CN110262044B - Diffraction-free two-dimensional optical lattice period adjustment system based on zoom lens - Google Patents

Abstract

The invention relates to a non-diffraction two-dimensional optical lattice period adjustment system based on a zoom lens, comprising a laser, a first half-wave plate, a lens group for beam expansion, a beam splitting prism, a second half-wave plate, and a spatial light modulator , a first lens, a reticle, a mirror, a second lens, a zoom lens, a third lens and a detector. After the light beam retaining the fundamental information is reflected by the mirror, it interferes with the second lens to form a non-diffraction two-dimensional optical lattice, and then passes through the zoom lens and the third lens in turn, and is imaged on the detector, wherein, In the zoom lens, the position of the back focal plane remains unchanged during focusing, and the distance between the zoom lens and the third lens is the sum of the back focal length of the zoom lens and the front focal length of the third lens; It can realize the continuous change of the magnification of the beam expander system, so as to realize the rapid and continuous adjustment of the period of the diffraction-free two-dimensional optical lattice.

Description

Diffraction-free two-dimensional optical lattice period adjustment system based on zoom lens

technical field

The invention relates to a fast and continuous adjustment system for the period of a diffraction-free two-dimensional optical lattice, in particular, it is aimed at assisting a light field regulation method based on a spatial light modulator, a multi-core optical fiber interference method and the like to generate a diffraction-free two-dimensional optical lattice. system.

Background technique

An optical lattice is a periodic pattern of potential wells produced by the intersecting interference of multiple laser beams. As early as 1989, Steven Chu and others at Bell Labs used two laser beams to propagate in opposite directions to generate an interfering standing wave field, and for the first time realized a one-dimensional optical lattice in an experiment. Subsequently, Grynberg et al. successfully obtained two-dimensional optical lattices and three-dimensional optical lattices by interfering with multiple laser beams according to certain rules, and theoretically summarized the conditions for the generation of optical lattices. However, the period of the wavelength order makes it difficult to distinguish between the optical lattice cells, and the restriction of the cell shape in all directions is not uniform, which seriously affects the application feasibility of this technology. In 2005, based on theoretical design, Prof. Eric Betzig creatively proposed two new structures, Sparse Lattices and Composite Lattices, which achieved high-quality amplification of the overall optical lattice, breaking through the wavelength-scale period. limit. Since then, the combination of optical lattices and non-diffraction beams has further enhanced the flexibility of the period adjustment of optical lattices, making it widely used in the fields of super-resolution microscopy, photonic lattice lithography, micro-nano manipulation, and surface measurement. application space.

The development of optical lattice technology is inseparable from the improvement of its periodic control ability. The period of an optical lattice is the spacing between each unit cell in the light field pattern, and this parameter has a significant impact on extended optical lattice applications. At present, the combination of optical lattices and non-diffraction beams can produce non-diffraction two-dimensional optical lattices. The period adjustment of such optical lattices has certain flexibility and has a theoretical basis for continuous period adjustment. However, in the period adjustment process of the diffraction-free two-dimensional optical lattice, it is often necessary to adjust the optical path structure to satisfy the theoretical conditions, that is, to adjust the position of the optical element or to replace the optical element. For example, a non-diffraction two-dimensional optical lattice can be generated using a light field control method based on a spatial light modulator. If a conventional method is used to adjust the period of a non-diffractive two-dimensional optical lattice, it is necessary to change the size of the mask in the optical path system, that is, to replace the mask. or changing the focal length of the lens behind the mask, that is, replacing the lens and adjusting the lens position for focusing. This method is inefficient, and the optical path structure needs to be changed every time the period of the diffraction-free two-dimensional optical lattice is changed, and the discontinuous change of the parameters of the optical path elements makes the continuous adjustment of the two-dimensional optical lattice period difficult to achieve. Therefore, in view of this situation, realizing the rapid and continuous adjustment of the period of the diffraction-free two-dimensional optical lattice can further enhance the ability to control the period of the two-dimensional optical lattice and facilitate its development of application fields.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a system that can realize fast and continuous adjustment of the period of a diffraction-free two-dimensional optical lattice. The technical solution is as follows:

