All-fiber and fiber compatible acousto-optic modulators with potential biomedical applications

All-fiber acousto-optic (AO) devices such as frequency shifters, phase, intensity and polarization modulators, tunable filters and multiplexers have been developed in the last decade mostly for their importance in fiber optic communication systems. However they can equally have potential uses in bio sensing and fiber based biomedical systems. We present the design, construction and performance of a number of all-fiber and fiber compatible acousto-optic modulators that particularly phase and polarization modulators and will address their potential uses in biomedicine. Among these components and devices, an all-fibre phase modulator acts on the phase of optical fields that propagate down the fibre core. To enhance the phase modulation, the acoustic energy is focused into the fiber core using an acoustic lens. Another high efficiency birefringence (or polarization) modulator was demonstrated that is designed to operate at the acoustic resonance frequency of the fiber. Fiber compatible devices were built using gradient index (GRIN) lenses that can couple the light into a fiber or between two fibers. Diffraction based and polarization GRIN modulators were demonstrated and AOMs of in-fiber gratings as well as ones made from glasses that exhibit large AO figure of merit. As a high frequency polarization, phase, intensity or wavelength modulators these devices have a great potential for use in polarimetric imaging, scanning of a fiber-optic OCT system, tuning the wavelengths in miniature hyperspectral imaging systems and sensors or for frequency-domain OCT.