Low-voltage optical devices based on liquid crystal photonic bandgap fibres

Photonic Crystal Fibers (PCFs) have appeared as a new class of optical waveguides, which have attracted large scientific and commercial interest during the last years. PCFs are microstructured waveguides, usually in silica, with a large number of air holes located in the cladding region of the fiber. The size and location of these air holes opens up for a large degree of design freedom within optical waveguide design. Further, the existence of air holes in the PCF gives access close to the fiber core and by introducing new materials into the air holes, a high interaction between light and hole material can be obtained, while maintaining the microstructure of the waveguide. In this paper, we describe what we call Liquid Crystal Photonic Bandgap Fibers, which are PCFs infiltrated with Liquid Crystals (LCs) in order to obtain increased fiber functionality. We describe a thermo-optic fiber switch with an extinction ratio of 60dB and tunable PBGs using thermo-optic tuning of the LC. These devices operate by the PBG effect and are therefore highly sensitive to the refractive index distributions in the holes.

Optical devices based on liquid crystal photonic bandgap fibres

We report on an ytterbium-doped fiber chirped-pulse amplification (CPA) system delivering millijoule level pulse energy at repetition rates above 100 kHz corresponding to an average power of more than 100 W. The compressed pulses are as short as 800 fs. As the main amplifier, an 80 μm core diameter short length photonic crystal fiber is employed, which allows the generation of pulse energies up to 1.45 mJ with a B-integral as low as 7 at a stretched pulse duration of 2 ns. A stretcher-compressor unit consisting of dielectric diffraction gratings is capable of handling the average power without beam and pulse quality distortions. To our knowledge, we present the highest pulse energy ever extracted from fiber based femtosecond laser systems, and a nearly 2 orders of magnitude higher repetition rate than in previously published millijoule-level fiber CPA systems.

Millijoule pulse energy high repetition rate femtosecond fiber chirped-pulse amplification system

Various embodiments include large cores fibers that can propagate few modes or a single mode while introducing loss to higher order modes. Some of these fibers are holey fibers that comprising cladding features such as air-holes. Additional embodiments described herein include holey rods. The rods and fibers may be used in many optical systems including optical amplification systems, lasers, short pulse generators, Q-switched lasers, etc. and may be used for example for micromachining.

Single mode propagation in fibers and rods with large leakage channels

Photonic crystal fibers are highly attractive as nonlinear media as they combine a large nonlinear coefficient and a highly customizable zero dispersion wavelength - flexibility not found in any other medium. However, the high dispersion slope at the zero-dispersion wavelength demonstrated so far is very limiting to the useful bandwidth. We propose a new fiber design comprising a hybrid core-region with three-fold symmetry that enables unprecedented dispersion control while maintaining low loss and a high nonlinear coefficient. The lowest dispersion slope obtained is 1·10-3ps/(km·nm2) or one order of magnitude lower than for conventional slope reduced nonlinear fibers. The nonlinear coefficient is more than 11 (W·km)-1 and loss below 7.9 dB/km at 1.55 µm has been achieved.

Dispersion flattened hybrid-core nonlinear photonic crystal fiber

We report on the design of a single-polarization single-transverse mode large mode area photonic crystal fiber. By including index-matched stress applying elements in the photonic cladding an ultra-broadband single polarization window is obtained while a large mode field area of ~700 microm(2) is maintained. Based on that design, an Yb-doped double-clad photonic crystal fiber is realized that combines low nonlinearity and single polarization properties. A first result of the high power operation using this fiber is demonstrated.

Stress-induced single-polarization single-transverse mode photonic crystal fiber with low nonlinearity

We demonstrate, for the first time, a highly nonlinear polarization maintaining photonic crystal fiber with zero dispersion at 1.55 /spl mu/m, nonlinear coefficient of 20 (Wkm)/sup -1/ and splice loss to standard technology fiber of 0.3 dB.

Highly nonlinear photonic crystal fiber with zero-dispersion at 1.55 /spl mu/m

Photonic crystal fibers consisting of a solid fused silica core surrounded by a regular array of sub-micron air-holes have been shown to operate with single mode core well above 30 μm in active laser geometries as well as passive beam delivery fibers. Novel designs based on the combination of stress applying elements that are index matched to the holey cladding have recently been emerged. In this report we summarize the properties of these polarization maintaining photonic crystal fibers. Beside the characterization of the polarizing window and birefringence, high power laser and amplifier configurations using these fibers are demonstrated and first experiments concerning the temperature sensitivity of the polarizing properties are presented.

Design and high power operation of a stress-induced single-polarization single-transverse mode LMA Yb-doped photonic crystal fiber

Recent development achievements in high power fiber laser designs and subassemblies have improved the performance and usability. Such achievements show the path for these fiber lasers out of the R&D labs and into industrial environments.

C. Jacobsen

Papers

Stress-induced single-polarization single-transverse mode photonic crystal fiber with low nonlinearity

Highly nonlinear photonic crystal fiber with zero-dispersion at 1.55 /spl mu/m

Design and high power operation of a stress-induced single-polarization single-transverse mode LMA Yb-doped photonic crystal fiber

Recent progress on photonic crystal fibers for high power laser applications