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This paper compares the performance of two polymeric substance, polyvinyl alcohol (PVA) and polyethylene oxide (PEO) as a host in graphene saturable absorber (SA) fabrication. By applying a low-cost solution casting method, graphene flakes which was prepared using the electro-chemical exfoliation technique will be mixed with PEO or PVA solvent as a host. Single concentration (12.04 wt.%) of graphene-PVA and graphene-PEO has been prepared for comparison. At 1.5 µm wavelength region, 2.8 meters erbium doped fiber (EDF) was applied as a gain medium in ring laser cavity setup. Generally, our measurement confirmed stable Q-switched pulses generation (>30 dB) for both SAs at 1.5 µm region. Evidently, the generated pulse by graphene-PVA at 1531.1 nm produced shorter pulse width of 1.85 µs as compared to 18.1 µs by graphene-PEO at maximum permissible pump power. Although smaller pulse energy was calculated for graphene-PVA, the ability of this type of SA to withstand higher pump-power proved its superiority as compared to its counterpart. Notably, this is the first ever effort that assess the performance of PVA and PEO host in graphene-based saturable absorption, particularly at 1.5 µm region.

There are many types of light source specifically bulbs in the market with different working principles. Each of them provides different intensity at different wavelength. In order to check energy efficiency, it is not appropriate to measure intensity at certain specific wavelength for the same power rating bulb. Therefore, this paper reported the averaging spectroscopy method for intensity measurement between 400-700 nm before comparison is carried out. It is observed that the light emitting diode (LED) bulb shows to be the most efficient light bulbs with the highest average light intensity compared to incandescent and fluorescent bulbs. Light stability test is also carried out and reported in this paper.

In this study, a novel and simple optical fiber sensor is proposed, simulated, and experimentally demonstrated for simultaneous measurement of high refractive index (RI) and temperature. The sensor consists of a section of single-mode-silica rod-single-mode (SSRS) fiber structure cascaded to fiber Bragg grating (FBG) (SSRS-FBG). The simultaneous measurement of high RI and temperature was realized in this study by monitoring the output power level and wavelength shift of the SSRS-FBG single dip transmission spectrum corresponding to different surrounding high RI and ambient temperature values. The experimental results showed that the cascaded sensor had a sensitivity of 108.07 dBm/RIU for high RI ranging at 1.45-1.531, while the temperature sensitivity was 9.31 pm/°C from 35 °C to 85 °C. This sensor is most suitable for high RI applications, such as for monitoring oil quality stored in terminal and power transformers.

Palm oil is an edible vegetable oil yielded from the mesocarp of the palm oil’s fruit. It is commonly used as cooking oil as compared to other cooking oil such as olive or coconut oil because it is inexpensive and has high oxidative stability when used for frying. However, after frequent frying, the oil undergoes some physical and chemical reactions which affect the quality. This leads to the formation of compound that is dangerous to human body which is called free fatty acid (FFA). Therefore, a measurement device needs to be developed to determine the quality of heated cooking oil. In this paper, a spectroscopy study using an open-path method which focus on the palm cooking oil is proposed to examine the reaction of palm oil upon prolonged heating process. Open-path method is a technique where the incident beam will travel through the sample (palm oil) before it is detected by a spectrometer. The result shows that the FFA samples have the optimum absorbance peak at the UV wavelength 339.15 nm and each prolonged heated oil show different absorbance value. Hence, there is a potential to develop an optical sensor to determine the quality of the heated cooking oil.

Fault detection and localization in optical fiber communication links are important in the optical access network (OAN) due to the passive nature of the network elements involved. Any failure in the link can resort to a huge amount of data loss in the network. However, deployment of fault detection and localization devices is extremely limited due to the reliability and financial implications of the devices. Several fault monitoring solutions in the OAN domain have been investigated by the researchers over the decades; the challenges for these monitoring techniques are the cost and complexity of their deployment. Thus, this work proposes a cost-effective solution for the detection and localization of a fault in the OAN based on Fiber-to-the-x (FTTx) network using optical reflectors. The reflected signal from the monitors in the network will be utilized to detect and locate the optical link with fault. Experimental results obtained show the techniques capability to detect and localized fault in the network, in-service over a distance of 20 km.

