Modulation instability initiated high power all-fiber supercontinuum lasers and their applications

Abstract

High average power, all-fiber integrated, broadband supercontinuum (SC) sources are demonstrated. Architecture for SC generation using amplified picosecond/nanosecond laser diode (LD) pulses followed by modulation instability (MI) induced pulse breakup is presented and used to demonstrate SC sources from the mid-IR to the visible wavelengths. In addition to the simplicity in implementation, this architecture allows scaling up of the SC average power by increasing the pulse repetition rate and the corresponding pump power, while keeping the peak power, and, hence, the spectral extent approximately constant. Using this process, we demonstrate >10W in a mid-IR SC extending from ∼0.8 to 4μm, >5W in a near IR SC extending from ∼0.8 to 2.8μm, and >0.7W in a visible SC extending from ∼0.45 to 1.2μm. SC modulation capability is also demonstrated in a mid-IR SC laser with ∼3.9W in an SC extending from ∼0.8 to 4.3μm. The entire system and SC output in this case is modulated by a 500Hz square wave at 50% duty cycle without any external chopping or modulation. We also explore the use of thulium doped fiber amplifier (TDFA) stages for mid-IR SC generation. In addition to the higher pump to signal conversion efficiency demonstrated in TDFAs compared to erbium/ytterbium doped fiber amplifier (EYFA), the shifting of the SC pump from ∼1.5 to ∼2μm is pursued with an attempt to generate a longer extending SC into the mid-IR. We demonstrate ∼2.5 times higher optical conversion efficiency from pump to SC generation in wavelengths beyond 3.8μm in the TDFA versus the EYFA based SC systems. The TDFA SC spectrum extends from ∼1.9 to 4.5μm with ∼2.6W at 50% modulation with a 250 Hz square wave. A variety of applications in defense, health care and metrology are also demonstrated using the SC laser systems presented in this paper.