silica containing some dopants) with ultraviolet light in the spatial shape of a standing wave pattern (→ interference). Such an index modulation can be produced by irradiating over some time interval a photosensitive (photorefractive) glass (e.g. to obtain a large reflection bandwidth or to obtain some amount of chromatic dispersion.įabrication of Volume Bragg Gratings The holographic method, applied to some photosensitive glass, is most common for the fabrication of volume Bragg gratings.Ī volume Bragg grating is some transparent medium where there is a periodic modulation of the refractive index in some region (principle of a volume hologram). There are chirped volume Bragg gratings (CVBG, CBG), i.e., devices where the Bragg wavelength is not constant, but varies continuously along the device. However, it is possible to have two or more Bragg gratings within the same volume of material. Normally, a device contains only a single grating.Therefore, such devices can also be operated at fairly high average power levels. Optical losses related to absorption or scattering of light are usually at a very low level.multiple J/cm 2 then allows for very high peak powers. The large beam area in combination with the relatively high optical damage threshold of e.g. The thickness of such devices (typically several millimeters) is sufficient for allowing substantial beam radii of e.g.The shape and width of the reflection spectrum (filter shape) can be tailored to some extent.In the case of an unchirped grating, it is determined by the length of the grating and the magnitude of the refractive index modulation. The peak reflectance is sometimes only a few percent, in other cases more than 99%.However, there are also transmitting Bragg gratings (TBG), where the diffracted beams on the same side of the device is the transmitted beams. 0.1 nm or 0.01 nm) – either directly back into the incoming beam or under some angle. below 1 μm, so that one can obtain reflection of light in some narrow optical bandwidth (e.g. Typically, one uses a very small grating period of e.g.For a different angle of incidence, hardly any reflection occurs. Some typical properties of volume Bragg gratings: Figure 1: A volume Bragg grating within a glass block reflects an incident beam, if the Bragg condition is met (left-hand side). They are also called bulk Bragg gratings or volume holographic gratings. Typically, such gratings are written into some photosensitive glass, and sometimes into crystal materials. in the form of a cube or a parallelepiped – in contrast to diffraction gratings made on the surface of an optical element or fiber Bragg gratings, where the grating is written into the core of an optical fiber. Volume Bragg gratings (also called volume holographic gratings) are Bragg gratings which are written inside some transparent material, e.g. How to cite the article suggest additional literature Definition: Bragg gratings written into some bulk material
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