• 专利附录
  • 专利说明
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    • 专利摘要:
    Invisibility device based on paraxial optics comprising at least four lenses (l1, l2, l3, l4) aligned according to an optical reference axis (eor), where the lenses (l1, l2, l3, l4) are configured for causing the concentration of received light rays during their travel between the input lens (l1) and the output lens (l4), so that between said input lens (l1) and said output lens (l4) is generated a region of invisibility (ir) through which light rays that have an axially symmetrical shape according to the reference optical axis (eor), where at least one of the lenses (l1, l2, l3, l4) is not lens (l3) of tunable focal distance that allows to control the position of an invisibility plane (pi) located behind said lens (l3) of tunable focal distance. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2645739A1
    申请号:ES201730100
    申请日:2017-01-30
    公开日:2017-12-07
    发明作者:Braulio GARCÍA CÁMARA；José Manuel Sánchez Pena；Rubén NÚÑEZ MARTÍN；Eduardo David VELASCO PÉREZ
    申请人:Universidad Carlos III de Madrid；
    IPC主号:
    专利说明:

    Tunable invisibility device based on paraxial optics OBJECT OF THE INVENTION
    The present invention belongs in general to the field of optics, and more particularly to the invisibility devices that are being developed in fundamentally academic environments and in research centers for various applications, such as military, advertising, biomedical, leisure industry, etc.
    The object of the present invention is a novel device capable of generating a region of invisibility with the particularity that the position of at least one invisibility plane can be modified thanks to the use of at least one tunable focal length lens. BACKGROUND OF THE INVENTION
    The important development of materials engineering in recent years, together with the progress of manufacturing techniques has allowed the generation of new nanostructured or metamaterial materials. The main characteristic of these materials is that they allow to achieve properties, in particular optical properties, that are not in nature. The versatility offered by these materials has allowed researchers to devise all kinds of devices to manipulate light, as described by H. Cheng, T.C. Chan and P. Shen in "Transformation optics and metamaterials", Nature Mater. 9, 387-396 (2010). Among these devices, some capable of producing the invisibility of objects, as described by J.B. Pendry, D. Schuring and D.R. Smith in "Controlling electromagnetic fields", Science 312, 1780-1782 (2006). There are also various patent documents that describe invisibility systems based on this type of materials. As an example, documents US9095043 B2 entitled "Electromagnetic cloak using metal lens" or 9166302 B2 entitled "Wideband electromagnetic cloaking systems" may be mentioned.
    However, these systems have as their main disadvantages their great complexity and the high cost involved in their design and manufacturing. In addition, it is necessary to design and generate a specific system for each object that you want to make invisible, or for a very limited area. This follows, for example, from the documents of J. Valentine et al. "An optical cloak made of dielectric", Nature Mater. 8, 568-571 (2009); L.H. Gabrielli et al. "Silicon
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    nanostructure cloak operating at optical frequencies ”Nature Photon. 3, 461-463 (2009); or X. Ni et al. "An ultrathin invisibility skin cloak for visible light", Science, 349, 1310-1314 (2015).
    In contrast to these complex systems, in 2014 Professors Choi and Howell of the University of Rochester (USA) developed and demonstrated an invisibility device based on paraxial optics capable of generating a region of invisibility with several planes of invisibility. In the document entitled "Paraxial ray optics cloaking," Opt. Express 22, 29465-29478 (2014) describe a system that consists of four commercial lenses aligned and conveniently adjusted following the laws of classical geometric optics. Note that, for the system to function properly, it is necessary that the distances between the lenses and the focal lengths of said lenses meet certain conditions. These conditions are called "invisibility conditions" in this document, and are described in more detail later in this document. This system is described in more detail in US patent application US 2016/0025956, where specific configurations consisting of 3 or 4 lenses are described.
    The Choi and Howell system has significant advantages over previous devices. It is an extremely simple system, which allows its implementation by almost anyone following fairly simple instructions. In addition, the materials necessary for its manufacture are very low cost. However, this system has the disadvantage that it is static. That is, once a system of this type is assembled, the region of invisibility remains fixed and unchanged, as well as the position of the different planes of invisibility associated. This supposes a great limitation as far as the possible commercial applications of the device. DESCRIPTION OF THE INVENTION
    The inventors of the present application have realized that the device proposed by Choi and Howell presents various limitations that complicate, if not completely prevent, its use in practice beyond an academic environment.
