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Optical filters are essential in a wide range of applications, including optical communications, electronics, lighting, optical sensors and photography. This article presents recent work which indicates that optical filters can be created from specialized nanoparticle suspensions. Specifically, this article describes a theoretical optimization process for designing nanofluid-based filters for hybrid solar photovoltaic/thermal (PV/T) applications. This particular application is suitable because nanofluids can be utilized as both volumetric solar absorbers and flowing heat transfer mediums. The nanofluid filters described in this work compare favorably with conventional optical filters for five photovoltaic (PV) cell alternatives: InGaP, CdTe, InGaAs, Si, and Ge. This study demonstrates that nanofluids make efficient, compact and potentially low-cost, spectrally selective optical filters. Solar collectors: Fluent combination Fluid-based optical filters could serve as efficient, compact and low-cost components for use in hybrid solar collectors. This is the finding of a recent theoretical study in which Robert Taylor at the University of New South Wales, Australia, together with colleagues in Australia and the USA, who studied the optical properties of nanoparticles suspended in liquids. These ‘nanofluids’ can be engineered to filter light (through selective absorption) for a variety of photovoltaic cells with expected efficiencies comparable to those offered by conventional solid-state filters. As fluids, the suspensions can also be used for transferring and storing thermal energy. These characteristics are helpful for improving the design of hybrid solar collectors, which combine photovoltaic conversion of light into electricity with direct-absorption of thermal energy.

This paper proposes a Faraday anomalous dispersion optical filter that uses rare earth-doped crystals to overcome the limitations of current atomic filtering technology, which include limited working wavelength and Doppler broadening. The paper analyses Er 3+ : LiYF 4 1530 nm as an example filter. The results show that the proposed filter achieves high transmission while maintaining an ultra-narrow bandwidth transmission spectrum. The maximum transmission efficiency reaches 94.8% with a transmission bandwidth of hundred trillions HZ. The position of the transmission peak can be tuned by adjusting the size of the magnetic field, enabling the conversion of the transmission spectrum between the line center and the line wing.

Hybrid emission filters, comprising an interference filter and an absorption filter, exhibit high excitation light rejection performance and can act as lensless fluorescent devices. However, it has been challenging to produce them in large batches over a large area. In this study, we propose and demonstrate a method for transferring a Si substrate, on which the hybrid filter is deposited, onto an image sensor by attaching it to the sensor and removing the substrate via plasma etching. Through this method, we can transfer uniform filters onto fine micrometer-sized needle devices and millimeter-sized multisensor chips. Optical evaluation reveals that the hybrid filter emits light in the 500 to 560 nm range, close to the emission region of green fluorescent protein (GFP). Furthermore, by observing the fluorescence emission from the microbeads, a spatial resolution of 12.11 μm is calculated. In vitro experiments confirm that the fabricated device is able to discriminate GFP emission patterns from brain slices.

In this paper, the samples of network of borate glass have been prepared by melt quenching technique and characterized. Optical characterization of the network was examined By UV–VIS spectroscopic technique. The results showed an increasing in refractive index, permittivity, extinction coefficient, dielectric constants, electric susceptibility and polarizability with increasing Co 3 O 4 content. Cobalt ions produced intense blue color in glass and used as optical filters in UV–VIS region. Fourier-transform infrared spectroscopy is used to characterize the local order and kind of forming structural units and provides information about the interaction between alkali metal ions and borate glass network. Addition modified oxide of cobalt oxide converts some of BO 3 to BO 4 units. Glass samples are exposed to melting and grinded so the resulted bands are very broadening and overlapping to analyze this overlap used deconvolution analysis technique. Cobalt-doped borate glass behaved as optical band pass filters, i.e., area, center, width and height of band pass.

Carbon monoxide (CO) is one of the toxic air pollution produced in incomplete combustion of carbon-containing fuels. At a certain threshold of concentration, this gas can harm the environments and affect the human health. Unfortunately, it cannot be detected by humans. In this study, CO gas detection has been designed and constructed using the principle of Non-Dispersive Infrared (NDIR). An incandescent light bulb is used to provide infrared source. An optical filter based on interferometry with a bandpass of about 4.63 μm is used to pass the light which corresponds to the CO gas absorption. The TPS 334 thermopile sensor is used to measure light intensity after gas absorption. The built-in RTD in the thermopile is involved to compensate the results of the gas concentration measurement. The experimental result shows that this NDIR sensor can measure CO gas concentration with a sensitivity of about 7 mV / ppm.

