Light field generation device and method based on nonlinear photonic crystal structure

Abstract

The invention relates to the technical field of non-linear optics and light field regulation and control, in particular to a light field generation device and method based on a non-linear photonic crystal structure, and the device specifically comprises a polaroid, a quarter-wave plate and a non-linear photonic crystal. The nonlinear photonic crystal comprises two structures, one structure is a photonic crystal structure meeting nonlinear Bragg diffraction conditions, and multiple annular light spots are generated; the other structure is a spiral structure capable of generating vortex light; through nonlinear optical modulation, fundamental frequency light passes through a polaroid and a quarter-wave plate in sequence, is focused and then enters a photonic crystal structure meeting the nonlinear Bragg diffraction condition and a spiral structure meeting the requirement for generating a vortex light vector light field to generate a nonlinear light field. The nonlinear light field comprises a nonlinear Bragg diffraction polarized light field and a nonlinear vortex vector light field. According to the invention, the Bragg diffraction polarized light field and the vortex vector light field can be simply, compactly and highly integrated, and the device plays an important role in high-dimensional information processing, quantum communication, sensing, miniaturized optical systems and the like.

Description

Technical Field

[0001] The present invention relates to the technical fields of nonlinear optics and optical field control, and in particular, to an optical field generation device and method based on a nonlinear photonic crystal structure. Background Art

[0002] In recent years, nonlinear optical effects have shown important application potential in the fields of optical field control, quantum information, and micro-nano photonics. Traditional nonlinear photonic crystals satisfy the quasi-phase matching condition by designing the nonlinear photonic crystal structure (periodic / quasi-periodic polarization), significantly improving the conversion efficiency of nonlinear processes such as frequency doubling and sum frequency. However, existing technologies mostly focus on the realization of single functions and it is difficult to simultaneously achieve the generation and dynamic control of complex nonlinear optical fields in a single structure. It often requires the cooperative control between multiple optical elements, inevitably causing problems such as complex system structure, cumbersome operation, and difficulty in integration.

[0003] In the prior art, the generation of nonlinear vector optical fields mostly adopts a cascaded scheme. Based on the idea of coherent superposition, researchers have designed many methods such as the Sagnac interference method, Mach-Zehnder interference method, and 4f system optical path interference method to generate vector optical fields with complex modes. First, a fundamental frequency vortex beam is generated by a linear element, and then frequency conversion is performed by a nonlinear crystal. Such a scheme is limited by the complexity of the fundamental frequency optical field mode and requires strict phase matching conditions for the linear and nonlinear processes, resulting in poor system flexibility and limited efficiency. How to directly utilize the cooperative effect of the polarization modulation of the fundamental frequency light and the internal polarization distribution in the crystal through the design of the intrinsic structure of the nonlinear photonic crystal to achieve the efficient output of nonlinear Bragg diffraction and vortex vector optical fields in the nonlinear photonic crystal is still a technical problem to be solved urgently.

[0004] Therefore, the present invention proposes an optical field generation device and method based on a nonlinear photonic crystal structure to solve the above problems. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention develops an optical field generation device and method based on a nonlinear photonic crystal structure. By innovatively designing two functionally integrated nonlinear photonic crystal structures and combining precise modulation of the laser polarization state, the technical bottlenecks of single function, low efficiency, and complex system in the traditional scheme can be broken through, providing an efficient and compact solution for nonlinear optical field control.

[0006] On the one hand, the technical solution for the present invention to solve the technical problem is an optical field generation device based on a nonlinear photonic crystal structure, and this device includes a polarizer, a quarter-wave plate, and a nonlinear optical crystal with a Bragg grating structure or a spiral structure; Through nonlinear optical modulation, the fundamental frequency light passes through a polarizer and a quarter-wave plate successively, and after being focused by a lens, it is incident on a nonlinear optical crystal with a Bragg grating structure or a spiral structure respectively to generate a nonlinear Bragg diffraction polarized light field and a nonlinear vortex vector light field.

[0007] Nonlinear photonic crystals are applicable to all crystals without a center of symmetry; The nonlinear light field is generated based on second-order nonlinear optical effects or third-order nonlinear effects. Second-order nonlinear optical effects include frequency doubling, sum frequency, or difference frequency, and third-order nonlinear effects include four-wave mixing.

