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iscover how distributed Bragg reflectors use layered structures to create no-go zones for light
In the growing demand for optical technology, distributed Bragg reflectors (DBRs) are showing their irreplaceable importance. DBR is a structure formed by multiple layers of alternating materials, and is widely used in optical fibers and waveguides. These structures are characterized by the different refractive indices of each layer, which causes light waves to reflect and refract between these layers, thus forming so-called optical forbidden zones, a phenomenon that has attracted the attention of many scientific researchers.
The optical forbidden zone refers to the phenomenon that light waves within a specific range cannot propagate in the structure, which enables DBR to effectively reflect light of specific wavelengths.
Structure and principle
Distributed Bragg reflectors consist of multiple layers of different materials whose refractive indices alternate. Whenever a light wave passes through the interface of these layers, partial reflection and refraction occur. When the vacuum wavelength of the light waves approaches four times the optical thickness, the interaction of these waves produces constructive interference, making the layer structure act as a high-quality reflector. This light-forbidden zone created by the layered structure is the core of DBR technology.
The boundary of each layer is a starting point for reflection and refraction for light waves, which makes DBR achieve high reflectivity at specific wavelengths.
Characteristics of light-exclusion zones
In a DBR, the reflected wavelength range is called the photonic stopband. Light within this range must obey specific propagation rules, meaning that light waves at these wavelengths are prohibited from propagating through the structure. This property makes distributed Bragg reflectors particularly important in a variety of optical devices, including lasers and fiber resonators.
Calculation of reflectivity
The calculation of DBR reflectivity involves the refractive index of multiple layers, as well as the thickness data of the layers. Generally, material choices such as titanium dioxide and silicon work well together, which allows for controllable reflectivity and light range. These reflective properties also have a profound impact on its use.
Reflection characteristics of TE and TM modes
DBR shows specific differences in reflectivity for the transverse electric mode (TE mode) and transverse magnetic mode (TM mode) at different incident angles and wavelengths. The TE mode is usually highly reflected by the structure, while the TM mode is relatively easy to penetrate. Such characteristics not only demonstrate the function of DBR as a polarizer, but also further promote the development of optical components.
Bio-inspired Bragg reflectorsBioinspired Bragg reflectors are 1D photonic crystals designed with inspiration from nature. This structure can not only produce structural colors, but can also be used to make low-cost gas/solvent sensors. When the holes in the structure are replaced by other substances, its color changes accordingly, which technically demonstrates the cutting-edge application of materials science.
ConclusionThese bioinspired structures demonstrate creativity in nature and offer new perspectives for the advancement of modern technology.
The research and application of distributed Bragg reflectors are not limited to the understanding of their principles, but also include how to use their unique optical properties to advance existing technologies. How interesting will the future be as materials science and optical engineering continue to advance?
