Heterodyne Mixing Research Articles

Quantitative determination of wheat moisture content based on microwave detection technique combined with multivariate data analysis

In this study, a new method is proposed for the quantitative detection of wheat moisture content based on double heterodyne mixing microwave transmission technique. First of all, the microwave detection device received the command from the computer and detected the wheat in the frequency domain of 2.5 GHz–11.5 GHz, while acquiring the transmission index corresponding to each frequency point. Then, competitive adaptive reweighted sampling (CARS) was used for coarse feature selection of the transmission index after least partial squares filtering, and Genetic Algorithm (GA) was used for secondary feature refinement of the coarse selected feature variables, and they were sorted and combined according to their weights. Finally, Support vector regression (SVR) was used to establish quantitative models with different combinations of feature variables to achieve rapid detection of wheat moisture content. The results showed that the CARS-GA-SVR model had better detection performance for wheat moisture content determination compared to the CARS-SVR model. Among them, the CARS-GA-SVR model had the best detection effect when the combination of feature variables is 6-dimensional, with coefficient of determination (RP2) of 0.9756 and relative prediction deviation (RPD) of 6.3234. Compared to the SVR model established by the full transmission index, the RPD improved from 3.7089 to 6.3234. The results reveal that rapid and high-precision detection of wheat moisture content can be achieved by using a self-made miniaturized microwave device combined with a suitable chemometric method.

Simultaneous analysis of mildew degree and aflatoxin B1 of wheat by a multi-task deep learning strategy based on microwave detection technology

This study proposes a novel qualitative and quantitative analysis method for wheat mildew degree and aflatoxin B1 (AFB1) by microwave detection technology combined with multi-task learning strategy. The team developed a miniaturized microwave detection device with double heterodyne mixing structure, and used this device to obtain the transmission indexes (amplitude and phase) of moldy wheat samples. A multi-task learning model based on convolutional neural network (CNN) structure was designed to realize the self-learning and model calibration of the transmission indexes, and to complete the classification and regression tasks of wheat mildew degree recognition and AFB1 content detection. The obtained results found that in the qualitative analysis, the accuracy, precision, recall, and F1-score of the fusion CNN model were all 100% during the prediction. In the quantitative detection, the RMSEP, RP2 and RPD of the fusion CNN model respectively were 2.0138 μg kg−1, 0.9807 and 7.2849. The overall results reveal that it is feasible to realize simultaneous analysis of the contamination level of wheat mycotoxins by microwave detection technology combined with deep learning, and the application of multi-task learning strategy can effectively avoid the waste of resources in the process of model calibration.

Analysis of coherent-OFDM modulation for FSO communication over distribution with pointing errors

In this paper, we have analyzed a proposed coherent-orthogonal frequency division multiplexing (Co-OFDM) free space optical (FSO) communication system under ▪ distribution channel model. The proposed Co-OFDM FSO system contains a heterodyne mixer at the receiver section, which is used to convert the optical frequency to radio frequency (RF). After that, a carrier recovery circuit is used and then a synchronization circuit is used to correct the timing and phase of the received signal. Here, we derived an ABER expression and outage probability expression for the Co-OFDM FSO communication system under ▪ distribution channel model. We analyzed the results for different atmospheric turbulence (AT) conditions, pointing errors and the number of subcarriers. We have analyzed the system outage probability with varying received optical power and pointing error for different SNR thresholds and also analyzed for different AT conditions. In the results, we observed that the ABER performance improves as AT conditions improve, as the number of subcarriers decreases and as the pointing error decreases. Also, we observed that when AT conditions get worse, then to get same outage probability, we have to increase the SNR threshold. We have compared the Co-OFDM FSO system with popular modulation techniques PAM and PPM under ▪ distribution channel model.

