Polymer optical fibers (POFs) have significant advantages over numerous sensing applications. The key element in developing sensor is by removing the cladding of the fiber. The use of organic solvent is one of the methods to create tapered POF in order to expose the core region. In this study, the etching chemicals involved is acetone, methyl isobutyl ketone (MIBK), and acetone-methanol mixture. The POF is immersed in 100%, 80%, and 50% of acetone and MIBK dilution. In addition, the mixture of acetone and methanol is also used for POF etching by the ratio 2:1 of the volume. Acetone has shown to be the most reactive solvent towards POF due to its fastest etching rate compared to MIBK and acetone-methanol mixture. The POF is immersed and lifted from the solution for a specific time, depending on the power loss properties for the purpose of producing unclad POF. In comparison to silica fiber optic, the advantages of POF in terms of its simple technique and easy handling enable it to produce unclad POF without damaging the core region. The surface roughness of the POF is investigated under the microscope after being immersed into different solvent. This method of chemical tapering of POF can be used as the fundamental technique for sensor development. Next, the unclad fiber is immersed into ethanol solutions in order to determine the reaction of unclad POF towards its surrounding. The findings show that this particular sensor is sensitive towards concentration changes ranging between 10 wt% to 50 wt%. � The Authors, published by EDP Sciences, 2017.

Plasmonic demodulation is a process where an optical signal due to the generation of surface plasmon polaritons (SPP) reacts with electrical domain, resulted an inverse relationship between them. In this study, fabrication processes of gold strip thin films on the glass substrates are presented. For an optimization purpose of electro-optics effect observation, the width of gold strip thin film is set as 0.5mm, which is equal to the laser beam spot diameter. First, the strip pattern is printed on a commercial transparent plastic slide. The pattern transfer process from plastic slide to glass slide is performed using UV light. Once the pattern is formed on the glass substrate, gold thin film with varies thicknesses namely 30nm, 50nm and 100nm are deposited by monitoring the sputtering time; via d.c. sputtering on the glass substrate which is partly coated with the positive photoresist. The photoresist is removed by immersing the coated glass slide in acetone solution for 15 minutes, follow with DI water for three seconds in an ultrasonic bath. This yields to the establishment of gold strip thin films with dimension of width 0.5mm � length 10mm. An optimal plasmonic demodulation process is successfully acquired by using gold metal strip with thickness of 30nm and higher laser power level, namely P=1.5mW. In a conclusion, we believe that the output of this study will contribute a significant impact to the development of the plasmonic demodulator as an active device. � 2015 IEEE.

Partial unclad fibers with diameters ranging from d=121µm to d=125µm were fabricated using standard telecommunications optical fiber (SMF28) via low cost mechanical swipe-off technique. Graphene oxide (GO) was deposited using drop casting method on the outer side of the partial unclad SMF. IR laser with excitation wavelengths of λ=1310nm and λ=1550nm were launched along the graphene-coated SMF. The sensitivity of graphene based macrobend unclad SMFs were investigated by introducing two different pH of aqueous environment with values of 3.5 (acidic) and 12.5 (alkaline) that acted as sensing media. The optimum power loss was obtained as smallest diameter of partial unclad SMF with d=121µm was appointed. As uncoated SMF was replaced with the GO coated SMF which had been immersed into 3.5pH liquid solution, it was found that the optical power losses were increased about 6.79dBm and 5.15dBm using laser with λ1=1310nm and λ2=1550nm respectively. The uncoated SMFs experienced the increment of power losses about 2.11dBm and 5.15dBm as they were soaked into the solution with pH=12.5 using similar laser of λ1 and λ2. It is noteworthy to highlight the significant of graphene’s employment on macrobend unclad SMF by using λ1=1310nm in which better sensitivity and selectivity represented by maximum changes of power losses were apparently observed for both solutions. The usage of λ=1550nm exhibited poor selectivity where the partial unclad SMF unable to differentiate two contrasting pH solution. In conclusion, graphene based macrobend fiber optic sensor for pH detection was successfully developed by employing partial unclad SMF with cladding diameter of d=121µm and laser wavelength of λ=1310nm due to the enhancement of evanescent field’s strength. © 2020 Trans Tech Publications Ltd, Switzerland.

