Abstract:
A method of controlling an ultra-short pulse system is described comprising controlling an optical power within the ultra-short pulse system and control-system controlling a width of an optical pulse. In some embodiments, the method also comprises tuning a compressor by controlling a number of passes of the optical pulse through a Bragg grating to control the width of the optical pulse output from the compressor. In other embodiments, the method may comprise tuning a multi-pass stretcher by controlling a number of passes of the optical pulse through a loop of the multi-pass stretcher to control the width of the optical pulse output from the multi-pass stretcher. A method of controlling an ultra-short pulse system may also comprise accessing a control system from a remotely located command station, communicating status information from the control system to the command station, and communicating information from the command station to the control system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/615,883, now U.S. Pat. No. 7,444,049, filed on Dec. 22, 2006 and entitled “Pulse Stretcher and Compressor Including a Multi-Pass Bragg Grating,” which claims the priority benefit of:
         U.S. Provisional Patent Application Ser. No. 60/761,736, filed on Jan. 23, 2006, entitled “METHOD OF DISPERSION COMPENSATION IN A CPA SYSTEM,”   U.S. Provisional Patent Application Ser. No. 60/762,284, filed on Jan. 25, 2006, entitled “USP LASER FIBER AMPLIFIER,”   U.S. Provisional Patent Application Ser. No. 60/763,002, filed on Jan. 26, 2006, entitled “SEED CONTROL IN ULTRA-SHORT PULSE LASER SYSTEMS,”   U.S. Provisional Patent Application Ser. No. 60/762,791, filed on Jan. 26, 2006, entitled “AMPLIFIER CONTROL IN ULTRA-SHORT PULSE LASER SYSTEMS” and   U.S. Provisional Patent Application Ser. No. 60/762,790, filed on Jan. 26, 2006, entitled “METHOD OF REMOTE ACCESS TO AN ULTRA-SHORT PULSE LASER SYSTEM.”       

     This application is related to
         co-pending U.S. patent application entitled “Bragg Fibers in Systems for the Generation of High Peak Power Light,” Ser. No. 11/112,256, filed Apr. 22, 2005, which in turn claims the benefit and priority of U.S. provisional patent application Ser. Nos. 60/635,734, filed on Dec. 13, 2004, and entitled “Bragg Fibers For The Generation Of High Peak Power Light,” and 60/636,376, filed on Dec. 16, 2004, and entitled “Bragg Fibers In Systems For The Generation Of High Peak Power Light;” and   co-pending U.S. patent application entitled “High Order Mode Optical Amplifier in an Ultrashort Pulse Laser System,” Ser. No. 11/491,219, filed on Jul. 20, 2006, which in turn claims the benefit and priority of U.S. Provisional Patent Application entitled “Chirped Pulse Amplifier System Including Tapered Fiber Bundle,” Ser. No. 60/793,960, filed on Apr. 20, 2006.   The disclosures of all of the above U.S. patents and patent applications are incorporated by reference herein.       

    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to stretching and compressing electromagnetic pulses, and more particularly laser pulses. 
     2. Description of Related Art 
     Chirped pulse amplification (CPA) is very useful for producing ultrashort-duration high-intensity pulses for use in high peak power ultrashort pulse laser systems. CPA increases the energy of an ultrashort laser pulse while avoiding optical amplifier damage. In this technique, the duration of the pulse is increased by first dispersing the ultrashort laser pulse temporally as a function of wavelength (a process called “chirping”) to produce a chirped pulse, then amplifying the chirped pulse, and then recompressing the chirped pulse to significantly shorten its duration. Lengthening the pulse in time reduces the peak power of the pulse and, thus, allows energy to be added to the pulse without reaching a damage threshold of the pulse amplifier and optical components. The amount of pulse amplification that can be achieved is typically proportional to the amount of pulse stretching and compression. Typically, the greater the amount of stretching and compression, the greater the possible pulse amplification. 
     A fiber Bragg grating may be used for chirping a pulse and recompressing the pulse. However, the amount of stretching or compression by the fiber Bragg grating is substantially fixed by the physical dimensions of the fiber Bragg grating. Thus, various sizes of fiber Bragg gratings are used for chirping and/or compressing pulses. In some fiber Bragg gratings, nominal adjustments to the pulse length may be provided by physically, mechanically, or thermally stretching the optical fiber of the fiber Bragg grating to modify the length of the optical fiber. Unfortunately, the amount of adjustment to the pulse length is relatively small and the optical fiber may suffer damage from the physical stress and strain of the stretching. There is, therefore, a need for improved systems and methods of stretching and compressing optical pulses. 
     SUMMARY OF THE INVENTION 
     Various embodiments of the invention include a CPA system for amplifying a chirped pulse to a high power. The CPA system is configured to stretch and/or compress the pulse using multiple passes through a Bragg grating. In various embodiments, the Bragg grating includes a fiber Bragg grating, a volume Bragg grating, a fiber Bragg grating, a volume fiber Bragg grating, a bulk grating, a chirped fiber Bragg grating (CFBG), a chirped volume Bragg grating (CVBG), a Gires-Tournois Interferometer (GTI) in planar waveguide, a Fabry-Perot GTI, and/or the like. As used in this application, the term Bragg grating is intended to further include a Bragg waveguide. In various embodiments, a Bragg waveguide could be a Bragg fiber, a fiber Bragg grating, and/or the like. Bragg fibers are characterized in U.S. patent application entitled “Bragg Fibers in Systems for the Generation of High Peak Power Light,” Ser. No. 11/112,256, filed Apr. 22, 2005. 
     The multiple passes of the pulse through the Bragg grating enable stretching and/or compression of the pulse multiple times. The number of passes through the Bragg grating determines the amount of stretching and/or compression of the pulse. For example, a pulse can be stretched by a greater amount using multiple passes than using a single pass. Likewise, the pulse can be compressed by a greater amount using multiple passes than using a single pass. The number of passes may be selected to control the amount of stretching and/or compression. 
