Patent Publication Number: US-11656406-B2

Title: Beam steering device and system including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 15/977,785, filed on May 11, 2018, which claims priority from Korean Patent Application No. 10-2017-0093688, filed on Jul. 24, 2017, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     Apparatuses consistent with exemplary embodiments relate to beam steering devices and systems including the same. 
     2. Description of the Related Art 
     Several methods have been proposed to steer a beam to a desired position. There is a mechanical method by which an element irradiated by a beam is mechanically rotated, and a non-mechanical method by which an optical phased array (OPA) is used to steer a beam. 
     Mechanical beam steering utilizes a motor or a microelectromechanical system (MEMS) structure to steer the beam to the desired position. Mechanical beam steering using a motor steers light emitted from a laser diode or from a light-emitting diode while rotating an entire component. Mechanical beam steering using such a motor may increase the volume and cost of a steering system, and noise may be generated by use of the motor. 
     Also, beam steering using a MEMS structure provides only a small viewing angle, and when light of high power is irradiated, a transmission distance of the light may be reduced due to stress applied to a mirror. Also, a vibration problem may occur and thus, the application of this type of beam steering may be limited. Due to the characteristics of a driving method, an operation response time may be slow—i.e. more than several microseconds. 
     On the other hand, as a non-mechanical method using an OPA, there is a method of using interference of a bundle of beams in the form of a waveguide and a method of using a nanostructure as a reflector. In an OPA method using the waveguide, a driving pixel must be provided for each waveguide for electric or thermal driving, and a driver for a driving pixel must be provided, and thus the required circuitry and the device as a whole are complicated and the processing price may increase. In addition to the complexity of the driving pixel, a reflection method using a nanostructure has the problem of long distance detection due to low reflection efficiency, which makes it difficult to put it into practical use. 
     SUMMARY 
     One or more exemplary embodiments may provide a beam steering device to which a transmission type meta structure is applied and a system including the beam steering device. 
     Additional exemplary aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented exemplary embodiments. 
     According to an aspect of an exemplary embodiment, a beam steering device includes a plurality of transmission type optical modulation devices provided to steer an incident beam in different directions, wherein each of the plurality of transmission type optical modulation devices includes: a phase modulator including a nanoantenna in which a plurality of nanostructure rows in which a plurality of nanostructures are connected to each other are arranged and a meta surface including the plurality of nanostructure rows; and a plurality of drivers provided to independently apply an electric signal in unit of the nanostructure row to control a phase change of each of the plurality of nanostructure rows. 
     Each of the plurality of nanostructure rows may form a line type phase modulator, wherein the line type phase modulator includes an array of line type phase modulators that modulate a phase in unit of a line. 
     The plurality of nanostructure rows may be arranged one-dimensionally (i.e. in a one-dimensional array) in each of the plurality of transmission type optical modulation devices. 
     The plurality of transmission type optical modulation devices may include a first transmission type optical modulation device and a second transmission type optical modulation device, and wherein, when a nanostructure row provided in the first transmission type optical modulation device is referred to as a first nanostructure row and a nanostructure row provided in the second transmission type optical modulation device is referred to as a second nanostructure row, a plurality of first nanostructure rows are arranged in a first direction and a plurality of second nanostructure rows are arranged in a second direction. 
     The first transmission type optical modulation device and the second transmission type optical modulation device may be arranged such that the first direction which is an arrangement direction of the plurality of first nanostructure rows and the second direction which is an arrangement direction of the plurality of second nanostructure rows cross with each other. 
     The first transmission type optical modulation device and the second transmission type optical modulation device may have the same structure and are arranged to steer an incident beam in directions crossing each other to steer the incident beam two-dimensionally. 
     The plurality of transmission type optical modulation devices may have the same structure and are arranged to steer the incident beam in different directions. 
     The plurality of transmission type optical modulation devices may be arranged on the same beam path in different planes to steer the incident beam two-dimensionally by a combination of the plurality of transmission type optical modulation devices. 
     The plurality of transmission type optical modulation devices may be spaced apart from each other. 
     The plurality of transmission type optical modulation devices may have a combined structure. 
