In this paper, two D-band (110 similar to 170 GHz) monolithic millimeter-wave integrated circuit ( MMIC) amplifiers have been designed and realized using 90-nm InAlAs/InGaAs/InP high gain electron mobility transistors ( HEMT) technology. The amplifiers are developed in common source and microstrip technology. The three-stage MMIC amplifier A is designed based on device A and measured on wafer with a small-signal peak gain of 11.2 dB at 140 GHz and 3-dB-bandwidth is 16 GHz with a chip size of 2.6 mm x1.2 mm The two-stage MMIC amplifier B is designed based on device B and measured on wafer with a small-signal peak gain of 15.8 dB at 139 GHz and 3-dB-bandwidth is 12 GHz and the gain is higher than 10 dB from 130 GHz to 150 GHz with a chip size of 1.7 mm x 0.8 mm The amplifier B also shows an excellent noise character with noise figure of 4.4 dB when the associated gain of 15 dB is acquired at 141 GHz and the average noise figure is about 5.2 dB over the bandwidth. The amplifier B exhibits a higher gain-per-stage, competitive gain-area ratio and lower noise figure. The successful realization of MMIC amplifiers is of great potential for receiver-front-end applications at D-band.
A composition dependent model based on the Cr-W alloy structure has been studied to make it possible to be put into practical application. In terms of the optical properties of the Cr-W alloy with defined composition, a simpler 4-layered structure with single Cr-W alloy absorption layer has been designed to show the merit of high photon-to-heat conversion efficiency in the broad spectral region of 300 similar to 1 000 nm.
This paper introduces two designs of balanced frequency triplers in 0.68 THz and 1.00 THz bands. The proposed triplers are based on discrete antiparallel Schottky diodes and quartz glass instead of terahertz integrated circuit. The merits of this work are attributed to the improvement of the diode model, the thinned quartz glass film and the machining accuracy of the waveguide. The improved LEC diode model considers not only the current-voltage ( I/V) and capacitance-voltage ( C/V) but also plasma resonance and skin effect. The quartz glass film is thinned to 15um and can be used for up to 1.2 THz. The machining accuracy of the waveguide is ( +/- 3 ) mu m for terahertz applications with channel size 60 mu m. The measurement shows a peak output power above 160 mu W and 60 mu W for the 0.68 THz and 1.00 THz triplers, respectively. Moreover, the efficiencies of the 0.68 THz and 1.00 THz triplers are around 1% and 0. 6% correspondingly. The output frequency bandwidths are both more than 10%.
The tunable high performance multi-channel wavelength demultiplexer ( WDM) based on metal-insulator-metal ( MIM) plasmonic ring resonators is designed and numerically investigated. By the resonant theory of ring cavity, we find that the channel wavelength of WDM can be easily manipulated by adjusting the radius and refractive index of the ring cavity, which is in good agreement with the results obtained by finite element method (FEM) simulations. The multi-channel WDM structure consisting of a plasmonic waveguide and several ring resonators increases the transmission up to 80% at telecommunication regime, which is two times higher than the results reported in a recent literature. The proposed compact multi-channel wavelength demultiplexer can find more applications for the ultra-compact WDM systems in highly integrated telecommunication circuits.
In this paper, an approach of beam power combining based on quasi-optical technology is proposed. It has advantages of low loss, high combining efficiency and relatively easy manufacturing. The analysis, simulation and experimental results are presented at short millimeter waves. High combining efficiency has been obtained.
Active millimeter wave imaging (AMWI) is an efficient way to detect dangerous objects concealed under clothes. However, because the images acquired by AMWI are often obscure and some of concealed objects are small in size, the automatic detection and localization of the objects remain as a challenging problem. Yao Di first employed convolutional neural networks (CNNs) and used a dense sliding window method to detect concealed objects. In this paper, the author presents two improvements over Yao's work: 1) Using contextual information to suppress interference and improve detection probability: 2) Using a two-step search method instead of exhaustive search to reduce the computational complexity. To reduce the computational complexity, the author first uses a CNN in vertical direction to filter the interference and obtain the vertical position of the concealed object, then uses another CNN to determine the horizontal position of the concealed object. To make use of big window containing contextual information, the author uses IoG (intersection-over-ground-truth) instead of IoU (Intersection-over-Union) to define positive and negative samples in training and testing process. Experimental results show that the proposed method will make the length of computational time reduced to about 30% of that of the exhaustive search while achieving better detection performance.
