Optical Fourier Research Articles

Effects of drying processes on starch-related physicochemical properties, bioactive components and antioxidant properties of yam flours.

The effects of five different drying processes, air drying (AD), sulphur fumigation drying (SFD), hot air drying (HAD), freeze drying (FD) and microwave drying (MWD) for yams in terms of starch-related properties and antioxidant activity were studied. From the results of scanning electron microscopy (SEM), polarized optical microscopy (POM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR), the MWD sample was found to contain gelatinized starch granules. The FD yam had more slow digestible (SDS) and resistant starches (RS) compared with those processed with other modern drying methods. The bioactive components and the reducing power of the dried yams, were lower than those of fresh yam. When five dried samples were compared by principal component analysis, the HAD and SFD samples were observed to have the highest comprehensive principal component values. Based on our results, HAD would be a better method for yam drying than the more traditional SFD.

MEMS squeezer for the measurement of single cell rupture force, stiffness change, and hysteresis

A MEMS squeezer able to compress single living cells underwater until rupture was designed and tested. The relatively large motion range of the device in aqueous media (~2.5 µm) allows provoking cell disruption while measuring cell mechanical properties before and after membrane rupture. An AC driven electrothermal micro actuator with mechanical amplification pressed single cells against a reference back spring. Deformations of the cell and the reference spring were measured with nanoscale resolution using optical Fourier transform techniques. The motion of the reference spring divided by the cell deformation provides the cell stiffness relative to the reference spring constant. An abrupt change in the cell stiffness and the appearance of cracks indicated the cell wall rupture force was reached. A total of 22 baker’s yeast cells (Saccharomyces cerevisiae) were squeezed with the micro device. The average force necessary to rupture the cell membrane was 0.47 ± 0.1 µN. Before rupture the cells had an average stiffness of 9.3 ± 3.1 N m−1; the post-rupture stiffness dropped to 0.94 ± 0.57 N m−1. Cell hysteresis was also measured: cells squeezed and released before reaching the rupture force showed residual deformations below 100 nm, while cells squeezed past the rupture force and then released showed residual deformations between 490 and 990 nm.

Time Lens-Based Optical Fourier Transformation for All-Optical Signal Processing of Spectrally-Efficient Data

We review recent progress in the use of time lens-based optical Fourier transformation for advanced all-optical signal processing. A novel time lens-based complete optical Fourier transformation (OFT) technique is introduced. This complete OFT is based on two quadratic phase-modulation stages using four-wave mixing, separated by a dispersive medium, which enables time-to-frequency and frequency-to-time conversions simultaneously, thus performing an exchange between the temporal and spectral profiles of the input signal. Using the proposed complete OFT, several advanced all-optical signal processing schemes for spectrally-efficient systems and networks have been achieved, including all-optical generation, detection and format conversion of spectrally-efficient signals. The spectrally-efficient signals in this paper mainly refer to efficiently multiplexed signals with a high symbol rate per Hz, such as orthogonal frequency division multiplexing, Nyquist wavelength-division multiplexing (Nyquist-WDM), and Nyquist optical time division multiplexing (Nyquist-OTDM) signals.

Discussion on comparative analysis and a new attack on optical asymmetric cryptosystem.

This paper presents two different aspects of cryptanalysis of the optical phase-truncated Fourier transform (PTFT)-based cryptosystem. In the first part, a comparative study is carried out for a specific attack on the PTFT-based scheme in different optical transformation domains. In the second part, a new attack algorithm is proposed. The existing attack algorithms devised for the PTFT-based cryptosystem require knowledge of both the encryption keys for successful retrieval of phase through phase-retrieval algorithms to extract information about the plaintext. The proposed new attack method eliminates the requirement of one of the encryption keys to carry out the attack on the PTFT-based scheme. The numerical results support the proposed method.

Unraveling the Mystery of Stöber Silica's Microporosity.

Puzzling aspects of the microporous structure of Stöber silica, including inconsistencies in the BET specific surface area and the long measurement time required for N2 adsorption, hinder further research on and potential applications of this material. In this work, Stöber silica samples prepared using systematic and detailed post-treatment methods were characterized by N2 adsorption, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma optical emission spectrometry, elemental analysis, and Fourier transform infrared spectroscopy. We have found that the often overlooked sample preparation conditions may be the main causes that perplex the gas adsorption characterization results of Stöber silica samples. The pore-blocking processes associated with a variety of sample treatment methods are discussed in detail. Strong evidence for the particle growth model and pore-blocking mechanism involving ethoxyl groups, Si species, and condensation of silanols is provided. A remarkable result is that the measurement time is shortened from 1 month in our previous work to 2-3 days for samples with large specific surface areas. A suitable post-treatment condition is recommended to obtain microporous Stöber silica with a short measurement time, including water washing, low temperature drying without a vacuum, and a short storage time.

