D. S. Patil

A new technique for the reduction of the power loss in the Y-branch optical power splitter

A new technique for the reduction of the optical power loss at the branching point of the rib waveguide Y-branch power splitter on silicon substrate has been proposed. The rib height of the waveguide nearby the branching point is increased which causes the decrease in the effective index of the region lying between the two output branches nearby the branching point. The beam propagation method is applied for the analysis of the rib waveguide Y-branch optical power splitter. It is inferred from this analysis that the value of the power loss can be reduced by ∼50% by decreasing the effective index.

Mode confinement and near field intensity analysis in a GaN-based blue–green laser diode

Field intensity analysis of a GaN-based channel substrate planer blue–green laser diode has been carried out at a 507 nm wavelength for better optical confinement to explore its applicability in optical storage. Our analysis reveals that a thin active layer does not support higher order modes. However, an active layer thickness of 0.23 µm supports the fundamental transverse mode and mode 1. The change in the geometry of the channel region provides guiding effects along the X-direction in a structure. It was found that an increase in the channel depth causes an increase of the effective refractive index in a nonlinear manner and the confinement factor increases in a nonlinear manner with the active layer thickness. It is inferred from our analysis that an increase in aluminium mole fraction in the clad leads to an excellent confinement of near field intensity, which has been attributed to an increase of refractive index step. The full width at half maximum (FWHM) of near field intensity was found to be 0.35 and 0.31 µm corresponding to aluminium mole fractions of 5% and 15%, respectively. The near field intensity distribution in the channel waveguide (3D) along the X- and Y-directions clearly shows confinement at the centre of the active region.

Computer analysis and optimization of physical and material parameters of the blue laser diode

The computer analysis and optimisation of various physical and material parameters of the blue laser diode have been presented. Numerical analysis of basic electrical equations, which include Poissons equation and current continuity equations for the electrons and holes, has been carried out using finite difference method. The wave equation is solved using effective index method to obtain transverse electric field. Using rate equation for photons, photon density is determined and the empirical value of free carrier loss coefficient has been determined so as to satisfy oscillation conditions. We have optimised the physical parameters and material parameters for the emission wavelength of 477 nm for the first time by considering ZnSe as an active layer material and ZnMgSSe as a clad.

Analysis of near-and far-field intensities in ZnO based heterostructure waveguides

Analysis of near- and far-field intensities in a simple double heterostructure of ZnO/Mg x Zn1 − x O and hybrid double heterostructure of Al x Ga1 − x N/ZnO have been carried out at 375 nm wavelength. Near- and far-field intensity distribution along the junction plane has been studied as a function of mole fractions of Mg and Al for varying active layer thickness. The spread of the near- and far-field intensities has been estimated and articulated as full width at half maximum (FWHM). For near-field, FWHM was found to be decreasing nonlinearly with increase of Mg mole fraction in the simple heterostructure and increasing in a nonlinear manner with the increase of Al mole fraction in the hybrid heterostructure. FWHM deduced from our analysis was 0.355 µm for 7% and 0.156 µm for 27% Mg mole fraction. For the hybrid heterostructure, the FWHM values estimated were 0.1275 and 0.1397 µm, respectively. Confinement factor as a function of mole fractions and active layer thickness has been explored and it was found to be increasing with active layer thickness. The FWHM of far-field intensity shows a vertical divergence of 26○ and showed a minor variation with the active layer thickness. Finally, it is inferred from our analysis that confinement of the near-field was strongly influenced by the mole fraction and the active layer thickness while the far-field was weakly influenced.

Deposition and characterization of SiON films using HMDS for photonics applications

Silicon oxynitride (SiON) films were deposited using a thermal chemical vapour deposition (CVD) system in the temperature range of 760 to 820 °C with hexamethyldisilazane (HMDS), ammonia (NH3) and oxygen (O2) precursors. The deposited films were characterized by using ellipsometry, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy and energy dispersive analysis of x-rays (EDAX). The effect of deposition temperature on the physical and optical properties of deposited SiON films has been analysed. It has been observed that the refractive index of the deposited films increases with corresponding increase in deposition temperature. The compressive stress decreases in accordance with increase in deposition temperature. The peak position of Si–O–Si stretching vibration moves towards a lower wave number while FWHM increases with increase in the deposition temperature. The peak intensity of Si–H, Si–OH and N–H stretching peaks found to reduce with increasing the deposition temperature. This may be an indication of improvement in the quality of the deposited films. EDAX clearly shows the peaks corresponding to Si, N and O, which confirm successful growth of SiON films. These deposited silicon oxynitride films exhibit a very well controlled refractive index in the range of 1.54–1.74, which is very attractive for the application of SiON in photonic wave-guide devices.

Optimization of the structural parameters of a power combiner for a high-power blue laser diode

The computer analysis and optimization of structural parameters of a power combiner and a blue laser diode have been carried out to obtain high power. Initially, the structural and material parameters of a single blue laser diode have been optimized at the emission wavelength of 507 nm. For this analysis and optimization, the electrical and optical equations have been solved in the self-consistent manner. The power obtained from two such blue laser diodes has been coupled to a power combiner to obtain high power. The beam propagation method has been applied for the propagation of modes through the combiner and the computation of the output power. It is pragmatic from the present analysis that output power from the combiner is 33.95 mW, which is about double that of the power obtained from a single blue laser diode of 17 mW by proper optimization of the structural parameters of the combiner for minimum losses.

