Also known as microstructured optical fiber, it has attracted wide attention in recent years. Its cross section has a complex refractive index distribution and usually contains holes with different arrangements. These holes have the same size as the wavelength of light wave and run through the whole device. Light waves can be confined to the core of optical fiber. Photonic crystal fiber has many peculiar properties. For example, only one mode of transmission can be supported in a wide bandwidth range; The arrangement of pores in the cladding region has great influence on the model performance; The asymmetric arrangement of holes can also produce great birefringence effect, which makes it possible for us to design high-performance polarization devices.

Put forward the concept

The concept of photonic crystal first appeared in 1987. At that time, it was proposed that the electronic band gap of semiconductors has a periodic dielectric structure similar to optics. One of the most promising fields is the application of photonic crystals in optical fiber technology. The main topic it involves is the periodic microstructure of high refractive index fibers (they usually consist of air holes with silicon dioxide as the background material). This kind of optical fiber is usually called photonic crystal fiber (pcfs), and this new optical waveguide can be conveniently divided into two different groups. The first type of optical fiber has a high refractive index core (usually solid silicon) and is surrounded by a two-dimensional photonic crystal cladding. These optical fibers have properties similar to those of traditional optical fibers, and their working principle is to form waveguides through total internal reflection (tir). Compared with traditional refractive index conduction, the effective refractive index of photonic crystal cladding allows the core layer to have a higher refractive index. Therefore, it is important to pay attention to these so-called internal total reflection photonic crystal fibers (TIR-PCF).

In fact, it is completely independent of the photonic band gap (

porphobilinogen

) effect. The photonic crystal cladding of another kind of fiber, which is completely different from tir-pcfs, shows photonic band gap effect, which is used to control the light beam in the core layer. These optical fibers (PBG-PCF) show considerable performance, the most important of which is the ability to control and guide the beam propagation in the core with refractive index lower than the cladding. In contrast, the total internal reflection photonic crystal fiber (tir-pcfs) was the earliest one, while the real photonic band gap conductive fiber (pbg-pcfs) was only recently proved by experiments.