Photonic crystal fiber (PCF) is a new type of optical fiber that adds a unique dimension to fiber design possibilities, enabling the previously unthinkable in fiber optics. The mode and the band-diagram analysis by conventional electromagnetic methods had proven the advantages of the PCF. When this new product couples to the existing optical fiber systems or vice versa, the important issue is the coupling efficiency. From among the available numerical techniques, the FDTD method seems to be the most reliable for such a task. The method does not force any assumptions on the behavior of the propagating light. It solves Maxwell’s equation in time domain and space domain directly and is readily applicable to problems like transmissions through refractive index discontinuities and multiple reflections on interfaces. The paper will present FDTD simulation results of the coupler and analysis of the calculated coupling efficiency on coupler design parameters.
We present the state of the art for commercial design and simulation software in the 'front end' of photonic circuit design. One recent advance is to extend the flexibility of the software by using more than one numerical technique on the same optical circuit. There are a number of popular and proven techniques for analysis of photonic devices. Examples of these techniques include the Beam Propagation Method (BPM), the Coupled Mode Theory (CMT), and the Finite Difference Time Domain (FDTD) method. For larger photonic circuits, it may not be practical to analyze the whole circuit by any one of these methods alone, but often some smaller part of the circuit lends itself to at least one of these standard techniques. Later the whole problem can be analyzed on a unified platform. This kind of approach can enable analysis for cases that would otherwise be cumbersome, or even impossible. We demonstrate solutions for more complex structures ranging from the sub-component layout, through the entire device characterization, to the mask layout and its editing. We also present recent advances in the above well established techniques. This includes the analysis of nano-particles, metals, and non-linear materials by FDTD, photonic crystal design and analysis, and improved models for high concentration Er/Yb co-doped glass waveguide amplifiers.
Threshold reduction and enhanced mode selectivity are demonstrated in pulsed GaN-based lasers upon the introduction of 5(lambda) /4 air/nitride Bragg gratings defined by focused ion beam (FIB) etching. A 13% reduction in threshold current is obtained from a laser with a 5 micrometers wide ridge by introducing a deep-etch air/nitride mirror. The presence of a reduced-depth Bragg grating, etched across 4 micrometers wide ridge structure using a lower FIB dose, results in single-peak spectral characteristics for currents up to 1.14(DOT)ITh. The introduction of the Bragg mirrors always results in a broadening of the near field parallel to the epitaxial planes.
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