Monolithic electronic-photonic integrated circuits for free-space sensors and receivers
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Authors
Rollinson, John
Issue Date
2024-05
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Electrical engineering
Alternative Title
Abstract
Over the past decade, commercial semiconductor foundries have driven continual advance-ment in the chip-scale miniaturization of optical devices co-integrated alongside CMOS elec-
tronics on a single piece of silicon. Such monolithic electronic-photonic integrated circuit
(EPIC) platforms have become the foundation of state-of-the-art high-speed fiber optic links,
driving bandwidths towards 200 Gbit/s/λ while simultaneously reducing energy-per-bit. Be-
yond data communications, the devices and features offered by these processes can readily
be applied to a range of alternative applications, such as spectroscopy, imaging, quantum
photonics, LiDAR, free-space communications, and biomedical sensing. The availability of
low-loss, wide-optical-bandwidth silicon nitride layers exposes a range of applications beyond
the commercial near-infrared (NIR) bands, ranging from visible to NIR+ wavelengths, while
monolithic integration of CMOS electronics enables leading-edge integration density, power
efficiency, bandwidth, and noise performance.
A common challenge among many EPIC applications is coupling free-space light into
the chip. This dissertation presents the design and optimization of a free-space EPIC re-
ceiver targeting high sensitivity, scalability, and low power consumption. The receiver entails
a novel inverse-designed passive coupling scheme, optimized photodetectors, and a low-noise
analog front-end (AFE) for conversion of the incident light to voltage. While various free-
space coupling techniques have previously been demonstrated, existing approaches tend to
suffer from either high power consumption, large area requirements, poor scalability, packag-
ing complexity, or fabrication incompatibility. A new photonic antenna technique, consisting
of distributed arrays of grating couplers, is developed in this work to address the limitations
of the prior art. By aggregating the outputs of multiple collectors through photonic power
combining networks, the photonic antenna collection area scales independently of the pho-
todetector noise floor, facilitating the creation of high-sensitivity receivers. Inverse design,
a robust photonic device optimization methodology, is employed to realize low-loss, highly
compact components exceeding the performance of traditional manual designs. A composite
topological inverse design technique is developed to further improve power combining perfor-
mance by enabling the realization of complex, multi-objective device transformations using
scattering matrix decomposition.
In tandem with improvements in photonic coupling, the readout electronics are noise-
minimized to achieve high signal-to-noise ratio. The photodetector noise current and ca-
pacitance are reduced through empirical study while the transimpedance amplifier utilizes
capacitive-matching and equalization to reduce the white noise contribution. To demonstrate
the efficacy of this monolithic electronic-photonic receiver/sensor architecture, a 16-pixel di-
rect time-of-flight (ToF) LiDAR receiver is designed and fabricated in a commercial EPIC
platform. The receiver pixels operate on the integrated plenoptic sensor principle, wherein
gratings tuned to different coupling angles provide angular discrimination of reflected light
from a pulsed flood-illumination source. Using the grating array antenna and the low-noise
AFE scheme, the fabricated receiver demonstrates an 8× improvement in receiver sensitiv-
ity over a prior plenoptic sensor using ∼1/10 of the area. The LiDAR sensor captures
short-range, privacy-preserving indoor ToF measurements, demonstrating >5 m range with
excellent ambient light rejection. While the device functions well as a LiDAR sensor, the
co-optimized EPIC architecture presented here applies to broad free-space coupling appli-
cations. The discussion concludes by proposing modifications to the receiver design for
alternative applications along with areas for further improvements in sensitivity and noise
performance.
Description
May2024
School of Engineering
School of Engineering
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY