System and method for object remote sensing

Abstract

A method for object remote sensing comprising the steps: Generating (160) a spatially polarization-inhomogeneous light beam and directing the beam towards a distant object; Receiving (170) an output light beam comprising the spatially polarization-inhomogeneous light beam after the light beam has contacted the remote object by a polarimetry receiver; measuring (180) an electric field of the output light beam; and Determining (190) changes in a spatially inhomogeneous state of the polarization of the output light beam to determine spatial features of the remote object.

Description

INFORMATION REGARDING RELATED APPLICATIONS

[0001] This application claims priority to Provisional Application No. 62 / 082,716 filed November 21, 2014, which is incorporated herein by reference. BACKGROUNDTechnical field

[0002] The present invention relates to object remote sensing and, more particularly, to systems and methods for object remote sensing by measuring the change in the spatially inhomogeneous state of polarization of a spatially inhomogeneously polarized light beam. Description of the state of the art

[0003] There are various known processing systems and methods for remote sensing objects. For example, Light Detection and Ranging (LIDAR) can be used to obtain topographical information about an object. LIDAR involves measuring the time of flight of a light beam to and from an object. However, LIDAR reduces the feature resolution to the magnitude of the light beam's flex, resulting in reduced resolution as the distance to the object increases.

[0004] Optical angular momentum (OAM) spectroscopy has also been used for object remote sensing. In OAM spectroscopy, a light beam is directed at the object of interest, and the OAM spectrum resulting from the subsequent light-matter interaction is measured. While OAM spectroscopy achieves higher resolution compared to LIDAR, OAM spectroscopy requires very fine and complex control of liquid crystal-on-silicon spatial light modulators at the transmitter and / or receiver sides to generate and measure the optical OAM spectrum. Furthermore, OAM spectra are difficult to measure accurately due to high sensitivity to misalignment and crosstalk. Therefore, a system and method for object remote sensing that delivers accurate high-resolution and real-time feature detection would be highly advantageous.

[0005] From US 2009 / 00284835 A1 an imaging microscope for imaging a surface with an acousto-optical system is known which generates inhomogeneously polarized beams which are scattered from the surface, focused on imaging spots and then detected by a detector. SUMMARY

[0006] A method for object remote sensing comprising the steps of generating a spatially polarization-inhomogeneous light beam and directing the beam toward a remote object. The method further includes the step of receiving an output light beam comprising the spatially polarization-inhomogeneous light beam after the light beam has contacted the remote object, with a polarimetry receiver. The electric field of the output light beam is measured, and changes in the spatially inhomogeneous state of polarization of the output light beam are determined. The spatial features of the remote object can be determined from the changes in the spatially inhomogeneous state of polarization of the output light beam.

[0007] A system for object remote sensing, including a spatially polarization-inhomogeneous light beam generation unit configured to generate a spatially polarization-inhomogeneous light beam and direct the light beam toward a remote object. The system further includes a polarimetry receiver configured to receive an output light beam comprising the spatially polarization-inhomogeneous light beam after the light beam has contacted the remote object. The polarimetry receiver includes a processor, memory, and an interface. The memory is configured to store a calculation module that calculates an electric field of the output light beam and determines changes in the spatially inhomogeneous state of polarization of the output light beam.

