Optimization control of modulation-instability gain in photonic crystal fibres with two zero-dispersion wavelengths

We design three kinds of photonic crystal fibres （PCF） with two zero-dispersion wavelengths （ZDWs） using the improved full vector index method （FVIM） and finite-difference frequency domain （FDFD} techniques. Based on these designed fibres, the effect of fibre structure, pump power and wavelength on the modulation instability （MI） gain in the anomalous dispersion region close to the second ZDW of the PCFs is comprehensively analysed in this paper. The analytical results show that an optimal MI gain can be obtained when the optimal pump wavelength （1530 nm） is slightly shorter than the second ZDW （1538 nm） and the optimal pump power is 250 W. Importantly, the total MI gain bandwidth has been increased to 260 nm for the first time, so far as we know, for an optimally-designed fibre with ∧ = 1.4 nm and d/∧ = 0.676, and the gain profile became much smoother. The optimal pump wavelength relies on the second ZDW of the PCF whereas the optimal pump power depends on the corporate operation of the optimal fibre structure and optimal pump wavelength, which is important in designing the most appropriate PCF to attain higher broadband and gain amplification.

Device Length Dependency of Cross Gain Modulation and Cross Phase Modulation in Semiconductor Optical Amplifier

The cross gain modulation, the cross phase modulation and their recovery time in the SOAs with the various lengths were experimentally investigated. It was found that these values strongly depended on the device length.

Ultrafast Raman fiber laser:a review and prospect

Ultrafast Raman fiber laser has been proved to be an effective method to obtain ultrafast optical pulses at special wavelength.Yet,compared with conventional rareearth doped counterparts,it is challenging for Raman fiber lasers to generate pulses with high pulse energy and short pulse duration.Here,we review three categories of ultrafast Raman fiber laser technologies and give detailed discussions on the advantages and challenges of each.In regards to mode-locking,different saturable-absorbers-based fiber lasers are compared and their common problem resulting from long cavity length are discussed.In terms of synchronously-pumping,several approaches to match the repetition rate of pulsed pump with the length of Raman fiber cavity are discussed,while the technical complexity of each method is analyzed.Moreover,the recently developed technology termed as nonlinear optical gain modulation(NOGM)is introduced,which turns out to be a simple and quality solution to generate highenergy femtosecond pulses with wavelength agility.Compared with the others,NOGM gathers various advantages including simple structure,long-term stability,high pulse energy and short pulse duration,which may effectively promote application expansion of ultrafast Raman fiber laser in the near future.

Micro EEG/ECG signal's chopper-stabilization amplifying chip for novel drycontact electrode

Facing the body＇s EEG（electroencephalograph, 0.5–100 Hz, 5–100 μV） and ECG＇s（electrocardiogram,〈 100 Hz, 0.01–5 mV） micro signal detection requirement, this paper develops a pervasive application micro signal detection ASIC chip with the chopping modulation/demodulation method. The chopper-stabilization circuit with the RRL（ripple reduction loop） circuit is to suppress the ripple voltage, which locates at the single-stage amplifier＇s outputting terminal. The single-stage chopping core＇s noise has been suppressed too, and it is beneficial for suppressing noises of post-circuit. The chopping core circuit uses the PFB（positive feedback loop） to increase the inputting resistance, and the NFB（negative feedback loop） to stabilize the 40 dB intermediate frequency gain. The cascaded switch-capacitor sample/hold circuit has been used for deleting spike noises caused by non-ideal MOS switches, and the VGA/BPF（voltage gain amplifier/band pass filter） circuit is used to tune the chopper system＇s gain/bandwidth digitally. Assisted with the designed novel dry-electrode, the real test result of the chopping amplifying circuit gives some critical parameters： 8.1 μW/channel, 0.8 μVrms（@band-widthD100 Hz）, 4216–11220 times digitally tuning gain range, etc. The data capture system uses the NI CO＇s data capturing DAQmx interface,and the captured micro EEG/ECG＇s waves are real-time displayed with the PC-Labview. The proposed chopper system is a unified EEG/ECG signal＇s detection instrument and has a critical real application value.