CN111399202B - Spatial light modulator coupling device without zero-order diffracted light - Google Patents

Abstract

The invention belongs to the field of spatial light field regulation and control, and relates to a spatial light modulator coupling device without zero-order diffraction light, which comprises a sealing box, an asymmetric triangular reflector and a spatial light modulator; the asymmetric triangular reflector and the spatial light modulator are oppositely arranged and are arranged in the sealing box; the sealing box is provided with a light inlet hole and a light outlet hole; the incident light is emitted from the light outlet after sequentially passing through the light inlet, the asymmetric triangular reflector, the spatial light modulator and the asymmetric triangular reflector. The invention provides a spatial light modulator coupling device without zero-order diffraction light, which can regulate and control a high-precision light field, can inhibit zero-order light beams without a spatial filter, is modularized and compact and is easy to combine with other systems.

Description

Spatial light modulator coupling device without zero-order diffracted light

technical field

The invention belongs to the field of spatial light field regulation, and relates to a spatial light modulator coupling device, in particular to a spatial light modulator coupling device without zero-order diffracted light.

Background technique

The invention of the laser in 1960 greatly promoted the development of natural scientific research, such as laser life science, optical information processing, optical micro-nano processing and many other laser-based scientific research fields emerged. The main limitation of ordinary commercial lasers is that the output mode is fixed, generally a fundamental mode Gaussian beam, which cannot meet the requirements of modern scientific research and applications for the specific distribution of optical field amplitude, phase and polarization state. The spatial light field modulation technology based on the spatial light modulator to control the spatial parameters of the light field converts the fundamental mode Gaussian beam into a novel arbitrary structured light field, which promotes optical information storage, optical micro-nano processing, optical communication, optical microscopy and optical micro- Rapid developments in areas such as manipulation. Commonly used light field control devices mainly include digital micromirror device (Digital Micromirror Device, DMD), deformable mirror (Deformable Mirror, DM) and liquid crystal spatial light modulator (Spatial Light Modulator, SLM). In scientific research, liquid crystal spatial light modulators have become the most widely used devices due to their high utilization of light energy. The liquid crystal spatial light modulator uses the birefringence characteristics of liquid crystal molecules to modulate the phase distribution of the light field, thereby controlling the intensity and polarization characteristics of the light field. The optical anisotropy of liquid crystal molecules makes the phase modulation depth of the light field related not only to the optical axis orientation of liquid crystal molecules, but also to the polarization state of incident light. A liquid crystal spatial light modulator is a polarization selective device that modulates only incident light with a specific polarization state, usually linearly polarized light in the horizontal direction. Among them, the most commonly used reflective liquid crystal spatial light modulators have two working modes: normal incidence and small-angle incidence, as shown in Figure 1 and Figure 2, respectively. For the normal incidence mode, a non-polarized beam splitter prism (NPBS in Figure 1) needs to be used to realize phase modulation, which leads to the optical energy utilization rate of the system being lower than 25%. rarely used. In order to maximize the utilization of light energy, researchers often use a small angle of incidence. Small angle of incidence will reduce the precision of light field regulation. Theoretically, the larger the incident angle, the lower the accuracy. In order to ensure the accuracy of light field regulation, the incident light angle is usually required to be small. For example, the German HoloEYE company requires the angle to be less than 6°, while the Japanese Hamamatsu company requires the angle to be less than 10°. The complete separation of the incident light and the outgoing light in the small-angle incidence mode will cause the laser beam to travel a long distance, such as d1 in Figure 2. At the same time, considering the size of the optical components used for collimating and separating the two beams, such a system has scattered optical paths and occupies a large space, thereby reducing the stability of the system. In addition, due to the grid structure of the liquid crystal spatial light modulator, that is, the fill factor cannot reach 100%, after the incident light is modulated by the spatial light modulator, an unmodulated zero-order beam will be generated, reducing the quality of the light field. Therefore, the zero-order beam needs to be suppressed. A common method is to use a spatial filter (aperture in Figure 3) to allow only the modulated light field (+1st order beam in Figure 3) to pass, and block the zeroth order beam (0th order beam in Figure 3). This ensures that the final system only has the modulated light field distribution. The introduction of spatial filters not only increases the complexity of the coherence, but also makes it difficult to implement in specific applications. For example, in femtosecond laser processing, excessive optical power density can burn out the spatial filter placed on the focal plane of the lens. In addition, the introduction of the spatial filter will increase the exit angle of the modulated light (+1 order) and reduce the modulation accuracy.

