Showing papers on "Dynamic range published in 2016"
TL;DR: In this paper, a three degree-of-freedom (3DoF) microelectromechanical system (MEMS) resonant sensing device consisting of three weakly coupled resonators with enhanced sensitivity to stiffness change is presented.
Abstract: This paper reports a three degree-of-freedom (3DoF) microelectromechanical systems (MEMS) resonant sensing device consisting of three weakly coupled resonators with enhanced sensitivity to stiffness change. If one resonator of the system is perturbed by an external stimulus, mode localization occurs, which can be detected by a change of modal amplitude ratio. The perturbation can be, for example, a change in stiffness of one resonator. A detailed theoretical investigation revealed that a mode aliasing effect, along with the thermal noise floor of the sensor and the associated electrical system ultimately limit the dynamic range of the sensor. The nonlinearity of the 3DoF sensor was also analyzed theoretically. The 3DoF resonator device was fabricated using a silicon on insulator process. Measurement results from a prototype device agreed well with the predictions of the analytical model. A significant, namely 49 times, improvement in sensitivity to stiffness change was evident from the fabricated 3DoF resonator sensor compared with the existing state-of-the-art 2DoF resonator sensors, while the typical nonlinearity was smaller than ±2% for a wide span of stiffness change. In addition, measurements indicate that a dynamic range of at least 39.1 dB is achievable, which could be further extended by decreasing the noise of the device and the interface electronics. [2015-0020]
73 citations
TL;DR: It is demonstrated that the novel all-optical akinetic ultrasound sensor achieves a exceptionally low peak noise equivalent pressure (NEP) values of 2 Pa over a 20 MHz measurement bandwidth while maintaining a flat frequency response, and a detection bandwidth up to 22.5 MHz (-6 dB).
Abstract: A novel all-optical akinetic ultrasound sensor, consisting of a rigid, fiber-coupled Fabry-Perot etalon with a transparent central opening is presented. The sensing principle relies exclusively on the detection of pressure-induced changes of the refractive index in the fluid filling the Fabry-Perot cavity. This enables resonance-free, inherently linear signal detection over a broad bandwidth. We demonstrate that the sensor achieves a exceptionally low peak noise equivalent pressure (NEP) values of 2 Pa over a 20 MHz measurement bandwidth (without signal averaging), while maintaining a flat frequency response, and a detection bandwidth up to 22.5 MHz (−6 dB). The measured large full field of view of the sensor is 2.7 mm × 1.3 mm and the dynamic range is 137dB/Hz or 63 dB at 20 MHz bandwidth. For different required amplitude ranges the upper amplitude detection limit can be customized from at least 2 kPa to 2 MPa by using cavity mirrors with a lower optical reflectivity. Imaging tests on a resolution target and on biological tissue show the excellent suitability of the akinetic sensor for optical resolution photoacoustic microscopy (OR-PAM) applications.
67 citations
TL;DR: A novel perception-based quantization to remove nonvisible information in high dynamic range (HDR) color pixels by exploiting luminance masking so that the performance of the High Efficiency Video Coding (HEVC) standard is improved for HDR content.
Abstract: The human visual system (HVS) exhibits nonlinear sensitivity to the distortions introduced by lossy image and video coding. This effect is due to the luminance masking, contrast masking, and spatial and temporal frequency masking characteristics of the HVS. This paper proposes a novel perception-based quantization to remove nonvisible information in high dynamic range (HDR) color pixels by exploiting luminance masking so that the performance of the High Efficiency Video Coding (HEVC) standard is improved for HDR content. A profile scaling based on a tone-mapping curve computed for each HDR frame is introduced. The quantization step is then perceptually tuned on a transform unit basis. The proposed method has been integrated into the HEVC reference model for the HEVC range extensions (HM-RExt), and its performance was assessed by measuring the bitrate reduction against the HM-RExt. The results indicate that the proposed method achieves significant bitrate savings, up to 42.2%, with an average of 12.8%, compared with HEVC at the same quality (based on HDR-visible difference predictor-2 and subjective evaluations).
56 citations
TL;DR: In this paper, the authors used an atomic accelerometer onboard an aircraft to achieve one-shot sensitivities of 2.3 × 10−4 g over a range of ∼ 0.1 g.
