Faisal Rafiq Mahamd Adikan | University of Malaya, Malaysia (original) (raw)
Papers by Faisal Rafiq Mahamd Adikan
21st Annual Conference British Liquid Crystal Society (BLCS 2007), 2007
Liquid crystal-based integrated optical devices offer the potential for high speed and dynamicall... more Liquid crystal-based integrated optical devices offer the potential for high speed and dynamically tunable optical switches in modern telecommunications networks. Here, electrically tunable devices have major advantages over their thermal counterparts, with superior response times and low operating voltages (~100V). Our approach to achieving such devices is to fabricate planar optical waveguides with integrated Bragg gratings via direct UV writing1 into silica-on-silicon samples with evanescent field coupling into a liquid crystal overlay through an etched window (Fig. 1(a)). Such electrically tunable devices work on the principle of shifting the Bragg wavelength by modifying the effective index of a waveguide in a multilayer substrate. Electrically controlled liquid crystal birefringence modifies the waveguide effective index, producing a Bragg wavelength shift. In our early samples, Merck 18523 nematic liquid crystal is used as it has a compatible refractive index to silica (n=1.49 at λ=1550nm). Homeotropic alignment of the liquid crystal is provided by application of a surfactant layer.
Phys Rev E Stat Nonlin Soft Matter Phys, 2012
Spreading of evaporative liquid drops in a thin porous layer has been studied. The entire spreadi... more Spreading of evaporative liquid drops in a thin porous layer has been studied. The entire spreading process can be divided into three distinct phases according to the change of the wetted porous region size. The first phase is characterized by the expansion of the wetted porous region and shrinking of the liquid drop. Contact line pinning is observed in the wetted porous region in the second phase even with the liquid drop totally absorbed into the porous layer. The third phase sees the shrinkage of the wetted porous region until it is not observable. Based on these observations, a model is devised to simulate the spreading of a liquid drop under the studied conditions. Partial differential equations are used to describe the relation between liquid drop volume and other important parameters of a fluid flow, including maximum wetted region diameter achieved, time taken to reach each spreading process phase, and evaporation rate. Calculated results are in good agreement with the experimental data.
Chinese Optics Letters, 2011
Spectral hole burning (SHB) effects in a gain-flattened erbium-doped fiber amplifier (EDFA) are d... more Spectral hole burning (SHB) effects in a gain-flattened erbium-doped fiber amplifier (EDFA) are demonstrated to be significant in the presence of large signal power around the 1530-1532-nm wavelength range. These are the first effects reported in a setup employing equivalent power level distribution of 40 channels ranging from 1530 to 1561 nm. To explain this, the introduction of a new local population variable into the laser equation is required to support the original inversion ratio that is determined by the pump lasers. In the analysis section, spectroscopic parameters and high signal powers are considered to be other contributing parameters to the change in the gain characteristics. An improvement to this theoretical basis is suggested by implementing mathematical modeling to validate similarities between the gain shape of simulation to that obtained in the experiment.
Optik, 2013
In this work, fabrication and characterization of a single-mode vinyltriethoxysilane (VTES) based... more In this work, fabrication and characterization of a single-mode vinyltriethoxysilane (VTES) based hybrid organic-inorganic sol-gel ridge waveguide is reported. VTES based hybrid sol-gel material has been deposited by multiple spin-coating process on quartz substrate. Channel waveguides have been fabricated by UV photopolymerization followed by wet etching process. Optical guided mode was observed to ensure the single mode condition while cut-back technique was performed for loss propagation measurement. Optical propagation losses were measured to be 1.6 dB/cm at 1.31 μm wavelength. This value shows that this material is a promising choice for the development of integrated optical circuits for telecommunication field.
Sense and fibrelity: next generation optical biosensors. At SET for Britain, London, UK, 12 Dec 2006., 2006
Biosensors now play a vital and essential role in medicine, industry and the environment, providi... more Biosensors now play a vital and essential role in medicine, industry and the environment, providing routine analysis, crucial monitoring, and early detection of problems and crisis points.
Biosensors are increasingly finding applications in homeland security, as well as in bio/pharmaceutical research. The market for biosensors is forecast to swell to £5.7 billion in 2007, with an annual growth rate of around 10 per cent [1], as new techniques address the issues of accuracy, response time, ease of use and cost, which currently determine specific implementation
in different sectors. Solutions based on integrated optics -- lab-on-chip and microfluidics -- are now gaining an
increasing foothold on the biosensor market.
