Measured Wavelength Range Research Articles

Setup for characterising the spectral responsivity of Fabry–Pérot-interferometer-based hyperspectral cameras

Hyperspectral cameras capture the spectral power distribution of the objects in the imaged view via dozens of narrow-band spectral channels of the camera. Knowledge of the spectral responsivity of the channels is essential when interpreting the acquired hyperspectral data and assessing its reliability. The spectral responsivity of the camera channels may vary within the image area. This paper presents a measurement setup and data analysis routine for characterising the spectral responsivity of a hyperspectral camera. This method was used to characterise the spectral responsivity of a Fabry–Pérot-interferometer-based hyperspectral camera. The characterisation method implemented in this study was able to reveal several channel leaks in the measured wavelength range. In the image area there is an approximately 1.5 nm shift in the channel wavelengths, and up to 10% variation in the channel bandwidths. The expanded uncertainties (k = 2) for the measured channel bandwidths, sensitivities and wavelengths were 7.9%, 9.5% and 0.64 nm, respectively.

Extension of the Measurable Wavelength Range for a Near-Infrared Spectrometer Using a Plasmonic Au Grating on a Si Substrate.

In this paper, we proposed near-infrared spectroscopy based on a Si photodetector equipped with a gold grating and extended the measurable wavelength range to cover 1200–1600 nm by improving a spectrum derivation procedure. In the spectrum derivation, photocurrent data during alteration of the incidence angle of the measured light were converted using a responsivity matrix R, which determines the spectroscopic characteristics of the photodetector device. A generalized inverse matrix of R was used to obtain the spectrum and to fit a situation where multiple surface plasmon resonance (SPR) peaks appeared in the scanning range. When light composed of two wavelengths, 1250 nm and 1450 nm, was irradiated, the two wavelengths were distinctively discriminated using the improved method.

Ellipsometric study on optical properties of hydrogen plasma-treated aluminum-doped ZnO thin film

Aluminum-doped zinc oxide (AZO) thin films were prepared by radio frequency (RF) sputtering at room temperature, and then post-treated by hydrogen (H2) plasma at different durations. After H2 plasma treatment under the condition of 10 W, 200 °C and 3.0 Hours, the resistivity showed a dramatically decrease from 1.6 Ω cm to 3.4 × 10−3 Ω cm, while the transmittance at the wavelength of 550 nm was improved from 90.5% to 96.0%. The optical constants of H2 plasma-treated AZO thin films were detailed characterized by a varied angle spectroscopic ellipsometer. The results show that the refractive index n decreases in the entire measured wavelength range of 350–1100 nm, while the extinction coefficient k decreases in the short wavelength range and changes negligibly at the long wavelength range. These results can provide guidelines for the design and optimization of AZO thin film-based optoelectronic applications.

Polydimethylsiloxane: Optical properties from 191 to 1688 nm (0.735–6.491 eV) of the liquid material by spectroscopic ellipsometry

Polydimethylsiloxane (PDMS) is an important polymer with numerous applications. Herein, the authors report the optical function(s) of PDMS from 191 to 1688 nm as determined from reflection spectroscopic ellipsometry (SE) and transmission ultraviolet-visible data. Two commercial samples of liquid PDMS (PDMS700 and PDMS2000) with molecular weights of 700–1500 g/mol and 2000–3500 g/mol, respectively, were analyzed. Both samples were linear polymers terminated with silanol groups. The optical functions determined from the two materials were essentially identical. Both the reflection and transmission measurements obtained from these materials required special experimental considerations. For the reflection SE measurements, these included roughening (frosting) the inside of the vessel that held PDMS and the need to level the instrument instead of the samples. The transmission measurements were obtained via a dual cuvette approach that eliminated the effects of the cuvettes and their interfaces. In addition to analyzing the data from the individual samples, the SE data from the samples were considered together in a multisample analysis (MSA). Because both samples of PDMS were transparent over the measured wavelength range, and because of the relatively wide wavelength range considered, the optical functions here were fit with Sellmeier models. This produced a good fit for the MSA with a mean squared error value of 1.68. The optical functions obtained in this work agreed well with previously reported values. For example, for the MSA, the authors obtained the following nx values, where x is the wavelength in nanometers: n300 = 1.443, n500 = 1.407, and n1000 = 1.393.