[0008] These and other features and advantages will become apparent from the following detailed descriptions and illustrative embodiments thereof, which should be read in conjunction with the accompanying drawings BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The disclosure will provide details in the following description of preferred embodiments with reference to the following figures, wherein: Fig. 1 is a block / flow diagram illustrating a system for remote sensing of objects; Fig. 2 is another block / flow diagram illustrating another system for remote object sensing in accordance with the present principles; Fig. Figure 3 is an illustrative example of imaging produced by the polarimetry receiver in accordance with the present principles; Fig. Figure 4 is an illustrative example of Stokes parameters calculated by the polarimetry receiver in accordance with the present principles; FIG. is an illustrative example of a full electric field reconstruction generated by the polarimetry receiver in accordance with the present principles; Fig. 6 is a vector mode spectrum determined by the polarimetry receiver in accordance with the present principles; Fig. Figure 7 is a flowchart illustrating a method for remote sensing objects in accordance with the present principles; Fig. 8 is a flowchart illustrating a method for generating a spatially polarization-inhomogeneous light beam in accordance with a preferred embodiment; and Fig. 9 is a flowchart illustrating a method for receiving the output light beam by a polarimetry receiver in accordance with a preferred embodiment. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0010] In accordance with the present principles, systems and methods are provided for remote object sensing by detecting features of the remote object based on changes in the spatially inhomogeneous state of polarization of a spatially polarization-inhomogeneous light beam directed toward the remote object and subsequently received by a polarimetry receiver. The polarimetry receiver is configured to measure the spatially inhomogeneous state of polarization of the spatially inhomogeneous electric field of the light beam emitted by the remote object and to calculate the changes in the spatially inhomogeneous state of polarization to determine the spatial features of the remote object. The system obtains high-resolution, real-time information regarding important spatial features of the remote object.

[0011] Embodiments described herein may be entirely hardware, entirely software, or may include both hardware and software elements, which may include, but are not limited to, firmware, pre-programmed software, microcode, etc.

[0012] Embodiments may include a computer program product accessible from a computer-usable or computer-readable medium that provides program code for use by or in connection with a computer or instruction execution system. A computer-usable or computer-readable medium may include any apparatus that stores, communicates, propagates, or transports the program for use by or in connection with the instruction execution system, instruction execution apparatus, or instruction execution device. The medium may be magnetic, optical, electronic, electromagnetic, infrared, or a semiconductor system (or apparatus or device to or propagation medium).The medium may include a computer-readable storage medium such as a semiconductor or solid-state memory, a magnetic tape, a removable computer diskette, random access memory (RAM), read-only memory (RPM), a fixed magnetic disk, and an optical disk, etc.

[0013] A data processing system suitable for storing and / or executing program code may include at least one processor coupled directly or indirectly to storage elements via a system bus. The storage elements may include local memory used during actual execution of the program code, mass storage, and cache memory providing temporary storage of at least some program code to reduce the number of times code must be retrieved from mass storage during execution. Input / output or I / O devices (including but not limited to keyboards, displays, pointing devices, etc.) may be connected to the system either directly or through intermediary I / O controllers.

[0014] Network adapters may also be coupled to the system to allow the data processing system to connect to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the types of network adapters currently available.

[0015] Reference is now made to the drawings, in which like reference numerals designate like or similar elements, and first to Fig. 1 is a block / flow diagram illustrating a system 100 for optically detecting a remote object 106, shown by way of example in accordance with one embodiment of the present principles. The system 100 may include a spatially polarization-inhomogeneous light beam generation unit 102 configured to generate a spatially polarization-inhomogeneous light beam and direct the light beam toward a remote object 106. A "spatially polarization-inhomogeneous beam," also referred to as a "vector" beam, is a light beam having a polarization state that is different at each spatial point transverse to the beam, i.e., not along its propagation direction.

[0016] As in Fig. 2, in one embodiment, the inhomogeneous light beam generating unit may be a laser beam generator 108. The laser beam generator 108 may consist of various known devices configured to generate light beams with spatially polarization-homogeneous light. The inhomogeneous light beam generating unit 102 may further include an optical fiber 110, such as a single-mode optical fiber, configured to guide the spatially polarization-homogeneous light beam from the laser beam generator 108. In a preferred embodiment, the inhomogeneous light beam generating unit 102 may include a lens 112 configured to receive the light beam from the optical fiber 110 and collimate the light beam.

[0017] The generation unit 102 may further include a Q-plate 114. A Q-plate is a birefringent liquid crystal plate with a patterned transverse optical axis. The Q-plate 114 is configured to transform the light beam received by the lens 112 into spatially polarization-inhomogeneous light. The Q-plate is configured to generate a specific inhomogeneous state of polarization for the light beam, which depends on the pattern of the Q-plate.