    In the first place, since it is a static device formed by conventional lenses, once the assembly is done, the region of invisibility remains fixed and unalterable. Therefore, if the user wishes to modify the position of an invisibility plane, for example to make visible a certain object initially located within the region of invisibility, or vice versa, to make invisible an object initially located outside the region of
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    Invisibility, it will be necessary to physically replace one or more of the lenses that constitute the assembly. This implies inconveniences such as the necessary time and work, and in practice it constitutes an important limitation in relation to its potential commercial application.
    Secondly, sometimes there are environmental parameters that can affect the focal length of the lenses, such as the working temperature. This means that, even after careful design and assembly of the invisibility device, a modification of the ambient temperature can cause changes in said invisibility region. Because of this, alterations in the position of the invisibility planes can occur, and as a result objects that were initially invisible may become visible, or objects that were initially visible may become invisible. These unwanted changes in the region of invisibility also constitute a major drawback for the commercial application of this device.
    The inventors of the present application have developed a solution for this problem that is based on a device similar to that described by Choi and Howell where at least one of the conventional static lenses is replaced by a tunable lens of varying focal length. The modification of the focal length of said tunable lens allows the user to cause the invisibility condition to be fulfilled or not fulfilled, which allows the system to function in such a way that the invisibility planes are in certain positions. As a result of the system's exit from the invisibility condition, at least one invisibility plane located immediately behind the tunable lens changes position or fades. The result is that an object located in the position of said invisibility plane can be made visible or invisible at will simply by acting on the tunable lens.
    Additionally, the inventors of the application have developed a feedback system designed to automatically maintain the invisibility condition of the system regardless of possible changes in the focal lengths of the lenses that make up the device, for example because of variations in the conditions environmental. That is, the system "pursues" the condition of stability against disturbances capable of modifying the optimum working point, so that it ensures that a certain plane of invisibility behind the tunable lens remains motionless in its original position.
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    Some terms that will be used throughout the following description are described below.
    Paraxial optics: Paraxial optics refers to optical systems in which the paths of light rays that pass through the device form small angles relative to the reference optical axis. This allows certain approaches (sin θ ≈ θ, tan θ ≈ θ, cos θ ≈ 1) to be used that simplify the mathematical analysis of the system.
    Light beam: Any of the terms "light beam", "light beam", "light rays", etc. refers to the set of rays of light that pass through the device. According to the known conditions of paraxial optics, these light rays form an angle with the reference optical axis less than a certain threshold angle. This set of light rays therefore crosses the entire device longitudinally from the input lens to the output lens. This term may refer to said set of light rays at any point along the optical reference axis of the device depending on the context in which it is used.
    Conventional or static lens: This is a lens that does not allow a controlled modification of its refractive index and / or its geometry, and therefore its focal length. A static lens is usually made of materials such as glass, quartz or polished plastic. Note that, although these lenses are not intended to modify the focal length, it can vary uncontrollably as a result of environmental conditions.
    Tunable lens: This is a lens whose geometry or focal length can be modified at will thanks to the variation of some physical parameter, such as electric current, voltage, temperature, pressure, or others. Its focal length is also affected by environmental conditions.
    Lens: This generic term refers generally to both conventional and tunable lenses. In addition, the term lens not only refers to individual lenses themselves, but also to lens assemblies designed to carry out the function of a single lens, or to correct certain unwanted optical effects associated with the use of an individual lens.
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    Region of invisibility: This is a region of space, located within an essentially cylindrical or conical volume located between the input lens and the output lens of the device of the present invention, through which no light rays pass. The invisibility region is generated as a consequence of the concentration of the light rays in the direction of the reference optical axis, so that in the outer portion of said essentially cylindrical or conical volume a region appears through which said rays do not pass. The invisibility region has axial symmetry and its size is larger when the rays are more concentrated.
