40GBASE QSFP+ (Quad Small Form-Factor Pluggable) transceivers are widely provided all round the world. These modules offer various high-density and low-power 40 Gigabit Ethernet connectivity options for data centre, high performance computing networks, enterprise core and distribution layers and service provider applications. Among so many options, such as QSFP-40G-SR4, QSFP-40G-LR4, QSFP-40G-ER4, WSP-Q40GLR4L, etc., QSFP-40G-LR4 is well know as it can support link lengths of up to 10 km over single mode fibre. It enables high-bandwidth 40G optical links over 12-fibre parallel fibre terminated with MPO/MTP multifibre female connectors. The following will talk about one of QSFP-40G-LR4: QSFP LR4 PSM (Parallel Single Mode).

Main Features of QSFP LR4 PSM

The QSFP LR4 PSM is a parallel 40G Quad Small Form-Factor Pluggable optical module. It offers increased port density and saves cost for total system. This module provides 4 independent transmit and receive channels. It can support 4×10 Gbps operation for an aggregate data rate of 40 Gbps on 10km of single mode fibre. It can also support 1x40G optical links over 12-fibre parallel fibre terminated with MPO/MTP connectors. But the ribbon cable with MPO/MTP connector should have proper alignment instead of being twisted. The module operates with single +3.3 V power supply. With a 2-wire serial interface, it allows to send and receiver more complex control signals and to receiver digital diagnostic information. If there are some channels not used, then the unused channels can be shut down for maximum design flexibility. This transceiver module with form factor, optical/electrical connection and digital diagnostic interface is compliant with Multi-Source Agreement (MSA). It can meet the harshest external operating conditions including temperature, humidity and EMI interference (Electromagnetic Interface). For example, its operating case temperature ranges from 0 to 70 ℃。

Working Principle of QSFP LR4 PSM

This QSFP LR4 PSM is a parallel single mode optical transceiver with an MTP/MPO fibre ribbon connector. This transceiver module offers 4 transmit and 4 receive channels and each can support 10.3125 Gbps data rates (as shown in the following figure). The transmitter accepts electrical input signals compatible with Common Mode Logic (CML) levels. All input data signals are differential and internally terminated. The receiver converts the input signals via a photo detector array into parallel electrical output signals. And the outputs signals are also voltage compatible with Common Mode Logic (CML) levels. All signals are differential and support a data rates up to 10.3 Gbps per channel.

Each module offers 7 low speed hardware control pins (including the 2-wire serial interface): ModSelL (Module Select), SCL (Serial Clock), SDA (Serial Data), LPMode (Low Power Mode), IntL (Interrupt), ResetL, and ModPrsL (Module Present). Here just introduces several pins.

ModSelL is an input pin. When held low by the host, the module responds to 2-wire serial communication commands. The ModSelL allows the use of multiple QSFP+ modules on a single 2-wire interface bus–individual ModSelL lines for each QSFP+ module must be used.

SCL and SDA are required for the 2-wire serial bus communication interface and enable the host to access the QSFP+ memory map.

LPMode pin is used to set the maximum power consumption to protect the host. If the hosts are able to cool higher power modules, such modules will be accidentally inserted.

FS.COM QSFP-40G-LR4 is designed for use in 40 Gigabit Ethernet links over single mode fibre. It’s compliant with QSFP+ MSA and IEEE 802.3ba 40GBASE-LR4. LR4 PSM is one of QSFP-40G-LR4 modules. All these cost-effective transceivers have to be tested before shipping to ensure full compatibility and to offer the best customer service.