Composite Optical Waveguide Research Articles

Fast fabrication, gas sense characteristics and kinetics of cubic Ti-BIPA-TC-MOF film composite optical waveguides

A cubic Ti-metal-organic framework (MOF) ([Ti2–(TpA)2–H2BIPA]), constructed from a titanium metal centre and a benzo-imidephenanthroline tetracarboxylic acid (H4BIPA–TC) ligand was photo-inductively grown on the surface of a titanium dioxide (TiO2) composite optical waveguide (COWG) substrate and the influence of photo-inductive growth period on the [Ti2–(TpA)2–H2BIPA] film surface morphology, optical properties and gas adsorption/sensing characteristics was investigated. The results showed that [Ti2–(TpA)2–H2BIPA] formed a cubic structure after grew for only 5 min. As an ideal gas adsorbent, it exhibits a specific response to ethylenediamine (EDA) among various benzene, amine and acid gases, due to the intrinsic electron deficiency, rich COOH active sites of the Ti–BIPA–TC–MOF–5 frame and the higher molar refractive indexes or dipoles of EDA than other gases. In the EDA concentration range from 10 ppt to 100 ppm, the Ti–BIPA–TC–MOF–5 film COWG exhibited a rapid, repeatable response. Moreover, the Ti–BIPA–TC–MOF–5 film COWG was relatively stable, within 17 d of EDA detection, the response intensity was almost constant and slightly decreased within 40 d. In a static gas adsorption stage at 283–313 K, the EDA gas adsorption behaviour of the Ti–BIPA–TC–MOF–5 film is consistent with the pseudo-second-order kinetic model.

A novel TiO2-modified THPP-BCP composite optical waveguide sensor for the determination of ethylenediamine at ppb level.

Composite thin films OWG sensors show higher sensitivity than single film-based OWG sensors, making them particularly useful in the detection of trace gases. In this work, we developed a new tetra hydroxyphenyl porphyrin (THPP)-bromocresol purple (BCP)/TiO2 gel composite film-based OWG (THPP-BCP/TiO2-OWG) sensor for identifying ethylenediamine (EDA) gas. The fabricated sensor was characterized using ultraviolet and infrared spectroscopy and atomic force microscopy. The test result shows that the response of the THPP-BCP/TiO2-OWG composite film sensor to analytes was 3-4 times higher than that of the single film THPP-OWG sensor. The THPP-BCP/TiO2-OWG sensor exhibited excellent selectivity and remarkable response to EDA gas at a concentration of < 1ppb at room temperature, with fast response (1s) and recovery (3s) times. The high refractive index TiO2 film contributes to OWG's sensitivity, while the THPP and BCP's sensitivity to bases further increased the sensor's response to EDA gas. The combination of THPP-BCP thin film and TiO2 gel film provides a powerful platform for OWG sensors that are highly sensitive, specific, and stable in the detection of trace gases.

Composite optical waveguide sensor based on porphyrin@ZnO film for sulfide-gas detection

Composite optical waveguide sensor based on porphyrin@ZnO film for sulfide-gas detection

Development of composite optical waveguide based on azobenzene-modified titanium metal-organic framework film for study of gas adsorption kinetics.

This study investigates the fabrication and gas adsorption kinetics of an azobenzene (AZB)-modified titanium metal-organic framework (AZB@Ti-MOF) film composite optical waveguide (COWG) that recognizes ethylenediamine (EDA) gas. After modification with AZB, the surface of the Ti-MOF film became rough and evolved from a hemispherical structure to a petal-like structure; a large pore size and small specific surface area accompanied the evolution of the surface morphology. The AZB@Ti-MOF film COWG exhibited a positive response to EDA gas co-existing with the same concentration (1000 ppm) of benzenes, amines, and acidic gases. It is postulated that charge transfer occurs when the AZB@Ti-MOF film COWG adsorbs EDA gas, leading to significant strengthening of the intramolecular hydrogen bonds as EDA works as an electron donor. Incomplete or prolonged EDA desorption from the film surface at room temperature resulted in a decrease in the surface sensitivity of the COWG AZB@Ti-MOF film. The kinetics of EDA adsorption were examined using pseudo-first-order and pseudo-second-order (PSO) kinetic models. The EDA adsorption kinetics fit well with the PSO model. As measured at room temperature, the adsorption capacity (qe) per unit surface of the AZB@Ti-MOF films was 46.50 × 10-2 µg·cm-2.