Abstract: Inertial sensors based on cold atom interferometry exhibit many interesting features for applications related to inertial navigation, particularly in terms of sensitivity and long-term stability. However, at present the typical atom interferometer is still very much an experiment—consisting of a bulky, static apparatus with a limited dynamic range and high sensitivity to environmental effects. To be compliant with mobile applications further development is needed. In this work, we present a compact and mobile experiment, which we recently used to achieve the first inertial measurements with an atomic accelerometer onboard an aircraft. By integrating classical inertial sensors into our apparatus, we are able to operate the atomic sensor well beyond its standard operating range, corresponding to half of an interference fringe. We report atom-based acceleration measurements along both the horizontal and vertical axes of the aircraft with one-shot sensitivities of 2.3 × 10−4 g over a range of ∼ 0.1 g. The same technology can be used to develop cold-atom gyroscopes, which could surpass the best optical gyroscopes in terms of long-term sensitivity. Our apparatus was also designed to study multi-axis atom interferometry with the goal of realizing a full inertial measurement unit comprised of the three axes of acceleration and rotation. Finally, we present a compact and tunable laser system, which constitutes an essential part of any cold-atom-based sensor. The architecture of the laser is based on phase modulating a single fiber-optic laser diode, and can be tuned over a range of 1 GHz in less than 200 μs.
51 citations
TL;DR: The two-dimensional pixel detector JUNGFRAU as mentioned in this paper is designed for high performance photon science applications at free electron lasers and synchrotron light sources, and it is developed for the SwissFEL currently under construction at the Paul Scherrer Institut, Switzerland.
Abstract: The two-dimensional pixel detector JUNGFRAU is designed for high performance photon science applications at free electron lasers and synchrotron light sources. It is developed for the SwissFEL currently under construction at the Paul Scherrer Institut, Switzerland. The detector is a hybrid pixel detector with a charge integration readout ASIC characterized by single photon sensitivity and a low noise performance over a dynamic range of 104 12 keV photons. Geometrically, a JUNGFRAU readout chip consists of 256×256 pixels of 75×75 μm2. The chips are bump bonded to 320 μm thick silicon sensors. Arrays of 2×4 chips are tiled to form modules of 4×8 cm2 area. Several multi-module systems with up to 16 Mpixels per system will be delivered to the two end stations at SwissFEL. The JUNGFRAU full scale readout ASIC and module design are presented along with characterization results of the first systems. Experiments from fluorescence X-ray, visible light illumination, and synchrotron irradiation are shown. The results include an electronic noise of ~50 electrons r.m.s., which enables single photon detection energies below 2 keV and a noise well below the Poisson statistical limit over the entire dynamic range. First imaging experiments are also shown.
49 citations
TL;DR: In this paper, an analytical and experimental study on low-noise piezoelectric thin film resonators that utilize the delta-E effect of a magnetostrictive layer to measure magnetic fields at low frequencies is presented.
Abstract: We present an analytical and experimental study on low-noise piezoelectric thin film resonators that utilize the delta-E effect of a magnetostrictive layer to measure magnetic fields at low frequencies. Calculations from a physical model of the electromechanical resonator enable electrode designs to efficiently operate in the first and second transversal bending modes. As predicted by our calculations, the adapted electrode design improves the sensitivity by a factor of 6 and reduces the dynamic range of the sensor output by 16 dB, which significantly eases the requirements on readout electronics. Magnetic measurements show a bandwidth of 100 Hz at a noise level of about 100 pTHz−0.5.
47 citations
TL;DR: In this paper, a microwave-coupled ring resonator with a wide dynamic range is studied for use in sensing applications, which is well suited for low-cost, real-time low-power, and CMOS compatible sensing technologies.
Abstract: A highly sensitive, microwave-coupled ring resonator with a wide dynamic range is studied for use in sensing applications. The resonator's structure has two resonant rings and, consequently, two resonant frequencies, operating at 2.3 and 2.45 GHz. Inductive and capacitive coupling mechanisms are explored and compared to study their sensing performance. Primary finite element analysis and measurement results are used to compare the capacitive and inductive coupled ring resonators, demonstrating sensitivity improvements of up to 75% and dynamic range enhancement up to 100% in the capacitive coupled structure. In this work, we are proposing capacitive coupled planar ring resonators as a wide dynamic range sensing platform for liquid sensing applications. This sensing device is well suited for low-cost, real-time low-power, and CMOS compatible sensing technologies.
