Remote characterization of nonlinear distortions in ultrashort pulses transmitted through dynamic fiber optic links

Ultrashort pulse sources are complex and resource-intensive. To reduce overhead and simplify operations, we had previously developed a method to deliver ultra-short pulses through fiber-optic links to multiple locations and to characterize them remotely using a compact detector module. We created a pulse pair with varying delays at the central location using a pulse shaper before launching them into the fiber links and measured the first and second-order autocorrelations at the satellite location. However, this method proved inadequate for detecting the effects of optical nonlinearities as the spectral broadening seen by a pulse pair with varying degrees of overlap differs from that of a pair of pulses undergoing nonlinear broadening separately. To overcome this drawback, we propose to launch a variable-delay pulse pair with no temporal overlap to avoid combined nonlinear distortions in the fiber link and measure the autocorrelations at the output by adding a fixed-delay interferometer to our detector module. The in-house fabricated fixed-delay element consisted of a quartz plate with its surfaces coated by partially reflecting Bragg mirrors. Using this modified setup, we have been able to detect the nonlinear distortions encountered by sub∼400fs pulses in the delivery links.