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Interval between adjacent planar waveguides and light intensity emitted from waveguide surface were the primary two factors affecting light distribution characteristics in the planar waveguide flat-plate photobioreactor (PW-PBR). In this paper, the synergy effect between light and nitrate in the PW-PBR was realized to simultaneously enhance microalgae growth and lipid accumulation. Under an interval of 10 mm between adjacent planar waveguides, 100% of microalgae cells in regions between adjacent waveguides could be illuminated. Chlorella vulgaris growth and lipid accumulation were synchronously elevated as light intensities emitted from planar waveguide surface increasing. With an identical initial nitrate concentration of 18 mM, the maximum lipid content (41.66% in dry biomass) and lipid yield (2200.25 mg L −1 ) were attained under 560 μmol m −2 s −1 , which were 86.82% and 133.56% higher relative to those obtained under 160 μmol m −2 s −1 , respectively. The PW-PBR provides a promising way for microalgae lipid production. [ABSTRACT FROM AUTHOR]

An essential impact which can improve the indoor environment and save on power consumption for artificial lighting is utilization of daylight. Optical fiber daylighting technology offers a way to use direct daylight for remote spaces in a building. However, the existing paradigm based on the precise orientation of sunlight concentrator toward the Sun is very costly and difficult to install on the roof of buildings. Here, we explore an alternative approach using mirror-coated lens array and planar waveguide to develop a flat optical fiber daylighting system (optical fiber daylighting panel) with lateral displacement Sun-tracking mechanism. Sunlight collected and reflected by each mirror-coated lens in a rectangular lens array is coupled into a planar waveguide using cone prisms placed at each lens focus. This geometry yields a thin, flat profile for Sunlight concentrator. Our proposed concentrating panel can be achieved with 35 mm thickness while the concentrator's width and length are 500 mm × 500 mm. The commercial optical simulation tool (LightToolsTM) was used to develop the simulation models and analyze the system performance. Simulation results based on the designed system demonstrated an optical efficiency of 51.4% at a concentration ratio of 125. The system can support utilizing a lateral displacement Sun-tracking system, which allows for replacing bulky and robust conventional rotational Sun-tracking systems. This study shows a feasibility of a compact and inexpensive optical fiber daylighting system to be installed on the roof of buildings. [ABSTRACT FROM AUTHOR]

A simple, compact, low cost and highly sensitive refractive index sensor based on single mode leaky planar waveguide is reported. An optical waveguide fabricated on glass substrate has been proposed to construct the sensor. In this structure Cytop works as guiding layer while Teflon forms the cladding layers. Propagation of light in Cytop layer is strongly affected by the refractive index of external medium placed on top of Teflon layer. If the refractive index of the medium is close to or greater than that of Cytop, there is leakage of power from Cytop layer to external medium which affects the transmittance of the waveguide. The structure can be designed to have strong variation in transmittance with the refractive index of external medium and, thus, can be utilized as a highly sensitive refractive index sensor for biomedical applications. In this paper we have carried out the designs of such refractive index sensor for various biological and chemical applications. We design a sensor having sensitivity of the order of 10 4 dB/RIU. Fabrication of the sensor can be carried out by using spin coating technique. Long sensing range, high sensitivity, simple manufacturing process and compactness make the sensor attractive for diverse applications. [ABSTRACT FROM AUTHOR]

A biosensor experimental set-up based on a silicon oxide/ silicon nitride/ silicon oxide waveguide operating as polarization interferometer was designed, built, and tested. The operation principle of the proposed sensor lies in the detection of a phase shift between p -and s -components of polarized light. The mode of operation of the proposed sensor is similar to that of Mach-Zehnder interferometer, while its design is much simpler and does not require splitting the waveguide into two arms. The refractive index sensitivity of the polarization interferometer sensor in the range of 1200 radians per refractive index unity (RIU) was evaluated. Several biosensing tests were conducted on detection of aflatoxin B1 in direct immunoassay with specific antibodies immobilized in the sensing window. Binding of 0.01 ng/ml (10 ppt) of aflatoxin B1 appeared to cause a phase shift of approximately one period. This is a remarkably high sensitivity (especially for direct immunoassay format) which the detection of mycotoxins in much lower concentrations in ppt level. [ABSTRACT FROM AUTHOR]

Highly transparent YAG/10at.%Yb:YAG/YAG planar waveguide ceramics were fabricated by the non-aqueous tape casting and solid-state reactive sintering technology. The tapes are relatively homogeneous and the green body shows a dense structure without distinct interfaces after the treatment of debinding and cold isostatic pressing. YAG/10at.%Yb:YAG/YAG ceramics with almost full dense structure were obtained by vacuum-sintering at 1760 °C for 30 h. For the mirror-polished sample with the thickness of 3.5 mm, the In-line transmittance was measured to be 83.6% at the visual wavelength of 400 nm. The diffusion distance of the Yb 3+ ions was about 215 μm along the thickness direction of the ceramics. In the lasing experiments, the YAG/10at.%Yb:YAG/YAG planar waveguide ceramics were end-pumped by a 976 nm semiconductor diode laser and enabled efficient continuous-wave lasers, which resulted in a maximum output power of 1.6 W and a slope efficiency of 34.4% at 1030 nm. [ABSTRACT FROM AUTHOR]

