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Summary Testicular microlithiasis (TML) is an incidental finding at ultrasonography of the scrotum. A link between testicular microlithiasis and testicular cancer has been suggested. However, the majority of studies are retrospective using ultrasonography with minor data on health status and life style characteristics. Our objective was to investigate if lifestyle and health are associated with TML. In 2014, we conducted a self‐administered questionnaire survey including 1538 men, who all due to testicular/scrotal symptoms had an ultrasound investigation of the scrotum during 2004–2013. The men were divided into men with TML and men without. The 23‐items questionnaire included items on age, height, weight, lifestyle (alcohol consumptions, smoking habits, workload, exercise and food), previous diseases in the testicles, pain and consumption of analgesics. The prevalence of TML was 12.8%. Overall, lifestyle factors did not vary between men with or without TML. However, men with TML did consume more crisp than men without. Development of TML was not associated to classic life style factors such as alcohol consumption, smoking habits, or mothers smoking during pregnancy. Also, age and height could not be linked to presence of TML. We did find, however, that men with TML experienced less physical activity and consumed more crisp than men without TML. Since ingestion of crisps has potential carcinogenic effect (acrylamide), this finding needs confirmation in a separate study.

Power scaling of fiber laser systems requires the development of innovative active fibers, capable of providing high pump absorption, ultralarge effective area, high-order mode suppression, and resilience to thermal effects. Thermally induced refractive index change has been recently appointed as one major limitation to the achievable power, causing degradation of the modal properties and preventing to obtain stable diffraction-limited output beam. In this paper, the effects of thermally induced refractive index change on the guiding properties of a double-cladding distributed modal filtering rod-type photonic crystal fiber, which exploits resonant coupling with high-index elements to suppress high-order modes, are thoroughly investigated. A computationally efficient model has been developed to calculate the refractive index change due to the thermo-optical effect, and it has been integrated into a full-vector modal solver based on the finite-element method to obtain the guided modes, considering different heating conditions. Results have shown that the single-mode regime of the distributed modal filtering fiber is less sensitive to thermal effects with respect to index-guiding fibers with the same effective area. In fact, as the pump power is increased, their single-mode regime is preserved, being only blue-shifted in wavelength.

Summary form only given. Ultrafast ps and fs laser systems using ROD fiber amplifiers delivering megawatts of peak power and several hundreds of watts in average power have attracted significant academic and industrial interest in recent years. However, the power scaling has reached a temporary limit caused by thermal effects, which has set a limit of average power scaling of these amplifiers due to so called modal instabilities (MIs) [1]. New types of fiber designs with very large cores have been suggested to increase the average power limit [2, 3]. One way of achieving this, is using resonant structures [3], however it is often speculated that these structures are sensitive to temperature causing unstable beam quality under high thermal load (high power extraction pr unit length).A 25-ps mode-locked linearly polarized seed source at 1032 nm (40MHz rep rate, 16 W average power) is used to seed a distributed mode filtering ROD fiber with 90μm core diameter. The ROD fiber shows excellent power conversion efficiency as shown in Fig. 1 with almost linear slope and the MI threshold level is observed at 314 W of average output power corresponding to ~320kW of peak power. Optical to optical conversion efficiency is 69% and the mode quality is stable below the MI threshold. No non-linear effects are observed and the ASE is suppressed by ~35dB, shown in Fig.1. The experiments are modeled using a semi-analytical approach [4, 5], where a nonlinear coupling constant that depends on the thermo-optical effect is determined. χ is combined with FEM-calculated mode distributions to predict the onset of modal instabilities for this particular fiber design.We demonstrate that a ROD fiber design having a resonant structure can deliver efficient and linear amplification to high average output power without suffering from thermal load induced beam quality degradation. In addition, we evaluate the influence of the noise of the seed source on the MI threshold level. We model the MI threshold for this fiber and show good agreement between measurements and simulations, when the MIs are seeded by system dependent noise.

Photonic crystal bandgap fibers employing distributed mode filtering design provide near diffraction-limited light outputs, a critical property of fiber-based high-power lasers. Microstructure of the fibers is tailored to achieve single-mode operation at specific wavelength by resonant mode coupling of higher-order modes. We analyze the modal regimes of the fibers having a mode field diameter of 60 µm by the cross-correlated (C(2)) imaging method in different wavelength ranges and evaluate the sensitivity of the modal content to various input-coupling conditions. As a result, we experimentally identify regimes of resonant coupling between higher-order core modes and cladding band. We demonstrate a passive fiber design in which the higher-order modal content inside the single-mode guiding regime is suppressed by at least 20 dB even for significantly misaligned input-coupling configurations.

