We propose and demonstrate a novel four-wavelength erbium-doped fiber laser using four-wave mixing (FWM). By inserting a length of highly nonlinear photonic crystal fiber (HNPCF) in the laser cavity and using two fiber Bragg gratings as the wavelength-selecting components, four stable wavelengths with equal spacing have been realized at room temperature. The energy-conversion-induced loss caused by the FWM, which happens in the HNPCF among the two oscillating laser lines and the FWM products, is believed to contribute to the stable multiwavelength operation by suppressing the wavelength competition between the two laser lines.
Picosecond soliton pulse train has been obtained from a passively mode locked erbium-doped ring fiber laser. The passive mode-locking mechanism that is at play in this laser relies on the modulational instability (MI) theory. By accurately adjusting the polarization setting of the circulating cavity light, the repetition rate can be tuned from 58 to 114GHz. Theoretical explanation is also given.
We report the temperature-independent measurement of displacement based on the chirp tuning of a fiber grating and a specially designed cantilever. The 3-dB bandwidth of the chirped grating changes linearly with displacement and is independent of the temperature. The displacement can be monitored directly by measuring the reflected light from the chirp grating. A linear displacement response of 37.063 mV/mm was obtained. The fluctuation of the output signal is less than 5% for a temperature range from 20 to 60°C without any temperature compensation technique. The sensor has potentially low cost due to its simple structure.
We report on a narrow band optical fiber filter utilizing a multimode fiber Bragg grating and fiber mode scrambler in order to tune its reflectivity that is useful as variable optical reflector and strain sensor. A change of reflectivity from 81% to 2% is achieved. We develop a novel fiber Bragg grating strain sensor that allows strain to be applied in the portion of the multimode fiber without grating. Particular advantages of this strain sensor are simple design, low system cost and high sensitivity. A strain sensitivity of 0.0013%/microstrain in change of reflectivity and large dynamic range (0-7,000 microstrain) are demonstrated. The strain sensitivity can be improved greatly by using efficient mode conversion structure in the device.
A temperature-independent displacement sensor is demonstrated using a chirped fiber grating and a specially designed cantilever. The 3-dB bandwidth of the chirped grating changes linearly with displacement and is independent to the temperature. Linear displacement response of 37.063mV/mm was obtained. By measuring the reflected light from the chirp grating, the displacement can be monitored directly. The sensor has potentially low cost due to its simple structure.
The polymeric cross-linked hydrogel doped with dye 4- nitroaniline was prepared. The nonlinear optical properties of this material has been studied. The optical storage effects and the dynamic lens effects in this dye doped hydrogel under laser radiation have been observed. It is reasonable to show that this dye doped polymer get will find some applications in optical signal processing.