Spectral comparison of diffuse PAR irradiance under different tree and shrub shading conditions and in cloudy days

Spectral Solar Photosynthetically Photon Flux Density (PPFD) (380 to 780 nm) reaching the surface of a plant in different lighting conditions has been analyzed in order to better understand the different photosynthetic performance of plants depending on their spatial situation and the vegetation surrounding.A comparison between the shadow of several trees in a sunny day and the case of a cloudy day in an open space has been studied. Three isolated trees (a palm tree, an olive tree and a shrub oleander) and a tipuana grove have been studied.The study has been developed in Valencia (Spain) during January and February 2017. A portable Asensetek Standard ALP-01 spectrometer with a measurement wavelength range of 380 to 780 nm, has been used. Conditions with higher PPFD received are found to be, apart from those of a sunny day, those for cloudy day (with a spectral maximum in the Green region of the spectrum), and those for individual trees and shrub shadows in a sunny day (with a spectral maximum in the Blue region). The case in which less amount of PPFD is received is that under the shadow of tipuana grove (with a spectral maximum in the Infrared region of the spectrum). In fact the order of magnitude in which the PPFD in a cloudy day exceeds the PPFD under the tipuana grove shade is up to 20.

Silver-Stabilized Guanine Duplex: Structural and Optical Properties.

Recent experimental duplexes of DNA stabilized by Ag cations, pairing homostrands of guanine-guanine, cytosine-cytosine, adenine-thymine, and thymine-thymine, display much higher stability than the Watson-Crick paired DNA duplexes; these broaden the range of applications for DNA nanotechnology. Here we focus on silver-stabilized guanine duplexes in water. Using hybrid quantum mechanics/molecular mechanics simulations, we propose an atomic structure for the Ag+-mediated guanine duplex with two nucleobases per strand, G2-Ag2+-G2. We then compare experimental and time-dependent density functional theory-simulated electronic circular dichroism (ECD) spectra to validate our results. Both experimental and simulated ECD share two negative peaks around 220 and 280 nm, with no positive signal in the measured wavelength range. We found that the left- or right-handed disposition of bases in the structure has a decisive effect on the signs of the ECD. We conclude that G2-Ag2+-G2 is left-hand-oriented, and extrapolation of this orientation to longer strands gives rise to a left-hand-oriented parallel helix stabilized by interplanar H bonds.

Interannual variations in aerosol microstructure parameters according to data of sun photometer measurements in Tomsk

Results of studying the time variations in aerosol microstructure parameters retrieved by inverting the spectral measurements of the aerosol optical depth are presented. The input data were obtained at the Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences using SP-type sun photometers during periods of observations in 2003–2006 and 2011–2014. During the first period, aerosol optical depth was measured at 13 wavelengths in the range 0.37–4 μm. In the second period, the upper boundary of the wavelength range of measurements was 2.14 μm. The total amount of data processed had been more than 7000 hourly average spectra. The aerosol microstructure parameters, such as the geometric cross section, volume concentration, and average particle radius, were analyzed.

Wide-field mid-infrared hyperspectral imaging of adhesives using a bolometer camera

By combining a bolometer detector with an imaging-type interferometer, an inexpensive, easy-to-handle wide-field mid-infrared hyperspectral imaging apparatus was produced. We measured the distributions of four types of thin adhesive layers on an aluminium plate and analysed the results using correlation coefficients to visualise the distribution of various adhesives that cannot be discerned by the naked eye or conventional methods such as visible/near-infrared spectroscopic/fluorescent photography. The measurement wavelength range, obtained spectrum’s wavenumber resolution, and measurement time was 8–14 μm, about 9 cm−1, and about 30 s, respectively. Using conventional methods, adhesives could not be distinguished from the others. By using this method, we found that adhesives could be precisely distinguished by setting an appropriate threshold value for the correlation coefficient. Thus, our approach can accurately measure the spatial distribution of different types of adhesive that cannot be discriminated by conventional methods.

Single walled carbon nanotube/Si heterojunctions for high responsivity photodetectors

Single walled carbon nanotube/n-Si (SWCNT/n-Si) hetero-junctions have been obtained by depositing SWCNT ultra-thin films on the surface of an n-Si substrate by dry transfer method. The as obtained junctions are photo sensitive in the measured wavelength range (300–1000 nm) and show zero bias responsivity and detectivity values of the order of 1 A W−1 and 1014 Jones respectively, which are higher than those previously observed in carbon based devices. Moreover, under on–off light excitation, the junctions show response speed as fast as 1 μs or better and noise equivalent powers comparable to commercial Si photomultipliers. Current–voltage measurements in dark and under illumination suggest that the devices consist of Schottky and semiconductor/semiconductor junctions both contributing to the fast and high responses observed.

Genetic-algorithm-optimized wideband on-chip polarization rotator with an ultrasmall footprint.

