Metal-clad Optical Waveguide Research Articles

Experimental study of DC Kerr effect of chalcogenide glass film by free space coupling method

Chalcogenide glass is an important nonlinear optical material that has attracted much attention in the areas of integrated photonics, supercontinuum sources, and all-optical switches in recent years. However, the current research mainly focuses on the nonlinear effect excited by light, and the research on its properties under the action of a DC field is still deficient. Here, a metal-cladding optical waveguide, which is composed of a chalcogenide glass film coated on a glass substrate, is presented to analyze the quadratic electro-optic (QEO) effect of the chalcogenide glass film. The DC Kerr coefficient and the whole components of the QEO tensor of the sample were experimentally determined by the free space coupling method.

Adsorption independent silver colloids index measurement with metal-cladding optical waveguide

The refractive index measurements of silver nanoparticles colloids can provide chemical composition and nanostructure details. Although the standard surface plasmon resonance (SPR) approach improves index measurement precision, it is restricted by silver nanoparticles adsorption and incapable of detecting the colloid index due to the evanescent nature of the surface wave. Herein, a method utilizing metal-cladding optical waveguide (MCOW) was proposed to measure the volume refractive index of silver nanoparticles colloids, importantly, which is independent of particle adsorption. The experimental results show that the sensitivity of the refractive index measurement using the MCOW approach is at least 10−6 RIU (Refractive Index Unit) owing to the oscillating ultrahigh-order modes, this work not only presents a high-sensitivity, high-yield, simple-to-process, and effective refractive index measuring technique, but also recommends a more practical and adaptable colloidal particle characterization approach.

Metal-Clad Waveguide Resonance Sensor Using a Mesoporous TiO2 Thin Film as the Chemical Sensitive Core Layer

A metal-clad optical waveguide sensor based on guided-mode resonance spectroscopy has been developed using a mesoporous TiO2 film as the chemical-sensitive core layer. The sol–gel block copolymer templated mesoporous TiO2 films are ∼275 nm thick, supporting both the transverse electric (TE) and transverse magnetic (TM) modes and thus providing the sensor with the TE- and TM-related dual sensitivities. Both the TE- and TM-mode resonance wavelengths (λR) at the same incident angle were obtained by broadband attenuated total reflection spectroscopy. The film porosity was determined to be ∼0.535 by using the combination of Fresnel formula and Bruggeman approximation to fit the measured values of λR. The TE- and TM-related sensitivities of the sensor to the two analytes of elaidic acid (EA) and Cr6+ were measured at the same incident angle. For each analyte, the TM-related sensitivity is higher than that with the TE-related one. The two sensitivities can be calibrated with each other. Moreover, by adjusting th...

Second-harmonic generation in a metal-clad nonlinear optical waveguide.

Efficient optical nonlinear effects in waveguides play an important role in integrated photonic functionalities. The dispersion characteristics need to be well designed to satisfy the phase-matching condition of the interacting waves in waveguides. Here we demonstrate a novel phase-matching process of second-harmonic generation (SHG) in a symmetrical metal-cladding optical waveguide (SMCOW) with a nonlinear guiding layer. Ultrahigh order modes in SMCOWs possess small propagation constants, and can be actively tuned to satisfy the phase-matching condition via free-space coupling. We establish a model of SHG in the SMCOW and experimentally verify it as well. This mechanism could also be applied to or referenced in other nonlinear frequency conversion processes.

Enhanced Raman spectroscopy by a double cavity metal-cladding waveguide

In order to double the mode density to increase the Raman scattering efficiency, a double cavity structure was introduced to the metal-cladding optical waveguide (MCW) chip. This novel double cavity MCW inherits all the merits of the MCW, such as free space coupling, large detection area, and polarization independence. Furthermore, attributed to the doubled mode density, more incident energy is coupled into the guiding layer and results in a larger enhancement of the Raman scattering. Since the distribution of the electric field is sensitive to the refractive index profile of the two cavities, the proposed structure can be further optimized to concentrate all of the energy to the sample cavity. Experimental verification via four liquid samples of a different refractive index is carried out in support of the above hypothesis.

