Abstract:
Multi-band 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 
     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 
     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. 
     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 47K temperature, requiring cryogenic electronics. 
     SUMMARY 
     According to one embodiment, the THz receiver is composed from a resonator wave input structure able to select the frequency, angle of incidence and polarization of the incident THz photons and harvest their energy loading the field inside resonating structure. The resonant structure said antenna has a device of discharging its energy into a set of shaped conductive beads generically called plasmon amplifier. 
     According to another embodiment the beads of the plasmon amplifier is operating as a voltage amplifier and applies its output the potential over the gate of an ultra low field effect active device, perturbing a reference signal generically called “carrier” passing through this active device. 
     According to another embodiment the field effect active device is optimally 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 internal noise supposed to produce a symmetric perturbation. 
     To minimize the electronic noise in the input stages cryogenic temperature is recommended. 
     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. 
     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. 
     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 
         FIG. 1  shows the resonator structure input stage—principia diagram 
         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. 
         FIG. 3  shows a magnified cross section through the MOS/BET-FET gate and solid-state compact voltage amplifier 
         FIG. 4  shows the signal schematic flow diagram from the THz input resonator to ADC 
         FIG. 5  shows the real-time on flow digital analog converter for microwave and THz applications with fast data acquisition in a schematic diagram. 
         FIG. 6  shows the multi-band module array that constitutes the elementary spectral detection unit 
         FIG. 7  shows a composite detection element using several multi-band modules, placed to detect different polarization planes. 
         FIG. 8  shows the principle of THz detection based on nonlinear carrier perturbation 
         FIG. 9  shows the schematic diagram of the signal flow from detection to imaging system data storage 
     
    
    
     DETAILED DESCRIPTION 
     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 best match the power transfer. 
       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. 
     In  FIG. 1  a modified “yagi” like resonator device comprises central support  1  grounded and 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. 
     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. 
     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. 
     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. 
     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 . 
     The voltage buildup on the beads  7  is driven through the passages  10 ,  11  towards the solid-state passive voltage pre-amplifier made with plasmonic structures. 
       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. The input resonator structure output stage shown in  FIG. 1  fuses with the input stage of the plasmon amplifier represented by the beads  22 ,  24 ,  32 . 
     The central resonator axis  20  is the connected to the bottom support with the role in shielding and voltage reference and is in contact with the central support  1  in  FIG. 1 . 
     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. The components  22 ,  21 ,  28  and  29  in the compact version of construction are the same with the components  7 ,  6 ,  11 ,  10  while  20 ,  26 ,  27  are a continuation of  1 ,  9  and  8  respectively. 
     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 structure delimited by surface  28  to resonate on a different frequency than the right side structure delimited by surface  29  modifying the shape of the frequency band. 
     The beads cascade  22 , 24 , 32  respectively  23 ,  25 ,  31  sustained and/or embedded on dielectric layers, or wires to maintain the right position to get the maximal voltage amplification. 
     The cascade has the number of beads given by the dimensions of the gate  31 ,  32  of the MOS-FET or ballistic FET formed using the last bead of the structure, and the wavelength that determines the dimensions of the entry beads  22 ,  23 . The bids ratio, shape, positioning and the loss factors in the structural materials is given the voltage amplification coefficient. 
     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. 
     The metallic  34 , 35  structure covers the FET active structure  38 ,  39  with the role of shielding the FET operating intermediary frequency in MHz to GHz domain. 
     The contacts and the mechanical structure of the electronics is made small and&#39;planar placed in locations  36 ,  37  giving the minimal interference in the gate&#39;s space. 
     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  32  and  31  acting on active layers  38 ,  39  making the THz power extractionat the necessary level to influence the current passing through. 
     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”. 
     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. 
     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 . 
     The structure presented in  FIG. 2  takes the THz selected signal prepared by the input structure in  FIG. 1  and by a nonlinear process uses it to perturb a much lower reference frequency running in MHz or GHz domain, where the electronic devices are naturally operating making the function of a down-converter. 
       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 making the 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 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 optimal voltage amplification. 
     The FET&#39;s source  54  and the drain  53  are conductive layers screening the active semiconductor layer underneath constituting the elements, of the transistor junction like structure commanded by the gate  52  and placed in such a manner to make the noise rejection factor big, and no perturbation to be transmitted from below. 
     The “transistor” has various substrates like metallic plating  54 ,  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 electric conductivity purposes and heat homogenization. 
     To enhance the detection properties a special shaped FET have to be developed by bending the actual thin structure along 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 electro-magnetic field. This setup has the role to convert the voltage generated by the “plasmon amplifier” into a low frequency signal in the form of a carrier signal amplitude perturbation compatible with the actual electronics. 
       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 and match polarization and frequency. The selected wave by matching wave length and polarization builds up the voltage in the resonator, that is further transmitted and amplified through the chain of beads  72  ( 50 ,  51 ,  52  in  FIG. 3 ) towards the gate 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. 
     The perturbed—carrier—signal is transferred through an adapter circuit  75  to be further amplified in a secondary stage  76  and applied to a double comparator  77  that extracts the perturbation only. In this way is performed a down transition from the THz domain to MHz or GHz domain making the signal compatible with a no dead time analog digital converter  78  that digitizes the signal and stores it into a multiple access buffer memory. There is the process computer, called imager, that takes the data from this buffer memory and process it in accordance with the detection structure, calibration and code. 
       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  output to a chain of converters  92  similar to  81 . 
     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 processing in real time providing the compact data to various computer buses  95 . 
       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 with the highest frequency and minimal dimensions  103 , with an intermediary frequency  104 , or with the lowest frequency and bier dimensions  105 , etc. The elemental unit  102  of the assembly  101  is obtained by building tight together the input resonator structure  70  in  FIG. 4  followed by the solid state “plasmon amplifier”  72  in  FIG. 4  sticked into resonator, with the amplification elements  74  to  77  mounted compact on the active element  74  build with the plasmon resonator incorporated over its gate, all together being packed in a single case. 
     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 step 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 assembly&#39;s carrier frequency and the real time visualization at the human eye speed. 
       FIG. 7   a  shows another embodiment of the invention regarding the multi-band modules that might be grouped based on shape in various combinations creating units in octagons  110  while  FIG. 7   b  shows possible resonators grouping combinations in hexagons  111 , trapezes  112 , parallelograms, rhombs  113  and other centered polygons. The resonant polarization selective structures may provide various bands and polarization combinations (planar, circular, elliptic) even detecting the polarization advance rotation versus left (levogir) in  114  or right (dextrogir) in  115 . The structures may be prisms or pyramids matching in planar or curved surfaces to morph on the shape of the supporting surface. 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/or stereoscopy. 
     Knowing, based on recent measurements, that the photon has a finite dimension and length containing about 10 thousands to 1 billion oscillations and a specific with and shape, 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. 
       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. 
     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. 
     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. 
       FIG. 9  presents a synthesis of the THz signal detection method with the main embodiments. The fact 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. 
     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 . The input resonator features as central frequency, bands with and position, directivity and polarization will be application dependent and subject to design optimization. 
     The plasmonic amplifier output is attacking the gate of a shaped active element  134  that runs through a special shaped signal generically called “carrier” in a low frequency domain, lower than its cut-off or maximum operating frequency of the electronics used. The THz signal is perturbing the “carrier” signal 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 carrier signal perturbed by the THz frequency and the original unperturbed carrier signal is applied to a differential amplifier  135  and the integrated THz perturbation signal is extracted and applied to the ADC converter  136 . 
     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.