     Beam steering optics may be configured for directing the pulse through the Bragg grating multiple times. For example, the beam steering optics may direct the pulse through multiple paths within a volume Bragg grating. In some embodiments, the beam steering optics includes a switch configured to control the number of times a pulse passes through a Bragg grating. In some embodiments, a pulse may traverse multiple Bragg gratings, each multiple times. In some embodiments, a volume Bragg grating is configured to both stretch and compress a pulse multiple times, using beam steering optics to direct the pulse through appropriate paths. In some embodiments, the pulse is amplified between passes through the Bragg grating. In various embodiments, the Bragg grating, beam steering optic components, amplifiers, delay lines, switches, and/or the like may be mounted and/or fabricated on a wafer. 
     Various embodiments of the invention include a laser system comprising a source configured to emit a pulse, a Bragg grating configured to receive the pulse and compress the pulse to generate a compressed pulse, and beam steering optics configured to direct the compressed pulse into the Bragg grating one or more times to further compress the compressed pulse. 
     Various embodiments of the invention include a laser system comprising a source configured to emit a pulse, a Bragg grating configured to receive the laser pulse and stretch the pulse to generate a stretched laser pulse, and beam steering optics configured to direct the stretched pulse into the Bragg grating one or more times to further stretch the stretched pulse. 
     Various embodiments of the invention include a system comprising a volume Bragg grating configured to receive a laser pulse, and beam steering optics configured to direct the laser pulse into the volume Bragg grating two or more times, each of the two or more times being to compress the laser pulse, or direct the laser pulse into the volume Bragg grating two or more times, each of the two or more times being to stretch the laser pulse. 
     Various embodiments of the invention include a system comprising a Bragg grating configured to receive a pulse and output a compressed or stretched the pulse, and a switch configured to receive the compressed or stretched pulse from the Bragg grating and, in a first state, to direct the compressed or stretched pulse one or more times into the Bragg grating for further compression or stretching to produce a multiply stretched or multiply compressed pulse and, in a second state, to direct the multiply compressed or multiply stretched pulse as an output pulse. 
     Various embodiments of the invention include a method comprising receiving a pulse in a Bragg grating, compressing the pulse using the Bragg grating to generate a compressed pulse, directing the compressed pulse into the Bragg grating, and further compressing the compressed pulse one or more times using the Bragg grating to generate a multiply compressed pulse. 
     Various embodiments of the invention include a method comprising receiving a pulse in a Bragg grating, stretching the pulse using the Bragg grating to generate a stretched pulse, directing the stretched pulse into the Bragg grating, and further stretching the stretched pulse one or more times using the Bragg grating to generate a multiply stretched pulse. 
     Various embodiments of the invention include a method comprising receiving a pulse in a first Bragg grating, stretching the pulse using the first Bragg grating two or more times to generate a multiply stretched pulse, amplifying the multiply stretched pulse to generate an amplified pulse, and compressing the amplified pulse two or more times using a second Bragg grating. 
     Various embodiments include a method of controlling a high-power ultra-short pulse system containing a seed source generator generating seed pulses, a pulse stretcher, a power amplifier, a compressor, and a control system, where the pulse stretcher increases a duration of the seed pulses, the power amplifier amplifies a power of the stretched pulses, and the compressor decreases a duration of the amplified pulses. The method comprises controlling at least one of average power output of the compressor to a specified value, output pulse repetition rate to a specified value, compressor output pulse energy to a specified value, and pulse power output of the compressor to a specified value. The method also comprises control-system controlling of at least one of power output of the stretcher, power output of the power amplifier, power output of a seed pulse amplifier optically located between the stretcher and the pulse picker, pulse picker output pulse repetition rate, pulse picker EOM bias current to minimize pulse picker output power level at a given seed amp pump-current, and a half-wave plate position to minimize optical power losses in the compressor. 
     Various embodiments include a method of using remote communication with a high-power, ultra-short pulse ablation system containing a seed source generator configured for generating seed pulses, a pulse stretcher, a power amplifier, a compressor, and a control system. The pulse stretcher increases the duration of the seed pulses, the power amplifier amplifies the power of the stretched pulses, and the compressor decreases the duration of the amplified pulses. Various embodiments also include a method of remotely accessing the control system of the high-power, ultra-short pulse system from a remotely located command station and two-way communication between the command station and the control system. Various embodiments can furnish status information from the ultra-short pulse system to the command station and provide information from the command station to the ultra-short pulse system. In some embodiments, information from the command station includes at least one of remote updating of software of the control system, remotely improving operations of an application of the ultra-short pulse system, remote maintenance of the ultra-short pulse system, remotely controlling operation of an application, and remotely controlling operation of an ultra-short pulse system test. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram illustrating various embodiments of a chirped pulse system. 
         FIG. 1B  is a block diagram illustrating various embodiments of a chirped pulse system including a tunable multi-pass compressor. 
         FIG. 2  is a block diagram illustrating a chirped pulse amplifier including a multi-pass Bragg grating in which the pulse is both stretched and compressed, according to various embodiments. 
         FIG. 3  is a block diagram of alternative embodiments of the chirped pulse amplifier of  FIG. 1A , illustrating details of a multi-pass stretcher and a multi-pass compressor. 
         FIG. 4  is a block diagram illustrating further details of the multi-pass compressor of  FIG. 1A , according to various embodiments including a multi-pass Bragg grating. 
         FIG. 5A  is a block diagram illustrating further details of the multi-pass stretcher of  FIG. 1A , according to various embodiments including a multi-pass loop. 
         FIG. 5B  is a block diagram illustrating further details of the multi-pass stretcher of  FIG. 1A , according to various embodiments including a Bragg waveguide. 
         FIG. 5C  is a block diagram illustrating further details of the multi-pass stretcher of  FIG. 1A , according to various embodiments including a Bragg waveguide and a reflector. 
         FIG. 5D  is a block diagram illustrating further details of the multi-pass stretcher of  FIG. 1A , according to various embodiments including a Bragg waveguide and a reflector. 
         FIG. 6  is a block diagram illustrating alternative embodiments of a fiber Bragg grating used for stretching a pulse. 
         FIG. 7  is a flow diagram illustrating methods for stretching a pulse, according to various embodiments. 
         FIG. 8  is a flow diagram illustrating methods for compressing a pulse, according to various embodiments. 
         FIG. 9  is a block diagram of a method of tuning the stretching of a pulse, according to various embodiments. 
