Fabrication and characterization of dye mixture doped polymer optical fiber as a broad wavelength optical amplifier

Rhodamine 6G and Rhodamine B dye mixture doped polymer optical fiber amplifier (POFA), which can operate in a broad wavelength region (60 nm), has been successfully fabricated and tested. Tunable operation of the amplifier over a broad wavelength region is achieved by mixing different ratios of the dyes. The dye doped POFA is pumped axially using 532 nm, 10 ns laser pulses from a frequency doubled Q-switched Nd: YAG laser and the signals are taken from an optical parametric oscillator. A maximum gain of 22.3 dB at 617 nm wavelength has been obtained for a 7 cm long dye mixture doped POFA. The effects of pump energy and length of the fiber on the performance of the fiber amplifier are also studied. There exists an optimum length for which the amplifier gain is at a maximum value.     

短腔的高浓度掺铒光纤激光器

本文提出采用高浓度掺铒光纤的短腔环形光纤激光器,研制出铋铝共掺和铋镓铝共掺两种石英基高浓度掺铒光纤,这两种掺铒光纤的吸收系数在1530 nm处分别达到了66.3dB/m和59.5dB/m.利用这两种石英基高浓度掺铒光纤,采用环形结构制作出了短腔的光纤激光器,光纤激光器中铒光纤长度分别仅为30 cm和90 cm.对采用这两种高浓度掺铒光纤制作的光纤激光器的输出特性进行了测试和分析.实验结果表明,采用铋镓铝共掺的掺铒光纤制作的光纤激光器具有更高的输出功率和斜率效率,在980 nm泵浦源输出功率330 mW时可以实现15 dBm的激光输出,激光器的斜率效率达到了22%.     

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.     

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 single longitudinal mode S-band fiber laser using a 3 m length of erbium-doped fiber

In this paper a tunable single-longitudinal mode (SLM), short-wavelength band (S-band) fiber laser using a conventional erbium-doped fiber (EDF) with a length of 3?m and a step index erbium dopant profile as opposed to the commonly used depressed cladding erbium-doped fiber (DC-EDF) is proposed and demonstrated. The proposed SLM fiber laser has a tuning range of 1496 to 1507?nm in a ring configuration using two 0.15?m of EDF which acts as saturable absorbers (SAs). The highest peak power measured is about ?0.6?dBm at a wavelength range of 1502 to 1507?nm. The measured signal-to-noise ratio (SNR) is approximately 74?dB for the same wavelength range. The line-width of the SLM output is measured to be 140?kHz.     

SOA-based multi-wavelength source

A simple fiber laser configuration based on a semiconductor optical amplifier (SOA) is proposed for obtaining multi-wavelength oscillation at room temperature, in which a Sagnac loop mirror is used as the wavelength selective component. The SOA has a flat gain of approximately 23dB within a bandwidth of 12 nm at a small input signal power. The loop mirror was constructed using a 3dB coupler and polarization maintaining fiber (PMF). The output spectrum of the proposed laser can be adjusted by controlling the bias current of the SOA and is quite stable at room temperature. At a bias current of 150 mA, six lines are obtained with at least ?40 dBm output power and 25dB signal-to-noise ratio (SNR). The channel spacing and number of lines is determined by the length of polarization maintaining fiber (PMF) used in the loop mirror. The channel spacing of the proposed laser is 1.49 nm with a PMF 3 m. The multi-wavelength comb output can also be tuned by adjusting the operating temperature of the SOA. The multi-wavelength laser has the advantage of a simple configuration, stability at room temperature, a broad wavelength band, and no need for optical pump lasers.     

A novel optical device with wide-bandwidth wavelength conversionand an optical sampling experiment at 200 Gbit/s

This paper reports the characteristics of our proposed prototype optical parametric diffuser (OPD). An OPD is based on the theory of four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). However, to improve the conversion bandwidth and FWM efficiency, the gain bandwidth is spread and the gain peak wavelengths are set to a wavelength near the FWM light on the short-wavelength side by combining different MQW active layers. We measured the optical gain characteristics; the fiber-to fiber gain was 16.1 dB and the gain bandwidth over 8 dB was 117 nm when driven at 200 mA dc, and 190 nm when driven by an 800 mA pulse current. In a wavelength-conversion experiment, a high conversion efficiency of ⩾-20 dB was obtained across a detuning wavelength bandwidth of 43 nm. A clear waveform was obtained in an optical sampling experiment to measure 200 Gbit/s optical data sequences     

Fiber Bragg grating flow sensors powered by in-fiber light

This paper presents an active fiber Bragg grating temperature and flow sensor based on self-heated optical hot wire anemometry. The grating sensors are directly powered by optical energy carried by optical fibers. In-fiber diode laser light at 910 nm was leaked out from the fiber and absorbed by the surrounding metallic coating to raise the temperature and change the background refractive index distribution of the gratings. When the diode laser is turned off, the grating is used as a temperature sensor. When the diode laser is turned on, the resonance wavelength and spectral width change of the self-heated grating sensor is used to measure the gas flow velocity. The grating flow sensors have been experimentally evaluated for different grating length and input laser power. The grating flow sensors have demonstrated a 0.35- m/s sensitivity for nitrogen flow at atmosphere pressure.     

