Showing papers on "Dynamic range published in 2019"

Fast and Sensitive Terahertz Detection Using an Antenna-Integrated Graphene pn Junction.

Abstract: Although the detection of light at terahertz (THz) frequencies is important for a large range of applications, current detectors typically have several disadvantages in terms of sensitivity, speed, operating temperature, and spectral range. Here, we use graphene as a photoactive material to overcome all of these limitations in one device. We introduce a novel detector for terahertz radiation that exploits the photothermoelectric (PTE) effect, based on a design that employs a dual-gated, dipolar antenna with a gap of ∼100 nm. This narrow-gap antenna simultaneously creates a pn junction in a graphene channel located above the antenna and strongly concentrates the incoming radiation at this pn junction, where the photoresponse is created. We demonstrate that this novel detector has an excellent sensitivity, with a noise-equivalent power of 80 pW/[Formula: see text] at room temperature, a response time below 30 ns (setup-limited), a high dynamic range (linear power dependence over more than 3 orders of magnitude) and broadband operation (measured range 1.8-4.2 THz, antenna-limited), which fulfills a combination that is currently missing in the state-of-the-art detectors. Importantly, on the basis of the agreement we obtained between experiment, analytical model, and numerical simulations, we have reached a solid understanding of how the PTE effect gives rise to a THz-induced photoresponse, which is very valuable for further detector optimization.

5.7 A 256×256 40nm/90nm CMOS 3D-Stacked 120dB Dynamic-Range Reconfigurable Time-Resolved SPAD Imager

Abstract: Light Detection and Ranging (LIDAR) applications pose extremely challenging dynamic range (DR) requirements on optical time-of-flight (ToF) receivers due to laser returns affected by the inverse square law over 2-3 decades of distance, diverse target reflectivity, and high solar background [1]. Integrated CMOS SPADs have a native DR exceeding 140dB, typically extending from the noise floor of few cps to 100’s Mcps peak rate. To deliver this DR to downstream DSP, large SPAD time-resolved imaging arrays must count and time billions of single photon events per second demanding massively parallel on-chip pixel processing to achieve practical I/O power consumption and data rates. Hybrid Cu-Cu bonding offers a mass-manufacturable platform to implement these sensors by providing high-fill-factor SPADs optimised for NIR stacked on dense nanoscale digital processors [2]. Stacked sensor architectures involving pixel-level histogramming, on-chip peak detection and TDC/processor resource sharing are now being investigated [3–5].

Wide-band parametric amplifier readout and resolution of optical microwave kinetic inductance detectors

Abstract: The energy resolution of a single photon counting microwave kinetic inductance detector can be degraded by noise coming from the primary low temperature amplifier in the detector's readout system. Until recently, quantum limited amplifiers have been incompatible with these detectors due to the dynamic range, power, and bandwidth constraints. However, we show that a kinetic inductance based traveling-wave parametric amplifier can be used for this application and reaches the quantum limit. The total system noise for this readout scheme was equal to ∼2.1 in units of quanta. For incident photons in the 800–1300 nm range, the amplifier increased the average resolving power of the detector from ∼6.7 to 9.3 at which point the resolution becomes limited by noise on the pulse height of the signal. Noise measurements suggest that a resolving power of up to 25 is possible if the redesigned detectors can remove this additional noise source.

Dynamic Measurements Using FDM 3D-Printed Embedded Strain Sensors.

Abstract: 3D-printing technology is opening up new possibilities for the co-printing of sensory elements. While quasi-static research has shown promise, the dynamic performance has yet to be researched. This study researched smart 3D structures with embedded and printed sensory elements. The embedded strain sensor was based on the conductive PLA (Polylactic Acid) material. The research was focused on dynamic measurements of the strain and considered the theoretical background of the piezoresistivity of conductive PLA materials, the temperature effects, the nonlinearities, the dynamic range, the electromagnetic sensitivity and the frequency range. A quasi-static calibration used in the dynamic measurements was proposed. It was shown that the temperature effects were negligible, the sensory element was linear as long as the structure had a linear response, the dynamic range started at ∼ 30 μ ϵ and broadband performance was in the range of few kHz (depending on the size of the printed sensor). The promising results support future applications of smart 3D-printed systems with embedded sensory elements being used for dynamic measurements in areas where currently piezo-crystal-based sensors are used.

