Manufacturing process for a spiral phase plate to influence optical signals

Abstract

Manufacturing process of a spiral phase plate for influencing optical signals, characterized in that by ablation with homogenized laser radiation (8) of at least one laser (1) by means of - two disk-shaped and circular masks (2, 3) arranged one after the other in the laser radiation (8) in the beam direction, rotatable in the axis of the laser radiation (8) in connection with a drive (4, 5) connected to a control device (7), each with at least one cutout with at least one curved edge and / or at least one opening (10) with at least one curved edge, - a third mask arranged in the laser radiation (8) in the beam direction of the laser (1) after the two masks (2, 3) as first mask (2) and second mask (3) and - an imaging optical device located in the beam direction of the laser (1) after the masks (2, 3) provides at least one depression in a body (6) such that the bottom of the depression has at least one groove, at least one step, at least one flat surface, at least one spherical surface, at least one free-formed surface or a combination thereof and the diameter of the depression is limited or the edge geometry of the depression is influenced by means of the third mask.

Description

[0001] The invention relates to a manufacturing process for a spiral phase plate for influencing optical signals.

[0002] One method for increasing the data transmission rate is so-called OAM (Orbital Angular Momentum) multiplexing, which uses OAM modulators. For example, patent EP 3 188 382 A1 discloses an optical switching device, an optical crossing node, and an optical signal switching method that use OAM modulators in the form of spatial light modulators. These can be based on liquid crystal silicon technology to modulate the spatial phase distribution of an incident optical signal. Other technologies include a thin-film hologram technology and a special prism technology, which are only named as such.

[0003] German publication DE 689 17 998 T2 discloses a device for laser corneal reshaping, wherein several disc-shaped and circular masks, each with multiple openings, are arranged successively in the direction of the laser beam and rotatable in the direction of the laser radiation. The device creates a depression whose base can have a cross-sectional combination of a groove, a step, a flat surface, a spherical surface, or a free-form surface.

[0004] The publication EP 2 327 503 A1 discloses a method and a device for structuring a solid surface coated with a hard material using lasers. The surface being processed is, in particular, the surface of an embossing tool. Specifically, an aperture and a mask can be used, which are arranged sequentially in the laser beam.

[0005] Publication WO 2009 / 012 789 A1 relates to a device consisting of a pair of specially designed plate-shaped diffracting optical elements arranged sequentially parallel to each other. An arrangement at a specific distance can, for example, function as a lens, axicon, phase shifter, or spiral phase plate. A spiral phase plate can have a recess which may exhibit at least one curvature in cross-section.

[0006] The invention specified in claim 1 is based on the objective of designing a manufacturing process in such a way that at least one depression with a definable structure can be introduced into a body for influencing optical signals by ablation with laser radiation from at least one laser.

[0007] This problem is solved by the features listed in claim 1.

[0008] The manufacturing process of a spiral phase plate for influencing optical signals, wherein a depression is created by ablation with laser radiation from at least one laser, is characterized in particular by the fact that the at least one depression can be created with a specific structure.

[0009] This is achieved by ablation with homogenized laser radiation from at least one laser using -two disc-shaped and circular masks arranged one after the other in the laser beam direction, rotatable in the axis of the laser beam in conjunction with a drive connected to a control device, each with at least one cutout with at least one curved edge and / or at least one opening with at least one curved edge, -a third mask arranged in the laser radiation in the direction of the laser beam after the two masks as first mask and second mask and -an imaging optical device located downstream of the masks in the direction of the laser beam at least one depression is thus introduced into a body, that the bottom of the depression has at least one groove, at least one step, at least one flat surface, at least one spherical surface, at least one free-formed surface or a combination thereof, and that the diameter of the depression is limited or the edge geometry of the depression is influenced by means of the third mask.

[0010] The opening or cutout can, for example, be in the shape of a circular sector with at least one straight line connecting the circular arc, one curve connecting the circular arc, or a combination thereof.

[0011] The body thus produced has a depression with a bottom that, in cross-section, has a groove, a step, a curve, or a straight line, each individually, multiple times, or in a combination thereof. The depression is therefore a depression created by means of the laser radiation of the laser using at least two disk-shaped and circular masks arranged successively in the laser beam direction, rotatable on the axis of the laser radiation, each with at least one cutout and / or at least one opening.

