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Exploring the Fundamentals of Fiber Optics Technology

Exploring the Fundamentals of Fiber Optics Technology

Fiber optics technology uses glass or plastic fibers to transmit light signals. It is based on the principle of total internal reflection, which allows light to travel through the fiber without signal loss. This is integral to various applications, including fiber lasers and interferometric setups. By using fiber optics, both stability and convenience are significantly increased compared with standard breadboard setups. The use of fiber optics has increased significantly in a wide range of applications, including medical devices, sensing, and industrial automation.

How Do Fiber Optics Work?

There are three main types of standard fiber cables: single-mode, polarization-maintaining and multimode. Single-mode fiber cables have a small core and are designed in such a way that they support only a single propagation mode. A single-mode fiber is often used to connect the optical setups of interferometers, for example. Meanwhile, multimode fiber cables have larger cores, allowing for the propagation of multiple light modes. You are more likely to find multimode fibers in spectrometry, microscopy, quantum computers and other imaging applications.

If you bend both single- and multi-mode fibers, however, the state of polarization of the light exiting the fiber will change. Polarization-maintaining fibers, or PM fibers, are used to maintain the polarization of light as it propagates through the fiber. This is achieved by introducing strong built-in birefringence, creating two orthogonal polarization axes with different propagation constants. The linear polarization of light coupled into one of these axes is subsequently maintained. Linearly polarized laser radiation is conventionally coupled into the slow axis because of its lower sensitivity to fiber bending.

By carefully controlling the fiber geometry and material properties, as well as carefully confectioning the fiber with adequate connectors, it is possible to maintain a high polarization extinction ratio (PER). This is the ratio between the optical powers coupled to the two polarization axes of the fiber. Polarization-maintaining fibers are widely used in applications where polarization control is critical, such as interferometers, and polarization-sensitive optical coherence tomography. Their unique properties make them essential components in many advanced photonic systems.

Beyond the fiber optic cable itself, there are several key components for ensuring high PER, high coupling efficiencies, and long-term component stability in a fiber optic system.
Fiber connectors are used to connect fibers to receptacles – for example that of a fiber coupler. FC-type connectors are standard for PM fibers, as they provide a robust and reproducible connection – even for PM fibers.

  • Fiber collimators are used to convert a divergent beam of light into a collimated beam. This is useful in many applications, including laser surgery and optical sensing.
  • Fiber couplers or laser beam couplers are used to couple into fiber cables. The laser beam coupler has to produce a diffraction-limited spot that matches the mode field of the fiber to achieve maximum coupling efficiency. They also need to be optimized for high pointing stability and long-term stability.
  • Fiber patch cables are fully confectioned fiber cables that include fiber connectors. They are typically available in different lengths and as single-mode, PM, and multimode. Standard fiber cables usually are Ø 3mm fiber cables with Aramid strain-relief or cables with Ø 900 µm buffer only.
  • Fiber ports, in this context, are synonymous with fiber couplers. Often they are the optical setup’s entry and exit points.
  • Fiber Port Clusters are compact opto-mechanical units that split one or multiple fiber-coupled sources into multiple output fiber cables with high efficiency and variable splitting ratio.
  • PM fibers is the short form for polarization-maintaining fibers and are used in applications where polarization is critical. In these fibers, the polarization is maintained, even when the fiber is bent or twisted. PM fibers are used in sensing, interferometry, and telecommunications applications.

Looking for Fiber Optic Solutions?

The future of fiber optics technology looks bright, and it will continue to transform the way we live and work. Contact a Schäfter+Kirchhoff team member today to learn how our cutting-edge components can take you to the next level. From fiber collimators to polarization analyzers, we have everything you need to revolutionize your system. Get in touch today.

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