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Channel waveguides with diffraction gratings at their input and output for light injection and extraction, respectively, constitute the key components for applications in integrated optics and photonics. Here, we report for the first time on such fluorescent micro-structured architecture entirely elaborated on glass by sol-gel processing. This architecture particularly takes advantage of a high-refractive index and transparent titanium oxide-based, sol-gel photoresist that can be imprinted through a single photolithography step. This resist enabled us to photo-imprint the input and output gratings on a photo-imprinted channel waveguide doped with a ruthenium complex fluorophore (Rudpp). In this paper, the elaboration conditions and optical characterizations of derived architectures are presented and discussed with respect to optical simulations. We firstly show how the optimization of a two-step deposition/insolation sol-gel procedure leads to reproducible and uniform grating/waveguide architectures elaborated on rather large dimensions. Then, we show how this reproducibility and uniformity govern the reliability of fluorescence measurements in waveguiding configuration. These measurements demonstrate that: (i) our sol-gel architecture is well adapted to the efficient channel–waveguide/diffraction grating coupling at the Rudpp excitation and emission wavelengths; (ii) it enables an efficient propagation of the emission signal in the core of the waveguide allowing its photo-detection after extraction through the output grating; and (iii) it is affected by very reduced parasitic mechanisms, such as propagation losses and photobleaching features. This work constitutes a promising preliminary step toward the integration of our architecture in a microfluidic platform for further fluorescence measurements in liquid medium and waveguiding configuration. [ABSTRACT FROM AUTHOR]

Space-selective laser-induced crystallization of glass enables direct femtosecond laser writing of crystal-in-glass channel waveguides having nearly single-crystal structure and consisting of functional phases with favorable nonlinear optical or electrooptical properties. They are regarded as promising components for novel integrated optical circuits. However, femtosecond-laser-written continuous crystalline tracks typically have an asymmetric and strongly elongated cross-section, which causes a multimode character of light guiding and substantial coupling losses. Here, we investigated the conditions of partial remelting of laser-written LaBGeO5 crystalline tracks in lanthanum borogermanate glass by the same femtosecond laser beam which had been used for their writing. Exposure to femtosecond laser pulses at 200 kHz repetition rate provided cumulative heating of the sample in the vicinity of the beam waist sufficient to provide space-selective melting of crystalline LaBGeO5. To form a smoother temperature field, the beam waist was moved along the helical or flat sinusoidal path along the track. The sinusoidal path was shown to be favorable for tailoring the improved cross-section of the crystalline lines by partial remelting. At optimized laser processing parameters, most of the track was vitrified, and the residual part of the crystalline cross-section had an aspect ratio of about 1:1. Thermal-induced stress emerging during the tailoring procedure was efficiently eliminated by fine post-annealing. The proposed technique suggests a new way to control the morphology of laser-written crystal-in-glass waveguides by tailoring their cross-section, which is expected to improve the mode structure of the guided light. [ABSTRACT FROM AUTHOR]

A method for calculating parameters of rectangular waveguides using separation of variables is presented. The method makes it possible to calculate multilayer Bragg waveguides with an arbitrary number of layers and an arbitrary composition as photonic crystal structures with defect. A result of the numerical calculation of the dispersion diagram of such a structure is given. This result is in good agreement with the earlier published data on the study of similar structures.

Space-selective laser-induced crystallization of glass enables direct femtosecond laser writing of crystal-in-glass channel waveguides having nearly single-crystal structure and consisting of functional phases with favorable nonlinear optical or electrooptical properties. They are regarded as promising components for novel integrated optical circuits. However, femtosecond-laser-written continuous crystalline tracks typically have an asymmetric and strongly elongated cross-section, which causes a multimode character of light guiding and substantial coupling losses. Here, we investigated the conditions of partial remelting of laser-written LaBGeO5 crystalline tracks in lanthanum borogermanate glass by the same femtosecond laser beam which had been used for their writing. Exposure to femtosecond laser pulses at 200 kHz repetition rate provided cumulative heating of the sample in the vicinity of the beam waist sufficient to provide space-selective melting of crystalline LaBGeO5. To form a smoother temperature field, the beam waist was moved along the helical or flat sinusoidal path along the track. The sinusoidal path was shown to be favorable for tailoring the improved cross-section of the crystalline lines by partial remelting. At optimized laser processing parameters, most of the track was vitrified, and the residual part of the crystalline cross-section had an aspect ratio of about 1:1. Thermal-induced stress emerging during the tailoring procedure was efficiently eliminated by fine post-annealing. The proposed technique suggests a new way to control the morphology of laser-written crystal-in-glass waveguides by tailoring their cross-section, which is expected to improve the mode structure of the guided light.