Experimental demonstration of uncompressed 4K video transmission over directly modulated distributed feedback laser‐based terahertz wireless link

AbstractWe demonstrate the transmission of uncompressed 4K videos over the photonics‐based terahertz (THz) wireless link using a directly modulated distributed feedback laser diode (DFB‐LD). For optical heterodyne mixing and data modulation, a DFB‐LD was employed and directly modulated with a 5.94‐Gb/s non‐return‐to‐zero signal, which is related to a 6G‐serial digital interface standard to support ultra‐high‐definition video resolution. We derived the optimal frequency of the THz carrier by varying the wavelength difference between DFB‐LD output and Tunable LD output in the THz signal transmitter to obtain the best transmission performances of the uncompressed 4K video signals. Furthermore, we exploited the negative laser‐to‐filter detuning for the adiabatic chirp management of the DFB‐LD by the intentional discrepancy between the center wavelength of the optical band‐pass filter and the output wavelength of the DFB‐LD. With the help of the abovementioned methods, we successfully transmitted uncompressed 4K video signals over the 2.3‐m wireless transmission distance without black frames induced by time synchronization error.

Label-free single-cell counting and characterization in the GHz-range

Abstract We demonstrate operation of a micropore based flow cytometer in the radio-frequency range. Apart from simply counting micron sized particles, such as cells, with close to nano-second resolution this counter offers the additional benefit of delivering insight into the intracellular environment. Such non-invasive screening of the cell’s interior based on analysing amplitude and phase of the signal is helpful in characterizing the biological activity of cells. In detail we are using heterodyne mixing to demodulate the temporal impedance changes, which are induced by cells translocating through a micropore embedded in a radio-frequency circuit. This allows us to measure every amplitude and phase modulation induced by a translocation event. Herein, we compare the Jurkat cells (human T lymphocytes) recordings with a control group of polystyrene beads. As the cells are measured on a single cell level, the variations on the measured amplitude and phase signals are used, herein, to sense morphological cell changes in real time.

Photon correlation spectroscopy with heterodyne mixing based on soft x-ray magnetic circular dichroism

Many magnetic equilibrium states and phase transitions are characterized by fluctuations. Such magnetic fluctuation can in principle be detected with scattering-based x-ray photon correlation spectroscopy (XPCS). However, in the established approach of XPCS, the magnetic scattering signal is quadratic in the magnetic scattering cross section, which results not only in often prohibitively small signals but also in a fundamental inability to detect negative correlations (anticorrelations). Here, we propose to exploit the possibility of heterodyne mixing of the magnetic signal with static charge scattering to reconstruct the first-order (linear) magnetic correlation function. We show that the first-order magnetic scattering signal reconstructed from heterodyne scattering now directly represents the underlying magnetization texture. Moreover, we suggest a practical implementation based on an absorption mask rigidly connected to the sample, which not only produces a static charge scattering signal but also eliminates the problem of drift-induced artificial decay of the correlation functions. Our method thereby significantly broadens the range of scientific questions accessible by magnetic x-ray photon correlation spectroscopy.

Heterodyne mixing in self-local oscillator plasmonic diodes

We investigate the possibility of using the n+nn+ diodes to produce Gunn oscillations. According to our results, we suggest our device as a possible unipolar device for heterodyne detection or emission, since it may act as a detector for terahertz radiation as well as high-frequency local oscillator. For this purpose, we present an investigation of InGaAs n+nn+ vertical diodes about the presence of high-frequency self-oscillations as well as the effect of mixing induced either by an optical beating or by an electrical excitation in the presence, in both cases, of a dc bias.

Unlocking synchrotron sources for THz spectroscopy at sub-MHz resolution.

Synchrotron radiation (SR) has proven to be an invaluable contributor to the field of molecular spectroscopy, particularly in the terahertz region (1-10 THz) where its bright and broadband properties are currently unmatched by laboratory sources. However, measurements using SR are currently limited to a resolution of around 30 MHz, due to the limits of Fourier-transform infrared spectroscopy. To push the resolution limit further, we have developed a spectrometer based on heterodyne mixing of SR with a newly available THz molecular laser, which can operate at frequencies ranging from 1 to 5.5 THz. This spectrometer can record at a resolution of 80 kHz, with 5 GHz of bandwidth around each molecular laser frequency, making it the first SR-based instrument capable of sub-MHz, Doppler-limited spectroscopy across this wide range. This allows closely spaced spectral features, such as the effects of internal dynamics and fine angular momentum couplings, to be observed. Furthermore, mixing of the molecular laser with a THz comb is demonstrated, which will enable extremely precise determinations of molecular transition frequencies.