Efficient microfluidic photocatalysis in a symmetrical metal-cladding waveguide.

In this paper, a symmetrical metal-cladding optical waveguide based microfluidic chip with a self-organized and free-standing TiO2 nanotube membrane was utilized to perform efficient photocatalysis. The chip has a microchannel bonded with TiO2 nanotube coated glass. The employment of microfluidic chip for hydrolysis reaction can enable the transfer of mass and photons. Moreover, the incorporation of the double metal-cladding waveguide enhances the light-matter interaction and effectively improves the efficiency of photocatalysis.

Aluminum Nanoholes for Optical Biosensing.

Sub-wavelength diameter holes in thin metal layers can exhibit remarkable optical features that make them highly suitable for (bio)sensing applications. Either as efficient light scattering centers for surface plasmon excitation or metal-clad optical waveguides, they are able to form strongly localized optical fields that can effectively interact with biomolecules and/or nanoparticles on the nanoscale. As the metal of choice, aluminum exhibits good optical and electrical properties, is easy to manufacture and process and, unlike gold and silver, its low cost makes it very promising for commercial applications. However, aluminum has been scarcely used for biosensing purposes due to corrosion and pitting issues. In this short review, we show our recent achievements on aluminum nanohole platforms for (bio)sensing. These include a method to circumvent aluminum degradation—which has been successfully applied to the demonstration of aluminum nanohole array (NHA) immunosensors based on both, glass and polycarbonate compact discs supports—the use of aluminum nanoholes operating as optical waveguides for synthesizing submicron-sized molecularly imprinted polymers by local photopolymerization, and a technique for fabricating transferable aluminum NHAs onto flexible pressure-sensitive adhesive tapes, which could facilitate the development of a wearable technology based on aluminum NHAs.

Analysis and experimental investigation of the temperature property of sensors based on symmetrical metal-cladding optical waveguide

Symmetrical metal-cladding waveguide (SMCW) is a kind of new waveguide construction, and it consists of a planar glass slab sandwiched in two metal films with different thicknesses. The metal in this structure is usually a noble metal, such as Au, Ag and Cu etc. One of the characteristics of the glass is the sub-millimeter thickness, which is useful for exciting the ultrahigh order mode. Since the SMCW structure was proposed, it has received much attention from the researchers for its excellent characteristics of free-space coupling technique and ultrahigh order mode excitation. This free-space coupling technology has a higher sensitivity compared with the end-face coupling, prism coupling and grating coupling techniques. The ultrahigh order mode is very sensitive to the incident light wavelength, the thickness of guiding layer and the refractive index, but not sensitive to polarization. Based on the thermal-optical effect and thermal expansion effect of metal film and guiding layer materials, we research the temperature property of the SMCW structure. Researching methods include simulation analysis and experimental demonstration. First, we calculate the relation of the thickness and dielectric property of metal films, and the thickness and refractive index of the guiding layer with the temperature. Results show that these four factors are nearly proportional to the temperature difference. Then, we simulate the relationship of the reflectivity of the SMCW structure with those four factors by means of single-factor investigation under spectral and angular interrogation mode of operation, and find that the temperature-dependence of thickness of the guiding layer makes the chief contribution to the waveguide function of SMCW. Meanwhile, we analyze the sensitivity of the sensors based on SMCW structure, and the result shows that the sensitivity of this kind of sensor can be up to 21.89 pm/K (spectral mode) and 1.449×10-3 rad/K (angular mode). Finally, we demonstrate the simulation results by experiment. In our experiment, a series of reflectivity is measured at temperatures varying from 320 to 380 K, and the value is expressed in the form of voltage output of PSD (position sensitive diode). The sensor shows a good linearity and a high average resolution of 0.517×10-3 rad/K; furthermore, we fit the experimental data and get the linear function between angle shifts and temperature difference of Δθ = 0.02965×ΔT. So, once the temperature has any minute variation, it will easily give a change in the resonance incident angle and show the effect of sensor. Owing to the advantages of high sensitivity, low cast and easy fabrication, the temperature sensor based on SMCW will be a promising sensor in many fields.