A theoretical study on the perfect absorbers working in the far-infrared region with SU8 based multiple-layer metamaterials has been demonstrated. The perfect absorbers consist of periodic array of metal particles, SU8 dielectric spacing layer and a thicker metallic bottom layer. Through the LC model and the finite element numerical simulation methods, we studied the performance of the absorber. With finely tuned parameters, such like the thickness of the SU8 dielectric layers, the periodicity of the metal particles array, and the length of the metal particles, the near perfect absorption up to similar to 100% at the wavelength range between 20 mu m to 30 mu m for far infrared can be achieved. Based on these results, further design for the double-resonator absorber has been provided. Dual band perfect absorption can be accurately and independently obtained by adjusting the particle size of the upper and the lower metal layers. Moreover, the wavelength of the perfect absorption is also almost independent of the incident angle. These phenomena can be attributed to the multiple reflections between the thick metallic bottom layer and metal particle layers separated by SU8 dielectric layer, which can also be explained using a LC model as the resonant absorption in the metal-dielectric-metal cavities.
A cylindrical gyrotron cavity is designed and optimized with a high order mode TE34,10- to deliver an output power of megawatts level at 140 GHz. Analysis on mode competition indicates that the two adjacent modes TE33,10- and TE31,11+ involve in competition and cause significant decreasing of output power of TE34,10-. To suppress the competition hysteresis loops of TE31,11+ and TE33,10- with TE34,10- are calculated, which indicates TE34,10- can inhibit growth of the other two modes with decreasing magnetic field from its low efficiency single mode oscillation zone, while it turned out just the opposite with increasing magnetic field due to the earlier oscillation of the competitors. Based on the results, a multimode time-dependent calculation including 42 modes is carried out with magnetic field dropping from 5.59 T to 5.51 T, the results show that mode competition is successfully suppressed, the operation mode TE31,10- realizes stable single mode oscillation with an output power of 0.96 MW and an electron efficiency of 36.7% at 140 GHz.
In this paper, the double-layer harmonic diffractive element (HDE) structure is investigated and the optimization procedure is based on the equation of diffraction efficiency of the double-layer diffractive optical element. The diffraction efficiency of the system in the designed middle and far infrared wavebands is larger than 99%, which improves the image contrast and the imagequality significantly. A new dual-band infrared double-layer HDE telescope is designed, which can work in the middle and far infrared wavebands. It is shown that the system approximately attains diffraction limit and is easy to processed.
In this work, Ga doped ZnO (GZO) /CdS bilayer films were prepared on p-Si substrate by magnetron sputtering to form GZO /CdS /p-Si heterojunction device. The structural, optical and electrical properies of the nanocrystalline GZO/CdS bilayer films were studied by XRD, SEM, XPS, UV-VIS spectrophotometer and Hall effect measurement. The J-V curve of GZO /CdS /p-Si heterojunction device shows good rectifying behavior. And the value of I-F/I-R (I-F and I-R stand for forward and reverse current, respectively) at +/- 3 V is found to be as high as 21. The results indicate that the nanocrystalline GZO /CdS /p-Si heterojunction possesses good diode characteristic. High photocurrent density is obtained under a reverse bias. The nanocrystalline GZO/CdS/p-Si heterojunction device exhibits clear photovoltaic effect. Because the lattice constant of CdS is between GZO and Si, it can be used for a buffer layer between GZO and Si, to effectively reduce the interface states between GZO and p-Si. Therefore, we observed the clear photovoltaic effect of GZO/CdS/p-Si heterojunction.
Thin films of crystalline V2O5 nanoflakes were prepared through atomic layer deposition (ALD) process. The film thickness was verified to play a critical role in determining structural morphology, optical bandgap and Raman vibration of crystalline V2O5 thin films. Two optical bandgaps observed at about 2. 8 eV and 2.4 eV result from two growth stages during ALD preparation. We expect that these results help to understand the growth control of ultrathin films and their functional devices.
