Loose-Tube VS. Tight-Buffered Fiber Optic Cable

It is known that fiber optic cable has been the preferred medium for the data center backbone due to channel capacity and scalability, total immunity to electromagnetic interference (EMI) and radio frequency interference (RFI), elimination of the crosstalk inherent in copper cabling (like twinax cable), smaller diameter, and ease of installation, particularly when using pre-terminated modular trunk cables. Selecting the right type of fiber optic cable boils down to the applications and the installation. This post will introduce and compare two fiber optic cable types based on different cable constructions—loose-tube and tight-buffered fiber optic cable.

Loose-Tube Fiber Optic Cable Overview

In loose-tube construction, the fiber is laid helically into semi-rigid tubes, allowing the cable to stretch without stretching the fiber itself, which can protect the fiber from tension during laying and due to temperature changes. Loose-tube fiber may be “dry block” or gel-filled. Dry block offers less protection to the fiber than gel-filled, but costs considerably less. Loose-tube fiber cable comes in various fiber counts that typically range from 6 to 144, with some manufacturers offering higher counts up to 216 fibers. Except a 6-fiber cable, the fibers are grouped into sets of 12 for maximum density.

Structure of Loose-Tube Cable

The following image shows the main components used to construct a Loose-tube cable.

• Multiple 250um coated bare fibers in loose tube.
• One or more loose tubes holding 250um bare fibers. Loose tube stranded around the central strength member.
• Moisture blocking gel in each loose tube for water blocking and protection of 250um fibers.
• Central strength member in the center of the cable and is stranded around by loose tubes.
• Aramid Yarn as strength member.
• Ripcord for easy removal of outer jacket.
• Outer jacket(PVC is most common for outdoor cables because of its moisture resistant, abrasion resistant and stable over wide temperature range characteristics).

Advantages of Loose-Tube Cable

• Extreme Temperature Resistant: Loose-tube cable establishes a strain-free environment for the optical fiber by mitigating the influence of external effects, which makes it perform well at extreme temperatures. Besides, this characteristic also enhances the performance of the loose-tube cable design under a variety of mechanical forces, such as tensile, flexure, twisting, crush, etc.
• Water-blocking Characteristic: As we all know, the core fiber of loose-tube cable is surrounded with a dry water-swellable tape and yarns, or with a gel, which can effectively stop the entry and migration of water.
• UV Protection: The outer jacket of loose-tube cable consists of carbon black, which can provide maximum ultraviolet protection, making the cable able to withstand direct exposure to ultraviolet sunlight in aerial installations.

Tight-Buffered Fiber Optic Cable Overview

Instead of a loose tube, the fiber may be embedded in a heavy polymer jacket, commonly called “tight buffer” construction. Tight-buffered cables are offered for a variety of applications, but the two most common are “breakout” and “distribution”. Tight-buffered cable comes in fiber counts ranging from 2 to 144 fibers, with larger fiber counts featuring fiber subunits of 6 or 12 fibers within the cable. For example, a 144-fiber cable usually has twelve 12-fiber subunits while a 36-fiber cable could have six 6-fiber subunits or three 12-fiber subunits.

Structure of Tight-Buffered Cable

The following image shows the structure of tight-buffered cable.

• Multiple 900um tight-buffered fibers stranded around the central strength member.
• Central strength member in the center of the cable.
• Aramid Yarn(trade name Kevlar) wrapped around the fibers for physical protection and cable pulling.
• Ripcord for easy removal of outer jacket.
• Outer jacket or sheath(usually PVC).

Advantages of Tight-Buffered Cable

• Easy to Install: Tight-buffered cables are easier to install, because there is no messy gel to clean up and they don’t require a fan-out kit for splicing or termination. You can crimp connections directly to each fiber.
• Higher Survivability Standard: Based on military technology for survival under mechanical and environmental stresses.
• Flexibility: No stiff strength member is needed, making the cable more flexible. The cable is also “tight bound” allowing it to be pulled around multiple bends or hung vertically without causing “fiber axial migration”.

Which One to Choose—Loose-Tube or Tight-Buffered?

After we have introduced these two types of fiber optic cables, people may wonder which one is the best for their project. Actually, these two cable types are deployed in different applications.

