This paper presents a high-directionality optical grating antenna for chip-level LiDAR applications. The antenna, designed on a silicon-nitride-nitride platform, consists of two vertically stacked grating layers with a nitride waveguide layer in between. By optimizing the grating periods, duty cycles, and the relative offset between the grating layers using a particle swarm optimization algorithm, a directionality of 87.8% (0.56 dB) at 1550 nm wavelength and a minimum coupling loss of 1.7 dB were achieved. The performance of the antenna was demonstrated in a chip-to-chip transceiver configuration using a coherent detection system. With a transmitter output power of 10 dBm, the system achieved a signal-to-noise ratio of 17.7 dB and 13.2 dB at screen distances of 20 m and 40 m, respectively. These results highlight the potential of the proposed antenna for long-range, chip-level LiDAR applications.
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.
Optical phased array (OPA) has been widely employed across various applications, including light detection and ranging. Nevertheless, OPA faces significant limitations, such as excessive power consumption, complex control systems, and challenging packaging formats, which hinder its further development. Focal plane arrays (FPAs) have garnered increasing attention due to their absence of these drawbacks. However, FPAs currently face a dilemma as their ranging performance fails to meet application requirements. To address this issue, this paper presents a novel structure featuring small-scale receiving array and high directional antenna design. Utilizing this chip, we showcase a scanning range of 5.98° and a coherent detection capability of 6 meters.
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 great potential in the fields of light detection and ranging, free-space optical communication, laser imaging and biosensors due to their excellent characteristics such as all-solid-state structure, fast scanning speed, good stability, high resolution and low cost. According to the radar equation, the transmit power will directly determine the maximum ranging distance of optical phased arrays. Limited by nonlinear effects and damage threshold, it is difficult to further increase the input optical power of Si-based OPA above 30 dB. Therefore, fully utilizing the input optical power of OPA is an important issue in the research. In this paper, we demonstrate a novel three-layer silicon antenna for OPA, which consists of a upside grating layer, a waveguide layer and a downside grating layer from top to bottom. In the simulation, we found that the upward directivity of the antenna is greater than 60% in a large wavelength range of 1413 nm to 1875 nm. In addition, the maximum upward directivity of the antenna is 94.68% at 1599nm. The above result is beneficial to increase the output power of the phased array and eliminate the blind area in the field of view when the beam is scanned to the point of destructive interference. Overall, the above results show that the design proposed in this paper has great potential for application.
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.
Light detection and ranging (LiDAR) technique is always a building block in the fields of sensing, mapping and autonomous driving navigation. Beam steering devices, which are used for light emission and reception, play a key role in LiDAR system. Lens-assisted beam-steering (LABS) is one of the most competitive candidates among various beam steering technologies. Compared with conventional integrated optical phased array (OPA), LABS unit is with lower optical loss and meanwhile lower control complexity. In this paper, we demonstrate a highly integrated LABS chip based on micro-ring optical switch array with a wide field of view (FoV, 30°×40°) and a narrow beam divergence (<0.1°). A 32×32 micro-ring optical switch array connected with a 1×1024 optical antenna array is integrated in the silicon photonic chip with an overall size of 6×14 mm2. Incident light is routed to one antenna by the micro-ring optical switch array and emitted into the free space, and the emergent light is collimated and steered by a cylindrical lens fixed above the optical antenna array subsequently. On this basis, one-dimensional steering is achieved by switching light to different antennas, while steering in the other dimension is realized via wavelength tuning. Under this circumstance, only two micro-ring switches need to be turned on at one time, leading to a significant reduction of optical loss and control complexity of the proposed chip. Notably, our work demonstrates the feasibility of large-scale integration of optical switch array within LABS chip by adopting compact micro-ring switches, paving a new path for miniatured beam scanners.
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.
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.
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.
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
A room temperature four-channel hybrid laser array was realized by using selective area metal bonding method, which is able to evanescently couple the light from InGaAsP multi-quantum well laser diodes into the slotted silicon waveguide. The output wavelength of this hybrid laser can be accurately tuned to 1538.6 nm, 1540.5 nm 1544.9 nm and 1550 nm through controlling the waveguide width of each channel. A typical threshold current of one channel was of 20 mA and the corresponding side-mode suppression ratio was of 20 dB. Moreover, one advantage of such slotted structures is the ease in fabrication, thus making this type of devices as a promising candidate for wavelength division multiplex in future optical communication system.
