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Ian H. White

Publications and source records attributed to Ian H. White.

17 recordsLinked to original sources
arXiv2026

Proof-or-Stop: Don't Trust the Agent, Trust the Evidence -- Loop Engineering for Verifiable Evidence-Gated Lifecycle Control

Autonomous coding agents increasingly execute multi-step software work, but lifecycle states such as reviewed, tested, DONE, and ready-to-merge remain claims unless supported by current evidence. We present Proof-or-Stop Lifecycle Control, a method that permits lifecycle transitions only when fresh, tracked-source-state-bound, mechanically verifiable evidence satisfies the relevant gate. The method treats agent outputs as claims rather than lifecycle state, and uses proof operationally to mean gate-admissible evidence under a stated trust model, not semantic program correctness. We evaluate an open-source implementation through mechanism tests, a powered control-policy ablation, and operated self-application evidence. The unattended-loop engine passed 10 of 10 scenarios with zero false-DONE, and local-key receipt bundles rejected 18 tamper classes with zero false accepts. In a 9,240-cell ablation, the pre-registered A4 versus A2-prime comparison reduced visible-pass/hidden-fail amplification from 31 of 1,800 injected cells under a compute-budgeted naive loop to 2 of 1,800 under the gated loop, a 1.6 percentage-point improvement in not-amplified rate with a 95 percent confidence interval of [0.8, 2.5]. A near-compute A3 versus A4 comparison, 14 of 1,800 versus 2 of 1,800, indicates that the gain is associated with enforcing review as a lifecycle gate rather than merely adding a reviewer. The self-application corpus contains 565 stories and 1,007 review findings, with 94.8 percent resolved, plus a 68-row high/critical cross-vendor exhibit. These results support Proof-or-Stop as a model-agnostic, host-neutral control layer for deciding which autonomous-agent claims a lifecycle may act on. The evaluation is limited to one model family, 24 ablation tasks, and a self-hosted corpus.

cs.AI↗
arXiv2025

Dynamic Power Allocation For NOMA-Based Transmission in 6G Optical Wireless Networks

OWC has been considered as a key enabling technology to unlock unprecedented speeds of communication, supporting high demands of data traffic. In this paper, infrared lasers are used as optical transmitters operating in an indoor environment under eye safety regulations due to their high modulation speed. To provide efficient multiple access service, NOMA-based transmission is implemented to multiplex messages intended to multiple users in the power domain and maximize the spectral efficiency of our laser-based OWC network. In particular, a BIA outer precoder is designed to coordinate the transmission among multiple APs and determine the precoding matrices for groups of users potential formed according to NOMA principles. For effective use of NOMA, an optimization problem is formulated to maximize the sum rate of the network through forming optimum groups under certain joint conditions, efficient power allocation, high quality of service for each weak and strong users, and high overall system performance. Such optimization problems are defined as max-min fractional programs difficult to solve in practice. Therefore, a dynamic application for NOMA is introduced using two algorithms. First, a RF-aided dynamic algorithm is designed to form multiple groups, where users exchange binary variables among them through an RF system to establish distance-based weight edges, which are used as a metric for the grouping process. Second, a dynamic power allocation is proposed to determine the optimum power allocated to each group, while the users belonging to a certain group receive their traffic demands regardless of their classification as weak or strong. The results show the convergence of the proposed dynamic application to the optimum solution, and its high performance in terms of sum rate, fairness, and energy efficiency compared to counterpart schemes.

eess.SY↗
arXiv2025

Observation of generic U(m) non-Abelian holonomy in photonics

Non-Abelian geometric phases form the foundation of fault-tolerant holonomic quantum computation. An "all-geometric" approach leveraging these phases enables robust unitary operations in condensed matter systems. Photonics, with rich degrees of freedom, offer a highly promising platform for non-Abelian holonomy. Yet, achieving universal unitary transformations in photonic holonomy remain elusive. Intrinsic positive real couplings in dissipationless photonic waveguides restrict holonomy to special orthogonal matrices, falling short of universal quantum gates or arbitrary linear operations. Here, we introduce artificial gauge fields (AGFs) to enable complex-valued couplings, expanding photonic holonomy to the full unitary group. We realize generic U(2) transformations and synthesize higher dimensional U(m) operations (up to U(4)) in integrated photonics. Our results open doors toward the transformative "all-geometric-phase" approach in photonic computing in both classical and quantum realms.