A Surface-Scattering-Based Composite Optical Waveguide Sensor for Aerosol Deposition Detection

Aerosol is a suspension of fine chemical or biological particles in the air, and it is harmful, easily causing air pollution, respiratory diseases, infrastructure corrosion, and poor visibility. Therefore, the development of advanced optical sensors for real-time detection of aerosol deposition is of great significance. In this work, a prism-coupled composite optical waveguide (COWG) sensor for aerosol deposition detection based on surface scattering is proposed and demonstrated theoretically and experimentally. The COWG consists of a single-mode slab glass waveguide locally covered with a tapered thin film of high-index metal oxide. The tapered film can greatly enhance the evanescent field through the adiabatic transition of the fundamental transverse electric (TE0) mode between the uncovered and film-covered regions, thereby enabling the COWG to serve as a simple yet highly sensitive evanescent-wave scattering sensor for sensitive detection of aerosol deposition. The COWG with a tapered layer of Ta2O5 was prepared by masked sputtering, aerosol salt particle deposition on the COWG was successfully detected, and the influence of surface water droplets on the COWG sensor performance was analyzed. The experimental results indicate that the sensitivity of the COWG is 30 times higher than that of the bare glass waveguide.

Surface-modified Ti-MOF/TiO2 membrane and its gas-sensing characteristics

A titanium metal–organic framework/titanium dioxide (Ti-MOF/TiO2) composed membrane was fabricated by light inductive growth of Ti-MOF ([Ti2-(TpA)2-NDI] n ; TpA = terephthalic acid, NDI = 1,8,4,5-naphthalene-tetracarboxdiimide) on a titanium dioxide film composite optical waveguide (COWG) substrate. The Ti-MOF/TiO2 membrane conforms to a mesoporous structure with a 24 nm pore size and a 108 nm thickness through continuous growth for 40 min under 340 nm ultraviolet light illumination. Under ambient conditions, in terms of COWG sensors, Ti-MOF/TiO2 exhibited the greatest response to ethylenediamine (EDA), followed by nitrogen dioxide (NO2), methylamine and trimethylamine, when exposed to 15 types of benzenes, amines and acidic gases. To improve response selectivity, the Ti-MOF/TiO2 film was modified with 1,3,3-trimethylindolinonaphthospirooxazine (SP), forming an SP@Ti-MOF/TiO2 COWG. This modified COWG showed improved selectivity response by showing robust response to EDA and a negligible response to others. When an EDA gas molecule was adsorbed on the surface of the membrane, charge transfer between them preferentially occurred, leading to a change in the optical parameter. The surface-modified SP@Ti-MOF/TiO2 COWG showed a fast (3 s) and reversible response with a wide detection range (0.1–1000 parts per billion) to EDA gas without the interference of benzene, toluene, xylene, styrene and chlorobenzene; acidic gases; and other amines.

