Patent Publication Number: US-8111458-B2

Title: Optical device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This patent application claims priority from a Japanese patent application No. 2008-002595 filed on Jan. 9, 2008, the contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an optical device. More particularly, the present invention relates to an optical device including phasors. 
     2. Related Art 
     A depolarization plate obtained by laminating three wavelength plates having a predetermined phase difference and an in-plane azimuthal angle has been known as disclosed, for example, in Japanese Patent Application Publication No. 2006-113123. This depolarization plate functions as a ¼ wavelength plate in the wideband wavelength range between 400 nm and 700 nm. Moreover, there has been known a depolarization plate that is divided into two portions by a border line passing through the center of the depolarization plate, in which one side of the depolarization plate is a ½ wavelength plate an optical axis of which is parallel or perpendicular to the border line and the other side is a ½ wavelength plate an optical axis of which has an angle with the border line of 45 degrees, as disclosed, for example, in Japanese Patent No. 2995989. 
     Since the depolarization plate disclosed in Japanese Patent Application Publication No. 2006-113123 converts a ray of linearly-polarized light into a ray of circularly-polarized light (or elliptically-polarized light), it is impossible to acquire light obtained by scrambling a polarized component of the linearly-polarized light. Moreover, in the technique of Japanese Patent No. 2995989, it is impossible to obtain depolarized light on the whole face perpendicular to a direction in which light travels. 
     SUMMARY 
     Therefore, it is an object of an aspect of innovations of the present invention to provide an optical device that can solve the foregoing problems. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention. 
     That is, according to an aspect related to the innovations herein, one exemplary an optical device may include: a plurality of first phasors having substantially the same phase delaying axis as each other; and a plurality of second phasors having substantially the same phase delaying axis as each other in a direction different from that of the first phasors and providing a phase difference substantially the same as that provided by the first phasors, in which the plurality of first phasors and the plurality of second phasors are arranged on substantially the same face, a density of the first phasors is substantially the same as a density of the second phasors, and a spatial distribution of the density of the first phasors and a spatial distribution of the density of the second phasors are substantially uniform. 
     The summary does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view exemplary showing an optical system  100  according to an embodiment. 
         FIG. 2  is a view exemplary showing a cross section that is parallel to a propagation direction of incident light in an optical element  110 . 
         FIG. 3  is a view exemplary showing cross sections that are perpendicular to propagation directions of incident light in a first phasor array  210  and a second phasor array  220 . 
         FIGS. 4A and 4B  are views showing other examples of arrangement of phasors in the first phasor array  210  and the second phasor array  220 . 
         FIG. 5  is a view showing another example of a cross section that is perpendicular to the propagation direction of incident light in the optical element  110 . 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The embodiments of the invention will now be described based on the preferred embodiments, which do not intend to limit the scope of the present invention, but just exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention. 
       FIG. 1  shows an example of an optical system  100  according to an embodiment. An object of the optical system  100  is to generate light of which polarized components are substantially removed. The optical system  100  includes a light source  150 , a lens system  130 , and an optical element  110 . The lens system  130  includes a plurality of lenses  131  to  133  and a diaphragm  135 . The lens system  130  collects light generated from the light source  150 . In addition, the lens system  130  and the optical element  110  function as an optical device according to the present invention. 
     The light source  150  may be a polarized light source for emitting polarized light. The polarized light includes completely polarized light and partially polarized light. Specifically, the polarized light may be light of which degree of polarization is larger than a predetermined value. As an example, the light source  150  may be a laser source. The light generated from the light source  150  is incident on the lens  131 . The light passing through the lens  131  is diaphragmed by the diaphragm  135 . 
     The optical element  110  is provided in the vicinity of the diaphragm  135 . The optical element  110  substantially removes depolarized components of the light that is emitted from the light source  150  and is diaphragmed by the diaphragm  135 . The light passing through the optical element  110  is changed into light having a predetermined beam diameter by means of the lens  132  and the lens  133 . 
       FIG. 2  shows an example of a cross section that is parallel to a propagation direction of incident light in the optical element  110 . The optical element  110  has a first phasor array  210  and a second phasor array  220 . The optical element  110  is formed by disposing the first phasor array  210  and the second phasor array  220  along the propagation direction of incident light. In addition, the outgoing face of light on the second phasor array  220  may be in contact with the incoming face of light on the first phasor array  210 . In addition, as described below, as an example, the first phasor array  210  may be a ½ phasor array in which a plurality of ½ phasors is arranged, and the second phasor array  220  may be a ¼ phasor array in which a plurality of ¼ phasors is arranged. 