[0008] The structure of the nonlinear photonic crystal is an artificially designed spatially ordered crystal with a periodically varying nonlinear susceptibility The modulation range of the nonlinear susceptibility is , and the period of the spatially ordered structure satisfies the phase matching condition, and the phase matching condition is as follows: , where Δk represents the wave vector mismatch between the fundamental frequency light and the nonlinear light field.

[0009] The dimensionality of the nonlinear photonic crystal structure includes one-dimensional, two-dimensional, or three-dimensional, and the structural distribution of the nonlinear photonic crystal includes a lattice distribution structure, a linear periodic grating structure, a circular surface structure, and / or an elliptical surface structure.

[0010] The size range of the structural unit of the nonlinear photonic crystal structure in any direction is: 0.5 µm - 100 µm.

[0011] On the other hand, the present invention also provides a method for generating a light field based on a nonlinear photonic crystal structure, which is applied to a device for generating a light field based on a nonlinear photonic crystal structure, and includes the following steps: Step 1: Prepare nonlinear photonic crystals with Bragg grating structures and spiral structures that satisfy the quasi-phase matching condition respectively; Step 2: A laser beam is emitted by a laser. The laser beam is fundamental frequency light illumination, which is linearly polarized light or circularly polarized light. The laser beam passes through a polarizer and a quarter-wave plate successively to convert the fundamental frequency light illumination emitted by the laser into modulated fundamental frequency light illumination, and the modulated fundamental frequency light illumination is light with an arbitrary polarization state; Step 3: Fix the nonlinear photonic crystal on a three-dimensional platform. After the modulated fundamental frequency light is irradiated on the nonlinear photonic crystal, the light passes through the nonlinear photonic crystals of the two structures respectively to generate a nonlinear Bragg diffraction polarized light field and a nonlinear vortex vector light field.

[0012] Step 1 is specifically as follows: Prepare samples with Bragg grating structures and helical structures, cut the nonlinear material in any direction, and polish the laser incident or exit surface to obtain samples with the required prepared structures; Prepare a nonlinear photonic crystal structure inside the polished sample. The processing and preparation methods of the nonlinear photonic crystal structure include femtosecond laser direct writing technology and ion implantation methods.

[0013] Step 1 further includes: Obtain polarized light fields with different polarization directions by adjusting the structural parameters of the nonlinear Bragg grating structure; Adjust the polarized light field by performing periodic design according to the quasi-phase matching relationship, designing the period and layer spacing of the Bragg grating; Adjust the topological charge number of the helical structure to obtain vector light fields with different orbital angular momenta; Design the number of helical periods according to the vector light field of the required vortex light, and at the same time control the quasi-phase matching condition to compensate for the wave vector mismatch, and obtain a nonlinear vortex vector light field.

[0014] Step 2 is specifically as follows: The laser beam emitted by the laser is incident on the polarizer to generate linearly polarized light; The linearly polarized light is incident on the quarter-wave plate, and the fast axis of the quarter-wave plate forms or or non a preset included angle with the polarization direction of the linearly polarized light. The polarization states of the laser beams corresponding to different included angles are linearly polarized light, circularly polarized light, and elliptically polarized light; Generate elliptically polarized light with a specific ellipticity by configuring the azimuth angle of the quarter-wave plate under the condition of keeping the total light intensity unchanged.

[0015] Step 3 is specifically as follows: The nonlinear photonic crystal structure is either coated with an anti-reflection film or not; By adjusting the incident angle of the fundamental frequency light with different polarization states, change the period of the nonlinear photonic crystal structure, so that the fundamental frequency light and the nonlinear light field satisfy the quasi-phase matching condition, and then obtain a nonlinear light field with a nonlinear frequency conversion effect.

[0016] The effects provided in the invention content are only the effects of the embodiments, rather than all the effects of the invention. The above technical solutions have the following beneficial effects: The non-linear photonic crystal structure prepared by the present invention is based on the non-linear frequency conversion theory. Through methods such as laser processing and ion implantation, an annular grating structure or a spiral structure with a spatially periodic distribution is formed inside the non-linear photonic crystal. The reciprocal lattice vector G = 2π / Λ provided by the periodic Λ distribution in the structural space can satisfy the phase matching condition to achieve efficient non-linear frequency conversion. At the same time, the non-linear photonic crystal structure performs spatial modulation on the converted laser, and a required non-linear polarized light field or vortex light field can be obtained. The present invention provides a simple, compact and highly integrated method and device for generating non-linear vector light fields based on non-linear photonic crystal structures, which can enhance the non-linear frequency conversion efficiency while obtaining non-linear vector light fields, and play an important role in high-dimensional information processing, quantum communication, sensing and miniaturized optical systems, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention.

