Optical Filtering Effect Research Articles

Stable and Tunable Erbium Ring Laser by Rayleigh Backscattering Feedback and Saturable Absorber for Single-Mode Operation

This work demonstrates a high-quality erbium-doped fiber (EDF) ring laser in the L-band gain range by combining the Rayleigh backscattering (RB) feedback signal and unpumped EDF induced saturable absorber (SA) filter. The optical filter effect induced by the RB feedback injection and EDF SA could generate single-longitudinal-mode (SLM) behavior and shrink the linewidth to sub-kHz. The output linewidth, power, and optical-signal-to-noise ratio (OSNR) of the fiber ring laser were also shown within the 42 nm wavelength bandwidth of 1565.0 to 1607.0 nm. Also, the instabilities of output power and central wavelength of each lasing lightwave were analyzed with a measurement time of 45 min.

Enhancing Solar Photovoltaic Panel Performance in India's Tropical Climate: An Experimental Study on the Influential Effects of Optical Filters

<p>Due to the increasing global energy demand and consequent climate change from burning fossil fuels, researchers are getting more focused on renewable energies as a potential solution to the world's energy problems. Solar energy is a prominent form of sustainable energy. The solar photovoltaic power generation system’s electrical performance is negatively influenced by several factors, including the impact of solar irradiance, incident angle, temperature, dust accumulation on the top of the solar cell, cracks in the solar panel, shadowing, shunt resistance, solar cell materials, load mismatch, maintenance and cleaning schedule, spectral mismatch loss, and cable loss. The direct environmental factors that have the biggest impact on efficiency are the effects of sun irradiance and temperature. This empirical investigation examined the impact of optical filters on the electrical efficiency of a 40W polycrystalline solar PV panel in India while considering real-time ambient conditions. Through the utilization of an optical filter, the solar PV panel's temperature is diminished, hence enhancing the output power of the solar panel. Based on the experimental findings, the utilization of a transparent plexiglass sheet equipped with a coolant system installed on the solar panels leads to a drop in the average operating temperature of the solar PV module by up to 6°C. Additionally, the output power is enhanced by up to 10W in comparison to the reference solar panel’s output performance.</p>

Experimental investigation of the effect of optical filters on the performance of the solar photovoltaic system

Researchers are becoming more interested in renewable energies as a viable answer for today’s energy needs due to the rising demand for energy and climate changes brought on by the use of fossil fuel resources. One of the most significant sources of renewable energy is solar energy. Photovoltaic systems are used to convert the received solar radiation to electricity. Low overall performance throughout the operational time caused by raising the solar cells’ temperature is one of the most significant problems with the use of photovoltaic systems. In this experimental work, the influence of optical filters on the performance of photovoltaic panels was studied under Sharjah meteorological conditions. In this study, a 50 W solar PV module’s outdoor performance characteristics were analyzed. This case study employed a Plexiglas sheet, a box filled with air and water, and affixed it directly to the top surface of the PV panel to demonstrate the impact of the Plexiglas as an optical filter on the electrical productivity of the PV panel in relation to the variation in temperature caused by the filters. By imposing optical filters, and therefore lowering the temperature of the system, this work shows promising results in boosting the performance of the PV module. Module current drops dramatically as solar irradiance is blocked, yet panel voltage rises for filter-covered panels compared to the reference panel. In terms of fill factor and electrical efficiency, there has been a noticeable improvement. The voltage at maximum power, electrical efficiency, and maximum output power increased significantly. The average efficiencies of a reference PV module, a plexiglass-sheet-covered PV module, and a plexiglass-air-box-covered PV module are 7.02%, 7.5%, and 8.12%, respectively. In comparison to the reference module’s average efficiency of 6.66%, the covered PV module with plexiglass water box averages 6.74%

Temporal coherence in an unbalanced SU(1,1) interferometer.

