We demonstrated pulse compression at 1 μm based on the use of microstructured optical fibers. Two different approaches have been investigated. On the first hand, we used fibers with negative group velocity dispersion at the laser emission to obtain self-compression based on solitonic effect. On the second hand, we used fibers with zero-dispersion at the laser emission to generate very broad spectra (by self-phase modulation) recompressed afterward using prism-based compressor. We studied experimentally and theoretically these two techniques of compression with a special care regarding their limitations. For the experiments, the compressions have been obtained using a home-made diode-pumped Yb:SYS laser producing 110-fs pulses directly injected in the microstructured optical fibers. We demonstrated compressed pulses as short as 20-fs centered at 1070 nm which is to our best knowledge the shortest pulses obtained with a diode-pumped system in this wavelength range.

A new type of optical pulse shaper for arbitrary waveform generation is demonstrated, based on fiber Bragg grating and micro-electro-mechanical system (MEMS) technologies. This is an on-chip device which is compact, robust, monolithic, and programmable and can be used for a variety of applications such as higher order dispersion compensation in fiber communication links and high-energy pulse amplification.

We report a self-starting stretched-pulse mode-locked all-fiber erbium ring laser with high output pulse energy. In this laser, to increase the output pulse energy a piece of positive-dispersion singlemode fiber with large core diameter is used to lower the nonlinearity in the positive dispersion section of the laser cavity. Pulses with ~0.6 nJ single-pulse energy and less than 100 fs was achieved.

We demonstrate a sub-100 fs frequency doubled fiber laser operating at 810 nm. The laser produces 60 mW of average power at a repetition rate of 50 MHz. Extremely low amplitude noise (below 0.1%) and compact size makes this source ideal replacement for low power ultrafast Ti:Spphire lasers.

We report on the high power fiber based amplification of parabolic pulses. The output is compressed using transmission gratings to 300 fs and an average power of 38 W at 75 MHz repetition rate.

The fiber based generation of nearly transform-limited 10-ps pulses with 200 kW peak power (97 W average power) based on SPM-induced spectral compression is reported. Efficient second harmonic generation applying this source is also discussed.

We are developing an all fiber laser system optimized for providing input pulses for short pulse (1-10ps), high energy (~1kJ) glass laser systems. Fiber lasers are ideal solutions for these systems as they are highly reliable and once constructed they can be operated with ease. Furthermore, they offer an additional benefit of significantly reduced footprint. In most labs containing equivalent bulk laser systems, the system occupies two 4’x8’ tables and would consist of 10's if not a 100 of optics which would need to be individually aligned and maintained. The design requirements for this application are very different those commonly seen in fiber lasers. High energy lasers often have low repetition rates (as low as one pulse every few hours) and thus high average power and efficiency are of little practical value. What is of high value is pulse energy, high signal to noise ratio (expressed as pre-pulse contrast), good beam quality, consistent output parameters and timing. Our system focuses on maximizing these parameters sometimes at the expense of efficient operation or average power. Our prototype system consists of a mode-locked fiber laser, a compressed pulse fiber amplifier, a “pulse cleaner”, a chirped fiber Bragg grating, pulse selectors, a transport fiber system and a large flattened mode fiber amplifier. In our talk we will review the system in detail and present theoretical and experimental studies of critical components. We will also present experimental results from the integrated system.

We report a 120 W, linearly polarized, single-mode Yb-doped fiber laser operating at 10 MHz pulse repetition rate. To produce narrow linewidth and high peak power, a fiber oscillator power amplifier (FOPA) configuration is used. With an Yb-doped large mode area (LMA) fiber, the FOPA has generated up to 2.4 kW peak power and less than 20 pm linewidth without the onset of nonlinear effects at 5 ns pulse duration. 120 W average output power corresponding to a slope efficiency of 71% with respect to the launched power has been generated. The beam quality is 1.1 times diffraction-limited and the polarization extinction ratio is better than 95%. No linewidth broadening beyond the 20 pm instrumental resolution or nonlinear effects are observed at 120 W output power. The diffraction-limited beam quality from the FOPA allows us to use LBO crystals to achieve efficient second harmonic generation (SHG) without “gray tracking” problems. The frequency doubling of 110 W FOPA output has generated 60 W, near-diffraction-limited, linearly polarized green output. With two LBO crystals at noncritical phase-matching, a maximum of 54.5% doubling efficiency has been demonstrated. The overall electrical efficiency to green output is 10%.

