Abstract:
Optical fiber including a core, a cladding surrounding the core, having a refractive index lower than the core, and polarization beam splitter layers in an incident part and emission part at opposite ends of the core, for transmission of a particular polarized beam, for maintaining a polarization direction of an incident beam to enhance an optical utilization efficiency, and projection display system including a beam source of a polarization direction, an optical fiber for reflecting the laser beam to transmit the laser beam therethrough, and maintaining the polarization direction, vibration means connected to the optical fiber at least one or more than point, for vibrating the optical fiber, to vary a phase of the laser beam passing through the optical fiber, a display panel, and a projection optical system for enlarging and projecting the picture from the display panel onto a screen, thereby providing an excellent picture quality.

Description:
[0001]    This application claims the benefit of the Korean Application Nos. P2001-40460, and P2001-40461, both filed on Jul. 6, 2001, which are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to optical fiber, and more particularly, to optical fiber that can prevent polarization variation for enhancing an optical efficiency, and a projection display of the same that can provide a high picture quality.  
           [0004]    2. Background of the Related Art  
           [0005]    In general, the optical fiber is a fibrous waveguide for transmission of a light widely used in optical communication, optical measurement, optical transmission, and the like.  
           [0006]    A basic principle of the optical fiber is total reflection of a light. That is, a light passing through two media of different refractive indices refracts at an interface of the two media, when a relation as shown in an equation (1) comes into existence, which is called as Snell&#39;s Law where n1, and n2 denote refractive indices of the two media, and θ1 denotes an incident angle and θ2 denotes a refraction angle.  
             n 1 sin θ1 =n 2 sin θ2  
           [0007]    That is, when the light progresses from a medium with a high refractive index to a medium with a low refractive index, there is a specific incident angle at which the refraction angle is 90°, and for an incident angle greater than the specific angle, the light is reflected at the interface of the two media, which is called as total reflection.  
           [0008]    The optical fiber employs such a total reflection, and FIG. 1 illustrates a related art optical fiber.  
           [0009]    Referring to FIG. 1, the related art optical fiber is provided with a core  11  in a central part, and a cladding  12  surrounding the core  11 . For causing total reflection, the refractive index of the core  11  is made higher than the refractive index of the cladding  12 . Therefore, the light incident to the core  11  progresses as the light is totally reflected along the core  11  according to a condition of the total reflection.  
           [0010]    However, it is matter of course that the light progressing along the core  11  is involved in phase change, with a change a polarization direction. Particularly, when the optical fiber is stressed by bending, or heat, or an external pressure, the optical fiber is involved in change of the refractive index, with further change of the phase. Therefore, though the related art optical fiber transmits a photo energy effectively, the related art optical fiber has a problem in that the related art optical fiber changes a polarization direction. In application fields of the polarization, an effective use of the polarization light has been difficult due to a loss caused by the polarization change of the optical fiber.  
           [0011]    In the meantime, for maintaining a fixed polarization direction, even a single mode optical fiber is employed. However, the single mode optical fiber is required to be thinner than a few μm, has a limitation in a length thereof, and is susceptible to an external pressure or a stress caused by bending.  
           [0012]    Meanwhile, as a display system for realizing a large sized screen, there is a projection display system in which a small picture is enlarged, and projected onto a large screen. Of the projection display systems, a projection display system employing a laser as a light source is under development, of which structure will be explained, briefly.  
           [0013]    Referring to FIG. 2A, one exemplary related art projection display system is provided with a laser beam source  21  for emitting a laser beam, an illuminative optical system  22 , a display panel  23 , and an optical projection system  24 . The display panel  23  displays a picture by controlling an amount of the laser beam in response to an electrical signal, and the picture is enlarged, and projected onto the screen  25  through the optical projection system  24 .  
           [0014]    Referring to FIG. 3B, another exemplary related art projection display system is provided with a laser beam source  31 , an optical system  32 , an AOM  33  for controlling a transmission amount of a laser beam in response to an electric signal related to a picture signal, a polygonal mirror  34  for providing a horizontal image by scanning the laser beam, and a galvanometer  35  for providing a vertical image by repetitive up and down rotation at a fixed angle. That is, the projection display system displays a picture on the screen  36  by rotation and angle combination of the galvanometer  35 , and the polygon mirror  34 .  
           [0015]    The foregoing projection display system enhances clarity and reproducibility of colors, displays a picture with colors close to natural colors, and reproduces a clear picture quality as the picture has a high contrast.  
