Optical Pass Filter Research Articles

Spectral shaping of an ultrafast ytterbium fiber laser via a passive intracavity optical filter: a simple and reliable route to sub-45 fs pulses.

We investigate the use of passive intracavity optical filters for controlling the laser output spectrum of a polarization-mode-locked, ultrafast ytterbium fiber laser. The overall lasing bandwidth is increased or extended by strategic choice of the filter cutoff frequency. Overall laser performance, including pulse compression and intensity noise, is investigated for both shortpass and longpass filters with a range of cutoff frequencies. The intracavity filter not only shapes the output spectra, but also provides a route for overall broader bandwidths and shorter pulses in ytterbium fiber lasers. These results demonstrate that spectral shaping with a passive filter is a useful tool to routinely achieve sub-45fs pulse durations in ytterbium fiber lasers.

Liquid crystal based active wavelength filter for phase-sensitive optical time domain reflectometry.

This study proposes a liquid-crystal-based active wavelength filter for phase-sensitive optical time domain reflectometry to mitigate the amplified spontaneous emission (ASE) noise and accurately match the passband with the light source. The validity of the proposed system was verified using comparative experiments with conventional passive optical filters. The experiment showed an increase in signal-to-noise ratio (SNR) of up to 2.21 dB compared with passive filters. Additionally, the proposed system can effectively eliminate ASE noise, resulting in an SNR of 12.99 dB.

Influence of graphene nanopowder impurities on the structural and optical properties of sodium borate copper-based glass: Towards UV/NIR shielding materials

Graphene nanopowder was used as an unconventional additive to the studied oxide glasses, where it was added to the raw components of the copper-sodium borate glass by weight% according to the chemical formula :[(B2O3)0.6mol%(Na2O)0.3mol%(Cu2O3)0.2mol%]+(Graphene)x, where x = 0, 0.2, 0.4, 0.6 and 1 g. Then, the traditional melt quenching method was considered for the glass preparation process. X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Ultraviolet–Visible spectra UV–Vis, and the electron spin resonance (ESR) were used for the characterization processes. According to the XRD patterns, the prepared samples have been divided into two categories, pure glassy samples (x < 0.6 g), and glass-ceramic samples (x ≥ 0.6 g). The FTIR showed the presence of the structural groups BO3 and BO4 as well CO. Also, FTIR showed a conversion from BO3 to BO4 when the content of graphene increased, which means a decrease in the number of nonbridging oxygen atoms NBOs. The deconvolution parameters showed an increase in the relative area of the band assigned to the OH and CH2 groups. According to ESR spectral analysis, Cu2+ ions should occupy octahedral sites with tetragonal distortion as the ground state, where the effective g values and the peak-to-peak width were computed and linked with the structural variation of the prepared samples. The UV–Vis optical measurements showed that the as-prepared glasses/glass-ceramics could act as an optical pass filter in the region of the visible light, as well as good candidates for UV- and NIR shielding applications.

Investigation of the temperature and magnetic field effect on the Cesium D1 atomic line filter characteristics

Atomic spectral line filter is a narrow band pass optical filter which has many applications in quantum and laser systems. By engineering the system parameters like gas temperature and intensity of magnetic field, the filter with desired characteristics could be obtained. In this work, an atomic spectral line filter for Cesium D1 line (894.6nm) is implemented and characterized. The effect of system parameters on the filter transmission and its bandwidth is investigated. It is observed that by applying a magnetic field of 390 Gauss and adjusting the gas cell temperature on 40°C, a single peak filter with maximum filter transmission and FWHM of 0.24 GHz could be obtained.

