Study On C-band Tunable Single-frequency Fiber Laser

Ultra-high-speed(400G/1T) coherent optical communication networks which require higher transmission rates and more complex modulation formats call for the laser has ultra- narrow linewidth(<100 k Hz),high SNR(>40 d B)and tunable function. The single-frequency fiber lasers have narrower linewidth,higher SNR and compact all-fiber design than the Semiconductor single-frequency lasers,which have the potential to be the light source of the high-speed coherent communication systems. In this thesis,tunable single-frequency fiber lasers are studied. The tunable single-frequency fiber laser which wavelengths meet the ITU-T standard C-band channels is structured. The specific research contents are as follows.Firstly,the design of tunable single-frequency fiber laser is proposed. The detail scheme is followed.(1)Obtain single-frequency laser output of different lasing wavelengths by controlling different pump chip switch,which will achieve the scheme of coarse tuning output wavelength.(2)Use high-gain phosphate fiber as laser gain medium,which will shorten the cavity length and achieve the scheme of output characteristics of the single-frequency laser.(3)Use the precise temperature control which will achieve the scheme of precisely controlled output wavelength of single-frequency fiber laser.Secondly,through using the ITU-T standard C-band channels, four single-frequency fiber laser cavities of different lasing wavelengths are structured, which constitute the tunable single-frequency fiber lasers. Output characteristics of the tunable single-frequency fiber laser are measured. The result of single-frequency,linewidth < 3 k Hz,side-mode suppression ratio(SMSR)> 65 d B,output power > 14 m W,RIN <-135 d B/Hz,polarization extinction ratio(PER)> 21 d B are achieved. In order to precisely controlling the output laser wavelength,we also setup experiments on the wavelength tuning of a single-frequency fiber laser through temperature controlling and stretching narrowband fiber grating by using PZT.Finally,in order to increase the output power of the tunable single-frequency fiber laser,the amplifier based on Er3+/Yb3+ co-doped phosphate fiber is investigated experimentally. By comparing the experimental results,the optimized 4 cm gain fiber length is achieved,and the output characteristics were analyzed and discussed. The tunable single-frequency fiber laser features single frequency as well as narrow linewidth(k Hz), while keeping all the merits(output power>13 d Bm,SMSR>60 d B, RIN of-135 d B/Hz). With compact size,lower cost and excellent performance,our tunable single-frequency fiber laser is expected to be applied to next-generation communication network.