Optical Fiber Link Design requirements

The optical link design essentially is putting the various optical components, so that information can be transmitted satisfactorily. The satisfactoriness of the transmission can be defined in terms of some characteristic parameters.The user generally specifies the distance over which the information is to be sent and the data rate to be transmitted. The Designer then has to find the specification of the system components.

The designer generally has to define some additional criteria either as per the standards or as per the user specifications.

The Design criteria are given in the following.

Primary Design Criteria

• Data Rate
• Link length

Additional Design Parameters

• Modulation format eg Analog/digital
  • • • • • • • Depends upon the type of signals user want to transmit. For example if it is a TV signal, then may be analog transmission is more suited as it requires less bandwidth and better linearity. On the other hand if data or sampled voice is to be transmitted, digital format may be more appropriate.
              • The digital signals have to be further coded to suite the transmission medium and for error correction.
• System fidelity: BER, SNR
  • • • • • • • The system fidelity defines the correctness of the data received at the receiver.
              •  For digital transmission it is measured by the Bit Error Ratio (BER) . The BER is defined as:-
              • 
              • In optical system, the BER has to be less than 10E-9
              • For analog system, the quality parameter is the Signal-to-noise (SNR) ratio. In addition, there is a parameter called the inter-modulation distortion, which describes the linearity of the system.