Polarization control of light waves is an important technique in optical communication and signal processing. On-chip polarization rotation from the fundamental transverse-electric (TE00) mode to the fundamental transverse-magnetic (TM00) mode is usually difficult because of their large effective refractive index difference. Here, we demonstrate an on-chip wideband polarization rotator designed with a genetic algorithm to convert the TE00 mode into the TM00 mode within a footprint of 0.96 μm ×4.2 μm. In simulation, the optimized structure achieves polarization rotation with a minimum conversion loss of 0.7dB and the 1-dB bandwidth of 157nm. Experimentally, our fabricated devices have demonstrated the expected polarization rotation with a conversion loss of ∼2.5 dB in the measured wavelength range of 1440-1580nm, where the smallest value reaches ∼2 dB. The devices can serve as a generic approach and standard module for controlling light polarization in integrated photonic circuitry.

Investigations of thermal annealing role on the optical properties of Zn-In-Se thin films

Zn-In-Se (ZIS) thin films were prepared by sequential evaporation of its elemental sources on the glass substrates. The effect of thermal annealing under nitrogen environment on the optical properties of the films was discussed. In addition to the comparative study of three different annealing temperatures, the results were analyzed by relating with their structural and compositional characteristics. The optical analyses were based on the observed interference fringes on their transmission spectra of the films. The refractive indices were calculated by means of envelope method (EM) and the continuity of the refractive indices was evaluated by three-term Cauchy fitting process. From the results of the refractive index calculations, the real and imaginary part of the dielectric constant were determined. The optical absorption coefficients of the films were found in the range of 103–104cm−1 over the visible and near-infrared region and by using these values, the extinction coefficients were calculated. Moreover, the band gap values were calculated from the corresponding Tauc plots, and the refractive index dispersion over the measured wavelength range was investigated with single-oscillator model (SOM) and the related parameters were obtained.

Direct fabrication of cone array microstructure on monocrystalline silicon surface by femtosecond laser texturing

Improving the utilization ratio of sunlight is a key factor for the development of solar cell. In this paper, a quasi uniform cone-array-like microstructure was directly fabricated on monocrystal silicon surface in atmosphere by using an alternative femtosecond laser texturing technique. The fabricated cone array like microstructure has a spike depth of up to 8 μm and is able to substantially reduce light reflection due to the effective optical coupling between the incident light with the cone array like microstructure. Compare to planar silicon wafer, the relative reflectance of the cone array structure has been decreased to less than 9% in the measured wavelength range from 400 to 1000 nm. This may be a promising method for the optimal fabrication of surface-microstructure photovoltaic material, such as solar cell, infrared sensor, etc.

Birefringence of the new fluoride borates Ba2Na3[B3O6]2F and Ba7(BO3)4−yF2+3y in the Na, Ba, B//O, F quaternary reciprocal system

The birefringence of the new Ba2Na3[B3O6]2F (BNBF) (P63/m) and Ba7(BO3)4−yF2+3y (P63) phases has been investigated. Coefficients of the Sellmeier equations have been determined. Parallel [B3O6]3− rings in the Ba2Na3[B3O6]2F structure generate the major anisotropic polarizabilities and produce large birefringence Δn=0.1097−0.0428 from 350nm to 5μm, comparable to that of commercial birefringent crystal α-BaB2O4. A new flux for growing a high quality BNBF crystal has been proposed. In the measured wavelength range from 266nm to 1.7μm noncentrosymmetric phase Ba7(BO3)4−yF2+3y (y=0.49) exhibits low birefringence Δn=0.0111−0.0037 which can be accounted for non-coplanar arrangement of the anionic groups in the structure. Low birefringence prevents the use of this crystal for nonlinear optical applications, since phase-matching conditions for second harmonic generation can not be reached.

Integrated High-Performance Two-Stage Ratiometric Wavelength Monitors on Silicon

We design and fabricate an integrated high-performance two-stage ratiometric wavelength monitors (RMWMs) on silicon. The first stage is a coarse wavelength monitor with a wide working range based on two unbalanced Mach–Zehnder interferometers acting as edge filters. The second stage is a fine wavelength monitor with picometer wavelength resolution utilizing two tunable microrings acting as edgefilters. The highest measured wavelength resolution can reach 1.6 pm in a 0.7-nm-wide wavelength range for the fine wavelength monitor. The working wavelength range can reach about 55 nm with a resolution of 0.1 nm for the coarse wavelength monitor. By thermally tuning the resonant wavelengths of microrings, we can obtain high resolution on the whole 9.6-nm free spectral range of the microrings. The influence of perturbation of temperature is also discussed. This letter can solve the problem that the measurable wavelength range and resolution limit each other in a conventional RMWM.