Doppler Measurement of Modulated Light for High Speed Vehicles.

Technical details associated with a novel relative motion sensor system are elaborated in the paper. By utilizing the Doppler effect, the optical sensor system estimates the relative motion rates between the sensor and the moving object equipped with modulating light sources and relatively inexpensive electrical components. A transimpedance amplifier (TIA) sensing circuit is employed to measure the Doppler shift exhibited by the amplitude modulated light sources on the moving platform. Implementation details associated with the amplitude modulation and photo-detection processes are discussed using representative hardware elements. A heterodyne mixing process with a reference signal is shown to improve the signal-to-noise ratios of the Doppler shift estimation processing pipeline. Benchtop prototype experiments are used to demonstrate the utility of the proposed technology for relative motion estimation applications.

A Photonic Based Multiband Signal Generation, Transmission and processing for 5G ROF front-haul

This work proposes the generation of multi-band K-band, V-band, W-band of millimeter-wave (mm-wave) and its transmission performance through the standard SMF of various lengths. The optical frequency multiplication (OFM) principle is used for multi-band signal generation by the optical modulator’s non-linear characteristic. The frequency doubling, quadrupling, and six-tupling are done for multi-band generation. The generated multi-band is modulated with downlink data at the central station and transmitted through the conventional Radio over Fiber (RoF) network. The received signal is photo-electrically converted by heterodyne mixing with the local oscillator according to the user’s requirement. The transmission performance is analyzed at the receiver end for varying lengths of SMF. The simulation analysis result shows that the RoF system holds good for multi-band transmission of 30, 60, 90 GHz for about 40 km. The power penalty for 30, 60, 90 GHz signal from B-T-B to 40 km is -3.79 dB, -4.847 dB, -6.33 dB.

The effects of nonlinear thermal fluctuation and series junction array on high-T c superconducting terahertz mixer performance

Sensitive high-T c superconducting (HTS) heterodyne receivers are envisioned as promising technologies for terahertz (THz) communication and sensing applications due to the lack of power efficient sources in the band. HTS device properties, particularly the noise temperature, are dependent on complicated factors that include multiple noise sources as well as the interaction between Josephson junction and radio-frequency (RF) networks. We report investigations on the device properties of an HTS THz mixer in the presence of nonlinear thermal fluctuation and series junction array. By using the three-port analysis method, it is observed that the Planck and quantum noises representing nonlinear thermal fluctuation plays a significant role in the cases of smaller fluctuation parameters and higher signal frequencies. The influence of series junction array on mixer performance is also studied, which shows that there is an optimum junction number dependent on the normalized RF source impedance. The measured results of a broadband antenna-coupled HTS single-junction mixer agree well with that obtained by numerical simulation. The results predict that noise performance, conversion gain and operating bandwidth would be considerably improved if a series junction array with a suitable junction number is used for heterodyne mixing.

Demonstration of a wideband submillimeter-wave low-noise receiver with 4–21 GHz IF output digitized by a high-speed 32 GSps ADC

We report on a 275–500 GHz heterodyne receiver system in combination with a wideband intermediate-frequency (IF) backend to realize 17 GHz instantaneous bandwidth. The receiver frontend implements a heterodyne mixer module that integrates a superconductor-insulator-superconductor (SIS) mixer chip and a cryogenic low-noise preamplifier. The SIS mixer is developed based on high-current-density junction technologies to achieve a wideband radio frequency (RF) and IF bandwidth. The IF backend comprises an IF chain divided into two channels for 4.0–11.5 GHz and 11.3–21.0 GHz and an analog-to-digital converter (ADC) module that is capable of high-speed sampling at 32 Giga samples per second with 12.5 GHz bandwidth per channel and an effective number of bits of 6.5. The IF backend allows us to simultaneously cover the full 4–21 GHz IF range of the receiver frontend. The measured noise temperature of the receiver frontend was below three times the quantum noise (hf/kB) over the entire RF band. A dual-polarization sideband-separating receiver based on this technique could provide up to 64 GHz of instantaneous bandwidth, which demonstrates the possibility of future wideband radio astronomical observations with advanced submillimeter-wave heterodyne receivers.