Dichromatic properties of a magnetic fluid thin layer

In the paper, we investigate spectral dependence of transmittance of a thin layer of a magnetic fluid with Fe2O3 nanoparticles and transformer oil ITO 100 as base fluid, as a function of its thickness. Thin layer samples of the magnetic fluid with various thicknesses were prepared using standard microscope glass slides and spacers with defined thicknesses ranging from 25 µm to 530 µm. The stable spatial localization of the thin layer was ensured due to the existence of a surface tension emerging at the interface between the magnetic fluid surface and surfaces of the microscope glass slides. The transmittance as a function of the layer thickness was investigated in visible (VIS) and near-infrared (NIR) spectral ranges and spectral dependence of the coefficient of absorption of the magnetic fluid was determined, too. At the same time, the change of color of the layers depending on their thicknesses was evidenced. The results show the transmittance dependence on the thin layer thickness can be used to design magnetic fluid-based passive optical attenuators and filters.

Broadband Photonic RF Channelizer With 92 Channels Based on a Soliton Crystal Microcomb

We report a broadband radio frequency (RF) channelizer with up to 92 channels using a coherent microcomb source. A soliton crystal microcomb, generated by a 49 GHz micro-ring resonator (MRR), is used as a multi-wavelength source. Due to its ultra-low comb spacing, up to 92 wavelengths are available in the C band, yielding a broad operation bandwidth. Another high-Q MRR is employed as a passive optical periodic filter to slice the RF spectrum with a high resolution of 121.4 MHz. We experimentally achieve an instantaneous RF operation bandwidth of 8.08 GHz and verify RF channelization up to 17.55 GHz via thermal tuning. Our approach is a significant step towards the monolithically integrated photonic RF receivers with reduced complexity, size, and unprecedented performance, which is important for wide RF applications ranging from broadband analog signal processing to digital-compatible signal detection.

Model Predictive Controller Design of a Wavelength-Based Thermo-Electrical Model of a Photovoltaic (PV) Module for Optimal Output Power

As it stands, in terms of environmental impact and efficiency, photovoltaic (PV) energy has appeared to be a potential renewable power source that notably contends with the traditional power generation schemes. More so, a noteworthy factor that contrariwise influences the PV module efficiency is the PV module temperature. Therefore, the more the PV module temperature increases, the lesser the PV module efficiency. More importantly, the impact of undesired spectrum wavelengths on the PV module temperature is further reduced by passive optical filters, nonetheless, active optical filters which is more superior to the passive type, based on the PV module temperature and output power during the day, dynamically change the cut-off wavelength. Consequently, the efficiency as well as the lifecycle is both enhanced by controlling the active optical filter so as to attain optimal output power. Therefore, in this paper, a wavelength-based thermo-electrical model of a PV module was designed and simulated, the essence of this model is mainly to predict the impact of each module wavelength on both the temperature and the output power of the PV module. In view of this, since the output power is affluence by the module temperature, it is expedient to design a controller that locates the optimal cut-off spectral wavelength to lessen the module temperature whereas getting the most out of the output power over a period of time. In this vein, we designed a Model Predictive Controller whose objective is to maximize the output power by simply controlling the input power through filtering the spectrum wavelength for a photovoltaic (PV) system. The design and simulation of the plant model as well as the MPC controller were carried-out on MATLAB/Simulink environment.

Enhancement of PV performance using optical solar spectrum splitting

ABSTRACT The mismatch between the spectral response of PV cells and the available solar radiation results in conversion losses which increase its temperature and hence decreases its photoelectric efficiency. Employing spectral beam splitting by using optical filters for pass or reflect the wanted parts of the solar radiation spectrum for the PV operation may represent a promising solution. This work aims to assess the effect of using “Short pass Filter” and “UV Hot Mirror” as an optical filter on the performance of PV cells. This was achieved by installing three small identical PV modules, each of 1 W. The first panel was the standard one that was used for comparison purposes, the second panel was fitted by a short pass optical filter, such that all incident solar radiation is and only useful portion of the solar spectrum will reach the PV. The solar radiation that reaches the third panel was filtered by UV hot mirror that reflects ultraviolet and visible light. It was found that the short pass filtered panel and the hot filtered Panel caused a drop in the temperature by 6°C and 10°C, respectively. The average efficiency of the reference panel is 6.9% while it is for the short pass filtered panel 7.1% and 12% for the Hot UV Filtered Panel. Comparing the obtained results with previous results, it may be concluded that this solar splitting method is a promising one to be used to enhance the PV performance.