SUMMARY OF THE INVENTION

In order to solve the problems of scattered optical paths and zero-order beam filtering in the background art, the present invention provides a high-precision light field control device that can suppress zero-order light beams without a spatial filter, and the spatial light field control device is modular and compact. A zero-order diffracted light-free spatial light modulator coupling device that is easily integrated with other systems.

In order to achieve the above object, the present invention adopts the following technical solutions:

A coupling device for a spatial light modulator without zero-order diffracted light, characterized in that: the coupling device for a spatial light modulator without zero-order diffracted light comprises a sealed box, an asymmetric triangular reflector and a spatial light modulator; the The asymmetric triangular reflector and the spatial light modulator are oppositely arranged and placed inside the sealing box; the sealing box is provided with a light entrance hole and a light exit hole; the incident light passes through the light entrance hole, the asymmetric triangular reflector and the spatial light modulation in sequence. and the asymmetric triangular reflector, and then exit from the light exit hole.

The positional relationship between the asymmetric triangular reflector and the spatial light modulator satisfies: d2≥d1;

in:

d1 is the vertical distance from the intersection of the incident light incident to the spatial light modulator and the outgoing light modulated by the spatial light modulator to the spatial light modulator;

d2 is the vertical distance from the vertex of the asymmetric triangular reflector to the spatial light modulator.

The relationship between the vertex angle α of the asymmetric triangular reflector and the exit angle β of the laser beam modulated by the spatial light modulator is: α=90°+β/2.

The above-mentioned asymmetric triangular reflector includes a first reflection waist surface and a second reflection waist surface connected with the first reflection waist surface; the incident light sequentially passes through the light entrance hole, the first reflection waist surface, the spatial light modulator and the second reflection waist surface The apex of the asymmetric triangular reflector is the connection point of the first reflection surface and the second reflection surface.

The angle between the first reflection waist surface and the axis of the sealing box is 45°; the angle between the second reflection waist surface and the axis of the sealing box is γ, where γ=45°+β/2.

The apex angle α of the asymmetric triangular reflector is 93°˜95°, and the included angle γ between the second reflection waist surface and the axis of the sealing box is 48°˜50°.

The first reflection waist surface and the second reflection waist surface are both coated with a high reflection film.

The light incident hole and the light exit hole are concentric.

The above-mentioned coupling device for the spatial light modulator without zero-order diffracted light further comprises a threaded hole arranged on the sealing box.

The above-mentioned threaded holes are evenly distributed in the circumferential direction of the light incident hole and/or the circumferential direction of the light exit hole with the connection line between the light incident hole and the light exit hole as the center.

The advantages of the present invention are:

The invention provides a spatial light modulator coupling device without zero-order diffracted light, comprising a sealed box, an asymmetric triangular reflector and a spatial light modulator; the asymmetric triangular reflector and the spatial light modulator are oppositely arranged and placed in a sealed box Inside the box; a light entrance hole and a light exit hole are arranged on the sealed box; the incident light passes through the light entrance hole, the asymmetric triangular reflector, the spatial light modulator and the asymmetric triangular reflector in sequence and then exits from the light exit hole. The two sides of the sealed box are provided with light-passing holes through which the incident light and the outgoing light pass; the asymmetric triangular reflector is arranged on the incident light path and the outgoing light path of the spatial light modulator for coupling the incident light and the outgoing light. The asymmetric triangular reflector The surfaces of the two asymmetric surfaces are coated with a highly reflective film. The invention simultaneously realizes the vertical incidence of the laser beam and the small-angle exit of the modulated beam, suppresses the zero-order beam without a spatial filter, and solves the problems of discrete components, system instability, etc. Problems such as difficulty in suppressing zero-order beams. Under the premise of high-efficiency coupling of input and output laser beams, the invention avoids the interference of zero-order beams, greatly compresses the space occupied by the optical path of the spatial light field control, makes the entire space light field control device miniaturized and compact, and greatly reduces the The volume and weight of the whole machine is very beneficial to the modularization and instrumentation of the system.

