Showing papers on "Spectrum analyzer published in 2019"

In-situ Measurement Methodology for the Assessment of 5G NR Massive MIMO Base Station Exposure at Sub-6 GHz Frequencies

Abstract: As the roll-out of the fifth generation (5G) of mobile telecommunications is well underway, standardized methods to assess the human exposure to radiofrequency electromagnetic fields from 5G base station radios are needed in addition to existing numerical models and preliminary measurement studies. Challenges following the introduction of 5G New Radio (NR) include the utilization of new spectrum bands and the widespread use of technological advances such as Massive MIMO (Multiple-Input Multiple-Output) and beamforming. We propose a comprehensive and ready-to-use exposure assessment methodology for use with common spectrum analyzer equipment to measure or calculate in-situ the time-averaged instantaneous exposure and the theoretical maximum exposure from 5G NR base stations. Besides providing the correct method and equipment settings to capture the instantaneous exposure, the procedure also comprises a number of steps that involve the identification of the Synchronization Signal Block, which is the only 5G NR component that is transmitted periodically and at constant power, the assessment of the power density carried by its resources, and the subsequent extrapolation to the theoretical maximum exposure level. The procedure was validated on site for a 5G NR base station operating at 3.5 GHz, but it should be generally applicable to any 5G NR signal, i.e., as is for any sub-6 GHz signal and after adjustment of the proposed measurement settings for signals in the millimeter-wave range.

Bio-Physical Modeling, Characterization, and Optimization of Electro-Quasistatic Human Body Communication

Abstract: Human body communication (HBC) has emerged as an alternative to radio wave communication for connecting low power, miniaturized wearable, and implantable devices in, on, and around the human body. HBC uses the human body as the communication channel between on-body devices. Previous studies characterizing the human body channel has reported widely varying channel response much of which has been attributed to the variation in measurement setup. This calls for the development of a unifying bio-physical model of HBC, supported by in-depth analysis and an understanding of the effect of excitation, termination modality on HBC measurements. This paper characterizes the human body channel up to 1 MHz frequency to evaluate it as a medium for the broadband communication. The communication occurs primarily in the electro-quasistatic (EQS) regime at these frequencies through the subcutaneous tissues. A lumped bio-physical model of HBC is developed, supported by experimental validations that provide insight into some of the key discrepancies found in previous studies. Voltage loss measurements are carried out both with an oscilloscope and a miniaturized wearable prototype to capture the effects of non-common ground. Results show that the channel loss is strongly dependent on the termination impedance at the receiver end, with up to 4 dB variation in average loss for different termination in an oscilloscope and an additional 9 dB channel loss with wearable prototype compared to an oscilloscope measurement. The measured channel response with capacitive termination reduces low-frequency loss and allows flat-band transfer function down to 13 KHz, establishing the human body as a broadband communication channel. Analysis of the measured results and the simulation model shows that instruments with 50 Ω input impedance (Vector Network Analyzer, Spectrum Analyzer) provides pessimistic estimation of channel loss at low frequencies. Instead, high impedance and capacitive termination should be used at the receiver end for accurate voltage mode loss measurements of the HBC channel at low frequencies. The experimentally validated bio-physical model shows that capacitive voltage mode termination can improve the low frequency loss by up to 50 dB, which helps broadband communication significantly.

Simultaneous Measurement of Electric and Magnetic Fields With a Dual Probe for Efficient Near-Field Scanning

Abstract: A near-field scanning is usually time-consuming to map the electromagnetic field along the surface of a device. In this communication, a dual probe is proposed with a U-shaped loop to sense radio frequency (RF) magnetic and electric fields simultaneously, so that the one-time scanning by the dual probe can replace the two-time scanning by single-detector probes. Different from the traditional near-field scanning by using a single-detector probe and spectrum analyzer, the proposed scanning can be achieved by the two-output probe and a two-port vector network analyzer connecting to the probe. The efficient near-field scanning measurements of the electric and magnetic field on a conductor-backed coplanar waveguide transmission line and an RF power divider by using the dual probe are in agreement with those by using two single-detector probes.

