The mechanical properties (such as length, shape, and stiffness) of a photomechanical material change when exposed to light. A key feature of such materials that would make them suitable for futuresque applications such as ultra-smart morphing materials is the fact that various parts of the material can communicate with other parts of the material using light. Additionally, each part of the material acts as a sensor and can change shape. These proprieties taken together can be used to make a highly-intelligent neural network that has the ability to change its physical form based on sensory data.
Potential Technological Applications
Photomechanical materials are far from being a technology. Present research seeks to set the scientific foundations for making a novel new material that has the ability to morph in response to stress or light. In contrast to common materials that are made of atoms or molecules, and interact through electric fields, Kuzyk has envisioned a system made of microscopic units that each communicate with all others using light, imbuing the system with enormous processing power and intelligence. Add to each unit the ability to respond to stress and perform actuation, and the system gains the ability to intelligently morph into complex structures.
Such a material would fill a new realm of applications. Just as a series of pictures on a piece of film can be projected onto a screen to show motion on a two-dimensional plane, the highly interconnected smart material could be made to go through a series of shapes leading to true 3-dimensional animations of a solid material. One that could be touched.
For example, automobile designers could use such materials to continually change the shape of a model to test its aerodynamics or aesthetics; a chair could be made to automatically change shape to accommodate any body type; and an exact replica of an individual could be made from information sent from a distance. Having your Uncle Joe's three-dimensional solid-body facsimile sitting next to you in casual conversation would be far more advanced than picture phones, which transmit only two-dimensional images. Other applications would include noise cancellation wallpaper, reconfigurable air craft wings, ultra-stable platforms for precision manufacturing or characterization, and reconfigurable optical filters.
 M. G. Kuzyk, Polymer Fiber Optics: Materials, Physics, and Applications, CRC Press, Taylor & Francis Group, Boca Raton (2007).
Since the end materials are far from reality, present work seeks to take the initial steps by setting a series of milestones that would demonstrate the feasibility of this totally new material concept. The approach taken by researchers is hierarchical in nature, which begins with a demonstration of the fundamental building blocks, followed by studies of how a small number of the building blocks interact with each other when interconnected with light. The goal of such studies studies culminates with the development of fabrication methods that can be used to make a bulk material from a collection of microscopic building blocks.
The fundamental physics underlying these materials and technologies is, for the most part, in place; that is, photomechanical materials exist, interferometers with photomechanical materials can be built into polymer fibers, and a series of gratings can be written into a fiber to make a network of interacting units. The challenge lies in understanding how to build a system from optimized units that works together to provide the desired function.
The fundamental building block is a polymer fiber-optic interferometer containing a nonlinear-optical and photomechanical material -- thus simultaneously having the ability to manipulate light, sense stress, and apply anisotropic stress to its surroundings. Such devices have been dubbed Photomechanical Optical Devices (POD). A POD simultaneously responds optically and mechanically to yield mechanical/optical multistability, logic, stress/temperature sensing, optical/mechanical memory, positioning, and more – all of which have been separately demonstrated.
A network of PODs, interconnected by light signals along a fiber, would in principle form the thread of an ultra-smart material with functionality that goes well beyond present materials paradigms. In contrast to a neural network, in which each neuron is connected to a small number of neighbors, a linear array of PODS along an optical fiber would interact with all others, processing information, reacting to stress and responding by selectively passing light and stressing the surroundings.
The tutorial that follows traces the hisotry of photomechnical effects, describes recent advances in photomehcnical materials, and reviews technological demonstrations that show the feasibility of this interesting new field.