Eye-safe lidar receiver using Er3+: Fiber optical preamplifier

We have demonstrated a 15 dB lidar receiver detection sensitivity improvement by employing an Er3+-doped fiber preamplifier as the input to an InGaAs P-I-N photodiode. This eye-safe, 1550 nm detection system can significantly improve lidar system performance. It will be shown that it is comparatively easier at 1550 nm than at 1064 nm to achieve a higher detection sensitivity for a lidar system using a fiber preamplifier in comparison with that using an avalanche photodiode(APD). The reason is that the Er:fiber preamplifier performs better than a Nd:fiber preamplifier, while the InGaAs APD is less sensitive in comparison with a Si APD. In a lidar receiver using a fiber preamplifier, the beam coupling efficiency from free-space mode to a single-mode fiber is the critical parameter. For moderate target velocities, an automatic front-end alignment system using piezoelectric transducers can be effected to yield a good coupling efficiency. The design and preliminary test results of such a lidar receiver will be discussed in terms of optimized optical filter bandwidth, optical preamplifier gain and noise figure, and input saturation level.