In this paper, an improved technique for a centralized fault monitoring and detection in Gigabitcapable Passive Optical Network using fiber Bragg grating sensor is proposed. The technique detects fault once it occurs at the vulnerable locations in the fiber optic distribution link by the proposed Fiber Bragg Grating devices. The scheme uses an amplified Erbium Doped Fiber Amplifier monitoring signal in the C-band and a uniform Fiber Bragg Grating with different Bragg wavelengths and reflectivities as the branch identifiers in the network. The reflected signal from the optical sensor is analyzed at the Optical Line Terminal in the Central Office by an Optical Spectrum Analyzer to determine the branch with rupture in the network. The simulated result obtained shows that the system can monitor and detect a fault in the Feeder Fiber link, up to 20 km at optical power received of −44 dBm. The scheme is capable of detecting a fault in the various optical distribution network at the remote node in the customer’s end, at minimum optical power received of −58 dBm with negligible effects on data signal transmission.

In order to avoid service level agreement violation in a passive optical network, effective failure detection and localization is of paramount importance for early fault identification. In this paper, we focus on a technique that can be used to detect and identify a failure in the physical layer using fiber Bragg grating (FBG) sensor integrated with machine learning (ML) technology. A kernel-based support vector machine trained model is purposely developed to detect and identify faulty optical link in PON. The technique relies on the retrieved optical reflected signal from the FBG sensors which are further elaborated by the ML algorithm using MATLAB. The dataset for the training and testing of the proposed model is generated in a simulated $1 \times 4$ Gigabit passive optical network, with a monitoring power of −4.16 dBm at a distance of 20 km. Optimal parameters of the support vector are selected with the help of cross-validation, thus leading to the optimized non-linear decision boundary. The proposed approach is tested on a number of datasets generated from the FBG sensors and demonstrates that the model achieves a 97 to 99% accuracy compared with the observed optical reflected spectra from the FBG sensors using an optical spectrum analyzer (OSA). The model which is not too complex, could avoid the use of costly OSA when embedded into the network controller in a software define network and minimizes the monitoring cost.

In this paper, the surface roughness characteristic of D-shaped optical fibre sensors with its effects on the sensitivity has been studied. The ULTRAPOL end and edge polishing system was used with some modifications to fabricate the D-shaped sensors with planar sensing zone from the single-mode optical fibres. The mean surface roughness of 343, 96, 25 and 9 nm was estimated at the sensing zone of the D-shaped sensors which were sequentially polished with 30, 9, 3 and 0.5 µm grit size polishing films, respectively. From the experimental results, it has been observed that surface roughness of the sensing zone does not exhibit the significant effects on the output signal strength, whereas the sensitivity of the D-shaped sensors nonlinearly related with the surface roughness of the sensing zone. The designed D-shaped optical fibre sensors have potential applications in biomedical and chemical industries.

In this study a technique for a centralized fault monitoring and detection in Gigabit-capable Passive Optical Network (G-PON) using fiber Bragg grating (FBG) sensor is proposed. The technique detects fault once it occurs at the vulnerable locations in the fiber optic distribution link by the proposed FBG devices. Monitoring signal in the C-band is reflected by a uniform FBG with different Bragg wavelengths and reflectivities. The FBGs serve as branch identifiers in the network. The reflected signal from the FBGs is analyzed at the Optical Line Terminal (OLT) in the Central Office (CO) by an Optical Spectrum Analyzer (OSA), to identify the branch with rupture in the network. The simulated result obtained shows that the system can monitor, and detect a fault in the physical layer of the optical distribution network with negligible effects on data signal transmission.

An all‐fiber Mach‐Zehnder interferometer based on symmetrical offset coreless silica fiber (CSF) is proposed and demonstrated for temperature sensing. The sensor is constructed by a symmetrical offset splicing of a short CSF section between two CSF sections. Thus, two distinct optical paths are created inside and outside of the offset section resembling a Mach‐Zehnder interferometer. For temperature sensing, the offset gap is filled with refractive index liquid with high thermo‐optic coefficient of 3.34 × 10−4. Measurement is established by monitoring wavelength shift resulting from interference of modes between the two distinct optical paths. A very high temperature sensitivity of 3220 pm/°C has been achieved with a short sensor length of 1.5 mm. Due to its compact size and high sensitivity, the proposed structure would be an attractive option for low temperature measurement such as for human body temperature monitoring.

