Ahmad Ashrif A. Bakar

Development of Phase Detection Schemes Based on Surface Plasmon Resonance Using Interferometry

Surface plasmon resonance (SPR) is a novel optical sensing technique with a unique ability to monitor molecular binding in real-time for biological and chemical sensor applications. Interferometry is an excellent tool for accurate measurement of SPR changes, the measurement and comparison is made for the sensitivity, dynamic range and resolution of the different analytes using interferometry techniques. SPR interferometry can also employ phase detection in addition to the amplitude of the reflected light wave, and the phase changes more rapidly compared with other approaches, i.e., intensity, angle and wavelength. Therefore, the SPR phase interferometer offers the advantages of spatial phase resolution and high sensitivity. This work discusses the advancements in interferometric SPR methods to measure the phase shifts due to refractive index changes. The main application areas of SPR sensors are demonstrated, i.e., the Fabry-Perot interferometer, Michelson interferometer and Mach-Zehnder interferometer, with different configurations. The three interferometers are discussed in detail, and solutions are suggested to enhance the performance parameters that will aid in future biological and chemical sensors.

Multi-wavelength Brillouin-Raman ring-cavity fiber laser with 22-GHz spacing

We experimentally demonstrate a multi-wave length Brillouin-Raman fiber laser configured in a ring-cavity resonator. Interactions between stimulated Brillouin scattering and Raman amplification in a dispersion compensating fiber, attributed to the generation of 16 output channels at injected Raman pump unit power of 650 mW and Brillouin pump power of 2.0 mW. The first output channel has a peak power of 14.8 mW. By discriminating the even-order Brillouin Stokes signals from circulating in the resonator, the generated output channels were found to have wavelength spacing of ∼22 GHz. The output channels were also found to have average optical signal-to-noise ratio value of 11.7 dB.

Single-stage gain-clamped L-band EDFA with C-band ASE saturating tone

We demonstrate a single-stage gain-clamped L-band Erbium-doped fiber amplifier with 1480 nm pump wavelength. The gain-clamping technique is achieved by utilizing the backward propagation of C-band amplified spontaneous emission (ASE). This unwanted noise is reflected back into the optical amplifier and its intensity is adjusted using the variable optical attenuator. The C-band ASE sets the population inversion level along the Erbium doped-fiber and limits the L-band signal amplification to a specific value. The whole optical bandwidth in L-band can be employed for signal amplification since the saturating tone is out of the band. The gain dynamic range of 11.7 dB is obtained between 21.7 and 10.0 dB with noise figure of less than 5.5 dB for signal power up to 2 dBm.

Recent Advances in Shape-Controlled Synthesis of Noble Metal Nanoparticles by Radiolysis Route

This paper focuses on the recent advances on radiolysis-assisted shape-controlled synthesis of noble metal nanostructures. The techniques and protocols for producing desirable shapes of noble metal nanoparticles are discussed through introducing the critical parameters which can influence the nucleation and growth mechanisms. Nucleation rate plays a vital role on the crystallinity of seeds while growth rate of different seeds’ facets determines the final shape of resultant nanoparticles. Nucleation and growth rate both can be altered with factors such as absorbed dose, capping agents, and experimental environment condition to control the final shape. Remarkable physical and chemical properties of synthesized noble metal nanoparticles by controlled morphology have been systematically evaluated to fully explore their applications.

Performance of 18 channel CWDM system with inline Semiconductor Optical Amplifier

Semiconductor Optical Amplifier (SOA) is used for a 2.5Gbps Coarse Wavelength Division Multiplexing (CWDM) transmission in O to L-band (1271-1611 nm). Analysis of the proposed topology is conducted using Optisystem software. In this paper, discussions on the gain spectrum and the quality of signal of an optically amplified 18 channel system are provided. A wideband travelling wave SOA which operates as an inline amplifier resulted in wide 3 dB bandwidth of 200 nm. The overall quality of signal at the receiver is evaluated with the Q factor value. Better performance based on Q factor analysis is obtained at larger lengths of the first fiber span and a flat gain over 11 CWDM channels is obtained.

Real-time monitoring and fault locating using amplified spontaneous emission noise reflection for tree-structured Ethernet passive optical networks

Abstract. Nowadays, optical networks are becoming dense while detecting faulty branches in the tree-structured networks has become problematic. Conventional methods are inconvenient as they require an engineer to visit the failure site to check the optical fiber using an optical time-domain reflectometer. An innovative monitoring technique for tree-structured network topology in Ethernet passive optical networks (EPONs) by using the erbium-doped fiber amplifier to amplify the traffic signal is demonstrated, and in the meantime, a residual amplified spontaneous emission spectrum is used as the input signal to monitor the optical cable from the central office. Fiber Bragg gratings with distinct center wavelengths are employed to reflect the monitoring signals. Faulty branches of the tree-structured EPONs can be identified using a simple and low-cost receiver. We will show that this technique is capable of providing monitoring range up to 32 optical network units using a power meter with a sensitivity of −65  dBm while maintaining the bit error rate of 10−13.