The presence of near-field indicates the existence of evanescent waves, which is one of the important requirements for the development of an optical sensor. This study was carried out to identify the presence of near-field and far-field as monochromatic light propagated through various structures and sizes of apertures. The confocal microscopy setup consisted of He-Ne laser with 633nm of excitation wavelength, apertures (slits and numerous sizes of pinholes), objective lens, projected screen and silicon photodetector. The near-field and far-field were determined by calculating the Fresnel number, FN as assorted size and design of apertures were added in the setup. The presence of far-field was identified with the usage of slits (single slits and double slits) represented by the value of FN, which was less than 1(FN?1). As the aperture was replaced with pinholes with diameters within 30?m and 1.2mm, the near-field was resulted (FN?1). Value of FN became greater as distance x between lens and pinholes increased. We also discovered a significant finding where the field intensities I were decreased with increment of distance x for the near-field, and vice versa (far-field). By using an extrapolating technique, it was found that the near-field can be created by using pinhole with a diameter of a < 1.46mm. In conclusion, the discovery of this work proves an excellence role of pinholes in confocal microscopy setup in creating the evanescent waves for optical sensing applications. � 2019 Akademi Sains Malaysia.

Zinc oxide (ZnO) thin films have become technologically important materials due to their wide range of electrical and optical properties. The characteristics can be further adjusted by adequate doping processes. The effect of dopant concentration of Al, heating treatment and annealing in reducing atmosphere on the optical properties of the thin films is discussed. Undoped and aluminum-doped zinc oxide (AZO) thin films are prepared by the sol-gel method. Zinc acetate dihydrate, 2-methoxyethanol and monoethanolamine are used as precursor, solvent and stabilizer. In the case of AZO, aluminum nitrate nanohydrate is added to the precursor solution with an atomic percentage equal to 0 %, 1 %, 2 % and 3 % of Al. The multi thin layers are transformed into ZnO upon annealing at 450 �C and 500�C. The optical properties such as transmittance, absorbance, band gap and refractive index of the thin films have been investigated by using UV-Visible Spectroscopy (UV-Vis). The results show that the effect of aluminium dopant concentration on the optical properties is depend on the post-heat treatment of the films. By doping with Al, the transmittance spectra in visible range increased and widen the band gap of ZnO which might due to Burstein-moss effects.

Optical sensor based on surface plasmon resonance are widely used for various applications. In this paper, an optimization of EM waves polarization modes for the occurrence of SPR by using a modified optical waveguiding assembly has been discussed. A 633 nm of linearly polarized He-Ne laser was appointed as a light source. The polarization modes were controlled by rotating the position of He-Ne laser. It was found that the optimum SPR signal with reflectance, R = 0.21 a.u and SPR angle, ?SPR = 48� can be obtained as the position of laser was rotated at 90�, with the presence of polarizer. The location of the critical angle was observed at ?C = 46�. For the validation purpose, a simulation based on Fresnel equation was conducted where the percentage difference between the experimental and theoretical results were analyzed. The percentage difference between experimental and theoretical results for both ?SPR and ?C were 9.09% and 15.00% respectively. In conclusion, an excellent agreement between the theoretical and experimental findings proved the stability of this SPR setup, where the EM waves polarization can easily be controlled by manipulating the position of laser. � The Authors, published by EDP Sciences, 2017.

Kretschmann-based surface plasmon resonance (K-SPR) sensing approach using planar thin metal films offer distinct advantages over other label-free sensing techniques in the visible region. SPR phenomenon occurs due to the propagation of electromagnetic waves along the surface of the thin metal layers. Practically, some refractive index changes on the dielectric sample layer will cause changes in surface plasmon polaritons (SPP). The main purpose of using this coupling technique is to match the light-wave vector wave with the SPP vector wave. This paper will give an overview of the design and development of SPR-based sensors utilizing the angular interrogation Kretschmann configuration for detecting the presence of various analytes such as urea, creatinine, glucose, ethanol and uric acid in the visible region. Various sensor layers such as 50-nm thick gold (Au), MoS2/graphene, Au/graphene oxide, Ag/ITO and Au/Ag/ZnO thin films were used to detect the analytes at 633 nm, 670 nm and 785 nm visible electromagnetic wavelengths. Output characteristics such as the reflectivity, full width at half maximum (FWHM), sensitivity, Q factor and Figure of merit (FOM) of the sensors were analyzed. Results of this study was obtained using Lumerical's Finite Difference Time Domain (FDTD) and experimental characterization was obtained using Bionavis SPR equipment; available at IMEN, UKM. � 2019 IEEE.