Simplified White Blood Cell Differential: An Inexpensive, Smartphone- and Paper-Based Blood Cell Count.

Sorting and measuring blood by cell type is extremely valuable clinically and provides physicians with key information for diagnosing many different disease states including: leukemia, autoimmune disorders, bacterial infections, etc. Despite the value, the present methods are unnecessarily costly and inhibitive particularly in resource poor settings, as they require multiple steps of reagent and/or dye additions and subsequent rinsing followed by manual counting using a hemocytometer, or they require a bulky, expensive equipment such as a flow cytometer. While direct on-paper imaging has been considered challenging, paper substrate offers a strong potential to simplify such reagent/dye addition and rinsing. In this work, three-layer paper-based device is developed to automate such reagent/dye addition and rinsing via capillary action, as well as separating white blood cells (WBCs) from whole blood samples. Direct onpaper imaging is demonstrated using a commercial microscope attachment to a smartphone coupled with a blue LED and 500 nm long pass optical filter. Image analysis is accomplished using an original MATLAB code, to evaluate the total WBC count, as well as differential WBC count, i.e., granulocytes (primarily neutrophils) vs. agranulocytes (primarily lymphocytes). Only a finger-prick of whole blood is required for this assay. The total assay time from finger-prick to data collection is under five minutes. Comparison with a hemocytometry-based manual counting corroborates the accuracy and effectiveness of the proposed method. This approach could be potentially used to help make blood cell counting technologies more readily available, especially in resource poor, point-of-care settings.

Cavity Enhanced Organic Photodiodes with Charge Collection Narrowing

AbstractColor discrimination in photodetection is conventionally achieved using broadband‐absorbing inorganic semiconductors with passive optical filters. Organic semiconductors show promise to deliver narrowband spectral responses due to their tunable optical properties. While achieving narrow‐absorbing organic semiconductors is an ongoing endeavor in the synthetic chemistry community, charge collection narrowing is introduced as a “material‐agnostic” technique to realize narrowband spectral responses using broadband absorbers such as blends of organic semiconductors, inorganic nanocrystals, and perovskites in a photodiode architecture. Charge collection narrowing in organic semiconductors demands photoactive junction thicknesses on the order of a few micrometers causing fabrication difficulties and limitations in device metrics such as frequency bandwidth. In this work it is shown that electrical inversion can result in charge collection narrowing in organic photodiodes with active layer thicknesses on the order of hundreds of nanometers and hence much easier to achieve via high throughput solution processing techniques. Additionally, it is shown that an indium tin oxide/gold electrode with modified work function acts as a cavity mirror, further narrowing the spectral response and at the same time delivering an extremely selective cathode, suppressing the dark current dramatically. Nearly voltage independent detectivities of 1013 Jones are achieved with an active sensing area of 0.2 cm2.

Experiment of Multispectral Sensing Sensor for Urban Road Materials in Outdoor Environment

This research is the first attempt to conduct several experiments of multispectralsensing sensor for urban road materials in outdoor environment. This research aims to classifyfive urban road materials that are aggregates, asphalts, concrete, clay, natural fibre includingvegetation and water. There were 9 cameras in the multispectral sensing sensor. Seven cameraattached with narrow band optical filter with the centre spectrum at 710nm, 730nm, 750nm,800nm, 870nm, 905nm and 950nm. One camera attached with 720 nm normalization band useshigh pass optical filter. Another camera attached with UV/IR cut optical filter works as a RGBcamera. The images results, that have been taken, are processed in MATLAB to get the imagingindex results from the multispectral system. Naïve Bayes classifier is used in Weka to classifythe urban road materials with vegetation and water. The first classification and testing thatclassifies five urban road materials with vegetation and water have accuracy results ranged from0 % to 32% while the accuracy results without vegetation and water have better accuracy resultsranged from 0 % to 55 %.