We investigate the temporal dynamics of Modal instabilities (MI) in ROD fiber amplifiers using a 100 μm core rod fiber in a single-pass amplifier configuration, and we achieve ~200W of extracted output power before the onset of MI. Above the MI threshold, we investigate the temporal dynamics of beam fluctuations in both the transient and chaotic regime. We identify a set of discrete frequencies in the transient regime and a white distribution of frequencies in the chaotic regime. We test three identical rods using a multiple ramp-up procedure, where each rod is tested in three test series and thermally annealed between each test series. We find that the MI threshold degrades as it is reached multiple times, but is recovered by thermal annealing. We also find that the test history of the rods affects the temporal dynamics.

We analyze the modal properties of an 85μm core distributed mode filtering rod fiber using cross-correlated (C 2 ) imaging. We evaluate suppression of higher-order modes (HOMs) under severely misaligned mode excitation and identify a single-mode regime where HOMs are suppressed by more than 20dB.

The modal instability (MI) threshold is estimated for four rod fiber designs by combining a semi-analytic model with the finite element method. The thermal load due to the quantum defect is calculated and used to numerically determine the mode distributions on which the expression for the onset of MIs is highly dependent. The relative intensity noise of the seed laser in an amplifier setup is used to seed the mode coupling between the fundamental and higher order mode, and lead to MI threshold values of 174 W – 348 W of extracted output power for the four rod fibers having core diameters in the range 53 μm – 95 μm.

The effects of thermally-induced refractive index change on the guiding properties of different large mode area fibers have been numerically analyzed. A simple but accurate model has been applied to obtain the refractive index change in the fiber cross-section, and a full-vector modal solver based on the finite-element method has been used to calculate the guided modes of the fibers operating at high power levels. The results demonstrate that resonant structures added to the fiber cross-section can be exploited to provide efficient suppression of high-order modes with a good resilience to thermal effects.

Thermally induced nonlinear mode coupling leads to transverse mode instability (TMI) in high power fiber amplifiers. A numerical model including altering mode profiles from thermal effects and waveguide perturbations predicts a TMI threshold of ~100W.

A large-mode-area Ytterbium-doped photonic crystal fiber amplifier with build-in gain shaping is presented. The fiber cladding consists of a hexagonal lattice of air holes, where three rows are replaced with circular high-index inclusions. Seven missing air holes define the large-mode-area core. Light confinement is achieved by combined index and bandgap guiding, which allows for single-mode operation and gain shaping through distributed spectral filtering of amplified spontaneous emission. The fiber properties are ideal for amplification in the long wavelength regime of the Ytterbium gain spectrum above 1100 nm, and red shifting of the maximum gain to 1130 nm is demonstrated.

We report on an ytterbium doped single mode distributed mode filtering rod fiber in an amplifier configuration delivering high average output power, up to 292 watts, using a mode-locked 30ps source at 1032nm with good power conversion efficiency. We study the modal stability of the output beam at high average output power levels and demonstrate a 44% power improvement before the threshold-like onset of mode instabilities by operating the rod fiber in a leaky waveguide regime. We investigate the guiding dynamics of the rod fiber and explain the improved performance by thermally induced refractive index profile change.

A large-mode-area Ytterbium-doped photonic crystal fiber amplifier with efficient suppression of amplified spontaneous emission is presented. The fiber cladding consists of a hexagonal lattice of air holes, where three rows are replaced with circular high-index inclusions. Seven missing air holes define the large-mode-area core. Light confinement is achieved by combined index and bandgap guiding, which allows for single-mode operation and distributed spectral filtering of amplified spontaneous. The fiber properties give control of the gain shape and are ideal for amplification in the long wavelength regime of the Ytterbium gain spectrum above 1100 nm.