[0018] Figure 1 FIG. is a schematic diagram of a multi-layer annular Bragg grating structure obtained by the device and method of the present invention.

[0019] Figure 2 FIG. is a schematic diagram of a spiral structure obtained by the device and method of the present invention.

[0020] Figure 3 FIG. is a schematic diagram of an experimental device for generating a non-linear Bragg diffraction polarized light field based on an annular Bragg grating structure; Figure 4 FIG. is a schematic diagram of an experimental device for generating a non-linear vortex vector light field based on a spiral structure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In order to clearly illustrate the technical features of the present solution, the present invention will be described in detail below through specific embodiments and in conjunction with its accompanying drawings. The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below.

[0022] Embodiment 1 An optical field generating device based on a non-linear photonic crystal structure, the device includes a polarizer, a quarter-wave plate, and a non-linear optical crystal with a Bragg grating structure or a spiral structure; The non-linear optical crystal with a Bragg grating structure satisfies the non-linear Bragg diffraction condition, and the non-linear optical crystal with a spiral structure satisfies the vortex light vector generation condition; Through nonlinear optical modulation, the fundamental frequency light passes through a polarizer and a quarter-wave plate successively, and after being focused by a lens, it is incident on a nonlinear optical crystal with a Bragg grating structure or a spiral structure respectively to generate a nonlinear Bragg diffraction polarized light field and a nonlinear vortex vector light field.

[0023] Nonlinear photonic crystals are applicable to all crystals without a center of symmetry; Nonlinear optical fields are generated based on second-order nonlinear optical effects or third-order nonlinear effects. Second-order nonlinear optical effects include frequency doubling, sum frequency, or difference frequency, and third-order nonlinear effects include four-wave mixing.

[0024] The structure of the nonlinear photonic crystal is an artificially designed spatial order crystal with a periodically varying nonlinear susceptibility The modulation range of the nonlinear susceptibility is , and the period of the spatial order structure satisfies the phase matching condition, and the phase matching condition is as follows: , where Δk represents the wave vector mismatch between the fundamental frequency light and the nonlinear optical field.

[0025] The dimensionality of the nonlinear photonic crystal structure includes one-dimensional, two-dimensional, or three-dimensional, and the structural distribution of the nonlinear photonic crystal includes a lattice distribution structure, a linear periodic grating structure, a circular curved surface structure, and / or an elliptical curved surface structure.

[0026] The size range of the structural unit of the nonlinear photonic crystal structure in any direction is: 0.5 µm - 100 µm.

[0027] Example 2 A method for generating an optical field based on a nonlinear photonic crystal structure, applied to an optical field generating device based on a nonlinear photonic crystal structure, includes the following steps: Step 1: Prepare nonlinear photonic crystals with Bragg grating structures and spiral structures that satisfy the phase matching condition respectively; Step 2: A fundamental frequency light beam is emitted by a laser, polarized as linearly polarized light or circularly polarized light. The laser beam passes through a polarizer and a quarter-wave plate successively to convert the fundamental frequency light emitted by the laser into modulated fundamental frequency light, and the modulated fundamental frequency light is light with an arbitrary polarization state; Step 3: Fix the nonlinear photonic crystal on a three-dimensional platform. After irradiating the modulated fundamental frequency light on the nonlinear photonic crystal, the light passes through the nonlinear photonic crystals of the two structures respectively to generate a nonlinear Bragg diffraction polarized light field and a nonlinear vortex vector light field.

[0028] Step 1 is specifically as follows: Prepare samples with Bragg grating structures and spiral structures, cut non-centrosymmetric nonlinear crystal materials in any direction, and polish the laser incident or exit surfaces to obtain samples with the desired prepared structures; Prepare a multi-layer Bragg grating structure and a spiral structure of a nonlinear photonic crystal structure in the polished crystal sample. The processing and preparation method of the nonlinear photonic crystal structure includes femtosecond laser direct writing technology and ion implantation method.

