arXiv subjects

Paul Yu

Publications and source records attributed to Paul Yu.

10 recordsLinked to original sources

arXiv2022

Realization of a wide steering end-fire facet optical phased array using silicon rich silicon nitride

The design, fabrication, and characterization of a 16-element optical phased array (OPA) using a high index (n = 3.1) silicon rich silicon nitride (SRN) is demonstrated. We present one-dimensional beam steering with end-fire facet antennas over a wide steering range of >115{\deg} at a fixed wavelength of 1525 nm. A spot size of 0.11{\deg} has been measured at boresight, consistent with theory. We demonstrate SRN as a viable material choice for chip-scale OPA applications due to its high thermo-optic coefficient, high optical power handling capacity due to negligible two-photon absorption (TPA), wide transparency window, low propagation loss, and CMOS compatibility.

physics.optics↗

arXiv2021

Keyless Authentication for AWGN Channels

This work establishes that the physical layer can be used to perform information-theoretic authentication in additive white Gaussian noise channels, as long as the adversary is not omniscient. The model considered consists of an encoder, decoder, and adversary, where the adversary has access to the message, a non-causal noisy observation of the encoder's transmission, and unlimited transmission power, while the decoder observes a noisy version of the sum of the encoder and adversary's outputs. A method to modify a generic existing channel code to enable authentication is presented. It is shown that this modification costs an asymptotically negligible amount of the coding rate, while still enabling authentication as long as the adversary's observation is not noiseless. Also notable is that this modification is not (asymptotically) a function of the statistical characterization of the adversary's channel and furthermore no secret key is required, hence paving the way for a robust practical implementation. Using these results, the channel-authenticated capacity is calculated and shown to be equal to the non-adversarial channel capacity. While this modular scheme is designed for use in the given channel model, it is applicable to a wide range of settings.

cs.IT↗

arXiv2021

Efficient and compact thermo-optic phase shifter in silicon-rich silicon nitride

The design, fabrication, and characterization of low loss ultra-compact bends in high index (n = 3.1 at {\lambda} = 1550 nm) PECVD silicon rich silicon nitride (SRN) is demonstrated and utilized to realize efficient, small footprint thermo-optic phase shifter. Compact bends are structured into a folded waveguide geometry to form a rectangular spiral within an area of 65 x 65 \mum2 possessing a total active waveguide length of 1.2 mm. The device features a phase shifting efficiency of 8 mW/{\pi} and a 3 dB switching bandwidth of 15 KHz. We propose SRN as a promising thermo-optic platform combining the properties of silicon and silicon stoichiometric nitride

physics.app-ph↗

arXiv2020

Thermo-Optic Properties of Silicon-Rich Silicon Nitride for On-chip Applications

We demonstrate the thermo-optic properties of silicon-rich silicon nitride (SRN) films deposited using plasma-enhanced chemical vapor deposition (PECVD). Shifts in the spectral response of Mach-Zehnder Interferometers (MZIs) as a function of temperature were used to characterize the thermo-optic coefficients of silicon nitride films with varying silicon contents. A clear relation is demonstrated between the silicon content and the exhibited thermo-optic coefficient in silicon nitride films, with the highest achievable coefficient being as high as (1.65+/-0.08) x 10-4 K-1. Furthermore, we realize an SRN Multi-Mode Interferometer (MMI) based thermo-optic switch with over 20 dB extinction ratio and total power consumption for two-port switching of 50 mW.

physics.app-ph↗

arXiv2020

Authentication Against a Myopic Adversary

We consider keyless authentication for point-to-point communication in the presence of a myopic adversary. In particular, the adversary has access to a non-causal noisy version of the transmission and may use this knowledge to choose the channel state of an arbitrarily-varying channel between legitimate users; the receiver is successful if it either decodes to the correct message or correctly detects adversarial interference. We show that a channel condition called U-overwritability, which allows the adversary to make its false message appear legitimate and untampered with, is a sufficient condition for zero authentication capacity. We present a useful way to compare adversarial channels, and show that once an AVC becomes U-overwritable, it remains U-overwritable for all "less myopic" adversaries. Finally, we show that stochastic encoders are necessary for positive authentication capacity in some cases, and examine in detail a binary adversarial channel that illustrates this necessity. Namely, for this binary channel, we show that when the adversarial channel is degraded with respect to the main channel between users, the no-adversary capacity of the underlying channel is achievable with a deterministic encoder. Otherwise, provided the channel to the adversary is not perfect, a stochastic encoder is necessary for positive authentication capacity; if such an encoder is allowed, the no-adversary capacity is again achievable.

