Micro bimorph cantilever switches for tuning integrated optical systems

We propose to use a self aligning technology (Figure 1) to integrate micro bimorph cantilevers with tips with respect to e.g. the holes in a photonic band gap (PBG) microresonator coupling section in order to perturb its evanescent field [1]. Using a simplified process, we first fabricated bimorph cantilevers on top of silicon, by surface micromachining techniques in which the upper electrode is a thin layer of Chromium on the top of a thick layer of dielectric material which is Silicon Rich Nitride (SiN). The resonance frequencies and pull in voltages of these electrostatically actuated bimorph cantilevers with off-state deflection [2] are analysed and it is found that the higher resonance frequencies come at the price of larger switching voltages (Figure 2-3). This allows for fabrication of relative stiff cantilevers with resonance frequencies in the MHz range to interact with the evanescent field of PBG crystals in which the mechanical elements start to play a role typically with a distance <400 nanometers. We have also fabricated bimorph cantilevers without tips, integrated on top of various optical systems like ring resonators, photonic crystals and planar waveguides. Analytical and numerical models are developed to predict the resonance frequencies and the pull-in voltages of these switches, including the effect of undercut and validated it with experimental data. We have observed selective wavelength on/off switching by perturbing the near band edge resonance of a waveguide grating with a 20 μm wide silicon nitride AFM cantilever, without using its tip area (Figure 4). The observed mechanical perturbation allows 15 dB on/off switching of a specific wavelength and a wavelength tuning of approximately 60 pm. In conclusion, here we describe the technology for fabricating integrated bimorph switches, the optimization studies of the cantilever designs and measurements of mechano-optical interactions using an AFM based cantilever. These optical switches have potential application in the field of elecommunication networks

Mechanical tuning of optical race-track ring resonators

This paper presents the fabrication and mechanical characterization of electrostatically actuated micro bimorphs integrated with race-track ring resonators, for optical tuning applications. The bimorphs, having an upward deflection in the off-state, are integrated by surface micromachining techniques with race-track ring resonators fabricated on Silicon On Insulator (SOI) wafers. Using electrostatic actuation, these bimorphs are pulled into the evanescent field of the ring resonator thereby modulating the propagation properties. Pull-in voltages of the bimorphs have been measured statically and the effect of electrostatic spring softening (ESS) on the resonance frequency has been measured dynamically. The resonance wavelength of the optical ring resonator could be tuned by 50 pm by applying an 8.5 V DC voltage to a 40 μm long bimorph, bringing it into close proximity of the ring resonator waveguide. To the best of our knowledge, this is the first experimental demonstration of tuning of race track ring resonators by integrated, electrostatically actuated bimorphs.\ud \u

Integration of Micro-cantilevers with Photonic Structures for Mechano-optical Wavelength Selective Devices

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. Mechanooptical modulation is investigated in three different types of optical devices, viz. a microring 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

Bimorph based Active Joints for Nanometre scale Actuation

In this work the modelling of a micro bimorph cantilever which is composed of a Silicon Nitride cantilever beam coated on top with a thin Chromium layer is described. The structure functions as a vertical electrostatic actuator for nanometre displacements with stress induced upward curvature in the off-state. A detailed description of the optimisation of the resonance frequency of the cantilever as a function of the thickness of the chromium layer and the deflection of the cantilever is presented. The developed model suggests that resonance frequencies of several MHz can be obtained for structures providing nanometre scale stroke

Optimised Frequency Range of Active Joints for Nanometre Range Stroke

This paper describes the modelling of a micro bimorph cantilever which is composed of a Silicon Nitride cantilever beam coated on top with a thin Chromium layer. The structure functions as a vertical electrostatic actuator for nanometre displacements with stress induced upward curvature in the off-state. A detailed description of the optimisation of the frequency of the cantilever as a function of the thickness of the chromium layer and the deflection of the cantilever is presented. The developed model suggests that resonance frequencies of several MHz can be obtained for structures providing up to 300 nm stroke

Mechano-optical wavelength tuning in a photonic crystal microcavity with sub-1 V drive voltage

A micro-bimorph cantilever with self-aligned nano-tips is monolithically integrated with a photonic crystal based device using optical and deep-UV lithography techniques. Upon electrostatic actuation, the dielectric nano-tips perturb the optical field providing electromechano-optical modulation of light. Static tuning of the optical transmission spectra by more than 600 pm is measured with a sub – 1 V drive voltage, resulting in a modulation as high as 21 dB. The observed strong electromechano-optical effect may find application in power efficient devices for optical communication networks, e.g. as wavelength routing element

Integrated self-aligned tips for dispersion tuning in a photonic crystal micro-cavity

A micro-bimorph cantilever is monolithically integrated with a photonic crystal micro-cavity based device, using surface micro-machining techniques. The integrated cantilever is equipped with self-aligned dielectric tips with respect to the holes of the photonic crystal and on electrostatic actuation, the tips move into the holes, providing electro-opto-mechanical modulation of guided waves. The device is designed to operate in the C-band of the telecommunication wavelengths and constitute a promising candidate for future integrated optical devices

Micro bimorph cantilever switches for tuning integrated optical systems

We propose to use a self aligning technology (Figure 1) to integrate micro bimorph cantilevers with tips with respect to e.g. the holes in a photonic band gap (PBG) microresonator coupling section in order to perturb its evanescent field [1]. Using a simplified process, we first fabricated bimorph cantilevers on top of silicon, by surface micromachining techniques in which the upper electrode is a thin layer of Chromium on the top of a thick layer of dielectric material which is Silicon Rich Nitride (SiN). The resonance frequencies and pull in voltages of these electrostatically actuated bimorph cantilevers with off-state deflection [2] are analysed and it is found that the higher resonance frequencies come at the price of larger switching voltages (Figure 2-3). This allows for fabrication of relative stiff cantilevers with resonance frequencies in the MHz range to interact with the evanescent field of PBG crystals in which the mechanical elements start to play a role typically with a distance <400 nanometers. We have also fabricated bimorph cantilevers without tips, integrated on top of various optical systems like ring resonators, photonic crystals and planar waveguides. Analytical and numerical models are developed to predict the resonance frequencies and the pull-in voltages of these switches, including the effect of undercut and validated it with experimental data. We have observed selective wavelength on/off switching by perturbing the near band edge resonance of a waveguide grating with a 20 μm wide silicon nitride AFM cantilever, without using its tip area (Figure 4). The observed mechanical perturbation allows 15 dB on/off switching of a specific wavelength and a wavelength tuning of approximately 60 pm. In conclusion, here we describe the technology for fabricating integrated bimorph switches, the optimization studies of the cantilever designs and measurements of mechano-optical interactions using an AFM based cantilever. These optical switches have potential application in the field of elecommunication networks

Optimisation study of micro cantilevers for switching of photonic band gap crystals

We propose to use electrostatically actuated micro bimorph cantilevers with tips for nanometric perturbations in the evanescent field of various resonators and photonic band gap crystals (PBG) using a self aligning technology. Since in PBG and in other high optical index contrast structures the interaction of evanescent field with mechanical elements start to play a role typically with a distance <400 nanometers, the required cantilever strokes for switching can be accordingly small. This allows for fabrication of relative stiff cantilevers with resonance frequencies in the MHz range. In this contribution we describe the technology for such devices, the optimization studies of the cantilever designs and measurements of mechano-optical interactions using an AFM based cantilever