We present, for the first time based on our knowledge, a novel in-fiber optical phase modulator that is inherently broadband, efficient, and polarization-maintaining (PM). The modulator is a 25 mm long section of a D-shaped cladding PM fiber with half of its silica cladding replaced with an electro-optic (EO) silicone gel. A phase modulation of more than pi rad has been demonstrated. We describe techniques that enable the long-distance exposure of the fiber core, microfabrication of on-fiber electrodes, a low refractive index EO cladding material for replacing silica fiber cladding, and accurate phase measurement utilizing a Sagnac interferometer.
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