Fabrication and Surface Modification of Niobium Metal–Organic Framework Membrane and its Gas Sensing Application

AbstractThe niobium metal–organic framework (Nb‐MOF = [Nb2(bdc)2(NDI)]n) membrane, constructed from terephthalic acid(bdc) and 1,8,4,5‐naphthalenetetracarboxdiimide (NDI), is in this work grown on the surface of lithium niobate (LiNbO3) film composite optical waveguide (COWG) substrate using UV‐light illumination method. After growing for 20 min, the Nb‐MOF membrane forms as a graphene‐like structure with 50 nm pore size and 96 nm thickness. At room temperature (25 °C), in terms of COWG sensors, Nb‐MOF exhibits the greatest response to H2S and SO2, followed by ethylenediamine (EDA) and NO2, coexistence with 15 kinds of benzenes, amines, and acidic gases. In order to improve its response selectivity, the spirooxazine (SP) is embedded into the Nb‐MOF frame, and a SP@Nb‐MOF membrane COWG with smooth‐snowflake imprinted surface is obtained. In gas sensing performance, the obtained COWG shows the greatest response to H2S, while the response of SO2, NO2, and other gases are obviously diminished. When the SP@Nb‐MOF membrane exposes to H2S gas, proton‐transfer and morphology modulation are induced. The presented sensor also shows a wide detection range (1 × 104–0.1 ppb), fast response (4 s), and long‐term stability of 120 d to H2S at room temperature (25 °C) and 25% relative humidity.

A Temperature Sensor Based on Composite Optical Waveguide

We propose a temperature sensor, which consists of a composite optical waveguide (COW) sandwiched between two single mode fibers (SMFs). The COW is formed by side polishing a capillary optical fiber (COF) and filling with polydimethylsiloxane (PDMS). Unlike the conventional fixed sensing structure, the Mach-Zehnder interferometer (MZI) and multimode interferometer (MMI) can be selectively formed by adjusting different fusion splicing parameters, so as to produce a blunt or sharp tapered fusion structure between the SMF and the COF. Because of the high thermo-optic coefficient of PDMS and the high-order modes excited by the tapered fusion structure, the MZI and MMI sensors are very sensitive to temperature. The experimental results show that within the temperature measurement range from 16 °C to 80 °C, several resonance wavelengths of the MZI and MMI sensors exhibit a remarkable blue shift with the increase of temperature. The maximum temperature sensitivities of the MZI and MMI sensors can reach −0.50 nm/ °C and −0.88 nm/ °C, respectively. The humidity sensitivity of the sensor is −0.10 nm/%RH. However, in the process of temperature measurement, humidity has little influence on the sensitivity of the sensor. Due to the advantages of compact size, flexible structure, and high sensitivity, the sensor has great application potential in monitoring the changes of environment and living temperature.

Waveguide length and pump power effects on the amplification of europium aluminum doped polymer

Mosquito method is used to fabricate a 50 μm core diameter graded index (GI) multimode Eu-Al doped polymer composite optical waveguide amplifier. In this paper, waveguide length and pump power are varied with an input signal of - 30 dB m. Under a 532 nm laser excitation, 16.27 dB optical gain under an optimal 10 cm waveguide length is observed from forward pumping amplification for a threshold pump power of 23 dB m. Also, the waveguide has been characterized to be 0.83 dB/cm at 617 nm wavelength.

A Polarimetric Interferometer Based on Composite Optical Waveguide for Refractive Index Detection

A sensitive interference refractive index sensor based on composite optical waveguide (COWG) was developed. Sol-gel technique was used to prepare TiO2 sol, and the TiO2 film was fixed on the surface of single-mode potassium ion-exchange (PIE) optical waveguide (OWG) by dip-coating and annealing treatment to fabricate an interference refractive index sensor device. The interference between the zeroth-order transverse electric (TE0) and magnetic (TM0) modes of the laser beam which transport in the COWG caused phase-difference change (Δϕ) of output light signals. Refractive index sensitivity of TiO2/PIE COWG chip was examined by injecting aqueous NaCl solutions and distilled water in turn to detect its Δϕ. Experimental results show that, for the TiO2/PIE COWG its refractive index sensitivity is SRI = (573.09 × 2π)/RIU in the refractive index ranges of 1.3386∼1.36. The sensor sees the advantages of high sensitivity, compact size, simple fabrication, as well as low cost.