Influence of Temperature on Reflectivity of Symmetrical Metal-Cladding Optical Waveguide

The influence of temperature on the reflectivity of symmetrical metal-cladding optical waveguide (SMCOW) is studied theoretically by means of single-factor investigation under spectral and angular interrogation mode of operation. The theoretical model for temperature dependence of reflectivity includes the temperature dependence of refractive index and thickness of guiding layer, the temperature dependence of the metal film thickness and metal-dielectric function. It is found that the effect of temperature on the reflectivity of SMCOW is mainly attributed to the temperature dependence of refractive index and thickness of guiding layer; on the contrary, the temperature properties of metal film hardly contribute to the influence of temperature on the reflectivity. Based on the analysis, the sensitivities of SMCOW with guiding layer made up of different optical glasses are computed under both spectral and angular interrogation. This letter is supposed to provide direction in designing SMCOW sensors against the temperature variation.

Spontaneous-Emission Coupling from an Excited Atom into a Symmetrical Metal-Cladding Optical Waveguide

We consider the coupling behavior which transfers the energy of the spontaneous emission from an atom embedded in free space into a symmetrical metal-cladding optical waveguide. The ratio for spontaneous emission into the waveguide modes is derived by using a compact form of Green's function for a multilayer. Up to 90% of the spontaneous emission energy fed into the waveguide is demonstrated when the atom is positioned above the waveguide in a limited space range.

Metal-clad optical waveguide fluorescence device for the detection of heavy metal ions

We developed Hg 2+ -sensing chips by decorating the external surface of metal-clad optical waveguides with a monolayer of Hg 2+ -sensitive fluorescent molecular probes. The emission properties of the original water-soluble form of the molecule were previously found to be selectively quenched in the presence of Hg 2+ ions. The fabricated samples were tested with optical waveguide fluorescence spectroscopy by putting them in contact with a 5-μM water solution of Hg 2+ ions and recording the emission spectra versus incubation time. The estimate of the limit of detection was 150 nM. A preliminary evaluation of the selectivity of the structure was also performed by using Cd 2+ as possible interfering analytes.

Determination of trace chromium (VI) using a hollow-core metal-cladding optical waveguide sensor

A biosensor capable of highly sensitive detection of trace chromium (VI) with a simple hollow-core metal-cladding waveguide (HCMW) structure is theoretically modeled and experimentally demonstrated. Owing to the high sensitivity of the excited ultrahigh-order modes in the waveguide, a tiny variation of the extinction coefficients in the waveguide guiding layer where the chromate ions reacts with the diphenylcarbazide (DPC) can lead to a significant change of light intensity in the reflection spectrum. The experimental results indicate that using the proposed method, the chromium (VI) sensitivity detection limit can be as low as 1.2 nM, which represents a 16-fold improvement compared to the surface plasmon field-enhanced resonance light scattering (SP-RLS) method, and a 4-fold improvement compared to the flame atomic absorption spectrometry and fluorimetry spectroscopy, respectively.

All-optical modulator based on a ferrofluid core metal cladding waveguide chip

We propose a novel optical intensity modulator based on the combination of a symmetrical metal cladding optical waveguide (SMCW) and ferrofluid, where the ferrofluid is sealed in the waveguide to act as a guiding layer. The light matter interaction in the ferrofluid film leads to the formation of a regular nanoparticle pattern, which changes the phase match condition of the ultrahigh order modes in return. When two lasers are incident on the same spot of the waveguide chip, experiments illustrate all-optical modulation of one laser beam by adjusting the intensity of the other laser. A possible theoretical explanation may be due to the optical trapping and Soret effect since the phenomenon is considerable only when the control laser is effectively coupled into the waveguide.

Conical reflection of light during free-space coupling into a symmetrical metal-cladding waveguide

Novel conical reflection of light by a thick three-layered metal-clad optical waveguide is observed. A symmetrical metal-cladding optical waveguide is used, which exhibits extraordinary conical reflection during free-space coupling of light to the waveguide. The phenomenon is attributed to the leakage of excited ultrahigh-order guided modes and their inter- and intramode coupling interaction.