High Flux Passive Imaging With Single-Photon Sensors

Abstract: Single-photon avalanche diodes (SPADs) are an emerging technology with a unique capability of capturing individual photons with high timing precision. SPADs are being used in several active imaging systems (e.g., fluorescence lifetime microscopy and LiDAR), albeit mostly limited to low photon flux settings. We propose passive free-running SPAD (PF-SPAD) imaging, an imaging modality that uses SPADs for capturing 2D intensity images with unprecedented dynamic range under ambient lighting, without any active light source. Our key observation is thatthe precise inter-photon timing measured by a SPAD can be used for estimating scene brightness under ambient lighting conditions, even for very bright scenes. We develop a theoretical model for PF-SPAD imaging, and derive a scene brightness estimator based on the average time of darkness between successive photons detected by a PF-SPAD pixel. Our key insight is that due to the stochastic nature of photon arrivals, this estimator does not suffer from a hard saturation limit. Coupled with high sensitivity at low flux, this enables a PF-SPAD pixel to measure a wide range of scene brightnesses, from very low to very high, thereby achieving extreme dynamic range. We demonstrate an improvement of over 2 orders of magnitude over conventional sensors by imaging scenes spanning a dynamic range of 10^6:1.

80 km Fading Free Phase-Sensitive Reflectometry Based on Multi-Carrier NLFM Pulse Without Distributed Amplification

Abstract: Long range phase-sensitive optical time domain reflectometer (ϕ-OTDR) sensing mainly employs distributed amplification in the sensing fiber. It requires the light to be injected into both ends of the sensing fiber, which reduces the degree of freedom in embedding the fiber into structures. To overcome this problem, the key factors that affects the signal-to-noise ratio (SNR) in ϕ-OTDR system based on matched filter is analyzed thoroughly, and a single-ended long-range ϕ-OTDR that does not require distributed amplification is proposed. In this system, two key techniques are adopted for SNR improvement. To boost the pulse energy and suppress the self-phase modulation, the distortion of the amplified pulse is rectified by using iterative predistortion method; to mitigate the influence of the interference fading and the stimulated Brillouin backscattering, a three-carrier pulse is employed. In combination with the non-linear frequency modulation technique which yields a 42.7 dB side lobe suppression ratio, these approaches guarantee an achievable ϕ-OTDR of 80 km sensing range, 2.7 m spatial resolution, 49.6 dB dynamic range in the experiment. To the best of authors’ knowledge, this is the first time that a ϕ-OTDR without optical amplification in the sensing fiber is realized over such a long sensing range.

Optical Fiber Refractive Index Sensor With Low Detection Limit and Large Dynamic Range Using a Hybrid Fiber Interferometer

Abstract: A refractive index (RI) fiber sensor with low detection limit but large dynamic range is proposed and demonstrated using an exposed core microstructured optical fiber. The exposed-core fiber is highly birefringent due to its asymmetry and also supports multimode propagation; thus, can be used simultaneously as a Mach-Zehnder and Sagnac interferometer. The Mach-Zehnder interference is significantly more phase sensitive to RI due to a longer effective path length difference. This leads to a lower detection limit compared to that for the Sagnac interferometer, which has a larger free spectral range that allows the dynamic range of the RI measurement to be extended. By combining these two interferometers, the proposed sensor achieves a detection limit of as low as 6.02 × 10−6 refractive index units (RIU) while maintaining a large dynamic range from 1.3320 to 1.3465 RIU. The proposed sensor also has the advantages of biocompatibility, low cost, high stability, small size, ability to operate remotely and to be fabricated.