[0012] The manufacturing process is based on two masks, the first and second masks, positioned within the laser beam. By introducing two independently rotatable masks (apertures) into the laser beam, it can be precisely shaped. Material is ablated from the surface of the object according to the geometry of the laser beam. For example, two semicircular masks, positioned one above the other at a right angle, together form a resulting mask in the shape of a circular sector. The opening angle of this sector can be influenced by rotating one of the two masks. This allows structures similar to a spiral staircase or several intertwined spiral staircases to be incorporated into optical materials.

[0013] The manufacturing process is advantageously characterized by the fact that, through rotation and possible relative movement of two masks, a mask projection method for direct laser structuring is provided. This allows for the fabrication of spiral phase plates with feature sizes in the millimeter and micrometer range. The process enables both the simple fabrication of regularly segmented microspiral phase plates and the fabrication of microspiral phase plates with irregular configurations. Furthermore, lenses, Fresnel lenses, or Fresnel zone plates can also be fabricated and thus realized.

[0014] The use of spiral phase plates represents a method for increasing data transmission rates, known as OAM (Orbital Angular Momentum) multiplexing. The light transmitting the data is imprinted with a spiral phase distribution and thus an orbital torque. Individual phase modulation leads to an individual orbital torque and can therefore be used to separate transmission channels. This setup extends the direct laser microstructuring process, particularly excimer laser microstructuring, based on the mask projection method, to enable the fabrication of spiral phase plates (SPPs) with such an individual configuration (topological batch / number of steps / modulation depth / regular and irregular division).Another advantage is that structures can be manufactured in such a way that they can also have a focusing effect. The configuration of the spiral phase plates can be controlled via the process parameters and process control, so that even irregular spiral phase plates can be produced.

[0015] The structuring process is based on mask projection technology. Using a pulsed excimer laser, a specific amount of material is ablated with each laser pulse, depending on the laser and material parameters. Homogenizing the laser beam ensures that the laser pulse fluence is distributed homogeneously across the entire mask area and thus also in the image plane of the imaging system. Therefore, the ablation depth is uniform throughout the entire ablation area. This area is defined by the mask geometry. In general, the depth of the microstructures depends on the laser pulse fluence and the number of pulses per area. A helical phase shift can be generated by manipulating the optical thickness of a transparent material. The microstructure required for this is comparable to a spiral staircase.The fabrication of these three-dimensional microstructures requires precise control of the structuring depth within the ablation area, particularly in the direction of rotation. This can be achieved by combining two semicircular masks arranged in a row. Both masks can be rotated independently by separate drives.

[0016] Advantageous embodiments of the invention are specified in claims 2 and 3.

[0017] The body can be an optical body made of plastic or glass, or it can be a crystal.

[0018] The body can have at least two depressions with identical or differently shaped bottoms.

[0019] An embodiment of the invention is shown in principle in the drawings and is described in more detail below.

[0020] They show: Fig. 1. A device for introducing at least one depression into a body for influencing optical signals, Fig. 2 a mask with an opening in the shape of a circular segment, Fig. 3 a mask with an opening in the form of a circular segment with a curve connecting the circular arc and Fig. 4 two masks and a converging lens in the laser beam as well as an image of the resulting mask geometry on a body surface.

[0021] In the following exemplary embodiment, a method and a device for introducing at least one depression into a body for influencing optical signals by ablation with laser radiation from at least one laser are explained in more detail.

[0022] A device for introducing at least one depression in a body 6 for influencing optical signals by ablation with laser radiation 8 of at least one laser 1 consists essentially of the laser 1, two masks 2, 3 in the form of a first mask 2 and a second mask 3, drives 4, 5 in the form of a first drive 4 and a second drive 5 and a control device 7.

[0023] The Fig. Figure 1 shows a device for introducing at least one depression into a body 7 for influencing optical signals in a schematic representation.

[0024] In the direction of the laser beam 8 of the laser 1, the first mask 2 and the second mask 3 are arranged sequentially so as to be rotatable along the axis of the laser beam 8. Furthermore, the first mask 2 is connected to the first drive 4 and the second mask 3 to the second drive 5. The drives 4 and 5 are connected to the control unit 7, which is primarily a data processing system. This allows the masks 2 and 3 to be rotated together or independently of each other. For processing, the workpiece 6 is located on a carrier. This carrier is connected to a positioning device 9, enabling rotation and / or movement in the x and y directions. The positioning device has a drive mechanism for these movements, which is connected to the control unit 7.

[0025] They show the Fig. 2 a mask 2, 3 with an opening 10 in the form of a circular segment and the Fig. 3 a mask 2, 3 with an opening 10 of a circular sector with a curve connecting the circular arc, each in a principal representation.

