We present a model and a rigorous method to calculate the transmission coefficient of silicon micro-rings with complex waveguide cross-section including non-linear effects and self-heating, with very short simulation times. The method is applied to the design of MRRs in the SISCAP platform with high Q and reduced non-linearity, namely due to two photon absorption and free carrier absorption. We demonstrate that the free carrier diffusion in rib waveguides and Shockely-Read-Hall recombination play a fundamental role in reducing the impact of non-linearities in the ring.

Replacing conventional electrical interconnects with optical counterparts at on-board and in-package length scales requires compact photonic integrated circuits (PICs) capable of scaling to aggregate capacities of 1Pbps with 0.1pJ/bit energy consumption at a range of ambient temperatures [1]. Photonic input-output can easily wavelength division multiplex (WDM) over enormous bandwidths without incurring any extra propagation loss; this allows staggering single line rates while using modest channel rates, which alleviates driver/receiver implementation. Silicon photonics is an attractive platform for this application due to its compact waveguide bends, its scalability and maturity, and its ability to serve as a substrate for other photonic materials that aid in the production of low-loss waveguides along with efficient photodetectors, modulators, and lasers [2]. Figure 25.1.1 illustrates the photonic architecture of a transceiver that serves as a milestone towards this goal. A 20-wavelength quantum dot mode-locked laser (QD-MLL) comb source has its outputs coupled to separate 1Tbps silicon photonic PICs. One technology, microring modulators (MRMs), has emerged from silicon photonics to produce extremely dense PICs. They are resonant based structures which can modulate a single wavelength out of summation of multiple wavelengths, which removes multiplexers from the system. Instead, the transmitter (TX) separates even and odd channels of the comb source to separate ring banks. Each bank has 10 MRM which operate at 26.4Gbps NRZ with a 5.6% forward error correction (FEC) overhead. The modulated odd and even comb lines are interleaved together, and a shallow 210MHz clock signal is encoded onto all channels for optical clock transmission via a variable optical attenuator (VOA). The 500G lanes then pass through quantum dot semiconductor optical amplifiers (QD-SOAs) before being polarization multiplexed onto a single 1T port for propagation over polarization-maintaining (PM) fiber. The receiver (RX) portion of the PIC polarization demultiplexes the two 500G lanes; a small fraction of the power of each channel is sent to a photodiode (PD) that detects the clock signal. The rest of the power is deinterleaved, and then each individual 25G channel is demultiplexed by a corresponding WDM ring resonator filter with a high-speed PD receiver on its drop port. The RF driver for the transceiver is flip chip bonded directly to the PIC to conserve energy. Additionally, the ring resonator filters in the PIC require circuitry to actively align themselves to the QD-MLL comb lines; 3D integration is used to reduce footprint.

The architecture and component technology of a low power,high capacity,short reach optical interconnect are detailed.Measurements from high-performance 300 mm silicon photonics components that comprise the system are shown,along with a quantum-dot mode-locked laser 20-channel comb source with free space wall plug efficiencies up to 17％,advanced packaging techniques for 3D silicon photonic-electronic integration,and schematics for integrated electronics that control the photonic integrated circuits.Techniques for operating such a system in the presence of changing ambient temperature are addressed.Experiments on a 1 Tbps design are conducted with an optical link experiment indicating sub-picojoule/bit energy consumption at scale.

We report pump-probe experiments for measuring free carrier lifetime in Si and Si/poly-Si microrings and compare results with trap-assisted Shockley-Read-Hall recombination model.

A means of athermalizing unbalanced Mach-Zehnder interferometers on a 300 mm silicon photonics foundry platform utilizing Si and SiN layers to produce the path imbalance is demonstrated. This technique can be applied to all other forms of finite impulse response filters, such as arrayed waveguide gratings. Wafer scale performance of fabricated devices is analyzed for their expected performance in the target application: odd-even channel (de)-interleavers for dense wavelength division multiplexing links. Finally, a method is proposed to improve device performance to be more robust to fabrication variations while simultaneously maintaining athermality.

A high-power, single-mode laser structure based on screening of supermodes in vertically coupled waveguides is proposed and demonstrated in the $1.3 \mu \text{m}$ wavelength range. This supermode-screening (SuMoS) laser operates in a single large mode with low ellipticity that is ideal for optical coupling and high optical power at the facet. Fabricated Fabry-Pérot lasers demonstrated low loss ( $\sim $ 1 cm $^{-1}$ ), high power ( $>$ 500 mW), reasonable power conversion efficiency ( $>$ 20%), and good coupling to a lensed optical fiber ( $>$ 80%).

We report pump-probe measurements of time resolved optical transmission spectra of Si and Si/poly-Si microrings after high free carrier densities have been generated by two-photon absorption of the pump pulse. From measurements, we can extract the recovery dynamics of free carrier absorption, refractive index dispersion, generated free carriers and finally the effective initial free carrier lifetimes. The method is validated by comparing modelling and simulations with measurements; the obtained results are in very good agreement with what predicted by the Shockley-Read-Hall recombination model for trap assisted recombination. We also propose a method for determining the empirical relations for free carrier absorption and refractive index dispersion in poly-Si waveguides.

