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Silicon nitride (SiN) waveguides with ultra-low optical loss enable integrated photonic applications including low noise, narrow linewidth lasers, chip-scale nonlinear photonics, and microwave photonics. Lasers are key components to SiN photonic integrated circuits (PICs), but are difficult to fully integrate with low-index SiN waveguides due to their large mismatch with the high-index III-V gain materials. The recent demonstration of multilayer heterogeneous integration provides a practical solution and enabled the first-generation of lasers fully integrated with SiN waveguides. However, a laser with high device yield and high output power at telecommunication wavelengths, where photonics applications are clustered, is still missing, hindered by large mode transition loss, non-optimized cavity design, and a complicated fabrication process. Here, we report high-performance lasers on SiN with tens of milliwatts output power through the SiN waveguide and sub-kHz fundamental linewidth, addressing all the aforementioned issues. We also show Hertz-level fundamental linewidth lasers are achievable with the developed integration techniques. These lasers, together with high-Q SiN resonators, mark a milestone towards a fully integrated low-noise silicon nitride photonics platform. This laser should find potential applications in LIDAR, microwave photonics and coherent optical communications. Achieving high output power and low noise integrated lasers is a major challenge. Here the authors experimentally demonstrate integrated lasers from a Si/SiN heterogeneous platform that shows Hertz-level linewidth, paving the way toward fully integrating low-noise silicon nitride photonics in volume using real devices for lasing. [ABSTRACT FROM AUTHOR]

Silicon photonics is advancing rapidly in performance and capability with multiple fabrication facilities and foundries having advanced passive and active devices, including modulators, photodetectors, and lasers. Integration of photonics with electronics has been key to increasing the speed and aggregate bandwidth of silicon photonics based assemblies, with multiple approaches to achieving transceivers with capacities of 1.6 Tbps and higher. Progress in electronics has been rapid as well, with state-of-the-art chips including switches having many tens of billions of transistors. However, the electronic system performance is often limited by the input/output (I/O) and the power required to drive connections at a speed of tens of Gbps. Fortunately, the convergence of progress in silicon photonics and electronics means that co-packaged silicon photonics and electronics enable the continued progress of both fields and propel further innovation in both. [ABSTRACT FROM AUTHOR]

Implementing optical-frequency combs with integrated photonics will enable wider use of precision timing signals. Here, we explore the generation of an octave-span, Kerr-microresonator frequency comb using hybrid integration of an InP distributed-feedback laser and a SiN photonic-integrated circuit. We demonstrate electrically pumped and fiber-packaged prototype systems, enabled by self-injection locking. This direct integration of a laser and a microresonator circuit without previously used intervening elements, such as optical modulators and isolators, necessitates understanding self-injection-locking dynamics with octave-span Kerr solitons. In particular, system architectures must adjust to the strong coupling of microresonator backscattering and laser-microresonator frequency detuning that we uncover here. Our work illustrates critical considerations toward realizing a self-referenced frequency comb with integrated photonics. [ABSTRACT FROM AUTHOR]

Silicon photonics offer a low-cost platform for large-scale RF system integration. Spur-free dynamic range (SFDR) for analog and RF photonic components is limited by electrical and optical characteristics of the p- and n- junction used to produce plasma dispersion. We propose a silicon ring modulator and demonstrate design conditions that balance the phase change between the DC Kerr and plasma dispersion effects to produce a broadband, linear electro-optical conversion. A linear phase shifter is tested within a ring modulator and an SFDR of 98 dB $\cdot$ Hz $^{2/3}$ is measured. With predistortion, the SFDR increases to 108 dB $\cdot$ Hz $^{2/3}$. In addition, the ring supports discrete multitone modulation with 16-QAM subcarriers at a 47 Gbps data rate over a 16 GHz bandwidth. [ABSTRACT FROM AUTHOR]

We present an extensive analysis of the physical mechanisms responsible for the degradation of 1.3- $\mu \text{m}$ InAs quantum dot lasers epitaxially grown on Si, for application in silicon photonics. For the first time, we characterize the degradation of the devices by combined electro-optical measurements, electroluminescence spectra, and current-voltage analysis. We demonstrate the following original results: when submitted to a current step-stress experiment: 1) QD lasers show a measurable increase in threshold current, which is correlated to a decrease in slope efficiency; 2) the degradation process is stronger, when devices are stressed at current higher than 200 mA, i.e., in the stress regime, where both ground-state and excited-state emission are present; and 3) in the same range of stress currents, an increase in the defect-related current components is also detected, along with a slight decrease in the series resistance. Based on the experimental evidence collected within this paper, the degradation of QD lasers is ascribed to a recombination-enhanced defect reaction (REDR) process, activated by the escape of electrons out of the quantum dots. [ABSTRACT FROM AUTHOR]

