Microring Modulator Research Articles

Highly reliable integrated W-band transmitter based on an on-chip dual-mode DFB laser and cascaded microring modulators

We propose an integrated W-band transmitter enabled by an integrated dual-mode distributed feedback (DFB) laser and cascaded silicon photonic microring modulators for next-generation wireless communication. 10 Gb/s error-free intensity modulation and direct detection W-band transmission are achieved in experiments by using the dual-mode DFB laser and two free-running lasers. Moreover, we conduct an experiment of dual-carrier modulation based on cascaded microring modulators, achieving 3 dB signal-to-noise ratio improvement and better signaling integrity for wireless communication. The proposed photonic integrated W-band transmitter will be a viable solution for a high-speed and low-power wireless communication system.

Silicon multi-mode micro-ring modulator for improved robustness to optical nonlinearity.

Due to the resonant nature and silicon's strong optical nonlinearity, the system's performance of silicon micro-ring modulators can be seriously affected by the input optical power. In this Letter, we proposed and experimentally demonstrated a multi-mode silicon micro-ring modulator to mitigate its optical nonlinear effects by operating in the TE1 mode. The TE1 mode features a high nonlinear threshold compared with the TE0 mode because of its larger waveguide loss and larger mode effective area. Under the condition of 10 mW optical input power, the resonance spectrum maintains a good symmetric Lorentz shape. The resonant wavelength shifts less than one resonance linewidth, showing an improved robustness to optical nonlinearity compared with regular silicon micro-ring modulators.

Improving Linewidth and Extinction Ratio Performances of Lithium Niobate Ring Modulator Using Ring‐Pair Structure

Electro‐optic modulators lie at the heart of complex integration and high‐density electro‐optic systems. One of the representative electro‐optic modulators is thin‐film lithium niobate‐based microring modulator which has demonstrated advantages of compact footprint, low optical loss, and high modulation efficiency. However, the linewidth and extinction ratio of ring modulators are fundamentally limited by the ring losses and coupling, respectively. To this end, a novel type of electro‐optic modulators with ring‐pair structure on thin‐film lithium niobate platform is proposed, which brings substantial improvement of linewidth and extinction ratio. The ring‐pair modulator exhibits a larger linewidth up to 22 GHz, 1.74 times larger than that of the single‐ring resonator with same design parameters. Moreover, the experimental results also reveal that the added‐up extinction ratio of ring‐pair resonator goes beyond 30 dB, much larger than that in an individual ring resonator. These advantages of ring‐pair modulators pave a new way for the application of compact ring‐based modulators with large working wavelength window and high extinction ratio, to be exploited in quantum optics, programmable nanophotonics and optical sensors, etc.

Versatile Tunning of Compact Microring Waveguide Resonator Based on Lithium Niobate Thin Films

With the advancement of modulation technology and the requirement for device miniaturization and integration, lithium niobate on insulator (LNOI) can be a versatile platform for this pursuit, as it can confine the transmitted light at the nanoscale, leading to a strong light–matter interaction, which can sensitively capture external variations, such as electric fields and temperature. This paper presents a compact microring modulator with versatile tuning based on X-cut LNOI. The LNOI modulator equipped with electrodes with a coverage angle of 120∘ achieved a maximum electro-optic (EO) tuning efficiency of 13 pm/V and a maximum extinction ratio of 11 dB. The asymmetry in the static or quasi-static electro-optic tuning of the microring modulator was also analyzed. Furthermore, we measured the thermal-optic effect of the device with a sensitivity of 26.33 pm/∘C, which can potentially monitor the environment temperature or compensate for devices’ functional behavior. The demonstrated efficient and versatile compact microring modulator will be an important platform for on-chip active or passive photonic components, microring-based sensor arrays and integrated optics.

Resonant plasmonic micro-racetrack modulators with high bandwidth and high temperature tolerance

Resonant modulators encode electrical data onto wavelength-multiplexed optical carriers. Today, silicon microring modulators are perceived as promising to implement such links; however, they provide limited bandwidth and need thermal stabilization systems. Here we present plasmonic micro-racetrack modulators as a potential successor of silicon microrings: they are equally compact and compatible with complementary-metal–oxide–semiconductor-level driving voltages, but offer electro-optical bandwidths of 176 GHz, a 28 times improved stability against operating temperature changes and no self-heating effects. The temperature-resistant organic electro-optic material enables operation at 85 °C device temperature. We show intensity-modulated transmission of up to 408 Gbps at 12.3 femtojoules per bit with a single resonant modulator. Plasmonic micro-racetrack modulators offer a solution to encode high data rates (for example, the 1.6 Tbps envisioned by next-generation communications links) at a small footprint, with low power consumption and marginal, if no, temperature control.