46 citations
TL;DR: A new multi-channel CMOS amperometric ADC featuring pixel-level architecture for gas sensor arrays featuring digital modulation of input currents and an incremental ΣΔ ADC to achieve wide dynamic range and high sensitivity with very high power efficiency and compact size is presented.
Abstract: Airborne pollutants are a leading cause of illness and mortality globally. Electrochemical gas sensors show great promise for personal air quality monitoring to address this worldwide health crisis. However, implementing miniaturized arrays of such sensors demands high performance instrumentation circuits that simultaneously meet challenging power, area, sensitivity, noise and dynamic range goals. This paper presents a new multi-channel CMOS amperometric ADC featuring pixel-level architecture for gas sensor arrays. The circuit combines digital modulation of input currents and an incremental $\Sigma\Delta$ ADC to achieve wide dynamic range and high sensitivity with very high power efficiency and compact size. Fabricated in 0.5 $\mu\text{m}$ CMOS, the circuit was measured to have 164 dB cross-scale dynamic range, 100 fA sensitivity while consuming only 241 $\mu\text{W}$ and 0.157 $\text{mm}^{2}$ active area per channel. Electrochemical experiments with liquid and gas targets demonstrate the circuit’s real-time response to a wide range of analyte concentrations.
44 citations
TL;DR: How real-time and sequential high dynamic range microscopy facilitates automated three-dimensional neural segmentation is demonstrated, making the technique particularly relevant for longitudinal imaging in the presence of physiological motion and/or for quantification of in vivo fast tracer kinetics during functional imaging.
Abstract: In conventional confocal/multiphoton fluorescence microscopy, images are typically acquired under ideal settings and after extensive optimization of parameters for a given structure or feature, often resulting in information loss from other image attributes. To overcome the problem of selective data display, we developed a new method that extends the imaging dynamic range in optical microscopy and improves the signal-to-noise ratio. Here we demonstrate how real-time and sequential high dynamic range microscopy facilitates automated three-dimensional neural segmentation. We address reconstruction and segmentation performance on samples with different size, anatomy and complexity. Finally, in vivo real-time high dynamic range imaging is also demonstrated, making the technique particularly relevant for longitudinal imaging in the presence of physiological motion and/or for quantification of in vivo fast tracer kinetics during functional imaging.
38 citations
TL;DR: The proposed architecture's low noise, wide bandwidth, and wide dynamic range make it ideal for measurements of highly nonlinear electrochemical and electrophysiological systems.
Abstract: An integrated current measurement system with ultra wide dynamic range is presented and fabricated in a 180-nm CMOS technology. Its dual-mode design provides concurrent voltage and frequency outputs, without requiring an external clock source. An integrator-differentiator core provides a voltage output with a noise floor of 11.6 fA/ $\sqrt{\text{Hz}}$ and a $-3$ dB cutoff frequency of 1.4 MHz. It is merged with an asynchronous current-to-frequency converter, which generates an output frequency linearly proportional to the input current. Together, the voltage and frequency outputs yield a current measurement range of 155 dB, spanning from 204 fA (100 Hz) or 1.25 pA (10 kHz) to 11.6 μA. The proposed architecture's low noise, wide bandwidth, and wide dynamic range make it ideal for measurements of highly nonlinear electrochemical and electrophysiological systems.
36 citations
TL;DR: A fiber-optic thermometer based on dual Fabry-Perot interferometers made from the same material, but with different cavity lengths, which enables unambiguous recognition of the dense fringes associated with the thick FPI over the free-spectral range determined by the thin FPI is proposed.