Normal spectral emissivity of GH536 (HastelloyX) in three surface conditions

The normal spectral emissivity of GH536, a nickel-based superalloy, is measured using a FT-IR spectrometer in the wavelength range 1–15μm at moderate and high temperature (400–1200K), as well as the samples with partially oxidized and flame treatment processed. It is found that the emissivity of GH536 decreases with the increasing of emission wavelength, which is well predicted by the electromagnetic wave theory, and increases linearly when the temperature rises. The emissivity of the other two samples with partially oxidized and flame treatment processed is also investigated in details. The results of the partially oxidized sample indicate that oxidation can enhance the emissivity significantly and alter the wavelength dependence trend. And the results of the flame treatment processed sample shows that the impurities and defects caused by the fire treatment process moderately increase the emissivity. The experimental data of GH536 is compared with the results calculated using Hagen-Rubens equation, which shows an inconsistence at high temperature condition. Therefore, a modified emissivity model is proposed, which has a good agreement in measured wavelength range at moderate and high temperature condition.

Investigation of the optical properties of LiTi_2O_4 and Li_4Ti_5O_12 spinel films by spectroscopic ellipsometry

The spinel lithium titanates materials Li4Ti5O12 and LiTi2O4 were fabricated by pulsed laser deposition. High quality and single phase thin films were successfully grown, thus opening the door for a systematic investigation of the optical properties of the spinel system Li1+xTi2-xO4 (0≤ x ≤1/3). The microstructure of Li1+xTi2-xO4 films were characterized by X-ray diffraction and atomic force microscope. The optical properties of the films were studied by spectroscopic ellipsometry at room temperature. The refractive index, extinction coefficient, and the thickness of the films were obtained by fitting the experimental data over the entire measured wavelength range. The results show that the two spinel oxides exhibit absolutely different dispersion trends in the visible region. The optical band gap of Li4Ti5O12 is about 3.14eV. The crystal-field energy splitting of LiTi2O4 is about 2.09eV between the eg and the t2g orbitals.

Direct optical measurements of far- and deep-ultraviolet surface plasmon resonance with different refractive indices.

The surface plasmon resonance (SPR) of Al thin films was investigated by varying the refractive index of the environment near the films in the far-ultraviolet (FUV, 120-200 nm) and deep-ultraviolet (DUV, 200-300 nm) regions. An original FUV-DUV spectrometer that adopts an attenuated total reflectance (ATR) system was used. The measurable wavelength range was down to the 180 nm, and the environment near the Al surface could be controlled. The resultant spectra enabled the dispersion relationship of Al-SPR in the FUV and DUV regions to be obtained. In the presence of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) on the Al film, the angle and wavelength of the SPR became larger and longer, respectively, compared to those in air. These shifts correspond well with the results of simulations performed using Fresnel equations.

Ultra-broadband and low-loss 3 dB optical power splitter based on adiabatic tapered silicon waveguides.

A broadband, low-loss and polarization-insensitive 3 dB optical power splitter based on adiabatic tapered silicon waveguides is proposed and investigated. 3D-FDTD simulation results show that the splitter achieves an output transmission efficiency of nearly 50% over an ultra-broad wavelength range from 1200 to 1700 nm. The device is fabricated, and experimental results show that the splitter exhibits a low excess loss of <0.19 dB for the TE polarization and <0.14 dB for the TM polarization over the entire measured wavelength range from 1530 to 1600 nm, while having an adiabatic taper length of only 5 μm. In addition, the measured power uniformity of the cascaded 1×8 splitter is only 0.47 dB, and 0.17 dB for the TE and TM polarizations, respectively. With the advantages of low loss, broad bandwidth, and compact size, the proposed splitter is a promising element for large-scale silicon integrated photonic circuits.

Wavelength‐resolved measurement of gain recovery in an erbium‐doped fiber amplifier

ABSTRACTWe report on wavelength‐resolved measurements of gain recovery in an erbium‐doped fiber amplifier using a wavelength‐selectable distributed feedback (DFB) laser as a light source. Recovery profiles of the gain are obtained for a wavelength range from 1528 to 1559 nm by applying a single‐wavelength pump‐probe method. Although the recovery time slightly decreases as the wavelength increases, it is nearly constant over the measured wavelength range. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:751–754, 2016

High contrast circular grating reflector on silicon-on-insulator platform.

A compact circular high contrast grating (HCG) reflector with a footprint of only 4.03 μm×4.32 μm on 220 nm silicon-on-insulator (SOI) platform is proposed and experimentally demonstrated. The proposed device breaks the high wavelength selectivity limitation for the conventional grating reflectors on a thin SOI platform by using the circular structure in a compact region. In addition, the device provides a high polarization selectivity over a wide wavelength range which is useful for applications such as tunable laser cavities and resonators to provide wide tuning range and high polarization stability. The circular structure based HCG reflector has an ultra-wide operational bandwidth (Δλ) of over 385 nm with the center wavelength (λ) set at 1550 nm, providing a Δλ/λ=24.83%. An average reflectance high of 94.15% is observed from 1525 to 1610 nm in the experimental measurement. The polarization extinction ratio is greater than 13 dB over the entire measured wavelength range.