Integrated photonic computing promises revolutionary strides in processing power, energy efficiency, and speed, propelling us into an era of unprecedented computational capabilities. By harnessing the innate properties of light, such as high-speed propagation, inherent parallel processing capabilities, and the ability to carry vast amounts of information, photonic computing transcends the limitations of traditional electronic architectures. Furthermore, silicon photonic neural networks hold promise to transform artificial intelligence by enabling faster training and inference with significantly reduced power consumption. This potential leap in efficiency could revolutionize data centers, high-performance computing, and edge computing, minimizing environmental impact while expanding the boundaries of computational possibilities. The latest research on our silicon photonic platform for next-generation optical compute accelerators will be presented and discussed.
This work investigates the effects of the confinement factor on the linewidth enhancement factor in hybrid silicon quantum dot comb lasers, which is a key parameter involved in frequency comb generation. Experiments are performed on two laser devices sharing the same gain material with slightly different cavity designs resulting in different confinement factors. The results highlight that a lower confinement factor leads to a smaller carrier-induced refractive index variation and a larger differential gain, together resulting in a smaller linewidth enhancement factor, which in turn translates into different sets of performance regarding the feedback applications. This paper brings novel insights on the fundamental aspects of quantum dot comb lasers and provides new guidelines of future on-chip light sources for integrated wavelength-division multiplexing applications.
We present a novel technology wherein memristors are heterogeneously integrated with optoelectronic devices on a silicon photonic platform. We present results on memristor integrated microring modulators and lasers with non-volatile memory. Furthermore, multiple devices are combined with optical waveguides to create photonic integrated circuits with neuromorphic computing. By pairing non-volatile memory devices directly with silicon photonics, we can integrate memory, computing, and high-speed optical interconnects all together on the same chip.
Increasing the throughput of a transmitter by scaling out to multiple wavelengths in high bandwidth density links, such as those found in data centers or high performance compute clusters, is beginning to gain traction for two reasons. First, increasing the data rate per wavelength by both increasing the baud rate (>50G) and by increasing the number of bits per symbol (PAM-4) consumes more power and increases latency, from having to use a powerful FEC. Second, a technological advantage, in achieving tight integration of lasers with silicon based photonics, has reduced laser coupling losses and tighter control on laser wavelengths, which in turn allows for greater utilization of the available optical bandwidth. In this talk, we will review our current and past efforts in realizing multi-wavelength laser sources heterogeneously integrated on silicon as a means to generate fully integrated transmitters with bandwidth capacity in excess of 1Tbps over 40 channels. We will also discuss some of the recent results from our MOSCAP microring modulators and Si-Ge/ quantum dot based avalanche photodetectors that enable a fully integrated heater-free compact transceiver. The estimated power consumption for the optical components in such a transmitter is around 1pJ/bit, which is roughly a 10x reduction compared to the state-of-the-art.
On-chip integration of semiconductor lasers have shown a growing interest in recent years, especially for the development of photonic integrated circuits (PICs) which are of paramount importance for high-speed communication within and between data centers, and fast on-board data exchanges. For all these applications, a key challenge remains the stability of the laser sources integrated on a PIC in presence of external optical feedback with the view to avoid integrated bulky and costly optical isolation. In this study, the effects of external optical feedback are investigated in hybrid InAs/InP quantum dot comb lasers on silicon. The design of the cavity includes a semiconductor optical amplifier section, a saturable absorber and an on-chip external cavity incorporating a vertical coupler. We measured the resulting feedback properties with respect to the operation conditions (bias current and voltage) and to the length of the saturable absorber. We show that under most operating conditions, the laser remains stable against optical feedback, only few regimes of operation occur, which either improve or degrade the frequency comb and/or the radio-frequency beatnote power of the laser.
Coherent Ising machines have been proposed as a promising platform for combinatorial optimization. Initial fiber-based, FPGA-assisted instantiations experimentally outperform quantum annealers based on superconducting qubits in speed and energy-efficiency due their ability to have programmable all-to-all connectivity between the Ising nodes. Since then, multiple flavors of coherent Ising machines have been proposed based on silicon photonics. In this talk, we will compare and contrast these integrated Ising machines with their table-top setup counterparts and their upcoming competitors in digital and analog electronics. Moreover, we will explain how large-scale problems can be mapped to small-scale integrated Ising cores.