Sains Malaysiana, 2001
The dependence of erbium-doped fiber amplifier (EDFA) performance on amplifier self-saturation is... more The dependence of erbium-doped fiber amplifier (EDFA) performance on amplifier self-saturation is studied by tuning the pump wavelength over a 5 nm band centered at 980 nm. Gain and noise figure are degraded at the peak pump absorption wavelength, which shows the strongest effect of amplifier self-saturation. It is shown experimentally that tuning the pump wavelength away from the peak pump absorption provides 1 -2 dB improvement in pump to-signal conversion. The effect of amplifier self-saturation is also dependent on the signal wavelength where high gain and noise figure penalties are obtained at 1530 nm (± 5 nm) band.
3th European Conference on Integrated Optics (ECIO 2007), 2007
We present our recent developments in direct-UV-written integrated optical devices, based on app... more We present our recent developments in direct-UV-written integrated optical devices, based on
applications in telecommunications, material characterisation, and optical sensing. The inherent advantages of
this channel definition technique over traditional etching based approaches are reiterated and demonstrated in
the production of small angle, low loss X-couplers with negligible polarisation dependence. Interfering two
focussed UV spots also provides us with the capability to simultaneously define a channel waveguide and Bragg
grating, opening new device and application opportunities. Such structures provide a method to quantify the
photosensitivity effects observed in conventional multilayer substrates, and assess the core uniformity of a novel
‘flat-fibre’ format recently developed within the ORC. We will also discuss electrically tuned Bragg gratings via
liquid crystal overlayers, displaying a dynamic range in excess of 100GHz for use in dynamic optical networks.
Scientific Research and Essays, 2011
A simple noise-speech discrimination method in time domain is presented. The random signal noise ... more A simple noise-speech discrimination method in time domain is presented. The random signal noise characteristics were studied in time domain. Using the characteristics information, in real time processing, a simple algorithm to detect starting and ending point of speech samples in time domain is being demonstrated. Out of 100 attempts, about 94% of successful attempts of noise-speech discrimination have been obtained with white noise background by choosing the critical thresholds values.
3rd International Conference on Photonics, ICP 2012, 2012
Although commercial tunable optical filters with integrated electronic controls are available, it... more Although commercial tunable optical filters with integrated electronic controls are available, it costs much more than a manually tunable filter. This paper aims to demonstrate a simple procedure on mounting a manually tunable bandpass filter (TBF), with a mathematical model to represent the relation between the sensor's output and the central wavelength of the filter. A position sensor is used to match the central wavelength of the filter and the sensor's output. This results in a simple mount to actuate the TBF and the position of the wavelength is simply translated in terms of the output voltage. Although the accuracy of the system is not commercial grade, a rudimentary setup with promising results can be observed. We present the mount using very simple components, utilizing motorized actuation, with an analog voltage output which can bear any desired resolution for digitization. Finally, a mathematical model is developed to represent the wavelength-voltage relation. This setup paves way for researchers to log the central wavelength from tunable filters without the need for any equipment, at a much lower cost compared to its commercial counterparts.
Optics Express, 2012
An all-optical generation of a millimeter wave carrier from a multiwavelength Brillouin-erbium fi... more An all-optical generation of a millimeter wave carrier from a multiwavelength Brillouin-erbium fiber laser is presented. Four-channel output with spacing of about 21.5 GHz is generated from the fiber laser by controlling the gain in the cavity. A dual-wavelength signal with spacing correspondent to six orders of Brillouin frequency shift is obtained by suppressing the two channels at the middle. Heterodyning these signals at the high-speed photodetector produces a millimeter wave carrier at 64.17 GHz. Temperature dependence characteristic of Brillouin frequency shift realize the flexibility of generated millimeter wave frequency to be tuned at 6.6 MHz/ °C.
Electronics Letters, 2007
A method for fabricating planar silica substrates via modified chemical vapour deposition (MCVD) ... more A method for fabricating planar silica substrates via modified chemical vapour deposition (MCVD) and a modified fibre drawing technique is presented. Long lengths of planar material are generated from a single substrate offering a potentially low-cost alternative to existing planar substrate deposition processes. Buried straight and splitting waveguide channels, as well as Bragg gratings, are inscribed in the planar material using direct UV-writing technology, and the results are reported.