Spoof Surface Plasmon Polaritons Based Reconfigurable Band-Pass Filter

Abstract: This letter reports the design and analysis of the bandwidth (BW) reconfigurable band-pass filter using spoof surface plasmon polaritons at THz/microwave frequency. The designed filter consists of a spoof SPP T-shape resonator in which tuning has been introduced using variable capacitor device (having a cutoff frequency in THz regimes). Even and odd mode analysis has been carried out for a better understanding of the phenomenon. The proposed concept of variable bandwidth at a THz frequency in the SSPP structure has been demonstrated through Co-EM simulation. For the experimental validation of the proposed approach, the filter has been designed at microwave frequency, developed on a 60 mil (1.52 mm) thick microwave laminate, and characterized using a Keysight Field-Fox analyzer N9918A . In THz and microwave frequency regime, the designed filter has 3-dB BW reconfigurability of 20 GHz (0.41–0.43 THz) and 300 MHz (100–400 MHz) with the insertion loss of ~3 dB and ~1.7 dB–3.2 dB, respectively. The proposed reconfigurable bandpass filter will have an important role in the design and development of plasmonic circuits and systems.

Fully integrated CMOS-compatible polarization analyzer

Abstract: Abstract Polarization measurement has been widely used in material characterization, medical diagnosis and remote sensing. However, existing commercial polarization analyzers are either bulky schemes or operate in non-real time. Recently, various polarization analyzers have been reported using metal metasurface structures, which require elaborate fabrication and additional detection devices. In this paper, a compact and fully integrated silicon polarization analyzer with a photonic crystal-like metastructure for polarization manipulation and four subsequent on-chip photodetectors for light-current conversion is proposed and demonstrated. The input polarization state can be retrieved instantly by calculating four output photocurrents. The proposed polarization analyzer is complementary metal oxide semiconductor-compatible, making it possible for mass production and easy integration with other silicon-based devices monolithically. Experimental verification is also performed for comparison with a commercial polarization analyzer, and deviations of the measured polarization angle are <±1.2%.

Optimized design, calibration, and validation of an achromatic snapshot full-Stokes imaging polarimeter

Abstract: An achromatic snapshot full-Stokes imaging polarimeter (ASSIP) that enables the acquisition of 2D-spatial full Stokes parameters from a single exposure is presented. It is based on the division-of-aperture polarimetry using an array of four-quadrant achromatic elliptical analyzers as polarization state analyzer (PSA). The optimization of PSA is addressed for achieving immunity of Gaussian and Poisson noises. An extended eigenvalue calibration method (ECM) is proposed to calibrate the system, which considers the imperfectness of retarder and polarizer samples and the intensity attenuation of polarizer sample. A compact prototype of ASSIP operating over the waveband of 450-650 nm and an optimized calibration setup are developed. The achromatic performance is evaluated at three bandwidths of 10, 25, and 200 nm, respectively. The results show that the prototype with an uncooled CMOS camera works well at each bandwidth. The instrument matrix determined at the narrower bandwidth is more applicable to the wider one. The uncertainties of the calibrated instrument matrices and reconstructed Stokes parameters are improved by using the extended EMC at each bandwidth. To speed up the acquisition of high-contrast images, wide bandwidth along with short exposure time is preferable. The snapshot capability was verified via capturing dynamic scenes.

Resource-efficient analyzer of Bell and Greenberger-Horne-Zeilinger states of multiphoton systems

Abstract: We propose a resource-efficient error-rejecting entangled-state analyzer for polarization-encoded multiphoton systems. Our analyzer is based on two single-photon quantum-nondemolition detectors, where each of them is implemented with a four-level emitter (e.g., a quantum dot) coupled to a one-dimensional system (such as a micropillar cavity or a photonic nanocrystal waveguide). The analyzer works in a passive way and can completely distinguish ${2}^{n}$ Greenberger-Horne-Zeilinger (GHZ) states of $n$ photons without using any active operation or fast switching. The efficiency and fidelity of the GHZ-state analysis can, in principle, be close to unity, when an ideal single-photon scattering condition is fulfilled. For a nonideal scattering, which typically reduces the fidelity of a GHZ-state analysis, we introduce a passively error-rejecting circuit to enable a near-perfect fidelity at the expense of a slight decrease of its efficiency. Furthermore, the protocol can be directly used to perform a two-photon Bell-state analysis. This passive, resource-efficient, and error-rejecting protocol can, therefore, be useful for practical quantum networks.

