Characterization of a multiwavelength Brillouin-erbium fiber laser based on a linear cavity configuration

We experimentally demonstrate a simple method for generating a multiwavelength Brillouin comb by utilizing a linear cavity of hybrid Brillouin-erbium fiber lasers (BEFLs). The optimization of Brillouin pump wavelength, power, and erbium gain played a significant role in determining the maximum number of Brillouin Stokes signals generated. Simultaneous and stable multiple-wavelength laser output of 22 lines with 10.88-GHz channel spacing has been obtained with good flatness. Various parameters such as 980-nm pump power, Brillouin pump wavelength, and Brillouin pump power that affect the performance of a multiwavelength BEFL system have been investigated. An analysis of the tuning range of the system is presented.     

Double spacing multi-wavelength L-band Brillouin erbium fiber laser with Raman pump

A new multi-wavelength Brillouin erbium fiber laser (BEFL), which operates in the L-band region with double frequency Brillouin spacing, is demonstrated. This design uses a Raman pump (RP) and a piece of 2?km highly nonlinear fiber as a gain medium. The double frequency spacing is achieved by employing a dual ring configuration, which is formed by utilizing a four-port circulator that removes the odd-order Stoke signals. Twenty Stokes and seventeen anti-Stokes lines, which have optical signal to noise ratio (OSNR) greater than 15?dB, are generated simultaneously with a spacing of 0.16?nm when Brillouin pump and RP powers were fixed at the optimum values of 8 dBm and 40?mW, respectively. The BEFL can be tuned in the range between 1591?nm to 1618?nm. The proposed configuration increases the number of lines generated and the OSNR, and thus allows a compact multi-wavelength laser source to be realized.     

Bismuth-based Brillouin/erbium fiber laser

A multi-wavelength Brillouin/erbium-doped fiber laser (BEFL) operating in the 1573 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a bismuth-based erbium-doped fiber (Bi-EDF) approximately 215 cm long and a single mode fiber (SMF) of various lengths to generate an optical comb with a spacing of approximately 0.089 nm. Two 3 dB couplers were used to form a looping arm in the system in order to produce cascaded Brillouin Stokes waves as internal feedback for multi-wavelength operation. A stable output laser comb with 10 lines at more than ??13 dBm was obtained with 4.85 dBm Brillouin pump power and two 140 mW pumps at 1480 nm. The 1480 nm pumps' power and SMF length have a significant effect on the number of wavelengths and on the output power of the generated wavelength comb.     

Dual wavelength erbium-doped fiber laser using a tapered fiber

A tapered fiber is fabricated by heating and stretching a piece of optical fiber after the polymer protective cladding has been removed. An equidistant comb-like transmission spectrum, with a spacing of 1.6?nm and an extinction ratio of more than 5?dB, was obtained by the tapered fiber due to the multibeam interferences of the cladding modes. The tapered fiber was applied in a ring erbium-doped fiber laser (EDFL) to generate dual-wavelength lasing oscillations. The EDFL operates at wavelengths of 1557.0?nm and 1558.6?nm with a stable peak power and a signal-to-noise ratio of more than 40?dB.     

光纤饱和吸收体稳频窄线宽光纤激光器

结合光纤饱和吸收体与光纤光栅法布里-珀罗标准具,研制出了全光纤结构1550nm单频窄线宽掺铒光纤环形激光器.采用两个976nm激光二极管双向抽运作为抽运源,高掺杂浓度铒光纤作为增益介质,以行波腔消除空间烧孔效应,利用光纤光栅法布里-珀罗标准具窄带选模特性,以10m长低掺铒光纤饱和吸收体稳频,得到了十分稳定的窄线宽激光输出.激光器抽运阈值功率21mW,在抽运光功率为145mW时输出光功率39mW,斜率效率30%,信噪比大于50dB.采用延迟自外差方法精确测量光纤激光器线宽小于10kHz.     

Tunable S-band output based on Raman shift in dispersion shifted fiber

A tunable short-wavelength band Raman fiber laser using a dispersion shifted fiber as the nonlinear medium is proposed and demonstrated. This approach provides an alternative to the common method of using depressed-cladding, erbium-doped fibers as the gain medium in S-band fiber lasers. The proposed laser has a tuning range of 1508 to 1534?nm as well as an average peak power of about ?11.3?dBm within the range 1518–1530?nm. A high signal-to-noise ratio of approximately 70 dB is obtained from the system at this range.     

