Fabrication of a truly single mode, low loss and polarization maintaining HC-PCF is reported. This fiber has a 50 nm
wide strictly single mode region with good polarization holding (h-parameter below 10-4 m-1) and low loss (<20 dB/km).
High-power fiber lasers and amplifiers have gained tremendous momentum in the last 5 years. Many of the traditional manufacturers of gas and solid-state lasers are now pursuing the fiber-based systems, which are displacing the conventional technology in many areas. High-power fiber laser systems require reliable fibers with large cores, stable mode quality, and good power handling capabilities-requirements that are all met by the airclad fiber technology. In the present paper we go through many of the building blocks needed to build high-power systems and we show an example of a complete airclad laser system. We present the latest advancements within airclad fiber technology including a new 100 μm single-mode polarization-maintaining rod-type fiber capable of amplifying to megawatt power levels. Furthermore, we describe the novel airclad-based pump combiners and their use in a completely monolithic 350 W cw fiber laser system with an M2 of less than 1.1.
We present two low-loss 7-cell core hollow-core photonic crystal fibers (HC-PCF) with intrinsic single mode properties
around 1550 nm. By reducing the number of surface modes within the bandgap these fibers can be operated close to the
short wavelength bandgap edge. It is well known that by omitting a core tube in HC-PCF fabrication of a surface mode
free bandgap can be achieved. We found by experimental as well as numerical, investigation that using a core tube with
a wall thickness reduced to between 60-70 % is sufficient to have a surface mode free short wavelength bandgap edge.
The transmission and mode properties of the fabricated fibers are examined experimentally and compared to numerical
High-power fiber lasers and amplifiers have gained tremendous momentum in the last five years, and many of the
traditional manufactures of gas and solid-state lasers are pursuing the attractive fiber-based systems, which are now
displacing the old technology in many areas. High-power fiber laser systems require specially designed fibers with large
cores and good power handling capabilities - requirements that are all met by the airclad fiber technology. In the present
paper we go through many of the building blocks needed to build high-power systems and we show an example of a
complete airclad laser system. We present the latest advancements within airclad fiber technology including a new 70
μm single-mode polarization-maintaining rod-type fiber capable of amplifying to MW power levels. Furthermore we
describe the novel airclad based pump combiners and their use in a completely monolithic 350 W CW fiber laser system
with an M2 of less than 1.1. Finally, we briefly touch upon the subject of photo darkening and its origin.
Fiber lasers deliver excellent beam-quality and high efficiency in a robust and largely maintenance-free format, and are now able to do so with output powers in the kilowatt regime. Consequently, fiber lasers have become an attractive alternative to solid-state and gas lasers for e.g. material processing like welding, cutting and marking.
The all-glass air-clad photonic crystal fibers (PCFs) combine large mode-field diameters (currently up to 40 μm), high numerical aperture (typically in the 0.6-0.65 range), high pump absorption (30 dB/m demonstrated in ytterbium) and excellent high-power handling (kW CW and mJ pulses demonstrated). These properties have made this fiber type one of the most promising candidates for the future high-power fiber laser and amplifier systems that are expected to replace many of the traditional systems in use today.
To utilize the high numerical aperture and large mode-field diameters of the air-clad PCFs, special care must be taken in the system integration. In this paper, we will show examples of how these fibers can be integrated in laser and amplifier sub-assemblies with standard fiber pump-interfaces for use with single-emitter diodes or diode-bar pump sources. Moreover, we report on the most recent advances in fiber design including rod-type fibers and broadband polarizing ytterbium-doped large-mode-area air-clad fibers. Finally, we will review the latest results on PCF-based amplifier and laser configurations with special focus on high-power CW systems and high-energy pulsed configurations.
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.
Light sources with a broad spectral output and diffraction limited beam quality have a wide variety of present and future applications. A few of particular interest are hyperspectral laser radar for environmental monitoring, active hyperspectral imaging for detection and identification of objects, and speckle-free illumination. With the exception of systems based on amplified femto- or picosecond lasers, which are large and extremely complicated, pulse energies from supercontinuum laser sources have been limited to <10 microJoules which is generally not sufficient for the applications listed above. We present a simple technique to generate broadband light spanning several hundred nanometers in the near infrared with pulse energies of ~1 mJ, an improvement of approximately two orders of magnitude. The system is comprised of a Q-switched Nd:YAG laser and a very large mode area photonic crystal fiber. A combination of cascaded stimulated Raman scattering, four wave mixing, and self-phase modulation is responsible for the spectral broadening. Possibilities of scaling the output to the ~10 mJ level as well as extending the spectral coverage to the visible and mid-infrared will also be discussed.
Air-clad photonic crystal fibers hold promise to bring the single mode power levels past the 1kW limit through the utilization of extremely high numerical apertures, large mode field diameters and short fiber lengths. Here we discuss design, fabrication and handling issues of such fibers.
We report on recent progress in the design and application of
vertical-cavity surface-emitting lasers (VCSELs) for optical
interconnect applications in the 850 nm emission wavelength
regime. Ongoing work toward parallel optical interconnect modules
with channel data rates of 10 Gbit/s is reviewed and performance
results of flip-chip integrated two-dimensional VCSEL arrays are
presented. 10 Gbit/s speed as well as low thermal resistance of
the lasers has been achieved. As a possible alternative to
graded-index multimode fibers, we show 10 Gbit/s data
transmission over 100 m length of a novel, entirely undoped
multimode photonic crystal fiber. The use of VCSELs with output powers in the 10 mW range is demonstrated in a 16-channel free-space optical (FSO) module and VCSELs with even higher output power are shown to provide possible FSO connectivity up to data rates of 2.5 Gbit/s.
The emission spectra of several commercial InGaAlP laser diodes operating in the visible range are investigated. Large free-running linewidths on the hundred MHz level and relaxation oscillations at frequencies up to 2 GHz were observed in the field spectra. Linewidth reduction to less than one MHz has been achieved with resonant optical feedback on the cost of strong relaxation oscillations. With a short extended cavity configuration we could get both narrow linewidths on the MHz level and strong damping of the relaxation oscillations. Keeping the cavity length short, stable operation was achieved without any additional anti-reflection coating of the laser diode. A combination of the two methods gave additional strong reduction in the laser linewidth to roughly 50 kHz. To demonstrate the feasibility of the short extended cavity lasers in the visible range, the calcium intercombination line at 657 nm was reported with high resolution using an atomic beam apparatus.