Monolithic Photonic Integrated Circuit Research Articles

Silicon-thulium hybrid microdisk lasers with low threshold and wide emission wavelength range.

We demonstrate low-threshold and wide emission wavelength range hybrid-integrated silicon-thulium microdisk lasers based on a pulley-coupled design. The resonators are fabricated on a silicon-on-insulator platform using a standard foundry process and the gain medium is deposited using a straightforward, low-temperature post-processing step. We show lasing in 40- and 60-µm diameter microdisks with up to 2.6 mW double-sided output power and bidirectional slope efficiencies of up to 13.4% with respect to 1620 nm pump power launched to the bus waveguides. We observe thresholds less than 1 mW versus on-chip pump power and both single-mode and multimode laser emission spanning across wavelengths from 1825 to 1939nm. These low threshold lasers with emissions over a > 100 nm range open the door to monolithic silicon photonic integrated circuits with broadband optical gain and highly compact and efficient light sources in the emerging ∼1.8-2.0 µm wavelength band.

Coupling of Photon Emitters in Monolayer WS2 with a Photonic Waveguide Based on Bound States in the Continuum

On-chip light sources are an essential component of scalable photonic integrated circuits (PICs), and coupling between light sources and waveguides has attracted a great deal of attention. Photonic waveguides based on bound states in the continuum (BICs) allow optical confinement in a low-refractive-index waveguide on a high-refractive-index substrate and thus can be employed for constructing PICs. In this work, we experimentally demonstrated that the photoluminescence (PL) from a monolayer of tungsten sulfide (WS2) could be coupled into a BIC waveguide on a lithium-niobate-on-insulator (LNOI) substrate. Using finite-difference time-domain simulations, we numerically obtained a coupling efficiency of ∼2.3% for an in-plane-oriented dipole and a near-zero loss at a wavelength of 620 nm. By breaking through the limits of 2D-material integration with conventional photonic architectures, our work offers a new perspective for light-matter coupling in monolithic PICs.

Three-dimensional inter-layer optical signal transmission realized by a monolithically integrated semiconductor-based carrier transport structure.

In this study, we proposed and demonstrated a brand new type of monolithic photonic devices which realizes the three-dimensional (3D) all-optical switching for inter-layer signal transmission. This device is composed of a vertical Si microrod which serves as optical absorption material within a SiN waveguide in one layer and as an index modulation structure within a SiN microdisk resonator lying in the other layer. The ambipolar photo-carrier transport property in the Si microrod was studied by measuring the resonant wavelength shifts under continuous-wave laser pumping. The ambipolar diffusion length can be extracted to be 0.88 µm. Based on the ambipolar photo-carrier transport in a Si microrod through different layers, we presented a fully-integrated all-optical switching operation using this Si microrod and a SiN microdisk with a pump-probe technique through the on-chip SiN waveguides. The switching time windows for the on-resonance operation mode and the off-resonance operation mode can be extracted to be 439 ps and 87 ps, respectively. This device shows potential applications for the future all-optical computing and communication with more practical and flexible configurations in monolithic 3D photonic integrated circuits (3D-PICs).

Monolithic Photonic Integrated Circuit Based on Silicon Nitride and Lithium Niobate on Insulator Hybrid Platform

Monolithic Photonic Integrated Circuits In article number 2200121, Yonghui Tian, Guanghui Ren and co-workers experimentally demonstrate a monolithic photonic integrated circuit (PIC) for high-speed data communication application on the thin-film lithium niobate on insulator (LNOI) platform. The proposed PIC shows high data modulation rate of 70 Gbps for single channel and the total data throughput reaches up to 280 Gbps, which opens up new avenues for achieving large-scale monolithic integration on the LNOI platform in future.

A Review of Photonic Systems-on-Chip Enabled by Widely Tunable Lasers

Photonic Integrated Circuits (PICs) on indium phosphide have matured significantly over the past couple of decades and have found use in many system applications. Some PIC efforts on other group III-V substrates have also been initiated. In numerous cases, the usefulness of these PICs is because of the reduction in size, weight, and power they provide, but in many cases also because of the higher performance made possible by the improved relative phase stability among optical paths as well as the reduction of inter-element coupling losses. In this paper, as part of this special issue in tribute to Prof. Daniel Dapkus, we focus on monolithic PICs that provide a system function, especially those that incorporate and build on widely-tunable laser technology as a key element. Some of the early widely-tunable laser work is reviewed, and a selection of past system-on-a-chip developments is presented as background. Then, more recent system-on-a-chip advances performed by the author’s groups are reviewed in more detail. Key advances are highlighted.

