Source Intensity Fluctuations Research Articles

Field experimental mode-pairing quantum key distribution with intensity fluctuations.

The mode-pairing quantum key distribution (MP-QKD) protocol, which can achieve high key rates over long distances without phase locking, is a potential candidate for implementing intercity QKD. However, achieving precise control of the light source intensity in a field MP-QKD experiment is an exceedingly challenging task. In this Letter, we study the decoy-state MP-QKD protocol with light source intensity fluctuations. Furthermore, we propose a statistical analysis method based on the T-distribution to calculate confidence intervals of intensity fluctuations. Finally, in the field MP-QKD experiments, considering intensity fluctuations and the finite size effect, we obtain secure key rates of 1.03 × 10-6 bit/pair and 3.64 × 10-6 bit/pair for the symmetric (195.8 km) and asymmetric (127.7 km) cases, respectively.

Ratiometric optical oxygen sensor based on perovskite quantum dots and Rh110 embedded in an ethyl cellulose matrix

Ratiometric optical sensor gas sensing continues to develop optical sensing techniques and materials used in various industrial and environmental applications. This research focuses on a new ratiometric optical sensor using the development of new material of FAPbI3 perovskite QDs and a simple method to detect oxygen (O2) gas. FAPbI3 perovskite QDs are used as an indicator of oxygen gas, and rhodamine 110 (Rh 110) is a reference material in a ratiometric optical sensor. All of the sensing and reference materials are embedded in an ethyl cellulose (EC) matrix and coated on the surface of the filter paper. Using a UV LED with a central wavelength of 380 nm as the excitation light source, the emission spectra results show that the emission wavelengths of the oxygen-sensitive dye (O2) FAPbI3 perovskite QDs do not overlap with the Rh 110 reference signal. Thus, oxygen concentration can be measured using a ratiometric fluorescence reference-based approach. The sensing signal will be obtained in the presence of analyte gas in the ratiometric sensitivity of R0/R100, where R0 and R100 represent the luminescence intensity detected in 100% nitrogen and 100% oxygen concentrations, respectively. The experimental results show the optical oxygen sensor's sensitivity as R0/R100 = 12.7. In addition, the response time and recovery of the oxygen gas sensor produced are 75 s and 93 s, respectively. The use of a new type of FAPbI3 perovskite QDs material has been successfully developed in the optical ratiometric sensor for oxygen gas. The sensor proposed in this study has a low cost and easy fabrication process. The effect of spurious fluctuations in the excitation source intensity can be suppressed by the ratiometric optical sensing method.

Optical wavelength meter with machine learning enhanced precision

A photonic implementation of a wavelength meter typically applies an interferometer to measure the frequency-dependent phase shift provided by an optical delay line. This work shows that the information to be retrieved is encoded by a vector restricted to a circular cone within a 3D Cartesian object space. The measured data belong to the image of the object space under a linear orthogonal map. Component impairments result in broken orthogonal symmetry, but the mapping remains linear. The circular cone is retained as the object space, which suggests that the conventional conic section fitting for the wavelength meter application is a premature reduction of the object space from R3 to R2. The inverse map, constructed by a learning algorithm, compensates impairments such as source intensity fluctuation and errors in delay time, coupler transmission, and photoreceiver sensitivity while being robust to noise. The simple algorithm does not require initial estimates for all parameters except for a broad bracket of the delay; further, weak nonlinearity introduced by uncertain delay can be corrected by a robust golden search algorithm. The phase-retrieval process is invariant to source power and its fluctuation. Simulations demonstrate that, to the extent that the ten parameters of the interferometer model capture all significant impairments, a precision limited only by the level of random noise is attainable. Applied to measured data collected from a fabricated Si3N4 wavelength meter, greater than an order of magnitude improvement in precision compared with the conventional method is achieved.

Characterization of State-Preparation Uncertainty in Quantum Key Distribution

To achieve secure quantum key distribution, all imperfections in the source unit must be incorporated in a security proof and measured in the lab. Here we perform a proof-of-principle demonstration of the experimental techniques for characterising the source phase and intensity fluctuation in commercial quantum key distribution systems. When we apply the measured phase fluctuation intervals to the security proof that takes into account fluctuations in the state preparation, it predicts a key distribution distance of over 100 km of fiber. The measured intensity fluctuation intervals are however so large that the proof predicts zero key, indicating a source improvement may be needed. Our characterisation methods pave the way for a future certification standard.

Supercontinuum intensity noise coupling in Fourier transform photoacoustic spectroscopy.

