Eric Tremblay

Proof of principle demonstration of a self-tracking concentrator

We present to the best of our knowledge the first successful demonstration of a planar, self-tracking solar concentrator system capable of a 2-dimensional angular acceptance of over 40°. The light responsive mechanism allows for efficient waveguide coupling and light concentration independently of the angle of incidence within the angular range. A coupling feature is created at the focal spot of the optical system by locally melting a phase change material which acts as an actuator due to the large thermal expansion. A dichroic prism membrane reflects the visible light so that it is efficiently coupled into a waveguide at the point of the created coupling feature. We show simulation results for concentration and efficiency, validated by an experimental proof of concept demonstration of a self-tracking concentrator array element. Simulations show that a system based on this approach can achieve 150X effective concentration by scaling the system collecting area to reasonable dimensions (40 x 10 cm²).

Thermal phase change actuator for self-tracking solar concentration

We present a proof of principle demonstration of a reversible in-plane actuator activated by focused sunlight, and describe a concept for its use as a self-tracking mechanism in a planar solar concentrator. By actuating at the location of focused sunlight and splitting the solar spectrum for actuation energy, this phase change device aims to provide the adaptive mechanism necessary to efficiently couple concentrated solar light from a lens into a planar lightguide in a manner that is insensitive to incidence angle. As a preliminary demonstration we present a planar actuator array capable of in-plane deflections of >50μm when illuminated with focused light from a solar simulator and demonstrate solar light activated frustrated total internal reflection (FTIR) with the actuator array. We further propose how this solar induced FTIR effect can be modified using a dichroic facet array to self-adaptively couple and concentrate solar light into a planar lightguide.We present a proof of principle demonstration of a reversible in-plane actuator activated by focused sunlight, and describe a concept for its use as a self-tracking mechanism in a planar solar concentrator. By actuating at the location of focused sunlight and splitting the solar spectrum for actuation energy, this phase change device aims to provide the adaptive mechanism necessary to efficiently couple concentrated solar light from a lens into a planar lightguide in a manner that is insensitive to incidence angle. As a preliminary demonstration we present a planar actuator array capable of in-plane deflections of >50 μm when illuminated with focused light from a solar simulator and demonstrate solar light activated frustrated total internal reflection (FTIR) with the actuator array. We further propose how this solar induced FTIR effect can be modified using a dichroic facet array to self-adaptively couple and concentrate solar light into a planar lightguide.

Self-tracking solar concentrator with an acceptance angle of 32°

Solar concentration has the potential to decrease the cost associated with solar cells by replacing the receiving surface aperture with cheaper optics that concentrate light onto a smaller cell aperture. However a mechanical tracker has to be added to the system to keep the concentrated light on the size reduced solar cell at all times. The tracking device itself uses energy to follow the suns position during the day. We have previously shown a mechanism for self-tracking that works by making use of the infrared energy of the solar spectrum, to activate a phase change material. In this paper, we show an implementation of a working 53 x 53 mm(2) self-tracking system with an acceptance angle of 32° ( ± 16°). This paper describes the design optimizations and upscaling process to extend the proof-of-principle self-tracking mechanism to a working demonstration device including the incorporation of custom photodiodes for system characterization. The current version demonstrates an effective concentration of 3.5x (compared to 8x theoretical) over 80% of the desired acceptance angle. Further improvements are expected to increase the efficiency of the system and open the possibility to expand the device to concentrations as high as 200x (C(geo) = 400x, η = 50%, for a solar cell matched spectrum).

Light induced fluidic waveguide coupling.

We report on the development of an opto-fluidic waveguide coupling mechanism for planar solar concentration. This mechanism is self-adaptive and light-responsive to efficiently maintain waveguide coupling and concentration independent of incoming lights direction. Vapor bubbles are generated inside a planar, liquid waveguide using infrared light on an infrared absorbing glass. Visible light focused onto the bubble is then reflected by total internal reflection (TIR) at the liquid-gas interface and coupled into the waveguide. Vapor bubbles inside the liquid are trapped by a thermal effect and are shown to self-track the location of the infrared focus. Experimentally we show an optical to optical waveguide coupling efficiency of 40% using laser light through a single commercial lens. Optical simulations indicate that coupling efficiency > 90% is possible with custom optics.

Curved Holographic Combiner for Color Head Worn Display

A volume hologram recorded with a lens array is proposed as a color transflective screen for Head Worn Display (HWD) systems. Design, fabrication as well as proof of concept are reported. Light from a single MEMS-based projector is efficiently diffracted towards the eye with an angular spread given by the numerical aperture of the lenses forming the lens array. Using a dual-focus contact lens, full color high-resolution images are added to the HWD users normal vision. A full color system with a 55 degrees lateral field of view is demonstrated. This screen offers the possibility for small footprint and large field of view HWDs.