This work is devoted to the study of the pyroelectric effect on the properties of optical waveguides formed in a lithium niobate crystal by proton exchange. In the present work, we studied the cessation effect of the radiation channeling during thermocycling of Y-splitters samples. We examined the spectral dependence of optical losses on the wavelength using an optical spectrum analyzer. The results demonstrate that in the range of 1530–1570 nm, all wavelengths are suppressed equally. The optical frequency domain reflectometry shows that the increase of optical losses is observed along the entire waveguide, but not only at the Y-splitting point, as supposed earlier. [ABSTRACT FROM AUTHOR]

We report on the fabrication of filament damages in Yb-doped phosphate glass by femtosecond laser pulses. The uneven index modification was obtained using a 20× optical microscope objective with 0.4 numerical apertures. The multimode fields of original channel waveguides were investigated and in good agreement with the simulation results, whose structures can be regarded as a kind of beam splitters. Under the optical pump at 976 nm, the end region of the original filament shows continuous wave laser oscillation. The elongated and uniform filaments were fabricated by introducing a circular aperture, so that the guiding performance of tradition-channel single mode was achieved. Both large-mode-area waveguides are expected to find applications in optical communications and high-power lasers and amplifiers. [ABSTRACT FROM AUTHOR]

Silicon photonics is the most important technological platform for creating a variety of functional optical elements, including promising types of optical sensors. Moreover, in recent years, 20% of all publications on silicon photonics are devoted to the development of various versions of optical sensors. Their advantage steams from the combination of high technical parameters with the possibility of mass production using CMOS technology of microelectronics and nanophotonics. A brief description of various technological solutions of the last decade that provide progress in the development of optical sensor characteristics is given. Special attention is paid to new promising sensor designs based on bimodal technology, which promises a significant increase in sensor sensitivity by means of equalizing the group delay of a pair of different optical modes propagating through the waveguide structure. The review will be useful for domestic and foreign researchers working in the field of sensor development. [ABSTRACT FROM AUTHOR]

This work is devoted to the study of the pyroelectric effect on the properties of optical waveguides formed in a lithium niobate crystal by proton exchange. In the present work, we studied the cessation effect of the radiation channeling during thermocycling of Y-splitters samples. We examined the spectral dependence of optical losses on the wavelength using an optical spectrum analyzer. The results demonstrate that in the range of 1530–1570 nm, all wavelengths are suppressed equally. The optical frequency domain reflectometry shows that the increase of optical losses is observed along the entire waveguide, but not only at the Y-splitting point, as supposed earlier.

This article presents a numerical model of field-assisted Ag+-Na+ ion exchange in glass, used to determine Ag+ ion concentration contours in cross-sections of channel waveguides. Space charge density was used as a modeling parameter, with different values adopted separately under the mask and in the region of the mask window. Based on the results of simulations, it can be stated that the space charge distribution under the mask has a decisive influence on the diffusion range of Ag+ ions into the glass and on the shape of silver ion concentration contours corresponding to the maximum range of Ag+ ions diffusion. Charge generated within the diffusive structure influences the shape of silver ion concentration contours near the mask's edge and affects the thickness of the polarized layer under the mask within the waveguide's optical structure. Modeling results indicate a significant influence of factors affecting space charge density distribution in glass on the results of forming channel waveguides in the field-assisted process. [ABSTRACT FROM AUTHOR]

Featured Application: The results can have application in fiber optic gyroscopes to avoid the breakdown during the fast heating of device. It is shown that the termination of the channeling of the fundamental radiation mode in the waveguide can be observed upon heating of an optical integrated circuit based on proton exchange channel waveguides formed in a lithium niobate single crystal. This process is reversible, but restoration of waveguide performance takes tens of minutes. The effect of the waveguide disappearance is observed upon rapid heating (5 K/min) from a low temperature (minus 40 °C). This effect can lead to a temporary failure of navigation systems using fiber optic gyroscopes with modulators based on a lithium niobate crystal. [ABSTRACT FROM AUTHOR]

A flagship application of miniaturized chemical optical (CO) sensors is the real-time monitoring of cell cultures in the biomedical field. Most of these devices are based on fluorescence variations when a fluorophore encapsulated in the sensor is brought into contact with an analyte. In this context, micro-structured architectures involving light coupling between a channel waveguide and diffraction gratings appear a promising way to propose integrated devices with enhanced detection sensitivity. In this paper, we report for the first time on such micro-structured architecture entirely elaborated through a sol-gel route. This work particularly highlights the potential of a high refractive index titanium oxide based sol-gel photoresist that can be imprinted through a single photolithography step (selective insolation/development) to form a given pattern, thus avoiding multi-step and rather costly traditional lithographic procedures. We firstly present a simplified two-step process taking advantage of this photoresist and leading to micro-structured architectures composed of diffraction gratings imprinted on channel waveguides. Both components of these architectures have been optimized on the basis of opto-geometrical characterizations and modeling. Then channel waveguide/diffraction grating coupling assessments are presented and discussed, showing that light coupling can effectively be achieved in the sol-gel architectures. This work constitutes a first step that opens the route to new CO sensors in channel waveguide configuration. • A two-step deposition/insolation sol-gel procedure is developed. • The sol-gel procedure takes advantage of a photosensitive TiO 2 -based resist. • Selective insolation yields a channel waveguide/diffraction grating architecture. • Light coupling between the waveguide and the grating is demonstrated. • The sol-gel architecture is intended for integration in chemical optical sensors. [ABSTRACT FROM AUTHOR]