We investigate the noise transfer mechanism from the light source intensity fluctuations to the acoustic signal in Fourier transform photoacoustic spectroscopy (FT-PAS). This noise coupling is expected to be reduced in FT-PAS compared with conventional Fourier transform spectroscopy, as only the specific spectral components that are absorbed by the probed sample contribute to the noise level. We employ an incoherent supercontinuum (SC) light source in our experiments and observe a linear relation between the sample gas concentration and the detected noise level, which significantly reduces the influence of the SC noise on the detection limit. Based on our experimental results, we derive a model for the noise level, which establishes the foundation for practical sensitive implementation of FT-PAS.

Diffraction-based overlay metrology using angular-multiplexed acquisition of dark-field digital holograms.

In semiconductor device manufacturing, optical overlay metrology measures pattern placement between two layers in a chip with sub-nm precision. Continuous improvements in overlay metrology are needed to keep up with shrinking device dimensions in modern chips. We present first overlay metrology results using a novel off-axis dark-field digital holographic microscopy concept that acquires multiple holograms in parallel by angular multiplexing. We show that this concept reduces the impact of source intensity fluctuations on the noise in the measured overlay. With our setup we achieved an overlay reproducibility of 0.13 nm and measurements on overlay targets with known programmed overlay values showed good linearity of R2= 0.9993. Our data show potential for significant improvement and that digital holographic microscopy is a promising technique for future overlay metrology tools.

Distortion-corrected phase demodulation using phase-generated carrier with multitone mixing.

We present a novel phase generated carrier (PGC) demodulation technique for homodyne interferometers which is robust to modulation depth variations and source intensity fluctuations. By digitally mixing the waveform with a multitone synthetic function (a linear combination of harmonics of the modulating signal), distortion can become negligible even in presence of large variations of the modulation depth. The technique only requires two mixers and can also provide the DC component of the phase in real time, without needing any previously recorded data or ellipse-fitting algorithms. We validate the technique with simulated waveforms and with experimental data from a wavelength metering experiment using an integrated unbalanced interferometer on-chip, showing that the technique corrects distortion without increasing the noise with respect to the standard PGC technique.

In-process roughness quality inspection for metal sheet rolling

A reliable in situ inspection of working rolls’ surface quality requires fast roughness measurements with >0.5 m2/min on a nanometer scale. A speckle-based measurement approach is realized using a high-speed pulse laser and FPGA-based image processing to inspect surface areas with a diameter of 1 cm without motion blur with 200 Hz. As a result, a roughness resolution below 0.5 nm is demonstrated under manufacturing conditions, which mainly results from light source intensity fluctuations. The surface quality inspection is finally validated on the rolling wheel in a reconditioning process to detect the tool roughness distribution and respective tool wear.

Performance of photoelectron spin polarimeters with continuous and pulsed sources: from storage rings to free electron lasers.

In this work the experimental uncertainties concerning electron spin polarization (SP) under various realistic measurement conditions are theoretically derived. The accuracy of the evaluation of the SP of the photoelectron current is analysed as a function of the detector parameters and specifications, as well as of the characteristics of the photoexcitation sources. In particular, the different behaviour of single counter or twin counter detectors when the intensity fluctuations of the source are considered have been addressed, leading to a new definition of the SP detector performance. The widely used parameter called the figure of merit is shown to be inadequate for describing the efficiency of SP polarimeters, especially when they are operated with time-structured excitation sources such as free-electron lasers. Numerical simulations have been performed and yield strong implications in the choice of the detecting instruments in spin-polarization experiments, that are constrained in a limited measurement time. Our results are therefore applied to the characteristics of a wide set of state-of-the-art spectroscopy facilities all over the world, and an efficiency diagram for SP experiments is derived. These results also define new mathematical instruments for handling the correct statistics of SP measurements in the presence of source intensity fluctuations.

Ratiometric, filter-free optical sensor based on a complementary metal oxide semiconductor buried double junction photodiode

We report a complementary metal oxide semiconductor integrated circuit (CMOS IC) with a buried double junction (BDJ) photodiode that (i) provides a real-time output signal that is related to the intensity ratio at two emission wavelengths and (ii) simultaneously eliminates the need for an optical filter to block Rayleigh scatter. We demonstrate the BDJ platform performance for gaseous NH3 and aqueous pH detection. We also compare the BDJ performance to parallel results obtained by using a slew scanned fluorimeter (SSF). The BDJ results are functionally equivalent to the SSF results without the need for any wavelength filtering or monochromators and the BDJ platform is not prone to errors associated with source intensity fluctuations or sensor signal drift.

Raw data normalization for a multi source inverse geometry CT system.

