Nor Hafizah Ngajikin

Performance Analysis of Bootstrap Transimpedance Amplifier For Large Windows Optical Wireless Receiver

Due to optical wireless link power budget considerations, the receiver is required to have a large collection area. One of the main noise mechanisms in wideband preamplifiers employing large area detectors is the noise due to the low pass filter formed by the detector capacitance and the input impedance to the preamplifier. Typical large photodetection area commercial detectors has capacitance are around 100-300 pF compared to 50pF in fiber link. Hence, techniques to reduce the effective detector capacitance are required in order to achieve a low noise and wide bandwidth design. In this paper analysis on the bootstrap transimpedance amplifier (BTA) for input capacitance reduction is reported. This technique offers the usual advantages of the transimpedance amplifier together with an effective capacitance reduction technique for optical wireless detector

WIDE RANGE OF ELECTROSTATIC ACTUATION MEMS FPOTF

By employing Microelectromechanical system (MEMS) technology, Fabry-Perot Optical Tunable Filter (FPOTF) with hybrid tuning mechanism, varying d and altering incident angle is presented. The proposed structure consists of a ∞oating dual membrane FPOTF with capability to be tuned at difierent light incident angles. Three electrostatic cavities have been designed to perform this task independently. This technique is capable to increase the tuning range up to 2/3 of capacitance gap with additional doubly range of incident angle. Optic, mechanic and electrostatic analysis of the proposed structure has been validated by simulation. Analysis in optical performance shows the tuning range enhancement is about 1.92% for §2 - mirror tilting at 6 - initial angle compared to conventional dual beam MEMS FPOTF. This analysis validates the principle of hybrid tuning method.

Peak to Average Power Ratio (PAPR) Reduction in OFDM System

Orthogonal frequency division multiplexing (OFDM) is a special form of multi-carrier modulation which is robust against the multipath effect, intersymbol interference (ISI) and high spectral efficiency. However, peak to average power ratio (PAPR) is a major drawback in the system since this leads to the distortion problem in the linear devices such as the power amplifier (PA). Thus, the PAs require a backoff which is approximately equal to the PAPR for distortionless transmission. This decreases the efficiency for amplifiers. Hence, reducing the PAPR is the main focus of this paper. One of the available PAPR solutions is clipping. In the technique, the efficiency does not depend on the number of carriers. This paper investigates the effectiveness of the clipping technique by focusing on the performance of PAPR value with different values of clipping ratios (CRs) and the relationship between PAPR value and bit error rate (BER)

Performance Analysis of MIMO-CDMA System

Nowadays, the demand on communication system is towards high capacity and faster data transmission with minimum error or losses. In wireless communication, multiple input multiple output (MIMO) is one of the techniques that can increase spectral efficiency and link reliability. Therefore, the performance of MIMO-CDMA with comparison to conventional code division multiple access (CDMA) system has been analyzed. The simulations models are simulated with different number of antenna which are two transmit-two receive (2Tx2Rx) and four transmit-four receive (4Tx4Rx). System specification is based on voice application. The simulation results shows that the proposed MIMO-CDMA (2Tx2Rx) is improved by 43% of BER and MIMO-CDMA (4Tx4Rx) improved by 63% of BER performance compared to conventional CDMA. Capacity performance of MIMO-CDMA (2Tx2Rx) improved by 50% and MIMO-CDMA (4Tx4Rx) improved by 75% compared to conventional CDMA

High Sensitivity of Balloon-Like Bent MMI Fiber Low-Temperature Sensor

A novel low cost and simple temperature sensor based on multimode interference (MMI) is formed by a successive singlemode fiber (SMF)-bent multimode fiber (MMF)-SMF structure. Due to the small curvature radius of bent MMF section mimicking a balloon shape, MMI effect from the core is spreading into coating. The high temperature sensitivity is mainly due to the large thermo-optical coefficient of the existing acrylate coating of the MMF fiber. A temperature sensitivity of up to -2060 pm/°C and -25.1 nW/°C for wavelength- and intensity-based interrogation, respectively, have been achieved in the range between 27 °C and 31 °C. This sensor is most suitable in high sensitivity and low-temperature application such as the measurement of human body temperature.

Measurements of ozone absorption cross section with ratiometric and non-ratiometric methods

In ultraviolet absorption spectroscopy, absorption cross section (ACS) is a parameter important for calculating ozone concentrations. In this work we have determined the ACS at the room temperature and normal pressure. The ozone con- centration has been recorded in the region 450-989 ppm, using a compact aluminium gas cell of 5 cm optical path length. We have also compared the results derived with the ratiometric and non-ratiometric methods based on the Beer-Lambert law. Our experimental results demonstrate that the non-ratiometric method can compete with the ratiometric method whenever the measuring times are relatively short.

Incident Angle Approach to Sensitivity Enhancement for Ozone Sensor

The design and mathematical model of a reflective type optical gas sensor is presented. Light source is radiated at an incident angle for 10 cm gas cell with an internal diameter of 0.4 cm. At an incident angle of 1o, optical path length obtained is 342.7886 cm, at 27o incident angle, optical path length is 10.4926 cm and at an incident angle of 28o, optical path length is 9.9631 cm. The model is most efficient at lower incident angles, precisely between (1o and 27o). Effects of variation in diameter and length of gas cell are also demonstrated.

Pressure Dependence of Ozone Absorption Cross Section

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.

Sensitivity and response time of an ozone sensor

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.

Optical path length, temperature, and wavelength effects simulation on ozone gas absorption cross sections towards green communications

Ozone is a green house gas. Ozone absorption cross sections have been reported with discrepancies and inconsiste ncies. In this paper, simultaneous effects of the optical path length and temperature variations on ozone gas absorption cross sections are investigated at different wavelengths. HITRAN 2012, the latest available line list on spectralcalc.com simulator, is used in this study to simulate ozone gas absorption cross sections in relation to the simultaneous effects of the optical path length and temperature at the wavelengths of 603 nm and 575 nm. Results obtained for gas cells with the optical path length from 10 cm to 120 cm show that the decrease in temperatures from 313 K to 103 K results in the increase in ozone gas absorption cross sections. At wavelengths of 603 nm and 575 nm, the percentage increase of ozone gas absorption cross sections is 1.22% and 0.71%, respectively. Results obtained in this study show that in the visible spectrum, at co nstant pressure, ozone gas absorption cross sections are dependent on the temperature and wavelength but do not depend on the optical path length. Analysis in this work addresses discrepancies in ozone gas absorption cross sections in relation to the temperature in the visible spectrum; thus, the results can be applied to get optimal configuration of high accuracy ozone gas sensors.