Mid-infrared sources based on the soliton self-frequency shift

We present a method to maximize the soliton self-frequency shift (SSFS) in microwires with diameter profiles varying nonuniformly along the soliton propagation path. The method is divided into two steps. The first step consists in selecting the input microwire diameter that leads to the highest rate of frequency shift per unit of propagation length. The second step consists in increasing gradually the microwire diameter along the soliton path to suppress dispersive wave emission and maintain a large rate of frequency shift per unit of propagation length. We first propose and apply a rule to select the initial diameter using the adiabatic theory. The optimal diameter profile is then achieved by maintaining the redshifting soliton at a fixed spectral separation from the zero-dispersion wavelengths. The optimized profile supports solitons with different input energies that allow a wavelength shift up to 650 nm from the 2100 nm pump wavelength in a 20 cm microwire length. We compare our results with the SSFS generated in microwires with uniform diameter profile to illustrate the enhancement of wavelength shift in the designed nonuniform microwire. (C) 2012 Optical Society of America