     The phase modulator may include an active layer having a refractive index varying according to an electrical control and a nanoantenna on the active layer, and wherein the nanostructure row and the active layer corresponding to the nanostructure row form a line type phase modulator. 
     The active layer may include a region having a carrier concentration varying depending on an applied voltage. 
     The active layer may include a transparent conductive oxide, a transition metal nitride, LiNbO 3 , LiTaO 3 , potassium tantalate niobate (KTN), lead zirconate titanate (PZT), or a polymer material having an electro-optic characteristic. 
     The beam steering device may further include an insulating layer between the active layer and the nanoantenna. 
     According to an aspect of another exemplary embodiment, a Light detection and Ranging (LiDAR) system includes: a light source unit; the beam steering device configured to two-dimensionally steer light from the light source unit to an object; and a sensor unit configured to receive light steered in the beam steering device, irradiated to the object, and then reflected from the object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other exemplary aspects and advantages will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG.  1    schematically shows an exemplary structure of a beam steering device according to an exemplary embodiment; 
         FIG.  2    is a cross-sectional view illustrating an exemplary stack structure of a phase modulator applied to the beam steering device of  FIG.  1   ; 
         FIG.  3    shows a process by which a beam steering device two-dimensionally steers an incident beam according to an exemplary embodiment; 
         FIG.  4    shows a process by which a beam steering device two-dimensionally steers an incident beam according to an exemplary embodiment; 
         FIG.  5    is a conceptual diagram for explaining a principle of beam steering by a beam steering device according to an exemplary embodiment; 
         FIGS.  6 A,  6 B, and  6 C  show exemplary shapes of nanostructures according to an exemplary embodiment; 
         FIGS.  7  and  8    are cross-sectional views of exemplary stack structures of a phase modulator applied to a beam steering device according to an exemplary embodiment; and 
         FIG.  9    is a block diagram showing a schematic configuration of a LiDAR system according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a beam steering device and a system including the beam steering device according to exemplary embodiments will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like devices, and the sizes and thicknesses of the respective devices may be exaggerated for convenience of explanation. On the other hand, the exemplary embodiments described below are merely illustrative, and various modifications are possible from these embodiments. Hereinafter, when a layer is described as being provided on “on”, “upper portion”, or “above” of a substrate or other layer, the layer may be on the substrate or directly on another layer, and another layer may be present therebetween. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of devices, modify the entire list of devices and do not modify the individual devices of the list. 
       FIG.  1    schematically shows an exemplary structure of a beam steering device  10  according to an exemplary embodiment. 
     Referring to  FIG.  1   , the beam steering device  10  includes a plurality of transmission type optical modulation devices, for example, first and second transmission type optical modulation devices  100  and  200 , provided to steer an incident beam in different directions. Although a case in which the beam steering device  10  according to an exemplary embodiment includes two transmission type optical modulation devices, that is, the first and second transmission type optical modulation devices  100  and  200 , will be described as an example, the embodiment is not limited thereto, and three or more transmission type optical modulation devices may be arranged to steer the incident beam in different directions. 
     Each of the first and second transmission type optical modulation devices  100  and  200  is a transmission type meta device having a meta surface formed of a nanoantenna. The nanoantenna may be driven in units of nanostructure rows  110  and  210  in which a plurality of nanostructures are connected to each other. That is, in the first and second transmission type optical modulation devices  100  and  200 , the nanoantenna may have a configuration in which a plurality of nanostructure rows  110  and  210  are arranged and may be independently driven in units of the nanostructure rows  110  and  210 . Each of the plurality of nanostructure rows  110  and  210  includes a plurality of nanostructures connected to each other and extending in one dimension. 
     Each of the first and second transmission type optical modulation devices  100  and  200  may include a phase modulator including the plurality of independently driven nanostructure rows  110  and  210  and a plurality of drivers  150  and  250  that control a phase by independently applying an electric signal in units of the nanostructure rows  110  and  210 . Thus, the nanoantenna may have a structure in which the plurality of nanostructure rows  110  and  210  are arranged in an array, and the nanostructure rows  110  and  210  and active layers  130  and  230  corresponding to the nanostructure rows  110  and  210  form a line type phase modulators, such that the phase modulator may have a structure including the line type phase modulators that modulates the phase in units of lines. 
