We demonstrate optical bistability in InP/InAlGaAs multi-quantum well(MQW) semiconductor ring lasers(SRL) which
are fabricated by the use of inductively coupled plasma reactive ion etching (ICP-RIE) and can be used in a multi-ring to
achieve all-optical storage. Unlike other international reports, the observed optical bistability has unidirectional regime
started directly from the threshold, skip the first two regimes and greatly reduce the injection current required in
applications. The device described in this article achieves threshold current 56mA which is quite low compared to other
reported devices, and some analysis and experiments on the etching depth have been done.