Equilibrium mode distribution

About: Equilibrium mode distribution is a research topic. Over the lifetime, 928 publications have been published within this topic receiving 14939 citations.

Simulation and analysis of mode staff excitation during “O”-band optical signal launching to graded multimode fiber with large central defect of refractive index profile via standard singlemode fiber

Abstract: We present modified technique for differential mode delay map measurement. Here according to well-known methods a fast laser pulse is also launched into a tested multimode fiber (MMF) via single mode fiber (SMF), which scans core of MMF under precision offset positions. However unlike known technique formalized in ratified standards, proposed modification differs by addition scanning of the output end of tested MMF by short tail of SMF. Therefore for each radial offset position at the input/output MMF ends, the shape of pulse response of launched optical signal is recorded, that provides to get more informative differential mode delay map. This work presents some results of experimental approbation of proposed modified technique for differential mode delay map measurement.

Dispersion compensation device

Abstract: The present invention is a dispersion compensation device capable of varying dispersion compensation amount with a simple configuration. The device includes a first mode light conversion section capable of converting input light into light of higher mode, a dispersion compensation section capable of performing dispersion compensation on the higher mode light outputted from the first mode light conversion section corresponding to the status of mode of the higher mode light, a second mode light conversion section capable of converting the light of higher mode dispersion-compensated in the dispersion compensation section into light of original mode, and a mode control section capable of variably controlling the status of mode of the higher mode light converted in the first mode light conversion section, and controlling to convert the higher mode light from the dispersion compensation section to the light of original mode in the second mode light conversion section.

Highly efficient 90μm core rod fiber amplifier delivering >300W without beam instabilities

Abstract: 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.

Novel methods of intracavity beam shaping

Abstract: Methods of shaping laser beams within the laser resonator are studied. The simplest form of shaping is the spatial modegeneration inherent in the laser cavity due to the geometry of the resonator in conjunction with gain to compensate forroundtrip losses, such as diffraction and output coupling. Typically the fundamental mode or multimode behavior isexhibited from such configurations. Passive mode shaping can be accomplished by introducing static amplitude or phasemasks. An example of an amplitude mask is provided in order to generate a higher-order spatial mode. Active mode shapingcan be accomplished by altering the optical pump distribution. This case is studied experimentally with a diode-end-pumpedNd:YVO 4 laser and compared to modeling of expected Hermite-Gaussian mode generation. Active mode shaping allows thepreferred mode distribution to be altered in real time. Additional shaping can be done following the resonator to modify aHermite-Gaussian mode into a psuedo-Laguerre-Gaussian mode. This work also shows that using the coherent propagationmethod of Gaussian beam decomposition is capable of modeling and describing intracavity beam shaping.Keywords: laser beam shaping, transverse modes, solid-state lasers, laser resonator, coherent propagation, Hermite-Gaussianmode, Laguerre-Gaussian mode