    Invisibility plane: Within the invisibility region, it is a plane perpendicular to the reference optical axis and located at a point corresponding to a local maximum concentration of light rays (also called focus), so that the size of the region of invisibility in that plane presents a local maximum. When the light rays are essentially concentrated on a single point of the optical reference axis, a virtually complete invisibility plane is obtained except for the cut-off point of the plane with said optical reference axis. Note that, on occasion, when the invisibility plane is mentioned, reference is not strictly made to the plane in a geometric sense, but rather to a volume of small thickness around the plane of geometric invisibility, which can accommodate a certain object that one wishes to make invisible.
    Before / after: These terms will be interpreted based on the direction of the path traveled by the light rays. That is, when referring to a first element located "before" a second element, or a second element located "after" a first element, it is understood that said elements are located in positions such that light rays Incoming in the device go first through the first element and then through the second element. In other words, the first element is closer to the input of the device of the invention than the second element. In addition to the terms "before / after" similar ones may be used, such as "anterior / posterior", "front / rear", "after", etc.
    Position: This term refers to the location of a certain element along the optical reference axis.
    Invisibility condition: This term refers generically to the relationships between the focal lengths of the lenses and the distances between the lenses
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    that allow a correct functioning of the system with a certain position
    of the planes of invisibility. For example, according to Choi and Howell the
    invisibility condition for a system consisting of four lenses can
    be summarized in (see Fig. 1):
    a) d1 = d3; f1 = f4; f2 = f3 (the system is symmetric)
    b) d1 = f1 + f2
    c) d2 = 2 f2 (f1 + f2) / (f1 – f2)
    The technical features of the preamble of the independent claim of the present invention correspond essentially to the Choi and Howell system described in the scientific article and the patent application mentioned above in this document. However, the device of the invention is not necessarily restricted to the use of four lenses, since a larger number of lenses can be used in an equivalent manner.
    A first aspect of the present invention is directed to a device that essentially comprises the following elements:
    a) An input lens that receives light rays.
    b) At least one first intermediate lens.
    c) At least a second intermediate lens.
    d) An output lens through which light rays come out.
    These lenses are aligned along an optical reference axis, according to the type of typical configuration of paraxial optics based systems.
    The distance between the lenses and their focal distances are selected such that each ray of light received by the input lens, according to an input direction, exits through the output lens according to an output direction essentially parallel to said input direction, provided that the angle of said input direction relative to the optical reference axis is less than a threshold angle. This condition allows that, when an observer looks through the device in a direction essentially parallel to the optical axis of reference or that forms a small angle relative to it, an object located at the entrance of the device looks the same way at the exit Of the device. Threshold angle
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    mentioned is the usual one to be able to use the paraxial approximation, and it can take values of approximately 5º-10º.
    In addition, the lenses are configured to cause the concentration of the light rays received during their travel between the input lens and the output lens, so that between said input lens and said output lens a region of invisibility is generated by the one that does not pass the light rays that have an axially symmetrical shape along the optical reference axis. The light rays can converge essentially at one or more points of the reference optical axis located between the input lens and the output lens, so that the invisibility region can contain virtually complete invisibility planes except for the point itself of cutting of the plane with the optical axis of reference.
    Until now, a static invisibility device of the type described by Choi and Howell has been described. Note that although explicit reference is made to a device consisting of four lenses, it would be possible to design similar devices with any larger number of lenses, so the system is scalable as long as it meets certain relationships of the classical geometric optics that give rise to to the condition of invisibility. While the invisibility condition for a four-lens system has been described so far, it would be possible to generalize it for a larger number of lenses. In that case, the device would include more than two intermediate lenses.
    Well, regardless of the number of lenses, the main distinguishing feature of the present invention in relation to said prior art device is that at least one of the lenses of the device of the present invention is a tunable focal length lens that allows to control the position of an invisibility plane located behind said tunable focal length lens.
    In effect, the modification of the focal length of the tunable lens causes a change in the path of the light rays that pass through it. If in an initial configuration where the invisibility condition is met there is an invisibility plane located in a certain position after the tunable lens, when the focal distance of the tunable lens is modified, the invisibility condition system is exited. That is, the paths of light rays along the device are modified such that the concentration positions of the light rays in the portion of the device after said tunable lens change. As a consequence, the position of the invisibility plane behind the tunable lens changes, or it
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    it fades, so that an object located on that plane that was initially invisible becomes visible. Note that the same device can include more than one tunable lens, which would allow controlling the position of more than one invisibility plane.
