@MISC{Szödényi_bulkdiffraction, author = {Ákos Szödényi}, title = {Bulk diffraction grating LIX}, year = {} }
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Abstract
Technologies and new concepts for optical networking are advancing rapidly as a result of notable progresses in all-optical technologies and emerging bandwidth greedy applications. Telecom operators are forced, in consequence, to adapt in the near future, their deployed optical fiber communication systems so as to cope with these challenging advances. Deploying "islands" wherein the optical signals benefit from the advantages of transparency may be more feasible than replacing totally the current conventional digital systems by alloptical technologies. In this paper the size of a metropolitan "transparent island" (the "island" is in the non transparent network "ocean") is assessed by computer simulations depending on the architecture of the all-optical add/drop multiplexer (OADM) used. In effect, three architectures of OADM were on focus to compare between their performances after cascading several optical nodes. Optical signal quality represented by BER estimation is used as the metric that determines the size of a transparent island. To the best of my knowledge, this is the first time an estimation of the size (hop number) of transparent islands is given depending on applied optical devices used and the target BER. Three optical filter types Multiplexing and demultiplexing functions both employ narrowband filters, cascaded and combined in other ways to achieve the desired result. Particular techniques that have been used to perform such filtering include thin film filters, fiber Bragg or bulk gratings and integrated optics (AWG). Diffraction grating (mux) A bulk-optic diffraction grating [1] reflects light at an angle proportional to wavelength and the underlying physical principle is constructive and destructive interference. For each wavelength of incident light, there is an angle for which light waves reflecting from individual grating lines will differ in phase by exactly one wavelength-spacing. At this angle, the intensity contribution from each line will add constructively, so this will be the angle of maximum transmission for that specific incident wavelength. Designing a mux or demux using a diffraction grating is a matter of positioning the input and output optics to select the desired wavelength. Although they are difficult to manufacture and expensive, devices based on diffraction gratings have an insertion loss that is essentially independent of the number of channels, rendering this technology one of the more promising for high channel count systems. However, polarization control requires critical attenuation.