MSM-PMD as correlation receiver in a new 3D-ranging system

摘要

This contribution describes a ranging system based on a new kind of optical sensor, called the Photonic Mixer Device (PMD). This unit combines fast optical sensing and modulation of incoherent light signals in one component part by its unique and powerful principle of operation. The key feature of this new sensor is the direct detection of the correlation value between the light and an electrical reference signal as an analog voltage value. The realized ranging system is based on the following concept: A laser diode or LED is modulated with a PN-code sequence and the reference signal consists of the same PN-code sequence. With a delay unit the phase of the reference signal is shifted until the PMD-sensor returns an expected correlation value. The delay between the reference and the reflected light signal implies information concerning the distance to the reflecting object. An array of these sensors provides a 3D-ranging system, that could be used for, e.g., collision avoidance in new traffic control systems or in product monitoring systems. Fast modulation of the laser and the PMD provides a high distance resolution. Nowadays PMD-realizations are based on standard CMOS-technology, but we also keep investigation in a new kind of PMD based on MSM-technology (metal-semiconductor-metal). The MSM-sensor got the outstanding feature of a very high bandwidth. It should cope with modulation frequencies up to 1 GHz. Equipped with this feature the attained resolution may be very fine. In this paper we propose the advantages of this system, including the useful qualities of using a PN-code sequence. The experimental results of the new ranging system, including the MSM-PMD-device, are the main focus.