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.
To meet the requirements of high dynamic range applications of LiDAR, this paper designs the silicon avalanche photodetector (Si APD) with large linear gain, which can reduce the difficulty of subsequent APD circuits and improve the accuracy of laser ranging. In this paper, a planar n+-p-π-p+ avalanche photodetector (APD) is formed by ion implantation and annealing process, based on a silicon intrinsic substrate wafer. And the device structure is optimized to improve the maximum gain value in linear mode. Based on this, a new trench with an ion implantation type guard ring is designed to enhance the linear gain range. The simulation results show that the device operates in the wavelength range of 400~1100 nm and reaches the peak response at 700 nm. The breakdown voltage is 153 V, and the dark current at 90% breakdown voltage is 1.47 nA. The gain range is 2~101 under 32~138 V bias, with a large gain dynamic range and good linearity of gain, which is beneficial for the subsequent amplification circuit. Meanwhile, the calculation shows that the input optical power of APD device corresponding to the optical current compression degree of -1 dB is -16 dBm, which has good linearity in the range of -70~-16 dBm, which is beneficial to improve the overall performance of LIDAR.
A 976nm fiber-coupled diode laser module based on stepped prisms and polarization beam combiner is proposed in this paper to solve the mismatch of beam quality in both directions of diode lasers. The beam size was compressed on the fast and slow axis without using a prism stack for beam shaping. Based on that, a laser stack of eight mini bars was coupled into a fiber with a core diameter of 200 μm and a numerical aperture of 0.22. The simulation results show that the output power of the fiber-coupled module is 597 W, the brightness is almost 12.5 MW/(cm2 ·sr), and the optical-to-optical conversion efficiency is 93.28%. The fiber-coupled module proposed in this paper can not only achieve high power outputs but is also widely used in the fields of material processing and industrial.
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%.
The smile effect of the laser bar increases the difficulty of laser beam coupling and limits its application. In this paper, the smile effect in the high-power laser on the microchannel cooler (MCC) and the method of reducing the smile effect by balancing the thermal-induced stress are studied. The model of diode laser packaging with MCC is established based on the finite-element method (FEM). The effect of the thickness of the N-foil on the smile effect and stress is analyzed. The bar is bent into a convex shape after the bar is bonded to the heat sink, according to the simulation. With the increase of the thickness of the N-foil, the bar deformation gradually decreases, and then the middle part of the bar reversely increases. The thermal-induced stress on the bar is balanced by optimizing the thickness of the N-foil. The minimum deformation was less than 0.2 μm.
Photonic crystal laser diode bars have the advantages of low vertical divergence angle and high resistance to catastrophic optical mirror damage. However, with the increase of output power, the waste heat problem is becoming more serious, affecting the further improvement of laser performance. Therefore, it is of great significance to study the thermal characteristics of bars. In this paper, the fluid-solid coupling conjugate heat transfer model of a microchannel cooled photonic crystal laser diode bar is established through the Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) numerical methods. The transient thermal behavior, steady-state characteristics, and temperature distribution of photonic crystal laser diode bars under continuous (CW) operating states are studied in detail. The simulation results show that the junction temperature is 55.48°C, and the thermal resistance is 0.48 K/W. The closer the emitter is to the bar center, the easier the thermal crosstalk occurs. In the experiment, the continuous output power of the photonic crystal laser bar is 112.13 W at 120 A, the junction temperature is 57.14 °C, and the thermal resistance is 0.50 K/W. The simulations of bars are consistent with the experiment.
The lateral leakage current is influenced by the height of ridge waveguide. We design two structures to restrict the lateral leakage current of ridge diode lasers, called ‘step-ridge’ structure and ‘groove-ridge’ structure. In order to obtain a better output electrical characteristic, we optimize the geometry of the two structures. For ‘step-ridge’ structure, we simulate various step-widths (including up-step widths and down-step widths). For ‘groove-ridge’ structure, we simulate different widths of groove and distances between injection section and groove. The lateral leakage currents of both two structures were calculated under the same injection current. In conclusion, both two structures can effectively reduce the leakage carrier by at most 80%, the ‘step-ridge’ diode lasers can improve around 6.5% wall-plug efficiency, but the ‘groove-ridge’ diode lasers would reduce the wall-plug efficiency at the same time.
