Photodetector Signal Research Articles

Nanodisplacement Measurements of Piezoelectric Flextensional Actuators Using a New Interferometry Homodyne Method

Piezoelectric flextensional actuator (PFA) devices are increasingly being applied in precision mechanics, such as nanotechnology equipments, electronic microscopy instruments, cell manipulation systems, and microsurgery tools. These PFAs need to be characterized by measuring the produced nanodisplacements, and optical interferometry is well established as an accurate and precise technique for this application. In this paper, a new and efficient method for optical phase detection, here named generalized J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> /J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> method, is presented. As in the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> /J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> conventional method, the new method is based on information contained in the photodetected signal spectrum when the drive voltage is sinusoidal and has a known frequency. The dynamic range of this method is from 0.26 to 100π rad (and higher), and only a limited number of frequencies in the magnitude spectrum of the photodetected signal are used, without the need to know the phase spectrum. The method has the advantages of being simple, passive homodyne, self-consistent, and immune to fading. Using the new method, two novel PFAs prototypes, designed using topology optimization method, are tested in terms of displacement linearity (relative to applied voltage) and frequency response.

Near video-rate linear Stokes imaging with single-pixel detectors

In this work we demonstrate a polarization sensitive computational imaging system based on a digital micro-mirror device (DMD) and several single-pixel photodetectors. By taking advantage of computational imaging techniques, the light measured by each single-pixel detector can reconstruct a 2D image for a specific linear polarization state. Using the rapid frame-rate of the DMD to continuously project a series of spatially orthogonal illumination patterns, near video-rate reconstructions can be achieved. In addition we extend this approach to provide full-colour images through a process of sequential colour selection (RGB). Taking the difference between photodetector signals from orthogonal linear polarization states, we obtain images corresponding to the linear Stokes parameters. We apply this rapid polarization sensitive imaging system to inert and biological material. Since the spatial information in the images reconstructed by this approach are determined by the projection system, rather than the detectors, the approach provides perfect pixel registration between the various polarization selective images and associated Stokes parameters. Furthermore, the use of single-pixel detectors and the large operational bandwidth afforded by DMDʼs means that the approach can readily be extended for imaging at wavelengths where detector arrays are unavailable or limited.

Quantification of rolling circle amplified DNA using magnetic nanobeads and a Blu-ray optical pick-up unit.

We present the first implementation of a Blu-ray optical pickup unit (OPU) for the high-performance low-cost readout of a homogeneous assay in a multichamber microfluidic disc with a chamber thickness of 600 μm. The assay relies on optical measurements of the dynamics of magnetic nanobeads in an oscillating magnetic field applied along the light propagation direction. The laser light provided by the OPU is transmitted through the sample chamber and reflected back onto the photo detector array of the OPU via a mirror. Spectra of the 2nd harmonic photo detector signal vs. the frequency of the applied magnetic field show a characteristic peak due to freely rotating magnetic nanobeads. Beads bound to ~1 μm coils of DNA formed off-chip by padlock probe recognition and rolling circle amplification show a different dynamics and the intensity of the characteristic peak decreases. We have determined the optimum magnetic bead concentration to 0.1mg/mL and have measured the response vs. concentration of DNA coils formed from Escherichia Coli. We have found a limit of detection of 10 pM and a dynamic range of about two orders of magnitude, which is comparable to the performance obtained using costly and bulky laboratory equipment. The presented device leverages on the advanced but low-cost technology of Blu-ray OPUs to provide a low-cost and high-performance magnetic bead-based readout of homogeneous bioassays. The device is highly flexible and we have demonstrated its use on microfluidic chambers in a disc with a thickness compatible with current optical media mass-production facilities.

Analysis of structural–technological limitations in silicon circuits for reading photodiode signals in the IR region

This paper presents the results of a study of the scientific and engineering principles of the creation of silicon multiplexers intended for reading out and preprocessing photodetector signals in the IR ranges 8–14 and 3–5 μm. The noise equivalent temperature difference is estimated for far-IR photodetectors based on silicon multiplexers with linewise and framewise accumulation of signals from HgCdTe photodiodes (PDs). The features of how the structural–technological limitations in the silicon readout circuits affect the characteristics of the IR photodetectors are analyzed for a wide range of parameters of HgCdTe PDs and a wide range of technological design norms for fabricating silicon multiplexers.

