Novel mechanical alignment and component fabrication for wavelength-selective optical switches
Growing demand for internet bandwidth is driving an expansion of the optical switching infrastructure in the global telecom network. Two-dimensional free-space wavelength selective switches (WSSs) offer significantly increased integration over current linear WSS technology, providing a step change in switching capacity. The fabrication of two-dimensional WSSs presents significant optomechanical challenges. This thesis develops a range of novel alignment and fabrication techniques necessary to construct an experimental two-dimensional WSS system. Where necessary these techniques are further developed to enable the cost-effective volume manufacture of commercial switching products based on this technology.
An overview of the role of a WSS in a wavelength-division-multiplexed telecom network is first provided. The operating principles and optical specification of the experimental WSS system are then described. The optomechanics require a unique combination of accuracy, stability and modularity, combined with the unique 2D architecture. An evaluation is made of the optomechanical techniques used for comparable systems. This demonstrates that three key areas of research are necessary to achieve the optomechanical requirements for the experimental WSS system.
The first key task is the characterisation and development of the two-dimensional waveguide arrays required to realise the input and output ports. Both conventional single-mode fibres and waveguides fabricated with ultrafast-laser inscription (ULI) are investigated. The ULI waveguide technology is verified as an enabling technology for the volume manufacture of two-dimensional WSSs. The second key task is the development of passive alignment techniques for the micro-optical input-output assembly, using the precision afforded by mechanical parts fabricated with a ULI-etching process. These are shown to achieve micron-level accuracy without the need for external equipment. This has substantial implications for a range of fields beyond precision optics. The final task is the metrology, mounting and alignment of the bulk optics in the relay system. Novel kinematic and semikinematic mounting schemes are modelled, fabricated and experimentally verified. They then allow the WSS to be rapidly aligned to the required accuracy, enabling it to achieve optical performance superior to that of commercial products using conventional WSS technology.