Monolithic Photonic Integrated Circuit Based on Silicon Nitride and Lithium Niobate on Insulator Hybrid Platform

Lithium niobate on insulator (LNOI) has been demonstrated as a promising platform for photonic integrated circuits (PICs), thanks to its excellent properties such as strong electro‐optic effect, low material loss, and wide transparency window. Herein, a monolithic PIC for high‐speed data communication application on a lithium‐niobate‐etchless platform with silicon nitride (Si3N4) as a loading material is proposed and demonstrated. The fabricated PIC consists of four racetrack resonator modulators and a pair of four‐channel mode (de)multiplexers, which shows high data modulation rate of 70 Gbps for single channel and the total data throughput reaches up to 280 Gbps. To the best of knowledge, this is the first demonstration of PIC consisting of high‐speed electro‐optical modulators and (de)multiplexers with such high data capacity on Si3N4‐LNOI hybrid platform, which opens up new avenues for achieving large‐scale monolithic integration on LNOI platform in future.

Demonstration of a 2 × 800 Gb/s/wave Coherent Optical Engine Based on an InP Monolithic PIC

We report on the development of a two-channel digital coherent optics (DCO) module, based on a monolithic InP photonic integrated circuit (PIC) transceiver and SiGe application-specific integrated circuit (ASIC), paired with a real-time 7 nm digital signal processing (DSP) ASIC. The high-performance coherent optical engine, which utilizes digital Nyquist subcarriers and probabilistic constellation shaping (PCS) techniques, enables long-haul and ultra-long-haul transmission distances over mixed fiber and amplifier types. This work discusses the performance of a DCO unit operating at multiple data rates over three practical real-world-like network distances. 800 Gb/s data transmission over a 1,000 km standard single mode fiber link was achieved using a 96 GBd, PCS-64QAM modulation format. Results of extended reaches of over 2,400 km and 5,000 km are also presented with data rates of 600 Gb/s and 400 Gb/s, respectively.

InP high power monolithically integrated widely tunable laser and SOA array for hybrid integration.

We present a monolithic InP-based photonic integrated circuit (PIC) consisting of a widely tunable laser master oscillator feeding an array of integrated semiconductor optical amplifiers that are interferometrically combined on-chip in a single-mode waveguide. We demonstrate a stable and efficient on-chip coherent beam combination and obtain up to 240 mW average power from the monolithic PIC, with 30-50 kHz Schawlow-Townes linewidths and >180 mW average power across the extended C-band. We also explored hybrid integration of the InP-based laser and amplifier array PIC with a high quality factor silicon nitride microring resonator. We observe lasing based on gain from the interferometrically combined amplifier array in an external cavity formed via feedback from the silicon nitride microresonator chip; this configuration results in narrowing of the Schawlow-Townes linewidth to ∼3 kHz with 37.9 mW average power at the SiN output facet. This work demonstrates a new approach toward high power, narrow linewidth sources that can be integrated with on-chip single-mode waveguide platforms for potential applications in nonlinear integrated photonics.

Tunable V-Cavity Lasers Integrated With a Cyclic Echelle Grating for Distributed Routing Networks

We demonstrate a monolithic InP-based photonic integrated circuit (PIC) consisting of four tunable V-cavity lasers (VCLs), a cyclic echelle diffraction grating router (EDGR) and four semiconductor optical amplifiers (SOAs). Quantum-well intermixing (QWI) technique is used to produce three different bandgap energies on the chip. Single VCL with 30 nm tuning range at 1.3 μm wavelength band and up to 40 dB side-modesuppression ratio (SMSR) is experimentally demonstrated. The chip has a 4.5 nm channel spacing and 18 nm free-spectral range (FSR). Measured spectrum of all the 16 input-output combinations show cyclic response.

Growth of high quality Ge-on-Si layer by using an ultra-thin LT-Si buffer in RPCVD

Ge epitaxial layer on Si substrate becomes more attractive for Si-based monolithic photonic integrated circuit (PIC). Low threading dislocation density and low surface roughness play a vital role in realizing the fabrication of the Ge optoelectronic devices. In this study, an ultra-thin LT-Si buffer for the deposition of Ge layer was investigated with regard to Ge layer’s crystallinity, symmetrical characteristic, threading dislocation density, and surface roughness. As a result, Ge epitaxial film has low threading dislocation density (TDD=5×106cm−2) and smooth surface (RMS = 0.68nm) in 5µm×5µm scan field with the Ge epitaxial layer thickness of about 1µm. What’s more, it was grown in a short time by using an ultra-thin LT-Si buffer layer without using chemical mechanical polishing (CMP), high temperature annealing, H2 annealing or cyclic annealing. In addition, room temperature direct gap photoluminescence was observed from intrinsic tensile-strained (0.21%) Ge-on-Si layer and bandgap narrowing in Ge epitaxial layer is 85meV.