A diffraction-free two-dimensional optical lattice period adjustment system based on a zoom lens, comprising a laser, a first half-wave plate, a lens group for beam expansion, a beam splitting prism, a second half-wave plate, a spatial light modulator, a first Lens, reticle, mirror, second lens, zoom lens, third lens and detector, the laser is emitted from the laser, the polarization direction is adjusted by the first half-wave plate, the beam is expanded by the lens group, and then passed through the beam splitting prism and the first half-wave plate. The two-half-wave plate reaches the spatial light modulator, and the spatial light modulator performs phase modulation on it and returns to the beam splitting prism and reflects it into the back optical path. The beam is Fourier-transformed by the first lens, and the frequency domain information is displayed at the mask. The mask filters the frequency domain information and only retains the base-level information. After the beam with the base-level information is reflected by the mirror, it interferes with the second lens to form a diffraction-free two-dimensional optical lattice, and then passes through the zoom lens in turn. and the third lens, and imaging on the detector, wherein the zoom lens, the position of its back focal plane remains unchanged during focusing, and the distance between the zoom lens and the third lens is the back focal length of the zoom lens The sum of the front focal length of the third lens; by adjusting the focal length of the zoom lens, the continuous change of the magnification of the beam expander system can be realized, so that the rapid and continuous adjustment of the period of the diffraction-free two-dimensional optical lattice can be realized.

Preferably, the maximum and minimum focal lengths of the zoom lens should be selected according to the period adjustment requirements: if the period needs to be enlarged and adjusted, the minimum focal length of the zoom lens should be smaller than the focal length of the third lens; if the period needs to be reduced and adjusted, the zoom The maximum focal length of the lens should be greater than the focal length of the third lens.

The present invention proposes an optical path design scheme including a zoom lens period adjustment system, which realizes the rapid and continuous adjustment of the period of a diffraction-free two-dimensional optical lattice, and the designed optical path system has the following beneficial effects:

(1) The adjustment of the period of the diffraction-free two-dimensional optical lattice has continuity. Since the focal length of the zoom lens can be continuously adjusted, it is guaranteed that the parameters of the optical path element can be continuously changed, which facilitates the realization of the diffraction-free two-dimensional optical lattice. The effect of continuous adjustment of the cycle.

(2) More efficient, no need to make changes to the optical path structure that has been built, and no need to change the structural position of the optical path components, just adjust the focal length of the zoom lens in situ to achieve no diffraction The rapid change of the period of the two-dimensional optical lattice is simple and easy to implement, and the adjustment efficiency is improved.

(3) The period adjustment system with zoom lens is simple in structure, easy to install, and can be easily embedded into various systems that can generate non-diffraction two-dimensional optical lattices, providing the system with the ability to quickly and continuously adjust the period of non-diffraction two-dimensional optical lattices .

(4) High-quality rapid and continuous amplification of diffraction-free two-dimensional optical lattices is achieved, which can help the technology to cope with various applications and measurement situations.

Description of drawings

Figure 1 Schematic diagram of the generation of a diffraction-free two-dimensional optical lattice

Figure 2 Schematic diagram of the structure of the period adjustment system with zoom lens

Figure 3 Schematic diagram of zooming of the zoom lens

Fig. 4 Schematic diagram of the period adjustment system of a zoom lens with a period adjustment system for adjusting the period of a non-diffraction two-dimensional optical lattice

Figure 5 Schematic diagram of the optical path of the optical field control method based on the spatial light modulator adding a period adjustment system with a zoom lens

Figure 6 The effect of adjusting the period of the non-diffraction two-dimensional optical lattice by using the period adjustment system with the zoom lens The lattice period becomes larger

Reference numerals are explained as follows: structured light source 1, lens 2, detector 3, zoom lens 4, lens 5, laser 6, half-wave plate 7, lens 8, lens 9, lens 10, lens 11, beam splitting prism 12, Half-wave plate 13 , spatial light modulator 14 , lens 15 , mask 16 , mirror 17 .