Wideband DFS Measurement Using a Low-Frequency Reference Signal

Abstract: A novel Doppler frequency shift (DFS) measurement system based on a cascaded modulator topology is presented. It is capable to measure both the object speed and moving direction on an electrical spectrum analyzer with the use of a fixed low-frequency reference signal. It has a simple single-laser and single-photodetector structure, a robust performance and a wide operating frequency range, which is only limited by the optical modulator bandwidth. Experimental results are presented that demonstrate DFS ranging from −100 kHz to +100 kHz with an error of less than ±0.1 Hz at different microwave signal frequencies. Over 35 dB suppression in unwanted frequency components present at the system output is also demonstrated.

Multichannel Electrical Impedance Spectroscopy Analyzer with Microfluidic Sensors

Abstract: Impedance spectroscopy is a common approach in assessing passive electrical properties of biological matter. However, several problems appear in microfluidic devices in connection with the requirement for high sensitivity of signal acquisition from small volume sensors. The developed compact and inexpensive analyzer provides impedance spectroscopy measurement from three sensors, both connected in direct and differential modes. Measurement deficiencies are reduced with a novel design of sensors, measurement method, optimized electronics, signal processing, and mechanical design of the analyzer. Proposed solutions are targeted to the creation of reliable point-of-care (POC) diagnostic and monitoring appliances, including lab-on-a-chip type devices in the next steps of development. The test results show the good working ability of the developed analyzer; however, also limitations and problems that require attention and further improvement are appointed.

Ultrafast and ultrahigh-resolution optical vector analysis using linearly frequency-modulated waveform and dechirp processing

Abstract: We propose and experimentally demonstrate an ultrafast and ultrahigh-resolution optical vector analyzer (OVA) using linearly frequency-modulated (LFM) waveform and dechirp processing. An optical LFM signal, achieved by modulating an electrical LFM signal on an optical carrier via carrier-suppressed optical single-sideband (OSSB) modulation, is separated into two portions. One portion (denoted as the reference signal) directly goes through the reference path, and the other (denoted as the probe signal) undergoes magnitude and phase changes by an optical device under test (DUT) in the measurement path. After balanced photodetection, the reference signal and the probe signal are mixed to perform a dechirp operation. A relatively low-frequency electrical signal is generated, which can be sampled by a low-speed analog-to-digital converter. As a result, the frequency responses of the DUT can be extracted at a high speed by post digital signal processing. Thanks to the large chirp rate of the electrical LFM signal and the dechirp processing, the proposed LFM-based OVA enables ultrafast measurement speed and ultrahigh frequency resolution. We perform an experiment in which a narrowband tunable optical filter is characterized. The measurement speed reaches 1 ns/point, and the frequency resolution is 1.6 MHz.

Tera-sample-per-second single-shot device analyzer.

Abstract: With the ever-increasing need for bandwidth in data centers and 5G mobile communications, technologies for rapid characterization of wide-band devices are in high demand. We report an instrument for extremely fast characterization of the electronic and optoelectronic devices with 27 ns frequency-response acquisition time at the effective sampling rate of 2.5 Tera-sample/s and an ultra-low effective timing jitter of 5.4 fs. This instrument features automated digital signal processing algorithms including time-series segmentation and frame alignment, impulse localization and Tikhonov regularized deconvolution for single-shot impulse and frequency response measurements. The system is based on the photonic time-stretch and features phase diversity to eliminate frequency fading and extend the bandwidth of the instrument.

Ion cyclotron emission diagnostic system on the experimental advanced superconducting tokamak and first detection of energetic-particle-driven radiation.

