Fiber Connector Type: SC APC vs SC UPC

With the rapid development of fiber networks, fiber connectors have become an essential assembly to cater for high-performance fiber optic system. There are various fiber connector types in the market, such as LC, ST, SC, MPO/MTP and so on, among which, SC is one of the most commonly used fiber connectors. Further Classifying SC by polishing type, we have SC APC connector and SC UPC connector. This article will introduce SC APC vs SC UPC and illustrate their difference for your selection guide.

SC APC vs SC UPC: What Refers to SC?

SC is the abbreviation of Subscriber Connector, sometimes also refers to Square Connector or Standard Connector. SC is a type of fiber optic connector with snap (push-pull coupling) coupling type and a 2.5 mm diameter ferrule, which is popularly used in single mode duplex system for its high performance and accurate alignment.

SC APC vs SC UPC: What Refers to APC and UPC?

Generally speaking, SC APC connector and SC UPC connector are distinct from each other based on fiber end face. SC APC connector is polished with an 8-degree angle, while SC UPC connector is polished with no angle, which causes difference in light reflection. SC UPC connector adopts an extended polish method to realize finer fiber surface finish, which brings much lower back reflection (ORL) and thus provides much more reliable signal in data center, digital TV and telephone. Although SC UPC connector has low insertion loss and wide range of application, there are some applications requiring for higher return loss, no less than 60 dB or even higher. In this circumstance, SC APC connector can make the need and consistently perform well due to the 8-degree angle.


Figure 1: This photo shows a SC APC connector.

SC APC vs SC UPC: What Are the Differences?

As mentioned above, we know SC APC and SC UPC varies from polishing style, which is a difference in the manufacturing process. But in the actual usage, what are the distinct features of SC APC and SC UPC connectors and how to choose from them? Here are some clues.

·Return Loss Value

With a SC UPC connector installed on the end of a fiber, reflected light is reflected straight back to the light source. However, with a SC APC connector, reflected light is reflected at an angle into the outer cladding layer rather than straight back towards the light source. This different way of reflection of reflected lights brings about different return loss value. SC APC connector is standardized with a return loss value as -60dB or higher, while SC UPC connector as -50dB or higher.

·Insertion Loss Value

Another specification to consider about fiber connector is insertion loss. Lower the insertion loss, better the performance. Someone prefer SC UPC connector, because they hold the view that SC UPC connector is easier to realize low insertion. This is true on account of less air gaps in SC UPC connector than SC APC connector. However, modern technique has made insertion loss value of SC APC connector as low as SC UPC connector.


SC APC connector is commonly used in applications that are much more sensitive to return loss, and requires for high precision signal, such as FTTX (Fiber To The X), video delivery through RF signal, WDM (wavelength division multiplexing) applications and analogue equipment like CCTV. For applications less sensitive to return loss and no other particular demands are required, a SC UPC connector can work as equal effectively as a SC APC connector.


Figure 2: This photo shows a SC UPC connector.

·Other Reference

While SC APC connector is green, SC UPC connector is blue. Besides, the first is much more expensive than the latter one for the optical performance of SC APC much better than SC UPC connector. Other factors to think is the ease of use and your personal needs.


This article touches the concept of several items: SC, APC connector and UPC connector. Then it explains why SC APC connector is distinct from SC UPC connector from several aspects. It is improper to say one SC connector type wins the other for there are lots of consideration under specific circumstances. Simply put, people choose from these two SC connectors according to their personal need. Taking the factors of optical performance, cost and application in usage into consideration, one can make the best choice.

LC Connector Introduction

Fiber optic connectors are used to the mechanical and optical means for cross connecting fibers. Fiber optic connectors can also be used to join fiber cables to transmitters or receivers. There have been many types of connectors developed for fiber cable. Single mode networks have used FC or SC connectors in about the same proportion as ST and SC in multimode installations. But LC connector with smaller size and higher performance has become popular and the connector choice for optical transceivers for systems operating at gigabit speeds. The following text gives a detailed introduction of LC connector.

History of LC Connector

LC stands for Lucent Connector, as the LC connector was developed by Lucent Technologies as a response to the need by their primary customers, the telcos, for a small, low insertion loss connector. Then the LC design was standardized in EIA/TIA-604-10 and is offered by other manufacturers.

SC connector and LC connector

Advantages of LC Connector

There are solid reasons that the LC is the preferred connector for high-performance network. From the appearance, LC connect is like a mini size of SC connector. LC connector borrows split-sleeve construction and a cylindrical ferrule (usually ceramic) from SC connector. LC connector has a push-and-latch design providing pull-proof stability in system rack mounts. The picture on the right shows the appearance of SC connector and LC connector.