Abstract: The paradox between a large dynamic range and a high resolution commonly exists in nearly all kinds of sensors Here, we propose a fiber-optic thermometer based on dual Fabry–Perot interferometers (FPIs) made from the same material (silicon), but with different cavity lengths, which enables unambiguous recognition of the dense fringes associated with the thick FPI over the free-spectral range determined by the thin FPI Therefore, the sensor combines the large dynamic range of the thin FPI and the high resolution of the thick FPI To verify this new concept, a sensor with one 200 μm thick silicon FPI cascaded by another 10 μm thick silicon FPI was fabricated A temperature range of −50°C to 130°C and a resolution of 68×10−3°C were demonstrated using a simple average wavelength tracking demodulation Compared to a sensor with only the thick silicon FPI, the dynamic range of the hybrid sensor was more than 10 times larger Compared to a sensor with only the thin silicon FPI, the resolution of the hybrid sensor was more than 18 times higher
TL;DR: For the implementation of an all fiber observation network for submarine seismic monitoring, a tri-component geophone based on Michelson interferometry is proposed and tested.
Abstract: For the implementation of an all fiber observation network for submarine seismic monitoring, a tri-component geophone based on Michelson interferometry is proposed and tested. A compliant cylinder-based sensor head is analyzed with finite element method and tested. The operation frequency ranges from 2 Hz to 150 Hz for acceleration detection, employing a phase generated carrier demodulation scheme, with a responsivity above 50 dB re rad/g for the whole frequency range. The transverse suppression ratio is about 30 dB. The system noise at low frequency originated mainly from the 1/f fluctuation, with an average system noise level -123.55 dB re rad / Hz ranging from 0 Hz to 500 Hz. The minimum detectable acceleration is about 2 ng / Hz , and the dynamic range is above 116 dB.
19 Jun 2016
TL;DR: High-precision individual cell tuning was experimentally demonstrated, for the first time, in analog integrated circuits redesigned from a commercial NOR flash memory, and relies on a write-verify algorithm, using a compact model of cell's dynamics.
Abstract: High-precision individual cell tuning was experimentally demonstrated, for the first time, in analog integrated circuits redesigned from a commercial NOR flash memory. The tuning is fully automatic, and relies on a write-verify algorithm, with the optimal amplitude of each write pulse determined from runtime measurements, using a compact model of cell's dynamics, fitted to experimental results. The algorithm has allowed tuning of each cell of a 100-cell array to any desired state within a 4-orders-of-magnitude dynamic range. With 10 write pulses, the average tuning accuracy is about 3%, while with 35 pulses the precision reaches ∼0.3%. Taking into account the dynamic range, the last number is equivalent to ∼1,500 levels, i.e. 10+ bits.
TL;DR: A new approach to display HDR IR images with contrast enhancement by using the local edge-preserving filter and an adaptive Gamma transformation to adjust the gray distribution of the base layer, and stretch the detail layer based on a human visual effect principle.
TL;DR: This work proposes a 25 kHz 3rd-order continuous-time ΔΣ modulator utilizing a 5-bit SAR quantizer, enabling noise coupling to be possible in a typical nanoscale CMOS 65 nm technology with VDD of 1 V.
Abstract: As technology scales, integrating high resolution ADCs into high fidelity mixed signal systems becomes challenging in advanced CMOS processes. Cascading integrators to achieve high-order filter structures limits the modulation index and compromises on stability at the expense of added hardware and power consumption. To optimize the maximum stable amplitude (MSA) to accommodate a larger input dynamic range, the supply rails have to be expanded, which limited technology choices to those of a larger feature size. This work proposes a 25 kHz 3rd-order continuous-time $\Delta \Sigma $ modulator (CT $\Delta \Sigma \text {M}$ ) utilizing a 5-bit SAR quantizer, enabling noise coupling (NC) to be possible in a typical nanoscale CMOS 65 nm technology with VDD of 1 V. Mismatches in SAR comparator and DAC array are mitigated with a proposed calibration scheme while CM mismatches are solved by a floating differential charge storage capacitor (FDCSC) coupling method. To allow sufficient time for SAR bit cycling and noise charge feedback settling, 1 Ts excess loop delay (ELD) is compensated with digital differentiation that minimizes both the power and complexity of the auxiliary feedback DAC. The prototype obtained DR/SNR/SNDR of 103.1 dB/100.1 dB/95.2 dB while dissipating 0.8 mW, hence achieving a FoMSNDR and FoMschreier of 0.34 pJ/level and 177.9 dB, respectively.
TL;DR: In this paper, a pixel based on a three-transistor active pixel sensor has two linear responses and a logarithmic response using additional circuits, and the photogate surrounding the n+/p-sub photodiode exists for the second linear response.
