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Protect Fiber-Optic Cable from UV
and IR damage with Hot Mirrors and Cold Mirrors.

How are hot mirrors and a cold mirrors used to prevent UV and IR radiation from damaging fiber-optic cable?

 

Recently we’ve been getting a few questions about the effects of UV and IR radiation on optical fiber that is often used in high speed local area fiber-optic communications equipment and image displays or lighting systems. So we thought it was about time we shared a basic synopsis of the effects and a few methods by which to prevent unwanted radiation from destroying costly equipment or delaying expensive projects.

 

It’s important to understand what optical fiber is. Optical fiber is made of either glass, plastic or polycrystalline materials such as quartz and is intended to carry visible or infrared light from one end of the fiber to the other. The optical fiber is coated with a transparent cladding to enhance the refractive index of the fiber and is then surrounded by a buffer and a jacket for mechanical protection. The optical fiber functions by having light emitted from a source, such as a high energy arc lamp, diode laser or LED, coupled into the core of the fiber, which contains and directs the light to the other end of the optical fiber where it can be read as data or displayed as an image.

 

The various compositions of optical fiber have different strengths and weaknesses. For instance optical fiber used in long distance communication, such as those making up the backbones of the internet, are very likely composed of germanium dioxide doped silica glass, which has the benefit of a lower optical attenuation, but is often very expensive to implement when compared to Plastic optical fiber (POF) due to the special handling and installation techniques required.

 

Optical fiber has many practical applications from medical surgical headlamps to high end communications channels. For some industrial, medical or sensing applications where larger cores are needed than in standard data communications, a plastic-clad silica fiber or polymer-clad silica fiber (PCS) is used. Optical fiber is used in many different applications, many of which require that the light passing through the optical fiber be as bright as possible. This is often achieved through the use of high energy arc lamps.

 

The low cost of implementation for POF and PCS make them preferable to glass optical fiber in many different applications. One thing that makes them less preferable is their susceptibility to UV and IR radiation damage. The damage from high energy UV photons takes the form of solarization of the core and/or cladding which can discolor the fiber thus causing signal degradation. Solarization can form physical defects in the fiber which can selectively absorb the visible light spectrum which adversely affect the transmittance efficiency of the fiber. In extreme cases, the fiber core face can be burned, all but destroying the fiber’s functionality.

 

Quartz and glass optical fibers have an advantage of being more resistant to the effects of UV and IR damage, but are not immune to the effects of high irradiance levels of UV light. While arc sources are the brightest, they are also the most damaging. However, even lower power sources can cause UV and IR damage. There are a few ways to effect the prevention of this damage, but one of the most effective is to use a combination of hot and cold mirrors.

 

26_G01-682 Standard Hot Mirror_smallHot mirrors can be used to protect the fiber by reflecting the UV and IR wavelengths away from the fiber while transmitting visible light. This will allow most of the desired light to be used in the application while the harmful UV radiation is prevented from damaging the fiber.

 

23_G01-444 UV Cold Mirror_smallCold mirrors can also be used to protect the optical fiber by reflecting the desired visible light to the fiber and passing the harmful IR wavelengths on to a disposal method. Even better than using just one of these mirrors is to use both, as each kind of mirror is not perfect, using them in conjunction with each-other allows for a greater degree of protection, while retaining the light needed for the application.

 

One way to achieve the use of a hot mirror and cold mirror is to set the cold mirror at a 45 degree angle to the light source such that the visible light is reflected toward the optical fiber and the IR wavelengths are passed through to an absorptive mechanism or a venting port. Then the hot mirror is placed between the cold mirror and the optical fiber so that the limited remaining harmful UV wavelengths are reflected away from the fiber.

 

Another method by which the hot mirror and cold mirror can be used is to coat the reflective backing of the light source with a combination coating, causing the IR and UV radiation to pass into the housing where it can be absorbed or vented.

 

For more information about Hot Mirror and Cold Mirror applications, please call our staff at 1-800-426-2864 or email us.

 

Abrisa Technologies is a recognized global supplier of high quality, fabricated glass components, optical thin film coatings, and custom glass solutions for a wide variety of industries. From our US based Abrisa Industrial Glass fabrication facility in Santa Paula, CA and our ZC&R Coatings for Optics division in Torrance, CA we serve diverse industries such as microelectronics and displays, semiconductor, military, automotive, aerospace, medical, biomedical and scientific R&D. We provide custom specialty flat glass and coating products for applications such as: flat panel display, touch and gesture recognition; visible to IR imaging and surveillance; entertainment, indoor and outdoor lighting; advanced instrumentation; and photonics.


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