Wavelength Error Research Articles

Correction of the wavelength error in transmission of a full-color holographic 3D image

When a digital holographic image represented by a sampled wavefield is transmitted and the wavelength used in the three-dimensional (3D) display devices does not agree exactly with the wavelength of the original image data, the reconstructed 3D image will differ slightly from the original. This slight change is particularly problematic for full-color 3D images reconstructed using three wavelengths. A method is proposed here to correct the holographic image data and reduce the problems caused by wavelength mismatch. The effectiveness of the method is confirmed via theoretical analysis and numerical experiments that evaluate the reconstructed images using several image indices.

MMF-SMF-MMF optic surface plasmon resonance sensor based on hexagonal plate-like [formula omitted] structure

The manuscript introduces a fiber-optic MSM SPR sensor employing a hexagonal plate-like structure of Co(OH)2/TiO2/Au for surface plasmon resonance (SPR) sensing. This article aims to improve it through optimization of material composition and structure. The MSM structure SPR sensors were fabricated on the surface of single-mode fiber optic using chemical precipitation and physical vapor deposition, where Co(OH)2 and TiO2 served as sensitive materials. The experimental results demonstrate that the proposed sensor exhibited significantly higher sensitivity and broader application potential than the gold film control group and the gold film/TiO2 control group. Specifically, the gold film control group had a sensitivity of 1778.44 nm/RIU, while the sensitivity of the TiO2/Au control group was 2230.9 nm/RIU. In contrast, the Co(OH)2/TiO2/Au structure SPR sensor had a sensitivity of 3106.5 nm/RIU, which is far superior to the two control groups. Moreover, the results of repeated measurements indicated that the resonant wavelength error was only within 2 nm. These findings suggest that the Co(OH)2/TiO2/Au structure SPR sensor has promising stability and repeatability, making it suitable for applications in various fields, including chemical sensing and biological sensing.

Phase space analysis of two-wavelength interferometry.

Multiple wavelength phase shifting interferometry is widely used to extend the unambiguous range (UR) beyond that of a single wavelength. Towards this end, many algorithms have been developed to calculate the optical path difference (OPD) from the phase measurements of multiple wavelengths. These algorithms fail when phase error exceeds a specific threshold. In this paper, we examine this failure condition. We introduce a "phase-space" view of multi-wavelength algorithms and demonstrate how this view may be used to understand an algorithm's robustness to phase measurement error. In particular, we show that the robustness of the synthetic wavelength algorithm deteriorates near the edges of its UR. We show that the robustness of de Groot's extended range algorithm [Appl. Opt.33, 5948 (1994)APOPAI0003-693510.1364/AO.33.005948] depends on both wavelength and OPD in a non-trivial manner. Further, we demonstrate that the algorithm developed by Houairi and Cassaing (HC) [J. Opt. Soc. Am. A26, 2503 (2009)JOAOD60740-323210.1364/JOSAA.26.002503] results in uniform robustness across the entire UR. Finally, we explore the effect that wavelength error has on the robustness of the HC algorithm.

The Effect of Spatial Velocity Gradients on Block-Matching Accuracy for Ultrasound Velocimetry

