Optical detection and logic devices with latching function

DETAILED DESCRIPTION It is object of the invention to provide improved apparatus and methods of optical detection and logic devices with latching functions optical logic devices and methods.
According to the present invention there is disclosed an optical logic device having a latching function, the device comprising: an interferometer having an input waveguide for the input of an input optical signal and an output waveguide operable to output an output optical signal having a signal state representative of a logic state determined in accordance with an interference condition of the interferometer; setting means operable to set the interference condition wherein the setting means is responsive to a further optical signal to change the interference condition to thereby change from one state to another the logic state represented by the output optical signal; and latching means operable to maintain the interference condition set by the setting means.
The interference conditions can conveniently be set by means of a phase modulating means such as a semi-conductor optical amplifier comprising one of the arms of the interferometer.
The further optical signal may conveniently be counter-propagated through the semi-conductor optical amplifier relative to the direction of propagation of a component of the input signal.
The non-linear effect of cross-modulation appearing in the semi-conductor optical amplifier then provides phase modulation of the component input optical signal which, under appropriate bias conditions of the semi-conductor optical amplifier, provides the required change of interference condition.
The latching means may be provided by dividing a feedback optical signal from the output signal and inputting the feedback optical signal to the interferometer so as propagate through the phase modulating means.
A latching function is thereby provided by maintaining the changed phase relationship after removal of the further optical signal.
The optical logic device may be reset by changing the interference condition to a state in which the output optical signal is nulled