Wide dynamic range homodyne interferometry method and its application for piezoactuator displacement measurements

Multiactuated piezoelectric flextensional actuators (MAPFAs) is a fast-growing technology in development, with a wide range of applications in precision mechanics and nanotechnology. In turn, optical interferometry is an adequate technique to measure nano/micro-displacements and to characterize these MAPFAs. In this work, an efficient method for homodyne phase detection, based on a well-known Bessel functions recurrence relation, is developed, providing practical applications with a high dynamic range. Fading and electronic noise are taken into account in the analysis. An important advantage of the method is that, for each measurement, only a limited number of frequencies in the magnitude spectrum of the photodetected signal are used, without the need to know the phase spectrum. The dynamic range for phase demodulation is from 0.2 to 100π rad (or 10 nm to 16 μm for displacement, using 632.8 nm wavelength). The upper range can be easily expanded by adapting the electronic system to the signal characteristics. By using this interferometric technique, a new XY nanopositioner MAPFA prototype is tested in terms of linearity, displacement frequency response, and coupling rate.

Algorithm for Excitation Optimization of Fabry–Pérot Filters Used in Swept Sources

We investigate the improvement in the nonlinearity of a conventional wavelength swept laser source on the basis of a fiber Fabry-Perot tunable filter using a well-established optimization method, simulated annealing (SA). The signal driving the filter is constructed from many short ramps of different slopes that are interconnected. The values of the slopes are optimized through the SA algorithm to achieve maximum amplitude for the Fourier transformed peaks of the photodetected interferometric signal.

A high dynamic range method for the direct readout of a dynamic phase change in homodyne interferometers

Piezoelectric flextensional actuators (PFAs) are an efficient alternative to systems that demand nano-positioning of devices, such as in nanotechnology. Optical techniques constitute an excellent choice for contactless measurement of nano-displacements. In particular, optical interferometry constitutes an adequate choice for characterizing PFAs. There are several types of interferometers, as well as optical phase demodulation methods, used in practice. One interesting class of demodulation methods uses the spectrum of the photo-detected signal and its intrinsic properties when there is a harmonically varying time-domain modulating signal. In this work, a low cost homodyne Michelson interferometer, associated with simple electronic circuits for signal conditioning and acquisition, is used. A novel dynamic phase demodulation method, named Jm&Jm + 2, is proposed, which uses only the magnitude spectrum of the photo-detected signal, without the need to know its phase spectrum. The method is passive, direct, self-consistent, without problems of phase ambiguity and immune to fading, and presents a dynamic range from 0.45 to 100 rad displacements (between 22.6 nm and 5 µm, for λ = 632.8 nm). When applied to the measurement of half-wave voltage in a proof-of-concept Pockels cell, it presents errors smaller than 0.9% when compared to theory. For the estimation of PFA displacement, it allows the measurement of linearity and frequency response curves, with excellent results.

Terahetz detection by heterostructed InAs/InSb nanowire based field effect transistors

Heterostructured InAs/InSb nanowire (Nw) based field effect transistors (FET) have been fabricated and tested as Terahetz radiation detectors. While responsivity and noise equivalent power compare with the ones of InAs nanowire detectors, the presence of small-gap InSb semiconductor gives rise to interesting physical effects such an increase of the detected signal with charge injection through the wire, at odds with standard FET-detectors. Additionally, the photodetected signal voltage changes its sign after a threshold gate bias, which we explain considering surface-related transport and field asymmetries imposed by the use of a lateral gate electrode.

A novel approach for realization of primary vibration calibration standard by homodyne laser interferometer in frequency range of 0.1 Hz to 20 kHz

The paper discusses the primary vibration calibration standard of NPL, India capable of calibrating the reference accelerometers in frequency range from 0.1Hz to 20kHz as per ISO 16063-11. The excitation subsystem produces constant vibration at a specified amplitude and frequency, while the measurement system uses NI interface for measuring the quadrature output. The acceleration level and voltage level at the calibration frequency f is determined by applying a Discrete Fourier Transform to the voltage and displacement signals, and then examining the spectral component at frequency f. A PC-based data acquisition system acquires the accelerometer voltage signal and analog quadrature interferometer photodetector signal pair as well as a digital quadrature pair whereby the software processes the demodulated photodetector signals to reconstruct the armature displacement. The validation of the calibration results for standard reference accelerometers with manufacturer results and uncertainty in calibration in entire frequency range 0.1Hz to 20kHz is reported in the present work.