[0029] The multi-layer annular Bragg grating structure and spiral structure are realized by artificially modulating the nonlinear optical crystal structure. The processing methods include femtosecond laser direct writing technology, ion implantation technology, local electric field polarization, etc., which can realize technologies for modulating the nonlinear susceptibility and phase of the crystal.

[0030] Step 1 further includes: Obtain polarization light fields with different polarization directions by adjusting the structural parameters of the nonlinear Bragg grating structure; Adjust the polarization light field by performing periodic design according to the quasi-phase matching relationship, designing the period and layer spacing of the Bragg grating; Adjust the topological charge number of the spiral structure to obtain vector light fields with different orbital angular momenta; Design the number of spiral periods according to the vector light field of the required vortex light, and at the same time control the quasi-phase matching condition to compensate for the wave vector mismatch, obtaining a nonlinear vortex vector light field, and the nonlinear effect of this light field is enhanced.

[0031] Step 2 is specifically as follows: The laser beam emitted by the laser is incident on the polarizer to generate linearly polarized light; The linearly polarized light is incident on a quarter-wave plate, and the fast axis of the quarter-wave plate forms or or non a preset included angle with the polarization direction of the linearly polarized light, so that the output light intensity remains constant. The polarization states of the laser beams corresponding to different included angles are linearly polarized light, circularly polarized light, and elliptically polarized light; Under the condition of keeping the total light intensity unchanged, generate elliptically polarized light with a specific ellipticity through the azimuth angle configuration of the quarter-wave plate.

[0032] Step 3 is specifically as follows: The nonlinear photonic crystal structure is coated with an anti-reflection film or not; By adjusting the incident angle of the fundamental frequency light with different polarization states, change the period of the nonlinear photonic crystal structure, so that the fundamental frequency light and the nonlinear light field satisfy the quasi-phase matching condition, and then obtain a nonlinear light field with a nonlinear frequency conversion effect.

[0033] The described Bragg grating structure is designed as a multi-layered ring structure. The grating periodic structure is distributed parallel to the crystal optical axis direction. The phase difference relationship is satisfied between rings. , where m is an integer, to achieve multi-order nonlinear diffraction spots; the grating periods between layers satisfy the phase difference relationship , where n is an integer, to achieve the nonlinear enhancement of diffraction spots. In this way, the periodic multi-layered ring-shaped nonlinear Bragg grating can generate a Bragg diffraction polarized light field with a quasi-phase matching effect.

[0034] The periodicity of the described spiral structure needs to satisfy the quasi-phase matching condition to compensate for the phase mismatch and ensure the effective phase accumulation of the light field generated during the nonlinear process, thereby improving the conversion efficiency; the spiral structure directly encodes the spiral phase in the nonlinear optical crystal through the spatially modulated nonlinear coefficient or geometric symmetry, enabling the output light field to carry orbital angular momentum and form a vortex vector light field; this process requires combining the phase matching for structural design to ensure efficient nonlinear frequency conversion and phase modulation, thereby achieving the nonlinear conversion from a Gaussian beam to a vortex light field.

[0035] It should be noted that for the design of the nonlinear crystal structure described in the present invention, only by fabricating the Bragg grating and the spiral structure inside or on the surface of the crystal structure, without other complex operations, can the generation and synchronous nonlinear enhancement of the Bragg diffraction polarized light field and the vortex vector light field be achieved, and the structure is highly integrated.

[0036] Embodiment 3 As Figure 1 and Figure 3 shown, in order to prove that the photonic crystal structure through the nonlinear Bragg diffraction condition in the method of the present invention can generate a nonlinear Bragg diffraction polarized light field, the following experiment is conducted: The selected nonlinear photonic crystal material is a z-plane cut quartz crystal with a thickness of 0.5 mm, and the optical surface of the crystal is polished. First, according to the condition required to satisfy the quasi-phase matching, the period of the ring-shaped Bragg grating is designed. The central diameter of the ring-shaped Bragg grating is 14 µm, the period of the grating is 7 µm, and the layer spacing is 4.2 µm; the preparation of the Bragg grating structure can adopt femtosecond laser direct writing technology, ion implantation method, chemical etching method, etc.

