High-power single-mode laser diodes around 795 nm are widely used in applications such as Rb atomic clocks and nuclear magnetic resonance imaging. We simulate a high-power single-mode semiconductor laser around 795 nm based on a supersymmetric structure. In the lateral direction, the mode stability characteristics are investigated by varying the three waveguides widths and the distances between the middle main waveguide and the two sub-waveguides. Since the left and right waveguides have different widths, the optimal distance from them to the main waveguide is also different. In order to ensure the single-mode operating of the laser, there is a pair of optimized distances from the left and right waveguides to the main waveguide. The distances from the left and right waveguides to the main waveguide are 1 μm and 1.2 μm, respectively, when the widths of the left waveguide, right waveguide and main waveguide are set as 2.3 μm, 3.5 μm and 6 μm, respectively. In the longitudinal direction, a laterally-coupled grating structure is used to achieve longitudinal mode selection. Such lasers are expected to be the next generation of high-power, narrow-linewidth, singlemode laser diodes.
Microdisks and micro-rings are commonly used micro-optical devices that greatly enhance the interaction between light and matter within a cavity due to their high-quality factor and small mode volume, making them widely used in microcavity optical sensing. By introducing parity-time (PT) symmetric structures into the microcavity, the coupling efficiency of the optical field inside the cavity can be improved, which is conducive to obtaining higher sensing sensitivity. We theoretically verify the feasibility of using a PT-symmetric micro-ring coupled microdisk composite cavity as an active sensor based on the characteristics of exceptional point (EP) enhanced sensing in PT-symmetric systems. Gain is introduced to the microdisk cavity by injecting current until the system undergoes PT symmetry breaking, i.e., when the sensor is at the EP, the transmission of light will exhibit a nonlinear enhancement effect due to the degeneracy of eigenvalues and corresponding eigenvectors of the system, making the signal more sensitive to changes in the sensing medium. The results obtained through the finite difference time domain method show that the intensity sensitivity of the PT-symmetric microcavity at the EP is improved by about 11.8 times compared with the conventional microcavity when the working wavelength is in the range of communication band and different concentrations of the same gas are injected into the air, which is expected to provide reference and insight for the further development of microcavities for refractive index sensing.
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.
With the development of optoelectronic technology, InGaAs/InP avalanche photodiodes (APDs) are more and more used in fiber-optic communication systems with high bit rates and long-distance transmission because of their advantages of high sensitivity, low noise, and high speed. When etching mesa-type InGaAs/InP APDs, the edges of the mesa sidewalls are susceptible to premature breakdown due to the increased electric field, which affects the device's performance. In this paper, a shallow-etched mesa-type InGaAs/InP APD with a guard ring structure is proposed in order to suppress edge breakdown. By using Silvaco TCAD software for simulation, the results show that the structure proposed in this paper can limit the active region in the center region, effectively suppress the edge electric field, make the electric field distribution more uniform, and suppress the uncertainty of breakdowns, so that the reliability of the device is greatly increased. The final optimized device has a punch-through voltage of 16 V and a breakdown voltage of 41.3 V. The device has a diameter of 80 μm. The dark current is about 2.02 nA, and the gain is 36 when the breakdown voltage is 95%.
Directly modulated semiconductor lasers (DMLs) with surface high-order grating have been designed, fabricated and measured. The output powers under different temperatures were measured, and there are almost no kinks among all the light-power curves. The threshold current is 22 mA with a slope efficiency of 0.21 mW/mA at 25 ℃. The side-mode suppression ratio (SMSR) over 30 dB is achieved. The wavelength red-shifting caused by current-induced heating is at a ratio of 0.03 nm/mA. Small signal response of this kind of lasers with surface high-order grating was measured at 25 ℃ and the -3 dB bandwidth is 11 GHz.
32-channel hybrid III-V/silicon laser arrays operating at C-band with 100GHz wavelength spacing are designed and simulated. Each channel of the hybrid III-V/silicon laser arrays includes III-V/silicon waveguide gain region with lateral sampled Bragg grating (LSBG) on silicon waveguide for selecting a single longitudinal mode, tapered III-V/silicon waveguide coupling region and silicon waveguide light output region. Light generated by III-V active region evanescently couples to the silicon waveguide, and outputs from the silicon waveguide. The seed grating’s period of LSBG is fixed and varing the sampled grating period of LSBG for selecting wavelength. The transfer matrix method is used to simulate LSBG’s parameters of hybrid III-V/silicon laser arrays. The simulation results show that 32- wavelengths are selected successfully by LSBG when the sampling grating periods are between 4.6 μm and 6.9 μm while the seed grating is fixed at 251 nm. Besides, the tapered III-V/silicon waveguide coupling region is designed and simulated by eigenmode expansion method of commercial software to convert the light spot size and increase the coupling efficiency from III-V to silicon waveguide. By optimizing the parameters, the coupling efficiency is up to 90% while hybrid III-V/silicon tapered waveguide length is fixed at 400μm
A three-dimensional tapered silicon-based spot-size converter is studied to improve the butt-jointed efficiency between the laser diode and the single-mode silicon waveguide. This kind of the spot-size converter can be fabricated while the ridge waveguide is etched. There is no need to regrow SiN or SiON on silicon. The optimized coupling efficiency between the spot-size converter and laser diode is over 0.8 at the wavelength of 1550 nm. This spot-size converter is useful for silicon photonics.
We designed and analyzed the ring resonators used as external optical cavities for hybrid tunable lasers based on silicon waveguides. The designed double-ring resonators (DRRs) for tunable lasers on silicon can provide a tuning range over 40 nm by micro-heaters, which cover the entire C-band with a high tuning accuracy.
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