Lasers used in optical interconnects in data centers require electro-absorption modulators (EAMs) with low energy consumption and cost. In this study, we designed and optimized EAM through numerical simulation. By optimizing the doping concentration in the separate confinement heterostructure (SCH) layer, we achieved an increase in the maximum extinction ratio (ER) from 44 dBm to 64 dBm and a reduction in the driving voltage from 3.8 V to 2.9 V. These results provide theoretical support for further reducing the energy consumption and cost of EAM in optical communication, especially in the current era of escalating data volume.
Distributed Feedback (DFB) semiconductor lasers with low Relative Intensity Noise (RIN) are in demand for high-power and narrow-linewidth applications. However, there is a lack of research on the compatibility of these features, together with RIN degradation at high temperature. In this paper, the RIN characteristics of InGaAsP multi-quantum-well DFB lasers are studied through theoretical calculation and numerical investigation, the results of which are very close. Based on numerical simulation, the epitaxy layers and optical cavity structures of DFB lasers are optimized to improve the RIN performance. The simulation results show that a high-power laser with an output power up to 400 mW and a narrow-linewidth laser with a linewidth below 300 kHz can obtain a peak RIN below -166 dB/Hz and -160 dB/Hz from 0.1 to 20 GHz, respectively, meeting the requirements of light sources for microwave photonics system and coherent optical transceiver system. In terms of thermal effect, buried heterostructure lasers could effectively mitigate the deterioration of RIN compared to ridge waveguide lasers due to better temperature characteristics.
Optical phased array has the advantages of low cost, small size, and high stability. It has broad application prospects in Lidar, free space optical communication, and so on. Among all of them, SiN photonic integrated circuit platforms have received much research. Compared to Si, SiN has smaller optical nonlinear effects and waveguide losses, allowing higher optical power to be emitted. However, the refractive index of SiN is smaller than Si. The pitch of SiN-based waveguides and waveguide grating antennas is larger to reduce crosstalk. This results in a smaller field of view for SiN optical phased arrays and reduces the power ratio of the main lobe to the total emission. In this work, we spaced two SiN waveguides with different propagation constants to reduce the coupling strength between adjacent waveguides. In the range of 1500 nm to 1600 nm, the crosstalk is smaller than -29 dB at the waveguide pitch of 2 μm. In this case, the field of view of the optical phased array reaches 43.89° × 8.47° (ψ × θ). For the optical phased array with 512 channels and a 1 mm long antenna, the divergence angle is 0.078° × 0.086° (Δψ × Δθ). The small spot achieves higher resolution and high point cloud density.
We propose a 128-channel SiN-Si dual-layer optical phased array (OPA) chip based on SOI substrate. It combines the low loss characteristics of SiN with the excellent modulation characteristics of Si. Compared with a Si single-layer OPA chip, it avoids the problem of high waveguide loss in the case of high input optical power due to the strong nonlinear absorption effect of Si. Therefore, our double-layer OPA has lower overall waveguide loss and can achieve high output power, which is conducive to long-distance detection. When it works, the beam is emitted from the end faces of its waveguides, with a radiation efficiency over 94%. Since the center spacing of the waveguides in the antenna area is close to the sub-micron scale, a large scanning range of 100.4° is achieved.
Si-based photonic integrated circuit is developing rapidly and has been widely used, such as optical communication, optical neural network, lidar and so on. However, Si has strong optical nonlinear effects, which limits the maximum transmitting optical power. It needs numbers of semiconductor optical amplifiers to expand the scale of the photonic integrated circuit because of the limited input optical power, which increases the complexity and cost of the Si-based photonic integrated circuits. Therefore, with much lower the waveguide loss and optical nonlinear effects than Si, SiN waveguide is able to transmit higher optical power and has received a lot of research. In this paper, a grating coupler based on SiN-Si dual-layer structure is proposed. It is composed of a layer of Si grating above the SiN waveguide layer. In the case of coupling from grating coupler to single-mode fiber, the minimum coupling loss is about -1.07 dB at 1563.5 nm, and the 1 dB bandwidth is over 100 nm. As to coupling from single-mode fiber to grating coupler, the minimum coupling loss is about -2.53 dB at 1553.4 nm, and the 1 dB bandwidth is about 65 nm. With the proposed grating coupler, it is able to effectively reduce the coupling loss between the single-mode fiber and the chip, increase the working bandwidth, and achieve higher input power. It is very helpful to reduce the complexity and cost of Si-based photonic integrated circuits, because of the reduced requirements for the number of semiconductor optical amplifiers. This will be useful in Si-SiN hybrid integration and SiN-based photonic integrated circuits.
