Research Of Ranging Method Based On Orthogonal Phase-locked Microwave Photonic Signal

With the increasing requirements for distance measurement, new distance measuring theories and methods are continuously proposed. And laser ranging is one of the subsequently developed ranging methods, which uses a laser as the light source. Because of its high resolution rate of the angle and good anti-interference ability, the multipath effect and clutter can be avoided so that such a method has a broad use in military and civilian fields. Phase laser ranging is one of the laser ranging, which has obvious advantages compared with other methods in the aspects of speed, precision, system construction and cost.Firstly, various methods of the laser ranging are introduced, including the pulse method, the feed-back method, the phase method and the interferometry method. The next part focuses on the phase ranging method, based on which the method of orthogonal locked ranging research based on microwave photonic signal is proposed. After the overall design of the measuring system, the selection of the key components in the system are introduced in detail, such as semiconductor lasers, Mach-Zehnder-Modulators (MZM), photodiode and so on.The proposed method of orthogonal locked ranging research based on microwave photonic signal in this paper is phase laser ranging essentially, and the system is a simple microwave photonic system with large bandwidth, low-loss and anti-electromagnetic interference and so on. An analog multiplier is used as a mixer in this system to pick up the phase difference which contains the information of distance to be detected. A radio frequency (RF) signal is first obtained from a modulated optical signal that is reflected by the target, and then mixed with the reference RF signal of the same frequency to extract their phase difference, which contains the ranging information. To improve the ranging accuracy, the frequency of the RF signal is swept to seek out the phase quadrature point between the microwave photonic signal and the reference signal, where the DC output of the mixer is minimum. As is known, the phase difference of two adjacent points is π. In this way, the distance measurement can be achieved by calculating the frequency difference between two adjacent phase quadrature points.The ranging method is verified by measuring two lengths of fiber repeatedly and achieved a high precision with a relative error less than3e-4. Last, the errors generated by the system are discussed and analyzed in the end.