Abstract:
Multiband polarized receiver-emitter THz domain visualization device that includes a group of elemental receiver units made from a resonant system sensitive to frequency and polarization, a micro-bead solid-state voltage amplifier in the gate of a differential FET system. The detection is based on the carrier perturbation method detected by a set of double gate comparator circuits that further generates an integrated signal driven to a digital analog converter. The signal from here is accessing event-based memory used to generate the 3D images. Multiple detection modules are coupled into a triangular detection element detecting a multitude of frequencies, in a cascade of bands from 2 mm to 1 micron. This THz chromatic detector is integrated in a surface morph array, or in an image area of a focusing device generating a pixel of information with band, amplitude, polarization and time parameters, driving to a complex 3D substance level visualizations.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/786,169, filled on Mar. 27, 2006, which is hereby incorporated by reference in this entity. 
     
    
     BACKGROUND 
       [0002]    During the past few decades, electromagnetic applications got a new dimension as solution to assure better communication and better imaging. The new instrumentation not only allowed to have better image, but to obtain images of the temperature distribution and more recently, of the molecular and atomic composition distribution. Developing visualization device in far Infra red presents tremendous advantages and focused the research of space agencies, defense and security as well many other private companies oriented to science. The THz wave emitters and receivers are less developed, compared to its neighboring bands (microwave and optical). During the past decade, THz waves have been used to characterize the electronic, molecular vibration and composition, properties of solid, liquid and gas phase materials to identify their molecular structures. 
         [0003]    The Terahertz domain is the most uncovered, because the energies are small to be detected by the majority of the actual devices, while the dimensions are in the sub-millimetric domain. The problem of the ratio Signal/Noise ratio is difficult because the energy of a single 1 THz photon is 4.1 meV equivalent to a 47 K temperature, requiring cryogenic electronics. 
       SUMMARY 
       [0004]    According to one embodiment, the THz receiver is composed from a resonator structure able to select after the frequency, angle of incidence and polarization the THz photons and harvest their energy loading the field inside the structure. The resonant structure said antenna has a device of discharging its energy into a set of shaped conductive beads generically called plasmon amplifier. 
         [0005]    According to another embodiment the beads amplifier is operating as a voltage amplifier and drives the potential over an ultra low field effect active device, passing a reference signal generically called “carrier”. 
         [0006]    According to another embodiment a field effect active device is shaped in order to increase the field effect inside and to produce a nonlinear characteristic similar to that of a rectifier device. The device will transform the presence of a THz signal into a strong perturbation giving a non-null integral compared with the noise that will produce a symmetric perturbation. To minimize the electronic noise in the input stages cryogenic temperature is recommended. 
         [0007]    According to a further embodiment the detected THz signal integrated over a carrier half period is further applied to an analog-digital converter having no-dead time and generating the binary value into a stack memory, from where various processing may be performed. The main processing will be a carrier down-frequency conversion to the imaging devices frame rate for real time visualization procedures, or background correction. 
         [0008]    According to another embodiment the resonant structures used for THz photon energy harvesting may be used for THz pulsed beam emission, if the same device is reversed, such as the differences in phasing of the carrier frequency to be transformed into a short transitory resonant structures loading pulse. 
         [0009]    The general aim of the development is to produce narrow band emitter receivers in THz domain that to open the way to applications in molecular domain visualization and localization. The fast electronic devices are meant to assure detection power for chemical reactions visualization in the domain down to nanoseconds. The applications are drastically enlarged if the power of pulsed selected frequency and polarization is added by the use of THz pulse generation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows the resonator structure input stage-principia diagram 
           [0011]      FIG. 2  shows in cross-section the resonator stage diagram coupling to the passive plasmonic electric field amplifier and this amplifier coupling to the active device. 