Smartphone near infrared monitoring of plant stress

The most widely used method for monitoring plant stress is the use of near infrared (NIR) spectrophotometry to calculate normalized difference vegetation index (NDVI), as defined by [NIR reflectance − red reflectance]/[NIR reflectance + red reflectance]. NDVI measures the chlorophyll absorption in the red spectrum relative to the scattering by cellular structure in NIR, and has been used to monitor vegetation health and subsequently its stress from aerial or satellite images. Rather than using an NIR spectrophotometer or an NIR camera that is rather expensive, we attempted to use a commercial smartphone, utilizing its (potentially unintended) ability in recognizing near infrared (NIR) color. Some of the most recent versions of smartphones have eliminated the NIR block filters on their cameras, and able to recognize NIR in their red pixels of CMOS array. Through attaching an inexpensive high pass filter at 800 nm to a smartphone camera, we were able to collect the NIR reflectance (with a high pass optical filter) and the red reflectance (without a filter), enabling NDVI assessments. This method was verified by measuring the NDVI values from a series of chlorophyll solutions, and showed a strong linear correlation with R2 = 0.948, corroborating the smartphone’s ability in evaluating NDVI. Using the leaves from three different plant species, the NDVI values were evaluated using the smartphone and compared with the plants’ chlorophyll contents using acetone extraction and subsequent spectrophotometry. A good linear relationship was found with R2 = 0.88–0.92. We further evaluated the NDVI values against the plants’ water contents (measured by oven-drying), showing the non-linear relationship with the NDVI saturation above 50% water content. The assay time was almost instantaneous, requiring only a smartphone and a high pass filter, thus allowing inexpensive, easy-to-use, rapid, and early prediction of plant stress that can be used for field and household applications.

Continuous Lubricant Film Thickness Measurement Between Piston Ring and Cylinder Bore

Measurement of film thickness between piston ring and cylinder bore has been a challenge for decades; laser-induced fluorescence (LIF) method was used by several groups, and promising results are obtained for the investigation of lubricant film transport. In this study, blue light generated by a laser source is transmitted to a beam splitter by means of a fiber optic cable and combined with another fiber optic line, then transmitted to the piston ring and cylinder bore conjunction. The light causes the fluorescence dye present in the lubricant to emit light in a longer wavelength, i.e., green. Reflected light is recollected; blue wavelength components are filtered out using a narrow band pass optical filter, and only components in the florescence wavelength is transmitted to a photomultiplier tube. The photomultiplier produces a voltage proportional to instantaneous lubricant film thickness. Then, the photomultiplier signal is calibrated for lubricant film thickness using a laser textured cylinder bore with known geometries. Additional marks were etched on the liner for calibration. The LIF system is adapted to a piston ring and cylinder bore friction test system simulating engine conditions. Static piston ring and reciprocating liner configuration of the bench test system allow the collection of continuous lubricant film thickness data as a function of crank angle position. The developed system has potential to evaluate new designs, materials, and surface properties in a controlled and repeatable environment.

TL/OSL properties of beta irradiated Al2O3:Tm3+ phosphor synthesized by microwave combustion method