[0018] As in Fig. As shown in Figure 2, the inhomogeneous light beam generation unit 102 directs the spatially polarization-inhomogeneous light so that it travels from the Q-plate 114 through a first free-space channel 111 and contacts the remote object 106. The light-matter interaction between the spatially polarization-inhomogeneous light beam 104 and the remote object 106 changes the spatial polarization content of the light beam 107 emitted by the remote object. These changes in spatial polarization of the light beam are characteristic of the features of the remote object 106 and can be used to determine the features of the remote object.

[0019] The system 100 may further include a polarimetry receiver 116. The polarimetry receiver may include one or more processors 130 and memory 132 for storing programs and applications. The polarimetry receiver 116 may further include a display 114 that allows a user to view images and interact with the system 100. The polarimetry receiver may further include an interface 146, which may include a keyboard, a mouse, a joystick, an optical device, or any other peripheral or control device to enable user feedback from and interaction with the system 100.While processor 130, memory 132, display 144, and interface 146 are specifically shown as components of polarimetry receiver 116, in other embodiments, one or more of these components may be located in other parts of system 100 and have connections as known in the art, such as a communications bus for connecting to the polarimetry receiver.

[0020] The polarimetry receiver 116 is configured to receive the spatially polarization-inhomogeneous light beam 107 output from the remote object 116 and to obtain measurements regarding the spatially inhomogeneous electric field of the output light beam. The polarimetry receiver 116 is further configured to determine changes in the spatially inhomogeneous state of the polarization of the spatially polarization-inhomogeneous light beam.

[0021] As in Fig. 2, the output light beam 107 from the distant object 16 passes through a second free space channel 115. While the second free space channel 115 is illustratively shown in the embodiment of Fig. 2 as a channel different from the first free-space channel 111, in some embodiments, the output light beam 107 from the remote object 106 may be reflected through the first free-space channel to the polarimetry receiver 116.

[0022] In the embodiment from Fig. 2, the polarimetry receiver may include a polarizer 118, such as a linear polarizer. The polarimetry receiver 116 may further include a quarter-wave plate 120 configured to change the polarization state of the light beam passing through it by converting the linearly polarized light into circularly polarized light.

[0023] The polarimetry receiver 115 may further include imaging optics 122 and a charge-coupled device (CCD) camera 124. The imaging optics are configured to receive the light beam from the quarter-wave plates 120 and output the beam to the charge-coupled device camera 124 for imaging. For example, in one embodiment, the imaging optics 122 are configured to image a 4f system onto a CCD camera 124.

[0024] Fig. 3 provides illustrative examples of images 126 generated by the CCD camera 124. In Fig. 3 represent, I0, I 45 , I 90 , and I 135 the intensities of an arbitrary vector light field, E(r,ϕ), obtained when the polarizer 118 is rotated by 0, 45, 90, and 135 degrees with respect to a Cartesian reference coordinate system.

[0025] The polarimetry receiver 115 is configured to measure the spatially inhomogeneous electric field to obtain a measurement-based reconstruction of the full electric field of the output light beam 107. In one embodiment, the polarimetry receiver 115 may be configured to measure the spatially inhomogeneous electric field using Stokes polarimetry. In this embodiment, the polarimetry receiver may determine the spatially inhomogeneous electric field by rotating the polarizer 118 with respect to a Cartesian reference coordinate to obtain four intensity values.

[0026] As in Fig. 3, the resulting intensities obtained when the polarizer 118 is rotated by 0, 45, 90, and 135 degrees are imaged using the imaging optics 122 onto the CCD camera 124 with stronger intensity proportional to lighter pixel outputs. While not shown in Fig. 3, the right and left circular polarization content of the electric field can also be measured using the quarter-wave plate 120, imaging optics 122 and CCD camera 124. While the Fig. 2-3 use Stokes polarimetry to measure the spatially inhomogeneous electric field, in other embodiments the system 100 may be configured to use other methods known in the art to measure the electric field of the output light beam 107.

