May 15 2014
A Bragg mirror, also known as a dielectric mirror, is a kind of mirror made up of alternating thin optical layers of two different materials. A quarter-wave mirror is the most commonly used Bragg mirror, consisting of optical layers whose thickness is exactly one-quarter of the design wavelength.
Bragg mirrors are usually manufactured using thin-film deposition techniques. Fiber Bragg gratings, which are used in fiber lasers and other fiber devices, are often manufactured by irradiating the fiber with ultraviolet light.
Basic Principle
The operation of Bragg mirrors depends on the interference of light reflected from the two different optical layers. The difference in length of the optical path of the reflections is generally half the design wavelength. However, the difference in phase shifts at a low-to-high index boundary is actually 180°, which indicates that the reflections are in phase.
Moreover, the alternating signs of the amplitude reflection coefficients of the optical layers results in the strong reflection of light, which interferes constructively. Thus, the reflectivity is calculated by the difference in refractive indices of the layer materials, and the reflection bandwidth is determined with respect to the difference in refractive indices.
Applications
The potential applications of Bragg mirrors include the following:
- Anti-reflection coatings
- Hot and cold mirrors
- Laser applications
- Thin-film beam splitters
Sources and Further Reading