In classical coherence theory, coherence time is typically related to the bandwidth of the optical field. Narrowing the bandwidth by optical filtering will result in the lengthening of the coherence time. In the case of a delayed pulse photon interference, this will lead to pulse overlap and recovery of interference, which is otherwise absent due to time delay. However, this is changed for entangled optical fields. In this Letter, we investigate how the temporal coherence of the fields in a pulse-pumped SU(1,1) interferometer changes with the bandwidth of optical filtering. We find that the effect of optical filtering is not similar to the classical coherence theory in the presence of quantum entanglement. A full quantum theory is presented and can explain the phenomena well.

Hardware-Efficient Blind Frequency Offset Estimation for Spectral-Efficient Digital Subcarrier Multiplexing Systems

For the digital subcarriermultiplexing (DSM) transmission, it is compulsory to realize the frequency offset estimation (FOE) and compensation (FOC) before the subcarrier de-multiplexing and the chromatic dispersion (CD) compensation (CDC). Here, we demonstrate a blind FOE method for the spectral-efficient DSM signals with a sharper root raised cosine (RRC) spectral shaping, with the capabilities of the transparent modulation format operation, a wide FOE range, and a high FOE accuracy. By reusing the spectral information for the CDC, the proposed FOE method is hardware efficient. Moreover, the proposed FOE method is numerically identified robust to transmission impairments, including the amplified spontaneous emission (ASE) noise, the optical filtering effect, and the accumulated CD, with an estimation error of less than 35 MHz under a FFT size of 2048. The correct function of the proposed FOE method is finally experimentally verified for 25 Gbaud 16QAM DSM signals under scenarios of both back-to-back (B2B) and standard single-mode fiber (SSMF) transmissions.

A hybrid system integrating solid oxide fuel cell and thermo-radiative-photovoltaic cells for energy cascade utilization

A novel hybrid system coupling solid oxide fuel cell (SOFC) with thermoradiative (TR) and photovoltaic (PV) cells is proposed, evaluated, and optimized for energy cascade utilization. Theories of electrochemistry, Planck radiative heat transfer, and first law of thermodynamics are applied to assess and optimize the performance of the hybrid system. Firstly, energy balance analysis is conducted to obtain suitable area ratio between the subsystems and the SOFC. A homo-structure InAs–InAs is chosen as an example of the TP-PV cells. The peak power density of 0.669 W cm −2 and the maximum efficiency of 0.770 and the relevant work conditions are achieved through parametric optimal analysis. It is also found that decreasing the leakage resistance of the SOFC can enhance electricity production and efficiency of the hybrid system. Secondly, a GaSb-InSb TP-PV cells are adopted to couple with the SOFC for performance enhancement. Finally, the positive effects of back surface reflector and the negative effects of irreversible heat transfers on the hybrid system are discussed. The obtained results are helpful for designing and optimizing the SOFC-TR-PV hybrid systems. • An SOFC-TR-PV hybrid system is proposed and studied to enhance power and efficiency. • An optimum structure of TP-PV cells is designed as GaSb-InSb. • The effects of optical filter and Newton's heat transfers on the system are revealed. • The maximum power and efficiency and the conditions are obtained under various cases. • The present work are of great importance to design and optimize the hybrid systems.

Performance evaluation of IEEE 802.15.7 CSK modulation under blue shift effect of optical receiver filters

In recent years, the use of light-emitting diodes (LEDs) in lighting, which has higher energy efficiency and longer-lasting environmentally friendly lighting compared to conventional lighting devices, has accelerated the development of a promising new technology for short-range wireless optical transmission called visible light communication (VLC). Besides other applications, VLC switches the LEDs at very high speeds to simultaneously realize indoor lighting and data transmission. But the intensity and color of the lighting may vary because of data transmission. Color shift keying (CSK) modulation defined in the IEEE 802.15.7 VLC standard guarantees constant light intensity and color. The CSK receiver uses a band-pass optical filter to separate the light channels. However, the transition band of optical filters shifts towards the blue wavelength depending on the incidence angle of the light which is called the blue shift effect. In this paper, the performance of the CSK receiver is investigated for the first time under the blue shift effect in the case of single and multiple transmitter LED cells. The numerical results show that the blue shift effect significantly decreases system performance. To eliminate the distorting effect, various methods and an adaptive equalizer-based CSK receiver are proposed. The proposed structures provide notable improvement.