           [0012]      FIG. 3  shows a magnified cross section through the MOS/BET-FET gate and solid-state compact voltage amplifier 
           [0013]      FIG. 4  shows the signal schematic flow diagram from the THz input resonator to ADC 
           [0014]      FIG. 5  shows the real-time on flow digital analog converter for microwave and THz applications with fast data acquisition in a schematic diagram. 
           [0015]      FIG. 6  shows the multi-band module array that constitutes the elementary spectral detection unit 
           [0016]      FIG. 7  shows a composite detection element using several multi-band modules, placed to detect different polarization planes. 
           [0017]      FIG. 8  shows the principle of THz detection based on nonlinear carrier perturbation 
           [0018]      FIG. 9  shows the schematic diagram of the signal flow from detection to imaging system data storage 
           [0019]      FIG. 10  shows the schematic diagram of reversible operating modes of the THz plasmon amplifier-resonator structure for emission. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The generic diagram of a high frequency transceiver is based on a selective resonant element called antenna that adapts the ether impedance of about 377 Ohm at certain frequency to the electronic device impedance adjusting the electric parameters to match the power of the electronic device that may present a multitude of functions. 
         [0021]      FIG. 1  shows a generic resonant structure is made from conductive material, as Gold, Silver, etc. and it may have different shapes from those in the drawing as an embodiment of the invention. The real object being designed considering the variations of the shapes and electric parameters associated with the operation frequency such as to maximize the quality factor of the resonator. 
         [0022]    In  FIG. 1  this modified “yagi” like device is made from the central support  1  grounded or in good connection with the electromagnetic vibrators  2  that have a role in frequency and polarization selection of the incident waves. The flat structures are preferred due to easiness of buildup by lithographic or chemical vapor deposition means. 
         [0023]    The antenna is using several vibrators  2 ,  3 ,  4 ,  5  or more which define the directivity, polarization, frequency band and the passive resonator signal amplification. The number of the resonator elements or the usage of phased parallel structures are mainly parametric design elements, and may be varied to meet the performance requirements of various designs. 
         [0024]    The electrode  2  only, or the entire structure may be embedded into a dielectric material as diamond, silicon, germanium, resin, glass or ceramic transparent to THz frequencies with role in compaction and surface hardening. 
         [0025]    The end electrode  6  is the receiver that has modified geometry allowing an enhanced voltage peak resonator made of shaped beads  7  with the dimension of about ⅛- 1/16 the wave length, as the alternative voltage near field distribution to look as quasi-continuum. 
         [0026]    The back reflector  14  has a lateral structure  12 ,  13  and signal passing grid holes  10 ,  11 , connected to a lateral funnel structure  8 ,  9 , which makes it look like a wave guide with the purpose to enhance the quality factor and the voltage on the beads  7 . 
         [0027]    The voltage from the beads is driven through the passages  10 ,  11  towards the solid-state passive voltage pre-amplifier that may be made with plasmonic structures. 
         [0028]      FIG. 2  shows another embodiment of the invention in a cross section through the solid-state preamplifier and the field effect and/or ballistic active element with role in voltage amplification and signal detection. 
         [0029]    The central resonator axis  20  is the connected to the bottom support with the role in shielding and voltage reference. 
         [0030]    The resonator beads  22 ,  23  (corresponding to  7  in  FIG. 1 ) are positioned on the support  21  ( 6  in  FIG. 1 ) and connected to the central support  20  ( 1  in  FIG. 1 ) and shaped such as the maximum voltage is obtained preferably towards the bottom surfaces  28 ,  29  ( 12 - 14  in  FIG. 1 ) that are shaped in such manner to maximize the quality factor of the resonator. 
         [0031]    The bottom of the array contains the reflector surface  28 ,  29  connected to the lateral funnel structure  26 ,  27  ( 9 ,  8  respectively). There is possible that the left side  28  to resonate on a different frequency than the right side  29  modifying the shape of the frequency band. 
         [0032]    The beads cascade  22 , 24 , 32  respectively  23 ,  25 ,  31  is sustained and/or embedded on dielectric layers, or wires in a position to get the maximal voltage amplification. The shape, dimensions and position of the beads are subject of optimization. 