     The phase modulator of the first transmission type optical modulation device  100  and the phase modulator of the second transmission type optical modulation device  200  may have a meta surface including the plurality of nanostructure rows  110  and  210  and may control the phase according to an electric signal independently applied to each nanostructure row from the plurality of drivers  150  and  250 . 
     The first transmission type optical modulation device  100  may include, for example, a first phase modulator and the first driver  150  disposed on a first substrate  101  that is transparent with respect to a wavelength used in the optical modulation device. The [example of the wavelength to which the substrate is transparent] first phase modulator may include the first active layer  130  having a refractive index that is variable according to application of an electrical signal, and a first nanoantenna in which the plurality of first nanostructure rows  110 , each including a plurality of nanostructures connected to each other, are arranged on the first active layer  130 . A first insulating layer  120  may be provided between the first active layer  130  and the first nanostructure row  110 . 
     The second transmissive type optical modulation device  200  may include, for example, a second phase modulator and the second driver  250  disposed on a second substrate  201  which is transparent with respect to a wavelength used in the optical modulation device. The second phase modulator may include the second active layer  230  having a refractive index that is variable according to application of an electrical signal, and a second nanoantenna in which the plurality of second nanostructure rows  210 , each including a plurality of nanostructures connected to each other, are arranged on the second active layer  230 . A second insulating layer  220  may be provided between the second active layer  230  and the second nanostructure row  210 . 
     The first and second drivers  150  and  250  may be provided to independently apply an electric signal to each the first nanostructure row  110  and the second nanostructure row  210 , respectively, thereby electrically controlling refractive indexes of the first and second active layers  130  and  230  corresponding to the first and second nanostructure rows  110  and  210 . 
     The first phase modulator and the second phase modulator of the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200  may include a phase modulator  300  having a structure as shown in  FIG.  2   . 
       FIG.  2    is a cross-sectional view illustrating an exemplary stack structure of the phase modulator  300  applied to the beam steering device  10  of  FIG.  1   . 
     Referring to  FIG.  2   , the phase modulator  300  may include, for example, an active layer  330 , having a refractive index that is variable according to an electrical signal applied thereto, disposed on a substrate  301  that is transparent with respect to a wavelength used in the phase modulator, and a nanoantenna  315  disposed on the active layer  330 . The phase modulator  300  may further include an insulating layer  320  between the active layer  330  and the nanoantenna  315 . The substrate  301  may correspond to the first substrate  101  and the second substrate  201  in  FIG.  1   . The active layer  330  may correspond to the first active layer  130  and the second active layer  230  in  FIG.  1   . The nanoantenna  315  may correspond to a first nanoantenna, in which the plurality of first nanostructure rows  110  are arranged, and a second nanoantenna, in which the plurality of second nanostructure rows  210  are arranged, in  FIG.  1   . The insulating layer  320  may correspond to the first insulating layer  120  and the second insulating layer  220  in  FIG.  1   . 
     The substrate  301  may be transparent with respect to the wavelength used in the modulator, and may be formed of any of various insulating materials such as a material containing silicon, a glass material, a plastic material, or the like. 
     The active layer  330  may be formed of a material having an optical characteristic that is variable depending on an external signal. The external signal may be an electrical signal. The active layer  330  may be formed of a transparent conductive oxide (TCO) such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), and gallium zinc oxide (GZO). Transition metal nitrides such as TiN, ZrN, HfN, and TaN may also be used. In addition, electro-optic materials such as LiNbO 3 , LiTaO 3 , potassium tantalate niobate (KTN), and lead zirconate titanate (PZT) having effective permittivity that is variable upon application of an electric signal may be used. Any of a variety of polymeric materials having an electro-optic characteristic may be used. 
