Mid-infrared supercontinuum generation for WDM applications using chalcogenide photonic crystal fiber

Abstract In this study, the design and characterization of a photonic crystal fiber (PCF) as a light source for a mid-infrared supercontinuum generation (SCG) is presented. This PCF is based on a highly nonlinear chalcogenide $${\text{As}}_{40}{\text{Se}}_{60}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mtext>As</mml:mtext> <mml:mn>40</mml:mn> </mml:msub> <mml:msub> <mml:mtext>Se</mml:mtext> <mml:mn>60</mml:mn> </mml:msub> </mml:mrow> </mml:math> background material with a hexagonal structure arrangement of air-holes rings. The PCF parameters such as the chromatic dispersion (D), the effective refractive index ( $${n}_{eff}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi>eff</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) and the nonlinear coefficient (γ) have been investigated. We study the stimulated SCG in two types of dispersion regimes: anomalous and all-normal dispersion (ANDi). We initiate the study by sending a 28.4 fs wide optical pulse with a peak power of 10 kW and a central wavelength of 2.8 µm through a 2 cm long PCF. In the anomalous dispersion, we demonstrate the generation of coherent and broadband SCG spectrum spanning the wavelength region from 1.6 to 7.8 µm. While, in the ANDi regime we demonstrate the generation of a broad, ultra-flat-top and highly coherent SCG spectrum extending from 2 to 4 µm at 6 dB spectral flatness. Thus, we achieve ultra-flat SCG spectrum source with a bandwidth as wide as 2400 nm within only 2 cm propagation length of the proposed PCF. This spectrum range is very suitable for variety of applications in mid-infrared region such as optical metrology, frequency comb generation, and optical coherence tomography (OCT). Results further demonstrate that with an applied pump power of 15 kW through the ANDi regime, a flat spectral bandwidth of 380 nm (wavelengths ranging from 1260 to 1640 nm) at just 3 dB spectral flatness is achieved. This band covers the five-telecommunication optical bands O-, E-, S-, C- and L-bands that comply with ITU-T-compliant wavelengths for wavelength division multiplexing (WDM) applications like coarse WDM (CWDM) and dense WDM (DWDM).