cs.IT↗

arXiv2020

Secret key authentication capacity region, Part II: typical authentication rate

This paper investigates the secret key authentication capacity region. Specifically, the focus is on a model where a source must transmit information over an adversary controlled channel where the adversary, prior to the source's transmission, decides whether or not to replace the destination's observation with an arbitrary one of their choosing (done in hopes of having the destination accept a false message). To combat the adversary, the source and destination share a secret key which they may use to guarantee authenticated communications. The secret key authentication capacity region here is then defined as the region of jointly achievable message rate, authentication rate, and key consumption rate (i.e., how many bits of secret key are needed). This is the second of a two part study, with the studies separated by how the authentication rate is measured. Here, the authentication rate is measured by the minimum of the maximum probability of false acceptance where the minimization is over all highly probable subsets of observations at the adversary. That is, consider the maximum probability of false authentication as a function of the adversary's observation, and the adversary's observation as a random variable. The authentication rate is then measured as the smallest number for which the probability that the maximum probability of false authentication is greater than said number is arbitrary small. This is termed typical authentication, since it only needs to consider adversarial observations which are typical with the transmission. Under this measure of authentication matching inner and outer bounds are determined.

cs.IT↗

arXiv2020

Secret key authentication capacity region, Part I: average authentication rate

This paper investigates the secret key authentication capacity region. Specifically, the focus is on a model where a source must transmit information over an adversary controlled channel where the adversary, prior to the source's transmission, decides whether or not to replace the destination's observation with an arbitrary one of their choosing (done in hopes of having the destination accept a false message). To combat the adversary, the source and destination share a secret key which they may use to guarantee authenticated communications. The secret key authentication capacity region here is then defined as the region of jointly achievable message rate, authentication rate, and key consumption rate (i.e., how many bits of secret key are needed). This is the first of a two part study, with the parts differing in how the authentication rate is measured. In this first study the authenticated rate is measured by the traditional metric of the maximum expected probability of false authentication. For this metric, we provide an inner bound which improves on those existing in the literature. This is achieved by adopting and merging different classical techniques in novel ways. Within these classical techniques, one technique derives authentication capability directly from the noisy communications channel, and the other technique derives its' authentication capability directly from obscuring the source.

cs.IT↗

arXiv2018

Inner Bound for the Capacity Region of Noisy Channels with an Authentication Requirement

The rate regions of many variations of the standard and wire-tap channels have been thoroughly explored. Secrecy capacity characterizes the loss of rate required to ensure that the adversary gains no information about the transmissions. Authentication does not have a standard metric, despite being an important counterpart to secrecy. While some results have taken an information-theoretic approach to the problem of authentication coding, the full rate region and accompanying trade-offs have yet to be characterized. In this paper, we provide an inner bound of achievable rates with an average authentication and reliability constraint. The bound is established by combining and analyzing two existing authentication schemes for both noisy and noiseless channels. We find that our coding scheme improves upon existing schemes.

cs.IT↗

arXiv2017

A TTL-based Approach for Content Placement in Edge Networks

Edge networks are promising to provide better services to users by provisioning computing and storage resources at the edge of networks. However, due to the uncertainty and diversity of user interests, content popularity, distributed network structure, cache sizes, it is challenging to decide where to place the content, and how long it should be cached. In this paper, we study the utility optimization of content placement at edge networks through timer-based (TTL) policies. We propose provably optimal distributed algorithms that operate at each network cache to maximize the overall network utility. Our TTL-based optimization model provides theoretical answers to how long each content must be cached, and where it should be placed in the edge network. Extensive evaluations show that our algorithm significantly outperforms path replication with conventional caching algorithms over some network topologies.

cs.NI↗

arXiv2016

Keyless authentication in the presence of a simultaneously transmitting adversary

If Alice must communicate with Bob over a channel shared with the adversarial Eve, then Bob must be able to validate the authenticity of the message. In particular we consider the model where Alice and Eve share a discrete memoryless multiple access channel with Bob, thus allowing simultaneous transmissions from Alice and Eve. By traditional random coding arguments, we demonstrate an inner bound on the rate at which Alice may transmit, while still granting Bob the ability to authenticate. Furthermore this is accomplished in spite of Alice and Bob lacking a pre-shared key, as well as allowing Eve prior knowledge of both the codebook Alice and Bob share and the messages Alice transmits.

cs.IT↗