The invention utilizes the asymmetric triangular reflector to realize the vertical incidence of the laser beam into the spatial light modulator and the small angle output of the modulated light; the asymmetric triangular reflector realizes the suppression of the zero-order beam that is not modulated by the spatial light modulator; It can guide and separate the incident light and the outgoing light in the smallest distance; the reflective spatial light field control module based on the coupled beam of the asymmetric triangular reflector has high light energy utilization and wide-band applicability, and is suitable for the visible light band to the mid-infrared wavelength. The light source within the range greatly expands the scope of application of the spatial light field control module. The incident light and the outgoing light of the present invention are parallel, which is very beneficial to the adjustment of the optical path of the system and the continuous expansion of functions. The present invention can be widely used in all spatial light field control systems using reflective spatial light modulators, such as optical tweezers systems, structured illumination microscopy systems, optical information processing and storage systems, and the like. In the present invention, the sealed box can block diffracted light of various orders generated after the laser beam is modulated by the SLM. In addition, the sealed airtight box helps to isolate the dust and avoid the lowering of the damage threshold caused by the SLM adsorbing too much dust, thereby effectively protecting the SLM. The present invention can set different apex angle α and waist surface 22 angle γ of the asymmetric triangular reflector, meet the requirements of vertical incidence of laser beam and small angle output of modulated light, and improve the accuracy of light field regulation.

Description of drawings

Fig. 1 is the schematic diagram of the normal incidence mode of the spatial light modulator SLM in the optical system;

Fig. 2 is the schematic diagram of the small-angle incident mode of the spatial light modulator SLM in the optical system;

3 is a schematic diagram of a zero-order light blocking scheme in a small-angle incident mode;

Fig. 4 is the principle schematic diagram of the spatial light modulator coupling device without zero-order diffracted light provided by the present invention;

FIG. 5 is a schematic structural diagram of using a plurality of spatial light modulators in series;

FIG. 6 is a schematic structural diagram of a preferred embodiment of a coupling device for spatial light modulator without zero-order diffracted light provided by the present invention.

Reference number:

1-spatial light modulator; 2-asymmetric triangular reflector; 3-sealed box; 21-first reflection waist; 22-second reflection waist; 31-light entrance hole; 32-light exit hole.

Detailed ways

The content of the present invention is described in further detail below in conjunction with the accompanying drawings and specific embodiments:

As shown in FIG. 4 , the present invention provides a spatial light modulator coupling device without zero-order diffracted light, comprising a sealed box 3 , an asymmetric triangular reflector 2 and a spatial light modulator 1 ; the asymmetric triangular reflector 2 and The spatial light modulator 1 is oppositely arranged and placed inside the sealing box 3; the sealing box 3 is provided with a light entrance hole 31 and a light exit hole 32; the incident light sequentially passes through the light entrance hole 31, the asymmetric triangular reflector 2, and the spatial light modulator 1 and the asymmetric triangular reflector 2 are then emitted from the light exit hole 32 .

The positional relationship between the asymmetric triangular reflector 2 and the spatial light modulator 1 satisfies: d2≥d1;

in:

d1 is the vertical distance from the intersection of the incident light incident to the spatial light modulator 1 and the outgoing light modulated by the spatial light modulator 1 to the spatial light modulator 1 (that is, d1 is the two beams when the incident light and the outgoing light are just separated. the vertical distance from the separation point to the SLM);

d2 is the vertical distance from the vertex of the asymmetric triangular reflector 2 to the spatial light modulator 1 .

The relationship between the vertex angle α of the asymmetric triangular reflector 2 and the exit angle β of the laser beam modulated by the spatial light modulator 1 is: α=90°+β/2.

The asymmetric triangular reflector 2 includes a first reflection waist surface 21 and a second reflection waist surface 22 connected with the first reflection waist surface 21; the incident light passes through the light entrance hole 31, the first reflection waist surface 21, and the spatial light modulator in sequence. 1 and the second reflection waist surface 22 are then emitted from the light exit hole 32; the vertex of the asymmetric triangular reflector 2 is the connection point of the first reflection surface and the second reflection surface.

The included angle between the first reflection waist surface 21 and the axis of the sealing box 3 is 45°; the included angle between the second reflection waist surface 22 and the axis of the sealing box 3 is γ, γ=45°+β/2. The vertex angle α of the asymmetric triangular reflector 2 is 93°˜95°, and the included angle γ between the second reflection waist surface 22 and the axis of the sealing box 3 is 48°˜50°. Both the first reflection waist surface 21 and the second reflection waist surface 22 are coated with a high reflection film. The light entrance hole 31 and the light exit hole 32 are concentric.

The coupling device of the spatial light modulator without zero-order diffracted light also includes threaded holes arranged on the sealing box, and the threaded holes are evenly distributed in the circumferential direction of the light incident hole 31 and the light incident hole 31 with the connection line between the light incident hole 31 and the light exit hole 32 as the center. /Or in the circumferential direction of the light exit hole 32, the arrangement of the threaded hole can facilitate docking with other optical components.