In this paper, graphene oxide (GO) was doped into SU-8 polymer to examine the functionalities of polymer waveguide material via dopant inclusion. In material preparation, step by step processes starting from cyclopentanone mixing will be explained. It is shown that doped material's refractive index can be tailored by having different weight percentage of GO. Finally, a single mode ridge waveguide loss of GO doped SU-8 has been characterized to be 1.9 dB/cm at 1550 nm wavelength.

This paper explains about the performance of graphene nanopowder (GNP) based saturable absorber (SA) at 1.5-micron region which is prepared by dissolution in polyvinyl alcohol (PVA) polymer. Two different GNP flakes thickness (AO2-8 nm and AO4-60 nm) are tested. By applying a solution casting method, three weight ratio of GNP to PVA (12.04, 8.03 and 3.11 wt.%) have been prepared and fabricated as a composite thin film. To characterize for the SA performance, 4 mm 2 area of GNP-PVA thin film is embedded in a 14 meters long ring cavity with 3 meters Erbium doped fiber (EDF) as a gain medium. Our characterization results show that the GNP-PVA thin film act as a Q-switcher which produce stable laser pulses for 12.04 wt.% with maximum repetition rate of 39.22 kHz and shortest pulse width of 11.79 µs. Meanwhile, unstable Q-switched pulses of 8.03 wt.% and 3.11 wt.% have been observed with recorded signal to noise ratio (SNR) of only 21 dB and 17 dB, respectively. The threshold pumping power for Q-switched lasing to emerge is recorded as low as 30 mW. Apparently, it shows that GNP concentration and flakes thickness in fabricated SA composite plays vital role in the performance of generated Q-switch laser, particularly at 1.5 µm region. Full Text: PDF References T. Hasan, Z. Sun, F. Wang, F. Bonaccorso, P.H. Tan, A.G. Rozhin, A.C. Ferrari, "Nanotube–Polymer Composites for Ultrafast Photonics", Adv. Mater. 21, 3874 (2009). CrossRef Q. Bao, H. Zhang, Y. Wang, Z. Ni, Y. Yan, Z.X. Shen, K.P. Loh, D.Y. Tang, "Atomic-Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers", Adv. Funct. Mater. 19, 3077 (2009). CrossRef Z. Luo, M. Zhou, J. Weng, G. Huang, H. Xu, C. Ye, Z. Cai, Opt. Lett. 35(21), 3709 (2010). CrossRef D. Popa, Z. Sun, T. Hasan, F. Torrisi, F. Wang, A.C. Ferrari, "Graphene Q-switched, tunable fiber laser", Appl. Phys. Lett. 98, 3106 (2011). CrossRef Y.M. Chang, H. Kim, J.H. Lee, Y. Song, "Multilayered graphene efficiently formed by mechanical exfoliation for nonlinear saturable absorbers in fiber mode-locked lasers", Appl. Phys. Lett. 97, 211102 (2010). CrossRef M. Jiang, Z. Ren, Y. Zhang, B. Lu, R. Zhang, J. Guo, Y. Zhou, J. Bai, "Passive Q-Switching with Graphene Saturable Absorber in Nd:YAG Operating at 1064nm", Mater. Sci. Forum 694, 700 (2011). CrossRef N. Hussin, M.H. Ibrahim, F. Ahmad, H. Yahaya, S.W. Harun, "Graphene Nanoplatelets (GnP)-PVA Based Passive Saturable Absorber", Telkomnika 15(2), 814 (2017). CrossRef F.C. Mat, M. Yasin, A.A. Latiff, S.W. Harun, Photonics Letters of Poland 9, 100 (2017). CrossRef E.K. Ng, K.Y. Lau, H.K. Lee, N.M. Yusoff, A.R. Sarmani, M.F. Omar, M.A. Mahdi, "L-band femtosecond fiber laser based on a reduced graphene oxide polymer composite saturable absorber", Opt. Mater. Express 11, 59 (2021). CrossRef N.H.M. Apandi, S.N.F. Zuikafly, N. Kasim, M.A. Mohamed, S.W. Harun, F. Ahmad, "Observation of dark and bright pulses in q-switched erbium doped fiber laser using graphene nano-platelets as saturable absorber", Bull. Electr. Eng. Inform. 8, 1358 (2019). CrossRef N.U.H.H.B. Zalkepali, N.A. Awang, Y.R. Yuzaile, Z. Zakaria, A.A. Latif and F. Ahmad, "Graphene Nanoplatelets as Saturable Absorber for Mode-locked Fiber Laser Generation", J. Adv. Res. Dyn. Control Syst. 12(2), 602 (2020). CrossRef X. Zhu and S. Chen, "Autoencoder-Based Transceiver Design for OWC Systems in Log-Normal Fading Channel", IEEE Photonics J. 11, 7105109 (2019). CrossRef

