伍拾貳、 光纖的衰減量也是以 dB 計值
光是一種能量，歸屬於功率項。
以下的是英文資訊，請自行參閱。
◾ Decibel ( 維基百科 ) [英文] http://en.wikipedia.org/wiki/Decibel
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“Electric power
dBm or dBmW
dB(1 mW) — power measurement relative to 1 milliwatt. XdBm = XdBW + 30.”
“Radio power, energy, and field strength
dBm
dB(mW) — power relative to 1 milliwatt. When used in audio work the milliwatt is referenced to a 600 ohm load, with the resultant voltage being 0.775 volts. When used in the 2-way radio field, the dB is referenced to a 50 ohm load, with the resultant voltage being 0.224 volts. There are times when spec sheets may show the voltage & power level e.g. -120 dBm = 0.224 microvolts.”
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◾ dBm ( 維基百科 ) [英文] http://en.wikipedia.org/wiki/DBm
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“Expression in dBm is typically used for optical and electrical power measurements, not for other types of power (such as thermal). A listing by power levels in watts is available that includes a variety of examples not necessarily related to electrical or optical power.”
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廠商資訊：
◾ Belden_Tech Info_Fiber Optic Cables [英文] http://www.belden.com/pdfs/TechInfo/techinfo.htm
◾ Belden_Tech Info_Fiber Optic Cables_Optical Power and Decibel Scales [英文] http://www.belden.com/pdfs/techinfo/TechOptical.htm
◾ Fluke Electronics_Learn About [英文] http://www.flukenetworks.com/learn-about
◾ Fluke Electronics_Learn About_Fibre Testing [英文] http://www.flukenetworks.com/Expertise/Learn-About/Fiber-Testing
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