Ultrafast All-Optical Cross-Switching Schemes as Logical Operations Based on Dual-Wavelength Interaction in Soft Glass Multicore Fiber

Coupled nonlinear waveguides represent a promising approach for all-optical signal processing tasks with useful applications in telecom, quantum information, and spectroscopy. This contribution focuses on a study of a multicore, highly nonlinear soft glass fiber with advantageous properties allowing self-switching [1] or cross-switching [2] of sub-100 fs pulses at low switching energies. Following our preliminary achievements, we performed an in-depth analysis of the dual-wavelength nonlinear switching potential of the fiber containing five separated dual-core units (DCUs) with different degrees of asymmetry (Fig. 1a). A complex study was performed, sequentially addressing all 5 DCUs under fiber length optimization and various control-signal beam input combinations. The experimental setup has been detailed in [2]. It consists of two synchronized fs sources operating at a 1 kHz repetition rate: 1) a 1030 nm, 250 fs control source from a commercial ultrafast Yb:CaF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> amplifier, and 2) a 1550 nm, 80 fs signal source from an optical parametric amplifier, pumped by the second harmonic of the basic amplifier. The two pulse sequences were combined into a single beam with a dichroic mirror, temporally synchronized, and the energy of the signal pulses was set to 100 pJ to ensure their linear propagation. The nonlinear switching was controlled by varying the control pulse energy in the range of 1–10 nJ, and the combined beams were coupled into the fiber using a 50x microobjective. The fiber's output facet was imaged onto the chip of an IR camera by another 40x microobjective. Independent alignment of the signal beam was ensured by a tunable telescope and a mirror situated before the dichroic mirror. Selective launching of the control and signal beams into one of the two fiber cores was realized in a way that allowed four combinations for each DCU. Series of signal field output spatial distributions were registered by the camera as a function of control pulse energy for each combination. After processing the results, graphs of dual-core signal extinction ratio (ER <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$=10\log(E_{1}/E_{2})$</tex> in dB, where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{1,2}$</tex> is the output energy in the corresponding core) vs. input control pulse energy were created, depending on DCU selection, control/signal input combination, and fiber length.