The Study On The Incoherent Combination Of Near-infrared Supercontinuum Source

The high brightness and broad spectrum of supercontinuum source make it have extensive application prospects in the fields of communication technology,spectroscopy,metrology,biomedicine,photoelectric countermeasures and so on.Supercontinuum generation in fiber amplifiers has both high output power and broad spectrum due to the synchronization of the power amplification and the signal wavelength broadening.Fiber amplifier has simple construction and high optical-optical efficiency.However,the highest output power level is limited by the redundant power leaked from the gain fiber and also the small core diameter of the output fiber.In order to increase the power of supercontinuum source,we study theoretically and experimentally the incoherent power combination of supercontinuum source based on Yb-doped fiber amplifier.The main content of the study is as follows:According to the fabrication method and design philosophy of fiber power combiner,a 7×1 combiner is simulated.The input and output optical fields at different wavelengths are calculated,which illustrates that the stimulated combiner has the same high power combining efficiency in the spectral range from 1060 nm to 1700 nm but the output beam quality deteriorates with increasing signal wavelength.The combining effects of light propagating in the center/surrounding input fibers of the combiner are also compared and the result illustrates that when the signal propagates in the surrounding input fibers,the power combining efficiency and output beam quality decreases simultaneously.When seven light beams are launched into the input fibers,the whole power combining efficiency of the input is higher than 98% covering the whole spectral region of 1060-1700 nm,which proves the feasibility of supercontinuum incoherent power combination.Based on the simulated design,a broadband fiber power combiner is fabricated.Seven high power fiber amplifiers are set up based on a picosecond pulsed laser as the seed and three-stage master oscillator power amplifier configuration.With the detailed structure of one amplifier is presented as an instance.Seven supercontinuum sources with output powers at one hundred level and spectra covering 1060-1700 nm are obtained in the seven main amplifiers with a seed pulse repetition frequency of 10 MHz and pulse width of 100 ps.The home-made fiber combiner is used in the incoherent power combination experiments.Two amplifiers are combined firstly with low output power.With the repetition frequency of the seed pulse tuned to be 1 MHz,the output spectra of the two amplifiers broaden to 1700 nm with low output power.The comparison of the output and the input spectra shows the combiner has the same power combining efficiency over 1060-1700 nm.Later high power experiment proceeds with using the seven amplifiers.When transmitting alone,the power combining efficiencies of each input supercontinuum source are all higher than 90% and the output spectra are almost the same as the input,which illustrates that the combiner works steadily when the input power of each input fiber is higher than 100 W.By combining the seven sources together,a beam of supercontinuum source with an output power of 802 W,spectrum covering 1060-1700 nm and beam divergence angle of 80 mrad is obtained in the output fiber.