Optical Waveguide Theory

Xu-dong Wang*,† and Otto S. Wolfbeis*,‡ †Department of Chemistry, Fudan University, 200433 Shanghai, P. R. China ‡Institute of Analytical Chemistry, Chemoand Biosensors, University of Regensburg, D-93040 Regensburg, Germany ■ CONTENTS Books, Reviews, and Articles of General Interest 204 Sensors for (Dissolved) Gases and Vapors 204 Hydrogen 204 Hydrocarbons 206 Oxygen 206 Carbon Dioxide 208 Nitrogen Oxides 208 Other Gases 208 Ammonia 209 Ethanol 209 Other Volatile Organic Compounds (VOC)s 210 Sensors for Humidity, Water Fractions, Hydrogen Peroxide, and Hydrazine 211 Humidity 211 Water Fractions in Organic Solvents 212 Hydrogen Peroxide 213 Sensors for pH Values, Ions, and Salinity 213 pH Values 213 Ions 214 Salinity and Ionic Strength 215 Sensors for Organic Species 216 Glucose Sensing 216 Sucrose 217 Oils 217 Other Organics 217 Biosensors 218 Nucleic Acid-Based Biosensors (DNAand Aptamer-Based) 218 Immunosensors 218 Enzymatic Biosensors 219 Other Biosensors 220 New Schemes and Materials 220 New Sensing Schemes 220 Molecularly Imprinted Polymer (MIP)-Based Sensors 221 Photonic Crystals 223 Author Information 223 Corresponding Authors 223 Notes 223 Biographies 223 Acknowledgments 223 References 223

Fiber-Optic Chemical Sensors and Biosensors (2013-2015).

We report on the capability of adaptive neuro fuzzy inference system (ANFIS) coupled with discrete wavelet transform (DWT) for the de-noising of absorption signals The proposed method is examined for the de-noising of a CO2 spectrum which is experimentally traced in the near-infrared around 157 μm This is performed by contaminating the spectrum with a various types of complicated noise figures produced by several approaches It is found that DWT-assisted ANFIS is quite sufficient for CO2 signal recovery that is obscured by a huge amount of unknown noises without need of using a prior estimation of the noise feature Eventually, enhanced signal-to-noise ratio of about 117 is obtained

Combination of discrete wavelet transform and ANFIS for post processing of spectroscopic signals

The potential and drawbacks of the apodized 2f/1f wavelength modulation spectroscopy are theoretically studied and experimentally characterized. We apply a near-infrared DFB-based laser spectrometer, tunable around the R(32) CO2 absorption line centered at 6369.408 cm−1. The performance of the apodized method is shown by minimizing the pressure deviation between the gauge and experimental pressures by using the beneficial effect of the scaling $$k$$
 -factor. This factor equalizes the experimental and simulated peak heights of the CO2 absorption trace. We found that when $$k$$
 -factor is varied up to its optimum value of ~200, a pressure deviation of nearly zero is obtained at a case pressure of 19 ± 0.5 mbar. Under such optimum condition a minimum uncertainty of ±1 mbar is also obtained for the pressure deviation. However, we further acquired that far from this optimum condition, compared to the common method, the apodized approach is also capable of reducing the pressure deviation by ~13.5 % at 20 ± 0.5 mbar of CO2 pressure, indicating the performance of the proposed method for precise pressure measurement of a gas sample, regardless of the optical limits.

Experimental characterization of apodized wavelength modulation spectroscopy for accurate quantitative measurement

Modulation index optimization for wavelength modulation spectroscopy

The performance of an optical sensor that employs an unbuffered polydimethylsiloxane (PDMS)-cladding fiber optic is demonstrated for the sensitive detection of CO2 gas in the near-infrared region for around 1.57 µm using the apodized 2f/1f wavelength modulation spectroscopy method. The permeability and diffusion characteristics of the PDMS fiber have been theoretically examined and numerically simulated. The results of the simulation are verified by an experimental setup containing a DFB laser source and 5-m-coiled unbuffered PDMS fiber placed in a pre-vacuumed cell filled with about 980 ± 10 Torr of pure CO2 gas. A minimum detectable absorption of ~0.9 × 10−4 is measured, corresponding to a detection sensitivity of ~4.5 × 10−11 
 $${\text{cm}}^{ - 1} /{\text{Hz}}^{1/2}$$
 . The effect of the scaling k-factor on the apodized signal is subsequently studied, showing close agreement between the simulation and experimental results.

Mehran Mohammadi Jozdani

Papers

Polymeric fiber sensor for sensitive detection of carbon dioxide based on apodized wavelength modulation spectroscopy