High-gain polarization-insensitive optical amplifier

A polarization-insensitive optical amplifier (PIOA) consisting of two serial semiconductor laser amplifiers (SLAs) is studied theoretically and experimentally. A polarization-insensitive isolator (PII) inserted between the two SLAs serves not only to eliminate the coupling cavity, but also to rotate any polarized forward light by 90°. Experimental results show a maximum fiber-to-fiber gain of 29 dB. PIOA gain deviation for the input polarization launch angle is just 0.6 dB compared to an original value of 5-6 dB in a single SLA. A theoretical analysis shows that it is necessary to achieve a PII rotation design error of less than 0.5° in order to suppress deviation below 0.1 dB. PIOA noise figure deviation, for the input signal polarization launch angle, was only 0.1 dB from both the experimental and theoretical results even though there was a rotation error of 2°