Optical analogue to digital converter

An analogue to digital converter according to any preceding claim in which the optical processing circuit of each processing channel comprises 2n/2 optical sub-circuits which each include an optical device, each sub-circuit arranged to provide at an output a digital optical output signal, each circuit having a non-linear relationship between the input signal intensity and the gain of the optical device whereby the sub-circuit has a threshold about which the device causes the digital output signal from that device to change state, each optical sub-circuit of a processing channel having a different threshold to any other optical sub-circuits in that processing channel.

An analogue to digital converter according to any preceding claim in which a said processing channel corresponding to the most significant bit of the output signal comprises a single optical sub-circuit arranged to provide at an output a digital optical output signal and having a non-linear relationship between the input signal intensity and gain of the optical sub-circuit such that the sub-circuit has a threshold at which the sub-circuit is arranged to change the state of digital output signal.

An analogue to digital converter according to any preceding claim in which at least one of said processing channels includes two or more pairs of optical sub-circuits, each having a different switching threshold T3,T1,T7,T5, each threshold corresponding to a different intensity level of the analogue input signal at which the output signal of the processing channel is arranged to change state, the output signals from each pair being input to the optical combining circuit which comprises at least two optical logic elements, each receiving the output from one of the pairs, and at least one further logic clement which is arranged to receive at an input the output of two of the logic elements.

An analogue to digital converter according to any preceding claim in which the or each optical logic element comprises an optical AND, NAND, OR, NOR and NOT element each formed from at least one semiconductor optical amplifier.

An analogue to digital converter according to any preceding claim which is arranged to produce a three bit digital optical output signal and comprises three processing channels, in which the processing channels comprise:

• a first processing channel having an optical processing circuit comprising one optical sub-circuit whose output corresponds to the most significant bit of the output signal,
• a second processing channel having an optical processing circuit comprising two optical sub-circuits, each having different thresholds, and both outputting an optical signal which is passed to a respective input of an optical combining circuit comprising an optical logic gate, the output of the logic gate corresponding to the next most significant bit of the output signal, and
• a third processing channel having an optical processing circuit comprising two pairs of optical sub-circuits, each having a different threshold, and the output of both pairs being passed to an optical combining circuit which comprises a pair of optical logic gates, each connected to the outputs of a respective one of the two pairs of optical sub-circuits, the combining circuit further comprising an OR gate which combines the output of the two logic gates, the output of the OR gate corresponding to the least significant bit of the digital output signal.

An analogue to digital converter according to any preceding claim in which each of the optical sub-circuits includes an optical device that has only a single switching threshold.

An analogue to digital converter according to any preceding claim in which the optical combining circuit comprises at least one semi-conductor optical amplifier.

An analogue to digital converter according to any preceding claim in which an optical splitter is provided which is arranged to receive the optical input signal from the input and splits the input signal into N optical sub-signals, each of the N processing channels being coupled to a respective one of the N processing channels.

An analogue to digital converter according to any preceding claim in which the digital output signal (140) represents a binary, twos complement binary or gray scale coding of the analogue optical input signal.