Nonlinear ultrafast switching based on soliton self-trapping in dual-core photonic crystal fibre

Abstract

In this paper, we present a systematic numerical study of a novel ultrafast nonlinear switching concept based on soliton self-trapping in dual-core (DC) photonic crystal fibre (PCF). The geometrical parameters of highly-nonlinear (HN) DC microstructure are optimized with regard to desired linear and nonlinear propagation characteristics. The comparable magnitude of fibre coupling length and soliton period is identified as a key condition for presented switching concept. The optimized DC PCF design is subjected to detailed nonlinear numerical study. Complex temporal-spectral-spatial transformations of 100 fs hyperbolic secant pulse at 1550 nm in the DC PCF are studied numerically employing a model based on coupled generalized nonlinear Schrödinger equations solved by a split-step Fourier method. For the optimized DC structure, mutual interplay of solitonic and coupling processes gives rise to nonlinear switching of self-trapped soliton. The output channel (fibre core) for the generated soliton can be controlled via the input pulse energy. For vertical polarization, the optimal soliton switching with extinction ratio contrast of 32.4 dB at 10.75 mm propagation distance is achieved. Even better switching contrast of 34.8 dB can be achieved for horizontal polarization at optimal propagation distance of 10.25 mm. Besides energy-controlled soliton self-trapping switching, the fibre supports also nonlinear polarization switching with soliton switching contrast as high as 37.4 dB. The proposed fibre holds a high application potential allowing efficient ultrafast switching of sub-nanojoule pulses at over-Tb/s data rates requiring only about 1 cm fibre length.

All-optical switching based on soliton self-trapping in dual-core high-contrast optical fibre

“…Therefore, assuming an in-coupling efficiency of 32 %, in-fibre pulse energies are required only at the level of 32 pJ. It represents an improvement by factor of 3 to 4 in comparison to the previous theoretical air-glass PCF study [7].…”

“…Figure 5. shows an example of the spectral propagation maps (in dB scale) for two input energies and in the both fibre cores at λ = 1550 nm and T FWHM = 100 fs, representing interesting switching performance. In this case, the same excitation parameters were used, as those reported in [7] where an air-glass PCF was considered. The lowest excitation energy leading to soliton self-trapping in the non-excited core was identified as 100 pJ, while the same behaviour occurred in the excited core for energies close to 112 pJ.…”

“…According to this expectation we decided to explore spectral range of 1400 -1800 nm in the context of switching performance to explore the excitation wavelength effects. Similarly, the pulse width effect was studied in the experimentally available range of 75 -150 fs, since we expected that it may influence also the character of the solitonic propagation (see equations (7) and (8)). We analysed the switching performance for different combinations of excitation wavelength and pulse width and compared to the case of 1550 nm, 100 fs.…”

Nonlinear performance of asymmetric coupler based on dual-core photonic crystal fiber: Towards sub-nanojoule solitonic ultrafast all-optical switching

“…A new generation DC PCF with hexagonal microstructure and enhanced nonlinear performance potential ( Fig. 1a) was self-designed [20]. In-house synthesized highly nonlinear glass (PBG08) with well determined linear and nonlinear properties was used for fabrication of the fiber samples in correspondence to the theoretical optimization process.…”

“…Strongly modulated spectra and narrower features are caused by higher soliton number (N~10 at 1 nJ in-coupled pulse energy), determined mainly by high nonlinear refractive index of the utilized glass. Considering the enhancement of n NL by 20-times, we expected even smaller switching energies in the case of totally symmetric structure [20]. However, in the real asymmetric structure, energies approaching 1 nJ are required to fulfill the nonlinear asymmetry balancing condition (5) in order to obtain true switching performance.…”