An Adaptive Method for Image Dynamic Range Adjustment

Abstract: In this paper, we relate the operation of image dynamic range adjustment to the following two tasks: 1) for a high dynamic range (HDR) image, its dynamic range will be mapped to the available dynamic range of display devices and 2) for a low dynamic range (LDR) image, its distribution of intensity will be extended to adequately utilize the full dynamic range of display devices. The common goal of both tasks is to preserve or even enhance the details and improve the visibility of scenes when being matched to the available dynamic range of a display device. In this paper, we propose an efficient method for image dynamic range adjustment with three adaptive steps. First, according to the histogram of the luminance map separated from the given RGB image, two suitable Gamma functions are adaptively selected to separately adjust the luminance of the dark and bright components. Second, an adaptive fusion strategy is proposed to combine the two adjusted luminance maps in order to balance the enhancement of the details in different regions. Third, an adaptive luminance-dependent color restoration method is designed to combine the fused luminance map with the original color components to obtain more consistent color saturation between the images before and after dynamic range adjustment. Extensive experiments show that the proposed method can efficiently compress the dynamic range of HDR scenes with good contrast, clear details, and high structural fidelity of the original image appearance. In addition, the proposed method can also obtain promising performance when being used to enhance LDR nighttime images and greatly facilitates the object (car) detection in nighttime traffic scenes.

High-Precision Time-of-Flight Determination Algorithm for Ultrasonic Flow Measurement

Abstract: Commercial time-of-flight (TOF) ultrasonic flowmeters (UFM) are rapidly expanding in the general industry. Among the different techniques that can be applied to determine the TOF of ultrasonic waves, the cross-correlation method presents numerous advantages, such as robustness for weak signals and noise suppression. However, the selection of an appropriate reference wave is presumably a key element in the precise measurement of TOF. In this paper, an algorithm to compute an accurate TOF is proposed. The form of the electric signal received by the transducer is obtained from an acoustically forced underdamped oscillator model, and the analytical solution of the model is proposed as a reference wave. In order to validate the effectiveness of this procedure, a UFM system is designed and tested in a flowmeter calibration test rig. It is demonstrated that the use of the presented scheme overcomes the average method limitations, and turns out to be a convenient solution in a wide range of conditions. Robust measurements of near-zero flow values are acquired, which allow the achievement of a high dynamic range. The error curve of the proposed system have been obtained, revealing that the absolute value of the relative errors is lower than 2% within all the spectrum of flow rates considered (from 0.2 to 150 $\text{m}^{3}$ /h). Results demonstrate that the algorithm provides high-precision measurements within a wide dynamic range. The algorithm is portable and versatile: it can be adapted to different types of transducers without the need of additional measurements, allowing adjusting parameters on-the-fly for an optimal performance of the ultrasonic flowmeter (UFM) system.

High dynamic range, heterogeneous, terahertz quantum cascade lasers featuring thermally-tunable frequency comb operation over a broad current range

Abstract: We report on the engineering of broadband quantum cascade lasers (QCLs) emitting at Terahertz (THz) frequencies, which exploit a heterogeneous active region scheme and have a current density dynamic range (Jdr) of 3.2, significantly larger than the state of the art, over a 1.3 THz bandwidth. We demonstrate that the devised broadband lasers operate as THz optical frequency comb synthesizers in continuous wave, with a maximum optical output power of 4 mW (0.73 mW in the comb regime). Measurement of the intermode beatnote map reveals a clear dispersion-compensated frequency comb regime extending over a continuous 106 mA current range (current density dynamic range of 1.24), significantly larger than the state of the art reported under similar geometries, with a corresponding emission bandwidth of 1.05 THz ans a stable and narrow (4.15 KHz) beatnote detected with a signal-to-noise ratio of 34 dB. Analysis of the electrical and thermal beatnote tuning reveals a current-tuning coefficient ranging between 5 MHz/mA and 2.1 MHz/mA and a temperature-tuning coefficient of -4 MHz/K. The ability to tune the THz QCL combs over their full dynamic range by temperature and current paves the way for their use as powerful spectroscopy tool that can provide broad frequency coverage combined with high precision spectral accuracy.

Optical vector analysis with attometer resolution, 90-dB dynamic range and THz bandwidth.

