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

Unit 6: Analog And Digital Links

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

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

Example link-loss budget 4

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

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.

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.

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

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

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

CNR versus optical power level 4

Multichannel Amplitude Modulation 5