We propose and numerically investigate a double-cladded athermal waveguide structure aiming at broadband low anomalous dispersion operation. Single-crystal aluminum nitride (AlN) is the core of the waveguide, cladding with silicon oxide (SiO2) and titanium dioxide (TiO2). TiO2 with a negative thermo-optic coefficient (TOC) is used to realize material thermal compensation for AlN. By optimizing the waveguide structure parameters, it shows a near-zero broadband effective TOC, ±4×10-6 /K over a 1770-nm bandwidth from 1830 to 3600 nm. Besides, it also has low anomalous dispersion, from -20 to 20 ps/nm/km in the same wavelength range. Different with the conventional strip waveguide, the waveguide is a double cladded structure, which is easy to fabricate in practice. Furthermore, this structure will not damage the single crystal state of aluminum nitride, maintaining its original excellent optical properties.
We propose an optical beam scanner based on an on-chip 1×100 micro-ring optical switch array. By adopting a combination of optical switch array and lens system, it can achieve beam steering. It uses a simple control circuit to achieve fast beam scanning. The simulation shows that its emission efficiency exceeds 95%, which is conducive to long distance scanning and detection. All the components of this scanner can be fabricated on SOI substrate except for the optical lens, so its cost is low and the overall size of the device can be greatly reduced .In addition, since there are no moving parts in our scanner, it has advantages in performance and service life compared with mechanical optical beam steering devices. These advantages make our scanner is promising in light detection and ranging (LiDAR) field and free space optical communication field.
For constructing functional photonic integrated circuits, it is expected to incorporate an efficient and compact laser source into the complementary metal-oxide-semiconductor platform. Monolithic integration of III-V submicron lasers on patterned SOI substrates by means of the aspect ratio trapping method is a promising solution. Here, we have designed submicron lasers with reversed ridge waveguides on patterned Si/SOI substrates by three dimensional finite difference time domain simulation, effectively confining the light into the submicron lasers without removing the top Si layer. The reversed ridge waveguide structure can be formed by extending the III-V materials out of the SiO2 trench. The high-quality InP reversed ridge waveguide epitaxial structures have been obtained. The results of the simulations show that the optical leakage loss is reduced to the order of 10-2. This provides a new approach to develop the silicon-based submicron lasers emitting at the telecom bands.
We have designed electrically pumped sub-micron lasers on the SOI substrates, and proposed to incorporate InP tunnel junctions into sub-micron lasers to reduce carrier absorption loss. Numerical simulations show that the sub-micron laser is able to support a stable optical guide mode with a metal absorption loss of 2.13 dB/cm. And after doping, carrier absorption loss of the sub-micron laser without a tunnel junction is 11.67 dB/cm while carrier absorption loss of the sub-micron laser with InP tunnel junction is 6.72dB/cm. By incorporating InP tunnel junction, carrier absorption loss of the sub-micron laser is reduced by 42% so that a lower lasing threshold is obtained. The optimization of metal absorption loss and carrier absorption loss are of great significance for electrically pumped lasing, which promotes the realization of silicon-optical full integration
Epitaxial growth of III-V compound semiconductors on Si has attracted significant attention for many years due to the potential for monolithic integration of III-V based optoelectronic devices with Si integrated circuits. There are three major problems for GaAs monolithic epitaxy on Si, respectively the large lattice mismatch, the difference in thermal expansion coefficient, and growth of a polar material on a nonpolar substrate. Various dislocation reduction techniques have been proposed, such as graded SiGe buffer layers, thermal cycles annealing (TCA), and strained-layer superlattices (SLs) as dislocation filters. Unfortunately, these methods generally require relatively thick epitaxial layers and/or complex epitaxial process. This study relates to the heteroepitaxy of GaAs on nanopatterned Si substrates using the selective aspect ratio trapping method. The dislocations originally generated at the GaAs/Si interface are mostly isolated by the SiO2 side wall. High-quality GaAs nanowires have been grown on Si(001) substrates by metal-organic chemical vapor deposition. A method of two-step epitaxy of GaAs is performed to achieve a high-quality GaAs layer with a 217 arcsec narrow FWHM of HRXRD. Material quality was confirmed by Scanning electron microscope (SEM) and transmission electron microscopy (TEM). We also simulated the distribution of the light field on the nanoscale GaAs layer surround by Ag films used the FDTD method. The light field confined well in the 250nm width GaAs nanowire which can be used in the nanolasers on Silicon as light sources.
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