In this paper, we propose a push-pull type double fiber Bragg gratings liquid level sensor. It consists with two-matched fiber Bragg gratings and converts the shift of optical wavelength into output power according to the matching relationship between transmission spectrum and reflection spectrum of gratings. The output power of the optical sensor is linearly changed with liquid level by utilizing the push-pull structure. The liquid level sensor achieves self-demodulation, which greatly simplifies the sensing structure.
A waveform generation scheme based on complex filter and frequency-time mapping is proposed. In the experiment, a programmable processor was used for the complex filter. The shape of the spectrum is controlled by the amplitude frequency response, and the second order phase is controlled by the phase frequency response to realize frequency-time mapping. In experiment, rectangular pulse, sawtooth pulse and comb lines are realized by adjusting the complex filter. The influence of dispersion and spectral 3dB bandwidth on the time domain waveform is also analyzed. The proposed waveform generation is dynamically adjustable due to the dispersion is continuously tunable.
We consider the continuous wave propagation in a highly dispersive and nonlinear medium wherein the wave
propagation is governed by the generalized nonlinear Schrodinger equation. We demonstrate the novel flat-top
modulational instability gain for a wide range of modulation frequencies in the anomalous dispersion regime of highly
dispersive and nonlinear media. We find that the resulting MI gain is independent of input power. Besides, we compare
the analytical results with those of numerical results.
The temporal characteristics of a fiber ring laser are reported. The laser has a simple configuration, which contains
an Erbium-doped fiber amplifier (EDFA), a polarization controller (PC) and a coupler. The EDFA has a high saturation
power of 27dBm to provide the gain in the cavity. The PC is used to control the polarization state of light. A 99/1
coupler is used to extract the laser output. There is no filter in the cavity to confine the spectrum of the laser. The simple
laser configuration can operate in different temporal modes with different pump power. In the self mode locking state,
the repetition rate is equal to the inverse of the round trip time of the cavity. The repetition rate of the laser can be
increased by increasing the pump power of the EDFA. This self mode locking phenomena is due to the homogeneous
gain medium in the cavity, rather than the nonlinear effect in the cavity. The nonlinear effect can suppress the self mode
locking phenomena by inserting a short length highly nonlinear fiber in the laser cavity.
A novel filter with tunable bandwidth and wavelength is introduced. Its bandwidth can be tuned by a transverse voltage. And its wavelength can be tuned by a longitudinal voltage. The main parameters that affect its properties are synthetically analyzed. Computer simulation results show that its transmission bandwidth is changeable and the transmission spectrum with rectangular working area is close to the ideal band-pass function. Experimentally, its free spectral range is more than 50nm. The tunable range of the center wavelength is about 50nm. The full width at half maximum can be tuned from 1.2nm to 50nm.