On-chip Light Research Articles

Heterogeneously integrated light emitting diodes and photodetectors in the metal-insulator-metal waveguide platform

Abstract We demonstrate heterogeneous integration of active semiconductor materials into the conventional passive metal-insulator-metal (MIM) waveguides to provide compact on-chip light generation and detection capabilities for chip-scale active nanophotonic platforms. Depending on its bias conditions, a metal-semiconductor-metal section can function as either a light emitting diode or a photodetector directly connected to the MIM waveguides. We experimentally verify the independent and combined operations of electrically-driven on-chip light sources and photodetectors.

Manipulating the non-Hermitian skin effect in optical ring resonators

Non-Hermitian skin effects (NHSEs) enrich the traditional band theories and give rise to unique non-Hermitian topological properties. Here, we reveal a different type of NHSE, termed the V-shaped NHSE, and explore an on-chip optical ring resonator platform to demonstrate the NHSE in telecommunication wavelength. By tuning the hopping and loss modulation, we work out a phase diagram that reveals the phase transition of the NHSE. Besides the conventional NHSE and the frequency-dependent bipolar NHSE, another type of NHSE is observed featuring an interesting V shape in its special skin states distribution. We further design a silicon ring resonator array with loss-assisted antiresonating coupling as the link resonators to demonstrate the nontrivial NHSE. The simulations show that one can tune the number of states piled up at different ends by switching the NHSE from conventional, bipolar to V-shaped types continuously. Our work enriches the NHSE phase transitions and implies potential in on-chip light modulation by the NHSE.

Nanoantennas for selectively switching on and off under different input phase distributions and wavelengths

Optical nanoantennas, as devices connecting free-space light and on-chip light, are important components of integrated photonic circuits. They are often used as optical couplers, and in optical routine of intermediate layers of IC chips. To have more degrees of freedom to manipulate the light scattering, we design a novel optical nanoantenna composed of subwavelength silicon pillars. The antenna can exhibit on and off scattering states under different input optical modes and exhibit opposite on-off characteristics at different wavelengths. The antenna is small in size and flexible in design, and has the potential to build a more flexible 3D optical link for photonic integrated circuits.

Anisotropic Van Der Waals 2D GeAs Integrated on Silicon Four-Waveguide Crossing

In-plane optical anisotropy plays a critical role in manipulating light in a wide range of planner photonic devices. In this study, the strong anisotropy of multilayer 2D GeAs is leveraged and utilized to validate the technical feasibility of on-chip light management. A 2D GeAs is stamped into an ultra-compact silicon waveguide four-way crossing optimized for operation in the O-optical band. The measured optical transmission spectra indicated a remarkable discrepancy between the in-plane crystal optical axes with an attenuation ratio of ∼3.5 (at 1330 nm). Additionally, the effect of GeAs crystal orientation on the electro-optic transmission performance is demonstrated on a straight waveguide. A notable 50% reduction in responsivity was recorded for devices constructed with cross direction compared to devices with a crystal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> -direction parallel to the light polarization. This extraordinary optical anisotropy, combined with a high refractive index ∼4 of 2D GeAs, opens possibilities for efficient on-chip light manipulation in photonic devices.

Topologically-optimized on-chip metamaterials for ultra-short-range light focusing and mode-size conversion

Abstract The concept of metamaterials offers a flexible pathway to manipulate the macroscopic behavior of light by delicately designed microscopic subwavelength structures, which has been recently introduced to integrated photonics to create devices with ultra-compact footprint, excellent performance or versatile functionalities. However, the conventional design approach of metamaterials, including two separated steps of subwavelength structure design and the assembly of unit cells, often encounters challenges when facing extreme design targets. In this work, we propose a hierarchical inverse design approach by cascading a conventional unit-cell-based design with a holistic topology optimization. As a proof-of-concept, we demonstrate ultra-short-range light focusing and mode-size conversion enabled by on-chip meta-lenses. The shortening of tapering region pushes higher numerical aperture of on-chip lenses, leading to the violation of locally periodic approximation used in meta-lens design and thus poor device performance, which fortunately, can be well compensated by the follow-up holistic optimization step. We experimentally realize mode-size squeezing by almost 20 times in a tapering region as short as 8 μm and 5 μm with low insertion loss and broadband performance. The proposed design scheme provides practical guidelines to design metamaterials as flexible on-chip wavefront control and light routing devices for various applications in fiber communication, sensing and optical computing.

