Showing papers by "Muttukrishnan Rajarajan published in 2004"

Rigorous comparison of parabolically tapered and conventional multimode-interference-based 3-dB power splitters in InGaAsP/InP waveguides.

Abstract: Design issues such as optical transmission, interference mechanisms, the splitting ratio, the polarization dependence, and the fabrication tolerances of a compact parabolically tapered multimode-interference (MMI)-based 3-dB power splitter on an InP-based deeply etched ridge waveguide, by use of the finite-element-based beam-propagation method, are presented. The benefits and drawbacks of the use of the tapered structure, in comparison with an untapered MMI-based 3-dB splitter, have also been investigated.

QoS constraints in bluetooth-based wireless sensor networks

Abstract: This paper investigates the case of a wireless sensor network deploying Bluetooth technology. The paper analyses main technological features of Bluetooth, such as error recovery, power consumption and connection establishment, and using some experimental results analyses their effect on the Quality of Service in the sensor network. The paper presents a case for a different view of QoS in sensor networks. We argue that the network availability, reliability and especially the originality (freshness) of data have emerged as crucial QoS issues in wireless sensor networking. The paper puts emphasis on master-side scheduling in Bluetooth and analyses using simulation the performance of three scheduling schemes in a sensor network model. We analyse the performance of the schemes in symmetric and asymmetric load environments and with different bit error probabilities. Two of the schemes are specially designed for sensor networks, and one of them, the Maximum Burst Delay First, shows very good results in the asymmetric load environment.

Mode beating in tapered high-power lasers

Abstract: The evolution of the optical beam profile along a high-power tapered semiconductor amplifier has been demonstrated by using a rigorous finite element-based and full-vectorial modal solution, coupled with the beam propagation approach. Numerically simulated results indicate that many higher order modes are generated and propagate along the tapered structure and their interference with the fundamental mode causes variations of the optical beam, both along the transverse and the axial directions, which significantly modify the output beam quality.

Design issues for directional coupler- and MMI-based optical microring resonator filters on InP

Abstract: The characterization and optimization of optical microring resonator-based optical filters on deeply etched GaInAsP-Inp waveguides, using the finite element-based beam propagation approach is presented here. Design issues for directional coupler- and multimode interference coupler-based devices, such as field evolution, optical power, phase, fabrication tolerance and wavelength dependence have been investigated.

Rigorous analysis of photonic crystal fibers by using a full-vectorial H-field-based finite element method

Abstract: Modal solutions for photonic crystal fibers with circular air-holes in a hexagonal array are presented, by using a rigorous full-vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, modal hybridness, modal birefringence and group velocity dispersion values are presented. The effect of external pressure on photonic crystal fibers is analyzed also by using the powerful finite element method. Modal solutions are obtained for both symmetric and asymmetric air-holes and the effect of pressure on the modal properties and mode degeneration are evaluated, presented and discussed.

Modal solutions of photonic crystal fibers by finite element method

Abstract: Modal solutions of photonic crystal fibers with both circular and rectangular air holes are presented by using a rigorous full vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations. 1. INTRODUCTION The photonic crystal fiber (PCF) (which is also known as ‘holey’ fiber), is a micro-structured fiber, where arrays of holes run along the waveguide length, having a more controllable fabrication parameters than standard single mode fiber. Increasing interest is being shown in such PCFs for a range of applications in optical communications, sensing and signal processing. These include the control and guidance of optical beams, taking advantage of their unique transmission characteristics, which include being continuously single-moded, with controllable spot-sizes and with tailored group velocity dispersion (GVD) characteristics. The optical properties of standard fibers are mostly controlled by two key parameters, the radius and the index difference between core and cladding. Single mode fiber can be designed by balancing these two parameters for different applications, for example in conventional low-loss telecommunication grade fibers or specialized fibers such as doped fibers with a smaller spot-size. However, the adjustment of the GVD properties is severely limited. By contrast in a PCF, the number of holes, their sizes, orientations and placements can provide an additional degree of freedom which is not present for conventional fiber. A wide range of potential applications is anticipated, exploiting the ability to tailor the GVD, the large spot-size for high power applications, and the smaller spot-size for improved nonlinear interactions, Raman amplification, Brillouin lasers, second harmonic generation, four-wave mixing, and creating polarization maintaining PCFs with higher modal birefringence and super continuum generation.

Modal hybridism of polarization maintaining photonic crystal fibers by using a full-vectorial finite element method

Abstract: The photonic crystal fiber (PCF) is a micro-structured fiber, where arrays of holes running along the waveguide length, has more controllable fabrication parameters than a standard single mode fiber. Increasing interest is being shown in such PCFs for a range of applications in optical communications, sensing and signal processing. This includes the control and guidance of optical beams, taking advantage of their unique transmission characteristics, including being continuously single-moded, with controllable spot-sizes and with tailored group velocity dispersion characteristics. To date, most of the research into these fibers has a strong experimental basis [1], which has recently been complemented by various modal solution approaches to their characterization, but mostly using scalar formulations or being limited to specific types of structures. The modal solution approach based on the powerful finite-element method (FEM) [2] is more flexible, can represent any arbitrary cross-section more accurately and has been widely used to find the modal solutions of a wide range of optical waveguides [2]. The optical modes in a high-index contrast PCF with two-dimensional optical confinement are also hybrid in nature. To accurately characterize such fibers a full-vectorial approach is necessary and a H-field based full vectorial approach [2] has recently been extended to study the polarization issues in such PCFs. Polarization dependent single mode operation, variation in the spot-size, modal field profiles, modal hybridism, birefringence, and the beat length have been calculated for these fibers. REFERENCES [1] J C Knight et al., Opt. Lett., 21, pp.1547-1549, 1997. [2] B M A Rahman and J B Davies, J. Lightwave Tech., 2, pp.682-688, 1984.

Design issues for directional coupler-based optical microring filters on InP waveguides

Abstract: The characterization of optical microring resonator-based optical filter on InP waveguides, using the finite element-based beam propagation approach is presented here. Design issues, such as, coupling, wavelength dependence, power and field evolution have been investigated.