1872 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 23, NO. 24, DECEMBER 15, 2011 Generation of Broadband Chaotic Laser Using Dual-Wavelength Optically Injected Fabry–Pérot Laser Diode With Optical Feedback Mingjiang Zhang, Tiegen Liu, Pu Li, Anbang Wang, Jianzhong Zhang, and Yuncai Wang Abstract—Chaotic laser with a flat power spectrum up to 32.3 GHz has been generated by using a dual-wavelength op- tically injected Fabry–Pérot laser diode with optical feedback. The Fabry–Pérot laser diode with fiber ring cavity is utilized to generate the chaotic light. The bandwidth of the chaotic laser, due to dual-wavelength optical injection, is enhanced roughly four times as much as that of the chaotic laser without optical injection. Index Terms—Bandwidth enhancement, broadband, chaos, op- tical feedback, optical injection, semiconductor lasers. I. INTRODUCTION C HAOTIC laser generated by the laser diodes has aroused considerable interest owing to its wide applications in optical chaos communications [1], chaotic lidar [2], optical time domain reflectometer (OTDR) [3], fast random bit gen- erator [4], [5], and photonic ultra-wideband signal generator [6]. However, the relaxation oscillation limits the bandwidth of the chaotic laser emitted from a laser diode with single optical injection or feedback. Thus some applications are much restricted in the range resolution of chaotic lidar, the bit rate of random sequence, and the transmission rate of optical chaos communications. Manuscript received June 27, 2011; revised August 23, 2011; accepted September 24, 2011. Date of publication October 03, 2011; date of current version November 23, 2011. This work was supported by the National Natural Science Foundation of China under Grant 60927007 and Grant 61108027, by the Shanxi Province Science Foundation for Youths under Grant 2010021003-4, and by the National Basic Research Program of China (973 Program) under Grant 2010CB327800. M. Zhang is with the Institute of Optoelectronic Engineering, Department of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China, and also with the Key Laboratory of Optoelectronics Infor- mation Technical, Ministry of Education, College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China (e-mail: zhangmingjiang@tyut.edu.cn). T. Liu is with the Key Laboratory of Optoelectronics Information Technical, Ministry of Education, College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China (e-mail: tgliu@tju.edu. cn). P. Li and A. Wang are with the Institute of Optoelectronic Engineering, De- partment of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China (e-mail: lipu8603@126.com; wangyc@tyut.edu.cn). J. Zhang is with the State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China, and also with the Institute of Optoelectronic Engineering, Department of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China (e-mail: zhajianzho@163.com). Y. Wang is with the Institute of Optoelectronic Engineering, Department of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China, and also with the State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China (e-mail: wangyc@tyut.edu.cn). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2011.2170560 Therefore, in past few years, some schemes for bandwidth enhancement of chaotic laser have been reported. For example, Lin et al. numerically studied the bandwidth enhancement of chaotic states in a semiconductor laser subject to optoelectronic feedback by using external optical injection [7]. Hosiny et al. represented chaos enhancement by injecting additional optical signals into an optically injected semiconductor laser [8]. Moreover, Yan reported a method to enhance chaotic carrier bandwidth of a delayed feedback semiconductor laser with an additive feedback light [9]. Uchida et al. demonstrated the bandwidth-enhanced chaos generation by injecting the chaotic light into a slave laser diode [10]. Takiguchi et al. numerically demonstrated that the bandwidth of the chaotic carrier in a semiconductor laser with optical feedback was expanded to be about three times by strong optical injection [11]. By using an additional single-beam optical injection, we achieved the bandwidth enhancement of chaotic signals generated from a distributed feedback laser diode with optical feedback [12] and also demonstrated a route to bandwidth-enhanced chaos [13]. Until now, to our best knowledge, no experimental results of bandwidth-enhanced chaotic laser over 25 GHz has been reported by using these schemes cited above. In this letter, we propose a method to generate broadband op- tical chaotic signals by using dual-wavelength optical injection Fabry–Pérot laser diode with optical feedback and experimen- tally demonstrate the generation of chaotic laser with bandwidth up to 32.3 GHz by this scheme. II. EXPERIMENTS A. Experimental Setup Fig. 1 shows the experimental setup. A Fabry–Pérot laser diode (FP-LD) subject to optical feedback with a fiber ring cavity is used to generate the chaotic light. The power of feedback light is adjusted by a variable attenuator (VA3) and an erbium-doped fiber amplifier (EDFA), and its polarization state is controlled by a polarization controller (PC3). Two distributed feedback laser diodes (DFB-LD1 and DFB-LD2) are employed to enhance the bandwidth of the chaotic light by injecting continuous-wave light into the FP-LD through two 50/50 couplers. The wavelength of each DFB-LD is adjusted by a temperature controller to achieve the optical frequency detuning to the FP-LD. The power and polarization state of the injection lights are controlled by VA1, PC1, VA2 and PC2, respectively. The output of the chaotic laser is converted into chaotic radio signals by a 50-GHz bandwidth photodetector ( XPDV2020). A 6 GHz bandwidth oscilloscope (LeCroy 1041-1135/$26.00 © 2011 IEEE