Silicon (Si) photonics research and development started more than 30 years ago and has intensified in the last 15 years as levels of device functionality, photonic integration, and commercialization have all increased [1]. The key drivers for using Si in photonics arise from the quality of wafers and the superior processing capabilities developed and funded by the microelectronics industry. It has the promise to revolutionize the photonics industry in the same way that CMOS design and processing revolutionized the microelectronics industry, by driving down photonic chip cost while enabling higher levels of photonic integration and functionality. Commercialization, so far, has focused on optical communication (Telecom [2] and data center [3]) and biosensing [4], with a wealth of future application areas, including high-performance computing [5], automotive (lidar) [6], optical switches [7], and artificial intelligence [8]. [ABSTRACT FROM AUTHOR]

Laser gain regions using quantum dots have numerous improvements over quantum wells for photonic integration. Their atom-like density of states gives them unique gain properties that can be finely tuned by changing growth conditions. The gain bandwidth can be engineered to be broad or narrow and to emit at a wide range of wavelengths throughout the near infrared. The large energy level separation of the dot states from the surrounding material results in excellent high-temperature performance and gain recovery at sub-picosecond timescales. The fact that the quantum dots are isolated from each other and act independently at inhomogeneously broadened wavelengths results in ultralow linewidth enhancement factors, highly stable broadband mode-locked lasers, single-section mode locking, and the possibility of reduced crosstalk between amplified signals at low signal injection and enhanced four-wave mixing at high signal injection. The high carrier confinement and areal dot density provide reduced sensitivity to crystalline defects allowing for long device lifetimes even when epitaxially grown on silicon at high dislocation densities. [ABSTRACT FROM AUTHOR]

Heterogeneous silicon photonics using wafer bonding is reaching maturity with commercial products for the data center market being shipped in volume. Here we give an overview of recent research in the area showing record device performance by using the best of both worlds: III–V for light generation and Si for guiding the light. Utilizing the flexibility of the heterogeneous silicon platform, narrow-linewidth widely tunable lasers as well as fully integrated mode locked lasers with record pulse powers and pulse duration were demonstrated. The ability to perform multiple die bonding with optimized epitaxially grown layer stacks was used to realize high-performance photonic integrated circuits both for communications and sensing. In addition to III–V materials, nonreciprocal materials such as, for example, Ce:YIG can be bonded, providing additional functionality such as on-chip isolators and reconfigurable on-chip circulators. On-chip isolation will become necessary with the increase in complexity of photonic integrated chips as photonic components such as lasers are sensitive to feedback effects. [ABSTRACT FROM AUTHOR]

Featured Application: Ultra-low-loss Si waveguide platform for heterogeneous integration with III/V. Integrated ultra-low-loss waveguides are highly desired for integrated photonics to enable applications that require long delay lines, high-Q resonators, narrow filters, etc. Here, we present an ultra-low-loss silicon waveguide on 500 nm thick Silicon-On-Insulator (SOI) platform. Meter-scale delay lines, million-Q resonators and tens of picometer bandwidth grating filters are experimentally demonstrated. We design a low-loss low-reflection taper to seamlessly integrate the ultra-low-loss waveguide with standard heterogeneous Si/III-V integrated photonics platform to allow realization of high-performance photonic devices such as ultra-low-noise lasers and optical gyroscopes. [ABSTRACT FROM AUTHOR]

Abstract: Lithium niobate on insulator (LNOI) technology is revolutionizing the lithium niobate industry, enabling higher performance, lower cost and entirely new devices and applications. The availability of LNOI wafers has sparked significant interest in the platform for integrated optical applications, as LNOI offers the attractive material properties of lithium niobate, while also offering the stronger optical confinement and a high optical element integration density that has driven the success of more mature silicon and silicon nitride (SiN) photonics platforms. Due to some similarities between LNOI and SiN, established techniques and standards can readily be adapted to the LNOI platform including a significant array of interface approaches, device designs and also heterogeneous integration techniques for laser sources and photodetectors. In this contribution, we review the latest developments in this platform, examine where further development is necessary to achieve more functionalities in LNOI integrated optical circuits and make a few suggestions of interesting applications that could be realized in this platform. [ABSTRACT FROM AUTHOR]

