Polarization optical device

Abstract

The present invention relates to a polarization optical device, comprising a substrate. Silicon pillars of different sizes are periodically arranged on the substrate, and each silicon pillar applies, on the basis of the size thereof, different phase shifts to incident light components of different wavelengths and different polarization state angles in incident light, so that the incident light components of different wavelengths and different polarization state angles converge at different focal points. The present invention achieves a broadband polarization lens function by means of the principles of independent phase control and achromatism, and facilitates the miniaturization of the polarization optical device.

Description

Polarization optical device TECHNICAL FIELD

[0001] The present application relates to the technical field of broadband polarization optics, in particular to a polarization optical device. BACKGROUND

[0002] Super surface is a two-dimensional plane structure composed of super atoms with special electromagnetic properties according to a certain arrangement, which can realize flexible control of amplitude, phase, polarization and other of incident light, and has strong light field manipulation ability. In recent years, polarization-related research has attracted widespread attention at home and abroad, and how to obtain the polarization information of broadband light is the core problem in this field.

[0003] Traditional detection technology needs to combine various complex optical devices such as polarizing plates, wave plates, lenses, etc. to modulate the polarization and wavefront of light, resulting in a complex and bulky system, which cannot meet the needs of miniaturization and integration. TECHNICAL PROBLEM

[0004] The technical problem to be solved by the present application is to provide a polarization optical device that can realize miniaturization of broadband polarization lenses. TECHNICAL SOLUTION

[0005] The technical scheme adopted by the present application to solve its technical problem is to provide a polarization optical device, comprising a substrate, the substrate is periodically arranged with silicon columns of different sizes to form a silicon column array, each silicon column applies different phase shifts to different wavelength and different polarization state angle incident light components in the incident light according to its size, so that the different wavelength and different polarization state angle incident light components converge at different focal points.

[0006] Further, the different focal points are located on the same focusing plane, and the focusing plane is perpendicular to the silicon column array.

[0007] Further, the silicon column array satisfies a set phase distribution:

[0008] ;

[0009] Wherein, is the phase shift applied by the current silicon column to the incident light component of wavelength and polarization state angle ;

[0010] is the distance from the optical center of the optical device to the focusing plane;

[0011] is the radial distance from the center position of the current silicon column to the focal point ; the wavelength , the polarization angle of the incident light component;

[0012] the distance from the focus point to the center of the focusing plane;

[0013] is a constant.

[0014] Further, the constant is obtained by using an optimization algorithm to solve the constant that minimizes the deviation of the phase distribution function from the known optimal phase distribution.

[0015] Further, the silicon pillar array is divided into a first region, a second region, a third region and a fourth region in clockwise order; the silicon pillars in the first region and the third region apply different phase shifts to the first incident light component and the second incident light component of the first waveband at two different polarization angles, so that the first incident light component converges at a first focus point and the second incident light component converges at a second focus point; the silicon pillars in the second region and the fourth region apply different phase shifts to the third incident light component and the fourth incident light component of the second waveband at two different polarization angles, so that the third incident light component converges at a third focus point and the fourth incident light component converges at a fourth focus point.

[0016] Further, the different focus points are located on the same focusing plane, which is perpendicular to the silicon pillar array, and the first focus point, the second focus point, the third focus point and the fourth focus point are respectively located at the center of the second quadrant, the fourth quadrant, the first quadrant and the third quadrant of the focusing plane, and the first quadrant, the second quadrant, the third quadrant and the fourth quadrant of the focusing plane correspond to the projection of the first region, the second region, the third region and the fourth region on the focusing plane respectively.

[0017] Further, the polarization angles of the first incident light component, the third incident light component, the second incident light component and the fourth incident light component increase by 45° in turn.

[0018] Further, the polarization angle of the first incident light component is an integer multiple of 45°.

[0019] Further, the arrangement period of the silicon pillar array is less than the working wavelength.

[0020] Further, the height of the silicon pillar is set to cover multiple 2π in its phase shift adjustment range.

[0021] Further, the cross section of the silicon pillar is rectangular or elliptical. Advantages

[0022] Compared with the prior art, the application has the following advantages and positive effects: the application uses polarization-dependent independent phase control and achromatic principle, arranges the silicon columns with different side lengths periodically based on the set phase distribution, and introduces a constant term related to wavelength and polarization state in the phase distribution function to achromatize, so that the super lens converges incident waves with different wavelengths and different polarization states at different focal points, thereby realizing miniaturization of the wide-frequency polarization lens. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of a metasurface unit in an embodiment of the application;

[0024] Figure 2 is a schematic diagram of the principle of a super lens in an embodiment of the application;

[0025] Figure 3 is a silicon column arrangement diagram in an embodiment of the application. Embodiments of the application

[0026] The application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not used to limit the scope of the application. In addition, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content taught by the application, and these equivalent forms also fall within the scope defined by the appended claims.

[0027] An embodiment of the application relates to a wide-frequency polarization optical device, comprising: a silicon substrate, different-sized silicon columns being periodically arranged on the upper part of the substrate, and the silicon columns being in the center of metasurface units.

[0028] In the metasurface unit shown in Figure 1, the cross section of the silicon column is an anisotropic cross section shape, preferably one of a rectangle or an ellipse, so that waveguide modes polarized along the x-axis and the y-axis have different equivalent refractive indices. Each silicon column will exert a polarization-dependent phase delay on the transmitted wave, and this anisotropy for orthogonal polarization states is the key to independent control.

