Microring Modulator Research Articles

The high‐efficiency co‐design and the measurement verification of high‐bandwidth silicon photonic microring modulator

The microring modulator (MRM) is a small-size and low-power component, which is the potential for the next-generation optical interconnection. By the theoretical analysis, increasing the electrical bandwidth, which is relevant to the cross section and the doping concentration of the doping region, is a better way to increase electro-optical (EO) bandwidth. Therefore, a new doping profile of the PN depletion region with 4 doping concentration levels is introduced considering the electrical bandwidth. Based on the new doping profile, the MRM with the 160 μm length and the 0.33 and 0.2 μm coupling space are determined considering the trade-off between the EO bandwidth, quality factor (Q), extinction ratio, area of MRM, and power consumption. Moreover, the MRM is characterised and is applied in a wavelength division multiplexing transmitter. By the measurement, the transmitter with the designed MRM could transmit PAM4 signal at 52 Gbps rate, which indicates the MRM could be potential for the 50 Gbps/ch optical interconnection.

C-band 67 GHz silicon photonic microring modulator for dispersion-uncompensated 100 Gbaud PAM-4.

A very-high-bandwidth integrated silicon microring modulator (MRM) designed on a commercial silicon photonics (SiP) platform for C-band operation is presented. The MRM has a 3 dB electro-optic (EO) bandwidth of over 67 GHz and features a small footprint of 24 µm × 70 µm. Using the MRM, we demonstrate intensity modulation-direct detection (IM-DD) transmission with 4-level pulse amplitude modulation (PAM-4) signaling of over 100 Gbaud. By utilizing the optical peaking effect and negative chirp in the MRM, we extend the transmission distance, which is limited by the fiber-dispersion-induced frequency fading. Using a standard single-mode fiber (SSMF) for transmission across distances of up to 2 km, we measured the data transmission of 100 Gbaud PAM-4 signals with a bit error rate (BER) under the general 7% hard-decision forward-error correction (HD-FEC) threshold. The MRM enables an extended transmission distance for 100 Gbaud signaling in the C-band without dispersion compensation.

Sub-wavelength tunneling barrier in rib waveguide microring modulators with vanishing bending losses.

Silicon photonics ring resonators in rib waveguide configuration are among the most important components for wavelength-division-multiplexed communication networks. While the rib waveguide enables simple electrical connectivity in microring modulators and add-drop multiplexers, it also results in unacceptable bending losses once the circumference is shrunk below a few micrometers, limiting achievable free spectral ranges and resonant enhancements. We introduce a sub-wavelength tunneling barrier at the critical radius at which the conformally mapped effective index of the slab exceeds that of the waveguide in order to suppress these bending losses, while increasing the resonator's resistance only slightly. The fundamental working principle is explained and illustrated with a design study based on the finite difference eigenmode method. Three-dimensional finite difference time domain simulations verify the design and a proof-of-concept microring modulator is modeled based on the novel geometry.

Heterogeneous integrated phase modulator based on two-dimensional layered materials

Silicon nitride, with ultralow propagation loss and a wide transparency window, offers an exciting platform to explore integrated photonic devices for various emerging applications. It is appealing to combine the intrinsic optical properties of two-dimensional layered materials with high-quality optical waveguides and resonators to achieve functional devices in a single chip. Here we demonstrate a micro-ring resonator-based phase modulator integrated with few-layer MoS 2 . The ionic liquid is employed directly on the surface of MoS 2 to form a capacitor configuration. The effective index of the composite MoS 2 – SiN waveguide can be modulated via adjusting bias voltages to achieve different charged doping induced electro-refractive responses in MoS 2 film. The maximum effective index modulation of the composite MoS 2 – SiN waveguide can be achieved to 0.45 × 10 − 3 . The phase tuning efficiency is measured to be 29.42 pm/V, corresponding to a V π L of 0.69 V·cm. Since the micro-ring resonator is designed near the critical coupling regime, the coupling condition between the bus waveguide and micro-ring resonator can also be engineered from under-coupling to over-coupling regime during the charged doping process. That can be involved as a degree of freedom for the coupling tailoring. The ability to modulate the effective index with two-dimensional materials and the robust nature of the heterostructure integrated phase modulator could be useful for engineering reliable ultra-compact and low-power-consumption integrated photonic devices.