Carbon dioxide mid-infrared sensing based on Dy3+-doped chalcogenide waveguide photoluminescence.

Climate-active gases, notably carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), display fundamental absorption bands in the mid-infrared (mid-IR). The detection and monitoring of those gases could be enabled by the development of mid-IR optical sources. Broadband mid-IR on-chip light emission from rare-earth-doped chalcogenide photonic integrated circuits could provide a compact, efficient, and cost-effective gas sensing solution. Mid-IR photoluminescence of dysprosium-doped selenide ridge waveguides obtained under optical pumping at a telecommunication wavelength (∼1.3 µm) is investigated for Dy3+ ion concentrations in the 2500-10,000 ppmw range. CO2 detection at around 4.3 µm is then demonstrated based on absorption of this broadband mid-IR emission.

A sub-wavelength Si LED integrated in a CMOS platform

A nanoscale on-chip light source with high intensity is desired for various applications in integrated photonics systems. However, it is challenging to realize such an emitter using materials and fabrication processes compatible with the standard integrated circuit technology. In this letter, we report an electrically driven Si light-emitting diode with sub-wavelength emission area fabricated in an open-foundry microelectronics complementary metal-oxide-semiconductor platform. The light-emitting diode emission spectrum is centered around 1100 nm and the emission area is smaller than 0.14 μm2 (~varnothing 400 nm). This light-emitting diode has high spatial intensity of >50 mW/cm2 which is comparable with state-of-the-art Si-based emitters with much larger emission areas. Due to sub-wavelength confinement, the emission exhibits a high degree of spatial coherence, which is demonstrated by incorporating the light-emitting diode into a compact lensless in-line holographic microscope. This centimeter-scale, all-silicon microscope utilizes a single emitter to simultaneously illuminate ~9.5 million pixels of a complementary metal-oxide-semiconductor imager.

Photon-pair generation in a lossy waveguide

Abstract An on-chip quantum light source based on spontaneous four-wave mixing is an essential element for developing quantum photonic integrated circuit technology, which has the advantage of no connection loss owing to the integration of the source into photonic circuits. The waveguide-based quantum light source inevitably causes propagation loss owing to imperfections in the fabrication process, but the propagation loss effects on photon-pair generation have not been extensively studied. In this study, propagation loss effects were examined using theoretical and experimental methods. In theory, the performance of quantum light sources, such as brightness, heralding efficiency, and coincidence-to-accidental ratio, strongly depend on propagation loss. We fabricate several waveguides with a moderate propagation loss of 2.2 dB/cm to investigate the loss dependence and ascertain that the brightness, heralding efficiency, and coincidence-to-accident ratio strongly correlate with the length of the optical waveguide. The maximum coincidence-count brightness occurred at an optimization length of 1/α, where α is the absorption coefficient. In contrast, the single-count brightness shows slightly different waveguide length dependence owing to loss-induced one-photon states. We expect that the results obtained in this study will greatly assist in determining the proper waveguide length for photon-pair generation according to the source’s application fields. The results will be helpful in the development of a quantum light source suitable for practical and quantum optical integrated circuits and will lead to the development of high-fidelity quantum technologies.

On-chip ultraviolet second-harmonic generation in lithium-tantalate thin film microdisk

The compact and reliable ultraviolet (UV) source has attracted remarkable attention for its potential use in optical measurement systems, high-density optical storage, and biomedical applications. We demonstrate ultraviolet generation by frequency doubling in a lithium-tantalate-on-insulator (LTOI) microdisk via modal phase matching. The 50-µm-diameter microdisk was milled by a focused ion beam (FIB) and followed by chemo-mechanical polishing (CMP) to smooth the disk surface and edge, and the Q-factor reaches 2.74×105 in the visible band. On-chip UV coherent light with a wavelength of 384.3 nm was achieved, which shows great promise for using LTOIs in integrated ultraviolet source platforms.

High-performance all-inorganic CsPbBr3 quantum dots with a low-threshold amplified spontaneous emission.