A multi-source inverse-geometry CT (MS-IGCT) system consists of a small 2D detector array and multiple x-ray sources. During data acquisition, each source is activated sequentially, and may have random source intensity fluctuations relative to their respective nominal intensity. While a conventional 3rd generation CT system uses a reference channel to monitor the source intensity fluctuation, the MS-IGCT system source illuminates a small portion of the entire field-of-view (FOV). Therefore, it is difficult for all sources to illuminate the reference channel and the projection data computed by standard normalization using flat field data of each source contains error and can cause significant artifacts. In this work, we present a raw data normalization algorithm to reduce the image artifacts caused by source intensity fluctuation. The proposed method was tested using computer simulations with a uniform water phantom and a Shepp-Logan phantom, and experimental data of an ice-filled PMMA phantom and a rabbit. The effect on image resolution and robustness of the noise were tested using MTF and standard deviation of the reconstructed noise image. With the intensity fluctuation and no correction, reconstructed images from simulation and experimental data show high frequency artifacts and ring artifacts which are removed effectively using the proposed method. It is also observed that the proposed method does not degrade the image resolution and is very robust to the presence of noise.

Optical sensor for reducing influence of intensity fluctuations on output stability

High-precision optical measurements depend on the optical sensor's stability. Light source's intensity fluctuations are the dominant cause for output instability of the sensor. In order to address this issue, we have developed an optical sensor for reducing influence of the intensity fluctuations on the output stability. The sensor comprises a light source generating smoothly modulated intensity, a measuring channel, a reference channel, and a beam splitter dividing the light source intensity between the channels. The reference channel opens the measuring channel when the light source intensity equals a specific value and the measuring channel converts the input intensity into the output of the sensor. The sensor was designed and studied experimentally at a wave- length of 635 nm and a modulation frequency of 285 Hz. With the sensor, the influence of the intensity fluctua- tions on the output stability was reduced 110 times and the relative rms instability of 4.5 × 10 −5 was obtained. Techniques to achieve the instability of 1.0 × 10 −5 are also shown.©TheAuthors.PublishedbySPIEunderaCreativeCommons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its

SPR based fibre optic biosensor for phenolic compounds using immobilization of tyrosinase in polyacrylamide gel

We present a surface plasmon resonance (SPR) based fibre optic biosensor for the detection of phenolic compounds (potentially bio-hazardous) in aqueous solution. The sensing probe was prepared by depositing silver film onto optical fibre core via thermal evaporation technique followed by the immobilization of enzyme, tyrosinase, also known as poly phenol oxidase (PPO), using gel entrapment technique. The response characteristics of the biosensor towards different phenolic compounds were determined using wavelength interrogation technique. Experimental results of SPR spectra show a red shift in the resonance wavelength on increase in the concentration of the phenol compounds in aqueous samples. Further, the sensitivity of the sensor decreases as the concentration of the phenolic compounds increases. The biosensor also manifests optimum activity at pH 7. The sensor has high sensitivity, wider operating range, reusability and reproducibility of results which make the sensor compatible for practical applications. Since the sensor is based on wavelength interrogation it is immune to source intensity fluctuation. Further, the probe is fabricated on optical fibre it has additional advantages such as probe miniaturization, low cost, capability of online monitoring and remote sensing, immunity to electromagnetic field and biocompatibility.

Extracting surface wave attenuation from seismic noise using correlation of the coda of correlation

AbstractExtracting surface wave travel time information from the cross‐correlation (CC) of seismic ambient noise has been a great success and remains fast growing. However, it is still challenging to exploit the amplitude content of the noise CC. Although spatial average is able to constrain somewhat meaningful attenuation using noise CC amplitudes, clear bias is observed when spatially varying attenuation is estimated with the traditional noise CC calculation methods. Perhaps the key lies in the development of novel techniques that can mitigate the effect of the uneven distribution of natural noise sources. In this paper, we propose a new method to use the correlation of the coda of correlation of noise (C3) for amplitude measurement. We examine the ability of the method to retrieve surface wave attenuation using data from selected line array stations of the USArray. By comparing C3‐derived attenuation coefficients with those estimated from earthquake data, we demonstrate that C3 effectively reduces bias and allows for more reliable attenuation estimates from noise. This is probably because of the fact that the coda of noise correlation contains more diffused noise energy, and thus, the C3 processing effectively makes the noise source distribution more homogeneous. When selecting auxiliary stations for C3 calculation, we find that stations closer to noise sources (near the coast) tend to yield better signal‐to‐noise ratios. We suggest to preprocess noise data using a transient removal and temporal flattening method, to mitigate the effect of temporal fluctuation of the noise source intensity, and to retain relative amplitudes. In this study, we focus our analysis on 18 s measurements.

Normalization schemes for ultrafast x-ray diffraction using a table-top laser-driven plasma source

We present an experimental setup of a laser-driven x-ray plasma source for femtosecond x-ray diffraction. Different normalization schemes accounting for x-ray source intensity fluctuations are discussed in detail. We apply these schemes to measure the temporal evolution of Bragg peak intensities of perovskite superlattices after ultrafast laser excitation.

