Patent Publication Number: US-2019179130-A1

Title: Simultaneous multi-magnification reflective telescope utilizing a shared primary mirror

Description:
BACKGROUND OF THE INVENTION 
     Modern tactical aircraft use a number of imaging aids to assist the crew in viewing a scene, selecting targets in the scene, and directing weapons against the selected targets. Visible, infrared, and/or specific spectral bands imaging devices are used in various applications to form an image of the scene. The type of imaging spectrum depends upon the mission, weather conditions, the nature of the scene, as well as other factors. 
     One form of an optical system includes several lenses having varying magnification. The lenses are arranged at proper positions by a positioning mechanism along an optical path to achieve desired effects by a lens mount assembly. It is critical that the lenses be properly aligned by the mechanism, which often is difficult to access to adjust the lenses. There is presently a need for an optical system including a reflective telescope that has at least two simultaneous magnifications, one magnification for the purpose of imaging incoming light and one or two magnifications for outgoing light, such as a pulsed laser and/or a continuous wave illuminating laser without having the laser pass through an intermediate image plane. 
     There are two known approaches to provide simultaneous magnifications within the optical system. One approach includes coaxial systems having an imaging system and a laser system that uses the same telescope optics at the expense of lowered optical transmission in both imaging and laser modes. Another approach includes separate aperture systems with dedicated apertures for each function, on an embedded system that causes field of view issues due to aperture separation. 
     SUMMARY OF INVENTION 
     One aspect of the present disclosure is directed to an optical system comprising a housing and a laser coupled to the housing. The laser is configured to generate a beam of electromagnetic radiation. The optical system further comprises a multi-magnification reflective telescope coupled to the housing. The multi-magnification reflective telescope is configured to simultaneously direct the beam of electromagnetic radiation along a laser output path toward a target and to receive a reflected target image along an imaging optical path. The optical system further comprises one or more detectors coupled to the housing. Each detector is configured to selectively receive the target image from the multi-magnification reflective telescope. 
     Embodiments of the optical system further may include configuring the housing to have a window through which the beam of electromagnetic radiation travels toward the target and through which the target image is received. The one or more detectors may include a mid-wave infrared (MWIR) camera, a short-wave infrared (SWIR) camera and a day television (DTV). The multi-magnification reflective telescope includes a case, a shared primary mirror coupled to the case, and a secondary mirror coupled to the case. The shared primary mirror may be configured to expand the beam of electromagnetic radiation and the secondary mirror may be configured to direct the beam of electromagnetic radiation to and to receive the target image from the shared primary mirror. The multi-magnification reflective telescope further may include an eyepiece and a beam splitter coupled to the case, the eyepiece and the beam splitter being configured to direct the beam of electromagnetic radiation from the laser to the secondary mirror. The eyepiece may be selected to increase a magnification of the beam of electromagnetic radiation from 9× to 20×. The multi-magnification reflective telescope further may include a tertiary mirror coupled to the case, with the tertiary mirror being configured to direct the target image from the secondary mirror and the beam splitter. The tertiary mirror may be selected to increase a magnification of the target image up to 12× magnification. The multi-magnification reflective telescope further may include a fast steering mirror coupled to the case, the fast steering mirror being configured to direct the target image from the tertiary mirror to one or more detectors simultaneously. 
     Another aspect of the disclosure is directed to a method of simultaneously generating a beam of electromagnetic radiation and receiving a reflected target image. In one embodiment, the method comprises: generating a beam of electromagnetic radiation; directing the beam of electromagnetic radiation along a laser output path toward a target; receiving a target image; and directing the target image along an imaging optical path to one or more detectors simultaneously, the directing the target image being achieved simultaneously with the directing the beam of electromagnetic radiation. 
     Embodiments of the method further may include one or more detectors having a mid-wave infrared (MWIR) camera, a short-wave infrared (SWIR) camera and a day television (DTV). Directing the electromagnetic radiation and directing the target image may be achieved by way of a multi-magnification reflective telescope including a case, a shared primary mirror coupled to the case, and a secondary mirror coupled to the case. The shared primary mirror may be configured to expand the beam of electromagnetic radiation and the secondary mirror may be configured to direct the beam of electromagnetic radiation to and to receive the target image from the shared primary mirror. The multi-magnification reflective telescope further may include an eyepiece and a beam splitter coupled to the case, with the eyepiece and the beam splitter being configured to direct the beam of electromagnetic radiation from the laser to the secondary mirror. The multi-magnification reflective telescope further may include a tertiary mirror coupled to the case, with the tertiary mirror being configured to direct the target image from the secondary mirror and the beam splitter. The multi-magnification reflective telescope further may include a fast steering mirror coupled to the case, with the fast steering mirror being configured to direct the target image from the tertiary mirror to one or more detectors simultaneously. 
