Investigation On Wideband Chaos Of Monolithically Integrated Semiconductor Laser With Optical Injection

Recently, the chaos draws considerable attention due to its promising applications in secure communication, fast random-bit generation, radar, etc. Through introducing external disturbances such as optical feedback, optical injection, optoelectronic feedback or current modulation, a chaotic system based on semiconductor lasers(SLs) can be established for realizing chaotic signal output. In early researches, most of the SLs-based chaotic systems are usually constituted by discrete components. As one kind of photonic integrated circuits(PICs), the monolithically integrated semiconductor lasers(MISLs) have attracted intensive attention due to their unique virtues such as smaller size, lower cost, more stable, and better for mass production. Through specific design and manufacture, MISLs can output different dynamical states by selecting suitable current injection. Within the application of SLs-based chaotic systems, chaotic signal bandwidth is a crucial factor. Due to the restriction by the relaxation oscillation frequency of the DFB section in a MISL, the bandwidth of the chaotic signal generated by a solitary MISL is usually at a level of 10 GHz, which sometimes may not meet the requirements in some special applications such as beyond 10 Gb/s high-speed optical chaotic communication and ultra-high-speed random number generation. In order to overcome the bandwidth restriction by the relaxation oscillation frequency of the active region in SLs, various optical injection schemes are proposed to enhance the bandwidth of the chaotic signal. However, most of relevant investigations on the chaos bandwidth enhancement focus on those SLs-based chaotic systems, and pay little attention on a MISL chaos system.Wide bandwidth chaotic signal generation in a three-section monolithically integrated semiconductor laser(MISL) under external optical injection is investigated experimentally. And the MISL is composed of a distributed feedback(DFB) section, a phase(P) section and an amplification(A) section. Through evaluating the effective bandwidth of chaotic signals, the influences of the optical injection on the bandwidth of chaotic signal from the MISL are analyzed. The experimental results indicate that, for the currents of the DFB section(IDFB), the phase section(IP) and the amplification section(IA) are fixed at 70.00 m A, 34.00 m A and 23.22 m A, respectively, the effective bandwidth of chaos signal generated by the solitary MISL can reaches 14.36 GHz. After an external optical injection is introduced into the MISL under such conditions, the effective bandwidth of the generated chaotic signal can be beyond 2.5 times of that in the solitary MISL. Furthermore, the effects of the injection ratio and the frequency detuning on the effective bandwidth of the generated chaotic signal and the states of laser output are also discussed, respectively. When fixing the frequency detuning, with the increase of injection ratio, the effective bandwidth rapidly increases firstly, and then slowly increases to a relative stable value. When fixing the injection ratio and the absolute values of frequency detuning are relative small, the dynamical states are very sensitive to the variation of the frequency detuning and the effective bandwidths change dramatically. However, when the absolute value of frequency detuning possesses relative large values, the output is usually chaos and the effective bandwidth can beyond 36 GHz.