Abstract: A passive and noninvasive diagnostic system based on high-frequency B-dot probes (HFBs) has been designed and developed for the measurement and identification of ion cyclotron emission (ICE) in the Experimental Advanced Superconducting Tokamak (EAST). Details of the hardware components of this system including HFBs, direct current blockers, radio frequency splitters, filters, and power detectors as well as data acquisition systems are presented. A spectrum analyzer is used in addition to the ordinary speed acquisition card for data registration and analysis. The reliability of a HFB based diagnostic system has been well validated during the 2018 spring experiments on the EAST. ICE signals corresponding to fundamental cyclotron frequency of hydrogen ions and harmonics of deuterium ions were observed in experiments where deuterium plasmas were heated with deuterium neutral beams. The field dependence of ICE has been verified by recent experiments with three different background magnetic fields. The observed ratio of the ICE frequency is consistent with the ratio of the magnetic field intensity within measurement errors of a few percent.

Center Frequency and Bandwidth Reconfigurable Spoof Surface Plasmonic Metamaterial Band-Pass Filter

Abstract: In this study, we report a design concept to obtain center frequency and bandwidth reconfigurable spoof surface plasmon polaritons (SSPP) band-pass filter using T-shaped spoof SPP resonator. The design, analysis, and implementation of the proposed filter have been given with detailed mathematical analysis. Tuning has been performed using varactor diode which is introduced at different positons in the T-shaped resonator. Since spoof SPP has high field confinement and enhancement, hence it offers low crosstalk and mutual coupling as compared with conventional microstrip which is desirable to make low-loss system. The filter has been fabricated using a 1.52-mm-thick microwave laminate and characterization has been done using Keysight Field-Fox analyzer N9918A. The fabricated filter has a reconfigurable center frequency from 4.2 to 4.4GHz with insertion loss ~4.2 dB and bandwidth reconfigurable from 4.12 to 4.52GHz with ~3.8 dB insertion loss in the tuning range. The proposed reconfigurable band-pass filter will pave an important role in the designing and developing of the flexible plasmonic circuits and systems.

Time-division-multiplexed observation bandwidth for ultrafast parametric spectro-temporal analyzer.

Abstract: Parametric spectro-temporal analyzer (PASTA) has been demonstrated as a powerful tool for ultrafast spectrum measurement with superior frame rate and resolution. Compared with other time-stretch-based counterparts, the temporal focusing mechanism enlarges the initial condition and enables the observation of arbitrary waveform, especially the emission spectrum. However, due to the limited conversion bandwidth of the parametric mixing-based time-lens, the observation bandwidth of PASTA is constrained within the C (conventional) band, which hinders its practical applications. To overcome this constraint, both stokes and anti-stokes conversions of the parametric mixing process are leveraged, and the concept of time division multiplexing (TDM) is introduced to ensure their separability. Therefore, the TDM-based PASTA system successfully demultiplexes the C band and L (long) band spectra in two adjacent temporal frames. It is capable of reconstructing the wavelength-to-time sequence for arbitrary waveform over a record 58-nm observation bandwidth, which can be further improved by optimizing the filters and amplifiers. Meanwhile, both of these two bands achieve 20-pm resolution, 10-MHz frame rate, and -30-dBm sensitivity. Moreover, this TDM concept can also be applied to other parametric mixing-based temporal imaging systems to enlarge the working wavelength band, such as temporal magnification.

High-resolution continuum-source electrothermal atomic absorption spectrometer for simultaneous multi-element determination in the spectral range of 190–780 nm

Abstract: We have built a prototype atomic absorption spectrometer with an electrothermal atomizer and continuum light source for simultaneous multi-element determination. The spectral instrument consists of two parallel working Paschen-Runge polychromators having resolutions of 10 and 30 pm in the wavelength ranges of 190–350 and 350–780 nm, respectively. The instrument is equipped with a recording system, which consists of two assemblies of 14 linear CCD arrays each, connected to an analyzer for simultaneous acquisition of the emission spectra from each array. The continuum spectrum light source is a laser-driven xenon arc lamp, and the atomizer is a longitudinally heated graphite furnace with a programmable power supply. The spectrometer permits full wavelength range spectral acquisition with a temporal resolution of 2 ms. The hard- and software provide simultaneous direct determination of the number of elements in the solutions within four orders of magnitude concentration range.