Uniform amplitude multi-wavelength single-longitudinal-mode Brillouin–erbium fiber lasers

A multi-wavelength single-longitudinal-mode (SLM) Brillouin–erbium fiber laser has been proposed and demonstrated by using the broadband linear gain and the narrow band gain of stimulated Brillouin scattering both in Er-doped fiber. Eight orders of lased Stokes have been observed with relatively uniform amplitudes and rigid spacing of 11?GHz. Each Stokes frequency works on SLM operation owing to very short oscillating cavity. The output signal-to-noise ratio is as high as 50?dB. The hybrid gain of two mechanisms in Er-doped fiber is helpful to improve the flatness of the multi-wavelength combs.     

非对称光纤反射镜的可调谐光纤激光器

提出一种非对称窄带光纤环形反射镜结构的可调谐掺铒光纤激光器。980nm泵浦光对掺铒有源光纤进行抽运,高双折射光纤、偏振控制器（PC）和光纤耦合器构成窄带光纤反射镜,窄带光纤反射镜和普通光纤反射镜组成激光谐振腔,利用窄带光纤反射镜工作带宽纳米量级的特性得到单纵模激光。调整偏振控制器改变反射镜对不同波长的反射率,实现可变波长的激光输出。实验表明,该激光器的工作带宽为8nm,120mW泵浦光条件下最大输出功率为4mW,3dB带宽（脉冲的半高宽度）小于0．2nm,边模抑制比为20dB以上,在1527nm～1535nm的波长范围内观察到稳定激光输出。     

Investigation of the effects of SOA locations in the linear cavity of an O-band Brillouin SOA fiber laser

An investigation into the effect of semiconductor optical amplifier (SOA) location in an O-band Brillouin SOA fiber laser (BSFL) was performed. Better output peak power flatness was generated by placing the SOA after the nonlinear medium, which is a 20?km true wave fiber (TWF) than placing it before the TWF. A maximum power of six flat output peaks with average power of ?22.0?dBm for a BP (Brillouin pump) wavelength of 1320?nm was obtained, generated from a BSFL with a SOA located after the TWF, compared with three flat Stokes signals with the SOA before the TWF at a BP wavelength of 1310?nm. The flat peak power output for the O-band Brillouin fiber laser is important, especially in producing a good O-band source.     

Technique for continuous tuning of optical fiber lasers

For the first time to the authors' knowledge, we have demonstrated how thermally controlled overcoupled fused fiber couplers and fiber loop mirrors based on these couplers can be used as broadband tuning elements in a fiber laser cavity. No bulk optical elements play any role in this technique. Temperature tuning the coupler results in a shift in the coupling ratio or in the effective output coupler transmission. For a fixed pump source, and for a given laser cavity, this shift causes the lasing wavelength to shift. We have continuously tuned an Er silica fiber laser in this manner over the range of 1527-1570 nm in a ring configuration, and, using a fiber loop mirror with these couplers in a linear Tm silica fiber laser cavity, we have achieved more than 50-nm broadband tuning over the range of 1850-1910 nm. The tuning range and the sensitivity to temperature depend on the degree of overcoupling of the loop mirror coupler.     

All fiber on-axis coupling scheme between single mode fiber and GRIN fiber

In this paper we present a simple and novel method to maximize on-axis coupling efficiency to radially symmetric fibers without the need for extra free space optical elements. The method is based on inserting a segment of step-index multimode fiber (MMF), cleaved to a particular length, between the input fiber and the output fiber (OF). The MMF segment modifies the input field to match the guided modes in the OF. Using this technique we show that, by inserting an appropriate length MMF segment, it is theoretically possible to obtain a coupling coefficient as high as ?0.8 dB between a single mode fiber and a graded index ring-shaped fiber and ?0.32 dB for a multi-shell fiber. Our experimental measurements showed good agreement with theoretical predictions for the ring fiber.     

