaotic laser array generated by this invention; Figure 3 This is a schematic diagram of quantitative analysis based on mode coupling in three-dimensional coordinates.

[0015] Wherein: 1-Laser line reflector, 2-Gain medium, 3-First lens, 4-Aperture, 5-Second lens, 6-Metasurface, 7-Partial reflector. Detailed Implementation

[0016] Example 1: A time-delay-free chaotic laser array generation system based on metasurface coupling, such as Figure 1 As shown, the optical system includes, from front to back, a laser line reflector 1, a gain medium 2, a first lens 3, an aperture 4, a second lens 5, a metasurface 6, and a partial reflector 7, all arranged coaxially at the same height. The rear focal plane of the first lens 3 coincides with the front focal plane of the second lens 5; this coinciding plane is called the common focal plane. The aperture 4 is placed at the common focal plane. The laser line reflector 1 is placed on the front focal plane of the first lens 3. The gain medium 2 is placed between the laser line reflector 1 and the first lens 3. The partial reflector 7 is placed on the rear focal plane of the second lens 5. The metasurface 6 is placed between the laser line reflector 1 and the first lens 3.

[0017] In use, the laser beam is reflected back and forth in the laser resonant cavity formed by the laser line reflector 1 and the partial reflector 7, which extends the working length of the gain medium 2, suppresses the spontaneous emission of photons, and thus increases the photon number density in the cavity. The gain medium 2 has an energy level structure that forms population inversion, providing optical gain. The first lens 3 and the second lens 5 together form a self-imaging system, which changes the wavefront distribution of the incident light, so that any paraxial light can be reflected back and forth in the cavity without overflowing out of the cavity, increasing the working area of ​​the gain medium 2, realizing the mode field output of a large array, and the aperture 4 acts as an angular selector, making the system a self-imaging cavity with an adjustable number of modes.

[0018] The principle of this utility model is explained as follows: Within a degenerate cavity laser, the resonant frequency of the intrinsic mode. v qmn for ; in: q The longitudinal modulus ordinal number representing the intrinsic mode. m , n The two transverse modulus ordinal numbers representing the intrinsic modes, c The speed of light in a vacuum L The optical length of the degenerate cavity laser; A The angular transmission factor of a degenerate cavity laser; D This is the angle retention factor for a degenerate cavity laser.

[0019] Forward transmission transformation matrix from laser line mirror 1 to output coupler 7 M 1 is: ; in, A 1. B 1. C 1. D 1 represents the position transmission factor, tilt transmission factor, angle transmission factor, and angle holding factor for forward transmission of the system.

[0020] Similarly, the reverse transmission transformation matrix from the output coupling mirror 7 to the plane mirror 1... M 2 is: .

[0021] in, A 2. B 2. C 2. D2 represents the position transmission factor, tilt transmission factor, angle transmission factor, and angle holding factor for the system's reverse transmission.

[0022] The system's cyclic matrix M for: ; in: A , B , C , D These are the position transfer factor, tilt transfer factor, angle transfer factor, and angle retention factor of the resonant cavity. For a degenerate cavity, A = D =1, at this time: ; That is, the resonant frequency of the cavity is independent of the transverse mode number. Under the same longitudinal mode, countless transverse modes oscillate simultaneously, and each mode is an independent laser mode.

[0023] Due to the limitations of the cavity's geometric dimensions and diffraction losses, the specific number of transverse modes is determined by... N =( πN f ) 2 Given, where the Fresnel number is: ; in: a The system aperture radius refers to the radius of the end faces on both sides of the gain medium 2 within the degenerate cavity. l It is the distance between the two apertures, and in a degenerate cavity laser, it refers to the length of gain medium 2. λ It is the laser wavelength.

[0024] Preferably, in this embodiment, the front and rear focal lengths of the first lens 3 and the second lens 5 are both 20 cm, the distances between the aperture 4 and the second lens 5 and between the aperture 4 and the first lens 3 are both 20 cm, the distance between the laser line reflector 1 and the first lens 3 is 20 cm, the distance between the partial reflector 7 and the second lens 5 is 20 cm, the distance between the gain medium 2 and the laser line reflector 1 is 10 cm, and the distance between the metasurface 6 and the partial reflector 5 is 1 mm.

[0025] like Figure 2 As shown, the generated laser arrays A to G are arranged in a ring shape, and the distance between the center of the ring and the array unit is... r= 1.5 mm, the angle between the lines connecting any two array elements and the center of the ring. =45°, the array units are coupled to each other through nearest-neighbor coupling, and chaos is generated through nonlinear interaction. The beam profile of the laser array unit is circular with a diameter of 0.75 mm, and the distance between each array unit is... d =1 mm, coupling coefficient is 0.1.

[0026] In metasurface 6, the angles of refraction and reflection satisfy the generalized Snell's law: ; Where: θ i and θ t These are the incident angle and the exit angle, n i and n t These are the refractive indices of the incident and exit spaces, respectively. The exit and reflection angles of a plane wave incident on metasurface 6 depend not only on the incident angle, the incident medium, and the exit medium, but also on the wavelength λ and the phase gradient. It is related that by designing a phase gradient in a two-dimensional plane, light waves can be controlled to be emitted and reflected at any angle.

[0027] In this embodiment, a metasurface 6 is used within the cavity to simultaneously generate a laser array and couple modes. The metasurface 6 acts as a beam deflector, its array elements altering the distribution of the incident light wavefront to achieve directional reflection and partial transmission. The metasurface 6 has a transmission efficiency of 80%, directional ±1st order diffraction efficiencies of 10% each, and a spatial directional reflection angle of ( ). α , β , γ When incident light rays strike the metasurface 6, part of the light is transmitted and output, while the other part is directionally reflected into the optical paths of two adjacent modes, thus achieving mode coupling.