[0037] When femtosecond laser direct writing is selected, the laser light source for etching the Bragg grating is: Ti:Sapphire regenerative amplifier (Spitfire, Spectra Physics), with a wavelength of 800 nm, a repetition frequency of 1 kHz, a pulse width of 100 fs, and a maximum pulse energy of 6 mJ. Inside the processing platform, there is a rotatable half-wave plate controlled by a computer. Combined with a Glan laser polarizer, it can accurately control the single-pulse energy of the laser used for processing the sample. The polarization direction of the laser beam can also be controlled by the half-wave plate and focused into the sample through a 20x microscope objective lens with a numerical aperture of 0.5. The nonlinear quartz crystal used is placed on a three-dimensional moving processing platform controlled by a computer with a processing accuracy in the sub-micron range. The quartz crystal can translate along the x-axis perpendicular to the femtosecond laser beam on the processing platform, and at the same time, the sample can move up and down along the z-axis. After setting the required result size using a computer, femtosecond laser etching can be performed.

[0038] The wavelength of the laser source for characterization is 355 nm, the repetition frequency is 100 kHz, and the pulse width is 100 ps. After the laser source passes through a polarizer and a quarter-wave plate of 355 nm in sequence, the obtained circularly polarized light is focused by a convex lens and vertically irradiated onto the nonlinear Bragg grating structure. By rotating the polarizer and the quarter-wave plate to meet the phase-matching condition, a nonlinear Bragg diffraction polarized light field with a wavelength of 177.3 nm can be generated.

[0039] Example 4 As Figure 2 and Figure 4 shown, in order to prove that the method of the present invention can generate a nonlinear vortex vector light field with a frequency-doubling effect by satisfying the spiral structure for generating a vortex light vector light field, the following experiment is carried out: The selected nonlinear photonic crystal material is an x-cut, 1-mm-thick lithium niobate (LiNbO3) crystal, and the light-passing surface of the crystal is polished. First, according to the conditions required to satisfy quasi-phase matching, the pitch of the spiral structure is designed to be 7 µm and the spiral radius is 10 µm; the preparation of the spiral structure can adopt femtosecond laser direct writing technology, ion implantation method, chemical etching, etc. In the experiment, the femtosecond laser direct writing technology method is selected; the femtosecond laser etches to form a spiral structure with a periodic refractive index distribution in the z direction of the nonlinear crystal. The laser source used for etching the spiral in the experiment is: wavelength 1030 nm, repetition frequency 76 kHz, and pulse width 300 fs. The used LiNbO3 crystal is placed on a three-dimensional moving processing platform controlled by a computer, and the lateral offset angle in each layer, i.e., the z-y plane, is Δθ = 2πl / N, where N is the total number of layers and l is the number of rotation turns.

[0040] The wavelength of the laser source for characterization is: wavelength 1064 nm, repetition frequency 1 MHz, and pulse width 400 fs. After modulating the laser source, the circularly polarized light is focused by a convex lens and vertically irradiated onto the position where the structure is located. By adjusting the polarizer, a nonlinear vortex vector light field with a frequency-doubling (532 nm) effect can be generated.

[0041] Although the specific embodiments of the invention have been described above in conjunction with the accompanying drawings, they are not intended to limit the scope of protection of the present invention. Based on the technical solutions of the present invention, various modifications or variations that can be made by those skilled in the art without creative efforts are still within the scope of protection of the present invention.

Claims

1. An optical field generating device based on a non-linear photonic crystal structure, characterized in that: The device includes a polarizer, a quarter-wave plate, and a nonlinear optical crystal with a Bragg grating structure or a spiral structure; Through nonlinear optical modulation, the fundamental frequency light passes through the polarizer and the quarter-wave plate successively, and after being focused by a lens, it is incident on the nonlinear optical crystal with a Bragg grating structure or a spiral structure respectively to generate a nonlinear Bragg diffraction polarized light field and a nonlinear vortex vector light field.

2. The light field generating device based on a nonlinear photonic crystal structure according to claim 1, characterized in that: The nonlinear photonic crystal is applicable to all crystals without a center of symmetry; The nonlinear light field is generated based on the second-order nonlinear optical effect or the third-order nonlinear effect. The second-order nonlinear optical effect includes frequency doubling, sum frequency, or difference frequency, and the third-order nonlinear effect includes four-wave mixing.

