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Time-resolved simulation of a pulse reflecting from a Bragg mirror. A distributed Bragg reflector (DBR) is a reflector used in waveguides, such as optical fibers.It is a structure formed from multiple layers of alternating materials with different refractive index, or by periodic variation of some characteristic (such as height) of a dielectric waveguide, resulting in periodic variation in the ...
Typically the grating period is the same size as the Bragg wavelength, as shown above. For a grating that reflects at 1,500 nm, the grating period is 500 nm, using a refractive index of 1.5. Longer periods can be used to achieve much broader responses than are possible with a standard FBG. These gratings are called long-period fiber grating ...
Increasing current in the gain region causes a red shift in laser output due to heating. The reflectivity curve of the passive grating does not change. As a result, the grating will experience loss of reflectivity at the longer wavelengths, and eventually will induce a discontinuous blue shift in the wavelength to find a higher gain mode.
The structure builds a one-dimensional interference grating (Bragg scattering), and the grating provides optical feedback for the laser. This longitudinal diffraction grating has periodic changes in refractive index that cause reflection back into the cavity. The periodic change can be either in the real part of the refractive index or in the ...
The reflectivity of a dielectric mirror is based on the interference of light reflected from the different layers of a dielectric stack. This is the same principle used in multi-layer anti-reflection coatings , which are dielectric stacks which have been designed to minimize rather than maximize reflectivity.
A Bragg grating is an example of this type of photonic crystal. One-dimensional photonic crystals can include layers of non-linear optical materials in which the non-linear behaviour is accentuated due to field enhancement at wavelengths near a so-called degenerate band edge.
More complex designs using multiple layers can achieve low reflectivity over a broad band, or extremely low reflectivity at a single wavelength. Constructive interference in thin films can create a strong reflection of light in a range of wavelengths, which can be narrow or broad depending on the design of the coating.
The grating waveguides consists of many waveguides, each having a constant length increment (ΔL). Light is coupled into the device via an optical fiber (1) connected to the input port. Light diffracting out of the input waveguide at the coupler/slab interface propagates through the free-space region (2) and illuminates the grating with a ...