Selective Optical Filters Research Articles

Thermal management of tungsten by spectrally selective thin film optical filters under laser illumination

Surface temperature management of refractory metals, such as Tungsten, is crucial for their use in high-temperature applications like aerospace, defense, and laser instruments. In this study, distributed Bragg reflectors (DBR) were utilized to reduce the temperature caused by intense laser illumination. To address this problem, we developed a coupled optical and thermal model and investigated multiple factors, including material composition, morphology, architecture, and source-related parameters, such as wavelength. Our results indicate that our DBR coating designs can significantly decrease the temperature of the Tungsten.

Experimental investigation of photovoltaic performance with compound parabolic solar concentrator and fluid spectral filter

Spectral splitting technology can prevent a photovoltaic cell (PV) overheating ability and efficiency loss. The solar spectrum is split into two portions using this technology: the first produces electricity, while the second generates heat. The present research offers the design and performance evaluation of a novel PV-thermal (PV/T) system based on a compound parabolic concentrator (CPC) and a selective absorptive fluid-based optical filter. Different experiments are conducted to indicate the impact of 1, 3, and 5 cm air gaps between the optical filter and PV on the system's average outputs. In addition, the impact of tilting the solar concentrator on the system's performance was also investigated. Finally, a simulation of the cell's electrical performance was produced. Experimental findings demonstrated that all CPC-PV systems with an optical filter have a greater electrical efficiency of about 17% compared to 13.1% and 7.1% for no-filter CPC-PV systems and bare PV cells, respectively. The 3-cm air gap case also demonstrated the most significant electrical, thermal, and overall efficiency improvements, with average values of 17.1, 21.0, and 32.8%, respectively. Additionally, the inclined position of the CPC outperforms the horizontal position. Theoretical results, in terms of electrical performance, supported the experimental findings.

A dental implant-on-a-chip for 3D modeling of host-material-pathogen interactions and therapeutic testing platforms.

The precise spatiotemporal control and manipulation of fluid dynamics on a small scale granted by lab-on-a-chip devices provide a new biomedical research realm as a substitute for in vivo studies of host-pathogen interactions. While there has been a rise in the use of various medical devices/implants for human use, the applicability of microfluidic models that integrate such functional biomaterials is currently limited. Here, we introduced a novel dental implant-on-a-chip model to better understand host-material-pathogen interactions in the context of peri-implant diseases. The implant-on-a-chip integrates gingival cells with relevant biomaterials - keratinocytes with dental resin and fibroblasts with titanium while maintaining a spatially separated co-culture. To enable this co-culture, the implant-on-a-chip's core structure necessitates closely spaced, tall microtrenches. Thus, an SU-8 master mold with a high aspect-ratio pillar array was created by employing a unique backside UV exposure with a selective optical filter. With this model, we successfully replicated the morphology of keratinocytes and fibroblasts in the vicinity of dental implant biomaterials. Furthermore, we demonstrated how photobiomodulation therapy might be used to protect the epithelial layer from recurrent bacterial challenges (∼3.5-fold reduction in cellular damage vs. control). Overall, our dental implant-on-a-chip approach proposes a new microfluidic model for multiplexed host-material-pathogen investigations and the evaluation of novel treatment strategies for infectious diseases.

Widely Tunable RF Signal Generation Using an InP/Si3N4 Hybrid Integrated Dual-Wavelength Optical Heterodyne Source

Photonics-based techniques spearhead the generation of high-frequency signals in the millimeter-and Terahertz wave, crucial for ultrabroadband mobile wireless link development. Photonic integration is enabling to provide the photonic approach with added advantages of energy-efficiency, flexibility and scalability, in addition to signal quality. We present an optical heterodyne system based on a novel dual laser module containing two InP-Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> hybrid lasers with intracavity wavelength selective optical filters with output optical power per laser of up to 15 dBm (31 mW), wide wavelength tuning of about 60 nm, and narrow optical linewidth below 100 kHz. To the best of our knowledge, we present for the first time the continuous-wave generation of RF frequencies over a wide tuning range from C-band (4 GHz – 8-GHz) to W-band (75 GHz – 110 GHz) achieving record low RF electrical linewidth around 108 kHz and long-term drift < 12 MHz with two free-running lasers. This is the best beat-note linewidth obtained with such an integrated source in a free-runnning regime and with a wide tuning range ever reported.

