A bandwidth-tunable optical passband filter with tunable attenuation is proposed. The filter, composed of a transmission liquid crystal array and high-resolution diffraction grating, was successfully demonstrated based on the compact spatial light design. Experimental results showed that the bandwidth, wavelength, and attenuation could be tuned by controlling the voltage applied on the liquid crystal array. The insertion loss was less than 3 dB; the attenuation tuning range was from 0 to 15 dB. The bandwidth tuning range was from 50 to 5000 GHz, which covered the full C band. The filter can meet the technical requirements of colorless-directionless-contentionless-flexible reconfigurable optical add/drop multiplexer.

In this Letter, microwave generation based on frequency multiplication with fiber ring loop modulation and microwave photonic filters is proposed and experimentally demonstrated. High-order microwave harmonics can be generated and enhanced by the fiber ring loop modulation formed by incorporating a Mach–Zehnder modulator (MZM) into a fiber ring structure. Cascaded fiber ring based microwave photonic filters (FRMPFs) are adopted to filter out the desirable harmonics. In our work, with a driving signal of 2.835 GHz, the fourth-order harmonic with a frequency of 11.34 GHz is generated by using two cascaded FRMPFs.