Monolithic photonic integrated circuit with a GaN-based bent waveguide

Integration of a transmitter, waveguide and receiver into a single chip can generate a multicomponent system with multiple functionalities. Here, we fabricate and characterize a GaN-based photonic integrated circuit (PIC) on a GaN-on-silicon platform. With removal of the silicon and back wafer thinning of the epitaxial film, ultrathin membrane-type devices and highly confined suspended GaN waveguides were formed. Two suspended-membrane InGaN/GaN multiple-quantum-well diodes (MQW-diodes) served as an MQW light-emitting diode (MQW-LED) to emit light and an MQW photodiode (MQW-PD) to sense light. The optical interconnects between the MQW-LED and MQW-PD were achieved using the GaN bent waveguide. The GaN-based PIC consisting of an MQW-LED, waveguides and an MQW-PD forms an in-plane light communication system with a data transmission rate of 70 Mbps.

Mode-locked laser with pulse interleavers in a monolithic photonic integrated circuit for millimeter wave and terahertz carrier generation.

This Letter presents a photonics-based millimeter wave and terahertz frequency synthesizer using a monolithic InP photonic integrated circuit composed of a mode-locked laser (MLL) and two pulse interleaver stages to multiply the repetition rate frequency. The MLL is a multiple colliding pulse MLL producing an 80 GHz repetition rate pulse train. Through two consecutive monolithic pulse interleaver structures, each doubling the repetition rate, we demonstrate the achievement of 160 and 320 GHz. The fabrication was done on a multi-project wafer run of a generic InP photonic technology platform.

AlGaN/AlN integrated photonics platform for the ultraviolet and visible spectral range.

We analyze a photonic integrated circuit (PIC) platform comprised of a crystalline AlxGa1-xN optical guiding layer on an AlN substrate for the ultraviolet to visible (UV-vis) wavelength range. An Al composition of x~0.65 provides a refractive index difference of ~0.1 between AlxGa1-xN and AlN, and a small lattice mismatch (< 1%) that minimizes crystal dislocations at the AlxGa1-xN/AlN interface. This small refractive index difference is beneficial at shorter wavelengths to avoid extra-small waveguide dimensions. The platform enables compact waveguides and bends with high field confinement in the wavelength range from 700 nm down to 300 nm (and potentially lower) with waveguide cross-section dimensions comparable to those used for telecom PICs such as silicon and silicon nitride waveguides, allowing for well-established optical lithography. This platform can potentially enable cost-effective, manufacturable, monolithic UV-vis photonic integrated circuits.

Low-Cost AWG-Based Fundamental Frequency Mode-Locked Semiconductor Laser for Multichannel Synchronous Ultrashort Pulse Generation

We report a low-cost arrayed waveguide grating (AWG) based mode-locked semiconductor laser designed for multichannel synchronous ultrashort pulse generation. Both the fabrication process and chip characterization results are discussed in detail. By deploying a bundle active-passive photonic integration technique, only one regrowth step is required to monolithically integrate a semiconductor optical amplifier array, an AWG, and a common saturable absorber on a single InP substrate. Combined with a shallow ridge waveguide structure common for both active and passive sections and formed in a single dry etching process, our process allows the fabrication of the monolithic photonic integrated circuit chip in a much simplified process. The fabricated device demonstrated multichannel mode-locking operation at a repetition frequency of 4.1 GHz in a fundamental mode-locking regime under both passive mode-locking and synchronous hybrid mode-locking conditions. Timing jitter as low as 1 ps was obtained, and preliminary pulse chirping characteristics were analyzed by a frequency-resolved optical gating technique. The exhibited performance makes our device a promising candidate as a multichannel ultrashort pulse optical source for future cost-effective high-speed optical networking and signal processing applications.

Fully integrated multi-optoelectronic synthesizer for THz pumping source in wireless communications with rich backup redundancy and wide tuning range.

We report a monolithic photonic integrated circuit (PIC) for THz communication applications. The PIC generates up to 4 optical frequency lines which can be mixed in a separate device to generate THz radiation, and each of the optical lines can be modulated individually to encode data. Physically, the PIC comprises an array of wavelength tunable distributed feedback lasers each with its own electro-absorption modulator. The lasers are designed with a long cavity to operate with a narrow linewidth, typically <4 MHz. The light from the lasers is coupled via an multimode interference (MMI) coupler into a semiconductor optical amplifier (SOA). By appropriate selection and biasing of pairs of lasers, the optical beat signal can be tuned continuously over the range from 0.254 THz to 2.723 THz. The EAM of each channel enables signal leveling balanced between the lasers and realizing data encoding, currently at data rates up to 6.5 Gb/s. The PIC is fabricated using regrowth-free techniques, making it economic for volume applications, such for use in data centers. The PIC also has a degree of redundancy, making it suitable for applications, such as inter-satellite communications, where high reliability is mandatory.