Optics Communications, 2013
An enhanced pump delivery scheme for L-band remote erbium-doped fiber/Raman (R-EDFA/Raman) hybrid... more An enhanced pump delivery scheme for L-band remote erbium-doped fiber/Raman (R-EDFA/Raman) hybrid amplifier utilizing stimulated Raman scattering (SRS) is demonstrated. The technique benefits from the use of higher-order pumps that are realized by generating C-band SRS and ultra-long Raman fiber laser (ULRFL). A section of passive erbium-doped fiber is deployed at the end of the transmission span to exploit the ULRFL pump for additional amplification. Gain clamping effect is observed at the R-EDFA and passive EDF due to saturation from the higher-order pumps. Tuning the pump wavelengths to a region away from the amplification bandwidth could remove the gain-clamping effect and produce maximum gain performance.
International Journal of Molecular Sciences, 2012
Heavy metal oxide glasses, containing bismuth and/or lead in their glass structure are new altern... more Heavy metal oxide glasses, containing bismuth and/or lead in their glass structure are new alternatives for rare eart (RE) doped hosts. Hence, the study of the structure of these vitreous systems is of great interest for science and technology. In this research work, GeO2-PbO-Bi2O3 glass host doped with Er3+/Yb3+ ions was synthesized by a conventional melt quenching method. The Fourier transform infrared (FTIR) results showed that PbO and Bi2O3 participate with PbO4 tetragonal pyramids and strongly distort BiO6 octahedral units in the glass network, which subsequently act as modifiers in glass structure. These results also confirmed the existence of both four and six coordination of germanium oxide in glass matrix.
9th International Conference on Laser Ablation, Tenerife, Spain, 2007
We report on the observation of confocal micro-luminescence originated by defects created in dire... more We report on the observation of confocal micro-luminescence originated by defects created in direct UV written silica-on-silicon waveguides. Spatial and spectral analysis of the visible luminescence bands was performed with 488nm excitation. This has revealed the UV formation of different defects which are related to the different compositions of core and cladding layers.
Optics Communications, 2013
This paper demonstrates a method to remove the gain ripple profile specifically for a two-segment... more This paper demonstrates a method to remove the gain ripple profile specifically for a two-segment fiber optical parametric amplifier arising from the dispersion differences between the fiber gain medium and the standard single mode fiber attached to the optical components. This is achieved by using a simple design that incorporates a gain smoothening filter at the mid-stage of the amplifier. This simple yet practical method is useful when isolators are adopted for stimulated Brillouin scattering suppression but it comes with the expense of parametric gain.
3rd International Conference on Photonics, ICP 2012, 2012
Fabrication of High Index Guiding Photonic Crystal Fiber is demonstrated using stack-and-draw tec... more Fabrication of High Index Guiding Photonic Crystal Fiber is demonstrated using stack-and-draw technique. Novel rapid preform connecting method is presented, replacing an important process in conventional fabrication of microstructured fiber. Fabricated Photonic Crystal Fiber has core size of 5.77μm and displays low loss single-mode guiding in communication band.
Journal of Lightwave Technology, 2012
A physical micromachining technique is demonstrated in a low-loss flat-fiber substrate to fabrica... more A physical micromachining technique is demonstrated in a low-loss flat-fiber substrate to fabricate a multimode interference (MMI) device. The flat-fiber substrate is a low-index-contrast material; however, by making use of two physically micromachined trenches, lateral confinement is achieved providing high index contrast for the MMI region. A 1$\,\times\,$3 MMI device exhibiting 1.89 dB of excess loss has been demonstrated.
Optical Materials, 2012
A dual layer Benzocyclobutene (BCB) polymer with tailored refractive index values is successfully... more A dual layer Benzocyclobutene (BCB) polymer with tailored refractive index values is successfully fabricated using different curing processes, forming a platform for integrated optical devices. The dual layer BCB polymer could potentially solve the high index contrast issue associated with existing glass-polymer structure, which require sub-micron precision when producing single-mode waveguides. Although the two BCB layers display similar physical properties, they have significantly different optical and chemical characteristics. The different curing processes for the undercladding and core layers led to these differences. Single mode waveguides fabricated via photolithography were also demonstrated with an average propagation loss of 2 dB/cm.
