In-depth Understanding of Fiber Optic Cables

The commitment to fiber optic technology has spanned more than 30 years, and nowadays a high level of glass purity, fiber optic cable, has been achieved owing to the continuous research and development. This purity, combined with improved system electronics, enables to transmit digitized light signals over hundreds of kilometers with high performance, offering many advantages in fiber optic systems. This text provides an overview of the construction, categories, and working principles of this fiber optic cable.

Construction of Fiber Optic Cable

Fiber optic cable generally consists of fiver elements : the optic core, optic cladding, a buffer material, a strength material and the outer jacket. Here, much more detailed information is attributive to the optic core and optic cladding which are both made from doped silica (glass).

The Optic Core and Cladding Details

The optic core is the light-carrying element at the center of the cable, and the optic cladding surrounds the optic core. Their combination makes the principle of total internal reflection possible. Besides, a protective acrylate coating then surrounds the cladding. In most cases, the protective coating is a dual layer composition: a soft inner layer that cushions the fiber and allows the coating to be stripped from the glass mechanically, and a harder outer layer that protects the fiber during handling, particularly the cabling, installation, and termination processes. This coating protects the glass from dust and scratches that can affect fiber strength.

Optic Core and Cladding, makes reflection possible

Categories of Fiber Optic Cable

There are two general categories of fiber optic cable: single-mode fiber (SMF) and multi-mode fiber (MMF).

MMF was the first type of fiber to be commercialized. It has a core of 50 to 62.5 µm in diameter much larger than SMF, allowing hundreds of modes of light to propagate through the fiber simultaneously. Additionally, the larger core diameter of MMF facilitates the use of lower-cost optical transmitters (such as light emitting diodes or vertical cavity surface emitting lasers) and connectors, more suitable for relatively shorter-reach application. Take 1 Gigabit Ethernet (GbE) applications for example, MMF is deployed to establish 550m link length with 1000BASE-SX SFPs (eg. Cisco Meraki MA-SFP-1GB-SX).

SMF, in contrast, has a much smaller core, approximately 8 to 10 µm in diameter, which allows only one mode of light at a time to propagate through the core. It’s designed to maintain spatial and spectral integrity of each optical signal over longer distances, permitting more information to be transmitted. Similarly, as for 1GbE applications, SMF is able to realize 70km reach with 1000BASE-ZX SFPs, like GLC-ZX-SM, a product compatible with Cisco listed in Fiberstore.


Working Principles of Fiber Optic Cable

The operation of a fiber optic cable is based on the principle of total internal reflection. Light reflects (bounces back) or refracts (alters its direction while penetrating a different medium), depending on the angle at which it strikes a surface.

This principle comes at the center of how fiber optic cable works. Controlling the angle at which the lightwaves are transmitted makes it possible to control how efficiently they reach their destination. Lightwaves are guided through the core of the fiber optic cable in much the same way that radio frequency (RF) signals are guided through coaxial cable. The lightwaves are guided to the other end of the fiber being reflected within the core. The composition of the cladding glass related to the core glass determines the fiber’s ability to reflect light. That reflection is usually caused by creating a higher refractive index in the core of the glass instead of in the surrounding cladding glass, creating a waveguide. The refractive index of the core is increased by slightly modifying the composition of the core glass, generally by adding small amounts of a dopant. Alternatively, the waveguide can be created by reducing the refractive index of the cladding using different dopants.


In fiber optic cables, the light can carry more information over longer distances than the amount carried in a copper or coaxial medium or radio frequencies through a wireless medium. With few transmission losses, low interference, and high bandwidth, fiber optic cables are the ideal transmission medium. Fiberstore offers various kinds of fiber optic cables, including SMF and MMF types, simplex and duplex fiber optic cables, indoor distribution cables and outdoor loose tube cables, etc. For more information about fiber optic cables, you can visit Fiberstore.

Single Fiber – Why Choose it for Gigabit Optical Communications?