         FIG. 10  is a block diagram of a method of tuning the compression of a pulse, according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a block diagram illustrating various embodiments of a chirped pulse system generally designated  100 . The chirped pulse system  100  includes a pulse source  110 , an optional multi-pass stretcher  120 , an amplifier  130  and an optional multi-pass compressor  140 . The pulse source  110  is configured to generate a pulse having a duration, amplitude, mode, and phase profile. In various embodiments, the pulse source  110  comprises, for example, a ring laser, a laser oscillator, a chirped pulse source, a quasi-continuous wave laser, or the like. In some embodiments, the pulse source  100  generates a chirped pulse. In these embodiments, multi-pass stretcher  120  is optional. Chirped pulse system  100  includes at least one of the multi-pass stretcher  120  and the multi-pass compressor  140 . For example, in some embodiments the multi-pass stretcher  120  is replaced by a single-pass stretcher of the prior art. These embodiments include the multi-pass compressor  140 . 
     The multi-pass stretcher  120  is configured to receive the pulse from the pulse source  110  and includes one or more Bragg gratings through which the pulse is directed one or more times. In various embodiments, the pulse traverses at least one Bragg grating multiple times, and may pass through multiple Bragg gratings one or more times each. 
     The Bragg grating may be fabricated using a photorefractive glass that has an altered refractive index in areas that have been exposed to UV light. The areas of altered refractive index may be arranged so as to stretch and/or compress a pulse. Optionally, the path of the pulse through the Bragg grating determines whether the pulse is stretched or compressed. In some embodiments the Bragg grating is a chirped volume Bragg grating (CVBG) configured to stretch (or chirp) a pulse. 
     The volume Bragg grating optionally includes a cross-sectional aspect ratio in which one dimension is significantly larger than another dimension. For example the volume Bragg grating may have a cross-sectional height of microns and a cross sectional width on the order of one or more millimeters. In these embodiments, the volume Bragg grating may act as a single mode waveguide in one dimension and as a bulk optic in another dimension. In various embodiments, the cross-sectional dimensions may be in ratios of at least 1:1, 1:5, 1:10, 1:50, 1:100, 1:500, 1:1000, 1:5000, and 1:10,000. Embodiments with aspect ratios greater than 1:1 may be particularly suited for fabrication on a wafer. 
     The amplifier  130  is configured to receive the stretched pulse from the multi-pass stretcher  120  and amplify the pulse. In some embodiments, the amplifier  130  is configured to amplify the pulse between passes through a Bragg grating of the multi-pass stretcher  120 . In various embodiments, the amplifier  130  includes a doped fiber amplifier, a semiconductor optical amplifier, a double-clad fiber amplifier, a photonic crystal fiber amplifier, Raman amplifier, and/or the like. In some embodiments, the amplifier  130  comprises a tapered fiber bundle amplifier. Further details of an amplifier including a tapered fiber bundle may be found within U.S. Provisional Patent Application Ser. No. 60/793,960, entitled “Chirped Pulse Amplifier System Including Tapered Fiber Bundle.” In some embodiments, the amplifier comprises a high order mode fiber amplifier such as that described in U.S. patent application Ser. No. 11/491,219, entitled “High Order Mode Optical Amplifier in an Ultrashort Pulse Laser System.” 
     The multi-pass compressor  140  is configured to receive the amplified pulse from the amplifier  130  and includes one or more Bragg gratings configured to receive the amplified pulse one or more times. In various embodiments, the amplified pulse traverses at least one Bragg grating multiple times, and may pass through multiple Bragg gratings one or more times each. The temporal dispersion caused by the Bragg grating may be controlled by stretching the Bragg grating using a mechanical stretcher or a temperature controller. For example, if the Bragg grating is a volume Bragg grating its dispersion properties may be controlled by heating or cooling the volume Bragg grating. In some embodiments, the multi-pass compressor  140  is replaced by a single-pass compressor of the prior art. These embodiments include the multi-pass stretcher  120 . 
       FIG. 1B  is a block diagram illustrating various embodiments of a chirped pulse system generally designated  101  and including a tunable multi-pass compressor. The chirped pulse system  101  in  FIG. 1B  differs from the chirped pulse system  100  in  FIG. 1A  in that the chirped pulse system  101  includes a tunable multi-pass compressor  150  and/or an optional second stage compressor  160 . The chirped pulse system  101  is an alternative embodiment of the Chirped pulse system  100 . The tunable multi-pass compressor  150  and/or an optional second stage compressor  160  represent alternative embodiments of the multi-pass compressor  140 . The tunable multi-pass compressor  150  is configured to be tuned by controlling the number of passes of the pulse through a Bragg grating, and thus, controlling the output pulse width. In some embodiments, the tunable multi-pass compressor  150  is configured to provide fine control of the pulse width and the second stage compressor  160  is configured to provide coarse compression. In various embodiments, the second stage compressor  160  includes a single pass compressor or a multi-pass compressor. The second stage compressor  160  optionally includes a Bragg grating, e.g. a fiber Bragg grating or a Bragg waveguide. In some embodiments, chirped pulse system  101  is configured such that the second stage compressor  160  receives a pulse from the amplifier  130  and the output of the second stage compressor  160  is received by the tunable multi-pass compressor  150 . In these embodiments, the pulse may be substantially compressed prior to being received by the tunable multi-pass compressor  150 . 
       FIG. 2  is a block diagram illustrating part of chirped pulse system  100 , according to various embodiments. These embodiments include a multi-pass Bragg grating in which the pulse is both stretched and compressed. In  FIG. 2 , a chirped pulse amplifier includes a single Bragg grating which is used for both stretching a pulse using multiple passes and for compressing a pulse using multiple passes. The path of the pulse through a multi-pass Bragg grating determines whether the pulse is stretched or compressed. The pulse may be directed through a multi-pass stretching path in the Bragg grating for stretching the pulse. Further, the pulse may be directed through a multi-pass compression path in the same Bragg grating resulting in compression of the pulse. 
     The embodiments illustrated in  FIG. 2  include a chirped pulse amplifier  200  including a multi-pass Bragg grating  220  in which the pulse is both stretched and compressed, according to various embodiments. The chirped pulse amplifier  200  includes embodiments of the multi-pass stretcher  120 , the amplifier  130  and the multi-pass compressor  140 . Specifically, the chirped pulse amplifier  200  includes beam steering optic components  210 , a multi-pass Bragg grating  220 , and the amplifier  130 . The multi-pass Bragg grating  220  is part of both multi-pass stretcher  120  and multi-pass compressor  140 . 
