We have developed a LIDAR system with a sensor head which, although it includes a scanning mechanism, is less than
20 cc in size. The system is not only small, but is also highly sensitive.
Our LIDAR system is based on time-of-flight measurements, and incorporates an optical fiber. The main feature of our
system is the utilization of optical amplifiers for both the transmitter and the receiver, and the optical amplifiers enable
us to exceed the detection limit set by thermal noise. In conventional LIDAR systems the detection limit is determined
by the thermal noise, because the avalanche photo-diodes (APD) and trans-impedance amplifiers (TIA) that they use
detect the received signals directly. In the case of our LIDAR system, the received signal is amplified by an optical fiber
amplifier before reaching the photo diode and the TIA. Therefore, our LIDAR system boosts the signal level before the
weak incoming signal is depleted by thermal noise. There are conditions under which the noise figure for the
combination of an optical fiber amplifier and a photo diode is superior to the noise figure for an avalanche photo diode.
We optimized the gains of the optical fiber amplifier and the TIA in our LIDAR system such that it would be capable of
detecting a single photon. As a result, the detection limit of our system is determined by shot noise.
We have previously demonstrated optical pre-amplified LIDAR with a perfect co-axial optical system. For this we
used a variable optical attenuator to remove internal reflection from the transmission and receiving lenses. However, the
optical attenuator had an insertion loss of 6dB which reduced the sensitivity of the LIDAR. We re-designed the optical
system such that it was semi-co-axial and removed the variable optical attenuator. As a result, we succeeded in scanning
up to a range of 80 m.
This small and highly sensitive measurement technology shows great potential for use in LIDAR.