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Tunable Erbium-doped Fiber Laser Based On Sagnac Loop

Posted on:2015-10-16Degree:MasterType:Thesis
Country:ChinaCandidate:N LuFull Text:PDF
GTID:2298330467955380Subject:Communication and Information System
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With the rapid development of optical communication technology, people have becomeincreasingly demanding on large-capacity, long-distance transmission communication systems.Advantages of fiber lasers are increasingly apparent. Especially, the tunable erbium-dopedfiber laser attracts much attention because of its widely tuning range, stability, good laserquality, low lasing threshold and high conversion efficiency, and is widely used incommunications, fibre optical sensors, medical treatment, military and other important areas.In this paper, the tunable erbium-doped fiber lasers were studied, and two ring cavity tunableerbium-doped fiber lasers were designed. The main contents include:1. The background and significance of the subject are summarized. We briefly introduceand classify tunable lasers and fiber Sagnac loop, and summarize their research status andresults.2. From the view of lasing condition, resonant cavity, pump and threshold characteristics,this paper expounds the principle of fiber lasers. Several common optical elements areanalysed utilizing Jones matrix theory. Three typical filters are made theoretical derivationand simulation.3. A switchable dual-wavelength erbium-doped fiber laser based on Sagnac loop insertedwith two FBGs is proposed. The wavelength selection element consists of two fiber Bragggratings (FBGs), a polarization controller (PC) and a3dB coupler forming a Sagnac loopinserted with two FBGs(FBG-FSI), and selects the lasers satisfying the Bragg wavelength. Byadjusting the PC, we can change the wavelength-dependent loss to control single-anddouble-wavelength laser output. In addition, effect of different coupling ratios in FBG-FSI ontransmission characteristics of the filter is studied. When the coupling ratio is50:50, filterperformance is the best. In this case,980nm laser diode (LD) acts as the pump source. Atroom temperature, stable single-and double-wavelength lasers are achieved. Within two hours,the maximum fluctuation of peak power is less than0.7dB, and side mode suppression ratios(SMSR) are41.10dB and39.88dB, respectively.4. A cascading filter composed of Sagnac loop and M-Z is designed. The experimentalperiod of comb spectra of packaged M-Z filter is2.2nm and the bandwidth of eachtransmission peak is approximately1nm. By adjusting the DC driving voltage joining to M-Z,the comb spectra can move around. The experimental length of polarization maintaining fiber(PMF) is10m, and the period of comb spectra of Sagnac loop filter with a segment of PMF is0.42nm, which is about one fifth of that of M-Z. And there are surely two transmission peakswithin the bandwidth of the each transmission peak of M-Z. The Sagnac loop and M-Z arecascaded, and transmission spectrum is simulated and observed through experiment. Theresult shows that experimental result is consistent with the simulation result. A tunable erbium-doped fiber laser based on cascading filtering of Sagnac loop and M-Z is firstlyproposed. A segment of15km long single mode fiber is adding to the resonator to generatenonlinear effect to stabilize dual-wavelength output and obtain multi-wavelength lasers. Theexperiments suggest that3dB bandwidth of all the lasers are less than0.07nm, the peakpowers are more than-17dBm, SMSRs are more than32dB and the maximum powerfluctuation of single and double wavelength are1.2dB and1dB, respectively. In addition, athree-wavelength laser is also achieved. By adjusting the driving voltage and the PC in theSagnac loop, that every wavelength can be tunable continuously is achieved.
Keywords/Search Tags:erbium-doped fiber lasers, tunable, Sagnac loop, fiber Bragg grating, M-Z filter, cascading filtering
PDF Full Text Request
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