How does a CSFP Transceiver work?

CSFP transceiver stands for Compact Small Form-factor Pluggable Transceiver. CSFP transceiver is a dual channel bi-directional transceiver module. The optical signals are transmitted and received on a single strand of the single mode fiber optic cable. CSFP is used to increase the port usage on the communication equipment. Furthermore, it is also used in FTTH (Fiber To The Home) solutions.

CSFP transceivers have the same form factor as normal SFP transceivers, the cage and casing designs are also identical. CSFP can be installed in the SFP port of the communication equipment if it is supported by the equipment.

A CSFP connects to two bi-directional SFP transceivers on the far end of the communication link. Figure 1 shows the connectivity between a CSFP and bi-directional transceivers. Single strands of single mode optical fiber cable connect to the bi-directional SFP transceivers. These single strands of fiber optic carry both transmit and receive signals. CSFP provides two uplinks with speed up to 1Gbps each and consume the space of a single SFP transceiver. The port density can be doubled on high-end communication equipment. This results is cost-savings and increases the efficiency of the equipment.

Let us now dig deeper into the working principle of the CSFP transceivers. CSFP transceivers and bi-directional SFP transceivers have one or more WDM filters that split the optical source into two wavelengths. One wavelength is used for transmitting the signal and other is used for receiving the signal. CSFP and bi-directional transceivers usually operate on 1310nm, 1490nm and 1550nm wavelengths. The wavelengths used to transmit and receive signal is mentioned on the CSFP or bi-directional transceiver. It is to be noted here that the right combination of SFPs is required for proper operation. For example, if the CSFP is transmitting on 1310nm and receiving on 1490nm then the bi-directional SFP that is to be connected with it should receive on 1310nm and transmit on 1490nm. Otherwise the Tx/Rx pair will not work. The bi-directional transceivers connecting to the CSFP transceiver should be the same as both the channels of CSFP transceiver use same wavelengths to transmit and receive.

Figure 2 illustrates the high level diagram of a CSFP transceiver’s working. The light source is split into two wavelengths, the transmit wavelength and the receive wavelength. Both the wavelengths can travel on a single strand of single mode optical fiber cable, thus enabling bi-directional communication. The other channel has similar assembly. In other words, a CSFP combines two bi-directional SFPs in space of one.

As evident from the details mentioned above, CSFP transceiver is very useful in high density networks where the number of uplinks and downlinks are high in number and bandwidth requirements are up to 1Gbps. Use of CSFP transceivers can greatly increase efficiency and reduce the capital expenditure involved in the installation of new communication links.

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