All fiber MOPA laser-pumped,continuous-wave,mid-infrared,singly-resonant optical parametric oscillator based on periodically poled MgO-Doped LiNbO<Subscript>3</Subscript>

We report a continuous-wave (CW) mid-infrared singly resonant optical parametric oscillator (SRO) based on periodically poled MgO-doped LiNbO₃ (PPMgLN) pumped by a high power, single frequency fiber laser in master oscillator-power amplifier (MOPA) configuration at 1.064 μm. Using four-mirror ring OPO cavities, at the PPMgLN’s grating period of 30.5 μm and the temperature of 23°C, we achieved the maximum idler output power of 7.2 W at 3.4 μm when the pump power was 52.8 W. The total power-conversion efficiency from the pump to the idler in this experiment is about 13.6%, and corresponds to ∼44% of quantum-limited performance.     

Self-grown fiber fabrication by two-photon photopolymerization

We demonstrate a new fiber growth mechanism in a photocurable resin by ultrafast laser illumination. A high-repetition rate (∼1 MHz) ultrafast laser beam at the wavelength of ∼523 nm was focused into an ultraviolet photocurable resin to trigger two-photon photopolymerization process. Time-resolved shadowgraphs and scattered light imaging revealed that the curing commenced in the neighborhood of the geometric focal point of the laser beam and that the fiber growth progressed mostly towards the laser source. The cured fiber was thinner and longer than the profile of the focused laser beam, facilitated by nonlinear propagation and absorption of the ultra-fast laser beam. The achieved aspect ratio of the fiber was higher than 180 with ∼10 μm mean diameter, and the average growth rate was up to ∼2 mm/s.     

Sub-nanosecond single-frequency 10-kHz diode-pumped MOPA laser

A single-axial-mode, passively Q-switched (PQS) diode-pumped Nd:YAG laser, generating a diffraction-limited beam train of ≈40–60 μJ, ∼500-ps pulses with adjustable repetition rate in the range 1–10 kHz, was efficiently amplified by a single side-pumped Nd:YVO₄ bounce amplifier. After double-pass amplification, ≈1-MW pulse peak power with 577-ps duration and 545-μJ energy was achieved, still maintaining diffraction-limited beam performance. The average output power was 5.45 W at 10 kHz, corresponding to 13% extraction efficiency. The high brightness of this laser system seems ideal for nonlinear optics and some particular laser processing applications.     

126-W all-fiberized single-mode laser from an 11-μm small-core fiber

We demonstrate a 126-W all-fiberized single-mode laser from an 11-μm small-core fiber. The active fiber is a strictly single-mode fiber that produces pure single-mode. The optical to optical efficiency of the fiber laser is 68.2% with ASE suppressed by a factor of ∼35 dB and no power-roll. The output power is only limited by the available pump source, scaling the pump power may achieve much higher output power using the 11 μm small-core fiber.     

A novel-configuration multi-wavelength Brillouin erbium fiber laser and its application in switchable high-frequency microwave generation

A novel configuration of compound-cavity multi-wavelength Brillouin erbium fiber laser is proposed and experimentally demonstrated. With an incident optical carrier power of 8 dBm, at least 14 lasing lines are obtained with a wavelength spacing of ∼0.08 nm. Stability and power uniformity of the multi-wave-length lasing are ensured by the flat hybrid gain of Brillouin and erbium, the compound-cavity structure, and the four-wave mixing suppression using a long (10 km) single-mode fiber. A stable and frequency-switchable microwave can be achieved by incorporating a fiber Bragg grating filter to select the desired nth-order Stokes wave and beating it with the optical carrier at a photodetector. In our experiment, the 1st-4th-order Stokes waves are filtered respectively and hence a high-quality microwave with a switchable frequency from ∼10 to ∼40 GHz and a tuning step of ∼10 GHz is achieved. The signal-to-noise ratio is measured to be >25 dB.     

