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 intensityEr3+-doped fiber is usually inserted into the fiber communication line by splicingGain 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 SignalsRZ and NRZ FormatsA 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 CommunicationAmplitude 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(2f0t), 10 is represented by sin(2f0t+), 01 is represented by sin(2f0t+/2), and 11 is represented by sin(2f0t+3/2).
Analog Quadrature Amplitude Modulation (AQAM) A low-pass filter removes the high frequency terms containing cos(4f0t), leaving only the I(t) term.
Example of Digital 8-QAMIn 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 (Cont)