Study of a fiber optic humidity sensor based on agarose gel

An optical fiber humidity sensor was fabricated using a hydrophilic gel (agarose) deposited on the tapered plastic optical fiber (POF). The sensing element, agarose, can absorb and exude moisture from/to the ambience, thereby altering its refractive index and changing its ability to modulate the intensity of light that propagates through the fiber. Thus, the operating principle of the sensor is based on the intensity modulation technique, which utilizes a tapered POF probe coated with agarose that is sensitive to humidity. The POF, which was fabricated using an etching method, has a waist diameter of 0.45 mm and tapering length of 10 mm. As the relative humidity varies from 50% to 80%, the output voltage of the sensor with agarose gel of 0.5% weight content decreases linearly from 2.24 mV to 1.55 mV. The agarose-based sensor produces a sensitivity of 0.0228 mV/%, with a slope linearity of more than 98.36%. The tapered fiber with agarose gel of 1% weight content produces a sensitivity of 0.0103 mV/% with a slope linearity of more than 94.95% and a limit of detection of 2.635%, while the tapered fiber with agarose gel of 1.5% weight content produces a sensitivity of 0.0079 mV/% with a slope linearity of more than 98.53% and a limit of detection of 6.853%. The fiber with agarose gel of 0.5% weight content shows higher sensitivity compared to that of 1% and 1.5% due to the effect of pore size, which changes with concentration. The results demonstrate that agarose-based optical fiber sensors are both sensitive and efficient for economical and flexible measurements of humidity.     

低损耗双锥光纤的制备与光学特性研究

利用熔拉法制备了双锥光纤,系统地研究了拉制过程中拉制距离、拉制速度、氢气流量等参数与双锥光纤光学传输特性关系,实验表明,拉制距离控制在30mm-32mm,拉制速度在0.15mm/s,氢气流量在140-150之间时,可以得到损耗在0.5dB-0.7dB,锥腰直径介于0.6μm-2.5μm的低损耗双锥光纤。利用自行制备的双锥光纤进行微球腔耦合实验,得到微球腔良好的透射谱线。该范围内的双锥光纤可以高效激发微球腔回廊模式,对微球腔的应用以及双锥光纤在光传感应用方面具有指导意义。     

Linear control of the spectral characteristics of wavelength-selective components with a high-index tapered thin-film planar waveguide and a single-mode half-coupler

A simple system of linearly tunable fiber-film wavelength-dependent components is demonstrated that includes a linearly tapered high-index thin-film planar waveguide (PWG) evanescently coupled by a single-mode-fiber half-coupler. We present experimental and theoretical results for the linear tuning of spectral responses such as coupled power, resonance position (lambda(0)), and fiber output-light polarization through position shifting of the linearly tapered PWG, in the direction of the propagating light in the fiber, over the half-coupler block. We achieved almost linear control of the spectral response by changing the temperature of mixture-of-oils and overlay-doped poly(methyl methacrylate) PWG's when the refractive index of the system decreases with temperature. The variation in thickness of the tapered film is along the direction of the interaction length of the system. Linear tapered PWG's that comprised a mixture of oils, BK7 glass, and overlay-doped PMMA with high refractive indices were fabricated that could operate the device at lower and higher modes. We investigated the dependence of tuning lambda(0) on the PWG mode. Tuning by shifting of a linear tapered PWG over a fiber half-block is mode dependent, whereas tuning by changing the refractive index of a uniform PWG is mode independent. Wavelength shift Dlambda(0) is found to decrease with an increase in the resonant PWG mode number m for linearly tapered PWG's. A fiber-to-asymmetric linear tapered-PWG coupler, which maintains the taper slope to within a specific limit, can function as a linearly tunable polarizer for the light in the fiber.     

Generation of stable and narrow spacing dual-wavelength ytterbium-doped fiber laser using a photonic crystal fiber

Abstract

We demonstrate the design and operation of novel narrow spacing and stable dual-wavelength fiber laser (DWFL). A 70-cm ytterbium-doped fiber has been chosen as the gain medium in a ring cavity arrangement. Our design includes a short length photonic crystal fiber, acting as a dual-wavelength stabilizer based on its birefringence coefficient and nonlinear behavior and tunable band pass filter (TBPF) to achieve narrow spacing spectrum lasing. Our laser output is considered to be highly stable, with power fluctuation less than 0.8 dB over a period of 15 min. The flexibility and tunability of TBPF, together with polarization controller enable the spacing tuning of the DWFL from 0.03 nm up to 0.07 nm for 1040 nm region, and 0.10 nm up to 0.40 nm for 1060 nm region. The tunable wavelength spacing shows the flexibility of the DWFL in addition to stable and reliable properties of fiber laser in 1-μm region.     

