Photonics and Nanotechnology

The following sections are included:

• PREFACE

• CONTENTS

In this paper the capacitance-voltage characteristics of InN quantum dots embedded in AlGaN/GaN heterostructure has been studied. This work has been done for the InN quantum dots with different quantum dot size, and energy dispersion and for the AlGaN/GaN heterostructures with different Al mole fraction and number of quantum wells in different temperatures. The presence of InN quantum dot will cause Gaussian shape in capacitance-voltage characteristics approximately, where the peak of curves can evidence the position of quantum dots in the structures. Our calculation results show the Gaussian shape (or negative differential capacitance) is much higher at low temperature and for quantum dots with low energy and higher size dispersion.

Nano-focus beam applications of short wavelength approximately 220 nm now play important roles in engineering and industrial sections. At present, light sources at approximately 220 nm are commercially available but large size, difficult to maintain, and expensive. Compact wavelength tunable and cost effective light sources at approximately 220 nm are required. Laser diode with sum-frequency generation methods are employed to generated the shorter wavelength approximately 220 nm. This paper presents comparison of second harmonic generation schemes using a nonlinear optic crystal and two types of laser diode, which are a 440 nm single mode blue laser diode and a 450 nm multimode Fabry-Perot blue laser diode, has potential to generate wide tunable coherent deep ultraviolet-c at approximately 220 nm. Using the blue laser diode with the sum-frequency technique, a high second harmonic power is hardly observed due to low conversion efficiency. The best performance of second harmonic generation using blue laser diode, nonlinear optic crystal, and an high-Q external cavity laser diode was observed as 1.1 µW second harmonic ultraviolet-c power at 224.45 nm ultraviolet-c wavelength and 5.75 nm ultraviolet wavelength tunability. In addition, the improvement of increasing second harmonic power approximately 220 nm and the limitation of wavelength tuning of short wavelength are also theoretically discussed in this paper.

Analytical expression is proposed for evaluating the performances of sampled gratings. Accuracy of this expression has been verified by simulated reflectivity spectrum with the transfer matrix method. A new technique of multiplex reflection-spectrum envelope concatenation is introduced to demonstrate a 23-channel grating with uniform characteristics in all channels. The proposed technology can densify sampled grating both in spectral channels number and in spatially physical corrugation.

The formation of In_0.53Ga_0.47As/InP single quantum well with narrow well width grown by Organometallic Vapor Phase Epitaxy is verified by photoluminescence spectroscopy. PL spectra exhibit the e(1)-hh(1) transition in the well. PL measurement was conducted at various temperatures from 15 K to 200 K in order to investigate the important temperature-dependent parameters of this structure. Important parameters such as activation energies responsible for the photoluminescence quenching and broadening mechanisms are achieved. Because of small thermal activation energy of 15.1 meV in the narrow well, carriers can escape from the well to the barrier states. The dependence of PL width on temperature revealed that Inhomogeneous mechanism is the dominant mechanism for the broadening of PL peak and homogeneous mechanism is responsible at high temperature due to electron-phonon interaction.

The ground state transition energy as various temperatures of a single quantum well structure has been calculated. The numerical technique called shooting method was developed to get eigen values and eigen functions. Pässler's model and Aspnes's equation are adopted to calculate the energy gap(E_g) of Al_0.3Ga_0.7As and GaAs respectively. Our calculation has been tested by comparing the results to PL experimental data of Al_0.3Ga_0.7As/GaAs single quantum well. Good agreement has been found in the low temperature range (less than 40 K) and fair result has been obtained in the range of temperature higher than 40 K.

In this paper, we design the ring resonator filters such as moving average (MA), autoregressive (AR) and autoregressive moving average (ARMA) filters. These filters are designed as add/drop filter, channel selection and dispersion compensator. The transfer functions of optical filters are derived using Z-transforms.

This paper proposes a system of signal security using the optic series waveguide micro ring resonator, where the chaotic noise generation and cancellation can be performed. The required communication signals can be multiplexed with the generated chaotic noise in a micro ring resonator before transmission. The required information can be recovered via optic series waveguide micro ring resonator by a specific user at the output port of the waveguide micro-ring resonator. Simulation results obtained have shown the potential of applications which is closed to the practical applications, especially, the required information can be retrieved by the specified users. The ring parameters used with the ring radii are ranged between 10–20 µm, κ₁ = κ₂ = 0.0225 and n₂ = 2.2 × 10^-15 m²/W. The simulation results obtained have shown the potential of using such a proposed device for tunable band-pass and band-stop filters, which can be used for the information security in the system by the optic series waveguide micro ring resonator.

