Exploring Fiber Patch Connectors: LC, SC, ST, and More

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By Ben Hamlitsch, Technical and Product Innovation Manager RCDD, FOI at trueCABLE

Over the past two decades, the techniques for terminating copper Ethernet Category cables have remained largely unchanged. Whether in the past or in the present, you'll still encounter 8P8C RJ45 connectors on Ethernet patch cords and keystone jacks connected to patch panels. The color coding standards, T568A and T568B, remain steadfast in guiding the wiring sequence for proper connections. Unlike fiber optics, it's important to note that directly splicing copper Ethernet cables for extensions is nearly impossible; you must use a connector or patch panel while adhering to strict length limitations.

In contrast, extending and terminating fiber optic cables involves different methods. When an installer needs to extend a fiber link without the need for frequent connections, fibers are spliced together using either fusion or mechanical methods. However, at locations requiring plug-and-play capabilities, a connector must be applied. The evolution of fiber optic connectors is remarkable, with various types being incompatible with one another, and some connectors gradually being phased out. Choosing the appropriate type of connector hinges mainly on equipment needs and somewhat on the installation environment.

In this post, we will explore:

• Simplex vs Duplex Connector Styles
• FC, SC, LC, ST, and MPO/MTP Connectors

Simplex vs Duplex

To grasp the variety of available connectors, it's essential to understand assembly styles. Connectors are primarily categorized into two styles: simplex and duplex. While this may sound complex, it’s quite simple. Simplex refers to a single connector attached to a single fiber, whereas duplex comprises two single connectors housed together, often in a plastic casing. The term "zip cord" describes duplex fiber optic cords, which connect two fiber patch cords within a single jacket that can easily be separated.

Ultimately, the choice between simplex and duplex styles depends on your endpoint equipment and configuration. It's crucial to clarify that simplex and duplex do not pertain to single-mode or multi-mode fibers or specific connector types like LC or SC. In summary, each connector type manages a single fiber strand, regardless of assembly.

Here are a couple of images to visualize the differences:

Left: Duplex connector assembly. Right: Simplex connector assembly. Both are of the LC type.

FC Connectors

FC connector attached to a single-mode fiber in duplex format.

The FC connector is one of the oldest types of fiber optic connectors, originating from the term "Ferrule Connector," but it's also associated with "Fiber Channel." This metallic, screw-on connector offers exceptional resistance to vibrations and accidental disconnections. In terms of analogs, it is similar to the F-Connector used with coaxial cables. The FC connector utilizes a connector key and requires careful insertion to avoid damage to the fiber's end face. Its popularity is waning due to advancements in connector technology and precision manufacturing costs. Nonetheless, it still has its place in robotic and industrial environments where robustness is critical.

SC Connectors

SC connectors are prevalent in today's fiber optic landscape, although their dominance is increasingly challenged by the more compact LC connectors, which are better suited for high-density applications. The acronym SC stands for "Subscriber Connector," as it is commonly found at endpoints in residential and commercial installations. They are also referred to as "Standard Connectors."

SC connector in simplex format attached to single-mode fiber.

SC connectors feature a plastic push-pull design paired with a locking tab. This design makes them easy to insert and remove, boasting resistance to accidental disconnections, albeit not completely vibration-proof. They are more forgiving than FC connectors regarding the potential for end-face damage during reconnections. However, a drawback is their size, as they utilize a 2.50mm ferrule.

LC Connectors

As small form-factor connectors gain traction due to their space-saving advantages, the LC connector stands out. The LC, short for “Lucent Connector,” is efficiently designed to occupy half the space of SC connectors, incorporating a keyed, pull-proof design. Similar to SC, it utilizes a latch that secures the cable in place, but its compactness contributes significantly to its growing popularity in high-density installations.

SC connector to the left; LC connector to the right. Notice the size difference!

LC connectors are typically associated with fiber optic transceivers, which are devices that facilitate the translation of electrical signals to optical pulses, enhancing versatility. It's common for Ethernet switch manufacturers to exclude transceivers from switches, as they depend on the specific fiber optic installation you’re pursuing, often dictated by the lengths and speeds needed. This approach reduces the initial price of the switch while offering an expandable system that aligns nicely with a variety of fiber technologies. The flexibility of LC connectors and transceivers is revolutionizing the fiber optic market by making it accessible to smaller installations and DIY enthusiasts.

ST Connectors

Next up is the ST connector, which stands for "Straight Tip." This type is constructed from metal and employs a bayonet-style connection. The design resembles a twist-and-lock mechanism, akin to the BNC connectors commonly used in audio and video applications.

ST connectors on the left compared to an SC duplex assembly on the right.

ST connectors are neither pull-proof nor wiggle-proof, and they rank lowest in reliability among fiber termination options. Their usage has diminished significantly as more advanced connectors, including SC and LC, take precedence. Like FC and SC connectors, ST connectors also employ a 2.50mm ferrule.

MPO/MTP Connectors

Thus far, we've only discussed connectors terminating on a single fiber strand. However, there are indeed connectors designed for multiple strands, allowing for efficient and streamlined connections. A common approach for deploying fiber optic cables involves running high-fiber-count cables into telecommunications rooms (TRs), where various termination options can be implemented to connect your equipment seamlessly:

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• Using high-fiber-count cables with unconnected fibers to splice each fiber to a pigtail equipped with SC or LC connectors on the other end. This labor-intensive process complicates installations and increases the risk of mistakes.

• Utilizing a pre-connectorized high-fiber-count cable featuring an MPO/MTP connector, plugging it into fan-out cables that accommodate 12 to 24 SC or LC connectors. These factory-made solutions simplify installation, allowing users to take advantage of "plug and play" efficiency.

The term MPO stands for Multi-Fiber Push-On, a widely recognized connector type within the industry. MPO connectors may come in male or female forms. MTP connectors fall under the MPO classification but represent a specific brand. While all MTP connectors qualify as MPOs, not all MPOs can be classified as MTPs, as MTP is a registered trademark of US Conec. MTP connectors improve upon the standard MPO design by offering enhanced latching systems and precision fiber alignment.

Both MPO and MTP connectors operate similarly, accommodating two rows of fibers (up to 24) in a single termination. However, variations between MPO patch cords exist, each customized according to installation needs and equipment characteristics. Here are a couple of examples:

MPO to MPO cable on the left. MPO to LC connector fan-out on the right.

In conclusion, we’ve provided a concise overview of various connector styles that you may encounter. The most commonly found connectors in practice today include SC, LC, and MPO, while the use of others is steadily declining. In future discussions, we'll delve deeper into topics such as end-face polishing types (PC, UPC, APC) and the color coding standards that help distinguish between cable types. For now, I’ll say:

HAPPY NETWORKING!

trueCABLE provides this information through our website, including the "Cable Academy" blog and live chat support, to assist our customers and visitors, adhering to our website's terms and conditions. While the information is focused on data networking and electrical issues, it does not constitute professional advice, and any reliance on such material is at your own risk.