Abstract:
In a staring infrared countermeasures system, wherein the improvement comprises a semiconductor material emitter for providing a specific infrared wavelength to provide protection against an infrared radiation guided missile.

Description:
RELATED APPLICATIONS 
     This Application claims rights under 35 USC §119(e) from U.S. Application Ser. No. 61/156,117 filed Feb. 27, 2009, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to starring infrared countermeasure (IRCM) systems and more particularly to methods and apparatus for producing infrared (IR) radiation for use in such systems. 
     BACKGROUND OF THE INVENTION 
     There is broad recognition of the threat posed by heat (IR energy) seeking missiles to both military and commercial aviation. In the mid 1970&#39;s, defensive systems were rapidly developed and deployed to increase military aircraft battlefield survivability. These systems were highly successful in countering IR-missile threats and have proven themselves invaluable to both military and commercial sectors. These older prior art systems are based on a multi-spectral sources filtered to provide desired IR-missile jam wavelengths. The source must provide significant modulated energy emission, to provide appropriate jamming effectiveness. A major benefit of many older systems is that they are always “ON” and continually providing “staring” protection. The source emission can be tailored to the signature of the platform being protected or provide radiated fields of protection dictated by the geometry of the emitter. The “staring” characteristic ordinarily provides “JAM in the TUBE” protection. That is, missiles affected by such prior art staring systems typically can not launch since the missile&#39;s guidance system can not ‘lock’ onto the desired target. 
     A drawback to some such prior art systems is that they may be specifically designed for protection against what is referred to as Band I IR missile threats. IR missile technology has evolved to include improved jamming rejection and changes in spectral sensitivity (wavelength); this necessitates new methods to oppose the new threats. These newer IR-missiles are referred to as Band IV threats. To address the advanced technology, infrared countermeasures (IRCM) have followed with increasingly complex and sophisticated protection solutions that basically discards the older technologies. Today&#39;s advanced IRCM includes integrated missile warning and precision guided laser jamming technology. The latest Directional Infrared Countermeasure (DIRCM) systems direct high intensity modulated IR lasers on the incoming missile&#39;s dome, thus jamming the guidance control system. DIRCM systems differ from Staring systems in that they are significantly more complicated than the older staring systems. In addition, DIRCM systems must be cued by an advanced missile warning system prior to attempting to point and jam with sufficient precision and apply Energy on Target (EoT) to defeat the threat in a moving and turbulent environment. These complexities and the addition of many interrelated subsystems (i.e. Missile Warning, Gimbal, Tracking Camera, Cryogenic Coolers, and Lasers etc.) inherently increase life cycle cost and reduce system reliability. Consequently, the bulk of our military force&#39;s aircraft fleet is unprotected against advanced IR missiles. Many aircraft in our current military aircraft fleets, however, are still protected with such older staring IRCM systems. 
     A need, therefore, exists for still better and economic ways to protect aircraft from the more advanced IR guided missile threats being developed. 
     SUMMARY OF INVENTION 
     According to the present invention, the benefits of prior art staring systems and the advancement of Semiconductor IR-Source technology are combined to provide a semiconductor infrared lamp (SIR-Lamp) emitting multiple wavelengths and with sufficient power capable of deterring Bands I, II and IV threats. This invention thus provides a semiconductor infrared lamp that provides an upgrade to conventional Staring IRCM systems by providing a platform protection against modern IR-missile threats. 
     More specifically, the semiconductor infrared lamp is constructed by loading a number of individual light emitting diode lasers around the periphery of a ring or disk, with a number of rings stacked on top of each other around a central cooling pipe or chamber to provide sufficient output for countermeasuring incoming missiles. In one embodiment the 360° protection in a horizontal plane has a vertically restricted staring field of view, whereas by bending the peripheries of rings carrying the diode lasers, the staring field of view can be increased to as much as 160°, and in some cases greater, to provide near spherical coverage. There are two major products this technology has direct application towards: 1) the AN/ALQ-144 countermeasure set and the AN/ALQ-157 infrared countermeasure system. 
