Sven Brueckner

Splicing Ge-doped photonic crystal fibers using commercial fusion splicer with default discharge parameters.

A novel technique for splicing a small core Ge-doped photonic crystal fiber (PCF) was demonstrated using a commercial fusion splicer with default discharge parameters for the splicing of two standard single mode fibers (SMFs). Additional discharge parameter adjustments are not required to splice the PCF to several different SMFs. A low splice loss of 1.0 approximately 1.4 dB is achieved. Low or no light reflection is expected at the splice joint due to the complete fusion of the two fiber ends. The splice joint has a high bending strength and does not break when the bending radius is decreased to 4 mm.

Optical switch based on a fluid-filled photonic crystal fiber Bragg grating

We report the implementation of an in-fiber optical switch by means of filling a fluid into the air holes of a photonic crystal fiber with a fiber Bragg grating. Such a switch can turn on/off light transmission with an extinction ratio of up to 33 dB within a narrow wavelength range (Bragg wavelength) via a small temperature adjustment of +/-5 degrees C. The switching function is based on the temperature-dependent coupling between the fundamental core mode and the rod modes in the fluid-filled holes resulting from the thermo-optic effect of the filled fluid.

Toward photonic crystal fiber based distributed chemosensors

Different structures of photonic crystal fibers (PCF) have been investigated for application as intrinsic optical gas sensors. The fiber is used both as waveguiding structure and as sample containment. Advantages and drawbacks of solid core and hollow core PCF structures will be discussed. Theoretical assessment for the sensitivity of the investigated fiber types will be given. The calculated sensitivity of the solid core PCF will be reviewed using the fiber as methane sensor. A laser micro-drilling technology is used to perform first samples for quasi-distributed PCF chemical sensing.

Fiber Bragg grating inscription in pure-silica and Ge-doped photonic crystal fibers

We report on fiber Bragg gratings (FBGs) inscribed in pure-silica and Ge-doped photonic crystal fibers (PCFs) with a two-beam interference technique and a femtosecond or excimer laser. Such a technique enables the inscription of FBGs for different Bragg wavelengths with high flexibility. Effects of H(2)-loading and Ge doping on the efficiency of grating inscription were investigated by measuring the development of Bragg wavelength and attenuation in the transmission spectra with an increased exposure dose. H(2)-loading dramatically enhances the laser-induced index modulation not only in Ge-doped PCFs but also in pure-silica PCFs. We observed a reversible Bragg wavelength shift during femtosecond pulse irradiation, which indicates an internal temperature rise of approximately 77 degrees C.

Limits of light guidance in optical nanofibers

Reducing the waist of an optical fiber taper to diameters below 1 microm can be interpreted as creating an optical nanofiber with propagation properties different from conventional optical fibers. Although there is theoretically no cutoff of the fundamental mode expected, a steep decline in transmission can be observed when the fiber diameter is reduced below a specific threshold diameter. A simple estimation of this threshold diameter applicable to arbitrary taper profiles and based on the diameter variation allowing adiabatic transmission behavior is introduced and experimentally verified. In addition, this threshold behavior is supported by investigating the variation of the power distribution of the nanofiber fundamental mode as a function of the fiber diameter.

Thermo-Optic Switching Effect Based on Fluid-Filled Photonic Crystal Fiber

We report a thermo-optic switching effect with a high extinction ratio of 30 dB by means of filling a fluid into air holes of a solid-core photonic crystal fiber (PCF). Such an effect can perform a turn on-off operation of the transmitted light via a small temperature adjustment of ±10°C. The switching function attributes to the absorption of the filled fluid in combination with the interaction between the core mode and the excited ¿fluid rod¿ modes, resulting from the thermo-optic effect of the filled fluid.

Arrays of Regenerated Fiber Bragg Gratings in Non-Hydrogen-Loaded Photosensitive Fibers for High-Temperature Sensor Networks

We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index modification has shown to become more stable after the regeneration up to temperatures of 600 °C. With the use of an interferometric writing technique, it is possible also to generate arrays of regenerated fiber Bragg gratings for sensor networks.

Investigating Transverse Loading Characteristics of Microstructured Fiber Bragg Gratings With an Active Fiber Depolarizer

In this letter, the transverse loading characteristics of Bragg gratings in microstructured optical fibers were investigated by use of an active fiber depolarizer. Increasing transverse load shifts the Bragg wavelength to longer wavelengths; its sensitivity to transverse load decreases with increasing volume of air holes around the fiber core. Such transverse loading characteristics were found to be dependent on the fiber orientations.

Laser induced fluorescence of calcium fluoride upon 193 nm and 157 nm excitation

The combination of in situ transmission and laser induced fluorescence (LIF) measurements of CaF2 at 193 nm and 157 nm laser irradiation reveals a correlation between selected fluorescence bands and the laser transmission. At 193 nm irradiation, the fluence dependent transmission |dT/dH| of calcium fluoride shows a significant dependence on the temporal pulse shape of the laser source. Furthermore, a quantitative correlation between transmission properties and fluorescence intensity of calcium fluoride is reported for the first time in case of a LIF band at around 740 nm. Newly defined LIF detection conditions yield a remarkable increase of the sensitivity for bands with short lifetimes. Furthermore, different excitation mechanisms for the investigated fluorescence bands are found from both, fluence and pulse number dependent LIF measurements. At 157 nm irradiation, a fluence dependence of the transmission (|dT/dH|,T0) is obtained which is comparable to that of 193 nm excitation. LIF investigations at 157 nm excitation reveal an increase in complexity of the spectra compared to those of 193 nm excitation. It is found that the LIF spectra at 157 nm excitation mostly consist of the same bands as for 193 nm irradiation. Some samples, however, show a LIF band vanishing relative to its intensity at 193 nm excitation or the appearance of new bands characteristic only for 157 nm excitation. From comparing two calcium fluoride samples at 193 nm and 157 nm irradiation it is assumed that the presence of a characteristic 157 nm excited LIF band at around 225 nm is responsible for a drop in transmission at 157 nm.

Fiber Bragg gratings in small-core Ge-Doped photonic crystal fibers

We report about fiber Bragg gratings (FBGs) inscribed in a small-core Ge-doped photonic crystal fibers with a UV laser and a Talbot interferometer. We systematically investigated the responses of such FBGs to temperature, strain, bending, and transverse-loading. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. The bending and transverse-loading properties of the FBGs depend strongly on the fiber orientations.