One of the most ambitious goals of modern astronomy is to uncover signs of extraterrestrial biological activity, primarily achieved through spectroscopic analysis of light emitted by exoplanets to identify specific atmospheric molecules. Most exoplanets are indirectly identified through techniques like transit or Doppler shift of the host star's flux. Long-term surveys have yielded statistical insights into the occurrence rates of different planet types based on factors such as radius/mass, orbital period, and the spectral type of the host star. Initial estimates of terrestrial planets within the habitable zone have also emerged. However, the difficulty of detecting light from these exoplanets leaves much unknown about their nature, formation, and evolution. As the number of rocky exoplanets around nearby stars rises, questions about their atmospheric composition, evolutionary trajectory, and habitability increase. Direct measurement of an exoplanet's atmospheric composition through its spectral signature in the infrared can provide answers. Measuring the infrared spectrum of these planets poses significant challenges due to the star/planet contrast and very small angular separation from their host stars. Previous research showed that space-based telescopes are mandatory, and unless large primary mirrors (>30m in diameter) can be sent into space, interferometric techniques become essential. Combining light from distant telescopes with interferometric techniques allows access to information at minimal angular separation, operating within the diffraction limit of individual telescopes. Successful demonstrations of on-ground nulling interferometry open a new era for such space-based missions. They are vital to sidestep and tackle these scientific questions. We recently initiated a new study with the European Space Agency to explore the design parameters and the performances related to an interferometric concept based on a single spacecraft and sparse multiple sub-apertures. Launch constraints are linked to the use of an Ariane 6 launch vehicle. Our parametric study covers a range of 1-4 m for the diameter of the telescope and a 10-60 m baseline. The most promising concept working in the infrared range (3-20μm) will be highlighted. This study is conducted by TUDelft in cooperation with KULeuven, CSL/ULiège, and Amos with the support of the European Space Agency.

During the last few years, one of our main research topics has been developing a new type of spectropolarimeter intended for space applications. Initially analyzed numerically, the instrument has a compact, stable design without rotating components. The entire Stokes vector can be determined in a single shot in a vast spectral range. The simulations proved that the modulation schemes that can be obtained for this instrument are close to the optimal form. The objective of the current research is the experimental validation of this instrument. Here, we present the first results for determining the instrumental matrix and the demodulation results for a s eries of polarization states. In conclusion, we present the possible further developments of that project.

This paper proposes a novel approach to improve the performance of free-space optical communication intersatellite links by combining fundamental Gaussian and higher-order Laguerre-Gaussian beams. We present a comprehensive mathematical model to analyze the system’s performance, including received power statistics, average bit error probability, and outage probability. To generate the desired beam profiles, we propose an optical system capable of creating a superposition of orthogonally polarized Laguerre-Gaussian beams that yield the far-field irradiance distributions that optimize the communication performance. Our theoretical analysis demonstrates that the combination of fundamental Gaussian and higher-order modes can significantly enhance system performance compared to conventional fundamental Gaussian beams. In some scenarios, the proposed approach offers savings on the order of 20% to 40% of the required transmitted power.

Intersatellite optical communication links will be crucial for the development of future global optical and quantum communication networks. Under the harsh space environment satellite optical terminals will suffer pointing jitter and wavefront errors. In this paper, the impact of the combination of these errors on the transmitter side is modeled. Combining the far-field diffraction patterns obtained through computational Fourier optics and the statistics of the pointing jitter, the received power statistics are derived numerically for different scenarios. The computational model is first used to evaluate the optimum nominal parameters of the transmitted beam. Then, several optical aberrations are added to the transmitted beam and their impact on the communication performance is evaluated through the average bit error rate.

Reflectance spectroscopy is a technique widely used to investigate the composition and physical properties of a surface. The spectro-polarimetry adds the investigation of the polarimetric state of the light, while keeping the spectroscopy dependency. This technique is currently limited for the characterization of the surface, but can bring another clue on the composition and physical properties of the studied surface. We present here the design of a novel ellipsometer, optimized for the investigation of the polarization state of the light reflected by a granular surface. This instrument is able to measure the linear and circular components of the polarization over a wide spectral range from the ultraviolet to near-infrared and at a wide choice of geometrical configuration. The wide spectral range is achieved with the use of a photoelastic modulator acting like a retardance waveplate over the whole working range. Spectro-polarimetric investigations of terrestrial and extra-terrestrial samples will have application to mineralogical investigations, planetary surface explorations, and improve our understanding of the Solar System.