     As a result, replacing the conventional heating rod in the ALQ-144 with a series of laser rings vacuum-sealed in a lamp configuration can provide high intensity infrared radiation with specifically designed wavelengths and with energy levels to afford protection and without mechanically rotating parts. Likewise with the ALQ-157 removing the arc-lamp and replacing it with the semiconductor-IR lamp provides the additional protection. The difference between the two systems is that the ALQ-144 relies on dual spinning “chopper” sleeves to provide a mechanical driven modulated source. The ALQ-157 modulates the lamp by electrically pulsing the lamp with high current. Both have disadvantages overcome by the laser-lamp proposed in this invention. 
     It is noted that with the ALQ-144 the mechanical spinning devices are not required to modulate the infrared radiation for producing a jam code. Also note that the semiconductor lasers are modulated in one embodiment to provide the required modulated jamming radiation. Additionally, since the semiconductor output can be tailored as to wavelength there is very little unproductive energy since there is no white light to filter. Also, there are no covert filters needed and no moving parts to wear and fail. This coupled with the fact that there is no warm up period as is the case with prior heating rods makes the subject system highly desirable. Likewise, the ALQ-157 existing lamps require pre-heating before modulation occurs. With the pre-heating, the depth of modulation does not fall to zero. However, this phenomenon also is eliminated with the subject semiconductor-IR lamp since the modulation depth is zero. 
     Since the jam codes are electrically modulated into the output of the lasers, there is considerable freedom as to the shape of the pulses in both the frequency as well the amplitude domain. In addition, Band IV and Band I diodes can be separately modulated for in band jam code efficiency. Finally, the pump laser provides approximately 18% to 26% wall socket to IR emission efficiency as compared to 2%, when utilizing the prior heated tube broadband IR sources or arc-lamps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the subject invention will be better understood in connection with the Detailed Description, in conjunction with the Drawings, of which: 
         FIG. 1  is a diagrammatic of the ALQ-144 and top view of a prior art IR source that includes a heated tube; 
         FIG. 2  is a diagrammatic illustration of the assembly of  FIG. 1  showing in perspective and cutaway views the fixed IR source and modulating elements surrounding it; 
         FIG. 3  is a diagrammatic illustration of a staring, always-on infrared, jamming system showing a jamming module composed of the elements of  FIGS. 1 and 2 ; 
         FIG. 4  is a diagrammatic illustration of the utilization of the module of  FIG. 3  aboard a helicopter to provide enough IR jamming radiation to mask the heat signature produced by the helicopter; 
         FIG. 5  is a diagrammatic illustration of the ALQ-157 arc-lamp based system with base and cover open to show the replaceable lamp; 
         FIG. 6  is a diagrammatic illustration of the ALQ-157 of  FIG. 5  mounted to a helicopter; 
         FIG. 7  is a diagrammatic illustration of the use of multiple single emitter diode laser bars arranged around the peripheries of multiple stacked rings or disks carried in an evacuated housing that are used as to provide a replacement for the traditional fixed IR source; 
         FIG. 8  is a diagrammatic illustration of laser distribution for effective coverage to mask platform signature; 
         FIG. 9  is a diagrammatic illustration of a laser diode bar for use in the semiconductor  1 R lamp of  FIG. 7 , with the angles depicted being typical and variable depending on construction of the semiconductor materials; 
         FIG. 10  is a diagrammatic illustration of the subject replacement assembly showing the utilization of diode rings stacked about an inner tube to provide a stacked ring assembly; 
         FIG. 11  is a diagrammatic illustration of a semiconductor infrared diode laser source that can be substituted for the traditional heated tube or arc-lamp sources in a jamming module, in which Band I/IV ring assemblies are assembled about the inner tube of  FIG. 10  into a housing through which airflow or cooling materials are introduced; 
         FIG. 12  is a diagrammatic illustration of the completed semiconductor laser diode IR source in which the stacked rings of  FIG. 10  are housed within an outer sleeve capped with end cap heat exchangers at either end and apertured in the center to provide for the introduction and exhaust of air; 