physics.optics↗
arXiv2025

BIA Transmission in Rate Splitting-based Optical Wireless Networks

Optical wireless communication (OWC) has recently received massive interest as a new technology that can support the enormous data traffic increasing on daily basis. In particular, laser-based OWC networks can provide terabits per second (Tbps) aggregate data rates. However, the emerging OWC networks require a high number of optical access points (APs), each AP corresponding to an optical cell, to provide uniform coverage for multiple users. Therefore, inter-cell interference (ICI) and multi-user interference (MUI) are crucial issues that must be managed efficiently to provide high spectral efficiency. In radio frequency (RF) networks, rate splitting (RS) is proposed as a transmission scheme to serve multiple users simultaneously following a certain strategy. It was shown that RS provides high data rates compared to orthogonal and non-orthogonal interference management schemes. Considering the high density of OWC networks, the application of RS within each optical cell might not be practical due to severe ICI. In this paper, a new strategy is derived referred to as blind interference alignment-rate splitting (BIA-RS) to fully coordinate the transmission among the optical APs, while determining the precoding matrices of multiple groups of users formed beforehand. Therefore, RS can be implemented within each group to manage MUI. The proposed BIA-RS scheme requires two layers of power allocation to achieve high performance. Given that, a max-min fractional optimization problem is formulated to optimally distribute the power budget among the groups and the messages intended to the users of each group. Finally, a power allocation algorithm is designed with multiple Lagrangian multipliers to provide practical and sub-optimal solutions. The results show the high performance of the proposed scheme compared to other counterpart schemes.

eess.SY↗
arXiv2025

A Novel Terabit Grid-of-Beam Optical Wireless Multi-User Access Network with Beam Clustering

In this paper, we put forward a proof of concept for sixth generation (6G) Terabit infrared (IR) laser-based indoor optical wireless networks. We propose a novel double-tier access point (AP) architecture based on an array of arrays of vertical cavity surface emitting lasers (VCSELs) to provide a seamless grid-of-beam coverage with multi-Gb/s per beam. We present systematic design and thorough analytical modeling of the AP architecture, which are then applied to downlink system modeling using non-imaging angle diversity receivers (ADRs). We propose static beam clustering with coordinated multi-beam joint transmission (CoMB-JT) for network interference management and devise various clustering strategies to address inter-beam interference (IBI) and inter-cluster interference (ICI). Non-orthogonal multiple access (NOMA) and orthogonal frequency division multiple access (OFDMA) schemes are also adopted to handle intra-cluster interference, and the resulting signal-to-interference-plus-noise ratio (SINR) and achievable data rate are derived. The network performance is studied in terms of spatial distributions and statistics of the downlink SINR and data rate through extensive computer simulations. The results demonstrate that data rates up to 15 Gb/s are achieved within the coverage area and a properly devised clustering strikes a balance between the sum rate and fairness depending on the number of users.