The distribution functions of characteristic quantities for random noise signal of photodetector

Based on the random process of the photodetector noise signals {Vi}, the different characteristics of the two parts of the random measurementstability constant part and random fluctuation part are analyzed. A new mathematical model of the random noise signal is established. The theoretical analysis shows that the statistical distributions must obey the relationship of nonlinear transform. The distribution laws of the different characteristic quantities in the same random process are studied experimentally, such as, the amplitude of extreme, the amplitudes of the rising edge and falling edge, the interval between extreme points, the difference between adjacent amplitudes, the product value of the quantities and the quotient value of the quantities. And the statistical distribution of these characteristic quantities matches well with the form of the lognormal distribution. From the theoretical and experimental results we can conclude that the lognormal distribution plays an important role in describing the random fluctuation part characteristic of random process.

Photonic approach to the simultaneous measurement of the frequency, amplitude, pulse width, and time of arrival of a microwave signal

A photonic approach to the simultaneous measurement of the frequency, pulse amplitude (PA), pulse width (PW), and time of arrival (TOA) of an unknown pulsed microwave signal is proposed and demonstrated. The measurement is performed based on optical carrier-suppressed modulation, complementary optical filtering, low-speed photodetection, and electrical signal processing. A proof-of-concept experiment is carried out. A frequency measurement range of 2-11 GHz with a measurement error for frequency, PA, PW, and TOA within ±0.1 GHz, ±0.05 V, ±1 ns, and ±0.16 ns is achieved.

Optical-fiber pulse rate multiplier for ultralow phase-noise signal generation

In this Letter we report on an all optical-fiber approach to the synthesis of ultralow-noise microwave signals by photodetection of femtosecond laser pulses. We use a cascade of Mach-Zehnder fiber interferometers to realize stable and efficient repetition rate multiplication. This technique increases the signal level of the photodetected microwave signal by close to 18 dB. That in turn allows us to demonstrate a residual phase-noise level of -118 dBc/Hz at 1 Hz and -160 dBc/Hz at 10 MHz from a 12 GHz signal. The residual noise floor of the fiber multiplier and photodetection system alone is around -164 dBc/Hz at the same offset frequency, which is very close to the fundamental shot-noise floor.

Sensor noise informed representation of hyperspectral data, with benefits for image storage and processing

Many types of hyperspectral image processing can benefit from knowledge of noise levels in the data, which can be derived from sensor physics. Surprisingly, such information is rarely provided or exploited. Usually, the image data are represented as radiance values, but this representation can lead to suboptimal results, for example in spectral difference metrics. Also, radiance data do not provide an appropriate baseline for calculation of image compression ratios. This paper defines two alternative representations of hyperspectral image data, aiming to make sensor noise accessible to image processing. A "corrected raw data" representation is proportional to the photoelectron count and can be processed like radiance data, while also offering simpler estimation of noise and somewhat more compact storage. A variance-stabilized representation is obtained by square-root transformation of the photodetector signal to make the noise signal-independent and constant across all bands while also reducing data volume by almost a factor 2. Then the data size is comparable to the fundamental information capacity of the sensor, giving a more appropriate measure of uncompressed data size. It is noted that the variance-stabilized representation has parallels in other fields of imaging. The alternative data representations provide an opportunity to reformulate hyperspectral processing algorithms to take actual sensor noise into account.

四象限探测器位移测量的标定方法

A method for real-time,quick calibration of four-quadrant photodetector(QD) signals in optical tweezers system is provided.The experimental results indicate that the method is feasible and precise.Its instability is less than 1%.In addition,the effect of the bead depth on calibration factor is investigated experimentally,and it is found that the calibration factor decreases when the bead depth increases.The method can be used to monitor the stability of the optical tweezers system.

