Mach-Zehnder Lattice Research Articles

Efficient layout-aware statistical analysis for photonic integrated circuits.

Fabrication variability significantly impacts the performance of photonic integrated circuits (PICs), which makes it crucial to quantify the impact of fabrication variations before the final fabrication. Such analysis enables circuit and system designers to optimize their designs to be more robust and obtain maximum yield when designing for manufacturing. This work presents a simulation methodology, Reduced Spatial Correlation Matrix-based Monte-Carlo (RSCM-MC), to efficiently study the impact of spatially correlated fabrication variations on the performance of PICs. First, a simple and reliable method to extract physical correlation lengths, variability parameters that define the inverse of the spatial frequencies of width and height variations over a wafer, is presented. Then, the process of generating correlated variations for MC simulations using RSCM-MC methodology is presented. The methodology generates correlated variations by first creating a reduced correlation matrix containing spatial correlations between all the circuit components, and then processing it using Cholesky decomposition to obtain correlated variations for all circuit components. These variations are then used to conduct MC simulations. The accuracy and the computation performance of the proposed methodology are compared with other layout-dependent Monte-Carlo simulation methodologies, such as Virtual wafer-based Monte-Carlo (VW-MC). A Mach-Zehnder lattice filter is used to study the accuracy, and a second-order Mach-Zehnder filter and a 16x16 optical switch matrix system are used to compare the computational performance.

Polarization-insensitive silicon nitride Mach-Zehnder lattice wavelength demultiplexers for CWDM in the O-band.

Polarization-insensitive silicon nitride (SiN) 4-channel wavelength (de)multiplexers based on Mach-Zehnder interferometer lattice filters for coarse wavelength division multiplexing (CWDM) in the O-band are demonstrated in a SiN-on-silicon photonic platform. For the best-performing device, the insertion loss was < 2.8 dB, the inter-channel crosstalk was < -11.5 dB for a polarization scrambled input, and the passband shift between the orthogonal polarizations was < 1.5 nm. Across the 200mm wafer, the die-averaged insertion loss and maximum crosstalk were 3.1 dB and -10.6 dB, respectively. The higher-than-expected crosstalk was due to dimensional variations. This work shows the potential of SiN photonic circuits for CWDM without polarization diversity.

Drive-noise-tolerant broadband silicon electro-optic switch

We report a broadband digital electro-optical switch, based upon a multi-stage Mach-Zehnder lattice design in silicon-on-insulator. A digital switching response is demonstrated, engineered through apodization of the coupling coefficients between stages. The digital switching behavior results in crosstalk lower than -15 dB for drive-voltage noise levels in excess of 300 mV(pp), which exceeds the noise tolerance of a conventional single-stage Mach-Zehnder switch by more than six-fold. In addition, the digital design enables a larger maximum 'on'-state extinction (below -26 dB) and lower 'on'-state free-carrier-induced insertion loss (less than 0.45 dB) than that of the single-stage switch. The noise-tolerant, low-crosstalk switch can thus play a key role within CMOS-integrated reconfigurable optical networks operating under noisy on-chip conditions.

Design of a digital, ultra-broadband electro-optic switch for reconfigurable optical networks-on-chip

We present a novel design for a noise-tolerant, ultra-broadband electro-optic switch, based on a Mach-Zehnder lattice (MZL) interferometer. We analyze the switch performance through rigorous optical simulations, for devices implemented in silicon-on-insulator with carrier-injection-based phase shifters. We show that such a MZL switch can be designed to have a step-like switching response, resulting in improved tolerance to drive-voltage noise and temperature variations as compared to a single-stage Mach-Zehnder switch. Furthermore, we show that degradation in switching crosstalk and insertion loss due to free-carrier absorption can be largely overcome by a MZL switch design. Finally, MZL switches can be designed for having an ultra-wide, temperature-insensitive optical bandwidth of more than 250 nm. The proposed device shows good potential as a broadband optical switch in reconfigurable optical networks-on-chip.

Compact Wavelength-Selective Functions in Silicon-on-Insulator Photonic Wires

We present a number of compact wavelength-selective elements implemented in silicon-on-insulator (SOI) photonic wires. These include arrayed waveguide gratings (AWGs), Mach-Zehnder lattice filters (MZLFs), and ring resonators. The circuits were fabricated with deep UV lithography. We also address the sensitivity of photonic wires to phase noise by selectively broadening the waveguides, and demonstrate this in a compact AWG with -20 dB crosstalk and an insertion loss of 2.2 dB for the center channels

Synthesis of all-optical microwave filters using Mach-Zehnder lattices

A synthesis algorithm which generates the set of coupling ratios required to produce a desired time-domain window response using an all-optical Mach-Zehnder lattice network Is presented. The analysis assumes incoherent interference of the lightwaves within the structure. The window coefficients are dictated by the coupling ratios of the couplers forming the lattice, leading to a simple structure comprising only passive components. Since its impulse response (IR) is finite, the filter will be stable, and the algorithm is capable of generating a wide range of responses In terms of their extinction ratios and passbands. The theory has been validated by experiment.