Selective wavelength optical filters from mixed polymorph and binary integration of MoO3 multilayer structures

In this report, a systematic study of mixed polymorph and binary integration of MoO3 multilayer structures has been given. The spin-coated multilayer nanorods (hexagonal and orthorhombic) of MoO3 are fabricatedon glass substrates and TiO2 coated glass substrate at different temperatures, i.e., 300 °C and 500 °C. The microstructure and surface analysis of the deposited films were characterized by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The optical properties of the films were characterized by UV–visible absorption spectrophotoscopy and theoretical analysis of the transmittance data. The optical bandgap falls between the wavelength range from 225 nm to 310 nm. Due to the optical bandgap in UV region and good transmission properties in the visible region, the fabricated thin-film structures may be developed as selective wavelength optical filters, which can control the unwanted distribution of UV radiation.

Spectral irradiance primary scale realization and characterization of deuterium lamps from 200 to 400 nm.

To meet the increasing metrology demand of spectral irradiance in the short UV spectral range, a new spectral irradiance scale from 200 to 400 nm was realized at National Institute of Metrology (NIM) based on a high-temperature blackbody BB3500M, and a group of stable deuterium lamps are used as the transfer standards. Accurate real-time temperature of a blackbody is derived to reduce the temperature drift during the measurement period. A combination of an absolute and relative measurement system is designed to reduce repeatability uncertainty, and a selective optical filter method is used to remove fluorescence with a peak at 330 nm. A seven-point bandwidth novel correction method based on differential quadrature formula is put forward to correct the bandwidth error of the monochromator. The expanded uncertainties of the new spectral irradiance scale are 5.3% at 200 nm, 1.8% at 250 nm, 1.9% at 330 nm, and 3.6% at 400 nm, respectively. In the overlap wavelength from 250 to 400 nm, the average deviation between two types transfer standards, deuterium lamps and tungsten halogen lamps, is verified to be 0.39%, which are consistent with the associated measurement uncertainties.

Resin Made Long-Period Fiber Grating Structure for Tunable Optical Filter inside Single-Mode Fiber

The rectangular-structured resin with one of its triangular long-period fiber grating surface is designed and printed out by using a high resolution 3D printer, so called long-period fiber grating (LPFG) resin. This LPFG resin is directly pressed on the bare single-mode fiber by a digital force meter to filter out partial band of light inside the fiber. The grating period is expanded by tilting the resin from the initial fiber axis. The optical filter is observed as resonant wavelengths from the broadband wavelength. The results show that the resonant wavelength shift is a linear function of the grating period with the coefficient of determination over 0.99. The proposed scheme has a great potential to be employed as a sensor such as a selective optical filter and a buried intrusion sensor.

Improvement of the Quality of Life in Patients with Age-Related Macular Degeneration by Using Filters.

Background: Age-related macular degeneration (AMD) is a disease with an increasing incidence due to the general aging of the population that decreases the patient’s quality of life. This work aims to study whether selective cut optical filters improve the AMD patient’s quality of life. Methods: Prospective and longitudinal study in 79 patients. Visual acuity, contrast sensitivity, and the line differences in the Colenbrander test were measured. Patients answered The National Eye Institute 25-Item Visual Function Questionnaire (NEI VFQ-25), which measures the quality of life related to vision before and after using cut optical filters. Results: There was an improvement of 5.99 points (3.7–8.3) in NEI VFQ-25 after wearing filters. This improvement was 4.0 points for 450-nm filters and 12.7 points for 511-nm filters. For patients with visual acuity (VA) < 0.25, results of NEI VFQ-25 increased by 10.11 points (1.19–19.02) and for patients with late AMDs, results increased by 5.33 points (1.31–9.35). Conclusions: Selective filters improve the quality of life of patients with AMD. The success rate in the fitting of filters is better for those with VA lower than 0.25 and those with late or advanced AMD.