Abstract: Optical vector analysis (OVA) capable of achieving magnitude and phase responses is essential for the fabrication and application of emerging optical devices. Conventional OVA often has to make compromises among resolution, dynamic range, and bandwidth. Here we show an original method to meet the measurement requirements for ultra-wide bandwidth, ultra-high resolution, and ultra-large dynamic range simultaneously, based on an asymmetric optical probe signal generator (ASG) and receiver (ASR). The ASG and ASR remove the measurement errors introduced by the modulation nonlinearity and enable an ultra-large dynamic range. Thanks to the wavelength-independence of the ASG and ASR, the measurement range can increase by 2 N times by applying an N-tone optical frequency comb without complicated operation. In an experiment, OVA with a resolution of 334 Hz (2.67 attometer in the 1550-nm band), a dynamic range of > 90 dB and a measurement range of 1.075 THz is demonstrated. Typical methods for optical vector analysis have tradeoffs among resolution, dynamic range, and bandwidth. The authors use an asymmetric optical probe signal generator and receiver to perform attometer resolution measurement over a THz of bandwidth while maintaining high dynamic range, aiming to characterize emerging optical devices.

Deep learning enabled laser speckle wavemeter with a high dynamic range

Abstract: The speckle pattern produced when a laser is scattered by a disordered medium has recently been shown to give a surprisingly accurate or broadband measurement of wavelength. Here it is shown that deep learning is an ideal approach to analyse wavelength variations using a speckle wavemeter due to its ability to identify trends and overcome low signal to noise ratio in complex datasets. This combination enables wavelength measurement at high precision over a broad operating range in a single step, with a remarkable capability to reject instrumental and environmental noise, which has not been possible with previous approaches. It is demonstrated that the noise rejection capabilities of deep learning provide attometre-scale wavelength precision over an operating range from 488 nm to 976 nm. This dynamic range is six orders of magnitude beyond the state of the art.

Distributed Dynamic Strain Sensing via Perfect Periodic Coherent Codes and a Polarization Diversity Receiver

Abstract: Rayleigh scattering-based dynamic strain sensing with high spatial resolution, fast update rate, and high sensitivity is highly desired for applications such as structural health monitoring and shape sensing. A key issue in dynamic strain sensing is the tradeoff between spatial resolution and the Signal-to-Noise Ratio (SNR). This tradeoff can be greatly relaxed with the use of coding. A sequence of optical pulses is injected into the fiber and the detected backscattered signal is cross correlated with the original signal. With the use of coding, SNR is indeed improved, but if the sequence is not well chosen, the resulting Peak to Sidelobe Ratio (PSR) can be rather low. An excellent choice of codes are biphase Legendre sequences which offer near Perfect Periodic Autocorrelation (PPA). Other common issues in Rayleigh scattering-based sensing techniques are signal fading and dynamic range. The former issue can occur due to destructive interference between lightwaves that are scattered from the same spatial resolution cell and, in coherent detection schemes, when the polarization states of the backscattered light and the reference light are mismatched. The latter issue is a concern in phase sensitive schemes which require signal jumps not to exceed $2\pi$ . In this paper, a biphase Legendre sequence with 6211 pulses is used in conjunction with polarization diversity scheme and a PM fiber. The setup provides two independent measurements of the sensing fiber complex profile and achieves highly sensitive, distributed dynamic strain sensing with very low probability of fading. In addition, the system can handle both very large perturbation signals and very small perturbation signals. The system operated at a scan rate of $\sim$ 107 kHz and achieved spatial resolution of $\sim$ 10 cm and sensitivity of $\sim 1.1\text{mrad}/\sqrt{\text{Hz}}$ . The ratio between the powers of the maximum and minimum excitations that can be measured by the system is 136 dB.

One-bit Unlimited Sampling

Abstract: Conventional analog–to–digital converters (ADCs) are limited in dynamic range. If a signal exceeds some prefixed threshold, the ADC saturates and the resulting signal is clipped, thus becoming prone to aliasing artifacts. Recent developments in ADC design allow to overcome this limitation: using modulo operation, the so called self-reset ADCs fold amplitudes which exceed the dynamic range. A new (unlimited) sampling theory is currently being developed in the context of this novel class of ADCs. In this paper, we make a further step in this direction by coupling modulo sampling with one-bit Σ∆ quantization, or, in other words, consider one-bit unlimited sampling. We show that our scheme overcomes the dynamic range limitations of conventional one-bit quantizer, where no recovery guarantees are possible if the signal’s dynamic range substantially exceeds the range of its one-bit output. We provide a constructive recovery algorithm for bandlimited signals from one-bit modulo samples complemented with a bound on the reconstruction error.

