We present a soliton order preservation mechanism leading to broad tunability with high energy conversion efficiency (ECE) from a fiber-based soliton self-frequency shift (SSFS) system. Here, a pulse compressing fiber, placed before the Raman shifting nonlinear fiber (NLF), acts as a soliton order preserver. Thanks to this passive mechanism, the soliton order at the input of the NLF is preserved within 2.080% is maintained over a tunable range as large as 180 nm in a passive fiber-based SSFS system. Solitons are also tunable up to 320 nm in the wavelength range of1.96-2.28 µm with ECE>50%. Such a soliton order preservation mechanism that enables a high ECE while maintaining a broad soliton tunability is of utmost practical interest for wavelength conversion systems.

Emerging applications in the mid-infrared (MIR) stimulate the growth and development of novel optical light sources. Soliton self-frequency shift (SSFS) in soft glass fiber currently show great potential as an efficient approach towards the generation of broadly tunable femtosecond pulses in the MIR. In this work, we demonstrate highly efficient tunable soliton source based on SSFS in chalcogenide glass. We show a simple and fully fiberized system to generate these continuously tunable Raman solitons over a broad spectral range of 2.047-2.667 μm, which consumes no more than 87 pJ per pulse. The spectral measurements suggest that the generated pulses are as short as 62 fs with a maximum power conversion efficiency of 43%. This result is realized thanks to an 8 cm long As2S3 microstructure optical fiber tapered into a microwire. Thanks to their broad transparency, their high nonlinearity and their adjustable chromatic dispersion, chalcogenide microwires are promising components for the development of compact, low power consumption and highly efficient MIR optical sources.