Abstract: A new pixel structure is proposed for wide dynamic range CMOS image sensors. A pixel based on a three-transistor active pixel sensor has two linear responses and a logarithmic response using additional circuits. The photogate surrounding the n+/p-sub photodiode exists for the second linear response. The logarithmic response is due to the biased MOS cascode. The proposed pixel was designed and fabricated using a 0.35- $\mu \text{m}$ 2-poly 4-metal standard CMOS process. The dynamic range of the pixel is higher than 106 dB. A test chip with a pixel pitch of $10 \times 10~\mu \text{m}^{2}$ and a $160 \times 120$ pixel array is evaluated.
TL;DR: The results of static and dynamic experiments demonstrate that the voltage curves of static experiments are similar to those of dynamic experiments; therefore, the static data can be used to simulate the dynamic curves.
Abstract: A novel method for proximity detection of moving targets (with high dielectric constants) using a large-scale (the size of each sensor is 31 cm × 19 cm) planar capacitive sensor system (PCSS) is proposed. The capacitive variation with distance is derived, and a pair of electrodes in a planar capacitive sensor unit (PCSU) with a spiral shape is found to have better performance on sensitivity distribution homogeneity and dynamic range than three other shapes (comb shape, rectangular shape, and circular shape). A driving excitation circuit with a Clapp oscillator is proposed, and a capacitance measuring circuit with sensitivity of 0.21 V p - p / pF is designed. The results of static experiments and dynamic experiments demonstrate that the voltage curves of static experiments are similar to those of dynamic experiments; therefore, the static data can be used to simulate the dynamic curves. The dynamic range of proximity detection for three projectiles is up to 60 cm, and the results of the following static experiments show that the PCSU with four neighboring units has the highest sensitivity (the sensitivities of other units are at least 4% lower); when the attack angle decreases, the intensity of sensor signal increases. This proposed method leads to the design of a feasible moving target detector with simple structure and low cost, which can be applied in the interception system.
TL;DR: The proposed adaptive spot search method enables expanding the dynamic range of an SHWFS with a single shot and short processing time and is quantitatively evaluated by numerical simulations.
Abstract: A Shack-Hartmann wavefront sensor (SHWFS) that consists of a microlens array and an image sensor has been used to measure the wavefront aberrations of human eyes. However, a conventional SHWFS has finite dynamic range depending on the diameter of the each microlens. The dynamic range cannot be easily expanded without a decrease of the spatial resolution. In this study, an adaptive spot search method to expand the dynamic range of an SHWFS is proposed. In the proposed method, spots are searched with the help of their approximate displacements measured with low spatial resolution and large dynamic range. By the proposed method, a wavefront can be correctly measured even if the spot is beyond the detection area. The adaptive spot search method is realized by using the special microlens array that generates both spots and discriminable patterns. The proposed method enables expanding the dynamic range of an SHWFS with a single shot and short processing time. The performance of the proposed method is compared with that of a conventional SHWFS by optical experiments. Furthermore, the dynamic range of the proposed method is quantitatively evaluated by numerical simulations.
TL;DR: All-digital frequency synthesis architectures with phase and polar Σ-Δ modulation feedback loops are introduced as a means to overcome the inherent spectral-quality limitations of forward-dithered all- digital frequency synthesizers represented by the family of pulse direct digital synthesizers.
Abstract: All-digital frequency synthesis architectures with phase and polar $\Sigma$ – $\Delta$ modulation feedback loops are introduced as a means to overcome the inherent spectral-quality limitations of forward-dithered all-digital frequency synthesizers represented by the family of pulse direct digital synthesizers. The spectrum of dithered pulse direct digital synthesizers is derived first, with and without modulation, as well as that of their variations with multiple dithered paths and with colored dithering resulting in lower noise level. The limited dynamic range achieved by forward-dithered all-digital frequency synthesizers motivates the introduction of phase and polar $\Sigma$ – $\Delta$ modulation feedback loop architectures which are modeled and analyzed to derive their noise transfer functions. Extensive MATLAB simulation illustrates the suppressed near-in noise and the high spurs-free dynamic range the two $\Sigma$ – $\Delta$ schemes can achieve and the wideband spurs-free output of the polar one. Detailed analysis and implementation aspects of the techniques are outside the scope of the paper.