In this paper, we present an experimental investigation of all-optical switch using a symmetric Mach-Zehnder interferometer (MZI) combined with double fiber ring resonators. Here, we replace the ordinary-fiber ring resonator on one arm of MZI by a 980 nm-laser pumped erbium-doped fiber (EDF) ring resonator to form an EDFA. When adjusting the EDF pump power up we note increasing in switching power. Experimental results indicate that using MZI with double EDF ring, switching power is lowered significantly to nanowatt level in comparison with that of MZI with a single EDF ring of milliwatt level.

A new technique of an entangled photon pair generation and regeneration characterization using an all fiber optic scheme is investigated. The proposed system is consisted of a fiber optic ring resonator. The Kerr nonlinearity effect in the fiber ring resonator is exploited for the generation of two independent beams. The advantage of such a system is that it requires a simple arrangement without any optical pumping part and bulky optical components. Polarized light pulse trains are launched randomly into a nonlinear fiber optic ring resonator. Where the superpositions of light pulses in a nonlinear fiber optics ring resonator are randomly occurred which is formed the entangled photon pairs. A polarization controller controls polarization states of light pulses while circulating in the ring resonator. The entangled photons are seen on the avalanche photo-detector. Then the output of the entangled photon states recovery by using a fiber ring resonator incorporating an erbium-doped fiber (EDF) has been investigated. We have shown that the weak entangled photon states can be recovered after circulating in the amplified fiber optic medium. The results obtained have shown that this system can be used to achieve the recovered polarization entangled states with the obtained high gain. The amplifying noise has also been detected and seen on the spectrum output. This is affected to the entangled photon visibility, which is discussed.

We propose the results of optical Kerr effects in fiber grating for the measurement resolution. When the high power laser is launched into fiber grating, optical Kerr effects are induced in grating region then the effective refractive index is changed depending on the input power. The results that are given by the mathematical simulation, have shown the relation between the reflectivity and Bragg wavelength. All results can be used to analyze and improve the resolution of measurement system for fiber grating sensors and its applications.

This paper presents a new concept of quantum-chaotic encoding of light travelling in a fiber optic ring resonator. The Kerr nonlinear effects type of light in a fiber optic ring resonator is induced, and the four-wave mixing of the propagating waves at resonance occurred. The output signals can generate the double security which one is the quantum bits i.e. code, and the other is the chaotic signal/code. The proposed system has shown the potential of using for communication security, where the double security via the quantum-chaotic encoding can be performed.

Coupling of highly elliptical laser diode emission into single mode fiber using two spherical ball lenses is investigated and the effectiveness of the mode matching with the circular mode field of the fiber is realized. Coupling efficiency is theoretically analyzed by employing ray and Gaussian beam optics. A 100% coupling efficiency is obtained at an optimum working distance of 3.5 mm. the coupling efficiency is found to be largely affected by the angular, lateral and transversal offsets. It can also be controlled significantly by optimizing the lenses separation distance. The experimental measurements agree with the theoretical calculations. However, the maximum coupling efficiency obtained is around 75% due to some practical limitations regarding the positioning of ball lenses and their separation. From the variations of coupling efficiency with lateral, transversal and angular offsets, the effective mode matching is inferred. Laser welding technique with active alignment facilities have been used in the alignment and attachment of all the coupling components. Laser welding pulse parameters have been optimized for reliable weld yields.

We present the interesting results of nonlinear behaviors of light within a nonlinear ring resonator system, where optical and electrical signals conversion in frequency, wavelength and time domains can be made by using the chaotic signals generated within the micro ring system. There are three forms of applications using the chaotic behaviors are presented. Firstly, a new system of the simultaneous fast and slow light generation using a soliton pulse propagating within the nonlinear micro ring resonators. Secondly, we propose the simple system of an extreme narrow light pulse generation by using a soliton pulse circulating in the integrated micro ring devices. Finally, a simple system of fast light generation by using a soliton pulse circulating in the integrated micro ring devices is proposed. Using such a system, an attosecond pulse and beyond can be easily generated.

The following sections are included:

• AUTHORS INDEX