![]() In many cases, the end faces of the volume Bragg grating are optically polished and anti-reflection coated in order to avoid parasitic reflections. Some thermal development may follow the irradiation. The angle between the two beams, together with the optical wavelength and the refractive index of the glass, determines the period of the obtained interference pattern. Essentially, two narrow-linewidth ultraviolet light beams are superimposed in the material, having somewhat different propagation directions. 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. ![]()
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