Diffractive optical element

Abstract

Diffractive optical element The invention relates to smart diffractive elements, namely diffraction gratings and 2D photonic crystals, which optical response can be modified externally via applied magnetic field. This is achieved by magnetic shape memory effect of the used materials. The magnetic shape memory materials serve directly as building blocks in which the diffraction element is fabricated, or as substrates. This innovative approach allows the fabrication of wirelessly programable smart optical elements, which can function in temperature unstable environment, for applications in novel optical systems for computer logic, display technology, sensors of magnetic field, etc.

Description

[0001] Diffractive optical element

[0002] Field of the invention

[0003] The invention relates to the diffractive optical elements which optical response, in terms of their diffraction, reflectance, transmittance or spectral dispersion, can be changed and controlled externally utilizing external magnetic field and magnetic shape memory materials.

[0004] Background of the invention

[0005] The advancement of optical technology has given rise to the need for smart optical components or micro-optical devices, exemplified by smart diffractive elements (SDEs), such as gratings or 2D photonic crystals, in the evolution of next-generation optical devices. These devices can be dynamically tuned through external excitation to achieve the beam splitting of incident light. This is due to the change in the periodicity and lateral geometry of the element, which modifies the necessary diffraction conditions for constructive and destructive optical interference. The exceptional adjustable performance of SDEs is largely attributed to the widespread use of liquid crystal materials in their construction as stated in the document with the reference doi:10.1002 / adma.201606000. The flexible diffraction grating, constructed with liquid crystal materials, effectively accomplishes the task of switching the grating structures. However, owing to constraints in the tensile properties of the liquid crystal material, modulation of the period of the diffraction grating is typically unattainable.

[0006] Active or smart materials are substances capable of altering their properties when subjected to physical disturbances. This promises a playground for dynamic control of lateral geometries of diffractive optical elements making them smart. However, the applicability of many of these materials is limited due to their stimulation constrains. Shape-memory materials (SMMs), including alloys and polymers, are materials responsive to stimuli, capable of automatically reacting to changes in the surrounding environment in a predetermined fashion. These materials can be temporarily deformed and fixed into an arbitrary shape, subsequently regaining their permanent shape when exposed to stimuli, including heat, light, and pH. A novel diffractive optical element based on shape-memory polymers started to appear recently, utilizing thermally induced shape memory effect, as stated in the document with the reference doi: 10.1002 / marc.202100863 or 10.1021 / acsami.2cl8901. Nevertheless, such approach requires the external source of heat, resulting in the wired technical solution. Moreover, such element can function only in temperature stabilized environment, which significantly narrows its application potential.

[0007] Similar to traditional SMMs, magnetic shape memory materials (MSMMs), including alloys known from following document: US 10,290,405B2 and polymers, undergo a significant and reversible shape change linked to a structural reorientation in magnetic field. However, unlike conventional SMMs, which rely on temperature or voltage as the control parameter, MSMMs are influenced by a magnetic field.

[0008] MSMMs boast advantages such as not requiring lubrication and being operational at cryogenic temperatures. This capability enables them to function effectively in environments like outer space for millions of cycles.

[0009] As a result, MSMMs have garnered attention in contemporary automation dominated by micro-actuators and micro-sensors, known from the following documents: US 10,581,345B2. They outperform current active materials used in precision actuators by offering lower stiffness, higher bandwidth, increased accuracy, and reduced power requirements compared to alternative materials. This demonstrates that MSMM technology holds the potential for the fabrication of SDEs. The object of the invention is to provide a smart diffraction element with the ability to dynamically and reversibly change their optical response, in terms of diffraction pattern, reflective, transmissive and spectral properties externally and wirelessly via magnetic shape memory effect.

[0010] Summary of the invention

[0011] The object is achieved by design and fabrication of diffractive optical element from magnetic shape memory material or to use magnetic shape memory material as a substrate for optical diffractive layer.

[0012] The invention herein disclosed is a diffractive optical element that changes its shape under applied external magnetic field based on the magnetic shape memory effect.

