arXiv subjects

Joshua J. Collier

Publications and source records attributed to Joshua J. Collier.

4 recordsLinked to original sources

arXiv2026

Long baseline optical interferometric imaging with active phase stabilization

Astronomical observations allow us to better our understanding of the universe. As we observe smaller and more distance features, we run into the diffraction limit of our observation system. This limit is a function of the wavelength observed and the size of the primary aperture used. We can synthesize a larger primary aperture by implementing interferometry. Long baseline optical interferometry would lead to significant improvements in astronomical imaging resolution. Building optical interferometers with free space baselines becomes significantly more difficult as the baseline increases. A promising alternative is to use optical fiber to connect telescopes. Fiber-based interferometers are much more susceptible to phase noise than their free-space counterparts due to inhomogeneities in the fiber medium. This leads to significant degradation of interferometric signals used for astronomical measurements. We implement phase stabilization techniques used in quantum communications to stabilize an optical interferometer with a 170km pseudo-baseline. We use a quantum optimal measurement technique with this interferometer to resolve the extent of a source four times smaller than the diffraction limit of the system within 1.5% error. These results bring the potential for a full-scale on-sky long baseline interferometer significantly closer. A 350km baseline optical interferometer at 1550nm would allow us to resolve sub microarcsecond features in the universe.

physics.optics↗

arXiv2026

On-sky binary source hypothesis testing beyond the diffraction limit using spatial mode demultiplexing based detection

Improving the resolution of telescope systems will provide the opportunity to study new physical phenomena in previously unobserved environments. Spatial mode de-multiplexing (SPADE) based imaging is a promising and rapidly evolving technique for pushing the resolution of optical telescopes beyond the diffraction limit. A key application of this technique is for near-optimal hypothesis testing for the presence of secondary and extended sources in the sub-diffraction regime. We present the first demonstration of a binary-SPADE based hypothesis testing instrument deployed on-sky. In our proof-of-principle experiment, based on mode demultiplexing with a double clad fiber coupler, we demonstrate detection of a binary star system separated below the diffraction limit. We perform measurements in the photon-starved regime where no image can be formed by traditional direct imaging. We find the scaling of the system's type II error rate (the ``binary source miss" chance) was heavily limited by unbalanced loss in our double-clad fiber coupler when compared to the idealized quantum limits. Despite this the evaluated type II error is always lower than a perfect direct imaging measurement. We expect that if this instrument is scaled to larger aperture telescope systems the effects of atmospheric turbulence will further degrade this system's performance.

astro-ph.IM↗

arXiv2025

Phase stabilization for long baseline interferometry of incoherent optical sources

The maximum baseline, and therefore resolution, of optical astronomical interferometers is limited by attenuation and phase noise within the optical path between the apertures and beam combiner, as well as the practical challenges of constructing optical delay lines more than a few hundred meters in length. We implement off-band phase stabilization on two fiber optic links of 85~km, creating a total baseline of 170~km. We show that the system is able to effectively phase stabilize signals from an incoherent pseudo-thermal source with a bandwidth of 11.2~nm. We are able to reduce the phase noise by 4-5 orders of magnitude between 1 and 100~Hz such that we could resolve an applied phase difference of 0.16~cycles per second with continuous measurement. We show that, with phase stabilization active, the interferometer is able to recover both first-order and second-order photon correlations. These results demonstrate the feasibility of this technique for long-baseline optical and quantum astronomical interferometers. The present results are limited by chromatic dispersion within the fiber, which can be mitigated using dispersion compensating modules.

physics.optics↗

arXiv2025

Super resolving binary-source hypothesis testing with a double-clad fiber coupler

We present a technique for binary spatial mode demultiplexing, using a double-clad fiber coupler as an optical mode sorter, for hypothesis testing for one or two point sources in an incident optical field. By directly coupling an optical field through a double-clad fiber coupler, we demultiplex the field into the fundamental mode and a superposition of higher-order modes. We use the ratio of multi-mode to single-mode power to distinguish between single and double point sources. In a tabletop demonstration of the technique, we demonstrate the capability to accurately identify the presence of two sources separated below the Rayleigh limit for relative brightnesses from 0 dB to -20 dB. For sources with less than 5 dB difference in their relative powers, our imaging protocol can correctly determine the presence of a second optical source even when the two sources have separations 50x smaller than the Rayleigh limit. These results highlight the potential of this technique as a simple tool for super-resolving classification of a pair of point emitters, especially in the context of astronomical imaging for binary systems.

physics.optics↗