Lec-9 Optical Amplifier and Detector (10-Mar-2011)

Lec-9 Optical Amplifier and Detector (10-Mar-2011) -...

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Photonic Network By Dr. M H Zaidi Optical Amplifiers …Continued 1
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Photonic Network By Dr. M H Zaidi Review of Previous Lecture Optical amplifiers are a key component in long haul optical communication Amplifiers are majorly of four types Electro optic regenerators Erbium-doped optical amplifiers (EDFA) Raman Amplifiers Semiconductor optical amplifiers (SOA) Pump powers required for L-band EDFAs are much higher than their C-band counterparts. 2
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Photonic Network By Dr. M H Zaidi EDFA – Multi Stage Designs PUMP PUMP Input Signal Output Signal Er 3+ Doped Fiber Optical Isolator Optical Isolator Optical Isolator 1st Active Stage Co-pumped 2nd Active Stage Counter-pumped Er 3+ Doped Fiber 3
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Photonic Network By Dr. M H Zaidi EDFA – Multi Stage Designs 1 st stage gives high gain, low noise 2 nd stage give high output power Combined both, we get a high gain and high power output signal with low noise. Also multiple pumps give failure recovery benefits. Optical isolator/filter can be placed in between to flatten the gain or remove pump signal. 4
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Photonic Network By Dr. M H Zaidi EDFA - Advantages EDFAs have high pump power utilization (>50%) Directly and simultaneously amplify a wide wavelength band (> 80 nm) in the 1550 nm region, with a relatively flat gain. Flatness can be improved by gain-flattening optical filters Gain in access of 50 dB Low noise figure Transparent to optical modulation formats Suitable for long haul applications Demerit EDFAs are not small and cannot be integrated with other semiconductor devices 5
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Photonic Network By Dr. M H Zaidi Stimulated Raman Scattering If two or more signals at different wavelengths are injected into a fiber, SRS causes power to be transferred from the lower-wavelength channels to the higher-wavelength channels. This coupling of energy from a lower wavelength signal to a higher-wavelength signal is a fundamental effect that is also the basis of optical amplification and lasers. 6
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Photonic Network By Dr. M H Zaidi Stimulated Raman Scattering 7 Fig: The effect of SRS. Power from lower-wavelength channels is transferred to the higher- wavelength channels Fig: SRS gain coefficient as a function of channel separation
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By Dr. M H Zaidi Raman Amplifiers Raman Amplification is based on the Stimulated Raman Scattering (SRS) phenomenon. Raman gain spectrum is fairly broad and the peak of the gain is centered about 13 THz below the frequency of the pump signal used. Unlike EDFAs, we can use the Raman effect to provide gain at any wavelength. Raman amplification can potentially open up other bands for WDM, such as the 1310 nm window, or the so-called S-band lying just below 1528 nm. Also, we can use multiple pumps at different wavelengths and different powers simultaneously to tailor the overall Raman gain shape. Another major concern with Raman amplifiers is crosstalk
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Lec-9 Optical Amplifier and Detector (10-Mar-2011) -...

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