MITSUBISHI

MITSUBISHI LASER DIODESML5XX1 A SERIESFOR OPTICAL INFORMATION SYSTEMSII SIN vs. optical feedback ratioS/N vs. optical feedback ratio, where the frequencyis 20kHz and the bandwidth is 300Hz is shown inFig.13.That where the frequency is 10MHz and thebandwidth is 300kHz is shown in Fig.14.The S/N value is the worst value at casetemperatures of 25"C to 50 "C.Fig. 13 S/N vs. optical feedback ratiof=20kHz. BW=300Hz. Tc=25-50C70al1:lz"-en 100---0--lmW-·~·-2mW-··~··-3mW---&--4mW110Hf----+----+-----l····.···.5mW1204~--~~~~~~~~~~~.o O. 01 O. 05 O. 10. 2 O. 5 1 2 5 10Optical feedback ratio. Rf (%)Fig. 14 S/N vs. optical feedback ratio50 f=10MHz, BW=300kHz, Tc=25-50'C60z"- en---0-- lmW-.~.- 2mW90HI------1-----+-----I-··~ ..-3mW---&-- 4mW..··.····5mW100 Lfj-J'-:-~-:-.I.:c:-:'....,...,.'_,,__:_'_:,...............J-~_,J.o 0.01 0.050.10.2 0.5 1 5 10Optical feedback ratio. Rf (%)III Astigmatic distanceThere seems to be a difference in luminous pointin the parallel and perpendicular direction with thelaser beam. This distance between the two pointsin the astigmatic focal distance. Therefore, whenthe laser beam is focused, there is a difference infocal point in the two directions, making it difficultot converge the beam spot to the diffraction limit.The typical astigmatic focal distance at NA = 0.7of ML5XXl A is shown in Fig.15.The LD position which minimizes the horizontaland vertical spot diameters is obtained. Theastigmatic distance is the difference in moveddistances thus obtained.Fig. 15 Astigmatic distance10r-,---~----~--r_~-----,\ Po=3mW cw, I\ I'. \\ NA=0.7\ \ : perpendicular\ \ ~direction ," \ :\ "\~ \ ' I5r--~+-~~.--+~,-~~-~-1"\'" ., ......\ .... .4" "-parallel, ! - direction' .. 'Astigmatic--;oI---++E- distance 6.8 /1 mLD moving distance (/1 m)2-79