Abstract:
An optical pattern projection system and method use lasers and diffractive optical components to provide illumination and demarcation for airports, helipads, waterways, emergence route, pedestrian cross, as well as aid for search and rescue operations. The diffractive optical components produce an illumination pattern in the spatial domain and can use either passive or active optical elements.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]     The present application claims the benefit of U.S. Provisional Patent Application No. 60/622,609, filed Oct. 28, 2004, whose disclosure is hereby incorporated by reference in its entirety into the present disclosure. 
     
    
     FIELD OF INVENTION  
       [0002]     This invention generally relates to a light projection apparatus, and more specifically to a light projection apparatus employing lasers and diffractive optical components for applications in lighting, marking and demarcation enhancement.  
       BACKGROUND OF THE INVENTION  
       [0003]     The utilization of a laser to generate a uniformly illuminated line for lighting, marking and demarcation can date back to the early 1970s, wherein Veres described a gas laser based illumination system for providing center and edge stripes for an airport runway in U.S. Pat. No. 3,866,032. The advantages of laser based lighting and marking apparatus include high brightness, good beam quality, long lifetime and low power consumption.  
         [0004]     Later development in this field can be found in U.S. Pat. No. 4,700,912 to Corbett, U.S. Pat. Nos. 6,007,219 and 6,688,755 to O&#39;Meara, and U.S. Pat. No. 6,320,516 to Reason. In these references, a conventional refractive optical component, such as a glass plano-convex cylindrical lens, is used to convert the laser output from a spot into an illumination line.  
         [0005]     To produce a complex pattern, such as a multi-stripe start line for an airport runway, multiple laser sources or refractive lenses have to be used, which adds to possibility of failure to the whole system. Certain complicated patterns, including some signs, are impossible to generate by conventional refractive optical components.  
       SUMMARY OF THE INVENTION  
       [0006]     It is thus an object of the present invention to avoid the above-noted deficiencies of the prior art.  
         [0007]     In particular, it is an object of the present invention to allow the creation of more complicated patterns than have been possible in the prior art.  
         [0008]     It is another object of the present invention to avoid the use of unnecessarily complicated systems and their failure rate.  
         [0009]     To achieve the above and other objects, the present invention uses diffractive optical components for optical pattern projection for lighting, marking and demarcation enhancement.  
         [0010]     The diffractive optical component is a beam shaping and steering device capable of modulating the phase or amplitude of the wavefront of an optical beam, such as that from a laser or a light emitting diode (LED). The phase or amplitude modulation is performed in a micro scale with a spatial dimension much smaller than the size of the optical beam. As a result, the modulated optical beam can produce any complicated illumination pattern on a target plane. The diffractive optical component can be fabricated using holographic recording methods or wafer-based micro-fabrication techniques that are generally adopted in current semiconductor industry. The diffractive efficiency of the component can reach a level of &gt;90%.  
         [0011]     It is yet another object of the present invention to provide a yellow colored diode-pumped solid-state laser (DPSSL) for lighting, marking and demarcation enhancement. Previously demonstrated yellow laser airport lighting apparatuses for hold-line demarcation utilize either a He—Ne gas laser, which is limited by available power, or a composite yellow colored laser beam generated by combining a green colored DPSSL at 532 nm and a red colored diode laser at 635-670 nm, which suffers from a color uniformity problem. By adopting dual infrared wavelength generation and nonlinear frequency mixing technology, this invention discloses a true yellow colored DPSSL at wavelength regime of 560-600 nm for lighting, marking and demarcation enhancement.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Preferred embodiments of the present invention will be set forth in detail with reference to the drawings, in which:  
         [0013]      FIG. 1  illustrates the mechanical layout of an exemplary optical pattern projection apparatus;  
         [0014]      FIG. 2  illustrates one operation mode of the optical pattern projection apparatus, wherein a multi-stripe line pattern is projected on an airport runway;  
         [0015]      FIG. 3  illustrates the mechanism for complex illumination pattern generation utilizing micro-scale optical phase modulation;  
         [0016]      FIG. 4 ( a ) illustrates a dynamically reconfigurable diffractive optical component employing a liquid crystal modulator; and  
         [0017]      FIG. 4 ( b ) illustrates a dynamically reconfigurable diffractive optical component employing micro-electro-mechanical systems (MEMS).  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Preferred embodiments of the present invention will now be set forth in detail with reference to the drawings.  
         [0019]     In one preferred embodiment of the current invention as shown in  FIG. 1 , the optical pattern projection apparatus comprises a waterproof housing  10  with three compartments, i.e., a laser compartment  11 , an electronic compartment  12 , and an optional battery compartment  13 . The laser compartment  11  further comprises a true yellow colored DPSSL  14  mounted on a heat sink  15 , and a diffractive optical component  16  to modulate the phase/amplitude of the laser beam in spatial domain and produce a desired illumination pattern on the target surface. The modulated laser beam is delivered to the target surface through a transparent window  17 . Depending on the application requirements, a lens or a group of lenses may be inserted between the laser  14  and the diffractive optical component  16  for beam expansion and collimation.  