A planar waveguide-based array immunosensor (PWAI) was described, allowing measurements of up to twenty-four analytes in eight separate channels rapidly, sensitively and simultaneously. In this system, a linear laser light created by a line generator was coupled into a planar optical waveguide via a beveled angle, forming eight individual total internal reflection (TIR) lines. A multi-channel microfluidics cell was employed to isolate the parallel TIR lines physically so as to form eight independent flow channels on the same chip, avoiding the cross-reactivity of antibodies and supporting various bioassay conditions. By employing fluorescent detection with fluorophore-labeled antibodies binding to the surface of the waveguide with the analyte derivative covalently attached, the array immunoassays can realize the multi-analyte biosensing. A model was proposed to guide the design of such a planar waveguide-based evanescent wave biosensor. The proposed system was confirmed with the comparable sensitivity with previously reported waveguide biosensor. In addition to being a multi-channel analytical device for the highly sensitive detection of contaminants, the proposed evanescent wave PWAI can provide the dynamic surface-based biomolecular interaction information regarding the affinity and kinetics with high sensitivity. [ABSTRACT FROM AUTHOR]

Industrially manufactured planar waveguides doped with light scattering nanoparticles, which can dilute and redistribute the intense incident light within microalgae suspension more uniformly, were introduced into a flat-plate photobioreactor (PBR) with a width of 25 cm to alleviate the adverse effect of poor light penetrability on microalgae growth. Compared with the flat-plate PBR without waveguides, the illumination surface area per unit volume in the proposed PBR was increased by 10.3 times. During the whole cultivation period, the illuminated volume fractions in the proposed PBR were 21.4–410% higher than those in the flat-plate PBR without waveguides. Consequently, attributed to the optimized light distribution in the proposed PBR, a 220% improvement in biomass production was obtained relative to that in the flat-plate PBR without waveguides. Furthermore, higher light output intensities emitted from the planar waveguide surfaces and increased microalgae growth rates were achieved by decreasing the length of planar waveguides. [ABSTRACT FROM AUTHOR]

Erbium (Er)-doped ytterbium garnet [(ErYb)AlO; x = 0.005, 0.02 and 0.1, YbAG] planar waveguides have been prepared by an aqueous sol-gel method using polyvinylpyrrolidone as a gelling agent. The thermal behavior of gel was studied by thermogravimetry and differential thermal analysis. The phase composition of the films was determined using X-ray diffraction. Surface analysis was carried out by atomic force microscopy. A pure infrared emission of Er ions was observed in all prepared films. Light propagation was studied by m-line spectroscopy using several wavelengths (633, 964, 1311 and 1552 nm). The minimum coating cycles to observe one propagated mode at 1552 nm were determined to be 7. The sol-gel-derived Er:YbAlO seems to be a promising material for light amplifiers in the IR region. Graphical Abstract: [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of planar waveguides in an Er-doped tungsten-tellurite glass by implantation of 3.5 MeV N+ ions. Implantations were carried out in a wide fluence range of 1·1016 ÷8 ·1016 ions/cm2. Waveguides were characterized by m-line spectroscopy and spectroscopic ellipsometry. Irradiation-induced refractive index modulation saturated around a fluence of 8 ·1016 ions/cm2. Waveguides operating at 1550 nm were obtained in that material using 3.5 MeV N+ ion implantation.

A birefringence compensation technique based on angled star couplers in arrayed waveguide grating (AWG) is experimentally investigated in silica-on-silicon waveguide with B-Ge codoped upper cladding. A 16-channel AWG with 100-GHz channel spacing is designed and fabricated. The star couplers are designed according to Rowland circle construction with an oblique incident/diffraction angle. Five different polarization compensation parameters corresponding to different incident/diffraction angles are employed to investigate the stress-induced birefringence. The experimental results confirm that the polarization-dependent wavelength shift (PDλ) can be tuned by varying the incident/diffraction angle at the star couplers, and a birefringence-free AWG can be achieved without any additional fabrication process.

The research aim of this work is to develop a simple and highly sensitive optical biosensor for detection of mycotoxins. This sensor is built on a planar waveguide operating on the polarization interferometry principle, i.e., detecting a phase shift between p- and s-components of polarized light developed during the binding of analyte molecules. The operation of the proposed sensor is similar to that of a Mach–Zehnder interferometer, while its design is much simpler and it does not require splitting the waveguide into two arms. The refractive index sensitivity of the polarization interferometer sensor was in the range of 5200 radians per refractive index unit (RIU). Several tests were conducted to detect ochratoxin A (OTA) at different concentrations in direct immunoassay with specific antibodies immobilized in the sensing window. The lowest concentration of OTA of 0.01 ng/mL caused a phase shift of nearly one period. The results obtained prove high sensitivity of the sensors, which are capable of detecting even lower concentrations of mycotoxins at the ppt (part-per-trillion) level.

Due to the remarkable properties of chalcogenide (Chg) glasses, Chg optical waveguides should play a significant role in the development of optical biosensors. This paper describes the fabrication and properties of chalcogenide fibres and planar waveguides. Using optical fibre transparent in the mid-infrared spectral range we have developed a biosensor that can collect information on whole metabolism alterations, rapidly and in situ. Thanks to this sensor it is possible to collect infrared spectra by remote spectroscopy, by simple contact with the sample. In this way, we tried to determine spectral modifications due, on the one hand, to cerebral metabolism alterations caused by a transient focal ischemia in the rat brain and, in the other hand, starvation in the mouse liver. We also applied a microdialysis method, a well known technique for in vivo brain metabolism studies, as reference. In the field of integrated microsensors, reactive ion etching was used to pattern rib waveguides between 2 and 300 μm wide. This technique was used to fabricate Y optical junctions for optical interconnections on chalcogenide amorphous films, which can potentially increase the sensitivity and stability of an optical micro-sensor. The first tests were also carried out to functionalise the Chg planar waveguides with the aim of using them as (bio)sensors.