We report our recent progress in designing and manufacturing new, completely monolithic, linearly polarized, continuous wave (CW) fiber lasers that provide more than 300W of output power in a near diffraction limited, single transverse mode, spectrally stabilized output beam having a narrow line-width. The demonstrated design is simple and practical: the monolithic laser cavity may consist of only a coil of polarization maintaining (PM), large mode area (LMA) active fiber having a fiber Bragg grating (FBG) at one end and a fiber cleave at the other end. Proper selection of the coil diameter enables gain in only one polarization mode so as to provide the linearly polarized output. Fiber lasers built using this novel technique do not require any external polarizing components or the use of polarizing fiber. Such compact and robust fiber lasers are suitable for a variety of applications, such as multi-kW power scaling through coherent beam combining, nonlinear wavelength conversion processes using a variety of nonlinear materials, etc.

We have doped the core of Ytterbium (Yb) laser fibers additionally with Neodymium (Nd) to exploit wavelength-multiplexed high-power pump systems, which are commercially available. By pumping such a Nd:Yb-codoped fiber with the 808/940/978 nm-diode system, we could demonstrate CW output powers of more than 1 kW with high laser slope efficiency. In order to get a better understanding of this laser medium, we studied the fluorescence and the laser behavior of Nd:Yb fibers with different rare earth concentrations in comparison to a fiber doped solely with Nd. A theoretical model for the calculation of the fluorescence decay curve and spectrum as well as the laser characteristic and wavelength was developed, that takes the energy transfer process from Nd to Yb ions into account. Comparing the experimental and theoretical results, the behavior of the Nd:Yb high power fiber laser is understood as a collective emission of both ion types within the same wavelength region. These investigations contribute to the optimization of high power fiber lasers under the viewpoint of thermal load.

100W linear-polarized single-mode CW emission is demonstrated in an all-fiber format at 1566 nm. The Yb³⁺/Er³⁺ doped fiber laser has an extinction ratio >20 dB and M²<1.1. Using an Yb-Er doped multi-mode fiber, the laser provides > 13% overall electrical efficiency and less than 4 nm linewidth without the onset of Yb ions generation at wavelength range of 1060-1080 nm. There are no saturation effects due to pump or nonlinear phenomena. Parasitic lasing is suppressed with fiber laser cavity design and specialty filters.

Fiber lasers are pumped by fibercoupled, multimode single chip devices at 915nm. That’s what everybody assumes when asked for the type of fiber laser pumps and it was like this for many years. Coming up as an amplifier for telecom applications, the amount of pump power needed was in the range of several watts. Highest pump powers for a limited market entered the ten watts range. This is a range of power that can be covered by highly reliable multimode chips, that have to survive up to 25 years, e.g. in submarine applications. With fiber lasers entering the power range and the application fields of rod and thin disc lasers, the amount of pump power needed raised into the area of several hundred watts. In this area of pump power, usually bar based pumps are used. This is due to the much higher cost pressure of the industrial customers compared to telecom customers. We expect more then 70% of all industrial systems to be pumped by diode laser bars. Predictions that bar based pumps survive for just a thousand hours in cw-operation and fractions of this if pulsed are wrong. Bar based pumps have to perform on full power for 10.000h on Micro channel heat sinks and 20.000h on passive heatsinks in industrial applications, and they do. We will show a variety of data, “real” long time tests and statistics from the JENOPTIK Laserdiode as well as data of thousands of bars in the field, showing that bar based pumps are not just well suitable for industrial applications on high power levels, but even showing benefits compared to chip based pumps. And it’s reasonable, that the same objectives of cost effectiveness, power and lifetime apply as well to thin disc, rod and slab lasers as to fiber lasers. Due to the pumping of fiber lasers, examples will be shown, how to utilize bars for high brightness fiber coupling. In this area, the automation is on its way to reduce the costs on the fibercoupling, similar to what had been done in the single chip business. All these efforts are part of the JENOPTIK Laserdiode’s LongLifeTechnologie.

