Silicon Microring Resonator Research Articles

A 5 × 200 Gbps microring modulator silicon chip empowered by two-segment Z-shape junctions

Optical interconnects have been recognized as the most promising solution to accelerate data transmission in the artificial intelligence era. Benefiting from their cost-effectiveness, compact dimensions, and wavelength multiplexing capability, silicon microring resonator modulators emerge as a compelling and scalable means for optical modulation. However, the inherent trade-off between bandwidth and modulation efficiency hinders the device performance. Here we demonstrate a dense wavelength division multiplexing microring modulator array on a silicon chip with a full data rate of 1 Tb/s. By harnessing the two individual p-n junctions with an optimized Z-shape doping profile, the inherent trade-off of silicon depletion-mode modulators is greatly mitigated, allowing for higher-speed modulation with energy consumption of sub-ten fJ/bit. This state-of-the-art demonstration shows that all-silicon modulators can practically enable future 200 Gb/s/lane optical interconnects.

Experimental demonstration of a flexible-grid 1 × (2 × 3) mode- and wavelength-selective switch using silicon microring resonators and counter-tapered couplers

Experimental demonstration of a flexible-grid 1 × (2 × 3) mode- and wavelength-selective switch using silicon microring resonators and counter-tapered couplers

Giant optical absorption of a PtSe2-on-silicon waveguide in mid-infrared wavelengths.

Low-dimensional platinum diselenide (PtSe2) is a promising candidate for high-performance optoelectronics in the short-wavelength mid-infrared band due to its high carrier mobility, excellent stability, and tunable bandgap. However, light usually interacts moderately with low-dimensional PtSe2, limiting the optoelectronic responses of PtSe2-based devices. Here we demonstrated a giant optical absorption of a PtSe2-on-silicon waveguide by integrating a ten-layer PtSe2 film on an ultra-thin silicon waveguide. The weak mode confinement in the ultra-thin waveguide dramatically increases the waveguide mode overlap with the PtSe2 film. Our experimental results show that the absorption coefficient of the PtSe2-on-silicon waveguide is in the range of 0.0648 dB μm-1 to 0.0704 dB μm-1 in a spectral region of 2200 nm to 2300 nm wavelengths. Furthermore, we also studied the optical absorption in an ultra-thin silicon microring resonator. Our study provides a promising approach to developing PtSe2-on-silicon hybrid optoelectronic integrated circuits.

Photonic Neural Networks Based on Integrated Silicon Microresonators

Recent progress in artificial intelligence (AI) has boosted the computational possibilities in fields in which standard computers are not able to perform adequately. The AI paradigm is to emulate human intelligence and therefore breaks the familiar architecture on which digital computers are based. In particular, neuromorphic computing, artificial neural networks (ANNs), and deep learning models mimic how the brain computes. There are many applications for large networks of interconnected neurons whose synapses are individually strengthened or weakened during the learning phase. In this respect, photonics is a suitable platform for implementing ANN hardware owing to its speed, low power dissipation, and multi-wavelength opportunities. One photonic device that could serve as an optical neuron is the optical microring resonator. Indeed, microring resonators exhibit a nonlinear response and the capability for optical energy storage, which can be used to implement fading memory. In addition, their characteristic resonant behavior makes them extremely sensitive to input wavelengths, which promotes wavelength division multiplexing (WDM) applications and enables their use as WDM-based synapses (weight banks) in the linear regime. Remarkably, using silicon photonics, photonic integrated circuits can be fabricated in volume and with integrated electronics onboard. For these reasons, here, we describe the physics of silicon microring resonators and arrays of microring resonators for application in neuromorphic computing. We describe different types of ANNs, from feedforward networks to photonic extreme learning machines, and reservoir computing. In addition, we discuss hybrid systems in which silicon microresonators are coupled with other active materials. This review introduces the basics and discusses the most recent developments in the field.

Cryogenic optical packaging using photonic wire bonds

The widespread adaptation of systems relying on optically controlled quantum information will require reliable and efficient multi-channel fiber-to-chip connections that function at cryogenic temperatures. Here we demonstrate low loss (2 dB per channel) connections between a single mode fiber array and tapered silicon waveguides down to 5 K using polymer based photonic wire bonds (PWBs). A method is described for assembling the silicon chip and fiber array such that the PWB connections are robust to temperature cycling and cryostat bakeout. The threshold power handling capability of the PWBs is greater than 4 dBm, sufficient to demonstrate optical bistability in silicon microring resonators coupled to the waveguides at 5 K.