       FIG. 3  shows an example of cross sections that are perpendicular to a propagation direction of incident light in the first phasor array  210  and the second phasor array  220 . The first phasor array  210  includes first phasors  311   a  and first phasors  311   b  (hereinafter, referred to as first phasors  311 ), and second phasors  312   a  and second phasors  312   b  (hereinafter, referred to as second phasors  312 ). The first phasor array  210  is formed by arranging a plurality of units on a face, in which each unit includes the first phasor  311   a , the first phasor  311   b , the second phasor  312   a , and the second phasor  312   b.    
     In addition, a lattice of the first phasor array  210  shown in  FIG. 3  shows either of the first phasor  311  and the second phasor  312  in the present invention, and an arrow in the lattice shows a direction of a phase delaying axis of each phasor. As shown in  FIG. 3 , the first phasors  311  have a phase delaying axis in the direction of the y axis, and the second phasors  312  have a phase delaying axis in a direction forming a 45 degree angle with the y axis. 
     In this manner, the second phasors  312  have a phase delaying axis in a direction different from that of the first phasors  311 . Specifically, the phase delaying axis of the first phasors  311  and the phase delaying axis of the second phasors  312  substantially form an angle of 45 degrees. Moreover, the second phasors  312  provides substantially the same phase difference as that of the first phasors  311 . Specifically, the first phasors  311  and the second phasors  312  may be ½ wavelength plates. In addition, the first phasors  311  and the second phasors  312  are arranged on substantially the same face. In addition, it is sufficient that the first phasors  311  and the second phasors  312  be arranged on substantially the same face, and thus it is not necessary that both phasors be arranged on completely the same face. 
     The second phasor array  220  includes third phasors  321   a  and third phasors  321   b  (hereinafter, referred to as third phasors  321 ), and fourth phasors  322   a  and fourth phasors  322   b  (hereinafter, referred to as fourth phasors  322 ). The second phasor array  220  is formed by arranging a plurality of units on a face, in which each unit includes the third phasor  321   a , the third phasor  321   b , the fourth phasor  322   a , and the fourth phasor  322   b . In addition, the third phasors  321  and the fourth phasors  322  provide a phase difference different from that provided by the first phasors  311  and the second phasors  312 . Moreover, the fourth phasors  322  provides substantially the same phase difference as that of the third phasors  321 . Specifically, the third phasors  321  and the fourth phasors  322  may be ¼ wavelength plates. 
     In addition, a lattice of the second phasor array  220  shown in  FIG. 3  shows either of the third phasor  321  and the fourth phasor  322  in the present invention similarly to the first phasor array  210 , and an arrow in the lattice shows a direction of the phase delaying axis. As shown in  FIG. 3 , the third phasors  321  have a phase delaying axis in the direction of the x axis, and the fourth phasors  322  have a phase delaying axis in the y-axis direction forming 90 degrees to the direction of the x axis. In this manner, the fourth phasors  322  have a phase delaying axis in a direction different from that of the third phasors  321 . As an example, the phase delaying axis of the third phasors  321  is substantially perpendicular to the phase delaying axis of the fourth phasors  322 . Moreover, the third phasors  321  and the fourth phasors  322  are arranged on substantially the same face. In addition, it is sufficient that the third phasors  321  and the fourth phasors  322  be arranged on substantially the same face, and thus it is not necessary that both phasors be arranged on a completely same face. 
     In this manner, the first phasor array  210  is formed by arranging the first phasors  311  and the second phasors  312  in a matrix. Moreover, the second phasor array  220  is formed by arranging the third phasors  321  and the fourth phasors  322  in a matrix. Then, the first phasor array  210  in which the first phasors  311  are arranged on a face and the second phasor array  220  in which the fourth phasors  322  are arranged on a face are arranged along a propagation direction of incident light. 
     In addition, in the first phasor array  210 , densities of the first phasors  311  and the second phasors  312  may be substantially the same, and the spatial distribution of the density of the first phasors  311  and the spatial distribution of the density of the second phasors  312  may be substantially uniform. In addition, density may be the number of phasors per unit area, or may be the area occupied by phasors per unit area. 
