Photonic crystals (PhCs) are periodically structured electromagnetic media, generally characterised by not permitting light of defined ranges of frequency to propagate through the structure. These disallowed ranges of frequency are known as photonic band gaps. The intentional introduction of defects into the crystal gives rise to localized electromagnetic states that provide a mechanism for the control of the propagation of photons through PhCs. In the case of one dimensional (1-D) PhCs, the introduction of a single defect into a finite PhC results in the formation of a resonant cavity structure, a so-called microcavity. The ease of fabrication and scope for integration make 1-D PhCs good candidates for the future applications of PhCs in light transmission systems and, as such, these structures are the focus of the research reported here. The aim of this thesis is to report a practical study of passive 1-D PhC devices and thereby extend the base of measurements that support and extend the results of theory and simulation. Various types of 1-D PhC structures have been fabricated using electron beam lithography and inductively coupled plasma technologies in a clean-room environment. The fabricated structures in effect demonstrate a first or primitive level of integration of 1-D PhCs with another optical device, namely a ridge waveguide. Measurements were performed by butt-coupling from a single mode fibre taper of the transmission characteristics of the resulting integrated waveguides, whilst a Side-band measurement method for very high resolution (0.2pm) microcavity characterisation was invented during the measurement process. A multiple wavelength transmission optical filter transmitting at the telecommunication wavelengths of 1310nm and 1550nm, and which could be used in a WDM system was demonstrated. The effect of introducing mode matching structures to minimize II the scattering loss and boost the quality factor value was investigated. Optimum positioning of the tapers produced a significant enhancement of Q. Finally, a narrow pass band filter constructed from coupled cavities was fabricated and characterised. A quasi-flat transmission peak with a pass band width of just 4nm was observed.
|Date of Award||1 Dec 2007|
|Supervisor||Duncan Allsopp (Supervisor)|
- nano fabrication
- photonic crystals
- optical measurement