Fourier based partial least squares algorithm: new insight into influence of spectral shift in "frequency domain".

Abstract: Developments in analytical chemistry technology, especially the combination between the partial least squares and spectroscopy, have contributed significantly to predicting the chemical concentrations and discriminating similar chemical analytes. However, spectral shift is an unwanted but inevitable factor for the spectroscopic analyzer, especially in practical application, which decreases the method's accuracy and stability. To remove the term of spectral shift completely and increase the robustness of spectroscopic analysis method, Fourier transform based partial least squares method was proposed. The approach used Fourier transform first to transform the spectral shift in the "time domain" to the phase term in the "frequency domain." The module of the Fourier transformed spectra was then calculated. As a result, the phase term was removed (the module of the phase term is 1), which means the spectral shift term was removed completely. Finally, the spectra modules were used to build the model and validate. The approach's advantages are: (i) that the approach provides a new insight to treat the spectral shift in spectroscopic analyzer; (ii) that the model is insensitive to spectral shift; (iii) that the approach makes partial least squares combined with spectroscopy more suitable for practical application, rather than lab experiment, because spectral shift is permitted, which means the decreased requirements of measure environment. As an example, blood species discrimination, using Raman spectroscopy, was used in order to demonstrate this approach's effectiveness.

Diffuse Correlation Spectroscopy Analysis Implemented on a Field Programmable Gate Array.

Abstract: Diffusive correlation spectroscopy (DCS) is an emerging optical technique that measures blood perfusion in deep tissue. In a DCS measurement, temporal changes in the interference pattern of light, which has passed through tissue, are quantified by an autocorrelation function. This autocorrelation function is further parameterized through a non-linear curve fit to a solution to the diffusion equation for coherence transport. The computational load for this non-linear curve fitting is a barrier for deployment of DCS for clinical use, where real-time results, as well as instrument size and simplicity, are important considerations. We have mitigated this computational bottleneck through development of a hardware analyzer for DCS. This analyzer implements the DCS curving fitting algorithm on digital logic circuit using Field Programmable Gate Array (FPGA) technology. The FPGA analyzer is more efficient than a typical software analysis solution. The analyzer module can be easily duplicated for processing multiple channels of DCS data in real-time. We have demonstrated the utility of this analyzer in pre-clinical large animal studies of spinal cord ischemia. In combination with previously described FPGA implementations of auto-correlators, this hardware analyzer can provide a complete device-on-a-chip solution for DCS signal processing. Such a component will enable new DCS applications demanding mobility and real-time processing.

Collinear Acousto-Optic Filtration With Electronically Adjustable Transmission Function

Abstract: An acousto-optic system containing collinear acousto-optic filter fabricated from calcium molybdate crystal and a positive electronic feedback was examined. The feedback signal is formed due to the optical heterodyning effect that appears for the special geometry of polarizer and analyzer polarization planes mutual orientation between which the collinear filter is located. It is shown that the feedback circuit electrical parameters variation enable controlling the spectral characteristics of the acousto-optic collinear filtration, resulting in enhancing the maximal spectral resolution and transmission function side lobes suppression.

Measurement Methodology for Determining the Optimal Frequency Domain Configuration to Accurately Record WiFi Exposure Levels

Abstract: Radiofrequency fields are usually measured in order to be compared with electromagnetic exposure limits defined by international standardization organizations with the aim of preserving the human health. However, in the case of WiFi technology, accurate measurement of the radiation coming from user terminals and access points is a great challenge due to the nature of these emissions, which are noncontinuous signals transmitted in the form of pulses of short duration. Most of the methodologies defined up to now for determining WiFi exposure levels use or take as reference exposimeters, broadband probes, and spectrum analyzers without taking into account that WiFi signals are not continuously transmitted. This leads to an overestimation of the radiation level that cannot be considered negligible when data of the actual exposure are needed. To avoid this, other procedures apply empirical weighting factors that account for the actual duration of burst transmissions. However, this implies the implementation of additional measurements for calculating the weighting factors, and thus, increases the complexity of the work. According to this, it was still necessary to define the frequency domain measurement setup that is optimal for obtaining realistic WiFi signal values, without requiring the performance of additional recordings. Thus, the definition of an appropriate methodology to achieve this goal was established as the main objective of this paper. The set of tasks carried out to identify such a configuration, as well as the limitations obtained for other measurement settings, are deeply explained in this paper.

