Glass & Optical Fiber

Mass flow control and pressure control instruments are used in preform manufacturing, fiber drawing and ribbon forming processes. Manufacturers of optical fiber and components depend on Alicat for their fast control speeds, which help ensure a uniform product, while benefiting from ease of use features like customization/optimization, high turndown ratios and industrial automation (IIoT).

Preform Manufacturing

Preforms are the layered cylinders of glass, made on lathes using chemical deposition vapor flows, burners for heating and melting glass and pressure control to retain the shape while it is being formed. Once complete, the preforms are stood upright in drawing towers and the lower end is drawn as a fiber, which is coated and taken up on a drum winder. Preforms incorporate both the core light transmission layers and the cladding, different layers of refractive density that keep the beam of light traveling down the fiber, instead of leaking out the sidewalls, even if the fiber bends and loops.

Manufacturers use MFCs to:

  • Control fuel gas flows to burners – MFCs for H2, O2, Air, Acetylene, etc.
  • Control flow of deposition gases – MFCs control carrier gases like N2. Ar and vapor of GeCl4, SiCl4, BoCl3, SF6
  • Lay down process to compact layers against the core – MFCs for control of Cl2 and dual valve pressure controllers for pressure control to keep core from collapsing

Performance requirements:

  • Repeatability, accuracy, and fast response are key competencies for MFCs in preform manufacturing
  • High turndown ratio reduces costs and complexity


  • constant, stable flow must be maintained during pressure and temperature fluctuations
  • potentially a high temperature environment
  • leak rate
  • corrosive gas compatibility
  • fewer units-lower cost

Fiber drawing

Fiber drawing is the means of heating the end of a glass preform, and shaping the melting end into a cone that creates a continuous stream of molten glass which descends and cools into a fiber, which must then be guided in a way that will not break or alter it, while checking the thickness and adding layers to protect it.

In fiber draw processes, manufacturers use flow and pressure control to:

  • Flow control in the furnace to prevent degradation of the element – MFCs to control Ar, N2
  • Other curing processes in the system – MFCs to control the flow of N2, O2, Air, Ar
  • Pressure control of the coating materials – PCs to control head pressure which determines thickness

Performance requirements:

  • Repeatability and accuracy in the mass flow controllers to ensure a consistent product
  • Fast response of control in the event of gas supply changes in the fuel gas mix and draw furnace
  • Pressure control in the coaters
  • Accuracy for pressure controllers


  • Accurate mass flow measurement in burner gas mixing
  • Precise control of gas inside the furnace
  • Repeatable control of gas to curing processes
  • Precise control of pressure during the layering of polymeric coating

Fiber ribbon. Individual fibers are a little thicker than a human hair.

Ribbon forming

Combining fibers into packaged strips of fibers for easy installation in groups, like ribbon cables of electrical wires.

  • Mass flow controllers for control of process gases – N2, O2, Air. The gases control the cure rate of the polymers used to combine the individual fibers into the ribbon.
  • Pressure controllers can be used to control head pressure of polymer dispensing system.


  • Mass flow controller with high repeatability and fast response
  • Pressure Controllers with fast response and accuracy


  • Constant flow during pressure and temperature fluctuations
  • Potentially high temp environment
  • Corrosive gas compatibility

Customizing to optimize your performance

Depending on your need, and the step in fiber manufacturing, here’s a list of options to consider.

Large flow ranges

  • MFCs like our MC Series mass flow controllers have a 200 to one turndown ratio, meaning you can use one to span your full range, instead of buying multiples. This saves costs and reduces complexity!

Automation integration

  • Consider our offerings of industrial protocols. Although our standard instruments come with analog AND serial communications built in, most of our melted glass customers are using one of the industrial ethernet protocols like EtherNet/IP, DeviceNet, EtherCAT or Modbus TCP/IP. You can find more on our communications page.

Pressure control in a closed system

  • If you’re maintaining back pressure or pressure inside a preform while it’s on the lathe, you may want a controller that is able to maintain pressure and also vent pressure in case of over pressure of a closed system. Take a look at Alicat’s dual valve pressure controllers.

Stable control of mass flow in your burner controls

  • Alicat mass flow controllers are the fastest in the world. With flow stabilization as fast as 50 ms or less, it doesn’t matter that your pressure is fluctuating, your process will be rock steady.
  • If your pressure might fluctuate, you might be interested in our low-pressure-drop Whisper™ models. They leave you with plenty of pressure to use for your process.

Alicat MCRW high-flow "Whisper" series mass flow controller, shown with downstream valve
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