Advanced applications, including voice and data convergence, as well as storage area networking, are putting burdens on today’s fiber optic networking infrastructure, especially on the fiber cabling. With speeds in data centers now increasing from 10Gbps to 40Gbps, to 100Gbps, and 120Gbps, etc., different fiber technologies are required for Gigabit optical communications, like single strand fiber (simplex fiber cable) and duplex fiber cable. This text mainly introduces the single strand fiber, a relatively simple solution chosen for fiber optimization, and its benefits that drive the need to deploy single strand fiber for Gigabit optical communications.

Single Fiber Technologies

Single strand fiber, just as its name shows, uses one strand of glass instead of two dedicated strands with one for receiving and the other for transmitting. It doubles the capacity of the installed fiber plant, which in turn doubles the per fiber return on investment (ROI) with no need for more physical fiber.

Early single fiber solutions were based on single wavelength directional coupler technologies. With these solutions, the same wavelength (1310nm for up to 50km or 1550nm for longer distances) travels in each direction (transmit & receive). At the edges, the two signals are coupled into a single fiber strand with a directional coupler (splitter-combiner). This coupler identifies the direction of the two signals (ingress or egress) and separates or combines them. This kind of solution is normally very reliable and cost effective, as long as special installation and connector type (APC -angle polished connector) requirements are observed. Otherwise, this solution is prone to reflections when traversing patch panels and in the cases of fiber cuts or dirty connectors.

single fiber 1310nm TX/1510nm Rx

In recent years, a new single strand fiber technology has emerged based on two wavelengths traveling in opposite directions. External WDM couplers (multiplexers) combine or separate the two wavelengths at the edges. As technology progressed, the external passive WDM coupler became integrated into a standard interface fixed optic transceiver.

Single Fiber SFP (Small Form Pluggable)

The growing demand of single fiber solutions driven by the Ethernet bandwidth has led to the development of a wide range of single fiber pluggable SFP transceivers. These hot-pluggable optic transceivers are designed in small-form factor for high-density solutions, covering many industrial protocols and allowing flexibility in distance choices. Besides, they provide advanced optical performance, Digital Diagnostics Monitoring (DDM). Commonly-used single SFPs include 1000BASE-LX SFPs (eg.EX-SFP-1GE-LX shown below), 1000BASE-ZX SFPs, etc.

EX-SFP-1GE-LX,single fiber SFP

Single Fiber Benefits

The benefits of the single strand versus the dual strand fiber implementation can be considerable.

  • Operational and Capital Expense Savings

Single fiber solutions, like any other fiber optimization methods, affect both the capital expenses (CAPEX) and the operational expenses (OPEX). For fiber users like carriers and enterprises that lease dark fiber from their provider rather than owning the fiber plant, the OPEX savings is extremely significant by avoiding avoid the need to install additional fiber strands to accommodate growth without imposing limitations due to engineering capabilities.

  • Fiber Run — Engineering Cost

The design and engineering of a fiber run is a complex process. It may require crossing roads or freeways, which leads to possible thorough design, and inflexible work scheduling. The deployment cost might include trenching or other expenses. In many cases, the price of labor, services, and licenses required to install new cabling can far exceed the cost of the media and supporting electronics.

  • Fiber Termination and Accessories Cost

New fiber runs require terminating and connecting any fiber strand. This process requires qualified labor that will polish, connectorize, and test every fiber strand. Reducing the number of terminated fiber strands by half results in a significant cost reduction.

  • Network Reliability and Maintenance Cost

Reliability and availability are key in any communications system. Use of single fiber pluggable-based transceivers in an existing dual fiber link opens the possibility of creating redundant link solutions. In fiber assembly, a larger number of fiber strands increase the chance of fiber failure. The larger the fiber strands are, the higher the failure chances are, thus the maintenance cost increase accordingly. This can be reduced through the simplicity of single fiber technology.


Single fibers are considered as the simple way for fiber optimization, for they not only double the capacity of the installed fiber plant, but also help to achieve overall savings in Gigabit optical communications. Fiberstore offers single fibers available in both single-mode and multi-mode versions, which are all quality assured. In addition, single fiber optical transceivers can also be found in Fiberstore, such as 1000BASE-LX SFP (EX-SFP-1GE-LX mentioned above), 10GBASE-ZR SFP+ (SFP-10G-ZR). For more information about single fibers, you can visit Fiberstore.