Block matching serves as the foundation for ultrasound velocimetry techniques such as blood speckle tracking and echo-particle image velocimetry. Any spatial velocity gradients (SVGs) inside a block-matching pair will result in tracking error, due to both the finite block size and the ultrasound point-spread-function. We assess, using an in silico sinusoidal flow phantom, the effect of SVG magnitude and beam-to-flow angle on block-matching bias and precision. Secondarily we assess the effect that SVGs have on velocimetry bias when using angled plane-wave compounding. The magnitude and angle of SVGs were varied by adjusting the wavelength and direction of a sinusoidal flow profile. Scatterers displaced by this flow profile were used for simulating ultrasound radio frequency data at discrete time points. After beamforming, the 2-D flow field was estimated using block matching. Two imaging sequences were tested, a single plane-wave and a three-angled plane-wave. Smaller sinusoidal flow wavelengths resulted in increased bias and reduced precision, revealing an inverse relationship between sinusoidal flow wavelength and tracking error, with median errors ranging from 69%-90% for the smallest flow wavelengths (highest SVGs) down to 3%-5% for the largest (lowest SVGs). The SVG angle was also important, in which lateral SVGs (with axially oriented flows) resulted in significant speckle decorrelation and high tracking errors in regions with high SVGs. Conversely, axial SVGs (laterally oriented flow) experienced higher bias in the peak velocity regions of the flow profile. Coherent compounding resulted in higher velocity errors than using a single transmission for lateral SVGs but not for axial SVGs. The highest SVGs that could be measured with ≤10% error was when the sinusoidal flow wavelength was less than 20 times the ultrasound pulse wavelength. The clinical significance is that the high SVGs present in high kinetic energy flows, such as severe carotid stenosis and aortic regurgitation, will limit the ability to accurately quantify the velocities in these flow structures.

LED array microscopy system correction method with comprehensive error parameters optimized by phase smoothing criterion.

LED array microscopy is a novel computational imaging technique that can achieve two-dimensional (2D) phase imaging and three-dimensional (3D) refractive index imaging with both high resolution and a large field of view. Although its experimental setup is simple, the errors caused by LED array position and light source central wavelength obviously decrease the quality of reconstructed results. To solve this problem, comprehensive error parameters optimized by the phase smoothing criterion are put forward in this paper. The central wavelength error and 3D misalignment model with six freedom degree errors of LED array are considered as the comprehensive error parameters when the spatial positional and optical features of arbitrarily placed LED array are unknown. Phase smoothing criterion is also introduced to the cost function for optimizing comprehensive error parameters to improve the convergence results. Compared with current system correction methods, the simulation and experimental results show that the proposed method in this paper has the best reconstruction accuracy, which can be well applied to an LED array microscope system with unknown positional and optical features of the LED array.

Graphene/Polyaniline Film Optical Fiber Ammonia Gas Sensor With Excellent Sensing Performance

The possibility to improve the detection index of the optical ammonia gas sensors on the basis of the graphene/polyaniline (graphene/PANI) coated Mach–Zehnder interferometric optical fiber structure with etched thinned core fiber(e-TCF) is investigated. Based on the analysis of the output wavelength, a significant increase in sensitivity and stability of the ammonia sensors is achieved by using TCF. Experimental results show that its sensitivity is -27.8 pm/ppm, the response time is 32 s, dip wavelength error is lower than ±0.02 nm, and the dip intensity error is lower than ±0.002 dB in the stability test. This research illustrates that the proposed sensor has numerous advantages, including small size, strong anti-electromagnetic interference, and excellent repeatability characteristics. Furthermore, it can be applied in biomedical detection applications as it can improve the detection resolution of ammonia concentration at room temperature.

Optical non-volatile correction of SERS wavelength using optical pumping

In this paper, we propose a reconfigurable two-dimensional photonic crystal (PC) made from a new ultralow loss phase change material for detecting and imaging applications of surface-enhanced Raman scattering (SERS). The proposed all-dielectric structure is composed of identical holes periodically distributed on Sb2S3 as a substrate, tuned by optical pumping. The proposed PC is investigated using full-wave simulation of the CST with the finite-difference frequency domain method over a wide bandwidth of optical wavelengths. In this study, compensation for the error of the Fano resonance wavelength due to the fabrication process is realized through tuning optical pumping applied to the configuration. Also, the numerical results show the designed PC supports two high-quality Fano resonance modes, leading to uniform and high field enhancement with a SERS enhancement factor of 1.23 × 1012, which is significant for the application of SERS enhancement.

Polarized light diffuse reflectance FT-NIR MEMS spectrometer enabling the detection of powder samples through a thin plastic layer.