This work discusses synthesis of stable α-phase of Al2O3:Tm3+ by combustion method using temperature controlled microwave oven. The crystalline phase was analyzed by X-ray diffraction (XRD) technique and average crystallite size was found to be 147 nm. Observations using scanning electron microscope (SEM) image suggest formation of agglomerated particles and energy dispersive x-ray spectroscopy (EDS) confirmed the incorporation of Tm3+ in Al2O3. Thermoluminescence emission (TLE) spectrum of γ – irradiated Al2O3:Tm3+ shows characteristic emissions of Tm3+, Cr3+ and Mn4+. TL glow curves of γ – irradiated Al2O3:Tm3+ exhibit a prominent peak at 453 K along with a shoulder at 496 K. The glow curves of β – irradiated Al2O3:Tm3+ were studied in different emission regions using U340 + BG39 (UV band pass), CS759 + BG39 (Blue band pass) and BG39 (Visible band pass) optical glass filters. A prominent peak was observed at 471 K in for all mentioned emission regions and an additional shoulder was observed at 511 K with CS759 + BG39 and BG39 filters. TL glow curve of β – irradiated Al2O3:Tm3+ using only BG39 filter had more counts than CS759 + BG39 and U340 + BG39 filters. Further, the effect of Tm3+ impurity on TL response was studied. TL kinetic parameters were estimated by using computerized glow curve deconvolution (CGCD) technique. The activation energy and frequency factor of prominent peak (471 K) were found to be 1.31 eV and 3.50 × 1013 s−1 respectively. Optically stimulated luminescence (OSL) characteristics of β – irradiated Al2O3:Tm3+ were studied using U340 + BG39 and CS759 + BG39 filters. Highest OSL intensity was observed in UV. OSL curves were deconvoluted by general order decay equation. Life time and photoionization cross section of the traps responsible for OSL were found to be 5.30 s and 3.98 × 10−18 cm2 respectively. The process of ionization of electron from Tm3+, electron trap in host lattice and its recombination mechanism is proposed. Phosphorescence decay of beta irradiated sample was also studied. The lifetime of phosphorescence decay was found to be 140 s for the prominent peak and TL intensity decays 25% after the phosphorescence. TL/OSL dosimetric properties viz. linearity with dose, reusability and minimum detectable dose of the phosphor were characterized for medical dosimetry application.

Optical Filter Enabled Continuous Disinfection of Hospital Rooms Using Multi-Sensor Feedback Aided Light Source

In this paper, We have implemented an efficient technique for the inactivation of pathogens in the air and on the surfaces of the hospital rooms. These rooms are the main source of the bacterial diseases spreading in the locality and thereby contaminating the environment. So, a new method is taken into account which uses the wavelength light centered at 405 nm for the disinfection process. The inactivation process of bacteria’s is caused by the 405 nm light which targets the intra-cellular porphyrin of the pathogens which absorbs the light and bacteria’s are eliminated due to the generation of reactive oxygen species in their body. This process has been successfully achieved by the proposed model system. This system uses the light source assembly as a primary source that emits the white light in the broad spectrum which ranges from 450-475 nm that lies in the visible spectrum region. Then this broad spectrum white light is passed through the high-intensity narrow band pass optical filter which reduces the wavelength in the range of 400-410 nm having wavelength centered at 405 nm. Along with this, a multi-sensor adaptive feedback network is also applied to the system which changes the intensity level of the disinfecting light depending on the density of the bacteria’s present in the room. This adaptive nature of the system helps in reducing the power consumption by the system which is necessary in case of continuous disinfection process. This method holds an upper hand over the ultraviolet light devices (UV-C) technique which uses the wavelength in the range of 254-360 nm for the disinfection process. Since the 405 nm light lies in the visible spectrum, hence it is safe to use in presence of a person in the room, thus making the system a continuous process for the disinfection.

Ion dynamics of a laser produced aluminium plasma at different ambient pressures

Plasma is generated by pulsed laser ablation of an Aluminium target using 1064 nm, 7 ns Nd:YAG laser pulses. The spatial and temporal evolution of the whole plasma plume, as well as that of the ionic (Al2+) component present in the plume, are investigated using spectrally resolved time-gated imaging. The influence of ambient gas pressure on the expansion dynamics of Al2+ is studied in particular. In vacuum (10−5 Torr, 10−2 Torr) the whole plume expands adiabatically and diffuses into the ambient. For higher pressures in the range of 1–10 Torr plume expansion is in accordance with the shock wave model, while at 760 Torr the expansion follows the drag model. On the other hand, the expansion dynamics of the Al2+ component, measured by introducing a band pass optical filter in the detection system, fits to the shock wave model for the entire pressure range of 10−2 Torr to 760 Torr. The expansion velocities of the whole plume and the Al2+ component have been measured in vacuum. These dynamics studies are of potential importance for applications such as laser-driven plasma accelerators, ion acceleration, pulsed laser deposition, micromachining, laser-assisted mass spectrometry, ion implantation, and light source generation.

