Difference Between 40G QSFP+ Transceiver with LC Interface and MTP/MPO Interface

---

 

Data transmission with higher density
and bandwidth has become the trend under present networking environment. With
40 Gigabit Ethernet commonly deployed in most data centers, various network
devices designed for 40 Gigabit Ethernet (GbE) link are available on the
market. Among them, 40G QSFP+ transceivers play an important role in driving
the bandwidth to a mounting point. There are mainly two interfaces adopted by 40G
QSFP+ transceivers—MTP/MPO and LC. What is the difference between these
two interface types? This article will have an analysis of the 40G QSFP+
transceivers with LC interface and 40G QSFP+ transceivers with MTP/MPO
interface.

 

40G QSFP+ Transceivers With LC
Interface

From the figure below, we can easily
understand the working principle of 40G QSFP+ transceivers with LC interface.
In the transmit side, 4 channels of 10G serial data streams at different
wavelengths are passed to laser drivers. The laser drivers control directly
modulated lasers (DML) with wavelengths. Then the output of the four DMLs are
optically multiplexed to a SMF through an industry-standard LC connector,
combining as 40G optical signal. In the receive side, the 40G optical signal is
demultiplexed into four individual 10G optical data streams at different
wavelength. And each wavelength light is collected by a discrete photo diode
and amplified by a TIA, and then outputted as electric data. In this process, a
4-wavelength CWDM multiplexer and demultiplexer is used over a pair of
single-mode fibers. For transmission distance of this type of 40G QSFP+
transceiver, take 40G LR4 QSFP+ transceiver as an example, it can support an
optical link length up to 10 kilometers over the single mode fiber.

 

40G QSFP+ Transceivers With MTP/MPO
Interface

We can easily understand the working principle
of 40G QSFP+ transceiver with MTP/MPO interface from the figure below. In the
transmit side, the transmitter converts parallel electrical input signals into
parallel optical signals through the use of a laser array. Then the parallel
optical signals are transmitted parallelly through the multimode fiber ribbon
terminated with MPO/MTP fiber optic connector. In the receive side, the
receiver converts parallel optical input signals via a photo detector array
into parallel electrical output signals. Generally, 40G QSFP+ transceivers with
MTP/MPO interface are utilized for short distance transmission over multimode
fiber (MMF), like 40G SR4 QSFP+ transceiver, it can support a link length up to
100 meters on OM3 cable and 150 meters on OM4 cable.

 

Note: there are also some 40G QSFP+
transceivers with MTP/MPO interface supporting long distance transmission over
SMF. For example, 40G LR4 PSM QSFP+ transceiver, a parallel single-mode optical
transceiver with an MTP/MPO fiber ribbon connector, it offers four independent
transmit and receive channels, each capable of 10G operation for an aggregate
data rate of 40G over SMF. That is to say, eight single-mode fibers are used to
achieve parallel transmission, with transmission distance up to 10 kilometers.
From the perspective of cost, this kind of 40G QSFP+ transceivers cost more
than 40G QSFP+ transceivers with LC interface. Besides, in the data center
fiber infrastructure, MTP patch panel has to be used to accommodate MTP cables,
which would cost more than LC connectors and regular SMF cables.

 

4x10G Connectivity

For the 40G QSFP+ transceivers with LC
interface, they cannot be split into 4x10G as they use 4 wavelengths on a pair
of single-mode fibers and do not lend themselves to “splitting” into 4 pairs
without substantial complexity to split out the wavelengths. For the 40G QSFP+
transceivers with MTP/MPO interface, they can be used in 4x10G connectivity via
an external 12-fiber parallel to 2-fiber duplex breakout cable, which connects
the 40G module to four 10G optical interfaces.

 

Conclusion

Generally speaking, the 40G QSFP+
transceivers with LC interface are used for long distance transmission over
single-mode fiber (SMF), and 40G QSFP+ transceivers with MTP/MPO interface are
utilized for short distance transmission over multimode fiber (MMF). However,
for some 40G QSFP+ transceivers with MTP/MPO interface, such as 40GBASE-LR4 PSM
QSFP+ transceiver, it can support long distance transmission over SMF.