III-V-on-silicon photonic devices for optical communication and sensing

In the paper, we review our work on heterogeneous III-V-on-silicon photonic components and circuits for applications in optical communication and sensing. We elaborate on the integration strategy and describe a broad range of devices realized on this platform covering a wavelength range from 850 nm to 3.85 μm

Heterogeneous Integrated Photonic Transceiver on Silicon

The demand for high-speed and low-cost short-distance data links, eventually for chip-level optical communication, has led to large efforts to develop high density photonics integrated circuits (PICs) to decrease the power consumption and unit price. Particularly, silicon based photonic integration promise future high-speed and cost-effective optical interconnects to enable exascale performance computers and datacenters. High-level integration of all photonics components on chip, including high speed modulators and photodetectors, and especially lasers, is required for scalable and energy efficient system topology designs. This is enabled by silicon-based heterogeneous integration approach, which transfers different material systems to the silicon substrate with a complementary metal–oxide–semiconductor (CMOS) compatible process. In this thesis, our work focuses on the development of silicon photonic integrated circuit in the applications of high speed chip level optical interconnects. A full library of functional devices is demonstrated on silicon, including low threshold distributed feedback (DFB) lasers as a low power laser source; high extinction ratio and high speed electroabsorption modulators (EAM) and ultra-linear Mach-Zehnder interferometer (MZI) modulators for signal modulation in the data transmitter; high speed photodetectors for the data receiver; and low loss silicon components, such as arrayed waveguide grating (AWG) routers and broadband MZI based switches. The design and characterization of those devices are discussed in this thesis. A highly integrated photonic circuit can be achieved with co-design and co-process of all types of functional photonic devices. Selective die bonding method is performed to integrate multiple III-V dies with different band-gap onto a single photonic die. A reconfigurable network-on-chip circuit was proposed and demonstrated, with state-of-the-art high-speed silicon transceiver chip. With over 400 active and passive components heterogeneously integrated on silicon, photonic circuit with multiple- wavelength-division multiplexing (WDM) transceiver nodes achieved a total capacity up to 8×8×40 Gbps. This high capacity and dense integrated heterogenous circuit shows its potential as a solution for future ultra-high speed inter- and intra-chip interconnects

CMOS Integration of High Performance Quantum Dot Lasers For Silicon Photonics

Integration of III-V components on Si substrates is required for realizing the promise of Silicon Photonic systems. Specifically, the direct bandgap of many III-V materials is required for light sources, efficient modulators and photodetectors. Several different approaches have been taken to integrate III-V lasers into the silicon photonic platform, such as wafer bonding, direct growth, butt coupling, etc. Here, we have devised a novel laser design that overcomes the above limitations. In our approach, we use InAs quantum dot (QD) lasers monolithically integrated with silicon waveguides and other Si photonic passive components. Due to their unique structures, the QD lasers have been proven by several groups to have the combination of high temperature stability, large modulation bandwidth and low power consumption compared with their quantum well counterparts, which makes it an ideal candidate for Si photonic applications. The first section of this dissertation introduces the theory and novelty of QD lasers, the DC and RF characterization methods of QD lasers are also discussed. The second section is focused on the growth of QD gain chip which a broadband gain chip based on QD inhomogeneous broadening properties was demonstrated. In third section, the lasers devices are built on Si substrate by Pd wafer bonding technology. Firstly, a ridge waveguide QD laser is demonstrated in this section which have better heat dissipation and lower threshold current compared to the unbonded lasers. In section four, a on Si comb laser is also developed. Due to inhomogeneous broadening and ultrafast carrier dynamics, InAs quantum dots have key advantages that make them well suited for Mode-locked lasers (MLLs). In section five, a passively mode-locked InAs quantum dots laser on Si is achieved at a repetition rate of ~7.3 GHz under appropriate bias conditions. In section six, a butt-joint integration configuration based on QD lasers and silicon photonics ring resonator is tested by using to translation stage. In order to achieve the on chip butt-joint integration, an on chip laser facet was created in section seven. A novel facet etching method is developed by using Br-ion beam assist etching (Br-IBAE). In section eight, a Pd-GaAs butt-joint integration platform was proposed, a hybrid tunable QD laser which consist of a QD SOA gain chip butt joint coupled with a passive Si3N4 photonic integrated circuit is proof of concept by using an external booster SOA coupled with a Si3N4 ring reflector feedback circuit. The final section summarized the work discussed in this thesis and also discussed some future approaches by using QD lasers integrated with silicon photonics integrated circuits based on the Pd-GaAs wafer bonding butt-joint coupled platform

Widely-tunable and ultra-stable hybrid-integrated diode lasers

This thesis describes our investigation into diode lasers based on hybrid integration with frequency-selective waveguide feedback circuits. Deploying intra-cavity ring resonators as feedback filters, implemented using low-loss Si3N4 waveguides, enables single-mode laser operation with wavelength tunability over very wide ranges. Using high-Q ring resonators for cavity length extension is also very effective for improving the laser’s short-term frequency stability, which shows as an ultra-narrow intrinsic (Schawlow-Townes) linewidth. We demonstrate in this thesis that these lasers are also continuously tunable, that the spectral coverage can be extended from the infrared to the visible range, and that these lasers can be frequency locked to optical references to greatly enhance their long-term frequency stability

Integrated Pockels Laser

The development of integrated semiconductor lasers has miniaturized traditional bulky laser systems, enabling a wide range of photonic applications. A progression from pure III-V based lasers to III-V/external cavity structures has harnessed low-loss waveguides in different material systems, leading to significant improvements in laser coherence and stability. Despite these successes, however, key functions remain absent. In this work, we address a critical missing function by integrating the Pockels effect into a semiconductor laser. Using a hybrid integrated III-V/Lithium Niobate structure, we demonstrate several essential capabilities that have not existed in previous integrated lasers. These include a record-high frequency modulation speed of 2 exahertz/s (2.0$\times$10$^{18}$ Hz/s) and fast switching at 50 MHz, both of which are made possible by integration of the electro-optic effect. Moreover, the device co-lases at infrared and visible frequencies via the second-harmonic frequency conversion process, the first such integrated multi-color laser. Combined with its narrow linewidth and wide tunability, this new type of integrated laser holds promise for many applications including LiDAR, microwave photonics, atomic physics, and AR/VR

Hybrid integrated semiconductor lasers with silicon nitride feedback circuits

Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth as well as compatibility for embedding into integrated photonic circuits are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si3N4 in SiO2) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around 1.55 um wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser.Comment: 25 pages, 16 figure

Damping of relaxation oscillations,photon-photon resonance, and tolerance to external optical feedback of III-V/SiN hybrid lasers with dispersive narrow band mirror

We address the stability of a tunable hybrid laser based on a III-V Reflective Semiconductor Optical Amplifier (RSOA) edge-coupled with a Silicon Photonic (SiPh) dispersive mirror through a model of time-delayed algebraic differential equations that accounts for the narrow band mirror. Our results allow to (i) analyze the stability of single mode lasing, (ii) quantify the impact of the mirror bandwidth on the damping of the laser relaxation oscillations and the emergence of photon-photon resonance, and (iii) study the tolerance of the laser to the external optical feedback. Thanks to this analysis, we find a mirror design that gives ultra-high stability up to an external feedback level of −10 dB. The aim of the work is providing a tool for understanding and interpreting the dynamics of these lasers and design configurations for isolator-free operation