     For example, the first phasor array  210  may have substantially the same number of the first phasors  311  and the second phasors  312 , and the first phasors  311  and the second phasors  312  may be equally arranged on substantially the same face in a predetermined pattern. In addition, the first phasors  311  and the second phasors  312  may be arranged in random order. In addition, the first phasor  311  and the second phasor  312  may have substantially the same area. Moreover, the area occupied by the first phasors  311  in the first phasor array  210  and the area occupied by the second phasors  312  in the first phasor array  210  may be substantially the same. 
     Moreover, similarly, in the second phasor array  220 , densities of the third phasors  321  and the fourth phasors  322  may be substantially the same, and the spatial distribution of the density of the third phasors  321  and the spatial distribution of the density of the fourth phasors  322  may be substantially uniform. In addition, density may be the number of phasors per unit area, or may be the area occupied by phasors per unit area. 
     For example, the second phasor array  220  may also have substantially the same number of the third phasors  321  and the fourth phasors  322 , and the third phasors  321  and the fourth phasors  322  may be equally arranged in a predetermined pattern. In addition, the third phasors  321  and the fourth phasors  322  may be arranged in random order. In addition, the third phasors  321  and the fourth phasors  322  may have substantially the same area. Moreover, the area occupied by the third phasors  321  in the second phasor array  220  and the area occupied by the fourth phasors  322  in the second phasor array  220  may be substantially the same. In addition, it is preferred that densities of the first phasors  311 , the second phasors  312 , the third phasors  321 , and the fourth phasors  322  be substantially the same. 
     In addition, the third phasors  321   a  and the first phasors  311   a  are aligned along the propagation direction of incident light so that the incident light passing through the third phasors  321   a  passes through the first phasors  311   a . Moreover, similarly, the fourth phasors  322   a  and the second phasors  312   a  are aligned along the propagation direction of incident light so that the incident light passing through the fourth phasors  322   a  passes through the second phasors  312   a . Moreover, the third phasors  321   b  and the first phasors  311   b  are also aligned similarly. The fourth phasors  322   b  and the second phasors  312   b  are also aligned similarly. In this manner, each of phasors including the plurality of first phasors  311  and the plurality of second phasors  312  is arranged along the propagation direction of incident light together with at least one of phasors including the plurality of third phasors  321  and the plurality of fourth phasors  322  which are included in the second phasor array  220 . 
     Then, a density of the first phasors  311  and the third phasors  321  respectively arranged along the propagation direction of incident light, a density of the first phasors  311  and the fourth phasors  322  arranged along the propagation direction of incident light, a density of the second phasors  312  and the third phasors  321 , and a density of the second phasors  312  and the fourth phasors  322  may be substantially the same. In other words, the densities of a set of the first phasors  311  and the third phasors  321  that are aligned, a set of the first phasors  311  and the fourth phasors  322  that are aligned, a set of the second phasors  312  and the third phasors  321  that are aligned, and a set of the second phasors  312  and the fourth phasors  322  that are aligned may be substantially the same. 
     Stokes parameters (S′ 0 , S′ 1 , S′ 2 , S′ 3 ) for outgoing light after passing through the optical element  110  are expressed by the following equation. In addition, in the following equation, Stokes parameters for incoming light are (S 0 , S 1 , S 2 , S 3 ), the angle of the optical axis for the phasors included in the second phasor array  220  is θ 1 , the angle of the optical axis for the phasors included in the first phasor array  210  is θ 2 , and the retardation for the second phasor array  220  is Δ. 
     
       
         
           
             
               
                 
                   
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     By means of the above equation, when the incident light is respectively linearly-polarized light, elliptically-polarized light, and circularly-polarized light, Stokes parameter for light passing through the third phasors  321  and the first phasors  311 , light passing through the fourth phasors  322  and the first phasors  311 , light passing through the third phasors  321  and the second phasors  312 , and light passing through the fourth phasors  322  and the second phasors  312  are respectively computed. 