     The active layer  330  may include a region  335  in which a concentration of charge carriers is variable depending on whether a voltage is applied. The carrier variable region  335 , within which the carrier concentration is variable, may be formed in the active layer  330 , in a region adjacent to the insulating layer  320 , i.e., at a position close to a boundary between the insulating layer  320  and the active layer  330 . In the case of the first and second transmission type optical modulation devices  100  and  200  of  FIG.  1   , as shown in  FIG.  3   , the first active layer  130  and the second active layer  230  may respectively include carrier variable regions  135  and  235  in which the carrier concentration is variable in regions adjacent to the first and second insulating layers  120  and  220 . 
     The carrier concentration of the carrier variable region  335  is variable depending on an applied voltage. The variable carrier concentration may change the permittivity of the active layer  330 , specifically, a dielectric constant property with respect to a wavelength, such that a mode of modulating light incident on the phase modulator  300  may be adjusted. 
     The permittivity of the active layer  330  has a value that varies with the wavelength. A relative permittivity ε r  with respect to the permittivity ε 0  of vacuum is referred to as a dielectric constant, and a real part of the dielectric constant of the active layer  330  represents a value of 0 in a predetermined wavelength band. The wavelength band in which the real part of the dielectric constant has a value of 0 or very close to 0 is referred to as an epsilon near zero (ENZ) wavelength band. A dielectric constant of most materials is a function of wavelength and may be expressed as a complex number. A dielectric constant of vacuum is 1, and in the case of a typical dielectric material, the real part of the dielectric constant is a positive number greater than 1. In the case of metal, the real part of the dielectric constant may be a negative number. In most wavelength bands, a dielectric constant of most materials has a value greater than 1, but, in a particular wavelength, the real part of the dielectric constant may have a value of 0. 
     When the real part of the dielectric constant has a value of 0 or very close to 0, the material having the dielectric constant is known to have a specific optical characteristic. An operating wavelength band of the phase modulator  300  of the exemplary embodiment may be a region including the ENZ wavelength band of the active layer  330 . That is, by similarly setting a resonance wavelength band of the nanoantenna  315  and the ENZ wavelength band of the active layer  330 , a range of controlling the optical modulation performance by the applied voltage may be further increased. 
     The ENZ wavelength band of the active layer  330  may vary depending on the carrier concentration formed in the carrier variable region  335 . In order to utilize the ENZ wavelength band of the active layer  330 , the electrical signal applied to the phase modulator  300  may be controlled through a driver  350  such that the resonance wavelength band of the nanoantenna  315  is similar or identical to a wavelength band representing the ENZ property of the active layer  330 . 
     The nanoantenna  315  is an artificial structure having sub-wavelength dimensions (e.g. dimensions less than any wavelength of RF, infrared light or visible light), and strongly interacts with light in a predetermined wavelength band. In this regard, the term “sub-wavelength” refers to a dimension smaller than a wavelength of light to be modulated by the phase modulator  300 , that is, the operating wavelength of the nanoantenna  315 . For example, the wavelength of light to be modulated by the phase modulator  300  may be any wavelength of RF, infrared light or visible light. Any dimension of a shape of the nanoantenna  315  may be a sub-wavelength dimension. 
     The above-described function of the nanoantenna  315  is known to be caused by surface plasmon resonance occurring at a boundary between a conductive material and a dielectric material. A resonance wavelength varies depending on a detailed shape of the nanoantenna  315 . 
     In the phase modulator  300  according to an exemplary embodiment, the nanoantenna  315  may have a shape comprising the plurality of first and second nanostructure rows  110  and  210  are arranged as shown in  FIG.  1   , where each of the first and second nanostructure rows  110  and  210  comprise a plurality of nanostructures connected to each other. The nanostructures may have any of various shapes. 
     The nanoantenna  315  may be implemented as a conductive nanoantenna. That is, a highly conductive metal material that may generate surface plasmon excitation with a conductive material forming the first and second nanostructure rows  110  and  210  in  FIG.  1    may be employed. For example, the nanoantenna  315  may be formed of at least one selected from Cu, Al, Ni, Fe, Co, Zn, Ti, ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), silver (Ag) and gold (Au) and may include an alloy including at least one of these. Also, a highly conductive two-dimensional material, such as graphene, or a conductive oxide may be employed. The conductive nanoantenna  315  may have a small thickness so as to be able to transmit a wavelength used in the phase modulator. 