A fiber optic sensor for monitoring mercuric (Hg2+) ions in the aqueous sample have been developed based on modified cladding. To fabricate a D-shaped sensing zone onto the multimode optical fiber lengthwise polishing was utilized using a mechanical end and edge polishing system. The produced sensing region has dimensions of 10 mm × 125 μm × 62 μm (l × w × h). A 2 μm thin layer of Al2O3 nanoparticles sensitized with 4-(2-pyridylazo)-resorcinol was deposited onto the sensing element of multimode fiber optic sensor to make it sensitive and selective for Hg2+ ions. The analytical results demonstrate that the sensing device has a linear response for Hg2+ ions concentration over a range from 4 to 16 ppm along with a 4 ppm limit of detection in an aqueous sample at room temperature. The selectivity of the sensor is examined for the recognition of Hg2+ ions in presence of other cations such as zinc and/or lead ions up to 16 ppm in an aqueous solution. The main merits of this fabricated sensor are easy and safe installation, rapid response, enhanced linear response range, and better selectivity towards Hg2+ ions.

This article explains about the development of an optical sensor system to detect and measure ammonia emission in the agricultural field. At initial stage, an open path optical technique where a cylindrical chamber is used to detect low concentration of ammonia in the UV region. The methodology describing the working principle of the sensor and the wavelengths combination technique to enhance the Lower Detection Limit of the measurement. The result demonstrates that the developed optical sensor is able to measure ammonia concentration at around 212 nm. It also shows that by combining intensities at 2 adjacent wavelengths, the Lower Detection Limit has been improved to 2.25 ppm and 1 s response time is retained. Then the system is tested to monitor ammonia pollution in the cattle barn in Tipperary, Ireland. It shows that the developed system is able to detect and measure very low ammonia concentration which is below 2 ppm.

As optical fibre reaches deeper into passive optical network (PON) in fibre-to-the-x (FTTx) networks, maintaining the integrity of these networks is indeed imperative. Essentially, best practices have been established throughout the installation and verification of the fibre access network. Equally significant is monitoring the optical fibre performance degradation in-service to ascertain efficient service delivery, as well as to guarantee service level agreement. Nevertheless, a minor failure in PON may lead to massive loss of data stemming from inherent passivity of network elements in optical distribution network, thus resulting in customer dissatisfaction and escalated operational expenses borne by network operators. Unfortunately, testing and monitoring optical layer have become rather intricate due to the rapid evolution of PON technology. Hence, an efficient optical layer monitoring system equipped with complete monitoring capabilities may substantially enhance the quality of service. Having that said, this study presents a review pertaining to the progress on the performance of available approaches for optical link monitoring system in PON. Recent advances in improving the performance of the optical link monitoring system, such as measurement accuracy, measurement speed, signal-to-noise (SNR) ratio, spatial resolution, and dynamic range, were investigated. Additionally, the performances of the existing approaches based on optical monitoring specifications were compared to identify an ideal monitoring framework. Finally, this paper discusses several challenges and prospects for future endeavours in formulating an effective optical link monitoring system in PON.

Safety enhancement of airport runway surfaces can avoid unnecessary runway closure and airplane accidents due to foreign object debris. Millimeter-wave linear cell radar system empowered by radio-over-fiber network system is a promising solution for surveillance of the runway surfaces within 10 s. Currently, 96-GHz linear cell radar system has been already installed with four radio access units in Narita International Airport, Japan, as a field trial test. For the application of the linear cell radar system to Kuala Lumpur International Airport as a field trial in a tropical region, some fundamental characteristics need to be measured and analysed before installation of the linear cell radar system. In this paper, we show the summary of the field trial in Kuala Lumpur International Airport, Malaysia and Universiti Teknologi Malaysia, Malaysia.

peer-reviewed An improved and compact gas sensor using mid-infrared spectroscopy for highly responsive Carbon Dioxide (CO2) detection is presented. The sensing principle is based on open-path direct absorption spectroscopy in the mid-infrared region. The improved reflective structure of optical gas sensor consists of low cost and compact components. Several gas cell configuration which includes SISO, 2-MISO, 4-MISO and 8-MISO were simulated using ZEMAX®12 using non-sequential ray tracing technique to get the optimum radius of the reflective curved surface. Sensitivity analysis has shown that the optimised structure of 4-MISO yields the highest sensitivity and power efficiency of -0.2895%-1 and 12.298% respectively. The developed gas sensing system using the optimised gas cell has shown the capability of accurately detecting CO2 concentration between 1.5% and 5.8% with no cross-sensitivity with other gases present in the gas cell. The newly developed CO2 sensor exhibits high responsivity with the recorded rise time and fall time of less than 1 second respectively.

