Description:
Rollball’s RDSFP28-XX25G-LRD SFP28 transceiver is designed for use in 25-Gigabit Ethernet links up to 10km over single mode fiber. The module consists of DWDM EML Laser, PIN and Preamplifier in a high-integrated optical sub-assembly. Digital diagnostics functions are available via a 2-wire serial interface, as specified in SFF-8472.This module is designed for single mode fiber and operates at a nominal wavelength of 100GHz ITU Grid, C Band DWDM wavelength.
The module optical connection is duplex LC and shall be compatible with SFP+ 28Gbps and backward compatible with legacy 10G SFP+ pluggable. The SFP28 DWDM LR module is a dual directional device with a transmitter and receiver plus a control management interface (2-wire interface) in the same physical package. 2-wire interface is used for serial ID, digital diagnostics and module control function.
The transmitter converts 25Gbit/s serial PECL or CML electrical data into serial optical data compliant with the 25GBASE-LR standard.  An open collector compatible Transmit Disable (Tx_Dis) is provided.  Logic “1” or no connection on this pin will disable the laser from transmitting.  Logic “0” on this pin provides normal operation.  The transmitter has an internal automatic power control loop (APC) to ensure constant optical power output across supply voltage and temperature variations.  An open collector compatible Transmit Fault (Tx_Fault) is provided. TX_Fault is module output contact that when high, indicates that the module transmitter has detected a fault condition related to laser operation or safety.  The TX_Fault output contact is an open drain/collector and shall be pulled up to the Vcc_Host in the host with a resistor in the range 4.7-10 kΩ.  TX_Disable is a module input contact. When TX_Disable is asserted high or left open, the SFP28 module transmitter output shall be turned off. This contact shall be pulled up to VccT with a 4.7 kΩ to 10 kΩ resistor.
The receiver converts 25Gbit/s serial optical data into serial PECL/CML electrical data.  An open collector compatible Loss of Signal is provided.  Rx_LOS when high indicates an optical signal level below that specified in the relevant standard.  The Rx_LOS contact is an open drain/collector output and shall be pulled up to Vcc_Host in the host with a resistor in the range 4.7-10 kΩ, or with an active termination.  Power supply filtering is recommended for both the transmitter and receiver.   The Rx_LOS signal is intended as a preliminary indication to the system in which the SFP28 is installed that the received signal strength is below the specified range. Such an indication typically points to non-installed cables, broken cables, or a disabled, failing or a powered off transmitter at the far end of the cable.