Time-gated down-/up-conversion emission of Ho–CeO2 and Ho, Yb–CeO2 nanoparticles

Herein, we report the luminescence properties of (1%) Ho and (1%) Ho, (20%) Yb–CeO2 nanoparticles, investigated by time-resolved luminescence spectroscopy at 300 and 80K temperatures. The emission was measured over a broad detection range, from visible (450nm) up to infrared (1500nm) with excitation ranging from 210 to 1000nm. The structural properties were characterized by X-ray diffraction, Raman, Diffuse Reflectance Optical and Diffuse Reflectance Fourier Transform Infrared spectroscopies. The up-conversion emission of Ho–CeO2 and Ho, Yb–CeO2 using excitation wavelengths of 646.6, 759, 918and 971nm, respectively, were described in terms of time-gated up-conversion emission and excitation spectra, as well as up-conversion emission decays. Under short gate/ short delay conditions, the contribution of the 5F3 and 5F5 energy levels to the red emission of Ho at 630–680nm could be separated. The role of CeO2 charge transfer band as a selective antenna sensitizer as well as back transfer of excitation from Ho to Yb was also discussed. The mechanisms involved in the up-conversion emission of Ho and Ho, Yb–CeO2 were interpreted as ground state absorption followed by excited state absorption and energy transfer, respectively. For Ho, Yb–CeO2, a tunable red to green up-conversion emission ratio from 0.5 to 3.6 was also observed by increasing the power density of ~4 to 48W/cm2 of a cw laser diode at 980nm.

Effectiveness of phase-conjugated twin waves on fiber nonlinearity in spatially multiplexed all-optical OFDM system

Abstract In this paper, we investigate the effectiveness of using phase-conjugated twin waves (PCTWs) technique to mitigate fiber nonlinear impairments in spatially multiplexed all-optical orthogonal frequency division multiplexing (AO-OFDM) systems. In this technique, AO-OFDM signal and its phase-conjugated copy are directly transmitted through two identical fiber links. At the receiver, the two signals are coherently superimposed to cancel the phase noise and to enhance signal-to-noise ratio (SNR). To show the effectiveness of proposed technique, a spatially multiplexed AO-OFDM system is demonstrated by numerical simulation. AO-OFDM signal and its phase conjugated copy are optically generated by using optical coupler-based inverse fast Fourier transform (OIFFT)/fast Fourier transform (OFFT). The generated signal includes 29 subcarriers where each subcarrier is modulated by 4-quadrature amplitude modulation (4QAM) format at a symbol rate of 25 Gsymbol/s. The results reveal that transmission performance is considerably improved where the transmission distance of the proposed system is increased by ∼45% as compared to that of original system without PCTWs technique.

Microscope system with on axis programmable Fourier transform filtering

We propose an on-axis microscope optical system to implement programmable optical Fourier transform image processing operations, taking advantage of phase and polarization modulation of a liquid crystal on silicon (LCOS) display. We use a Hamamatsu spatial light modulator (SLM), free of flickering, which therefore can be tuned to fully eliminate the zero order component of the encoded diffractive filter. This allows the realization of filtering operation on axis (as opposed to other systems in the literature that require operating off axis), therefore making use of the full space bandwidth provided by the SLM. The system is first demonstrated by implementing different optical processing operations based on phase-only blazed gratings such as phase contrast, band-pass filtering, or additive and substractive imaging. Then, a simple Differential interference contrast (DIC) imaging is obtained changing to a polarization modulation scheme, achieved simply by selecting a different incident state of polarization on the incident beam.

Structural Properties and Antifungal Activity against Candida albicans Biofilm of Different Composite Layers Based on Ag/Zn Doped Hydroxyapatite-Polydimethylsiloxanes.