     In the chirped pulse amplifier  200 , a pulse  205 , from pulse source  110 , is directed through a stretching path  212  in the multi-pass Bragg grating  220  using one or more beam steering optics  210 . In various embodiments, the beam steering optics  210  include beam splitters, optical fibers, phase rotators, prisms, reflectors, lenses, tapered fiber bundles, Bragg waveguides, optical combiners, and/or the like. The multi-pass Bragg grating  220  is configured to receive the pulse  205  and output a stretched pulse  215 . The beam steering optics  210  are configured to further direct the stretched pulse  215  again into the stretching path  212  in the multi-pass Bragg grating  220  for additional stretching. After being stretched two or more times the multi-pass Bragg grating  220  outputs the stretched pulse  215  as a multiply-stretched pulse  225 . 
     The multiply-stretched pulse  225  may be directed using one or more beam steering optics  210  to the amplifier  130 . The amplifier  130  is configured to amplify the multiply stretched pulse  225  and output an amplified pulse  235 , as described elsewhere herein. The amplified pulse  235  may be directed, using beam steering optics  210 , to the multi-pass Bragg grating  220  for compression. 
     The beam steering optics  210  are further configured to direct the amplified pulse  235  into a compression path  242  in the multi-pass Bragg grating  220  for generating a compressed pulse  245 , and to direct the compressed pulse  245  again into the compression path  242  in the multi-pass Bragg grating  220  for additional compression. After being compressed two or more times the compressed pulse  245  is output as a multiply-compressed pulse  255 . 
     In  FIG. 2 , the pulse  205 , the stretching path  212  and the compression path  242  are depicted as spatially offset for purposes of illustration. However, a practitioner with ordinary skill in the art will recognize that in some embodiments, there may not be a spatial offset between the stretching path  212  and the compression path  242  and that they may overlap within the multi-pass Bragg grating  220 . In various embodiments, the multi-pass Bragg grating  220 , the amplifier  130 , the pulse source  110 , and/or the one or more of the beam steering optics  210  may be mounted and/or fabricated on a wafer. 
       FIG. 3  is a block diagram of alternative embodiments of the chirped pulse amplifier of  FIG. 1A , illustrating details of a multi-pass stretcher and a multi-pass compressor. In these embodiments, beam steering optics are used for directing a pulse through multiple paths within volume Bragg gratings to stretch and/or compress the pulse. In some embodiments, the multiple paths through a volume Bragg grating may be separated in space using the beam steering optics. 
     In the embodiment illustrated in  FIG. 3 , the multi-pass stretcher  120  includes an optional lens  310 , beam steering optics  210 , and an optional first volume Bragg grating  320  configured to stretch a pulse  305  multiple times. The multi-pass compressor  140  includes an optional lens(es)  310 , beam steering optics  210  and a second optional volume Bragg grating  320 ′ configured to compress an amplified pulse  335  multiple times. The pulse source  110  is configured to provide a pulse  305 . The lens  310  may be used to configure the pulse  305  to converge or diverge. The pulse  305  may be directed to the first volume Bragg grating  320  using one or more beam steering optics  210 . The first volume Bragg grating  320  is configured to receive the pulse  305  from the pulse source  110  and output a stretched pulse  315 . The stretched pulse  315  may be directed, using the beam steering optics  210 , into the first volume Bragg grating  320  again for additional stretching. The stretched pulse  315  may be further stretched one or more times in the first volume Bragg grating  320  and output as a multiply-stretched pulse  325 . 
     The multiply-stretched pulse  325  may be directed using one or more beam steering optics  210  to the amplifier  130 . The amplifier  130  is configured to amplify the multiply stretched pulse  325  and output an amplified pulse  335 . The amplified pulse  335  may be directed, using beam steering optics  210  and/or a lens(es)  310 , to the second volume Bragg grating  320 ′. 
     The second volume Bragg grating  320 ′ is configured to receive the amplified pulse  335  from the amplifier  130  and output a compressed pulse  345 . The compressed pulse  345  may be directed, using one or more beam steering optics  210 , into the second volume Bragg grating  320 ′ again for additional compression. The compressed pulse  345  may be further compressed one or more times in the second multi-pass Bragg Grating  320 ′ and output as a multiply-compressed pulse  355 . 
     In various embodiments, the volume Bragg gratings  320  and/or  320 ′, the amplifier  130 , pulse source  110 , one or more lenses  310  and/or the one or more of the beam steering optics  210  may be mounted and/or fabricated on a wafer. 
     The volume Bragg gratings  320  and  320 ′ are illustrated in  FIG. 3  as single gratings. However, the volume Bragg gratings  320  and/or  320 ′ may be configured as multiple gratings, configured to receive one or more passes of a pulse. In some embodiment, at least one of the volume Bragg gratings  320  and/or  320 ′ is configured to receive two or more passes of a pulse. 
       FIG. 4  is a block diagram illustrating further details of the multi-pass compressor  140  of  FIG. 1A , according to various embodiments including a multi-pass Bragg grating. In these embodiments, a pulse is received by a volume Bragg grating at an incident angle configured such that the pulse passes through a path including multiple reflections along the interior of the volume Bragg grating. The number of reflections may be determined from the incident angle of the pulse and the width of the volume Bragg grating. A lens may be disposed in the path of the incident pulse and configured to provide for conditioning the pulse, e.g. adjusting convergence or divergence of the pulse. 
     In the embodiments illustrated by  FIG. 4 , the multi-pass compressor  140  includes beam steering optics  210 , an optional lens  310 , a volume Bragg grating  430 , and an optional volume Bragg grating  440 . The pulse source  110  is configured to emit an incident pulse  405  and the beam steering optics  210  are configured to direct the incident pulse  405  toward the volume Bragg grating  430  at an incident angle  410  with respect to a normal  460  to a plane of the volume Bragg grating  430 . An optional lens  310  is configured to provide for divergence or convergence of the incident pulse  405 . 