Efficient 330-Gb/s PAM-8 modulation using silicon microring modulators.

We propose and demonstrate a high-efficiency silicon microring modulator for next-generation optical transmitters operating at line rates above 300 Gb/s. The modulator supports high-order PAM-8 modulation up to 110 Gbaud (330 Gb/s), with a driving voltage of 1.8 Vpp. The small driving voltage and device capacitance yields a dynamic energy consumption of 3.1 fJ/bit. Using the modulator, we compare PAM-8 with ultrahigh baud rate PAM-4 of up to 130 Gbaud (260 Gb/s) and show PAM-8 is better suited for 300-Gb/s lane rate operation in bandwidth-constrained short-reach systems.

Towards a high-density photonic tensor core enabled by intensity-modulated microrings and photonic wire bonding

We propose a photonic processing unit for high-density analog computation using intensity-modulation-based microring modulators (IM-MRMs). The output signal at the fixed resonance wavelength is directly intensity modulated by changing the extinction ratio (ER) of the IM-MRM . Thanks to the intensity-modulated approach, the proposed photonic processing unit is less sensitive to the inter-channel crosstalk. Simulation results reveal that the proposed design offers a maximum of 17-fold increase in wavelength channel density compared to its wavelength-modulated counterpart. Therefore, a photonic tensor core of size 512 times 512 can be realized by current foundry lines. A convolutional neural network (CNN) simulator with 6-bit precision is built for handwritten digit recognition task using the proposed modulator. Simulation results show an overall accuracy of 96.76%, when the wavelength channel spacing suffers a 3-dB power penalty. To experimentally validate the system, 1000 dot product operations are carried out with a 4-bit signed system on a co-packaged photonic chip, where optical and electrical I/Os are realized using photonic and electrical wire bonding techniques. Study of the measurement results show a mean squared error (MSE) of 3.09times 10^{-3} for dot product calculations. The proposed IM-MRM, therefore, renders the crosstalk issue tractable and provides a solution for the development of large-scale optical information processing systems with multiple wavelengths.

Advances in silicon photonics for high-capacity optical interconnects - INVITED

We review our recent progress on advanced silicon photonic devices and photonic circuits, including advanced grating couplers, modulators, mode and polarization division multiplexing and integrated optical signal processors for use in high capacity data center interconnects. The use of shifted polysilicon overlay gratings on waveguide grating couplers to improve coupling efficiency and polarization independence will be described. We also present our recent results on silicon microring and silicon-germanium electroabsorption modulators for 100Gbaud data transmission and their use polarization and mode division multiplexed optical fiber interconnects. We present novel integrated optical signal processors which can unscramble the mixing of polarization and mode data lanes that will occur after fiber transmission and demonstrate 400Gb/s per wavelength intensity modulation direct-detection silicon photonic transceivers.

Self-Stabilized 50 Gb/s Silicon Photonic Microring Modulator Using a Power-Independent and Calibration-Free Control Loop

This paper demonstrates the possibility of automatically stabilizing the working condition of an integrated Silicon Photonics microring modulator with a novel dithering-based control scheme. The proposed feedback strategy leverages a real-time acquisition of the modulator non-linear transfer function (TF) and operates by setting the target locking point to the zero of the TF second derivative, i.e. where the ring slope is maximum. This results in a control algorithm that is both power-independent and calibration-free. The paper shows that the operating point identified in this way has a negligible difference with respect to the optimum working condition of minimum Transmitter Penalty normally targeted and that the employed dithering signal does not affect the modulation quality. The control performances, made possible by an FPGA-based platform ensuring a 30 ms response time, are assessed in a 50 Gbit/s routing scenario, demonstrating effective compensation of wavelength and thermal variations and successful transmission even in demanding environments.

