J.E. Caplen

158-microJ pulses from a single-transverse-mode, large-mode-area erbium-doped fiber amplifier.

We report the amplification of 10-100-pJ semiconductor diode pulses to an energy of 158 microJ and peak powers >100 kW in a multistage fiber amplifier chain based on a single-mode, large-mode-area erbium-doped amplifier design. To our knowledge these results represent the highest single-mode pulse energy extracted from any doped-fiber system.

High-energy single-transverse-mode Q-switched fiber laser based on a multimode large-mode-area erbium-doped fiber.

We demonstrate that appropriately designed doped multimode fibers provide robust single-mode output when used within a fiber laser cavity. Using a novel large-mode-area fiber, we demonstrate what we believe to be record single-mode (M(2) <1.2) pulse energies of >0.5 mJ from a Q -switched fiber laser and even higher pulse energies (as high as 0.85 mJ) with slightly compromised spatial-mode quality (M(2)<2.0) . This approach offers significant scope for extending the range of single-mode output powers and energies that are achievable from fiber-laser-amplifier systems.

Fabrication and characterization of Yb/sup 3+/:Er/sup 3+/ phosphosilicate fibers for lasers

Fabrication process of efficient Yb/sup 3+/,Er/sup 3+/ codoped phosphosilicate fibers by modified chemical vapor deposition (MCVD) combined with the solution doping technique is studied in detail. We show that the process can be adapted to incorporate low viscosity phosphate glass and some important issues in the fabrication process are discussed. These include the sensitive presintering pass. We also report on the fabrication of a low loss all-glass double clad Yb/sup 3+/:Er/sup 3+/ codoped fiber. We explain how we evaluate the fibers and discuss the effect of the ytterbium to erbium concentration ratio on the laser characteristics. Finally, we present results of some investigations into the mechanisms which can affect the efficiency of the lasers, and show that the detrimental up-conversion from the metastable level of the erbium ions is dramatically reduced by the presence of the ytterbium ions.

Efficient single-frequency fiber lasers with novel photosensitive Er/Yb optical fibers

Boron- and germanium-doped highly photosensitive cladding is used in a novel design to achieve photosensitive Er/Yb-doped fibers, permitting short, strong gratings (length approximately 1 cm, reflectivity >99%) to be written without hydrogenation. The high absorption at 980 nm in Er/Yb fibers permits efficient pump absorption over a short device length, which is ideal for achieving highly efficient single-frequency fiber lasers. Both single-frequency Bragg-grating reflector and distributed-feedback lasers with slope efficiencies of 25% with respect to launched pump power have been realized in such fibers.

Yb 3+ -ring-doped fiber for high-energy pulse amplification

We report what is to our knowledge the first demonstration of pulse amplification in a cw-pumped fiber in which the doped gain medium has a ring shape surrounding a single-mode core. For a given pump power, ring doping reduces the gain and hence the power lost to amplified spontaneous emission. Thereby, a significantly larger amount of energy can be stored in the amplifier. Using an Yb(3+)-doped fiber pumped by 540 mW of power at 1000 nm, we measured 69 microJ of extracted pulse energy at 1047 nm, the highest value reported to date from a single-mode Yb(3+)-doped fiber. We predict that a fiber cladding pumped by a diode bar can produce pulse energies in excess of 1 mJ.

Femtosecond pulse amplification in cladding-pumped fibers

Femtosecond pulse amplification in a cladding-pumped fiber amplifier is demonstrated for the first time to our knowledge. Using a cladding-pumped erbium-doped fiber power amplifier and a passively mode-locked fiber seed oscillator in conjunction with an all-fiber chirped-pulse amplification system, we obtain 380-fs near-bandwidth-limited pulses with an average power of 260 mW. The pulse repetition rate is varied between 5 and 50 MHz, and pulse energies as high as 20 nJ are generated.

HIGH-POWER CHIRPED-PULSE ALL-FIBER AMPLIFICATION SYSTEM BASED ON LARGE-MODE-AREA FIBER GRATINGS

We describe the fabrication of chirped gratings in a specially developed photosensitive large-mode-area fiber and report the use of these components in a picosecond all-fiber chirped-pulse-amplification circuit. We demonstrate the generation of microjoule energy pulses with peak powers in excess of 500 kW, which we believe to be a record peak power from an all-fiber system.

Cladding-pumped fiber laser\amplifier system generating 100 /spl mu/J energy picosecond pulses

In addition to enabling the construction of high-power femtosecond amplifiers, doubleclad fibers may also be applied toward the construction of high-performance fiber oscillat o r ~ . ~ An example of a cladding-pumped Er/% fiber laser capable of generating 100 fs pulses with repetition rates up to 50 MHz and average powers of 15 mW is shown in Fig. 1. Here simple broad-stripe diode lasers may be used as pump sources. The autocorrelation and corresponding pulse spectrum are shown in Fig. 2. Wavelengths around 1.55 pm are useful because of the availability of reliable pump sources, however other emission wavelengths compatible with cladding pumping have also been demonstrated, namely Nd and Yb-doped fiber lasers. Though their emission wavelengths are in the positive dispersion regime of silica glass, compact soliton type fiber lasers may still be constructed by adding chirped fiber Bragg gratings for dispersion compensation to the cavity.6 In fact passively modelocked soliton-type fiber lasers may in principle be demonstrated in the whole trans100

Broad-area diode-pumped 1 W femtosecond fiber system

Summary form only given. High-average-power 310-fs pulses were obtained with an all-fiber chirped pulse amplification (CPA) system. Both the oscillator and the power amplifier are based on Er/Yb-doped fiber for cladding-pumping with broad-area laser diodes. A single 10-cm-long fiber grating is employed in the CPA system as a compact femtosecond-pulse stretcher/compressor.

High-energy high-average-power femtosecond fiber system using a QPM-grating pulse compressor

We demonstrate a simple and compact chirped pulse amplification (CPA) circuit for boosting both the accessible powers and energies from a femtosecond fiber amplifier. The system is based on a novel pulse compressor, chirped period quasi-phase-matched (QPM) grating, implemented in electric-field poled lithium niobate. A QPM grating compressor is unique in that it combines second-harmonic generation (SHG) and pulse compression in one crystal.