Photonic Integrated Circuits Research Articles

High Efficiency O‐band Preamplified Receiver Integrated with Semiconductor Optical Amplifier and Uni‐travelling Carrier Photodiode for Passive Optical Network

With the continuous increase in data traffic and enormous consumption of data in terms of video on demand services and cloud computing, there is an increasing demand for high speed and high sensitivity short reach receivers for passive optical networks (PON) access network which are point to multi‐point networks. Avalanche photodiodes (APD) are the standard receivers in PON networks due to their high sensitivity and low cost. However, it is currently not clear if they can provide high bandwidth above 40 GHz with good performance (gain, noise, etc.). Furthermore, standard PIN photodiodes do not provide sufficient sensitivity for PON networks. Therefore, in this article a SOA‐UTC receiver is proposed, which is a photonic integrated circuit (PIC) comprising a semiconductor optical amplifier (SOA) for optical preamplification and a high‐speed uni‐travelling‐carrier (UTC) photodiode for opto‐electronic conversion. A very high responsivity of 140 A W−1 is demonstrated, with a polarization dependent loss (PDL) around 1 dB and a 3 dB bandwidth of 48 GHz, which is very promising for future PON network with 50 Gbit s−1 capacity and above.

Thermal flux manipulation on the silicon photonic chip to suppress the thermal crosstalk

The integration density of silicon photonic integrated circuit (PIC) is ultimately constrained by various crosstalk mechanisms on the chip. Among them, the most prominent limiting factor is the thermal crosstalk due to the wide use of the thermo-optic effect. High-density silicon PICs strongly demand an advanced structure with better thermal crosstalk suppression ability than the traditional air isolation trench. Inspired by the thermal-metamaterial based on the scattering-cancellation method, we demonstrate a closed heat shield (CHS) structure on a silicon PIC chip, which can manipulate the thermal flux to bypass the temperature-sensitive silicon photonics components. The on-chip CHS structure is a bilayer cylindrical shell fabricated by the standard silicon photonics processing flow. Its outer and inner shell layers are formed by a 6-μm-wide interconnection metal and 4-μm-wide air trench, respectively. Plenty of temperature-sensitive micro-ring resonators inside the CHS are used to probe the temperature profile. The measurement results show that the CHS can reduce the local temperatures by 50%/44%/36% at the locations 29/41/83 μm away from the external heater. In contrast, the conventional air trench of the same dimension reduces the local temperatures by 32%/28%/21% at the same positions. In addition, the response time of the thermal field inside the CHS is around one-half of that in the conventional air trench. Furthermore, the simulation result indicates that if the outer shell of the CHS can contact with the silicon substrate by utilizing the through-silicon-via structure, the thermal crosstalk suppression ability can be improved significantly.

Photonic Weyl Waveguide and Saddle-Chips-like Modes.

Topological Weyl semimetals are characterized by open Fermi arcs on their terminal surfaces, these materials not only changed accepted concepts of the Fermi loop but also enabled many exotic phenomena, such as one-way propagation. The key prerequisite is that the two terminal surfaces have to be well separated, i.e., the Fermi arcs are not allowed to couple with each other. Thus, their interaction was overlooked before. Here, we consider coupled Fermi arcs and propose a Weyl planar waveguide, wherein we found a saddle-chips-like hybridized guiding mode. The hybridized modes consist of three components: surface waves from the top and bottom surfaces and bulk modes inside the Weyl semimetal. The contribution of these three components to the hybridized mode appears to be z-position-dependent rather than uniform. Beyond the conventional waveguide framework, those non-trivial surface states, with their arc-type band structures, exhibit strong selectivity in propagation direction, providing an excellent platform for waveguides. Compared with the conventional waveguide, the propagation direction of hybridized modes exhibits high z-position-dependency. For example, when the probe plane shifts from the top interface to the bottom interface, the component propagating horizontally becomes dimmer, while the component propagating vertically becomes brighter. Experimentally, we drilled periodic holes in metal plates to sandwich an ideal Weyl meta-crystal and characterize the topological guiding mode. Our study shows the intriguing behaviors of topological photonic waveguides, which could lead to beam manipulation, position sensing, and even 3D information processing on photonic chip. The Weyl waveguide also provides a platform for studying the coupling and the interaction between surface and bulk states.