Engineered second-order nonlinearity in silicon nitride

The lack of a bulk second-order nonlinearity (χ(2)) in silicon nitride (Si3N4) keeps this low-loss, CMOS-compatible platform from key active functions such as Pockels electro-optic (EO) modulation and efficient second harmonic generation (SHG). We demonstrate a successful induction of χ(2) in Si3N4 through electrical poling with an externally-applied field to align the Si-N bonds. This alignment breaks the centrosymmetry of Si3N4, and enables the bulk χ(2). The sample is heated to over 500°C to facilitate the poling. The comparison between the EO responses of poled and non-poled Si3N4, measured using a Si3N4 micro-ring modulator, shows at least a 25X enhancement in the r33 EO component. The maximum χ(2) we obtain through poling is 0.30pm/V. We observe a remarkable improvement in the speed of the measured EO responses from 3 GHz to 15 GHz (3 dB bandwidth) after the poling, which confirms the χ(2) nature of the EO response induced by poling. This work paves the way for high-speed active functions on the Si3N4 platform.

4 × 25 Gb/s PAM4 optical transmitter for micro‐ring modulator with thermal control

AbstractThe explosive growth of bandwidth demands of data center and super‐computing systems spur the appliance and development of optoelectronic‐based solutions such as micro‐ring modulator (MRM) transmitters, and advanced modulation schemes such as four‐level pulse‐amplitude modulation (PAM4). In this paper, a 4 × 25 Gb/s PAM4 MRM transmitter fabricated in 0.13 μm SiGe BiCMOS technology is presented. It consists of four‐channel MRM driver and thermal control loop. Capacitor and resistor degeneration techniques and inductor peaking techniques are adopted to expand channel bandwidth. Meanwhile, the predistortion technique is utilized to compensate for MRM nonlinearity, and auto gain control (AGC) circuits to enable the MRM driver to realize a fixed differential output swing of 3.5 Vpp. Furthermore, a thermal control method based on analog to digital converter, digital to analog converter, and logic control circuits is proposed to compensate for the temperature sensitivity of MRM. The measurement results show that the 25 Gb/s nonreturn‐to‐zero optical eye achieves an extinction ratio of 5.63 dB, and the PAM4 eye can be observed up to 40 Gb/s.

Ultra-Wide Free-Spectral-Range Silicon Microring Modulator for High Capacity WDM

Silicon microring modulators (MRM) are a promising technology for next generation datacenter interconnects, where migration to higher data capacities will require the increasing use of wavelength division multiplexing (WDM). However the periodic repetition of wavelength resonances, and the limited free-spectral range (FSR) of MRMs, can limit the number of WDM channels when we use the wavelength selectivity of the MRM to modulate a particular wavelength from frequency comb sources or other multi-wavelength sources propagating in the bus waveguide. In this paper, we realize an ultra-compact, high bandwidth, CMOS compatible MRM which has an ultra-wide FSR of 4 THz, 3-dB electro-optic (EO) bandwidth of >67 GHz and which can operate at high datarates for standard single mode fiber transmission in the C-band. Using the modulator, we demonstrate 100 Gbaud PAM-4 intensity modulation-direct detection (IM-DD) with 4 wavelengths within a single FSR in the wavelength range of 1540 nm–1570 nm. The bit-error-rate (BER) of the transmission was below the general 7% hard-decision forward-error correction (HD-FEC) of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> .

T-shaped silicon waveguide coupled with a micro-ring resonator-based Fano resonance modulator.

Fano resonance has an asymmetric and sharp resonance peak near the resonance wavelength, enhancing optical modulation performance. Here, a Fano resonant silicon optical modulator with a micro-ring resonator (MRR) coupled with a T-shaped waveguide is designed. Compared with an MRR modulator, a Fano resonance-based modulator has a smaller wavelength range of changes in optical intensity (from 0a.u. to 1a.u.). Under the condition of achieving the same light intensity change, Fano resonance only needs to shift the wavelength by 0.07 times compared with MRR. By optimizing the doping section and the Fano resonance line shape, the modulation depth of the Fano modulator is 12.44dB, and an insertion loss of 0.41dB is obtained. Moreover, it improves the modulation linearity. This modulator provides a new idea, to the best of our knowledge, for the single-cavity Fano resonance modulator.