Analysis of Optical Properties of GaN/AlGaN Quantum Well Ultra-Violet Laser Diode Using 6X6 Hamiltonian

The Quantum well structures have exhibited significant utility in the fabrication of advanced laser devices. The Gallium nitride semiconductor and its alloy particularly AlGaN based quantum structures are having important applications in optical data storage systems and the visible displays. Due to tailoring of wide band gap energy the spectrum obtained is from visible to ultraviolet wavelength range. We had thoroughly investigated the influence of Aluminum mole fraction variation in AlxGa1-xN under a biased condition for GaN/AlGaN based quantum heterostructure optical properties. Here, we had used 6X6 Hamiltonian to realize these properties. The 6X6 Hamiltonian has been chosen to include the many body effect in the calculation and to enhance the accuracy of the optimized results. The paper is focused to reveal the Aluminum mole fraction dependence of near and far filed intensities, peak optical gain, carrier concentration, and optical confinement factor. The effective index method has been used in determination of the optical field intensity in the near and far regimes. The variation in Aluminum mole fraction produces disparity in carrier concentration; hence, we have obtained the spontaneous emission and optical gain as a function of photon energy for different carrier density. The piezoelectric effect on GaN quantum well due to AlGaN barriers has been included through Poisson equation. This Poisson equation has been solved in a self-consistent manner along with Schrödinger and subsequently carrier concentrations have been deduced with a high accuracy using our simulation tools developed in MATLAB.

Single Crystalline a-Axis Mg Doped ZnO Thin Films Prepared by Sol-Gel Technique for Optoelectronics Applications

Single crystalline a-axis Mg doped ZnO thin films (MgxZn1-xO) were successfully prepared by sol-gel spin coating method using Zinc acetate, Magnesium acetate as precursors with ethanol as a solvent. The prepared solutions were used to deposit the films on silicon (100) substrate for different mole concentrations (x = 0.1 to 0.33). All deposited films were annealed at 450 0C to get dense crystalline films. X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis by X-ray (EDAX), Fourier Transform Infrared Spectroscopy (FTIR), Ellipsometry and semiconductor characterization system with probe station were used to characterize the deposited films for structural, chemical, optical, mechanical and electrical properties. The intense absorption peak was observed in the IR spectra for all deposited films showing bond position of fundamental ZnO peak for all Mg mole concentrations. From the XRD spectra, it revealed that the deposited films were single crystalline and a-axis oriented. EDAX spectra clearly showed the peak of Mg along with Zn and O indicating the successful incorporation of Mg into the ZnO. The refractive index was successfully tailored from 1.6 to 1.11 corresponding to 0.1 to 0.33 Mg mole concentration. The refractive index was found to be decrease with an increase in Mg mole concentration. I-V characteristics shows decrease in current with increase in the Mg mole concentration. Significant effect was not observed on thickness of deposited films due to the varying Mg mole fraction. Through SEM image, it was noted that the uniform film of Mg doped ZnO was deposited on the silicon substrate. Our results explore the applicability of MgZnO as cladding layer material to form effective and efficient heterostructure with ZnO as an active layer for the optical wave-guide applications.

Modeling and Simulation of GaN/AlGaN Laser and Temperature Dependent Analysis of Physical Parameters

The computer aided simulation tools have been developed using static device modeling approach for the analysis and optimisation of various physical parameters of the semiconductor lasers.The optical field distribution in various layers across the device is obtained by solving the wave equation. The modal analysis of optical confinement in three layer slab waveguide structure is carried out to obtain the optimized set of structural parameters for maximum intensity at 375 nm wavelength. The basic electrical equations have been implemented in discretized form and solved numerically to obtain the electrostatic potential and quasi Fermi potential at various nodes across the finite difference mesh of the device structure. The self consistent solution of basic electrical and optical equations has been obtained by iterative solution procedure. Recombination rates which have dependency on carrier concentration and recombination coefficient have been determined using various models at individual mesh points of the device. Temperature dependent analysis of recombination coefficient, band gap, refractive index, threshold current density, near field intensity, mirror loss in cavity, effective index has been carried out to explore applicability of nitride lasers at higher temperatures.

Computer Aided Simulation Tools for the Analysis of Semiconductor Lasers

The computer aided simulation tools have been developed for the analysis and optimisation of various physical parameters of the semiconductor lasers. For computer analysis, Poissons equation and current continuity equations have been numerically solved iteratively to obtain electrostatic potential and quasi-Fermi potentials at various positions in the device structure respectively. The wave equation has been solved to obtain the optical field for the transverse electric mode and the rate equation for photons has been solved to obtain photon density. The operational mechanism of the device is fully understood using this tool by graphical representation of output characteristics. The current flow in the device is restricted to less distribution width due to self focusing effect for greater magnitude of current or operating voltage. The peak value of optical intensity value for 807 nanometer exactly lies at the centre of the active region, which confirms the optical confinement.