Traveling-wave Electrode Research Articles

Simulation for Optical Response of High-Speed Traveling Wave Electro-Optic Polymer/TiO2 Multilayer Slot Waveguide Modulators

In this paper, we analyze a traveling wave electrode as it drives a high-speed electro-optic (EO) polymer/TiO 2 multilayer slot waveguide modulator by simulation. To enhance its mode confinement, the EO polymer is clipped by TiO2 slot waveguide films, and the electrode atop the active region and connection transmission line are optimized to match the impedance at 50 Ω. The optical response is over 200 GHz at 3-dB bandwidth with a 1-cm-long electrode. By comparison, the optical response with silicon TiO2 layers is only 20 GHz with transverse electric (TE) polarized light.

Monolithic Tunable Coupled-Cavity WDM Transmitter in a Generic Foundry Platform

We present the monolithic integration of an extended tuning range coupled-cavity laser with traveling-wave Mach–Zehnder modulators in a low-cost generic photonic foundry platform for 10 Gb/s operation. Using an intra-cavity Michelson interferometer combined with on-chip reflectors, the coupled-cavity laser shows a tuning range of 25 nm. The modulator building blocks with optimized traveling wave electrodes exhibit efficient modulation and 8.5-GHz electro-optic bandwidth, enabling 10 Gb/s ON–OFF keying. We demonstrate error-free operation of the tunable transmitter in a full photonic circuit environment. The laser modulator combination neither requires Bragg grating formation for wavelength tuning nor additional growth steps for multiquantum-well material in the modulator section and is therefore well suited for cost effective foundry platforms specifically for low-cost applications.

Low driving voltage Mach-Zehnder interference modulator constructed from an electro-optic polymer on ultra-thin silicon with a broadband operation.

An electro-optic (EO) polymer waveguide using an ultra-thin silicon hybrid has been designed and fabricated. The silicon core has the thickness of 50 nm and a width of 5 μm. The waveguide was completed after covering the cladding with the high temperature stable EO polymer. We have demonstrated a low half-wavelength voltage of 0.9 V at the wavelength of 1.55 μm by using a Mach-Zehnder interference modulator with TM mode operation. The measured modulation corresponded to an effective in-device EO coefficient of 165 pm/V. By utilizing the traveling-wave electrode on the modulator the high-frequency response was tested up to 40 GHz. The 3 dB modulation bandwidth was measured to be 23 GHz. In addition, the high frequency sideband spectral measurement revealed that a linear response of the modulation index against the RF power was confirmed up to 40 GHz signal.

InP基矩形马赫-曾德高速电光调制器行波电极设计与测试

InP基矩形马赫-曾德高速电光调制器行波电极设计与测试

Over 67 GHz Bandwidth and 1.5 V Vπ InP-Based Optical IQ Modulator With n-i-p-n Heterostructure

We report novel high-bandwidth InP-based Mach–Zehnder modulator and in-phase/quadrature (IQ) modulators that we realized by combining an n-i-p-n heterostructure and a capacitively loaded traveling wave electrode. The extremely low electrical and optical loss structure enhances the 3-dB electro-optic bandwidth of over 67 GHz without degrading other properties such as driving voltage and optical loss. The modulator also exhibits a static extinction ratio of over 24 dB with a V π of less than 1.5 V for the entire C-band. Furthermore, we demonstrate the first 120-Gbaud rate IQ modulation without optical pre equalization, and 100-Gb/s non-return-to-zero on-off keying modulation with a dynamic extinction ratio of over 10 dB.

Linearity Characterization of a Dual–Parallel Silicon Mach–Zehnder Modulator

We report a high-linearity wideband dual–parallel silicon Mach–Zehnder modulator (MZM). This modulator consists of two carrier-depletion-based MZMs with a single-drive push–pull traveling wave electrode configuration. An analytic model is established to investigate the linearity property of the modulator. The measurement results show the modulator can effectively suppress third-order harmonics and third-order intermodulation distortions, with improved modulation linearity, compared to a single MZM.