TL;DR: In this paper, a high-resolution scanning superconducting quantum interference device (SQUID) microscope for imaging the magnetic field of geological samples at room temperature is presented, including the magnetically shielded box (MSB), the XYZ stage, data acquisition by the system, and initial evaluation of the system.
Abstract: We have developed a high-resolution scanning superconducting quantum interference device (SQUID) microscope for imaging the magnetic field of geological samples at room temperature. In this paper, we provide details about the scanning SQUID microscope system, including the magnetically shielded box (MSB), the XYZ stage, data acquisition by the system, and initial evaluation of the system. The background noise in a two-layered PC permalloy MSB is approximately 40–50 pT. The long-term drift of the system is approximately ≥1 nT, which can be reduced by drift correction for each measurement line. The stroke of the XYZ stage is 100 mm × 100 mm with an accuracy of ~10 µm, which was confirmed by laser interferometry. A SQUID chip has a pick-up area of 200 μm × 200 μm with an inner hole of 30 μm × 30 μm. The sensitivity is 722.6 nT/V. The flux-locked loop has four gains, i.e., ×1, ×10, ×100, and ×500. An analog-to-digital converter allows analog voltage input in the range of about ±7.5 V in 0.6-mV steps. The maximum dynamic range is approximately ±5400 nT, and the minimum digitizable magnetic field is ~0.9 pT. The sensor-to-sample distance is measured with a precision line current, which gives the minimum of ~200 µm. Considering the size of pick-up coil, sensor-to-sample distance, and the accuracy of XYZ stage, spacial resolution of the system is ~200 µm. We developed the software used to measure the sensor-to-sample distance with line scan data, and the software to acquire data and control the XYZ stage for scanning. We also demonstrate the registration of the magnetic image relative to the optical image by using a pair of point sources placed on the corners of a sample holder outside of a thin section placed in the middle of the sample holder. Considering the minimum noise estimate of the current system, the theoretical detection limit of a single magnetic dipole is ~1 × 10−14 Am2. The new instrument is a powerful tool that could be used in various applications in paleomagnetism such as ultrafine-scale magnetostratigraphy and single-crystal paleomagnetism.
25 Feb 2016
TL;DR: An image sensor capable of both single-photon detection and normal imaging providing us with a high dynamic range is a huge technological challenge.
Abstract: Continuous improvements in sensitivity have opened up applications for image sensors such as camcorders, digital still cameras, mobile phones, and surveillance cameras. Even though leading-edge image sensors have reached the noise floor of a few electrons [1,2], a thrust towards darker levels still continues down to an illumination level equivalent to being under a crescent moon (i.e., 10−2 down to 10−4 lux). This requires single-photon detection with typical digital cameras pixel size, i.e., 1.5 to 5µm. Although huge-size pixel [3] or single-photon avalanche photodiode (SPAD) based image sensors [4] have been presented for such a purpose, in general, both have to pay area and dark current penalties. Thus, an image sensor capable of both single-photon detection and normal imaging providing us with a high dynamic range is a huge technological challenge.
TL;DR: In this paper, the autodyne response of a frequency-stabilized microwave oscillator subjected to the action of its self-radiation reflected from an object is analyzed.
Abstract: The expressions describing the autodyne (AD) response are obtained with allowance for the internal noise of a frequency-stabilized microwave oscillator subjected to the action of its self-radiation reflected from an object. The results of analyzing the AD and noise characteristics of the stabilized oscillator built around the band-reflecting filter with resistive coupling are presented. The conditions leading to the appearance of the periodic non-stationarity of noise characteristics are established. It is demonstrated that frequency stabilization is ensured by a gain in dynamic range. The experimental data on unstabilized and stabilized hybrid-integral AD oscillators based on the two-mesa Gunn diode of 8-mm range are presented.
20 Mar 2016
TL;DR: Proposed burst-mode coherent detection scheme successfully receives 20 Gb/s SP-QPSK burst frames with preamble of 1.3 ms, transmitted over 40 km SMF, at high sensitivity and wide dynamic range of 21.7 dBm.