[0013] This invention herein disclosed relies on the fact that a change in the shape of optical diffractive element modifies the lateral geometry of diffractive pattern. This changes the conditions for destructive and constructive interference, resulting in the change of optical response of the device. The diffractive pattern of the element can be simple, such as simple diffraction grating, or complex, such as 2D photonic crystal.

[0014] The core of the invention is based on the fact that the magnetic shape memory material can change its shape under applied external magnetic field. This changes the lateral geometry of the diffraction element resulting in the changes of diffraction properties. Such approach has dual advantage. Firstly, the system can be controlled wirelessly on medium distances, and secondly, after the shape change the external magnetic field is no longer necessary to maintain this change. This provides a low power consumption device comparing to other approaches for variable diffractive optical elements, such as piezoelectric effect. Moreover, the change is reversible by the application of external magnetic field in opposite direction. In the preferred embodiment of the diffractive element based on the invention, the magnetic shape memory material is used as a substrate for a diffraction granting or 2D photonic crystal. A standard methods of deposition is utilized to deposit a granting material on top of the magnetic shape memory substrate. Afterwards the lithographic or ruling and indenting techniques is used to create diffraction pattern with lateral geometry. The changes in diffraction properties are achieved by deformation of the lateral geometry transferred from magnetic shape memory substrate to the grating structure on top.

[0015] In the preferred embodiment of the diffractive element based on the invention, the diffractive pattern of diffraction grating or 2D photonic crystal will be directly created in the magnetic shape material itself via lithographic, ruling or indenting techniques. The change of the lateral geometry will be induced directly through the change in the shape of magnetic shape memory material.

[0016] In the preferred embodiment of the diffractive element based on the invention a magnetic shape memory material used for the fabrication is from group Ni-Mn-Ga, Ni-Mn-Ga-X, Ni-Mn- Ga-X-Y, Ni-Mn-Ga-X-Y-Z, where the substituents X, Y and Z are the impurities from the group of chemical elements Fe, Cu, Co, Ti, V, Cr, Nb, W, Ta, Zn, In, Sn, B, or magnetic shape memory polymers composed of two types of magnetic particles Fe3O4 or NdFeB.

[0017] In the preferred embodiment of the diffractive element based on the invention the diffraction grating structure can have rectangular, sinusoidal, or blazed profile.

[0018] It should also be noted that preferred embodiments of the present invention may include coatings to increase optical reflectivity of diffractive elements. While the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the inventions and claims. Explanation of drawings

[0019] The present invention is explained in detail by means of the following figures where:

[0020] Fig. 1 shows a cross-sectional side view of a blazed diffraction grating made of magnetic shape memory material and the schematical light diffraction with no applied magnetic field,

[0021] Fig. 2 shows a cross-sectional side view of deformed blazed diffraction grating made of magnetic shape memory material and the schematical light diffraction with applied external magnetic field,

[0022] Fig. 3 shows a cross-sectional side view of a blazed diffraction grating where the magnetic shape memory material is used as a substrate and the schematical light diffraction with no applied magnetic field,

[0023] Fig. 4 shows a cross-sectional side view of deformed blazed diffraction grating where the magnetic shape memory material is used as a substrate and the schematical light diffraction with applied external magnetic field,

[0024] Fig. 5 shows a side view of representative 2D photonic crystal made of magnetic shape memory material and the schematical light diffraction with no applied magnetic field,

[0025] Fig. 6 shows a side view of deformed representative 2D photonic crystal made of magnetic shape memory material and the schematical light diffraction with applied external magnetic field,

[0026] Fig. 7 shows a side view of representative 2D photonic crystal where the magnetic shape memory material is used as a substrate and the schematical light diffraction with no applied magnetic field, Fig. 8 shows a side view of deformed representative 2D photonic crystal where the magnetic shape memory material is used as a substrate and the schematical light diffraction with applied external magnetic field.

