| High power single-longitudinal-mode (SLM) fiber laser with high opticalsignal-to-noise ratio (OSNR) have enormous applications such as remotesensing, ladar, coherent detection, and nonlinear optics. Recently, the outputpower of fiber lasers grew quickly, but SLM fiber lasers did not. SLM fiberlasers can be boosted to watt-level, but it is still a challenge to preserve highOSNR. Besides, the output power of SLM fiber laser is also limited by thebackward stimulated Brillouin scattering (SBS).Owing to narrow band gain of SBS, Brillouin fiber lasers (BFLs) with?10m cavity can operate at SLM status. Though the threshold of BFLs can bereduced to submilliwatt level, but he pump frequency has ot match the cavitymode. This causes a big trouble for practical operation owing to the inevitablefluctuation of pump frequency. Moreover, it is difficult to output large poweras the cavity is critically coupled. Hybrid BFLs i’ncluding active media dontneed the critically coupled resonator, and they are able to achieve large power.A1W SLM Brillouin/ytterbium fiber laser with60dB OSNR has beendemonstrated. However, for a hybrid BFL, the wavelength tenability islimited at the self-lasing range. Besides, it inevitably introduces amplified spontaneous emission (ASE) noise from active fibers. Different than hybridBFLs, the BFLs without active fibers have wider tunable range, higher OSNR,and narrower linewidth. A SLM BFL with12m length cavity has beenreported and shown stable output power. In this letter, only SMF is used inthe single pass cavity. By exploiting the high efficiency of SBS in fibers andthe large output ratio of the lasing cavity, we demonstrate a watt-level SLMtunable BFL with75dB OSNR.Brillouin fiber laser (BFL) with multiwavelength output attracts muchinterest owing to their potential applications in microwave generation, anddense wavelength-division-multiplexing (DWDM) system. Hybrid BFL withthe reverse-S cavity is first reported for uniform power distribution has beenreported. However, the simultaneously using of two gain media in one cavitywill inevitably introduces amplified spontaneous emission (ASE) noise toBrillouin Stokes (BS) and causes restriction from self lasing cavity modeoscillation. In order to suppress the self lasing cavity modes, many techniquesare investigated. Tunable multiwavelength BFL was proposed to effectivelyeliminate the self-lasing cavity, and thus avoid self-lasing mode oscillationfrom EDFA. Recently, a reverse-S-shaped tunable multiwavelength BFL wasproposed to effectively eliminate the self-lasing cavity mode where the11kmlength dispersion compensation fiber (DCF) was used as the Brillouin gainmedium. However, the existent tunable multiwavelength BFL either operatesat kilometers length ordinary fiber or at hundred meters length fiber but with high Brillouin gain fiber. As experimentally demonstrated, BFL with10?20meters length cavity could generate stable SLM output. Unfortunately, theprevious schemes to generate tunable multiwavelength BFL are not able tooperate when the cavity is cut short to10?20meters, because where theBrillouin threshold will skyrocket.Different from hybrid BFL, single pass SMF cavity BFL is proposed andfound its application in microwave generation and ultrahigh resolutionspectral anal’ysis. Brillouin pump (BP) doesnt resonate in single pass cavity,which reduces the complexity to match the mode of cavity, and thus the BFLoutput wavelength could be continually tunable. In this paper, a novel widelytunable multiwavelength BFL is proposed based on the cascading process ofBS generation in a single pass SMF cavity. The novelty mainly consists oftwo parts. Firstly, the broad band amplifier (EDFA) is separated from thesingle pass cavity which eliminates the restriction from self-lasing cavitymodes. Secondly, the feeding mechanism is new and effective. As the cavityloss keeping small, the low SBS threshold is preserved. Obviously, theproposed scheme is more effective than reverse-S shaped BFL in generatingmult-orders of BS. |
PDF Full Text Request