     Yet another aspect of the disclosure is directed to a multi-magnification reflective telescope of an optical system. In one embodiment, the reflective telescope comprises a case, a shared primary mirror coupled to the case, and a secondary mirror coupled to the case. The shared primary mirror is configured to expand a beam of electromagnetic radiation and the secondary mirror is configured to direct the beam of electromagnetic radiation to and to receive a reflected target image from the shared primary mirror. The multi-magnification reflective telescope is configured to simultaneously direct the beam of electromagnetic radiation along a laser output path toward a target and to receive a target image along an imaging optical path and to direct the target image to at least one of one or more detectors. 
     Embodiments of the multi-magnification reflective telescope further may include an eyepiece and a beam splitter coupled to the case, the eyepiece and the beam splitter being configured to direct the beam of electromagnetic radiation from the laser to the secondary mirror. The multi-magnification reflective telescope further may include a tertiary mirror coupled to the case, with the tertiary mirror being configured to direct the target image from the secondary mirror and the beam splitter. The multi-magnification reflective telescope further may include a fast steering mirror coupled to the case, with the fast steering mirror being configured to direct the target image from the tertiary mirror to at least one of the one or more detectors. The eyepiece may be selected to increase a magnification of the beam of electromagnetic radiation from 9× to 20×, and the tertiary mirror may be selected to increase a magnification of the target image up to 12× magnification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. Where technical features in the figures, detailed description or any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures, detailed description, and claims. Accordingly, neither the reference signs nor their absence are intended to have any limiting effect on the scope of any claim elements. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. The figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the invention. In the figures: 
         FIG. 1  is a schematic block diagram of a simultaneous multi-magnification reflective telescope utilizing a shared primary mirror of an embodiment of the present disclosure; 
         FIG. 2  is a cross-sectional elevational view of the multi-magnification reflective telescope revealing components of the reflective telescope; 
         FIG. 3  is a cross-sectional perspective view of the multi-magnification reflective telescope revealing components of the reflective telescope; 
         FIG. 4  is a cross-sectional elevational view of the multi-magnification reflective telescope showing a ray trace of a laser output path and a ray trace of an imaging optical path; 
         FIG. 5  is a ray trace of an imaging optical path and using 12× imaging with a 2.5× laser; and 
         FIG. 6  is a ray trace of an imaging optical path and a laser output path using 10× imaging with a 4× laser. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present disclosure are directed to simultaneous multi-magnification reflective telescope that utilizes a shared primary mirror. In one embodiment, the multi-magnification reflective telescope includes an additional refractive eyepiece and/or secondary mirror, which is added to a three mirror anastigmat design. An anastigmat lens is a compound lens corrected for the aberrations of astigmatism and curvature of field. Light is folded into the additional secondary mirror or refractive eyepiece forming a Galilean telescope, which does not have an intermediate image. The secondary telescopes have either a much smaller or larger magnification ratio than the original telescope. Refractive eyepiece designs have higher magnification and can simultaneously use the shared primary mirror with the imaging optics. Additional secondary designs have a lower magnification and obscure a portion of the secondary mirror from imaging optical use. The telescope is intended to be simultaneously used with the anastigmat telescope. 
     The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to embodiments or elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality of these elements, and any references in plural to any embodiment or element or act herein may also embrace embodiments including only a single element. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. 
     Referring to the drawings, and more particularly to  FIG. 1 , an optical system is generally indicated at  10 . In one embodiment, the optical system  10  includes a housing  12  configured to contain and mount components of the optical system  10 . The optical system  10  further includes a simultaneous multi-magnification reflective telescope, generally indicated at  14 , coupled to the housing  12 . The multi-magnification reflective telescope  14  utilizes a shared primary mirror that will be described in greater detail below. As shown, the optical system  10  further includes a laser  16  coupled to the housing  12 . The laser  16  is configured to generate a beam  18  of electromagnetic radiation to the multi-magnification reflective telescope  14  along a laser output path. The optical system  10  further includes a window  20  provided in the housing  12  through which the beam  18  of electromagnetic radiation travels during operation. Optical images travel back through the window  20  of the housing  12  in the form of a reflected target image  22  along an imaging optical path through the multi-magnification reflective telescope  14 . This target image  22  may be delivered to one of several detectors provided in the optical system  10 , including but not limited to a mid-wave infrared (MWIR) camera  24 , a short-wave infrared (SWIR) camera  26  and a day television (DTV)  28 . 