[0027] The polarimetry receiver may include a calculation module 128 configured to calculate measurements of the spatially inhomogeneous electric field. For example, in the embodiment where the spatially inhomogeneous electric field is measured using Stokes polarimetry, the calculation module 128 may be configured to calculate Stokes parameters 129 from the CCD camera images 126.

[0028] Fig. 4 shows examples of Stokes parameters 129 calculated from the images in Fig. 3. In one embodiment, the calculation module 128 may use equations 1-4 as shown below to determine the Stokes parameters. S0(r,ϕ)=l0(r,ϕ)+l90(r,ϕ) S1(r,ϕ)=l0(r,ϕ)−l90(r,ϕ) S2(r,ϕ)=l45(r,ϕ)−l135(r,ϕ) S3(r,ϕ)=lRCP(r,ϕ)−lLCP(r,ϕ) where I0(r, ϕ), I 45 (r,ϕ), I 90 (r,ϕ), I 135(r,ϕ) are the intensities of an arbitrary vector light field, E(r,ϕ), obtained when analyzed using the polarizer 118 rotated by 0, 45, 90, and 135 degrees with respect to a Cartesian reference coordinate system, and I RCP (r,ϕ), I LCP (r,ϕ) are the intensities of E(r,ϕ) obtained when its right and left circular polarization contents are analyzed using a quarter-wave plate, respectively.

[0029] The calculation module 128 may also be configured to determine the orientation angle and ellipsity of the electric field polarization state. In one embodiment, the calculation module 128 may use Equations 5-6 to determine these values. ψ(r,ϕ)=12tan−1(S2(r,ϕ)S1(r,ϕ)) χ(r,ϕ)=12sin−1(S3(r,ϕ)S0(r,ϕ)) where ψ(r,ϕ) and χ(r,ϕ) are respectively the angles of orientation and the ellipsity of the state of polarization at each spatial point (r, ϕ).

[0030] In one embodiment, the polarimetry receiver is configured to generate a full electric field reconstruction 134 using the polarimetry results. Fig. Figure 5 shows a full electric field reconstruction 134 generated by the polarimetry receiver using the polarimetry results.

[0031] In a preferred embodiment, the calculation module 128 may also be configured to determine the changes in the spatially inhomogeneous state of polarization of the spatially polarization-inhomogeneous light beam. For example, in one embodiment, the polarimetry receiver 116 is configured to determine the changes in the state of polarization of the spatially inhomogeneous light beam by measuring the vector mode spectrum of any light field. Vector modes are spatial modes of light that carry a spatially inhomogeneous state of polarization. The vector mode spectrum is a superposition of the vector modes. The polarimetry receiver 116 may be configured to determine the vector mode spectrum by measuring the optical power in each vector mode of the spectrum.

[0032] The polarimetry receiver 116 may be configured to calculate the vector mode power coefficients in each mode, resulting in a complete vector mode decomposition. For example, the power of each vector mode may be calculated using Equation 7 as shown below. |cl,γ(r)|2=12π∫02πE(r,ϕ)⋅Vl,γ(ϕ)dϕ

[0033] The set of vector mode power coefficients |c ℓ,γ (r)| 2 corresponding to the vector field E(r, ϕ) is the vector mode spectrum. The vector mode spectrum can be measured by determining the power of each vector mode in the spectrum.

[0034] In one embodiment, the polarimetry receiver 116 is configured to use the overlap integral 7 to calculate the power coefficients in each mode and determine the vector mode spectrum. Vector mode decomposition provides a complete measurement of the vector mode spectrum corresponding to the remote object 106.

[0035] Fig. Figure 6 shows a vector mode spectrum for a fully radially polarized beam obtained from the polarimetry results.

[0036] Based on the determined vector mode spectrum 136, the system 100 is configured to measure changes in the polarization state of the spatially polarization-inhomogeneous light beam. For example, in one embodiment, the vector mode spectrum of a light beam can be predetermined, such as based on the specific characteristics of the Q-plate through which the light beam passes. The vector mode spectrum of the light beam that has passed through the Q-plate but has not yet contacted the distant object can also be determined by a polarimetry receiver, varying the parameters of the light beam generation unit 102, or by other means known in the art. The vector mode spectrum of the light beam passing through the Q-plate.