Heterogeneous integration enables the construction of silicon (Si) photonic systems, which are fully integrated with a range of passive and active elements including lasers and detectors. Numerous advancements in recent years have shown that heterogeneous Si platforms can be extended beyond near-infrared telecommunication wavelengths to the mid-infrared (MIR) (2–20 μm) regime. These wavelengths hold potential for an extensive range of sensing applications and the necessary components for fully integrated heterogeneous MIR Si photonic technologies have now been demonstrated. However, due to the broad wavelength range and the diverse assortment of MIR technologies, the optimal platform for each specific application is unclear. Here, we overview Si photonic waveguide platforms and lasers at the MIR, including quantum cascade lasers on Si. We also discuss progress toward building an integrated multispectral source, which can be constructed by wavelength beam combining the outputs from multiple lasers with arrayed waveguide gratings and duplexing adiabatic couplers. [ABSTRACT FROM PUBLISHER]

Photonic-integrated circuits fabricated on a heterogeneously integrated silicon platform have demonstrated record levels of integration and communication capacity. As photonic-integrated circuits become larger and more complex, designing and analyzing them demand modeling and simulation methodologies employed in matured electronic design automation. In this paper, the development of compact models for the building blocks of a fabricated optical network-on-a-chip is introduced. These models are implemented in both SPICE-compatible electronics design automation tools and dedicated photonic-circuit simulators. Model validation is conducted at both device and link levels, allowing the circuit designer to study the impact of individual device design on the overall link performance, paving the path for model-based design optimization of photonic-integrated circuits. [ABSTRACT FROM PUBLISHER]

We theoretically analyze the use of fully integrated high- $Q$ ring cavities (intrinsic $Q \sim 1$ million) with widely tunable semiconductor lasers to realize narrow linewidth lasers. Different configurations are studied, including cases where the high- $Q$ cavity is external to the laser cavity and provides filtered optical feedback to the laser cavity and cases where the high- $Q$ cavity is an integral part of the laser cavity. We show that the current heterogeneous silicon platform should allow subkilohertz instantaneous linewidths, and we outline the advantages and disadvantages of different high- $Q$ cavity placements. [ABSTRACT FROM PUBLISHER]

(1) The former tells us that depending on the value of the coefficient X, the optical feedback induced frequency shift can exhibit two different behaviors: in the low feedback regime (X < 1), Eq. (19) has only one solution whereas for X < 1, Eq. (19) has more than one solution due to the increase of external cavity modes (ECM), in a number increasing with X hence increasing the modal competition and laser instabilities. This description is incorrect and thereby should be replaced by a correct description as follows The former tells us that depending on the value of the coefficient I X i , the optical feedback induced frequency shift can exhibit two different behaviors: in the low feedback regime ( I X i < 1), Eq. (19) has only one solution whereas for I X i > 1, Eq. (19) has more than one solution due to the increase of external cavity modes (ECM), in a number increasing with I X i hence increasing the modal competition and laser instabilities. [Extracted from the article]

In this paper, we review the current status of the hybrid silicon photonic integration platform with emphasis on its prospects for increased integration complexity. The hybrid silicon platform is maturing fast as increasingly complex circuits are reported with tens of integrated components including on-chip lasers. It is shown that this platform is well positioned and holds great potential to address future needs for medium-scale photonic integrated circuits. [ABSTRACT FROM PUBLISHER]

The device and integration technology for silicon photonic transmitters are reviewed in this paper. The hybrid silicon platform enables on-chip lasers to be fabricated with silicon photonic circuits and can be integrated in the CMOS back-end flow. Laser arrays from multiple die bonding and quantum well intermixing techniques are demonstrated to extend the spectral bandwidth from the laser array of the transmitter. Two modulator technologies, silicon modulators and hybrid silicon modulators, are also described. [ABSTRACT FROM PUBLISHER]

A hybrid silicon photonic integrated filter is proposed and demonstrated with a novel structure. This filter incorporates a ring resonator in one arm of a Mach–Zehnder interferometer making it possible to obtain a programmable filter response. The optical filter consists of a 5-mm-long delay loop made of low-loss silicon waveguides with integrated thermal modulators resulting in a 0.164-nm free spectral range with absolute phase tunability and gain elements that allow for the tuning of the filter Q factor. The microwave response of this integrated filter is measured and display tunability of 20 GHz. [ABSTRACT FROM PUBLISHER]