         [0020]     The DPSSL  14  comprises a laser crystal, such as Nd:YVO 4 , pumped by an 808 nm laser diode. The laser crystal produces two infrared laser beams at 1064 nm and 1342 nm, respectively. A nonlinear crystal, such as KTP, is employed to mix the two infrared laser beams and produce a yellow laser beam at 593.5 nm.  
         [0021]     The electronic compartment  12  comprises one or more electronic circuit boards  18  to drive the DPSSL and control its output intensity. An optional rechargeable battery  19  in the battery compartment  13  is used to provide power to the electronic circuit boards  18 . The housing  10  is mounted on a mounting unit  20 , which is adjustable in height and elevation angle to control the pattern projection manner.  
         [0022]     One exemplary operation mode of the optical pattern projection apparatus is illustrated in  FIG. 2 , wherein the optical pattern projection apparatus  30  is used to produce a multi-stripe line pattern  31  on an airport runway  32 . In this scheme, the elevated optical pattern projection apparatus  30  is placed on one side of the runway. The laser beam generated by the DPSSL  33  is diffracted and expanded by the diffractive optical component  34  (corresponding to the component  16  of  FIG. 1 ) into multiple sections  35  and projected onto the surface of the runway to form the multi-stripe line pattern  31 . Except as explicitly described herein, the disclosure of  FIG. 1  applies to the embodiment of  FIG. 2 .  
         [0023]     A more detailed illustration of the optical pattern projection mechanism is shown in  FIG. 3 , in which a diffractive optical component with binary phase modulation is employed. In  FIG. 3 , the laser beam  41  produced by a laser  40  is first collected and collimated by a lens  42 . The collimated laser beam  43  is then delivered to a diffractive optical component  44  (corresponding to the component  16  of  FIG. 1 ) with micro-scale thickness or refractive index modulation, which induces phase modulation on the wavefront of the output laser beam  45 . Except as explicitly described herein, the disclosure of  FIG. 1  applies to the embodiment of  FIG. 3 .  
         [0024]     For reasons of simplicity, the phase modulation is illustrated in a binary mode in  FIG. 3  (with a phase shift value of either 0 or π), although the present invention is not limited to such a binary mode. Thus, the light emitted from adjacent phase modulation elements will interfere either constructively or destructively to form bright and dark patterns on the target plane  46 . The diffractive optical component  44  can be viewed as a beam shaping and steering element, which adjusts the propagation direction and profile of the laser beam by varying the phase of its wavefront.  
         [0025]     In real applications, the diffractive optical component can adopt grayscale phase modulation as well as amplitude modulation to produce even more complicated illumination patterns. It can also work in a reflection mode where the output optical beam propagates in opposite direction of the input optical beam. With the rapid development of micro-fabrication technology, the spatial resolution of the diffractive optical component can reach the same order as the laser wavelength. Potentially, any desirable illumination patterns, such as numbers, characters, and figures, can be generated.  
         [0026]     In another embodiment of the current invention, the diffractive optical component is dynamically reconfigurable to produce different illumination patterns with the same laser module. One example is a liquid crystal based dynamic spatial phase/amplitude modulator configured as an array  50  of elements  52 , as illustrated in  FIG. 4 ( a ). Nematic or ferroelectric liquid crystal  54  is injected between two layers of electrodes  56 ,  58 . One layer of electrodes  58  is micro-patterned to form an electrode array. By applying different voltages on the electrodes, the orientation of the liquid crystal molecules will change correspondingly. Thus, the refractive index or absorption in each element  52  can be adjusted to modulate the wavefront of the optical beam. The desired pattern is then generated in a similar way as described in the first embodiment. The voltages applied on the electrodes can be dynamically reconfigured to generate different patterns.  
         [0027]     In another example of the embodiment, as illustrated in  FIG. 4 ( b ), an array of micro-electro-mechanical systems (MEMS) mirrors  62  is used instead of liquid crystal modulator to implement an array of elements  60 . The phase or amplitude modulation is produced by varying the positions or tilt angles of the micro-mirrors  62 .  
         [0028]     The array  50  or  60  can be used in place of the element  16  of  FIG. 1 .  
         [0029]     While some preferred embodiments of the present invention have been set forth in detail, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the invention. For example, the diffractive optical component may utilize both phase and amplitude modulation. Conventional refractive optical components may be used in combination with the diffractive optical component for light beam control. The dynamic spatial phase (amplitude) modulator may be realized using other technologies. The light source is not limited to diode-pump solid-state lasers. Therefore, the present invention should be construed as limited only by the appended claims.