The ferrule size of LC connector is 1.25 mm which is half the size of SC connector ferrule—2.5 mm. LC connector is rated for 500 mating cycles and its typical insertion loss is 0.25 dB. An interesting feature of the LC is that, in some designs, the ferrule can be “tuned” or rotated with a special tool after it has been assembled. This offers a considerable performance advantage. The design and performance of LC connector address the need for high density and low insertion loss.

Application of LC Connector

LC connector can be found in many places for termination and connection, especially SFP transceivers for gigabit transmission. For example, the optic interfaces of Cisco SFP transceivers are all LC connectors. Some other applications are as following:

Simplex and duplex LC connectors

  • Telecommunication networks
  • Local area networks
  • Data processing networks
  • Cable television
  • Fiber-to-the-home
  • Premises distribution
LC Connector Selection Guide

To meet the needs of market, there are various types of LC connectors provided now. During the selection of LC connector, transmission media should be the first factor to consider. LC connector favors single mode fiber optic cable. But it can also be used with multimode fiber optic cable. Signals sometimes are transferred over simplex fiber optic cable and sometime duplex fiber optic cable. Thus, LC connector has both simplex and duplex design. The picture above shows an APC simplex LC connector on the left and a UPC duplex LC connector on the right. Some other factors like polishing style (APC or UPC), hole size and cable diameter should not be ignored. For more details about LC connectors, you can visit Fiberstore which provides various LC connectors with high performance and low price.

Fiber Optic Connector: An Important Part of Fiber Optic Termination

Fiber optics are used for a variety of applications in the photonics industry. Fiber optics are typically connectorized for convenience of mating and coupling. These connectors come in many configurations and styles. A fiber optic connector that was lower loss, lower cost, easier to terminate or solved some other perceived problem is urgently needed to the industry. As a result, about 100 fiber optic connectors have been introduced to the marketplace, but only a few represent the majority of the market. Today, Fiberstore’s Blog are going to show you these commonly used fiber optic connectors.

fiber optic connector

Fiber Optic Connector Types
Commonly used fiber optic connector types include SC, FC, LC, ST, MU, E2000, MTRJ, SMA , DIN as well as MTP & MPO etc. They are widely used in the termination of fiber optic cables, such as fiber optic pigtail, fiber optic patch cables and so on.

LC connector LC Connector (Lucent Connector) — Ferrule diameter = 1.25mm. LC connectors are licensed by Lucent and incorporate a push-and-latch design providing pull-proof stability in system rack mounts. LC connectors are available in single mode and multimode. Externally LC connectors resemble a standard RJ45 telephone jack. Internally they resemble a miniature version of the SC connector. This type of connectors are commonly used in connecting SFP Transceiver Module in Router/Switch. For example, the optic interfaces of Cisco’s SFP transceivers are all LC connectors.
SC connector SC Connector (Subscriber Connector) — Ferrule diameter = 2.5mm. The SC connector is becoming increasingly popular in single-mode fiber optic telecom and analog CATV, field deployed links. But the most commonly used field is to connect GBIC (100Base-FX) in router/switch. The high-precision, ceramic ferrule construction is optimal for aligning single-mode optical fibers. The connectors’ outer square profile combined with its push-pull coupling mechanism, allow for greater connector packaging density in instruments and patch panels. The keyed outer body prevents rotational sensitivity and fiber endface damage. Multimode versions of this connector are also available. The typical insertion loss of the SC connector is around 0.3 dB.
ST connector ST Connector (Straight Tip) — Ferrule diameter = 2.5mm. ST connector’s high-precision, ceramic ferrule allows its use with both multimode and single-mode fibers. The bayonet style, keyed coupling mechanism featuring push and turn locking of the connector, prevents over tightening and damaging of the fiber end. The insertion loss of the ST connector is less than 0.5 dB, with typical values of 0.3 dB being routinely achieved. ST connector is used extensively both in the field and in indoor fiber optic LAN applications, eg. ODF (optical distribution frame). In addition, ST connector is also used to connect GBIC transceiver, usually for 100Base-F.
FC connector FC Connector (Ferrule Connector) — Ferrule diameter = 2.5mm. The FC has become the connector of choice for single-mode fibers and is mainly used in fiber-optic instruments, SM fiber optic components, and in highspeed fiber optic communication links. This high-precision, ceramic ferrule connector is equipped with an anti-rotation key, reducing fiber endface damage and rotational alignment sensitivity of the fiber. The key is also used for repeatable alignment of fibers in the optimal, minimal-loss position. Multimode versions of this connector are also available. The typical insertion loss of the FC connector is around 0.3 dB.
MU connector MU Connector (Miniature Unit) — Ferrule diameter = 1.25mm. MU is a small form factor SC. It has the same push/pull style, but can fit 2 channels in the same Footprint of a single SC. MU was developed by NTT. It is a popular connector type in Japan. Applications include high-speed data communications, voice networks, telecommunications, and dense wavelength division multiplexing (DWDM). MU connectors are also used in multiple optical connections and as a self-retentive mechanism in backplane applications.
MTRJ connector MTRJ Connector (Mechanical Transfer Registered Jack) — Ferrule diameter = 2.45×4.4 mm. MT-RJ is a duplex connector with both fibers in a single polymer ferrule. It uses pins for alignment and has male and female versions. Multimode only, field terminated only by prepolished/splice method.
E2000 connector E2000 Connector — Ferrule diameter = 2.5mm. E2000 connector is a plastic push-pull connector developed by Diamond. The E2000 was developed as an improvement on the SC connector design by having: a latch that retains the connector, a dust cap always in place, and a smaller size. The built in dust cap always stays on the connector protecting the ferrule and blocking harmful laser light when the connector is disconnected. E2000 is available for Singlemode and Multimode applications.
sma SMA Connector (Sub Miniature A) — Ferrule diameter = 3.14mm. Due to its stainless steel structure and lowprecision threaded fiber locking mechanism, this connector is used mainly in applications requiring the coupling of high-power laser beams into large-core multimode fibers. Typical applications include laser beam delivery systems in medical, bio-medical, and industrial applications. The typical insertion loss of an SMA connector is greater than 1 dB.
DIN connector DIN Connector — Ferrule diameter = 2.5mm. DIN connector is a metal screw on connector which is developed by Siemens. Deutsch Telecom mainly uses it. This is a good connector to use where the ruggedness of a metal screw on connector is required but
where there is not enough space for a FC Connector.
mtp&mpo connector MTP and MPO Connector — MTP and MPO are compatible ribbon fiber connectors based on MT ferrule which allow quick and reliable connections for up to 12 fibers. They are intended for installations that require many fiber connections. Up to 12 fibers in a ribbon are stripped to 125um cladding and inserted into 250um spaced parallel grooves. The ferrule also includes two 0.7mm diameter holes, running parallel to the fibers on the outer side of the ferrule. These two holes hold precision metal guide pins which align the fibers with tight tolerances. MTP and MPO connectors feature male and female connector design. Male connectors have two guide pins and female connectors do not. Both connector types need an adapter to mate a pair of male and female connectors. Because MTP and MPO connectors are trying to align so many fibers at once, their coupling loss are typically bigger than single fiber connectors.