     The incident pulse  405  enters the volume Bragg grating  430  through an aperture  420 . In some embodiments, the aperture  420  is normal to the incident pulse  405 . In the volume Bragg grating  430 , the incident pulse  405  is compressed to generate a compressed pulse  415 . The optional volume Bragg grating  440  is configured to both further compress the compressed pulse  415  and to reflect the compressed pulse  415  into the volume Bragg grating  430  for additional compression. The compressed pulse  415  may undergo multiple reflections within the volume Bragg gratings  430  and  440 , through an appropriate angle  410 . With each reflection, the compressed pulse  415  is further compressed. The compressed pulse  415  may be emitted as a multiply compressed pulse  425  from the volume Bragg grating  430  at an aperture  450 . 
     The number of reflections within the volume Bragg grating  430  may be dependent on the length of the volume Bragg grating  430  and/or the volume Bragg grating  440 . A greater length will result in a greater number of reflections. In some embodiments, the volume Bragg grating  430  and the volume Bragg grating  440  may be configured to emit the multiply compressed pulse  425  from the volume Bragg grating  440  instead of  430 . Thus, the length of the volume Bragg gratings  430  and/or  440  may be used to control the number of reflections. 
     The number of reflections within the volume Bragg grating  430  may also be dependent on the angle  410 . A smaller angle  410  may result in a greater number of reflections. Thus, the number of the reflections of the compressed pulse  415 , and therefore the width of the output pulse, may be tuned by adjusting the incident angle  410 . 
     In some embodiments, a reflector is disposed in place of the volume Bragg grating  440 . These embodiments optionally include a movable embodiment of aperture  450  disposed within the reflector. The number of reflections that a pulse experiences may be controlled by positioning the aperture  450 . For example, the aperture  450  may be positioned such that the compressed pulse  415  is reflected nine times before reaching the aperture  450 , or the aperture  450  may be positioned such that the compressed pulse  415  is reflected eleven times before reaching the aperture  450 . In one embodiment, the aperture  450  is movable to select between one and thirty-five reflections. Thus, the number of reflections, and the amount of compression, can be controlled by positioning the aperture  450 . 
     In  FIG. 4 , the volume Bragg gratings  430  and  440 , as illustrated, are configured to compress the incident pulse  405 . However, a one of ordinary skill in the art will recognize that the volume Bragg gratings  430  and  440  may be configured to stretch the pulse  405 . In various embodiments, the volume Bragg grating  430  and/or  440 , the lens  310 , the beam steering optics  210 , and/or the pulse source  110  may be mounted and/or fabricated on a wafer. 
     As illustrated in  FIGS. 3 and 4 , multiple passes within a Bragg grating may be accomplished by directing a pulse through multiple paths that are spatially separated, to stretch or compress the pulse. However, in some embodiments, the multiple paths through the Bragg grating may be separated in time instead of position. As illustrated in  FIGS. 5A-5D , and  6 , the separation in time of the multiple paths through the Bragg grating may be accomplished using a switch. Moreover, the switch may be used to select the number of passes through the Bragg grating, thus, determining the width of the stretched or compressed pulse. In various embodiments, a switch can be an optical switch, such as an acousto-optic modulator (AOM) switch, an electro-optic modulator (EOM) switch, or a 2×2 switch, or a mechanical switch such as a movable micro mirror, and/or the like. 
       FIG. 5A  is a block diagram illustrating further details of the multi-pass stretcher  120  of  FIG. 1A , according to various embodiments including a multi-pass loop  500 . The loop  500  includes a switch  520 , a circulator  540 , a fiber Bragg grating  550 , and an optional delay line  560 . In some embodiments, amplifier  130  is included within loop  500 . In other embodiments, amplifier  130  is separate from loop  500 . The switch  520  is configured to receive a pulse  515  from the pulse source  110  and direct a switched pulse  525  to the amplifier  130 . The amplifier may be configured to receive the switched pulse  525  and output an amplified pulse  535 . The amplified pulse  535  may be directed to the circulator  540 . 
     The circulator  540  is configured to direct the amplified pulse  535  into the fiber Bragg grating  550  or other Bragg grating. The fiber Bragg grating  550  is configured to receive the amplified pulse  535  from the circulator  540  and return a stretched pulse  545  to the circulator  540 . The circulator  540  is further configured to direct the stretched pulse  545  to the delay line  560 . The delay line  560  is configured to output a delayed pulse  555  to the switch  520 . 
     The same pulse can be directed around the loop  500  (i.e., from the switch  520 , through the amplifier  130 , the circulator  540 , the fiber Bragg grating  550  and the delay line  560 ) multiple times. For example, a delayed pulse received at the switch  520  can be directed again to the circulator  540 . In each pass through the elements in the loop  500 , the pulse is again (optionally) amplified by the amplifier  130 , and further stretched as a result of being directed into and out of the fiber Bragg grating  550 . 
     After one or more passes through the loop  500 , the state of the switch  520  may be changed such that the delayed pulse  555  is directed as an output pulse  565 , rather than towards the amplifier  130  and/or circulator  540 . Thus, the switch  520  may be used to control the number of times the pulse is directed through the loop  500 . In various embodiments, the switch  520  includes a counter, a timer, a sensor, and/or the like. The counter may be configured to count the number of times the compressed pulse is direct into the fiber Bragg grating  550 . The timer may be used to measure a delay time between changes in the state of the switch  520 . The amount of stretching applied to the pulse, and thus, the pulse width, can be tuned by controlling the number of times the pulse is directed through the elements in the loop  500 . Thus, the output pulse width of the loop  500  may be tuned by opening or closing the switch  520  at appropriate times. For example, in some embodiments, the loop  500  is designed to stretch the pulse using from one to one hundred passes, such that the width of the output pulse  565  may be tunable to one hundred different pulse widths. The loop  500  may be configured for selection of more or fewer than one hundred passes. 
     In various embodiments, the loop  500  may be used to stretch the pulse at least 1, 2, 10, 30, 100, or more times. In some embodiments, the pulse is attenuated, for example two percent, with each pass through the loop  500 . When the attenuation is two percent per pass, the pulse will be attenuated about fifty percent after thirty-four passes. However, the pulse may be amplified between passes, for example using the amplifier  130 , to compensate, or more than compensate, for the attenuation. 
     In various embodiments, the pulses  515 ,  525 ,  535 ,  545 , and/or  555  may be communicated between the switch  520 , the amplifier  130 , the circulator  540 , the fiber Bragg grating  550 , and/or the delay line  560  using beam steering optics described elsewhere herein. For example, a fiber optic, a high order mode fiber optic, and/or a tapered fiber bundle may be used to direct a pulse between any elements of the loop  500 , e.g., the switch  520  and the amplifier  130 , the amplifier  130  and the circulator  540 , the circulator  540  and the fiber Bragg grating  550 , the circulator  540  and the delay line  560 , and/or the delay line  560  and the switch  520 . 