Lateral-Zigzag PN Junction Enabled High-Efficiency Silicon Micro-Ring Modulator Working at 100Gb/s

We propose and demonstrate a novel lateral-zigzag PN junction for silicon modulator working in C and O bands. The designed PN junction exhibits characteristics of large bandwidth, high modulation efficiency, and easy fabrication. For demonstration, it is embedded in a 220 nm silicon rib waveguide on a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> thick buried oxide layer to form a micro-ring modulator. The measured 3 dB electro-optic bandwidth of the fabricated modulator is 42 GHz while the resistor-capacitor (RC) bandwidth is measured and calculated to be 174 GHz. Clear and open eye diagrams are obtained for 50 Gb/s non-return zero (NRZ) and 100 Gb/s four-level pulse amplitude modulation (PAM4) signals. The modulation power consumption is only 14 fj/bit.

A CMOS-Compatible Carrier-Injection Plasmonic Micro-Ring Modulator with Resonance Tuning by Carrier Concentration

A complementary metal-oxide-semiconductor (CMOS)-compatible carrier-injection plasmonic micro-ring modulator (CIPMRM) is designed and analyzed theoretically. The CIPMRM has a compacted footprint of 49.3 μm2 (R = 2 μm), a bit rate of 36.5 Gbps, insertion loss of −9.8 dB, a static extinction ratio of 21.7 dB, and energy consumption of 4.40 pJ/bit as 2.2 V peak-to-peak voltage is applied at 1550 nm. Besides, the method of resonance tuning by carrier concentration is proposed to compensate for the wavelength mismatch between the CIPMRM resonance and the laser, resulting from temperature and line width variation of the CIPMRM. This method has a faster response time and a greater ability to shift the resonant wavelength compared with the method of thermo-optic resonance tuning. The proposed scheme provides a route for realizing the compacted size modulator for optoelectronic integration.

A CMOS-Compatible Carrier-Injection Plasmonic Micro-Ring Modulator (CIPMRM) with Stable Performance as Temperature Varying around 60 K

A CMOS-compatible carrier-injection plasmonic micro-ring modulator (CIPMRM) is proposed and theoretically analyzed. It has a compacted footprint of 43.4 μm2 (R = 2 μm), a data rate of 45 Gbps, an insertion loss of −8 dB, a static extinction ratio of 22 dB, and an energy consumption of 4.5 pJ/bit when 2.5 V peak-to-peak voltage is applied. Moreover, it works well when temperature varies around 60 K. A method of tuning the resonant wavelength based on the carrier concentration is proposed here because the device is reliable when the linewidth varies within ±5%. CIPMRM provides a way to overcome the shortcomings of temperature and process sensitivity, which are characteristics of the photonic micro-ring modulator. It can be used in optoelectronic integration for its small size and stable performance.

240 Gb/s optical transmission based on an ultrafast silicon microring modulator

An ultrafast microring modulator (MRM) is fabricated and presented with V π · L of 0.825 V · cm . A 240 Gb/s PAM-8 signal transmission over 2 km standard single-mode fiber (SSMF) is experimentally demonstrated. PN junction doping concentration is optimized, and the overall performance of the MRM is improved. Optical peaking is introduced to further extend the EO bandwidth from 52 to 110 GHz by detuning the input wavelength. A titanium nitride heater with 0.1 nm/mW tuning efficiency is implemented above the MRM to adjust the resonant wavelength. High bit rate modulations based on the high-performance and compact MRM are carried out. By adopting off-line signal processing in the transmitter and receiver side, 120 Gb/s NRZ, 220 Gb/s PAM-4, and 240 Gb/s PAM-8 are measured with the back-to-back bit error ratio (BER) of 5.5 × 10 − 4 , 1.5 × 10 − 2 , and 1.4 × 10 − 2 , respectively. A BER with different received optical power and 2 km SSMF transmission is also investigated. The BER for 220 Gb/s PAM-4 and 240 Gb/s PAM-8 after 2 km SSMF transmission is calculated to be 1.7 × 10 − 2 and 1.5 × 10 − 2 , which meet with the threshold of soft-decision forward-error correction, respectively.

Quantized photonic neural network modeling method based on microring modulators

Photonic chips have great potential for neural network computing due to their fast speed, low power consumption, and parallelism. We propose a quantized neural network modeling method based on microring resonators (MRR). We analyze the optical properties of the MRRs and utilize lasers with different wavelengths as inputs of the neural network. The quantization aware method is adopted to train the neural network, and the stochastic search method is utilized to determine hyperparameters of the network. We transform the network parameters and hyperparameters into MRR parameters to simulate neural network matrix multiplication operations. Finally, we used the Mixed National Institute of Standards and Technology database for testing the proposed model. For 4-, 5-, and 6-bit quantization of weight parameters, we obtain classification accuracies of 94.23%, 94.73%, and 96.11%, respectively. Thus our study demonstrates the feasibility of building a neural network inference system using a microring structure and provides a theoretical support for applying MRRs in neural networks.