[0028] like Figure 3 As shown, a three-dimensional coordinate system is established to perform quantitative analysis of the mode coupling and obtain the three-dimensional spatial reflection angle.

[0029] Using the metasurface 6 as the XY plane and the optical axis as the Z-axis, a three-dimensional Cartesian coordinate system is established with mode A as the center. The corresponding coordinates of mode B on the second lens 5 are (x, y, z). Under the control of the metasurface 6, the incident light wave has a reflection angle of (α, β, γ), with the specific values ​​as follows: .

[0030] Therefore, we can design corresponding metasurfaces to generate refraction and reflection of incident beams at different angles, thereby flexibly controlling the interaction between array modes.

[0031] Preferably, the gain medium 2 can be Nd:YAG, Nd:YLF, Nd:YO4, or other Nd...3+ The doped gain medium has a concentration of 0.8 at%-1.2 at% and a thickness of 1-3 mm, and adopts a cylindrical or square structure. The aperture 4 can be installed between the first lens 3 and the second lens 5 or between the second lens 5 and part of the reflecting mirror 7; Laser line reflector 1 needs to be coated with a high reflectivity film for the laser wavelength, with a reflectivity >99.9% and a diameter of 25.4 mm or 50.8 mm; Some reflectors 7 can adopt a 7:3, 8:2, 9:1, etc., for the spectral splitting ratio of reflection and transmission. They need to be coated with reflective and transmission films for the laser wavelength, with a diameter of 25.4 mm or 50.8 mm. The first lens 3 and the second lens 5 can be plano-convex lenses or biconvex lenses, with a focal length of 20cm or 30cm and a diameter of 25.4mm or 50.8mm, and need to be coated with a high transmittance film layer for the laser wavelength.

[0032] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present utility model shall fall within the protection scope of the present utility model.

Claims

1. A time-delay-free chaotic laser array generation system based on metasurface coupling, characterized in that, The system includes, from front to back, a laser line reflector (1), a gain medium (2), a first lens (3), an aperture (4), a second lens (5), a metasurface (6), and a partial reflector (7). The laser line reflector (1) and the partial reflector (7) form a laser resonant cavity to extend the working length of the gain medium (2). The first lens (3) and the second lens (5) form a self-imaging system to increase the working area of ​​the gain medium (2). The back focal plane of the first lens (3) and the front focal plane of the second lens (5) overlap to form a common focal plane. The aperture (4) is placed at the common focal plane and serves as an angular selector, making the system a self-imaging cavity with adjustable mode number. The metasurface (6) serves as a beam deflection device to realize laser array generation and mode coupling.

2. The time-delay-free chaotic laser array generation system based on metasurface coupling according to claim 1, characterized in that, The distance between the gain medium (2) and the laser line reflector (1) is 10 cm, and the distance between the laser line reflector (1) and the first lens (3) is 20 cm; the front and rear focal lengths of the first lens (3) and the second lens (5) are both 20 cm, and the distances between the aperture stop (4) and the second lens (5) and between the aperture stop (4) and the first lens (3) are both 20 cm; the distance between the metasurface (6) and the partial reflector (7) is 1 mm, and the distance between the partial reflector (7) and the second lens (5) is 20 cm.

3. A time-delay-free chaotic laser array generation system based on metasurface coupling according to claim 1 or 2, characterized in that, The time-delay-free chaotic laser array generation system is used to generate a chaotic laser array with a ring distribution. Adjacent array units are coupled to each other in a nearest-neighbor coupling manner to achieve the generation of chaos through nonlinear interaction; the beam profile of the array units of the chaotic laser array is circular.

4. The time-delay-free chaotic laser array generation system based on metasurface coupling according to claim 3, characterized in that, The distance r = 1.5 mm between the ring center of the chaotic laser array and the array unit, and the included angle between the lines connecting two adjacent array units to the ring center. =45°, the diameter of the array unit of the chaotic laser array is 0.75 mm, the distance between adjacent array units is d=1 mm, and the coupling coefficient is 0.

1.

5. The time-delay-free chaotic laser array generation system based on metasurface coupling according to claim 1, characterized in that, The metasurface (6) has a transmission efficiency of 80% and a directional diffraction efficiency of 10% for ±1 order diffraction. It is used to transmit part of the incident light and reflect part of it into the optical paths of two adjacent modes to achieve mode coupling.

6. The time-delay-free chaotic laser array generation system based on metasurface coupling according to claim 1, characterized in that, The outer side of the laser line reflector (1) is coated with a high reflectivity film, and the reflectivity of the high reflectivity film is >99.9%; the first lens (3) and the second lens (5) are respectively plano-convex lenses or biconvex lenses, and the outer side of the first lens (3) and the second lens (5) are respectively coated with a high transmittance film; the splitting ratio of reflection to transmission of the partial reflector (7) is any one of 7:3, 8:2, and 9:

1.

7. The time-delay-free chaotic laser array generation system based on metasurface coupling according to claim 6, characterized in that, The diameter of the laser line reflector (1) is 25.4 mm or 50.8 mm; the focal length of the first lens (3) and the second lens (5) is 20 cm or 30 cm, and the diameter is 25.4 mm or 50.8 mm; the diameter of the partial reflector (7) is 25.4 mm or 50.8 mm.

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