         FIG. 13  is a diagrammatic illustration of a gallium antimony semiconductor laser device; 
         FIG. 14  is a diagrammatic illustration of the gallium antimony semiconductor device of  FIG. 13  showing the utilization of a P-type and N-type material mounted on a heat-sink cathode in which the junction between the N-type and P-type devices produces a laser beam in terms of photon beams; 
         FIG. 15  is a diagrammatic illustration of the completed single emitter semiconductor laser of  FIG. 14 , illustrating in perspective view a polished end of the single emitter to couple out the laser beam; 
         FIGS. 16A and 16B  are diagrammatic illustrations of a modulation comparison of arc-lamps vs semiconductor IR lamps; 
         FIG. 17  is a diagrammatic illustration of multiple laser diode bars around the periphery of a ring, in which the laser diode bars are arranged on both the top and bottom surfaces of the ring; 
         FIG. 18  is a diagrammatic and cross sectional view of the assembly of  FIG. 17  illustrating the utilization of a thermally conductive substrate for the top and bottom portions of the ring, also illustrating a chamber between the thermally conductive substrates; 
         FIG. 19  is a diagrammatic illustration of the output of the multi-element laser diode bars of  FIGS. 17 and 18 , illustrating that for each individual element there is an approximate 40° vertical field of view and an approximate lateral 12° field of view for each of the laser diode elements; and, 
         FIG. 20  is an embodiment of a subject invention in which selected rings on which the laser diode elements are located are dish-shaped such that the laser diode bars located at the periphery of these dish-shaped elements point in different directions, the composite providing an up to 160° field of view for the module. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , in the past in so-called “hot brick” jamming modules such as the ALQ-144, a fixed IR source  10  in the form of a heating tube is located centrally in a housing  12  that carries lenses  14  about its periphery. Internal to the housing is a carrier modulator  16  in the form of masks which block the output of the fixed IR source. 
     The laser jamming codes are provided by spinning housing  12  such that the output in any given direction is modulated through the utilization of lenses  14 , in much the same way that lighthouses modulate their beams. 
     Referring to  FIG. 2 , it can be seen that fixed IR source  10  is centrally located interior to the spin modulator lenses  14 , with the carrier modulator  16  and lenses  14  being disposed around the fixed IR source as illustrated. 
     The masking provided by the carrier modulator provides that radiation from the fixed IR source only be emitted in the directions illustrated by slots  18  between the carrier modulator masks, with the IR radiation being focused by the lenses to provide the required jamming signals. 
     As will be appreciated, this configuration requires moving parts, with the output of the fixed IR source in one embodiment being equivalent to white light. 
     As shown in  FIG. 3 , a module  20  comprised of the IR source, housing, masks and lenses of  FIGS. 1 and 2  is shown, with module  20  being secured to a base  22  readily mountable as illustrated in  FIG. 4  on an aircraft  24 , in this case a helicopter. Here the radiation emitted from module  20  is of sufficient power to mask out the thermal signature of the aircraft by providing modulated infrared radiation which when detected by a missile seeker causes the missile seeker to think that the aircraft is other than where it actually is. This countermeasuring causes the missile to go off course and miss the aircraft. 
     The modules of  FIGS. 1 through 4  correspond to conventional staring systems such as the AN/ALQ-144 system, with the expense and physical complexity of these modules adding to cost and maintenance problems. 
     Unlike the AN/ALQ-44, the AN/ALQ-157 of  FIG. 5  provides jam modulation by electrically modulating an arc-lamp  25 .  FIG. 5  depicts an AN/ALQ-157 with the cover  27  off and a base  29  securing the replaceable arc-lamp  25 . Cover filters  41  prevent unwanted (visible light) spectral responses, and reflectors  43  reflect energy in desired configuration depending on signature of the protected platform.  FIG. 6  illustrates a CH-46 U.S. Navy helicopter  45  with the AN/ALQ-157 module  47  of  FIG. 5  installed. 
