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A finite-difference time domain method for analysis in optical waveguides: The time stability determination
(2019-12-01)
Somkuarnpanit, Suripon
;
Wongtaycham, Chariya
This paper proposes a method how to determine the critical time step for use in Finite-Difference Time Domain (FDTD) analysis. Typically, the method is requires an appropriate time step in the calculation. The method is based on the criterion of stability increasing time must less than the time for the increasing propagation distance used in the calculation. For the large time step, the calculation would be diverged whereas the small time step would consumed huge execution time for getting a result. Therefore, we propose a method to determine the value of the critical time step of stability in the FDTD calculation for the optical slab waveguide. We investigate the maximum time step to provide the minimum time expensed in the calculation with maintaining the stability in the beam propagation. A ratio of the transversal step to the longitudinal step or vice versa, as greater than unity, F, and the fraction, A, of the stability time step are established for this method. Both parameters would simplified the derivatives terms of the electric and magnetic fields in the Maxwell's Equations. The execution time would reasonably decreased. Alternatively, the relationship between the A and the fraction number F was calculated and represented by A = 0.003F4 - 0.135F3 + 2.24F2 - 17.73F + 66.78. It is found that the maximum time step is limited at 50% of the propagation time through the guide. The critical time step, which is used in the FDTD calculation, can be determined by the fractional critical time step A. With the guide length/width ratio > 10, the fractional critical time step should be not more than 10%. To implement the graph, we chose F of 4, corresponding to A of 19%. So, the simulation does diverge when A of 20%. The simulated results at the critical A and the small A of 9.5% have the same beam patterns.
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Estimation of the Maximum Transmission Rate for the Silicon-Based Racetrack MicroResonator
(2019-06-01)
Somkuarnpanit, Suripon
;
Wongtaycham, Chariya
The maximal transmission rate for an optical signals getting through the devices can be determined directly from the impulse response outing from the device. This could be done by a simple tracing the behavior of an optical pulse transmitting through the device using the method of finite-difference time-domain (FDTD) The device consists of a straight coupling structure with a gap of 0.2 μm and a curved section with radius of 1 mm, with the cross section dimension of 0.4 μm × 0.4 μm for the optimal coupling. The device was set the straight sections, for the energy coupling, of 3 μm and the curved section with the curvature of 1 μm. An optical pulse train was launched into and observed the output from the device. To investigate the transient response, we observed the outputs for a number of round trips. We found that the coupling will get settled at the steady coupling power by letting the optical pulse traveling for a number of roundtrips. This behavior is similar to the energy accumulating in the capacitor and inductor for the electrical signal, which leads to the delay characteristics of the pulse response. Furthermore, the optical signal response along the time was also observed as the signals in Figure 2. When an optical pulse was launched into the device, the output pulse would gradually develop its power to a maximum level. And at the end of the input pulse, the output pulse would exponential decay. It needs approximately 2.5 ps for rising time to the maximum level, and 1.5 ps for the falling time down to the zero level. Namely, the pulse requires the totally minimal time of 4 ps. This implies that the device can transmit the maximal bit rate of 125 Gb/s.
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A Design of the Silicon-based Race Track Microcavity Resonator with Defined HPBW and FSR Using FDTD Method
(2019-06-01)
Wongtaycham, Chariya
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Somkuarnpanit, Suripon
Having investigated the characterization of the racetrack microcavity resonator base on the silicon substrate, we found the optimized dimensions of straight guide at wavelength 1.55 μm are thickness and width of 0.4 μm. Secondly, the spectral response is consequently calculated, which leads to two important relationships between half-power bandwidth (HPBW) against the coupling efficiency and free spatial range (FSR) against the racetrack round trip. With defined the operating region of the device by the parameters HPBW and FSR the radius of the curved section and the length of the straight section could be obtained. So, we could complete dimension of all sections of the device. An example of the design is also demonstrated. Suppose the following characteristics are required; HPBW of 5 nm and free spatial range, FSR, of 30 nm. HPBW of 5 nm would correspond to K of 0.223, or the length L of 3 μm whereas, FSR of 30 nm would correspond to X-{\text{rt}} of 18 μm. The obtained L of 3 μm and X-{\text{rt}} of 18 μm form the curve radius R of 1.9 μm. Having known the dimension the characteristics of the device is simulated. The obtained results are remarkably near to the required characteristics defined.
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New upper and lower bounds line of sight path loss model for mobile propagation in buildings
(2008-03-03)
Phaiboon, Supachai
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Phokharatkul, Pisit
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Somkuarnpanit, Suripon
This paper proposes a method to predict line-of-sight (LOS) path loss in buildings. We performed measurements in two different types of buildings at a frequency of 1.8 GHz and propose a new path loss model with its upper and lower bounds. The upper and lower bounds depend on max and min values of sampled path loss data. This makes our model limit path loss within the boundary lines. The model includes time-variant effects from the object movement from people in the building and cars in parking areas. These influence reasonably on wave propagation. The results have shown that the proposed model will be useful for the design of the indoor wireless communication systems. © 2007 Elsevier GmbH. All rights reserved.