eess.SP↗
arXiv2022

Multi-User Rate Splitting in Optical Wireless Networks

Optical wireless communication (OWC) has recently received massive interest as a new technology that can support the enormous data traffic increasing on daily basis. Laser-based OWC networks can provide terabits per second (Tbps) aggregate data rates. However, the emerging OWC networks require clusters of optical transmitters to provide uniform coverage for multiple users. In this context, multi-user interference (MUI) is a crucial issue that must be managed efficiently to provide high spectral efficiency. Rate splitting (RS) is proposed as a transmission scheme to serve multiple users simultaneously by splitting the message of a given user into common and private messages, and then, each user decodes the desired message following a certain procedure. In radio frequency (RF) networks, RS provides higher spectral efficiency compared with orthogonal and non-orthogonal transmission schemes. Considering the high density of OWC networks, the performance of RS is limited by the cost of providing channel state information (CSI) at transmitters and by the noise resulting from interference cancellation. In this work, a user-grouping algorithm is proposed and used to form multiple groups, each group contains users spatially clustered. Then, an outer precoder is designed to manage inter-group interference following the methodology of blind interference alignment (BIA), which reduces the requirements of CSI at RF or optical transmitters. For intra-group interference, RS is applied within each group where the users belonging to a given group receive a unique common message on which their private messages are superimposed. Furthermore, an optimization problem is formulated to allocate the power among the private messages intended to all users such that the sum rate of the network is maximized.

eess.SP↗
arXiv2022

Terabit Indoor Laser-Based Wireless Communications: LiFi 2.0 for 6G

This paper provides a summary of available technologies required for implementing indoor laser-based wireless networks capable of achieving aggregate data-rates of terabits per second as widely accepted as a sixth generation (6G) key performance indicator. The main focus of this paper is on the technologies supporting the near infrared region of the optical spectrum. The main challenges in the design of the transmitter and receiver systems and communication/networking schemes are identified and new insights are provided. This paper also covers the previous and recent standards as well as industrial applications for optical wireless communications (OWC) and LiFi.

cs.IT↗
arXiv2022

High-Speed Imaging Receiver Design for 6G Optical Wireless Communications: A Rate-FOV Trade-Off

The design of a compact high-speed and wide field of view (FOV) receiver is challenging due to the presence of two well-known trade-offs. The first one is the area-bandwidth trade-off of photodetectors (PDs) and the second one is the gain-FOV trade-off due to the use of optics. The combined effects of these two trade-offs imply that the achievable data rate of an imaging optical receiver is limited by its FOV, i.e., a rate-FOV trade-off. To control the area-bandwidth trade-off, an array of small PDs can be used instead of a single PD. Moreover, in practice, a large-area lens is required to ensure sufficient power collection, which in turn limits the receiver FOV (i.e., gain-FOV trade-off). We propose an imaging receiver design in the form of an array of arrays. To achieve a reasonable receiver FOV, we use individual focusing lens for each PD array rather than a single collection lens for the whole receiver. The proposed array of arrays structure provides an effective method to control both gain-FOV trade-off (via an array of lenses) and area-bandwidth trade-off (via arrays of PDs). We first derive a tractable analytical model for the SNR of an array of PDs where the maximum ratio combining has been employed. Then, we extend the model for the proposed array of arrays structure and the accuracy of the analytical model is verified based on several Optic Studio-based simulations. Next, we formulate an optimization problem to maximize the achievable data rate of the imaging receiver subject to a minimum required FOV. The optimization problem is solved for two commonly used modulation techniques, namely, OOK and direct current biased optical orthogonal frequency division multiplexing with variable rate quadrature amplitude modulation. It is demonstrated that a data rate of ~ 24 Gbps with a FOV of 15 is achievable using OOK with a total receiver size of 2 cm by 2 cm.

cs.IT↗
arXiv2022

A Tb/s Indoor MIMO Optical Wireless Backhaul System Using VCSEL Arrays

In this paper, the design of a multiple-input multiple-output (MIMO) optical wireless communication (OWC) link based on vertical cavity surface emitting laser (VCSEL) arrays is systematically carried out with the aim to support data rates in excess of 1 Tb/s for the backhaul of sixth generation (6G) indoor wireless networks. The proposed design combines direct current optical orthogonal frequency division multiplexing (DCO-OFDM) and a spatial multiplexing MIMO architecture. For such an ultra-high-speed line-of-sight (LOS) OWC link with low divergence laser beams, maintaining alignment is of high importance. In this paper, two types of misalignment error between the transmitter and receiver are distinguished, namely, radial displacement error and orientation angle error, and they are thoroughly modeled in a unified analytical framework assuming Gaussian laser beams, resulting in a generalized misalignment model (GMM). The derived GMM is then extended to MIMO arrays and the performance of the MIMO-OFDM OWC system is analyzed in terms of the aggregate data rate. Novel insights are provided into the system performance based on computer simulations by studying various influential factors such as beam waist, array configuration and different misalignment errors, which can be used as guidelines for designing short range Tb/s MIMO OWC systems.