High Dynamic Range, Heterogeneous, Terahertz Quantum Cascade Lasers Featuring Thermally Tunable Frequency Comb Operation over a Broad Current Range

Abstract: We report on the engineering of broadband quantum cascade lasers (QCLs) emitting at Terahertz (THz) frequencies, which exploit a heterogeneous active region scheme and have a current density dynamic range (Jdr) of 3.2, significantly larger than the state-of-the-art, over a 1.3 THz bandwidth. We demonstrate that the devised broadband lasers operate as THz optical frequency comb synthesizers, in continuous-wave, with a maximum optical output power of 4 mW (0.73 mW in the comb regime). Measurement of the intermode beatnote map reveals a clear dispersion-compensated frequency comb regime extending over a continuous 106 mA current range (current density dynamic range of 1.24), significantly broader than the state-of-the-art at similar geometries, with a corresponding emission bandwidth of ≈1.05 THz and a stable and narrow (4.15 kHz) beatnote detected with a signal-to-noise ratio of 34 dB. Analysis of the electrical and thermal beatnote tuning reveals a current-tuning coefficient ranging between 5 and 2.1 MHz/m...

A high dynamic range optical detector for measuring single photons and bright light

Abstract: Detecting light is fundamental to all optical experiments and applications. At the single photon level, the quantized nature of light requires specialised detectors, which typically saturate when more than one photon is incident. Here, we report on a massively-multiplexed single-photon detector, which exploits the saturation regime of a single click detector to exhibit a dynamic range of 123 dB, enabling measurement from optical energies as low as 10−7 photons per pulse to ∼ 2.5 × 105photons per pulse. This allows us to calibrate a single photon detector directly to a power meter, as well as characterize the nonclassical features of a variety of quantum states.

A Microwatt Dual-Mode Electrochemical Sensing Current Readout With Current-Reducer Ramp Waveform Generation

Abstract: An electrochemical sensing chip with an integrated current-reducer pattern generator and a current-mirror based low-noise chopper-stabilization potentiostat circuit is presented. The pattern generator, utilizing the current reducer technique and pseudo resistors, creates a sub-Hz ramp signal for the cyclic voltammetric (CV) measurement without large-size passive components. The proposed design adopts the chopper-stabilization and low-noise biasing technique for the potentiostat and a counter-based time-to-digital converter to reduce the amplitude noise effects and to convert the sensing current signal to digital codes for further data processing. The design is fabricated using a 0.18-μm CMOS process and achieves a 41 pA current resolution in the current range of ±5 μA while maintaining the R2 linearity of 0.998. The system consumes 16 μW from a 1.2 V supply when a 5 μA sensing current is detected. The power efficiency of the readout interface is 0.31, and the sensing current dynamic range is 108 dB. The design is fully integrated into a single chip and is successfully tested in the dual-mode (CA/CV) measurements with commercial gold electrodes in a potassium ferricyanide solution in sub-millimolar concentrations.

Design of PAM-DMT-Based Hybrid Optical OFDM for Visible Light Communications

Abstract: In this letter, a pulse-amplitude-modulated based hybrid optical orthogonal frequency division multiplexing (PHO-OFDM) scheme is proposed We use the high order quadrature-amplitude-modulation to replace the one-dimensional pulse-amplitude-modulated on the even subcarriers for compensating the data capacity weakness of the conventional pulse amplitude modulated discrete multitone (PAM-DMT) The combined time-domain PHO-OFDM signal has a larger amplitude range than the original PAM-DMT but with a reduced peak-to-average power ratio Besides that, a flexible power allocation method is introduced to the proposed PHO-OFDM systems to fully exploit the whole dynamic range of LEDs The simulation results show that, under the same average bit rate, the proposed PHO-OFDM scheme has a better bit error rate performance compared with the conventional PAM-DMT scheme, thus demonstrating its application potential in visible light communications

Simplified phase-stable dual-comb interferometer for short dynamic range distance measurement

Abstract: A simplified phase-stable dual-comb interferometer for absolute distance measurement within a short dynamic range is proposed in this paper. The experimental results demonstrate that stable phase-difference information and lower timing jitter can be obtained within a time delay of 2000 ns between the reference interference signal and measurement interference signal. Using the proposed technique, the time-of-flight (TOF) result can link directly to the carrier-wave interferometric (CWI) result in an average time of 20 ms and can reach 2 nm precision in 0.5 s averaging time. Millimeter-scale measurement dynamic range and nanometer-level precision can thus be achieved without additional noise suppression. This method can also be applied at different stand-off distances.