    The tunable lens can in principle be of any type as long as it allows the modification at will of its focal length by a user. There are various types of tunable lenses in the art depending on the physical parameter used for the modification of its refractive index or geometry. For example, according to preferred embodiments of the invention, the tunable lens can be chosen from the following: electrically tunable focal length lens, mechanically tunable focal length lens, and thermally tunable focal length lens.
    According to an especially preferred embodiment of the invention, the tunable lens used is a lens whose focal length changes depending on the electric current applied thereto. An example of such a lens is essentially formed by a container in which an optical fluid is stored and which is also provided with an electromagnetic actuator. To modify the focal length, the electric current through the electromagnetic actuator is operated, which in turn exerts a variable pressure on the vessel that stores the optical fluid. As a consequence, the trajectory of the light rays that cross the lens and therefore also its focal length is modified. In another preferred embodiment of the invention, the tunable lens may be based on a liquid crystal, which has electro-optical properties so that its refractive index varies under the application of an electric field.
    In addition, the fact that the device of the invention includes at least one tunable lens has the additional advantage that it is possible to implement a control loop to keep the position of at least one invisibility plane motionless regardless of variations in the environmental conditions cause changes in the focal length of the lens of the device. This makes it possible to ensure that an object that is desired to remain invisible, or visible, remains so even if the focal length of the integrating lenses changes unexpectedly due to environmental conditions.
    According to a preferred embodiment of the invention, a feedback system configured to keep an invisibility plane still is described. The tunable focal length lens is considered to be located in a first position of the optical reference axis and the invisibility plane is located in a second position of the optical reference axis,
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    where the second position is after the first position. Well, the feedback system includes:
    a) Means configured to obtain representative properties of the light rays in a third position of the optical reference axis, where the third position is located between the lenses immediately before and immediately after the second position.
    b) Means configured to control the focal length of the tunable lens so that said properties of the light rays remain unchanged in said third position, so that said invisibility plane is also kept unchanged in said second position.
    That is, it starts from a certain configuration of the device in which a tunable lens is located in a first position and a certain invisibility plane is in a desired position called second position. In that situation, in which the invisibility condition is met, certain representative properties of the beam of light rays that pass through the device in a third position between the lens immediately before the invisibility plane and the lens immediately after the invisibility plane. Note that this is necessary because, otherwise, it cannot be ensured that maintaining the properties of the beam of light in the third position also implies maintaining the position of the invisibility plane, since between the second position and the third position could be a lens whose properties have varied as a result of environmental conditions. This will become clearer later in this document from the description of particular examples referred to the figures.
    In any case, if the above conditions are met, it can be assumed that as long as the properties of the beam of light in said third position remain constant, the invisibility condition will be fulfilled and therefore the invisibility plane will remain immobile in the second position. Consequently, the relevant properties of the light beam are monitored, for example the size, shape, misalignment with respect to the reference optical axis, intensity, or others, so that any change in them can be detected. If a change in any of these properties is detected, it means that an alteration of the environmental conditions has caused the change in the focal length of some of the lens of the device, and that this in turn has caused the change in the light beam in the third position. Therefore, the system of
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    feedback acts on the tunable lens to modify its focal length so that the properties of the beam of light rays in the third position return to their original value, so that the system returns to the optimum working point initially established at which they are met Invisibility condition
    The described feedback system can be implemented in different ways, although preferably it comprises at least the following elements:
    a) A beam splitter located in the third position of the optical reference axis, which deflects a portion of the light rays outside said optical reference axis.
    b) A photodetector located outside the reference optical axis, which is configured to receive the deviated portion of the light rays and to determine the properties of said deviated portion of the light rays.
    c) A processing means connected to the photodetector, which is configured to receive from said photodetector the properties of said deviated portion of the light rays. The processing medium can be implemented through a microcontroller, a microprocessor, an FPGA, a DSP, an ASIC, or in general by any suitable device to carry out the functions described in this document.
    d) A drive means connected to the processing means and to the tunable lens, which is configured to receive from said processing means orders to modify the focal distance of said tunable lens so that the properties of the deviated portion of the light rays Stay unchanged. The drive means can be an independent element of the processing means, or it can be integrated into the processing medium itself as an output card or the like.