We demonstrate high current operation of an evanescently coupled Ge waveguide n-i-p photodetector grown on top of a Si rib waveguide. A 7.4 \mum\,\times \,500 \mum device was found to dissipate 1.003 W of power (125.49 mA at -8 V). 2-D thermal simulations of the device show that the relatively high thermal conductivities of the intrinsic Ge region and the p^+ doped Si layer result in efficient heat transfer and hence, lower absorber temperatures when compared to a similar InP based waveguide photodiode. Additionally, to determine the feasibility of these devices for analog photonic applications, we performed large signal and small signal radio frequency (RF) measurements as well as linearity measurements. At 1 GHz and 40 mA of photocurrent, a third order output intercept point (OIP3) of 36.49 dBm is measured. The maximum RF power extracted at 1 GHz is 14.17 dBm at 60 mA of photocurrent and 7 V reverse bias. [ABSTRACT FROM PUBLISHER]

With this review paper we provide an overview of the main degradation mechanisms that limit the long-term reliability of IR semiconductor lasers for silicon photonics applications. The discussion is focused on two types of laser diodes: heterogeneous III–V lasers bonded onto silicon-on-insulator wafers, and InAs quantum-dot lasers epitaxially grown on silicon. A comprehensive analysis of the reliability-oriented literature published to date reveals that state-of-the-art heterogeneous laser sources share with conventional laser diodes their major epitaxy-related degradation processes, such as the generation of non-radiative recombination centers or dopant diffusion, while eliminating cleaved facets and exposed mirrors. The lifetime of InAs quantum dot lasers grown on silicon, whose development represents a fundamental step toward a fully epitaxial integration of future photonic integrated circuits, is strongly limited by the density of extended defects, mainly misfit dislocations, protruding into the active layer of the devices. The concentration of such defects, along with inefficient carrier injection and excessive carrier overflow rates, promote recombination-enhanced degradation mechanisms that reduce the long-term reliability of these sources. The impact of these misfits can be largely eliminated with the inclusion of blocking layers. [ABSTRACT FROM AUTHOR]

This paper reviews the recent progress of hybrid silicon evanescent devices. The hybrid silicon evanescent device structure consists of III-V epitaxial layers transferred to silicon waveguides through a low-temperature wafer bonding process to achieve optical gain, absorption, and modulation efficiently on a silicon photonics platform. The low-temperature wafer bonding process enables fusion of two different material systems without degradation of material quality and is scalable to wafer-level bonding. Lasers, amplifiers, photodetectors, and modulators have been demonstrated with this hybrid structure and integration of these individual components for improved optical functionality is also presented. This approach provides a unique way to build photonic active devices on silicon and should allow application of silicon photonic integrated circuits to optical telecommunication and optical interconnects. [ABSTRACT FROM AUTHOR]

Quantum Dot Lasers: Directly Modulated Single-Mode Tunable Quantum Dot Lasers at 1.3 µm (Laser Photonics Rev. 14(3)/2020) In article number 1900348, Yating Wan and co-workers demonstrate directly modulated, single-mode, tunable InAs/GaAs quantum dot (QD) lasers at 1.3 µm wavelength range, by combining the advantages of QDs with a special designed half-wave coupled cavity structure. Without involving re-growth steps or sub-wavelength grating lithography, 27-channel wavelength switching was achieved with side-mode-suppression-ratio of around 35 dB and output power of over 9 mW. [Extracted from the article]

Ultra-high-speed photodetectors and printed-circuit antennas construct photonic transmitters. In this letter, we demonstrate a terahertz (THz) photonic transmitter: edge-coupled membrane photonic transmitters based on metal-semiconductor-metal traveling-wave photodetectors, which are fabricated with low-temperature-grown GaAs photoabsorption layers. With a membrane-based and edge-coupled structure, the demonstrated photonic transmitters can eliminate the requirement of Si lenses and attain an over 20 times higher optical-to-THz power conversion efficiency 2 × 10[sup -4] than vertical illuminated photonic transmitters with Si lenses at the same operation frequency. [ABSTRACT FROM AUTHOR]