Design and study of silicon microring resonator based all-optical binary-coded decimal adder

Design and study of silicon microring resonator based all-optical binary-coded decimal adder

Real-time reconfigurable on-chip photonic frequency decoder.

A group-delay-unit-based integrated silicon photonic integrated circuit (PIC) is employed as a reconfigurable analog radio frequency decoder, which provides a real-time temporal and spectral analysis of any arbitrary multi-tone signal in the micro- and mm-wave range. The circuit is based on cascaded Mach-Zehnder interferometer embedded silicon microring resonators as variable delay units. The temporal decoding of the multi-tone input signal is demonstrated by tuning the signal with respect to the ring resonator delay and resonance. A one-to-one conformal time-to-frequency mapping provides real-time spectral decoding of the signal under test without additional digital signal processing. The idea is validated by several experimental results with single-tone and two-tone input signals in a compact, low-power, silicon PIC. The proposed real-time temporal analog frequency decoder may be very intriguing for high-speed, low-latency wireless applications, such as autonomous driving and 6G.

A silicon micro-ring resonator with unprecedented large free spectral range via double injection

A silicon-on-insulator submicron multimode micro-ring resonator symmetrically coupled to two bus waveguides via bent asymmetrical directional coupler to achieve unprecedented-large FSR is proposed based on double-injection configuration. An analytical model based on the transfer matrix method is developed to analyze the proposed structure and the physical mechanism for the FSR enlargement is thoroughly analyzed. In addition, the coupling angle is cleverly selected to improve the spectral shape and the extinction ratio at the resonant wavelengths. Finite difference time domain simulations show that ultra large FSRs of 180 nm and 206 nm can be obtained.

Optically Transparent and Thermally Efficient 2D MoS2 Heaters Integrated with Silicon Microring Resonators

Thermal tuning of the optical refractive index in the waveguides to control light phase accumulation is essential in photonic-integrated systems and applications. In silicon photonics, microheaters are mainly realized by metal wires or highly doped silicon lines, placed at a safe distance (∼1 μm) from the waveguide to avoid considerable optical loss. However, this poses a significant limitation for heating efficiency because of the excessive free-carrier loss when a heater is brought closer to the optical path. In this work, we present a new concept of using optically transparent 2D semiconductors (e.g., MoS2) for realizing highly efficient waveguide-integrated heaters operating at telecom wavelengths. We demonstrate that a single-layer MoS2 heater with negligible optical absorption in the infrared can be placed in close proximity (only 30 nm) to the waveguide and show the best-reported power consumption of Pπ ∼ 7.5 mW for waveguide-integrated heaters (no thermal insulations) without sacrificing the optical insertion loss. The heater’s response time is ∼25 μs, which is limited by the Au/1L-MoS2 Schottky contact. Both the efficiency and response time can be further significantly improved by realizing 2D MoS2 heaters with Ohmic contacts. Our work shows clear advantages of employing 2D semiconductors for heater applications and paves the way for developing novel energy-efficient loss-less 2D heaters for on-chip photonic-integrated circuits.

Silicon microring resonator based all-optical 3-input majority gate and its applications

In this study, we propose an all-optical majority gate using silicon waveguide-based microring resonator for the first time to our knowledge. All-optical microring resonator based majority gate has attractive properties such as energy-efficient, ultra-high-speed, and compact which are essential for optical computing. We have designed different logic circuits such as AND, OR, NOR, NAND, and one-bit full adder by exploiting the majority gate with inverter circuits. Optoelectronic conversion which limits the operational speed is avoided in our design. The operational speed of our design is nearly 260 Gbps. The required pump power for switching is only 1.66 mW for micro-ring resonator based switch which is very less comparatively. These designs have been realized in MATLAB as well as in Ansys Lumerical finite difference time domain (FDTD) simulation platform. The "figure of merits" of the presented majority gate is achieved numerically through simulation. The obtained values of extinction ratio and contrast ratio are much higher for the proposed majority gate and the values are 28.11 dB and 32.88 dB, respectively. The on-off ratio is also high for single microring resonator and it is 38.2 dB.