Metal-clad optical waveguide sensor with anisotropic metamaterial

We propose a metal-clad optical waveguide (MCOW) sensor based on a four-layered structure with anisotropic metamaterial. The expressions of reflectance of the four-layered system are given and the properties of MCOW sensor are also analyzed by simulation results. The anisotropy of metamaterial brings lots of different properties compared with isotropic one. It can be found that six different parameters of the proposed MCOW sensor have different influence on the reflectance dips which provide more flexibility in designing this kind of sensors.

Magnetic modulation of magnetic-fluid based on the symmetrical metal-cladding optical waveguide

A new type of symmetrical metal-cladding optical waveguide structures is proposed.The guiding layer that supports the oscillating field is submillimeter scale and severs as the sample room.The water-based Fe3O4 magnetic fluid with a volume fraction of 0.15% is injected into the sample room.The ultrahigh order modes are excited by a 860 nm laser beam on the structure with small incident angle(5).Owing to the strong concentration of the magnetic field,the sensitivity of the ultrahigh-order modes is very high.The rise and fall time of magnetic fluid is 2 ms when 10 mT magnetic field is applied.

Wideband slow-light modes for time delay of ultrashort pulses in symmetrical metal-cladding optical waveguide

A widebandwidth optical delay line is a useful device for various fascinating applications, such as optical buffering and processing of ultrafast signal. Here, we experimentally demonstrated effective slow light of sub-picosecond signal over 10 THz frequency range by employing the wide slow light modes in thick symmetrical metal-cladding optical waveguide (SMCOW). Ultrahigh-order guided modes travelling as slow light in waveguide together with strong confinement provided by metal-cladding makes this scheme nearly material dispersion independent and compatible with wide bandwidth operation.

A Temperature Sensor Based on a Symmetrical Metal-Cladding Optical Waveguide

A compact temperature sensor based on a symmetrical metal-cladding optical waveguide using free-space coupling is proposed and demonstrated theoretically and experimentally. The symmetrical Au-cladding optical waveguide is based on a thin LiNbO3 slab sandwiched between two metal films, which serve as the coupling layer and reflecting panel, respectively. The sensitivity of this sensor of 9.08 × 10−2 deg/°C, 6.6 × 10−2 deg/°C and 4.8 × 10−2 deg/°C corresponding to 3238-order, 3237-order and 3236-order modes, respectively, are obtained. Higher resolution is predicted with a larger linear expansion coefficient material and a higher resolution θ/2θ goniometer.

Fabrication and study of a metal-clad planar waveguide based biosensor

A metal-clad planar optical waveguide biosensor having five layer structure has been fabricated to study the detection of Pseudomonas and Pseudomonas-like bacteria. This waveguide is designed to increase the overlap of the evanescent field extension from the sensor face with the micro-scale biological objects in the bulk solution, to place most of the entire volume of the bacteria within the evanescent field. The results presented here leads to a significant optimization of the important design parameters to sense micro-scale biological objects. We have compared our computed results with the results obtained by similar non-metallic clad biosensor. The effect of affinity-layer refractive index on the sensitivity of these planar waveguides is also studied. We have shown this for some special cases by obtaining reflection dips at the particular angle of incidence. Our observations show that the metal-clad planar optical waveguide biosensor having higher affinity refractive index will give better sensitivity than other similar non-metallic clad biosensor. The validation of metal-clad planar optical waveguide sensor for the detection of Pseudomonas aeruginosa bacterium is also made.

Microsecond-scale switching time of magnetic fluids due to the optical trapping effect in waveguide structure

Instead of the conventional method of monitoring the transmitted light through a ferrofluid film, in this study we use ferrofluids as the guiding layer in a double metal-cladding optical waveguide structure, and measure the reflected light intensity to investigate the chain formation speed (switching speed) in ferrofluids. We conclude that the ultrahigh-order mode-induced optical trapping effect may be the main reason for the observed fast switching time which is increased by at least three orders of magnitude when a magnetic field was applied.