     Also, the nanoantenna  315  may be formed of a dielectric material and may be implemented as a dielectric nanoantenna. A refractive index of the active layer  330  may be less than a refractive index of the dielectric nanoantenna. The dielectric nanoantenna may be formed of a material having a dielectric constant of 10 or more. 
     That is, the dielectric nanoantenna may exhibit high antenna efficiency by using Mie resonance due to displacement current. To this end, the dielectric nanoantenna may have a shape with sub-wavelength dimensions and may have a high permittivity, for example, a permittivity higher than the permittivity of the active layer  330 . 
     The term “sub-wavelength” refers to a dimension smaller than the wavelength of the light to be modulated by the phase modulator  300 . At least one dimension defining the shape of the dielectric nanoantenna may be a sub-wavelength dimension. For example, when the wavelength of the light to be modulated by the phase modulator  300  is λ, the sub-wavelength dimension may be less than 212. 
     When the nanoantenna  315  is implemented as a dielectric nanoantenna, the dielectric nanoantenna may have a refractive index greater than that of the active layer  330 . The dielectric nanoantenna may have a refractive index greater than the largest refractive index in a range in which the refractive index of the active layer  330  is variable according to application of an electrical signal. The dielectric constant of the dielectric nanoantenna may be, for example, 10 or more. 
     Meanwhile, any of various insulating materials may be used for the insulating layer  320  and may include, for example, SiNx, SiOx, Al 2 O 3 , or HfO 2 . 
     Referring to  FIG.  1   , the plurality of first nanostructure rows  110  provided in the first transmission type optical modulation device  100  may be arranged in a first direction and the plurality of second nanostructure rows  210  provided in the second transmission type optical modulation device  200  may be arranged in a second direction. 
     At this time, the first direction and the second direction may be directions which intersect each other. For example, the first transmission type light modulation device  100  and the second transmission type light modulation device  200  may be arranged such that the first direction, which is an arrangement direction of the plurality of first nanostructure rows  110 , and the second direction, which is an arrangement direction of the plurality of second nanostructure rows  210 , intersect each other.  FIG.  1    exemplarily shows a case in which the first and second transmission type optical modulation devices  100  and  200  are arranged such that the first direction, which is the arrangement direction of the first nanostructure rows  110  of the first transmission type optical modulation device  100 , corresponds to the x-axis direction, and the second direction, which is an arrangement direction of the plurality of second nanostructure rows  210  of the second transmission type light modulation device  200 , corresponds to the y-axis direction. As shown, the arrangement direction of the nanostructure rows, for example, the x-axis direction for the first nanostructure rows  110  of the first transmission type optical modulation device  100 , is perpendicular to the direction in which each of the nanostructure rows extends. As shown, each of the first nanostructure rows extends in the y-axis direction in the first transmission type optical modulation device  100 . 
     Alternately, when the plurality of transmission type optical modulation devices are configured as the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200 , the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200  may have the same structure and may be arranged to steer incident beams in directions intersecting each other. In this case, the incident beam may be two-dimensionally steered by a combination of the first and second transmission type optical modulation devices  100  and  200 . The beam steering device  10  according to an exemplary embodiment may thereby implement two-dimensional beam steering. 
     For two-dimensional beam steering by the beam steering device  10  according to an exemplary embodiment, it may be possible to steer in both the first direction and the second direction, for example, the x direction and the y direction. 
     The beam steering device  10  according to an exemplary embodiment may include, for example, the first and second transmission type optical modulation devices  100  and  200  corresponding to transmission type meta devices, configuring an x-direction steering unit as the first transmission type optical modulation device  100  and a y-direction steering unit as the second transmission type optical modulation device  200 . 
     The plurality of first drivers  150  may be connected to the plurality of first nanostructure rows  110  constituting the first nanoantenna of the first transmission type optical modulation device  100  so as to independently apply electric signals to each of the plurality of first nanostructure rows  110 , and thus an incident beam may be steered, for example, in the x-axis direction. The plurality of second drivers  250  may be connected to the plurality of second nanostructure rows  210  corresponding to the second nanoantenna of the second transmission type light modulation device  200  so as to independently apply electric signals to each of the plurality of second nanostructure rows  210 , and thus an incident beam may be steered, for example, in the y-axis direction. 