21st Annual Conference British Liquid Crystal Society (BLCS 2007), 2007
Liquid crystal-based integrated optical devices offer the potential for high speed and dynamicall... more Liquid crystal-based integrated optical devices offer the potential for high speed and dynamically tunable optical switches in modern telecommunications networks. Here, electrically tunable devices have major advantages over their thermal counterparts, with superior response times and low operating voltages (~100V). Our approach to achieving such devices is to fabricate planar optical waveguides with integrated Bragg gratings via direct UV writing1 into silica-on-silicon samples with evanescent field coupling into a liquid crystal overlay through an etched window (Fig. 1(a)). Such electrically tunable devices work on the principle of shifting the Bragg wavelength by modifying the effective index of a waveguide in a multilayer substrate. Electrically controlled liquid crystal birefringence modifies the waveguide effective index, producing a Bragg wavelength shift. In our early samples, Merck 18523 nematic liquid crystal is used as it has a compatible refractive index to silica (n=1.49 at λ=1550nm). Homeotropic alignment of the liquid crystal is provided by application of a surfactant layer.
Phys Rev E Stat Nonlin Soft Matter Phys, 2012
Spreading of evaporative liquid drops in a thin porous layer has been studied. The entire spreadi... more Spreading of evaporative liquid drops in a thin porous layer has been studied. The entire spreading process can be divided into three distinct phases according to the change of the wetted porous region size. The first phase is characterized by the expansion of the wetted porous region and shrinking of the liquid drop. Contact line pinning is observed in the wetted porous region in the second phase even with the liquid drop totally absorbed into the porous layer. The third phase sees the shrinkage of the wetted porous region until it is not observable. Based on these observations, a model is devised to simulate the spreading of a liquid drop under the studied conditions. Partial differential equations are used to describe the relation between liquid drop volume and other important parameters of a fluid flow, including maximum wetted region diameter achieved, time taken to reach each spreading process phase, and evaporation rate. Calculated results are in good agreement with the experimental data.
Chinese Optics Letters, 2011
Spectral hole burning (SHB) effects in a gain-flattened erbium-doped fiber amplifier (EDFA) are d... more Spectral hole burning (SHB) effects in a gain-flattened erbium-doped fiber amplifier (EDFA) are demonstrated to be significant in the presence of large signal power around the 1530-1532-nm wavelength range. These are the first effects reported in a setup employing equivalent power level distribution of 40 channels ranging from 1530 to 1561 nm. To explain this, the introduction of a new local population variable into the laser equation is required to support the original inversion ratio that is determined by the pump lasers. In the analysis section, spectroscopic parameters and high signal powers are considered to be other contributing parameters to the change in the gain characteristics. An improvement to this theoretical basis is suggested by implementing mathematical modeling to validate similarities between the gain shape of simulation to that obtained in the experiment.
Optik, 2013
In this work, fabrication and characterization of a single-mode vinyltriethoxysilane (VTES) based... more In this work, fabrication and characterization of a single-mode vinyltriethoxysilane (VTES) based hybrid organic-inorganic sol-gel ridge waveguide is reported. VTES based hybrid sol-gel material has been deposited by multiple spin-coating process on quartz substrate. Channel waveguides have been fabricated by UV photopolymerization followed by wet etching process. Optical guided mode was observed to ensure the single mode condition while cut-back technique was performed for loss propagation measurement. Optical propagation losses were measured to be 1.6 dB/cm at 1.31 μm wavelength. This value shows that this material is a promising choice for the development of integrated optical circuits for telecommunication field.
Sense and fibrelity: next generation optical biosensors. At SET for Britain, London, UK, 12 Dec 2006., 2006
Biosensors now play a vital and essential role in medicine, industry and the environment, providi... more Biosensors now play a vital and essential role in medicine, industry and the environment, providing routine analysis, crucial monitoring, and early detection of problems and crisis points.
Biosensors are increasingly finding applications in homeland security, as well as in bio/pharmaceutical research. The market for biosensors is forecast to swell to £5.7 billion in 2007, with an annual growth rate of around 10 per cent [1], as new techniques address the issues of accuracy, response time, ease of use and cost, which currently determine specific implementation
in different sectors. Solutions based on integrated optics -- lab-on-chip and microfluidics -- are now gaining an
increasing foothold on the biosensor market.