     As will be discussed in greater detail below with reference to  FIGS. 2 and 3 , the multi-magnification reflective telescope  14  includes a shared primary mirror  30  that is configured to expand the beam  18  of electromagnetic radiation prior to exiting the window  20  of the housing  12 . The multi-magnification reflective telescope  14  further includes a secondary mirror  32  that is configured to direct the beam  18  of electromagnetic radiation to and to receive the target image  22  from the shared primary mirror  30 . The multi-magnification reflective telescope  14  further includes an eyepiece  34  and a beam splitter  36 , which are configured to direct the beam  18  of electromagnetic radiation from the laser via mirrors  38 ,  40  to the secondary mirror  32 . The eyepiece  34  is selected to increase a magnification of the beam  18  of electromagnetic radiation anywhere from 9× to 20× based on the layout design of the shared primary mirror  30  and the secondary mirror  32 . In one embodiment, the eyepiece  34  is configured to magnify the beam of electromagnetic radiation 12×. 
     The beam splitter  36  further is configured to direct the target image  22  from the secondary mirror  32  to a tertiary mirror  42  of the multi-magnification reflective telescope  14 . The multi-magnification reflective telescope  14  further includes a multi-axis fast steering mirror  44  that is configured to direct the target image  22  from the tertiary mirror  42  to the detectors, e.g., MWIR camera  24 , SWIR camera  26  and DTV  28 , via beam splitter  46  and mirror  48 . Although the multi-axis fast steering mirror  44  of the multi-magnification reflective telescope  14  in the shown embodiment is configured to direct the target image  22  to one of the three shown detectors, it should be understood that the optical system  10  can be configured to accommodate any number of detectors. Also, the multi-axis fast steering mirror  44  of the multi-magnification reflective telescope  14  can be configured to vary the direction of the target image  22  based on the positions of detectors with respect to the multi-axis fast steering mirror  44 . 
     Referring to  FIGS. 2 and 3 , the components of the multi-magnification reflective telescope  14  are secured in a case or housing  50  that embodies a compact imaging and illuminating system (CIIS). In one embodiment, the compact CIIS provides detailed intelligence data from the visual and infrared spectrum in support of military and civilian operations. The compact CIIS can be configured to provide long-range surveillance, target acquisition, tracking, range finding and laser designation. 
     As shown, the case  50  is formed and configured to support the shared primary mirror  30 , the secondary mirror  32  and the tertiary mirror  42  in secure positions during operation. In one embodiment, the case  50  is fabricated from a suitable metal material, such as an aluminum alloy having the same coefficient of thermal expansion as the primary mirror  30 , secondary mirror  32  and tertiary mirror  42 . As shown, the shared primary mirror  30  is secured or coupled to the case  50  at an angle so that it receives the beam  18  of electromagnetic radiation along the laser output path from the secondary mirror  32  and directs the beam of electromagnetic radiation to the window  20  of the housing  12  ( FIG. 1 ). As mentioned above, the shared primary mirror  30  is configured to expand the beam  18  of electromagnetic radiation. The secondary mirror  32  is secured or coupled to the case  50  in a position across from the shared primary mirror  30 , the eyepiece  34  and the beam splitter  36 , each of which is also coupled to the case  50 . As described above, the eyepiece  34  may be selected based on the layout of the shared primary mirror  30  and the secondary mirror  32  to achieve a desired magnification of multi-magnification reflective telescope  14 . The tertiary mirror  42  is mounted on or coupled to the case  50  at a bottom of the case. The tertiary mirror  42  is used by the imaging detectors only, and can provide magnification of the target image  22 , e.g., magnification ranging from 3× to 12×. 
       FIG. 3  illustrates the multi-magnification reflective telescope  14  including single axis fast steering mirrors  52  disposed before the eyepiece  34  and coupled to the case  50 . Embodiments of each fast steering mirror of the single axis fast steering mirrors  52  may include a reflective surface, and may be configured to manipulate the reflective surface to control the direction of the reflection of the beam  18  of electromagnetic radiation produced by the laser off of the reflective surface. Each single axis fast steering mirror further may include a fixed base, a pivot flexure or bearing, which couples the reflective surface to the base, and several actuators each configured to move the reflective surface relative to the base. Each single axis fast steering mirror may be configured to manipulate the reflective surface to control a direction of the reflection of the beam of electromagnetic radiation, including light and infrared light, off of the reflective surface, and configured to steer the reflective surface as a unit. 
     The multi-magnification reflective telescope  14  further may include beam reducer optics  54  disposed before the single axis fast steering mirrors  52 . The beam reducer optics  54  is provided to fit the beam  18  of electromagnetic radiation generated by the laser  16  into a controlled laser beam. 
