1. Field of the Invention
The present invention relates to an optical transceiver, in particular, the invention relates to an optical transceiver with an enhanced electro-magnetic interference (hereafter denoted as EMI) tolerance.
2. Background Art
An optical transceiver generally includes a transmitter optical subassembly (hereafter denoted as TOSA) to transmit signal light, a receiver optical subassembly (hereafter denoted as ROSA) to receive another signal light, an electronic circuit communicating with the TOSA and the ROSA, and a housing to enclose the TOSA, the ROSA and the circuit therein. One type of the optical transceiver is called as the pluggable optical transceiver in which the optical transceiver may be plugged within a cage prepared in the host system without turning the electrical power of the system off.
FIG. 10 illustrates such a pluggable optical transceiver 100. The optical transceiver 100 shown in FIG. 10 is going to be set within the cage 102 on the circuit board 104 of the host system through the port 103a prepared in the face panel 103 of the system. The optical transceiver 100 provides an optical receptacle 106 in the front end thereof, into which an external optical connector 107 is set to secure the optical coupling between the external optical fiber in the optical connector 107 and active devices installed in the TOSA and the ROSA. The cage 102 provides an electrical connector in the deep end thereof. Setting the optical transceiver 100 within the cage, the electrical plug formed in the rear end of the optical transceiver 100 mates with the electrical connector in the cage to establish the communication path between the optical transceiver 100 and the host system.
The EMI radiation from electronic equipment has been a subject for a long time. Because the pluggable optical transceiver is used in an arrangement to be inserted within the cage, electro-magnetic interference (hereafter denoted as EMI) radiation may leak through a physical gap between the optical transceiver and the cage. In order to reduce such EMI radiation, the optical transceiver generally provides ground fingers or ground fins that makes in contact with the inner surface of the cage when the optical transceiver 100 is set in the cage.
A United States patent, the U.S. Pat. No. 7,491,090, has disclosed one type of elastic fingers attached to surround the optical receptacle. When the optical connector is set in the optical receptacle, the optical connector pushes the elastic finer outwardly to make in contact with the cage; while, the optical connector is released from the optical receptacle, the elastic finger is apart from the cage to facilitate the extraction of the optical transceiver from the cage. A Japanese Patent Application published as JP-2003-270492A has disclosed another type of an optical transceiver having a metal shield to fill a gap between the optical receptacle and the port.
Conventional mechanisms to reduce the EMI radiation are those described above; that is, the ground fingers surrounding the optical receptacle not only make in contact with the cage to fill the gap against the cage, or at least to narrower the gap, but also stables the chassis ground or case ground.
However, recent optical transceiver operates in a higher frequency, sometimes exceeding 10 GHz; a small gap causes the leak of the EMI radiation from the optical transceiver. For instance, misalignment between the face panel and the cage may leak the EMI radiation. Moreover, the conventional ground fingers inherently have a gap with respect to adjacent fingers, which may also cause the leak of the EMI radiation with higher frequencies. Further, the external optical connector set in the optical receptacle also forms a small gap against the inner wall of the optical receptacle. Although some optical connectors implement a member to shield such a gap, a small sized connector applied in recent systems often have no room to place such a shielding member.
Thus, a way to implement an auxiliary member to shield a small gap shows a limitation as the operating frequency becomes higher. The present invention is to provide a technique to reduce the EMI radiation from an optical transceiver independent of ways to cover the small gap.