Mode‐division multiplexing (MDM) is attractive to enhance the link capacity of optical interconnects by using multiple mode‐channels in multimode bus waveguides. As sharp waveguide bends are very important for realizing dense photonic integrated circuits, here ultra‐sharp multimode waveguide bends for MDM systems are proposed and demonstrated by using subwavelength grating waveguide structures on silicon. An ultra‐sharp S‐bend with a radius of 10 µm is realized for the first time to enable a low‐loss and low‐crosstalk MDM optical interconnect with three mode‐channels. For this proposed ultra‐sharp subwavelength grating multimode waveguide bend (SMWB) with a 90° bending angle, the theoretical excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.18–0.22 dB, and 0.3–0.5 dB, respectively, in a wavelength band of 1500–1600 nm. Meanwhile, inter‐mode crosstalks are very low (less than −30 dB) for all mode‐channels. For the fabricated 90°‐SMWB, the excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.2–0.4 dB, and 0.3–0.7 dB while the inter‐mode crosstalk is approximately −22 dB in a wavelength band of 1520–1600 nm. The proposed SMWB is also extended for more than three mode‐channels. An ultra‐sharp multimode waveguide bend with a radius as small as R = 10 µm is realized for the first time by using shallowly etched subwavelength grating structures, which enables a low‐loss and low‐crosstalk mode‐division multiplexing optical interconnect with three mode‐channels. It can be extended for more than three mode‐channels. [ABSTRACT FROM AUTHOR]

In article number 1800149, Lin Chang and co‐workers demonstrate a gallium‐arsenide‐on‐insulator platform for integrated nonlinear photonics. Waveguides on this platform have high nonlinear coefficients, large index contrasts and low propagation losses. Harnessing those properties, a second harmonic generation with a record normalized efficiency is achieved. This work paves a way to ultra‐high performance nonlinear photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Tremendous scientific progress has been achieved through the development of nonlinear integrated photonics. Prominent examples are Kerr frequency comb generation in microresonators, and supercontinuum generation and frequency conversion in nonlinear photonic waveguides. A high conversion efficiency is enabling for applications of nonlinear optics, including such broad directions as high‐speed optical signal processing, metrology, and quantum communication and computation. In this work, a gallium‐arsenide‐on‐insulator (GaAs) platform for nonlinear photonics is demonstrated. GaAs has among the highest second‐ and third‐order nonlinear optical coefficients, and the use of a silica cladding results in waveguides with a large refractive index contrast and low propagation loss for expanded designs of nonlinear processes. By harnessing these properties and developing nanofabrication with GaAs, a record normalized second‐harmonic efficiency of 13 000% W−1 cm−2 at a fundamental wavelength of 2 µm is reported. This work paves the way for high performance nonlinear photonic integrated circuits, which not only can transition advanced functionalities outside the lab through fundamentally reduced power consumption and footprint, but also enables future optical sources and detectors. A gallium‐arsenide‐on‐insulator platform for integrated nonlinear photonics is demonstrated on silicon substrate. Waveguides on this platform have high nonlinear coefficients, large index contrasts, and low propagation losses. By harnessing those properties, a second‐harmonic generation with a record‐normalized efficiency of 13 000% W−1 cm−2 is achieved. This work paves the way to high performance nonlinear photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Silicon photonics enables wafer-scale integration of optical functionalities on chip. Silicon-based laser frequency combs can provide integrated sources of mutually coherent laser lines for terabit-per-second transceivers, parallel coherent light detection and ranging, or photonics-assisted signal processing. We report heterogeneously integrated laser soliton microcombs combining both indium phospide/silicon (InP/Si) semiconductor lasers and ultralow-loss silicon nitride (Si3N4) microresonators on a monolithic silicon substrate. Thousands of devices can be produced from a single wafer by using complementary metal-oxide-semiconductor–compatible techniques. With on-chip electrical control of the laser-microresonator relative optical phase, these devices can output single-soliton microcombs with a 100-gigahertz repetition rate. Furthermore, we observe laser frequency noise reduction due to self-injection locking of the InP/Si laser to the Si3N4 microresonator. Our approach provides a route for large-volume, low-cost manufacturing of narrow-linewidth, chip-based frequency combs for next-generation high-capacity transceivers, data centers, space and mobile platforms. [ABSTRACT FROM AUTHOR]

The article focuses on development of non-linear frequency mixing strategies to approach shift from the electromagnetic (EM) waves, and mentions use of Lithium niobate for frequency mixing due to material properties. Topics discussed include lithium niobate photonics flexibility in EM waves, integrated photonic circuits created by heterogeneous integration of active materials, and role of the confining waveguides in lithium niobate.

Si photonics as an integration platform has recently been a focus of optoelectronics research because of the promise of low-cost manufacturing based on the ubiquitous electronics fabrication infrastructure. The key challenge for Si photonic systems is the realization of compact, electrically driven optical gain elements. We review our recent developments in hybrid Si evanescent devices. We have demonstrated electrically pumped lasers, amplifiers, and photodetectors that can provide a low-cost, scalable solution for hybrid integration on a Si platform by using a novel hybrid waveguide architecture, consisting of III-V quantum wells bonded to Si waveguides. [Copyright &y& Elsevier]