A Highly Cascadable Optically Bistable Device for Large Fan-out Optical Computing Applications

Smith et al have shown (1) that in order to ensure that the change in output from one bistable device is sufficient to switch the succeeding one, the technique know as ’hold and switch’ is desirable. This involves holding a device as close as possible to its switch point with one laser beam, and using the change in output from a previous similar device to induce switching, thus providing fully restoring logic. Due to the fact that the holding power cannot be made arbitrarily close to the switching power, and that a substantial "over switch" is required to avoid the effects of critical slowing down, there exists a fundamental limit upon the cascadability and fan out potential of conventional bistable devices. This is because their change in output power can only be less than or equal to their switching power. A better device would be one in which the change in output power could be significantly larger than the switching power. The twin cavity device (TCD) described here will be shown to possess this quality.