    The operation of this feedback system would be fundamentally the following. It starts from an initial state of the device to be maintained and in which the invisibility condition is met. In this initial situation, there is an invisibility plane located in a second position after the first position in which the tunable lens is located. The beam splitter, located in a third position adjacent to the position of the invisibility plane to be controlled, deflects a portion of the light rays that pass through the device from the direction of the reference optical axis. That portion
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    Deviated from the light rays, it affects a photodetector. A signal representative of the properties of the deviated portion of the light rays received by the photodetector is sent to the processing medium. Therefore, the processing means knows what are the properties of the deviated portion of the light rays that correspond to the fulfillment of the invisibility condition.
    Once the initial state to be maintained is established, the processing medium continuously receives the photodetector signal and monitors the properties of the deviated portion of the light rays. In case you detect any change, it will mean that there has been some modification in any of the lenses that make up the device and that it has left the invisibility condition. If this occurs, the processing means acts on the tunable lens to modify its focal length until the properties of the deviated portion of the light rays return to their original state. As a result, the device is returned to the invisibility condition in which the invisibility plane being controlled is in the initial position. BRIEF DESCRIPTION OF THE FIGURES
    Fig. 1 shows an example of a device according to Choi and Howell that is formed by four static lenses.
    Figs. 2a and 2b show an example of a device according to the present invention that has a tunable lens respectively in a situation in which the invisibility condition is met and a situation in which the invisibility condition is not met.
    Figs. 3a-3c show in several situations an example of a device according to the present invention that has a feedback system for maintaining the invisibility plane in a certain position.
    Figs. 4a-4c schematically show the appearance of the deviated portion of the incident light rays on the photodetector. PREFERRED EMBODIMENT OF THE INVENTION
    Two devices according to the present invention are described below, one without feedback system and the other with feedback system, referring to the figures
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    attached. Note that these are only examples, and therefore should not be considered limiting, the invention being limited only by the appended claims.
    Specifically, although the examples refer to invisibility devices formed by four lenses, the number of lenses of the device of the invention is not limited to four and may be more so long as their focal distances and the distances between them meet the relevant invisibility condition. in each case. In the same way, it is not necessary that the tunable lens is the one that is specifically in the third place of the device, but that it can replace any of the lenses that comprise it. Similarly, although the examples show a single tunable lens, the device of the invention can use more than one tunable lens, thus allowing to control the visibility / invisibility of more than one object located respectively in more than one invisibility plane. In addition, although the following examples show lenses having the same diameter, it should be interpreted that it is possible to implement the device of the invention using lenses of different diameters and introducing additional correction elements to make them compatible with the rest. The way in which this is carried out is known and common in this field, since the lenses necessary to carry out each assembly are not always commercially available with the same diameter. Finally, each lens of the device of the invention can be replaced by sets of two or more coupled lenses capable of exercising the same function as that.
    Fig. 2a shows a first example of a device, according to the present invention, specifically formed by four lenses (L1, L2, L3, L4), where the first lens (L1) or input lens, the second lens (L2), and the fourth lens (L4) or output lens is static, and the third lens (L3) is tunable. In this specific example, it is assumed that the tunable lens (L3) is of the type that allows the variation of its focal length as a function of the intensity of the electric current (I) applied to it. An arrow-shaped object has been placed at the entrance of the device, that is, to the left of the input lens (L1).
    The situation shown in Fig. 2a corresponds to compliance with the conditions of invisibility, which implies that it must be met that:
    a) d1 = d3; f1 = f4; f2 = f3 (I1)
    b) d1 = f1 + f2
    c) d2 = 2 f2 (f1 + f2) / (f1 – f2)
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    To do this, the specific values that adopt the parameters of the device shown in the
    Fig. 2a are:
    d1 = d3 = 275mm;
    d2 = 330 mm;
    f1 = f4 = 200mm;
    f2 = 75 mm
    Given these values, and taking into account equations a) -c), the focal length f3 (I1) of the tunable lens (L3) should adopt a value of 75 mm, equal to the focal length of the second lens (L2) . To do this, a certain current (I1) necessary for f3 (I1) = 75 mm is applied to the tunable lens (L3). It is easy to verify that in this way the device shown in Fig. 2a meets the invisibility conditions.