         [0033]    The cascade may have a number of beads given by the dimensions of the gate  31 ,  32  of the MOS-FET or ballistic FET and the wavelength that determines the dimensions of the entry beads  22 ,  23 . 
         [0034]    The cascade ratio, beads shape and materials will be driven by the voltage maximization criteria and fabrication possibilities. A meshed structure  30  will be used to create dipolar effects amplification of the voltage in the beads locations. 
         [0035]    The metallic  34 , 35  structure covers the FET structure  38 ,  39  with the role of shielding the FET operating intermediary frequency in MHz to GHz domain from the THz resonator frequency. 
         [0036]    The contacts and the mechanical structure of the electronics is made small and planar placed in locations  36 ,  37  giving the minimal interference in the gate&#39;s space. 
         [0037]    The funnel structure  30  and the beads  22 , 24 , 32  respectively  23 , 25 ,  31  are looking like a resonator “de-Q-ing” antenna, when matched, the resonator power is absorbed and transmitted through the metallic mesh funnel  30  in the FET gates  38 ,  39 . 
         [0038]    The active structure  38 , 39  is made by a tunneling electronics, ballistic transistor, field effect transistor, operating at a lower frequency in the MHz-GHz domain named “carrier”. 
         [0039]    The application of this high frequency variable voltage is increasing the scattering in one arm  36 , 38  while decreasing in the complementary one  37 , 39 . The electrostatic scattered electrons of the carrier frequency corroborated to the influenced arrays in the active material interface or junction perturbs the shape of the low frequency signal which integrates the detection in a pulse with a length in time shorter than ½ of the carrier period that represents an embodiment of the invention. The amplitude is proportional with the THz signal. 
         [0040]    The GHz perturbed signal is extracted through the communication spaces  40 ,  41 ,  45  in the comparator amplifier space  44 . The temperature is maintained constant by a “Peltier” cooling device  42  surrounded by thermal conductive materials, to keep cryogenic temperatures in the sensitive elements and so to minimize the electronic noise. Vacuuming the device makes the transition to the upper surface&#39;s temperature and applying thermal shunts on the heat leakage tracks. Finally, the signal detected on intermediary frequency is extracted from the module  44  through the gates  43 ,  46 . 
         [0041]      FIG. 3  shows another embodiment of the invention in a magnified cross section through the interface connection between the beads  50 , 51 , 52  ( 22 ,  24 ,  32  or  23 ,  25 ,  31  in  FIG. 2 ) cascade plasmonic voltage amplifier and the MOSFET gate  52  ( 38 , or  39  in  FIG. 2 ) is made such as the dimension of the last bead to be compatible with the gate dimension that is in the range of 50-100 nm. The scaling factor and beads number is set to adjust upwards to the resonator ( 22 ,  23  in  FIG. 2 ) dimensions and to obtain the maximal stable amplification. 
         [0042]    The FET&#39;s source  54  and the drain  53  are plated and screened, and the two active elements, generically called transistors gates  52  are placed in a symmetric manner to make the rejection factor big, and no perturbation to be transmitted from below. The “transistor” has various substrates like metallic plating  55 , a n-doped substrate  56 , a insulator layer, oxide layer  57 , and chip&#39;s substrate  58 . The metallic backing  60  is used for conductivity purposes and heat homogenization. 
         [0043]    Special shaped FET have to be developed as a thin wire bended together on the symmetry central axes forming a needle shaped tip for the gate of an appropriate radius to connect to the bead  51 . In this way the transistor will look like a needle tip getting out of the metallic surface. The diamond based electronics for very low currents may be used. The main idea is that with the tiny voltage a THz photon may create, to become able to perturb a lower frequency carrier signal in order to detect the presence and intensity of a specific THz electromagnetic field. 