High average power ultra-fast fiber chirped pulse amplification system

We report on a high-gain diode-pumped ytterbium-doped fiber-amplifier system delivering pulse energies in the 100-μJ range at high repetition rates (32 kHz) with nearly-diffraction-limited beam quality (M²∼1.7) at a 1060-nm center wavelength. Femtosecond seed-laser pulses are stretched in a commercially available single-mode fiber and compressed after amplification to subpicosecond pulse duration. In a multimode Yb-doped fiber amplifier we have demonstrated average powers of up to 22 W and single-pulse energies of up to 130 μJ. Received: 16 August 2000 / Revised version: 4 September 2000 / Published online: 8 November 2000     

Single mode MOPA structured all-fiber Yb pulse fiber amplifier at low repetition

We describe a mopa structured all-fiber 15 μm fiber amplifier cascade. A single-mode diode laser generating 1064 nm wavelength, several nanosecond pulses at 100 Hz repetition was adopted to seed a corepumping amplifier featuring a 6 μm core Yb-doped fiber. Multi-stage pulse-pumping technology was applied to eliminate ASE as much as possible and ease the heat load of the system that leads to the freedom of temperature control of the laser diode. The master oscillator-power amplifier (MOPA) generated 1064 nm, 18 ns pulse-width, 100 Hz repetition of 220 μJ single pulse energy, peak power >12 kW with single transverse output. The pulse energy of 220 μJ is the largest to date in the all-fiber MOPA amplifier with core diameter around 15 μm to our knowledge.     

Tunable Ytterbium-Doped Fiber Laser Based on a Mechanically Induced Long Period Holey Fiber Grating

We describe a tunable double-clad Yb-doped fiber laser based on a long period fiber grating mechanically induced in a section of single mode holey fiber inserted into the laser cavity. The mechanically induced long period holey fiber grating acts as a wavelength-selective fiber filter whose central wavelength, linewidth, and strength can be tuned by changing the period, the length of the grating, and the applied pressure. The fiber laser gives a ∼12.6 nm tuning range, from ∼1079:4–1092nm, with slope efficiencies of 18.7–26.3% at this wavelength range, with respect to the launched pump power.     

High gain double-pass L-band EDFA with dispersion compensation as feedback loop

We demonstrate an efficient double-pass L-band erbium-doped fiber amplifier (EDFA) incorporating chirped fiber Bragg grating (CFBG). The amplifier structure exploits the characteristics of CFBG to reflect the amplified signal back into the gain medium, filter out the recycled forward amplified spontaneous emission and block the residual 1480 nm pump power. The amplifier configuration has high gain and low noise figures as compared to double-pass EDFA using broadband mirror. The demonstrated amplifier has gain of more than 48 dB and low noise figure of less than 4 dB at low input signal power of −40 dBm.     

Tm:fiber laser in-band pumped Ho:LuAG laser with over 18 W output at 2124.5 nm

We describe efficient operation of a Ho:LuAG laser in-band pumped by a cladding-pumped narrow linewidth Tm fiber laser at ∼1907 nm. With 1.0 at % Ho³⁺-doped LuAG and an output coupler of 6% transmission, the laser had a threshold pump power of ∼0.85 W and generated 18.04 W of continuous-wave output power at 2124.5 nm for 35 W of incident pump power, corresponding to an average slope efficiency with respect to incident pump power of 53.4%.     

百瓦级全光纤结构单频掺铥主振荡功率放大器

报道了平均功率超过百瓦的单频掺铥全光纤结构主振荡功率放大器。使用线宽小于100kHz、中心波长为1.97μm的单频种子源进行级联放大,主放大器的斜率效率为50%。监测放大器的回光功率和光谱,没有发现受激布里渊散射以及其他非线性效应。通过增加泵浦功率,可以获得更高功率的掺铥单频放大输出。     

Nonlinear optical and optical limiting studies of alkoxy phthalocyanines in solutions studied at 532 nm with nanosecond pulse excitation