Tunable radiative cooling based on a stretchable selective optical filter

Radiative cooling has the potential to drastically improve a wide range of energy conversion and utilization processes on Earth. However, the lack of tunability may limit its application in practical scenarios such as buildings, vehicles, and textiles. In this paper, we propose a new, to the best of our knowledge, approach to achieve tunable radiative cooling through a stretchable multilayer filter. The cooling power can be continuously modulated by mechanical stretching, which only requires a small amount of energy. This filter can be combined with existing static radiative cooling systems to achieve efficient and continuous regulation of cooling power.

Engineering novel tunable optical high-Q nanoparticle array filters for a wide range of wavelengths.

The interaction of non-monochromatic radiation with arrays comprising plasmonic and dielectric nanoparticles has been studied using the finite-difference time-domain electrodynamics method. It is shown that LiNbO3, TiO2, GaAs, Si, and Ge all-dielectric nanoparticle arrays can provide a complete selective reflection of an incident plane wave within a narrow spectral line of collective lattice resonance with a Q-factor of 103 or larger at various spectral ranges, while plasmonic refractory TiN and chemically stable Au nanoparticle arrays provide high-Q resonances with moderate reflectivity. Arrays with fixed dimensional parameters make it possible to fine-tune the position of a selected resonant spectral line by tilting the array relative to the direction of the incident radiation. These effects provide grounds for engineering novel selective tunable optical high-Q filters in a wide range of wavelengths, from visible to middle-IR.

Angular Dependences of Transmission Spectra of Photonic-Crystal Films Based on Aluminum Oxide

The angular dependences of the transmission of a one-dimensional photonic crystal based on porous anodic aluminum oxide are studied in the wavelength range of 320–1200 nm. The possibility of using porous one-dimensional photonic crystals based on aluminum oxide as selective narrowband optical filters and mirrors is studied.

Угловые зависимости спектров пропускания фотонно-кристаллических пленок на основе оксида алюминия

AbstractThe angular dependences of the transmission of a one-dimensional photonic crystal based on porous anodic aluminum oxide are studied in the wavelength range of 320–1200 nm. The possibility of using porous one-dimensional photonic crystals based on aluminum oxide as selective narrowband optical filters and mirrors is studied.

Towards an on-chip optical microsystem for spectroscopic detection of gastrointestinal dysplasia

This paper presents a CMOS optical microsystem with a 4 × 4 photodiodes array and their readout electronics, based on 16 light-to-frequency converters, and 16 high selective optical filters, for spectrophotometric measurement of diffuse reflectance and fluorescence signals, applied to the detection of gastrointestinal dysplasia. The photodiodes array is based on n+/p-epilayer junction silicon photodiodes. Their readout electronics outputs a digital signal, with a frequency proportional to the photodiode current, featuring a sensitivity of 26 Hz/nA at 550 nm, a spectral resolution of 9 MHz and a power consumption of 1 mW. The optical filters are based on 16 thin-film narrow-band Fabry-Perot resonators, in which dielectric mirrors are used. They feature high transmittances and low full-width-half-maximum. Experimental measurements, using phantoms representative of the main absorbing, scattering and fluorescence properties of gastrointestinal tissues, proved the viability of the CMOS optical microsystem with the optical filters to extract those signals, when comparing the obtained results with commercial equipment. The implemented apparatus is ready to be used as a portable system on a surgery room to verify the total removing of gastrointestinal cancer tissue. Moreover, the developed approach is a step forward in the implementation of a gastrointestinal dysplasia detection miniaturized tool.

