A novel beam-shaping method which obtains nearly uniform illumination for a high-power Laser Diode (LD) stack is
introduced. Based on the properties of the angular distribution during the Gaussian beams propagate, a flat-topped beam
profile can be achieved by the superposition of Multi-tilted Gaussian beams. Due to the theory above, the individual
lensing techniques are introduced to shape the beams of the LD stack. Cylindrical lenses are used to control the
divergence-angle of the output beams. By adjusting the offset of each cylindrical micro-lens, each output beam on the
fast axis gains the different tilted emitting-angle. Meanwhile the beams on the slow axis are also shaped by a large
cylindrical lens. Thus the beam-shaping optical system is designed to reconfigure the beams of a high power LD stack to
form a Multi-tilted Gaussian beam shape for a 10°×10° field-angle illumination. The simulation results from ASAP
software show that uniform illumination can be obtained in the far-field district. With the proper uniformity and high
efficiency, the beam-shaping optical system we have proposed for high-power LD stacks can be well suitable for laser
illuminator in laser active imaging and detecting system.
Efficient beam shaping with uniform illumination is required in laser active imaging and detecting systems. In this paper, a beam-shaping method by superposition of tilted fundamental-mode Gaussian beams to produce nearly uniform illumination is proposed. The analytical formula for the average intensity of propagating multitilted Gaussian beams (MTGBs) is derived and used to study the uniformity of the beam profile with Fourier analysis. It is found that the MTGB maintains its flat-topped shape as it propagates and its uniformity is controlled by the parameters of fundamental-mode beams and superposition. Numerical examples are given. The method is used to reconfigure the beams of a high-power laser diode stack to form a MTGB shape for illumination of a 9×11.6-deg angular field. The simulation results from ASAP software show a shaping efficiency of 75%, and the rms deviation of the irradiance distribution from a flat-top shape is approximately 8%.
Proc. SPIE. 6838, Optoelectronic Devices and Integration II
KEYWORDS: Avalanche photodetectors, Semiconductor lasers, Monte Carlo methods, Time metrology, Ionization, Thulium, Avalanche photodiodes, Signal detection, Pulsed laser operation, Laser systems engineering
Several pulse response property of Avalanche photodiode (APD) were discussed in the paper, including the amplitude nonlinearity of large optical power signal input due to space-charge-effects, the reshape property and time domain property from the nonlinearity model of APD. In the pulse response measurement experiment, the APD was illuminated with a pulsed laser diode whose impulse width is several decades nanosecond with peak power up to decade watt. The experiment results showed the nonlinearity pulse response was well matched with the model numerical simulate result. The affect to the APD based range finder and Ladar was discussed and useful correction solution from the model was made especially for pulse TOF range finder.
It is convenient to apply three-dimensional (3D) detecting instruments to automatic drive, virtual reality modeling,
terrain reconnaissance, etc. It is presented that a new high-speed camera which achieves one three-dimensions image by
only one light pulse in this paper. It has a measurement range of one kilometer and a distance resolution of five meters.
This camera is composed with a pulse laser and three receivers which are made up with a Micro Channel Plate (MCP)
and a Charge Coupled Device (CCD) each. These parts are mature commercial productions that provide low cost and
high reliable to the 3D camera. As soon as the pulse laser emits a light pulse, the three receivers are modulated with
synchronistical control circuits. A 3D picture can be calculated by three different density images which are obtained by
that. The one-light-pulse-one-picture mode gives a flexible way to work with a gate signal. A 3D camera working with
high-speed gate signal can achieve high-speed photography easily. A mathematic model is established to describe
measurement range, distance detection precision and space resolving of the camera. The best modulation functions of the
receivers are given with consideration of white noise by Euler-Lagrange equation. Due to the best modulation function
we give a scheme is follows: The first receiver is modulated by a const gain, the second one is modulated by a linearly
increasing gain and the last one is modulated by a linear decreasing gain. This combination achieve both low noise and
simple structure. Because of the simple structure, several fibers which we named amending fibers can be used to amend
error of receiver modulation and synchronistical error. Analysis of the detection precisions of the camera and continuous
wave detection systems are carried out both in time domain and frequency domain. The results indicate pulse laser can
increase the detection range by suppressing background light greatly and decreasing imaging time. But it achieves lower
precision if the background light is faintness. Simulation experiment results are presented in this paper. A 1.4 kilometers
fiber was used in this experiment to simulate a 700 meters distant, a Laser Diode (LD) is employed to simulate the pulse
laser. A high voltage modulation circuit was designed to modulate the gain of MCP to implement the modulation
function. The experiment results with and without amending fibers indicated that the primary noises come from CCD and
the high voltage modulation circuit. The amending fibers can weaken the circuit errors in some degree. Future
improvement is described in the end of the paper also.
A novel three-dimensional (3D) camera concept system could capture 3D image with thousands of pixels at range of
several kilometer in real time was presented. The camera used a pulse laser to illuminate the scene, a solid-stat chargecouple
device(CCD) sensor, and sample cumulation technology based on a gated binary image intensifier. The
cumulation charges captured in CCD carried the information of range. The system was designed to have some significant
advantages, such as low cost, simply schemes, high speed mainly limited to the speed of CCD frame capture. Potential
applications include navigation of autonomous helicopter, large target identification, sensing and guidance, auto collision
avoidance, robotic vision, atmospheric sensing and topography. In the paper, we discussed the fundamental principle and
schemes of the 3D camera system based on sample cumulation and presented the feasible experiment result with a photo
multiplier tube with binary character to simulate one pixel of the 3D camera system. Then we discussed the factors
which influence the quality of 3D image according to the experiment result.