We report our results on the nonlinear optical and optical limiting properties of two alkoxy phthalocyanines namely 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine and 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine zinc(II) studied at a wavelength of 532 nm using 6 ns pulses. Using the standard Z-scan technique we observed that both the phthalocyanines exhibited negative nonlinearity as revealed by the signature of closed aperture data. The magnitude of the nonlinear refractive index n₂ evaluated from the closed aperture data was ∼ 1.61×10^-11 cm²/W for the free-base phthalocyanine and ∼ 1.56×10^-11 cm²/W for the metallic phthalocyanine. Open aperture Z-scan data indicates strong nonlinear absorption in both the phthalocyanines with measured nonlinear coefficients of ∼ 1650 cm/GW and ∼ 1850 cm/GW respectively. We also report optical limiting properties of these phthalocyanines with limiting thresholds (I_1/2) of ∼ 0.5 J/cm². Our studies suggest that these phthalocyanines are one of the best molecules for nonlinear optical applications studied recently. PACS 42.65.-k; 42.70.Jk, 42.65.Jx     

SOA nonlinearities in 4 × 25 Gb/s WDM pre-amplified system for 100-Gb/s Ethernet

A simulation analysis of the impact that the nonlinear response of a semiconductor optical amplifier (SOA) has in a four-channel WDM pre-amplified transmission system is presented in the framework of the recently proposed extended-reach (40-km, 4 × 25 Gb/s) 100 Gb Ethernet link. Channel spacing values ranging from 200 to 800 GHz, and fiber losses between 0 and −20 dB are considered. A maximum power penalty of 4.5 dB is predicted for short fiber lengths and for the tightest channel plan. For short fiber lengths, the penalty drops by about 0.8 dB when moving from 400 to 800 GHz; whereas for long fiber lengths, the penalty increases by 0.2 dB, provided that an average dispersive fiber is utilized. The widely spaced channel plan then represents the best choice in terms of the analyzed physical effects to implement the next-generation 100 GbE link. Further, our numerical investigation includes a discrimination analysis that confirms cross-gain modulation as the main overall SOA nonlinear impairment in the analyzed architecture, and establishes ultra-fast carrier heating-induced FWM as responsible for the system performance difference observed as a function of channel spacing. The difference practically vanishes for fiber lengths above 30 km. Finally, the proposal of an equation that fits the simulated power spectrum density of the first-order four-wave mixing-generated product as a function of channel spacing is presented as an aid to validate our numerical results.     

Stimulated brillouin scattering of electromagnetic ion cyclotron waves in a plasma

Using the fluid model for the nonlinear response of ions, we have studied the nonlinear scattering of an electromagnetic ion cyclotron wave off the ion acoustic wave in a plasma. The low frequency nonlinearity arises through the parallel ponderomotive force on ions and the high frequency nonlinearity arises through the nonlinear current density of ions. For a typical nonisothermal plasma (T _e/T _i∼10) the threshold for this instability in a uniform plasma is ∼1mW/cm². At power densities ≳10² W/cm², the growth rate for backscatter turns out to be ∼10⁴s⁻¹.     

Generation of ultraviolet broadband light in a single-mode fiber

Ultraviolet broadband light spanning 337–405 nm was produced in a single-mode optical fiber primarily by stimulated Raman scattering. Pulses of 4 ns duration at 337 nm were coupled into a 50 m long ultraviolet-grade fiber featuring single-mode operation in the 320–450 nm range. Significant spectral broadening was achieved with pulses of only ∼10 W peak power. Our experiments demonstrate the potential for a source with ∼10⁴ times the spectral radiance of a quartz tungsten halogen lamp, which is currently used for many applications in this wavelength range. PACS 42.65.Ky; 42.81.Wg     

Telecom-grade fiber laser-based difference-frequency generation and ppb-level detection of benzene vapor in air around 3 μm