3. The light field generating device based on a nonlinear photonic crystal structure according to claim 1, characterized in that: The nonlinear photonic crystal structure is an artificially designed spatially ordered crystal with a periodically varying nonlinear susceptibility The modulation range of the nonlinear susceptibility is The period of the spatially ordered structure satisfies the phase matching condition, and the phase matching condition is as follows: ， Wherein, Δk represents the wave vector mismatch between the fundamental frequency light and the nonlinear light field.

4. The light field generating device based on a nonlinear photonic crystal structure according to claim 1, characterized in that: The dimensionality of the nonlinear photonic crystal structure includes one-dimensional, two-dimensional, or three-dimensional, and the structural distribution of the nonlinear photonic crystal includes a lattice distribution structure, a linear periodic grating structure, a circular curved surface structure, and / or an elliptical curved surface structure.

5. The light field generating device based on a nonlinear photonic crystal structure according to claim 1, characterized in that: The size range of the structural unit of the nonlinear photonic crystal structure in any direction is: 0.5 µm - 100 µm.

6. A method for generating an optical field based on a nonlinear photonic crystal structure, applied to an optical field generating device based on a nonlinear photonic crystal structure as described in claim 1, characterized in that, It includes the following steps: Step 1: Prepare nonlinear photonic crystals with a Bragg grating structure and a spiral structure that satisfy the quasi-phase matching condition respectively; Step 2: A laser beam is emitted by a laser. The laser beam is the fundamental frequency light illumination, which is a linearly polarized light or a circularly polarized light. The laser beam passes through the polarizer and the quarter-wave plate successively, and the fundamental frequency light illumination emitted by the laser is converted into the modulated fundamental frequency light illumination. The modulated fundamental frequency light illumination is light with an arbitrary polarization state; Step 3: Fix the nonlinear photonic crystal on a three-dimensional platform. After the modulated fundamental frequency light is irradiated on the nonlinear photonic crystal, the light passes through the nonlinear photonic crystals of the two structures respectively to generate a nonlinear Bragg diffraction polarized light field and a nonlinear vortex vector light field.

7. A method for generating an optical field based on a nonlinear photonic crystal structure according to claim 6, characterized in that, Step 1 is specifically as follows: Prepare samples with a Bragg grating structure and a spiral structure, cut the nonlinear material in any direction, and polish the laser incident or exit surface to obtain the samples of the required prepared structure; Prepare a nonlinear photonic crystal structure inside the polished sample. The processing and preparation methods of the nonlinear photonic crystal structure include femtosecond laser direct writing technology and ion implantation method.

8. A method for generating an optical field based on a nonlinear photonic crystal structure according to claim 7, characterized in that, Step 1 also includes: Adjust the structural parameters of the nonlinear Bragg grating structure to obtain polarized light fields with different polarization directions; Adjust the polarized light field by performing periodic design according to the quasi-phase matching relationship and designing the period and layer spacing of the Bragg grating; Adjust the topological charge number of the spiral structure to obtain vector light fields with different orbital angular momenta; Design the spiral period number according to the required vector light field of the vortex light, and at the same time control the quasi-phase matching condition to compensate for the wave vector mismatch to obtain a nonlinear vortex vector light field.

9. A method for generating an optical field based on a non-linear photonic crystal structure according to claim 8, characterized in that, Step 2 is specifically as follows: The laser beam emitted by the laser is incident on the polarizer to generate linearly polarized light; Incident linearly polarized light onto a quarter-wave plate, and the fast axis of the quarter-wave plate forms a or NOR preset included angle with the polarization direction of the linearly polarized light. The polarization states of the laser beams corresponding to different included angles are linearly polarized light, circularly polarized light, and elliptically polarized light; Under the condition of keeping the total light intensity unchanged, elliptically polarized light with a specific ellipticity is generated by the azimuth angle configuration of the quarter-wave plate.

10. A method for generating an optical field based on a nonlinear photonic crystal structure according to claim 9, characterized in that, Step 3 is specifically as follows: The nonlinear photonic crystal structure is coated with an antireflection film or not; By adjusting the incident angle of the fundamental frequency light with different polarization states, the period of the nonlinear photonic crystal structure is changed, so that the fundamental frequency light illumination and the nonlinear light field satisfy the quasi-phase matching condition, and then a nonlinear light field with a nonlinear frequency conversion effect is obtained.

Images