Binding Affinity of a Highly Sensitive Au/Ag/Au/Chitosan-Graphene Oxide Sensor Based on Direct Detection of Pb2+ and Hg2+ Ions

The study of binding affinity is essential in surface plasmon resonance (SPR) sensing because it allows researchers to quantify the affinity between the analyte and immobilised ligands of an SPR sensor. In this study, we demonstrate the derivation of the binding affinity constant, K, for Pb2+ and Hg2+ ions according to their SPR response using a gold/silver/gold/chitosan–graphene oxide (Au/Ag/Au/CS–GO) sensor for the concentration range of 0.1–5 ppm. The higher affinity of Pb2+ to binding with the CS–GO sensor explains the outstanding sensitivity of 2.05 °ppm−1 against 1.66 °ppm−1 of Hg2+. The maximum signal-to-noise ratio (SNR) upon detection of Pb2+ is 1.53, and exceeds the suggested logical criterion of an SNR. The Au/Ag/Au/CS–GO SPR sensor also exhibits excellent repeatability in Pb2+ due to the strong bond between its functional groups and this cation. The adsorption data of Pb2+ and Hg2+ on the CS–GO sensor fits well with the Langmuir isotherm model where the affinity constant, K, of Pb2+ and Hg2+ ions is computed. The affinity of Pb2+ ions to the Au/Ag/Au/CS–GO sensor is significantly higher than that of Hg2+ based on the value of K, 7 × 105 M−1 and 4 × 105 M−1, respectively. The higher shift in SPR angles due to Pb2+ and Hg2+ compared to Cr3+, Cu2+ and Zn2+ ions also reveals the greater affinity of the CS–GO SPR sensor to them, thus supporting the rationale for obtaining K for these two heavy metals. This study provides a better understanding on the sensing performance of such sensors in detecting heavy metal ions.

Flat gain, wide bandwidth of in-line semiconductor optical amplifier in CWDM Systems

Abstract Semiconductor optical amplifier (SOA) is one of the commonly used amplifiers in optical networks. This paper reviews the SOA implementation in coarse wavelength division multiplexing (CWDM) systems, which includes the explanation of the fundamental concepts such as the configuration, principle of operation as amplifiers, and the performance in different CWDM topologies. Simulation using OptiSystem software was carried out to determine the gain saturation at high input power and longer wavelengths. It shows that SOA implementation in CWDM networks is capable of providing flat gain for 40 nm wavelength span.

A Novel Technique Employing Tapered Fiber Bragg Grating to Solve the Axial/Transverse Forces Crosstalk in Microsurgical Instruments

This paper demonstrates the capability of retinal microsurgical instruments constructed with customized fiber Bragg gratings (FBGs) sensors to completely decouple the transverse and axial force components. In contrast to the constantly shifting Bragg wavelength, FBG bandwidth can only be tuned when a nonuniform strain/temperature distribution is applied. Using a tapered FBG (TFBG) at the neutral axis of the instrument makes the bandwidth tune-ability possible by applying forces both transversely and axially, while the bandwidth of the outer/lateral standard FBG (SFBG) due to the fiber symmetry remains insensitive to axial forces. Therefore, the crosstalk (transverse forces) in the TFBG can be easily filtered out when mixed forces are applied simultaneously. Tapered fiber mode analysis is carried out to calculate the local modes and is used in the analytic coupled-mode solution. Transfer-matrix method, then, is developed to analyze the reflected spectrum of the TFBG. We provide a developed mathematical model algorithm to show how force vectors can be measured. Tuning the reflected bandwidth is directly corresponding to the amount of the reflected optical power. Thus, the results show that the simulated needle sensors are able to measure transverse and axial forces with a sensitivity of 0.049 and 0.0026 dBm/mN, while the SFBG is insensitive to the axial forces. This novel method is applicable for microsurgical applications, i.e., vascular and cochlear implant surgeries and catheterization procedures.

Electrocardiographic signal detection using self-mixing interferometer technique with customized electro-optic phase modulator

This paper demonstrates the viability of using self-mixing interferometer technique with a customized electro-optic phase modulator to detect the electrocardiographic signals on surface skin. The signals were recorded under two different optical feedback levels where the self-mixing technique operated under strong optical feedback regime was preferred due to the clear advantage of stability and linear relationship between the input and output signal.