We discuss a fiber Bragg grating laser sensor in which the measurement of an intermodal beating frequency is used for the Bragg gratings (BG) interrogation. The linear cavity of the laser is formed by one reference BG at one side and one or several sensing BGs at the opposite side of the cavity. For this report we used two sensing BGs. In the laser with one BG at each cavity side the beating frequency is defined by the distance between BGs. If two sensing BGs are used, the beating frequency is defined by both the distances between the reference BG and each of the sensing BGs and by a ratio between sensing BGs reflections at the laser wavelength. So, when the reflection of sensing BGs is shifted by temperature or strain, the beating frequency is changed. We discuss the experimental results obtained for the laser sensor with the total cavity length equal to 4277 m; the distance between the sensing BGs was 47 m. A RF spectrum analyzer with 100-kHz bandwidth was used that allows the measurement of three first harmonics. We found that the beating frequency can be moved from the value corresponding to the 4277-m cavity to the value corresponding to the 4230-m cavity by shifting the maximum reflection of the sensing BGs. The narrowest spectrum equal to 52 Hz was obtained when the tuned delay was incorporated into the cavity. A shift of the maximum BG reflection less then 0.05 nm was detected.

We have developed pulsed fiber laser with computer controlled pulse duration and multi-kilowatt output peak power in a diffraction-limited beam. The diode laser as a master oscillator and Yb-based fiber amplifiers were used in a MOPFA configuration. The output pulse duration can be arbitrary selected in the range from 4ns to over 200ns with 1ns resolution. Pulse duration does not depend on the repetition rate and remains the same for all operational frequencies in the range from 10kHz to over 140kHz. The short length of the large mode area Yb-doped fiber was used to amplify the generated pulses to over 40kW peak power and several watt of the average power. The output pulse-to-pulse energy instability was less than 1% for all operational frequencies. Due to the single mode design of the delivery fiber, the measured output beam quality M² was found to be smaller than 1.05. The developed laser presents a solid-state design to be used in the industrial environment for applications where primary requirements are the beam quality, high repetition rate, small pulse-to-pulse energy instability and reliable laser operation on the real factory floor.

Low lying obstacles present immediate danger to both military and civilian helicopters performing low-altitude flight missions. A LADAR obstacle detection system is the natural solution for enhancing helicopter safety and improving the pilot situation awareness. Elop is currently developing an advanced Surveillance and Warning Obstacle Ranging and Display (SWORD) system for the Israeli Air Force. Several key factors and new concepts have contributed to system optimization. These include an adaptive FOV, data memorization, autonomous obstacle detection and warning algorithms and the use of an agile laser transmitter. In the present work we describe the laser design and performance and discuss some of the experimental results. Our eye-safe laser is characterized by its pulse energy, repetition rate and pulse length agility. By dynamically controlling these parameters, we are able to locally optimize the system’s obstacle detection range and scan density in accordance with the helicopter instantaneous maneuver.

Pr-Yb doped ZBLAN glass optically pumped with NIR shows visible fluorescence generated by an up-conversion process. With diode laser pumping, laser emission from a single-mode Pr-Yb doped ZBLAN fiber has been achieved at 492, 520, 605, 635 and 717 nm. This makes it possible to build all solid state visible fiber lasers. Solutions for building color-switchable fiber lasers by the aid of an external resonator or by manipulation of the reflectivity of a dielectric mirror are discussed. Experiments with switching between two wavelengths are presented. A fiber laser with switchable emission from 10 mW at 492 nm to > 10 mW at 635 nm is introduced. The laser output noise is less than 1 % rms, the beam quality is M² < 1.3, and the spectral width is < 1 nm (FWHM). Switching between 492 nm and 520 nm is also demonstrated. All wavelengths are generated within the same fiber resulting in identical boresight directions for different colors, and 100 % pointing stability. Fluorescence microscopy in life sciences is a typical application for this kind of laser.

For the first time, a >10W single-mode Tm-doped amplifier is demonstrated. The all fiber format is optimized for single frequency signals in the 1800 - 2020 nm band. Natural Tm ³⁺ gain bandwidth is shifted towards the 1800nm and 2000nm region by selecting the fiber composition and length. No SBS-related issues were observed at levels of >10W of output power while using a single-frequency seed source. A simple model allowing the prediction of amplifier gain is presented.