We present room-temperature continuous-wave lasing of 1.31 μm multi-quantum well lasers on a novel defect-free heterogeneous III-V-on-silicon integration platform. The epitaxially grown laser structure on the platform shows significantly low dislocation density of 9.5×104 cm-2, leading to a minimal threshold current density of 813 A/cm2. These results bring promise to create multi functionalities like source, modulation and detection, etc. on such a defect-free, low-cost, large-scale substrate for Datacom applications.
Optical interconnect is essential for massive data communication in rapidly developed data center and high-performance computing infrastructures. Large bandwidth, high energy efficiency and low latency are intrinsic advantages in optics. But they are also present R&D challenges under new requirements such as low total solution cost and reliable operation in harsh computing environment. Recently we have developed hybrid microring lasers on silicon to enable high integration density, compact chip size, and potentially volume and cost-effective production in a CMOS foundry. Novel structures such as thermal shunts and hybrid metal-oxide-semiconductor (MOS) capacitors were integrated into the laser cavity to allow over 100 oC cw operation and "zero-power" laser wavelength and power control. Special CMOS driver with equalization functionality for direct microring laser modulation with good signal integrality was also designed and fabricated in a 65 nm foundry process. For the first time, we integrated all these designs and chips together to demonstrate a 5-channel hybrid transmitter with 0.5 nm channel spacing and overall 70 Gb/s direct modulation rate. A novel direct photon lifetime modulation with much larger bandwidth than conventional injection current modulation by modulating bias on the MOS capacitor is demonstrated for the first time as well. Finally we review our on-going progress on migrating the similar design from a standard quantum well laser active region to a superior quantum-dot one for further improved temperature and dynamic performance.
Initially, we’ll discuss an SOI based, carrier injection micro-ring modulator. The static optical and electrical characteristics of this device will be reviewed and described. Thermal control and modulation mechanisms with pre-emphasis will be outlined. Automated wafer-lever optical/electrical results from volume foundries (Leti and STMicro) used for PDK/Verilog model development will be reviewed, along with experimental data on direct modulation to 25 Gb/s, crosstalk at various DWDM channel separations, and demonstrations with an external quantum-dot based comb laser with 80 and 50GHz channel spacing.
Following this, our work on directly modulated hybrid quantum-well ring lasers will be reviewed in design, fabrication. Experimental results for modulation at 12.5 Gb/s/channel, integration with MOS capacitor for wavelength control and modulation and a thermal shunt for temperature management will highlight the advantages of this technology that may be exploited. Subsequently, our work on hybrid quantum-dot based comb lasers for on-chip DWDM sources will be discussed in their details of physical operation, demonstrating successful mode-locking and noise-free operation across the 20-80C thermal range. Our work on the integration of on-chip APDs from a CMOS-compatible processes will also be reviewed, demonstrating error-free operation at 12.5 Gb/s and 25 Gb/s with a sensitivity of -26dBm and -16dBm, respectively. The use of APDs will drastically decrease the overall power consumption of the interconnect, lowering total cost of ownership. Finally, our most recent progress on integration of the silicon photonics with CMOS by a flip-chip will be reviewed showing high-speed modulation and thermal control for a multi-channel DWDM transceiver.
The evolution of computing infrastructure and workloads has put an enormous pressure on datacenter networks. It is
expected that bandwidth will scale without increases in the network power envelope and total cost of ownership.
Networks based on silicon photonic devices promise to help alleviate these problems, but a viable development path for
these technologies is not yet fully outlined. In this paper, we report our progress on developing components and
strategies for datacenter silicon photonics networks. We will focus on recent progress on compact, low-threshold hybrid
Si lasers and the CWDM transceivers based on these lasers as well as DWDM microring resonator-based transceivers.
Hybrid silicon platform provides a solution to integrate active components (lasers, amplifiers, photodetectors, etc.) with
passive ones on the same silicon substrate, which can be used for building an optical interconnect system. Owing to the
advantages in footprint, power consumption, and high-speed modulation, hybrid silicon microring lasers have been
demonstrated as a potential candidate for on-chip silicon light source. In this paper we review the progress to improve
the performance of recently demonstrated compact microring lasers with ring diameter of 50 μm. A simple approach to
enhance optical mode and electron-hole recombination, which results in threshold reduction and efficiency improvement
is developed. This is done by appropriately undercutting the multiple quantum well (MQW) region to force carriers to
flow towards the outer edge of the microring for better gain/optical mode overlap. We observe a reduction of the
threshold of over 20% and up to 80% output power enhancement. The model and the experimental results highlight the
benefits, as well as the negative effects from excessive undercutting, including lower MQW confinement, higher modal
loss and higher thermal impedance. A design rule for MQW undercutting is therefore provided. Application as on-chip
optical interconnects is discussed from a system perspective.