Loose-tube cable is specifically designed for harsh environments. It has a water-resistant gel that surrounds the fibers, which helps the fibers from moisture, making the cable ideal for harsh, high-humidity environments where water or condensation can be a problem. The gel-filled tubes can also expand and contract with temperature changes. Loose-tube cable has a higher tensile strength than tight-buffered cable. But it is not the best choice when cable needs to be routed around multiple bends, which is often true in indoor applications. Excess cable strain can force fibers to emerge from the gel.

Tight-buffered cable is optimized for indoor applications. Because it’s sturdier than loose-tube cable, it is more available for moderate-length LAN/WAN connections or long indoor runs, and even direct burial. Tight-buffered cable is also recommended for underwater applications.

Summary

Choose the right cable types for your applications can effectively improve network performance and ensure the life span of the whole project. FS.COM offers a wide range of loose-tube and tight-buffered cables in different fiber counts and with single-mode fiber or multimode fiber. For more detailed information, please visit FS.COM.

What Makes Direct Attach Cable Preferable for 40/100G Migration?

As new applications, devices and architectures continue to demand ever higher speed networks, 40G and 100G Ethernet links are rapidly coming on line. Many vendors have put forward various solutions for 40/100G migration, including optical transceivers (like QSFP+ or QSFP+ 28), fiber cabling (like MPO/MTP breakout cable or MPO/MTP harness cable), and copper cables (like direct attach cable). Among these solutions, direct attach cable with unique advantages is more preferable for 40/100G migration. But why? The following part will explain the reasons in details.

What Is Direct Attach Cable?

Direct attach cable (DAC), also known as twinax cable, is a fixed assembly supporting high data speed that uses a small form-factor connector module as an optical transceiver at the either end of a length of cable. Generally, direct attach cable can be active and passive. The former one has active electronic components in the optical modules to improve the signal quality, while the latter one is mainly just a straight “wire” and contains a few components. With low cost, low power consumption and low latency, DAC has become popular in network industry and widely applied in storage area network, data center and higher performance computing connectivity to achieve the migration to 40/100G. The image below shows Cisco QSFP-H40G-CU1M compatible 40G QSFP+ Passive Direct Attach Copper Cable.

Unique Features of Direct Attach Cable

With many unique features, direct attach cable can satisfy the increasing demand for high speed data transmission. The main features of DAC are described in the following text.

• Low Price—DACs are much cheaper than the regular optics. Because the “transceiver” on both ends of DACs are not real optics. Compared with regular optical transceivers, the small form-factor connector modules are without expensive optical lasers and electronic components, and they’re just used to transmit the optical signals. Accordingly, the cost of DACs will be much lower. Besides, DACs in some case can be an alternative to optical transceivers as it eliminates the separable interface between transceiver modules and optical cable. Thus, direct attach cable is a more cost effective solution for 40/100G applications.
• Power Saving—A small electrical component is used in both active direct attach cable and passive direct attach cable to identify the modules on the end and cable type to the Ethernet interface. Compared to optical transceivers, DACs with this component consumes very litter power.
• Enough Data Rate for Various Applications—With the appearance of optical fibers which can support high data speed and achieve good performance in networks, many people may think that copper has been out of sight. Actually, DAC can also provide high speed input and output data. Currently, DACs are most commonly used for 10G and 40G applications. And with the development of technology, some direct attach cable can be used to achieve data transmission of 100G, or even 120G.
• Interchangeability—With the advancement of copper cable technology, copper DACs are interchangeable and hot swappable with fiber optic modules.

Summary

With a wide range of 40/100G solutions available on the market, direct attach cable becomes the preferable one for 40G/100G applications, since it takes the advantages of cost and power saving, enough data rate for various applications and excellent interchangeability. With the increasing demand for higher bandwidth, direct attach cables are continuing evolving. Fiberstore, as a professional manufacturer and supplier of optical equipment, has various direct attach cables in stock, such as 10G SFP+ DACs, 40G QSFP+ DACs, and 100G QSFP28 DACs. If you want to upgrade your network to 40/100G with direct attach cables, please visit FS.COM.