High-power fiber amplifiers for pulsed applications require large mode area (LMA) fibers having high pump absorption and near diffraction limited output. This improves the limiting factor of nonlinear effects, while maintaining good beam quality. Photonic crystal fibers allow realization of short LMA fiber amplifiers having high pump absorption through a pump cladding that is decoupled from the outer fiber. However, achieving ultra low NA for single-mode (SM) guidance is challenging, and thus different design strategies must be applied to filter out higher order modes (HOMs). The novel distributed modal filtering (DMF) design presented here enables SM guidance, and previous results have shown a SM mode field diameter of 60 μm operating in a 20 nm SM bandwidth. The DMF rod fiber has high index ring-shaped inclusions acting as resonators enabling SM guidance through modal filtering of HOMs. Large preform tolerances are compensated during the fiber draw resulting in ultra low NA fibers with very large cores. In this paper, design optimization of the SM bandwidth of the DMF rod fiber is presented. Analysis of band gap properties results in a fourfold increase of the SM bandwidth compared to previous results, achieved by utilizing the first band of cladding modes. This covers of a large fraction of the Yb emission band, where wavelengths of 1030 nm and 1064 nm can be included.

We present recent development of photonic crystal fiber amplifiers containing photonic bandgap structures for enhanced spectral and modal filtering functionality.

High-power fiber amplifiers for pulsed applications require large mode area (LMA) fibers having high pump absorption and near diffraction limited output. Photonic crystal fibers allow realization of short LMA fiber amplifiers having high pump absorption through a pump cladding that is decoupled from the outer fiber diameter. However, achieving ultra low NA for single mode (SM) guidance is challenging, thus different design strategies must be applied. The distributed modal filtering (DMF) design enables SM guidance in ultra low NA fibers with very large cores, where large preform tolerances can be compensated during the fiber draw. Design optimization of the SM bandwidth of the DMF rod fiber is presented. Analysis of band gap properties results in a fourfold increase of the SM bandwidth compared to previous results, achieved by utilizing the first band of cladding modes, which can cover a large fraction of the Yb emission band including wavelengths of 1030 nm and 1064 nm. Design parameters tolerating refractive index fabrication uncertainties of ± 10-4 are targeted to yield stable SM bandwidths.

We demonstrate a high power fiber (85 μm core) amplifier delivering up to 292 Watts of average output power using a mode-locked 30 ps source at 1032 nm. Utilizing a single mode distributed mode filter bandgap rod fiber, we demonstrate 44% power improvement before the threshold-like onset of mode instabilities by operating the rod fiber in a leaky waveguide regime. We investigate the guiding dynamics of the rod fiber and report a distinct bandgap blue-shifting as function of increased signal power level. Furthermore, we theoretically analyze the guiding dynamics of the DMF rod fiber and explain the bandgap blue-shifting with thermally induced refractive index change of the refractive index profile.

We present a simple fabrication method for embedding gold nanoparticles (GNPs) in a microfiber with two main advantages. The GNPs are positioned within the microfiber securing maximum enhancement of the electrical field and protection of the GNPs from the surroundings; moreover incoupling losses to the microfiber are reduced significantly by integrating a single mode fiber in the device. The average enhancement factor of the electric field within one unit cell of the microfiber due to the GNPs is estimated to 17.4. This enhancement leads to an enhanced Kerr effect near the plasmon resonance frequency. The fabrication method is demonstrated without GNPs.

Dye-doped polymer photonic crystal (PhC) lasers fabricated by combined nanoimprint and photolithography are studied for their reproducibility and stability characteristics. We introduce a phase shift in the PhC lattice that substantially improves the yield of single wavelength emission. Single mode emission and reproducibility of laser characteristics are important if the lasers are to be mass produced in, e.g., optofluidic sensor chips. The fabrication yield is above 85% with highly reproducible wavelengths (within 0.5%), and the temperature dependence on the wavelength is found to be −0.045 or −0.066 nm K-1, depending on the material.

The influence of index contrast variations for obtaining single-mode operation and low threshold in dye doped polymer two dimensional photonic crystal (PhC) lasers is investigated. We consider lasers made from Pyrromethene 597 doped Ormocore imprinted with a rectangular lattice PhC having a cavity in the middle of the crystal structure. We demonstrate that the index contrast, neff,high/neff,low, is an essential parameter for achieving low threshold, and we identify a trade-off between low threshold and single-mode operation.

In this work, a thorough numerical analysis of the impact of thermally-induced waveguide changes on the Single-Mode (SM) regime of the distributed modal filtering (DMF) photonic crystal fiber (PCF) has been performed by employing a full-vector modal solver based on the finite-element method, capable of taking into account the refractive index change on the fiber cross-section due to thermo-optic effect. Simulation results have been compared with those obtained for other rod-type fibers with a similar mode field diameter of about 65 μm.