Other Tricks

Laser

When we discuss our work in fiber optics with people who are not communications contractors or installers, many people assume we work with medical fiber optics because that’s the fiber optics most people are familiar with. Medical applications of fiber optics in diagnostics and surgery are common, and many people have had some experience with them.

But the uses of fiber optics outside communications are much broader. Fiber is used for lighting, laser surgery and welding, replacing spark plugs, detonating bombs and many types of devices to sense physical parameters such as sound, pressure, chemical content, etc. Airplanes and ships even use gyroscopes made with fiber optics. This month, we’ll review some of these other applications.

Light bright

One of the first uses for fiber optics was illumination. Make a fairly large (~3 mm) bundle of fibers and polish both ends. Then, put a bright light at one end with a lens to focus the light into the bundle and light will come out the other end. The light can be focused with a lens at the other end.

This method of illumination can provide a bright light in hard-to-reach spaces, with the advantage that it isolates the light source’s heat from what is illuminated. This is a big advantage when looking at sensitive or delicate objects. Some fibers also radiate light from the fiber’s edges, creating illumination  that looks very much like a neon light. Therefore, it can be used for applications similar to neon tubes, such as signs. 

Fiber optic lighting uses nonconductive glass or plastic fibers, so it also can be used to provide lighting in areas where electrical lighting is dangerous, such as around swimming pools or in explosive atmospheres.

Pass the remote 

Another application for fiber optics was remote imaging. If we carefully arrange that bundle of fibers in a series of rows on one end and exactly duplicate the arrangement on the other—a coherent bundle—we can use this fiber array for imaging. Each fiber acts like a pixel in a digital display by creating an image with the resolution of the number of fibers. Lenses on each end help create the image views and some fibers, usually around the outside, can be used to carry light to illuminate the subject being viewed. That’s how medical endoscopes work, but the same technique is used for inspecting inside machinery that would otherwise have to be disassembled to inspect.

Cutting in 

Couple enough power into the fibers, or even into a single fiber, and you can do laser surgery, which is a good solution for some tricky operations such as inside human joints. Laser surgery has one big advantage: the heat from the laser cauterizes tissue and minimizes bleeding. Special probes help perform unique surgery, such as one that will insert devices, such as a fiber mesh, to repair internal tears such as hernias. 

Other fiber optic probes contain sensors made from fiber optics. In medical applications, fiber sensors can measure color, pressure or chemical content, such as oxygen in blood, allowing doctors to examine inside the body without major surgery or disturbing normal body functions.

Couple even more power into a fiber, and you can laser-weld and cut. You can also use this technique to create bomb detonators. One note of caution: When you get to these power levels, dirt or contamination on the ends of a fiber can be an even bigger problem than in communications. At these power levels, the dirt can explode and damage or destroy the fibers.

Fiber optic medical applications are not just for imaging or surgery. All those high-tech medical devices must communicate. High-resolution digital X-rays, CAT, MRI or PET scans and other medical-diagnostic tests generate large amounts of data to be sent to specialists for analysis. Many of those big diagnostic machines generate increased electromagnetic interference, which is another advantage of communications over fiber optics for both internal and external connections. We can probably safely say that every major hospital uses plenty of fiber optics for communications. And those cables and systems are installed by typical fiber optic installers.

Some of the most interesting fiber optic applications are for sensors in the outside world. In some cases, the fiber itself is the sensor, but, in others, it is simply used to transport light to the sensor. Fiber optic sensors can monitor high-voltage transmission lines, find leaks on pipelines, measure physical conditions for deep well drilling and listen for submarines off the coast.

We will cover some of these applications in more detail in future columns.

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor

Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.

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