         [0044]      FIG. 4  shows the complete detection sequence of the THz receiver an embodiment of the invention. The THz photons are hitting the resonator cavity  70 , having the grounded funnel wall structure  71  ( 8 ,  9  in  FIG. 1 ) such to function like an open wave guide, with the special resonant structure in the middle to select the right wave with matching polarization and frequency. The selected wave with the matching wave length and polarization builds up the voltage in the resonator, which is further transmitted and amplified through the chain of beads  72  ( 50 ,  51 ,  52  in  FIG. 3 ) towards the gates of the low current MOS-FET like structure  73  and  74  ( 38 ,  39  in  FIG. 2 ) operating in the nonlinear domain of their characteristics and asymmetrically varying their equivalent resistance and perturbing the alternating carrier MHz-GHz frequency. 
         [0045]    The carrier-perturbed signal is further amplified in a secondary stage  76  and applied to a double comparator  77  that extracts the perturbation only. In this way a down transition to the THz domain down to MHz or GHz domain with a no dead time digital anagogic converter  78  digitizes the signal and stores into a multiple access buffer memory. There is the process computer takes the data from this buffer memory and process it in accordance with the detection structure and calibration. 
         [0046]      FIG. 5  shows another embodiment of the invention, in the schematic diagram of the zero-dead-time analog digital converter  80  composed from several direct converting modules  81 ,  92  based on comparators  85  which generates a digital line  87  outputs applied in a buffer  88  from where is converted in hexadecimal signal  89 . The signal  82  representing the perturbation is entering an impedance adapter  83  and is applied to the parallel structure of comparators  85  to take the reference from the voltage divider  84  powered in very stable conditions. The signal is also applied to a delay line  86  and a new differential amplifier  90  in which the reference is dynamically build so only the truncation difference is amplified and passes through by  91  to a chain of converters  92 . 
         [0047]    A plurality of 2 n  amplifiers chain producing at each stage the most significant n bits can be connected in series until the last significant bits become meaningless. These bits are grouped in a data bus and sent to a multiple direct access memory buffer  93 ,  94 . The memory module  94  is used for online neural processing in real time providing the compact data to various computer buses  95 . 
         [0048]      FIG. 6  shows an assembly of the THz band detection device as one embodiment of this invention that consists in a solid-assembly of the devices described in the previous figures each operating on a defined frequency, with controlled polarization and directivity, representing a unit  103 ,  104 ,  105 , etc. 
         [0049]    The individual devices were compacted in a triangular structure, scanning all the range in dedicated frequency bands. This creates a triangular multi-band module  100  according to an embodiment of this invention. The frequency sweep will determine the shape of the triangle. The electronics have been attached on all the receivers in the module. This device makes possible fast monitoring at the carrier frequency and the real time visualization at the human eye speed. 
         [0050]      FIG. 7  shows another embodiment of the invention according with the multi-band modules that might be grouped based on shape in various combinations creating units in octagons  110 , hexagons  111 , trapezes  112 , parallelograms, rhombs  113  and other centered polygons. They may provide various bands and polarization combinations even detecting the polarization advance spin versus left or right  114 ,  115 . The structures may be prisms or pyramids matching in planar or curved surfaces to morph on the shape. This multiple band controlled polarization array makes possible the signature analysis for molecular identification with temperature and density evaluation. The plurality of such cells used makes possible various type of visualization from planar imaging as human eye, to fly eye or tri-dimensional material localization with various visualization routines to become accessible to humans as pseudo-color and stereoscopy. 
         [0051]    Knowing, based on recent measurements, that the photon has a finite dimension and length containing about 10 thousands to 1 billion oscillations and a with roughly shaped by the Heinsenberg&#39;s incertitude principle applied to fermions, the invention makes various combinations to detect the polarization and locality of bunches of photons. This module establishes multi-band, multi-polarization information usable for material chemical identification based on pseudo-chromatics analysis where it is possible. There is also known that the THz domain is well populated so a background extraction of the thermal photons will be required. The plurality of frequencies contributes to a good evaluation of the Plank thermal emission curve and extraction in order to enhance contrast for molecular distribution and state visualization. 
