Study of ultrafast optical signal processing using polarization bistable VCSELs

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We investigated mainly the following three topics to create new nonlinear optical functional devices based on the pitchfork bifurcation bistable operation of vertical-cavity surface-emitting lasers (VCSELs) and injection of spin-polarized electrons.(1)We studied the bistable switching between the two orthogonal polarization modes existing in the VCSEL with a squared shape waveguide. As one important all-optical signal processing, we have shown by our simulations that the 3R function (Retiming, Reshaping, and Regenerating) can be obtained using such a VCSEL. This 3R regeneration has a large optical gain of 16 dB for 10 Gbit/s and the optical gain was reduced with an increase in bit rate. The ON-OFF ratio is improved by the 3R regeneration up 100 Gbit/s.(2)We have proposed the optical buffer memory using a two-dimensional array of the ultrafast polarization bistable VCSELs. Optical buffer memory is an important device for photonic packet switching. First, the polarization of the VCSELs are reset by an optical reset pulse. Ultrafast optical signals are converted to spatially parallel signals and injected into the VCSELs together with optical set pulses. Only when the optical signals and the optical set pulses are simultaneously injected into the VCSELs, the VCSELs change their polarization. Therefore, the VCSELs emit the outputs with the polarizations which depend on '0' and '1' of the input signal. The output signal pulses are created from the CW 0°output of the VCSELs and are converted to an ultrafast optical signal.(3)We investigated the electric field dependence of electron spin relaxation during transport in GaAs at 10K. Spin polarizations of photogenerated electrons were measured before and after drifting in the 2μm region of GaAs under photoluminescence from quantum wells. We have found direct evidence that the electron spin relaxation during the drift is accelerated in the higher electric field.