     The beam steering device  10  according to an exemplary embodiment may include transmission type optical modulation devices, and thus the first and second transmission type optical modulation devices  100  and  200  may be positioned on the same beam path on different planes. Also, two-dimensional beam steering may be realized by using the first and second transmission type optical modulation devices  100  and  200  having the same structure and arranging nanostructure rows to cross each other, that is, at 90 degree angles to each other. 
       FIG.  3    shows a process by which the beam steering device  10  steers an incident beam two-dimensionally according to an exemplary embodiment. 
     Referring to  FIG.  3   , the first nanostructure rows  110  are arranged in the x direction in the first transmission type optical modulation device  100 , the second nanostructure rows  210  are arranged in the y direction in the second transmission type optical modulation device  200 , and the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200  are sequentially arranged from a side in which a beam is incident. 
     When the beam is incident on the first transmission type optical modulation device  100 , since the first driver  150  controls an electric signal applied to the first nanostructure rows  110 , a traveling direction of the incident beam may be controlled in an x-z plane by the first transmission type optical modulation device  100 . The beam steered in the x-z plane is then incident on the second optical transmission type optical modulation device  200 . Since the second driver  250  controls an electric signal applied to the second nanostructure row  210 , the traveling direction of the incident beam may be controlled in the y-z plane by the second transmission type optical modulation device  200 . Therefore, the beam transmitted through the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200  may be steered two-dimensionally. 
       FIGS.  1  and  3    illustrate a case in which there is a space between the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200 . Alternately, the first and second transmission type optical modulation devices  100  and  200  may be combined together, as shown in  FIG.  4   , instead of being spaced apart. 
     As shown in  FIG.  4   , when the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200  are combined together, for example, the second transmission type optical modulation device  200  may include an insulating layer, instead of the second substrate  201  of the first transmission type optical modulation device  100 . That is, an insulating layer is stacked on the first nanostructure row  110  of the first transmission type optical modulation device  100 , and the second phase modulator and the second driver  250  forming the second transmission type optical modulation device  200  may be formed on the insulating layer. 
       FIG.  5    is a conceptual diagram for explaining a principle of beam steering by the beam steering device  10  according to an exemplary embodiment.  FIG.  5    shows an example of a beam steering principle in an optical modulation device in which nanostructure rows are arranged in an x direction, for example, the first transmission type optical modulation device  100 . 
     Each of the plurality of first nanostructure rows  110  included in a first phase modulator of the first transmission type optical modulation device  100  may modulate differently depending on an electrical signal applied from the first driver  150  corresponding to a phase of incident light Li. Modulated light Lm output by the first transmission type optical modulation device  100  may be perpendicular to a transition line LL connecting phase values of the adjacent first nanostructure rows  110 . 
     When a phase transition of the adjacent first nanostructure rows  110  is linear, an adjacent phase difference is Asp, and a distance between the adjacent first nanostructure rows  110  is d, the incident light Li of a wavelength  2  is steered in an angular direction θ defined as follows.
 
sin θ=Δϕλ/2 πd  
 
     The angular direction θ is a direction forming an angle θ with respect to the z direction in an x-z plane. 
     According to the above conditions, the voltage applied to each of the first nanostructure rows  110  may be set to form a desired phase transition. 
     The voltage, for example, V 1  to V 9 , applied to each of the first nanostructure rows  110  may be controlled individually. Since the angle formed by the transition line LL with the x-axis may be adjusted, a direction of the modulated light Lm in which the incident light Li is steered may be adjusted in the x-z plane. 
     By the same principle, the voltage applied to each of the second nanostructure rows  210  of the second transmission type optical modulation device  200  may be controlled individually and a modulated light by the second transmission type optical modulation device  200  may be adjusted by an angle formed by a transition line connecting phase values by the adjacent second nanostructure rows  210  with respect to they direction, and thus a direction of a modulated beam in which the beam incident on the second transmission type optical modulation device  200  is steered may be adjusted in the y-z plane. 
