X2 Optics are a standardized form factor for 10 Gbps fiber optics transponders.
Both 10G Ethernet and 10G Fibre Channel versions are available. X2 optics are used in datacom optical links only (not telecom), and they are smaller than XENPAK transponders. The electrical interface to the host board is also standardized and is called XAuI (4 x 3.125 Gbps ). X2 optics are essentially an enhanced version of the Xenpak. It also has the same connector as a Xenpak (SC). Cisco introduced the X2 form factor and HP is producing them as well. Although X2 optics are quite old and bulky, they are still used in the newer product line of Cisco, i.e. the ASR 9000 series. The reason for this is that Cisco has not officially offered the SFP+ for longer distances or a SFP+ for DWDM. The X2 optics come in 4 different versions: SX, LX, EX and ZX. The SX version will work on Multi Mode fiber, the LX, EX and ZX work only on Single Mode fiber.
The LX will reach a maximum range of 10km, the EX of 40km and the ZX of 80km. X2 optics alway shave a Tx (sending laser) and a Rx side (receiver). The difference between the sending power (in dB) and the receiving power (in dB) is called the power budget and will determine the distance an optic can cover, where the laser light (in nanometers) also has an important role. Recently, Cisco offered the X2-10GB-T with has a normal RJ45 / Copper port and can produce speeds of 10G over CAT7 cable. Solid Optics offers the complete CWDM and DWDM spectrum for X2 optics. X2 optics are also available as a Bidi optic, which has only 1 SC plus and will work on 1 single strand of single fiber. In addition, Form Factor Converters are available for the X2 optics which allows the end user to convert (2) SFP 1G ports out of (1) X2. Utilizing the X2 converter, you can use the X2 optics as 10G or as a double SFP 1G, creating more flexibility for the end customer.