    With this configuration, the light beam enters from the input of the device in the first lens (L1) essentially parallel to the optical reference axis (EOR), focuses on the space between the first lens (L1) and the second lens ( L2) and reaches said second lens (L2), refocuses to a lesser extent than before in the space between the second lens (L2) and the third lens (L3) and reaches said third lens (L3), and returns to focus on the space between the third lens (L3) and the fourth lens (L4) and reaches said fourth lens (L4), after which the light beam again takes a direction parallel to the optical reference axis (EOR). Therefore, an observer located at the exit of the device, to the right of the output lens (L4), sees the object in the form of an arrow essentially in the same way as if there were no distance between the input lens (L1) and the output lens (L4).
    It can be seen that a region of invisibility (IR) is formed in the areas between lenses in which the light rays approach the optical reference axis (EOR). This invisibility region (RI) has cylindrical symmetry around the reference optical axis (EOR) and has the resulting form of subtracting the essentially conical volume occupied by the rays of light along its displacement, from the essentially cylindrical volume between the lens input (L1) and the output lens (L4). The invisibility region (RI) described has three invisibility planes called (pi1, pi2, PI), one between each pair of lenses, although we will see that in Fig. 2 only the invisibility plane (PI) located between the third lens (L3) and the output lens (L4). The formation of this region of invisibility (RI) and the planes of invisibility (pi1, pi2, PI) does not affect the image of the arrow that an observer sees at the exit of the device.
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    Well, in the aforementioned invisibility plane (PI) an essentially flat obstacle (O) has been arranged, in this example a sheet of graph paper, with its edge just adjacent to the optical reference axis (EOR). That is, the sheet of paper (O) essentially covers the middle of the path that the rays of light would follow when passing through the device if they were all their path parallel to the optical reference axis (EOR). However, because all the light rays are focused on the optical reference axis (EOR) itself at the level of the invisibility plane (PI), the sheet of paper (O) is invisible to an observer on the right Of the device. The observer sees the image of the complete arrow.
    Fig. 2b shows a configuration of the same device of Fig. 2a where the current (I) that controls the focal length of the tunable lens (L3) has been operated, and that passes from (I1) to (I2). As a consequence, this focal length has increased and invisibility conditions are no longer met. The invisibility plane (PI) has varied in position and possibly its size has decreased (the actual trajectories of the light rays in the figure are not represented), that is, the light rays are no longer focused on a single point but that occupy a greater surface area of said invisibility plane (PI). In any case, part of the light rays that pass through the device affect the sheet of paper (O), which therefore blocks part of the image that an observer sees at the exit of the device. The observer sees an image similar to that shown, where the sheet of paper partially covers the image of the arrow.
    In short, it is easy to appreciate how the device of the invention makes it possible to make an obstacle (O) properly located in the device of the invention visible or invisible at will. The time required to modify the focal length of the tunable lens (L3) is very small, of the order of milliseconds, so that a visual effect is achieved in which the obstacle (O) suddenly appears or disappears.
    Fig. 3a shows a second example of a device similar to that of Fig. 2a except that it also includes a feedback system designed to maintain the conditions of invisibility even if changes occur in the focal length of the lenses (L1, L2, L3 , L4) that compose it. A complete description of those elements of the device that are equivalent to those described in relation to Fig. 2a is omitted here, describing in detail only the elements that make up the feedback system.