Wide-band Parametric Amplifier Readout and Resolution of Optical Microwave Kinetic Inductance Detectors

Abstract: The energy resolution of a single photon counting Microwave Kinetic Inductance Detector (MKID) can be degraded by noise coming from the primary low temperature amplifier in the detector's readout system. Until recently, quantum limited amplifiers have been incompatible with these detectors due to dynamic range, power, and bandwidth constraints. However, we show that a kinetic inductance based traveling wave parametric amplifier can be used for this application and reaches the quantum limit. The total system noise for this readout scheme was equal to ~2.1 in units of quanta. For incident photons in the 800 to 1300 nm range, the amplifier increased the average resolving power of the detector from ~6.7 to 9.3 at which point the resolution becomes limited by noise on the pulse height of the signal. Noise measurements suggest that a resolving power of up to 25 is possible if redesigned detectors can remove this additional noise source.

A 196μW, Reconfigurable Light-to-Digital Converter with 119dB Dynamic Range, for Wearable PPG/NIRS Sensors

Abstract: This paper presents a low power, reconfigurable, high dynamic range (DR), light-to-digital converter (LDC) for wearable PPG/NIRS recording. The LDC converts light into the time domain with a dual-slope mode integrator, followed by a counter-based time-to-digital converter. This architecture merges the functionalities of a conventional transimpedance amplifier and ADC, while quantization in time domain significantly improves the DR. The inherent low pulse repetition frequency (PRF) of LDC also reduces the LED power. Furthermore, the DR of the LDC can be easily reconfigured by re-programming the counting step size or the PRF of the LEDs, allowing optimal power consumption for different DR scenarios. The IC achieves a maximum DR of 119dB while only consuming $196 \mu \mathrm {W}($ including 2X LEDs). The IC is validated with PPG and NIRS tests, using photodiodes (PDs) and silicon photomultipliers (SiPMs) respectively.

Coherent Full-Duplex Double-Sided Two-Way Ranging and Velocity Measurement Between Separate Incoherent Radio Units

Abstract: This paper presents a novel coherent full-duplex (FD) double-sided two-way ranging (CFDDS-TWR) technique for wireless locating and velocity measurement between separate radio units. The idea presented here is a quantum leap in wireless locating since it enables coherent ranging, continuous phase tracking, and velocity measurement between wireless units that operate incoherently with separate low-cost crystal oscillator clock sources. Frequency modulated continuous wave chirp sequences are exchanged in a FD manner between two radio units. The signals transmitted from two radio units are received, respectively, by each of the two units and down-converted in a mixer with the receiver’s own transmit signal to generate a beat signal in each unit. The two beat signals are then processed together, after one beat signal is transmitted to the partner unit. Phase coherent range and Doppler phase measurements can be conducted between incoherent radio units. The presented CFDDS-TWR technique also offers options for reducing noise-like distortions caused by mixing the products of uncorrelated phase noise. We show both analytically and experimentally that the described compensation method reduces the noise level and enhances the dynamic range of the ranging signals tremendously—as evidenced by an improvement of around 24 dB in our results. These unique signal and synchronization properties show that the CFDDS-TWR method is a highly accurate measurement approach. Results acquired with a 24-GHz test system in a 7- to 17-m range demonstrate a standard deviation in range and velocity of 0.25 mm and 0.05 mm/s, respectively.