In this work we represent a highly efficient (>20%) CW second harmonic generation in PPKTP and PPLN crystals. As a fundamental source we used a high power (>24W) single-frequency (<50kHz linewidth) linearly polarized CW Er:Yb fiber laser. This laser was used in a single pass schematic to achieve more than 5W average power SHG in 780nm. Single pass conversion efficiency of >20% for PPLN and >7% for PPKTP was demonstrated. We also demonstrate a possibility of single mode fiber delivery for this SHG source with excellent beam quality (M² <1.1). Pump power dependency of conversion efficiency and other SHG characteristics for PPLN and PPKTP would be presented and compared.

We discuss the dramatic development of high-power fiber laser technology in recent years and the prospects of kilowattclass single-frequency fiber sources. We describe experimental results from an ytterbium-doped fiber-based multihundred-watt single-frequency, single-mode, plane-polarized master-oscillator power amplifier (MOPA) operating at 1060 nm and a similar source with 0.5 kW of output power, albeit with a degraded beam quality (M² = 1.6) and not linearly polarized. Experiments and simulations aimed at predicting the Brillouin limit of single-frequency system with a thermally broadened Brillouin gain are presented. These suggest that single-frequency MOPAs with over 1 kW of output power are possible. In addition, the power scalability of a simple single-strand fiber laser to 10 kW is discussed.

The effect of temperature variation along a high power fiber amplifier on the SBS threshold is considered theoretically. We show that for an end-pumped rare-earth doped double-clad fiber the inhomogeneous distribution of temperature, which is caused by absorption of pump radiation, may result in total suppression of SBS even for output powers well above 200 W.

Stimulated Brillouin Scattering (SBS) is a polarization-dependent, nonlinear process that is often the limiting factor for high-power fiber laser applications. We report the results of experiments measuring the SBS thresholds and the SBS gain bandwidths in several passive optical fibers. Fibers with nearly identical mode-field diameters and loss coefficients from different manufacturers were selected. Observations from these experiments indicate that the SBS gain coefficient for fibers from different manufacturers varied significantly resulting in a 70% deviation in SBS threshold. Also, polarization-maintaining (PM) fiber exhibited a significant increase in the SBS threshold for a linearly polarized pump beam that is launched into the PM fiber at 45° relative to the fiber's slow axis. This increase in threshold was not mirrored in non-PM fiber. These results suggest that the polarization multiplier in the SBS threshold equation may be highest when a PM fiber is used with the appropriate launch conditions, rather than a non-PM conventional single-mode fiber. We will present the experimental results and a theoretical model demonstrating the polarization dependent gain properties in both PM and non-PM fiber.

Significant progress has been recently reported on beam combining of arrays of fiber and semiconductor lasers using both coherent (phased array) and wavelength (spectral) techniques. The choice between these two classes of beam-combining techniques has implications for the degree of control required on the array elements and on the optical system that is using the beam-combined array. Coherent beam combining imposes more stringent requirements on array-element control (spectrum, phase, amplitude, and polarization) than wavelength combining. Also, wavelength-combined systems should degrade more gracefully than coherent systems and require fewer changes to optical systems as the number of elements is varied.

Coherent beam combining of many fiber lasers realizes power and brightness scaling. We have proposed and demonstrated highly efficient coherent beam combining of N fiber lasers by Y-shaped array coupled with fused fiber couplers. Power-summed single beam output is obtained from one of the N fiber ports with the lowest loss by selective excitation of one of the N constructive-interference supermodes. The basic characteristics of the coherent array, scalability of power summation, and bandwidth narrowing property will be presented. A 2.65-W fiber laser with only a 12-MHz bandwidth has been obtained by arraying eight 10-nm-bandwidth erbium-doped fiber lasers with an 85% addition efficiency. The characteristic bandwidth narrowing by the Vernier effect can be applied to high-power, narrowband fiber laser beyond nonlinearity limitations. By threshold control of the supermodes, high-speed (>1 kHz), high-contrast-ratio (>100) coherent control of beam direction has been demonstrated in the N=8 coherent array. An electro-optically-driven, 8-channel variable optical attenuator array was implemented in the output ports, and the thresholds were controlled electrically. No requirements of complicated phase-control optics/electronics and perfect single beam formation without side lobes are unique advantages. Mass-free and reaction-free properties will be quite useful in material processing and space communications.