Growing interest in free-space optical communication, due to the high bandwidth and security provided by these links, has generated the necessity of designing high-performance satellite terminals. In order to develop these terminals, the opto-thermo-mechanical phenomena that appear in the space environment and their effect on optical communication links have to be understood in detail. A review of the opto-thermo-mechanical phenomena occurring in spaceborne terminals is presented, describing the relevance of each of them. The methods found to compute the impact on the communication performance due to opto-thermo-mechanical phenomena are collected by building the bridge between the optical and communication performance parameters. Finally, techniques available to mitigate the detrimental effects of these phenomena are classified, and the relevant research challenges are identified.

The light emitted or reflected by a medium can exhibit a certain degree of polarization. Most of the time, this feature brings valuable information about the environment. However, instruments able to accurately measure any type of polarization are hard to build and adapt to inauspicious environments, such as space. To overcome this problem, we presented recently a design for a compact and steady polarimeter, able to measure the entire Stokes vector in a single shot. The first simulations revealed a very high modulation efficiency of the instrumental matrix for this concept. However, the shape and the content of this matrix can change with the characteristics of the optical system, such as the pixel size, the wavelength or the number of pixels. To assess the quality of the instrumental matrices for different optical characteristics, we analyze here the propagation of errors, together with the impact of different types of noise. The results show that the instrumental matrices are converging towards an optimal shape. On this basis, the theoretical limits of sensitivity on the Stokes parameters are inferred.

A novel method for space object identification is proposed, based on full Stokes spectropolarimetry in the visible and near-infrared wavelength range. Space objects that have been previously detected and are illuminated by the sun can be observed with a telescope to simultaneously obtain intensity, spectra, and polarimetry, and compose light curves of these parameters as function of time. The intention is to thus assign a unique identification, or at least a classification to these objects. Single, double, and multiple reflections of sunlight off the space object (natural or artificial objects, including debris) will introduce spectrally dependent polarisation into the scattered light, the spectral signature of which is affected by the complex refractive index of the scattering materials and the geometry. The simultaneous measurement of the full Stokes vector allows separation of the light source unpolarised spectral signatures on the one hand from the polarisation spectral features on the other hand. To illustrate the concept, we have performed a number of simulations for double scattering off a small selection of materials, for a large range of scattering geometries. Examples of individual scattering geometries and statistical summaries of all geometries are presented. A demonstrator spectropolarimeter is being built, we present an overview of the design and the high level planning, as well as some predicted performance parameters.

Photonic structuration is an efficient way to improve light harvesting in multiple optoelectronic applications. In this study, photonically structured TiO2 is considered as a photoanode layer for perovskite solar cells to enhance light absorption through the excitation of quasi-guided modes within the photoactive perovskite material, while optimizing the charge collection in the photovoltaic assembly and therefore its global efficiency. Practically, polystyrene beads of various diameters are used as hard templating sacrificial agents for the design of inverse-opal TiO2 through spin-coating protocols. The positive impact of the porous photonic structuration in comparison with compact, unstructured photoactive layers is demonstrated. An optimum of light absorption is shown for hybrid TiO2-perovskite structures composed of ∼400 nm diameter TiO2 hollow spheres filled with CH3NH3PbI3, confirming recent numerical predictions. However, electronic-related countereffects are observed in consecutively assembled solar cells when pore dimensions exceed the estimated diffusion length of electrons in the infiltrated perovskite material. Upper conversion efficiency is obtained with solar cells composed of ∼220 nm diameter large TiO2 pores filled with CH3NH3PbI3.

Light management is an important area of photovoltaic research, but little is known about it in perovskite solar cells. The present work numerically studies the positive effect of structuring the photo-active layer of perovskite material. This structuration consists of a hybrid absorbing layer made of an uniform part and an opal-like part. A genetic algorithm approach allows us to determine the optimal combination among more than 1.4 x 10⁹ potential combinations. The optimal combination provides an internal quantum efficiency of 98.1%, nearly 2% higher than for an equivalent unstructured photo-active layer. The robustness of the optimum against potential experimental deviations, as well as the angular dependency of the proposed structure, are examined in the present study.

Perovskite solar cells have shown a tremendous interest for photovoltaics since the past decade. However, little is known on the influence of light management using photonic crystals inside such structures. We present here numerical simulations showing the effect of photonic crystal structuring on the integrated quantum efficiency of perovskite solar cells. The photo-active layer is made of an opal-like perovskite structure (monolayer, bilayer or trilayer of perovskite spheres) built in a TiO₂ matrix. Fano resonances are exploited in order to enhance the absorption, especially near the bandgap of perovskite material. The excitation of quasi-guided modes inside the absorbing spheres enhances the integrated quantum efficiency and the photonic enhancement factor. More specifically, a photonic enhancement factor as high as 6.4% is predicted in the case of spheres monolayer compared to an unstructured perovskite layer. The influences of sphere’s radius and incident angle on the absorbing properties are also estimated. Those numerical results can be applied to the nascent field of photonic structuring inside perovskite solar cells.