Modern medicine is still struggling to find new and more effective methods for fighting off viruses, bacteria and fungi. Among the most dangerous and at times life-threatening fungi is Candida albicans. Our work is focused on surface and structural characterization of hydroxyapatite, silver doped hydroxyapatite and zinc doped hydroxyapatite deposited on a titanium substrate previously coated with polydimethylsiloxane (HAp-PDMS, Ag:HAp-PDMS, Zn:HAp-PDMS) by different techniques: Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectroscopy (GDOES) and Fourier Transform Infrared Spectroscopy (FTIR). The morphological studies revealed that the use of the PDMS polymer as an interlayer improves the quality of the coatings. The structural characterizations of the thin films revealed the basic constituents of both apatitic and PDMS structure. In addition, the GD depth profiles indicated the formation of a composite material as well as the successful embedding of the HAp, Zn:HAp and Ag:HAp into the polymer. On the other hand, in vitro evaluation of the antifungal properties of Ag:HAp-PDMS and Zn:HAp-PDMS demonstrated the fungicidal effects of Ag:HAp-PDMS and the potential antifungal effect of Zn:HAp-PDMS composite layers against C. albicans biofilm. The results acquired in this research complete previous research on the potential use of new complex materials produced by nanotechnology in biomedicine.

Effect of capping agent on the particle size of CdSe nanoparticles.

CdSe nanoparticles were synthesized by green route and chemical route methods. In the green route method the samples were capped by starch and in the chemical route method the samples were capped by mercaptoacetic acid (MAA). The samples were characterized by powder X- ray diffraction (XRD) and transmission electron microscopy (TEM). Both the samples showed zinc blend structure. The optical absorption spectra and Fourier transform infrared (FTIR) spectra were also studied. A blue shift was seen in the absorption spectra as compared with the bulk as well as the sample capped by starch. TEM images showed agglomeration for the starch-capped sample as compared with the MAA-capped sample. The particle size for the sample capped by MAA was found to be less as compared with the starch-capped sample. A blue shift in the photoluminescence (PL) spectra was also recorded for the samples prepared by the chemical route as compared with the sample prepared by the green route as well as the bulk. The PL peak shifted towards the red side and increase in the peak intensity occurred with the change in the excitation wavelength. Change in PL intensity was observed with different pH at 685 nm. Copyright © 2016 John Wiley & Sons, Ltd.

Recent Advances on the Optical Properties of Zinc-Doped Antimony Sulphide (Sb2S3) Thin Films

The influence of zinc (Zn) impurities at different concentrations on the properties of antimony sulphide (Sb2S3) thin films grown using the solution growth technique is reported. The films were grown at room temperature of 28oC, a deposition time of 2 h, and an initial pH of 4.40. The films were then doped with different concentrations of Zinc impurities (0.25 -1.0M) and then annealed at annealing temperatures ≤ 400 oC. The films were characterised using optical spectroscopy and Fourier transform infrared spectroscopy (FTIR) to investigate the transmittance, absorbance and reflectance versus wavelength measurements, X-ray diffractometry (XRD) to study the structural properties, Scanning electron microscopy (SEM) to investigate the morphological properties, and Rutherford Backscattering (RBS) techniques for the compositional analysis. The results indicate that the film thickness was in the range 0.3 -1.5μm, with an increase in the film thicknesses of the doped layers compared to the as-deposited films. The transmittances of the doped layers were found to be reduced compared to the as-deposited films. The results of the optical analysis show that the films had direct energy band gap with optical absorption coefficient (α) > 104 cm-1 in both the doped and as-grown layers. The refractive index was typically ≤ 3.6, with higher values obtained from the doped layers. The values of the energy band gap were in the range suitable for application in solar photovoltaic and photonic devices.

(Invited) In Operando Optical Studies of Solid Oxide Electrochemical Cells

Solid oxide fuels cells (SOFCs) are promising devices for fuel flexible and efficient power generation. The high temperatures (>700 oC) required enable operation on hydrocarbon fuels but avoiding degradation by carbon deposition remains a challenge. In operando optical methods, including Raman and Fourier Transform infrared emission spectroscopy (FTIRES) and near infrared thermal imaging (NIRTI), have been developed to characterize and understand molecular and material processes in SOFCs in order to improve their performance and durability. Recent results include studies of SOFCs on methane operating under various reforming conditions. Dry reforming, using carbon dioxide, which is also simulated biogas, reveals a high degree of anode activity based on substantial cooling of the anode but also reduced carbon formation compared to unreformed methane. An intermediate amount of anode cooling and carbon formation is observed with steam reforming. Related studies have been carried out to assess the effectiveness of carbon removal by steam and carbon dioxide using a new, duplex method in which NIRTI and FTIRES are performed simultaneously. Also, NIRTI has been used in conjunction with near ambient pressure X-ray photoelectron spectroscopy (APXPS) to identify spatially resolved regions where the emission intensity changes are observed due to ceria reduction during water electrolysis. The results are consistent with the APXPS results and interpretation for the reaction. The observations also provide an example of emissivity rather than temperature changes observed with high temperature thermal imaging in solid oxide electrochemical cells.