On-chip wavelength division multiplexing filters using extremely efficient gate-driven silicon microring resonator array

Silicon microring resonators (Si-MRRs) play essential roles in on-chip wavelength division multiplexing (WDM) systems due to their ultra-compact size and low energy consumption. However, the resonant wavelength of Si-MRRs is very sensitive to temperature fluctuations and fabrication process variation. Typically, each Si-MRR in the WDM system requires precise wavelength control by free carrier injection using PIN diodes or thermal heaters that consume high power. This work experimentally demonstrates gate-tuning on-chip WDM filters for the first time with large wavelength coverage for the entire channel spacing using a Si-MRR array driven by high mobility titanium-doped indium oxide (ITiO) gates. The integrated Si-MRRs achieve unprecedented wavelength tunability up to 589 pm/V, or VπL of 0.050 V cm with a high-quality factor of 5200. The on-chip WDM filters, which consist of four cascaded ITiO-driven Si-MRRs, can be continuously tuned across the 1543–1548 nm wavelength range by gate biases with near-zero power consumption.

Spectra reconfiguration of a silicon microring resonator via double injection with different angles.

A reconfigurable silicon microring filter, which is constructed by cascading a tunable Mach-Zehnder interferometer and a double injected silicon microring resonator with a variable input angle, is proposed and investigated. The spectra reconfigurations of the optical filter were simulated and analyzed using the transmission matrix method. The results show that when keeping the perimeter of the microring constant, the free spectral range (FSR) of the filter can be multiplied by adjusting the angle between the two injections. Moreover, by changing the coupling coefficients of the microring and the optical power ratio between the two injections, different types of spectral responses such as square, sinusoidal, and flat-top interleaver can be obtained. The device is simple and easy to integrate, and its capabilities to expand the FSR and spectral reconfiguration may have great potential in reconfigurable integrated optic chips.

Automated sample-to-answer system for rapid and accurate diagnosis of emerging infectious diseases

Automated sample-to-answer systems that promptly diagnose emerging infectious diseases, such as zoonotic diseases, are crucial to preventing the spread of infectious diseases and future global pandemics. However, automated, rapid, and sensitive diagnostic testing without professionals and sample capacity and type limitations remains unmet needs. Here, we developed an automated sample-to-answer diagnostic system for rapid and accurate detection of emerging infectious diseases from clinical specimens. This integrated system consists of a microfluidic platform for sample preparation and a bio-optical sensor for nucleic acid (NA) amplification/detection. The microfluidic platform concentrates pathogens and NAs in a large sample volume using adipic acid dihydrazide and a low-cost disposable chip. The bio-optical sensor allows label-free, isothermal one-step NA amplification/detection using a ball-lensed optical fiber-based silicon micro-ring resonator sensor. The system is integrated with software to automate testing and perform analysis rapidly and simply; it can distinguish infection status within 80 min. The detection limit of the system (0.96 × 101 PFU) is 10 times more sensitive than conventional methods (0.96 × 102 PFU). Furthermore, we validated the clinical utility of this automated system in various clinical specimens from emerging infectious diseases, including 20 plasma samples for Q fever and 13 (11 nasopharyngeal swabs and 2 saliva) samples for COVID-19. The system showed 100% sensitivity and specificity for detecting 33 samples of emerging infectious diseases, such as Q fever, other febrile diseases, COVID-19, human coronavirus OC43, influenza A, and respiratory syncytial virus A. Therefore, we envision that this automated sample-to-answer diagnostic system will show high potential for diagnosing emerging infectious diseases in various clinical applications.

A Multi-layered GaGeTe Electro-Optic Device Integrated in Silicon Photonics

Electrically tunable devices contribute significantly to key functions of photonics integrated circuits. Here, we demonstrate the tuning of the optical index of refraction based on hybrid integration of multi-layered anisotropic GaGeTe on a silicon micro-ring resonator (Si-MRR). Under static applied (DC) bias and transverse-electric (TE) polarization, the device exhibits a linear resonance shift without any amplitude modulation. However, for the transverse-magnetic (TM) polarization, both amplitude and phase modulation is observed. The corresponding wavelength shift and half-wave voltage length product <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$(V_{\pi} . l)$</tex-math></inline-formula> for the TE polarization are -1.78 pm/V and 0.9 V.cm, respectively. These values are enhanced for the TM polarizations and correspond to - 6.65 pm/V and 0.28 V.cm, respectively. The dynamic radio frequency (RF) response of the devices was also tested at different bias conditions. Remarkably, the device exhibits a 1.6 MHz and 2.1 MHz response at 0 V and 7 V bias, respectively. Based on these findings, the integration of 2D GaGeTe on the silicon photonics platform has great potential for the next generation of integrated photonic applications such as switches and phase shifters.

