High Polarization Dependence Research Articles

High-performance vector torsion sensor based on high polarization-dependent in-fiber Mach-Zehnder interferometer.

We propose a high-performance vector torsion sensor based on an in-fiber Mach-Zehnder interferometer (MZI), which consists of a straight waveguide inscribed in the core-cladding boundary of the SMF by a femtosecond laser in only one step. The length of the in-fiber MZI is 5 mm, and the whole fabrication time does not exceed 1 min. The asymmetric structure makes the device have high polarization dependence, and the transmission spectrum shows a strong polarization-dependent dip. Since the polarization state of the input light entering the in-fiber MZI varies with the twist of the fiber, torsion sensing can be achieved by monitoring the polarization-dependent dip. Torsion can be demodulated by both the wavelength and intensity of the dip, and vector torsion sensing can be achieved by setting the appropriate polarization state of the incident light. The torsion sensitivity based on intensity modulation can reach 5763.96 dB/(rad/mm). The response of dip intensity to strain and temperature is weak. Furthermore, the in-fiber MZI retains the fiber coating, so it maintains the robustness of the complete fiber structure.

Fabrication of Superconducting Mid-Infrared Photodetectors With Dipole Nanoantennas

We have proposed using nanoantennas with superconducting detector to improve the response performance of infrared detectors. Dipole nanoantennas that have an NbN load resistance were fabricated to evaluate the antenna properties. By using electromagnetic simulation, the antenna length was set at 2400 nm for the operation around 7-μm wavelength. The antennas were evaluated by using Fourier transform infrared spectroscopy. In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The results of the simulation qualitatively agreed with the results of the experiment. The antenna effective area was also evaluated, and the area was estimated to be approximately 5.4 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 1420 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . We have fabricated a prototype of midinfrared (MIR) photodetectors that were formed with 45 dipole antennas with an NbN strip. The antennas were placed within an area of 20 × 20 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and they were connected by bias line in series. By the irradiation of MIR (λ = 4.9 μm) light, the responses with high polarization dependence values caused by antenna effect were observed.

400-Channel 25-GHz-spacing SOI-based planar waveguide demultiplexer employing a concave grating across Cand L-bands

The 400-channel 25-GHz-spacing SOI-based planar waveguide demultiplexer employing a concave grating across C- and L-bands is proposed in this paper. For the high polarization dependence, the waveguides are designed for supporting the TE mode only. To reduce the spherical aberration of the concave grating, the values of the maximum half divergent angle of the light source and minimum effective half width of the fundamental mode of the ridge waveguide are determined. We use a design example to show the spectral characteristics of the proposed design. Simulation results show that the proposed design provides better spectral characteristics and smaller die size.