The polarization control of silicon photonic integrated devices is an urgent problem caused by the birefringence effect due to the structural asymmetry of the silicon (Si) waveguide (450 nm × 220 nm), which results in polarization loss, polarization mode dispersion, and wavelength polarization related issues. This work presents a proposal for a compact silicon hybrid plasmonic waveguide (HPW) polarization controller. The proposed design includes two sets of Bragg gratings, placed within different material layers of the polarization controller. By changing the relative positions of the two sets of Bragg gratings, the absorption problem generated by the hybridized modes can be reduced or even eliminated, thus the reflection spectrums of the TE and TM polarization mode are optimized. Besides, one polarization mode of TE mode and TM mode has a high reflectivity, while the other polarization mode has a high transmission by designing different grating periods and other parameters. Based on the simulations and design, the silicon HPW polarization controller has an optimal length of 23.247 microns when used as a TM-mode polarization reflector, and the corresponding optimal length is 19.694 microns when used as a TE-mode polarization reflector. At the working wavelength, the polarization extinction ratio (ER) and insertion loss (IL) of the TM-mode polarization reflector are greater than 28.1 dB and less than 0.087 dB, respectively, and the ER and IL of the TE-mode polarization reflector are greater than 18.9 dB and less than 0.085 dB, respectively. Compared with conventional silicon waveguide polarization controllers, TE mode and TM mode separation, selection, transmission, and reflection of the proposed silicon HPW polarization controller can be achieved with a compact size. In the future, will be potential for widespread applications for this technology in both silicon photonic devices and silicon photonic integrated circuits.
The beam quality of the semiconductor laser is influenced by the structure of the laser's own waveguide as well as the beam shaping system. The cylindrical lens is used to compress the laser beam in the fast-axis direction in optically pumped source applications. Significant spectral deterioration occurs during the shaping of the laser beam. The spectrum of the laser split into some small peaks and misaligned with the absorption peaks of the crystal, resulting in a decrease in the overall absorption efficiency. In this paper, the reasons of spectral deterioration are investigated, and the spectral characteristics are optimized by varying the the output facet coating film’s reflectivity of the semiconductor laser chip. An improvement scheme for spectral deterioration of high power semiconductor lasers after beam shaping is proposed. The experiment results shows that the deterioration of the spectrum is significantly eliminated when the coating film’s reflectivity is adjusted from 0.88% to nearly 15%. A 976nm high power semiconductor laser chip with 7.16% reflectivity coating film has the highest slope efficiency. Due to a trade-off between spectral quality and the slope efficiency, it is necessary to choose an appropriate coating film’s reflectivity on the output facet surface to achieve both high output power and good spectra. This has important application prospects in future solid-state laser pump source applications.
Couplers have always been crucial in integrated optics, particularly in silicon-based integrated optics, where silicon-based couplers are used to couple silicon-on-insulator (SOI) waveguides and common single-mode optical fibers. However, direct coupling between single-mode fibers and silicon waveguides causes significant coupling losses due to the huge difference in mode spot size. In this research work, we propose a novel cantilever-based silicon-on-insulator edge coupler. A silicon waveguide with a cantilever structure is first created on an SOI wafer, and then silicon dioxide (SiO2) and silicon nitride (Si3N4) layers are alternatively placed on top of it and etched into ridge waveguide shapes. At the same time, the dimensions of the silicon waveguide in the longitudinal direction (light transmission direction) taper to form a tapered waveguide, and the refractive index of the Si3N4 tapers in the longitudinal direction as the longitudinal length of the Si3N4 shortens layer by layer from bottom to top. The coupling efficiency of a single-mode fiber with a mode field diameter of 10.4 μm and the SOI silicon waveguide exceeded 91%. The silicon coupler was simulated and constructed using the finitedifference method in time domain (FDTD) and the eigenmode expansion (EME) method. This highly effective SOI silicon coupler is crucial for silicon optical integration and may be used in a variety of situations, including optical computing, optical sensing, and optical communication.
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