The effect of biochar, hydrochar particles and dissolved organic matter on the photodegradation of metribuzin herbicide in aquatic media

Biochar and hydrochar particles and/or dissolved organic matter (DOM) may participate in several decomposition and transport processes of organic pollutants, thus their effect on aqueous photolysis of metribuzin (MBZ), selected as a potential pesticide pollutant of water systems, has been studied. Chars have been characterized by several techniques in order to correlate physicochemical characteristics with observed photodegradation rates. Biochar presented a micro-mesoporous graphitic structure with high surface area, and lower amounts of oxygen functional groups while hydrochar presented coral like structure, low surface area, incomplete carbonization and higher amounts of oxygen functional groups. MBZ photolysis was enhanced in the presence of low concentration levels (50 mgL−1) of char particles and DOM while an inhibitory effect was observed for higher concentrations (100–400 mgL−1). DOM from hydrochar present a stronger optical filter effect than biochar DOM while the biochar matrix and DOM present the higher ability to generate hydroxyl radicals (•OH) and singlet oxygen (1O2), respectively. The participation of different ROS in photodegradation pathways for each matrix was studied also by scavenging experiments. The overall effect on photodegradation rate was the result of counterplay between the decrease of direct photolysis due to the light attenuation and the occurrence of indirect photolysis reaction paths via the generated ROS depending on the role of char matrix and DOM to act as source or sink for the ROS. The results demonstrate the significant and dissimilar role of char matrices and dissolved organic matter on the photo degradation rate of organic pollutants in aquatic matrices.

Light-driven artificial neuron models based on photoswitchable systems

Neuromorphic engineering devises and implements surrogates of neurons to contrive brain-like computing machines. This work presents the design and computational analysis of two artificial neuron models based on photochromic compounds. The first system is a model of a pacemaker neuron. It consists of two direct thermally reversible photochromic compounds that interplay mutually through inner optical filter effects. The two photochromic compounds give rise to oscillations if they have specific spectral and dynamical properties. The second system consists of three thermally reversible photochromic compounds. They interact through a structure of negative feedback actions based on the inner filter effect, which mimics the chemical relationships established between the three genes involved in the biochemical “Repressilator”. Hence, this system is named “Optical Repressilator”. For specific chemical composition and values of the parameters characterizing the photochromic compounds, it is a valuable model of a phasic photo-excitable neuron.

Simultaneous transmission/absorption photometry of particle-laden filters from wildland fires during the Biomass Burning Observation Project (BBOP) field campaign

Transmissivity and absorptivity measurements were carried out simultaneously in the visible (wavelength of 532 nm) at laboratory conditions using particle-laden filters obtained from a three-wavelength particle/soot absorption photometer (PSAP). The particles were collected on filters from wildland fires over the Pacific Northwest during the Department of Energy Biomass Burning Observation Project (BBOP) field campaign in 2013. The objective of this investigation was to apply this measurement approach, referred to as simultaneous transmission/absorption photometry (STAP), to estimate the aerosol extinction coefficient from actual field-campaign filter aerosol, and compare results with the PSAP. The STAP approach offers several advantages over the PSAP, including estimation of the extinction coefficient from temperature measurements (avoiding the complexities associated with filter reflectivity/scattering measurements), as well as determination of the filter optical properties and filter effects on particle absorption (resulting in particle absorption enhancement).The experimental arrangement included a laser probe beam impinging normal to the particle-coated surface of a vertically mounted filter, and a thermocouple placed flush in the middle of (and in thermal contact with) the filter uncoated back surface. With this simple arrangement, the transmissivity and absorptivity were determined simultaneously at a given laser beam wavelength. The measurement repeatability was better than 0.3 K (95% confidence level) for temperature and 0.4 mW for laser power. The limit of detection for the extinction coefficient was estimated to be (8–12) Mm−1 (95% confidence level) at about 1.9 mW laser power. The extinction coefficient was determined through measurement of both PSAP blank and exposed filters. Filters were obtained from nine different aircraft flights conducted during the BBOP campaign, representing different flight patterns, days, stages of burning, landscapes, and wildland fires. The STAP extinction coefficient matched the darkness of the filter coating, however the PSAP-filter results did not follow the same order. Although there were differences in transmissivity between the two techniques, the estimated values for absorption coefficient were in good agreement.