cs.IT↗
arXiv2021

Safety Analysis for Laser-based Optical Wireless Communications: A Tutorial

Light amplification by stimulated emission of radiation (laser) sources have many advantages for use in high data rate optical wireless communications. In particular, the low cost and high-bandwidth properties of laser sources such as vertical-cavity surface-emitting lasers (VCSELs) make them attractive for future indoor optical wireless communications. In order to be integrated into future indoor networks, such lasers should conform to eye safety regulations determined by the international electrotechnical commission (IEC) standards for laser safety. In this paper, we provide a detailed study of beam propagation to evaluate the received power of various laser sources, based on which as well as the maximum permissible exposure (MPE) defined by the IEC 60825-1:2014 standard, we establish a comprehensive framework for eye safety analyses. This framework allows us to calculate the maximum allowable transmit power, which is crucial in the design of a reliable and safe laser-based wireless communication system. Initially, we consider a single-mode Gaussian beam and calculate the maximum permissible transmit power. Subsequently, we generalize this approach for higher-mode beams. It is shown that the M-squared-based approach for analysis of multimode lasers ensures the IEC eye safety limits, however, in some scenarios, it can be too conservative compared to the precise beam decomposition method. Laser safety analyses with consideration of optical elements such as lens and diffuser, as well as for VCSEL array have been also presented. Skin safety, as another significant factor of laser safety, has also been investigated in this paper. We have studied the impacts of various parameters such as wavelength, exposure duration and the divergence angle of laser sources on the safety analysis by presenting insightful results.

cs.IT↗
arXiv2017

Bandwidth and Offset Launch Investigations on a 1.4 m Multimode Polymer Spiral Waveguide

Bandwidth measurements are conducted on a 1.4 m long spiral polymer multimode waveguide for a SMF and 50/125 um MMF launch and for different input offsets. The waveguide exhibits a bandwidth of at least 30 GHz for all input types, yielding a bandwidth-length product of at least 42 GHzxm, while no impact is observed on the waveguide performance due to the different spatial input offsets. The results indicate that data transmission at data rates even higher than 25 Gb/s can be achieved over such structures, thereby demonstrating the potential of multimode polymer waveguide technologies in short-reach board-level datacommunication links.

physics.ins-det↗
arXiv2017

Loss and Bandwidth Studies on Multimode Polymer Waveguide Components for On-Board High-Speed Optical Interconnects

Optical interconnects play a key role in the implementation of high-speed short-reach communication links within high-performance electronic systems. Multimode polymer waveguides in particular are strong candidates for use in passive optical backplanes as they can be cost-effectively integrated onto standard PCBs. Various optical backplanes using this technology and featuring a large number of multimode polymer waveguide components have been recently demonstrated. The optimisation of the loss performance of these complex waveguide layouts becomes particularly important at high data rates (>=25 Gb/s) due to the associated stringent power budget requirements. Moreover, launch conditions have to be carefully considered in such systems due to the highly-multimoded nature of this waveguide technology. In this paper therefore, we present thorough loss and bandwidth studies on siloxane-based multimode waveguides and waveguide components (i.e. bends and crossings) that enable the implementation of passive optical backplanes. The performance of these components is experimentally investigated under different launch conditions for different waveguide profiles that can be readily achieved through fabrication. Useful design rules on the use of waveguide bends and crossings are derived for each waveguide type. It is shown that the choice of waveguide parameters depends on the particular waveguide layout, assumed launch conditions and desired link bandwidth. As an application of these studies, the obtained results are employed to optimise the loss performance of a 10-card shuffle router and enable >=40 Gb/s data transmission.