     Therefore, the directions of the modulated beams steered by the first transmission type optical modulation device  100  and the second transmission type optical modulation device  200  may be two-dimensionally adjusted. 
     Nanostructures of the first nanostructure row  110  and the second nanostructure row  210  of to the beam steering device  10  according to an exemplary embodiment may have any of various shapes, for example, as shown in  FIGS.  6 A through  6 C . 
     As shown in  FIG.  6 A , a nanostructure  410  may have a cross shape, and lengths in two directions forming the cross shape may be the same or different. 
     As shown in  FIG.  6 B , a nanostructure  420  may have a star shape in which a plurality of bars are crossed. 
     As shown in  FIG.  6 C , a nanostructure  430  may be formed by cross-shaped nano holes.  FIG.  6 C  shows a reverse shape of  FIG.  6 A  but is not limited thereto. For example,  FIG.  6 C  may be formed in a reverse shape of  FIG.  6 B  or in another reverse shape. 
     A nanostructure may be a combination of two or more of the illustrated shapes, or may be formed in any of various other shapes. 
     An example in which a phase modulator applied to the first and second transmission type optical modulation devices  100  and  200  of the beam steering device  10  according to an exemplary embodiment is formed as a stacked structure of the active layer  33  including the carrier variable region  335 , the insulating layer  320 , and the nanoantenna  315  as shown in  FIG.  2    is described above, but any of various embodiments may be possible. 
     For example, the phase modulator applied to the first and second transmission type optical modulation devices  100  and  200  of the beam steering device  10  according to an exemplary embodiment may be a structure in which a first semiconductor layer  450  of a first conductivity type and a second semiconductor layer  460  of a second conductivity type, opposite to that of the first semiconductor layer  450 , are stacked on the substrate  301 , which is transparent with respect to a wavelength used in the modulator, to form a p-n junction, and the nanoantenna  315  is provided thereon as shown in  FIG.  7   . 
     Also, the phase modulator applied to the first and second transmission type optical modulation devices  100  and  200  of the beam steering device  10  according to an exemplary embodiment may be a structure in which the active layer  470  is formed of an electro-optic (EO) material or a thermal-optic (TO) material on the substrate  301 , which is transparent with respect to the wavelength used in the modulator, and the nanoantenna  315  is provided directly on the active layer  470  as shown in  FIG.  8   . 
     The active layer  470  may be formed of an electro-optic material, for example, LiNbO 3 , LiTaO 3 , potassium tantalate niobate (KTN), or lead zirconate titanate (PZT) having effective permittivity that is variable when an electric signal is applied thereto. Also, any of a variety of polymeric materials having an electro-optic characteristic may be used. 
     An example in which the beam steering device  10 , according to an exemplary embodiment, includes first and second transmission type optical modulation devices  100  and  200  as a plurality of transmission type optical modulation devices such that arrangement directions of nanostructure rows of the first and second transmission type optical modulation devices  100  and  200  intersect each other is described and shown above. In the case in which the beam steering device  10  includes three or more transmission type optical modulation devices as the plurality of transmission type optical modulation devices, the arrangement directions of nanostructure rows may be at different angles, and an incident beam may be steered two-dimensionally by adjusting an electric signal applied to each nanostructure row. 
       FIG.  9    is a block diagram showing a schematic configuration of a LiDAR system  1000  according to an exemplary embodiment. 
     Referring to  FIG.  9   , the LiDAR system  1000  includes a light source unit  1200  that emits light, a beam steering device  1300  that steers the light emitted from the light source unit  1200  toward an object OBJ, and a sensor unit  1400  that senses the light reflected from the object OBJ. 
     The LiDAR system  1000  may further include a control unit  1100  that adjusts a phase profile of the beam steering device  1300  and a signal processing unit  1500  that processes a signal sensed by the sensor unit  1400 . 
     The light source unit  1200  irradiates light to be used for analyzing a position and a shape of the object OBJ. The light source unit  1200  may include a light source that generates and emits light having a predetermined wavelength. The light source unit  1200  may include a light source such as a laser diode (LD), a light-emitting diode (LED), a superluminescent diode (SLD), etc. that generates and irradiates light in a wavelength band suitable for analyzing the position and the shape of the object OBJ, for example, light in an infrared band wavelength. The light source unit  1200  may generate and irradiate light in a plurality of different wavelength bands. The light source unit  1200  may generate and irradiate pulsed light or continuous light. 