    The tunable lens (L3) is located in a position here called first position (P1) while the position of the invisibility plane (PI), in the state in which
     F.OEPM30 / 01 / 2017F.Effective Application No.30 / 01/2017

    they meet the conditions of invisibility, it is called second position (P2). The second position (P2) is after the first position (P1). In a third position (P3) located between the first position (P1) and the second position (P2) there is a beam splitter (DH) configured to deflect a portion of the light rays that pass through the device. The deflected portion of the light rays is directed by the beam splitter (DH) towards the sensitive surface of a photodetector (FD). The photodetector (FD) is in turn connected to a processing medium (MP), and the processing medium (MP) is connected to a drive means (MA). The drive means (MA) is connected to the tunable lens (L3), such that it injects the necessary current according to the orders received from the processing medium (MP).
    In the situation shown in Fig. 3a, the actuation means (MA) is injecting a certain current (I1) into the tunable lens (L3) which makes the focal distance of said tunable lens (L3) 75 mm. Under these conditions, the status of the device is the same as that shown in Fig. 2a, the invisibility conditions are met, and the invisibility plane (PI) is in the second position (P2). The sheet of paper (O), which is located in the second position (P2), remains invisible, and an observer located at the exit of the device sees the image of the complete arrow.
    In this situation, the portion of the light rays deflected by the beam splitter (DH) affects the photodetector (FD) according to certain properties. For example, the deflected portion incident in the photodetector (FD) may be a circumference or ellipse centered at a certain point, with a given diameter and a determined intensity, as schematically shown in Fig. 4a. This data is transmitted from the photodetector (FD) to the processing medium (MP), which stores it as the reference properties corresponding to compliance with the invisibility condition. In the initial setting of the device, these properties of the deviated portion of the light rays correspond to the current (I1), which in turn corresponds to a focal distance of the tunable lens (L3) of 75 mm.
    However, it can happen that for uncontrollable reasons there is a change in environmental conditions, for example the temperature, which affects the values of the focal length of one of the lenses (L1, L2, L3, L4). Static lenses (L1, L2, L4) vary little compared to this type of changes, but this is not the case with the tunable lens (L3), whose value can change and thus move away from the value of 75 mm corresponding to compliance with the conditions of invisibility even though the excitation intensity is maintained at the initial value of (I1).
     F.OEPM30 / 01 / 2017F.Effective Application No.30 / 01/2017

    This situation is shown in Fig. 3b. An increase in temperature has significantly modified the value of the focal length of the tunable lens (L3), which has increased, and as a consequence the position of the invisibility plane (PI) is no longer coincident with the second position (P2). Therefore, due to a mechanism similar to that described in relation to Fig. 2b, the sheet of paper (O), which is in the second position (P2), has become visible to an observer located at the exit of the device. On the other hand, it is evident to appreciate that if the position of the focus - that is, the position of the invisibility plane (PI) - moves, the beam of light rays must necessarily also change as it passes through the third position (P3 ). This is detected by the photodetector (FD) through the deviated portion of the light rays.
    For example, we can assume that the ellipse located at a certain point, with a certain size and a certain intensity shown in Fig. 4a corresponds to the deviated portion of the light rays in the initial state when the sensitive surface of the photodetector is affected (FD) After the change in the focal length of the tunable lens (L3), this ellipse may have changed in size, increasing (Fig. 4b, the dotted line represents a circumference equal to that of Fig. 4a) or decreasing (Fig. 4c, the dotted line represents a circle equal to that of Fig. 4a). As a result, the processing medium (MP) orders the drive medium (MA) to change the current applied to the tunable lens (L3) until it reaches a I'1 value in which the ellipse returns to the situation of Fig. 4a. Since the ellipse returns to the initial form, the beam of light rays in the third position (P3) of the device is also identical to what it was in the initial position, and that means that the invisibility plane (PI) has returned to its initial position, as shown in Fig. 3c. That is, with the change in environmental conditions, it is necessary to apply a current I’1 to the tunable lens (L3) so that its focal length is 75 mm.