A highly sensitive and selective optical waveguide sensor based on a porphyrin-coated ZnO film

A highly sensitive and selective optical sensor device based on a porphyrin-coated ZnO thin film/K+ ion-exchanged glass composite optical waveguide (COWG) layer was developed. The surface of the ZnO film was coated with a thin film of 5,10,15,20-tetrakis-(4-methoxyphenyl) porphyrin by the spin-coating or immersion method. The optical properties of the films were probed by UV–vis and Fourier-transform infrared spectroscopies. The gas sensing performance was also examined in detail. The high sensitivity, room temperature operation, good selectivity, and reproducibility of the sensor render it a promising candidate for industrial use and in environmental monitoring.

Detection of diethyl chlorophosphate using a composite optical waveguide sensor

A highly sensitive composite optical waveguide sensor was developed for diethyl chlorophosphate vapor detection.

Improved light emitting UV curable PbS quantum dots-polymer composite optical waveguides

We present for the first-time light emitting ultraviolet (UV) curable active PbS quantum dots-polymer composite optical waveguides fabricated by vacuum assisted microfluidic (VAM) soft lithography technique. PbS quantum dots were synthesized by colloidal chemistry methods with tunable sizes resulting in light emissions in near infrared wavelengths. UV curable polymer of selective refractive index were synthesized facilitating waveguide mode confinement and good PbS quantum dots solubility. Photoluminescence of the composite exhibited ∼30 times better brightness than PbS-SU-8 composites. Light emitting multi-mode waveguides of about 50×42μm cross-sectional dimension were successful demonstrated. Light emitting single-mode waveguides were fabricated by VAM technique with sectional flow tapers.

Numerical investigation of a microfiber-plane-grating composite optical waveguide for gas refractive index sensing.

In this paper, we propose a microfiber-plane-grating composite optical waveguide (MPGCOW), which is formed by immobilizing a tapered microfiber on the surface of a plane grating with one defect, for gas refractive index (RI) sensing. Its optical properties and gas RI sensing properties are investigated by the finite difference time domain method. Results show that the MPGCOW has a photonic stop band and is very sensitive to the ambient gas RI variation. The largest gas RI sensing sensitivity of 486.67nm/RIU and detection limit of 2×10-6 are obtained by immersing the structure in the mixture gas of N2 and He with various mixture ratios.

Refractive-Index-Enhanced Raman Spectroscopy and Absorptiometry of Ultrathin Film Overlaid on an Optical Waveguide

Waveguide-based spectroscopic techniques utilizing evanescent wave as a probe are ideal tools for surface and interface analysis. However, practical applications of these techniques are largely limited by the weak effective signals resulting from the restricted strength of interaction between the evanescent wave and the ultrathin sample immobilized at the waveguide surface; this is especially the case in light of the evanescent-wave excited waveguide Raman spectroscopy. Hence, we present a non-surface-enhanced Raman spectroscopy (SERS) method in this work to enhance the Raman spectroscopy of ultrathin film overlaid on the waveguide surface by intensifying the evanescent wave–sample interaction via manipulating the refractive index (RI) of the waveguide superstrate. Polarization-controllable and highly reproducible Raman enhancement can be achieved for the 10-nm-thick copper phthalocyanine (CuPc) ultrathin film deposited on the surface of a composite optical waveguide (COWG), with the enhancement factors b...

Nonspecific detection of lead ions in water using a simple integrated optical polarimetric interferometer

Real-time detection of heavy metal ions in water was implemented by using a composite optical waveguide (COWG) based polarimetric interferometer. The COWG was made by local deposition of a tapered nanometric layer of high-index materials onto a single-mode slab glass waveguide, and it is a low-cost robust waveguide with a locally large modal birefringence. The COWG-based polarimetric interferometer operates with a single incident laser beam and uses the transverse electric and transverse magnetic modes as the sensing and reference beams, respectively, and it can easily detect 0.1 ppm lead(II) ions in water via nonspecific adsorption on the tapered layer of TiO2. The excellent linearity was obtained between the lead(II) concentration and the ratio of concentration to the phase-difference change (Δϕ), suggesting that adsorption of lead(II) ions on the TiO2 film follows the Langmuir isotherm model. The saturation adsorption leads to Δϕmax = 7.485π. By use of the eigenvalue equations for a homogeneous waveguide to fit the measured refractive-index (RI) sensitivity of the interferometer, the equivalent thickness of Teq = 26.05 nm for the tapered TiO2 layer used was achieved. With Teq = 26.05 nm and Δϕmax = 7.485π and the thickness of 0.264 nm for the lead(II) adlayer, the adlayer RI was derived to be nad ≈ 1.945 at the maximum coverage.