The Janus layered metamaterial modulated by liquid crystal with multitasking of different logic gates and mode-switching biosensing

A Janus layered metamaterial (JLM) operating in the terahertz (THz) region is proposed, which increases the direction dimension to manipulate the propagation of electromagnetic waves (EWs) through the introduction of nonlinear Kerr media. It achieves multi-scale multitasking with different logic gates and mode-switching biosensing, making a breakthrough on traditional single-function and single-scale THz devices. Due to the electro-optical effect, the liquid crystal (LC) is adjusted by the electric field, and the sharp transmission peak generated by the located defect mode resonance can be used to realize the forward scale logic product gate and the backward scale exclusive NOR gate. In addition, by locking the sharp transmission peak, the biosensing can have different detection ranges under the LC modulation. Therefore, when EWs propagate forward and backward, the mode switching of different biosensing categories with a glucose concentration of 300–550 g/l, creatinine concentration of 80.9–85.28 μmol/l, and the blood component in refractive index of 1.33–1.38 can be realized. The JLM proposed provides a possibility for the design of the chip-level compact optical integrated circuit and offers a new idea for multi-purpose biomedical detection, owning certain research value.

Optimization of the coupling efficiency under self-injection locking in a narrow linewidth hybrid wavelength tunable laser diode

In this study, a fiber Fabry–Perot (FFP) interferometer was connected to a hybrid wavelength-tunable laser diode consisting of a semiconductor optical amplifier chip and Si photonics chip, and spectral linewidth narrowing was achieved using the self-injection locking effect. The hybrid wavelength-tunable laser was equipped with a variable-reflectivity mirror, which allowed the optimization of κ, the coupling efficiency between the laser cavity and FFP interferometer. By optimizing κ, self-injection locking stabilized, and the linewidth was controlled between 4 and 300 kHz. This laser can be used to evaluate the linewidth required for communication systems such as digital coherent communication and the accuracy required for distance measurement.

Two-dimensional thin film lithium niobate photonic crystal waveguide for integrated photonic chips

The photonic crystal waveguide (PCW) possesses remarkable capabilities in manipulating light beams and light–matter interactions within the subwavelength range. This property renders it a highly promising structure for the miniaturization of optical devices. We delve into the mode characteristics in two-dimensional PCWs on thin film lithium niobate, establish the correlation between the single-mode region in the PCW and its photonic crystal duty cycle, and observe mode hybridization in the waveguide. A lithium niobate PCW with sidewall angles can realize single-mode transmission or mode conversion by adjusting the width of its defective waveguides, and it is theoretically and experimentally verified that a change in the width of the waveguide shifts the operating wavelength. The results of the mode analysis are useful in the design of waveguide structures for photonic crystal-based electro-optical modulators and optical sensors.

Continuously tunable silicon waveguide optical switched delay line based on grating-assisted contradirectional coupler

The integrated optical delay line plays a crucial role in microwave photonic chips. Continuous tunability is a growing trend in filtering and beamforming techniques of microwave photonics. Based on the silicon platform, we present and experimentally demonstrate an integrated continuously optical tunable delay line (OTDL) chip, which contains a 4-bit optical switched delay line (OSDL) and a thermally tunable delay line based on grating-assisted Contradirectional coupler (CDC). The OSDL can achieve stepwise optical delays, while the CDC is introduced to improve delay tuning resolution within one step delay of the OSDL. The combination of the two modules can realize tuning delays from 0 to 160 ps. Additionally, it is easy to increase the maximum delay by cascading more optical switches. The experimental results demonstrate that the proposed OTDL shows outstanding performance and good expansibility.

Monolithic back-end-of-line integration of phase change materials into foundry-manufactured silicon photonics

Monolithic integration of novel materials without modifying the existing photonic component library is crucial to advancing heterogeneous silicon photonic integrated circuits. Here we show the introduction of a silicon nitride etch stop layer at select areas, coupled with low-loss oxide trench, enabling incorporation of functional materials without compromising foundry-verified device reliability. As an illustration, two distinct chalcogenide phase change materials (PCMs) with remarkable nonvolatile modulation capabilities, namely Sb2Se3 and Ge2Sb2Se4Te1, were monolithic back-end-of-line integrated, offering compact phase and intensity tuning units with zero-static power consumption. By employing these building blocks, the phase error of a push-pull Mach–Zehnder interferometer optical switch could be reduced with a 48% peak power consumption reduction. Mirco-ring filters with >5-bit wavelength selective intensity modulation and waveguide-based >7-bit intensity-modulation broadband attenuators could also be achieved. This foundry-compatible platform could open up the possibility of integrating other excellent optoelectronic materials into future silicon photonic process design kits.