           [0016]    However, the projection display system can not but have interference of the laser beam on the screen  25  or  36  caused by coherence of the laser beam, forming glittering speckles on the screen  25  or  36  coming from regular phases of the laser beam, that deteriorates picture quality, contrast, and resolution.  
         SUMMARY OF THE INVENTION  
         [0017]    Accordingly, the present invention is directed to an optical fiber and a projection display system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0018]    An object of the present invention is to provide an optical fiber for maintaining a polarization direction of an incident beam to enhance optical utilization efficiency.  
           [0019]    Another object of the present invention is to provide a projection display system, in which a light utilization efficiency is enhanced by using the optical fiber, and speckles caused by laser beam interference is eliminated, for providing an excellent picture quality.  
           [0020]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0021]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the optical fiber includes a core, a cladding surrounding the core, having a refractive index lower than the core, and PBS (Polarization Beam Splitter) layers in an incident part and emission part at opposite ends of the core, for transmission of a particular polarized beam.  
           [0022]    The PBS layer is a multilayered thin film coated on the incident part, or the emission part, or a thin polarization plate bonded to the incident part, or the emission part. The PBS layers in the incident part and the emission part have the same polarization directions of transmissive laser beams.  
           [0023]    Therefore, according to the present invention, the beam incident to the core through the PBS layer in the incident part can not pass the PBS layer in the emission part but reflected into the core even if a polarization direction thereof is changed by external causes in the middle. If this process is repeated, a beam having the same polarization direction with the incident beam emits through the PBS layer in the emission part. At the end, the polarization direction of the emitted beam becomes the same with the polarization direction of the incident beam, thereby enhancing an optical utilization efficiency.  
           [0024]    In another aspect of the present invention, there is provided a projection display system including a beam source for emitting a laser beam of a polarization direction, an optical fiber for totally reflecting the laser beam to transmit the laser beam therethrough, and maintaining the polarization direction, vibration means connected to the optical fiber at least one or more than point, for vibrating the optical fiber, to vary a phase of the laser beam passing through the optical fiber, a display panel for controlling an amount of the laser beam from the optical fiber in response to an electric signal, to provide a picture, and a projection optical system for enlarging, and projecting the picture from the display panel onto a screen.  
           [0025]    As explained, there are PBS layers in the incident part and the emission part of the optical fiber, for transmission of laser beams of the same polarization direction.  
           [0026]    Thus, according to the present invention, when the vibration means applies vibration to the optical fiber, a phase of the laser beam becomes irregular. As a result, the laser beam interferes each other and the speckles are eliminated. In this instance, as has been explained, even if there may be a polarization loss caused by variation of the polarization direction of the laser beam, the PBS layers can secure an optical utilization efficiency higher than a certain level.  
           [0027]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention:  
         [0029]    In the drawings:  
         [0030]    [0030]FIG. 1 illustrates a related art optical fiber;  
         [0031]    FIGS.  2 A- 2 B illustrate related art projection display systems, schematically;  
         [0032]    [0032]FIG. 3 illustrates an optical fiber and a function thereof in accordance with a preferred embodiment of the present invention;  
         [0033]    [0033]FIG. 4 illustrates one example of an optical system having the optical fiber in FIG. 3 applied thereto;  
         [0034]    [0034]FIG. 5 illustrates a projection display system in accordance with a preferred embodiment of the present invention; and  
         [0035]    [0035]FIG. 6 illustrates an optical fiber and a function thereof in the projection display system in FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0036]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In explaining the present invention, same parts will be given the same names and reference symbols, and iterative explanation of which will be omitted.  
         [0037]    [0037]FIG. 3 illustrates an optical fiber and a function thereof in accordance with a preferred embodiment of the present invention, and FIG. 4 illustrates one example of an optical system having the optical fiber in FIG. 3 applied thereto.  
         [0038]    Referring to FIG. 3, the optical fiber of the present invention includes a core  110  for providing a transmission passage, a cladding  120  for surrounding the core  110 , and PBS (Polarization Beam Splitter) layers  115 , and  117  on both ends of the core  110 .  
         [0039]    The core  110  has an incident part  111  and an emission part  113  on opposite ends. The core  110  has a refractive index greater than the cladding  120 . Therefore, the light incident to the incident part  111  is totally reflected, to progress along the core  110  to the emission part  113 . The incident part  111  and the emission part  113  are tilted at an angle with respect to an axis of the core  110 .  
         [0040]    The PBS layer  115 , or  117  only transmits, or reflects a beam of a specific direction of polarization selectively. The polarization direction of a beam means a direction of vibration of the beam as the beam progresses, and the PBS layer ( 115 , or  117 ) is a kind of filter that transmits only a beam of a specific vibration direction.  
