Today, follow HX Fiber to explore how sand is transformed into optical fiber step by step:

Step 1: Understand the raw materials of optical fiber

Silicon is the most common element and the most important raw material

Silicon is the second most common element in the Earth's crust, mainly found in quartz in the form of silicon dioxide (the main component of sand), and is the basis of the semiconductor industry. Silicon is key to the development of the communications and information industries. Almost all chips are based on silicon, and 90% of integrated circuits use silicon substrates.

As the most critical material for current communications, the main component of optical fiber is silicon dioxide. Optical fiber communication is a communication method that uses light waves to transmit information in optical fibers. Due to the extremely high frequency of light, the capacity of optical fiber communication is very large, and optical fiber communication also has the advantages of strong anti-electromagnetic interference ability and low signal attenuation, so it is widely used in the field of modern communications.

The main component of optical fiber is silicon dioxide (SiO2). Silicon dioxide is an inorganic compound with high melting point and high hardness. It is also an important raw material for manufacturing optical fiber. In optical fiber communication, light waves are transmitted through optical fibers made of silicon dioxide, achieving fast, efficient and long-distance transmission of information.

Step 2: Choose sand

In nature, silicon mainly exists in the form of quartz sand. The crystal clear sand in river sand is the most suitable. Desert sand is gravel, saltpeter and dust are not suitable for extracting silicon, but high-quality river sand is a high-quality material for extracting silicon. Pure silicon rods are substrates for chip manufacturing, while purified silica is used to produce glass and optical fiber.

The sand required for optical fiber is more picky, quartz stone, calcium oxide, etc. We need to find suitable raw materials from nature.

The production process from sand to optical fiber includes the following steps:

Prepare raw materials: The main raw materials include quartz sand, alumina, calcium oxide, etc., among which quartz sand is the most important raw material, which is made of high-purity silica through a special process. These raw materials need to be crushed, screened, etc. to ensure the consistency of their quality and particle size.

As the most critical technology for communication optical cables, optical fiber preform is the most advanced technology.

Optical fiber preform is the original rod material that controls the performance of optical fiber. It is generally tens to hundreds of millimeters in diameter. Its inner layer is a high-refractive-index core layer, and its outer layer is a low-refractive-index cladding layer to meet the basic conditions for light wave transmission in the core layer. Optical fiber preform consists of a core rod and a cladding. There are four main production processes: modified chemical vapor deposition (MCVD), axial vapor deposition (VAD), rod-out chemical vapor deposition (OVD) and plasma chemical vapor deposition (PCVD). Among them, VAD and PCVD have a high comprehensive cost-effectiveness and gradually become the mainstream of production. The obtained optical fiber preform is placed in a high-temperature drawing furnace for heating and softening, and is drawn into glass fibers of different diameters with similar proportions. These glass fibers are what we often call optical fibers.

Optical fiber preform

The most critical technology in the production of optical fiber and cable - optical fiber preform production, is currently only produced by a few companies in the world: the methods for producing preforms include PCVD, OVD, and VAD. Although the methods are different, they all aim to obtain the optical fiber mother embryo - optical fiber preform. my country's Changfei Company and FiberHome Company both have the ability to produce optical fiber preforms, but with different processes. It is said that these two companies, both located in Wuhan, have produced nearly half of the world's optical fiber preforms.

Preparation of preform: Preform is one of the key materials for making optical fiber. The preparation process of preform includes steps such as sol injection, gel curing and sintering.

Optical fiber preform is a round glass rod like the one in the picture above. It looks like a one-piece structure, but in fact, the core layer in the middle and the cladding layer outside have different refractive indices, that is, the center is a glass with a high refractive index, and the surrounding is ordinary glass. The ratio is roughly the same as the relationship between the small cylinder and the large cylinder in the picture above, with a diameter ratio of about 8:125.

Because the core layer has a high refractive index, when the laser signal propagates in the core layer, it will propagate in the core layer. When it encounters the cladding, due to the different refractive indices, it will directly form a principle similar to mirror reflection, reflecting the laser signal back to the core layer. Therefore, the laser signal of optical communication always propagates in the core layer.