         [0052]      FIG. 8  shows another main embodiment of the invention, is the method of carrier perturbation used for THz detection, that consists in asymmetrical perturbation of the gate of a MOSFET or ballistic FET like active device of a special design by an ultra high frequency not even detectable by the normal operation of the component. 
         [0053]    The invention is based on the usage of a nonlinear active device that makes the difference between the presence of the THz wave and the thermal noise. At this frequency the perturbation have to be applied in the nonlinear characteristics  120  of the FET Response  123  which for a high frequency gate perturbation by a Voltage  121  the response  122  becomes asymmetric so the integral in the response time gives a non-null component. So, the intermediate frequency voltage  124  supposed as being a sinusoidal wave  125  will record a distortion like perturbation  126 , which will have a non null integral over the response time period of the comparator which have to be 3-10 shorter then the period of the carrier frequency in GHz. This will impose the timing of the illumination profile in THz bands. Faster modulation will be detected only by the cumulative effect. The requirement to minimize the electronic thermal noise in the input stages will drive to cryogenic resonator and plasmon amplifier devices and a good faceting of the beads with low electronic emission materials having low multipactor factor and low electron rattle noise. 
         [0054]    As conclusion of one of the main embodiments of the invention, the amplification is measuring the distortions of the perturbed GHz-MHz wave compared with a reference signal, and assumes proportionality with the THz signal&#39;s intensity. Other aspects of photon shape and duration effects remain to be clarified, as well as photon width and selectivity in the light of Heisenberg&#39;s equation remain to be clarified and observed and adjust at the device&#39;s buildup. 
         [0055]      FIG. 9  presents a synthesis of the THz signal detection method with the main embodiments. The concept that most of the conductors remains conductors even in various bands in the THz domain except for resonance where they have an anomalous behavior drives the application of the resonant structures in the THz domain as a main embodiment of the invention. 
         [0056]    The THz signal  130  is therefore according to the invention selected and amplified in the resonant structure  131 , and transmitted to the plasmonic amplifier  132 . 
         [0057]    The plasmonic amplifier is attacking the gate of a shaped active element  134  that runs a based special shaped frequency in a low frequency domain, lower than its cut-off frequency perturbing it as an asymmetric noise. This built in asymmetry makes the difference between the presence of the THz signal and the electronic noise being a kind of THz signal rectification as shown in  FIG. 8 . Further, the THz perturbed low frequency carrier and the original signal passing through an unperturbed device is applied to a differential amplifier  135  and the integrated THz perturbation signal is extracted and applied to the ADC converter  136 . 
         [0058]    The Analog-Digital Converter  136  has a no-dead time feature useful for continuous conversion the digital data extracted  137  is loading a stack memory. All the electronics  133  is closely mounted on a customized chip near the resonator. 
         [0059]      FIG. 10  presents another important feature of the plasmonic amplifier-electromagnetic resonator—the reversibility—of the composition from two perturbation signals, of a THz wave, by carrier differentiation into the plasmonic amplifier entry representing an embodiment of the invention. 
         [0060]    The fast signal generator  152  generates two carrier frequency signals slightly shifted in time  145 ,  147 , applied successive on the plasmonic amplifier entry  143  and  144  which combines them obtaining a solitron type variation  146 . This perturbation is transmitted back through the plasmonic amplifier  142 , loading the resonator  141  that discharges through a THz emission  140 . 
         [0061]    The device  150  is an electronic amplifier tube generating an electron beam  149  instead of an electric voltage shaped pulse, heating the capillary tube which forces it into a bunch pulse acting further on the plasmon amplifier entry  142  above and under the multipactor threshold and increasing the power of the THz emitter up to the limits of a pulsed power device able to illuminate with high THz narrow band intensities.