Design and Simulation of Ultra low loss Spiral Delay line for Integrated Optical Coherence Tomography

We report a design of 55 cm long spiral delay line at 850 nm wavelength. Propagation characteristics were simulated and analysed with fully vectorial Eigen Mode Expansion (EME) method. Bending losses were calculated and analysed for the optimization of minimum bending radius for reported structure. We have also simulated and analysed excess loss for a broadband of 200 nm at 850 nm operating wavelength. An excess loss of less than 0.2 dB is reported for the structure over the entire bandwidth range. The structure was further simulated for individual Transverse Electric (TE) and Transverse Magnetic (TM) modes and the analysis showed better results for TM mode. Reported structure is easy to fabricate, ultra-low loss and also broadband over 200 nm with a foot print of only 6×6 sq. mm. So, this design will improvise the reference arm section and will enhance the depth scanning of integrated optics based optical coherence tomography system.