Beer–Lambert law deviation is often observed. Here, we propose alternative wavelength 279.95 nm for ozone concentration measurement between 357 and 971 μL L−1 to preserve linearity. Sensor loses linearity below transmittance 0.2165, as sensor approaches saturation. We recommend measurement of ozone concentration above transmittance of 0.2165 for strong linear relation. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1013–1016, 2015

Accurate value of absorption cross section is required for correct measurement of ozone concentration. Measurement of ozone has been done at different altitude and pressure. However, previous work has failed to establish significant relation between pressure and ozone absorption cross section. Therefore, this work aims to establish relation between pressure and maximum ozone absorption cross section via spectralcalc.com gas cell simulator. Simulation results show maximum absorption cross section 1.148×10-21 m2 molecule-1 and maximum absorption wavelength 255.442 nm are independent of pressure changes from 0.1 atm to 3.0 atm. Thus, measurement of ozone concentration at maximum absorption wavelength is strongly recommended due to negligible pressure dependence.

A novel simple fiber sensor to sense liquid level is presented. The operation principle is based on the relative Fresnel reflective intensity. The sensor consists of a fiber splitter with the configuration of one input to multiple fiber outputs, i.e. 1×4, 1×8 and 1×12 arrangements that act as a discrete liquid level. A broadband source (BBS) is used as the light source supply. The total reflected power intensity is measured using a power meter. Experimental results show that the power intensity decreases as the level of liquid is increased. The sensor has a simple configuration, low cost, and it can be customized for a wide height measurement range spanning from a few centimeters up to a hundred meters.

In this paper, a low-cost fiber optic displacement sensor (FODS) using a bundle of plastic optical fiber (POF) as a probe is developed and presented. The sensor consists of a high power light emitting diode (LED) as light source, a probe with multiple receiving plastic optical fiber and a photodiode detector. The sensor is characterized at millimeter distance and the sensor output is analyzed from 0 mm to 13 mm displacement. The sensitivity of the sensor is found to be 5.38 mV/mm over 2.6 mm sensing range. The sensor is very useful for close distance target since it is highly sensitive at the front slope. The low development cost, high degree of sensitivity and simplicity of the design make it suitable for wide range of industrial applications.

There has been a surge in ozone gas relevance in agriculture, environment and in the industry. This has resulted in increased research activities in areas involving ozone gas generation, application, safety and sensing. In this manuscript we present reviews of selected recent works (2011–2015) on ozone gas sensors based on absorption spectroscopy. Issues addressed include sensors applications versus requirements; sensors performance versus limitations and cost of sensors. Outstanding research issues are also outlined. While the review is mainly biased towards sensing of ozone using conventional absorption spectroscopy, other methods such as photo acoustic, photo reductive, photo stimulated, metal oxides, electrochemical, chemical, solid state and resistive ozone sensors were also considered in light of their performance criteria. Generally, it was observed that new applications of ozone gas lead to new sensing research challenges. Several sensing parameters were repeatedly investigated and improved upon over the years. Some of these parameters include: selectivity, sensitivity, speed of response, cost of sensor, lower detection limit and portability.