In this paper we present results of an analysis of a method of effectively combining the output of a fiber array into a single beam by using a laser cavity in stable configuration. To couple the individual channels, our approach uses the nature of the high index modes with their spatial pattern resembling a combination of the sub-beams. The structure of such modes allows for very efficient matching (up to 97%) of the individual channels of the fiber array to an intra-cavity field distribution. As the high index mode has a spherical wavefront with π-phase shift between the nearest sub-beams this allows use of a simple phase corrector to form a diffraction limited output beam. In the configuration under analysis, the intra-cavity power per individual channel of the array is low enough to avoid damaging the fiber while the total output power is the sum of the power of all the channels. This paper describes the characteristics of the proposed fiber array beam coupling, in particular, the selection and stabilization of the chosen operating mode without losses in oscillation efficiency.

We review recent advances in Yb fiber lasers and amplifiers for high power short pulse systems. We go on to describe associated recent developments in fiber components for use in such systems. Examples include microstructured optical fibers for pulse compression and supercontinuum generation, and advanced fiber grating technology for chirped-pulse amplifier systems.

We have demonstrated 466 mW of 469 nm light from a frequency doubled continuous wave fiber laser. The system consisted of a 938 nm single frequency laser diode master oscillator, which was amplified in two stages to 5 Watts using cladding pumped Nd ³⁺ fiber amplifiers and then frequency doubled in a single pass through periodically poled KTP. The 3 cm long PPKTP crystal was made by Raicol Crystals Ltd. with a period of 5.9 μm and had a phase match temperature of 47 degrees Centigrade. The beam was focused to a 1/e² diameter in the crystal of 29 μm. Overall conversion efficiency was 11% and the results agreed well with standard models. Our 938 nm fiber amplifier design minimizes amplified spontaneous emission at 1088 nm by employing an optimized core to cladding size ratio. This design allows the 3-level transition to operate at high inversion, thus making it competitive with the 1088 nm 4-level transition. We have also carefully chosen the fiber coil diameter to help suppress propagation of wavelengths longer than 938 nm. At 2 Watts, the 938 nm laser had an M² of 1.1 and good polarization (correctable with a quarter and half wave plate to >10:1).

High-power, continuous-wave (CW) supercontinuum spanning from 1200 to 2100 nm has been generated in an all-fiber configuration. The output of a CW 8-W phosphosilicate fiber Raman laser at 1556 nm was efficiently converted to the supercontinuum in the successive high-nonlinear dispersion-shift fiber with the zero-dispersion wavelength of 1539 nm. The fiber-length and input-power dependences were investigated, and both the spectral broadening and continuum power are found to be strongly affected by the 2220-nm absorption band in silica. An average power of 6.8 W and a 20-dB bandwidth of 900 nm were obtained from the optimal 150-m fiber length. Very flat spectral intensity of 10±1 mW/nm from 1640 to 2015 nm is also a noteworthy feature. Raman-assisted four-wave mixing driven by modulation instability is the most possible mechanism of the presented CW supercontinuum generation and well explains the spectral cutoffs.

We report up to 7.2 W, 800 nm wide supercontinuum generation in a photonic crystal fiber. The pump laser is an Yb-doped fiber oscillator/amplifier generating up to 120 W output at 5~20 MHz repetition rate, with pulse duration of 5~100 ns. The experiment has demonstrated ~60% conversion efficiency for supercontinuum generation using nanosecond lasers. The maximum power is limited by the thermal lensing from the optical components.

High performance, short coherence length light sources with broad bandwidths and high output powers are critical for high speed, ultrahigh resolution OCT imaging. We demonstrate an all-fiber continuous-wave Raman light source based on a photonic crystal fiber, pumped by a continuous-wave Yb-fiber laser, which generates 330 mW output power and 140 nm bandwidths. The light source is compact, robust, turnkey and requires no optical alignment. In vivo high speed, ultrahigh resolution OCT imaging of tissues with < 5 μm axial resolution at 1.3 μm center wavelength is demonstrated.