A detailed description of the non-linear effects in silicon is needed when designing ring resonators in the silicon platform. The optical field propagating in the ring waveguide is strongly absorbed due to two-photon-absorption (TPA) and free-carrier-absorption (FCA), which become more prominent with increasing the input power in the ring. We present a new approach for the modelling of non-linear effects in silicon based ring resonators. We have numerically solved the non-linear problem coupling the variation of refractive index and loss due to TPA, FCA , self-heating and Shockley-Read-Hall (SRH) theory for trap-assisted recombination process. The model is validated by reproducing experimental measurements on a ring and a racetrack resonator having different Q-factors and waveguide cross-sections. As a result, we show that the SRH recombination is the origin of the dependence of free carrier lifetime on the power circulating in the ring and how this dependence is affected by the surface trap density and trap energy level. The model is then applied to the calculation of the maximum power that can incident the silicon rings designed for the Si PIC mirror of a hybrid III-V/Si widely tunable laser.

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.

We study the stability of a hybrid laser source consisting of a III-V reflective semiconductor optical amplifier (RSOA) edge-coupled to a silicon photonic mirror, based on two coupled high-Q microring resonators, providing a narrow band effective reflectivity. We simulate the laser dynamics through a model of time-delayed algebraic equations accounting for the frequency-selective mirror reflectivity, demonstrating single-mode emission, self-pulsing, and turbulent regimes. Further, we identify the regions of higher CW operation in terms of bias current and laser detuning with respect to the reflectivity peak. Finally, we test the CW laser stability with respect to optical feedback, mimicking the effect of spurious back-reflections from the passive parts of the circuit, and demonstrate ultra-stable CW operation for a sizeable range of detuning.

We report on how external cavity III-V/SiN hybrid lasers operate in regimes of ultra-damped relaxation oscillations or in CW unstable dynamical regimes (self-pulsing or approaching turbulence) as a consequence of mirror dispersion, non-zero linewidth enhancement factor, and four-wave mixing in the gain medium. The impact of the dispersive mirror bandwidth and different mirror effective lengths on the laser tolerance to external optical feedback is also discussed.

We report how external cavity III-V/Si hybrid lasers operate in regimes of ultra-damped relaxation oscillations or in turbulent and self-pulsing regimes. The different regimes are reached by detuning the lasing wavelength respect to the mirror effective reflectivity peak and are the consequence of the dispersive narrow band reflectivity of the silicon photonics mirror, the linewidth enhancement factor and four-wave mixing in the gain medium.

We report how external cavity III-V/Si hybrid lasers operate in regimes of ultra-damped relaxation oscillations or in unstable regimes as consequence to the dispersive mirror, non-zero linewidth enhancement factor and four-wave mixing in the gain medium. Tolerance to external optical feedback is also discussed.

We present a design of a tunable hybrid laser based on III-V Reflective Semiconductor Optical Amplifier (RSOA) and Silicon Photonics (SiPh) external mirror that represents a good trade off between high Wall-Plug Efficiency (WPE) and high tolerance to optical feedback caused by unwanted back reflections from the rest of the SiPh chip. The sensitivity to optical feedback of different configurations, an important issue in many SiPh applications, is evaluated through the calculation of the critical feedback level based on an effective Lang-Kobayashi model and the main results are validated through numerical simulations of laser dynamics. We conclude that hybrid lasers with long effective external cavities typically designed to reduce the laser linewidth can be also exploited to improve the tolerance to spurious optical feedback.

We compare the design of three different single mode laser structures consisting in a Reflective Semiconductor Optical Amplifier coupled to a silicon photonic external cavity mirror. The three designs differ for the mirror structure and are compared in terms of SOA power consumption and side mode suppression ratio (SMSR). Assuming then a Quantum Dot active material, we simulate the best laser design using a numerical model that includes the peculiar physical characteristics of the QD gain medium. The simulated QD laser CW characteristics are shown and discussed.

We present a novel reconfigurable comb laser design that enables channel sparing, and demonstrate its functionality in a III-V/Si external cavity configuration. The laser is comprised of a single shared tunable Si ring mirror Vernier-paired with an array of tunable channel ring filters each coupled to their respective reflective semiconductor optical amplifier. This comb laser is not only tunable, capable of shifting all comb lines together, but it is flexible, able to change the spacing of channels in the comb within a fixed grid defined by the ring mirror. This flexibility results in features not previously demonstrated in a comb, such as mixed channel spacing and channel sparing capability. This is a practical candidate for flexible, scalable wavelength division multiplexed links targeting the next generation of data centers for the cloud.

We present a novel 3.3-μm radius ring modulator design with dramatically reduced resonance wavelength variations. By implementing a multi-mode waveguide design for the ring waveguides, phase errors from processing non-idealities in waveguide width and etching depth are significantly reduced. Measured resonance wavelengths from four 200-mm wafers fabricated in a commercial 130-nm CMOS foundry showed a total of ~5-nm peak-to-peak variation, which is only about 1/6 of the free spectral range of the ring design. With this tighter control over the absolute resonance positions, the tuning range and tuning power requirements of the ring modulators can be significantly reduced, which in turn enhances their functionality for applications in high density, energy-efficient high-performance computing systems.

A 1550nm external-cavity hybrid III-V/SOI laser with a room-temperature threshold current of 18mA and output powers up to 4mW was demonstrated with a novel assembly technique. An edge-coupled 1x6 laser array was passively aligned with sub-micron positional tolerance.

We report a silicon interposer based 1×4 external-cavity hybrid III-V/Si laser array using a manufacturable back-end-of-the-line integration. All channels are individually-tunable and wavelength-stabilized with a threshold current of 14mA, output powers of >3mW, over 35dB side mode suppression ratio and less then 46kHz linewidth.