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Muti-layer fuzzy logic sets for mobile path loss in forests
(2007-08-08)
Phaiboon, Supachai
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Phokharatkul, Pisit
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Somkuarnpanit, Suripon
Mobile path loss prediction in forests using Multi-Layer fuzzy logic system (MLFS) is presented in this paper. The MLFS consists of a tree density decision layer which is a supervisory layer in order to select the next layers using fuzzy decision. The sub-predictions use a set of rule base that provide path loss prediction in each case of an environment. These crisp inputs are classified by the fuzzifier to fuzzy sets and then inferenced using fuzzy linguistic rule base into multi - output path loss slopes via de-fuzzifier. For this study, we classified the terrains into high-, medium-, low- density and grass area and used the simple linguistic rules for prediction of the path loss slopes. We performed measurements in different forest densities at a frequency of 1.8 GHz with base station antenna height in a range of 3, 4, and 5 m above ground while the receiving antenna height was fixed at 1.8 m above ground. The results have shown that fuzzy logic approach provides more accurate prediction of path loss slopes than that of conventional empirical mathematic models. The proposed models will be useful for the local wireless network and micro-cell design of mobile communication systems in forests. ©2006 IEEE.
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Fading analysis of vegetation density effects on path loss for 1.8 GHZ cellular mobile with low base station antenna height
(2006-12-01)
Phaiboon, Supachai
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Pitithammawong, Kitti
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Chulajata, Tatcha
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Somkuarnpanit, Suripon
This paper presents studies of propagation characteristics in a suburban forest based on a measurement campaign at a frequency of 1.8 GHz. We investigated how tree density affected the fast fading characteristic depending on tree density and base station antenna height in a range of 3, 4, and 5 m above ground while the receiving antenna height was fixed at 1.8 m above ground. Three categories were studied: high density area, low density areas and grass area. Measurement of the receiver signal over 120 s intervals for a stationary mobile were used to obtain the distribution functions for the fading. We found that the distributions followed a Rician distribution, whose K-factor depended on tree density and transmitter height.
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Mobile path loss prediction model for forest areas using MIMO fuzzy logic system
(2006-09-01)
Phaiboon, Supachai
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Phokharatkul, Pisit
;
Kittitummawong, Piti
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Somkuarnpanit, Suripon
This paper proposes a method to predic mobile path loss in forests using MIMO fuzzy logic system. The multi-input was classified into seven input parameters defined as, X1 is number of trees/m2 and X2 to X7 are tree structure parameters. These crisp inputs are classified by fuzzifier to fuzzy sets and then inferenced using fuzzy linguistic rule base into multi - output path loss slopes via de-fuzzifier. For this study, we classified the terrains into high-, medium-, low- density and grass area and used the simple linguistic rules for prediction the path loss slopes. We performed measurements in different forest densities at a frequency of 1.8 GHz with base station antenna height in a range of 3, 4, and 5 m above ground while the receiving antenna height was fixed at 1.8 m above ground. The results have shown that fuzzy logic approach provides more accurate prediction of path loss slopes than that of conventional empirical mathematic model. The proposed models will be useful for the local wireless network and micro-cell design of mobile communication systems in forests.
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Microwave line-of-sight path loss prediction on urban street by fuzzy logic model
(2005-12-01)
Phaiboon, Supachai
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Phokharatkul, Pisit
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Somkuarnpanit, Suripon
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Boonpiyathud, Sitchai
This paper proposes a method to model the path loss characteristics on urban streets in the microwave band. We applied the concept of fuzzy logic to predict path losses. The input fuzzy sets were classified into five sets, namely 1) Distance between transmitter and receiver, 2) Frequency, 3) Time of day, 4) Transmitting antenna height and 5) Receiving antenna height. These inputs are then inferenced into output path loss via linguistic rules which were trained by measurement. To check the proposed model, we compared the fuzzy prediction with the same and an another measurement. The results show that the fuzzy logic models provided a better prediction. © 2005 IEEE.
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Upper-and lower-bound path-loss modeling for indoor line-of-sight environments
(2005-01-01)
Phaiboon, Supachai
;
Phokharatkul, Pisit
;
Somkuarnpanit, Suripon
;
Boonpiyathud, Sitchai
This paper proposes a method to predict line-of-sight (LOS) path loss in buildings. We performed measurements in two different type of buildings at a frequency of 1.8 GHz and propose upper-and-lower bounds path loss models which depend on max and min values of sample path loss data. This makes our models limit path loss within the boundary lines. The models include time-variant effects such as people moving and cars in parking areas with their influence on wave propagation that is very high. The results have shown that the proposed models will be useful for the system and cell design of indoor wireless communication systems. © 2005 IEEE.
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An optical fiber feeder system and performance for cellualar microcell 800MHz CDMA systems
(2001-12-01)
Phaiboon, Supachai
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Somkuarnpanit, Suripon
This paper proposes an optical fiber feeder system for use in cellular microcell 800MHz CDMA systems, as well as its performance. The RF signal of the CDMA system is converted into the optical signal, which can be delivered in the optical fiber. We analyze the system performance in terms of CNR (carrier to noise ratio) and SER (symbol error rate) using theoretical modeling as well as numerically calculation of the CDMA system compared with the intensity modulation. It is found that the optical feeder system for the CDMA system has got higher CNR than that of the system with intensity modulation, especially at low power level e.g. CNR more than 80dB for received optical power of -40dBm. This would provide a consequence of relatively low error rate in signal detection.

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