Deep subwavelength plasmonic graphene nanoribbon waveguides for telecommunication frequencies are proposed. The mode properties of graphene nanoribbon waveguides with varied chemical potential are numerically investigated in terms of the effective indices and the propagation length of the plasmonic modes. A refractive index as high as 4980 is obtained on the plasmonic mode along the nanoribbon waveguide with a width of 3 nm at a frequency of 190 THz, and the normalized mode area on the scale of 10−8(1/λ0)2. An embedded graphene nanoribbon waveguide was also proposed and it is that the optical characteristic can be tuned by adjusting the chemical potential of graphene. The proposed structure can be a fundamental component of the future integrated plasmonic circuit system.
We investigated the etching process especially for the integrated InGaAs/InP multiquantum-well laser. Two different
ways of etching process were demonstrated, which are RIE followed by selective wet etching and selective wet etching
only. The latter one showed ideal interface between active region and passive waveguide after regrowth. This etching
process is simpler and more effective than the first one. Using this process, we also fabricated a 1.79-μm DBR laser with
350-μm active region and 400-μm passive waveguide. The output power and threshold current and were demonstrated as
a function of temperature. The wavelength tuning characters were investigated with current and temperature changes. It
is demonstrated that this etching process can be successfully used to fabricate integrated photonic devices with
InGaAs/InP materials and the DBR laser can be a candidate for gas sensing system due to the single mode and large
tuning range.
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.
An evanescently-coupled, hybrid InGaAsP-Si laser operating at 1.55 μm is presented by selective area metal bonding (SAMB). The III-V laser, fabricated on a p-InP substrate with a semi-insulating InP:Fe buried heterostructure (BH), serves to provide optical gain. On the SOI wafer, a 3-μm wide and 500-nm high Si waveguide is formed and the bonding metal (AuSn alloy) is selectively deposited in the regions 6 μm away from the Si waveguide on each side. The InGaAsP gain structure is flip-chip bonded onto the patterned SOI wafer using SAMB method which separates laterally the optical coupling area and the metal bonding area to avoid strong light absorption by the bonding metal. The hybrid laser runs with a maximum single-sided output power of 9 mw at room temperature. The slope efficiency of the hybrid laser is about 0.04 W/A, 4 times that of the laser before bonding which indicates that the light confinement is improved after the bonding. The hybrid laser has achieved 10 °C contimuous wave (CW) lasing. A near-field image of the hybrid laser is studied. As the inject current increases, the light spot markedly shifts down to the Si waveguide and covers the Si waveguide region, which demonstrates that the light generated in the III-V active region is coupled into the Si waveguide. This method allows for different III-V devices to be bonded onto any desired places on a SOI substrate. The simplicity and flexibility of the fabrication process and high yield make the hybrid laser a promising light source.
This paper reports on the mode-locked operation of a 980-nm external-cavity passively mode-locked laser with
extremely narrow RF linewidth. Optical pulses with 10-ps pulse duration were generated at a repetition rate of 955 MHz, with an average output power of 39.3 mW – which corresponds to a peak power of 4.1 W, generated directly from the oscillator. The RF spectrum displays a -3dB RF linewidth of only ~40 Hz, as well as a 60-dB dynamic contrast,
revealing the exceptionally low-noise fundamental mode-locked operation of this laser. At a repetition rate of ~1 GHz,
the highest peak power of 5.26 W was achieved, albeit with an increased -3dB RF linewidth of ~100 Hz. The two-section chip incorporated an active region with a dual InGaAs quantum well sandwiched by an asymmetrical waveguide, and was operated at room temperature. By taking advantage of the broad tunability of the repetition rate which externalcavity lasers can afford, we also investigated the limits of stable fundamental mode-locked operation at the lowest repetition rates (or maximum external cavity lengths).
A novel mode-beating DBR laser with dual-mode lasing is fabricated. The DBR laser has four parts, a front gain section, a phase section, a DBR grating section, and a rear gain section. When the current of the front gain section is above the threshold, the device is working in single-mode. Dual-mode lasing can be obtained by adjusting the current of the rear gain section. The power difference between the two modes can be less than 1 dB. An optical down-conversion technique was used to measure the beating frequency. The mode-beating frequency of the two modes is about 93 GHz, and the 3- dB linewidth of the mode-beating RF spectrum of the laser when free-running is about 5 MHz. Moreover, the wavelength of the dual-mode can be tuned synchronously when the current injected into the DBR grating section is adjusted. The wavelength tuning range of the device is at least 3 nm.
A 1.65μm three-section Distributed Bragg Reflective (DBR) laser for CH4 gas sensor was reported. Wide tunable range
covering R3 and R4 methane absorption line manifolds. Wavelength tunable properties and temperature stability were
characterized and analyzed. Several advantages were demonstrated compared with traditional DFB laser in harmonic
detection method.
