arXiv subjects

Stephanos Yerolatsitis

Publications and source records attributed to Stephanos Yerolatsitis.

At least 19 recordsLinked to original sources

arXiv2026

The Photonic Lantern Nuller: from concept to laboratory and on-sky demonstrations

This thesis work presents the conceptual design and experimental characterization of the Photonic Lantern Nuller instrument, which uses a multimode-to-single-mode demultiplexing waveguide to cancel out starlight while maintaining planet light, allowing for the direct characterization of planets at a telescope's diffraction limit. The PLN was experimentally characterized in the lab, where it was further enhanced using common-path wavefront sensing and control techniques, and then demonstrated on sky at the Subaru Telescope. Highlights include measured in-lab null-depths of $\sim 10^{-4}$ in three out of four ports simultaneously and on-sky null-depths of approximately $\sim 10^{-1}$ (limited by jitter and atmospheric residuals). We provide an overview of these results and discuss avenues for future work.

astro-ph.IM↗

arXiv2026

Experimentally-determined performance limits for joint imaging and wavefront sensing with a photonic lantern

The photonic lantern (PL) is a focal-plane wavefront sensor (WFS) that can be used for second-stage control of extreme adaptive optics (AO) systems. While the number of sensed modes and the dynamic range with respect to each mode have been relatively well characterized, little attention has been paid to the PL's sensitivity, i.e. how measurement noise impacts the accuracy of PL wavefront reconstruction. We compute the PL's sensitivity to photon noise as a function of spatial frequency, and compare it to existing WFSs, using simulations as well as experiments on the muirSEAL testbed. We further assess these metrics in the case where only a subset of PL ports are available for wavefront sensing. In this configuration, the remaining ports are used to spatially and spectrally reconstruct the observed scene using algorithms such as SPADE. Using more ports for wavefront sensing enables greater aberration sensitivity but leaves less spatial information for image reconstruction. This allows us to trade off between fewer samples with smaller aberrations and more samples with larger aberrations. This work sets the stage for AO system design incorporating the PL as a joint WFS and imager.

astro-ph.IM↗

arXiv2026

Wavelength-Dependent Evolution of Full-Field Transfer Matrices in Photonic Lanterns

A fiber-based photonic lantern can couple an array of single-mode optical fibers to the guided modes of a multimode fiber, with the mapping between the single-mode fibers and guided modes fully described by a complex-valued transfer matrix. Recent experimental studies have reported strong wavelength-dependent evolution of this matrix in non-mode-selective photonic lanterns, yet a quantitative physical explanation for this behavior has not previously been demonstrated. Here, we present direct measurements of the wavelength-dependent encoding transfer matrix of a photonic lantern across the range 1525 nm to 1575 nm using off-axis holographic imaging, enabling high-fidelity recovery of both amplitude and phase. Beyond measurement, we introduce a physically grounded propagation model and numerical simulation that quantitatively reproduces the observed wavelength evolution and provides a unified physical explanation for behavior reported in prior experimental work. The model identifies differential modal phase accumulation in the multimode section as the dominant mechanism governing spectral evolution and shows that increasing the length of the multimode end systematically accelerates the phase evolution of the transfer matrix with wavelength. These results establish a direct and predictive link between photonic lantern geometry and spectral response, providing a design framework for tailoring lanterns either to enhance sensitivity to closely spaced wavelengths or to enforce uniform response over broad bandwidths for spectroscopic and imaging applications.

physics.optics↗

arXiv2025

Multi-node quantum key distribution network using existing underground optical fibre infrastructure

Quantum key distribution (QKD) offers unconditional information security by allowing two distant users to establish a common encryption key resilient to hacking. Resultingly, QKD networks interconnecting critical infrastructure and enabling the secure exchange of classified information, can provide a solution to the increasing number of successful cyberattacks. To efficiently deploy quantum networks, the technology must be integrated over existing communication infrastructure, such as optical fibre links. Yet, QKD poses stringent requirements on the conditions of the network over which it is deployed. This work demonstrates the first quantum communication network in Cyprus via the deployment of a multi-node quantum network, exploiting existing commercial underground optical fibre. The network employs bidirectional occupation of fibres and wavelength multiplexing in a ring architecture to achieve, with minimal use of dark fibres, high-rate QKD. Results obtained reveal consistent key generation rates across all nodes, confirming reliable operation in a real-world environment. This deployment highlights the feasibility of leveraging existing telecom infrastructure for quantum-secured communication, marking a significant step toward scalable and cost-effective quantum networks suited for critical applications.