Sains Malaysiana, 2001
The dependence of erbium-doped fiber amplifier (EDFA) performance on amplifier self-saturation is... more The dependence of erbium-doped fiber amplifier (EDFA) performance on amplifier self-saturation is studied by tuning the pump wavelength over a 5 nm band centered at 980 nm. Gain and noise figure are degraded at the peak pump absorption wavelength, which shows the strongest effect of amplifier self-saturation. It is shown experimentally that tuning the pump wavelength away from the peak pump absorption provides 1 -2 dB improvement in pump to-signal conversion. The effect of amplifier self-saturation is also dependent on the signal wavelength where high gain and noise figure penalties are obtained at 1530 nm (± 5 nm) band.
3th European Conference on Integrated Optics (ECIO 2007), 2007
We present our recent developments in direct-UV-written integrated optical devices, based on app... more We present our recent developments in direct-UV-written integrated optical devices, based on
applications in telecommunications, material characterisation, and optical sensing. The inherent advantages of
this channel definition technique over traditional etching based approaches are reiterated and demonstrated in
the production of small angle, low loss X-couplers with negligible polarisation dependence. Interfering two
focussed UV spots also provides us with the capability to simultaneously define a channel waveguide and Bragg
grating, opening new device and application opportunities. Such structures provide a method to quantify the
photosensitivity effects observed in conventional multilayer substrates, and assess the core uniformity of a novel
‘flat-fibre’ format recently developed within the ORC. We will also discuss electrically tuned Bragg gratings via
liquid crystal overlayers, displaying a dynamic range in excess of 100GHz for use in dynamic optical networks.
Scientific Research and Essays, 2011
A simple noise-speech discrimination method in time domain is presented. The random signal noise ... more A simple noise-speech discrimination method in time domain is presented. The random signal noise characteristics were studied in time domain. Using the characteristics information, in real time processing, a simple algorithm to detect starting and ending point of speech samples in time domain is being demonstrated. Out of 100 attempts, about 94% of successful attempts of noise-speech discrimination have been obtained with white noise background by choosing the critical thresholds values.
3rd International Conference on Photonics, ICP 2012, 2012
Although commercial tunable optical filters with integrated electronic controls are available, it... more Although commercial tunable optical filters with integrated electronic controls are available, it costs much more than a manually tunable filter. This paper aims to demonstrate a simple procedure on mounting a manually tunable bandpass filter (TBF), with a mathematical model to represent the relation between the sensor's output and the central wavelength of the filter. A position sensor is used to match the central wavelength of the filter and the sensor's output. This results in a simple mount to actuate the TBF and the position of the wavelength is simply translated in terms of the output voltage. Although the accuracy of the system is not commercial grade, a rudimentary setup with promising results can be observed. We present the mount using very simple components, utilizing motorized actuation, with an analog voltage output which can bear any desired resolution for digitization. Finally, a mathematical model is developed to represent the wavelength-voltage relation. This setup paves way for researchers to log the central wavelength from tunable filters without the need for any equipment, at a much lower cost compared to its commercial counterparts.
Optics Express, 2012
An all-optical generation of a millimeter wave carrier from a multiwavelength Brillouin-erbium fi... more An all-optical generation of a millimeter wave carrier from a multiwavelength Brillouin-erbium fiber laser is presented. Four-channel output with spacing of about 21.5 GHz is generated from the fiber laser by controlling the gain in the cavity. A dual-wavelength signal with spacing correspondent to six orders of Brillouin frequency shift is obtained by suppressing the two channels at the middle. Heterodyning these signals at the high-speed photodetector produces a millimeter wave carrier at 64.17 GHz. Temperature dependence characteristic of Brillouin frequency shift realize the flexibility of generated millimeter wave frequency to be tuned at 6.6 MHz/ °C.
Electronics Letters, 2007
A method for fabricating planar silica substrates via modified chemical vapour deposition (MCVD) ... more A method for fabricating planar silica substrates via modified chemical vapour deposition (MCVD) and a modified fibre drawing technique is presented. Long lengths of planar material are generated from a single substrate offering a potentially low-cost alternative to existing planar substrate deposition processes. Buried straight and splitting waveguide channels, as well as Bragg gratings, are inscribed in the planar material using direct UV-writing technology, and the results are reported.
