Guiding light by and beyond the total internal reflection mechanism

This thesis reports a series of techniques the author has developed to model various waveguiding structures, including the conventional planar and channel waveguides working by, and the advanced structures working beyond the TIR mechanism. Hence, this thesis contains both the methods and their applications to model and study the standard guided-wave and the advanced leaky-wave structures. The methods include mode solvers based on finite difference method (FDM) and finite element method (FEM), furnished with transparent boundary conditions (TBCs) for both guided and leaky modes. Based on the developed techniques, structures as simple as planar waveguides up to as complicated as photonic crystal fibers (PCFs) can be modeled rigorously

Enhancing the Performance of Integrated Optical Sensor by Slow-light: Theoretical Study on Ring-Resonator Based Structures

In this work, the performance of three kinds of integrated optical ring-resonator based slow-light structures for sensing applications is theoretically studied using the transfer matrix method and the complex transmission coefficient approach. Enhancement of sensing performance due to the slowlight phenomenon is quantitatively formulated. The modeling results show that using realistic structure parameters, a refractive index detection limit of one order better than the state of the art Mach-Zehnder interferometer sensing structure is possible by the inclusion of such a slow-light structure. The role of ring(s) attenuation constant in limiting the usable light slowness and the achievable sensor resolution is also discussed. For a sufficiently small ring attenuation constant, the optimal sensing performance of a single resonator circuit can be better than that of multiple resonator circuits, while offering less fabrication complexities, cleaner spectra, shorter device length, and higher figure of merit

Finite element analysis of photonic crystal fibers

A finite-element-based vectorial optical mode solver, furnished with Bayliss-Gunzburger-Turkel-like transparent boundary conditions, is used to rigorously analyze photonic crystal fibers (PCFs). Both the real and imaginary part of the modal indices can be computed in a relatively small computational domain. The leakage loss, the dispersion properties, the vectorial character, as well as the degeneracy of modes of the fibers can be studied through the finite element results. Results for PCFs with either circular or non-circular microstructured holes, solidor air-core will be presented, including the air-core air-silica Bragg fiber. Using the mode solver, the single-modeness of a commercial endlessly single-mode PCF was also investigated

Noise and resolution in IO interferometric sensing

The paper presents a general theory for sensing devices, relating noise and device parameters to resolution of modal index changes. The theory is applied to optimise the length of a few integrated optics sensing devices, being a Mac-Zehnder interferometers and two Fabry-Perot implementations. The results enable the determination of the maximum attainable resolution, and show the crucial importance of loss

Modelling of microstructured waveguides using a finite-element-based vectorial mode solver with transparent boundary conditions

Finite element vectorial optical mode solver is used to analyze microstructured waveguides in a relatively small computational domain. The presentation will consider the computational method, as well as the applications of it on a number of waveguides with 2-D cross section where microstructures are employed

A finite element characterization of a commercial endlessly single-mode photonic crystal fiber: is it really single mode?

One of interesting properties of photonic crystal fibers (PCFs) is their possibility to be single-moded over a wide wavelength range, down to UV, while still having a reasonably large modal profile. Such properties are attractive for applications like optical sensing, interferometry, and transport of white light. PCFs, which is designed specially for such property are known as the endlessly single-mode (ESM-) PCFs [1].\ud However, the ESM property requires the holey cladding of a PCF to have a small air-filling factor. Such a requirement indeed creates problems for PCF manufacturers, as it does not go in harmony with other equally important properties of the PCF. A small air filling factor implies large leakage loss. So, the characteristics of commercially available ESM-PCFs, in fact come out from compromises between the desirable endlessly-single-modeness and the low leakage loss properties. Hence, depending on the type of applications, the term ESM itself could mislead its users, if the endlessly single modeness is presumed without proper precautions.\ud In this work, using a vectorial finite-element leaky mode solver published recently [2], several dominant leaky modes of a commercial ESM-PCF [3] were investigated. Although the leakage loss of the fundamental mode is already 6 orders lower (on a dB/unit-length scale) than that of the nearest higher order modes, the leakage losses of these higher order modes are still quite low, which might still be significant, especially for short wavelength and short fiber-length applications. In addition to the ordinary-fiber-like hybrid core modes, the existence and significance of unusual modes like cladding-resonance modes and core-cladding-resonance modes were also numerically observed. Based on the loss discrimination between the most dominant and the nearest higher order mode, we set-up a criterion for the single-modeness. Using that measure, we verified the single-modeness of the corresponding ESM-PCF and found that the endlessly single-modeness is valid only for a relatively long fiber, typical of local area network applications. This finding implies that applications employing short fiber-length, working in short wavelength regimes, should be prepared for significant effects of the higher order modes, e.g. by employing a mode stripper to suppress their effects. We suggest that ESM-PCF for short fiber-length applications need to be designed differently from those for long fiber-length applications.\ud \ud References\ud [1]. T.A. Birks, J.C. Knight, and P.S.J. Russell, “Endlessly single-mode photonic crystal fiber,” Opt. Lett., Vol. 22, No. 13, pp. 961-963, 1997.\ud [2]. H.P. Uranus and H.J.W.M. Hoekstra, “Modelling of microstructured waveguides using a finite-element based vectorial mode solver with transparent boundary conditions,” Opt. Express, Vol. 12, No. 12, pp. 2795-2809, 2004.\ud [3]. www.crystal-fibre.com/datasheets/ESM%20-%2012%20-%2001.pdf\u

Direct experimental observation of pulse temporal behavior in integrated-optical ring-resonator with negative group velocity

We report a direct experimental observation of pulse temporal behavior in an integrated optical two-port ring-resonator circuit as a function of coupling strength, including the transition across the critical coupling point. We demonstrate the observation of pulse ‘advancement’ in the negative v_g regime and pulse delay in the positive v_g regime. We also observed a smooth transition of the pulse shape from highly negative to highly positive v_g (or vice versa) through a pulse splitting phenomenon. The observed phenomena agree well to theoretical simulations