         [0041]    The PBS layer  115 , or  117  may be a multilayered thin film directly coated on the incident part  111  or the emission part  113 , or a thin polarization plate bonded to the incident part, or the emission part  113 . The lights transmissive through the PBS layer  115  in the incident part and the PBS layer  117  in the emission part have the same polarization direction.  
         [0042]    The function of the optical fiber of the present invention will be explained.  
         [0043]    As an example, it is assumed that the PBS layer  115 , or  117  transmits an S wave beam  41 , and reflects a P wave beam  43 . Of course, it is possible that a PBS layer having a property opposite to the foregoing PBS layer can be provided depending on designer.  
         [0044]    When the S wave beam  41  is incident to the incident part  111 , the S wave beam  41  transmits the PBS layer  115 , and incident to the core  110 . Then, the S wave beam  41  progresses to the emission part  113  along the core  110 .  
         [0045]    In this instance, while the S wave beam  41  progresses along the core  110 , the S wave beam  41  is involved in a phase change, such that a polarization direction of the S wave beam  41  is changed. Particularly, when the optical fiber is bent, or an external cause, such as heat or pressure, is applied to the optical fiber, the change of the polarization direction will be greater. As a result, a part of the S wave beam  41 , failing to maintain a proper polarization direction, is changed to the P wave beam  43 , resulting in a state in which the S wave beam  41  and the P wave beam  43  are mixed in the core  110 .  
         [0046]    Thereafter, the S wave beam  41  and the P wave beam  43 , progressing along the core  110 , come to meet the PBS layer  117  in the emission part, when the P wave beam  43  is reflected, and progresses toward the incident part  111  along the core  111  again, while the S wave beam  41 , transmits the PBS layer  117 , and progresses to a destination.  
         [0047]    Eventually, the P wave beam  43 , failed to pass through the optical fiber, goes back and forth between the incident part  111  and the emission part  113 , during which process, the P wave beam  43  is changed to the S wave beam  41  again due to a polarization direction change.  
         [0048]    Then, the S wave beam  41  transmits the PBS layer  117  in the emission part, and progresses to the destination.  
         [0049]    If such a process is repeated, the S wave beam  41  incident through the incident part  111  becomes the S wave beam  41  finally without any loss by repeating the change process, even if the S wave beam  41  is changed to the P wave beam  43  in the middle of the process. That is, the polarization direction of the emitted beam is maintained the same as the polarization direction of the incident beam.  
         [0050]    Therefore, by minimizing an optical loss caused by the change of polarization direction, both the efficiency of beam utilization and an output can be enhanced.  
         [0051]    In the meantime, if the incident beam is the P wave beam  43 , the same result can be obtained by using PBS layer  115 , or  117  which transmits the P wave beam  43  and reflects the S wave beam  41 .  
         [0052]    The foregoing optical fiber has a variety of optical applications. As an example, FIG. 4 illustrates an optical measuring instrument having the optical fiber of the present invention applied thereto.  
         [0053]    Referring to FIG. 4, the optical measuring instrument includes a beam source  51 , a plurality of optical systems  52 , and  53 , an optical fiber  100 , and detector  54 . As the beam source  51 , a laser having a single polarization direction is employed. There are PBS layers  115 , and  117  in the incident part and the emission part of the optical fiber  100 , respectively.  
         [0054]    The operation of the optical measuring instrument will be explained, briefly.  
         [0055]    A laser beam from the beam source  51  is incident to the optical fiber  100  through the optical system  52 . The laser beam emits from the optical fiber  100  in a polarization direction identical to the polarization direction of the incident beam maintained by the PBS layers  115 , and  117 . Then, the laser beam is directed to the detector  54  through the optical system  53 . In this instance, in view of characteristics of the optical fiber  100 , an output of the detector  54  can be enhanced without a loss of the laser beam.  
         [0056]    A projection display system having the optical fiber of the present invention applied thereto will be explained, in detail. FIG. 5 illustrates a projection display system in accordance with a preferred embodiment of the present invention, and FIG. 6 illustrates an optical fiber and a function thereof in the projection display system in FIG. 5.  
         [0057]    Referring to FIGS. 5 and 6, the projection display system includes a beam source  61  for emitting a laser beam having a fixed polarization direction, an optical fiber  100  for transmission of the laser beam while the polarization direction is maintained, vibration means  130  for applying vibration to the optical fiber  100  artificially, a display panel  64  for controlling an amount of the laser beam from the optical fiber by means of an electric signal, to provide a picture, and a screen  66  for displaying the picture from the display panel  64 .  