     Referring to  FIG. 4 , a trace pattern of the beam  18  of electromagnetic radiation along the laser output path is represented by solid lines, and a trace pattern of the target image  22  along the imaging optical path is represented by dashed lines. As shown, the beam  18  of electromagnetic radiation generated by the laser  16  enters the multi-magnification reflective telescope  14  via the mirrors  38 ,  40  shown in  FIG. 1 . Specifically, electromagnetic radiation enters the multi-magnification reflective telescope  14  through the eyepiece  34  and the beam splitter  36 . The eyepiece  34  can be selected to increase the magnification of the laser path output to a desired magnification. The beam  18  of electromagnetic radiation is then directed to the secondary mirror  32 , which reflects the beam  18  of electromagnetic radiation to the shared primary mirror  30 . The beam  18  of electromagnetic radiation is then directed to the window  20  of the housing  12  of the optical system  10  shown in  FIG. 1  toward a field of view target. As the beam  18  of electromagnetic radiation travels along the laser output path within the multi-magnification reflective telescope  14 , the laser beam is expanded as it is directed toward the field of view target. 
     Simultaneously to the transmission of the beam  18  of magnetic radiation along the laser output path, the target image  22  is reflected back to the multi-magnification reflective telescope  14  through the window  20  and toward the shared primary mirror  30 . The target image  22  is reflected by the shared primary mirror  30  toward the secondary mirror  32 , which in turn directs the target image  22  to the beam splitter  36 . The beam splitter  36  directs the target image  22  toward the tertiary mirror  42 , which can be selected to increase the magnification of the target image  22 . The target image  22  is reflected by the tertiary mirror  42  toward the multi-axis fast steering mirror  44 , which in turn directs the target image  22  toward the beam splitter  46  and the mirror  48  ( FIG. 1 ). The target image  22  is then directed to one of the three detectors  24 ,  26  and  28  by configuring the beam splitter  46  and the mirror  48 . 
     Several case embodiments may be used to house the components of the multi-magnification reflective telescope. For example, one exemplary case may be configured to secure components of an unobscured, free aperture, higher magnification CIIS design. In another example, the case may be configured to secure components of a centrally obscured, free aperture, higher magnification CIIS design. 
     As referenced above, the tertiary mirror  42  of the multi-magnification reflective telescope  14  may be configured to vary the magnification of the target image  22  directed to the detectors  24 ,  26  and  28 , based on the layout of the shared primary mirror  30  and the secondary mirror  32 . 
     For example, in another embodiment,  FIG. 5  illustrates a trace pattern of a beam  18  of electromagnetic radiation along the laser output path that is represented by solid lines in which the beam of electromagnetic radiation is magnified 2.5×.  FIG. 5  further illustrates a trace pattern of the target image  22  along the imaging optical path that is represented by dashed lines in which the target image is magnified 12×. In the shown embodiment, the beam  18  of electromagnetic radiation generated by the laser  16  enters the multi-magnification reflective telescope  14  through an insertion mirror  60  and an alternative secondary mirror  62 . The beam  18  of electromagnetic radiation is then directed to the shared primary mirror  30 , and through the window  20  toward a field of view target. Simultaneously to the transmission of the beam  18  of magnetic radiation along the laser output path, the target image  22  is reflected back to the multi-magnification reflective telescope  14  through the window  20  and toward the shared primary mirror  30 . The target image  22  is reflected by the shared primary mirror  30  toward the secondary mirror  32 , fold mirrors  64  and  66 , and to the tertiary mirror  42 . The target image  22  is then reflected toward the multi-axis fast steering mirror  44 , the beam splitter  46  and the mirror  48 , and ultimately directed to one or more of the three detectors  24 ,  26 ,  28 . 
     In another example,  FIG. 6  illustrates a trace pattern of a beam  18  of electromagnetic radiation along the laser output path that is represented by solid lines in which the beam of electromagnetic radiation is magnified 4×.  FIG. 6  further illustrates a trace pattern of the target image  22  along the imaging optical path that is represented by dashed lines in which the target image is magnified 10×. 
     A multi-magnification reflective telescope  14  of an optical system  10  may be used to perform a method of simultaneously generating a beam of electromagnetic material and receiving a target image. The method includes generating a beam  18  of electromagnetic radiation with a laser  16 . The method further includes directing the beam  18  of electromagnetic radiation along a laser output path toward a target by passing the beam through components of the multi-magnification reflective telescope  14 , including, but not limited to an insertion mirror  60 , an alternative secondary mirror  62 , and a shared primary mirror  30 . Next, the method includes receiving a target image  22  by the multi-magnification reflective telescope  14  of the optical system  10 , and directing the target image along an imaging optical path to at least one of several detectors, e.g., detectors  24 ,  26  and  28 , via the primary shared mirror  30 , the secondary mirror  32 , a fold mirror  68 , the tertiary mirror  42  and the multi-axis fast steering mirror  44  of the reflective telescope. The directing the target image  22  can be achieved simultaneously with the directing the beam  18  of electromagnetic radiation. 
     It should be understood that any number of configurations can be achieved, based on the layout of the shared primary mirror  30  and the secondary mirror  32 , and the other components of the optical system  10 . 
     Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only, and the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.