A lightwave communication link, operating at a wavelength of 1.5 m and a bit rate of 1Gb/s has a receiver consisting of a cascaded optical amplifier,...

 A lightwave communication link, operating at a wavelength of 1.5 μm and a bit rate of 1Gb/s has a receiver consisting of a cascaded optical amplifier, narrow optical filter, and photodetector. It ideally takes at least 130 photons/bit to achieve 10−15 bit error rate.

(a) How many photons per bit would it take to achieve the same error rate at 10 Gb/s?

(b) At this wavelength 1 mW of power is carried by 7.5×1015 photons per second. What is the received power level for 10−15 bit error rate at 1 Gb/s? (Express the answer in dBm).