cs.ET↗
arXiv2016

High-Bandwidth and Large Coupling Tolerance Graded-Index Multimode Polymer Waveguides for On-board High-Speed Optical Interconnects

Optical interconnects have attracted significant research interest for use in short-reach board-level optical communication links in supercomputers and data centres. Multimode polymer waveguides in particular constitute an attractive technology for on-board optical interconnects as they provide high bandwidth, offer relaxed alignment tolerances, and can be cost-effectively integrated onto standard printed circuit boards (PCBs). However, the continuing improvements in bandwidth performance of optical sources make it important to investigate approaches to develop high bandwidth polymer waveguides. In this paper, we present dispersion studies on a graded-index (GI) waveguide in siloxane materials designed to deliver high bandwidth over a range of launch conditions. Bandwidth-length products of >70 GHzxm and ~65 GHzxm are observed using a 50/125 um multimode fibre (MMF) launch for input offsets of +/- 10 um without and with the use of a mode mixer respectively; and enhanced values of >100 GHzxm are found under a 10x microscope objective launch for input offsets of ~18 x 20 um^2. The large range of offsets is within the -1 dB alignment tolerances. A theoretical model is developed using the measured refractive index profile of the waveguide, and general agreement is found with experimental bandwidth measurements. The reported results clearly demonstrate the potential of this technology for use in high-speed board-level optical links, and indicate that data transmission of 100 Gb/s over a multimode polymer waveguide is feasible with appropriate refractive index engineering.

cs.ET↗
arXiv2015

Pulse generation with ultra-superluminal pulse propagation in semiconductor heterostructures by superradiant phase transition enhanced by transient coherent population gratings

This paper reports the observation of ultra-superluminal pulse propagation in GaAs/AlGaAs multiple contact heterostuctures in a superradiant emission regime, and shows definitively that it is a different class of emission from conventional spontaneous or stimulated emission. It is shown that coherent population gratings induced in the semiconductor medium under strong electrical pumping have great impact in causing a decrease of the group refractive index in the range of 5-40%. This decrease is much greater than that which would be observed due to conventional carrier depletion or chirp mechanisms. The decrease in refractive index in turn causes faster-than-c propagation of femtosecond pulses. The measurement also shows unequivocally the exist of coherent amplification of electromagnetic pulses in semiconductors at room temperature, the coherence being strongly enhanced by interactions of the light with coherent transient gratings locked to carrier gratings. This pulse generation technique can be anticipated to have great potential in applications where highly coherent femtosecond optical pulses must be generated on demand

cond-mat.str-el↗
arXiv2012

Observation of the formation of long-range order during superradiant emission in a high-density e-h system

The transition of atomic, electronic, or e-h systems to quantum phases is an extraordinary process when both microscopic and macroscopic properties of the system undergo fundamental changes. Bose-Einstein condensation, has been observed in a number of physical systems, including super-cold atomic gases and solid- state quasiparticles. The most typical example of equilibrium condensation is the superconducting state of Cooper pairs in metals. However, in many cases the lifetime of particles or quasiparticles under study is finite, ranging from picoseconds to milliseconds. And even in this case condensation is possible. It is generally understood at present that coherence and off-diagonal long-range order in the density matrix are the most important characteristic features of condensed quantum states. Phase coherence established over microscopic distances is an intrinsic property of all Bose condensates. Experiments featuring interference between either two condensates or two separate parts of the same condensate are often considered as more convincing than observation of the macroscopic occupation of the ground state. The formation of long-range order and spatial phase coherence can be measured by studying interference patterns using either a Michelson interferometer or Young double slit arrangement. Here we present experimental results of observation of long-range temporal and spatial coherence of a macroscopically ordered state of a high-density e-h system in GaAs during the generation of femtosecond superradiant emission at room temperature

cond-mat.str-el↗