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.

A dual optical time domain reflectometry (OTDR) system, which employs two different continuous waves at the optical line terminal and a pair of fiber Bragg gratings at the end of each optical network unit, is proposed in a time-division multiplexing passive optical network (PON). The proposed scheme accomplishes the fiber fault monitoring by comparing the different wavelength’s testing curves. Complete complementary code is utilized to measure multiple wavelength signals simultaneously with only one receiver and to improve the dynamic range of this system. The PON system consisting of 20 km feeding fiber and a 1:16 splitter is investigated by the experiments. The experimental results show that the faulty branch can be successfully identified by using our scheme. What is more, we also demonstrate that our scheme can be applied to the multi-stage PON.