The surfaces of the two waist surfaces of the asymmetric triangular reflector 2 used in the present invention are coated with high-reflection films, and the two sides of the sealing box 3 close to the two waist surfaces of the asymmetric triangular reflector 2 are respectively provided with light-transmitting holes as the whole space light The input end and output end of the field, namely the light entrance hole 31 and the light exit hole 32 of the sealing box 3, the light entrance hole 31 and the light exit hole 32 are arranged concentrically; the asymmetric triangular reflector 2 and the spatial light modulator 1 are adjusted in position and distance It is fixed in the sealed box 3, and the specific position is set so that the two waist surfaces of the asymmetric triangular reflector 2 are arranged on the incident light path and the outgoing light path of the spatial light modulator 1 for coupling the incident light and the outgoing light.

The angle between the first reflection waist surface 21 and the horizontal line NN' is 45°, and the angle at which the laser beam perpendicular to the horizontal line NN' is reflected on the spatial light modulator after being reflected by the first reflection waist surface 21 is 0°, that is, the vertical incidence angle is 0°. ; the angle γ between the second reflection waist surface 22 and the horizontal line NN' and the outgoing angle β of the laser beam after the laser beam is modulated by the spatial light modulator satisfy the relationship γ=45°+β/2; The vertex angle α and the outgoing angle β of the laser beam modulated by the spatial light modulator satisfy the relational expression α=90°+β/2.

The two asymmetric waist surfaces of the asymmetric triangular reflector 2 are both silver-plated reflecting surfaces. The incident light A is reflected by the first reflecting waist surface 21 and then vertically irradiated onto the spatial light modulator 1 (SLM) to be modulated, and the modulated light is irradiated. to the second reflection girdle 22 and reflected out. From the geometric relationship, if the incident light is perpendicular to the centerline NN' of the asymmetric triangular reflector 2 and the spatial light modulator 1, the laser beam will be vertically incident on the spatial light modulator 1 after being reflected by the first reflection waist surface 21. On the liquid crystal panel, the laser beam modulated by the spatial light modulator loaded with the blazed grating phase hologram emerges at a small angle β, and is finally reflected by the second reflection waist surface 22, and finally the outgoing light B and the incident light A are obtained. parallel. The zero-order light beam C that is not modulated due to the grid structure of the spatial light modulator will return to the first reflection waist surface 21 along the original path, and finally exit through the hole 31 to achieve separation from the exit light B. The angle γ between the second reflection waist surface 22 and the horizontal line NN' and the exit angle β of the laser beam modulated by the spatial light modulator satisfy the relationship γ=45°+β/2; the vertex angle α of the asymmetric triangular reflector 2 The outgoing angle β of the laser beam modulated by the spatial light modulator satisfies the relational expression α=90°+β/2. In order to satisfy the small angle output of the modulated laser beam from 6° to 10°, the value range of γ is 48° to 50°, and the value range of α is 93° to 95°. Place the vertex of the asymmetric triangular reflector 2 as far as possible where the incident light and the outgoing light are just separated (the O point in Figure 3, that is, d2=d1), which can greatly reduce the propagation distance of the laser beam and compress the system space.

The vertex angle of the asymmetric triangular reflector 2 can be designed as α=93°, then the incident angle of the incident light irradiating the spatial light modulator SLM is 0°, and the exit angle of the laser beam modulated by the spatial light modulator SLM is 6° °. If the diameter D of the incident light spot is 10mm, the minimum distance that the incident light and the outgoing light are completely separated is d1=D/tan(β)=8/tan(6°)≈95.1mm. Considering the processing accuracy of the vertex angle of the asymmetric triangular reflector 2, the actual distance d2 from the asymmetric triangular reflector 2 to the SLM liquid crystal panel can be set as 100 mm. The incident light and the outgoing light are parallel, which is very beneficial to the adjustment of the optical path of the system and the continuous expansion of functions.

In the present invention, the asymmetric triangular reflector 2 and the spatial light modulator SLM are installed in the sealed box 3 to form a modular compact spatial light field control device, which can effectively reduce the quality of the spatial light field control device and improve the system quality. Device transfer is easy, while modular devices facilitate instrumentation and commoditization of the system. Through such a design, the entire spatial light field control module has very good compatibility and scalability, and can be easily combined with other optical systems; the compact design is also conducive to the application of spatial light field control technology in special fields, such as Space experiments that have extremely high requirements on system quality and stability.

