光纤通信 Solutions (1)

Solutions （1）

1.1 A receiver requires 10mW as input power. If all the system losses add up to 50dB, then how much power is required from the source?

P?P?50?dB??10lg?in??in?105?mW??Pin?106?mW?

?10?10

1.2 There are 1010 photons per second incident on a photodetector at wavelength 0.8?m, Computer the power incident on the detector. If this detector converts light to current at a rate of 0.65mA/mW, what current is produced?

Nh10?6.626?10W??P??tt1I?RP?0.65?2.48?10?9?1.6nAc10?343?108?0.8?10?6?2.48?10?9

1.3 The power incident on a detector of light is 100nW. (a) Determine the number of photons per second incident on the detector if the wavelength is 800nm. (b) Repeat the calculation if the wavelength is 1550nm. (c) Which wavelength requires the most photons to produce the 100nW of power?

Pt100?10?9?1a)N???4.02?10118c3?10h6.626?10?34??0.8?10?6 ?9Pt100?10?1b)N???7.8?10118c3?10h6.626?10?34??1.55?10?6 c) 1550nm波长需要更多的光子。

1.4 To operate properly, a fiber optic receiver requires -34dBm power.

The system losses total 31dB from the light source to the receiver. How much power does the light source emit (in mW)？

PdBm?AdB??34dBm?PdBm?AdB?34dBm?31dB?34dBm??3dBm P?0.5mW