Abstract
All-optical control of Surface Plasmon Polaritons (SPPs) can switch light with high speed and a large signal to noise ratio. We demonstrate 25 ps-time scale switching of continuous wave light by pump pulses copropagating in the same single mode fiber at different wavelengths near 1550 nm. The switching is due to hot carriers from the SPPs in a 45 nm-thin gold coating on the fiber cladding. The SPPs are generated by pump pulses coupled from the core to cladding modes by a tilted fiber Bragg grating (TFBG). Hot carriers modify the complex permittivity of the metal coating on a time scale of the order of picoseconds and hence the cladding mode resonance wavelengths of the TFBG. A probe light signal copropagating in the same fiber can therefore be modulated by the transmission resonance shifts. With 25 ps pulses at 1540.4 nm and 1 MHz and 50 mW average power, the modulation depth of a CW probe at 1543.4 nm copropagating in the core reached 4.5% ± 1% with a pulse width broadened to 56 ps. Under these conditions, the pump power density was 0.147 GW/cm2 in the metal layer, for a conversion efficiency as high as 30% ± 7% per GW/cm2. Since many other plasmonic and nonlinear active materials can be deposited on fiber claddings, we believe that this very simple all-fiber configuration to perform all-optical switching of core-guided light in single mode fibers by plasmon-modulated resonances has strong potential applications in studies of light-matter interactions over fast and ultrafast time scales.
Highlights
Surface Plasmon Polaritons (SPPs) provide an effective way to confine electromagnetic fields to sub-micrometer thick layers near the surface of metals, and excitation of SPP at femtosecond time scales can initiate a cascade of linear and nonlinear processes with multiple outcomes such as nonradiative decay to carriers and phonons and radiative decay via emission of photons.1–4 Such processes have opened new avenues toward the realization of ultrafast nanophotonic devices for all-optical signal processing in high speed telecommunication networks, but one of the major challenges is how to achieve fast and efficient switching or modulation of light by SPPs without excessive insertion losses in fiber or optical waveguide systems
When generating SPPs by interband transition pulsed pumping on the other hand, hot carriers are generated on femtosecond time scales in the metal and they strongly modify the complex permittivity on the same time scale
The spectral width over which the SPP excitation is possible for an optimal gold thickness and low roughness is still quite larger than the wavelength spacing between the grating resonances of the modes of the fiber cladding which means that pumping and probing of the complex permittivity can be carried out simultaneously with different wavelengths copropagating simultaneously in the single mode core
Summary
Surface Plasmon Polaritons (SPPs) provide an effective way to confine electromagnetic fields to sub-micrometer thick layers near the surface of metals, and excitation of SPP at femtosecond time scales can initiate a cascade of linear and nonlinear processes with multiple outcomes such as nonradiative decay to carriers and phonons and radiative decay via emission of photons. Such processes have opened new avenues toward the realization of ultrafast nanophotonic devices for all-optical signal processing in high speed telecommunication networks, but one of the major challenges is how to achieve fast and efficient switching or modulation of light by SPPs without excessive insertion losses in fiber or optical waveguide systems. Surface Plasmon Polaritons (SPPs) provide an effective way to confine electromagnetic fields to sub-micrometer thick layers near the surface of metals, and excitation of SPP at femtosecond time scales can initiate a cascade of linear and nonlinear processes with multiple outcomes such as nonradiative decay to carriers and phonons and radiative decay via emission of photons.1–4 Such processes have opened new avenues toward the realization of ultrafast nanophotonic devices for all-optical signal processing in high speed telecommunication networks, but one of the major challenges is how to achieve fast and efficient switching or modulation of light by SPPs without excessive insertion losses in fiber or optical waveguide systems. When generating SPPs by interband transition pulsed pumping on the other hand, hot carriers are generated on femtosecond time scales in the metal and they strongly modify the complex permittivity on the same time scale. Such changes can be used to build modulators and switches from nonlinear effects in guided wave interferometers and resonators operating at sub-picosecond time scales. The issue with interband pumping is that it necessitates pump photons at wavelengths much shorter than the telecommunication bands in the near infrared
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