Effect of optical filters and light source spectra on the spectral luminous efficiency function measurement

During the measurement of spectral luminous efficiency function $$V\left( \lambda \right)$$, monochromatic visual stimuli of higher luminance can be obtained by narrow band optical filters with broad band light sources, compared to monochromators. However, the distortion of $$V\left( \lambda \right)$$ is inevitably caused due to the bandwidth of the optical filters. In this paper, the effect of optical filters and light source spectra on the spectral luminous efficiency function $$V\left( \lambda \right)$$ measurement is studied. Filters with different spectral transmittances and light sources with different spectral power distributions are considered in the model to simulate visual sensitivity experiment. Compared with real $$V\left( \lambda \right)$$, the distortion of the simulated $$V\left( \lambda \right)$$ caused by the bandwidth of filters is quantitatively evaluated with the aid of a quality indicator, mismatch error $$f'$$. Results and conclusions in this paper can be used as a guide to optimize the design of the visual sensitivity experiments for $$V\left( \lambda \right)$$ measurement.

Visual and non-visual properties of filters manipulating short-wavelength light.

PurposeOptical filters and tints manipulating short‐wavelength light (sometimes called ‘blue‐blocking’ or ‘blue‐attenuating’ filters) are used in the management of a range of ocular, retinal, neurological and psychiatric disorders. In many cases, the only available quantification of the optical effects of a given optical filter is the spectral transmittance, which specifies the amount of light transmitted as a function of wavelength.MethodsWe propose a novel physiologically relevant and retinally referenced framework for quantifying the visual and non‐visual effects of these filters, incorporating the attenuation of luminance (luminous transmittance), the attenuation of melanopsin activation (melanopsin transmittance), the colour shift, and the reduction of the colour gamut (gamut reduction). Using these criteria, we examined a novel database of spectral transmittance functions of optical filters (n = 121) which were digitally extracted from a variety of sources.ResultsWe find a large diversity in the alteration of visual and non‐visual properties. The spectral transmittance properties of the examined filters vary widely, in terms of shapes and cut‐off wavelengths. All filters show relatively more melanopsin attenuation than luminance attenuation (lower melanopsin transmittance than luminous transmittance). Across the data set, we find that melanopsin transmittance and luminous transmittance are correlated.ConclusionsWe suggest that future studies and examinations of the physiological effects of optical filters quantify the visual and non‐visual effects of the filters beyond the spectral transmittance, which will eventually aid in developing a mechanistic understanding of how different filters affect physiology. We strongly discourage comparing the downstream effects of different filters on, e.g. sleep or circadian responses, without considering their effects on the retinal stimulus.

Aqueous photochemical degradation of mefenamic acid and triclosan: role of wastewater effluent matrices.

In this study, photochemical degradation of two emerging pharmaceutical chemicals, mefenamic acid (MF) and triclosan (TCS), was investigated to clarify the role of treated wastewater effluent matrices on their environmental photolysis. Target compounds were individually exposed to simulated sunlight in different media: ultrapure buffered water and synthetic field water with treated municipal wastewater effluent. The results in ultrapure buffered water showed that the direct photolysis processes in aquatic environments are not relevant to the elimination of MF. However, in samples containing treated wastewater effluent, photochemical degradation of MF was clearly enhanced. Our results indicate that MF undergoes indirect photolysis by reactive intermediates produced in an effluent matrix. Further quenching experiments suggested that photochemically produced hydroxyl radicals and excited triplet state dissolved organic matter drive the degradation of MF. In contrast to MF, TCS photochemical degradation proceeds through rapid direct photolysis. TCS was quickly degraded in ultrapure buffered water but it is considerably hampered in samples containing wastewater effluent. The declined degradation of TCS in the synthetic field water was discussed in terms of underlying optical filter effects by coexisting chromophoric substances. Results emphasize the importance of taking local water chemistry into consideration when predicting natural attenuation of pharmaceutical chemicals in receiving areas.

