7. Optical Fiber Communication Systems. Inter-Continental Optical Fiber Communications.
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Transcript of 7. Optical Fiber Communication Systems. Inter-Continental Optical Fiber Communications.
7. Optical Fiber Communication Systems
Inter-Continental Optical Fiber Communications
Optical Fiber Communication Systems and Fiber Sensors (Example of Measuring the Gap of Bridge)
Attenuation and Dispersion in Silica Fiber
Erbium Doped Fiber Amplifier (EDFA)
• Er3+ ions doped into the core region of an optical fiber to achieve light amplification need (stimulated emission > absorption) population inversion required (N2> N1)
• Optical gain, Gop=K(N2 –N1), where K is a constant depends on pumping intensity
• Er3+-doped fiber is usually inserted into the fiber communication line by splicing
• Gain efficiency : 8-10 dB/mW
Classification of Optical Fibers
Theory of Step-index Fiber
Theory of Step-index Fiber (Cont’)
Single-mode Operation of Step-index Fiber
Coupling from LD to Fiber
Fiber Lens to Improve Coupling Efficiency
Optical Fiber Splice and Mismatches in a Fiber-to-fiber Connection
Digital Signals—RZ and NRZ Formats
• A return-to-zero (RZ) format is the signal returns to zero between each pulse. The signal is self-clocking.
• A non-return-to-zero (NRZ) format does not have a rest state. NRZ is not inherently a self-synchronizing code, thus some additional synchronization technique must be used for avoiding bit slip.
Some Digital Modulations in Communication
• Amplitude Shift Keying (ASK)
• Frequency Shift Keying (FSK)
• Phase Shift Keying (PSK)
• Quadrature Amplitude Modulation (QAM)
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
Quadrature PSK (QPSK)
• In the example shown in the right figure, 00 is represented by sin(2πf0t), 10 is represented by sin(2πf0t+π), 01 is represented by sin(2πf0t+π/2), and 11 is represented by sin(2πf0t+3π/2).
Analog Quadrature Amplitude Modulation (AQAM)
A low-pass filter removes the high frequency terms containing cos(4πf0t), leaving only the I(t) term.
Example of Digital 8-QAM
• In this 8-QAM example, eight different modulation states using 4 phase angles and 2 amplitudes: one at 50% modulation; the other at 100%. (4 phases X 2 amplitudes = 8 modulation states).
• In QAM, the constellation diagram is a useful representation. The constellation points are usually arranged in a square grid.
Example of Constellation Diagram in 16-QAM
Examples of Constellation Diagrams in QAMs
Example of 8-QAM Optical Fiber Communication System
Eye Diagram
Eye Diagram (Cont’)