Study on ultra-fast optical memories using semiconductor lasers

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We have investigated mainly the following four topics to create ultra-fast optical memories by using laser diodes.(1) Polarization switching in strained quantum well laser diodes.The TE-TM mode switching in laser diodes was achieved using GaAsP/AlGaAs tensely strained quantum well for TM mode gain enhancement. The electrodewas devid into two, i.e., a main electrode and a control electrode. The device showed S-shaped polarization bistability in the light vs. current curves, when the control current was changed at the fixed main current.(2) Theoretical estimation of switching speed of polarization bistability.We showed by the numerical analysis using traveling-wave rate equations that flip-flop operation with bit rates of higher than 100Gbit/s can be achieved by pitchfork bifurcation polarization bistability in vertical-cavity surface-emitting lasers (VCSELs).(3) Experimental demonstration of pitchfork bifurcation polarization bistability in VCSELsPitchfork bifurcation polarization bistability has been observed experimentally in a VCSEL for the first time. All-optical flip-flop operation has been successfully demonstrated by injecting the trigger light inputs having the two orthogonal polarizations. When a 0ﾟ (90ﾟ) trigger pulse is injected, the VCSEL changes its polarization from 90ﾟ (0ﾟ) to 0ﾟ (90ﾟ). The laser oscillation with 0ﾟ (90ﾟ) polarization continues even when the injection of the 0ﾟ (90ﾟ) tigger pulse was stoped.(4) Ultra-fast all-optical flip-flop operationWe demonstrated high-speed all-optical flip-flop operation using VCSELs by injecting optical trigger pulses having two orthogonal polarizations. We successfully obtained a 5.3GHz all-optical flip-flop operation with injection power of only - 120muW.We also obtained bistable polarization switching by injecting - 3.5ps ultra-short optical pulses generated from a mode-locked Ti : Sapphire laser.