All-inorganic halide perovskite CsPbX3(X = Br/Cl/I)quantum dots have gained a considerable attention in the optoelectronic fields. However, the high cost and poor stability of the prepared CsPbX3 quantum dots (QDs) are inevitable challenges for their future practical applications. And the high-performance CsPbX3 QDs are always needed. Herein, a facile and low-cost synthesis scheme was adopted to prepare the CsPbBr3 QDs modified by lead bromide (PbBr2) and tetraoctylammonium bromide (TOAB) ligands at room temperature in open air. The prepared CsPbBr3 QDs exhibited a high photoluminescence quantum yield (PLQY) of 96.6% and a low amplified spontaneous emission (ASE) threshold of 12.6 µJ/cm2. Stable ASE intensity with little degradation was also realized from the CsPbBr3 QDs doped with PMMA. Furthermore, the enhanced ASE properties of the CsPbBr3 QDs-doped PMMA based on distributed feedback (DFB) substrate was achieved with a lower threshold of 3.6 µJ/cm2, which is 28.6% of that of the (PbBr2 + TOAB)-treated CsPbBr3 QDs without PMMA. This work exhibits a promising potential in the on-chip light source.

On-chip light trapping in bilayer moiré photonic crystal slabs

The optical response of bilayer moiré photonic structures can be precisely controlled by varying the lattice geometry. Bilayer moiré photonic crystal slabs exhibit flat bands in the optical band structure, where the optical modes have zero group velocity. They also give rise to momentum-independent light-trapping of Bloch waves in both transverse and vertical directions, leading to high quality-factors (Q=109) and small mode volumes (V=0.12 λ2). The large Q and small V lead to a large Purcell enhancement (FP=1035), providing opportunities for low-threshold lasing, enhancement of optical nonlinearities, and quantum information processing.

Electrically induced adiabatic frequency conversion in an integrated lithium niobate ring resonator.

Changing the frequency of light outside the laser cavity is essential for an integrated photonics platform, especially when the optical frequency of the on-chip light source is fixed or challenging to be tuned precisely. Previous on-chip frequency conversion demonstrations of multiple GHz have limitations of tuning the shifted frequency continuously. To achieve continuous on-chip optical frequency conversion, we electrically tune a lithium niobate ring resonator to induce adiabatic frequency conversion. In this work, frequency shifts of up to 14.3 GHz are achieved by adjusting the voltage of an RF control. With this technique, we can dynamically control light in a cavity within its photon lifetime by tuning the refractive index of the ring resonator electrically.

Locally Structured On-Chip Optofluidic Hollow-Core Light Cages for Single Nanoparticle Tracking.

Nanoparticle tracking analysis (NTA) is a widely used methodology to investigate nanoscale systems at the single species level. Here, we introduce the locally structured on-chip optofluidic hollow-core light cage, as a novel platform for waveguide-assisted NTA. This hollow waveguide guides light by the antiresonant effect in a sparse array of dielectric strands and includes a local modification to realize aberration-free tracking of individual nano-objects, defining a novel on-chip solution with properties specifically tailored for NTA. The key features of our system are (i) well-controlled nano-object illumination through the waveguide mode, (ii) diffraction-limited and aberration-free imaging at the observation site, and (iii) a high level of integration, achieved by on-chip interfacing to fibers. The present study covers all aspects relevant for NTA including design, simulation, implementation via 3D nanoprinting, and optical characterization. The capabilities of the approach to precisely characterize practically relevant nanosystems have been demonstrated by measuring the solvency-induced collapse of a nanoparticle system which includes polymer brush-based shells that react to changes in the liquid environment. Our study unlocks the advantages of the light cage approach in the context of NTA, suggesting its application in various areas such as bioanalytics, life science, environmental science, or nanoscale material science in general.

Electrically pumped InP/GaAsP quantum dot lasers grown on (001) Si emitting at 750 nm.

Excellent performance of InAs quantum dot (QD) lasers grown on Si in the datacom and telecom bands has been reported in recent years. InP QD lasers on Si with emission wavelength at 650 nm-750 nm are seldom explored. In this paper, we report the growth and room temperature lasing of electrically pumped InP/GaAsP QD lasers directly grown on (001) Si emitting at 750 nm. The lowest threshold current density obtained is ∼650 A/cm2, measured on a 2 mm × 70 µm device. Moreover, the highest operating temperature of the InP QD laser grown on the GaAs/Si template is above 95°C. This 750 nm near red on-chip light source for the monolithic integration of Si photonics is potentially applicable in display, bio-photonics, and spatial mapping.

Step-like beam scanning in a slow-light grating beam scanner for a FMCW LIDAR.

