Analysis of Wave Propagation Eigenproblem in Metamaterial Structures
PhD. Thesis defined for Mr. Ehsan Faghihifar
Analysis and Design of Optical Splitters based on
Subwavelength Structures using Silicon on Insulator
PhD. Thesis defined for Mr. Kamal Arik
Abstract :
Optical couplers (as optical combiners or splitters) are of great importance in photonic integrated circuits (PICs) and widely used in telecommunication systems. Couplers are used in PICs to combine, i.e. spatially overlap optical fields or divide (splitters) the field from one waveguide into two or more paths. Various types of optical splitters have been proposed in literature including adiabatic couplers, Directional couplers, Y-junctions and multimode interference (MMI) couplers. However, design and implementation of a polarization-independent, broadband and compact optical splitter is still a challenge.
A polarization beam splitter (PBS) is one of the most important polarization-handling devices for separating/combining TE and TM polarizations. Various structures have been presented for the realization of on-chip PBSs by using MMI structures and evanescent coupling structures. However, one should know that it is still a challenge to realize compact on-chip polarization-handling devices with excellent performances, including low excess loss (EL) and high extinction ratio (ER) in a broad wavelength band.
In general, the project pursues two goals in the silicon on insulator (SOI) platform. Firstly, we propose two polarization-independent, broadband and compact power splitters with different operating functions using subwavelength structures in which the dispersion characteristic of the subwavelength grating waveguide (SWG) is engineered to achieve the design. Secondly, broadband PBSs based on asymmetrical directional coupler (ADC) and Machzehnder interferometer (MZI) are proposed. The basic idea is to manipulate the phase-matching condition of both polarizations. As a result, two orthogonal polarizations will be separated in short distance.
Keywords: Integrated Photonics, Silicon Photonics, Power Splitters, Polarization Splitters
Design and implementation of vector- sum phase shifter for WLAN application
MSc. Thesis defined for Mr. Mohammad Mehdi Janforoz
Abstract :
On the demand of higher directivity, higher throughput and less interference, phased array systems and MIMO have become attractive to reach these goals. The advantages of phased array systems include the ability to perform electronic beam steering and arbitrary pattern synthesis. Phase shifters and variable gain amplifiers are used in order to reach These advantages. In this thesis, a ‘’ C‘’ band (4.8 GHz-6.2 GHz) vector-sum phase shifter using HMIC technology for realizing a phased array receiver is designed. This phase shifter can change signal phase and amplitude. The main blocks of this phase shifter are low-insertion phase and low-noise variable gain amplifier, which consists of current steering and current reuse topology with techniques for compensation of insertion phase, quadrature hybrid (branch line coupler) and Wilkinson power divider (combiner). Design specifications for variable gain amplifier are: low-insertion phase (below 13 degree), low-noise figure (below 4.9dB) and high dynamic range (about 24dB).
The designed circuit has maximum gain about 25dB and insertion phase bellow 11 degree. All of the passive sections are designed with microstrip transmission line on RO4003 for low insertion loss. ADS momentum planar EM simulator and CST studio is used to design and validate the schematic simulation results. The results of The signal constellation have 1024 different points and its RMS phase and gain error are 0.85 deg and 0.02 respectively. To show the designed phase shifter’s ability in pattern synthesizing, two uniform and chebyshev patterns are plotted.
Keywords: vector-sum phase shifter, phased array, low-insertion phase and low-noise variable gain amplifier
