Need For Optical Elements Research Articles

A very low-cost pulse-amplitude modulated chlorophyll fluorometer

The quantum yield of photosystem II (ϕPSII) is an important metric to determine a plant’s light use efficiency and to detect plant stresses. Commercial instruments that measure ϕPSII exist, but their cost may prevent widespread adoption. We present the design and realization of a chlorophyll fluorometer capable of measuring ϕPSII that uses a minimal set of optical components and relies on low-cost electronics with total component costs below USD 300. A consumer grade 405 nm laser diode obviates the need for optical elements in the excitation path, and an avalanche photodiode ensures high sensitivity. In addition, an emission filter and a collimating lens are needed. We demonstrate sensor linearity and actinic light immunity with fluorescence reference standards, and we compare our device to a commercial instrument to assess accuracy: With three plant species (Spathiphyllum, Heuchera, and Hosta) and under actinic light variations from zero to 450 μmolm−2s−1, reported ϕPSII from both instruments correlated with R2=0.87. Implications of our design choices, their costs, and alternatives are discussed.

Performing Calibration of Transmittance by Single RGB-LED within the Visible Spectrum.

Spectrophotometry has proven to be an effective non-invasive technique for the characterization of the pollution load of sewer systems, enabling compliance with new environmental protection regulations. This type of equipment has costs and an energy consumption which make it difficult to place it inside a sewer network for real-time and massive monitoring. These shortcomings are mainly due to the use of incandescent lamps to generate the working spectrum as they often require the use of optical elements, such as diffraction gratings, to work. The search for viable alternatives to incandescent lamps is key to the development of portable equipment that is cheaper and with a lower consumption that can be used in different points of the sewer network. This research work achieved the following results in terms of the measured samples: First, the development a calibration procedure that enables the use of RGB-LED technology as a viable alternative to incandescent lamps, within the range of 510 to 645 nm, with high accuracy. Secondly, demonstration of a simple method to model the transmittance value of a specific wavelength without the need for optical elements, achieving a cost-effective equipment. Thirdly, it provides a simple method to obtain the transmittance based on the combination of RGB colors. Finally its viability is demonstrated for the spectral analysis of wastewater.

Optical diode activity in an axially asymmetric nonlinear medium incorporated with phenothiazine and silver nanoparticles

In order to overcome the limitations posed by electronic devices, and to fulfill the need for optical elements in integrated photonic circuits, it is crucial to develop an optical analogue of an electronic diode which is one of the most basic elements of electronic circuits. Asymmetric light transmission is essential for fabricating such an all-optics based system. Different structures and configurations have been proposed for exhibiting asymmetric photonic signal transmission but found ineffective due to their complex structure and/or relatively large size. Here we discuss the results of theoretical investigation and consequent experimental realization of a nonlinear thin-film multilayer device that exhibits passive anisotropic optical transmission an optical analogue of electronic diode. This optical diode requires neither a magnetic field nor strong input fields for the diode action, whereas many conventional optical diode systems fail to work under ambient conditions and are unsuitable for integration into optical circuits. The system proposed here is based on axially asymmetric nonlinear absorption in an orderly arranged thin saturable absorber and a thin reverse saturable absorber. The variation of optical diode action on changing the parameters such as linear transmittance, nonlinear absorption coefficients and saturation intensity are theoretically simulated to understand how the forward and reverse transmittances change with the parameters. The experimental demonstration of the diode activity has been accomplished using single beam open aperture z-scan technique at an on-axis input intensity of ~0.27 GW/cm2, where the saturable absorber was Ag nanoparticles prepared by liquid phase laser ablation technique and the reverse saturable absorber was Phenothiazine-Ag composite. The system exhibited good non-reciprocity in this range 0.14–0.42 GW/cm2 and the observed non-reciprocity factor at 0.27 GW/cm2 on-axis input intensity is around 3. Due to a large bandwidth, good chemical and thermal stability, cost-effectiveness and large-scale integration with existing fabrication technologies, this optical diode based on axial asymmetry in nonlinear absorption is a good candidate for future all optical communications and computing.