A fundamental W-band voltage-controlled oscillator (VCO) featuring high output power and wide tuning range has been successfully designed. The VCO was fabricated utilizing 0. 8 mu m InP DHBT technology. The DHBT exhibits peak f(r) of 170 GHz and f(m)(ax) of 250 GHz. The VCO core implemented a balanced Colpitts-type topology modified for high-requency application. An additional buffer amplifier stage was connected with the core to further boost output power as well as eliminate the load pulling effect. The DHBT base-collector P-N junction at reverse bias was chosen as a varactor diode to realize a wide frequency tuning. The measured results demonstrate that the oscillation frequency of the proposed VCO can be tuned between 81 similar to 97. 3 GHz, which is a relative tuning bandwidth of 18. 3 %. Over this frequency range the oscillator has a maximum output power of 10.2 dBm, and the power variation is less than 3.5 dB. A phase noise of -88 dBc/Hz@ 1MHz is obtained at the highest tuning frequency.
Stray light control is an important technical indicator of an optical system' s performance. The stray light in infrared optical systems includes not only external stray light, but also the internal radiation stray light. The conventional initial system design method limited to an "object-image" conjugate relationship cannot properly take account of stray light. This paper presents a triple conjugate optical system design method for "object-image", "object-intermediate real image" and "entrance pupil-exit pupil" triple conjugate relationships that minimizes the influences of internal and external stray light to provide good stray light control performance. With this method, an off-axis three-mirror anastigmatic infrared optical system with F/# = 4, linear field of view = 7 degrees, point source transmission less than 5 x 10(-4), and cold iris efficiency 96% was designed and imaged good pictures in orbit.
Flexible high-efficiency III-V multijunction solar cells are being developed for use in unmanned Aerial Vehicles (UAVs), wearable devices and space applications. The solar cell epitaxial layers are grown on GaAs substrate by metalorganic chemical vapor deposition (MOCVD) and then are transferred to flexible substrates by cold bonding and epitaxial lift-off process (ELO). Through the design of ELO apparatus and a large number of experiments on the optimal parameter, GaAs solar cell structure can be effectively separated from 4-inch GaAs wafer without defects and degradation in performance. Recently, 30 cm(2) large area flexible GaInP/GaAs/InGaAs 3-junciton solar cells on 50 mu m polyimide film achieved a 1-sun, AMO conversion efficiency of 31.5% with an open-circuit-voltage of 3.01 V, a short-circuit current-density of 16.8 mA/cm(2), and a fill factor of 0.845. By using the very light PI substrate, the unit weight of the solar cell is only 168.5 g/m(2) and the specific power is up to 2 530 W/kg.
A terahertz quasi-optical detector has been presented, which is mainly composed of a GaAs antenna-coupled Schottky diode chip and a highly resistive silicon lens. In order to reduce the ohmic loss, the standard terahertz Schottky diode fabrication process has been improved by forming the antenna patterns on the semi-insulating GaAs layer. Experimental responsivity and DSB conversion loss of the quasi-optical detector are 1 360 similar to 1 650 V/W and 10.6 similar to 12.5 dB at 335 similar to 350 GHz range, respectively. The noise equivalent power (NEP) is estimated to be 1.65 similar to 2 pW/Hz(1/2). Imaging experiments based on this quasi-optical detector have been carried out in both direct- and heterodyne-detection modes, successfully demonstrating its potential in terahertz imaging applications.