A wide range analysis of spectroscopic ozone gas sensor is conducted in order to obtain specific affected wavelength when 616 ppm to 999 ppm of ozone concentration is released into 5 cm gas cell of transmission type. It is observed that by employing different wavelength in ultraviolet region based on spectroscopic ozone detection, obvious differences of transmittance value are obtained for each particular wavelength. Consideration with Twyman-Lothian equation, specific wavelength at 239 nm, 240 nm, 241 nm, 242 nm, 278 nm, 279 nm, 280 nm, 281 nm is proven to achieve wide range of ozone detection when low relative error of concentration is achieved by value of transmittance in range between 0.25 and 0.5.

peer-reviewed The optimized structure of CO2gas sensor has been simulated consists of low cost components and easy for fabrication. The structure is based on reflective type gas cell using aluminium material. Optimization was made on radius of aluminium surface to enhance the performance of the sensor. The results show that the gas sensor is fully optimized and able to detect higher power efficiently. It is proven that the optimized CO2gas sensor of 8-Multiple-Input-Single-Output (MISO) has capability to gain power of at least 1.0 Watt with 12.5% efficiency. However, Single-Input-Single-Output (SISO) has shown greater efficiency as it can detect 29.1% of total power supplied with the lowest Merit Function (MF) value of 0.648. PUBLISHED peer-reviewed

Laboratory design of an ozoneconcentration regulator which is build on the theory of continuity equation forgas flow in parallel pipes in conjunction with the ozone elimination potentialsof an ozone destructor is presented. At an initial oxygen flow rate of 33.33 cm3s-1,ozone concentration was generated andvaried between 429.30 parts per million (ppm) to 3826.60 ppm. Similarly at an initial oxygen flow rate of 25cm3s-1, ozone concentration was generated and varied between 387.30 ppm to4435.20 ppm. Effect of flow meter when the ozone concentration was set toapproximate 1000 ppm were investigatedand reported. Fine tuning of the regulator is necessary to ensureconcentration stability for long duration experimental work. DOI: http://dx.doi.org/10.11591/telkomnika.v13i2.6952

The effect of inlet radius of a transmission type optical gas cell on its response time is reported. Six gas cells of varying lengths, and internal radius of 0.32cm were considered at first and then other internal diameters were also investigated afterwards. The effect of inlet radius is easily discernible at all velocities considered; however it is more pronounced at lower flow rates. At a velocity of 16.79cm/s of ozone gas, and for a target sensing time of ≤ 0.5 seconds; we observed that the inlet radius requirements for gas cells of varying lengths and varying internal diameters is not the same for a specific target sensing speed. The length and the internal radius of a gas cell are proportional to its inlet radius.

Ultraviolet absorption spectroscopy is reliable for ozone concentration measurement. Concentration range and optical path length are inversely related based on theoretical calculation and observation of previous work. However, gas cells for ozone application are typically not expandable. In addition, they incur cost for custom fabrication. Here we design a reconfigurable brass gas cell that may interchange optical path length between 5.6 cm and 10.8 cm. Components are available at low cost, easy to joint and ready to use. Theoretical background and gas cell structure are discussed. Practical transmittance values between e-0.65 and e-0.05 are proposed for theoretical calculation of concentration via Beer-Lambert law. The concentration values are used in SpectralCalc.com gas cell simulation to obtain transmittance. Both approaches yield comparable result. Simulation result shows concentration range of 5.6 cm optical path length gas cell (31.82 ppm to 413.67 ppm) is wider than concentration range of 10.8 cm optical path length gas cell (16.50 ppm to 214.49 ppm). Simulation condition is at transmittance from 0.5291 to 0.9522, sampling wavelength 253.65 nm, temperature 300 K and pressure 1 atm. Thus, we strongly recommend short optical path length gas cell (5.6 cm) for wide range of concentration measurement (31.82 ppm to 413.67 ppm).

Sensor response time T (90) or speed of response is mathematically a function of the rate of diffusion of a gas sample in an absorption spectroscopic gas cell. Increasing the rate of diffusion increases the speed of response and vice versa. In this article, we present the design and analytical results on the response time of a reflective type ozone gas sensor. The variables of length and cross sectional area were interplayed to optimise the rate of diffusion. Two optical reflectors were employed in increasing the path length of the sensor; this resulted in the simultaneous reduction of the effective cell length and an increase in the diameter of the gas cell (cylindrical structure). Ozone diffusion in the 30 cm length of gas cell has been simulated to be 0.01713 ppm cm3/secs in comparison to 0.01023 ppm cm3/sec for a single reflector gas cell, which shows an enhancement of the sensor response time.

The use of optical retro-reflectors in improving the sensitivity and response time of an optical sensor based on optical absorption spectroscopy for the measurement of ozone gas is presented. Two optical retro-reflectors are employed in the design of a 30cm and 20 cm absorption gas cells. Our analysis shows that, in the 30cm gas cell, a sensitivity of 0.0451ppm and 0.0901ppm is achievable while in the 20cm gas cell we can achieve a sensitivity value of 0.0681ppm. However these sensitivity values are dependent on the optical density of the sensor. In general gas cell with wider diameters has potentials for a faster response time.

