There are 40GBASE-SR4 QSFP + transceivers and 40GBASE-LR4 QSFP + transceivers. It's known that 40GBASE-SR4 uses a parallel multimode fiber (MMF) link to achieve 40 G. It offers 4 independent transmit and receive channels, each capable of 10 G operation for an aggregate data rate of 40G over 100 meters of OM3 MMF or 150 meters of OM4 MMF. While for 40GBASE-LR4 QSFP + transceivers, there are two kinds of links. One is coarse wavelength division multiplexing and the other is parallel single-mode fiber. What's the difference?
40GBASE-LR4 coarse wavelength division multiplexing QSFP + Transceiver
QSFP-40GE-LR4, one of 40GBASE-LR4 coarse wavelength division multiplexing QSFP + transceivers, is compliant to 40GBASE-LR4 of the IEEE P802.3ba standard. The optical interface is a duplex LC connector. It can support transmission distance up to 10 km over single-mode fiber by minimizing the optical dispersion in the long-haul system.
This transceiver converges 4 inputs channels of 10 G electrical data to 4 coarse wavelength division Multiplexing optical signals by a driven 4-wavelength distributed array (DFB) laser array, and then multiplexes them into a single channel for 40 G optical transmission, propagating out of the transmitter module from the SMF. Reversely, the receiver module accepts the 40 G coarse wavelength division multiplexing optical signals input, and demultiplexes it into 4 individual 10G channels with different wavelengths. The central wavelengths of the 4 coarse wavelength division multiplexing channels are 1271, 1291, 1311 and 1331 nm as members of the coarse wavelength division multiplexing wavelength grid defined in ITU-T G694.2. Each wavelength channel is collected by a discrete photo diode and output as electric data after being amplified by a transimpedance amplifier (TIA).
40GBASE-LR4 PSM QSFP + Transceiver
Different from coarse wavelength division multiplexing QSFP + transceiver which uses a LC connector, parallel single-mode QSFP + is a parallel single-mode optical transceiver with an MTP / MPO fiber ribbon connector. It offers 4 independent transmit and receive channels, each capable of 10 G operation for an aggregate data rate of 40 G over single-mode fiber about 10 km. The cable can not be twisted to keep proper channel to channel alignment.
In a parallel single-mode QSFP +, the transmitter module accepts electrical input signals and the receiver module converls analog optical input signals via a photo detector array into parallel electrical output signals. The receiver module. All data signals are differential and support a data rates up to 10.3 G per channel.
Difference of Two Links
What's the difference of these two links? From the perspective of optical transceiver module structure, parallel single-mode looks more cost effective because it uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. Beside, its array-fiber coupling to an MTP connector is relatively simple. From the perspective of infrastructure, parallel single mode is more expensive, because when the link distance is long, parallel singlemode uses 8 optical singlemode fibers while coarse wavelength division multiplexing uses only 2 optical singlemode fibers. For more about their differences, please see the following table:
What's more, in the data center fiber infrastructure, the patch panel has to be changed to accommodate MTP cables. This would cost more than LC connectors and regular single mode fiber cables. Beside, it's not easy to clean MTP connectors. So coarse wavelength division multiplexing is more profitable and popular for 40GBASE-LR4 QSFP + link.
For 40GBASE-LR4 QSFP + transceivers, both coarse wavelength division multiplexing link and parallel single mode link can reach the transmission distance of 10 km. 40GBASE-LR4 CWDM QSFP + transceivers use a duplex LC connector via 2 optical sm fibers. And 40GBASE-LR4 parallel single mode QSFP + transceivers use an MTP / MPO fiber ribbon connector via 8 optical sm fibers. So, there is no need to make any changes to upgrade 10 G fiber cable plant to 40 G connectivity, which is more cost-effective. Fiberstore provides wide brand compatible 40 G coarse wavelength division multiplexing QSFP + transceivers, such as Juniper compatible JNP-QSFP-40G-LR4 and HP compatible JG661A. Each fiber optic transceiver has been tested to ensure its compatibility and interoperability.