Evaluation of complex copper ore sorting: Effect of optical filtering on particle recognition

In mixed and multi-component mineral systems, the reflectance spectra of individual minerals interfere with the reflectance/absorbance features of other minerals and random spectra can form. This contradictory case causes difficulty in implementing ore sorting to certain minerals. Hence, filtering out certain wave lengths may prevent this situation which makes it difficult for an ore sorter to perform a selective and efficient separation. The scope of this study is to investigate the feasibility of the optical filtering to enhance the differences in the reflectance features of mineral grains, and to compare the possible separation performances of the ore sorters under the best filtered and unfiltered conditions.Within the experimental studies, a new experimental setup which runs its uniquely coded software was designed. Additionally, an adjustable filter cartridge apparatus was developed enabling to mount the wavelength specific filters in front of the conventional sensors which support universal f-mount type lenses. A representative sample batch consisting of 31 grains of complex copper ore was prepared. Filtered and unfiltered images of each grain in between 450 and 1650 nm wavelength range were acquired carefully with the designed experimental setup. Following the data extraction by imaging studies, each particle was weighed, ground, and analyzed to determine chemical compositions. Thus, the reflectance values and chemical analysis data of each particle with each filter were obtained. Principal component analysis (PCA), partial least square analysis (PLS) and stepwise multiple linear regression (SMLR) methods were used to evaluate the resulting data in order to establish meaningful relationships between dominant chemical contents and reflectance values of each individual particle. Hence, the effect of using optical filters in altering the differences among the reflectance values of complex copper ore grains has been determined. Following the determination of best filters and wave lengths, projected product qualities of a conjectural optical sorting operation integrated with optical filters have been analytically investigated. It was concluded that an alteration in the relationship between % sulphide content and reflectance values was observed over 1500 nm wavelengths in comparison to the unfiltered and other filtered conditions. Evaluation of the overall results showed that up to 73.30% of Au, 96.14% of Ag, and 86.24% of CuFeS2 in feed can be recovered when a long-pass 1500 nm filter was used.

Direct laser writing of vertical junctions in graphene oxide films for broad spectral position-sensitive detectors

Abstract Heterostructures with built-in electric fields are crucial for charge separation and lateral photovoltaic effect in current position-sensitive detectors (PSDs), which have to be produced by combining semiconductors with metal or other semiconductors to form various vertical junctions (e.g. Schottky junctions) via complicated and high-cost manufacture processes. In the present work, it was found that vertical junctions can be directly written and patterned inside graphene oxide (GO) films with gradient C/O ratios by laser scribing due to the optical filter effect of the films and the formation of reduced GO (rGO) layers. Such junctions were verified to show the capability for high-precision position sensing on the micrometer scale, owing to the lateral photovoltaic effect. These self-powered laser-scribed PSDs can exhibit a small nonlinearity of <5.4%, which is far less than the acceptable level of 15%. A fast response time of about 1 ms can be obtained under a zero bias voltage, which is the fastest speed among the photodetectors based on pure rGO. Electron lateral diffusion in the upper layers of the laser-scribed devices was found to play a main role. These suggest that laser-scribed vertical junctions inside rGO are promising for high-precision displacement sensing, with the capability of low cost, flexibility, and passive operation mode.

Transmitter power control for a multicarrier visible light communication system

AbstractHigher bandwidth becomes a major challenge in the development and implementation of visible light communication systems as transmission rates increase. One way of increasing bandwidth is through wavelength division multiplexing in multicarrier systems that use red, green, and blue light‐emitting diodes to produce white light. However, these systems often suffer from low performance as a result of crosstalk interference, mainly caused by the imperfect nature of optical filters used to discriminate between the colors. This paper demonstrates the use of centralized transmitter power control to predict the trends in the performance of a multicarrier visible light communication system that employs red and blue light emitting diodes. We have shown that, using a model that takes into consideration the effects of optical filters used for detection of colors at the receiver, one is able to predict the trends in the overall system's performance. This enables us to adequately determine the optimal power levels in the red and blue channels, which will result in the best overall performance of the system. Our model can be used in the design and implementation of multicarrier systems to minimize the crosstalk, which improves the performance, and lead to efficient higher bandwidth. The model is first implemented in computer simulations and then tested on an experimental set‐up to validate the results.

