MITSUBISHI

MITSUBISHI LASER DIODESML4XX5 SERIESFOR OPTICAL INFORMATION SYSTEMSI Light output vs. monitoring output characteristicThe laser diodes emit beams from both of theirmirror surfac~s, front and rear surfaces. The rearbeam can be used for monitoring power of frontbeam since the rear beam is proportional to thefront one. Fig.7 shows an example of light outputvs. monitoring photocurrent characteristics.When the front beam output is 3mW, themonitor output becomes 0.35mA.Fig. 7 Light output VS.432/17 /vmonitoring output currentV /VI Astigmatic distanceThere seems to be Ii difference in luminous pointin the parallel and perpendicular direction with thelaser beam. This distance between the two pointsis the astigmatic focal distance. Therefore, whenthe laser beam is focused, there is a difference infocal point in the two directions, making it difficultto converge the beam spot to the diffraction limit.The typical astigmatic focal distance at NA = 0.7of ML4XX5 is shown in Fig.S.The LD position which minimizes the horizontaland vertical spot diameters is obtaained. Theastigmatic distance is the difference in moveddistances thus obtained.E-3I~~.~..8.CI)100.1 0.2 0.3 0.4 0.5Monitoring output 1m (mA)Fig. 8 Astigmatic distancePo =3mWCWI'NA=0.7,I,II, , . perpendicular~ V direction" 1"• . - ..... ' ~~~~.'I ,",I5o a\,:1 -.... ,.... ~'Astigmr~ distance 5.6 It m\ , ~ directionI I I10 20 30LD moving distance (It m)2-43