     As an example, when the incident light is linearly-polarized light having (S 1 , S 2 , S 3 )=(0.5, 0.3, 0.0), (S 1 , S 2 , S 3 ) components of the Stokes parameter for outgoing light passing through the above combined phasors are (0.4, −0.4, −0.14), (0.4, −0.4, 0.14), (−0.4, 0.4, −0.14), and (−0.4, 0.4, 0.14). When these (S 1 , S 2 , S 3 ) components for the outgoing light are added every component, it becomes that S 1 =0, S 2 =0, and S 3 =0. Therefore, the optical element  110  can substantially remove the polarization of the incident light of the above linearly-polarized light. 
     Moreover, when the incident light is elliptically-polarized light having (S 1 , S 2 , S 3 )=(−0.5, 0.7, 0.5), (S 1 , S 2 , S 3 ) components of the Stokes parameter for the outgoing light passing through the above combined phasors are (−0.25, −0.45, 0.85), (0.45, 0.25, −0.85), (0.25, 0.45, 0.85), and (−0.45, −0.25, −0.85). When these (S 1 , S 2 , S 3 ) components for the outgoing light are added every component, it becomes that S 1 =0, S 2 =0, and S 3 =0. Therefore, the optical element  110  can also substantially remove the polarization of the incident light of the above elliptically-polarized light. 
     Moreover, when the incident light is circularly-polarized light having (S 1 , S 2 , S 3 )=(0, 0, −1), (S 1 , S 2 , S 3 ) components of the Stokes parameter for the outgoing light passing through the above combined phasors are (0.71, 0.71, 0.0), (−0.71, −0.71, 0.0), (−0.71, −0.71, 0.0), and (0.71, 0.71, 0.0). When these (S 1 , S 2 , S 3 ) components for the outgoing light are added every component, it becomes that S 1 =0, S 2 =0, and S 3 =0. Therefore, the optical element  110  can also substantially remove the polarization of the incident light of the above circularly-polarized light. 
     In addition, the outgoing light obtained by passing through the optical element  110  microscopically has a polarized component. Therefore, a light diffusing section that diffuses a ray of light passing through the first phasor array  210  and the second phasor array  220  may be provided in the optical system  100 . In addition, the light diffusing section may be provided in contact with the first phasor array  210 . The light diffusing section may overlap light passing through the combinations of the above phasors by diffusing the outgoing light from the optical element  110 . For example, the light diffusing section may diffuse the outgoing light from the optical element  110  to light which is diffused in the size order of the unit of the first phasor  311   a , the first phasor  311   b , the second phasor  312   a , and the second phasor  312   b  or the unit of the third phasor  321   a , the third phasor  321   b , the fourth phasor  322   a , and the fourth phasor  322   b . Moreover, the lens system  130  may have an optical characteristic for diffusing the outgoing light from the optical element  110 , and thus may function as a light diffusing section. A light diffusing section may diffuse outgoing light in the size order of a predetermined beam diameter when light is collected. 
       FIGS. 4A and 4B  show other examples of arrangement of the phasors in the first phasor array  210  and the second phasor array  220 . Arrows in lattices showing the first phasor array  210  in  FIG. 4A  show the directions of phase delaying axes for phasors located at the positions corresponding to the first phasor  311   a , the first phasor  311   b , the second phasor  312   a , and the second phasor  312   b  shown in  FIG. 3  among the phasors included in the first phasor array  210 . Moreover, arrows in lattices showing the second phasor array  220  in  FIG. 4A  show the directions of phase delaying axes for phasors located at the positions corresponding to the third phasor  321   a , the third phasor  321   b , the fourth phasor  322   a , and the fourth phasor  322   b  shown in  FIG. 3  among the phasors included in the second phasor array  220 . The second phasor array  220  in the present example has a phase delaying axes in the same directions as that of the second phasor array  220  shown in  FIG. 3 . 
     Moreover, similarly to  FIG. 4A , arrows in lattices showing the first phasor array  210  in  FIG. 4B  show the directions of phase delaying axes for phasors located at the positions corresponding to the first phasor  311   a , the first phasor  311   b , the second phasor  312   a , and the second phasor  312   b  shown in  FIG. 3  among the phasors included in the first phasor array  210 . In the configuration shown in  FIG. 4B , the phase delaying axis of the second phasors  312   a  is substantially perpendicular to the phase delaying axis of the second phasors  312   b . Even in this configuration, the phase delaying axis of the second phasors  312   a  and the phase delaying axis of the second phasors  312   b  together form an angle of substantially 45 degrees with the phase delaying axis of the first phasors  311   b . In addition, the second phasor array  220  shown in  FIG. 4B  has a phasor array similar to that of the second phasor array  220  shown in  FIG. 4A . 