Preliminary study to measure gaseous ozone concentration using ultraviolet absorption spectroscopy is presented. Firstly, background of ozone is introduced. Next, fundamental theory behind ultraviolet absorption spectroscopy is discussed based on Beer-Lambert’s Law and absorption spectrum of ozone. After that, absorption cross section of ozone is simulated via spectralcalc.com. Temperature of system is varied. Peak absorption cross section and peak absorption wavelength are found to be 1.166 ´ 10-21 m2 molecule-1 and 255.376 nm respectively at 300 K and 0 torr. Absorption cross section in ultraviolet region shows slight variation of at most 1.286 per cent when temperature is changed from 200 K to 300 K. Around room temperature, peak absorption cross section simulated in current work is consistent with previous work, because relative error is found to be small in between 1.630 per cent and 3.087 per cent. Unlike previous work, absorption of light by ozone is detected in ultraviolet region only due to weak absorption in visible region.

Simulasi penapis optik untuk 1310nm panjang gelombang dan 1510nm operasi pada pandu gelombang optik planar berdasarkan bahan–bahan baru VTT yang berasal sol–gel menggunakan teknik MMI disajikan dalam tulisan ini. Bahan simulasi telah menunjukkan bahawa, pada prinsipnya, mirip dengan kecekapan penapisan dari bahan lain yang dilaporkan dalam peranti MMI, dalam kes pemusnahan nisbah (ER), ia dicatatkan sebanyak 18.4dB dan 21.6dB untuk panjang gelombang 1310 nm dan 1550 nm, masing–masing. Sementara itu, kehilangan masukan (IL) adalah sekitar 1.43–1.64 dB untuk kedua operasi penapisan. Struktur ini terdiri daripada dua bahagian kaskad MMI, iaitu mekanisma gangguan umum (GI) dan mekanisma gangguan berpasangan (PI). Kelebihan peranti berasaskan MMI dan bahan–bahan yang berasal sol–gel dibahas dalam makalah ini. Prinsip pencorakan sendiri, ciri–ciri bahan yg digunakan dan struktur akhir penapis berasaskan MMI ini juga ada ditunjukkan dalam makalah ini. Kata kunci: Gelombang pandu optik; penapis gelombang; MMI; mekanisma gangguan umum; mekanisma gangguan berpasangan; mekanisma gangguan; bahan–bahan terbitan sol–gel Simulation of optical wavelength filter for 1310nm and 1510nm operation on planar optical waveguides based on new VTT sol–gel derived material using Multimode Interference (MMI) technique is presented in this paper. Simulations of the material have demonstrated that in principle, similar filtering efficiency to other materials reported in MMI devices, in terms of extinction ratio (ER), it was simulated to be 18.4 and 21.6 dB for the wavelengths of 1310nm and 1550 nm, respectively. Meanwhile, the simulated insertion loss (IL) is around 1.43–1.64 dB for both filtering operations. The structure consists of two cascaded MMI sections, employing General Interference (GI) and Paired Interference (PI) mechanisms. The advantages of MMI based devices and sol–gel derived materials are discussed in this paper. The self–imaging principle, material characterizations and the final design of MMI based filter structure are also demonstrated in this paper. Key words: Optical waveguide; wavelength filter; MMI; general interference mechanism; paired interference mechanism; interference mechanisms; sol–gel derived material

peer-reviewed A compact and low-cost gas sensor using absorption spectroscopy for Carbon Dioxide (CO2) measurement is presented. The sensing principle is based on open-path direct absorption spectroscopy in the mid-infrared range. The improved reflective structure of optical gas sensor consists of low cost and compact components, such as filament emitter, multispectral pyroelectric detector, Calcium Fluoride (CaF2) window and aluminium curve reflective surface. In the previous investigation, the optimized gas cell structure was simulated using ZEMAX®12 software prior to fabrication for measuring CO2 gas concentration. The developed gas sensing system using the optimized gas cell structure has shown the capability of accurately detecting CO2 concentration. The sensor utilizes a CaF2 narrow bandpass (NBP) filter for detection of CO2 gas with no cross-sensitivity with other gases present in the gas cell. The repeatability of sensor’s response of detecting CO2 was tested with response times were calculated as being less than 1 second.