Red–Green–Blue Light Emission from Composition Tunable Semiconductor Micro‐Tripods

AbstractMicro/nanoscale lasers that span the entire visible spectrum, especially those in red, green, and blue colors, are not only essential for a variety of optical devices but also have important applications in visible color communication, multi‐color fluorescence sensing, and wavelength division multiplexing. Despite the great efforts made to achieve multi‐color lasing using a variety of approaches, on‐chip white light emission and even red, green, and blue multi‐color lasers still suffer from considerable challenges in micro‐nano structures. Here, CdSxSe1−x, CdS, and ZnS micro‐tripod structures are successfully prepared using chemical vapor deposition approaches. The micro‐photoluminescence (µ‐PL) spectra and PL‐mapping of these micro‐tripods reveal various emissions at 630, 508, and 460 nm, respectively. Additionally, white‐light emissions based on these composition‐tunable tripods are realized through an end‐coupling structure system. Moreover, room‐temperature modes tunable lasers are observed clearly from three legs of these micro‐tripods, with a low threshold of ≈48.39 µJ cm−2 and a high quality factor of 1227.3. The realization of micro‐tripods‐based lasers may provide an innovative way for highly integrated photonic circuits and communications.

Recent Progress in Nanophotonic Light Sources

It is increasingly crucial in the information era to rapidly transmit and process vast quantities of data. However, conventional electronic integrated circuits that operate at rates below 10 GHz encounter significant challenges in effectively managing parallel signals. How can information be transmitted more quickly? Photonic integrated circuits (PICs) are the solution. PICs have the capability of processing multiple signals in parallel on a single optical waveguide by multiplexing wavelength, polarization, and angular momentum. This enables PICs to transmit at speeds exceeding 100 GHz, showing the potential to increase processing speeds while simultaneously reducing power levels. Nevertheless, one drawback of photonic devices is that they are typically several orders of magnitude larger than electronic devices. Consequently, nanophotonics researchers have been working to make photonic devices smaller without compromising their ability to control light. Advances in nanoscale light sources can present a viable solution to overcome these obstacles. With the formation of long-lasting, spatially confined resonances in nanocavities, it is possible to precisely manipulate far-field radiation. In this article, we provide an overview of the recent achievements in nanophotonic light sources, including topological nanolasers and single-photon emitters.

A Multiplex "Disposable Photonics" Biosensor Platform and Its Application to Antibody Profiling in Upper Respiratory Disease.

Photonic technologies promise to deliver quantitative, multiplex, and inexpensive medical diagnostic platforms by leveraging the highly scalable processes developed for the fabrication of semiconductor microchips. However, in practice, the affordability of these platforms is limited by complex and expensive sample handling and optical alignment. We previously reported the development of a disposable photonic assay that incorporates inexpensive plastic micropillar microfluidic cards for sample delivery. That system as developed was limited to singleplex assays due to its optical configuration. To enable multiplexing, we report a new approach addressing multiplex light I/O, in which the outputs of individual grating couplers on a photonic chip are mapped to fibers in a fiber bundle. As demonstrated in the context of detecting antibody responses to influenza and SARS-CoV-2 antigens in human serum and saliva, this enables multiplexing in an inexpensive, disposable, and compact format.

Heralded Three-Photon Entanglement from a Single-Photon Source on a Photonic Chip.

In the quest to build general-purpose photonic quantum computers, fusion-based quantum computation has risen to prominence as a promising strategy. This model allows a ballistic construction of large cluster states which are universal for quantum computation, in a scalable and loss-tolerant way without feed forward, by fusing many small n-photon entangled resource states. However, a key obstacle to this architecture lies in efficiently generating the required essential resource states on photonic chips. One such critical seed state that has not yet been achieved is the heralded three-photon Greenberger-Horne-Zeilinger (3-GHZ) state. Here, we address this elementary resource gap, by reporting the first experimental realization of a heralded 3-GHZ state. Our implementation employs a low-loss and fully programmable photonic chip that manipulates six indistinguishable single photons of wavelengths in the telecommunication regime. Conditional on the heralding detection, we obtain the desired 3-GHZ state with a fidelity 0.573±0.024. Our Letter marks an important step for the future fault-tolerant photonic quantum computing, leading to the acceleration of building a large-scale optical quantum computer.