We have developed a nonmechanical beam scanner equipped with a Si photonics slow-light grating toward an on-chip frequency-modulated continuous-wave light detection and ranging (FMCW LIDAR) device. An optical beam is scanned thermo-optically, but it is also shifted sensitively to the frequency modulation, which is inconvenient for FMCW LIDAR. In this study, we canceled this shift and obtained step-like beam scanning with synchronized thermo-optic signals, which was confirmed in space-time-domain beam observations. The step-like scanning allows finer angular resolution of the range profile.

Spatially resolving amplitude and phase of light with a reconfigurable photonic integrated circuit

Photonic integrated circuits play a pivotal role in many applications. Particularly powerful are circuits based on meshes of reconfigurable Mach–Zehnder interferometers as they enable active processing of light. This meets demands accross different fields, from communication to signal and information processing and sensor applications. Here, we use a reconfigurable photonic integrated circuit to realize a spatially resolving detector of amplitudes and phases of an electromagnetic field distribution. This is achieved by optically sampling free-space beams with a carefully designed input interface and subsequently processing the resulting on-chip light within the photonic mesh of interferometers. To perform measurements of this kind, we develop and experimentally implement a versatile method for the calibration and operation of such integrated photonics based detectors. Our technique works in a wide parameter range, even when running the chip off the design wavelength. Amplitude, phase, and polarization sensitive measurements are of enormous importance in modern science and technology, providing a vast range of applications for such integrated detectors.

Femtojoule femtosecond all-optical switching in lithium niobate nanophotonics

Optical nonlinear functions are crucial for various applications in integrated photonics, including all-optical information processing1, photonic neural networks2,3 and on-chip ultrafast light sources4,5. However, the weak native nonlinearity of most nanophotonic platforms has imposed barriers for such functions by necessitating large driving energies, high-Q cavities or integration with other materials with stronger nonlinearity. Here we effectively utilize the strong and instantaneous quadratic nonlinearity of lithium niobate nanowaveguides for the realization of cavity-free all-optical switching. By simultaneous engineering of the dispersion and quasi-phase matching, we design and demonstrate a nonlinear splitter that can achieve ultralow switching energies down to 80 fJ, featuring a fastest switching time of ~46 fs and a lowest energy–time product of 3.7 × 10−27 J s in integrated photonics. Our results can enable on-chip ultrafast and energy-efficient all-optical information processing, computing systems and light sources.

A bright and spectrally multiplexed on-chip quantum light source

A bright and spectrally multiplexed on-chip quantum light source

Heterogeneously integrated quantum-dot emitters efficiently driven by a quasi-BIC-supporting dielectric nanoresonator

Bound states in the continuum (BICs) can make subwavelength dielectric resonators sustain low radiation leakage, paving a new way to minimize the device size, enhance photoluminescence, and even realize lasing. Here, we present a quasi-BIC-supporting GaAs nanodisk with embedded InAs quantum dots as a compact bright on-chip light source, which is realized by heterogeneous integration, avoiding complex multilayered construction and subsequent mismatch and defects. The emitters are grown inside the nanodisk to match the mode field distribution to form strong light–matter interaction. One fabricated sample demonstrates a photoluminescence peak sustaining a quality factor up to 68 enhanced by the quasi-BIC, and the emitting effect can be further promoted by improving the epilayer quality and optimizing the layer-transferring process in the fabrication. This work provides a promising solution to building an ultracompact optical source to be integrated on a silicon photonic chip for high-density integration.

Multi-wavelength injection locked semiconductor comb laser

Quantum dot lasers on silicon have gained significant interest over the past decade due to their great potential as an on-chip silicon photonic light source. Here, we demonstrate multi-wavelength injection locking of InAs/GaAs quantum dot Fabry–Perot (FP) lasers both on GaAs and silicon substrates by optical self-injection via an external cavity. The number of locked laser modes can be adjusted from a single peak to multiple peaks by tuning wavelength dependent phase and mode spacing of back-injected light through a Lyot filter. The multi-wavelength injection locked laser modes exhibit average optical linewidth of ∼ 20 kHz , which are narrowed by approximately three orders of magnitude from their free-running condition. Furthermore, multi-wavelength self-injection locking via an external cavity exhibits flat-top optical spectral properties with approximately 30 stably locked channels under stable operation over time, where the frequency detuning is less than 700 MHz within 40 min. Particularly, FP lasers by direct epitaxial growth on silicon substrates are self-injection locked as a flat-top comb source with tunable free spectral range from approximately 25 to 700 GHz. The reported results emphasize the great potential of multi-wavelength injection locked lasers as tunable on-chip multi-wavelength light sources.