[0029] According to the transmission phase control principle, the phase shifts and exerted by the metasurface unit on the x and y polarized wave components in the incident light are determined by the side lengths and of the silicon column along the x and y directions, respectively. The metasurface can be regarded as a birefringent device with its principal axes along the x and y directions, and the required transmission phase and ​By setting the column height h, the phase control range of the unit structure covers multiple 2π phases, and the period p is set to be less than the working wavelength to avoid the generation of high-order diffraction and reduce energy loss.

[0030] The function expression of the entire super lens phase distribution is as follows:

[0031]

[0032] Wherein, is the phase shift imposed by the current silicon column on the incident light component of wavelength , polarization state angle , is the distance from the optical center of the optical device to the focusing plane, is the radial distance from the center position of the current silicon column to the focal point , is the preset focal point of the incident light component of wavelength , polarization state angle , is the distance from the focal point to the center of the focusing plane, is a constant related to wavelength and polarization state, so that the super lens realizes achromatic focusing within a certain wide frequency.

[0033] In order to find the appropriate constant , the error function in formula (2) is used to evaluate the deviation E of the theoretical phase distribution function of each incident light component from the known optimal phase distribution, that is, the phase distribution obtained by arranging the closest super surface unit in the super surface unit library on the entire super lens plane, and the particle swarm algorithm is used for feedback iteration to solve the optimal constant that minimizes the deviation E, thereby minimizing the inaccuracy of phase control required for focusing light on each focal point. The error function is:

[0034]

[0035] Each silicon column can independently control the incident orthogonal polarized light, so it is necessary to realize multi-dimensional phase distribution design for multiple wavelengths and polarization states. Under the determined phase distribution, the most suitable silicon column is selected at each position in the super surface unit library to form the wide frequency polarization super lens of the embodiment.

[0036] As shown in FIG. 2, after the phase distribution of the super lens is determined, light is incident from the bottom, and different wavelengths and polarization states of light are respectively converged on different focal points by the designed device. The entire super lens is divided into four functional areas:

[0037] For blue and green wave bands, the X-polarized light and Y-polarized light (corresponding to 0° and 90°) of green light are respectively focused on the second quadrant and the fourth quadrant center of the focusing plane; the 45° polarized light and 135° polarized light of blue light are respectively focused on the first quadrant and the third quadrant center of the focusing plane.

[0038] Figure 3 shows the arrangement of silicon columns at the center of the hyperlens, the four quadrants have different functions, the first quadrant focuses the X-polarized green light on the second quadrant center of the focusing plane, and the other second, third, and fourth quadrants successively converge the 45° polarized blue light, Y-polarized green light, and 135° polarized blue light to the third, fourth, and first quadrant center of the focusing plane. When the super surface unit library cannot cover the required polarization angle, the required phase shift can be achieved by rotating the silicon column, for example, in order to control the 45°-135° polarization state, the silicon columns in the second and fourth quadrants can be rotated by 45°, while the silicon columns in the first and third quadrants remain at a rotation angle of 0°.

Claims

1. A polarizing optical device, characterized by, The application relates to a silicon pillar array, which comprises a substrate, and a plurality of silicon pillars of different sizes arranged on the substrate in a periodic manner, each silicon pillar imparting different phase shifts to different wavelength and polarization angle components of incident light according to the size of the silicon pillar, so that the different wavelength and polarization angle components of incident light converge at different focal points.

2. The optical device of claim 1, wherein, The different focal points are located in the same focal plane, and the focal plane is perpendicular to the silicon pillar array.

3. The optical device of claim 2, wherein, The silicon pillar array satisfies a set phase distribution: ； wherein For the current silicon post to wavelength , polarization state angle a phase shift imposed by the incident light component of the light, the distance of the optical center of the optical device to the focusing plane, to the center of the current silicon column to the focal point a radial distance of the focal point for wavelength , polarization state angle a preset focal point of the incident light component of the light, for the focal point a distance to the center of the focal plane, The phase distribution is a constant.

4. The optical device of claim 3, wherein, the constant is obtained as an optimal estimate of the constant that minimizes the deviation of the phase distribution function from a known optimal phase distribution using an optimization algorithm ​ 5. The optical device of claim 1, wherein, The silicon pillar array is divided into a first region, a second region, a third region and a fourth region in a clockwise direction; the silicon pillars in the first region and the third region impart different phase shifts to first incident light components and second incident light components of a first waveband with two different polarization angle components, so that the first incident light components converge at a first focal point and the second incident light components converge at a second focal point; the silicon pillars in the second region and the fourth region impart different phase shifts to third incident light components and fourth incident light components of a second waveband with two different polarization angle components, so that the third incident light components converge at a third focal point and the fourth incident light components converge at a fourth focal point.

6. The optical device of claim 5, wherein, The different focal points are located in the same focal plane, and the focal plane is perpendicular to the silicon pillar array, and the first focal point, the second focal point, the third focal point and the fourth focal point are respectively located at the centers of the second quadrant, the fourth quadrant, the first quadrant and the third quadrant of the focal plane, and the first quadrant, the second quadrant, the third quadrant and the fourth quadrant of the focal plane correspond to the projections of the first region, the second region, the third region and the fourth region on the focal plane.

7. The optical device of claim 6, wherein, The polarization angle of the first incident light component, the third incident light component, the second incident light component and the fourth incident light component increases by 45 degrees in sequence.

8. The optical device of claim 6, wherein, The polarization angle of the first incident light component is an integer multiple of 45 degrees.

9. The optical device of claim 1, wherein, The arrangement period of the silicon pillar array is less than the working wavelength.

10. The optical device of claim 1, wherein, The cross section of the silicon pillar is rectangular or elliptical.

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