In this paper we review the recent progress in developing compact microring lasers on the hybrid silicon platform.
A simplified self-aligned process is used to fabricate devices as small as 15 μm in diameter. The optically-pumped,
continuous wave (cw) devices show low threshold carrier density, comparable to the carrier density to reach material
transparency. In the electrically-pumped lasers, the short cavity length leads to the minimum laser threshold less than 5
mA in cw operation. The maximum cw lasing temperature is up to 65 °C. Detailed studies in threshold as a function of
coupling coefficient and bus waveguide width are presented. Surface recombination at the dry-etched exposed interface
is investigated qualitatively by studying the current-voltage characteristics. Ring resonator-based figures of merits
including good spectral purity and large side-mode suppression ratio are demonstrated. Thermal impedance data is
extracted from temperature-dependent spectral measurement, and buried oxide layer in silicon-on-insulator wafer is
identified as the major thermal barrier to cause high thermal impedance for small-size devices. The demonstrated
compact hybrid ring lasers have low power consumption, small footprint and dynamic performance. They are promising
for Si-based optical interconnects and flip-flop applications.
A compact electrically-pumped hybrid silicon microring laser is realized on a hybrid silicon platform. A simplified, selfaligned,
deep-etch process is developed to result in low-loss resonator with a high quality factor Q>15,000. Small
footprint (resonator diameter=50 μm), electrical and optical losses all contribute to lasing threshold as low as 5.4 mA and
up to 65 °C operation temperature in continuous-wave (cw) mode. Outcoupling- and bus waveguide width-dependent
studies are conducted for optimizing device structure. A simple qualitative study in current-voltage (IV) characteristic
shows that dry etching through active region leads to <3× more leakage current at the same reverse bias than wet etch
counterpart. It indicates a relatively good interface with tolerable surface recombination from deep dry etch. The
spectrum is single mode with large extinction ratio (>40 dB) and small linewidth (<0.04 nm) observed. The unique
bistability operation in ring resonator structure is also demonstrated.
A bending directional coupler is presented to enhance the evanescent coupling between a compact deeply-etched III-V/Si
hybrid microring laser and its small Si bus waveguide. With the present design, one could realize a sufficient evanescent
coupling between the III-V/Si hybrid microring even when the gap between the microring and the bus waveguide is
relatively large gap (~ 400nm). This makes the fabrication easier.
Single wavelength hybrid silicon evanescent lasers are described based on wafer bonding III-V multiple quantum wells
to gratings patterned on a silicon waveguide. Distributed Bragg feedback and distributed Bragg reflector lasers are
demonstrated integrated with passive silicon waveguides showing thresholds as low as 25mA and output powers as high
as 11mW around 1600nm wavelength.
Abstract 100 mm wafer bonding of InP-based structure and silicon-on-insulator wafers is presented with the use of a lowtemperature
(300 °C) O2 plasma-assisted wafer bonding process. An efficient vertical outgassing channels (VOCs) design
is developed to eliminate the fundamental obstacle of interfacial voids in bonding due to intrinsic chemical reactions.
Generated gas species of H2O and H2 can quickly diffuse to VOCs, etched through-holes to buried oxide layer (BOX), and
absorbed by the BOX layer owing to the open network structure and large gas permeability. The interfacial void density is
reduced from 55,093 cm-2 down to 3 cm-2, more than five orders of magnitude reduction for appropriate design of VOCs.
Uniform patterning of VOCs leads to no outgassing "dead zone" across the entire bonding area, and decrease of the
thermal mismatch-induced interfacial strain potentially as well, which both result in the wafer scale-independent bonding.
In addition, we present distributed feedback silicon lasers realized on the hybrid silicon evanescent platform. The laser
operates continuous wave with a single mode output at 1600 nm. A continuous wave (CW) low threshold of 25 mA with a
maximum output power of 5.4 mW is demonstrated at 10 °C. The obtained side mode suppression ratio of 50 dB, 3.6
MHz linewidth, and over 100 nm single mode operation band are comparable to those of commercial III-V DFB devices.
These highly single mode lasers may find applications in computer interconnect.
