The effects of dynamic weather on the transmission of a pulsed 2.09-μm laser beam across a 1-km coastal channel are presented. Tests were conducted at the University of Central Florida's Townes Institute Science & Technology Experimentation Facility (TISTEF). By collecting data before, during, and after the morning quiescent period, diverse atmospheric conditions are explored, including periods of clear and cloudy skies and calm and turbulent optical paths. Spatial variations of the laser beam in response to temperature fluctuations and atmospheric turbulence were captured by an infrared camera positioned at the target site. Recorded data were analyzed to assess changes in beam diameter and beam wander relative to range conditions. A suite of weather sensors provided air temperature, wind speed, and solar irradiance. A line-of-sight scintillometer quantified optical turbulence by providing estimates of the refractive-index structure parameter (Cn2), ranging from 2×10–15 m–2/3 to 4×10–13 m–2/3. Data obtained from range sensors provided inputs for new split-step wave-optics simulations. This work presents the first known comparison of 2-μm laser propagation with the simulation software “High Energy Laser - Performance Estimation Test Technology (HEL-PETT)” developed by Coherent Aerospace & Defense. Experimental results agree well with simulations. Data also revealed the quantitative effects of small, dense cloud cover on range conditions: one-minute cloud cover had no effect on range temperature, optical turbulence, or laser beam properties, whereas four-minute cloud cover generated distinct changes in these properties.
This effort designed and tested new algorithms and deployable scintillometer hardware for ocean optical turbulence characterization. Novel features include a hand-deployable design, a non-laser optical source, a rapidly adjustable propagation length, and a collocated multi-instrument environmental sensor package. Undersea testing was contingent on several accomplishments, including developing robust algorithms and data logging methods, integrating compact optics and electronics, and engineering handheld-sized pressure vessels suitable for field experimentation. The test assembly was deployed in 428-m Pacific Ocean water from a small boat. Direct measurements revealed the ocean’s refractive-index structure parameter (Cn2 from 1.9×10−11 m−2/3 to 2.3×10−10 m−2/3) and the inner scale of optical turbulence (l0 from 0.5 mm to 1.5 mm). Onboard temperature, depth, beam attenuation, and backscattering sensors corroborated key regions of interest, namely the thermocline. By integrating turbulence, temperature, depth, attenuation, and backscattering measurements within a single hand-portable assembly, we increased our understanding of ocean optical dynamics while demonstrating the practicality of a low size, weight, and power scintillometer.
The inherent and apparent optical properties (IOPs and AOPs) of seawater limit the performance of free-space optical (FSO), underwater wireless optical communication (UWOC), and imaging systems. Absorption, scattering, and downwelling irradiance are three such properties that influence system performance and often evolve independently. In situ measurements of multiple IOPs and AOPs would provide environmental sensing for fielded optical systems, but such comprehensive measurements are typically expensive or impractical. This effort analyzed existing oceanographic data sets to uncover wavelength-dependent correlations between IOPs, AOPs, test depths, and ocean depths. We then employed machine learning (ML) methods to predict the optical properties of diffuse attenuation (Kd) and backscatter (bb) using beam attenuation (c) and compared these results to ground-truth values. Predicted values of Kd and bb were well matched to their ground-truth data. Furthermore, we demonstrate ML-based Jerlov optical water type classification using beam attenuation as the optical data input. With our methods validated, we collected new optical data sets and processed them using our ML models. Results are promising and indicate future in situ classification and prediction capability. To highlight one practical application, we present a preliminary ML-enabled performance estimator for a generic FSO or UWOC system.
Optically active rare-earth Neodymium (Nd) ions are integrated in Niobium (Nb) thin films forming a new quantum memory device (Nd:Nb) targeting long-lived coherence times and multi-functionality enabled by both spin and photon storage properties. Nb is implanted with Nd spanning 10-60 keV energy and 1013-1014 cm-2 dose producing a 1- 3% Nd:Nb concentration as confirmed by energy-dispersive X-ray spectroscopy. Scanning confocal photoluminescence (PL) at 785 nm excitation are made and sharp emission peaks from the 4F3/2 -< 4I11/2 Nd3+ transition at 1064-1070 nm are examined. In contrast, un-implanted Nb is void of any peaks. Line-shapes at room temperature are fit with Lorentzian profiles with line-widths of 4-5 nm and 1.3 THz bandwidth and the impacts of hyperfine splitting via the metallic crystal potential are apparent and the co-contribution of implant induced defects. With increasing Nd from 1% to 3%, there is a 0.3 nm red shift and increased broadening to a 4.8 nm linewidth. Nd:Nb is photoconductive and responds strongly to applied fields. Furthermore, optically detected magnetic resonance (ODMR) measurements are presented spanning near-infrared telecom band. The modulation of the emission intensity with magnetic field and microwave power by integration of these magnetic Kramer type Nd ions is quantified along with spin echoes under pulsed microwave π-π/2 excitation. A hybrid system architecture is proposed using spin and photon quantum information storage with the nuclear and electron states of the Nd3+ and neighboring Nb atoms that can couple qubit states to hyperfine 7/2 spin states of Nd:Nb and onto NIR optical levels excitable with entangled single photons, thus enabling implementation of computing and networking/internet protocols in a single platform.