     In this manner, it is preferred that the phase delaying axes of the second phasors  312  relatively has an angular difference of substantially 45 degrees to the phase delaying axes of the first phasors  311 . Moreover, the direction of a phase delaying axis of each phasor is not limited to a specific direction in a specific coordinate system. Moreover, an angular difference between the angle of the phase delaying axis of the third phasors  321  and the angle of the phase delaying axis of the first phasors  311  may be optional. Moreover, in the above example, the first phasor array  210  and the second phasor array  220  are arranged along the propagation direction of incident light in the order corresponding to the second phasor array  220  and the first phasor array  210 , but they may be arranged along the propagation direction of incident light in the order corresponding to the first phasor array  210  and the second phasor array  220 . 
       FIG. 5  shows another example of a cross section that is perpendicular to the propagation direction of incident light in an optical element  110 . The optical element  110  includes a plurality of first phasors  511   a  and  511   b  (hereinafter, referred to as first phasors  511 ), a plurality of second phasors  512   a  and  512   b  (hereinafter, referred to as second phasors  512 ), a plurality of third phasors  521   a  and  521   b  (hereinafter, referred to as third phasors  521 ), and a plurality of fourth phasors  522   a  and  522   b  (hereinafter, referred to as fourth phasors  522 ). 
     In addition, the first phasors  511  and the second phasors  512  may be ½ wavelength plates similarly to the first phasors  311  and the second phasors  312 , and the third phasors  521  and the fourth phasors  522  may be ¼ wavelength plates similarly to the third phasors  321  and the fourth phasors  322 . In addition, the angles of phase delaying axes of the first phasors  511 , the second phasors  512 , the third phasors  521 , and the fourth phasors  522  may be respectively equal to those of the first phasors  311 , the second phasors  312 , the third phasors  321 , and the fourth phasors  322 . Moreover, similarly to the first phasors  311  and the second phasors  312 , a density of the first phasors  511  may be substantially the same as a density of the second phasors  512 , and the spatial distribution of the density of the first phasors  511  and the spatial distribution of the density of the second phasors  512  may be substantially uniform. 
     Moreover, similarly to the third phasors  321  and the fourth phasors  322 , a density of the third phasors  521  may be substantially the same as a density of the fourth phasors  522 , and the spatial distribution of the density of the third phasors  521  and the spatial distribution of the density of the fourth phasors  522  may be substantially uniform. In this manner, the optical element  110  according to the present example has a function similar to that of the optical element  110  as described with reference to  FIGS. 1 to 3  except that the plurality of third phasors  521  and the plurality of fourth phasors  522  are arranged on the same face together with the plurality of first phasors  511  and the plurality of second phasors  512 . 
     Moreover, as shown in the present drawing, the first phasors  511  and the second phasors  512  are alternately arranged in the direction of the x axis so as to form a λ/2 plate row. Moreover, the third phasors  521  and the fourth phasors  522  are alternately arranged in the direction of the x axis in the direction perpendicular to the lined direction of the first phasors  511  and the second phasors  512  on the λ/2 plate row, so as to form a λ/4 plate row, in which the λ/4 plate row is provided in contact with the λ/2 plate row. Then, the λ/2 plate rows and the λ/4 plate rows having the same array are alternately arranged in the direction of the y axis, in order to form the optical element  110 . The polarized light can be sufficiently removed even by the optical element  110  having such an arrangement. 
     Although the present invention has been described by way of an exemplary embodiment, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and the scope of the present invention. It is obvious from the definition of the appended claims that embodiments with such modifications also belong to the scope of the present invention. 
     The claims, specification and drawings describe the processes of an apparatus, a system, a program and a method by using the terms such as operations, procedures, steps and stages. When a reference is made to the execution order of the processes, wording such as “before” or “prior to” is not explicitly used. The processes may be performed in any order unless an output of a particular process is used by the following process. In the claims, specification and drawings, a flow of operations may be explained by using the terms such as “first” and “next” for the sake of convenience. This, however, does not necessarily indicate that the operations should be performed in the explained order.