A tunable optical rail is embedded into the cavity of a nonlinear-polarization-rotation （NPR） mode-locked fiber laser to generate a sampling pulse with different repetition frequencies and realize bit-rate-adaptive software synchronous optical sampling. Two ultrashort pulses （20.26677 and 20.22900 MHz） are derived, and a 100-MHz data signal is sampled twice with these pulses based on sum-frequency generation （SFG） in periodically poled lithium niobate （PPLN）. The eye diagram is successfully recovered, and an estimated bit rate of 102.22 MHz is derived. This method is feasible for bit rates ranging from 200 MHz to 1 GHz, with 〈3% relative error.
We investigate the multilevel modulation for red-green-blue light emitting diode （RGB LED）. A simple approach for extracting soft values from the modulation is proposed. The mapping way from bits to the modulated symbols for the multilevel modulation is also investigated. The modified modulation is obtained through the brute force. Based on the Monte Carlo simulations, the proposed approach and modified modulation are confirmed and better bit error rate （BER） performances are obtained.
A software synchronous optical sampling system is constructed based on sum frequency generation （SFG） in periodically poled lithium niobate （PPLN）. Five gigahertz of a non-return-to-zero （NRZ） data signal is sampled by sampling pulse with the repetition frequency of 29.31 MHz. The power of the SFG light is set at 23 dBm, and an eye diagram is successfully recovered. A band-pass filter is added before the sampling pulse is subjected to erbium-doped fiber amplifier to reduce gain competition and ensure a high power level of SFG.