Hollow waveguide integrated laser spectrometer for 13CO2/12CO2 analysis.

Abstract: Using hollow waveguide hybrid optical integration, a miniaturized mid-infrared laser absorption spectrometer for 13CO2/12CO2 isotopologue ratio analysis is presented. The laser analyzer described focuses on applications where samples contain a few percent of CO2, such as breath analysis and characterization of geo-carbon fluxes, where miniaturization facilitates deployment. As part of the spectrometer design, hollow waveguide mode coupling and propagation is analyzed to inform the arrangement of the integrated optical system. The encapsulated optical system of the spectrometer occupies a volume of 158 × 60 × 30 mm3 and requires a low sample volume (56 µL) for analysis, while integrating a quantum cascade laser, coupling lens, hollow waveguide cell and optical detector into a single copper alloy substrate. The isotopic analyzer performance is characterized through robust error propagation analysis, from spectral inversion to calibration errors. The analyzer achieves a precision of 0.2‰ in 500 s integration. A stability time greater than 500 s was established to allow two-point calibration. The accuracy achieved is 1.5‰, including a contribution of 0.7‰ from calibrant gases that can be addressed with improved calibration mixtures.

A Multichannel FRA-Based Impedance Spectrometry Analyzer Based on a Low-Cost Multicore Microcontroller

Abstract: Impedance spectrometry (IS) is a characterization technique in which a voltage or current signal is applied to a sample under test to measure its electrical behavior over a determined frequency range, obtaining its complex characteristic impedance. Frequency Response Analyzer (FRA) is an IS technique based on Phase Sensitive Detection (PSD) to extract the real and imaginary response of the sample at each input signal, which presents advantages compared to FFT-based (Fast Fourier Transform) algorithms in terms of complexity and speed. Parallelization of this technique has proven pivotal in multi-sample characterization, reducing the instrumentation size and speeding up analysis processes in, e.g., biotechnological or chemical applications. This work presents a multichannel FRA-based IS system developed on a low-cost multicore microcontroller platform which both generates the required excitation signals and acquires and processes the output sensor data with a minimum number of external passive components, providing accurate impedance measurements. With a suitable configuration, the use of this multicore solution allows characterizing several impedance samples in parallel, reducing the measurement time. In addition, the proposed architecture is easily scalable.

How to Increase the Analog-to-Digital Converter Speed in Optoelectronic Systems of the Seed Quality Rapid Analyzer

Abstract: This invention is relevant when working as part of optoelectronic systems, including non-destructive quality control of forest seeds. The possibility of synthesis of the ultrafast optical analog-to-digital converter (ADC) providing conversion of analog information to digital in the sub-GHz range is considered. The functional scheme of the optical ADC, containing technologically well-developed optical elements is given; the principle of operation is described in detail. The possibility of increasing the speed of the ADC to make it potentially possible for optical data processing schemes is shown.

Spectral Analysis of Sounds by Acoustic Hearing Analyzer

Abstract: It is shown that the transient evoked otoacoustic emission in response to a short (broadband) sound impulse is an impulse function of the auditory canal, middle ear, and cochlea of the inner ear. Its form corresponds to the basic functions form of wavelet representations of the "convexity" type, which are characterized by a shift (delay) in time, position and shift of position. It is established that the division into frequency groups, which is the main property of hearing, does not occur in the central nervous system, as previously thought, but in an acoustic auditory analyzer. It is a correlation filter with many inputs - transverse fibers and exits of the outer hair cells to the nerve fibers. The acoustic system of the acoustic analyzer is a unique correlation filter, i.e. a kind of patent of nature.

