Acousto-Optic Double Side-Band Amplitude Modulation of a Fiber Bragg Grating in a Four-Holes Suspended-Core Fiber

A dynamic multiwavelength reflection filter is acoustically induced by the reflectivity modulation of a fiber Bragg grating in a suspended-core fiber. The fiber composed by four air holes is combined with a specially designed acousto-optic modulator to increase the modulation efficiency and to reduce significantly the device size. The effect of the two strongest modulator modes on the grating is evaluated at 374 and 474 kHz. The high-frequency acoustic waves are amplitude modulated by a low-frequency signal from 100 to 500 Hz, generating resonant wavelengths peaks in the grating spectrum. The modulated grating reflectivity is experimentally characterized in the spectral domain. The modulation depth, bandwidth, and number of the induced resonances are tuned by the voltage and frequency of an electrical signal. Up to 15 wavelength peaks with a spectral bandwidth of ~5 pm and a modulation depth up to 74% are generated, indicating new possibilities for compact and fast all-fiber acousto-optic devices.