Study On The Intensity Noise Of Erbium Doped Fiber Laser

Because of the advantages of band widely, noise lowly and gain highly, efficiency highly and so on, Erbium-doped fiber laser (EDFL) is widely used in optical fiber sensing and optical communication field. With the higher and higher demand about the sensitivity of interferometric fiber-optic sensors, as one important factor which influences its detection sensitivity, it is become concerned hot about the intensity noise of EDFL. So it is also become an important topic about suppressed the nose intensity of the EDFL. Based on the above consideration, the main work of this paper is:1,It is Explained the development and the characteristics of the fiber laser. It is necessary to describe the research of the intensity noise of the EDFL and focus on the intensity noise of the optical fiber laser research. In the meantime, it is introduced the related research of the intensity noise of the optical fiber laser, home and abroad. The basic theory of fiber laser in particular EDFL is introduced and several typical cavity structures of EDFL are included.2,The basic characteristics of intensity noise of the fiber laser is introduced。Focusing on analyzing the relaxation oscillation which is the main factor of influencing the intensity noise of the EDFL, besides, the reason about the relaxation oscillation is explained. According to the rate equations, it is analyzed the factor of effecting the relaxation oscillation, the phenomenon of the relaxation oscillation is affected by the pump-rate fluctuations and cavity-loss fluctuations. At last, some methods are showed to suppress the intensity noise of the EDFL in experiment.3,The pump laser can be controlled to influence the EDFL's intensity noise. The optoelectronic feedback is used to suppress the intensity noise of the EDFL:at the first, the output of the EDFL is sampled by PD. and then the phase and amplitude of the feedback signal is adjusted by the feedback circuit, finally the feedback signal is coupled to the pump drive, then the output power of the pump laser is modulated, in order to suppress the intensity noise of the EDFL. To do this has very good suppression for the low and medium frequency noise of EDFL. The relaxation oscillation peak of intermediate frequency (about 30 KHz) is reduced to about 35dB, and the low frequency band (below 20 KHz) falls to about 10dB averagely. Therefore, these methods in the largely suppressed the intensity noise of EDFL. Through optoelectronic feedback and the development of a new type of pump circuit, the output of EDFL gains a flat noise output spectrum line which is better than-121dB/Hz.4,Some new questions are proposed based on previous work, which point out the direction of future work about suppressed the intensity noise of EDFL.