A Nonlinear Transmission Line Model for Simulating Distributed SIS Frequency Multipliers

Superconductor/insulator/superconductor (SIS) jun-ctions have extremely nonlinear electrical properties, which makes them ideal for a variety of applications, including heterodyne mixing and frequency multiplication. With SIS mixers, the SIS junctions normally have circular cross sections, but they can also be fabricated in the form of microstrip transmission lines, known as distributed SIS junctions (DSJs). By using a DSJ as an open-circuit stub, it is possible to create a large SIS junction with a low effective input reactance. This is beneficial for SIS frequency multipliers because their output power is proportional to the area of the junction. It is challenging, however, to simulate the behavior of DSJs because they have to be modeled as transmission lines and the model has to take into account the quasiparticle tunneling current, which is a nonlinear function of the ac voltage. In this article, we present a new nonlinear transmission line model to accurately describe the behavior of DSJs and to simulate the performance of distributed SIS frequency multipliers (DSMs). This model is compared to experimental data from a recent DSM device and good agreement is found between the dc tunneling currents and the output powers at the second harmonic. Based on this success, an improved DSM design is proposed that has a higher output power and a higher conversion efficiency than previous designs.

Terahertz-Wave Generation Based on Optical Frequency Comb and Single Mach-Zehnder Modulator

A novel Terahertz-wave (THz-wave) generation on the strength of optical frequency comb and single push-pull Mach-Zehnder modulator (MZM) with a pair of transmitter and receiver in 0.4-THz band is proposed. The advantages of the optical frequency comb based on phase modulator (PM) 1 and PM2 in series includes the uncomplicated operation and good stability to produce numerous subcarriers at 25-GHz intervals. THz-wave is generated based on two comb lines derived from the same optical frequency comb. One comb line is used as an optical local oscillator (LO) and the other is served as signal carrier for data modulation for heterodyne mixing. We investigate the generation and transmission of a 0.4 THz THz-wave signal carrying 4 Gbaud quadrature-phase-shift-keying (QPSK) or 1 Gbaud 16 quadrature amplitude modulation (16-QAM) data over back-to-back (BTB) transmission or 10 km standard single-mode fiber (SSMF) transmission, with the bit-error-rate (BER) performance below the hard decision forward error correction (HD-FEC) threshold of 3.8e-3.

340 GHz Double-Sideband Mixer Based on Antenna-Coupled High-Temperature Superconducting Josephson Junction

Wireless communication and sensing are moving from microwave, millimeter-wave into the terahertz (THz) frequency regime to meet the fast growing demand of ultrahigh data-rate communications and super resolution imaging. Faced with severe atmospheric absorption attenuation and the lack of power efficient transmitting source at the higher band, ultrasensitive and cost-effective receiver frontend technology is required for advanced THz wireless systems. To date, the most sensitive heterodyne mixers, the key components of frontend receiver systems, are based on low-temperature superconducting materials that operate at liquid helium (4.2 K) temperature range, requiring expensive and bulky cryogenic cooling systems thus hindering them from commercial applications such as wireless communications and sensing. In this article, we present a 340 GHz double-sideband fundamental mixer based on thin-film antenna-coupled high-temperature superconducting (HTS) Josephson junction that operates at a much higher temperature range attainable with smaller and cheaper cryocoolers. Based on our innovative work in terms of advanced device circuit and on-chip antenna designs, accurate parametric simulation analyses, and Josephson junction parameter optimizations, the reported mixer exhibits a measured noise temperature of 470 and 780 K at operating temperatures of 20 and 40 K respectively at 340 GHz, a performance significantly higher than any HTS THz mixers reported to date.

