A tunable self-mixing chaotic laser based on high frequency electro-optic modulation
Introduction
Light that is injected into a laser cavity will mix with the original laser in the cavity, resulting in a change in the laser resonance frequency and output power. For different injection conditions, the laser output will show a number of nonlinear states, such as a locked state, single periodic oscillation, double periodic oscillation, multi periodic oscillation, quasi-periodic oscillation or a chaotic state. Therefore, optical injection has been widely applied in laser self-mixing measurements, fiber active sensing, laser radar, mode-locked lasers, etc. [1], [2], [3], [4], [5], [6].
Optical injection is an important way to generate a chaotic laser [7], [8], [9]. Optical chaos refers to the unstable random outputs of the modes running in a laser cavity. This chaos is due to the addition of a disturbance, i.e., a new degree of freedom, to a stable-running optical cavity [10], [11], [12], [13]. A chaotic laser has a very broad bandwidth, high frequency and high degree of autocorrelation because of its intrinsic randomness. Chaotic laser has many great applications in optical security communication, optical information storage, comprehensive sensing, optical simulation, optical processing of chaotic phenomena in nature [14], [15], [16], [17], [18], [19], etc. Many researchers have focused on the development of chaotic lasers. Kumar et al. studied the dynamic characteristics of erbium-doped laser loss in an annular cavity and obtained the output of a chaotic laser by adjusting the loss intensity and other factors [20]. Mirg et al. adopted a ring laser system consisting of two erbium-doped fibers and obtained the output of an ultrabroadband chaotic laser of 12.5 GHz [21]. The Lucas group studied the nonlinear dynamics of an ytterbium femtosecond fiber laser and found that a chaotic laser can be produced in a quasi-mode-locked state [22]. In an all-fiber optical system, the laser can also be used to produce a chaotic signal by inserting a grating or a delay fiber in the light path, and modulating the light path with a circuit signal, and so on [23], [24], [25], [26], [27]. In the above researches, the chaos laser has been obtained in the optical fiber system, and the mechanism of chaos generation and chaos bandwidth expansion have been deeply analyzed, that we know the time delay and the frequency modulation of the pump laser in a laser cavity influence the bandwidth of the chaotic laser importantly. However, the effect of frequency modulation on the bandwidth of chaotic laser still needs to be further studied. Because the frequency modulated light injection is a convenient way for us to obtain the actively controllable chaos optical system. In the key applications, the broadband frequency carrying capacity of chaotic laser is of great value.
In this paper, we propose a tunable self-mixing chaotic laser based on high frequency electro-optic modulation. The laser dynamics system is designed to be a double ring resonator. One ring is the main laser resonance, and the other is for optical feedback injection with electro-optic modulation, which provides two degrees of freedom for the main laser. A kinetic equation is created to understand the formation of the chaotic laser with different optical feedback modulations. Spectral responses and chaotic series are experimentally studied. The bandwidth and the autocorrelation of the chaotic series corresponding to different modulation frequencies are analyzed. The modulation effect of chaotic laser frequency bandwidth is observed, and the method of tunable chaotic laser frequency bandwidth is obtained.
Section snippets
System designed and theoretical analysis
The diagram of the designed chaotic system is shown in Fig. 1. We use a pump laser at the wavelength of 980 nm as the source providing the energy for the erbium-doped fiber (EDF). The pump radiation is directed to a wavelength division multiplexer (WDM) and then passes through the EDF. The radiation is filtered by an FBG and runs in a wave band of 1550−1552 nm, then it passes through an optical coupler (OC-1), and it is separated into two parts by the OC-1 (20%:80%). Eighty percent of the light
Experimental results and discussion
The experimental system is constructed according to the diagram shown in Fig. 1. One part of the experimental system consists of the pump, WDM (980/1550-FBT), erbium-doped fiber, FBG, OC-1, and OC-2, which can produce a stable laser. The other part of the experimental system consists of OC-1, EOM, VOA and OC-2, which can achieve photoelectric modulation of the signal and couple with the first part. The last part of the experimental system consists of EDFA, PD and ESA (KEYSIGHT EXA Signal
Conclusions
In this paper, we have proposed and constructed a self-mixing laser system based on optical feedback frequency modulation, and demonstrated the generation of chaotic laser theoretically and experimentally. The chaos is caused by the disturbance of the degree of freedom of laser resonance caused by the change of injected optical feedback frequency. By tuning the frequency from 10 MHz to 10 GHz, we have obtained an ultra-wide band chaotic signal range from 0.8 GHz to 24 GHz, and also the
CRediT authorship contribution statement
Xuejie Mu: Conceptualization, Methodology, Software, Writing - original draft. Zhi Yan: Writing - review & editing. Yarong Yu: Software. Haitao Yan: Supervision, Writing - review & editing. Daofu Han: Investigation, Resources, Data curation, Funding acquisition, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Programs No. 61765010 and 61675964).
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