EDFA control

VME design
Ethernet NIC design
Motor control

EDFA and Raman technologies are the mainstay of the telecommunications optical amplification industry. Implementation of these technologies require practical solutions to a number of control and monitoring problems. Typical control of these amplifiers involve an analog interface to a number of pump lasers and their associated temperature control circuitry. Simple in concept but subtle issues could cause problems in practice. Careful design with respect to power distribution, stability and noise analysis are required in addition to a workable error compensation scheme.

Optical amplification systems involve dynamic control of a variety of components to optimize performance:

  • Total power adjustment
  • EDFA gain tilt using attenuators and pump power adjustment
  • AGC control of pump powers to allow optical channel add/drop
  • channel power equalization using dynamic optical filters
  • variable dispersion compensation using FBG technology

Depending on the line rate transmitted through the fiber one or more of these control elements are present in the amplifier. A 40Gbps amplifier typically provides concurrent control of all four of these elements. A 10Gbps amplifier may only need to provide total pump power, tilt control and perform some sort of AGC.

Output optical power control is a direct function, within limits, of the amount of current driven through the pump lasers. The driver circuit must provide a clamping function to prevent overdriving the laser which will result in damage to these expensive devices. Operation of the driver circuit begins with the EDFA processor determining a desired drive level. This information passes to the control circuit either in digital or analog form. The control circuit converts the drive level into a current and uses a feedback loop to stabilize the current.

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Email: djy@tracecircuits.com

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