Transmission Spectra and Optical Properties of a Mesoporous Photonic Crystal Based on Anodic Aluminum Oxide

Optical properties of a one-dimensional photonic-crystal film with a lattice period of ≈380 nm formed by electrochemical etching of an aluminum foil are investigated. Experimental data on the spectra of transmission and reflection in the region of the first, second, and third stop bands of anodic photonic crystal of aluminum oxide are compared with a theoretical dependence obtained from the well-known dispersion relation. The possibility of creating selective narrow-band optical filters based on mesoporous one-dimensional photonic crystals is analyzed. The conditions of enhancement of an electromagnetic field of laser radiation at 532 nm under normal incidence on a photonic-crystal surface are established. The possibility of generation of optical harmonics under the conditions of sharp increase in the effective field of the driving radiation in a mesoporous photonic crystal of anodic aluminum oxide filled with lithium iodate is analyzed.

Structural Color for Additive Manufacturing: 3D-Printed Photonic Crystals from Block Copolymers.

The incorporation of structural color into 3D printed parts is reported, presenting an alternative to the need for pigments or dyes for colored parts produced through additive manufacturing. Thermoplastic build materials composed of dendritic block copolymers were designed, synthesized, and used to additively manufacture plastic parts exhibiting structural color. The reflection properties of the photonic crystals arise from the periodic nanostructure formed through block copolymer self-assembly during polymer processing. The wavelength of reflected light could be tuned across the visible spectrum by synthetically controlling the block copolymer molecular weight and manufacture parts that reflected violet, green, or orange light with the capacity to serve as selective optical filters and light guides.

Photo-ignition process of multiwall carbon nanotubes and ferrocene by continuous wave Xe lamp illumination.

This work aims to investigate and characterize the photo-ignition phenomenon of MWCNT/ferrocene mixtures by using a continuous wave (CW) xenon (Xe) light source, in order to find the power ignition threshold by employing a different type of light source as was used in previous research (i.e., pulsed Xe lamp). The experimental photo-ignition tests were carried out by varying the weight ratio of the used mixtures, luminous power, and wavelength range of the incident Xe light by using selective optical filters. For a better explanation of the photo-induced ignition process, the absorption spectra of MWCNT/ferrocene mixtures and ferrocene only were obtained. The experimental results show that the luminous power (related to the entire spectrum of the Xe lamp) needed to trigger the ignition of MWCNT/ferrocene mixtures decreases with increasing metal nanoparticles content according to previously published results when using a different type of light source (i.e., pulsed vs CW Xe light source). Furthermore, less light power is required to trigger photo-ignition when moving towards the ultraviolet (UV) region. This is in agreement with the measured absorption spectra, which present higher absorption values in the UV–vis region for both MWCNT/ferrocene mixtures and ferrocene only diluted in toluene. Finally, a chemo-physical interpretation of the ignition phenomenon is proposed whereby ferrocene photo-excitation, due to photon absorption, produces ferrocene itself in its excited form and is thus capable of promoting electron transfer to MWCNTs. In this way, the resulting radical species, FeCp2+∙ and MWCNT−, easily react with oxygen giving rise to the ignition of MWCNT/ferrocene samples.

Fine tuning of optical signals in nanoporous anodic alumina photonic crystals by apodized sinusoidal pulse anodisation.

In this study, we present an advanced nanofabrication approach to produce gradient-index photonic crystal structures based on nanoporous anodic alumina. An apodization strategy is for the first time applied to a sinusoidal pulse anodisation process in order to engineer the photonic stop band of nanoporous anodic alumina (NAA) in depth. Four apodization functions are explored, including linear positive, linear negative, logarithmic positive and logarithmic negative, with the aim of finely tuning the characteristic photonic stop band of these photonic crystal structures. We systematically analyse the effect of the amplitude difference (from 0.105 to 0.840 mA cm-2), the pore widening time (from 0 to 6 min), the anodisation period (from 650 to 950 s) and the anodisation time (from 15 to 30 h) on the quality and the position of the characteristic photonic stop band and the interferometric colour of these photonic crystal structures using the aforementioned apodization functions. Our results reveal that a logarithmic negative apodisation function is the most optimal approach to obtain unprecedented well-resolved and narrow photonic stop bands across the UV-visible-NIR spectrum of NAA-based gradient-index photonic crystals. Our study establishes a fully comprehensive rationale towards the development of unique NAA-based photonic crystal structures with finely engineered optical properties for advanced photonic devices such as ultra-sensitive optical sensors, selective optical filters and all-optical platforms for quantum computing.