100 Gb/s and 2 V V π InP Mach‐Zehnder modulator with an n‐i‐p‐n heterostructure

An ultra-high bandwidth (BW) and a low Vπ InP Mach-Zehnder modulator with an n-i-p-n heterostructure is proposed. The combination of the n-i-p-n heterostructure and the capacitive-loaded travelling-wave electrode provides a modulator with extremely low electrical loss. The device exhibits a 3 dB electro-optic BW of over 67 GHz and a Vπ of 2.0 V. A 100 Gb/s non-return-to-zero on–off keying modulation with an extinction ratio of over 10 dB is also realised.

Performance Study of optical Modulator based on electrooptic effect

In this paper, we have studied and derive performance parameter of highly integrated Lithium Niobate optical modulator. This is a chirp free modulator having low switching voltage and large bandwidth. For an external modulator in which travelling-wave electrodes length L imposed the modulating switching voltage, the product of Vπ and L is fixed for a given electro optic material Lithium Niobate. We investigate to achieve a low Vπ by both magnitude of the electro-optic coefficient for a wide variety of electro-optic materials. A Sellmeier equation for the extraordinary index of congruent lithium niobate is derived. For phase-matching, predictions are accmate for temperature between room temperature 250°C and wavelength ranging from 0.4 to 5µm. The Sellmeier equations predict more accmately refractive indices at long wavelengths. Theoretical result is confirmed by simulated results. We have analysed the various parameters such as switching voltage, device performance index, time constant, transmittance, cut-off frequency, 3-dB bandwidth, power absorption coefficient and transmission bit rate of Lithium Niobate optical Modulator based on electro -optic effect.

Modeling and optimization of a single-drive push–pull silicon Mach–Zehnder modulator

We present an equivalent circuit model for a silicon carrier-depletion single-drive push–pull Mach–Zehnder modulator (MZM) with its traveling wave electrode made of coplanar strip lines. In particular, the partial-capacitance technique and conformal mapping are used to derive the capacitance associated with each layer. The PN junction is accurately modeled with the fringe capacitances taken into consideration. The circuit model is validated by comparing the calculations with the simulation results. Using this model, we analyze the effect of several key parameters on the modulator performance to optimize the design. Experimental results of MZMs confirm the theoretical analysis. A 56 Gb/s on–off keying modulation and a 40 Gb/s binary phase-shift keying modulation are achieved using the optimized modulator.

Time-Domain Large-Signal Modeling of Traveling-Wave Modulators on SOI

Silicon photonic modulators have strong nonlinear behavior in phase modulation and frequency response, which needs to be carefully addressed when they are used in high-capacity transmission systems. We demonstrate a comprehensive model for depletion-mode Mach–Zehnder modulators (MZMs) on silicon-on-insulator, which provides a bridge between device design and system performance optimization. Our methodology involves physical models of p–n–junction phase-shifters and traveling-wave electrodes, as well as circuit models for the dynamic microwave-light interactions and time-domain analysis. Critical aspects in the transmission line design for high-frequency operation are numerically studied for a case of p–n–junction loaded coplanar-strip electrode. The dynamic interaction between light and microwave is simulated using a distributed circuit model solved by the finite-difference time-domain method, allowing for accurate prediction of both small-signal and large-signal responses. The validity of the model is confirmed by the comparison with experimental results for a series push–pull MZM with a 6 mm phase shifter. The simulation shows excellent agreement with experiment for high-speed operation up to 46 Gb/s. We show that this time-domain model can well predict the impact of the nonlinear behavior on the large-signal response, in contrast to the poor prediction from linear models in the frequency domain.

Low Power InP-Based Monolithic DFB-Laser IQ Modulator With SiGe Differential Driver for 32-GBd QPSK Modulation

An optical transmitter incorporating a monolithically integrated laser and a traveling wave electrode in-phase and quadrature modulator is presented. A co-designed SiGe differential driver was co-packaged for highest quality push-pull modulation. With only 0.1-dB coupling loss between the laser and the modulator, and a low modulator switching voltage the transmitter power consumption was 1.1 W, which fits the CFP4 (analog coherent optics) ACO module overall budget of 6 W. Without DSP for precompensation, FEC or equalization, 32 GBd QPSK with 3 V pp driving voltage and an error vector magnitude of <10% are presented. Operation with an optical signal-to-noise ratio larger than 14 dB is achieved before breaking the hard decision forward error correction threshold (3.8 × 10−3).