Unitary rotation and gyration of pixelated images on rectangular screens.

In the two space dimensions of screens in optical systems, rotations, gyrations, and fractional Fourier transformations form the Fourier subgroup of the symplectic group of linear canonical transformations: U(2)F⊂Sp(4,R). Here, we study the action of this Fourier group on pixelated images within generic rectangular Nx×Ny screens; its elements here compose properly and act unitarily, i.e., without loss of information.

Mn2+ doped ZnS quantum dots in ferroelectric liquid crystal matrix: Analysis of new relaxation phenomenon, faster optical response, and concentration dependent quenching in photoluminescence

Phase transitional, dielectric, electro-optical, polarizing optical microscopic, photoluminescence (PL), and Fourier transformed infrared (FTIR) spectroscopic measurements have been carried out on ZnS:Mn quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC). A new dielectric relaxation mode has been envisaged in FLC material due to the presence of 0.25 wt. % ZnS:Mn (40 mol. %) QDs. The characteristics of the new mode have been compared with those of the soft mode. A significant fastening of the electro-optical response (∼75%) has been observed in the case of 0.25 wt. % ZnS:Mn (20 mol. %) QDs doped FLC material. The induction of the new relaxation mode is attributed to the flexoelectric tilt fluctuations. The induced flexoelectric polarization in the FLC medium at the vicinity of QDs might be responsible for the enhanced spontaneous polarization in the FLC/QDs mixtures. Quenching in PL for the FLC/QDs mixtures has been observed, which strongly depends on Mn content in QDs. The change in FTIR spectra for the FLC/QDs composite clearly indicates the change in molecular dynamics of the pure FLC after the dispersion of QDs. The presented results will certainly pave a way to utilize QDs for obtaining faster response of the FLC material and potential material to tune the relaxation processes.

Quenching of photoluminescence and enhanced contrast of ferroelectric liquid crystal dispersed with Cd1−XZnXS/ZnS core/shell nanocrystals

We report the dispersion of Cd1−xZnxS/ZnS core/shell nanocrystals (NCs) in ferroelectric liquid crystal (FLC) into different concentrations. Absorbance of white light, photoluminescence (PL), contrast, polarizing optical microscopy and Fourier transformed infrared spectroscopy (FTIR) have been performed to disclose the nature of FLC/NCs composite. The presence of NCs, in different concentration, quenches the PL of FLC material. The mechanism of quenching is explained by the modified Stern–Volmer quenching equation. The maximum contrast for FLC/NCs was found at 0.25wt% of dopant concentration which is the optimized concentration of NCs in FLC from application point of view. Contrast was further supported by polarizing optical micrographs (POMs). The change in POM also indicates the change in molecular alignment of FLC owing to concentration of NCs which also affect the optical properties of composites. FTIR spectra reveal that the NCs strongly interact with FLC molecules and changes their molecular dynamics associated with the central core and aliphatic chain. The present FLC/NCs composite has potential application in ultraviolet to visible light conversion, ultraviolet light storage applications and high contrast PL displays.

Transmission performance improvement using random DFB laser based Raman amplification and bidirectional second-order pumping.

We demonstrate that a distributed Raman amplification scheme based on random distributed feedback (DFB) fiber laser enables bidirectional second-order Raman pumping without increasing relative intensity noise (RIN) of the signal. This extends the reach of 10 × 116 Gb/s DP-QPSK WDM transmission up to 7915 km, compared with conventional Raman amplification schemes. Moreover, this scheme gives the longest maximum transmission distance among all the Raman amplification schemes presented in this paper, whilst maintaining relatively uniform and symmetric signal power distribution, and is also adjustable in order to be highly compatible with different nonlinearity compensation techniques, including mid-link optical phase conjugation (OPC) and nonlinear Fourier transform (NFT).

An optical information processing-based idea for visual attention analysis

One of the challenges in visual attention analysis is to generate full-resolution saliency map in real time. Traditional methods usually design algorithms and implement in computer, and they have faced a troublesome problem in balancing the resolution and computational speed. Optical computing is considered to be a practical and efficient method, so we build an optical information processing-based system to achieve fast visual saliency extraction to generate full resolution saliency maps with fine details of boundaries. The whole system mainly consists of a Display as the input image source, optical Fourier Lens and spatial filters, an imaging sensor. The key of our method is frequency selection with two precise pinholes which treated as band-pass spatial filters. And the saliency map is finally obtained using simple calculation. According to the experimental results, and comparing with other famous approach, the results demonstrate that our system efficiently produce full resolution saliency maps with good boundaries.