     Referring to  FIG. 7 , fixed IR source  10  in one embodiment, a cesium-arc lamp, is replaced by a semiconductor infrared laser lamp  26  made up of disks or rings  30  carrying multiple laser diode bars  32 , each having a number of single emitter laser diodes. The rings carrying the laser diode bars are stacked in an IR transparent lamp housing  40  having end cap heat exchangers  48 . As will be discussed in connection with  FIG. 9 , the laser diode bars are capable of tens-of-watts each, and when stacked as illustrated, provide more than sufficient modulated infrared energy to counter a wide class of incoming missiles. As will be discussed, the field of view  46  of each of the individual single emitters shows that each individual emitter has a vertical component  47  and a horizontal component  49 . Because the laser diode bars are arranged around the periphery  34  of the disk, lamp  26  has a 360° staring field of view in the horizontal direction. 
     The amount of energy and the energy pattern can be tailored to provide protection where needed as illustrated in  FIG. 8 . The signature of an aircraft is not generally equally distributed but often follows a pattern such as that illustrated at  51 . The amount of energy of energy emitted by the semiconductor IR lamp can be tailored spatially as illustrated at  53  to emulate the unique signature of each platform being protected. This allows conservation of aircraft power. 
     Referring now to  FIG. 9 , and as will be discussed hereinafter, laser diode bars  32  are available and include individual laser diodes  33 , each having a P-type material  50  and an N-type material  52 , such that there is a laser emission from the junction between the two as illustrated at  35  in which the horizontal field of view  37 , in one embodiment is 12°, whereas the vertical field of view illustrated at  49  is 40°. These angles are typical but will vary depending on the construction of the wafer during fabrication. 
     These diode laser bars are derived from the technology used in laser welders and in one embodiment up to thirty single emitters can be located in a laser diode bar. 
     As will therefore be appreciated, semiconductor lasers from the laser-welding field which are capable of massive amounts of energy are packaged so as to provide a 360° staring coverage, with each bar having a sufficiently powerful output to effectively countermeasure incoming threats. 
     More particularly, referring to  FIG. 10 , a semiconductor laser diode IR lamp replaces the lamps in the modules of  FIGS. 1-4 . This IR source includes a laser diode ring or disk  30  having multiple laser diode bars  32  spaced about the periphery  34  of the disk. The disk is centrally apertured to provide a ring having a central aperture for the passage of an inner tube  36  there through, which is provided with an air stream or cooling material. It is the purpose of the subject invention that this semiconductor IR laser source can be substituted for the heating rod of  FIGS. 1 through 4  and the arc-lamp  25  of  FIG. 5 . Note, this IR source includes an inner tube assembly  38  on which the laser diode rings  30  are stacked as illustrated about inner tube  36 . 
     Referring to  FIG. 11 , as can be seen, laser diode rings  30  can be stacked and can be provided with modulated outputs in Band I, Band II and Band IV. In one embodiment these rings are stacked on an inner tube assembly contained within a transparent housing  40  which in one embodiment is evacuated, and through which an airflow  42  runs centrally and exhausts as illustrated at  44 . 
     The field of view of this IR source is illustrated at  46  for each of the single emitter laser diodes within each of the bars  32  located about the periphery of the laser diode rings. 
     Referring to  FIG. 12 , housing  40  includes an IR transparent outer sleeve  46 , with the outer sleeve capped by end cap heat exchangers  48  to provide the final semiconductor IR lamp of the subject invention. 
     Referring now to  FIG. 13 , each of the semiconductor laser diode bars are shown to include a gallium antimony layer  50  constituting a P-type material on which are patterned N-type materials  52  as illustrated. It is noted that the gallium antimony P-type layer is located on a heat-sink cathode  56 . 