PH-indicators doped polysaccharide LbL coatings for hazardous gases optical sensing

Sensitive layer-by-layer (LbL) coatings for optical detection of gaseous NH3 and HCl were prepared by self-assembly of oppositely charged polysaccharides (chitosan and λ-carrageenan) followed by doping LbLs with pH-sensitive dyes – bromothymol blue (BTB) and Congo red (CR). It has been shown that CR, being an amphoteric dye, diffuses into LbL films regardless of the charge of the outermost polyelectrolyte layer, and the dye loading increases linearly with the LbL film thickness, whereas BTB diffuses into LbL films only when the outermost layer is positively charged, and linearity between dye loading and film thickness holds only up to 8–12 double layers (DLs) deposited. Formation of dye-doped LbL coatings at the surface of K+/Na+ ion-exchanged glass has allowed fabrication of composite optical waveguide (OWG) gas sensor for detection of ammonia and hydrochloric acid vapors. The response time of BTB-doped composite OWG for ammonia detection was below 1s, and the detection limit was below 1ppm. CR-doped OWG sensors have shown high sensitivity to HCl vapor but slow relaxation time (up to several hours for 12DL LbL films).

Fiber-Optic Solution Concentration Sensor Based on a Pressure-Induced Long-Period Grating in a Composite Waveguide

A fiber-optic solution concentration sensor based on a pressure-induced long-period grating (LPG) in a composite optical waveguide is proposed. The composite waveguide consists of a standard single-mode fiber with its coating stripped away, a teflon-cannula and the medium to be measured. An experiment has been carried out to measure the concentration of the sodium chloride (NaCl) solution. The results show that the central resonant wavelengths of the LPG shift towards shorter wavelengths when the concentration of the NaCl solution increases. The central resonant wavelength of the LP14 cladding mode exhibits a total blue shift of 4.13 nm in the NaCl solution concentration range of 0–25%, which corresponds to a sensing sensitivity of 0.17 nm/%.

Optical properties and sensing applications of lithium iron phosphate thin films

A composite optical waveguide sensor, consisting of lithium iron phosphate (LiFePO4, LFP) as the sensing material, was constructed and utilized for the detection of volatile organic compound gases. Nano-LFP powder was prepared via the hydrothermal method and was subsequently utilized in a dip-coating procedure for the fabrication of LFP thin films. The effect of heat treating temperature on the refractive index of the thin films was studied. A glass optical waveguide gas sensor was fabricated by coating an LFP thin film on the surface of single-mode tin-diffused glass optical waveguide. The sensor was found to exhibit a linear response to xylene in the range of 50–1000ppm, with response times of less than 5s.

Refractive Index Sensing by Using Mechanically Induced Long-Period Grating

In this paper, a refractive index sensor using a mechanically induced long-period grating is proposed and experimentally demonstrated. The sensing element is based on a composite optical waveguide, which is made of a single-mode fiber, a Teflon-cannula, and the medium pending to test. The research shows that the resonant wavelength of the high- order mode coupling is sensitive to the refractive index of the liquid. The pressure applied on the experimental setup should keep constant in the refractive index measurements for different liquids, where the mode coupling is in the undercoupling state. The sensitivity of the sensor for LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> mode resonance is about 2.78 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> refractive index unit in the refractive index range from 1.33 to 1.43.