Efficient fiber coupling system for simultaneous beam shaping and wavelength combining based on misaligned stepped prism multiplexing.

Due to the substantial contrast in the output beam quality between the two directions of the semiconductor laser, efficiently coupling the beam directly into the fiber is difficult. In this study, an efficient shaping method based on step multiplexing of misaligned step prisms is proposed and investigated systematically. First, multiple laser stacks eliminate dark areas to improve the beam quality through the full utilization of the transmission and reflection surfaces of the misaligned stepped prisms, which also improves the efficiency of the stepped prisms. It also simultaneously realizes laser wavelength combining based on reflective surface multiplexing without affecting the quality of the beam on the premise of improving the output power. Finally, the whole beam shaping system is completed without using cut-transform-rearranging prisms. The method couples four groups of laser stacks into a single fiber with a fiber diameter of 400 µm and a numerical aperture of 0.22. It can be seen from the computer-simulated model outputs that the final fiber output power can reach 2255.4 W and that the system as a whole has a light-to-light translation rate of 88.1%.

Metasurface cutoff perfect absorber in a solar energy wavelength band.

We report a metasurface cutoff perfect absorber (MCPA) in the solar energy wavelength band based on the double Mie resonances generated from the silicon and gallium arsenide nanoring arrays grown on the Al layer in the solar energy wavelengths. A high average absorption of 0.910 in the absorption band and almost eliminated absorption in the nonabsorption band are realized within only 120 nm thick structures. The MCPA is of a sharp cutoff between the absorption and nonabsorption band, whose extinction ratio, extinction difference, and cutoff slope are 9.4 dB, 0.8, and 0.0019n m -1, respectively. The proposed MCPA suggests an efficient way to design a solar thermal absorber, which is of great importance in renewable energy, such as for solar thermal applications.

A broadband and polarization-independent metasurface perfect absorber for hot-electron photoconversion.

We report an ultra-broadband metasurface perfect absorber from the UV to NIR region based on TiN nanostructures. A polarization-independent experimental average absorption of 0.900 (0.921 in simulation) at the wavelength band from 300 nm to 1500 nm is realized with only an 82 nm-thick TiN layer with TiO2 and MgF2 on top, which is efficiently fabricated by utilizing double-beam UV interference lithography followed by sputter coating deposition. A TiN-TiO2 hot-electron photoelectric conversion system is also simulated. An IPCE of 4% is realized at the wavelength of 710 nm and the average IPCE is 2.86% in the wavelength range of 400 nm to 1500 nm. The demonstrated device suggests an efficient way of designing and fabricating broadband perfect absorbers, which has great application potential in efficient hot-electron optoelectronic and photocatalytic systems.

Compact beam shaping design based on polarization plane multiplexing of semiconductor lasers.

Fiber coupling is difficult due to the uneven beam parameter product between the vertical and horizontal axes of semiconductor lasers. A beam shaping technique based on the combination of the internal total reflection and polarization surface of a stepped prism is proposed to achieve filling the dark area of the beam and polarization merging, as well as enabling the polarization plane to be multiplexed and the utilization rate of the polarization plane to be increased. The proposed technology can couple three groups of stacked array semiconductor lasers into a single fiber, in which the center diameter is 200 µm, and the numerical aperture is 0.22. The simulation results indicated that the output power of 1099 W and optical-optical conversion productivity of 85.8% were achieved.

None sharp corner localized surface plasmons resonance based ultrathin metasurface single layer quarter wave plate.

We report on a non-sharp-corner quarter wave plate (NCQW) within the single layer of only 8 nm thickness structured by the Ag hollow elliptical ring array, where the strong localized surface plasmons (LSP) resonances are excited. By manipulating the parameters of the hollow elliptical ring, the transmitted amplitude and phase of the two orthogonal components are well controlled. The phase difference of π/2 and amplitude ratio of 1 is realized simultaneously at the wavelength of 834 nm with the transmission of 0.46. The proposed NCQW also works well in an ultrawide wavelength band of 110 nm, which suggests an efficient way of exciting LSP resonances and designing wave plates, and provides a great potential for advanced nanophotonic devices and integrated photonic systems.

All-dielectric ultra-thin metasurface angular filter.

An all-dielectric double-layer grid grating is proposed and demonstrated theoretically and experimentally to realize the angular filtering effect. The theoretical results show that the transmission of the double-layer grid grating drops sensitively, as the incident angle increases under TM incidence at the designed resonant wavelength. The transmission is almost 0 (i.e., the entire incident light is reflected) when the incident angle increases to over 12°, which exhibits excellent angular filtering behavior. Double-beam interference lithography and sputter coated depositions are utilized to fabricate the proposed angular filter. The experimental results show that the divergent angle of the transmitted beam through the angular filtering sample at the wavelength of 633 nm is 7.76°, and the transmission is as high as 0.936 at normal incidence. The ultra-thin all-dielectric angular filter is very easy to fabricate in a large area, which has important applications in directional lighting and image processing.

Flexible metasurface black nickel with stepped nanopillars.

We report on a monolithic, all-metallic, and flexible metasurface perfect absorber [black nickel (Ni)] based on coupled Mie resonances originated from vertically stepped Ni nanopillars homoepitaxially grown on an Ni substrate. Coupled Mie resonances are generated from Ni nanopillars with different sizes such that Mie resonances of the stepped two sets of Ni nanopillars occur complementarily at different wavelengths to realize polarization-independent broadband absorption over the entire visible wavelength band (400-760 nm) within an ultra-thin surface layer of only 162 nm thick in total. Two-step double-beam interference lithography and electroplating are utilized to fabricate the proposed monolithic metasurface that can be arbitrarily bent and pressed. A black nickel metasurface is experimentally demonstrated in which an average polarization-independent absorption of 0.972 (0.961, experiment) in the entire visible band is achieved and remains 0.838 (0.815, experiment) when the incident angle increases to 70°.

All-dielectric polarization-independent optical angular filter.

We report on an all-dielectric, polarization-independent angular filter with one-dimension (1D) photonic crystal (PC) composed of semiconductor compatible Si/SiO2 pairs. The near-symmetric directional band gap of p- and s-polarized components and Fabry-Pérot (F-P) resonances are utilized to realize efficient polarization-independent angular filtering for normal incidence. The proposed angular filter is designed and experimentally demonstrated in a large area (5 cm × 5 cm) with multilayer sputtering depositions. Experimental measurements show that a divergence angle of the polarization-independently transmitted beam through the angular filtering sample at 1550 nm is 2.2° only and the transmission is as high as 0.8 at normal incidence. The proposed and demonstrated angular filter suggests an effective way to design and implement semiconductor compatible, all-dielectric and polarization-independent angular filters in a fashion of simple structure and easy-fabrication, which is expected to have great applications in lighting, beam manipulation, optical coupling and optical communications.