       FIG. 5B  is a block diagram illustrating further details of the multi-pass stretcher of  FIG. 1A , according to various embodiments including a Bragg waveguide  570 .  FIG. 5B  differs from  FIG. 5A  in that a Bragg waveguide  570  is used to stretch the pulse, instead of the circulator  540  and the fiber Bragg grating  550 . In each pass through the elements in the loop  500 , the pulse is further stretched as a result of passing through the Bragg waveguide  570 , instead of being directed into the fiber Bragg grating  550  by the circulator  540 . 
       FIG. 5C  is a block diagram illustrating further details of the multi-pass stretcher of  FIG. 1A , according to various embodiments including a Bragg waveguide  570  and a reflector  580 .  FIG. 5B  differs from  FIG. 5A  in that a Bragg waveguide  570  and a reflector  580  is used to stretch the pulse, instead of the fiber Bragg grating  550 . In each pass through the elements in the loop  500 , the pulse is further stretched as a result of being directed into the fiber Bragg waveguide  570  by the circulator  540 . The reflector  580  may return the pulse back through the Bragg waveguide  570  to the circulator  540 . 
     In  FIGS. 5A-5C , the fiber Bragg grating  550  and Bragg waveguide are used configured to stretch a pulse. However, one of ordinary skill in the art will recognize that the fiber Bragg grating  550  may be configured to compress a pulse. Moreover, the pulse may be compressed multiple times in one Bragg grating for fine adjustment and compressed a large amount one time in another Bragg grating for a coarse adjustment. Embodiments of the loop  500  that are configured to compress a pulse typically do not include the amplifier  130 . 
       FIG. 5D  is a block diagram illustrating details of the tunable multi-pass compressor  150  and second stage compressor  160  of  FIG. 1B , according to various embodiments including a multi-pass loop  500 .  FIG. 5D  differs from FIG.  5 A in that the embodiments of loop  500  illustrated are configured to compress the pulse instead of stretch the pulse, and a second stage compressor  502  comprising a fiber Bragg grating  550 ′ is configured for further compressing the output pulse  565 .  FIG. 5D  further differs from  FIG. 5A  in that the optional amplifier  130  and the optional delay line  560  are omitted. In these embodiments, the loop  500  includes the switch  520 , the circulator  540 , and the fiber Bragg grating  550 . The loop  500  may further include the delay line  560  when configured for compressing a pulse. 
     The pulse can be compressed multiple times. The same pulse can be directed around the loop  500  (i.e., from the switch  520 , through the circulator  540 , the fiber Bragg grating  550  and back to the switch  520 ) multiple times. For example, a pulse received at the switch  520  can be directed again to the circulator  540 . In each pass through the elements in the loop  500 , the pulse again is directed into and out of the fiber Bragg grating  550  and thus, further compressed. After one or more passes through the loop  500 , the state of switch  520  may be changed such that the compressed pulse  545  is directed as an output pulse  565 , rather than towards the circulator  540 . 
     The compression of the pulse may be tunable. The amount of compressing experienced by the pulse, and thus, the pulse width, can be tuned by controlling the number of times the pulse is directed through the loop  500 , using the switch  520 . Thus, the output pulse width of the loop  500  may be tuned by opening or closing the switch  520  at appropriate times. For example, in some embodiments, the loop  500  may be designed to compress the pulse using from one to one hundred passes, such that the width of the output pulse  565  may be tunable to one hundred available pulse widths. The loop  500  may be configured for selection of more or fewer than one hundred passes. 
     In various embodiments, the loop  500  may be used to compress the pulse at least 1, 2, 10, 30, 100, or more times. In some embodiments, the pulse is attenuated, for example two percent, each pass through the loop  500 . When the attenuation is two percent per pass, the pulse will be attenuated about fifty percent after thirty-four passes. 
     Coarse and fine adjustment may be used to control the output pulse width. The second stage compressor  502  comprises a circulator  540  and the fiber Bragg grating  550 ′ and is disposed to compress the output pulse  565 . In some embodiments, the fiber Bragg grating  550 ′ in the second stage compressor  502  is configured to compress the pulse by a greater degree than a single pass through the fiber Bragg grating  550  in the loop  500 . Thus, the loop  500  may be used for fine adjustment of the compression of the pulse, whereas the second stage compressor  502  may be used for large scale compression of the pulse. In some embodiments, a multi-pass Bragg grating (e.g., a volume Bragg grating) may be used in the second stage compressor  502  instead of the fiber Bragg Grating  550 ′, for greater compression of the output pulse  565 . 
     In some embodiments, a volume Bragg grating, Bragg waveguide, or other Bragg grating may be substituted for the fiber Bragg grating  550  and/or the fiber Bragg grating  550 ′. In various embodiments, the switch  520 , the amplifier  130 , the circulator  540 , the fiber Bragg grating  550 , the delay line  560 , the pulse source  110 , and/or beam steering optic components may be mounted and/or fabricated on a wafer. 
       FIG. 6  is a block diagram illustrating details of the multi-pass stretcher  120  of  FIG. 1A , including one or more multi-pass path  600 , according to various embodiments. The multi-pass stretcher  120  includes one or more beam steering optics  210 , a volume Bragg grating  640 , a switch  650 , an optional delay line  560  and an optional volume Bragg grating  640 ′, which may be disposed to form the path  600  for a pulse  615 . In some embodiments, the volume Bragg grating  640  and/or  640 ′ could be replaced by a fiber Bragg grating or any other Bragg waveguide. The beam steering optic  210  is configured to receive the pulse  615  from the pulse source  110  and direct the pulse  615  to the volume Bragg grating  640 . The volume Bragg grating  640  may be configured to stretch the pulse  615  and return a stretched pulse  625 , via the beam steering optics  210 , the switch  650 , and the delay line  560 , to the volume Bragg grating  640 ′. The volume Bragg grating  640 ′ may further stretch the stretched pulse  625  and return the stretched pulse  625  to the switch  650  via the delay line  560 . In some embodiments, the volume Bragg grating  640  is replaced by a reflecting element. In these embodiments, Volume Bragg grating  640  may be used alone to stretch the Pulse  615 . 
