M. J. Andrejco

Broad-band erbium-doped fiber amplifier flattened beyond 40 nm using long-period grating filter

Broad-bandwidth amplification is essential for the construction of high-capacity multichannel communication systems. We describe a silica-based erbium doped fiber amplifier (EDFA) with a flat gain bandwidth exceeding 40 nm. The dual-stage EDFA includes a precisely designed inter-stage long-period fiber grating filter with more than 14-dB peak attenuation. By careful choice of the filter spectrum and fiber lengths, this EDFA is flat to within 1 dB over 40 nm while producing a noise figure below 4.0 dB and nearly +15-dBm output power.

11.2 dB SBS gain suppression in a large mode area Yb-doped optical fiber

11.2 dB suppression of stimulated Brillouin scattering (SBS) in an Yb-doped, Al/Ge co-doped large mode area (LMA) gain fiber is demonstrated with a ramp-like acoustic index profile exhibiting an acoustic index contrast of 0.09 and acoustic index slope of 0.01/μm.

Effect of heat and H 2 gas on the photo-darkening of Yb +3 fibers

Heating a photo-darkened ytterbium fiber causes a recovery in spectral transmission to the pre-darkened state. Exposure to H2 at high temperatures causes a permanent change in the visible transmission identical to that caused by photo-darkening.

Options for gain-flattened erbium-doped fiber amplifiers

We define two new figures of merit and use them to compare the best optical performance expected from ideal Er-doped fluoride fibre amplifiers (EDFFAs) and silica-based Er-doped fibre amplifiers (EDFAs). We use a computer model with measured spectral gain and loss parameters. It assumes homogeneous broadening and includes all known loss mechanisms.

Tapered fiber bundles for combining laser pumps (Invited Paper)

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.

Large-mode-area Er-doped fiber chirped-pulse amplification system for high-energy sub-picosecond pulses at 1.55 μm

We demonstrate a chirped-pulse amplification system generating 25 μJ compressed pulses at a center wavelength of 1552.5 nm. The seed module and the amplifier chain are all in-fiber (with a few small fiber-pigtailed free-space components), followed by a free-space diffraction grating pulse compressor. The amplifier chain contains a pre-amplifier and a booster whose gain fibers are 45/125 μm core/cladding-diameter, core-pumped Er-doped fibers. The pump lasers for both amplifiers are single-mode 1480 nm Raman lasers capable of up to 8 W output. The seed module generates up to 2 ns chirped pulses that are amplified and subsequently compressed to <800 fs duration. At a repetition rate of 50 kHz, the 2 ns pulses from the seed module were amplified to 72 μJ, resulting in 25 μJ after pulse compression. The corresponding peak power levels after the amplifier chain and compressor were 36 kW and 31 MW, respectively.

SBS suppression and acoustic management for high-power narrow-linewidth fiber lasers and amplifiers

This paper discusses the transverse acoustic index design of Yb-doped large mode area (LMA) LP01 optical fibers that provide ~10 dB of SBS threshold suppression relative to conventional LMA fibers with homogeneous elastic properties and equivalent optical effective areas Aeff. SBS suppression is achieved with a ramp-like negative acoustic lens structure that refracts the electrostrictive density fluctuations away from the optical mode thereby reducing the acousto-optic interaction that generates the stimulated light scattering. The fundamentals of the SBS process and its mitigation are briefly reviewed. Two figures-of-merit (FsOM) are identified to quantify the SBS suppression capability; the SBS reflectivity RSBS and the SBS threshold power Pth. An initial design of an SBS suppressing Yb-doped double clad fiber is incorporated in the power amplifier stage of a 200 W cw singlefrequency (SF) four stage master-oscillator power-amplifier (MOPA). The MOPA is also exercised as a pulsed amplifier and is utilized to measure the SBS reflectivities and thresholds in passive (i.e. un-pumped) fibers with ~100 ns pulses exhibiting peak powers up to ~250 W. In separate experiments, the SBS suppressing fibers are incorporated into the final stage of the pulsed four stage MOPA and the SBS reflectivities of the active gain fibers are measured. Pulsed SF MOPAs with peak pulsed power outputs ~900 W are demonstrated and confirm the kilowatt SF performance capability of these SBS suppressing fibers.

Increased amplifier efficiency by matching the area of the doped fiber region with the fundamental fiber mode

A significant improvement in the efficiency of high power large-mode area fiber amplifiers is demonstrated by improving the overlap of the doped region with the fundamental mode of the fiber

High-pulse energy MOPA using all-fiber components

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.

All-fiber 194 W single-frequency single-mode Yb-doped master-oscillator power-amplifier

A four-stage all-fiber single-frequency single-mode continuous-wave (cw) master- oscillator power-amplifier (MOPA) at 1083 nm is presented. Small mode area (SMA) and large mode area (LMA) amplifier stages are mode matched with a fiber mode converter (MC) and the signal and pumps are combined with tapered fiber bundles (TFBs). The final power stage uses a LMA Yb doped SBS-suppressing fiber. A single-frequency output power of 194 W is demonstrated with optical net and slope efficiencies of 68% and 80%, respectively.