Abstract: Proposed burst-mode coherent detection scheme successfully receives 20 Gb/s SP-QPSK burst frames with preamble of 1.3 ms, transmitted over 40 km SMF, at high sensitivity of −44.7 dBm with wide dynamic range of 21.7 dB.
TL;DR: This work presents a full-sampling direct analog-to-digital conversion FD-NIR imager, suitable for a wide-range of biophotonic applications where fast, accurate quantification of absolute optical properties is needed.
Abstract: Frequency domain near-infrared spectroscopy (FD-NIRS) has proven to be a reliable method for quantification of tissue absolute optical properties. We present a full-sampling direct analog-to-digital conversion FD-NIR imager. While we developed this instrument with a focus on high-speed optical breast tomographic imaging, the proposed design is suitable for a wide-range of biophotonic applications where fast, accurate quantification of absolute optical properties is needed. Simultaneous dual wavelength operation at 685 and 830 nm is achieved by concurrent 67.5 and 75 MHz frequency modulation of each laser source, respectively, followed by digitization using a high-speed (180 MS/s) 16-bit A/D converter and hybrid FPGA-assisted demodulation. The instrument supports 25 source locations and features 20 concurrently operating detectors. The noise floor of the instrument was measured at <1.4 pW/√Hz, and a dynamic range of 115+ dB, corresponding to nearly six orders of magnitude, has been demonstrated. Titration experiments consisting of 200 different absorption and scattering values were conducted to demonstrate accurate optical property quantification over the entire range of physiologically expected values.
TL;DR: This work has extended the theory behind linear optical differentiation and generalised it to nonlinear filters to create a new filter that can decouple the dynamic range from the sensitivity of this new wavefront sensor.
Abstract: Current wavefront sensors for high resolution imaging have either a large dynamic range or a high sensitivity. A new kind of wavefront sensor is developed which can have both: the Generalised Optical Differentiation wavefront sensor. This new wavefront sensor is based on the principles of optical differentiation by amplitude filters. We have extended the theory behind linear optical differentiation and generalised it to nonlinear filters. We used numerical simulations and laboratory experiments to investigate the properties of the generalised wavefront sensor. With this we created a new filter that can decouple the dynamic range from the sensitivity. These properties make it suitable for adaptive optic systems where a large range of phase aberrations have to be measured with high precision.
TL;DR: This paper presents a method to improve the dynamic range of white light interferometer (WLI) based polarization mode coupling (PMC) measurement system beyond 100 dB through eliminating interference beat noise and enhancing the tested interference intensity simultaneously.
Abstract: This paper presents a method to improve the dynamic range of white light interferometer (WLI) based polarization mode coupling (PMC) measurement system beyond 100 dB. The limitation of interference beat noise is overcame by analyzing in detail the inherent noises that have impacts on the detection sensitivity. An improved PMC measurement system and method are proposed for testing ultra-high polarization extinction ratio (PER) of polarization-related devices. The method can improve dynamic range dramatically through eliminating interference beat noise and enhancing the tested interference intensity simultaneously, which are verified theoretically and experimentally. In addition, a Y-junction with ~80 dB PER of LiNbO3 chip corresponding to a weak signal is tested as an application example. The results demonstrate that the high PER interferogram can be identified clearly and steadily with standard deviation 0.9 dB (3σ) @ ~80 dB. This proposed method is highly beneficial in fabrication and evaluation for polarization devices with ultra-high PER.
TL;DR: The dynamic range limitation of can be resolved by using multiple cameras that cover a large field of view instead of a single image sensor with a wide-angle lens and the dynamic range is expanded by 48-fold in this system.
Abstract: A new compact large field of view (FOV) multi-camera system is introduced. The camera is based on seven tiny complementary metal-oxide-semiconductor sensor modules covering over 160° × 160° FOV. Although image stitching has been studied extensively, sensor and lens differences have not been considered in previous multi-camera devices. In this study, we have calibrated the photometric characteristics of the multi-camera device. Lenses were not mounted on the sensor in the process of radiometric response calibration to eliminate the influence of the focusing effect of uniform light from an integrating sphere. Linearity range of the radiometric response, non-linearity response characteristics, sensitivity, and dark current of the camera response function are presented. The R, G, and B channels have different responses for the same illuminance. Vignetting artifact patterns have been tested. The actual luminance of the object is retrieved by sensor calibration results, and is used to blend images to make panoramas reflect the objective luminance more objectively. This compensates for the limitation of stitching images that are more realistic only through the smoothing method. The dynamic range limitation of can be resolved by using multiple cameras that cover a large field of view instead of a single image sensor with a wide-angle lens. The dynamic range is expanded by 48-fold in this system. We can obtain seven images in one shot with this multi-camera system, at 13 frames per second.