     Referring to  FIGS. 14 and 15 , junction of P-type layer  50  and N-type layer  52  provides a channel from which photons exit as photon beam  60 . It is noted that biasing for the single emitter semiconductor laser diodes is provided by a +ve terminal  62  and a −ve terminal  64 , with the −ve terminal  64  in one embodiment being the aforementioned heat-sink cathode  56 . Note the voltages +ve and −ve can be modulated by a modulator  66  to provide an appropriately coded output beam  60 . Thus in terms of  FIG. 15 , what can be seen is that a single emitter laser diode includes the ve terminal  62 , the N-type material  52 , the P type material  50  and the heat-sink cathode  56 , with output beam  60  being projected from a polished end  62  of the single emitter structure. 
     As can be seen in the modulation comparisons of  FIGS. 16A and 16B , the semiconductor IR-lamp beam of  FIG. 16B , is completely off at  69  when no voltage is applied, making the depth-of-modulation  67  turn completely off. This is unlike the arc-lamp modulation  71  of  FIG. 16A  that has residual heat and never turns completely off as illustrated at  73  due to a self signature. 
     Laser diode bars constructed with multiple single emitter laser diodes are illustrated in  FIG. 17  to be bonded to a circular conductive bond plate  72 , with the laser diode bars  70  positioned on either side of ring  30 . 
     As can be seen in  FIG. 18 , conductive plates  72  are positioned on a hollow thermally conductive substrate  74  that provides a chamber  76  between the top and bottom conductive plates. This structure along with central aperture  78  in the disk assembly provides for a centrally-located cooling chamber for each of the rings as well as to provide for passage of airflow through the disks for cooling purposes. 
     As can be seen in  FIG. 19  with the diode bars  70  mounted to rings  30 , the staring field of view for each of the individual or single element diode lasers is about 40° in the vertical direction and about 12° in the horizontal direction. 
     As will be appreciated, with the laser diode bars located on the periphery of a ring one achieves 360° coverage, here illustrated by double-ended arrow  80 . The vertical coverage is illustrated by double-ended arrow  78  and the horizontal coverage is illustrated by double-ended arrow  79 . 
     In order to extend the vertical coverage of the semiconductor IR source to a virtual sphere, as shown in  FIG. 20  ring  30 ′ and  30 ″ are dish-shaped in which one of the rings is upwardly bowed or offset from the central flat plane of the ring to orient the associated diode bars so that they point in the indicated directions for diode bars  70 ′ and  70 ″. It is noted that a central flat ring  30 ″ has the field of view described in  FIG. 14 . 
     Thus, for each of the diode bars there is a 40° vertical field of view angle as illustrated by double-ended arrow  90 . When the rings are dished as illustrated, the result is a 160° field of view as illustrated by double-ended around  92 . 
     Thus, the lasing region is virtually spherical for the subject IR source when the source is made up of a number of stacked dish-shaped elements about a flat disk element. 
     More specifically, the subject invention is directed to how existing IRCM lamp based systems can benefit from an integrated Band I/Band IV (even band II) lamp solution capable of protecting small to mid-size signature platforms. This idea breaks from traditional arc-lamp or heated element systems and employs semiconductor materials to provide specific IR wavelength protection against older and advanced IR missiles. 
     The welding industry has matured the use of semiconductor lasers, in the range of kilowatts of energy, packaged into very small form factors that provide sufficient heat to weld heavy metals. 
     The subject IRCM solution is provided by leveraging off of these laser technologies and techniques by taking bar-type multiple laser emitter bars and locating the emitters at the periphery of a disk to provide a 360° staring angle. 
     Recently, developments in Band IV materials have provided similar packaging technique opportunities as the matured laser welding devices. Demonstrated maturities of these separate wave length materials suggest that the technology is ready for a staring IRCM implementation. Combining the multiple wavelength types of semiconductor materials (laser diodes) into an IR source lamp configuration and construction provides an SIR-Lamp that emits Bands I and IV and if desired band II. 
     Those skilled in the art will appreciate that this invention may be used to upgrade conventional staring systems such as the AN/ALQ-144 system and the AN/ALQ-157 system, as well as maturing new systems that provides protection from the latest IR-seeking threats. 
