For Very Long Baseline Interferometry high-resolution imaging of exoplanets, an astrophotonic-based aperture synthesis concept is proposed for high-resolution direct imaging of exoplanets. A silicon photonic chip incorporates microheaters and optical phase shifters for precise control of delays and phase synchronization from widely separated receivers. A satellite laser guide star with a modulated optical signal serves as a global phase reference, enabling high-speed, high-stroke phase compensation and combining. The chip's design addresses challenges such as atmospheric turbulence and phase stability in optical frequencies. The study outlines the current proof-of-concept instrument status, measured performance, chip fabrication, and routes towards photonics-enabled exoplanet imaging.
Integrated photonics can be used for stable, cost-effective and precision instruments in astronomy. We present our development and testing of a silicon ring resonator as a tunable correlation filter, facilitating real-time gas contrast for specific molecules with low cross-sensitivity. Ring resonators for various gases in H-band, polarization-selective filters, and fiber-coupled prototypes are described. We present the first on-sky demonstration of silicon-on-insulator astrophotonics, and telluric CO2 absorption feature detection as a proof-of-concept using the 1.2m DAO telescope and REVOLT adaptive optics instrument. Comparisons with traditional spectrographs inform discussions on improving performance and extensions towards an observatory-class instrument for exoplanet biosignature detection.
The effects of spectral albedo on bifacial silicon heterojunction photovoltaic cell performance is explored in six locations in North America using an optoelectronic drift-diffusion model. We model seven spectral albedos using the scaled rear irradiance method and compare to broadband values. Cell performance varies geographically, with the maximum efficiency of 22.6% calculated for Cambridge Bay (69°N) with snow ground cover, and maximum output power of 216 W/m2 for Mexico City (20°N) with white sand. Neglecting spectral effects of albedo can under or over-estimate power by >2%, which can significantly impact system-level energy yield.
Bulk optical astronomical instruments face significant cost, complexity, flexure and alignment challenges with increasing next generation telescope sizes. Astrophotonics can mitigate these issues by using compact optical fiber or chip-based instruments. Here we present the design and development of a single-mode fiber coupled optical telescope system (ARTEMIS) designed for the demonstration of novel integrated astrophotonic instrumentation. Using a 4 cm fiber collimator as a telescope, we show on-sky measurements from an integrated astrophotonic chip. We have demonstrated the ability to detect <0.002% absorption depth changes of telluric CO2 lines using a sub-centimeter scale astrophotonic correlation spectroscopy chip with the sun as a background light source. These results provide a route towards demonstrating astrophotonic instrumentation on the larger 35 cm ARTEMIS telescope for the atmospheric characterization of smaller, fainter targets such as planets.
High sensitivity spectroscopy of astronomical targets is used for determining stellar radial velocities, exoplanet detection, and even exoplanet atmosphere sensing. However, high resolution spectrographs are bulky, highly complex and expensive instruments. While this bulk optical approach is versatile, fiber optic photonic instruments can be lower cost, more compact, and simpler to parallelize for multiple targets. Here we present a low-cost fiber-based correlation spectroscopy technique which can be used for simultaneously measuring radial velocity and molecular/atomic composition of astronomical targets. The correlation is achieved using a commercial, piezoelectrically tunable fiber Fabry-Pérot (FFP) filter that can be tuned from 1520 to 1620 nm. The output of the filter is measured using a single channel photodetector and processed using a lock-in amplifier. By adjusting the bias and modulation amplitude of the transmission spectrum of the FFP filter, the device can be optimized for maximum sensitivity to a certain absorption/emission line. We perform an on-sky demonstration using a 4.25 cm telescope to detect telluric CO2 with the sun as a background light source.
Using photonic devices, we developed a new approach to traditional spectroscopy where the spectral cross-correlation with a template spectrum can be done entirely on-device. By creating photonic devices with a carefully designed, modulated transmission spectrum, the cross-correlation can be carried out optically without requiring any dispersion, vastly simplifying the instrument and reducing its cost. The measured correlation lag can be used for detecting atomic/molecular species within and determining the radial velocity of a particular astrophysical object. We present an overview of two design approaches that are currently being developed that use different photonic platforms: silicon and fibre-based photonics. The silicon photonic approach utilizes ring resonators that can be thermo-optically modulated to carry out the cross-correlation. The fibre approach uses customized fibre Bragg gratings (FBGs) with transmission spectra that can be strain-modulated. Both approaches have been able to detect molecular gas in a lab setting, and we are now in the process of on-sky testing. Lastly, we discuss the future for these types of devices as their simplicity opens up the possibility of developing low-cost, purpose-built multi-object or integral field spectroscopic instruments that could make significant contributions to scientific programs requiring stellar RV measurements and exoplanet detections.
Determining the radial velocity and atmospheric composition of exoplanets is typically performed using dispersive spectroscopy. However, while this approach is versatile, spectrometers for such applications are complex, expensive and are bulky instruments. In contrast, tunable fiber-based filters are commercially available and can be used for low cost, passive remote gas sensing. In this work, we experimentally demonstrate Fabry-Pérot based correlation spectroscopy in a simple, low-cost, compact, and stable instrument package for astrophotonic gas sensing. We also show via simulation that exoplanet radial velocities can be determined simultaneously.
Bifacial photovoltaics present a clean and cheaper alternative to diesel generators for high-latitude remote communities; however, solar cells are typically tested at 0° angle of incidence, 25°C, and AM1.5, from which high-latitude conditions vary greatly. A bifacial silicon photovoltaic cell optimized for high-latitude conditions will improve energy yield for these systems. We integrate experimentally-derived cell parameters with a systems-level model capable of fixed-tilt and tracked energy yield predictions. We optimize to find the most efficient cell design for high-latitude environments in Sentaurus and SunSolve and determine the resulting improvement in energy yield for an entire panel in MATLAB.
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