Efficiency of a micro-bubble reflector based, self-adaptive waveguide solar concentrator

State of the art solar concentrators use free-space, non-imaging optics to concentrate sunlight. Mechanical actuators keep the focal spot on a small solar cell by tracking the sun’s position. Planar concentrators emerged recently that employ a waveguide slab to achieve high concentration by coupling the incident sunlight into the waveguide. We report on the development of an opto-fluidic waveguide coupling mechanism for planar solar concentration. The self-adaptive mechanism is light-responsive to efficiently maintain waveguide coupling and concentration independent of incoming light’s direction. By using an array of axicons and lenses, an array of vapor bubbles are generated inside a planar, liquid waveguide, one for each axicon-lens pair. The mechanism uses the infrared part of the solar spectrum on an infrared absorbing medium to provide the energy needed for bubble generation. Visible light focused onto the bubble is then reflected by total internal reflection (TIR) at the liquid-gas interface and coupled into the waveguide. Vapor bubbles inside the liquid are trapped by a thermal effect and are shown to self-track the location of the infrared focus. We show experimental results on the coupling efficiency of a single bubble and discuss the effect of angular coupling. Furthermore the effect of an array of bubbles inside the waveguide (as produced by a lensarray) onto the coupling efficiency and concentration factor is analyzed.

Gigapixel Imaging with the AWARE Multiscale Camera

Gigapixel cameras have been confined to specialized applications such as aerial photography and astronomical observatories. A simplified architecture would better suit terrestrial imaging and reduce instrument cost and complexity. Our gigapixel AWARE camera is based on monocentric multiscale optical design principles that produce high-resolution images with a field of view (FOV) limited only by vignetting. This design allows resolution to approach the theoretical diffraction limits for a given entrance pupil size and FOV.

Self-tracking planar concentrator using a solar actuated phase-change mechanism

In this paper we discuss optical considerations and present design simulation results for a self-tracking (passive) solar concentrator. The self-tracking mechanism uses a reversible in-plane paraffin thermal actuator to couple shortwavelength light into a lightguide at the position of the solar focus. By splitting the solar spectrum using a longpass dichroic faceted reflector for actuation energy, this device adaptively self-tracks and concentrates solar light into a planar waveguide.

Novel HMD concepts from the DARPA SCENICC program

Access to digital information is critical to modern defense missions. Sophisticated sensor systems are capable of acquiring and analyzing significant data, but ultimately this information must be presented to the user in a clear and convenient manner. Head-Worn Displays (HWDs) offer one means of providing this digital information. Unfortunately, conventional HWDs occupy significant volume and have serious performance limitations. To truly offer a seamless man/machine interface, the display must be able to provide a wide array of information in a manner that enhances situation awareness without interfering with normal vision. Providing information anywhere in the eyes field of view at resolutions comparable to normal vision is critical to providing meaningful information and alerts. Furthermore, the HWD must not be bulky, heavy, or consume significant power. Achieving these goals of the ideal wearable display has eluded optical designers for decades. This paper discusses the novel approach being developed under DARPAs SCENICC program to create a high resolution HWD based on using advanced contact lenses. This approach exploits the radically different concept of enhancing the eyes normal focus accommodation function to enable direct viewing of high resolution, wide field of view transparent image surfaces placed directly in front of the eye. Integrating optical components into contact lenses eliminates all of the bulky imaging optics from the HWD itself creating a high performance wearable display in a standard protective eyewear form factor. The resulting quantum advance in HWD performance will enable HWDs to expand well beyond their current limited rolls.

Demonstration of a 5x5 cm(2) self-tracking solar concentrator

Solar concentration is using optics in order to minimize the amount of expensive photovoltaic cell material needed. For concentration factors higher than approximately 4, tracking the sun’s position is needed to keep the focal spot on the solar cell. Based on recent developments using a waveguide slab to concentrate sunlight we propose and demonstrate a light responsive, self-tracking solar concentrator. Using a phase change material acting at the focal spot, it is possible to maintain efficient coupling into the waveguide, up to an angular range of +/- 20 degrees. The system uses the unused infrared part of the solar spectrum as energy for the phase change actuator to achieve its high acceptance angle. With a spectrally matched custom silicon solar cell attached to the waveguide slab, in which light is coupled, the visible part of the solar spectrum can be efficiently converted to electricity. A proof-of-concept single lens device was demonstrated in our previous work. Here we extend the principle to a 3x3 lens array demonstration device. The current demonstration device features an acceptance angle of +/- 16 degrees and an effective concentration factor of up to 20x.