We present a novel implementation of the lightwave synthesized frequency sweeper (LSFS) based on Ytterbium doped fiber amplifiers. The source can potentially be used for swept source optical coherence tomography (SS-OCT), which has recently been shown to have an improved signal to noise ratio compared to time domain OCT systems, and development of suitable swept wavelength sources is for this reason of utmost importance. Based on Ytterbium doped fiber amplifiers, the source operates in the 1-1.1 μm range, which makes it particular useful for ophthalmic applications of OCT. Previous studies of a LSFS based on Erbium doped fiber amplifiers (EDFAs), which can be operated with noise figures close to the fundamental quantum limit, showed that the scanning range was limited by the buildup of amplified spontaneous emission noise. In spite of Ytterbium doped amplifiers are fundamentally not able to approach the quantum limit, our fundamental experiments show performance comparable to EDFA based systems. The result of the experiments compare well with predictions given by a numerical concatenated amplifier model, hence validating the model and enabling us to use the model for future system optimization.

Chalcogenide glass fibers have been developed at NRL. Rare earth doped chalcogenide glass fibers emit strong IR emission and show potential for mid-IR and long-wave IR rare earth doped fiber lasers. In addition, undoped highly nonlinear chalcogenide glass fiber compositions have been developed with high Raman cross-sections and show potential for mid-IR and long-wave IR Raman fiber lasers.

In this invited paper, we will discuss the use of quantum dots as nonlinear optical elements in fiber laser sources. Furthemore, a review of the fabrication of the first low-loss (< 0.5 dB/cm) ion-exchanged waveguides in a quantum-dot-doped glass will be presented. We will discuss the coupling, propagation, absorption, and scattering losses in these waveguides. The near-field mode profile along with the refractive index profile of these waveguides will be presented. This PbS quantum-dot-doped glass was chosen due to its attractive optical gain and bleaching characteristics at wavelengths throughout the near infrared. This bleaching of the ground-state optical transition has been utilized for passive modelocking of a variety of lasers in the near infrared. In addition, we will discuss some of the potential integrated and fiber optics applications of our quantum-dot-doped waveguides.

A tapered fiber bundle is one of the leading approaches to coupling pump light into cladding-pumped fibers. This article compares it to other pump coupling schemes, and describes the tapered fiber bundle in detail. In addition tapered fiber bundles which maintain the polarization state of the signal and transform the size of the mode are described.

We report on the latest development within active photonic crystal fibers for high power lasers and amplifiers with special focus on how the fibers can be improved with both polarization-maintaining and polarizing properties. We describe rod-type fibers for which a record-high power extraction of 250W/m is achieved. Moreover, we describe how active characterization is used to optimize fibers for laser and amplifier sub-assemblies with respect to beam quality, efficiency and robustness. Finally, we illustrate how the fibers can be integrated with high NA tapers and passive air-clad fibers containing Bragg grating to form an all-fiber, alignment-free, high-power fiber laser subassembly.

Formatted diode bars are currently the preferred pump source for high-power fiber laser systems. In a formatted diode bar, the raw output of the diode bar is reformatted into a beam waist with a divergence, aspect ratio, and fill factor suitable for coupling into a conventional multimode fiber pigtail. The main drawbacks to formatted diode bar pump sources are cost, complexity and an inevitable tradeoff between coupling efficiency and source brightness. In this paper we describe how the Embedded Mirror Side Pumping (EMSP) technique allows the raw output of an unformatted diode bar to be used directly for side pumping double clad fiber (DCF) amplifiers. The EMSP technique allows the raw output of an unformatted diode bar to be coupled directly into the DCF inner cladding, without the same penalties in cost, complexity, coupling efficiency and loss of brightness. In particular, for applications at the 10 to 100 Watt power level and applications that require arrays of DCF amplifiers, diode bar EMSP will provide a very attractive alternative to systems based on formatted diode bar pump sources.

In the last years a dramatic increase of the output power of rare-earth-doped fiber lasers and amplifiers with diffraction limited beam quality has been observed. These demonstrates impressively that fiber lasers and amplifiers are an attractive and power scalable solid-state laser concept. The main limiting factors for the laser output power are the damage of the fiber ends, heating of the fiber due to the quantum defect and nonlinear effects. To overcome these problems, an increasing of the core diameter and keeping the fiber single mode, by using solid core step-index large-mode-area fibers, allow the power scaling beyond 1 kW at diffraction limited beam quality. A further scaling is possible by using novel highly doped air-clad photonic crystal fibers with increased mode field diameters of the active core. This type of fibers has several new preferable features. In our contribution we will discuss the advantages of microstructured fibers to reduce nonlinear effects inside the fiber and the possibility to scale the output power of fiber lasers and amplifiers with excellent beam quality. We also show experiments with pulsed fiber amplifier systems using these microstructured large mode area fibers.