Various metal oxide thin films, including TiO2, SnO2, MoO3, and NiO, grown by the electron-beam evaporation process, have been optimized for implementation as multilayered structures for infrared (IR) filter-based photonic cooler application. The filter and antireflection coating designs were based on various stacking configurations with titanium dioxide (TiO2) and tin dioxide (SnO2) used as seed layers. These designs were then optimized to achieve wideband optical transmission in the visible spectrum but cut off the infrared region. After deposition, the dual-layer filter configurations were characterized optically and structurally using ultraviolet–visible (UV–Vis) spectrometry, ellipsometry, three-dimensional (3D) profilometry, x-ray diffraction analysis, and scanning electron microscopy. A systematic comparison between these filters confirmed that stacking layers with TiO2 are the best candidate for photovoltaic modules as they demonstrate higher transmission and a clear cutoff after 1000 nm. Finally, computational analysis using OptiLayer software demonstrated a minimum optical reflectance of about 0.4% when coupling an oxide layer with a lower refractive index value (e.g., 1.4) with one having a higher refractive index (> 2). These results illustrate the promising potential of such films for IR filter-based photonic cooling of photovoltaics and/or smart windows.

In this paper, analysis of tunable optical filter based on Sagnac effect tuning is presented using a fiber-optic ring resonator (FORR) and the responses of the filters for different FORR and Sagnac loop parameters under steady-state conditions are investigated. Formulation of the optical filter response is presented by considering with/without single and multiple Sagnac loop effects. Effects of the FORR parameters of filter response are studied and analyzed under different parametric conditions for the maximum transmission intensity. The simulation results show that the filter responses are affected strongly by the Sagnac loop and the FORR parameters. With the Sagnac effect, it is shown that full-width at half maximum (FWHM) would increase by increasing the phase difference Δ from 0 to 0.20 radian, beyond which it will start decreasing. The difference in FWHM value in this range of Δ variations is found to be about 3.77 nm. Between the first and the second resonances at wavelengths 1395 and 1538 nm, the free spectral range (FSR) is found to be 140 nm. In multiple loops effects, by increasing the number of loop turn , the values of FSR would reduce. For Δ  = 0.3 and  = 1,  2,  3, the values of FSR are obtained as 144, 74, 47 nm, respectively.

The design for a metadevice on an optical platform combining two different applications is reported, namely optical filter and optical splitter. The platform is based on a dropping cavity placed in two-dimensional square photonic crystal (2D-PC). The PC-based optical filter consists of a periodic disposition of silicon (Si) cylinders in air, of radius r  = 0.2 a and a dielectric constant ε  = 12, while the PC-based splitter is composed of square alumina rods (Al 2 O 3 ) in air, of radius r  = 0.2 a and a dielectric constant ε  = 8.9. The two dropping PC waveguides, having the size w , are coupled via a cavity–ring resonator of thickness g. By controlling the geometrical parameters w and g, the incoming wavelength can be shifted or extinct.

The utilization of nanofluids and concentrating techniques in solar photovoltaic/thermal (PV/T) systems, to enhance the overall system performance, have been analysed explicitly in the last few years. More recently, nanofluid-based optical filters were integrated with photovoltaic (PV) systems for the effective utilization of solar spectrum, i.e. below and beyond the band-gap of PV cells. Therefore, to quantify the recent progress of spectral beam splitting-based hybrid PV/T systems (BSPV/T), a systematic review has been presented therein. The study highlights the technological and scientific advancement in BSPV/T in last two decades. Linear Fresnel mirror-based BSPV/T showed significant enhancement in the overall performance of hybrid PV/T system. Recently developed nanoparticle-laden BSPV/T system shows significant improvement in overall thermal efficiency of BSPV/T system, thanks to decoupling of thermal system and PV cell. Further, economic analysis, carbon footprint, and environmental assessment of BSPV/T are also discussed briefly. At the last, the authors have made an effort to identify the challenges, limitations, and prospective paths for future research in BSPV/T systems.

In this paper, a 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) material assisted one-dimensional photonic-crystal-based (1D-PhC) tunable optical filter is presented. The design comprises a bilayer 1D-PhC structure having DAST as an electro-optic material. The device parameters are configured to filter out the 632.8 nm wavelength from the reflection spectrum. The analysis shows that by illuminating the device with poly-chromatic light at an incident angle of 45.07°, the filtered wavelength exhibits transmission maxima having FWHM of less than 1nm. The analytical results also demonstrate the post fabrication 60 nm electrical tuning of the filtered wavelength by using only ±5 V applied potential. The structure also exhibits a very stable filter response up to 40% variations in optical thickness. Thus, the proposed design possesses the advantage in terms of low voltage wavelength tuning, stable response, easy fabrication and integration capability in integrated circuits.