Thermo-optical delay line for optical coherence tomography

Optical Coherence Tomography (OCT) is a powerful medical imaging technology. Its ability to non-invasively probe tissues in depth with high resolution has lead to applications in many fields of medicine, with a large potential for surgical guidance. One of the technological challenges impairing faster adoption of OCT is the relative complexity of the corresponding optical instrumentation, which translates into expensive and bulky setups. In this paper a compact fastscanning optical delay line based on the thermo-optical effect of silicon is studied. Although this effect has been applied to other optical components, the necessary frequency behaviour together with the relatively large scanning range required are unique to the application. Cycling speeds of over 1kHz and ranges of more than 1mm are needed for videorate acquisition of relevant tissue volumes. A structure is proposed to meet these specifications. A bulk micro machined freestanding waveguide is connected to the substrate by means of evenly spaced support beams. It is shown by means of the Finite Element Method that the geometrical parameters of the beams modulate the thermal behaviour of the waveguide. A linear trade-off between maximum working frequency and power dissipation for any given waveguide size and required scanning range has been found. Our results show that the proposed implementation of a fast-scanning delay line can match the requirements of Time Domain Optical Coherence Tomography.Electronic Instrumentation LaboratoryElectrical Engineering, Mathematics and Computer Scienc