Format Conversion Based On Cross-Phase Modulation In Silicon Nanowire Photonics Waveguides

Different optical networks require different optical modulation formats. Thanks to simple modulation and demodulation equipment and low cost, on-off keying (OOK) format is usually used in metropolitan area networks, while differential phase-shift keying (DPSK) is generally used in long-haul transmission networks due to its theoretical3-dB receiver sensitivity advantage for balanced detection and better tolerance in fiber nonlinearities. Thus, all-optical format converters are necessary at the interface of different networks to ensure that each optical network transmits optimal format.Because of its advantageous linear and nonlinear optical properties with the mature CMOS fabrication technology and tight mode confinement ability, silicon-on-insulator (SOI) is a promising platform for all-optical signal processing and optical device integration. This paper is mainly about the theory research on the modulation format convention from OOK to BPSK based on the cross phase modulation (XPM) in silicon waveguide.The theory model is established for XPM induced by interaction of two optical pulses in silicon nanowire waveguides. The nonlinear phase shift caused by XPM in silicon waveguides is numerically investigated by considering the influence of walk-off effect, group-velocity dispersion, and nonlinear losses including two-photon absorption (TPA) and free-carrier absorption (FCA). The nonlinear phase shift is tried to be enhanced through waveguide design and wavelength management. Low and flat dispersion is beneficial to acquiring a large nonlinear phase shift. The walk-off effect can be minimized by carefully choosing the zero dispersion wavelength of the used silicon waveguide and setting the signal and probe wavelengths symmetrically.Finally, the principle of format convention from OOK to BPSK based on XPM in silicon waveguides is provided. The difference is π between the maximum nonlinear phase shifts for the case that input signal is’1’and the case that the input signal is ’O’. Under this strategy format convention is realized from OOK to BPSK based on XPM in silicon waveguides. The performance of format converter is briefly analyzed.Our work provides some references for design and manufacture of integrated format converters in the future.