[0037] The polarimetry receiver 116 is configured to determine the differences between the calculated measurements of the spatially inhomogeneous electric field of the output light beam 107 and the vector mode spectrum of the light beam that has passed through the Q-plate (but has not yet contacted the remote object 106), and the differences are representative of features of the remote object 106, such as structural edges and corners of the remote object 106. This results in the detection of features of the remote object 106 by the system 100 in real time.

[0038] While the detection of the spatially inhomogeneous state of polarization of a spatially polarization-inhomogeneous light beam is described by way of example with specific reference to the determination of the vector mode spectrum, the spatially inhomogeneous state of polarization of the spatially polarization-inhomogeneous light beam and the changes in the state of polarization can be determined by measuring other characteristics or features of the light beam or by means known in the art.

[0039] As in Fig. As shown in Figure 7, the present invention is also directed to methods for remote sensing objects as described above. The method can be implemented using any combination of hardware and / or software.

[0040] Referring to Fig. 7, a method 150 for remote object sensing is shown by way of example in accordance with the present principles. In block 160, a spatially polarization-inhomogeneous light beam is generated and directed toward the remote object.

[0041] As in Fig. As shown in Figure 8, the generation of the spatially polarization-inhomogeneous beam may include the step of generating 162 a spatially polarization-inhomogeneous light beam. The spatially polarization-inhomogeneous light beam may then be guided 164 through an optical fiber. The light beam may then be received 166 by a lens that collimates the light beam. The collimated light beam may then be received 168 by a Q-plate that transforms the light beam into spatially polarization-inhomogeneous light.

[0042] The spatially polarization-inhomogeneous light beam then interacts with the distant object and the output light beam is received 10 by the polarimetry receiver as described in detail with reference to the system 100 of the present invention. As in Fig. As shown in Figure 9, the step of receiving the output light beam by a polarimetry receiver may include receiving 172 the output light beam from the remote object by a polarizer. The light beam from the polarizer may then be received 174 by a quarter-wave plate. The light beam may then pass 176 through imaging optics. After being received by imaging optics, the light beam is imaged 178 onto a charge-coupled device camera.

[0043] The output light beam is then measured 180 to obtain a reconstruction of the full electric field of the output light beam. As described in detail with reference to system 100, this can be achieved by Stocks polarimetry or by other means known in the art.

[0044] In block 190, the changes in the spatially inhomogeneous state of polarization of the output light beam are determined. For example, the changes in the spatially inhomogeneous state of polarization of the output light beam can be determined by measuring the vector mode power coefficients in each mode to determine the vector mode spectrum and comparing the measured vector mode spectrum with the vector mode spectrum of the light after it has passed the Q-plate. In one embodiment, the overlap integral from Equation 7 is used to determine the calculated power coefficients. Based on the determined changes in the spatially inhomogeneous state of polarization of the output light beam, features related to the distant object are detected.

[0045] While the above configuration and steps have been illustratively presented in accordance with one embodiment of the present principles, it is contemplated that other types of configurations and steps may also be utilized in accordance with the present principles. While various components have been illustratively described as separate components, the components may be formed in a variety of integrated hardware or software configurations. The foregoing is to be understood as illustrative and exemplary in all respects, but not restrictive, and the scope of the invention as described herein is to be determined not from the detailed description, but rather from the claims when interpreted to the fullest extent permitted by the patent laws.It is to be understood that the embodiments shown and described herein are merely illustrative of the principles of the present invention, and that those skilled in the art may implement various modifications without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention. Therefore, having described aspects of the invention with the details and specificity required by the patent statutes, what is claimed and protected by the patent is set forth below in the following claims.