Step PN Junction-Based Silicon Microring Modulator for High-Speed Application

Step PN Junction-Based Silicon Microring Modulator for High-Speed Application

Thin film lithium niobate electric field sensors.

We present our results for using thin film lithium niobate devices for electric field sensing applications. Micro-ring modulator and Mach-Zehnder modulator-based electric field sensors are demonstrated. Micro-ring resonator sensors can be used for low frequency (up to several GHz) electric field sensing applications and achieve a high sensitivity of 80 mV/(m Hz1/2) with a very compact size of 300μm, as limited by the intensity and phase noise of the used distributed feedback laser. A measurement bandwidth of 2.5GHz is measured for these sensors and is limited by the detector bandwidth. Alternatively, Mach-Zehnder modulators allow for perfect phase matching between the radio frequency signals and optical signals, and they can be used for electric field sensing up to several THz. A sensitivity of 2.2 V/(m Hz1/2) was obtained using our Mach-Zehnder electric field sensor with an interaction length of 600μm. The Mach-Zehnder sensor can sense electric fields with frequencies reaching 0.6THz based on the calculated results.

Recent Progress in Silicon-Based Slow-Light Electro-Optic Modulators.

As an important optoelectronic integration platform, silicon photonics has achieved significant progress in recent years, demonstrating the advantages on low power consumption, low cost, and complementary metal–oxide–semiconductor (CMOS) compatibility. Among the different silicon photonics devices, the silicon electro-optic modulator is a key active component to implement the conversion of electric signal to optical signal. However, conventional silicon Mach–Zehnder modulators and silicon micro-ring modulators both have their own limitations, which will limit their use in future systems. For example, the conventional silicon Mach–Zehnder modulators are hindered by large footprint, while the silicon micro-ring modulators have narrow optical bandwidth and high temperature sensitivity. Therefore, developing a new structure for silicon modulators to improve the performance is a crucial research direction in silicon photonics. Meanwhile, slow-light effect is an important physical phenomenon that can reduce the group velocity of light. Applying slow-light effect on silicon modulators through photonics crystal and waveguide grating structures is an attractive research point, especially in the aspect of reducing the device footprint. In this paper, we review the recent progress of silicon-based slow-light electro-optic modulators towards future communication requirements. Beginning from the principle of slow-light effect, we summarize the research of silicon photonic crystal modulators and silicon waveguide grating modulators in detail. Simultaneously, the experimental results of representative silicon slow-light modulators are compared and analyzed. Finally, we discuss the existing challenges and development directions of silicon-based slow-light electro-optic modulators for the practical applications.

High-speed silicon microring modulator at the 2 µm waveband with analysis and observation of optical bistability

Recently, significantly raised interests have emerged for the 2 µm waveband as an extended new window for fiber optic communication. Much research progress has been made on the photonic integrated circuits for the 2 µm waveband, especially on the CMOS-compatible silicon-on-insulator wafer. In this work, a silicon integrated microring modulator (MRM) with record high-speed performances at the 2 µm waveband was demonstrated. An L-shaped PN junction was specially designed for 2 µm to achieve a high modulation efficiency with V π L of 0.85 V · cm . The measured 3 dB bandwidth is 18 GHz, supporting up to 50 Gbps signaling at 2 µm. Additionally, optical bistability induced by the thermo-optical effect and nonlinear effects was analyzed theoretically and observed experimentally in the 2 µm MRM for the first time to our knowledge. Nonlinear coupled mode theory and the Runge–Kutta method were used to simulate the behaviors of bistability in the 2 µm MRM. The simulation and experimental results indicate that, when the MRM is launched by a high optical power, the distorted resonant spectrum under an optical bistable state deteriorates the modulation efficiency and signal performances. This work breaks the record of high-speed silicon MRM at 2 µm, drawing a promising prospect for the silicon photonic integration and high-speed interconnection at the 2 µm waveband, and it provides the referenceable analysis of optical bistability, which guides the design and experimental investigation of 2 µm MRM.

Polarization-Insensitive Silicon Microring Modulator for Single Sideband Modulation

We propose and experimentally demonstrate a polarization-insensitive single sideband modulator based on silicon microring modulators (MRM). The proposed modulator splits and modulates the two orthogonal polarization states of an input laser in a loopback structure, with an on-chip silicon polarization splitter rotator (PSR), overcoming the polarization dependence of the silicon photonic modulator. The IQ configuration of the modulator enables single sideband modulation, thus improving the resistance of the modulated signal to chromatic dispersion and extending the transmission reach. The adoption of an MRM relieves the bandwidth limitation in polarization-diverse versions of SiP Mach-Zehnder modulators (MZM). Our experiments validate the proposed modulator polarization insensitivity and transmission performance.