quant-ph↗

arXiv2025

On-sky demonstration of second-stage wavefront control with a photonic lantern

Ground-based direct imaging of exoplanets at high contrast requires precise correction of atmospheric turbulence using adaptive optics (AO). The planet-to-star contrast ratio at small angular separations from the host star is often limited by non-common-path aberrations (NCPAs) seen only in the science plane. The photonic lantern (PL) can be used to sense aberrations at the final science imaging plane. This enables a two-stage wavefront control architecture, in which the first-stage wavefront sensor senses atmospheric turbulence and the PL senses NCPAs and other aberrations not seen by the first stage. We demonstrate closed-loop control of residual wavefront errors using a non-dispersed PL after first-stage AO correction on the Shane 3m telescope at Lick Observatory. Our results show that non-dispersed PLs can be used for second-stage wavefront sensing, enabling performance improvements via minimally invasive retrofits to existing AO systems.

astro-ph.IM↗

arXiv2025

On-sky Demonstration of Subdiffraction-limited Astronomical Measurement Using a Photonic Lantern

Resolving fine details of astronomical objects provides critical insights into their underlying physical processes. This drives in part the desire to construct ever-larger telescopes and interferometer arrays and to observe at shorter wavelength to lower the diffraction limit of angular resolution. Alternatively, one can aim to overcome the diffraction limit by extracting more information from a single telescope's aperture. A promising way to do this is spatial mode-based imaging, which projects focal-plane field onto a set of spatial modes before detection, retaining focal-plane phase information crucial at small angular scales but typically lost in intensity imaging. However, the practical implementation of mode-based imaging in astronomy from the ground has been challenged by atmospheric turbulence. Here, we present the first on-sky demonstration of a subdiffraction-limited, mode-based measurement using a photonic lantern (PL)-fed spectrometer installed on the SCExAO instrument at the Subaru Telescope. We introduce a novel calibration strategy that mitigates time-varying wavefront error and misalignment effects, leveraging simultaneously recorded focal-plane images and using a spectral-differential technique that self-calibrates the data. Observing the classical Be star $β$ CMi, we detected spectral-differential spatial signals and reconstructed images of its H$α$-emitting disk. We achieved an unprecedented H$α$ photocenter precision of 50$μ$as in about 10-minute observation with a single telescope, measuring the disk's near-far side asymmetry for the first time. This work demonstrates the high precision, efficiency, and practicality of photonic mode-based imaging techniques to recover subdiffraction-limited information, opening new avenues for high angular resolution spectroscopic studies in astronomy.

astro-ph.IM↗

arXiv2025

Exploring the Capabilities of Astrophotonics for the Precise Alignment of Segmented Telescopes

The next generation of large telescopes for direct imaging of exoplanets will require segmented primary mirrors. Over both long and short timescales, these telescopes experience segment misalignments which degrade the final science image. Adaptive optics (AO) systems can be used to correct these aberrations in real time. AO systems require wavefront sensors (WFSs) that measure the phase of the incoming light in order to reconstruct optical aberrations. However, most WFSs used for sensing atmospheric turbulence cannot correctly detect aberrations induced by misalignments in segmented telescopes, as they show poor sensitivity to phase discontinuities. We investigate the potential of photonic lanterns (PLs), which are waveguides that allow for the low-loss transmission from multi-mode to multiple single-mode optical signals, for sensing segment misalignments at the focal plane. We assess the ability of PLs to measure piston offsets in segmented mirrors through both simulations and laboratory experiments. We simulate the photonic lantern and demonstrate linear reconstruction on segment pistons. Further, we train a neural network to reconstruct aberrations outside of the linear regime. We experimentally validate reconstruction of segment piston offsets on the Miniature Infrared SEAL (muirSEAL) testbed, which includes a segmented deformable mirror, a PSF imaging branch, and a PL. This work demonstrates the potential of the PL as a compact WFS for future space- and ground-based segmented-mirror telescopes.

astro-ph.IM↗

arXiv2025

Experimental validation of photonic lantern imaging and wavefront sensing performance

Photonic lanterns (PLs) are fiber-based waveguides that are capable of focal-plane wavefront sensing while simultaneously directing light to downstream science instruments. The optimal choice of wavefront reconstruction algorithm has yet to be determined, and likely depends on the particular observing scenario under consideration. Previous work in simulation suggests that PLs can be used for nonlinear wavefront sensing for several applications, including sensing the low-wind effect and correcting large-amplitude aberrations. We present the design of muirSEAL (miniature IR SEAL), a testbed designed to test PL wavefront reconstruction over Zernike modes and segmented-mirror offsets. We demonstrate throughput and linear wavefront reconstruction at multiple f-numbers. We further present initial laboratory imaging of a new photonic lantern fabricated at Lawrence Livermore National Laboratory.