     The stretched pulse  625  may be directed through the path  600  multiple times in a first state of the switch  650 , thus, producing a multiply stretched pulse. For example, the switch  650  may direct the stretched pulse  625  through the path  600  to the volume Bragg grating  640  again. In a second state of the switch  650 , the stretched pulse  625  is directed out of the path  600  as an output pulse  635 . In some embodiments, the switch  650  is configured to adjust the polarization of the pulse in order to control whether it is again directed into the volume Bragg grating  640  or directed as output. In each pass through the path  600 , the stretched pulse  625  is again directed in and out of the volume Bragg grating  640  and  640 ′ and thus, further stretched. The delay line  560  may be used to control distortion as the length of the stretched pulse  625  increases. In some embodiments, the embodiments of the multi-pass stretcher  120  illustrated in  FIG. 6  can include an embodiment of Amplifier  130  configured to amplify the stretched pulse  625  between passes though the volume Bragg grating  640  and/or volume Bragg grating  640 ′. 
     The width of the output pulse  635  may be tunable. For example, the amount of further stretching applied to the stretched pulse  625 , and thus, the width of the output pulse  635 , can be tuned by controlling the number of times the stretched pulse  625  is directed through the elements in the path  600 . Thus, the output pulse width of the path  600  may be tuned by changing the states of the switch  650  at appropriate times. For example, the path  600  may be configured to stretch the pulse  615  using from one to one hundred passes such that the width of the output pulse  635  may be tunable to select one of one hundred available pulse widths. The switch may be configured for selection from more or fewer than one hundred passes. 
     In various embodiments, the stretched pulse  625  may be directed between the switch  650 , the volume Bragg grating  640  and  640 ′, and/or the delay line  560  using beam steering optics  210  described elsewhere herein. In some embodiments, an optic fiber, for example a tapered fiber bundle, may be used to direct a pulse between any elements of the path  600 , e.g., the switch  650 , the volume Bragg grating  640  and  640 ′, the delay line  560  and/or other beam steering optics  210 . 
     In  FIG. 6 , the volume Bragg grating  640  and/or  640 ′ are illustrated as configured to stretch the pulse  615 . However, a practitioner with ordinary skill in the art will recognize that the volume Bragg grating  640  and/or  640 ′ may be configured to compress the pulse  615  in the path  600  instead of stretch the pulse  615 . Moreover, such a path  600  configured to compress a pulse may be coupled to a second stage compressor, such as that illustrated in  FIG. 5D . 
     In some embodiments, a volume Bragg grating or Bragg waveguide plus a reflector may be substituted for the volume Bragg grating  640  and/or  640 ′. In various embodiments, the volume Bragg grating  640  and/or  640 ′, the switch  650 , the delay line  560 , the beam steering optics  210  and/or the pulse source  110  may be mounted and/or fabricated on a wafer. 
     Various embodiments include methods for stretching or compressing a pulse including directing the pulse through a Bragg grating multiple times. The multiple passes through the Bragg grating result in further stretching or compression of the pulse to create multiply stretched or multiply compressed pulses. 
       FIG. 7  is a block diagram illustrating a method  700  for stretching a pulse, according to various embodiments. In step  710  a pulse is received by a Bragg grating (e.g., the fiber Bragg grating  550 , the volume Bragg grating  320 , Bragg waveguide  570 , and/or the like) from a pulse source. Beam steering optics (e.g., the beam steering optics  210 ) may be used to direct the pulse to the Bragg grating. In some embodiments, the beam steering optics include a lens configured to produce a converging or diverging pulse. In various embodiments, the beam steering optics are configured to rotate the pulse, split the pulse, amplify the pulse, delay the pulse, switch the pulse, reflect the pulse, modify polarization of the pulse, and/or the like. 
     In step  720 , a pulse (e.g., pulse  205 ) is stretched by a Bragg grating (e.g., Bragg grating  220 ) to produce a stretched pulse  215 . Optionally, the path that the pulse follows (e.g., the stretching path  212  or the compression path  242 ) into and out of the Bragg grating  220  determines whether the pulse is stretched compressed. The beam steering optics (e.g., beam steering optics  210 ) are configured to direct the pulse into the stretching path  212  through the Bragg grating  220  to stretch the pulse  205 . 
     In some embodiments, the length of the stretched pulse  215  may approach the length of the stretching path  212  into and out of the Bragg grating  220  as the stretched pulse  215  is stretched. In optional step  730 , the stretched pulse  215  is delayed to avoid distortion, truncation and/or the like. In some embodiments, the step  730  further includes amplifying the stretched pulse  215 . In some embodiments, the amount of stretching possible is limited by a length of a delay line, such as delay line  560 . Alternatively, the stretched pulse  215  is amplified instead of delayed in step  730 . 
     In step  740 , the stretched pulse  215  is redirected to the Bragg grating  220  using beam steering optics  210 . The stretched pulse  215  is redirected to the stretching path  212  through the Bragg grating  220  configured to stretch the stretched pulse  215  again. 
     In step  750 , the stretched pulse  215  is stretched further using the Bragg grating  220 , to produce a multiply stretched pulse. In some embodiments, the method  700  includes further stretching the stretched pulse  215  in the same Bragg grating  220 . For example, in a volume Bragg grating  220  multiple paths of the stretched pulse  215  through the Bragg grating  220  can be separated spatially. The beam steering optics  210  may be used to provide the spatial separation of the paths. In another embodiment, the multiple paths of the stretched pulse  215  through a fiber Bragg grating  220  may be separated in the time domain, using beam steering optics  210 , including a switch, e.g. the switch  520  illustrated in  FIG. 5A . In some embodiments, the method  700  includes directing the stretched pulse  215  into separate Bragg gratings  220 . 
     Although the method  700  for stretching a pulse is described as being comprised of various steps (e.g., receiving a pulse  710 , stretching the pulse  720 , delaying the pulse  730 , redirecting the pulse  740 , and further stretching the pulse  750 ), fewer or more steps may comprise the method  700  and still fall within the scope of various embodiments. For example, steps  730 - 750  may be repeated multiple times. 