[0027] Examples of the invention embodiments

[0028] It shall be understood that the specific cases of the invention embodiments described and depicted below are provided for illustration only and do not limit the invention to the examples provided here. Those skilled in the art will find or, based on routine experiment, will be able to provide a greater or lesser number of equivalents to the specific embodiments of the invention which are described here.

[0029] Example 1

[0030] The diffractive element shown in Fig 1 will be used as a dispersive element in spectrograph to broaden their effective detection spectral range in following steps: a) a blazed diffraction grating made from magnetic shape memory material 1 with the blazed angle for certain wavelength is placed in the monochromator and provides a certain diffraction pattern 3 of incident light beam 2. b) when the external field 5 is applied, the blazed angle of the grating 4 is changed due to the magnetic shape memory effect as shown if Fig. 2. This causes changed diffraction pattern 7 of the incident beam 6. The central diffraction wavelength is changed resulting in the shift of grating efficiency region, which will effectively broaden the effective spectral region of the monochromator. c) when the direction of the external magnetic field is reversed, the grating will come to the original shape with original diffraction properties.

[0031] The magnetic shape memory material has a composition of Ni-Mn-Ga. Example 2

[0032] The difference from Example 1 is the use of a magnetic shape memory material as a substrate 8, for diffractive geometry layer 9, which are deformed by magnetic shape memory effect 12, 13 and changing diffracted light 11, 16 of incident beam 10, 15, as illustrated in Fig. 3 and Fig. 4.

[0033] The magnetic shape memory material has a composition of Ni-Mn-Ga-Cu-Ti.

[0034] Example 3

[0035] A 2D photonic crystal made of a material with magnetic shape memory effect 17 with cylindrical hole lateral geometry 18 provides a light diffraction 20 of incident light beam 19. When the external magnetic field 22 is applied, the magnetic shape material is deformed by magnetic shape effect 21 resulting in deformed holes 23. This changes optical diffraction 25 of incident light beam 24, as illustrated in Fig. 5 and Fig 6. This procedure is fully reversable.

[0036] The magnetic shape memory material has a composition of polymer with magnetic particles NdFeB.

[0037] Example 4

[0038] The difference from Example 3 is the use of a magnetic shape memory material as a substrate 26 for 2D photonic crystal layer 27, which both become deformed 31, 32 after applied external magnetic field 33, which is changing the shape of the cylindrical holes 28, 34. This changes the optical diffraction 30, 36 of the incident light beam 29, 35 as illustrated in Fig. 7 and Fig. 8.

[0039] The magnetic shape memory material has a composition of polymer with magnetic particles Fe3O4. The above materials are not the only ones applicable. The skilled person will be able to routinely create materials meeting the composition from the group of materials Ni-Mn-Ga, Ni- Mn-Ga-X, Ni-Mn-Ga-X-Y, Ni-Mn-Ga-X-Y-Z, where the substituents X, Y and Z are the impurities from the group of chemical elements Fe, Cu, Co, Ti, V, Cr, Nb, W, Ta, Zn, In, Sn, B, or polymers with magnetic particles. The unifying property of all the possible materials is their magnetic shape memory.

[0040] Industrial applicability

[0041] Variable diffractive optical elements which optical properties can dynamically change and can be precisely controlled wirelessly by the application of external magnetic field will find their application in production of dispersive elements for spectrometers with broaden spectral efficiency, optical systems for computer logic where dynamic modulation of optical signal is required, display technology where spatial modulation of light beam is necessary, sensors of magnetic field, etc.

