Abstract: A system of detecting an occurrence of a trouble in an optical communication line having a plurality of nodes with a sending port and a receiving port, a plurality of 2-input & 2-output couplers and fibers connecting the nodes and the couplers for distributing any signal issued from a node to all the nodes. The coupler has an intersecting allocation between two inputs and two outputs. The intersection in the coupler makes the recurring signal pass only through a series of evanescent linkages of the couplers to the receiving port of the same node. When a trouble arises, the evanescent linkage is more likely to be broken down than the direct linkage and the node notices the trouble by the extinction of the recurring signal.

Abstract: An optical module has a connector housing and a photoelectric transfer unit received in the connector housing. The photoelectric transfer unit (photounit) has a lead frame, a photoelectric transfer element and an IC element for signal processing which are mounted on the lead frame. These elements are sealed in a transparent resin molding. The photoelectric transfer unit has six sides and has lead terminals protruding from one of the six sides. All sides of the unit except the side at which the lead terminals protrude are covered with a metal shield case formed with a hole as a light path leading to the photoelectric transfer element.

Abstract: An optical connector comprising a first housing for supporting a ferrule, a second housing having a ferrule holder into which the ferrule is inserted with a predetermined frictional resistance, a spring member for elastically pushing the ferrule into the ferrule holder against the frictional resistance at the time that load as the ferrule is brought into contact with the ferrule holder at a first predetermined stroke position has reached a first predetermined threshold value, and a pair of locking members contacting each other at a second predetermined stroke position, and when load of the contact at the second stroke position has reached a second predetermined threshold value, the contact at the second stroke position being released and then the first housing being further moved in the predetermined direction and the locking members being engaged with each other, wherein the second stroke position is set with respect to the first stroke position so that the locking members can contact each other prior to the