Dielectric-loaded graphene groove waveguide (DLGGW) structure is designed and the channel hybrid plasmonic modes are investigated in the terahertz domain. The proposed structure could effectively suppress the mode field confinement with relative low transmission loss due to the strong coupling between the dielectric mode and the channel graphene plasmonic mode. A typical propagation length is 37 . 8 μ m, and optical field is confined into an ultra-small area of approximately 52 μ m 2 at 1.5 THz. By changing the size of cylinder, the angle of the graphene groove, and the thickness of dielectric coating layer, the compromise between confinement and loss could be balanced flexibly. Unlike plasmons in noble metals, the propagation loss in DLGGW structure could be tuned by the graphene conductivity. Moreover, because of the imaginary part of graphene conductivity being positive, the proposed waveguide can propagate in a large terahertz frequency regime. This waveguide shows great applications in optical integrated devices, such as detectors, sensors and spectroscopy. [ABSTRACT FROM AUTHOR]

We numerically demonstrate mid-infrared supercontinuum generation in dispersion-engineered chalcogenide glass channel waveguide. The proposed ridge waveguide consists of arsenic pentasulfide (As 2 S 5 ) strip deposited on magnesium fluoride (MgF 2 ) substrate and air acting as an upper cladding. The structure parameters are calculated and optimized by using the fully vectorial finite-difference in the frequency-domain (FDFD) method Results indicates that the proposed waveguide exhibits an all normal dispersion (ANDi) profile over a wide spectral range with a zero dispersion wavelength (ZDW) around 2 μm. By solving the generalized nonlinear Schrödinger equation, we demonstrate supercontinuum generation extending from the near infrared to the mid infrared region. Indeed, a broad and perfectly coherent ultra-flat supercontinuum spectrum spanning the region from 700 to 5200 nm is successfully generated by using a 25 kW peak power 100 fs input pulse pumped at 2.5 μm, in a waveguide of 5 mm length. [ABSTRACT FROM AUTHOR]

It is shown that the termination of the channeling of the fundamental radiation mode in the waveguide can be observed upon heating of an optical integrated circuit based on proton exchange channel waveguides formed in a lithium niobate single crystal. This process is reversible, but restoration of waveguide performance takes tens of minutes. The effect of the waveguide disappearance is observed upon rapid heating (5 K/min) from a low temperature (minus 40 °C). This effect can lead to a temporary failure of navigation systems using fiber optic gyroscopes with modulators based on a lithium niobate crystal.

Channel optical waveguides and one-dimensional (1D) diffraction gratings are recorded by laser radiation with wavelengths of 450 and 532 nm within lithium niobate surface layers doped with iron and copper. The characteristics of induced elements are studied by light diffraction. The channel waveguides with widths from 40 to 70 μm are formed in lithium niobate sample with consecutive exposure of stripe-shaped areas. Planar 1D diffraction gratings localized at the surface are formed by its exposure through amplitude masks. Their characteristics are studied with light diffraction using the transmission geometry and at total internal reflection of light from the surface. [ABSTRACT FROM PUBLISHER]

We show numerically, how a chalcogenide planar waveguide designed to exhibit normal dispersion over a wide spectral range around the pump wavelength can produce relatively flat supercontinuum in the mid-infrared regime. A 1-cm-long channel waveguide, made using Ge11.5As24Se64.5 glass and pumped at 1.55 \mu \textm using short optical pulses with only 25 W peak power, produced a supercontinuum that was nearly 600 nm wide. Employing the same pump source with a peak power of 100 W, the supercontinuum could be extended to beyond 2.2 \mu \textm with a bandwidth of 1000 nm. By shifting the pump wavelength to 3.1 \mu \textm and using pulses with peak powers of up to 3 kW, the resulting ultraflat supercontinuum extended from 2 to 5.5~\mu \textm . Even a wider spectral range (1.8-6 \mu \textm ) can be realized if MgF2 glass is used for the lower cladding while maintaining power variations below 5 dB over the entire bandwidth. [ABSTRACT FROM AUTHOR]