Low Switching Voltage Mach–Zehnder Modulator Monolithically Integrated With DFB Laser for Data Transmission up to 107.4 Gb/s

We present a transmitter optical subassembly consisting of an InP-based travelling wave electrode Mach–Zehnder modulator monolithically integrated with a distributed feedback laser. At 56-Gb/s non-return-to-zero ON/OFF keying (NRZ-OOK), we achieve 3.5-km transmission before breaking the hard decision forward error correction threshold (3.8 ×10−3). 9-km transmission is achieved at 71.6-Gb/s 4-pulse–amplitude modulation (PAM4) and 5 km at 107.4 Gb/s PAM8. The modulation voltage is between 1.5 and 2 V, leading to overall power consumption of 171 mW for the NRZ-OOK case and 206 mW at PAM4 and PAM8.

Analysis of Optical and Electrical Tradeoffs of Traveling-Wave Depletion-Type Si Mach–Zehnder Modulators for High-Speed Operation

Fundamental limiting factors regarding high-speed performance of broadband depletion-type silicon (Si) Mach-Zehnder modulators (MZMs) are studied. Optical and electrical measurements of MZMs with traveling wave electrodes (TWE) reveal significant dependences between optoelectrical bandwidth and design parameters. An equivalent circuit model is implemented to fit measured modulator characteristics. Using the model, the limits of TWE depletion-type Si MZM systems are studied under the requirement of specific driving voltage. By comparing phase shifters with different doping concentration or junction position, we explore the fundamental optical and electrical tradeoffs which are limiting high-speed operation.

A Low-Voltage 35-GHz Silicon Photonic Modulator-Enabled 112-Gb/s Transmission System

We present a silicon photonic traveling-wave Mach–Zehnder modulator operating near 1550 nm with a 3-dB bandwidth of 35 GHz. A detailed analysis of traveling-wave electrode impedance, microwave loss, and phase velocity is presented. Small- and large-signal characterization of the device validates the design methodology. We further investigate the performance of the device in a short-reach transmission system. We report a successful 112-Gb/s transmission of four-level pulse amplitude modulation over 5 km of SMF using 2.2 ${\rm V}_{{\rm p} - {\rm p}} $ drive voltage. Digital signal processing is applied at the transmitter and receiver. 56-GBaud PAM-4 and 64-Gb/s PAM-2 transmission is demonstrated below a pre-FEC hard decision threshold of $4.4 \times 10^{-3}$ .

Silicon high-speed binary phase-shift keying modulator with a single-drive push–pull high-speed traveling wave electrode

We demonstrate binary phase shift keying (BPSK) modulation using a silicon Mach–Zehnder modulator with a π-phase-shift voltage (Vπ) of −4.5 V. The single-drive push–pull traveling wave electrode has been optimized using numerical simulations with a 3 dB electro-optic bandwidth of 35 GHz. The 32 Gb/s BPSK constellation diagram is measured with an error vector magnitude of 18.9%.

High-efficiency Si optical modulator using Cu travelling-wave electrode.

We demonstrate a high-efficiency and CMOS-compatible silicon Mach-Zehnder Interferometer (MZI) optical modulator with Cu traveling-wave electrode and doping compensation. The measured electro-optic bandwidth at Vbias = -5 V is above 30 GHz when it is operated at 1550 nm. At a data rate of 50 Gbps, the dynamic extinction ratio is more than 7 dB. The phase shifter is composed of a 3 mm-long reverse-biased PN junction with modulation efficiency (Vπ·Lπ) of ~18.5 V·mm. Such a Cu-photonics technology provides an attractive potentiality for integration development of silicon photonics and CMOS circuits on SOI wafer in the future.