Long Short Term Memory Neural Network (LSTMNN) and inter-symbol feature extraction for 160 Gbit/s PAM4 from silicon micro-ring transmitter

We propose and experimentally illustrate the use of Long Short Term Memory Neural Network (LSTMNN) and inter-symbol feature extraction (IFE) to recover 4-level pulse amplitude modulation (PAM4) data transmitted from a silicon micro-ring modulator (SiMRM) operated at 160 Gbit/s. Pre-hard-decision (HD) forward error correction (FEC) requirement (i.e. bit-error-rate, BER < 3.8 × 10−3) is achieved in the 160 Gbit/s PAM4 signal produced using a 47-GHz bandwidth SiMRM after 1 km single-mode-fiber (SMF) transmission.

Combo-PON OLT Transceiver Using Photonic Integration Technology

In this work, a prototype of 10G Combo-PON OLT transceiver based on photonic integrated circuits (PIC) is proposed and demonstrated. Key optical components for Combo-PON OLT transceiver, including high-power DFB laser, micro-ring modulator and WDM, have been developed and validated. The Combo-PON OLT transceiver integrated four XGS-PON/GPON ports and all ports comply with I-TUT G.984.2 Class C+ standard. The advantages and disadvantages of PIC in PON application are analyzed. The analysis shows that PIC can also provide a cost and power-efficient way to implement the next generation PON transceiver for high density PON ports.

Special issue “optical communications, sensing, and laser applications”

Special issue “optical communications, sensing, and laser applications”

Imaging of electromagnetic waves using a radio over fiber system including an Si photonics microring modulator array.

We propose an electromagnetic wave imaging system using Si photonics microring modulators (MRMs) as radio over fiber components. In this system, radio frequency signals detected at microwave probes are applied to the connected MRMs; an MRM is tuned to the laser wavelength using the thermo-optic effect to read-out through the optical transmission. By repeating this process for all MRMs and mapping the read-out signals in two dimensions, the distribution of electromagnetic waves can be visualized. Such system operation was demonstrated at 3.5 GHz in a 37.5 × 37.5 mm2 probing area, for which we confirmed the agreement with theoretical simulations.

Multi-Mode Transmitter Based on Silicon Microring Modulators

We propose and demonstrate a multi-mode transmitter based on cascaded silicon microring modulators (MRMs). By sharing bus waveguide at drop ports of the MRMs, data modulation and mode multiplexing could be achieved simultaneously, resulting in a simplified layout with compact size. For the proof-of-concept demonstration, multi-mode transmitter for TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> modes is fabricated. Transmission of non-return-to-zero on-off keying (NRZ-OOK) signals with the bit rate of 2 × 25 Gbps is experimentally demonstrated. Measured eye diagrams and bit error rate (BER) results indicate good transmission performance.

Polymer waveguide photonic interconnect for multichip communications-based heterogeneous integration

An on-package optical interconnect design is proposed for the first time, with silicon photonics in conjunction with the polymer-on-glass interposer technology to enable heterogeneous integration. Glass substrates are used for low-cost, high reliability packaging while silicon photonics allows for high-speed modulation and wavelength division multiplexing within a small footprint. By combining silicon-photonic and benzo-cyclobutene-on-glass interposer technologies, we propose a scalable on-package photonic interconnect that can provide data rates >224 Gb / s for medium-reach links. Our proposed interconnect considers microring modulators and high-speed detectors available in photonic-foundry processes. We present the power-budget analysis to identify the key limiting parameters toward achieving an energy consumption of < 1 pJ / bit.

Ultrahigh extinction ratio silicon micro-ring modulator by MDM resonance for high speed PAM-4 and PAM-8 signaling.

Due to the difficulty of controlling the waveguide loss in the doping region, high-speed silicon micro-ring modulators usually have limited extinction ratio. In this work, we present a mode-division-multiplexing (MDM) resonance-enhanced silicon micro-ring modulator with an ultrahigh extinction ratio. We used a two-mode micro-ring resonator and a mode conversion circular structure to trap the light twice within a single micro-ring resonator. Proof-of-concept high extinction ratio up to 55 dB was obtained. 30 Gb/s PAM-8 and 50 Gb/s PAM-4 signaling with a bit error rate below the hard-decision forward error correction (HD-FEC) threshold were demonstrated with the fabricated modulator, indicating great potential for high-order pulse amplitude modulation (PAM).