Optical filter requirements in an EML-based single-sideband PAM4 intensity-modulation and direct-detection transmission system.

The feasibility of a single sideband (SSB) PAM4 intensity-modulation and direct-detection (IM/DD) transmission based on a CMOS ADC and DAC is experimentally demonstrated in this work. To cost effectively build a >50 Gb/s system as well as to extend the transmission distance, a low cost EML and a passive optical filter are utilized to generate the SSB signal. However, the EML-induced chirp and dispersion-induced power fading limit the requirements of the SSB filter. To separate the effect of signal-signal beating interference, filters with different roll-off factors are employed to demonstrate the performance tolerance at different transmission distance. Moreover, a high resolution spectrum analysis is proposed to depict the system limitation. Experimental results show that a minimum roll-off factor of 7 dB/10GHz is required to achieve a 51.84Gb/s 40-km transmission with only linear feed-forward equalization.

Sub-GHz-resolution C-band Nyquist-filtering interleaver on a high-index-contrast photonic integrated circuit.

Modern optical communications rely on high-resolution, high-bandwidth filtering to maximize the data-carrying capacity of fiber-optic networks. Such filtering typically requires high-speed, power-hungry digital processes in the electrical domain. Passive optical filters currently provide high bandwidths with low power consumption, but at the expense of resolution. Here, we present a passive filter chip that functions as an optical Nyquist-filtering interleaver featuring sub-GHz resolution and a near-rectangular passband with 8% roll-off. This performance is highly promising for high-spectral-efficiency Nyquist wavelength division multiplexed (N-WDM) optical super-channels. The chip provides a simple two-ring-resonator-assisted Mach-Zehnder interferometer, which has a sub-cm2 footprint owing to the high-index-contrast Si3N4/SiO2 waveguide, while manifests low wavelength-dependency enabling C-band (> 4 THz) coverage with more than 160 effective free spectral ranges of 25 GHz. This device is anticipated to be a critical building block for spectrally-efficient, chip-scale transceivers and ROADMs for N-WDM super-channels in next-generation optical communication networks.

Performance testing of a spectral beam splitting hybrid PVT solar receiver for linear concentrators

A novel spectral beam splitting photovoltaic/thermal (PVT) solar receiver for linear concentrators has been developed capable of generating high-grade thermal energy concurrently with electricity. This paper evaluates the initial field testing of this receiver which combines a selective absorption heat transfer fluid (Propylene Glycol) with a band pass optical filter to achieve efficient spectral splitting. Wavelengths of light between 700nm and 1100nm are directed to the silicon PV cells, with the remaining wavelengths absorbed directly as heat. A prototype has been constructed and mounted to a parabolic trough concentrator with 42× geometrical concentration ratio. Results demonstrated considerable promise for this technique. High grade heat thermal efficiencies of 31% relative to the thermal beam splitting fraction were achieved at a receiver temperature of 120°C, with a total system efficiency of 50%. Electrical yields of approximately 3.8% relative to the total incident power were measured. While lower than expected we expect with minor modifications system efficiencies beyond 75% will be achievable.

STATISTICAL DESIGN CENTERING OPTIMIZATION OF 1D PHOTONIC CRYSTAL FILTERS

A statistical design centering approach is introduced, to achieve the optimal design center point of one-dimensional photonic crystal-based filters which are parts of several optoelectronic systems. Up to our knowledge, it is the first time that a design centering approach is applied to such a design problem. The proposed approach seeks nominal designable parameter values that maximize the probability of satisfying the design specifications (yield function). Thus, the achieved optimal design center point is much more robust to unavoidable designable parameter variations, occurring during fabrication process, for example. The yield maximization problem is formulated as an unconstrained optimization problem solved by derivative-free based-algorithm (NEWUOA) coupled with a variance reduction yield estimator to reduce large number of required system simulations. The flexibility and efficiency of the proposed design centering approach are demonstrated by two practical examples: band pass optical filter and spectral control filter. A comparison with Minimax optimization technique is also given.