         [0058]    There is an illumination optical system  62  in front of the optical fiber  100  for focusing the laser beam emitted from the beam source  61 , and there is a focusing optical system  63  in rear of the optical fiber  100  for focusing the laser beam from the optical fiber to the display panel  64 . There is a projection optical system  65  in rear of the display panel  64  for enlarging and projecting the picture from the display panel onto a screen  66 .  
         [0059]    As explained, the optical fiber  100  maintains the polarization direction of incident laser beam and the polarization direction of the emitted laser beams identical. To do this, the optical fiber  100  has the incident part  111  and emission part  113  at opposite ends of the optical fiber  100  tilted at predetermined angles with respect to an axis direction of the core  110 , in which the PBS layers  115 , and  117  are formed, respectively. The PBS layers  115 , and  117  transmit a laser beam of a specific polarization direction, and are formed of multilayered thin films coated on the incident part  111  and the emission part  113 , or polarization plates directly bonded to the incident part  111  and the emission part  113 , respectively.  
         [0060]    The vibration means  130  varies a phase of the laser beam passing through the optical fiber  100  irregularly by vibrating the optical fiber  100  artificially, for elimination of the speckle caused by coherence of the laser beam.  
         [0061]    To do this, the vibration means  130  includes an electrical or mechanical vibration source  131 , and a vibration transmission member  133  between the vibration source  131  and the optical fiber  100  for transmission of vibration from the vibration source  131  to the optical fiber  100 . As an example, there are two vibration transmission members  133  between the vibration source  131  and the optical fiber  100  shown in FIG. 5.  
         [0062]    As the display panel  64 , an LCD or a DMD (Digital Micromirror Device) may be employed. Taking a fact into account, that the beam directed to the display panel  64  is a laser beam, it is preferable that the display panel  64  is the LCD.  
         [0063]    The operation of the projection display of the present invention will be explained, in detail.  
         [0064]    At first, a laser beam having a polarization direction is emitted from the beam source  61 . It is preferable that the laser beam is R, G, B color lights for reproducing a color picture.  
         [0065]    Next, the laser beam is incident to the incident part in the optical fiber  100  through the illumination optical system  62 .  
         [0066]    Then, after the laser beam transmits the PBS layer  115 , the laser beam progresses toward the emission part  113  as the laser beam is totally reflected along the core  110 . In this instance, the vibration source  131  produces vibration, which is transmitted to the optical fiber  100  through the vibration transmission member  133 . The vibration causes a stress in the optical fiber  100  by deforming the optical fiber  100 , or acting as an external pressure, which changes the refractive index of the core  110  and/or the cladding  120 , that varies the phase of the laser beam, irregularly. This irregular variation of the phase of the laser beam implies a reduced coherence, which eliminates the speckles caused by interference of the laser beam.  
         [0067]    In the meantime, the polarization direction of a laser beam passing through the optical fiber  100  changes naturally, or by stress. Particularly, when the vibration means  130  applies a vibration, the polarization of the laser beam changes greatly. That is, a vibration direction of the laser beam varies irregularly with respect to a direction of progress. For an example, the laser beam from the beam source  61  is an S wave beam  41 , there is an unwanted P wave beam  43  formed in the optical fiber  100 . However, as explained, since there are the PBS layers  115 , and  117  in the incident part  111  and the emission part  113 , the P wave beam  43  is changed to the S wave beam  41  again, thereby eliminating the optical loss.  
         [0068]    Then, the laser beam from the optical fiber  100  is focused onto the display panel  64  through the focusing optical system  63 . The display panel  64  controls an amount of the laser beam, and presents a picture signal.  
         [0069]    Then, the picture signal is enlarged through the projection optical system  65 , and projected onto the screen  66 .  
         [0070]    As has been explained, the optical fiber and the projection display system thereof of the present invention have the following advantages.  
         [0071]    First, the PBS layers  115 , and  117  at opposite ends of the optical fiber permits to provide an emission beam having a polarization direction the same with the incident beam. Therefore, even if the optical fiber is bent, or a stress is occurred in the optical fiber by a temperature, or pressure, the optical fiber of the present invention can maintain the polarization direction, thereby enhancing an efficiency of utilization of light, and an output.  
         [0072]    Second, the artificial application of vibration to the optical fiber  100  having the PBS layers  115  and  117  formed therein, which varies a phase of the laser beam irregularly, eliminates speckles, thereby providing clean and clear picture quality.  
         [0073]    It will be apparent to those skilled in the art that various modifications and variations can be made in the optical fiber and the projection display system thereof of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.