We measured the diffraction efficiency response of two photorefractive polymer devices according to the duration of the single laser pulse used to record the hologram. The pulse duration was varied from 6 nanoseconds to 1 second, while the pulse energy density was maintained constant at 30 mJ/cm2. This changed the peak power from 5 ×109 mW to 30 mW. We observed a strong reciprocity failure of the efficiency according to the pulse duration, with a reduction as large as a factor 35 between 1 second and 30 μs pulse duration. At even lower pulse duration (< 30 μs), the efficiency leveled out and remained constant down to the nanosecond exposure time. The same behavior was observed for samples composed of the same material but with and without buffer layers deposited on the electrodes, and different voltages applied during the holographic recording. We explained these experimental results based on the charge transport mechanism involved in the photorefractive process. The plateau is attributed to the single excitation of the charge carriers by short pulses (τp < 30 μs). The increase of efficiency for longer pulse duration (τp > 30 μs) is explained by multiple excitations of the charge carriers that allows longer distance to be traveled from the excitation sites. This longer separation distance between the carriers increases the amplitude of the space-charge field, and improves the index modulation. The understanding of the response of the diffraction efficiency according to the pulse duration is particularly important for the optimization of photorefractive materials to be used at high refresh rate such as in videorate 3D display.
Photorefractive (PR) polymers change their index of refraction upon illumination through a series of electronic phenomena that makes these materials one of the most complex organic systems known. The refractive index change is dynamic and fully reversible, making PR materials very interesting for a large variety of applications such as holography and 3D display. In order to improve the recording speed and achieve videorate for our stereographic display application, we have introduced a new type of electrode geometry where the anode and cathode are in the same plane and are shaped as interpenetrating combs. This type of electrode geometry does not require the sample to be tilted with respect to the writing beams to record the hologram, which is a significant advantage. To monitor the highly non-homogeneous field resulting from this configuration, we used a multiphoton microscope to directly observe the chromophore orientation in situ upon the application of an electric field. Most recently, we developed a fast repetition rate laser (10kHz) where the pulse width can be adjusted from microseconds to milliseconds so that, in conjunction with a ns Q-switched Nd:YAG laser and an externally chopped CW laser, the diffraction efficiency of the material could be measured over 9 orders of magnitude. This measurement helps us better understand the mechanism of grating buildup inside photorefractive polymers.
KEYWORDS: Digital micromirror devices, Switches, Optical switching, Mirrors, Switching, Diffraction, Binary data, Data centers, Signal attenuation, Microelectromechanical systems
Presented here is a 32 × 32 optical switch for telecommunications applications capable of reconfiguring at speeds of up to 12 microseconds. The free space switching mechanism in this interconnect is a digital micromirror device (DMD) consisting of a 2D array of 10.8μm mirrors optimized for implementation at 1.55μm. Hinged along one axis, each micromirror is capable of accessing one of two positions in binary fashion. In general reflection based applications this corresponds to the ability to manifest only two display states with each mirror, but by employing this binary state system to display a set of binary amplitude holograms, we are able to access hundreds of distinct locations in space. We previously demonstrated a 7 × 7 switch employing this technology, providing a proof of concept device validating our initial design principles but exhibiting high insertion and wavelength dependent losses. The current system employs 1920 × 1080 DMD, allowing us to increase the number of accessible ports to 32 × 32. Adjustments in imaging, coupling component design and wavelength control were also made in order to improve the overall loss of the switch. This optical switch performs in a bit-rate and protocol independent manner, enabling its use across various network fabrics and data rates. Additionally, by employing a diffractive switching mechanism, we are able to implement a variety of ancillary features such as dynamic beam pick-off for monitoring purposes, beam division for multicasting applications and in situ attenuation control.
We present here the use the DMD as a diffraction-based optical switch, where Fourier diffraction patterns are used to steer the incoming beams to any output configuration. We have implemented a single-mode fiber coupled N X N switch and demonstrated its ability to operate over the entire telecommunication C-band centered at
1550 nm. The all-optical switch was built primarily with off-the-shelf components and a Texas Instruments
DLP7000™with an array of 1024 X 768 micromirrors. This DMD is capable of switching 100 times faster than currently available technology (3D MOEMS). The switch is robust to typical failure modes, protocol and bit-rate agnostic, and permits full reconfigurable optical add drop multiplexing (ROADM).
The switch demonstrator was inserted into a networking testbed for the majority of the measurements. The testbed assembled under the Center for Integrated Access Networks (ClAN), a National Science Foundation (NSF) Engineering Research Center (ERC), provided an environment in which to simulate and test the data routing functionality of the switch. A Fujitsu Flashwave 9500 PS was used to provide the data signal, which was sent through the switch and received by a second Flashwave node. We successfully transmitted an HD video stream through a switched channel without any measurable data loss.
Photorefractive composites derived from conducting polymers offer the advantage of dynamically recording holograms
without the need for processing of any kind. Thus, they are the material of choice for many cutting edge applications,
such as updatable three-dimensional (3D) displays and 3D telepresence. Using photorefractive polymers, 3D images or
holograms can be seen with the unassisted eye and are very similar to how humans see the actual environment
surrounding them. Absence of a large-area and dynamically updatable holographic recording medium has prevented
realization of the concept. The development of a novel nonlinear optical chromophore doped photoconductive polymer
composite as the recording medium for a refreshable holographic display is discussed. Further improvements in the
polymer composites could bring applications in telemedicine, advertising, updatable 3D maps and entertainment.
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