Optical communication network with passive monitoring

An optical communication network which comprises at least a first single-mode optical fiber, to be referred to as a primary fiber, for at least unidirectional transmission, at least at one signal wavelength, to be denoted .lambda..sub.s, from a first distribution node to a central office;

• a first multiplicity of optical network units, to be referred to as the first ONUs, located remotely from the central office, each ONU capable of transmitting and receiving data at least at the wavelength .lambda..sub.s, and each ONU comprising means for synchronizing the ONU transmissions such that a time-division-multiplexed signal is received at the central office;
• a first multiplicity of single-mode optical fibers, to be referred to as distribution fibers, for at least unidirectional transmission from the first ONUs to the first distribution node such that each ONU sends data via a respective one of the first distribution fibers;
• and
• first coupling means, located at the first distribution node, for passively combining transmissions from the first ONUs into the first primary fiber;
• CHARACTERIZED IN THAT:
• a) the first coupling means comprise a first coupler, to be referred to as a first Stage-1 coupler, which has a proximal end which includes at least one proximal port and a distal end which includes a plurality of distal ports;
• b) each first distribution fiber is optically coupled to one of the distal ports, and the first primary fiber is optically coupled to the proximal port of said coupler;
• c) the network further comprises a monitor;
• d) the network further comprises a first plurality of bypass lines, each said bypass line comprising an optical fiber having proximal and distal ends, the distal end optically coupled to a corresponding one of the first distribution fibers and the proximal end optically coupled to the monitor such that portions of at least some transmissions are received by the monitor without passing through the first Stage-1 coupler;
• e) the monitor comprises means for discriminating received transmissions based on a variable selection criterion;
• and
• f) the network further comprises passive optical means, optically coupled to the monitor and to one or more first bypass lines, for conforming transmissions in said bypass line or lines to a given value of the selection criterion.