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.     

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.     

Sensitive absorption spectroscopy by use of an asymmetric multiple-quantum-well diode laser in an external cavity

We have developed a broadly tunable diode laser system by employing custom-designed asymmetric multiple-quantum-well (AMQW) InGaAsP lasers in an external cavity configuration. Feedback is provided by a diffractive optical element with high coupling efficiency and wavelength selectivity, allowing for single-mode tuning of the output wavelength by varying the external cavity length. This tunable laser system was used experimentally to perform absorption spectroscopy on weak CO(2) lines over a broad wavelength region in the near infrared. An experimental tuning range of 80 nm has been observed for a laser cavity length of 600 mum, which is double the tuning range found with conventional, uncoated quantum-well lasers. We achieved a detection sensitivity of 5 x 10(-6) at 95% confidence over the wavelength range of 1.54-1.62 mum by employing a second-harmonic detection technique. The theoretical predictions of a broad gain profile from an ambipolar rate equation model are found to correspond to the experimentally observed increased tunability of the uncoated AMQW lasers.     

Application of macro-bending for flat and broad gain EDFA

Gain flattened C-band erbium-doped fiber amplifier (EDFA) is demonstrated using a macro-bending method. Various bending diameter and length of high concentration aluminosilicate EDFA are theoretically and experimentally analyzed. By varying the bending radius and the length of the doped fiber, the gain saturation effect as well as the energy transfer from shorter wavelength to a longer wavelength can be controlled to obtain a flattened and broadened gain profile in the C-band region. The amplifier uses a 9 m long erbium-doped fiber (EDF) with erbium ion density of 1.6 × 10²⁵ ions m^?3 and bending radius of 6.5 mm as a gain medium. The gain variation of the EDFA is obtained within ±1 dB over 25 nm bandwidth of C-band region.     

Tunable Tm-doped fiber ring laser operating at 1.9 μm band using force-induced fiber grating as wavelength tuner

We report wavelength-tunable operation of a Tm-doped silica fiber laser by using a force-induced long-period fiber grating (LPFG) formed in a fiber ring resonator. The laser output wavelength is tuned by moving the transmission passband that is generated between adjacent resonance wavelengths due to the force-induced LPFG. By changing the grating period around 900 μm, we control the laser output wavelength between 1845 and 1930 nm.     

L波段掺铒光纤超荧光光源和放大器研究

通过优化铒光纤长度,获得了平坦谱宽达30nm(0.7dB)的L波段超荧光光源,该光源具有7.21dBm的输出功率。在此基础上,研究L波段放大器增益特性,通过对铒光纤长度的进一步优化,用1480nm激光器作前向泵浦源,实验上获得了波长从1565nm~1595nm范围平坦的增益带宽,小信号增益可达22dB。     

High-power widely tunable thulium fiber lasers

Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides >150 W of average power, >50% slope efficiency, narrow output linewidth, and >100 nm tunability in the wavelength range around 2 μm.     

用差频腔产生覆盖633nm光谱的飞秒激光频率梳

飞秒激光频率梳被认为是连接光频和无线电频率的一个超精密齿轮,比较了自参考法锁相稳频飞秒激光频率梳和差频法单块结构飞秒激光频率梳的特点,前者光谱范围宽,但稳定性较差;后者稳定性较好,但光谱范围较窄。在差频腔单块结构飞秒激光频率梳的基础上,通过使用腔外压缩色散补偿方式压缩激光脉冲宽度,然后重新注入光子晶体光纤进行光谱扩展,获得了覆盖633nm波长的更宽的光谱范围,为633nm波长激光频率测量创造了条件。     

Switchable dual-wavelength single-longitudinal-mode erbium-doped fiber laser using an inverse-Gaussian apodized fiber Bragg grating filter and a low-gain semiconductor optical amplifier

We present a stable and switchable dual-wavelength erbium-doped fiber laser. In the ring cavity, an inverse-Gaussian apodized fiber Bragg grating serves as an ultranarrow dual-wavelength passband filter, a semiconductor optical amplifier biased in the low-gain regime reduces the gain competition of the two wavelengths, and a feedback fiber loop acts as a mode filter to guarantee a stable single-longitudinal-mode operation. Two lasing lines with a wavelength separation of approximately 0.1 nm are obtained experimentally. A microwave signal at 12.51 GHz is demonstrated by beating the dual wavelengths at a photodetector.     

