Hybrid-Integrated Tunable Hollow Waveguide DBR Laser
We propose a novel hybrid-integrated tunable laser with a hollow waveguide distributed Bragg reflector, enabling a wide continuous tuning with a single-tuning parameter. The wavelength tuning of hollow waveguide lasers is demonstrated for the first time.
Fabrication and characterization of hollow waveguide distributed bragg reflectors
We present the fabrication and characterization of a novel distributed Bragg reflector consisting of a grating loaded slab hollow waveguide. In this structure, we are able to obtain a high reflectivity even by using thin and short surface gratings because of the large contrast in refractive indices between a grating material and an air-core. We fabricated a slab hollow waveguide Bragg reflector with 620µm long, 190nm deep 1st-order circular grating composed of SiO2 exhibiting strong Bragg reflection at 1558nm with an air-core thickness of 10µm for TM mode. The peak reflectivity is 65% including fiber coupling loss, the 3dB bandwidth is 2.8nm and the grating-induced loss is less than 0.5dB.
Techno-economic analysis of solar thermal power plants using liquid sodium as heat transfer fluid
Abstract Solar thermal power plants with central receiver and thermal storage are expected to be one key technology in future electricity generation, because they are renewable and due to the thermal storage independent of the current solar radiation. State-of-the-art solar power plants often use molten nitrate salts as heat transfer fluid. The use of liquid sodium instead leads to lower electricity generation costs. Sodium has a high thermal conductivity and thus large heat transfer rates are possible. Hence, a smaller absorber surface is sufficient for the same thermal power. As a result, the sodium receiver achieves a higher efficiency at lower investment cost. Additionally, the aiming strategy, which reduces the peak heat flux on molten salt receivers isn’t necessary for sodium. Even at high heat flux densities, the absorber tubes will be cooled sufficiently due to the high heat transfer coefficients. Therefore, the sodium receiver in this analysis is designed for one single aim point, resulting in a heat flux density of q mean = 1.06 MW / m 2 and q peak = 2.99 MW / m 2 . The state-of-the-art system with molten salt considers q mean = 0.51 MW / m 2 and q peak = 1.0 MW / m 2 . The presented techno-economic analysis of two sodium based concepts compared to a reference system with molten salt results in up to 16% lower electricity generation costs.