We report a 40-μm core-diameter, Yb-doped, air-clad photonic crystal fiber laser operating continuous-wave with intrinsic single-transverse-mode beam quality (M² ~ 1.25). The laser was tunable over the 1020nm-1050nm range, exhibited a spectral linewidth <5GHz, was temporally stable and linearly polarized with a polarization extinction ratio >93%. The maximum output power obtained was ~14 W (limited by the available pump power).

We have demonstrated high power, linearly polarized output from an all-fiber laser using an integrated polarizing fiber. In this paper, we will detail the design, fabrication and operation of the single polarization fiber as well as the fiber laser experiments.

We report high pulse energy actively Q-Switched fibre laser systems in MOPA and single stage configurations. The system was comprised of a Q-Switched master oscillator and power amplifier in either GTwave or end pumped fibres. A number of different fibre lengths and core diameters were used to explore the laser capabilities. A Q-Switched master oscillator operating at 10 kHz repetition rate with typical pulse durations of 40-50 ns at ~ 1070 nm is demonstrated. The laser operation was investigated for pulse repetition rate from 10 to 100 kHz for higher average output powers. After the power amplifier pulse energies as high as 1.1 mJ were obtained.

Fiber lasers and amplifiers are used in a variety of applications either for scientific (spectroscopy, medicine...) or industrial applications (free space communications, laser marking and drilling ...). The combination of doped double clad fibers (DCF) and high power multimode semiconductors laser diodes technologies allows to achieve very high output power in very compact, robust and maintenance free systems. Yb ³⁺ doped DCF are well suited for 1μm wavelength amplification. In pulsed regime, achievable peak power can be strongly limited by nonlinear effects such as Kerr effect, Stimulated Raman Scattering (SRS) or Stimulated Brillouin Scattering (SBS). Consequently, the optimisation of optical amplifier architecture is required. In this paper, we demonstrate performances obtained for the generation of 2ns optical pulses up to >1.7kW peak power in a Master Oscillator Power Fiber Amplifier (MOPFA) configuration. The laser seed signal at 1060nm is emitted out of a single longitudinal mode source with spectral linewidth <0.2nm. The pulse repetition rate can be changed between 3 and 30MHz. The high power stage, based on a 2-stages architecture, allows to deliver >10W average output power with a good beam quality (M²<1.2). No significant limitation due to nonlinear effects of the type of the Kerr effect or SRS appears by means of the optimisation of the final stage’s fiber parameters. Results, such as a concentration of more than 80% of the total output power in a 1nm window around the central wavelength and above all an excellent conservation of the spectral properties of the seed source are demonstrated for a peak power of >1.7kW. These high performances are obtained in a fully-integrated device.

High power fiber lasers and amplifiers have received a significant amount of attention in recent years. Due to their stable beam characteristics, good thermal dissipation, and reduced weight compared to diode-pumped solid state lasers, they are finding more application spaces. One subset of this broad category of devices is pulsed sources operating in the mJ regime, which have a wide range of sensing and materials applications.

We have developed all fiber format pulsed lasers with bandwidth-limited emission and over 12kW peak power for the 1064nm and 1550nm wavelength ranges. The master oscillator followed by power fiber amplifier configurations were employed with operational frequencies from 100kHz to over 2MHz range and 2ns pulse duration. The pulse duration remains the same for all repetition rates. The designs of the low NA core fibers deployed ensure stable single spatial mode emission with 12μm and 14μm mode field diameter (MFD) for 1064nm and 1550nm correspondingly. The output emission bandwidth was below 0.1nm and pulse-to-pulse energy stability better than 1% were measured for all operational frequencies and output powers. Single mode fiber design of the fiber amplifiers ensured diffraction-limited output beam quality with M² less than 1.1. New lasers can be used for nonlinear frequency conversion to generate emission in the visible and UV parts of optical spectrum as well as in other applications.

We report a pulsed fiber source generating 1567 nm, spectrally narrow, ~2-ns pulses with maximum energy 303 μJ, average power of up to 12 W, and peak power > 130 kW.

