Experimental demonstration of a photonic-crystal-fiber optical diode

Two cascaded hollow-core photonic-crystal fibers with slightly shifted, but still overlapping, transmission peaks are shown to function as an optical diode for ultra-short laser pulses. Submicrojoule 100-fs Ti:sapphire laser pulses with a spectrum falling within the passband of one of the fibers, but outside the passband of the second fiber, experience spectral broadening due to self-phase modulation in the first fiber. A part of this self-phase-modulation-broadened spectrum is then transmitted through the second fiber. Identical short pulses propagating in the opposite direction are blocked by the second fiber with a shifted passband. A forward-to-backward signal ratio exceeding 40 is achieved with the created photonic-crystal fiber diode for 0.9-muJ, 100-fs pulses of 800-nm Ti:sapphire laser radiation.