MT-RJ = "Mechanical Transfer Registered Jack".
The "MT" in MT-RJ comes from the Mechanical Transfer (MT) ferrule. A ferrule is the component of a fiber connector that is used to align and protect the stripped end of a fiber. Ferrules can be made of glass, plastic, metal, or ceramic material.
The MT-RJ connector’s MT-type ferrule is made from precision-molded plastic and is based on multi-strand ferrule technology pioneered by NTT in Japan 10-20 years ago. Most other fiber connectors encountered in LAN applications use single-strand ferrules, so this is something that sets the MT-RJ connector apart.
The "RJ" in MT-RJ comes from the term Registered Jack (RJ). In the USA, telephone jacks are also known as registered jacks. Some examples are RJ-11, RJ-12, and RJ-45. The telephone connection interfaces (receptacle and plug) are registered with the U.S. Federal Communications Commission. They derive from interfaces that were part of AT&T's Universal Service Order Codes (USOC) and were adopted as part of FCC regulations (specifically Part 68, Subpart F. Section 68.502).
MT-RJ connectors are slightly smaller than the eight-pin RJ-45 modular connector used in making a copper 10/100/1000 Ethernet connection. The MT-RJ connector also uses a press-to-release latching mechanism similar to the one found on RJ-XX connectors. So including “RJ” in the name of the connector helps people to visualize the size of it and how it locks into place.
That’s probably more than you ever wanted to know about MT-RJ. There used to be a webpage devoted to MT-RJ (www.mtrj.com) but it doesn’t seem to be working lately.