Performance enhancement of on-chip optical switch and memory using Ge2Sb2Te5 slot-assisted microring resonator

Phase change material Ge2Sb2Te5 (GST) has recently emerged as a highly promising candidate for reconfigurable photonic devices owing to its non-volatility, high optical contrast, and fast transition speed between the amorphous and crystalline states. We propose a novel nonvolatile 1 × 2 optical switching and multi-level memory based on a GST slot-assisted microring resonator (MRR). GST slot is embedded in silicon microring resonator to enhance the light-matter interaction. The device demonstrates a low insertion loss of 0.7 dB in the amorphous state at the drop port and 0.1 dB in the crystalline state at the through port. The high extinction ratios of around 28.32 dB and 22.71 dB can be achieved at the drop and through ports, respectively. A multi-level photonic memory was proposed by combining MRR and a U-bend feedback loop embedded with GST slot. Free spectral range can be expanded from 21.6 nm to 43.2 nm by modifying the length of the feedback loop instead of the microring diameter. The minimum read contrast of 19% among each level can be achieved by changing two GST states individually for a reliable 4-level memory. The 2-level memory demonstrates a read contrast of 90% which is around 4.3 times higher than the traditional device. Our all-optical approach represents a significant step towards the development of low-loss and reliable photonic memory for neuromorphic computing and artificial intelligence.

Reconfigurable Low-Threshold All-Optical Nonlinear Activation Functions Based on an Add-Drop Silicon Microring Resonator

The realization of optical nonlinear activation functions (NAFs) is essential for integrated optical neural networks (ONNs). Here, we propose and experimentally demonstrate a photonic method to implement reconfigurable and low-threshold all-optical NAFs based on a compact and high-Q add-drop microring resonator (MRR) on silicon. In the experiment, four different NAFs including softplus, radial basis, clamped ReLU, and sigmoid functions are realized by exploiting the thermo-optical (TO) effect of the MRR. The threshold to implement NAFs is as low as 0.08 mW. As a demonstration, a handwritten digit classification benchmark task is simulated based on a convolutional neural network (CNN) using the obtained activation functions, where an accuracy of 98% is realized. Thanks to the unique advantages of ultra-compact footprint and ultralow threshold, the proposed nonlinear unit is promising to be widely used in large-scale integrated ONNs.

Programmable low-power consumption all-optical nonlinear activation functions using a micro-ring resonator with phase-change materials.

A programmable hardware implementation of all-optical nonlinear activation functions for different scenarios and applications in all-optical neural networks is essential. We demonstrate a programmable, low-loss all-optical activation function device based on a silicon micro-ring resonator loaded with phase change materials. Four different nonlinear activation functions of Relu, ELU, Softplus and radial basis functions are implemented for incident signal light of the same wavelength. The maximum power consumption required to switch between the four different nonlinear activation functions in calculation is only 1.748 nJ. The simulation of classification of hand-written digit images also shows that they can perform well as alternative nonlinear activation functions. The device we design can serve as nonlinear units in photonic neural networks, while its nonlinear transfer function can be flexibly programmed to optimize the performance of different neuromorphic tasks.

Implementation of all-optical synchronous and asynchronous binary up counters using silicon micro-ring resonator

All-optical synchronous and asynchronous binary up counters that employ silicon micro-ring resonator-based T flip-flops are proposed. An alternative approach to design all-optical synchronous and asynchronous binary up counters is also demonstrated using fewer optical components. The proposed design is theoretically realized in MATLAB simulation software at a very high operational speed of 260 Gbps. The performance of this design is validated through amplitude difference, contrast ratio, extinction ratio, amplitude modulation, on–off ratio, etc. The optimized values of the micro-ring resonator are achieved through numerical simulation, which will help to implement the proposed design practically.

Integrated thin-silicon passive components for hybrid silicon-lithium niobate photonics

A silicon photonics platform with a reduced silicon layer thickness, which is suitable for hybrid thin-film lithium niobate traveling-wave electro-optic modulators, is used to design low loss waveguides, precise directional couplers, high-quality-factor silicon microring resonators and broad-top coupled microring filters. These designs are verified with experimental measurements and show a way to include such components without requiring a second layer of crystalline silicon of different thickness for this purpose.

Modelling of one-bit Arithmetic Logic Circuit using silicon micro-ring resonator

All-optical technology overcomes the problems that arise in traditional digital circuits such as speed limitation, energy consumption and size. In this manuscript, we have implemented a one-bit arithmetic logic circuit employing all-optical silicon micro-ring resonator that utilizes the advantages over other all-optical techniques. The Arithmetic logic circuit is the core component of ultra-fast combinational circuits. The proposed arithmetic logic circuit is validated through MATLAB at about 260 Gbps. Performance of our design has been investigated by numerical simulation. The critical parameters of MRR are optimized on the basis of performance metrics.