Silicon-based traveling-wave photodetector array (Si-TWPDA) with parallel optical feeding.

We demonstrate silicon-based traveling-wave photodetector arrays (Si-TWPDAs) with parallel optical feeding by integrating multiple Germanium photodetectors. Such Si-TWPDAs feature the merit of high optical saturation power with remaining the large operation bandwidth. The impedance-matched traveling-wave electrode design takes into account the individual Ge photodetector loading effect. Optical waveguide delay lines are designed in order to balance the electrical phase delay of the traveling-wave electrode. The maximum linear photocurrent at -4V biased voltage are respectively 16 mA, 38 mA, and 65 mA with integrating 1, 2, and 4 photodetectors, upon the saturation power of 40 mW, 100 mW, and 160 mW. This corresponds to a normalized photocurrent generation of >0.32 mA/µm3 and a normalized saturation power of 0.8 mW/µm3. The extracted fiber access responsivity is ~0.42 A/W and the intrinsic responsivity of ~0.82 A/W. The measured 3-dB bandwidth for 4-channel TWPDA is ~20 GHz.

Microfluidic mixing on application of traveling wave electroosmosis

Microanalysis systems benefit from various advantages, such as their portable size, low cost, high accuracy, and short measurement times, prompting the development of numerous “lab-on-a-chip” techniques in recent decades. Biochemical applications of these techniques often require the rapid mixing of different fluid samples. This study presents a novel mixing technique using a four-phase traveling-wave electrode array. Traveling-wave electrode arrays subjected to alternating current (AC) signals are arranged on both sides of the microchannel walls, creating an overall chaotic mixing mechanism for a short microchannel and a low amplitude applied AC voltage. Numerical analyses reveal that the symmetric/asymmetric circulation zone can be generated by switching the phase-shift arrangement of the electrodes. The symmetric/asymmetric circulation zone involves convective and diffusive mixing mechanisms. The electrolyte conductivity, frequency, channel width and depth, and average inlet velocity affect the mixing performance. When the traveling-wave electrode arrays are implemented with 3D structures, the mixing efficiency is enhanced with a maximum achievable mixing quality of 98%.

Optimization and Demonstration of a Large-bandwidth Carrier-depletion Silicon Optical Modulator

We present the design, fabrication, and measurement of a high-speed carrier-depletion silicon optical modulator based on Mach-Zehnder Interferometer structure. Based on an equivalent circuit model, the traveling-wave electrode size and doping concentration of the PN junction are optimized to achieve a large modulation bandwidth. The modulation efficiency and optical loss at different positions of the PN junction are also simulated. The device is fabricated on silicon-on-insulator (SOI) with 0.13 μm CMOS technology. An insertion loss of 3.9 dB (resp. 6.2 dB) and a VπLπ of 1.62-2.05 V·cm (resp. 1.47-1.97 V·cm) are experimentally realized for 1 mm (resp. 2 mm) long phase shifter. By small signal measurement, the modulator exhibits a 3 dB bandwidth of 30 GHz and 19 GHz for 1 mm and 2 mm long phase shifter, respectively, which agrees well with the simulation results. The optical eye diagram with data rate up to 44 Gb/s is also demonstrated, showing potential in the application of high-speed optical interconnects.

Low-voltage, high speed, compact silicon modulator for BPSK modulation

A low voltage, high speed, compact silicon Mach-Zehnder Interferometer (MZI) modulator for Binary Phase Shift Keying (BPSK) modulation has been demonstrated. High modulation efficiency, VπLπ equals to 0.45V·cm, was obtained in a 1mm length device owing to a higher doping concentration and low-loss traveling-wave electrode. 25 Gb/s non-return-to-zero(NRZ)-BPSK with 6Vpp RF driving signal was achieved. Driven by a very low 3Vpp RF signal, the 10 Gb/s NRZ-BPSK was also realized benefiting from the high modulation efficiency and the low-voltage driving scheme. The power consumption for the BPSK modulation was as low as 0.118 W. These results prove that the silicon modulator is suitable for advanced communication system with low power consumption.