Polarized scattered light Fourier transform infrared (FTIR) spectroscopy is used for measuring the absorbance of highly scattering materials overcoming the multiple scattering effect. It has been reported for in vivo for biomedical applications and in-field for agricultural and for environmental monitoring. In this paper, we report a polarized light microelectromechanical system (MEMS)-based FTIR in the extended near infrared (NIR) that utilizes a bistate polarizer in a diffuse reflectance measurement setup. The spectrometer is capable of distinguishing between single backscattering from the uppermost layer and multiple scattering from the deep layers. The spectrometer has a spectral resolution of 64c m -1 (about 16nm at a wavelength of 1550nm) and operates in the spectral range of 4347c m -1 to 7692c m -1 (1300nm to 2300nm). The technique implies de-embedding of the MEMS spectrometer polarization response by normalizing its effect; this is applied on three different samples: milk powder, sugar, and flour in plastic bags. The technique is examined on different scattering size particles. The scattering particles diameter's range is expected to vary from 10µm to 400µm. The absorbance spectra of the samples are extracted and compared to the direct diffuse reflectance measurements of the samples, showing good agreement. By using the proposed technique, the calculated error for the flour was decreased from 43.2% to 2.9% at 1935nm wavelength. The wavelength error dependence is also reduced.

The Temperature Dependence of Hot Prograde Flows in Solar Active Regions

Using simultaneous observations from the EUV Variability Experiment (EVE) and imaging from the Atmospheric Imaging Assembly (AIA), we characterise the temperature dependence of apparent hot flows in solar active regions. The EVE instrument performs Sun-as-a-star spectroscopy and is composed of two spectrographs: MEGS-A and MEGS-B (Multiple EUV Grating Spectrograph-A, -B). It is known that EVE can measure wavelength shifts and thus can observe relative Doppler velocities in solar atmospheric plasmas over an extended temperature range. However, MEGS-A is affected by a known astigmatism effect (Chamberlin: Solar Phys.291, 1665, 2016); inhomogeneities in EUV brightness on the solar surface result in purely instrumental wavelength errors. We validate our methods by independently quantifying this effect and comparing to Chamberlin’s results, and we explore the wavelength dependence as an extension of his formula as derived for He ii 304 Å. MEGS-B is unaffected by this instrumental effect in any case, and this has allowed us to find evidence of hot prograde flows in active regions. Using our image-based models for the astigmatism and flows, we independently confirm our original MEGS-B result. We now extend our knowledge of the temperature dependence of these flows via the additional Fe emission lines available in MEGS-A. We find a monotonic increase of apparent flow speed with temperature up through lines of Fe xvi, nominally formed at about 6.4 MK.

Fiber Optic Voltage Sensor Based on Capacitance Current Measurement With Temperature and Wavelength Error Correction Capability

Traditional optical voltage transformers (OVTs) based on electro-optical and inverse piezoelectric effects are gradually exposing their accuracy and reliability issues. In contrast, fibers for measuring electricity have unique properties and significant advantages in the high-voltage power industry, especially fiber optic current sensor (FOCS), which has been widely used in the field of high-voltage measurement. As a result, a novel fiber optical voltage sensor (FOVS) is proposed, which uses FOCS to measure the current flowing through the capacitive voltage divider (CVD) and then calculates the primary voltage proportional to it. In order to solve the inherent temperature- and wavelength -dependent errors and achieve high accuracy, a novel closed-loop signal processing method, which aims to minimize the influence of temperature-sensitive components such as CVD, quarter waveplate, and sensing fiber on the measurement accuracy of the system, is presented. A 110-kV FOVS prototype with a rated voltage of 110/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$({3})^{1/2}$ </tex-math></inline-formula> kV and a rated frequency of 50 Hz is developed and tested. The results show that after temperature and wavelength correction, the accuracy reaches the metering class of 0.2% and protection class of 3P specified in GB/T20840.7-2007

Resolving Intrinsic Modulation Spectral Lines from Electro-Optic Modulation Spectra Based on Boosted Iterative Deconvolution