Detailed ways

The period adjustment system with zoom lens can realize the rapid and continuous adjustment of the period of the non-diffraction two-dimensional optical lattice. The pattern does not appear to diverge or contract. Although undiffracted light beams are not parallel light, they have similar properties to parallel light in some specific cases. For example, the commonly used parallel light beam expansion system (a lens group composed of two lenses with different focal lengths) can produce beam expansion effect on parallel light. The research of the present invention finds that it can also realize the overall enlargement of the non-diffraction two-dimensional optical lattice, which is the completion of the beam expansion. Tuning of diffraction-free two-dimensional optical lattice periods. The period of a diffraction-free two-dimensional optical lattice is determined by the wave vector direction of its interfering plane waves. The parallel beam expansion system can adjust the wave vector direction of the interference plane wave that produces the diffraction-free optical lattice, thereby producing a parallel beam similar to that of a parallel beam. magnification effect. Based on this, the present invention proposes a structure as shown in FIG. 2, by replacing the previous lens in the parallel light beam expansion system with a zoom lens to form a new periodic adjustment system, and beam expansion can be realized through the fast and continuous adjustment characteristics of the focal length of the zoom lens The rapid and continuous change of the magnification of the system enables the rapid and continuous adjustment of the period of the diffraction-free two-dimensional optical lattice.

Figure 1 is a schematic diagram of the generation of a non-diffraction two-dimensional optical lattice. The structured light source 1 is placed on the front focal plane of a lens 2, and then interference is completed through the lens 2 to form a non-diffraction two-dimensional optical lattice. In FIG. 1 , there are two factors that affect the period of the diffraction-free two-dimensional optical lattice, one is the structural parameters of the structured light source 1 , and the other is the focal length of the lens 2 . Using these two factors can realize the period adjustment, but it is more complicated. When changing the structure of the structured light source 1, it is unavoidable to change the optical path structure. For example, in the light field control method based on spatial light modulator, the shape and size of the mask should be replaced, and the position of the optical fiber should also be changed in the multi-core fiber method. to readjust. Changing the focal length of lens 2 means changing lenses with different focal lengths. Here, lens 2 cannot be replaced by a zoom lens, because the light beam entering lens 2 is not parallel light, and in order to form a two-dimensional optical lattice, lens 2 and light source 1 A certain distance must be maintained. To replace lenses with different focal lengths, to achieve refocusing, it is necessary to adjust the position of the lens. During the period adjustment process of the diffraction-free two-dimensional optical lattice, if the optical path structure needs to be continuously modified, the period adjustment efficiency will be low and inconvenient.

FIG. 2 is a periodic adjustment system with a zoom lens proposed by the present invention. The light beam first passes through the zoom lens 4 and then passes through the lens 5 . The ordinary parallel beam expansion system is a lens with two focal lengths determined, which can only magnify the non-diffraction two-dimensional optical lattice by a certain magnification, while the periodic adjustment system with zoom lens can realize the in-situ rapid and continuous adjustment of magnification. When the zoom lens is focused, as shown in Figure 3, because the zoom lens is often used in conjunction with detectors such as CCD, the focal length f on the image side is determined and unchanged, that is, the position of the focal plane on the image side is determined. Only the beam convergence angle α in the figure will change, which provides convenience for the zoom lens to cooperate with the latter lens in the beam expander system. The distance between the zoom lens and the lens is the sum of the focal length on the image side of the zoom lens 4 and the focal length on the object side of the lens 5. The change of α during focusing will lead to a corresponding change in the direction of the interference plane wave vector of the non-diffractive two-dimensional optical lattice, so that the The period of the diffraction-free two-dimensional optical lattice is changed, which is the key to the period adjustment of the system.

