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WO2018138401A1 - Dispositif d'invisibilité syntonisable reposant sur l'optique paraxiale - Google Patents

Dispositif d'invisibilité syntonisable reposant sur l'optique paraxiale Download PDF

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Publication number
WO2018138401A1
WO2018138401A1 PCT/ES2018/070058 ES2018070058W WO2018138401A1 WO 2018138401 A1 WO2018138401 A1 WO 2018138401A1 ES 2018070058 W ES2018070058 W ES 2018070058W WO 2018138401 A1 WO2018138401 A1 WO 2018138401A1
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WIPO (PCT)
Prior art keywords
lens
tunable
invisibility
light rays
focal length
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/ES2018/070058
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English (en)
Spanish (es)
Inventor
Braulio GARCÍA CÁMARA
José Manuel SÁNCHEZ PENA
Rubén NÚÑEZ MARTÍN
Eduardo David VELASCO PÉREZ
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Universidad Carlos III de Madrid
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Universidad Carlos III de Madrid
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Filing date
Publication date
Application filed by Universidad Carlos III de Madrid filed Critical Universidad Carlos III de Madrid
Publication of WO2018138401A1 publication Critical patent/WO2018138401A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection

Definitions

  • 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.
  • 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.
  • 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 HoweII 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.
  • 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.
  • 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 located behind the tunable lens remains motionless in its original position.
  • 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 ⁇ ⁇ ⁇ , tan ⁇ ⁇ ⁇ , eos ⁇ ⁇ 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.
  • a 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.
  • 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 optical reference 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.
  • a local maximum concentration of light rays also called focus
  • 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 that allow a correct functioning of the system with a certain position of the invisibility planes.
  • Fig. 1 the invisibility condition for a system consisting of four lenses can be summarized in (see Fig. 1):
  • 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.
  • 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.
  • Threshold angle mentioned is the usual one to be able to use the paraxial approximation, and it can take values of approximately 5 ° -10 °.
  • 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.
  • 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.
  • 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 it fades, so that an object located on that plane that was initially invisible becomes visible.
  • 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.
  • 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.
  • 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.
  • the electric current through the electromagnetic actuator is operated, which in turn exerts a variable pressure on the vessel that stores the optical fluid.
  • 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.
  • the device of the invention includes at least one tunable lens
  • 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.
  • a feedback system configured to keep an invisibility plane still.
  • 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, where the second position is after the first position.
  • the feedback system comprises: 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.
  • 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.
  • the system of 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 said optical reference axis Light rays. 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.
  • 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.
  • 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 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 focal length ⁇ 3 (li) of the tunable lens (L3) should adopt a value of 75 mm, equal to the focal length of the second lens (L2) .
  • 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).
  • a region of invisibility (Rl) is formed in the areas between lenses in which the rays of light approach the optical reference axis (EOR).
  • This region of invisibility (Rl) has cylindrical symmetry around the optical reference 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 (Rl) described has three invisibility planes called (ph, p ⁇ 2, Pl), one between each pair of lenses, although we will see that in Fig. 2 only the invisibility plane (Pl) located is controlled between the third lens (L3) and the output lens (L4).
  • this region of invisibility (Rl) and the planes of invisibility (ph, p ⁇ 2, Pl) does not affect the image of the arrow that an observer sees at the exit of the device.
  • 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).
  • 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 passes from () to ().
  • I current
  • L3 focal length
  • the invisibility plane (Pl) has varied in position and possibly its size has decreased (the actual paths 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 larger surface of said invisibility plane (Pl).
  • 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.
  • 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.
  • L1, L2, L3 , L4 the focal length of the lenses
  • the tunable lens (L3) is located in a position here called first position (P1) while the position of the invisibility plane (Pl), in the state in which they meet the conditions of invisibility, it is called second position (P2).
  • the second position (P2) is after the first position (P1).
  • a beam splitter (DH) 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).
  • the actuation means (MA) is injecting a certain current () into the tunable lens (L3) which makes the focal distance of said tunable lens (L3) 75 mm.
  • the status of the device is the same as that shown in Fig. 2a, the invisibility conditions are met, and the invisibility plane (Pl) 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.
  • the portion of the light rays deflected by the beam splitter (DH) affects the photodetector (FD) according to certain properties.
  • 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.
  • MP processing medium
  • these properties of the deviated portion of the light rays correspond to the current (), which in turn corresponds to a focal distance of the tunable lens (L3) of 75 mm.
  • Fig. 4a 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)
  • 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).
  • the processing medium (MP) orders the drive means (MA) to change the current applied to the tunable lens (L3) until it reaches a value ⁇ in which the ellipse returns to the situation of the 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 (Pl) 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 ⁇ to the tunable lens (L3) so that its focal length is 75 mm.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

La présente invention concerne un dispositif d'invisibilité reposant sur l'optique paraxiale qui comprend au moins quatre lentilles (L1, L2, L3, L4) alignées par rapport à un axe optique de référence (EOR), lesdites lentilles (L1, L2, L3, L4) étant configurées pour provoquer la concentration des rayons de lumière reçus pendant leur trajet entre la lentille (L1) d'entrée et la lentille (L4) de sortie, de sorte qu'entre la lentille (L1) d'entrée et la lentille (L4) de sortie se crée une région d'invisibilité (RI) à travers laquelle ne passent pas les rayons de lumière et qui a une forme axialement symétrique par rapport à l'axe de référence (EOR), au moins une des lentilles (L1, L2, L3, L4) étant une lentille (L3) à distance focale syntonisable qui permet de contrôler la position d'un plan d'invisibilité (PI) situé derrière ladite lentille (L3) à distance focale syntonisable.
PCT/ES2018/070058 2017-01-30 2018-01-26 Dispositif d'invisibilité syntonisable reposant sur l'optique paraxiale Ceased WO2018138401A1 (fr)

Applications Claiming Priority (2)

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ESP201730100 2017-01-30
ES201730100A ES2645739B2 (es) 2017-01-30 2017-01-30 Dispositivo de invisibilidad sintonizable basado en óptica paraxial

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101299079A (zh) * 2008-05-13 2008-11-05 上海市第二中学 一种基于几何光学的隐形装置及其设计
US20090316279A1 (en) * 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 (en) * 2014-07-24 2016-01-28 University Of Rochester Paraxial cloak design and device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101299079A (zh) * 2008-05-13 2008-11-05 上海市第二中学 一种基于几何光学的隐形装置及其设计
US20090316279A1 (en) * 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 (en) * 2014-07-24 2016-01-28 University Of Rochester Paraxial cloak design and device

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
CHOI, J. & HOWELL, J., PARAXIAL RAY OPTICS CLOAKING, vol. 22, no. 24, 18 November 2014 (2014-11-18), pages 29465 - 29478, XP055143680, [retrieved on 20171121] *
PENDRY, J. B. ET AL.: "CONTROLLING ELECTROMAGNETIC FIELDS", SCIENCE, vol. 312, 13 June 2006 (2006-06-13), pages 1780 - 1782, XP007907867, [retrieved on 20171121] *

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ES2645739B2 (es) 2018-11-26

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