Optical spectrum analysis is the most direct and effective method for characterizing electro-optic modulation spectra. According to the Rayleigh criterion, the best resolution of an optical spectrum analysis is limited by the point spread function of an optical spectrum analyzer (OSA) and the relative intensity of closely spaced spectral lines. In this paper, we propose a boosted iterative deconvolution (BID) method to resolve the intrinsic modulation of spectral lines from the measured optical carrier and modulation spectra. In our scheme, the electro-optic modulation spectrum is considered the convolution of the optical carrier spectrum and the intrinsic δ-function modulation spectrum, and the BID method enables fast and accurate extraction of the δ-function spectral lines from the measured modulation spectrum. The proof-of-concept experiment demonstrates that our method can improve the resolution of OSA by 10–30 p.m. at different relative intensities, with a best resolution of 10 p.m. in the iso-intensity case and wavelength errors of less than 2 p.m., which largely improves the measurement resolution and accuracy of the modulation spectrum.

Multimode interferometric sensor based on the no-core tellurite optical fiber for cryogenic temperature detection.

In this paper, a no-core tellurite optical fiber (NCTOF)-based sensor was proposed for cryogenic temperature detection in refrigeration process. The ultraviolet adhesive (UVA) dual-curing method was operated to stablish a sandwich-like composite structure, in which a section of NCTOF was compactly sandwiched between two segments of silica fiber to form multimode interference. The temperature sensing characteristics in cryogenic range were experimentally investigated by monitoring the transmission spectral movement, where a high sensitivity of 105.6 pm/°C was achieved in the range of -20-0 °C and 51.6 pm/°C in the range of -20-25 °C. The excellent performance was consistent with the simulation analysis. The maximum repeatability standard deviation and stability wavelength error of the sensor are 0.9799 pm/°C and 0.1676 nm, respectively. To the best of our knowledge, this is the first report on using tellurite optical fibers for cryogenic temperature detection, and the UVA dual-curing method provides a reliable solution for the integration and practical application of tellurite optical fiber. The proposed sensor is simple in structure, easy in fabrication, low in cost and excellent in performance. It can be expected to be used in food refrigeration, air-conditioning engineering, medical and health, industrial production, etc.

High-precision and wide-wavelength range FBG demodulation method based on spectrum correction and data fusion.

Optical fiber sensing technology plays an important role in the application of the sensing layer of the Internet of Things. The core of this technology is the demodulation of the fiber Bragg grating (FBG) sensing system. Since the FBG sensor utilizes the wavelength change to respond to the measured size, it is of great significance to improve the accuracy of the FBG wavelength demodulation. However, the demodulation performance of the current FBG wavelength demodulation method still has much room for improvement in terms of accuracy and stability. To this end, we propose a composite gas cell demodulation scheme based on spectrum correction and data fusion by using differential photodetectors, fitting extrapolation, data fusion methods, etc. The issue of low demodulation accuracy arising due to noise, temperature drift, spectral distortion, etc., was addressed to improve the demodulation performance of the FBG. In the experiment, four FBGs with different center wavelengths were used to verify their demodulation accuracy in the range of 1510-1590 nm. The maximum repeatability error of the FBG wavelength was measured to be 2.51 pm, and the linearity was as high as 99.9% or more; under the working environment of -20 °C to 60 °C, the maximum full-scale error did not exceed ±1.71 pm, which is improved by 54.3% compared with the traditional method.

