this research, an optical half-adder of silicon rods in the air platform with a wavelength of 1563 nm is proposed using a square-lattice photonic crystal (pc)-based structure. The corresponding structure has two input ports: A, B and two output ports: S, C, which has been designed and proposed by employing Nonlinear Kerr effect and two resonant cavities, and the ratio of the Silicone Rods per lattice constant, or lattice parameter is 0.211 and for the 1563 nm wavelength, the Band gap range of 1395 to 2066 nm was obtained. RSoft commercial software, plane wave expantion method and finite difference time domain are used for simulating the proposed structure. The Simulation indicated that the proposed resonance cavities-based structure could provide an optical half-adder performance without considering the logic gates that have already been mentioned in the former references. For the current structure, the maximum response time and the used level were obtained 3 and 2 ps, respectively.

In this research, to reduce the dispersion a new schemewas proposed for photonic crystal based optical fibers which resulted in nearly zero dispersion. Firstly the basic structures for photonic crystal fibers with circular and hexagonal arrangements were simulated with Lumerical software, which due to the lower dispersion of hexagonal arrangement, such a structure was chosen. By changing the shape and radius of holes and also the lattice constant, the dispersion was reduced to nearly zero values. In this thesis, a new design was proposed to decrease loss and dispersion of photonic crystal based optical fibers composed of six layers of holes. The radius of the air holes from the center of the fiber changes from 0.21 to 0.7 micrometers. The refractive index of 1.41 obtained from the simulation and the spatial distribution function for field intensity in the core showed that suitable confinement was occurred in the fiber center, and a loss of 3.34×10^-7dB/cm in 1550 nm wavelength confirmed this issue. The dispersion value of 0.026ps/nm.km in the mentioned wavelengths showed that the proposed structure has better performance compared with previous works. Effective Mode size has been obtained 7.93μm². The use of the circular air holes inside silicon resulted inthe simplification of the fabrication

In this thesis, a temperature sensor based on photonic crystal fiber is designed and simulated. For calculating the guided modes as well as electrical field destribution, Maxwell’s equations are solved by finite element method throu 5.2a version of Comsol Multiphysics software. For increasing the sensor sensitivity, a temperature sensitive liquid crystal with the thermo-optic coefficient of –4.65 x 10-4 /°C is infiltrated into the air holes of the second cladding ring. Simulation results show that complete coupling between two upper and lower supermodes inside the PCF, increases the core confinement loss and the temperature increament causes the blue shift of the peak confinement loss wavelength. According to the simulation results, the sensor demonstrates the sensitivity of S=-1.964 nm/°C with the correlation R2=0.999917, FWHM=7.2 nm and FOM=-0.272 /°C at the temperature range of 20 ~ 80 °C. Because of the same value of the sensor specifications for both X and Y polarizations, this sensor is suitable for real temperature measuring applications. In addition, by changing some PCF geometric parameters, performance characteristics of the sensor such as FWHM could be enhanced. Simulation results show a better performance of the propoused sensor in comparison with the latest studies.

In this research, an all optical flip flop based on photonic crystals is designed and simulated. Using finite difference time domain and plane wave expansion methods, electrical filed and photonic band gap are calculated respectively. Simulation is done with version 8.2 of RSoft software. The proposed device includes rod types with radius equal to 0.2 multiplied lattice constant where it is 575 nm. The proposed structure involves two inputs which are cross connected. Resonance phenomena is occurred at 1.586μm and 1.62μm for both cavities and resonance in one cavity causes to no resonance in another. Two biases are employed to solve the kipping data problem. The used area is 19μm*19μm and the rise time is 3.1ps for input signal. Simulation of the pr-oposed structure proves that the device can be assume as a flip flop for different states.

In this thesis, will discuss to design and simulate a light-emitting GaN diode using photonic crystals. To calculate the electric field intensity and efficiency of the device used Maxwell's equations solving by finite difference time domain method and 8.12 version of commercial Lumerical software. In this thesis, it was shown that by using a hole type photonic crystals and reducing total internal reflection one can improve the efficiency of a GaN light emitting diode by more than 2 factor. Using employing 15 periods of holes the efficiency of the device was improve by 2.1 factor for 400nm wavelength. In the photonic crystal structure the length to lattice constant relation and height of air holes were 0.5 and 210 nm respectively. Also the lattice constant was about 680 nm. To compare the simulation results with previous works, proposed structure at wavelength of 465 simulated and It was shown that using the lattic constant 574nm, height of air holes 210nm and length to lattice constant relation 0.54 efficiency of the device increased by 1.95 factor. the obtained results for 400 and 465 nm wavelengths showed that the proposed structure has better efficiency compared with previous works.

In this thesis an optical filter based on 1D photonic crystals was proposed for all optical communication systems. The proposed structure is tuned in the 1550 optical communication window. The transfer Matrix Method with Matlab code was used for performing the simulations effect of refractive index, number of layers, thickness of layers and incident angle on the out put wavelength of the proposed filter with narrow band width and high transmission efficiency was studied. The results show that at 1550 nm one can reach to 0.2 nm, 7750 and 100% for bandwidth, quality factor and transmission efficiency considering the simpler fabrication procedure of 1D photonic crystals the proposed device is suitable for wavelength division multiplexing systems.

In this project a new structure for designing photonic resonant cavity based all optical filters suitable for 1310 nm window has been proposed . The proposed filter was realized using a square lattice array of Si rods immersed in air which is suitable for TM polarization. RSOFT Photonic CAD was used for simulating the proposed device. The results show that at λ=1313 nm one can obtain bandwidth and quality factor equal to 0.37 nm and 3549. The transmission efficiency of the device is about 98%, Which shows very low loss. Total pot print of the structure is about 118.4 µm2, which proves the suitably of the proposed device integrated circuits.

