$in$ the $0\mathrm{.}85$ micron band, what $is$ the approximate attenuation after light has traveled down $1$ kilometer $of$ this fiber?

$2\mathrm{.}3dB$

None. There $isno$ attenuation foe this oart $of$ the electeomagnetic spectrum since $we$ use digital methods

$0\mathrm{.}125dB$

$0\mathrm{.}8dB$