High-speed, high-power double-clad fiber amplifiers

Summary form only given. Double-clad optical fibers are a robust, convenient medium for efficient optical amplification. Their compatibility with high-power semiconductor laser pump sources allows them to operate at saturated power levels of several watts, significantly higher than the level achievable with conventional diode-pumped fiber amplifiers. When coupled with a high-speed master oscillator, such an amplifier becomes an efficient high-speed, high-power optical transmitter. Such a source is of considerable interest for a high-speed space link. The transmitter consisted of a high-speed master laser diode, a high-gain fiber preamplifier, and a high-efficiency fiber power amplifier. The master oscillator was a Fabry-Perot laser diode centered at /spl lambda/=1072 nm, mounted in a high-speed, fiber-coupled package. The laser operated kink free to >50 mW and exhibited a 3-dB roll-off frequency of 11.1 GHz. Both the pre-amp and power amp were based on Yb-doped double-clad fibers pumped with /spl lambda/=915 nm fiber-coupled laser diodes. A polarization-independent optical isolator prevented feedback from the amplifier destabilizing the master oscillator. A free-space WDM module used to combine the signal and pump light into the core and cladding, respectively, of the pre-amp fiber, is shown.