177 dB linear dynamic range pixels of interest DSLR CAOS camera

Abstract: For the first time, demonstrated is an extreme linear Dynamic Range (DR) Pixels of Interest (POI) [i.e., Coded Access Optical Sensor (CAOS)] Digital Single Lens Reflex (DSLR) camera design that engages three different types of photosensors within one optomechanical assembly to smartly identify POI across a one billion to one light irradiance range. A pixelated CMOS sensor provides a limited DR and linearity image by engaging a moveable mirror placed between the Digital Micromirror Device (DMD) and the frontend imaging lens. Next using DMD control, non-POI light is directed away from the chosen point photodetector (PD) engaged for high DR POI image recovery, giving the PD an improved use of quantum well capacity. For brighter POI, a solid state photodiode point PD with an electronic gain controlled amplifier is engaged while for weaker light POI, a photomultiplier tube (PMT) with variable optical gain is deployed. POI imaging is achieved using time-frequency CAOS modes via DMD control and time-frequency correlation and spectral digital signal processing. A 123.4 dB linear DR POI recovery is achieved for a custom incoherent white light 36-patch target while a record 177 dB linear DR recovery is demonstrated for a single patch 633 nm laser target. For the first time, a 1023 POI frame, real-time 48 frames/s update rate CAOS imaging is demonstrated for tracking a changing focal spot moving laser target.

Ultrafast Large-Scale Chemical Sensing With CMOS ISFETs: A Level-Crossing Time-Domain Approach

Abstract: The introduction of large-scale chemical sensing systems in CMOS which integrate millions of ISFET sensors have allowed applications such as DNA sequencing and fine-pixel chemical imaging systems to be realised. Using CMOS ISFETs provides advantages of digitisation directly at the sensor as well as correcting for non-linearity in its response. However, for this to be beneficial and scale, the readout circuits need to have the minimum possible footprint and power consumption. Within this context, this paper analyses an ISFET based pH-to-time readout using an inverter in the time-domain as a level-crossing detector and presents a 32 × 32 array with in-pixel digitisation for pH sensing. The inverter-based sensing pixel, controlled by a triangular waveform, converts the pH response into a time-domain signal whilst also compensating for sensor offset and thus resulting in an increase in dynamic range. The sensor pixels interface to a 15-bit asynchronous column-wise time-to-digital converter (TDC), enabling fast asynchronous conversion whilst using minimal silicon area. Parallel outputs of 32 TDC interfaces are serialised to achieve fast data throughput. This system is implemented in a standard 0.18 $\,\mu$ m CMOS technology, with a pixel size of 26 $\mu$ m × 26 $\mu$ m and a TDC area of 26 $\mu$ m × 180 $\mu$ m. Additionally, we investigate the use of additional offset compensation by having half of the array implemented with the floating gate tied down via a well diode. Measured results demonstrate the system is able to sense reliably with an average pH sensitivity of 30 mV/pH, whilst being able to compensate for sensor offset by up to $\pm$ 7 V. A resolution of 0.013 pH is achieved and noise measurements show an integrated noise of 0.08 pH within 2–500 Hz and SFDR of 42.6 dB. The total power consumption of the system is measured to be 11.286 mW when operating at a high frame rate of 1 KFPS.

Distributed vibration measurement based on a coherent multi-slope-assisted BOTDA with a large dynamic range.

Abstract: We propose a novel technique to enhance the dynamic range of a coherent slope-assisted Brillouin optical time domain analysis. A multi-tone probe and a reference wave are launched into the fiber under test (FUT); after interacting with the pump pulse, the Brillouin gain, as well as the Brillouin phase shift of each tone, can be demodulated simultaneously. In light of this, the strain information can be determined by the Brillouin phase-gain ratio of each tone. In the experiment, a three-tone probe with a 60 MHz interval is used; effective measurement frequency span larger than 180 MHz is verified in a ∼2 km single-mode fiber with 2.5 m spatial resolution and 1.5 kHz sampling rate to strain. A vibration signal with 41 Hz frequency and 2546 μe amplitude is successfully demodulated.

Integration of a rapid scanning technique into THz time-domain spectrometers for nonlinear THz spectroscopy measurements.

Abstract: We have implemented a rapid scanning technique into THz time-domain spectrometers using an oscillating frictionless delay line, especially adapted for nonlinear THz experiments. Thereby we were able to increase the dynamic range of THz measurements in the frequency range from 40 to 200 cm-1 by up to 24 dB and reduce the scanning time by up to a factor of 200. We report here test measurements on TDS-setups at repetition rates of 80 MHz and 5 kHz. The dynamic range exceeds 64 dB, which allows to record even small changes in the THz absorption upon optical excitation by a THz probe, covering the frequency range of the intermolecular modes and the phonon bands. We demonstrate the potential of this technique for optical-pump THz-probe experiments using a 70 μm thick high-resistivity silicon, excited by 400 nm, ∼50 fs pulses as a sample.