A nonselective wet thermal oxidation technique for AlGaAs-containing heterostructures has been shown to enable the
fabrication of a variety of novel high-efficiency, high-power GaAs-based in-plane laser devices. Applied in conjunction
with a deep anisotropic dry etch, nonselective oxidation yields a simple, self-aligned high-index-contrast (HIC) ridge
waveguide (RWG) structure. The native oxide grown directly on the waveguide ridge simultaneously provides excellent
electrical insulation, passivation of the etch-exposed bipolar active region, and a low refractive index cladding, leading
to numerous laser performance benefits. The resulting strong lateral optical confinement at the semiconductor/oxide
interface (with refractive index contrast &Dgr;n~1.7) enables half-racetrack ring resonator lasers with a record small 6 &mgr;m
bend radius. A nearly circularly-symmetric output beam is demonstrated on narrow w=1.4 &mgr;m aperture width straight
stripe-geometry lasers with single spatial and longitudinal mode total power output of ~180 mW at 228 mA (9x
threshold). With the complete structural elimination of lateral current spreading, the excellent overlap of the optical field
with the gain region provides high slope efficiency performance (ranging from >1.0 W/A at w=1.4 &mgr;m to 1.3 W/A for
w=150 &mgr;m broad area stripes) for 300 K cw operation of unbonded, p-side up 808 nm InAlGaAs graded-index separate
confinement heterostructure (GRINSCH) active region lasers. Using the direct thermal oxidation of a dilute nitride
GaAsP/InGaAsN MQW active region, 1.3 &mgr;m emission GaAs-based HIC RWG lasers exhibit a >2X threshold reduction
and kink-free operation relative to conventional low-confinement devices. Other recent progress on the application of
nonselective oxidation to GaAs-based semiconductor lasers will be reported.
A simple, novel self-aligned deep etch plus wet thermal oxidization process is demonstrated which enables high-index-contrast (HIC) ridge waveguide (RWG) lasers fabricated in a high-efficiency, high-power AlGaAs/InAlGaAs/GaAs graded-index separate confinement heterostructure to operate with a curved half-ring resonator geometry having a bend radius as low as 10 μm. A wet thermal oxidation process modified through addition of <1% O2 to the N2 carrier gas is shown to smooth the sidewall roughness of etched AlGaAs ridge structures 10-100 fold as the oxidation front progresses inward. The reduction of propagation scattering loss due to the reduced sidewall roughness is examined. The thermal oxide grown on the deeply-etched RWG sidewalls and base also provides electrical isolation from the contact metallization, resulting in a simplified, self-aligned process, and yields a RWG structure which effectively prevents current spreading. The thermal oxide appears to be of sufficiently high quality to passivate the etched active region surface based on a comparative analysis of straight RWG lasers of varying stripe widths (w=5 to 150 μm) passivated with native-oxide vs. PECVD-deposited SiO2. For example, at w<15 μm, the SiO2-insulated devices have ~2X higher threshold current densities than the native-oxide devices for comparable bar lengths. The resulting high lateral optical confinement factor at the semiconductor/oxide interface (Δn=1.69) significantly enhances the laser gain and efficiency. A native-oxide-defined straight laser (w=7 μm, L= 452 μm) operates cw (300 K, unbonded, p-side up) with a threshold current of Ith=21.5 mA (Jth=679.5 A/cm2) and slope efficiency of 1.19 A/W (differential quantum efficiency = 78%) at a wavelength of ~813 nm.
A method and the device for obtaining a high peak output power laser with the ns-regime pulse are presented. A Q-switched laser with a novel configuration and a special Q-switched method for the resonator energy storage are proposed. We put a piece of glass with a small hole and special parameters into the resonator which is composed of two totally reflective mirrors in order to obtain the coupling output and realize the step alternation of Q value from "1" to "0" in the resonator. The photons emit out ofthe resonator after a transmission back and forth so as that the output laser pulses with a few ns lifetime are obtained. Simultaneously, the output laser distributes with a circle-axisymmetic pattern and demonstrates good space-transmission and focusing characteristics.
A novel technique and equipment for the diagnosis and treatment ofthe gastric cancer using violet laser to stimulate the traditional Chinese medicine photosensitizer are proposed. The photosensitizer's feature that it can gather together selectively inside the tumor tissues is utilized to test and treat the early-stage gastric cancer. The characteristic absorption spectrum and fluorescence emission spectrum of the traditional Chinese medicine photosensitizer are measured, and two violet light sources matching with the spectrums are proposed as well. One is "Hg-Xe" lamp with a special configuration at 433nm at the peak power, and the other is violet LD with a wavelength 405nm at the peak power, which exactly matches the absorption peak ofthe traditional Chinese medicine photosensitizer.
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