Jason C. C. Mak

Automatic Resonance Alignment of High-Order Microring Filters

Automatic resonance alignment tuning is performed in high-order series coupled microring filters using a feedback system. By inputting only a reference wavelength, the filter transmission is maximized on resonance, passband ripples are dramatically reduced, and the passband becomes centered at the reference. The method is tested on fifth-order microring filters fabricated in a standard silicon photonics foundry process. Repeatable tuning is demonstrated for filters on multiple dies from the wafer and for arbitrary reference wavelengths within the free spectral range of the microrings.

Binary particle swarm optimized 2 × 2 power splitters in a standard foundry silicon photonic platform

Compact power splitters designed ab initio using binary particle swarm optimization in a 2D mesh for a standard foundry silicon photonic platform are studied. Designs with a 4.8  μm×4.8  μm footprint composed of 200  nm×200  nm and 100  nm×100  nm cells are demonstrated. Despite not respecting design rules, the design with the smaller cells had lower insertion losses and broader bandwidth and showed consistent behavior across the wafer. Deviations between design and experiments point to the need for further investigations of the minimum feature dimensions.

FDTD-Compatible broadband surface impedance boundary conditions for graphene

Graphene is a material that has been the focus of much academic interest for its unique material properties. As understanding of graphene improves and fabrication of graphene based devices matures, there is a growing need for electromagnetic simulations of graphene to aid device design. A finite-difference time domain (FDTD) model of graphene is useful for characterizing relevant geometries over a wide range of frequencies, yet limited by the excessive computational resources needed to model this essentially two-dimensional lossy, dispersive medium. A natural alternative is the use of a broadband surface impedance boundary condition (SIBC) that includes both the inter and the intraband conductivity of graphene. This SIBC is developed using a vector-fitting extracted rational function expansion of graphenes surface conductivity, mapped into the time-domain and implemented as a system of field update equations.

Programmable Multiring Butterworth Filters With Automated Resonance and Coupling Tuning

We demonstrate a bandwidth and wavelength programmable silicon double microring optical filter that can be automatically, accurately, and repeatably set to an optimal Butterworth shape for maximum passband flatness. The algorithm uses a critical coupling condition to set the Butterworth shapes, followed by bandwidth tuning using a calibration dataset for the coupling coefficients. Silicon microrings with independently tunable phase shifts and coupling coefficients were designed for and fabricated at a foundry to demonstrate the method. Fabrication variations and thermal crosstalk are also compensated automatically.

Flip-chip integrated silicon Mach-Zehnder modulator with a 28nm fully depleted silicon-on-insulator CMOS driver

We present a silicon electro-optic transmitter consisting of a 28nm ultra-thin body and buried oxide fully depleted silicon-on-insulator (UTBB FD-SOI) CMOS driver flip-chip integrated onto a Mach-Zehnder modulator. The Mach-Zehnder silicon optical modulator was optimized to have a 3dB bandwidth of around 25 GHz at -1V bias and a 50 Ω impedance. The UTBB FD-SOI CMOS driver provided a large output voltage swing around 5 Vpp to enable a high dynamic extinction ratio and a low device insertion loss. At 44 Gbps, the transmitter achieved a high extinction ratio of 6.4 dB at the modulator quadrature operation point. This result shows open eye diagrams at the highest bit rates and with the largest extinction ratios for silicon electro-optic transmitter using a CMOS driver.

Automated calibration of high-order microring filters

We demonstrate the automated calibration of a 5th-order silicon microring filter using an optimization algorithm. The procedure only requires a single input wavelength and was implemented on a microcontroller with simple ADC and DAC circuitry.

A surface impedance boundary condition approach to the FDTD modeling of graphene

Graphene is a promising material for many applications, and electromagnetic modeling for graphene is needed to aid the design of graphene based devices. We present an approach for the finite-difference time-domain (FDTD) simulation of graphene improving on accuracy and computational efficiency. This is accomplished using a surface impedance boundary conditions (SIBC) to model graphene as a surface, eliminating the need to simulate the interior of the material. The vector-fitting technique is used in conjunction with FDTD to achieve accurate response over a broad range of frequencies.