Multi-channel 28-GHz millimeter-wave signal generation on a silicon photonic chip with automated polarization control

We propose and experimentally demonstrate an integrated silicon photonic scheme to generate multi-channel millimeter-wave (MMW) signals for 5G multi-user applications. The fabricated silicon photonic chip has a footprint of 1.1 × 2.1 mm2 and integrates 7 independent channels each having on-chip polarization control and heterodyne mixing functions. 7 channels of 4-Gb/s QPSK baseband signals are delivered via a 2-km multi-core fiber (MCF) and coupled into the chip with a local oscillator (LO) light. The polarization state of each signal light is automatically adjusted and aligned with that of the LO light, and then 7 channels of 28-GHz MMW carrying 4-Gb/s QPSK signals are generated by optical heterodyne beating. Automated polarization-control function of each channel is also demonstrated with ~7-ms tuning time and ~27-dB extinction ratio.

Photonic Vector Signal Generation Based on OEO and Optical Coherent QPSK Modulation

A novel scheme for photonic vector signal generation based on a self-starting optoelectronic oscillator (OEO) and optical coherent quadrature phase-shift keying (QPSK) modulation is proposed and experimentally demonstrated. The optical output sidebands of the OEO are employed for optical heterodyne mixing, where one first-order sideband is modulated by QPSK baseband data using a dual-parallel Mach–Zehnder modulator, followed by coherent detection so as to directly generate frequency-doubled K-band vector signals. In the experiment, a 19.9 GHz QPSK modulated vector signal with a bit rate of 100 Mb/s is generated when the OEO operates at 9.95 GHz. The generated signal is back demodulated with error vector magnitude (EVM) less than 7%.

High-Precision Displacement Sensing of Monolithic Piezoelectric Disk Resonators Using a Single-Electron Transistor

A single-electron transistor (SET) can be used as an extremely sensitive charge detector. Mechanical displacements can be converted into charge, and hence, SETs can become sensitive detectors of mechanical oscillations. For studying small-energy oscillations, an important approach to realize the mechanical resonators is to use piezoelectric materials. Besides coupling to traditional electric circuitry, the strain-generated piezoelectric charge allows for measuring ultrasmall oscillations via SET detection. Here, we explore the usage of SETs to detect the shear-mode oscillations of a 6-mm-diameter quartz disk resonator with a resonance frequency around 9 MHz. We measure the mechanical oscillations using either a conventional DC SET, or use the SET as a homodyne or heterodyne mixer, or finally, as a radio-frequency single-electron transistor (RF-SET). The RF-SET readout is shown to be the most sensitive method, allowing us to measure mechanical displacement amplitudes below 1E-13 m. We conclude that a detection based on a SET offers a potential to reach the sensitivity at the quantum limit of the mechanical vibrations.

50 GHz optical true time delay beamforming in hybrid optical/mm-wave access networks with multi-core optical fiber distribution

We propose and experimentally validate an optical true time delay beamforming scheme with straightforward integration into hybrid optical/millimeter (mm)-wave access networks. In the proposed approach, the most complex functions, including the beamforming network, are implemented in a central office, reducing the complexity and cost of remote antenna units. Different cores in a multi-core fiber are used to distribute the modulated signals to high-speed photodetectors acting as heterodyne mixers. The mm-wave carrier frequency is fixed to 50 GHz (V-Band), thereby imposing a progressive delay between antenna elements of a few picoseconds. That true time delay is achieved with an accuracy lower than 1 ps and low phase noise.

Waveguide integrated superconducting single-photon detector for on-chip quantum and spectral photonic application

With use of the travelling-wave geometry approach, integrated superconductor-nanophotonic devices based on silicon nitride nanophotonic waveguide with a superconducting NbN-nanowire suited on top of the waveguide were fabricated. NbN-nanowire was operated as a single-photon counting detector with up to 92 % on-chip detection efficiency in the coherent mode, serving as a highly sensitive IR heterodyne mixer with spectral resolution (f/df) greater than 106 in C-band at 1550 nm wavelength.