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Tunable microwave photonic filters based on double-sideband modulation and linear chirped fibre Bragg gratings

A continuously tunable microwave photonic filter with large dispersion is proposed by using bilaterally modulated and linearly chirped fibre Bragg gratings (LCFBG). A pair of LCFBGS were reverse-inserted into two arms of a Mach–Zehnder interferometer (MZI) to make a dual-tap band-pass filter. The free spectral range (FSR) can be adjusted by setting the basic time difference between two taps, adjusting the wavelength of the optical carrier and reflecting the microwave signal to different physical positions in the LCFBGs. A continuous tunability of the filter is validated. In our scheme, the FSR is adjusted from 33.6 MHz to 37.6 MHz with sub-megahertz accuracy and the adjustable range covering the whole range of over 100 MHz.