The usage method of the beam expander system with zoom lens is shown in Figure 4, and the period adjustment system with zoom lens is placed directly behind the lens 2 at a certain distance. The distance should not be too short, because the beams do not fully interfere at a short distance; nor should it be too long, because the non-diffracted beam generated in the actual experiment is not ideal, the non-diffracted distance is limited, and the interference pattern will dissipate if the distance is too long. The distance should preferably be near the image-side focal length of the lens 2 . Among them, a good non-diffraction two-dimensional optical lattice has been produced after the lens 2. Using its non-diffraction property, the periodic system including the zoom lens is embedded in it, and the rapid and continuous adjustment of the period of the non-diffraction two-dimensional optical lattice can be realized. .

Figure 5 shows the optical path of the light field control method based on the spatial light modulator with the addition of the period adjustment system of the zoom lens. The laser is emitted from the laser 6, and the polarization direction is adjusted through the half-wave plate 7. The lens 8/9/10/11 expands twice The beam passes through the beam splitter prism and the half-wave plate 13 to reach the spatial light modulator 14. The spatial light modulator performs phase modulation on it and returns to the beam splitter prism and reflects it into the back optical path. The lens 15 Fourier transforms the beam, and the mask plate The frequency domain information is displayed at 16, and the mask 16 filters the frequency domain information and only retains the base level information, and the base level information here is equivalent to the structured light source 1 constructed in FIG. 1 . After the light beam is reflected by the mirror 17, it interferes with the lens 2 to form a non-diffraction two-dimensional optical lattice. The zoom lens 4 and the lens 5 are embedded in the system to provide the ability to quickly and continuously adjust the period of the diffraction-free two-dimensional optical lattice, and complete the imaging on the detector 3 . It can be seen that the generation system including the period adjustment system of the zoom lens embedded in the diffraction-free two-dimensional optical lattice is simple and easy to implement, and has strong practicability.

Figure 6 is an example data of using a period adjustment system with a zoom lens to adjust the period of a two-dimensional optical lattice without diffraction. After the period adjustment system with a zoom lens is installed in the system, the focal length of the zoom lens can be adjusted manually to achieve no diffraction. Adjustment of the period of a two-dimensional optical lattice. The period of the lattice pattern collected in Figure 6(a) is 493.3 microns after graphic processing, and the period in Figure 6(b) is 565.0 microns. The zoom lens is adjusted to achieve the magnification effect of the two-dimensional optical lattice.

Claims (2)

1. A diffraction-free two-dimensional optical lattice period adjustment system based on a zoom lens, comprising a laser, a first half-wave plate, a lens group for beam expansion, a beam splitting prism, a second half-wave plate, a spatial light modulator, The first lens, the mask, the reflector, the second lens, the zoom lens, the third lens and the detector; the laser is emitted from the laser, the polarization direction is adjusted by the first half-wave plate, the beam is expanded by the lens group, and then passes through the beam splitter prism After reaching the spatial light modulator with the second half-wave plate, the spatial light modulator performs phase modulation on it and returns to the beam splitting prism and reflects it into the back optical path. The beam is Fourier transformed by the first lens, and the frequency domain is displayed at the mask. Information, the mask filters the frequency domain information and only retains the base-level information. After the beam with the base-level information is reflected by the mirror, it is then interfered by the second lens to form a non-diffraction two-dimensional optical lattice, and then zooms in turn. The lens and the third lens are imaged on the detector, wherein the position of the rear focal plane of the zoom lens remains unchanged during focusing, and the distance between the zoom lens and the third lens is the rear of the zoom lens. The sum of the focal length and the front focal length of the third lens; through the adjustment of the focal length of the zoom lens, the continuous change of the magnification of the beam expander system can be realized, so that the rapid and continuous adjustment of the period of the diffraction-free two-dimensional optical lattice can be realized. 2. The period adjustment system according to claim 1, wherein the maximum and minimum focal lengths of the zoom lens should be selected according to the period adjustment requirements: if the period needs to be enlarged and adjusted, the minimum focal length of the zoom lens should be smaller than the first focal length of the zoom lens. The three-lens focal length; if the period needs to be reduced, the maximum focal length of the zoom lens should be greater than the focal length of the third lens.

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