Coherence measurements of supercontinuum source based on a fiber laser and highly nonlinear dispersion shifted fiber

We constructed a passively mode-locked Er-doped fiber laser (PML-EDFL). It generates ∼ 1.3 ps pulses at a repetition rate of 12 MHz with an average output power of 0.7 mW. These pulses are amplified in a short Er-doped fiber amplifier (EDFA) which is composed of low nonlinearity EDF. The average power of amplified pulse is about 15 mW. And its pulse width is about 880 fs. An all-fiber supercontinuum (SC) is generated by putting the amplified fiber laser pulse at the wavelength of 1. 56 μm into the highly nonlinear dispersion shifted fiber (HN-DSF) whose zero dispersion wavelength is 1.537 μm and nonlinear coefficient is about 10.5/W/km at the input wavelength. The polarization state of the generated SC spectra is well defined such that it can be properly controlled by the polarization controller. By using a delayed pulsed method, we report an experimental study of the coherence of SC spectra generated through a HN-DSF. In this paper, the strong dependence of the spectral coherence on the HN-DSF length is observed experimentally. And optimal conditions for obtaining wide SC with high coherence are investigated in detail. We believed that our proposed all-fiber laser based SC source with high coherence has many important applications in recently developed frequency-domain measurement techniques such as optical coherence tomography (OCT), optical frequency domain imaging (OFDI), optical frequency domain reflectometry (OFDR) and their instrumentation.