       FIG. 8  is a block diagram illustrating a method  800  for compressing a pulse through spatially separated multiple paths, according to one embodiment. The steps  810 - 850  are similar to the steps  710 - 750  respectively, except that the pulse is compressed instead of stretched. 
     In step  810 , a pulse (e.g., the pulse  235 ) is received by the Bragg grating  220 . In step  820 , the pulse  235  is compressed by the Bragg grating  220 . The beam steering optics.  210  are configured to direct the pulse  235  through the compression path  242  in the Bragg grating  220 . 
     In optional step  830 , a compressed pulse, e.g., the compressed pulse  245  is delayed. In step  840 , the compressed pulse  245  is redirected, using the beam steering optics  210 , to the compression path  242  through the Bragg grating  220  for further compression. In step  850 , the compressed pulse  245  is further compressed using the Bragg grating  220 , to generate a multiply compressed pulse. In some embodiments, the pulse  235  can be compressed by the same Bragg grating  220  used for stretching an input pulse  205 , using the beam steering optics  210  to select the stretching path  212  or the compression path  242 , as described elsewhere herein. In some embodiments, the amount of compression that is possible is limited by the length of a delay line, such as delay line  560 . 
     Although the method  800  for stretching a pulse is described as being comprised of various steps (e.g., receiving a pulse in step  810 , compressing the pulse in step  820 , delaying the pulse in step  830 , redirecting the pulse in step  840 , and further compressing the pulse in step  850 ), fewer or more steps may comprise the method  800  and still fall within the scope of various embodiments. For example, the steps  840  and  850  may be repeated multiple times. 
     In  FIGS. 9 and 10 , the width of a stretched or compressed pulse may be tuned by turning a switch on or off at appropriate times. For example, the number of passes through a grating for stretching or compressing the pulse may be controlled using the switch to direct the pulse into the grating multiple times, or away from the grating. Thus, the switch can be used to control the width of the stretched or the compressed pulse. 
       FIG. 9  is a block diagram of a method  900  of tuning the stretching of a pulse, according to various embodiments. In a step  910 , a pulse (e.g., the pulse  515 ) is received by a fiber Bragg grating (e.g., the fiber Bragg grating  550 ). The pulse  515  may be directed to the fiber Bragg grating using beam steering optics  210 . In a step  920 , the pulse  515  is stretched using the fiber Bragg grating  550 . 
     A step  930  includes determining if a loop time has elapsed. The loop time is a time a pulse has been in a loop such as loop  500 . The longer the loop time, more times a pulse will have passed through a Bragg grating configured to stretch the pulse. Thus, the longer the loop time, the greater the stretching that will occur. For example, a timer may be coupled to the switch  520  and set to change the state of the switch  520  after a predetermined loop time has elapsed. If the loop time has not elapsed, the stretched pulse  545  is directed, e.g., using the switch  520 , to be stretched again. 
     In the optional step  940 , the stretched pulse  545  is delayed. As the length of the stretched pulse increases, as a result of multiple stretching steps, the delay may be useful in accommodating longer stretched pulses  545  from the fiber Bragg grating  550  and/or associated beam steering optics  210  to prevent truncation of the stretched pulse  545  when the switch  520  is changed to direct the stretched pulse  545  as output. In some embodiments, the step  940  further includes amplifying the stretched pulse  545 . Alternatively, the stretched pulse  545  is amplified instead of delayed in step  940 . 
     After the delay and/or amplification at step  940 , the stretched pulse  545  may be stretched again in step  920 , to generate a multiply stretched pulse. Optionally, step  940  is omitted and the stretched pulse  545  is stretched again at step  920 , directly after step  930 . The stretched pulse  545  may be stretched multiple times in a loop comprising the steps  920 ,  930 , and  940 . 
     If the loop time has elapsed at step  930 , the switch  520  may change state and the stretched pulse  545  is output at step  950 . In an optional step  960 , a sensor determines a property of the output pulse. In various embodiments, the property determined by the sensor in step  960  includes the length of the stretched pulse  545 , the intensity of the stretched pulse  545 , the power of the stretched pulse  545 , a wavelength of the stretched pulse  545 , and/or the like. Optionally, the loop time is changed based on the property determined in step  960 . 
     Although the method  900  for stretching a pulse is described as being comprised of various steps (e.g., receiving a pulse in step  910 , stretching the pulse in step  920 , determining if the loop time has elapsed in step  930 , delaying the pulse in step  940 , outputting the pulse in step  950 ), and sensing a property of the stretched pulse in step  960 , fewer or more steps may comprise the method  900  and still fall within the scope of various embodiments. 
       FIG. 10  is a block diagram illustrating a method  1000  of tuning the compression of a pulse, according to various embodiments. The steps  1010 - 1060  are similar to the steps  910 - 960  respectively, except where the method  1000  of  FIG. 10  differs from the method of  FIG. 9  in that the pulse is compressed instead of stretched, using multiple passes through s Bragg grating. 
     Although the method  1000  for compressing a pulse is described as being comprised of various steps (e.g., receiving a pulse  1010 , compressing the pulse  1020 , determining if the pulse length is correct  1030 , delaying the pulse  1040 , and outputting the pulse  1050 ), fewer or more steps may comprise the method  1000  and still fall within the scope of various embodiments. For example, steps  1020 - 1050  may be used for fine compression adjustment and a second stage compressor may follow step  1050  for coarse compression. 
     Several embodiments are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations are covered by the above teachings and within the scope of the appended claims without departing from the spirit and intended scope thereof. For example, the Bragg grating can be tuned mechanically, thermally, or using a piezo device. For example optically compression or expansion devices other than Bragg gratings may be used. Further, the systems and methods disclosed herein with reference to stretching a pulse may be adapted by one of ordinary skill in the art to compressing a pulse. Likewise, the systems and methods disclosed herein with reference to compressing a pulse may be adapted by one of ordinary skill in the art to stretching a pulse. For example, those examples including a fiber Bragg grating or volume Bragg grating may be adapted by reversing direction of the grating. Those examples including a Bragg waveguide may be adapted by changing the characteristics of the Bragg waveguide. The systems and methods described herein may be adapted to other types of pulse stretching and compressing optics, other than Bragg gratings. 
     The embodiments discussed herein are illustrative of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications or adaptations of the methods and or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the spirit and scope of the present invention. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated.