Holographic beam forming to generate and control multiple optical traps has proved successful using high-resolution spatial light modulators (SLMs). This type of beam control allows a multitude of traps to be independently controlled in three dimensions. Also, exotic beam shapes and profiles can be generated, which gives the optical trapping system even greater flexibility. Until recently, the generation of high resolution phase patterns has limited the speed of dynamic holographic optical trapping (HOT) systems. Today, video rate operation controlling hundreds of traps using 512x512 phase masks is possible and significantly faster operation is possible with fewer traps using less phase resolution. Therefore, phase-only liquid crystal modulator response is becoming the bottleneck. This paper discusses recent advances in SLM developments which address this issue.
Liquid crystal spatial light modulators, lenses, and bandpass filters are becoming increasingly capable as material and electronics development continues to improve device performance and reduce fabrication costs. These devices are being utilized in a number of imaging applications in order to improve the performance and flexibility of the system while simultaneously reducing the size and weight compared to a conventional lens. We will present recent progress at Sandia National Laboratories in developing foveated imaging, active optical (aka nonmechanical) zoom, and enhanced multi-spectral imaging systems using liquid crystal devices.
Unique liquid crystal (LC) spatial light modulators (SLM) are being developed for foveated imaging systems that provide wide field-of-view (FOV) coverage (±60° in azimuth and elevation) without requiring gimbals or other mechanical scanners. Recently, a transmissive-SLM- based system operating in the visible (532 nm) has been demonstrated. The LC SLM development is addressing implementation issues through the development of high figure-of-merit (FoM) LC materials and transmissive high-resolution SLMs. Transmissive SLM operation allows the foveated imaging configuration to be very compact using a very simple lens system. The reduction in the size, weight and cost of the imaging optics and in data acquisition/processing hardware makes the foveated approach attractive for small platforms such as unmanned airborne vehicles (UAVs) or missile seekers.
There are basically two types of high-resolution spatial light modulators (SLMs): reflective and transmissive. Obviously, the two types lend themselves to different optical configurations, where one might have advantages over the other for generating the dynamic multi-spot patterns needed by the micromanipulator. In addition, there are inherent performance and operational differences between the two, which has several implications. This paper compares reflective and transmissive high resolution SLMs as well as optical and electrical addressing schemes for operation in optical manipulation applications.
This paper presents the optical design and experimental demonstration of a compact, foveated, wide field-of-view (FOV) imaging system using two lenses and a liquid crystal spatial light modulator (SLM). The FOV of this simple doublet system is dramatically improved by the SLM, which can be programmed to correct all the geometrical aberrations at any particular field angle. The SLM creates a variation in the image quality across the entire FOV, with a diffraction-limited performance at the field angle of interest (similar to the foveated human vision). The region of interest can be changed dynamically, such that any area within the FOV of the system can be highly resolved within milliseconds. The wide FOV, compactness, and absence of moving parts make this system a good candidate for tracking and surveillance applications. We designed an f/7.7 system, with a 60° full FOV, and a 27 mm effective focal length. Only two lenses and a beam splitter cube were used along with a reflective SLM. The theoretical wavefront aberration coefficients were used to program the SLM, which was placed in the pupil plane of the system. A prototype was built and the system was experimentally demonstrated using monochromatic light and a CCD camera.
High-resolution, liquid-crystal spatial light modulators (SLMs) are being used as dynamic phase screens<sup>1,2</sup> for testing optical systems and as optical wavefront compensators<sup>3,4</sup> to dynamically correct distortions. An SLM provides hundreds of waves of adjustable phase modulation across the aperture of the device. Some of this phase adjustment can be used to compensate for distortions internal to the SLM such as backplane curvature. Because of modulo-2π operation, the dynamic range of the device is not significantly decreased by adding phase compensation, as long as the phase shift over the aperture is only a few waves. In this paper, we will discuss the techniques being used to determine the correct phase compensation for SLMs and how the compensation is being applied through the SLM control software.