In this research two optical beam splitters were proposed based on squre lattice and hexagonal lattice photonic crystal for TM and TM/TE mode. The squre lattice structure was composed of GaAs rodes immersed in air, which has three tunable outputs with loss as low as 0.31% in TM mode. In this structure, three defects were used for optical confinement and optical guiding. Also the hexagonal structure was composed of air pores created in Si substrate, which has two outputs ports. The minimum loss for TE and TM mods are 6.8% and 2.8% respectively. The footprints of proposed structures are less than 55µm2. Therefore they are suitble for optical integration. For performing the simulations we employ RSoft software and finite difference time domain and plan wave expantion method.

 In this research a numerical model based on drift and scattering has presented which can calculate gain and excess noise of avalanche photodiode with error of less than 7.5%. In this model process of drift and scattering was initiated by the injection of an electron into the multiplication region with clear electric field. Each electron after passing the dead space it may ionize. After impact ionization an electron- hole pair is generated. Similar to initial carrier each of the generated carriers pass the dead space without impact ionization and after passing dead space impact ionization might happen. This process continue through the multiplication region till all generated electrons and holes reach to edge od multiplication region. Then according to recorded results, number of impact ionization and gain of avalanche photodiode are simulated, after gain simulation, excess noise by using mentioned equations is counted.The simulation has been done using MATLAB and the results are compared with other reliable results obtained by reaserchers. Due to an error of less 7.5% in the calculation of excess noise can be said that drift-scattering model is able to simulate gain and excess noise of avalanche photodiode with acceptable accuracy without complication of other available models.

In this research, a kind of avalanche photodiode called tandem has presented which could significantly effect on excess noise parameter in photodiode.The main idea of this photodiode is repeat of several time multiplication region cascade. The cascade arrangement of different layers of multiplication region and rate of doping of them cause potential barrier. This barrier cause prevent of hole movement and decrease excess noise. Simulation of photodiode includes two sections: at first section a photodiode InAlAs-InGaAs whithout considering the repeat multiplication region simulated and excess noise was evaluated. At next section photodiode with repeat triplicate multiplication region, simulated. The silvaco software was used for simulation of structure and by using the resul ts of this software, gain and excess noise of photodiode computed with valid scientific data to examine the accuracy of simulation. Finally gain and excess noise of tandem Avalanche photodiode were compared with InAlAs-InGaAs photodiode. According to the results, tandem photodiode clarify the effect on excess noise factor and reduce 65% excess noise factor

 

In this project hexagonal and square lattice photonic crystal structures have been employed for designing optical filters suitable for optical communication systems in TE and TM mode. These structures are tunable at 1550 communication window. The results show that the square lattice has transmission efficiency and bandwidth equal to 93% and 0.9 nm respectively. By employing hexagonal lattice structure these values have been improved up to 97% and 0.3 nm respectively. These values are applicable according to IEEE 802.3 standard. The footprints of the proposed structures are less than 120 um2 so they are suitable for integration.

 In this thesis, temperature and strain sensors based on fiber bragg gratings were simulated using transfer matrix method. Here, the bragg grating is divided to sections in which input and output fields are described using matrix. Multiplying the matrices of all sections is used to extract the transmission and reflection spectra. Variation of period or refraction index of the structure dependant on temperature and strain is used to design temperature or strain sensors based on gaussian apodized bragg gratings. Simulation result illustrate that in spite of the simplicity of fabrication process for uniform Bragg grating, the reflection spectra possesses side lobes having a power of about 39% of the central wavelength. In order to suppress these side lobes the apodized gaussian bragg gratings is used. Results show that the side lobes will be omitted to the cost of decrement of 40% of reflection power in central wavelength using apodization.

 In this project, a 2D Monte Carlo model was used for simulating the electron hole components of optical output current and calculating the time response of a GaAs metal- semiconductor- metal detector for optical pulse. For this purpose a 2 valley model for electrons and a 2 band model for holes have been used. In the proposed model phonon and impurity scattering has been considered. The energy band assumed to be non-parabolic and the current mechanisms are tunneling and thermionic emission. By introducing a thin layer with 150 nm thickness and doping density of 6e16 cm-3 of the same type of the semiconductor, it has been shown that creation of an electrical field oppose to the direction of electrons at the end of the absorption layer results in the slight reduction of time response. By changing the position from 1.5 to 4.5 micron and doping density from 4e16 cm-3 to 1e17 cm-3 the peak current changes from 170µA to 300µA and fall time changes from 18 ps to 26 ps. In addition, the response current reduces from 27µA to 48µA. Comparing the obtained results with scientific reports confirms the validity of the proposed model.

In this research, a three-valley Monte Carlo method is used to simulate AlGaN-based Metal-Semiconductor-Metal photodetector. In the proposed model, energy bands are assumed to be non-parabolic. The scattering mechanisms taken into account are ionized impurity scattering, polar optical phonon scattering, piezoelectric scattering, deformation potential scattering, intervalley scattering and alloy scattering. Using this method, transient response and spectral responsivity of photodetector have been calculated. The simulation was done in two dimensions with MATLAB. To validate, the spectral responsivity of a device has been compared with the experimental data. The main goal of this research is to investigate factors affecting responsivity and transient response of the device. For this reason, the effect of device geometry, back-illumination and recessed electrodes are investigated. Finally, using these results, a structure is proposed to improve the responsivity of common devices. This structure is based on back-illumination in conjunction with recessed electrodes.