     The beam steering device  1300  may include a plurality of transmission type optical modulation devices arranged to independently modulate a phase of the incident light Li to steer the incident beam in different directions so as to steer the incident beam two-dimensionally. The beam steering device  1300  may have a configuration of the beam steering device  10  of the exemplary embodiment described above with reference to  FIGS.  1  to  8    or a modified configuration thereof. 
     Other optical members, for example, members for a path adjustment, for the wavelength division of light irradiated from the light source unit  1200 , or for an additional modulation, may be further arranged between the light source unit  1200  and the beam steering device  1300  and/or between the beam steering device  1300  and the object OBJ. 
     The control unit  1100  may control input signals to a plurality of drivers of the plurality of transmission type optical modulation devices included in the beam steering device  1300  so that the beam steering device  1300  has a phase profile desired to perform a beam steering function. The control unit  1100  may also control the beam steering device  1300  so that a steering direction of the beam steering device  1300  is sequentially controlled and the object OBJ is scanned. The beam steering device  1300  is capable of beam steering in a two dimensional direction by arranging the plurality of transmission type optical modulation devices that steer the incident beam in different directions on the same path and different planes, and thus the object OBJ may be scanned along the two-dimensional direction. Reflected light Lr reflected from the object OBJ while the object OBJ is being scanned is sensed by the sensor unit  1400 . A sensed optical signal may be transmitted to the signal processing unit  1500  and may be used for analyzing a presence of the object OBJ, a position, a shape, and the like. 
     The sensor unit  1400  may include an array of a plurality of sensors for detection of light that senses light reflected from the object OBJ. The sensor unit  1400  may include arrays of sensors capable of sensing light of a plurality of different wavelengths. 
     The signal processing unit  1500  may perform a predetermined operation from the optical signal detected by the sensor unit  1400 , for example, an operation for time-of-flight measurement, and determine a three-dimensional shape of the object OBJ from the predetermined operation. The signal processing unit  1500  may use various operation methods. For example, a direct time measurement method projects pulsed light onto the object OBJ, measures the time the light takes to be reflected by the object OBJ and returned with a timer, and obtains a distance. A correlation method projects pulsed light onto the object OBJ and measures a distance from brightness of the light reflected by the object OBJ and returned. A phase delay measurement method is a method of projecting continuous wave light such as a sine wave onto the object OBJ, detecting a phase difference of the light reflected by the object OBJ and returned and converting the detected phase different into a distance. The signal processing unit  1500  may include a memory for storing programs and other data required for such operations. 
     The signal processing unit  1500  may transmit information about a result of operations, that is, the shape and the position of the object OBJ, to other units. For example, the above information may be transmitted to a drive control unit or a warning system of an autonomous drive device employing the LiDAR system  1000 . 
     The LiDAR system  1000  may be used as a sensor for acquiring three-dimensional information about an object in real time, and thus may be applied to an autonomous driving device, for example, an unmanned vehicle, an autonomous vehicle, a robot, a drone or the like. The LiDAR system  1000  may be applied not only to an autonomous driving device but also to a black box or the like so that the LiDAR system  1000  may be used to detect front and rear obstacles at night, at a time at which it is difficult to identify an object with only an image sensor. 
     According to a beam steering device and a system to which the beam steering device is applied according to exemplary embodiments, a plurality of light modulation devices composed of a transmission type meta device are arranged on the same beam path of different planes to steer a beam in different directions, and thus the beam may be steered two-dimensionally. 
     Since the beam steering device is implemented as a transmission type structure, efficiency of a reflective type structure is good and a driver may be positioned outside a nanoantenna, and thus visibility may be wide and the configuration thereof may be simplified. 
     While the beam steering device  1300  including the plurality of transmission type optical modulation devices  100  and  200  that steer beams in different directions has been described with reference to the exemplary embodiments shown in the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims. It should be understood that exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.