Fast scan-fail device for class 1 operation of scanning micromirrors at a high laser power in the near-infrared region

Abstract

ABSTRACT With the availability and maturity of scanning micromirrors, a growing field of applications other than picoprojectors is emerging. The miniaturization potential of these scan based setups is most attractive for robotic vision and LIDAR imaging sensors for autonomous guided vehicles. The laser safety concept of picoprojectors is based on the eye blink reflex and high scanning frequencies (>10 kHz). However, in remote sensing applications, where infrared wavelengths and ve ry often lower scanning frequencies are a common choice, there is a demand for robust scan failure detection. According to IEC 60825 the maximum emission time of a 100 mW CW Laser at 900 nm must be below 5 µ s to be classified as a class 1 laser source. Sta te-of-the -art scan -fail devices, which are designed for laser light shows, only feature reaction times down to 1 ms . Therefore, to enable class 1 operation of a laser scanner, based on micromirrors, a detailed examination of all possible failure scenarios was performed and consequently a fast scan -fail device with a reaction time of less than 5 µ s was developed. The position of the micromirror is measured optically by focusing a laser diode to the micromirror and detecting the mirror position with a quadran t photodiode. To determine the current angular velocity of the micromirror the first derivative of the position signal is evaluated and monitored. This enables the eye -safe use of reasonably powered infrared lasers in low -cost scanning setups. Keywords: laser , safety, scanning , micromirror , MEMS, MOEMS, scan -fail device , scan failure