Rational engineering of nanoporous anodic alumina optical bandpass filters.

Herein, we present a rationally designed advanced nanofabrication approach aiming at producing a new type of optical bandpass filters based on nanoporous anodic alumina photonic crystals. The photonic stop band of nanoporous anodic alumina (NAA) is engineered in depth by means of a pseudo-stepwise pulse anodisation (PSPA) approach consisting of pseudo-stepwise asymmetric current density pulses. This nanofabrication method makes it possible to tune the transmission bands of NAA at specific wavelengths and bandwidths, which can be broadly modified across the UV-visible-NIR spectrum through the anodisation period (i.e. time between consecutive pulses). First, we establish the effect of the anodisation period as a means of tuning the position and width of the transmission bands of NAA across the UV-visible-NIR spectrum. To this end, a set of nanoporous anodic alumina bandpass filters (NAA-BPFs) are produced with different anodisation periods, ranging from 500 to 1200 s, and their optical properties (i.e. characteristic transmission bands and interferometric colours) are systematically assessed. Then, we demonstrate that the rational combination of stacked NAA-BPFs consisting of layers of NAA produced with different PSPA periods can be readily used to create a set of unique and highly selective optical bandpass filters with characteristic transmission bands, the position, width and number of which can be precisely engineered by this rational anodisation approach. Finally, as a proof-of-concept, we demonstrate that the superposition of stacked NAA-BPFs produced with slight modifications of the anodisation period enables the fabrication of NAA-BPFs with unprecedented broad transmission bands across the UV-visible-NIR spectrum. The results obtained from our study constitute the first comprehensive rationale towards advanced NAA-BPFs with fully controllable photonic properties. These photonic crystal structures could become a promising alternative to traditional optical bandpass filters based on glass and plastic.

Narrow stop band optical filter using one-dimensional regular Fibonacci/Rudin Shapiro photonic quasicrystals

One-dimensional deterministic aperiodic multilayered photonic crystals can be formed by stacking together dielectric layers of several different types according to substitutional generalized Fibonacci or Rudin Shapiro sequences. An efficient numerical technique based on calculus of transfer matrix of multiple layers is used to study the formation of optical gaps. The quasi-periodicic distribution gives some interesting optical properties and offers a multitude of adjacent pseudo-band gaps in different frequency range. The potential of photonic structure are explored by varying the structural parameters. The presence of band gaps due to long-range correlations. Further analysis shows that the central frequency of transmission band (stop band) can be changed by varying the type of distribution of two considered layers which formed the all quasi-photonic crystals cells and the order of quasiperiodic sequences. The structure is exploited to design selective optical filters with narrow band gaps and polychromatic stop band filters. These results make aperiodic photonic structures very attractive for the engineering of novel passive photonic.

Design and fabrication of SiO2/TiO2 and MgO/TiO2 based high selective optical filters for diffuse reflectance and fluorescence signals extraction.

This paper presents the design, optimization and fabrication of 16 MgO/TiO2 and SiO2/TiO2 based high selective narrow bandpass optical filters. Their performance to extract diffuse reflectance and fluorescence signals from gastrointestinal tissue phantoms was successfully evaluated. The obtained results prove their feasibility to correctly extract those spectroscopic signals, through a Spearman's rank correlation test (Spearman's correlation coefficient higher than 0.981) performed between the original spectra and the ones obtained using those 16 fabricated optical filters. These results are an important step for the implementation of a miniaturized, low-cost and minimal invasive microsystem that could help in the detection of gastrointestinal dysplasia.