astro-ph.IM↗

arXiv2025

Implicit Electric Field Conjugation with the Photonic Lantern Nuller

The Photonic Lantern Nuller (PLN) is an instrument concept designed to characterize exoplanets within a single beam-width from its host star. The PLN leverages the spatial symmetry of a mode-selective photonic lantern (MSPL) to create nulled ports, which cancel out on-axis starlight but allow off-axis exoplanet light to couple. The null-depths are limited by wavefront aberrations in the system as well as by imperfections in the lantern. We show that the implicit electric field conjugation algorithm can be used to reduce the stellar coupling through the PLN by orders of magnitude while maintaining the majority of the off-axis light, leading to deeper null depths (~10^{-4}) and thus higher sensitivity to potential planet signals. We discuss a theory for the tradeoff we observed between the different ports, where iEFC improves the nulls of some ports at the expense of others, and show that targeting one port alone can lead to deeper starlight rejection through that port than when targeting all ports at once. We also observe different levels of stability depending on the port and discuss the implications for practically implementing this technique for science observations.

astro-ph.IM↗

arXiv2024

Spectroscopy using a visible photonic lantern at the Subaru telescope: Laboratory characterization and first on-sky demonstration on Ikiiki (α Leo) and `Aua (α Ori)

Photonic lanterns are waveguide devices enabling high throughput single mode spectroscopy and high angular resolution. We aim to present the first on-sky demonstration of a photonic lantern (PL) operating in visible light, to measure its throughput and assess its potential for high-resolution spectroscopy of compact objects. We used the SCExAO instrument (a double stage extreme AO system installed at the Subaru telescope) and FIRST mid-resolution spectrograph (R 3000) to test the visible capabilities of the PL on internal source and on-sky observations. The best averaged coupling efficiency over the PL field of view was measured at 51% +/- 10% with a peak at 80%. We also investigate the relationship between coupling efficiency and the Strehl ratio for a PL, comparing them with those of a single-mode fiber (SMF). Findings show that in the AO regime, a PL offers better coupling efficiency performance than a SMF, especially in the presence of low spatial frequency aberrations. We observed Ikiiki (alpha Leo - mR = 1.37) and `Aua (alpha Ori - mR = -1.17) at a frame rate of 200 Hz. Under median seeing conditions (about 1 arcsec measured in H band) and large tip/tilt residuals (over 20 mas), we estimated an average light coupling efficiency of 14.5% +/- 7.4%, with a maximum of 42.8% at 680 nm. We were able to reconstruct both star's spectra, containing various absorption lines. The successful demonstration of this device opens new possibilities in terms of high throughput single-mode fiber-fed spectroscopy in the Visible. The demonstrated on-sky coupling efficiency performance would not have been achievable with a single SMF injection setup under similar conditions, partly because the residual tip/tilt alone exceeded the field of view of a visible SMF (18 mas at 700 nm). Thus emphasizing the enhanced resilience of PL technology to such atmospheric disturbances. The additional

astro-ph.IM↗

arXiv2024

Visible Photonic Lantern integration, characterization and on-sky testing on Subaru/SCExAO

A Photonic Lantern (PL) is a novel device that efficiently converts a multi-mode fiber into several single-mode fibers. When coupled with an extreme adaptive optics (ExAO) system and a spectrograph, PLs enable high throughput spectroscopy at high angular resolution. The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system of the Subaru Telescope recently acquired a PL that converts its multi-mode input into 19 single-mode outputs. The single mode outputs feed a R~4,000 spectrograph optimized for the 600 to 760 nm wavelength range. We present here the integration of the PL on SCExAO, and study the device performance in terms of throughput, field of view, and spectral reconstruction. We also present the first on-sky demonstration of a Visible PL coupled with an ExAO system, showing a significant improvement of x12 in throughput compared to the use of a sole single-mode fiber. This work paves the way towards future high throughput photonics instrumentation at small angular resolution.

astro-ph.IM↗

arXiv2024

Laboratory demonstration of a Photonic Lantern Nuller in monochromatic and broadband light

Photonic lantern nulling (PLN) is a method for enabling the detection and characterization of close-in exoplanets by exploiting the symmetries of the ports of a mode-selective photonic lantern (MSPL) to cancel out starlight. A six-port MSPL provides four ports where on-axis starlight is suppressed, while off-axis planet light is coupled with efficiencies that vary as a function of the planet's spatial position. We characterize the properties of a six-port MSPL in the laboratory and perform the first testbed demonstration of the PLN in monochromatic light (1569 nm) and in broadband light (1450 nm to 1625 nm), each using two orthogonal polarizations. We compare the measured spatial throughput maps with those predicted by simulations using the lantern's modes. We find that the morphologies of the measured throughput maps are reproduced by the simulations, though the real lantern is lossy and has lower throughputs overall. The measured ratios of on-axis stellar leakage to peak off-axis throughput are around 10^(-2), likely limited by testbed wavefront errors. These null-depths are already sufficient for observing young gas giants at the diffraction limit using ground-based observatories. Future work includes using wavefront control to further improve the nulls, as well as testing and validating the PLN on-sky.