     It will be appreciated that the present invention may also be employed in the upgrade of other conventional starring systems such as the AN/ALQ-157 system available from BAE Systems and the MATADOR® system available from BAE Systems in Ontario, Calif. 
     As is illustrated, the AN/AN/ALQ-144 heating rod can be replaced with a series of laser rings vacuum sealed in a SIR-Lamp configuration. The rings are populated with emitters of semiconductor material bars specifically designed to emit the wavelengths and energy levels required for protection. In an AN/ALQ-144 type system, the SIR-Lamp replacement does not require a mechanical spinning device to modulate the jam code. The subject innovation thus eliminates the need for more moving parts, environmental seals, and no covert filters. 
     The amount of energy emitted is dependent on the number of emitters packaged. For larger platforms, additional emitters are added to create larger SIR-Lamp sources. The goal is to provide sufficient protection for aircraft already deployed with current lamp based IRCM systems. 
     It will be appreciated that upgrading staring IRCM systems with an SIR-Lamp based system provides the user of such systems with the following advantages: 
     Added protection in Band I through IV; High reliable SIR-Lamp (laser welders last for thousands of hours) Tune-up maintenance can be “built in” to assure protection, Tune-up maintenance may result in repairable business model; Drastically reduced Self Signature, “S” resulting in much better signal to noise performance; No warm-up necessary due to the SIR-Lamp; Helicopters can fly with protection as soon as the system is turned on; Jam codes are constructed by electrical waveforms and pulses and not limited by heated devices; Higher efficiency system-Lower power DC aircraft systems can now be achieved; Eliminates moving parts to create jam codes as is used in the prior art AN/ALQ-144 system; Eliminates the need for high voltage and high current as is needed in the AN/ALQ-157 system and the MATADOR® system. 
     The semiconductor IR lamp of the present invention may be constructed in a similar way to prior art cesium-arc lamps that are currently fabricated, for example, by BAE Systems in Ontario, Calif. The basic construction involves an outer-envelope that transmits 2-5 μm, end caps to provide sleeve-support and hermaticity, an inner cavity that provides cooling, and rings that mount the semiconductor IR emitters. The vacuum can be backfilled with an inert gas to simultaneously provide the environmental sealing and increased heat transfer efficiency. The inner construction includes a cooling cylinder with rings attached. 
     Note there are advantages in using a laser available from nLight which uses an advanced indium phosphide (InP) material to provide a 2.1 μm pump laser using the industry typical semiconductor stacked-bars construction. This wavelength is ideal for a Band I solution. Coupling these techniques with the recent development in antimonide materials provides solutions for Band IV and/or Band II. 
     This approach provides an uncooled laser that will provide a series of Band IVa, Band IVb, Band II and a Band I solution. 
     The key to the subject invention is a series of IR semiconductor laser material rings. Each ring carries either single emitters or bars. The rings are dish-shaped to provide angular overlap. Preliminary performance calculations for such a construction follow: 
     1 bar=1 cm in length, 1 bar has 19 emitters; Divergence of a single emitter is approximately 40° fast axis, 12° slow axis @ 1/e^2; Results in approximately 30 bars around the periphery to provide 360° azimuth coverage; Mounting 15 bars each side of the ring would require approximately 2″ diameter. 
     Providing dish-shaped rings provides angular distribution with five rings providing “near-spherical” coverage. 
     Lab results indicate the emitters produce from 1 to 0.5 watts per emitter; 5 rings with 30 bars each and each bar has 19 emitters: 5×30×19=2,850 emitters; At 0.5 to 1.0 watts that is an estimated 1,425 watts to 2,850 watts of Band IV energy in a form factor equivalent package to the existing starring systems. 
     As discussed above, the semiconductor IR lamp of the present invention can provide bands IV, I and if desired band II protection for small and medium signature platforms. It has also been calculated that one single SIR-Lamp could provide power of 3,200 w/srad. It will also be appreciated that the present invention continues to provide a jam-in-tube defense and extends the life of a lamp based protection systems. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.