The influence of temperature, humidity and pressure on the measurement of exhaust gas CO concentration after pretreatment is analyzed. An on-line correction algorithm with multi-environment factors of neural network for the vehicle exhaust CO detection has been proposed. First, the exhaust gas sample data has been trained offline to build the BP neural network model, and then the real-time measured temperature, humidity, pressure and decimal absorption value of the samples have been put into the model for its online correction. Then the corrected CO concentration has been achieved, so the measurement error of the NDIR sensor caused by environmental changes has been solved. Through the prototype experiment, the simulation experiment and the comparison with SEMTECH-EcoStar, the maximum relative deviation of the CO with the concentration from 0 to 0.2% is 4.8% when the temperature range is from 30 to 50 degrees C, relative humidity is from 25 to 40%, the pressure is from 95 to 115 kPa. The experiments have been carried out in the vehicle field to get the correction factor between 0.8 and 1, which verifies the necessity and reliability of the method and provided effective technical support for the detection of the CO concentration of the high-temperature exhaust gas from motor vehicles.
Current studies on the relationship between carrier concentration in nano-scale semiconductor structure and its local conductance is mainly on parameters fitting. For above connection, existing models rely on artificial fitting parameters such as ideal factor. For above reason, derivation of carrier concentration though measured local conductance can not be done. In this work, we present a scheme to obtain the carrier concentration in narrow quantum wells (QWs). Cross-sectional scanning spreading resistance microscopy (SSRM) provides unparalleled spatial resolution (<10 nm, Capable of characterizing single QW layer) in electrical characterization. High-resolution local conductance has been measured by SSRM on molecular beam epitaxy-grown GaAs/AlGaAs QWs cleaved surface (110). Based on our experimental set-up, a model which describes conductance by the only argument, i.e. carrier concentration has been built. Using the model, our implementation derived carrier concentration from SSRM measured local conductance in GaAs/AlGaAs QWs ( doping level : 10(16)/cm(3 )- 10(18)/cm(3)). Relative errors of the results are within 30%.
A sub-10 mu m InGaAs (IGA) focal plane array (FPA), with cut-off wavelength of 2.6 mu m has been developed. The pixel pitch is reduced significantly comparing with that of reported extended wavelength IGA FPAs. To verify the feasibility of technology, the performance of sub-10 mu m IGA FPA was tested and compared with 30 mu m pixel pitch IGA FPA, which was fabricated from the same epitaxial material. The sub-10 mu m IGA FPA exhibits high performances in terms of dark current (0.45 nA @ V-R = 10 mV) and R(0)A (14.7 Omega . cm(2)) at room temperature. Its quantum efficiency can reach 63%. The comparable performances to 30 mu m pixel pitch IGA FPA illustrate that the sub-10 mu m IGA FPA fulfils the needs of large formats (>1 K x 1 K) and high densities in extended wavelength IGA detectors.
A modified folded groove waveguide called folded double ridge groove waveguide (FDRGW) is put forward for developing broadband high-power terahertz (THz) travelling-wave tube (TWT). A new transmission waveguide which is appropriate for this new kind of SWS as input and output energy coupler is proposed. It can be found from the high frequency characteristic simulation results that the folded double ridge waveguide SWS can increase the average interaction impedance and extend its operating bandwidth. In addition, the particle-in-cell (PIC) simulation results reveal that with the beam voltage of 27.4 kV and the beam current of 0.25 A, the average output power of the new folded double ridge groove waveguide TWT can reach 65.8 W and the corresponding gain is 27.21 dB at the center frequency 340 GHz. Therefore, the folded double ridge groove waveguide TWT could be used as wide-band and high-power terahertz radiation source.
This paper presents an improved small-signal model and a W-band monolithic low noise amplifier (LNA) using 100 nm InAlAs/InGaAs/InP-based high electron mobility transistors (HEMT) technology. For improving the fitting accuracy of S-parameters in low frequency, the small-signal model takes into account differential resistances of gate-to-source and gate-to-drain diodes, which modeled by resistances R-fs and R-fd. A W-band LNA monolithic millimeter-wave integrated circuit (MMIC) has been designed and fabricated based on this model to verify the feasibility of this model. The amplifier is measured on-wafer with a small-signal peak gain of 14.4 dB at 92.5 GHz and 3-dB bandwidth from 85 to 110 GHz. In addition, the MMIC also exhibits an excellent noise characteristic with the noise figure of 4.1 dB and the associate gain of 13.8 dB at 88 GHz. This MMIC amplifier shows wider 3-dB bandwidth and higher per-stage gain than others results at the similar band.