Mitsutoshi Maeda

System Design and Performance Characterization of a MEMS-Based Laser Scanning Time-of-Flight Sensor Based on a 256

This paper reports on a light detection and ranging (LIDAR) system that incorporates a microelectromechanical-system (MEMS) mirror scanner and a single-photon imager. The proposed architecture enables a high signal-to-background ratio due to pixel-level synchronization of the single-photon imager and the MEMS mirror. It also allows the receiving optics to feature a large aperture, yet utilizing a small MEMS device. The MEMS actuator achieves a mechanical scanning amplitude of ±4° horizontally and ±3° vertically, while the field of view of the overall sensor is 45 by 110. Distance images were acquired outdoors in order to qualitatively evaluate our sensor imaging capabilities. Quantitative ranging performance characterization carried out under 10 klx of ambient light revealed a precision of 14.5 cm throughout the distance range to 25 m, thus leading to a relative precision of 0.58%.

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We developed a LIDAR system with a sensor head as small as 22 cc, in spite of the inclusion of a scanning mechanism. This LIDAR system not only has a small body, but is also highly sensitive. Our LIDAR system is based on time-of-flight measurements, and it 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 enabled us to exceed the detection limit of thermal noise. In conventional LIDAR systems the detection limit is determined by 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, received signal is amplified by an optical fiber amplifier in front of the photo diode and the TIA. Therefore, our LIDAR system can boost 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 gain of the optical fiber amplifier and TIA in our LIDAR system such that it is capable of detecting a single photon. As a result, the detection limit of our LIDAR system is determined by shot noise. This small and highly sensitive measurement technology shows great potential for use in LIDAR with an optical preamplifier.

64-pixel Single-Photon Imager

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[1]. 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.

Highly sensitive lidar with a thumb-sized sensor-head built using an optical fiber preamplifier

In this paper we propose a direct diode laser (DDL) system consisting of laser diode (LD) bars, a planar lightwave circuit (PLC), and an optical fiber. We have developed a PLC as an optical power combiner and an LD mounting technology that is suitable for coupling to the PLC. A DDL system is presented that consists of six LD-PLC optical modules for the laser-welding of highly heat-resistant plastics. The total output power is in the 200 W class, with a spot diameter of 5.52 mm for the major axis and 5.00 mm for the minor axis at a focal length of 50 mm. The total output efficiency is 60.9% from the laser diode to the welding torch.

Improvement of highly sensitive lidar with a thumb-sized sensor-head built using an optical fiber preamplifier

A direct diode laser (DDL) system has been proposed, consisting of a laser diode (LD), planar lightwave circuit(PLC) and optical fibers. The output from one PLC module is a 320 um times 300 um bundle optical fibers, each fiber having a rectangular core of NA0.3. The output efficiency was 74.2% at the fiber end. This PLC module may be applied as the light source for DDL processing or for the excitation module of a fiber laser.