[0026] The masks 2 and 3 are circular discs, each having at least one opening 10 in the form of a circular sector. The circular sector can also include a chord in the form of a straight line (representation in the Fig. 2) or a curvature (representation in the Fig. 3) possess. With an arrangement of such masks 2, 3, a rotationally symmetrical recess can be created in the body 6. In one embodiment, a third mask can be arranged in the laser beam 8 in the beam direction of the laser 1 after the two masks 2, 3 as the first mask 2 and second mask 3, to limit the diameter or influence the edge geometry of the recess.

[0027] The Fig.Figure 4 shows two masks 2, 3 and a converging lens 11 in the laser beam as well as an illustration of the resulting mask geometry on the body 6 in a schematic representation.

[0028] In one embodiment, the laser radiation 8 of the laser 1 can in particular be a homogenized laser radiation 8 of the laser 1. In the beam direction of the laser 1 after the masks 2, 3, there is an imaging optical device in the form of a converging lens 11. This projects the geometry of the masks 2, 3 onto the body 6 and forms the depression.

[0029] With this device, depressions can be created by ablation using laser radiation 8 from laser 1 through microstructuring; these depressions can be rotationally symmetrical. The depression with the microstructure created in the body 6 by ablation with laser radiation 8 from laser 1 serves to influence optical signals. The microstructuring process used for this purpose is based on the technique of mask projection. By using, for example, a pulsed excimer laser system as laser 1, a specific amount of material is ablated with each laser pulse, depending on the laser and material parameters. By homogenizing the laser beam, the laser pulse fluence is distributed homogeneously throughout the entire mask area and thus also in the image plane of the imaging system. Therefore, the ablation depth is the same throughout the entire ablation area. This area is defined by the mask geometry.In general, the depth of the microstructures depends on the laser pulse fluence and the number of pulses per region. Generating a helical phase shift of an optical signal, for example, can be achieved by manipulating the optical thickness of a transparent material. The structure required for this is comparable to a spiral staircase. Fabricating these three-dimensional microstructures requires controlling the microstructuring depth within the ablation area, and especially in the rotational direction of masks 2 and 3. The microstructuring process begins with the calculation of the step angle and the sector angle. The latter defines the number of phase shifts in the modulated optical signal. Furthermore, the number of planes defines the step angle. Masks 2 and 3 are in a congruent position after system referencing. Subsequently, one of the masks 2 and 3 is rotated relative to the other until the sector angle is reached.This position is the starting state for the microstructuring of each sector, regardless of the sector angle. From this starting state, the sector angle is reduced by the step angle after each laser pulse. This process is repeated until the required number of steps is reached. In this way, for example, a spiral phase plate can be created.

[0030] In a body 6 for influencing optical signals, having at least one depression created by ablation with laser radiation 8 of at least one laser 1, the bottom of the depression has a groove, a step, a curve, or a straight line in cross-section, each individually, multiple times, or in a combination thereof. The bottom of the depression can thus have at least one groove in the form of a spiral or grooves in the form of spirally arranged parts. Furthermore, the bottom of the depression can be configured as a screw and / or with helically shaped parts. Additionally, at least one region of a surface of the spiral, the helical parts, the screw, or the helical parts can have a curve and / or a plane in cross-section. The body 6 can thus also have at least two depressions with identical or differently shaped bottoms.

[0031] Body 6 can be made of plastic, glass, or crystal.

Claims

[1] Manufacturing process of a spiral phase plate for influencing optical signals, characterized by , that by ablation with homogenized laser radiation (8) of at least one laser (1) by means of - two disk-shaped and circular masks (2, 3) arranged one after the other in the laser radiation (8) in the beam direction, rotatable in the axis of the laser radiation (8) in connection with a drive (4, 5) connected to a control device (7), each with at least one cutout with at least one curved edge and / or at least one opening (10) with at least one curved edge, - a third mask arranged in the laser radiation (8) in the beam direction of the laser (1) after the two masks (2, 3) as first mask (2) and second mask (3) and - an imaging optical device located in the beam direction of the laser (1) after the masks (2, 3) provides at least one depression in a body (6) such that the bottom of the depression has at least one groove, at least one step, at least one flat surface, at least one spherical surface, at least one free-formed surface or a combination thereof and the diameter of the depression is limited or the edge geometry of the depression is influenced by means of the third mask. [2] Method according to claim 1, characterized by that the body (6) is made of plastic or glass or that the body (6) is a crystal. [3] Method according to claim 1, characterized by , that at least two depressions with identical or differently shaped bottoms are provided in the body (6).

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