Characteristics and in vitro response of thin hydroxyapatite-titania films produced by plasma electrolytic oxidation of Ti alloys in electrolytes with particle additions.

The enhancement of the biological properties of Ti by surface doping with hydroxyapatite (HA) is of great significance, especially for orthodontic applications. This study addressed the effects of HA particle size in the electrolyte suspension on the characteristics and biological properties of thin titania-based coatings produced on Ti-6Al-4V alloy by plasma electrolytic oxidation (PEO). Detailed morphological investigation of the coatings formed by a single-stage PEO process with two-step control of the electrical parameters was performed using the Minkowski functionals approach. The surface chemistry was studied by glow discharge optical emission spectroscopy and Fourier transform infrared spectroscopy, whereas mechanical properties were evaluated using scratch tests. The biological assessment included in vitro evaluation of the coating bioactivity in simulated body fluid (SBF) as well as studies of spreading, proliferation and osteoblastic differentiation of MC3T3-E1 cells. The results demonstrated that both HA micro- and nanoparticles were successfully incorporated in the coatings but had different effects on their surface morphology and elemental distributions. The micro-particles formed an irregular surface morphology featuring interpenetrated networks of fine pores and coating material, whereas the nanoparticles penetrated deeper into the coating matrix which retained major morphological features of the porous TiO2 coating. All coatings suffered cohesive failure in scratch tests, but no adhesive failure was observed; moreover doping with HA increased the coating scratch resistance. In vitro tests in SBF revealed enhanced bioactivity of both HA-doped PEO coatings; furthermore, the cell proliferation/morphometric tests showed their good biocompatibility. Fluorescence microscopy revealed a well-organised actin cytoskeleton and focal adhesions in MC3T3-E1 cells cultivated on these substrates. The cell alkaline phosphatase activity in the presence of ascorbic acid and β-glycerophosphate was significantly increased, especially in HA nanoparticle-doped coatings.

Optical real-time Fourier transformation with kilohertz resolutions

Real-time Fourier transformation (RTFT) of signals is a fundamental concept that enables Fourier analysis at speeds beyond the limitations of conventional digital signal processing engines. In the optical domain, RTFT is commonly performed by inducing large amounts of group-velocity dispersion on the signal (time-varying light wave) of interest to map the signal’s frequency spectrum along the time domain. However, the optical frequency resolution of this method is typically restricted above the gigahertz range, which represents a critical limitation for applications in real-time spectroscopy, ultrafast detection, imaging and sensing, and, more particularly, for photonic-assisted generation and processing of radio-frequency (RF) signals. Here we propose a new concept for realization of RTFT that involves superposition of multiple signal replicas that are shifted simultaneously along the temporal and frequency domains, leading to an output temporal waveform that effectively maps the input optical spectrum. This configuration overcomes the frequency-resolution limitations of dispersion-based RTFT schemes, while providing the desired signal’s spectrum with minimal latency, equal to the inverse of the frequency resolution. We experimentally demonstrate a practical implementation of the concept on optical signals using a frequency shifted feedback (FSF) laser, achieving a frequency resolution of ≃30 kHz and a time–bandwidth product exceeding 400, while the predicted linearity of the frequency-to-time mapping process is shown over a 20 GHz bandwidth. The introduced concept should be of general interest for high-speed, real-time Fourier analysis, beyond the optical-domain implementation reported here; moreover, this work also paves the way for novel applications of FSF lasers in several areas, including high-precision metrology and optical or RF waveform synthesis and processing.

Optical vortex array in spatially varying lattice

We present an experimental method based on a modified multiple beam interference approach to generate an optical vortex array arranged in a spatially varying lattice. This method involves two steps which are: numerical synthesis of a consistent phase mask by using two-dimensional integrated phase gradient calculations and experimental implementation of produced phase mask by utilizing a phase only spatial light modulator in an optical 4f Fourier filtering setup. This method enables an independent variation of the orientation and period of the vortex lattice. As working examples, we provide the experimental demonstration of various spatially variant optical vortex lattices. We further confirm the existence of optical vortices by formation of fork fringes. Such lattices may find applications in size dependent trapping, sorting, manipulation and photonic crystals.