Point-by-point fiber gratings inscription by using high repetition rate femtosecond laser

Abstract

A point-by-point long period fiber grating inscription by using femtosecond photonic crystal fiber laser with high repetition rate has been studied experimentally. A fabrication platform was designed and built up, which was composed of a laser focusing system, a real-time imaging observation system and a precision three-dimensional positioning stage. In order to ensure quality of the fabricated fiber grating, the machining process was real-time monitored using a CCD camera and the transmission spectrum was real-time measured using a spectrometer. To reduce manual error in operation, a control program was coded by self-written LabVIEW program, which can realize the synchronous control of the 3D micro-positioning platform and the electronic high speed shutter. In the experiments, the femtosecond laser came from a high-power large-mode-area Yb3+-doped photonic crystal femtosecond fiber amplifier system, delivering laser pulses with an maximum power of 18W, a pulse width of 66.5fs, a central wavelength of 1040nm, and at a repetition rate of 52MHz after pulse compression. Fiber gratings with the duty ratio of 1/2 and the period of 400μm have been fabricated by point-by-point inscription technique. The measured transmission spectra indicate that the fiber gratings have good spectral properties. The experimental result exhibit the good micromachining ability of femtosecond photonic crystal fiber laser, which will lead to more and more applications in the future.