1. Subject Name: Optical Fiber Communication Subject Code: 10EC72
Prepared By: Sreepriya Kurup, Pallavi Adke, Sowmya L(TE)
Department: Electronics and Communication Engineering
Date: 10/11/2014
8/12/2014

2. Unit 6: Analog And Digital Links

3. Simplex point-to-point link
In analyzing the following key parameters are needed:
Desired Transmission Distance
The data rate
The bit error rate 1

4. Performance measurements
Performance measurements are carried out to ensure the desired level of
performance in the optical links. These are two analysis namely
The link power budget analysis
The rise time budget analysis
Optical power loss model 2

5. Example link-loss budget4

6. Mode-partition-noise effects
If in a multimode laser diode , the side modes are not sufficiently suppressed,
mode partition noise occurs.

7. Chirping & extinction-ratio penalties
The direct modulation of a laser gives rise to a phenomenon called chirping of pulses.
The extinction ratio of the laser is defined as the ratio of the output power for ‘1’ bit
and the output power for ‘0’ bit.

8. Multiple-reflection effects
Some of the components such as splices , couplers , connectors cause
discontinuity in the refractive index. When light travels through such an optical linksome power gets reflected back towards the source at these discontinuities.
This causes optical feedback and induces laser disabilities.

9. Overview of Analog Links
Analog link with major noise contributors at each stage 1

10. Carrier to Noise Ratio (CNR) It is defined as the ratio of rms carrier power to rms noise power at the input of the receiver. Carrier power
Laser diode response to analog signal modulation 2

11. The different types of noises are Photo detector noise Pre amplifier noises Relative Intensity Noise (RIN) 3

12. CNR versus optical power level4

13. Multichannel Amplitude Modulation5