Abstract-We investigate nonlinear carrier dynamics in a multiquantum-well semiconductor optical amplifier (SOA) in the context of ultrafast all-optical logic. A rate-equation model is presented that accounts for two-photon absorption, free-carrier absorption, self-and cross phase modulation, carrier heating, spectral, spatial hole burning, and self-and cross polarization modulation. The nonlinear refractive index dynamics is investigated theoretically and experimentally. We find nonlinear phase changes larger than radians, which recovers on a timescale in the order of 1 ps. We also investigate a nonlinear AND gate that consists of an SOA that is placed in an asymmetric Mach-Zehnder interferometer. We show that the gate can be operated using 800-fJ optical pulses with duration of 200 fs while having a contrast ratio larger than 11 dB.Index Terms-Optical logic, optical signal processing ultrafast carrier dynamics, semiconductor optical amplifier.
We, for the first time, present the ultrafast optical nonlinear response of a hydrogenated amorphous silicon (a-Si:H) wire waveguide using femtosecond pulses. We show cross-phase and cross-absorption modulations measured using the heterodyne pump-probe method and estimate the optical Kerr coefficient and two-photon absorption coefficient for the amorphous silicon waveguide. The pumping energy of 0.8 eV is slightly lower than that required to achieve two-photon excitation at the band gap of a-Si:H (approximately 1.7 eV). An ultrafast response of less than 100 fs is observed, which indicates that the free-carrier effect is suppressed by the localized states in the band gap.
We have developed a Mach-Zehnder interferometric all-optical switch employing intersubband transition in an InGaAs∕AlAs∕AlAsSb-coupled double quantum well waveguide. The recently discovered cross-phase modulation phenomenon was utilized as the switching mechanism; the nonlinear index of refraction for transverse electric polarized light is induced by intersubband optical excitation using transverse magnetic pump light. We demonstrate the demultiplexing operation of 160Gbit∕s data signals to 10Gbit∕s using this switch. At the input control pulse energy of 8pJ, the demultiplexed signals showed an extinction ratio better than 10dB, and an error-free demultiplexing was achieved.
We demonstrate a low-crosstalk 2 x 2 thermo-optic switch with silicon wire waveguides. The device is based on a 2 x 2 array of Mach-Zehnder interferometer (MZI) switches. Lowest crosstalk levels of -50 dB and -30 dB are obtained for 'bar' and 'cross' switching states, respectively. An intersection in the switch is important for low-crosstalk operation. The power consumption of one MZI element switch is 40 mW and the total power consumption of the device is at most 160 mW.
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