The power of circuit simulations for designing photonic integrated circuits

SUMMARYThe emerging of circuit‐level simulators for photonic integrated circuits (PICs) is driven by recent developments in technologies for integration of large‐scale monolithic PICs in both, silicon and InP technologies. For that reason, powerful circuit‐level simulators should be capable to model on the same circuit different types of sub‐components performing photonic, electronic or opto‐electronic, active or passive functions. In comparison with device‐level simulations, the use of realistic circuit‐level abstracted models facilitates rapid functional design without going into technological fabrication details and subsequent design flow. This accelerates the design process and decreases the number of runs to achieve the desired results. Detailed physical modeling remains limited to the design of some specific individual sub‐elements. Large‐scale PICs might comprise several thousands of elements. The circuit‐level abstraction also ensures that the simulation speed to achieve a certain simulation accuracy decreases reasonably slowly with the total number of photonic components in the modeled PIC. In this work, we present our solution for modeling PICs in the framework of the circuit‐level simulation tool VPIcomponentMaker™Photonic Circuits (Carnotstr. 6, 10587, Berlin, Germany, www.VPIphotonics.com). We demonstrate the combination of different simulation approaches in time domain, frequency domain and time‐and‐frequency domain for fast and accurate simulations. We discuss several diverse modeling benefits by means of application examples on silicon photonic PICs. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Light spectral filtering based on spatial adiabatic passage

We present the first experimental realization of a light spectral filter based on the spatial adiabatic passage technique. We demonstrate that a fully integrable CMOS-compatible system of three coupled identical total internal reflection silicon oxide waveguides with variable separation along their propagation direction can be used simultaneously as a low- and high-pass spectral filter within the visible range of wavelengths. Light is injected into the right waveguide, and after propagating along the system, long wavelengths are transferred into the left output, whereas short wavelengths propagate to the right and central outputs. The stopband reaches values up to −11 dB for the left output and approximately −20 dB for the right plus central outputs. The passband values are close to 0 dB for both cases. We also demonstrate that the filtering characteristics of the device can be controlled by modifying the parameter values, which define the geometry of the triple-waveguide system. However, the general filtering behavior of the system does not critically depend on technological variations. Thus, the spatial adiabatic passage filtering approach constitutes an alternative to other integrated filtering devices, such as interference or absorbance-based filters. Researchers have developed a waveguide-based scheme for filtering different wavelengths of light that suits chip-level integration. The approach, developed by Ricard Menchon-Enrich and co-workers from Barcelona, Spain, and Lausanne, Switzerland, relies on wavelength-dependent coupling between three closely spaced silicon oxide waveguides. When white visible light is launched into the right waveguide input, the red spectral components are transferred to the left waveguide output while green and blue components propagate to both right and central outputs. This ‘spatial adiabatic passage filter’ represents an alternative to filters that rely on either absorption or interference, which can be lossy or inconvenient to implement. Furthermore, because this filter is compatible with complementary metal–oxide–semiconductor fabrication, it could potentially be combined with other optical and electronic devices in a monolithic photonic integrated circuit.

Optical gain by simultaneous photon and phonon confinement in indirect bandgap semiconductor acousto-optical cavities

Optical gain that could ultimately lead to light emission from silicon is a goal that has been pursued for a long time by the scientific community. The reason is that a silicon laser would allow for the development of low-cost, high-volume monolithic photonic integrated circuits created using conventional CMOS technologies. However, the silicon indirect bandgap—requiring the participation of a proper phonon in the process of light emission—is a roadblock that has not been overcome so far. A high-Q optical cavity allowing a very high density of states at the desired frequencies has been proposed as a possible way to get optical gain. However, recent theoretical studies have shown that the free-carrier absorption is much higher than the optical gain at ambient temperature in an indirect bandgap semiconductor, even if a high-Q optical cavity is formed. In this work, we consider a particular case in which the semiconductor material is engineered to form an acousto-optical cavity where the photon and phonon modes involved in the emission process are simultaneously confined. The acousto-optical cavity confinement effect on the light emission properties is characterized by a compound Purcell factor which includes both the optical as well as the acoustic Purcell factor (APF). A theoretical expression for the APF is also introduced. Our theoretical results suggest that creating an acousto-optical cavity the optical gain can overcome the photon loss due to free carriers as a consequence of the localization of phonons even at room temperature, paving the way towards the pursued silicon laser.

RF/Photonic Link-on-Chip PIC

We present the design and the first experimental results from a new device where an entire RF/photonic link is fabricated as a monolithic photonic integrated circuit (PIC). This novel “link-on-chip” PIC can operate in a linear mode or a mixer mode, depending on its intended application.

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and also quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. A difference of this review from the other existing works on semiconductor VECSEL devices is that we will cover both the fundamental aspects and technological approaches of QD VECSEL devices. And lastly, the presented review here has provided a deep insight into useful guideline for the development of QD VECSEL technology and future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).