astro-ph.IM↗

arXiv2023

Mitigating Modal Noise in Multimode Circular Fibres by Optical Agitation using a Galvanometer

Modal noise appears due to the non-uniform and unstable distribution of light intensity among the finite number of modes in multimode fibres. It is an important limiting factor in measuring radial velocity precisely by fibre-fed high-resolution spectrographs. The problem can become particularly severe as the fibre's core become smaller and the number of modes that can propagate reduces. Thus, mitigating modal noise in relatively small core fibres still remains a challenge. We present here a novel technique to suppress modal noise. Two movable mirrors in the form of a galvanometer reimage the mode-pattern of an input fibre to an output fibre. The mixing of modes coupled to the output fibre can be controlled by the movement of mirrors applying two sinusoidal signals through a voltage generator. We test the technique for four multimode circular fibres: 10 and 50 micron step-index, 50 micron graded-index, and a combination of 50 micron graded-index and 5:1 tapered fibres (GI50t). We present the results of mode suppression both in terms of the direct image of the output fibre and spectrum of white light obtained with the high-resolution spectrograph. We found that the galvanometer mitigated modal noise in all the tested fibres, but was most useful for smaller core fibres. However, there is a trade-off between the modal noise reduction and light-loss. The GI50t provides the best result with about 60% mitigation of modal noise at a cost of about 5% output light-loss. Our solution is easy to use and can be implemented in fibre-fed spectrographs.

astro-ph.IM↗

arXiv2023

2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

Photonics offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile. Integrated astrophotonic devices stand to offer critical advantages for instrument development, including extreme miniaturization, as well as integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including for example the development of photonic lanterns, complex aperiodic fiber Bragg gratings, complex beam combiners to enable long baseline interferometry, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of (1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient integration of photonics with detectors, to name a few. In this roadmap, we identify 24 areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional instruments will be realized leading to novel observing capabilities for both ground and space platforms.

astro-ph.IM↗

arXiv2023

The path to detecting extraterrestrial life with astrophotonics

Astrophysical research into exoplanets has delivered thousands of confirmed planets orbiting distant stars. These planets span a wide ranges of size and composition, with diversity also being the hallmark of system configurations, the great majority of which do not resemble our own solar system. Unfortunately, only a handful of the known planets have been characterized spectroscopically thus far, leaving a gaping void in our understanding of planetary formation processes and planetary types. To make progress, astronomers studying exoplanets will need new and innovative technical solutions. Astrophotonics -- an emerging field focused on the application of photonic technologies to observational astronomy -- provides one promising avenue forward. In this paper we discuss various astrophotonic technologies that could aid in the detection and subsequent characterization of planets and in particular themes leading towards the detection of extraterrestrial life.

astro-ph.IM↗

arXiv2022

All-fibre wavefront sensor

We report on a tapered three-core optical fibre that can be used as a tip-tilt wavefront sensor. In this device, a coupled region of a few millimetres at the sensing tip of the fibre converts fragile phase information from an incoming wavefront into robust intensity information within each of the cores. The intensity information can be easily converted to linear wavefront error over small ranges, making it ideal for closed loop systems. The sensor uses minimal information to infer tip-tilt and is compatible with remote detector arrays. We explore its application within adaptive optics and present a validation case to show its applicability to astronomy.

astro-ph.IM↗

arXiv2021

3D-M3: High-spatial resolution spectroscopy with extreme AO and 3D printed micro-lenslets

By combining IFS with ExAO we are now able to resolve objects close to the diffraction-limit of large telescopes, exploring new science cases. We introduce an IFU designed to couple light with a minimal platescale from the SCExAO facility at NIR wavelengths to a SM spectrograph. The IFU has a 3D-printed MLA on top of a custom SM MCF, to optimize the coupling of light into the fiber cores. We demonstrate the potential of the instrument via initial results from the first on-sky runs at the 8.2 m Subaru Telescope with a spectrograph using off-the-shelf optics, allowing for rapid development with low cost.

astro-ph.IM↗

arXiv2021

An innovative integral field unit upgrade with 3D-printed micro-lenses for the RHEA at Subaru

In the new era of Extremely Large Telescopes (ELTs) currently under construction, challenging requirements drive spectrograph designs towards techniques that efficiently use a facility's light collection power. Operating in the single-mode (SM) regime, close to the diffraction limit, reduces the footprint of the instrument compared to a conventional high-resolving power spectrograph. The custom built injection fiber system with 3D-printed micro-lenses on top of it for the replicable high-resolution exoplanet and asteroseismology spectrograph at Subaru in combination with extreme adaptive optics of SCExAO, proved its high efficiency in a lab environment, manifesting up to ~77% of the theoretical predicted performance.

astro-ph.IM↗