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Abstract

An electrical multiplex data bus is operatively coupled to an optical multiplex data bus by means of a novel electro-optical converter arrangement to form a hybrid data transmission system in which the transition from the optical data bus to the electrical data bus or vice versa is transparent to the individual terminals and controllers connected thereto. The data on the electrical bus is encoded in a biphase Manchester II code. Within the optical portion of the system, the data is represented by three different levels of flux within the optical fiber transmission line. Since flux is a measure of the intensity of the light, it will never be less than zero; accordingly, the three flux levels may be 'zero', an intermediate value 'L', and a maximum value 'H'. A flux of zero then would correspond to a negative bi-phase electrical signal, a flux of H would correspond to a positive electrical signal and a flux of L would correspond to a transitory electrical signal that is undergoing a change of state from positive to negative (or vice versa). In one presently preferred embodiment, this is achieved by decomposing an electrical signal into two binary-valved components DATA and DATA* which respectively switch two separate externally controlled current sources such that a first current source establishes the L flux level and the sum of the two current sources establishes the H level; the current sources (and thus the flux levels) are adjusted to minimal values consistent with pre-established signal-to-noise thresholds.

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