Multistate Self-Electrooptic Effect Devices

We analyze and demonstrate novel multistate self electro-optic effect devices (M-SEEDs) containing several quantum well diodes in series. We show that a device with N diodes in series with a voltage source and illuminated by N light beams has N stable states corresponding to any one (and only one) of the diodes being highly transmissive. We show that this voltage-biased M-SEED can perform contention resolution in the sense required by analog systems (such as neural networks) because the diode illuminated by the weakest beam becomes the highly transmitting one on powering up the system. We further show that a current-biased M-SEED with N diodes in series with a current supply can have 2 sup N stable states, corresponding to any combination of diodes in their "transmitting" or "absorbing" states. This same device can also function as a binary image thresholder. Importantly, these M-SEEDs are multistable in multiple beams, in contrast to previous multistable optical devices that have multiple states for one beam. We also demonstrate electrically and optically enabled symmetric SEEDs (S-SEEDs) that comprise a pair of quantum well p-i-n diodes in series with a transistor or a third diode. This device is the equivalent of an electrical "tri-state" device that is used in some bus architectures.