Optical fibers are used to collect and deliver light in numerous applications, and they are also used to make instruments more sensitive as well smaller and easier to use.

From the beginning, optical fibers were used for medical imaging (endoscopes) to look inside the body to determine treatments. The use of fibers in the medical field has increased considerably: they are now used for laser surgery, laser scalpels, optical coherence tomography, kidney stone ablation, tumor ablation, skin treatment and many other treatments.

Fibers are finding uses in analytical instruments such as flow cytometry, DNA analysis, cell counting, confocal microscopy amongst others. Most of these instruments use fluorescent tags to detect abnormalities in cells. The intensity of fluorescent light from these is very small, in some cases in pW range. Fibers are used to collect the light and deliver it to photodetectors as well as deliver light from a laser to cell samples.

Optical fibers make excellent sensors as they are immune from electromagnetic radiation and can be used in environments where electronic sensors cannot be used.

There are basically two classes of fiber sensors:

1. intrinsic, where the fiber is the sensing element, and
2. extrinsic, where the fiber is used to relay the signals from a sensing element outside of the fiber.

Fibers can be used to sense almost everything and have been used to monitor stress, strain, temperature, pressure, current, voltage and used to measure chemicals. They are very useful in hazardous environments and have been used in diverse applications such as down-hole monitoring in oil and gas fields, structural monitoring of bridges, dams, buildings, and aircraft, to name a few.

Fibers form an integral part of optical switches where they are used as the conduit for information being switched. Optical switches are particularly important in data centers where the transfer of information needs to be performed as quickly as possible. Generally, information is transmitted using optical fibers and in conventional switches this information is switched from one channel to another by converting the optical signal to an electrical signal which is then switched to the required channel and then converted back to an optical signal which is then transmitted via another fiber. This process can be time consuming. To speed up the process of switching the information from one channel to another, a fully optical process is needed and used where the information is not converted from optical to electrical. This can be achieved via micro-electromechanical system (MEMS) technology where mirrors on a silicon chip can be used to switch the optical signal from one fiber to another in a 2D fiber array.

Fibers are finding increasing uses in the industrial setting where fiber lasers are used for cutting and welding as well as sensors on the industrial production lines. Laser welding and cutting requires the delivery of high power and the cutting/welding head needs to move in various patterns (depending on the cut or the weld required) therefore the fibers tend to have a large core diameter.