[0042] List of reference numerals

[0043] 1 blazed diffraction grating made from magnetic shape memory material without application of external magnetic field

[0044] 2 incident light beam

[0045] 3 diffracted light

[0046] 4 deformed blazed diffraction grating made from magnetic shape memory material after application of external magnetic field

[0047] 5 electromagnet coil generating external magnetic field

[0048] 6 incident light beam

[0049] 7 modified diffracted light

[0050] 8 substrate made from magnetic shape memory material

[0051] 9 blazed diffraction grating layer from different material than substrate without application of external magnetic field

[0052] 10 incident light beam

[0053] 11 diffracted light

[0054] 12 deformed blazed diffraction grating layer from different material than substrate after application of external magnetic field

[0055] 13 deformed substrate after application of external magnetic field

[0056] 14 electromagnet coil generating external magnetic field

[0057] 15 incident light beam

[0058] 16 modified diffracted light

[0059] 17 2D photonic crystal with cylindrical holes made from magnetic shape memory material without application of external magnetic field

[0060] 18 cylindrical hole

[0061] 19 incident light beam

[0062] 20 diffracted light

[0063] 21 deformed 2D photonic crystal made from magnetic shape memory material after application of external magnetic field electromagnet coil generating external magnetic field deformed cylindrical hole incident light beam modified diffracted light substrate made from magnetic shape memory material

[0064] 2D photonic crystal with cylindrical holes made in the layer from different material than substrate on top of the magnetic shape memory material substrate without application of external magnetic field cylindrical hole incident light beam diffracted light deformed substrate after application of external magnetic field deformed 2D photonic crystal with cylindrical holes made in the layer from different material than substrate on top of the magnetic shape memory material substrate after application of external magnetic field electromagnet coil generating external magnetic field deformed cylindrical hole incident light beam modified diffracted light

Claims

CLAIMS1. A diffractive optical element for optical response in the sense of optical diffraction, reflectance, transmission, spectral dispersion, comprising at least one optical diffractive layer with a diffractive pattern, and a substrate for supporting the optical diffractive layer, characterized in that, the substrate is of a magnetic shape memory material.

2. The diffractive optical element according to claim 1, characterized in that, the diffractive optical layer is of the magnetic shape memory material.

3. The diffractive optical element according to claim 1 or 2, characterized in that, the diffractive pattern of the diffractive optical layer is ID diffraction grating with sinusoidal, rectangular, or blazed profile.

4. The diffractive optical element according to claim 1 or 2, characterized in that, the diffractive pattern of the diffractive optical layer is 2D photonic crystal with square or triangular lattice of square shape or circular shape rods or holes.

5. The diffractive optical element according to any of claims 1 to 4, characterized in that, the magnetic shape memory material is with the composition from the group Ni-Mn-Ga, Ni- Mn-Ga-X, Ni-Mn-Ga-X-Y, Ni-Mn-Ga-X-Y-Z, where the substituents X, Y and Z are the impurities from the group of chemical elements Fe, Cu, Co, Ti, V, Cr, Nb, W, Ta, Zn, In, Sn, B.

6. The diffractive optical element according to any of claims 1 to 4, characterized in that, the magnetic shape memory material is magnetic shape memory polymer with magnetic particles FesC or NdFeB.

7. The diffractive optical element according to any of claims 1 to 6, characterized in that, the material of the diffractive optical layer is made of standardly used materials for diffraction gratings, especially gold, silver, aluminum.

8. A method of changing a lateral geometry of the diffraction pattern of a diffractive optical element formed according to any one of claims 1 to 7, characterized in that, the that the change of the lateral geometry is made by changing the shape of the material with magnetic shape memory.

9. A method of changing a lateral geometry of the diffraction pattern according to claim 8, characterized in that, the change of lateral geometry of the diffraction pattern is changed wirelessly by the application of external magnetic field to the material with magnetic shape memory.

10. A method of changing a lateral geometry of the diffraction pattern according to claim 9, characterized in that, the change of the lateral geometry of the diffraction pattern is reversible by application of the magnetic field in opposite direction.

11. A method of changing a lateral geometry of the diffraction pattern according to claim 9 or 10, characterized in that, the magnetic field can be applied to the magnetic shape memory material from either side of the diffractive optical element.

12. A method of changing a lateral geometry of the diffraction pattern according to any of claims 9 to 11, characterized in that, the magnetic field is generated by an electromagnet or mechanically rotatable permanent magnet.

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