An important part of the new fiber optic infrastructure involves fiber optic connectors. By mechanically coupling and aligning the fiber core so that light can pass through, fiber optic connectors affect insertion loss and return loss levels, installation time and overall fiber optic system cost. In fiber optic systems, LC fiber optic connectors, SC fiber optic connectors and MPO fiber optic connectors are generally used.
SC Fiber Optic Connectors feature a push-pull coupled end face with a spring-loaded ceramic ferrule and are ideal for data center applications.
The LC fiber optic connector (also push-pull fiber optic connector) came after the SC connector and has a smaller ferrule (hence the name "miniature fiber optic connector"). Its small size makes it ideal for dense data center racks and panels. MPO connectors are used for ribbon cables with 8 to 24 fibers.
Effect of Fiber Optic Connectors on Insertion Loss
Channel insertion loss in a fiber optic link depends on the length of the fiber and the number of connections. As shown below, the initial connection to the most commonly used SFP and QSFP optics is not considered part of the channel link loss.
Optical module connection
The multimode fiber (MMF) attenuation parameter used to calculate the channel insertion loss budget is 3.5 dB/km. Currently, the OM3/OM4/OM5 fiber optic cable specification in ANSI/TIA-568.3-D has been approved at 3.0 dB/km, which allows more headroom for the total link budget.
In an MMF link, the loss of the fiber optic connector will usually account for the majority of the channel insertion loss, especially in short-distance applications where the fiber attenuation is very small. Many MMF connections installed in data centers are pre-terminated at the factory and professionally polished.
LC Duplex is a fiber optic connector with a pair of MMF or single-mode fibers (SMF) that transmit data in two opposite directions, one in each fiber. It can be used for single-lane transceivers (such as 10G or 25G SFP), or for wavelength multiplexing in the same fiber pair (such as CWDM4, SWDM4 or BiDi).
mpo fiber optic connector
MPO array connectors support MMF and SMF types of parallel fiber connections. Typical use cases for MMF MPO-12 (eight fibers) are 40GBASE-SR4 and 100GBASE-SR4 transceivers, where four fibers are used as Tx (transmit) and the other four fibers are used as Rx (receive).
High fiber count MPO-16, MPO-24 and MPO-32 connectors have also been developed to support permanent trunk cabling and transceivers, such as 100GBASE-SR10 (20 fibers) and 400GBASE-SR16 (32 fibers).
Parallel single-mode (PSM) transceivers also employ this configuration, typically supporting distances of 500 m in data centers. MPO trunk cables are also used as horizontal permanent links in data centers for fiber aggregation.
Historically, insertion loss was much higher in SMF systems because the link was designed for longer distances. The attenuation in SMF is much lower than in MMF. Due to the much smaller core size, the insertion loss per SMF connection is significantly higher than that of an MMF connection.
lc fiber optic connector
LC duplex (single-lane or wavelength multiplexing) and MPO-12, MPO-16, MPO-24 and MPO-32 (parallel Fiber Channel) fiber optic connectors, we use an overpopulated launch condition model to compare MMF and Connection insertion loss between SMFs. Assuming light is uniformly distributed in the fiber core with a diameter of 2R, and the vertical core-to-core offset is Δr, then the connection insertion loss will be:
Connection insertion loss = 1-(2α-sin2α)/π, where α=cos-1(Δr/2R).
As shown below, the performance of single-mode fiber optic connectors is very prone to vertical misalignment. For example, a 1 µm vertical misalignment in a multimode fiber connector (diameter with a 50 µm core) would result in only a 2.5% loss (0.11 dB), whereas in an SMF connection it could result in a loss of over 14% (0.66 dB).