Wire drawing: The prepared optical fiber preform rod is placed in a high-temperature wire drawing furnace to heat and soften, and is drawn into glass fibers of different diameters with similar proportions. These glass fibers are what we often call optical fibers.

Of course, there will be equipment to control the melting temperature and drawing speed to ensure that the drawn optical fiber is uniform and the diameter meets the specifications. Then, after the drawn high-temperature glass fiber is cooled, a layer of glue is coated on the surface, which prevents the optical fiber from being too brittle and increases its flexibility.

Optical fiber comes in standard coils of certain lengths, such as 10 kilometers, or 25 kilometers, as shown in the coil above.

This forms the core of the optical fiber:

Core layer

Position: The core is located in the center of the optical fiber.

Composition: The core is made of high-purity silicon dioxide (SiO2) and is doped with a very small amount of dopants to increase the core's refractive index (n1) for light.

Function: The core's main function is to transmit optical signals. Since the core's refractive index is higher than the cladding, when light enters the core and meets certain conditions, the light will be totally internally reflected at the interface between the core and the cladding, and then transmitted forward along the core.

Cladding

Position: The cladding is tightly wrapped around the core.

Composition: The composition of the cladding is also high-purity silica with a very small amount of dopants. Its refractive index is slightly lower than that of the core (n1>n2).

Function: The cladding provides a reflection surface and light isolation for the transmission of light, ensuring that the optical signal can be transmitted in the core without leaking to the outside world. At the same time, the cladding also plays a certain mechanical protection role.

Coating

Location: The coating is the outermost layer of the optical fiber.

Composition: The coating is usually composed of materials such as acrylate, silicone rubber and nylon. The coating may include a multilayer structure such as a primary coating, a buffer layer and a secondary coating.

Function: The main function of the coating is to protect the optical fiber from water vapor erosion and mechanical abrasion. At the same time, the coating also increases the mechanical strength and bendability of the optical fiber, which helps to extend the service life of the optical fiber.

Subsequently, a protective layer is added to the outer layer of the optical fiber. The purpose of the colorful color is mainly to distinguish the order of the fiber cores. The colorful protective layer outside the optical fiber is actually the outer sheath of the optical fiber. Its materials are diverse, and the common ones include PE (polyethylene), PVC (polyvinyl chloride), PVDF (polyvinylidene fluoride), LSZH (low smoke halogen-free flame retardant), Plenum (flame retardant grade polyolefin) and Riser (shaft grade polyolefin). These materials each have their own characteristics and applicable environments, such as fire resistance, moisture resistance, weather resistance, etc.

The national standard for the fiber core sequence of BELLCORE is: blue, orange, green, brown, gray, white, red, black, yellow, purple, pink, cyan; (orange is also called orange) The color code must comply with the Munsell color code, which is also the most comprehensive color code arrangement in the world. The national standard full color spectrum: blue, orange, green, brown, gray, white, red, black, yellow, purple, pink, cyan. The loose tube sequence is: red from white to white.

Twelve optical fibers are bundled together, and a sleeve is formed on the outer layer through an injection molding machine. The 12 cores are encapsulated into a tube, and oil cake is injected in the middle to protect the optical fibers while filling the space.

In order to distinguish the multiple bundle tubes in the optical cable, different bundle tubes have different colors. This allows different optical fibers to be distinguished by group.

Multiple bundle tubes are connected to form optical cables of different specifications. If a 12-core optical cable has optical fibers in only one bundle tube, and if a 48-core optical cable has 12 cores in each of the four bundle tubes, different optical cable specifications are formed by analogy.

Generally, there is a reinforcing core in the middle of the optical cable, and there is also a case of a single-sided reinforcing core. A bundle tube is distributed around the reinforcing core and a sheath is added to form the optical cable. The commonly used optical cable reinforcing core is generally steel wire.

Before China mastered the production technology, the price of optical cables was extremely high. When Chinese companies mastered the production technology, the global price of optical cables dropped rapidly. Thanks to our optical cable manufacturers, especially national enterprises such as YOFC and FiberHome, for their contributions to my country's optical communication industry. Thanks to their continuous exploration of efficient production, the cost of fiber-to-the-home for each household has continued to decline, making China's optical communication penetration rate far ahead of the world.

Source: Dongguan HX Fiber Technology Co., Ltd