History of Different Connector Types
The ST connector is the oldest design of the connectors still in common use. It was the first connector to use a 2.5mm ferrule. The FC and DIN connectors improved on the ST connector by: isolating cable tension from the ferrule, keying the location of the ferrule for angle polishing, and threading onto the adapter for a more positive connection. The SC connector was then developed to eliminate having to screw and unscrew the connector every time and to reduce the cost by molding instead of machining the connector. A big advantage of this push/pull connector over a FC connector is that less room is required between connectors on patch panels. The E-2000 was developed as an improvement on the SC connector design by having: a latch that retains the connector, a dust cap always in place, and a smaller size. As patch panel densities increased the LC and MU connectors were developed to reduce the space required for connectors on patch panels. Both of these connectors use a 1.25mm ferrule. The MT-RJ connector was then developed to put transmit and receive fibers into one connector. This was the first connector to use the MT ferrule design as opposed to a 2.5mm or 1.25mm diameter ferrule. The MTP connector was then developed to increase fiber density even more. The MTP currently has 12 fibers in its MT ferrule however a 24-fiber version is under development.

There are many more influences that lead to the development of these different commonly used connector types. This is why all of the different connector types exist. In fact, there are not only these connector types. A multitude of specialty connectors are launched to the market for different application.

Connector Endface Preparation
Once the optical fiber is terminated with a particular connector, the connector endface preparation will determine what the connector return loss, also known as back reflection, will be. The back reflection is the ratio between the light propagating through the connector in the forward direction and the light reflected back into the light source by the connector surface. Minimizing back reflection is of great importance in high-speed and analog fiber optic links, utilizing narrow line width sources such as DFB lasers, which are prone to mode hopping and fluctuations in their output.

polishing type

Flat Polish — a flat polish of the connector surface will result in a back reflection of about -16 dB (4%).
PC Polish — the Physical Contact (PC) polish results in a slightly curved connector surface, forcing the fiber ends of mating connector pairs into physical contact with each other. This eliminates the fiber-to-air interface, there by resulting in back reflections of -30 to -40 dB. The PC polish is the most popular connector endface preparation, used in most applications.
UPC/SPC Polish — in the Super PC (SPC) and Ultra PC (UPC) polish, an extended polishing cycle enhances the surface quality of the connector, resulting in back reflections of -40 to -55 dB and < -55dB, respectively. These polish types are used in high-speed, digital fiber optic transmission systems.
APC Polish — the Angled PC (APC) polish, adds an 8 degree angle to the connector endface. Back reflections of <-60 dB can routinely be accomplished with this polish.

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