At the heart of EDFA technology is the Erbium Doped Fiber (EDF), which is a conventional Silica fiber doped with Erbium. When the Erbium is illuminated with light energy at a suitable wavelength (either 980nm or 1480nm) it is excited to a long lifetime intermediate state (see Figure 1), following which it decays back to the ground state by emitting light within the 1525-1565 nm band. If light energy already exist within the 1525-1565nm band, for example due to a signal channel passing through the EDF, then this stimulates the decay process (so called stimulated emission), resulting in additional light energy. Thus, if a pump wavelength and a signal wavelength are simultaneously propagating through an EDF, energy transfer will occur via the Erbium from the pump wavelength to the signal wavelength, resulting in signal amplification.

In its most basic form the EDFA optical amplifier consist of a length of EDF (typically 10-30m), a pump laser, and a component (often referred to as a WDM) for combining the signal and pump wavelength so that they can propagate simultaneously through the EDF. In principle EDFA’s can be designed such that pump energy propagates in the same direction as the signal (forward pumping), the opposite direction to the signal (backward pumping), or both direction together. The pump energy may either by 980nm pump energy, 1480nm pump energy, or a combination of both. Practically, the most common EDFA configuration is the forward pumping configuration using 980nm pump energy, as shown in Figure 2. This configuration makes the most efficient use of cost effective, reliable and low power consumption 980nm semiconductor pump laser diodes, thus providing the best overall design with respect to performance and cost trade-offs.

High Output Power with Class 1M Laser Safety

High capacity reconfigurable networks require high output power in order to maintain acceptable levels of OSNR. On the other hand, a major requirement for optical networks is that they comply with relevant laser safety standards, such as IEC 60825 parts 1 and 2, ITU-T G.664, and CDRH 21 CFR §1040.10. These standards dictate a maximum safe level of laser radiation, known as the Class 1M hazard level, above which exposure to radiation can be potentially harmful to skin and eyes. For EDFA’s operating in the C-Band, the Class 1M hazard level corresponds to a maximum theoretical output power of about 21.3 dBm. In practice however, the specified output power of a Class 1M EDFA should not exceed 20.5dBm, in order to take into account suitable safety margins.

For an EDFA to provide output power above 20.5 dBm, and still retain a Class 1M safety classification, it is necessary to provide an automatic power reduction (APR) mechanism that ensures reduction of output power upon occurrence of any event which could potentially lead to exposure to radiation above the Class 1M hazard level.

The Fiberstore VG EDFA In-line Amplifier Class 1M APR scheme is based on two independent detection mechanisms designed to detected any disruption in the output transmission line up to a distance of a few tens of kilometers, sufficiently far to cover that part of the transmission line where the signal power is above 20.5 dBm. Upon detection of such a disruption, the output power is decreased within 100 ms (in compliance with Class 1M requirements) to a level below 20.5 dBm. The APR hardware supports full redundancy of all critical components, such that there is no single point of failure which could lead to a situation where the EDFA remains operational, while the APR is not in operation.

A complementary feature to the APR mechanism is the automatic restart procedure (ARP). This ensures that when the fiber disruption that caused an APR event is corrected, the EDFA will automatically increase output power to the required level without need for manual operator intervention. These unique and patent protected mechanisms allow Fiberstore EDFAs to be classified as Class 1M laser products, while at the same time providing up to 26 dBm output power.

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