Optimization of the reflection in the optical coupling between high numerical aperture fibers and photonic integrated circuits

The optical coupling in silicon Photonic Integrated Circuits (PICs) remains one of the main topics in the improvement of the performance of these devices. Highly demanding parameter specifications, such as loss, reflection, and bandwidth, drive the continuous search for optimization. The use of High Numerical Aperture Fibers (HNA fibers) to couple light in small diameter mode edge couplers, is one of the existing technologies that address the coupling challenge. We demonstrate, using Eigenmode Expansion (EME) and Transfer Matrix Method (TMM) simulations, that the Optical Return Loss (ORL) of this coupling approach can be made as low as −45 dB for both Transverse Electric (TE) and Transverse Magnetic (TM) polarizations, simultaneously. The results from our TMM model agree well with a commercial solver one and are faster (six orders of magnitude) and more computationally efficient. It is shown that the refractive index in the TMM should be corrected to compensate for the Gouy phase shift in the non-guided sections of the optical coupling. Additionally, the reflection pattern, as a function of the gap between the fiber and the PIC, provides a way to control the distance of the fiber to avoid packaging-related problems.

Hybrid Graphene–Silicon Arrayed Waveguide Gratings for On-Chip Signal–Frequency Conversion

We present the design and simulations of a novel integrated device concept enabling a frequency conversion of a broad signal. The solution is based on a hybrid silicon–graphene photonic chip, which could be used for controlled spectrometry in low-cost devices. The device is based on a silicon-on-insulator (SOI) platform on which an arrayed waveguide grating (AWG) is designed for operation at the center wavelength of λ = 1800 nm. The AWG is spectrally separating one broad input signal to thirty-two-output channels with a channel spacing of 2.72 nm. The output signals are well separated and uniform with the extinction ratio and the standard deviation of 10.00 dB and 0.04, respectively. The 3 dB channel width is 1.34 nm, which is suitable for sensing applications with significant accuracy. After spacial and spectral separation, each output signal is then converted to one signal at 1480 nm wavelength through a graphene-based saturable absorber scheme. Therefore, the device allows the detection of each separated signal with a simple near-infrared camera on which the outputs are imaged using conventional optics, leading to a classical pixel/wavelength correspondence. Crossed-waveguide couplers are designed to combine the controlling signal at 1480 nm to each channel waveguide of the AWG. The combination of the signals saturates the graphene layer at the output waveguides, allowing the pass of the controlling wavelength. This device can be applied as a spectrometer in environmental sensing and monitoring with high efficiency and low cost.

Accelerating finite-difference frequency-domain simulations of inverse designed structures in nanophotonics using deep learning

The inverse design of nanophotonic devices is becoming increasingly relevant for the development of complex photonic integrated circuits. Electromagnetic first-order simulations contribute to the overwhelming computational cost of the optimization routines in established inverse design algorithms, requiring more efficient methods for enabling improved and more complex design process flows. Here we present such a method to predict the electromagnetic field distribution for pixel-discrete planar inverse designed structures using deep learning. Our model is able to infer accurate predictions used to initialize a conventional finite-difference frequency-domain algorithm and thus lowers the average time required for simulating the electromagnetic response of nanophotonic device layouts by up to 53% in iterative design process flows. We demonstrate the applicability of our deep learning method for the inverse design of photonic integrated powersplitters and mode converters, and we highlight the possibility of exploiting previous learning results in subsequent design tasks of novel functionalities via fine-tuning reduced data sets, thus improving computational speed further.

Passive wavelength selective polarization rotator in a hybrid waveguide platform

Polarization rotation and wavelength filtering are key functionalities used to build complex photonic integrated circuits. Both these functionalities have been demonstrated in various material and device platforms. We propose, for the first time, a fully passive wavelength selective polarization rotation in silicon nitride/amorphous silicon hybrid waveguide. We demonstrate TE0 → TM0 and TM0 → TE0 wavelength selective polarization rotator-cum-filter with a measured 3dB bandwidth of 14.8 nm. Further, we experimentally demonstrate a proof of concept for simultaneous coarse wavelength division multiplexing and polarization rotation for the first time in a passive configuration. We also show the feasibility of bandwidth engineering from 0.59 nm to 81 nm, enabled by the unique flexibility of the proposed hybrid waveguide.

Ultralow-loss optical interconnect enabled by topological unidirectional guided resonance.