Design considerations of photonic lanterns for diffraction-limited spectrometry

The coupling of large telescopes to astronomical instruments has historically been challenging due to the tension between instrument throughput and stability. Light from the telescope can either be injected wholesale into the instrument, maintaining high throughput at the cost of point-spread function (PSF) stability, or the time-varying components of the light can be filtered out with single-mode fibers (SMFs), maintaining instrument stability at the cost of light loss. Today, the field of astrophotonics provides a potential resolution to the throughput-stability tension in the form of the photonic lantern (PL): a tapered waveguide that can couple a time-varying and aberrated PSF into multiple diffraction-limited beams at an efficiency that greatly surpasses direct SMF injection. As a result, lantern-fed instruments retain the stability of SMF-fed instruments while increasing their throughput. To this end, we present a series of numerical simulations characterizing PL performance as a function of lantern geometry, wavelength, and wavefront error (WFE), aimed at guiding the design of future diffraction-limited spectrometers. These characterizations include a first look at the interaction between PLs and phase-induced amplitude apodization (PIAA) optics. We find that Gaussian-mapping beam-shaping optics can enhance coupling into 3-port lanterns but offer diminishing gains with larger lanterns. In the y and J band (0.97–1.35 µm) region, with moderately high WFE ( ∼ 10 % Strehl ratio), a 3-port lantern in conjunction with beam-shaping optics strikes a good balance between pixel count and throughput gains. If pixels are not a constraint, and the flux in each port will be dominated by photon noise, then larger port count lanterns will provide further coupling gains due to a greater resilience to tip-tilt errors. Finally, we show that lanterns can maintain high operating efficiencies over large wavelength bands where the number of guided modes at the lantern entrance drops, if care is taken to minimize the attenuation of weakly radiative input modes.

A design method of broadband metalens using time-domain topology optimization

Flat metalenses have attracted attention due to an increasing demand for compact electromagnetic devices. For such applications, broadband metalenses are highly desirable; however, conventional metalenses show relatively narrow band operation. Here, we propose a design method of free-form metalenses using topology optimization to operate with enhanced bandwidths. In contrast with preceding reports of topology optimization methods for metalenses, we developed a topology optimization method based on the time domain formulation to deal with broadband frequencies simultaneously. For this purpose, a group delay of optical pulses in the time domain, which is equivalent to the broadband phase matching condition in the frequency domain, is employed in the objective function. A level set based topology optimization method is applied to obtain a clear optimal configuration. To demonstrate the effectiveness of the proposed method, we provide design examples of metalens unit cells at millimeter frequency. We confirm that optimized unit cells of metalenses show superior performance compared to the conventional unit cells for both transmittance efficiency and phase error in broadband wavelength.

Broadband Mode (De)Multiplexer Formed With Phase-Matching of Multimode Access-Waveguide

A broadband mode (de)multiplexer [(De)MUX] is proposed and experimentally demonstrated based on a triple-waveguide coupler (TWC) with the phase-matching of a multimode access-waveguide. The tolerance to the operating wavelength and fabrication error of the proposed mode (De)MUX can be relaxed with the aid of the wider access-waveguide and the middle waveguide. The optimized mode (De)MUX is with a coupling length of $48~\mu $ m and a broad bandwidth of >122 nm with the mode crosstalk of <−15 dB. The optimized device was fabricated on a 220-nm-thick silicon-on-insulator platform and the measured results indicate that the operating bandwidth is 100 nm with the mode crosstalk lower than −14 dB.

A high-frequency non-resonant elliptical vibration-assisted cutting device for diamond turning microstructured surfaces