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.     

Tailored dispersion profile in controlling optical solitons in a tapered parabolic index fiber

We investigate the soliton dynamics in tapered parabolic index fibers via symbolic computation for a variety of dispersion profiles to inspect how a specific dispersion profile controls the optical soliton. By means of AKNS procedure, Lax pair is constructed for nonlinear Schrödinger equation with variable coefficients. Using obtained Lax pair, multi-soliton solutions are generated via Darboux transformation technique. Using multi-soliton solutions, soliton dynamics in tapered parabolic index fiber with the hyperbolic, Gaussian, exponential, and linear profiles are discussed. Results obtained in this study will be of certain potential application on construction of the nonlinear optical devices by soliton control. Results obtained in this study will be of certain value to the studies on the propagation and application of the soliton in the tapered parabolic index fiber and dispersion-managed fiber system.     

Wideband tunable Q-switched fiber laser using graphene as a saturable absorber

An ultra-wide wavelength tuning range, which covers three different band regions consisting of the S-, C-, and L-bands, is proposed and demonstrated for a graphene-based Q-switched erbium-doped fiber laser using a tunable bandpass filter as the wavelength tuning and filtering mechanism. A 3?m length of erbium-doped fiber is used as the gain medium in a ring laser cavity configuration, with absorption coefficients of between 11 and 13 dB?m^?1 at 980?nm and about 18?dB?m^?1 at 1550?nm. The tuning range of the Q-switching pulses covers a wide wavelength range of 58?nm, which spans from 1512.5?nm to 1570.5?nm. In addition, the lasing and Q-switching thresholds are considerably low, with respective values of ～11.0?mW and ～18.4?mW. A repetition rate of 55.3?kHz is obtained at the maximum pump power of 100.4?mW, together with pulse width and pulse energy of 1.6?μs and 25.8?nJ, respectively.     

Semiconductor optical amplifier-based multi-wavelength ring laser utilizing photonic crystal fiber

A multi-wavelength laser source is demonstrated with a semiconductor optical amplifier (SOA) as a gain medium. A multi-wavelength comb with equal spacing is achieved due to Fabry–Pérot modes of the SOA which oscillates in the ring cavity. A 100 m long photonics crystal fiber (PCF) is inserted in the ring cavity to provide a nonlinear gain by four-wave mixing (FWM) so that the output comb spectrum can be greatly broadened and flattened. The stability of the ring laser is also increased due to the efficient FWM phenomenon occurring in the PCF. The SOA-based laser can generate 35 lasing lines with equal spacing of 0.28 nm and extinction ratios of more than 30 dB at room temperature. The number of channels of the multi-wavelength laser can be controlled flexibly by changing the ratio of the coupler used in the ring cavity configuration as well as controlling the polarization state of the oscillating laser.     

S-band multiwavelength ring Brillouin/Raman fiber laser with 20 GHz channel spacing

We propose and demonstrate a tunable S-band multiwavelength Brillouin/Raman fiber laser (MBRFL) with a tuning range of between 1490 to 1530 nm. The proposed MBRFL is designed around a 7.7 km long dispersion compensating fiber in a simple ring configuration, acting as a nonlinear medium for the generation of multiple wavelengths from stimulated Brillouin scattering (SBS) and also as a nonlinear gain medium for stimulated Raman scattering (SRS) amplification. A laser source with a maximum power of 12 dBm acts as the Brillouin pump (BP), while two 1420 nm laser diodes with a total power of 26 dBm act as the Raman pumps (RPs). The MBRFL can generate a multiwavelength comb consisting of even and odd Stokes at an average power of -12 dBm and -14 dBm respectively, and by separating the even and odd Stokes outputs, a 20 GHz channel spacing is obtained between two consecutive wavelengths. Due to the four-wave mixing (FWM) effect, anti-Stokes lines are also observed. The multiwavelength comb generated is not dependent on the BP, thus providing high stability and repeatability and making it a highly potential source for many real-world applications. This is the first time, to the knowledge of the authors, that a tunable MBRFL has been developed using SRS to obtain gain in the S-band region.