A short pulse self-starting mode-lock fiber laser with femtosecond pulse width and high repetition rates is demonstrated. The oscillator features linearly cavity employing WDM system with a piece of Yb doped fiber. Semiconductor saturable absorber mirror (SESAM), with modulation depth of 30% and relaxation time of 4 ps, is employed. Two chirped fiber Bragg gratings are adopted. One FBG is placed in the cavity, with wide reflection near 1053nm. It compensates for the residual dispersion of the oscillator cavity elements and serves as an output coupler for the oscillator. The other FBG is placed out of the cavity to compress the pulse width further more. The length of laser cavity is around 10m. This modelock laser can self-start. Pulses as short as 225 fs pulse widths at repetition rates of 20 MHz are generated, with average output power is about 5mW. As all of the optical fiber components are small or bendable, the size of this laser is as tiny as Φ60mm×15mm.This femtosecond mode-lock all fiber laser affords a compact, novel and high-efficiency approach as seed source in the FrontEnd in inertial confinement fusion (ICF) laser illumination schemes.
Hi-Bi FBGs were employed and embedded in multi-layer composite films (Tedlar + Dacron +Mylar) to monitor temperature and tension. The temperature and tension characteristics of those embedded FBGs were demonstrated quantitatively. The Bragg wavelengths of embedded FBGs shift linearly with the temperature and tension loading on the multi-layer composite films. The slow-axis mode and the fast-axis mode of the Hi-Bi FBGs have different temperature sensitivity and tension sensitivity. The Hi-Bi FBGs have higher temperature sensitivity at low temperature than that at high temperature. Compared with non-embedded, the tension sensitivity of the embedded Hi-Bi FBG increased from 0.01424nm/N and 0.01439nm/N to 0.01516nm/N and 0.01532nm/N, respectively corresponding to the slow-axis mode and the fast-axis mode.
In this paper, a practical single-frequency high-repetition linearly-polarized eye-safe all-fiber laser with constant peak power is demonstrated. It is based on master-oscillator power amplifier (MOPA) system. A distributed feedback laser diode simulating at 1550nm with narrow linewidth of 2.3 kHz is employed as the seed source. It is modulated to a pulse laser with high repetition of 20 kHz and peak power of 10mW by an acousto-optic modulator (AOM). The pulse width is tunable between 100ns to 400ns. Two-stage cascade amplifier is established, which consists of a pre-amplifier and a power-amplifier. Amplified spontaneous emission (ASE) and stimulated billion scattering are well suppressed by special management. The output peak power of 30W is obtained, which has nearly diffraction-limited beam quality. It operates in linewidth of 1.2MHz, polarization-extinction ratio (PER) of 25dB and signal-to-noise ratio (SNR) of more than 40dB. Gain of the whole amplifier achieves nearly 35dB. Furthermore, an embedded control system (ECS) based on the WinCE operating system (OS) and the chip of S3C2440 is proposed. This control system based on closed-loop feedback technology makes the peak power keeping constant even the pulse width tunable, which is convenient for the end user of the radar. This robust portable laser is remarkable and fulfills the desire of coherent detection excellently.
The five of FBG were embedded in the PE sheath of a tether optical cable, which has about 18mm diameter and 7000mm length. The temperature and tension characteristics of the FBGs embedded in the polythene (PE) sheath had been demonstrated quantitatively. The Bragg wavelength of the embedded FBG shift linearly with the change of pulling force loaded on the tether optical cable and its tension sensitivity is about 3.75 pm/kg. The results of temperature experiment suggest the embedded FBG have been sensitized by PE material, so that its temperature sensitivity increase from 9.37pm/°C to about 12.51pm/°C.
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