Free space propagation and conventional optical systems such as lenses and mirrors all perform spatial unitary transforms. However, the subset of transforms available through these conventional systems is limited in scope. We present here a unitary programmable mode converter (UPMC) capable of performing any spatial unitary transform of the light field. It is based on a succession of reflections on programmable deformable mirrors and free space propagation. We first show theoretically that a UPMC without limitations on resources can perform perfectly any transform. We then build an experimental implementation of the UPMC and show that, even when limited to three reflections on an array of 12 pixels, the UPMC is capable of performing single mode tranforms with an efficiency greater than 80% for the first four modes of the transverse electromagnetic basis.

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Programmable unitary spatial mode manipulation

Materials with engineered thermal expansion, capable of achieving targeted area/volume changes in response to variations in temperature, are important for a number of aerospace, optical, energy, and microelectronic applications. While most of the proposed structures with engineered coefficient of thermal expansion consist of bi-material 2D or 3D lattices, here it is shown that origami metamaterials also provide a platform for the design of systems with a wide range of thermal expansion coefficients. Experiments and simulations are combined to demonstrate that by tuning the geometrical parameters of the origami structure and the arrangement of plates and creases, an extremely broad range of thermal expansion coefficients can be obtained. Differently from all previously reported systems, the proposed structure is tunable in situ and nonporous.

Origami Metamaterials for Tunable Thermal Expansion.

Soft adaptable materials that change their shapes, volumes, and properties in response to changes under ambient conditions have important applications in tissue engineering, soft robotics, biosensing, and flexible displays. Upon water absorption, most existing soft materials, such as hydrogels, show a positive volume change, corresponding to a positive swelling. By contrast, the negative swelling represents a relatively unusual phenomenon that does not exist in most natural materials. The development of material systems capable of large or anisotropic negative swelling remains a challenge. We combine analytic modeling, finite element analyses, and experiments to design a type of soft mechanical metamaterials that can achieve large effective negative swelling ratios and tunable stress-strain curves, with desired isotropic/anisotropic features. This material system exploits horseshoe-shaped composite microstructures of hydrogel and passive materials as the building blocks, which extend into a periodic network, following the lattice constructions. The building block structure leverages a sandwiched configuration to convert the hydraulic swelling deformations of hydrogel into bending deformations, thereby resulting in an effective shrinkage (up to around −47% linear strain) of the entire network. By introducing spatially heterogeneous designs, we demonstrated a range of unusual, anisotropic swelling responses, including those with expansion in one direction and, simultaneously, shrinkage along the perpendicular direction. The design approach, as validated by experiments, allows the determination of tailored microstructure geometries to yield desired length/area changes. These design concepts expand the capabilities of existing soft materials and hold promising potential for applications in a diverse range of areas.

Soft mechanical metamaterials with unusual swelling behavior and tunable stress-strain curves

Vibration and noise control using shunted piezoelectric transducers: A review

Inspired by the need to develop materials capable of targeted and extreme volume changes during operation, numerical simulations and experiments are combined to design a new class of soft architected materials that achieve a reduction of projected surface-area coverage during swelling.

Harnessing Buckling to Design Architected Materials that Exhibit Effective Negative Swelling

This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror may be used on its own, or as a segment of a larger mirror. The typical size of one segment is 100 to 200 mm; the production process relies on silicon wafers and thick film piezoelectric material deposition technology; it is able to lead to an actuation pitch of the order of 5 mm, and the manufacturing costs appear to grow only slowly with the number of degrees of freedom in the adaptive optics.

Modular bimorph mirrors for adaptive optics

This article presents a strategy for enhancing the performance of the synchronized switch damping on inductor technique used for the semiactive control of structural vibrations. This enhancement is...

Synchronized Switch Damping on Inductor and Negative Capacitance

Scale effects in active optics of large segmented mirrors

We discuss the concept of lightweight segmented bimorph mirrors for adaptive optics. The segment consists of a monocrystal silicon substrate actuated by an array of in-plane piezoceramic (PZT) actuators with honeycomb electrodes. We focus on technological aspects of the segment design that are critical for space applications and describe a single segment demonstrator. The morphing capability of the segment is evaluated experimentally. We also discuss the local deformations (dimples) associated with the shape of the electrodes acting on the PZT array.

Segmented bimorph mirrors for adaptive optics: segment design and experiment

This paper examines the active optics of future large segmented telescopes from the point of view of dynamic simulation and control. The first part of the paper is devoted to the modeling of the mirror. The model has a moderated size and separates the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary or residual response). The second part of the paper is devoted to control. The control strategy considers explicitly the primary response ofthe telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty. This approach is very fast and allows extensive parametric studies. The study is illustrated with an example involving 90 segments, 270 inputs, and 654 outputs.

Gonçalo Rodrigues

Papers

Modular bimorph mirrors for adaptive optics

Synchronized Switch Damping on Inductor and Negative Capacitance

Scale effects in active optics of large segmented mirrors

Segmented bimorph mirrors for adaptive optics: segment design and experiment

Active Optics of Large Segmented Mirrors: Dynamics and Control