Claims

[1] A method for object remote sensing comprising the steps: Generating (160) a spatially polarization-inhomogeneous light beam and directing the beam towards a distant object; Receiving (170) an output light beam comprising the spatially polarization-inhomogeneous light beam after the light beam has contacted the remote object by a polarimetry receiver; measuring (180) an electric field of the output light beam; and Determining (190) changes in a spatially inhomogeneous state of the polarization of the output light beam to determine spatial features of the remote object. [2] The method of claim 1, wherein Stokes polarimetry is used to measure the electric field of the output light beam [3] The method according to claim 1, wherein generating a spatially polarization-inhomogeneous light beam comprises the steps of: Generating (162) a spatially polarization-homogeneous light beam: guiding (164) the spatially polarization-homogeneous light beam through an optical fiber; Receiving (166) the spatially polarization-homogeneous light beam through a lens for collimating the light beam; and Receiving (168) a coordinated light beam by a Q-plate, which transforms the light beam into a spatially polarization-inhomogeneous light beam. [4] The method of claim 1, wherein receiving an output light beam includes the steps of: Receiving (172) the output light beam by a polarizer; Receiving (174) the output light beam by quarter-wave plates; Passing (176) the output light beam through imaging optics; and Imaging (178) the light beam onto a charge-coupled device camera. [5] The method of claim 2, further comprising the step of calculating Stokes parameters from the image generated by the charge-coupled device camera. [6] The method of claim 1, further comprising the step of measuring the angle of orientation and the ellipticity of the state of polarization of the output light beam. [7] The method of claim 1, wherein the changes in the spatially inhomogeneous state of polarization of the output light beam are determined by determining a vector mode spectrum of the output light beam and by comparing the vector mode spectrum of the output light beam with a vector mode spectrum of a light beam before contacting the remote object. [8] The method of claim 1, further comprising the step of generating a full electric field reconstruction of the output light beam. [9] The method of claim 7, wherein vector mode power coefficients are calculated to determine the vector mode spectrum of the output light beam [10] A system for object remote sensing, comprising: a spatially polarization-inhomogeneous light beam generating unit (100) configured to generate a spatially polarization-inhomogeneous light beam and to direct the light beam toward a distant object (106); and a polarimetry receiver (116) configured to receive an output light beam comprising the spatially polarization-inhomogeneous light beam after the light beam contacts the remote object, the polarimetry receiver including: a processor (130), memory and an interface (146), wherein the memory is configured to store a calculation module (128) which calculates an electric field of the output light beam and determines changes in a spatially inhomogeneous state of the polarization of the output light beam to determine spatial features of a distant object. [11] The system according to claim 10, wherein the spatially polarization-inhomogeneous light beam generating unit comprises: a laser beam generator (108) configured to generate light beams with spatially polarization-homogeneous light; an optical fiber (106) receiving the light beam from the laser beam generator; a lens (112) that receives and collimates the light beam from the optical fiber; a Q-plate (114), which receives the light beam from the lens and transforms the light beam into a spatially polarization-inhomogeneous light beam. [12] The system of claim 10, wherein the polarimetry receiver includes: a polarizer (118); a quarter-lambda plate (120); imaging optics (122); and a charge-coupled device camera (124). [13] The system of claim 10, wherein the polarizer is a linear polarizer. [14] The system of claim 10, wherein the polarimetry receiver is configured to determine the electric field of the output light beam using Stokes polarimetry. [15] The system of claim 10, wherein the polarimetry receiver is configured to measure the angle of orientation and the ellipsity of the state of polarization of the output light beam. [16] The system of claim 10, wherein the calculation module is configured to determine changes in the spatially polarization-inhomogeneous state of the polarization of the output light beam by determining a vector mode spectrum of the output light beam and by comparing the vector mode spectrum of the output light beam with a vector mode spectrum of a light beam before contacting the remote object. [17] The system of claim 10, wherein the polarimetry receiver is configured to generate a full electric field reconstruction of the output light beam. [18] The system of claim 16, wherein the polarimetry receiver is configured to calculate vector mode power coefficients to determine the vector mode spectrum of the output light beam.

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