A dual-depletion-region lumped electroabsorption modulator (DDR-LEAM) based on InP at 1550nm is designed and
fabricated. The measurement results reveal that the dual depletion region structure can reduce the device capacitance
significantly without any degradation of extinction ratio. The simulation results show that the highly doped charge layer
can concentrate almost all of the external applied voltage in MQW region and thus contribute to the identical extinction
ratio curves. The expected 3-dB bandwidth of the DDR-LEAMs using an equivalent circuit model is more than twice
lager than that of the conventional LEAM.
A novel EAM/PD monolithically-integrated optical logic element is presented. 5Gb/s optical logic AND gate operations
at about -2 V for non-return-to-zero (NRZ) signals with8.4dB extinction ratio and16mW absorbed optical power was
demonstrated.
All-optical clock recovery is a key technology in all-optical 3R signal regeneration (Re-amplification, Retiming, and Reshaping) process. In this paper, a monolithic integrated three-section amplified feedback semiconductor laser (AFL) is demonstrated as an all optical clock regenerator. We fabricated a three-section AFL using quantum well intermixing process without regrowth instead of butt-joint process. The tunable characteristics of three-section AFL were investigated, and all optical clock recovery for 40Gb/s return to zero (RZ) 231-1 pseudorandom binary sequence (PRBS) is demonstrated experimentally using AFL with time jitter about 689.2fs.
High performance InGaAsP/InGaAsP strained compensated multiple-quantum-well (MQW) electroabsorption
modulators (EAM) monolithically integrated with a DFB laser diode have been designed and realized by ultra low
metal-organic vapor phase epitaxy (MOVPE) based on a novel butt-joint scheme. The optimization thickness of upper
SCH layer for DFB and EAM was obtained of the proposed MQW structure of the EAM through numerical simulation
and experiment. The device containing 250μm DFB and 170μm EAM shows good material quality and exhibits a
threshold current of 17mA, an extinction ratio of higher than 30 dB and a very high modulation efficiency (12dB/V)
from 0V to 1V. By adopting a high-mesa ridge waveguide and buried polyimide, the capacitance of the modulator is
reduced to about 0.30 pF corresponding to a 3dB bandwidth more than 20GHz.
The narrow stripe selective growth of the InGaAlAs bulk waveguides and InGaAlAs MQW waveguides was first investigated. Flat and clear interfaces were obtained for the selectively grown InGaAlAs waveguides under optimized growth conditions. These selectively grown InGaAlAs waveguides were covered by specific InP layers, which can keep the waveguides from being oxidized during the fabrication of devices. PL peak wavelength shifts of 70 nm for the InGaAlAs bulk waveguides and 73 nm for the InGaAlAs MQW waveguides were obtained with a small mask stripe width varying from 0 to 40 μm, and were interpreted in considering both the migration effect from the masked region (MMR) and the lateral vapor diffusion effect (LVD). The quality of the selectively grown InGaAlAs MQW waveguides was confirmed by the PL peak intensity and the PL FWHM. Using the narrow stripe selectively grown InGaAlAs MQW waveguides, then the buried heterostructure (BH) lasers were fabricated by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good performance characteristics, with a high internal differential quantum efficiency of about 85% and an internal loss of 6.7 cm-1.
Unselective regrowth for fabricating 1.5-µm InGaAsP multiple-quantum well (MQW) distributed-feedback (DFB) buried heterostructure (BH) lasers is developed. The experimental results exhibit superior characteristics, such as a low threshold of 8.5 mA, high slope efficiency of 0.55 mW/mA, circular-like far-field patterns, the narrow linewidth of 2.5 MHz, etc. The high performance of the devices effectively proves the feasibility of the new method to fabricate buried heterostructure lasers.
A novel device of tandem multiple quantum wells (MQWs) electroabsorption modulators (EAMs) monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 mbar) selective area growth (SAG) MOCVD technique. Experimental results exhibit superior device characteristics with low threshold of 19 mA, output light power of 4.5 mW, and over 20 dB extinction ratio when coupled into a single mode fiber. Moreover, over 10 GHz modulation bandwidth is developed with a driving voltage of 2 V. Using this sinusoidal voltage driven integrated device, 10GHz repetition rate pulse with a width of 13.7 ps without any compression elements is obtained.
Width varied quantum wells show a more flat and wide gain spectrum (about 115nm) than that of identical miltiple quantum well. A new fabricating method was demonstrated in this paper to realize two different Bragg grating in an identical chip using traditional holographic exposure. A wavelength selectable DFB laser based on this material grown by MOVPE was presented. Two stable distinct single longitudinal mode of 1510nm and 1530nm with SMSR of 45 dB were realized.
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