Quadrupole mode plasmon resonance enabled subwavelength metal-dielectric grating optical reflection filters.

A metal-dielectric subwavelength grating structure was investigated for making single-peak narrow linewidth optical reflection filters in the near-infrared region. The subwavelength grating filter structure consists of a one-dimensional periodic array of metal (gold) and dielectric (Al2O3) elements on a dielectric substrate. Optimized reflection filters have a single reflection peak with ~10 nm linewidth in the infrared region over a wide spectral band. Finite-difference time-domain (FDTD) simulations and multipole analysis show that the narrow linewidth reflection is due to the coupling of the Rayleigh anomaly wave to the quadrupole plasmon resonance mode of the subwavelength metal-dielectric grating. Additionally, it was found that the contrast of the indices of refraction of two dielectric materials in the subwavelength structure is critical for realizing optical filter effect.

Tunable band (pass and stop) filters based on plasmonic structures using Kerr-type nonlinear rectangular nanocavity

We have proposed and numerically investigated two plasmonic structures for bandpass and band-stop filters. The bandpass filter is composed of two metal–insulator–metal (MIM) waveguides coupled to each other by a nonlinear rectangular nanocavity. The band-stop filter consists of an MIM waveguide side coupled to a Kerr-type nonlinear rectangular nanocavity. The optical filtering effect is verified by two-dimensional (2-D) finite-difference time-domain (FDTD) simulations. It is demonstrated that based on optical nonlinearity we can easily make the proposed filters tunable by properly adjusting the intensity of incident light without changing the dimensions of the structures. The simulation results revealed that within the transmission spectrum, the selected central wavelength and the bandwidth of the filter can be tuned by the input signal intensity. The proposed structures are suitable to be used as highly dense integrated optical circuits, where limitations on the dimensions of the filter structure are vital.

Vision-based keyhole detection in laser full penetration welding process

In a laser full penetration welding process, keyhole behavior affects the welding quality most. Due to the variation of wall thickness, constant welding speed and power will lead to partial penetration or over heat. So, effective monitoring and control method is needed to improve the quality of laser full penetration welding. In this paper, a vision based full penetration hole detection system is studied. The effects of exposure time, zooming lens, and optical filters on the quality of coaxial images are investigated. Among these factors, narrow bandwidth filters affect coaxial images most, because according to Plank law, workpiece under different temperature will emit light of different wavelengths, and the images under different narrow bandwidth filters reflect the temperature distribution of workpiece. The full penetration hole detection algorithm is developed based on region grow algorithm. Images of different welding speed and power are captured, and the relationship of the diameter of full penetration hole with welding speed and laser power is studied. The detection algorithm can identify partial penetration welding and laser cutting. It can be used to closed loop control of laser welding in future.

Theoretical Analysis of the Optical Filtering Effect on a Directly Modulated Reflective Semiconductor Optical Amplifier

The modulation bandwidth of a reflective semiconductor optical amplifier (RSOA) is limited by carrier lifetime. Therefore, it is hard to directly modulate an RSOA with high-speed electrical signals. We theorize that an optical filter can act as an optical equalizer, compensating for the narrow bandwidth limitation imposed by the RSOA. By modeling a time-varying RSOA with a modified transfer matrix method (TMM), we simulated 25 Gbps operation of an RSOA with optical filtering effects. We investigated the impact of detuning the center wavelength of the optical filter on the modulation of an RSOA. The numerical results show that it is possible to modulate an RSOA with an optical filtering effect at 25 Gbps without electronic equalization or digital signal processing.