Q3. (Total 25 marks) (a) Draw the simple structure and show the three key components of an optical receiver. Describe the functions of the three components. (6 marks) When there is no intersymbol interference(ISI) distortion and the dominant receiver noise is thermal noise, Q-factor at an optical receiver determines the receiver's bit error rate (BER) performance. If the responsivity of the photodetector used is R and the optical power for "" and "O" are P1 and Po respectively, and the root mean square(RMS) noise current for "" and "0" are ?i and ?0 respectively, what is the expression for Q? If the dominant noise for the receiver is thermal noise of the transimpedance amplifier, where should be the decision threshold for optimal signal detection? In an optical amplified system, where should be the optimal signal decision (b) threshold? (5 marks) Derive the power penalty for an optical receiving system if the extinction ratio r is not ideal. The extinction ratio is defined as r-Pi/Po and receiver noise is dominated by thermal noise. If the (c) extinction ratio is 3dB, how much is the power penalty? (5 marks) (d) Assuming Q-6 is required for achieving BER of 10 for a 10Gbit/s transmission system at 1550nm. For a receiver with PIN photodiode having responsivity of 0.85A/W and receiver transimpedance amplifier(TIA) equivalent input noise current density of 12pA/NHz, what is the minimum average power required by the receiver(receiver sensitivity)? If we use a DFB laser with transmitted power of -10dBm and the fibre loss is 0.2dB/km, what is the maximum transmission distance if we assume a system margin of 6dB? If the dispersion of the fibre at 1550nm is 17ps/nm/km and laser is modulated using an external modulator, will dispersion affect the performance of the transmission system? The power penalty caused by dispersion is less than dB if the rms pulse broadening is less than 30.6% of the bit period (9 marks)Q3. (Total 25 marks) (a) Draw the simple structure and show the three key components of an optical receiver. Describe the functions of the three components. (6 marks) When there is no intersymbol interference(ISI) distortion and the dominant receiver noise is thermal noise, Q-factor at an optical receiver determines the receiver's bit error rate (BER) performance. If the responsivity of the photodetector used is R and the optical power for "" and "O" are P1 and Po respectively, and the root mean square(RMS) noise current for "" and "0" are ?i and ?0 respectively, what is the expression for Q? If the dominant noise for the receiver is thermal noise of the transimpedance amplifier, where should be the decision threshold for optimal signal detection? In an optical amplified system, where should be the optimal signal decision (b) threshold? (5 marks) Derive the power penalty for an optical receiving system if the extinction ratio r is not ideal. The extinction ratio is defined as r-Pi/Po and receiver noise is dominated by thermal noise. If the (c) extinction ratio is 3dB, how much is the power penalty? (5 marks) (d) Assuming Q-6 is required for achieving BER of 10 for a 10Gbit/s transmission system at 1550nm. For a receiver with PIN photodiode having responsivity of 0.85A/W and receiver transimpedance amplifier(TIA) equivalent input noise current density of 12pA/NHz, what is the minimum average power required by the receiver(receiver sensitivity)? If we use a DFB laser with transmitted power of -10dBm and the fibre loss is 0.2dB/km, what is the maximum transmission distance if we assume a system margin of 6dB? If the dispersion of the fibre at 1550nm is 17ps/nm/km and laser is modulated using an external modulator, will dispersion affect the performance of the transmission system? The power penalty caused by dispersion is less than dB if the rms pulse broadening is less than 30.6% of the bit period (9 marks)Q3. (Total 25 marks) (a) Draw the simple structure and show the three key components of an optical receiver. Describe the functions of the three components. (6 marks) When there is no intersymbol interference(ISI) distortion and the dominant receiver noise is thermal noise, Q-factor at an optical receiver determines the receiver's bit error rate (BER) performance. If the responsivity of the photodetector used is R and the optical power for "" and "O" are P1 and Po respectively, and the root mean square(RMS) noise current for "" and "0" are ?i and ?0 respectively, what is the expression for Q? If the dominant noise for the receiver is thermal noise of the transimpedance amplifier, where should be the decision threshold for optimal signal detection? In an optical amplified system, where should be the optimal signal decision (b) threshold? (5 marks) Derive the power penalty for an optical receiving system if the extinction ratio r is not ideal. The extinction ratio is defined as r-Pi/Po and receiver noise is dominated by thermal noise. If the (c) extinction ratio is 3dB, how much is the power penalty? (5 marks) (d) Assuming Q-6 is required for achieving BER of 10 for a 10Gbit/s transmission system at 1550nm. For a receiver with PIN photodiode having responsivity of 0.85A/W and receiver transimpedance amplifier(TIA) equivalent input noise current density of 12pA/NHz, what is the minimum average power required by the receiver(receiver sensitivity)? If we use a DFB laser with transmitted power of -10dBm and the fibre loss is 0.2dB/km, what is the maximum transmission distance if we assume a system margin of 6dB? If the dispersion of the fibre at 1550nm is 17ps/nm/km and laser is modulated using an external modulator, will dispersion affect the performance of the transmission system? The power penalty caused by dispersion is less than dB if the rms pulse broadening is less than 30.6% of the bit period (9 marks)

(a) Draw the simple structure and show the three key components of an optical receiver. Describe the functions of the three components. (b) When there is no intersymbol interference (ISI) distortion and the dominant receiver noise is thermal noise, Q-factor at an optical receiver determines the receiver's bit error rate (BER) performance. If the responsivity of the photodetector used is R and the optical power for "1" and "0" are P and Po respectively, and the root mean square (RMS) noise current for "1" and "0" are 0 and respectively, what is the expression for Q? If the dominant noise for the receiver is thermal noise of the transimpedance amplifier, where should be the decision threshold for optimal signal detection? In an optical amplified system, where should be the optimal signal decision threshold? (c) Derive the power penalty for an optical receiving system if the extinction ratio r is not ideal. The extinction ratio is defined as 1-P/P, and receiver noise is dominated by thermal noise. If the extinction ratio is 3dB, how much is the power penalty? (d) Assuming Q-6 is required for achieving BER of 10 for a 10Gbit/s transmission system at 1550nm. For a receiver with PIN photodiode having responsivity of 0.85A/W and receiver transimpedance amplifier(TIA) equivalent input noise current density of 12pA/VHz, what is the minimum average power required by the receiver(receiver sensitivity)? If we use a DFB laser with transmitted power of -10dBm and the fibre loss is 0.2dB/km, what is the maximum transmission distance if we assume a system margin of 6dB? If the dispersion of the fibre at 1550nm is 17ps/nm/km and laser is modulated using an external modulator, will dispersion affect the performance of the transmission system? The power penalty caused by dispersion is less than 1dB if the rms pulse broadening is less than 30.6% of the bit period.