Lidar imaging systems are one of the hottest topics in the optronics industry. The need to sense the surroundings of every autonomous vehicle has pushed forward a race dedicated to deciding the final solution to be implemented. However, the diversity of state-of-the-art approaches to the solution brings a large uncertainty on the decision of the dominant final solution. Furthermore, the performance data of each approach often arise from different manufacturers and developers, which usually have some interest in the dispute. Within this paper, we intend to overcome the situation by providing an introductory, neutral overview of the technology linked to lidar imaging systems for autonomous vehicles, and its current state of development. We start with the main single-point measurement principles utilized, which then are combined with different imaging strategies, also described in the paper. An overview of the features of the light sources and photodetectors specific to lidar imaging systems most frequently used in practice is also presented. Finally, a brief section on pending issues for lidar development in autonomous vehicles has been included, in order to present some of the problems which still need to be solved before implementation may be considered as final. The reader is provided with a detailed bibliography containing both relevant books and state-of-the-art papers for further progress in the subject.

An Overview of Lidar Imaging Systems for Autonomous Vehicles

Single-mode fiber lasers with excellent beam quality and several-kilowatts output power are expected to realize both extraordinary processing speed and high aspect ratio in the material processing field. In this paper, we report an 8-kW output single-stage Yb-doped fiber laser with a BPP of 0.50 mm-mrad. The laser has a delivery fiber with a length of 3 m. To realize an 8-kW single-mode output without excess a stimulated Raman scattering threshold, fibers with a considerably large effective core area are employed. An ytterbium doped fiber is directly pumped by newly developed high-power laser diode modules with a total available pump power over 10 kW through a bi-directional pumping scheme. The laser has a high slope efficiency of 81%. The power of the SRS light around 1120 nm was 22 dB smaller than the fundamental laser power at 1070 nm. To the best of our knowledge, it is the smallest BPP with more than 8 kW output power pumped by an end-pumping regime. We believe the laser will contributes laser processing using a galvano scanner for high speed and high aspect ratio welding.

8-kW single-stage all-fiber Yb-doped fiber laser with a BPP of 0.50 mm-mrad

Spectroscopy of Yb-doped tungsten-tellurite glass and assessment of its lasing properties

We present results from our recent efforts on developing single-mode fused couplers in ZBLAN fibre. We have developed a custom fusion workstation for working with lower melting temperature fibres, such as ZBLAN and chalcogenide fibres. Our workstation uses a precisely controlled electrical heater designed to operate at temperatures between 100 – 250°C as our heat source. The heated region of the fibers was also placed in an inert atmosphere to avoid the formation of microcrystal inclusions during fusion. We firstly developed a process for pulling adiabatic tapers in 6/125 μm ZBLAN fibre. The tapers were measured actively during manufacture using a 2000 nm source. The process was automated so that the heater temperature and motor speed automatically adjusted to pull the taper at constant tension. This process was then further developed so that we could fuse and draw two parallel 6/125 μm ZBLAN fibres, forming a single-mode coupler. Low ratio couplers (1-10%) that could be used as power monitors were manufactured that had an excess loss of 0.76 dB. We have also manufactured 50/50 splitters and wavelength division multiplexers (WDMs). However, the excess loss of these devices was typically 2 - 3 dB. The increased losses were due to localised necking and surface defects forming as the tapers were pulled further to achieve a greater coupling ratio. Initial experiments with chalcogenide fibre have shown that our process can be readily adapted for chalcogenide fibres. A 5% coupler with 1.5 dB insertion loss was manufactured using commercial of the shelf (COTS) fibres.

Mid-IR fused fiber couplers

We report an industrial grade picosecond and femtosecond pulse Yb fiber lasers with >100 μJ pulse energy and hundreds of Watts of average power for improved laser machining speed of sapphire and glass. This highly efficient laser offers >25% wall plug efficiency within a compact 3U rack-mountable configuration plus a long >2m fiber delivery cable. Reconfigurable features such as controllable repetition rate, fine pulse duration control, burst mode operation and adjustable pulse energy permit the customer to tailor the laser to their application.

New generation of high average power industry grade ultrafast ytterbium fiber lasers

The world’s most powerful laser system for industrial applications would be presented. Ytterbium fiber laser combines record 101.3 kW output power, continuous-wave operational mode and an excellent beam quality. Beam parameter product (BPP) does not exceed 16 mm x mrad, when we use 300 μm x 10 m feeding fiber, or near 25 mm x mrad, when fiber-to-fiber output coupler with 500 μm x 50 m process fiber is used. Emission wavelength is 1070 nm. High wall-plug efficiency 35.4%, compact laser cabinet and total weight less than 3600 kg open the new opportunities in different industrial and mobile applications. Keywords—Lasers, fiber; Infrared and far-infrared lasers

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D. Mochalov

Papers

100 kW CW fiber laser for industrial applications