The application of high-performance VCSELs is extending from consumer electronics to automotive applications. Wet oxidation is an important technology in the fabrication of VCSELs. In this paper, we studied the wet oxidation process and mechanism in order to accurately control the oxidation aperture and improve the power and the conversion efficiency. Current density distributions of VCSELs with different oxide apertures are simulated based on COMSOL Multiphysics. In the experiment, the output power, conversion efficiency and threshold current of single junction and five-junction 940 nm VCSELs varying with oxide apertures are measured. Five-junction VCSELs exhibit maximum power conversion efficiencies are more than 60% and slope efficiency are more than 5.28W/A with oxide aperture from 9 to 15 μm under room temperature pulse condition (50 µs pulse width, 0.5% duty cycle). In addition, 385-element five-junction VCSEL array exhibits maximum power conversion efficiency of 53.45%. The five-junction VCSELs can be used as the basic laser source for the automotive applications.
Photonic crystal laser diodes are characterized by low divergence angle and high brightness, but thermal effects have become a major obstacle to further improvement of output power and efficiency. The thermal characteristics of high- power photonic crystal laser diodes are of great importance to improve the output power and increase the lifetime. In this paper, the physical heat dissipation model of a single photonic crystal laser diode with CS-mount package is established. Steady-state thermal characteristics simulations are performed using the Finite Element Method (FEM) and the influences of different parameters, such as solder, transition heat sink and heat sink on the thermal characteristics are analyzed. The simulation results show that the thickness and thermal conductivity of the heat sink materials are the main factors impacting the heat dissipation of the laser. The thermal resistance of the laser can be reduced effectively by using heat sink materials of high thermal conductivity. On the premise of ensuring wettability and reliability, the thickness of the solder layer should be decreased. A photonic crystal laser diode with a cavity length of 4 mm and a stripe width of 350µm based on an optimized heat dissipation structure is designed and fabricated. The CW output power of 41.9W, the vertical divergence angle of 18.48° and the thermal resistance of 1.54 K/W are obtained under the injection current of 50A at 20 ℃.
We design a 976nm fiber coupling module with 20 single-emitter diode lasers by ray tracing. Each emitter has an output power of 10 W. This is achieved by beam collimation of the fast and slow axis, fast-axis beam stacking using overlapping mirrors, and polarization beam combining. Through polarization multiplexing, the output power can be nearly doubled with no loss of beam quality. The core diameter of output fiber is 105μm with a numerical aperture (NA) of 0.22. Finally, the simulated result indicates that the module can have an output power over 190W. At the same time, the brightness of 14.43 MW∙cm-2∙str-1 and the coupling efficiency of 95% can be achieved.
High power and high beam quality laser sources are required in numerous applications such as nonlinear frequency conversion, optical pumping of solid-state and fiber lasers, material processing, and others. Here, we theoretically study and demonstrate a tapered laser diode with integrated metalens, which can greatly reduce the lateral far-field divergence of the device. A 980 nm tapered laser diode adopted in this design consists of a power-amplified tapered section and a narrow-ridged section, in which the latter restricts the lateral mode number, and the former is utilized to amplify the output power. The wavefront is carefully reshaped by preparing a one-dimensional (1D) trench metalens near the front facet of the tapered cavity. By precisely designing the length and width of the low refractive index elements at different positions, the approximate spherical wave formed by diffraction in the tapered cavity is transformed into an output plane wave while ensuring high transmittance (>90%), which reduces the divergence of the lateral far-field. The simulation results show that the lateral far-field divergence of the fundamental mode decreases from 3.2° to 2.0° (FWHM) after the integration of the metalens with a 500 μm length of tapered cavity.
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