As shown in FIG. 5 , when multiple spatial light modulators 1 need to be connected in series for simultaneous modulation of the amplitude, phase and polarization state of the optical field, the present invention can simply and quickly connect multiple spatial light modulators 1 in series (through the relay system (For example, the 4f system is common knowledge.) The device of the present invention (including the spatial light modulator 1) is connected in series) in one optical system to avoid system redundancy and confusion caused by the series connection of multiple spatial light modulators 1. Also, the added system complexity of the use of multiple spatial filters is avoided.

As shown in Figure 6, the PLUTO series spatial light modulator 1 and 93° asymmetric triangular reflector 2 (bottom: 52.8mm×25mm, height: 25mm) of the German HoloEYE company are installed in a small sealed box 3 (143mm×76mm×48mm), two clear holes are 1.035 inch-40 SM1 threads, and four 8×4-40UNC threaded holes are set at the center of the clear holes. The threaded holes can be easily connected with other optical elements. Device docking, such as for use with a 30mm cage system. The sealing box 3 can seal the whole device from dust and diffracted light spots.

Claims (9)

1. A spatial light modulator coupling device without zero-order diffracted light, characterized in that: the spatial light modulator coupling device without zero-order diffracted light comprises a sealed box (3), an asymmetric triangular reflector (2) and a spatial light modulator (1); the asymmetric triangular reflector (2) and the spatial light modulator (1) are oppositely arranged and placed inside the sealing box (3); The light hole (31) and the light exit hole (32); the incident light sequentially passes through the light entrance hole (31), the asymmetric triangular reflector (2), the spatial light modulator (1) and the asymmetric triangular reflector (2), The light exit hole (32) emits light; the asymmetric triangular reflector (2) includes a first reflection waist surface (21) and a second reflection waist surface (22) connected with the first reflection waist surface (21); the third reflection waist surface (22) The included angle between a reflection waist surface (21) and the axis of the sealing box (3) is 45°, the included angle between the second reflection waist surface (22) and the axis of the sealing box (3) is γ, the γ=45°+β/2. 2 . The spatial light modulator coupling device without zero-order diffracted light according to claim 1 , wherein the positional relationship between the asymmetric triangular reflector (2) and the spatial light modulator (1) satisfies: d2 . ≥d1; in: d1 is the vertical distance from the intersection of the incident light incident to the spatial light modulator (1) and the outgoing light modulated by the spatial light modulator (1) to the spatial light modulator (1); d2 is the vertical distance from the vertex of the asymmetric triangular reflector (2) to the spatial light modulator (1). 3 . The spatial light modulator coupling device without zero-order diffracted light according to claim 2 , wherein the vertex angle α of the asymmetric triangular reflector ( 2 ) is modulated by the spatial light modulator ( 1 ). 4 . The relationship between the exit angle β of the laser beam afterward is: α=90°+β/2. 4. The coupling device for a spatial light modulator without zero-order diffracted light according to claim 3, wherein the incident light passes through the light entrance hole (31), the first reflection waist (21), and the spatial light modulator in sequence. (1) and the second reflection waist surface (22) are emitted from the light exit hole (32); the vertex of the asymmetric triangular reflector (2) is the connection point of the first reflection surface and the second reflection surface. 5 . The spatial light modulator coupling device without zero-order diffracted light according to claim 4 , wherein the vertex angle α of the asymmetric triangular reflector ( 2 ) is 93° to 95°, and the first The included angle γ between the second reflection waist surface (22) and the axis of the sealing box (3) is 48°~50°. 6 . The spatial light modulator coupling device without zero-order diffracted light according to claim 5 , wherein the first reflection girdle ( 21 ) and the second reflection girdle ( 22 ) are both coated with high reflection membrane. 7 . The spatial light modulator coupling device without zero-order diffracted light according to any one of claims 1 to 6 , wherein the light entrance hole ( 31 ) and the light exit hole ( 32 ) are concentric. 8 . 8 . The zero-order diffracted light-free spatial light modulator coupling device according to claim 7 , wherein the zero-order diffracted light-free spatial light modulator coupling device further comprises a threaded hole provided on the sealing box. 9 . . 9 . The spatial light modulator coupling device without zero-order diffracted light according to claim 8 , wherein the threaded holes are evenly distributed around the connection line between the light entrance hole ( 31 ) and the light exit hole ( 32 ) as the center. 10 . in the circumferential direction of the light incident hole (31) and/or the circumferential direction of the light exit hole (32).

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