Optical amplifiers

Optical amplifiers

1. OPTICAL AMPLIFIERS BY TAFHIM BIN NASIR

2. An optical amplifier is a device which amplifies the optical signal directly without ever changing it to electricity. The light itself is amplified. Reasons to use optical amplifiers: Reliability Flexibility Wavelength Division Multiplexing(WDM) Low cost INTRODUCTION:

3. Necessity of Optical amplifiers Optical amplifiers boost up the power level of multiple light wave signals. To transmit a signal over long distances(>100km) , to compensate attenuation losses. Initially this was accomplished with an optoelectronic module consisting of regenerator, equalizer and an optical TX to send the data.

4. General applications of optical amplifiers In line optical amplifiers: In single mode link, the fiber dispersion may be small so that repeater can be eliminated. instead of regeneration of signal, simple amplification can be done . It is used to increase the distance between regenerative repeaters .

5. Power Amplifier The device which can be placed after the transmitter to boost the transmitter to boost the transmitted power is called as power amplifier. This provides increase in distance depending on the amplifier gain and fiber loss.

6. PREAMPLIFIER Optical amplifier being used as a front end preamplifier for an optical receiver. A weak optical signal is amplified before photo-detection so that signal to noise ratio degradation due to noise can be suppressed in the receiver . It provides a larger gain factor and BW.

7. BASIC CONCEPTS Most optical amplifiers are stimulated emission. An optical amplifier is basically a laser without feedback. O ptical gain is realized when the amplifier is pumped optically ( or electrically) to achieve population inversion. Gain depends on wavelength, internal light intensity and amplifier medium . Three types: semiconductor optical amplifiers, Raman amplifiers and Er + doped fiber amplifiers

8. E rbium- d oped  f iber   a mplifier ( EDFA )  is an optical  repeater device that is used to boost the intensity of optical signals being carried through a  fiber optic communications system . EDFA operates in the spectral band of 1530 to 1560 nm region. Active medium in an optical fiber amplifier consist 10 to 30 m length of optical fiber that has been lightly doped with a rare-earth element such as erbium( Er +) Erbium-doped Fiber Amplifier

9. A FIGURE OF EDFA DEVICE:

10. INSIDE AN EDFA:

11. Amplification Mechanism: Optical amplifier uses optical pumping. Pumping gives energy to electrons to reach the excited state. After reaching its excited state , the electrons must release some energy and drop to the lower level.

12. EDFAs include the ability: To pump the devices at several different wavelength . Low coupling loss to the compatible-sized fiber transmission medium. Highly transparent to signal format and bit rate.

13. Schematic Diagram of EDFA:

14. Semiconductor optical amplifiers Similar to laser diodes but the emission is triggered by input optical signal. Works in any wavelength . Have high noise resistance, compact and low power consumption. Cross talk between different wavelengths.

15. Semiconductor Amplifier An electrical current pass through the device that excites the electrons in the active region. when photon travel through the active region it can cause these electron to loose some of their extra energy in the form of

16. CONTINOUE.. more photons that match the wavelength of the initial ones. Therefore, an optical signal passing through the active region is amplified and is said to have experienced “gain”.

17. SOA: Amplification Process Semiconductor have valance and conduction band At thermal equilibrium valance band has higher population. Under population inversion condition band will have higher population . Population inversion is achieved by forward biasing the p-n junction .

18. RAMAN AMPLIFIERS Use stimulated Raman effect and pump laser whose frequency is equal to signal frequency plus frequency of chemical bond in the material. Because it is a nonlinear process, requires very high pump powers (watts). ARaman amplifier is a device which takes input Ws and amplified in the same direction or opposite direction with pump laser Wp .

19. Advantages of EDFA High gain(40-50) Low noise (3-5 dB) Low polarization sensitivity. EDFAs are fully compatible with the rest of the fiber optic transmission link.

20. Limitations: Large size. High pump power consumption (efficiency -10 dB/ 1 mw ).

21. Advantages of Raman Amplifier Low noise ( 3-5 dB) Wide gain bandwidth (up to 10 nm) Distributed amplification within the transmission fiber .

22. Limitations of Raman Amplifier Low gain. Requirement of high power pump.

23. Advantages of SOA Small size. Transmission bidirectional. smaller output power than EDFA Less expensive than EDFA.

24. Limitations of SOA Lower gain than EDFA. Higher noise than EDFA. High non-linearity .

25. CONCLUSION: Optical amplifiers perform a critical function in modern optical networks, enabling the transmission of many terabits of data over long distances of up to thousands of kilo-meters.

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