Optical 8‐ary phase shift keying modulation format generator based on three microring modulators

AbstractWe have proposed an 8PSK modulator based on three microring modulators (MRM). The design consists of three MRMs, each with a radius of 11.1 μm. Of these three, two MRMs are connected in parallel and they together generate a quadrature phase shift keying (QPSK) signal. While at the output port of the QPSK, a third MRM is connected in series works as an angle modulator, which is basically a 45° phase shift modulator; that is, the output of the MRM varies by 45° depending on the bit pattern fed to it, ‘0’or ‘1’ respectively. We have simulated and shown the performance of the proposed 8PSK modulator after transmitting the modulated signal through various lengths of optical. Constellation diagrams and eye diagrams at different fiber lengths are analyzed. Bit error rate (BER) versus optical signal to noise ratio curve shows that, 10−3 BER has been achieved at 13.5 dB optical signal to noise ratio.

Proposal of micro-ring resonator based PAM-4 modulator with variable ER

This paper presents a Microring modulator (MRM)-based 4-level Pulse Amplitude Modulation (PAM-4) with a variable extension ratio (ER). The calculated bit error rate for a 10 Gb/s PAM-4 eye diagram with the proposed MRM module in a back-to-back design. The system's efficiency was confirmed by the wide eye-diagram. At higher amplitude levels, eye-opening is reduced due to non-linearity. This issue is significantly compensated by employing a variable extension ratio at different amplitude levels, i.e., the transmitted power levels are varied. Each amplitude level has an uneven extension ratio varying from lower to higher.

Ultra-Compact Polarization Analyzer Based on Micro-Ring Resonators

Polarization measurement has been widely used in materials characterization. Conventional polarization analyzers (PA) based on free-space components are often bulky and require a stable platform. Taking advantage of silicon photonics, photonic integrated circuits for PA have been developed recently. In this letter, we propose and demonstrate an ultra-compact PA using a micro-ring modulator (MRM)-assisted interferometer with a chip size of ~0.12mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The fabricated devices show robust performance with measurement accuracy of ±2.3%.

Design and analysis of 2 × 1 photonic temporal multiplexer using SOI ring resonator for switching and logical applications

In this work, we designed a reconfigurable 2 × 1 temporal multiplexer (MUX) using a 1 × 1 microring modulator (MRM) configured in silicon on insulator (SOI) platform. To evaluate the performance of the MUX, logical operations such as NOT, OR, AND, NOR, and NAND are demonstrated. The numerical functionality of the device is assessed using the finite-difference beam propagation method (FD-BPM). The 1 × 1 MRM has a ring radius of 6 μm having a free spectral range (FSR) of 18 to 19 nm. The transmission characteristics and coupling factors of the all-pass and add-drop configuration are analyzed, especially for switching and logical circuit applications. The voltage tuning across the P-i-N junction is achieved by varying the carrier concentration across the intrinsic region, which corresponds to the change in refractive index. Various design parameters are tuned for this configuration, which offers a switching voltage of 0.79 V with modulation speed of 139 GHz. Further, the logical operations of OR, AND, NOR, and NAND with an extinction ratio of 10.25, 11.40, 18.83, and 16.06 dB is reported.

Ultra-low V pp and high-modulation-depth InP-based electro–optic microring modulator

A modulator is an essential building block in the integrated photonics, connecting the electrical with optical signals. The microring modulator gains much attention because of the small footprint, low drive voltage and high extinction ratio. An ultra-low V pp and high-modulation-depth indium phosphide-based racetrack microring modulator is demonstrated in this paper. The proposed device mainly comprises one racetrack microring, incorporating a semiconductor amplifier, and coupling with a bus waveguide through a multimode interference coupler. Traveling wave electrodes are employed to supply bidirectional bias ports, terminating with a 50-Ω impedance. The on/off extinction ratio of the microring reaches 43.3 dB due to the delicately tuning of the gain. An 11 mV V pp, a maximum 42.5 dB modulation depth and a 6.6 GHz bandwidth are realized, respectively. This proposed microring modulator could enrich the functionalities and designability of the fundamental integrated devices.

Nonreciprocal Light Propagation in a Cascaded All-Silicon Microring Modulator

Nonreciprocal Light Propagation in a Cascaded All-Silicon Microring Modulator