Optics Communications, 2013
An enhanced pump delivery scheme for L-band remote erbium-doped fiber/Raman (R-EDFA/Raman) hybrid... more An enhanced pump delivery scheme for L-band remote erbium-doped fiber/Raman (R-EDFA/Raman) hybrid amplifier utilizing stimulated Raman scattering (SRS) is demonstrated. The technique benefits from the use of higher-order pumps that are realized by generating C-band SRS and ultra-long Raman fiber laser (ULRFL). A section of passive erbium-doped fiber is deployed at the end of the transmission span to exploit the ULRFL pump for additional amplification. Gain clamping effect is observed at the R-EDFA and passive EDF due to saturation from the higher-order pumps. Tuning the pump wavelengths to a region away from the amplification bandwidth could remove the gain-clamping effect and produce maximum gain performance.
International Journal of Molecular Sciences, 2012
Heavy metal oxide glasses, containing bismuth and/or lead in their glass structure are new altern... more Heavy metal oxide glasses, containing bismuth and/or lead in their glass structure are new alternatives for rare eart (RE) doped hosts. Hence, the study of the structure of these vitreous systems is of great interest for science and technology. In this research work, GeO2-PbO-Bi2O3 glass host doped with Er3+/Yb3+ ions was synthesized by a conventional melt quenching method. The Fourier transform infrared (FTIR) results showed that PbO and Bi2O3 participate with PbO4 tetragonal pyramids and strongly distort BiO6 octahedral units in the glass network, which subsequently act as modifiers in glass structure. These results also confirmed the existence of both four and six coordination of germanium oxide in glass matrix.
9th International Conference on Laser Ablation, Tenerife, Spain, 2007
We report on the observation of confocal micro-luminescence originated by defects created in dire... more We report on the observation of confocal micro-luminescence originated by defects created in direct UV written silica-on-silicon waveguides. Spatial and spectral analysis of the visible luminescence bands was performed with 488nm excitation. This has revealed the UV formation of different defects which are related to the different compositions of core and cladding layers.
Optics Communications, 2013
This paper demonstrates a method to remove the gain ripple profile specifically for a two-segment... more This paper demonstrates a method to remove the gain ripple profile specifically for a two-segment fiber optical parametric amplifier arising from the dispersion differences between the fiber gain medium and the standard single mode fiber attached to the optical components. This is achieved by using a simple design that incorporates a gain smoothening filter at the mid-stage of the amplifier. This simple yet practical method is useful when isolators are adopted for stimulated Brillouin scattering suppression but it comes with the expense of parametric gain.
3rd International Conference on Photonics, ICP 2012, 2012
Fabrication of High Index Guiding Photonic Crystal Fiber is demonstrated using stack-and-draw tec... more Fabrication of High Index Guiding Photonic Crystal Fiber is demonstrated using stack-and-draw technique. Novel rapid preform connecting method is presented, replacing an important process in conventional fabrication of microstructured fiber. Fabricated Photonic Crystal Fiber has core size of 5.77μm and displays low loss single-mode guiding in communication band.
Journal of Lightwave Technology, 2012
A physical micromachining technique is demonstrated in a low-loss flat-fiber substrate to fabrica... more A physical micromachining technique is demonstrated in a low-loss flat-fiber substrate to fabricate a multimode interference (MMI) device. The flat-fiber substrate is a low-index-contrast material; however, by making use of two physically micromachined trenches, lateral confinement is achieved providing high index contrast for the MMI region. A 1$\,\times\,$3 MMI device exhibiting 1.89 dB of excess loss has been demonstrated.
Optical Materials, 2012
A dual layer Benzocyclobutene (BCB) polymer with tailored refractive index values is successfully... more A dual layer Benzocyclobutene (BCB) polymer with tailored refractive index values is successfully fabricated using different curing processes, forming a platform for integrated optical devices. The dual layer BCB polymer could potentially solve the high index contrast issue associated with existing glass-polymer structure, which require sub-micron precision when producing single-mode waveguides. Although the two BCB layers display similar physical properties, they have significantly different optical and chemical characteristics. The different curing processes for the undercladding and core layers led to these differences. Single mode waveguides fabricated via photolithography were also demonstrated with an average propagation loss of 2 dB/cm.