Microstructured Inline Optical Fiber Structure for Dispersion Control and Coherent Supercontinuum Generation

A microstructured optical fiber (MOF) structure with longitudinal dispersion variation is theoretically investigated for broad, coherent supercontinuum (SC) generation in the infrared (IR) region. The MOF possesses anomalous dispersion at 1550 nm but changes its dispersion to normal dispersion by a tapering process. The inline dispersion controlled structure provides a linear chirp and the subsequent pulse compression without additional components. The compressed pulse then seamlessly enters a short normal dispersion section for the coherent SC generation. Our simulation suggests that the inline structure can be as short as around 11.6 cm to realize the pulse compression and the SC generation. In particular, only 0.5-cm-long final normal dispersion section is required for the coherent SC generation, hence avoiding high background loss particularly in the spectral region above 2 $\mu\text{m}$, where silica glass absorption becomes considerably high. In the structure, the peak power of a pulse is enhanced by 14 times in the compression process, and the corresponding generated SC spectrum has a bandwidth of 1260 nm, extending to wavelengths above 2 $\mu\text{m}$. The simulation also shows that the generated spectrum is highly coherent. We experimentally demonstrated the dispersion shift from anomalous to normal dispersion with the microstructure fiber fabricated in-house.