A 600-MS/s DAC With Over 87-dB SFDR and 77-dB Peak SNDR Enabled by Adaptive Cancellation of Static and Dynamic Mismatch Error

Abstract: This paper presents a Nyquist-rate current-steering digital-to-analog converter that achieves a peak spurious-free dynamic range better than 87 dB and a peak signal-to-noise-and-distortion ratio better than 77 dB over a 265-MHz signal band. It is enabled by a fully integrated digital calibration technique that measures and cancels both static and dynamic mismatch errors over the first Nyquist band, and various circuit-level techniques that mitigate the effects of jitter and inter-symbol interference.

Analysis and Mitigation of Clipping Noise in Layered ACO-OFDM Based Visible Light Communication Systems

Abstract: Due to the limited dynamic range of the off-the-shelf electrical and optical components, deliberate digital clipping (DDC) is widely applied to optical orthogonal frequency division multiplexing (OFDM) based visible light communication systems. In this paper, we present a theoretical characterization of the layered asymmetrically clipped optical OFDM (ACO-OFDM) signals subject to peak clipping. We decouple a clipped $L$ -layer ACO-OFDM symbol to $L$ single-layer ACO-OFDM symbols, each corresponding to a layer, and show that these symbols are subject to symmetrical peak clippings at random levels. Using Bussgang’s theorem, the resulting attenuation factors and variances of the additive noise associated with each layer are derived. It is shown that the clipping noise caused by the DDC mainly falls onto the first layer, and its impact is gradually reduced in the subsequent layers. In order to combat the clipping noise, a novel receiver based on decision aided reconstruction is proposed. Simulation results show that the proposed receiver can effectively mitigate the clipping noise, leading to significant improvement of bit error rates over the conventional receiver.

Reactive Dedoping of Polymer Semiconductors To Boost Self-Powered Schottky Diode Performances.

Abstract: A facile and strategic junction tuning technology is reported to boost self-powered organic Schottky photodiode (OPD) performances by synergetic contributions of reactive dedoping effects. It is shown that dedoping poly(3-hexylthiophene-2,5-diyl) (P3HT) films with 1-propylamine (PA) solution significantly reduces not only acceptor-defect density but also intrinsic doping level, leading to dramatically enlarged depletion width of metal/polymer Schottky junctions, as confirmed by ultraviolet photoelectron spectroscopy and Mott-Schottky junction analyses. As a result, whole penetration regions of photons corresponding to absorption bands of P3HT can be fully covered by the depletion region of Schottky junctions, even without the assistance of external electric fields. In addition, it is shown that non-solvent exposure effects of PA dedoping further enable lower paracrystalline disorder and, thus, higher charge carrier mobility, by means of grazing incidence X-ray diffraction, field-effect mobility, and space-charge-limited current analyses. As a result of such synergetic advantages of the PA dedoping method, non-power-driven green-selective OPDs were demonstrated with a high specific detectivity exceeding 6 × 1012 Jones and a low noise-equivalent power of 5.05 × 10-14 W Hz-0.5. Together with a fast temporal response of 26.9 μs and a wide linear dynamic range of 201 dB, the possibility of realizing non-power-driven, near-ideal optimization of solution-processed OPDs with a facile dedoping method is demonstrated.

Background-free broadband absorption spectroscopy based on interferometric suppression with a sign-inverted waveform

Abstract: Background-free methods have potentially superior detection sensitivity because of their ability to take advantage of the full laser power; they are therefore attractive to spectroscopists. We implement background-free Fourier transform spectroscopy based on coherent suppression of the background using an interferometer, whereby the central peak of the interferogram is suppressed without losing molecular absorption signatures. This results in the appearance of peaks rather than dips in the measured spectrum. The technique can be used with a variety of broadband spectroscopies and features advantages such as a reduction in the required detector dynamic range, the capability to perform quantitative measurements, and strongly enhanced sensitivity down to the quantum limit. We validated our method experimentally by performing mid-infrared dual-comb spectroscopy with a mixture of multiple molecular species over a broad wavelength range of 3–5 μm.