We report on the development of a field deployable compact laser instrument tunable over ∼232 cm⁻¹ from 3.16 to 3.41 μm (2932.5–3164.5 cm⁻¹) for chemical species monitoring at the ppb-level. The laser instrument is based on widely tunable continuous-wave difference-frequency generation (DFG), pumped by two telecom-grade fiber lasers. DFG power of ∼0.3 mW near 3.3 μm with a spectral purity of ∼3.3 MHz was achieved by using moderate pumping powers: 408 mW at 1062 nm and 636 mW at 1570 nm. Spectroscopic performance of the developed DFG-based instrument was evaluated with direct absorption spectra of ethylene at 3.23 μm (∼3094.31 cm⁻¹). Absorption spectra of vapor-phase benzene near 3.28 μm (∼3043.82 cm⁻¹) were recorded with Doppler-limited resolution. Line intensities of the most intense absorption lines of the ν ₁₂ band near 3043.8 cm⁻¹ were determined to support development of sensitive mid-infrared trace gas detection of benzene vapor in the atmosphere. Detection of benzene vapor in air at different concentration levels has been performed for the first time using multi-pass cell enhanced direct absorption spectroscopy at ∼3.28 μm with a minimum detectable concentration of 50 ppb (1σ).     

Kilowatt-peak-power, single-frequency, pulsed fiber laser near 2 μm

We generated single-frequency pulses at kilowatt peak power from an all-fiber Tm-doped master oscillator power amplifier system, which is the first report of this kind (to the best of our knowledge) of a laser in the 2 μm region. Compared with the laser linewidth of seed pulses, spectral broadening by a factor of 3 was observed with the amplified pulses. This was attributed to self-phase modulation in passive pigtail fibers of the components (isolator and wavelength division multiplexing) that were placed after the fiber amplifier. The short pulse width (~7 ns) of the kilowatt-level pulses prevents an onset of stimulated Brillouin scattering in the long fiber. When launching the pulses into several-meter single-mode fiber, significant nonlinear spectral broadening occurs due to modulation instability in the fiber. This reaction is beneficial for generation of a mid- and long-wavelength IR supercontinuum in nonlinear IR fibers.     

High power Yb-fiber laser amplifier based on nonlinear chirped-pulse amplification at a repetition rate of 1 MHz

We report a high power fiber amplifier based on nonlinear chirped-pulse amplification(NCPA). To manage the nonlinearity,pulse shaping is introduced by self-phase modulation in the fiber stretcher with the help of spectral filtering. The third-order dispersion is compensated for by the nonlinear phase shift in the NCPA. With optimization, the system can output 382 fs pulse duration with 20 W average power at 1 MHz repetition rate. The long-term average power fluctuation is measured to be0.5% in 24 h, and the beam quality factor(M~2) is 1.25.     

NUMERICAL STUDY OF A RATIONAL HARMONICAL MODE-LOCKED SEMICONDUCTOR OPTICAL AMPLIFIER FIBER RING LASER

Based on the self-reproduction theory, a rational harmonic mode-locked semiconductor optical amplifier fiber ring laser was numerically investigated. The system parameters effects on pulse-amplitude equalization of rational harmonic mode locking was analyzed and the numerical result shows that the 2∼5 order rational harmonic mode-locked pulse with the small amplitude ripple can be obtained only by adjusting the system parameters.     

Optimally gain-flattened and dispersion-managed C + L-band hybrid amplifier using a single-wavelength pump laser

We propose a hybrid C-band erbium-doped fiber amplifier (EDFA) and L-band Raman fiber amplifier (RFA) using a single pump laser diode. The optimum pump sharing ratio to EDFA/RFA is 1/10 with a total pump power of 660 mW. Using multiple fiber Bragg gratings (FBGs) with various reflectivities at different positions along the dispersion compensation fiber, the optimum dispersion compensation and power equalization for C + L-band channels are simultaneously realized. With an input power of −20 dBm/ch, the signal power variation among the channels is reduced from 9.8 dB to less than ±0.5 dB. Two pump reflectors are introduced to increase the pumping efficiency.