Criteria for development of high sensitivity surface plasmon resonance (SPR) sensor depends on several factors such as types of metals, light polarization modes, light coupling techniques and thicknesses of metal film. This paper discussed the effect of light excitation wavelength ranging from ultra violet (UV) region to infrared (IR) region on SPR. Three regions have been classified such as UV region (from ?=200nm to ?380nm), visible region (from ?=400nm to ?=633nm) and IR region (from ?=870nm to ?=1550nm). Noble metal gold thin film with thickness of 50nm and refractive index of n=0.1759+3.3104k was deposited on top of BK7 triangular prism (n=1.51). Very weak SPR signal was generated as the excitation wavelength was set in UV region. The signal's strength increased about 26.63% with the increment of wavelength from ?=200nm until ?=380nm, resulting the blue-shifting of SPR angle from 54.03�to 43.48�. The greatest excitation of SPP was significantly observed as the visible light region was incident through the thin film gold-coated prism represented by the abrupt decreased of Rmin to 96.50% at ?=633nm. The SPR angle was red-shifted about 0.30�throughout this region. The SPR signal getting weaker as light excitation wavelength entered the IR region (from ?=870nm to ?=1550nm) indicated by the 64.34% inclination of Rmin. In this region, the SPR angle was remain red-shifted from ?SPR=44.97�until ?SPR=46.18�with the average increment of 0.31�for each wavelength. It can be concluded that the usage of red laser, ?=633nm able to enhance the maximum excitation of SPP. The remarkable outcome of this work shows the vital role of light excitation wavelength in generating strong SPR signal for various application such as sensor and optoelectronic device. � 2018 Author(s).

In recent years, there has been a significant interest in the development of optical waveguide modulators using Silicon-On-Insulator (SOI) substrates motivated by the potential to provide a reliable low-cost alternative to other photonic materials. Objective: In this paper, Multimode Interference (MMI) device is used to develop the MZI structure of the optical modulator. Meanwhile, the electrical part of the modulator utilizes the forward biased P-I-N structure. The effect of varying MMI width to the performance of the MZI optical modulator on SOI was investigated. The effect of varying MMI width to the insertion loss (IL), extinction ratio (ER) and modulation efficiency (V?L) of the device were carried out. Results: The investigated MMI widths are 22, 30 and 38 ?m. Smallest MMI width, which is 22 ?m has recorded the lowest value of insertion loss with 3.30 dB and the best extinction ratio of 25.60 dB. However, the best modulation efficiency was observed for the MMI width of 38 ?m with 0.1696 V.cm. Conclusion: Appropriate selection of MMI width is vital to ensure optimum performance of the MZI modulator. � 2015 IEEE.

Nowadays, surface plasmon resonance (SPR) sensor has been widely used in biosensing applications to detect the wide diversity of biomolecular interactions. There are few parameters need to be concerned in order to optimize the performance of SPR sensors such as film thicknesses, type of thin films and their configurations. In this study, we seek to determine the optimum thicknesses of hybrid thin films which consist of gold-graphene oxide layers for the enhancement of SPR sensor sensitivity. By using a theoretical approach, a WINSPALL 3.02 simulator had been used to investigate the effects of various thicknesses of hybrid configuration's thin films towards the excitation of surface plasmon polaritons (SPP). A layer of 3 nm protein was added to compare the maximum adsorption of the SPR sensor based on their configuration. It was found that the optimum thicknesses of gold and graphene oxide are 50 nm and 0.68 nm respectively for achieving best sensitivity. Thus, the sensitivity value for gold-GO thin films is higher than silver-GO which are 19.42 �/RIU and 5.45 �/RIU with FWHM = 2.28� and 0.64� respectively. � 2016 IEEE.

Surface plasmon resonance (SPR) can only be achieved if sufficient energy is provided at the boundary between metal and dielectric. An employment of prism as a light coupler by using Kretschmann configuration is one of the alternative for the production of adequate energy to be generated as surface plasmon polaritons (SPP). This work is carried out to investigate the effect of physical structure of the prism and its refractive index to the excitation of SPPs. A 50nm gold thin metal film with dielectric constant of ? =-12.45i+1.3 was deposited on the hypotenuse surface of the prisms. The physical structures of the prisms were varied such as triangular, conical, hemispherical and half cylindrical. These prisms were classified into two types of refractive indices (RI), namely n=1.51(type BK7) and n=1.77(type SF11). Based on SPR curve analyses, we discovered that strong SPR signals which consist of 82.98% photons were excited as SPPs can be obtained by using type-BK7 prism with physical structures of hemispherical or half cylindrical. From the view of selectivity ability as sensors, the usage of type-SF11 prisms (half cylindrical and hemispherical) able to enhance this impressive feature in which sharp SPR curves with small FWHM values were obtained. In conclusion, apart from properties of thin film materials, the physical structure of prisms and their RI values play crucial roles to obtain optimum SPR signal. High sensitivity SPR sensor can be established with the appointment of type-BK7 prisms (hemispherical or half cylindrical shape) as light couplers. � The Authors, published by EDP Sciences, 2017.