Effective supercontinuum generation by using highly nonlinear dispersion-shifted fiber incorporated with Si nanocrystals

The dispersion-shifted fiber (DSF) incorporated with Si nanocrystals (Si-NCs) having highly nonlinear optical property was fabricated to investigate the effective supercontinuum generation characteristics by using the MCVD process and the drawing process. Optical nonlinearity was enhanced by incorporating Si nanocrystals in the core of the fiber and the refractive index profile of a dispersion-shifted fiber was employed to match its zero-dispersion wavelength to that of the commercially available pumping source for generating effective supercontinuum. The non-resonant nonlinear refractive index, n2, of the Si-NCs doped DSF measured by the cw-SPM method was measured to be 7.03 x 10(-20) [m2/W] and the coefficient of non-resonant nonlinearity, gamma, was 7.14 [W(-1) km(-1)]. To examine supercontinuum generation of the Si-NCs doped DSF, the femtosecond fiber laser with the pulse width of 150 fs (at 1560 nm) was launched into the fiber core. The output spectrum of the Si-NCs doped DSF was found to broaden from 1300 nm to wavelength well beyond 1700 nm, which can be attributed to the enhanced optical nonlinearity by Si-NCs embedded in the fiber core. The short wavelength of the supercontinuum spectrum in the Si-NCs doped DSF showed shift from 1352 nm to 1220 nm for the fiber length of 2.5 m and 200 m, respectively.     

Development of a fiber-optic laser delivery system capable of delivering 213 and 266 nm pulsed Nd:YAG laser radiation for tissue ablation in a fluid environment

Ultraviolet (UV) lasers have the capability to precisely remove tissue via ablation; however, due to strong absorption of the applicable portion the UV spectrum, their surgical use is currently limited to extraocular applications at the air/tissue boundary. Here we report the development and characterization of a fiber-optic laser delivery system capable of outputting high-fluence UV laser pulses to internal tissue surfaces. The system has been developed with a view to intraocular surgical applications and has been demonstrated to ablate ocular tissue at the fluid/tissue boundary. The fifth (213?nm) and fourth(266?nm) harmonics of a Nd:YAG laser were launched into optical fibers using a hollow glass taper to concentrate the beam. Standard and modified silica/silica optical fibers were used, all commercially available. The available energy and fluence as a function of optical fiber length was evaluated and maximized. The maximum fluence available to ablate tissue was affected by the wavelength dependence of the fiber transmission; this maximum fluence was greater for 266?nm pulses (8.4?J/cm2) than for 213?nm pulses (1.4?J/cm2). The type of silica/silica optical fiber used did not affect the transmission efficiency of 266?nm pulses, but transmission of 213?nm pulses was significantly greater through modified silica/silica optical fiber. The optical fiber transmission efficiency of 213?nm pulses decreased as a function of number of pulses transmitted, whereas the transmission efficiency of 266?nm radiation was unchanged. Single pulses have been used to ablate fresh porcine ocular tissue. In summary, we report a method for delivering the fifth (213?nm) and fourth (266?nm) harmonics of a Nd:YAG laser to the surface of immersed tissue, the reliability and stability of the system has been characterized, and proof of concept via tissue ablation of porcine ocular tissue demonstrates the potential for the intraocular surgical application of this technique.     

单模硫系玻璃光纤的制备及其超连续谱的产生特性

硫系玻璃具有独特的红外光学性能和极高的光学非线性等特点, 使得硫系光纤成为中红外超连续谱产生的优选材料。基于二次挤压法制备了单模As-S光纤, 并利用飞秒脉冲和光参量放大器作为泵浦源研究了该光纤的中红外超连续谱的产生特性, 包括光纤长度、泵浦波长、泵浦功率对超连续谱产生的影响。结果表明该单模光纤具有较低的传输损耗和较小的材料色散分布; 相比于传统零色散点波长附近泵浦, 在正常色散区且杂质吸收峰附近泵浦也可获得脉冲的极大展宽(泵浦参数: 4.5 μm, 1 kHz, 150 fs, 光纤长度23 cm, 输出谱宽为1.5~8.7 μm@60 dB带宽); 较短长度的硫系光纤便可产生超宽频谱输出, 相反, 光纤长度越长输出频谱越窄且平坦性变差。