Summary thesis Shahina Shakkalakkal 2011

Summary

This thesis deals with the fabrication technology and mechano-optical characterisation of compact integrated wavelength selective optical devices for use in telecommunication applications. Upon electrostatic actuation, a mechanical element perturbs the optical evanescent field of a guided wave providing electro mechano-optical modulation of light. The silicon-on-insulator (SOI) based optical devices are fabricated in a silicon photonics fabrication platform called ePIXfab using deep-UV lithography. Further, using surface micromaching techniques, the mechanical elements are monolithically integrated with the optical devices in the MESA⁺ Cleanroom. Mechano-optical modulation is investigated in three different types of optical devices, viz. a micro-ring resonator, a photonic crystal slab waveguide and a photonic crystal microcavity based device. Owing to their ease of fabrication and low power consumption, electrostatically actuated curled micro-bimorph cantilevers are chosen as the mechanical perturbing element. The thesis concentrates on the characterisation of the mechanical elements, the development of integration technologies and mechano-optical characterisation of the integrated devices.

After introducing the purpose of the research, the first chapter explains the importance of matured silicon based technology for realising integrated optical devices. Further chapter two presents a review on the various optical modulation schemes, realised so far in literature. The relative merits of mechano-optical modulation schemes over existing alternative techniques such as those based on thermo-optic effects, electro-optic effects, plasma dispersion effects and liquid crystal infiltration are discussed.

A detailed analysis of the mechanical characterisation of curled micro-bimorph cantilevers is carried out in chapter three. The off-state tip deflections of the micro-cantilevers are optimised to an acceptable distance of <500 nm above the optical device, by considering various parameters such as length of the cantilever, upper electrode thickness and material. Further Galerkin based static and dynamic models are developed to predict various mechanical parameters of the curled micro-cantilever such as pull-in voltage, resonance frequency and resonance frequency shift by electrostatic spring softening. The predictions are validated against measured data.

A detailed explanation for a two mask fabrication scheme for integration of micro-cantilevers with race-track type micro-ring resonators is given in chapter four. Various fabrication related issues, of which a major one is related with the formation of stringers (unwanted residues left in the corners of a stepped surface), are addressed in this chapter. After discussing various existing stringer elimination methods, two novel alternative methods are proposed. Further the chapter demonstrates successful device realisation using one of these methods: i.e. utilising ultrasonic cleaning. The next chapter provides the mechano-optical characterisation of the micro-ring resonators integrated with micro-cantilevers. The mechanical characterisation includes analyses of both static and dynamic parameters such as off-state tip deflection, pull-in voltage, first order mode resonance frequency, quality factor, frequency shift by electrostatic spring softening etc. The device is near-critically damped, thus providing the fastest possible response for a device of given resonance frequency. Static optical tuning measurements demonstrate a wavelength shift of 122 pm and modulation depth of 18 dB for a 40 µm cantilever whereas dynamic measurements demonstrate optical switching with a rise time of 16 µs for a 100 µm cantilever.

A fabrication technology for integration of micro-cantilevers equipped with self-aligned tips with respect to the holes of a photonic crystal slab waveguide and photonic crystal micro-cavity based device is introduced in chapter six. Further both devices are mechano-optically characterised. An 80% throughput modulation in a photonic crystal slab waveguide is demonstrated. More importantly 560 pm wavelength tuning with 21 dB modulation in the third band edge of a photonic crystal microcavity based device is demonstrated. Finally chapter seven concludes the research described in the thesis with a discussion on possible future research.

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Home News Events Strategic Orientations research groups Publications PhD students Education MESA+ NanoLab Starting entrepreneurs Tech Park Industrial Partners Vacancies Links Sitemap Search	Summary thesis Shahina Shakkalakkal 2011 Summary This thesis deals with the fabrication technology and mechano-optical characterisation of compact integrated wavelength selective optical devices for use in telecommunication applications. Upon electrostatic actuation, a mechanical element perturbs the optical evanescent field of a guided wave providing electro mechano-optical modulation of light. The silicon-on-insulator (SOI) based optical devices are fabricated in a silicon photonics fabrication platform called ePIXfab using deep-UV lithography. Further, using surface micromaching techniques, the mechanical elements are monolithically integrated with the optical devices in the MESA⁺ Cleanroom. Mechano-optical modulation is investigated in three different types of optical devices, viz. a micro-ring resonator, a photonic crystal slab waveguide and a photonic crystal microcavity based device. Owing to their ease of fabrication and low power consumption, electrostatically actuated curled micro-bimorph cantilevers are chosen as the mechanical perturbing element. The thesis concentrates on the characterisation of the mechanical elements, the development of integration technologies and mechano-optical characterisation of the integrated devices. After introducing the purpose of the research, the first chapter explains the importance of matured silicon based technology for realising integrated optical devices. Further chapter two presents a review on the various optical modulation schemes, realised so far in literature. The relative merits of mechano-optical modulation schemes over existing alternative techniques such as those based on thermo-optic effects, electro-optic effects, plasma dispersion effects and liquid crystal infiltration are discussed. A detailed analysis of the mechanical characterisation of curled micro-bimorph cantilevers is carried out in chapter three. The off-state tip deflections of the micro-cantilevers are optimised to an acceptable distance of <500 nm above the optical device, by considering various parameters such as length of the cantilever, upper electrode thickness and material. Further Galerkin based static and dynamic models are developed to predict various mechanical parameters of the curled micro-cantilever such as pull-in voltage, resonance frequency and resonance frequency shift by electrostatic spring softening. The predictions are validated against measured data. A detailed explanation for a two mask fabrication scheme for integration of micro-cantilevers with race-track type micro-ring resonators is given in chapter four. Various fabrication related issues, of which a major one is related with the formation of stringers (unwanted residues left in the corners of a stepped surface), are addressed in this chapter. After discussing various existing stringer elimination methods, two novel alternative methods are proposed. Further the chapter demonstrates successful device realisation using one of these methods: i.e. utilising ultrasonic cleaning. The next chapter provides the mechano-optical characterisation of the micro-ring resonators integrated with micro-cantilevers. The mechanical characterisation includes analyses of both static and dynamic parameters such as off-state tip deflection, pull-in voltage, first order mode resonance frequency, quality factor, frequency shift by electrostatic spring softening etc. The device is near-critically damped, thus providing the fastest possible response for a device of given resonance frequency. Static optical tuning measurements demonstrate a wavelength shift of 122 pm and modulation depth of 18 dB for a 40 µm cantilever whereas dynamic measurements demonstrate optical switching with a rise time of 16 µs for a 100 µm cantilever. A fabrication technology for integration of micro-cantilevers equipped with self-aligned tips with respect to the holes of a photonic crystal slab waveguide and photonic crystal micro-cavity based device is introduced in chapter six. Further both devices are mechano-optically characterised. An 80% throughput modulation in a photonic crystal slab waveguide is demonstrated. More importantly 560 pm wavelength tuning with 21 dB modulation in the third band edge of a photonic crystal microcavity based device is demonstrated. Finally chapter seven concludes the research described in the thesis with a discussion on possible future research.