Grating couplers that interconnect photonic chips to off-chip components are crucial for various optoelectronics applications. Despite numerous efforts in past decades, the existing grating couplers are still far from optimal in energy efficiency and thus hinder photonic integration toward a larger scale. Here, we propose a strategy to achieve ultralow-loss grating couplers by using unidirectional guided resonances (UGRs), suppressing the useless downward radiation with no mirror on the bottom. By engineering the dispersion and apodizing the geometry of grating, we experimentally realize a grating coupler with a record-low loss of -0.34 dB and 1-dB bandwidth exceeding 30 nm at the telecom wavelength of 1550 nm and further demonstrate an optic via with a loss of only -0.94 dB. Given that UGRs ubiquitously exist in a variety of grating geometries, our work sheds light on a systematic method to achieve energy-efficient optical interconnect and paves the way to large-scale photonic integration.

Quasi van der Waals Epitaxy of Single Crystalline GaN on Amorphous SiO2/Si(100) for Monolithic Optoelectronic Integration.

The realization of high quality (0001) GaN on Si(100) is paramount importance for the monolithic integration of Si-based integrated circuits and GaN-enabled optoelectronic devices. Nevertheless, thorny issues including large thermal mismatch and distinct crystal symmetries typically bring about uncontrollable polycrystalline GaN formation with considerable surface roughness on standard Si(100). Here a breakthrough of high-quality single-crystalline GaN film on polycrystalline SiO2/Si(100) is presented by quasi van der Waals epitaxy and fabricate the monolithically integrated photonic chips. The in-plane orientation of epilayer is aligned throughout a slip and rotation of high density AlN nuclei due to weak interfacial forces, while the out-of-plane orientation of GaN can be guided by multi-step growth on transfer-free graphene. For the first time, the monolithic integration of light-emitting diode (LED) and photodetector (PD) devices are accomplished on CMOS-compatible SiO2/Si(100). Remarkably, the self-powered PD affords a rapid response below 250µs under adjacent LED radiation, demonstrating the responsivity and detectivity of 2.01×105 A/W and 4.64×1013Jones, respectively. This work breaks a bottleneck of synthesizing large area single-crystal GaN on Si(100), which is anticipated to motivate the disruptive developments in Si-integrated optoelectronic devices.

Coherent Imaging with Photonic Lanterns

Photonic lanterns (PLs) are tapered waveguides that gradually transition from a multimode fiber geometry to a bundle of single-mode fibers (SMFs). They can efficiently couple multimode telescope light into a multimode fiber entrance at the focal plane and convert it into multiple single-mode beams. Thus, each SMF samples its unique mode (lantern principal mode) of the telescope light in the pupil, analogous to subapertures in aperture masking interferometry (AMI). Coherent imaging with PLs can be enabled by the interference of SMF outputs and applying phase modulation, which can be achieved using a photonic chip beam combiner at the backend (e.g., the ABCD beam combiner). In this study, we investigate the potential of coherent imaging by the interference of SMF outputs of a PL with a single telescope. We demonstrate that the visibilities that can be measured from a PL are mutual intensities incident on the pupil weighted by the cross correlation of a pair of lantern modes. From numerically simulated lantern principal modes of a 6-port PL, we find that interferometric observables using a PL behave similarly to separated-aperture visibilities for simple models on small angular scales (<λ/D) but with greater sensitivity to symmetries and capability to break phase angle degeneracies. Furthermore, we present simulated observations with wave front errors (WFEs) and compare them to AMI. Despite the redundancy caused by extended lantern principal modes, spatial filtering offers stability to WFEs. Our simulated observations suggest that PLs may offer significant benefits in the photon-noise-limited regime and in resolving small angular scales at the low-contrast regime.

Mixing Materials for Integrated Photonic Innovation

Photonics, an ever-growing field since the invention of lasers in the 1960s, has been applied in wide-ranging applications such as optical communications, sensing, imaging and more. Photonic integrated circuits (PIC) are the next step to take this technology and shrink it onto a semiconductor chip, leading to more compact, cheaper, and lower power consumption solutions. However, integrated photonics faces the challenge of lacking a single material platform that encompasses all the desired properties, unlike its more mature electronic integrated circuit counterpart which uses silicon with a standardised fabrication process known as complementary metal oxide semiconductor (CMOS). To overcome this limitation, researchers are exploring hybrid and heterogeneous integration techniques. By combining the strengths of different photonic platforms, such as III-V materials for light emission, silicon for strong light guidance, silicon-nitride for visible light guiding, and lithium niobate for its modulating capabilities, integrated photonic technologies can harness the collective advantages and unlock new possibilities. “Light brings us the news from the universe.” — Sir William Bragg