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.
The operational parameters including the polarization controlling and the pump power in a nonlinear polarization rotation-based passively mode-locked fiber laser are studied in this paper.The carrier rate equations of the activated erbium-doped fiber are first employed together with the nonlinear Shro¨dinger equations to reveal the relation between the operational parameters and the output state of the passively mode-locked fiber laser.The numerical and experimental results demonstrate that the output state of the mode-locked laser varies with the polarization controlling and the pump power.The periodicity of the polarization controlling is observed.With given pump power,there exists a set of polarization controlling under which the ultra-short pulse can be generated.With given polarization controlling,the mode-locked state can be maintained generally except for some particular values of pump power.Three shapes of the output optical spectra from the fiber cavity can be identified when the pump power changes.The results in this paper provide a comprehensive insight into the operation of the nonlinear polarization rotation-based passively mode-locked fiber laser.
A novel design of optical sampling system has been developed by using sum-frequency generation （SFG） in a periodically-poled lithium niobate （PPLN） waveguide and using passive mode-locked fiber laser pulses as optical sampling pulses. The system achieved high temporal resolution and high sensitivity using a 30 mm length PPLN with quasi phase match period of 19.3 μm and 151 fs sampling pulses which were generated by passive modelock fiber laser based on nonlinear polarization rotation （NPR）. Clear eye-diagram of 10 Gbit/s non-return-to-zeros （NRZ） pseudorandom binary sequence （PRBS） optical signal were successfully reconstructed by this system.
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.