In recent years, research has begun to focus on the development of non-resonant elliptical vibration-assisted cutting (EVC) devices, because this technique offers good flexibility in manufacturing a wide range of periodic microstructures with different wavelengths and heights. However, existing non-resonant EVC devices for diamond turning can only operate at relatively low frequencies, which limits their machining efficiencies and attainable microstructures. This paper concerns the design and performance analysis of a non-resonant EVC device to overcome the challenge of low operational frequency. The structural design of the non-resonant EVC device was proposed, adopting the leaf spring flexure hinge (LSFH) and notch hinge prismatic joint (NHPJ) to mitigate the cross-axis coupling of the reciprocating displacements of the diamond tool and to combine them into an elliptical trajectory. Finite element analysis (FEA) using the mapped meshing method was performed to assist the determination of the key dimensional parameters of the flexure hinges in achieving high operational frequency while considering the cross-axis coupling and modal characteristics. The impact of the thickness of the LSFH on the sequence of the vibrational mode shape for the non-resonant EVC device was also quantitatively revealed in this study. Moreover, a reduction in the thickness of the LSFH can reduce the natural frequency of the non-resonant EVC device, thereby influencing the upper limit of its operational frequency. It was also found that a decrease in the neck thickness of the NHPJ can reduce the coupling ratio. Experimental tests were conducted to systematically evaluate the heat generation, cross-axis coupling, modal characteristics and diamond tool’s elliptical trajectory of a prototype of the designed device. The test results showed that it could operate at a high frequency of up to 5 kHz. The cross-axis coupling ratio and heat generation of the prototype are both at an acceptable level. The machining flexibility and accuracy of the device in generating microstructures of different wavelengths and heights through tuning operational frequency and input voltage have also been demonstrated via manufacturing the micro-dimple arrays and two-tier microstructured surfaces. High-precision microstructures were obtained with 1.26% and 10.67% machining errors in wavelength and height, respectively.

High-accuracy measurement system for the refractive index of air based on a simple double-beam interferometry.

A measurement system based on a simple double-beam interferometry is built to realize the measurement of air refractive index with high accuracy. The basic principle of the system is that, through measuring the change of optical path difference caused by rapid and smooth vacuumization, measurement of refractive index of air is converted to length measurement. Error correction and signal processing are studied to ensure high-accuracy measurement of the refractive index of air. Three applicable methods are used in system. The system based on the methods realize the subdivision and counting of interference fringe by software with three-error correction, error compensation for the end-window plates' thickness change caused by vacuumization, steady realization of high vacuum conditions. To verify the accuracy and reliability of the system, the measurement results are compared with that obtained from the method based on empirical Edlén's formula. Analysis result shows that the expanded measurement uncertainty of the system is U = 5×10-9, with k = 2. The system can be used to compensate the laser wavelength error caused by the refractive index of air with high accuracy.

An optical fiber sensor based on polyimide coated fiber Bragg grating for measurement of relative humidity

Humidity is an important parameter in many industry fields and accurate humidity measurement is of great significance to improve production efficiency and ensure product quality. This paper presents a sensing model and scheme for utilizing thermoplastic polyimide (PI) coated fiber Bragg grating (FBG). The humidity sensitive PI layer was firstly prepared and coated on the FBG. The humidity calibration experiment was designed to verify the sensor performance based the saturated salt solution method. The experimental results show this FBG humidity sensor can work steady in the relative humidity (RH) condition ranging from 11%RH to 83% RH, with the sensitivity of the sensor less than 2 pm/% RH and measurement uncertainty of ±1% RH in the temperature range of 30 °C to 70 °C. In order to solve the problem that the PI-coated FBG is both sensitive to the humidity and temperature (cross sensitivity problem), a novel method of temperature compensation has been proposed. The method uses the character that the coefficients of expansion of the PI-coated layer for humidity and temperature are linearly superimposed and obtains the temperature compensation coefficient by linear interpolation of the function relationship between the measured temperature and the FBG central wavelength shift. The analysis of experimental data shows that within the temperature variation range of 20 °C, this temperature compensation method can effectively guarantee the average wavelength errors within 0.03 nm without reference grating. In this way, it can extend the FBG humidity measurement under environmental temperature up to 90 °C making it possible for application in the measurement the humidity in the high temperature environment.

Laser wavelength metrology with low-finesse etalons and Bayer filters

We present a wavelength meter with picometer-scale resolution based on etaloning effects of inexpensive glass slides and the built-in color filters of a consumer grade CMOS camera. After calibrating the device to a commercial meter, we tested the device's calibration stability using two tunable visible lasers for a period of over 16 days. The wavelength error over that entire period has a standard deviation of 5.29 parts per million (ppm) about a most probable error of 0.90 ppm. Within 24 hours of calibration, this improves to 0.04 ppm with a standard deviation of 3.94 ppm.