Steering multiple laser beams using spatial light modulators (SLMs) creates unwanted diffraction and reflections that are not modulated by the SLM, which can make beam tracking difficult. A novel, to the best of our knowledge, and simple beam steering methodology is proposed, which aims at reducing the influence of this clutter while maintaining tracking performance. The beam(s) are deliberately defocused before steering with a superposition of a phase ramp and Fresnel lens (PRFL) phase screen on the SLM. As a result, the non-modulated reflections and diffracted light are decreased in relative intensity to the steered beam, in turn allowing simple and standard peak intensity and center of gravity (CG) algorithms for tracking. Hardware demonstration shows tracking performance using the PRFL remained on-par with more complex filtering approaches while adding no additional hardware. This method has potential to improve the communication performance of multi-beam laser communication terminals.

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Free-space optical communication has proven to have many advantages over traditional radio communications. For instance, the hardware power efficiency and limited beam spread increase data rates for lower power consumption. Furthermore, the technology does not suffer from decreased bandwidth due to crowding. Free-space optical communication is usually done using laser communication terminals. In the past the focus has been on increasing the data rates for a single link and this has led to an exponential rise in the data rate performance. However, these modules have been limited to single beams and are hence capable of only one link. This decreases the number of users, networking, and relay capabilities of optical communication satellites. The advent of MEMS Micro-Mirror Arrays (MMA) and Spatial Light Modulators (SLM) have allowed for compact and lightweight control of wavefronts. These applications would also allow for scalable independent steering of multiple laser beams. The Delft University of Technology is conducting a study of a compact and scalable multi-beam terminal using these beam steering methods[1]. The terminal consists of a MEMS MMA for high frequency response in the aperture with a high resolution SLM for the beam steering and shaping. This terminal is designed for spacecraft-to-ground and spacecraft-to-spacecraft duplex communications. It is expected to support up to 10 or more duplex links in one terminal and, therefore, suitable for usage in small satellites and mega-constellations. The high resolution can also be used for sub-aperture wavefront correction in future. This paper discusses the design of the multi-beam terminal.@en

Presentation at the 2nd optical wireless communication conference 28-9-2021@en

Introduction: The current COVID-19 pandemic has caused large shortages in personal protective equipment, leading to hospitals buying their supplies from alternative suppliers or even reusing single-use items. Equipment from these alternative sources first needs to be tested to ensure that they properly protect the clinicians that depend on them. This work demonstrates a test suite for protective face masks that can be realized rapidly and cost effectively, using mainly off-the-shelf as well as 3D printing components. Materials and Methods: The proposed test suite was designed and evaluated in order to assess its safety and proper functioning according to the criteria that are stated in the European standard norm EN149:2001+A1 7. These include a breathing resistance test, a CO₂ build-up test, and a penetration test. Measurements were performed for a variety of commercially available protective face masks for validation. Results: The results obtained with the rapidly deployable test suite agree with conventional test methods, demonstrating that this setup can be used to assess the filtering properties of protective masks when conventional equipment is not available. Discussion: The presented test suite can serve as a starting point for the rapid deployment of more testing facilities for respiratory protective equipment. This could greatly increase the testing capacity and ultimately improve the safety of healthcare workers battling the COVID-19 pandemic.

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