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Diffstat (limited to '1655/CH6/EX6.14.1/Example_6_14_1.sce')
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diff --git a/1655/CH6/EX6.14.1/Example_6_14_1.sce b/1655/CH6/EX6.14.1/Example_6_14_1.sce new file mode 100755 index 000000000..d661dd5d3 --- /dev/null +++ b/1655/CH6/EX6.14.1/Example_6_14_1.sce @@ -0,0 +1,9 @@ +// Example 6.14.1 page 6.42
+
+clc;
+clear;
+
+// This is example does not consist of any numerical computation
+
+printf("\nQuestion - What do you understand by single longitudinal mode laser or SLM? ")
+printf("\nAnswer - \nIn laser operation optical gain alone is not sufficient for laser operation but a minimum amount of gain is also necessary.\nThis gain can be achieved when laser is pumped above threshold level.\nIn simplest laser structure we have p-n junction.Active layer is sandwitched between p and n type layers of higher bandgap material. Such broad area semiconductor laser need high threshold current and light confinement becomes difficult.\nGain guided semiconductor laser limit the current injection over a narrow stripe thus overcome the problem of light confinement.They are also called stripe geometry lasers.\nIn index guided laser an in index step is introduced to form waveguide.\nIn buried heterostructure laser the active region in buried by layers of lower refractive indices.\nWhen width and thickness of the active layer is controlled, light can be made to emerge in a single spatial mode, but the problem arises when such lasers oscillate in many longitudinal modes in Fabry Perot cavity.\nThe spectral width obtained is about 2-4 nm which can be tolerated for 1.3 micrometer operation, but for systems operating near 1.55 micrometer at higher bit rates such multimode lasers can not be used. At such times laser which emit light in a single longitudnal mode are required to give higher bit rates than 1 Gb/s. They are called Single Longitudinal Mode (SLM) lasers.");
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