Difference between revisions of "Basics of Optical Communication Systems and WDM"
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typical delta for SM: 0.2->1% | typical delta for SM: 0.2->1% | ||
MM: 1->3%. | MM: 1->3%. | ||
| − | numerical aperture | + | numerical aperture = sqrt((n1^2)-(n2^2)) ~ n1*sqrt(2*delta) |
| + | small wavelength limit(or ray picture): if fibre core radius >> wavelength. | ||
Revision as of 14:45, 29 March 2010
Plastic fibres exist. capacity vs distance requirement drives us to move from copper cables to optical fibres. attenuation vs wavelength has minimas at telecom wavelength (1310nm and 1550nm). SONET - synchronous optical network. SDH - synchronous digital heirarchy. notation - OC-N => N x 51 Mbps STM-X => X x 155Mbps some standards OC-48 : 2.5Gbps OC-192 : 10Gbps OC-768 : 40 Gbps Bands O(original) band - 1260 <-> 1360nm E(Extended) band - 1360 <-> 1460nm S(Short) band - 1460 <-> 1530nm C(Conventional) band - 1530 <-> 1565nm L(Long) band - 1565 <-> 1625nm U(Ultra-long) band - 1625 <-> 1675nm At 1310nm (although not an exact minimum) there is zero pulse broadening. CWDM-coarse wavelength division multiplexing,DWDM-dense wavelength division multiplexing. coarse: span:1270->1610nm , spacing:20nm (ex. 1310,1490,1550). Dense: spacing:0.1->0.8nm. refractive index varies with wavelength and doping of the fibre. SM(single mode) core diameter: 8-10um, cladding: 125um. MM(multi mode) core diameter: 50-62.5um, cladding: 125um. step and graded index fibres. Index is graded to minimize pulse broadening. n_cladding = n_core*(1-delta) typical delta for SM: 0.2->1% MM: 1->3%. numerical aperture = sqrt((n1^2)-(n2^2)) ~ n1*sqrt(2*delta) small wavelength limit(or ray picture): if fibre core radius >> wavelength.