Instrument independent diffuse reflectance spectroscopy

Diffuse reflectance spectroscopy with a fiber optic probe is a powerful tool for quantitative tissue characterization and disease diagnosis. Significant systematic errors can arise in the measured reflectance spectra and thus in the derived tissue physiological and morphological parameters due to real-time instrument fluctuations. We demonstrate a novel fiber optic probe with real-time, self-calibration capability that can be used for UV-visible diffuse reflectance spectroscopy in biological tissue in clinical settings. The probe is tested in a number of synthetic liquid phantoms over a wide range of tissue optical properties for significant variations in source intensity fluctuations caused by instrument warm up and day-to-day drift. While the accuracy for extraction of absorber concentrations is comparable to that achieved with the traditional calibration (with a reflectance standard), the accuracy for extraction of reduced scattering coefficients is significantly improved with the self-calibration probe compared to traditional calibration. This technology could be used to achieve instrument-independent diffuse reflectance spectroscopy in vivo and obviate the need for instrument warm up and post∕premeasurement calibration, thus saving up to an hour of precious clinical time.

Correction of wavefront reconstruction errors caused by light source intensity instability in phase-shifting interferometry

In the recording process of phase-shifting interferometry, intensity fluctuation caused by light source instability may occur and then introduce amplitude and phase errors to the reconstructed object wavefront. A simple direct algorithm of digital data processing to correct these errors is proposed and satisfactorily verified by both computer simulations and optical experiments. This method can work without specific knowledge of the source intensity fluctuation, and it reduces both the amplitude and phase errors of the reconstructed wavefront by about two orders of magnitude in computer simulations.

InGaAs Spectrometer and F-P Filter Combined FBG Sensing Multiplexing Technique

A novel fiber Bragg grating (FBG) sensing multiplexing system based on the combination of InGaAs spectrometer and Fabry-Perot (F-P) filter (InGaAs/F-P) is proposed. The multiplexing system only demodulates FBG sensors whose peak wavelengths are shifting. The demodulation can be sequenced according to each sensor's priority, latency time and wavelength shifting. What is more, the monitor section of that system is not influenced by environmental temperature and source intensity fluctuations. At the average signal repeat rate of 6Hz, the average delay time of the conventional wavelength- and spatial-division combined system, the long period grating (LPG) combined system and the InGaAs/F-P system are 303, 97, and 6 ms, respectively. Simulation analysis and experiment work demonstrated that the InGaAs/F-P system is more rational and smart than other counterparts.

Width-tunable pulse generation using four-wave mixing in bismuth based highly nonlinear fiber

This communication reports a simple configuration for the implementation of a compact and all-fiber based width-tunable pulse generator using four-wave mixing (FWM) effect in only 1.9-m of bismuth oxide based highly nonlinear fiber (Bi-HNLF). The width- tunable pulses are generated at repetition rates of 5 and 10 GHz. In the performed experiment, the pulsewidth of a 5 GHz repetition rate pulse train is tuned from 83 to 23 ps whereas the pulsewidth of a 10 GHz repetition rate pulse train is continuously tuned from 32 to 18 ps. An analytical model is presented for width-tunable pulse generation and the results agree well with the experimental findings. The effects of pump source timing jitter and intensity fluctuation on pulse generation are discussed.

Optical Ratiometric Sensor for Alcohol Measurements

The need for low‐cost, robust alcohol sensors has increased with the renewed interest in alternative fuels as well as high‐throughput screening of biological processes involving the production of ethanol. The goal of this research was to develop a miniaturized optical ratiometric ethanol sensor to be used for in situ measurements. The sensor is based on the fluorescent dye Nile Blue Chloride. When in solution, the dye exhibits a single fluorescence peak. However, a dual emission peak is observed upon physical immobilization of the dye in the hydrogel poly(ethylene glycol) dimethacrylate. The dual emission allows for ratiometric measurements, thus circumventing drawbacks associated with fluorescence intensity measurements such as signal variations due to dye bleaching, source intensity fluctuations, etc. In developing this sensor we investigated ethanol sensitivity; alcohol selectivity; response time; and cross‐sensitivity with pH, polarity, and ionic strength. We found that the sensor is sensitive to a broad range of ethanol concentrations, namely 5% to 90% v/v. Due to the hydrogel's restrictive pore size, the sensor is sensitive to short‐chain alcohols such as methanol, ethanol, and propanol, but lacks sensitivity to larger alcohols such as butanol and hexanol. We also found the sensor maintains full functionality after autoclaving. Sensor sensitivity to alcohol in solutions of varying ionic strength is negligible, whereas the solvent's polarity must be controlled to maintain meaningful results. The sensor is most sensitive in acidic and neutral environments, indicating promising use for yeast‐ based alcohol fermentations.