     F.OEPM30 / 01 / 2017F.Effective Application No.30 / 01/2017
    权利要求:
    Claims (7)
    [1]
    1. Tunable invisibility device based on paraxial optics, comprising: - an input lens (L1) that receives light rays; -at least a first intermediate lens (L2); -at least a second intermediate lens (L3); and -a output lens (L4) through which the light rays come out, -where said lenses (L1, L2, L3, L4) are aligned in accordance with an optical axis
    reference (EOR),
    - where each ray of light received by the input lens (L1) according to an input direction exits through the output lens (L4) according to an output direction essentially parallel to said input direction, the input direction forming an angle relative to to the optical reference axis (EOR) below a threshold angle; Y
    - wherein the lenses (L1, L2, L3, L4) are configured to cause the concentration of the light rays received during their travel between the input lens (L1) and the output lens (L4), such that between said lens (L1) input and said output lens (L4) generates an invisibility region (RI) through which light rays that have an axially symmetrical shape along the optical reference axis (EOR), characterized by that
    - at least one of the lenses (L1, L2, L3, L4) is a tunable focal length lens (L3) that allows to control the position of an invisibility plane (PI) located behind said tunable focal length lens (L3) .
    [2]
    2. Tunable invisibility device (1) based on paraxial optics according to claim 1, wherein the tunable lens (L3) is chosen from the following: electrically tunable focal distance lens, mechanically tunable focal distance lens, and distance lens thermally tunable focal.
    [3]
    3. Tunable invisibility device (1) based on paraxial optics according to claim 2, wherein the tunable lens (L3) is a lens whose focal length changes depending on the electric current applied to it.
    [4]
    Four. Tunable invisibility device (1) based on paraxial optics according to claim 2, wherein the tunable lens (L3) is based on a liquid crystal whose refractive index varies under the application of an electric field.
     F.OEPM30 / 01 / 2017F.Effective Application No.30 / 01/2017

    [5]
    5. Tunable invisibility device (1) based on paraxial optics according to any of the preceding claims, which further comprises a feedback system configured to keep the invisibility plane (PI) still, where the focal distance lens (L3) tunable is located in a first position (P1) of the optical reference axis (EOR) and said invisibility plane (PI) is located in a second position (P2) of the optical reference axis (EOR), the second position (P2) being ) after the first position (P1), where said feedback system comprises:
    - means (DH, FD) configured to obtain representative properties of light rays in a third position (P3) of the optical reference axis (EOR), where the third position (P3) is located between the immediately anterior lenses (L3) and immediately after (L4) to the second position (P2); Y
    - means (MP, MA) configured to control the focal length of the tunable lens (L3) so that said light ray properties remain unchanged in said third position (P3), so that said invisibility plane (RI) is it also remains unchanged in said second position (P3).
    [6]
    6. Tunable invisibility device (1) based on paraxial optics according to claim 5, comprising:
    - a beam splitter (DH) located in the third position (P3) of the optical reference axis (EOR), which deflects out of said optical reference axis (EOR) a portion of the light rays;
    - a photodetector (FD) located outside the reference optical axis (EOR), which is configured to receive the deviated portion of the light rays and to determine the properties of said deviated portion of the light rays;
    - a processing medium (MP) connected to the photodetector (FD), which is configured to receive from said photodetector (FD) the properties of said deviated portion of the light rays; Y
    - a drive means (MA) connected to the processing means (MP) and the tunable focal length lens (L3), which is configured to receive from said processing means (MP) commands to modify the focal length of said lens (L3) ) tunable so that the properties of the deviated portion of the light rays remain unchanged.
    [7]
    7. Tunable invisibility device (1) based on paraxial optics according to claim 6, wherein said light ray properties are chosen from: size, shape, misalignment with respect to the reference optical axis (EOR ) and intensity.
     F.OEPM30 / 01 / 2017F.Effective Application No.30 / 01/2017
     FIGURES 
     F.OEPM30 / 01 / 2017F.Effective Application No.30 / 01/2017
     F.OEPM30 / 01 / 2017F.Effective Application No.30 / 01/2017
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    CN101299079A|2008-05-13|2008-11-05|上海市第二中学|Invisible apparatus and design based on geometrical optics|
    US20090316279A1|2008-05-30|2009-12-24|Searete Llc, A Limited Liability Corporation Of The State Of Delaware.|Emitting and focusing apparatus, methods, and systems|
    US20160025956A1|2014-07-24|2016-01-28|University Of Rochester|Paraxial cloak design and device|
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    PCT/ES2018/070058| WO2018138401A1|2017-01-30|2018-01-26|Tunable cloaking device based on paraxial optics|
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