Novel Lidar and Radar Development Using Photonic Microwave Generated from Nonlinear Dynamics of Semiconductor Lasers

• Main Authors: Cheng, Chih Hao, 鄭致灝
• Other Authors: Lin, Fan Yi
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/75826605100074872536

博士 === 國立清華大學 === 光電工程研究所 === 104 === Novel lidar and radar using photonic microwave generated from nonlinear dynamics of semiconductor lasers have been proposed and investigated. Benefitting from the photonic microwave, the techniques already developed in radar and lidar are possible to be integrated. The inherent properties of the laser light and microwave can also complement with each other to improve the performance of lidar and radar. In addition, based on nonlinear dynamics of semiconductor lasers, diverse photonic microwave covering from sinusoidal signals with linewidths of several Hz to non-periodic and wideband signals with bandwidths of several GHz can be obtained. In this dissertation, according to detection scenarios, the narrowband period-one (P1) state and broadband chaos state are explored for different lidar and radar applications. For lidar, a dual-frequency laser Doppler velocimeter (DF-LDV) based on the P1 state is investigated. By probing the target with the light-carried microwave, the DFLDV successfully shows the ability of speckle noise reduction and coherence enhancement. Compared with the conventional single-frequency laser Doppler velocimeter (SF-LDV), the velocity resolution of the DF-LDV is improved by 4 orders for a target with a longitudinal velocity vz = 4 cm/s, a transverse velocity vt = 5 m/s, and at a detection range of 108 m. To further improve the performance of the DF-LDV, a self-mixing DF-LDV (SM DF LDV) is proposed by incorporating the DF-LDV with the SM configuration. Benefitting from the SM configuration, the direction discriminability and high sensitivity are demonstrated. With few μW of optical power backscattered from a diffused target, an SNR of 23 dB is achieved without employing any avalanched photodetector or a photomultiplier tube. For radar, the chaos state with the electrical heterodyne technique is utilized to generate multiple orthogonal waveforms for the multiple-input-multiple-output (MIMO) radar application. The correlation between the heterodyned chaos signals are analyzed, which shows that the minimum frequency spacing of local oscillators for obtaining orthogonal heterodyned chaos signals is determined by the correlation time. With a correlation time of several μs, thousands of orthogonal chaos signals can be obtained. Furthermore, the electrical heterodyne technique is further extended to improve the quality of the chaos signal generated from a semiconductor laser subject to optical feedback. Through the heterodyne process, the power in the chaos spectrum can be redistributed to elevate the dip in the low frequency region and smooth out the loop frequency peaks. Therefore, the time delay signature (TDS) suppression and bandwidth enhancement can be achieved simultaneously. Compared to the original chaos, the amplitudes of the TDS and the effective bandwidths can be suppressed and enhanced up to 63% and 46% in average, respectively.