This study discussed the effect of nanocomposite film's thicknesses on the generation of SPR for detection of Pb2+ ions. Ag-GO nanocomposite film was deposited on the hypothenuse side of the triangular prism via Kretschmann configuration. The thicknesses of Ag-GO were varied between 50nm and 60nm by manipulating the Ag's thicknesses from 30nm to 50nm and GO's between 2nm and 10nm. The optimum SPR signal was obtained as thickness of Au-GO was fixed at 50nm with tAg=48nm and tGO=2nm resulting 75.77% of SPP excitation. As thicknesses of GO increased above 2nm and thicknesses of Ag were set less or more than 48nm, the SPP excitation became weaker. The sensitivity of SPR sensor shows a good agreement with the generation of SPP. The sensor exhibits the optimum sensitivity of s=0.452�/RIU with angle shifting of 0.905�as nanocomposite film under configuration of tAg=48nm: TGO=2nm and tAg=50nm: TGO=2nm were employed. In conclusion, the amplification of SPR sensor's sensitivity can be achieved by introducing 50nm nanocomposite films consist of �2nm thicknesses of GO. � 2018 IEEE.

This study proposed the development of hybrid Au-GO-GNP films for the enhancement of plasmon absorption in SPR sensing. Several thicknesses of Au at t=40nm, t=50nm and t=300nm were sputtered on the glass substrate. The hybridization of bilayer and trilayer films were formed by depositing GO-GNP layers and GNP-GO layers on top of various thicknesses of Au coated substrates. UV-Vis spectra analysis was conducted to characterize the plasmon absorption for each configuration. The plasmon absorption was successfully amplified by employing hybrid trilayer Au-GO-GNP with the thickness of Au film was fixed at t=50nm. It is noteworthy to highlight that the employment of bilayer and trilayer configurations are the key success to enhance the SPP excitation. Au-GNP and Au-GNP-GO results no significant outcome in comparison with Au-GO and Au-GO-GNP. A redshift of the absorbance wavelength evinces the presence of GO on Au-GO sample and GNP on Au-GO-GNP sample due to the surface reconstruction. It is important to emphasize that not all bilayer and trilayer configurations able to enhance the plasmon absorption where no significant output was obtained with the hybridization order of Au-GNP and Au-GNP-GO.

This work presents a study on the sensitivity of bare fiber Bragg grating (FBG) to detect ultrasonic frequencies under various temperature. Two infrared (IR) laser with excitation wavelength, λ=1310nm and λ=1550nm were employed. Various types of FBG with operating wavelength of 1546nm, 1550nm and 1554nm were used to identify the optimum design of sensor in detecting range of ultrasonic frequencies between 5kHz until 30kHz under various surrounding temperature from 20°C until 30°C. The principle of FBG vibration detection lies in the fact that spectral shift would occur due to the acoustic-induced variations in the medium. In this study, the ultrasonic signal had been investigated by monitoring the amplitude of optical output power. At 30°C, the bare FBG with operating wavelength of 1554nm using 1310nm light source exhibits the optimum performance in detecting ultrasonic vibration frequency, in which its sensitivity was obtained as P=0.10dBm. We believe that the sensitivity of the proposed sensor can be enhanced by introduce nanomaterials onto the FBG or by altering the physical structure of FBG. © Published under licence by IOP Publishing Ltd.

Plastic optical fiber sensing that coated with ZnO is developed and its interaction with ethanol and methanol solution is investigated. ZnO is synthesized sonochemically by using the bath type sonicator. The optical properties such as transmittance, absorbance and refractive index of ZnO is determined by using ultraviolet-visible (UV-Vis) spectrophotometer. Then, the cladding of plastic optical fiber (POF) is etched by using acetone solution, sand paper and deionized water. The unclad region is coated with ZnO and being immersed in the solution of ethanol and methanol in the range from 0 v/v% to 50 v/v%. The performance of ZnO coated POF is achieved by obtaining the output power value that transmitted via power meter. The result of this research is as the alcohol concentration increase, the output power value increase. Refractive index of ZnO is varied due to interaction between modified-cladding area and alcohol. Besides that, more light propagates inside the fiber when the sensor is tested under methanol solution compare to ethanol. Thus, the output power ratio increments as well as the sensor efficiency and shows the effectiveness of POF sensor to detect varied alcohol concentration. � 2020 Trans Tech Publications Ltd, Switzerland.