The relationship between the backward optical injection waveform and the mode-locked pulse shape of semiconductor optical amplifier fiber laser (SOAFL) is studied. The SOA plays both the roles of a gain medium and an optically controlled modulator in this work. The injected optical comb-like bright and dark pulse-train with 60-ps pulsewidth was generated using a Mach-Zehnder intensity modulator (MZM) which DC-biased voltage of 1.7 V and 7.2 V, respectively. The backward injection of optical dark pulse-train results in a wide gain-depletion width (and a narrow gain window) within one modulation period, which is necessary for perfect mode-locking the SOAFL. In opposite, the backward injection of short optical pulse of bright optical pulse-train only causes a less pronounced gain-depletion effect. Such a broadened gain window can hardly initiate the mode-locking process. The backward comb-like dark pulse-train modulation is much easier to initiate harmonic mode-locking in the SOAFL than the bright pulse-train or sinusoidal-wave injection, which generates pulsewidth as short as 15 ps at 1 GHz. After propagating through 195m-long dispersion-compensating fiber, the pulsewidth of the mode-locked SOAFL can be linearly compressed to 13.5 ps. The linewidth and time-bandwidth product of the compressed SOAFL pulses are 1.78 nm and 0.8, respectively. The pulsewidth can further be nonlinearly compressed by using a 4695m-long single-mode fiber. The shortest mode-locked SOAFL pulsewidth of 3.5 ps at repetition frequency of 1 GHz by using cross-gain modulation technique is reported for the first time.

The variations and trade-off between single-sided-band (SSB) phase noise and supermode noise (SMN) suppression ratio of an actively mode-locked erbium-doped fiber laser (EDFL) with intra-cavity semiconductor optical amplifier (SOA) based high-pass filter are discussed. The insertion of an SOA increases the SMN suppression ratio of the EDFL from 26 dB to 41.4 dB, however, the SSB phase noise at 100 kHz offset frequency from carrier is concurrently degraded from -114 dBc/Hz to -96 dBc/Hz. Such an operation also causes a broadening in the EDFL pulsewidth from 36 ps to 130 ps. The insertion of an optical bandpass filter (OBPF) further reduces the SSB phase noise to -110 dBc/Hz and improves the SMN suppression ratio to 43 dB. Theoretical simulation interprets that the optimized operation of the SOA based high-pass filter at nearly transparent current condition is mandatory to achieve a better SMN suppression ratio and minimize the SSB phase noise of the mode-locked EDFL without sacrificing its output pulsewidth.

Refractive index decrement was discovered in a fiber made from photo-thermo-refractive (PTR) glass. PTR glass is a fluorosilicate glass doped with cerium and silver which demonstrates refractive index change after UV exposure and thermal development due to precipitation of NaF nanocrystals in the irradiated areas. This glass is widely used for volume holographic optical elements recording. Photosensitivity in PTR optical fibers has been shown after exposure to radiation at 325 nm for about 1 J/cm2 followed by thermal development at 520°C. Refractive index difference between exposed and unexposed areas was about 1000 ppm. A Bragg mirror at 1088 nm was recorded in such fiber which showed narrow band reflection within 1 nm.

Fiber Lasers are emerging as a technically superior solution that is disruptive to conventional laser sources. Estimates place the 2005 market for Fiber Lasers at approximately $160Million, with growth potential of 100%/year for the next 3-4 years. Many of the applications envisage deployment where end-users have easy access to the benefits of the Fiber Laser source, without needing to understand the detailed physics and engineering behind the beam delivery. For these applications a comprehensive control platform with simple functional user interfaces is a significant competitive advantage. Depending on the nature of the particular application, effective controls can range from basic pump source management, to more detailed monitoring of multiple aspects of the lasing system to ensure the desired operating regime, and may even include feedback from external sensors to optimize delivery conditions.

Advances in high power fibre lasers and amplifiers and in novel non-linear fibres that can be readily integrated with such pumps have led to a family of high power super-continuum sources that extend throughout the complete window of transparency of silica based fibres. The systems have been operated femtosecond, picosecond and nanosecond as well as cw. Average powers of 10’s Watts can be easily achieved, giving flat spectral power densities in excess of 10’s mW per nm from 400 nm to beyond 2.2 μm.