KEYWORDS: Radio over Fiber, Reflection, Relative intensity noise, Analog electronics, Radio telescopes, Radio astronomy, Optical transmission, Connectors, Semiconductor lasers, Signal attenuation, Interference (communication)
Optical fibers, known for their immunity to electromagnetic interference, present a promising alternative to coaxial cables for long-range signal transmission in radio telescopes. This study introduces a cost-effective solution for analog signal transmission over fiber, specifically designed for radio astronomy applications. By modifying Small Form-factor Pluggable (SFP) modules, we developed a dual-channel Radio-over-Fiber (RFoF) system with a total cost under $100 USD. Our measurements indicate that the system meets the performance requirements of most radio telescope configurations and has reached technology readiness level 6. This manuscript details the design, modifications, and testing of the SFP modules, showcasing their potential benefits for radio astronomy.
Traditional optical astronomy is limited to the measurement of transient signals at time scales greater than ∼ 1ms due to the readout speed of detectors and read noise limitations to sensitivity in short exposures. The Ultra-Fast Astronomy Project (UFA)1, 2 explores much faster events in the sub-millisecond domain. We designed a single-photon imaging camera based on position-sensitive silicon photomultiplier (PS-SiPM) with a low-cost FPGA readout system to observe such events. The sensor operates in a photon-counting mode with time resolution on the order of 10ns and a spatial resolution of around 200μm. We present our camera’s electronic and mechanical design, the algorithm for data handling, and testing and calibration data.
In our Ultra-Fast Astronomy (UFA) program, we aim to improve measurements of variability of astronomical targets on millisecond and shorter time scales. In this work, we present initial on-sky measurements of the performance of silicon photomultiplier detectors (SiPMs) for UFA. We mounted two different SiPMs at the focal plane of the 0.7-m aperture Nazarbayev University Transient Telescope at the Assy-Turgen Astrophysical Observatory, with no filter in front of the detector. The 3 mm × 3 mm SiPM single-channel detectors have a field of view of 2.2716 ′ × 2.2716 ′ . During the nights of October 28–29, 2019, we measured sky background, bright stars, and an artificial source with a 100-Hz flashing frequency. We compared detected SiPM counts with Gaia satellite G-band flux values to show that our SiPMs have a linear response. With our two SiPMs (models S14520-3050VS and S14160-3050HS), we measured a dark current of ∼130 and ∼85 kilo counts per second (kcps), and a sky background of ∼201 and ∼203 kcps, respectively. We measured an intrinsic crosstalk of 10.34% and 10.52% and derived a 5σ sensitivity of 13.9 and 14 Gaia G-band magnitude for 200-ms exposures, for the two detectors, respectively. For a 10-μs window, and allowing a false alarm rate of once per 100 nights, we derived a sensitivity of 22 detected photons, or six Gaia G-band magnitudes. For nanosecond timescales, our detection is limited by crosstalk to 12 detected photons, which corresponds to a fluence of ∼155 photons per square meter.
We present program objectives and specifications for the first generation Ultra-Fast Astronomy (UFA) observatory which will explore a new astrophysical phase space by characterizing the variability of the optical (320 nm - 650 nm) sky in the millisecond to nanosecond timescales. One of the first objectives of the UFA observatory will be to search for optical counterparts to fast radio bursts (FRB) that can be used to identify the origins of FRB and probe the epoch of reionization and baryonic matter in the interstellar and intergalactic mediums. The UFA camera will consist of two single-photon resolution fast-response detector 16x16 arrays operated in coincidence mounted on the 0.7 meter Nazarbayev University Transient Telescope at the Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) located near Almaty, Kazakhstan. We are currently developing two readout systems that can measure down to the microsecond and nanosecond timescales and characterizing two silicon photomultipliers (SiPM) and one photomultiplier tube (PMT) to compare the detectors for the UFA observatory and astrophysical observations in general.
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