TL;DR: In this paper, an approach to implement photonic-assisted time-interleaved analog-to-digital conversion and its calibration method is presented, where analog modulated optical signal is divided into M channels, suffering different time delay induced by optical delay lines.
Abstract: An approach to implement photonic-assisted time-interleaved analog-to-digital conversion and its calibration method are presented. The analog modulated optical signal is divided into M channels, suffering different time delay induced by optical delay lines which provide great flexibility in producing time intervals and is then sampled by electronic analog-to-digital converters (ADCs). The channel mismatches resulting in performance degradation are estimated by a modified sine wave fitting method. The time mismatch and other mismatches are corrected by fine optical delay adjustment and digital processing, respectively. A four-channel photonic-assisted time-interleaved analog-to-digital converter (TIADC) system operating at 40 GSa s−1 was demonstrated experimentally. The photonic-assisted TIADC system was tested with a 6.31 GHz sine wave signal, exhibiting 40.3 dB signal-to-noise and distortion ratio (SINAD) and 57.6 dBc spurious-free dynamic range (SFDR). It is shown that the SINAD is dominated by the signal-to-noise ratio (SNR) of the analog optical link and the SFDR of the proposed system is limited by the linearity of the link.
TL;DR: A new electronic circuit design reducing the electronic noise of the photodetection circuit in the audio band is presented, which creates headroom for higher laser power and more squeezing to be observed in the future in GEO 600 and is applicable to other optics experiments.
Abstract: Current laser-interferometric gravitational wave detectors employ a self-homodyne readout scheme where a comparatively large light power (5–50 mW) is detected per photosensitive element. For best sensitivity to gravitational waves, signal levels as low as the quantum shot noise have to be measured as accurately as possible. The electronic noise of the detection circuit can produce a relevant limit to this accuracy, in particular when squeezed states of light are used to reduce the quantum noise. We present a new electronic circuit design reducing the electronic noise of the photodetection circuit in the audio band. In the application of this circuit at the gravitational-wave detector GEO 600 the shot-noise to electronic noise ratio was permanently improved by a factor of more than 4 above 1 kHz, while the dynamic range was improved by a factor of 7. The noise equivalent photocurrent of the implemented photodetector and circuit is about 5 µA/√Hz above 1 kHz with a maximum detectable photocurrent of 20 mA. With the new circuit, the observed squeezing level in GEO 600 increased by 0.2 dB. The new circuit also creates headroom for higher laser power and more squeezing to be observed in the future in GEO 600 and is applicable to other optics experiments.
TL;DR: N numerically and experimentally demonstrate the possibility of implementing the spatially varying transmission gradient using distributions of small pixels that are either transparent or opaque and the accuracy and consistency of a first-generation ODWS based on binary pixelated filters are experimentally demonstrated.
Abstract: Sensors measuring the spatial phase of optical waves are widely used in optics. The optical differentiation wavefront sensor (ODWS) reconstructs the wavefront of an optical wave from wavefront slope measurements obtained by inducing linear field-transmission gradients in the far-field. Its dynamic range and sensitivity can be adjusted simply by changing the gradient slope. We numerically and experimentally demonstrate the possibility of implementing the spatially varying transmission gradient using distributions of small pixels that are either transparent or opaque. Binary pixelated filters are achromatic and can be fabricated with high accuracy at relatively low cost using commercial lithography techniques. We study the impact of the noise resulting from pixelation and binarization of the far-field filter for various test wavefronts and sensor parameters. The induced wavefront error is approximately inversely proportional to the pixel size. For an ODWS with dynamic range of 100 rad/mm over a 1-cm pupil, the error is smaller than λ/15 for a wide range of test wavefronts when using 2.5-μm pixels. We experimentally demonstrate the accuracy and consistency of a first-generation ODWS based on binary pixelated filters.