A Spectrum Analyzer Based on a Low-Cost Hardware-Software Integration

Abstract: Instruments are a very important tool for the good comprehension of any science. In the engineering electrical field, most of the practice laboratories are equipped with a large set of devices. One of the major challenges to get a complete laboratory is the economic cost. Professional electronic devices as multi-meters, oscilloscopes or spectrum analyzers are quite expensive on the market. Fortunately, with the aid of software-defined radio (SDR), low-cost equipment can be built. A fundamental device in these projects is the RTL-SDR dongle. This electronic accessory captures wireless signals and puts them on a USB port. Therefore, with digital signal processing it is possible to get access to low-cost instruments like spectrum analyzers. In this work, an integration of hardware and software is presented. An application is developed with Python and implemented on a Raspberry Pi3 B+. This proposal captures, demodulates, and displays AM and FM signals. The signals obtained can be observed on frequency or time or can be recorded as well.

A Lagrangian interpolation-assisted direct laser absorption spectrum analyzer based on digital signal processor for methane detection

Abstract: A novel Lagrangian interpolation-based direct laser absorption spectroscopy (LI-DLAS) technique was presented to suppress noise in infrared gas detection by incorporating Lagrangian interpolation and nonlinear least-square fitting (NLLSF). An LI-DLAS analyzer was reported for methane (CH4) detection using a 1654 nm distributed feedback (DFB) laser, a compact digital signal processor (DSP), and a multi-pass gas cell (MPGC) with a 16 m optical path length. The performance of the developed LI-DLAS CH4 analyzer was evaluated by means of laboratory experiments. Compared with the traditional DLAS-based sensor without Lagrangian interpolation, the detection sensitivity was improved from 6 ppmv to 2 ppmv, and the detection stability was enhanced as the Allan–Werle deviation was dropped from 1.514 to 0.531 ppmv for a 1 s averaging time. Compared with a DLAS analyzer based on LabVIEW platform, the DSP-based CH4 analyzer shows the merits of compact size and low cost with potential filed-deployable applications in industrial monitoring and control.

Broadband spectral shaping using nematic liquid crystal

Abstract: We demonstrate what is, to our knowledge, the first implementation of nematic liquid crystal (LC) for spectral shaping of broadband light fields. A LC cell of several microns thickness is placed between a polarizer and an analyzer. By changing the analyzer angle, one can use the combined device as a spectral filter of different types, such as a notch filter, narrow-band filter etc. We also demonstrate that the source spectrum also gets manipulated by changing the LC cell thickness and by tuning the voltage applied across the LC cell, providing another degrees of freedom for shaping the broadband spectrum. Such important effect using liquid crystals can find technological applications in spectral shaping of light fields by making variable spectral filters, and in spectral switching based data communication schemes.

A Real-Time, 1.89-GHz Bandwidth, 175-kHz Resolution Sparse Spectral Analysis RISC-V SoC in 16-nm FinFET

Abstract: A 1.89-GHz bandwidth, 175-kHz resolution spectral analysis system-on-chip (SoC), integrating a subsampling analog-to-digital converter (ADC) frontend with a digital reconstruction backend and implementing a 21 600-point sparse Fourier transform based on the fast Fourier aliasing-based sparse transform (FFAST) algorithm has been co-designed by using the Constructing Hardware in a Scala Embedded Language (Chisel) and Berkeley Analog Generator (BAG) circuit generator frameworks in 16-nm CMOS. Three sets of $25\times $ , $27\times $ , and $32\times $ subsampling successive approximation register (SAR) ADCs acquire signal with ~5.4–6.3 effective number of bits (ENOB)/slice. The digital backend consists of mixed-radix 864-, 800-, and 675-point fast Fourier transforms (FFTs), a signal location estimator, and a peeling decoder that recovers aliased signals from a sparsely populated spectrum. A single-issue, in-order, fifth-generation reduced instruction set (RISC-V) Rocket processor interacts with the spectrum analyzer for post-processing and calibration. The ADC consumes 49.8 mW with a 3.78-GHz reference clock. At 400 MHz and 0.7-V digital supply voltage (VDD), the Rocket core and the FFAST digital signal processing (DSP) together consume 133.5 mW.