High-quality imaging is typically dependent upon well-focused optical systems. We present a method that linearizes defocus to provide a clear zero-crossing along the optical axis for structured light illumination (SLI) systems. Here, sinusoidal fringes are projected onto a quad target, a diffuse target with different heights along the optical axis in separate quadrants. Shifting the focus alters the fringe contrasts on the quad target. Best focus is achieved when the contrast between the different heights is balanced. The method was tested using a commercial SLI system and compared to a published phase-shifted reconstruction technique. The non-linear defocus behavior was efficiently linearized using the quad target method as evidenced by linear regressions. Finally, focal position estimates agreed well with the phaseshifted technique, thereby demonstrating viability of the method.
For the passed several years, the Naval Research Laboratory (NRL) has
been investigating the use of Carbon Fiber Reinforced Polymer (CFRP)
material in the construction of a telescope assembly including the optical
components. The NRL, Sandia National Laboratories (SNL), and
Composite Mirror Applications, Inc. (CMA) have jointly assembled a
prototype telescope and achieved “first light” images with a CFRP 0.4 m
aperture telescope. CFRP offers several advantages over traditional
materials such as creating structures that are lightweight and low
coefficient of thermal expansion and conductivity. The telescope’s
primary and secondary mirrors are not made from glass, but CFRP, as
well. The entire telescope weighs approximately 10 kg while a typical
telescope of this size would weigh quite a bit more. We present the
achievement of “first light” with this telescope demonstrating the imaging
capabilities of this prototype and the optical surface quality of the mirrors
with images taken during a day’s quiescent periods.
An active reflective component can change its focal length by physically deforming its reflecting surface. Such elements exist at small apertures, but have yet to be fully realized at larger apertures. This paper presents the design and initial results of a large-aperture active mirror constructed of a composite material called carbon fiber reinforced polymer (CFRP). The active CFRP mirror uses a novel actuation method to change radius of curvature, where actuators press against two annular rings placed on the mirror’s back. This method enables the radius of curvature to increase from 2000mm to 2010mm. Closed-loop control maintains good optical performance of 1.05 waves peak-to-valley (with respect to a HeNe laser) when the active CFRP mirror is used in conjunction with a commercial deformable mirror.
Optical zoom enables wide and narrow fields-of-view within a single optical system. Traditional zoom designs translate elements along the optical axis, a technique that is generally prohibitive for large diameter optics. Adaptive optical zoom (AOZ) alters system magnification via variable focal length elements, a technique that has the potential to facilitate zoom in large diameter systems. This paper details a novel optical theory developed to design AOZ systems. The developed theory modifies existing techniques for telescope objective design and third-order aberration determination to accommodate the additional degrees of freedom found with AOZ. The derived theory also enables a large-scale tradespace analysis, allowing optical design to begin from a broad perspective and optimize a particular design. Using the tradespace analysis, a Cassegrain AOZ objective with a 3.3Xzoom ratio is designed, demonstrating the capability and validity of the theory.
Micro-electro-mechanical systems (MEMS) deformable mirrors are known for their ability to correct optical aberrations,
particularly when the wavefront is expanded via Zernike polynomials. This capability is combined with adaptive optical
zoom to enable diffraction limited performance over broad spectral and zoom ranges. Adaptive optical zoom (AOZ)
alters system magnification via variable focal length elements instead of axial translation found in traditional zoom
designs. AOZ systems are simulated using an efficient approach to optical design, in which existing theories for
telescope objective design and third-order aberration determination are modified to accommodate the additional degrees
of freedom found with AOZ. An AOZ system with a 2.7× zoom ratio and 100mm entrance pupil diameter is presented to
demonstrate the validity and capability of the theory.
The Naval Research Laboratory and Sandia National Laboratories have been actively researching
the use of carbon fiber reinforced polymer material as optical elements in many optical systems.
Active optical elements can be used to build an optical system capable of changing is optical
zoom. We have developed a two-element optical system that uses a large diameter, thin-shelled
carbon fiber reinforced polymer mirror, actuated with micro-positioning motors, and a high
actuator density micro-electro-mechanical deformable mirror. Combined with a Shack-Hartmann
wavefront sensor, we have optimized this actuated carbon fiber reinforced polymer deformable
mirror's surface for use with a forthcoming reflective adaptive optical zoom system. In this paper,
we present the preliminary results of the carbon fiber reinforced polymer deformable mirror's
surface quality and the development of the actuation of it.
A common technique, referred to as channeled imaging polarimetry (CIP), enables the snapshot acquisition of the 2-
dimensional Stokes parameters of an arbitrary scene or sample. It achieves this by amplitude modulating the Stokes
parameters onto various interference-based spatial carrier frequencies. While this technique has utility, it often suffers
from low signal-to-noise ratios in remote sensing scenarios, since it requires narrow spectral bandwidth illumination (< 3
nm in the visible). This paper discusses one hardware implementation that can be utilized to overcome this limitation.
Consequently, an overview of the theoretical and experimental development of this system, a uniquely modified Sagnac
interferometer, is discussed. Both laboratory and outdoor data are included to demonstrate the instrument's ability to
measure polarization in arbitrary scenes. Inclusion of blazed diffraction gratings inside the interferometer enables whitelight
interference fringes to be generated. By incorporating these gratings, the operational bandwidth of the interference
fringes can exceed approximately 300 nm within the visible spectrum; two orders of magnitude greater than previous
CIP implementations. Lastly, by modifying the diffraction grating, the sensor becomes capable of snapshot multispectral
imaging. This is briefly discussed, with both a theoretical description and experimental data.