In a high-speed transmission and reception module for optical communication, for the connection between an optical device and a circuit substrate, a flexible substrate manufactured using a transmission line has heretofore been used for correcting a displacement between the optical device and the circuit substrate.
However, the above-described high-speed transmission and reception module for optical communication is hard to realize sufficient high-frequency characteristics at a communication speed more than 10 Gbps. To cope with the above-described problem, in the high-speed transmission and reception module for optical communication having a communication speed more than 10 Gbps, a relay substrate made of ceramic has been connected between the flexible substrate and the circuit substrate as a substrate for relay.
Proposed is a connector element for high frequency transmission in which parts having surfaces facing to each other are provided on conductors for constituting a ground line and signal line of the connector element and covered with dielectric materials (see, e.g., Japanese Laid-open Patent Publication No. 06-215819).
However, the above-described relay substrate made of ceramic is expensive. Further, precision is necessary for the connection between the relay substrate and any one of the flexible substrate and the circuit substrate, and also the time for assembly is necessary. Therefore, when the high-speed transmission and reception module for optical communication is manufactured, the assembly causes an increase in cost.
In the above-described connector element for high-frequency transmission, the connection shape to the substrate of a signal line and ground line constituting the transmission line is not sufficiently taken into consideration. Therefore, even if high-frequency transmission characteristics of the connector element are preferable, loss of high-speed signal may be caused by the connection to the substrate.