Simulation-based comparison of noise effects in wavelength modulation spectroscopy and direct absorption TDLAS

A simulative investigation of noise effects in wavelength modulation spectroscopy (WMS) and direct absorption diode laser absorption spectroscopy is presented. Special attention is paid to the impact of quantization noise of the analog-to-digital conversion (ADC) of the photodetector signal in the two detection schemes with the goal of estimating the necessary ADC resolution for each technique. With laser relative intensity noise (RIN), photodetector shot noise and thermal amplifier noise included, the strategies used for noise reduction in direct and wavelength modulation spectroscopy are compared by simulating two respective systems. Results show that because of the combined effects of dithering by RIN and signal averaging, the resolutions required for the direct absorption setup are only slightly higher than for the WMS setup. Only for small contributions of RIN an increase in resolution will significantly improve signal quality in the direct scheme.

Radio-frequency waveform generator with time-multiplexing capabilities based on multi-wavelength pulse compression

We demonstrate a new photonically assisted reconfigurable radio-frequency waveform generator. The setup is based on phase modulating a multi-wavelength pulse source and subsequent compression in a dispersive medium. Under the appropriate conditions, we show that the photodetected electrical signal is broadband and coherent. Specifically, we show that this system allows for the synthesis of a reconfigurable finite-impulse-response filter where the number of filter taps is given by the number of wavelengths available from the multi-wavelength source and the reconfiguration is determined simply by their power and wavelength separation. We also show that this technique allows for time-multiplexing the synthesized waveforms, thus leading to an effective switching speed fixed by the clock rate. In particular, we show transitions between synthesized waveforms with a frequency content > 60 GHz in periods shorter than 100 ps.

Primary phase calibration of laser-vibrometers with a single laser source

A set-up for the calibration of a heterodyne laser-vibrometer is described. By a distinctive optical set-up it is possible to use the laser of the device under test as the single source for the calibration device. In this way many difficulties of the optical adjustment usually encountered in set-ups for laser-vibrometer calibration are avoided and exceptionally low measurement uncertainties are achieved.This article describes the set-up for the case of a commercially available device which is additionally modified to provide the means for primary traceability. The measurement results are discussed for the analogue output usually used in industrial applications as well as for the output of the photodetector signal, which is used if the device is part of a primary calibration system. Special attention is given to the provisions necessary to achieve low measurement uncertainties.

Data recording system of a dispersion interferometer based on a CO2 laser

The data recording system of a multichannel double-pass dispersion interferometer based on a CO2 laser is described. This system has been designed to record the linear density of plasmas in a real-time mode with a time discreteness of 4 μs and resolution 〈NeL〉 ∼ 0.34 × 1013 cm−2 (Ne is the electron component of the plasma density, and L is the plasma size in the wave propagation direction) in the range of linear density variations of up to 1017 cm−2. The system is built from unified recording modules that use fast ADCs to record the shape of photodetector and modulator signals and FPGA-based digital units of dataflow processing to form results of measurements. The single-channel recording module of the dispersion interferometer has been tested under actual experimental conditions of the GDL gas-dynamic trap and the TEXTOR tokamak (Julich, Germany).

Time profile analysis of photodetector signals in multi read-out calorimetry with GHz samplers

We present possible applications of DAQ systems based on Domino Ring Samplers (DRS) for time profile analysis of photodetector signals used for present and future multiple read-out calorimeters. The example of an 80-channel system in preparation for dual read-out calorimetry (DREAM) is described.

Subterahertz noise signal generation using a photodetector and wavelength-sliced optical noise signals for spectroscopic measurements

We present a photonic technique for generating a subterahertz time-continuous noise signal, which provides not only fine resolution and a potential for broadband measurements but also a higher output power resulting in high signal to noise ratio for the spectroscopy measurement. To increase the output noise power at subterahertz frequencies, the optical noise is sliced with the arrayed waveguide gratings (AWGs), resulting in the power level of −126.1 dBm/Hz at 350 GHz, which is approximately 17 dB higher than that without the AWGs. Using the implemented subterahertz noise signal source, we demonstrate a simple spectroscopic measurement of the H2O absorption line at around 380 GHz.