Magnetooptical phase modulation in integrated Mach-Zehnder interferometric biosensors
B. Sepúlveda, G. Armelles and L. M. Lechuga
Sens. Act. A, 134, 2007, 339-347 - DOI: 10.1016/j.sna.2006.05.046
Abstract: The integrated Mach–Zehnder interferometric biosensors are one of the most promising optical biosensors due to their extreme sensitivity and possibility of integration in a lab-on-a-chip. However, the periodic response of the interferometric devices complicates the interpretation of experimental results due to the ambiguity and fading of the signal. To overcome these problems we present a phase modulation system based on the introduction of a periodic phase shift in the reference arm of the interferometers and the Fourier analysis of the output signal. This system allows the direct and unambiguous detection of the phase changes induced by the biosensing measurement. As phase modulation mechanism, we propose and theoretically analyze two different magneto-optic (MO) methods compatible with the standard microelectronic processes. The phase modulators are based on silicon-on-insulator (SOI) waveguides and yttrium iron garnets (YIG) as magnetic material. The first one exploits the non-reciprocal phase shifts induced in the TM guided modes when the orientation of the magnetization of an YIG layer is rotated within the plane of the layer. On the other hand, the MO phase modulation can also rely on the birefringence induced in magnetic liquids under an external magnetic field. We demonstrate that the MO phase modulation is compatible with SOI waveguides showing very high surface sensitivity in the biosensing measurements. In addition, the MO phase modulation can be achieved by using MO interaction lengths of only a few millimetres, facilitating the integration within the interferometric biosensors.