Abstract
In recent years, advancements in semiconductor optical amplifier (SOA) technology have solved many of the problems (e.g., polarization sensitivity[l] and low saturated output powers[2]) which have prevented their widespread deployment into optical networks. The most elusive and last remaining problem is the large crosstalk between channels in wavelength division multiplexing (WDM) and time division multiplexing (TDM) applications. The crosstalk arises from dynamic gain variations due to gain saturation. The most effective solution to these problems involves the use of a separate and simultaneous stimulated emission field in the SOA. Above threshold, the gain is clamped to the cavity losses and the effective carrier lifetime is significantly reduced due to stimulated emission. As a result, crosstalk, speed, and linearity of the SOA are significantly improved. Previous implementations of this gain-clamping approach to crosstalk reduction use a longitudinal lasing field[3-5] where a distributed Bragg reflector (DBR) or distributed feedback (DFB) laser structure is modified with lower reflectivities and then pumped above threshold. This approach, where laser light is collinear with the amplified signal, has a number of disadvantages. The creative challenge is to find a configuration where an "extra" lasing field can share the same gain medium and not hinder propagation of the signal beam through the device.
© 1996 Optical Society of America
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